TW202104079A - Graphite sheet and manufacturing method for the graphite sheet - Google Patents

Abstract

Disclosed herein are a thick graphite sheet and a method of preparing the same. The graphite sheet has a thickness of about 50 µm to about 100 µm and a second surface damage rate of about 0% to about 0.004%, as represented by Equation 2: Second surface damage rate (%) = {(B₁ /B₀ )×100}, ---(2) where B₀ is an area (in mm² ) of a graphite sheet specimen, as measured using an image of the graphite sheet specimen at 10× magnification and B₁ is an area (in mm² ) of a damaged region of the graphite sheet specimen, as measured using an image of the graphite sheet specimen at 10× magnification.

Description

Graphite sheet and manufacturing method of the graphite sheet

This application claims the Korean Patent Application No. 10-2019-0078274 filed with the Korean Intellectual Property Office on June 28, 2019 and the Korean Patent Application No. 10-2019 filed with the Korean Intellectual Property Office on September 26, 2019. The rights and interests of -0119181, the entire content of which is incorporated herein by reference in its entirety.

The invention relates to a thick graphite sheet and a preparation method thereof.

Graphite has good thermal conductivity and is highly favored as a means of heat dissipation. Specifically, artificial graphite prepared in the form of flakes has a thermal conductivity of about 2 to 7 times that of copper or aluminum, and is suitable for use as a heat dissipation tool for electronic devices.

Recently, with the reduction of weight and size, and the improvement of compactness and integration, the calorific value per unit volume of electronic devices has increased. This may have a direct adverse effect on the performance of the electronic device, such as a decrease in the operating speed of the semiconductor due to thermal load, a decrease in life due to deterioration of the battery, or the like.

As a method to solve this problem, a method of using relatively thick graphite sheets in electronic devices has been proposed. Compared with a conventional thin graphite sheet having a thickness of 30 μm or less, for example, such a thick graphite sheet has a larger heat capacity and can effectively dissipate heat even when the amount of heat generated by the electronic device is increased.

Artificial graphite sheets are usually prepared by carbonization and graphitization of polyimide films as precursors. Depending on the degree of thickness required, a thick polyimide film may be used, for example, a polyimide film having a thickness of 100 μm or more to prepare a thick graphite sheet.

However, the use of such thick polyimide films to prepare graphite flakes has the problem that it is difficult to obtain high-quality graphite flakes that have a smooth surface and will not damage the graphite structure during heat treatment, which will result in a decrease in yield.

It is believed to be caused by the assumption that the surface layer and the inside of the polyimide film are carbonized and graphitized almost at the same time. The graphite structure formed or being formed in the surface layer may be sublimated due to the thick polyimide film. Collapse or break due to gas. Another reason is that the graphite structure that has been formed or is being formed in the inner part of the middle of the membrane and the vicinity thereof may also collapse due to the significantly increased pressure caused by the relatively large amount of sublimation gas.

Therefore, there is a need for a technology that can prepare high-quality thick graphite sheets with good surface quality and complete graphite structures.

An object of the present invention is to provide a polyimide film capable of preparing graphite flakes with low brittleness and good surface quality while having the required large thickness, and a preparation method thereof.

Another object of the present invention is to provide a graphite sheet with low brittleness, good surface quality and thermal conductivity, and a desired large thickness, and a preparation method thereof.

The above and other objects of the present invention will become apparent by referring to the detailed description of the following embodiments.

1. An embodiment of the present invention relates to a polyimide film used for graphite sheets, which is formed of a polyimide film composition, and the polyimide film composition includes: polyimide; and The imidization catalyst, and the above-mentioned polyimide film has a thickness of about 100 µm to about 200 µm and a first surface damage rate of about 0% to about 0.004%. The first surface damage rate is represented by the following equation 1: A surface damage rate (%)={(A ₁ /A ₀ )×100}, ---(1) where A ₀ is the graphite sheet sample area measured using the graphite sheet sample image under 10 times magnification (in mm ² ), and A ₁ ^{is the damaged area (in mm 2} ) of the graphite flake sample measured using the graphite flake sample image under 10x magnification. The graphite flake sample is obtained by the following steps: The heating rate of 1 °C/min to about 5 °C/min is heated from about 15°C to about 1,200°C to carbonize the polyimide film sample with a size of 200 mm×25 mm; by using about 1.5 °C/min to about 5 °C/min heating rate from about 1,200 °C to about 2,200 °C, to make the carbonized polyimide film sample initial graphitization; by about 0.4 °C/min The heating rate of about 1.3 °C/min is heated from about 2,200 °C to about 2,500 °C to make the polyimide film sample that has been graphitized for the second time graphitization; and by heating at about 8.5 °C/min The heating rate to about 20°C/min is heated from about 2,500°C to about 2,800°C to graphitize the polyimide film sample that has undergone the secondary graphitization three times.

2. In Example 1, the molar ratio of the amide acid group of the polyamide acid to the amide catalyst in the polyimide film composition may be about 1:0.15 to about 1:0.20.

3. In embodiment 1 or 2, the polyimide film composition may include: 100 parts by weight of polyamic acid; and about 17 to about 36 parts by weight of the imidization catalyst.

4. In any one of embodiments 1 to 3, the polyimide film composition may further include about 1,500 ppm to about 2,500 ppm of inorganic filler relative to 100 parts by weight of polyimide acid, and the inorganic filler includes optional At least one of the group consisting of calcium carbonate, dicalcium phosphate, calcium hydrogen phosphate, barium sulfate, silicon oxide, titanium oxide, aluminum oxide, silicon nitride, and boron nitride.

5. Another embodiment of the present invention relates to a method for preparing a polyimide film for graphite flakes. The method includes: gelling the polyimide film at a temperature of 100°C to about 200°C. The imine film composition is formed by forming a polyimide film composition containing polyamide acid and an imidization catalyst into a film with a thickness of about 100 µm to about 200 µm; at a temperature of about 200°C to about 400°C The temperature of the gelled polyimide film composition for the first time; and at a temperature of about 300°C to about 500°C, the first time the polyimide film composition for the second Hypoimidization, wherein the polyimide film has a first surface damage rate of about 0% to about 0.004%, and the first surface damage rate is represented by Equation 1.

6. In Example 5, the molar ratio of the amide acid group of the polyamide acid and the amide catalyst in the polyimide film composition may be about 1:0.15 to about 1:0.20.

7. In embodiment 5 or 6, the polyimide film composition may include: 100 parts by weight of polyamic acid; and about 17 to about 36 parts by weight of the imidization catalyst.

8. In any one of embodiments 5 to 7, the polyimide film composition may further include about 1,500 ppm to about 2,500 ppm of inorganic filler relative to 100 parts by weight of polyimide acid, and the inorganic filler may include At least one of the group consisting of calcium carbonate, dicalcium phosphate, calcium hydrogen phosphate, barium sulfate, silicon oxide, titanium oxide, aluminum oxide, silicon nitride, and boron nitride.

9. A further embodiment of the present invention relates to a graphite sheet having a thickness of about 50 µm to about 100 µm and a second surface damage rate of about 0% to about 0.004%. The second surface damage rate is represented by the following equation 2. ： The second surface damage rate (%)={(B ₁ /B ₀ )×100}, ---(2) where B ₀ is the graphite sheet sample area measured using the graphite sheet sample image under 10 times magnification ( In mm ² ), and B ₁ ^{is the damaged area (in mm 2} ) of the graphite flake sample measured using the graphite flake sample image at a magnification of 10 times.

10. In Example 9, the graphite sheet may be formed of a polyimide film with a thickness of about 100 µm to about 200 µm.

11. In Embodiment 9 or 10, the graphite sheet can be obtained by carbonizing and graphitizing a polyimide film with a thickness of about 100 µm to about 200 µm.

12. In any of embodiments 9 to 11, the graphite sheet may have an in-plane thermal conductivity of about 800 W/m·K to about 1,200 W/m·K.

13. Another embodiment of the present invention relates to a method for preparing a graphite sheet, which comprises: preparing a carbonized sheet by heating a polyimide film from about 15°C to about 1,200°C, wherein the polyimide film The imine film is a polyimide film according to any one of Examples 1 to 4 or a polyimide film prepared according to any one of Examples 5 to 8; and the heating rate is gradually changed to Heat about 1,200°C to about 2,800°C to graphitize the carbonized sheet to prepare a graphite sheet with a thickness of about 50 µm to about 100 µm, wherein the graphite sheet has a second surface damage rate of about 0% to about 0.004% , The second surface damage rate is represented by equation 2.

14. In Example 13, the step of preparing the carbonized sheet may include thermally cracking the polyimide film by heating at a heating rate of about 1°C/min to about 5°C/min.

15. In embodiment 13 or 14, the step of graphitizing the carbonized sheet may include: performing the initial graphitization of the carbonized sheet by heating from about 1,200°C to about 2,200°C; and by heating from about 2,200°C to about 2,500°C, to perform the secondary graphitization of the primary graphitized carbonized sheet; and by heating from about 2,500°C to about 2,800°C, to perform the tertiary graphitization of the secondary graphitized carbonized sheet.

16. In Example 15, the step of first graphitizing the carbonized sheet can be performed at a heating rate of about 1.5 °C/min to about 5 °C/min; the step of making the primary graphitized carbonized sheet secondarily graphitized can be about The heating rate of 0.4 °C/min to about 1.3 °C/min is carried out; and the step of making the secondary graphitized carbonized sheet three-time graphitization can be carried out at a heating rate of about 8.5 °C/min to about 20 °C/min .

17. In any of embodiments 13 to 16, the polyimide film may have a thickness of about 100 µm to about 200 µm.

18. In any of embodiments 14 to 17, the graphite sheet may have an in-plane thermal conductivity of about 800 W/m·K to about 1,200 W/m·K.

The present invention provides a polyimide film that can be made into a graphite sheet with low brittleness and good surface quality, and at the same time has the required large thickness, a preparation method thereof, and a low brittleness, good surface quality and thermal conductivity, and at the same time Preparation method of graphite sheet with required large thickness.

Descriptions of known functions and configurations that may unnecessarily obscure the purpose of the present invention will be omitted.

It will be further understood that when the terms "comprises", "comprising", "includes" and/or "including" are used in this specification, they specifically refer to the feature The existence of components, integers, steps, operations, elements, components, and/or groups thereof, but does not exclude the presence or addition of one or more other characteristic components, integers, steps, operations, elements, components, and/or Its group. When the singular forms "a" and "an" are used in this specification, unless the context clearly indicates otherwise, it is also intended to include the plural form.

In addition, unless expressly stated otherwise, numerical values related to specific components should be interpreted as including tolerance ranges in the interpretation of the components.

It will be understood that although the terms "first", "second", etc. may be used herein to describe various elements, components, regions, layers and/or parts, these elements, components, regions, Layers and/or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section.

The expression "a to b" used herein to indicate a specific numerical range means "≥a and ≤b".

Polyimide film

An embodiment of the present invention relates to a polyimide film used for thick graphite sheets. The polyimide film used for thick graphite sheets according to the present invention is formed of a polyimide film composition. The polyimide film composition includes: polyimide acid; and an imidization catalyst, and it is Gelatinized and imidized polyimide film composition product.

The polyimide film used for thick graphite sheets according to the present invention has a thickness of about 100 µm to about 200 µm (for example, about 100 µm, about 110 µm, about 120 µm, about 130 µm, about 140 µm, about 150 µm, about 160 µm, about 170 µm, about 180 µm, about 190 µm, or about 200 µm) thickness, which is greater than the thickness of the traditional polyimide film, and therefore can be carbonized and graphitized to have a thickness of Graphite flakes of about 50 µm to about 100 µm (for example, about 50 µm, about 60 µm, about 70 µm, about 80 µm, about 90 µm, or about 100 µm).

In addition, the polyimide film for thick graphite flakes according to the present invention has about 0% to about 0.004% (for example, about 0%, about 0.001%, about 0.002%, about 0.003%, or about 0.004%). As another example, about 0% or about 0.001% to about 0.004%) of the first surface damage rate, as shown in Equation 1, and therefore can be made to have good surface quality and a thickness of about 50 µm to about 100 µm ( For example, about 50 µm, about 60 µm, about 70 µm, about 80 µm, about 90 µm, or about 100 µm) graphite flakes.

<Equation 1> Damage rate of the first surface (%)={(A ₁ /A ₀ )×100}, ---(1)

Where A ₀ is the area (in mm ² ) of the graphite flake sample measured using the graphite flake sample image under 10x magnification, and A _{1 is the graphite flake sample area measured using the graphite flake sample image under 10x magnification} The area of the damaged area (in mm ² ), the graphite sheet sample is obtained by the following steps: by measuring from about 1 °C/min to about 5 °C/min (for example, about 1 °C/min, about 2 °C /min, about 3°C/min, about 4°C/min, or about 5°C/min) heating rate from about 15°C to about 1,200°C to make the size 200 mm×25 mm Polyimide film samples are carbonized; by about 1.5 °C/min to about 5 °C/min (for example, about 1.5 °C/min, about 2 °C/min, about 2.5 °C/min, about 3 °C/min, about 3.5 °C/min, about 4 °C/min, about 4.5 °C/min, or about 5 °C/min) heating rate from about 1,200 °C to about 2,200 °C, to The carbonized polyimide film sample is graphitized for the first time; by about 0.4 °C/min to about 1.3 °C/min (for example, about 0.4 °C/min, about 0.5 °C/min, about 0.6 °C/min) C/min, about 0.7 °C/min, about 0.8 °C/min, about 0.9 °C/min, about 1 °C/min, about 1.1 °C/min, about 1.2 °C/min, or about 1.3 ° C/min) heating rate from about 2,200 °C to about 2,500 °C, to make the polyimide film sample after the primary graphitization secondary graphitization; and by using about 8.5 °C/min to about 20 °C/min (for example, about 8.5 °C/min, about 9 °C/min, about 9.5 °C/min, about 10 °C/min, about 10.5 °C/min, about 11 °C/min, about 11.5 °C/min, about 12 °C/min, about 12.5 °C/min, about 13 °C/min, about 13.5 °C/min, about 14 °C/min, about 14.5 °C/min, about 15 °C/min, about 15.5 °C/min, about 16 °C/min, about 16.5 °C/min, about 17 °C/min, about 17.5 °C/min, about 18 °C/min, about 18.5 ° C/min, about 19 °C/min, about 19.5 °C/min, or about 20 °C/min) heating rate from about 2,500 °C to about 2,800 °C, to make the secondary graphitized polymer The imine film sample is graphitized three times.

Specifically, the first surface damage rate can represent the surface damage rate measured on a graphite sheet sample. The graphite sheet sample is prepared by the following steps: by heating at about 1 °C/min to about 5 °C/min The rate is heated from about 15°C to about 1,200°C to carbonize the polyimide film sample with a size of 200 mm×25 mm; by heating at a rate of about 1.5 °C/min to about 5 °C/min Heat from about 1,200°C to about 2,200°C to graphitize the carbonized polyimide film sample for the first time; by heating at a heating rate of about 0.4 °C/min to about 1.3 °C/min from about 2,200° C is heated to about 2,500°C to second graphitize the polyimide film sample that has been graphitized for the first time; and by heating at a heating rate of about 8.5°C/min to about 20°C/min from about 2,500° C is heated to about 2,800°C to graphitize the polyimide film sample that has undergone secondary graphitization three times.

More specifically, the first surface damage rate can represent the surface damage rate measured on a graphite sheet sample prepared by the following steps: with a heating rate of about 1°C/min from about 15° C heat to about 1,200°C to carbonize a polyimide film sample with a size of 200 mm×25 mm and a thickness of 125 µm; the heating rate is about 1.5 °C/min from about 1,200°C to about 2,200°C for the first graphitization of the carbonized polyimide film sample; by heating from about 2,200°C to about 2,500°C at a heating rate of about 0.4 °C/min, the first graphitized polyimide film The secondary graphitization of the polyimide film sample; and the secondary graphitization of the polyimide film sample by heating it from about 2,500°C to about 2,800°C at a heating rate of about 8.5 °C/min.化.

In the first surface damage rate, A ₀ ^{is the graphite sheet sample area (in mm 2} ) measured using a digital camera at 10 times magnification, and A ₁ is the graphite sheet sample area measured at 10 times magnification. ^{The area of the damaged area (in mm 2} ) of the graphite flake sample measured by the graphite flake sample image acquired under the magnification.

In this article, it can be done by applying a filter with a 1 mm×1 mm square cell grid to the digital image of the graphite sheet sample at 10x magnification, and then calculating the square cells included in each area with the naked eye. Count, so as to carry out the measurement steps of each area.

Figure 4 is a diagram illustrating the area measurement method in the first surface damage rate measurement step represented by Equation 1. Referring to Figure 4, in the measurement step of the first surface damage rate represented by Equation 1, a digital image of the prepared graphite sheet under 10 times magnification is provided, and then a 1 mm×1 mm square cell grid The filter is used for the above-mentioned digital image, as shown in Figure 4(a). In this paper, each cell grid has an area of ^{1 mm 2.} In the first surface damage rate, A ₀ is measured by calculating the unit in which the graphite sheet occupies 50% or more of the unit area, as shown in Figure 4(b). Referring to Figure 4(b), because there are a total of 200 cells marked as blue are included in A ₀ , and A ₀ has a value of 200 mm ^2. In the first surface damage rate, _{A 1} is measured by calculating 50% or more of the unit area occupied by the graphite sheet among the units included _{in A 0 and} confirmed as damaged by visual inspection, as shown in Figure 4 (c ) Shown. Referring to Figure 4(c), because there are a total of 159 cells marked as yellow are included in A ₁ , and A ₁ has a value of 159 mm ^2. When _{the values of A 0} and A ₁ are put into Equation 1, the first surface damage rate measured on the exemplary 20 mm×10 mm graphite sheet sample in Fig. 4 is judged to be 79.5%.

The conventional polyimide film exhibits a high surface damage rate when used to prepare thick graphite sheets with a thickness of about 50 µm to about 100 µm, and it is therefore difficult to simultaneously ensure that the graphite sheets have the required large thickness and good surface quality. On the contrary, the polyimide film according to the present invention can be made into a graphite sheet with low brittleness and good surface quality while having the required large thickness.

The polyimide film composition contains polyimide acid and an imidization catalyst as shown below.

＜Polyamic acid＞

The polyimide of the polyimide film composition is used as a precursor to be converted into polyimide by the imidization catalyst. The polyamic acid may include any polyamic acid obtained by polymerizing a dianhydride monomer and a diamine monomer without limitation.

Examples of dianhydride monomers that can be used as raw materials for polyamide acid may include pyromellitic dianhydride (pyromellitic dianhydride), 2,3,6,7-naphthalenetetracarboxylic dianhydride (2,3,6,7- naphthalenetetracarboxylic dianhydride), 3,3',4,4'-biphenyltetracarboxylic dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride), 1,2,5,6-naphthalenetetracarboxylic dianhydride (1 ,2,5,6-naphthalenetetracarboxylic dianhydride), 2,2',3,3'-biphenyltetracarboxylic dianhydride (2,2',3,3'-biphenyltetracarboxylic dianhydride), 3,3',4,4 '-Benzophenonetetracarboxylic dianhydride (3,3',4,4'-benzophenonetetracarboxylic dianhydride), 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride (2,2-bis (3,4-dicarboxyphenyl)propane dianhydride), 3,4,9,10-perylenetetracarboxylic dianhydride (3,4,9,10-perylenetetracarboxylic dianhydride), bis(3,4-dicarboxyphenyl)propane Dianhydride (bis(3,4-dicarboxyphenyl)propane dianhydride), 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride (1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride) , 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride (1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride), bis(2,3-dicarboxyphenyl)methane dianhydride Anhydride (bis(2,3-dicarboxyphenyl)methane dianhydride), bis(3,4-dicarboxyphenyl)ethane dianhydride (bis(3,4-dicarboxyphenyl)ethane dianhydride), oxydiphthalic anhydride (oxydiphthalic anhydride) ), bis(3,4-dicarboxyphenyl)sulfone dianhydride (bis(3,4-dicarboxyphenyl)sulfone dianhydride), p-phenylene bis(trimellitic acid monoester anhydride) (p-phenylene-bis( trimellitic monoester acid anhydride)), B Ethylene-bis(trimellitic monoester acid anhydride)(ethylene-bis(trimellitic monoester acid anhydride)), bisphenol-A-bis(trimellitic monoester acid anhydride)(bisphenol-A-bis(trimellitic monoester acid anhydride) )), and at least one of its derivatives. Using these exemplary dianhydride monomers can obtain polyamide acid having both improved imidization efficiency and improved uniformity. In addition, these exemplary dianhydride monomers can be used alone or in mixtures thereof.

Examples of diamine monomers that can be used as raw materials for polyamide acid can include 4,4'-diaminodiphenylpropane (4,4'-diaminodiphenylpropane), 4,4'-diaminodiphenylpropane (4,4 '-diaminodiphenylmethane), benzidine, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenylsulfide, 3 ,3'-diaminodiphenylsulfone (3,3'-diaminodiphenylsulfone), 4,4'-diaminodiphenylsulfone (4,4'-diaminodiphenylsulfone), 4,4'-diaminodiphenylsulfone (4, 4'-oxydiphenylamine)(4,4'-diaminodiphenylether(4,4'-oxydianiline)), 3,3'-diaminodiphenylether(3,3'-oxydianiline)(3,3'- diaminodiphenylether(3,3'-oxydianiline)), 3,4'-diaminodiphenylether (3,4'-oxydianiline) (3,4'-diaminodiphenylether(3,4'-oxydianiline)), 1, 5-diaminonaphthalene (1,5-diaminonaphthalene), 4,4'-diaminodiphenyldiethylsilane (4,4'-diaminodiphenyldiethylsilane), 4,4'-diaminodiphenyldiethylsilane (4, 4'-diaminodiphenylsilane), 4,4'-diaminodiphenylethylphosphine oxide (4,4'-diaminodiphenylethylphosphine oxide), 4,4'-diaminodiphenyl-N-methylamine (4,4 '-diaminodiphenyl-N-methylamine), 4,4'-diaminodiphenyl-N-phenylamine (4,4'-diaminodiphenyl-N-phenylamine), 1,4-diaminobenzene (p-phenylenediamine) ( 1,4-diaminobenzene (p-phenylenediamine)), 1,3-diaminobenzene (1,3-diaminobenzene), 1,2-diaminobenzene (1,2-diaminobenzene), and its derivatives At least one of the group. Using these exemplary diamine monomers can obtain a polyamide acid having both improved imidization efficiency and improved uniformity. In addition, these exemplary diamine monomers can be used alone or in mixtures thereof.

For example, a molar ratio of about 1:0.9 to about 1:1.1 (for example, about 1:0.9, about 1:1, or about 1:1.1) can be used as the dianhydride monomer of the polyamide acid raw material Used with diamine monomer in the polymerization of polyamide acid. Within this range, a polyamide acid having both improved imidization efficiency and improved uniformity can be obtained.

Polyamide acid may have about 150,000 g/mol to about 1,000,000 g/mol (e.g., about 150,000 g/mol, about 200,000 g/mol, about 250,000 g/mol, about 300,000 g/mol, about 350,000 g/mol, About 400,000 g/mol, about 450,000 g/mol, about 500,000 g/mol, about 550,000 g/mol, about 600,000 g/mol, about 650,000 g/mol, about 700,000 g/mol, about 750,000 g/mol, about 800,000 g/mol, about 850,000 g/mol, about 900,000 g/mol, about 950,000 g/mol, or about 1,000,000 g/mol), especially about 170,000 g/mol to about 700,000 g/mol, more particularly about 190,000 A weight average molecular weight of g/mol to about 500,000 g/mol, but not limited to this. Within this range, polyamide acid can further improve the heat resistance and mechanical properties of the polyimide film according to the present invention.

Polyamide acid may have about 90,000 cP to about 500,000 cP (e.g., about 90,000 cP, about 100,000 cP, about 110,000 cP, about 120,000 cP, about 130,000 cP, about 140,000 cP, about 150,000 cP, about 160,000 cP, about 170,000 cP cP, approximately 180,000 cP, approximately 190,000 cP, approximately 200,000 cP, approximately 210,000 cP, approximately 220,000 cP, approximately 230,000 cP, approximately 240,000 cP, approximately 250,000 cP, approximately 260,000 cP, approximately 270,000 cP, approximately 280,000 cP, approximately 290,000 cP, Approximately 300,000 cP, approximately 310,000 cP, approximately 320,000 cP, approximately 330,000 cP, approximately 340,000 cP, approximately 350,000 cP, approximately 360,000 cP, approximately 370,000 cP, approximately 380,000 cP, approximately 390,000 cP, approximately 400,000 cP, approximately 410,000 cP, approximately 420,000 cP, about 430,000 cP, about 440,000 cP, about 450,000 cP, about 460,000 cP, about 470,000 cP, about 480,000 cP, about 490,000 cP, or about 500,000 cP), especially about 150,000 cP to about 400,000 cP, more particularly The viscosity is about 180,000 cP to about 300,000 cP, but not limited to this. Within this range, polyamide acid can further improve the heat resistance and mechanical properties of the polyimide film according to the present invention.

Polyamide acid can be dissolved in an organic solvent and used in the form of a polyamide acid solution. When the polyimide is used in the form of a polyimide solution, the polyimide film composition can further improve the processability and workability during the preparation of the polyimide film.

The organic solvent may include any organic solvent capable of dissolving polyamide acid, but is not limited thereto. In particular, the organic solvent may be an aprotic polar solvent.

Examples of aprotic polar solvents may include: amide solvents, such as N,N'-dimethylformamide (N,N'-dimethylformamide, DMF) and N,N'-dimethylformamide (N ,N'-dimethylacetamide, DMAc); phenolic solvents, such as p-chlorophenol (p-chlorophenol) and o-chlorophenol (o-chlorophenol); N-methyl-pyrrolidone (N-methyl-pyrrolidone, NMP); γ- Butyrolactone (γ-butyrolactone, GBL); and diglyme.

In addition to organic solvents, auxiliary solvents can be further used as needed to adjust the solubility of polyamide acid. Examples of auxiliary solvents may include toluene, tetrahydrofuran, acetone, methyl ethyl ketone, methanol, ethanol, and water.

When polyamic acid is dissolved in an organic solvent and used in the form of a polyamic acid solution, the polyamic acid solution may contain about 15 wt% to about 20 wt% (for example, about 15 wt%, about 16 wt%, About 17 wt%, about 18 wt%, about 19 wt%, or about 20 wt%) of polyamide acid (solid) and about 80 wt% to about 85 wt% (for example, about 80 wt%, about 81 wt%) %, about 82 wt%, about 83 wt%, about 84 wt%, or about 85 wt%). Within this range, the weight average molecular weight and viscosity of the entire polyimide solution can be easily adjusted while further promoting the formation of the polyimide film composition into a thin film.

＜Imidation catalyst＞

The imidization catalyst of the polyimide film composition is used to promote the conversion of polyimide into polyimide.

The imidization catalyst may include amine-based catalysts, such as aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines. heterocyclic tertiary amines). Among them, in terms of catalytic reactivity, heterocyclic tertiary amines may be preferable. Examples of heterocyclic tertiary amines may include quinoline, isoquinoline, β-picoline (BP), and pyridine. It can be used alone or in a mixture thereof.

In one embodiment, the imidization catalyst in the polyimide film composition can be used in the polyimide film composition with respect to 1 mol of the amide acid group of the polyamide acid, with a ratio of about 0.15 mol to about 0.2 mol (for example, about 0.15 mol). mol, about 0.16 mol, about 0.17 mol, about 0.18 mol, about 0.19 mol, or about 0.2 mol). Within this range, the imidization catalyst can make the polyimide film according to the present invention have a more regular matrix structure and further increase the crystallinity.

In another embodiment, the imidization catalyst in the polyimide film composition can be used in the polyimide film composition relative to 100 parts by weight of polyamic acid, in an amount of about 17 parts by weight to about 36 parts by weight (for example, about 17 parts by weight). , About 18 parts by weight, about 19 parts by weight, about 20 parts by weight, about 21 parts by weight, about 22 parts by weight, about 23 parts by weight, about 24 parts by weight, about 25 parts by weight, about 26 parts by weight, about 27 parts by weight , About 28 parts by weight, about 29 parts by weight, about 30 parts by weight, about 31 parts by weight, about 32 parts by weight, about 33 parts by weight, about 34 parts by weight, about 35 parts by weight, or about 36 parts by weight). . Within this range, the imidization catalyst can make the polyimide film according to the present invention have a more regular matrix structure and further increase the crystallinity.

＜Inorganic filler＞

In addition to the above-mentioned components, the polyimide film composition may further include an inorganic filler. The inorganic filler of the polyimide film composition is dispersed in the matrix of the polyimide film and sublimated after carbonization and/or graphitization of the polyimide film to induce foaming in the polyimide film . Therefore, due to the polyimide film structure in which the inorganic filler is uniformly dispersed in the polyimide matrix, the polyimide film can induce highly regularly arranged gaps therein. The gap created by foaming can improve the bending resistance of the graphite sheet prepared by using polyimide film. In addition, because the inorganic filler is sublimated after the carbonization and/or graphitization of the polyimide film, and the polyimide is converted into graphite, it is possible to obtain a graphite sheet with a highly regular and well-arranged structure. In addition, the inorganic filler can be used as a channel for releasing gas during its sublimation, thereby preventing surface defects and damage caused by foaming.

The inorganic filler may include any inorganic filler that can be sublimated at a temperature of about 1000° C. or higher without limitation. In particular, the inorganic filler may include at least one selected from the group consisting of calcium carbonate, dicalcium phosphate, calcium hydrogen phosphate, barium sulfate, silicon oxide, titanium oxide, aluminum oxide, silicon nitride, and boron nitride . Using these inorganic fillers can obtain graphite sheets with improved bending resistance and structural uniformity. These exemplary inorganic fillers can be used alone or in a mixture thereof.

The inorganic filler can be used in the polyimide film composition at about 1,500 ppm to about 2,500 ppm (e.g., about 1,500 ppm, about 1,600 ppm, about 1,700 ppm, about 1,800 ppm) relative to 100 parts by weight of polyamide acid. , About 1,900 ppm, about 2,000 ppm, about 2,100 ppm, about 2,200 ppm, about 2,300 ppm, about 2,400 ppm, or about 2,500 ppm). Within this range, the sublimation gas generated in the polyimide film after the carbonization and/or graphitization of the polyimide film can be smoothly discharged from the polyimide film, thereby further improving the use of polyimide The surface quality of the graphite sheet prepared by the film also enables the polyimide structure to be converted into an artificial graphite structure with higher efficiency.

The inorganic filler may have an average particle diameter of about 1.5 µm to about 4.5 µm (for example, about 1.5 µm, about 2 µm, about 2.5 µm, about 3 µm, about 3.5 µm, about 4 µm, or about 4.5 µm), but Not limited to this. Within this range, the inorganic filler can prevent the surface roughness of the polyimide film from being excessively reduced, and can further reduce the occurrence of bright spots caused by excessive foaming, thereby further improving the surface of the graphite sheet prepared using the polyimide film quality.

＜Additives＞

In addition to the above components, the polyimide film composition may further contain additives such as dehydrating agents.

The dehydrating agent promotes cyclization through the dehydration of polyamic acid. In particular, the dehydrating agent may include aliphatic acid anhydrides, aromatic acid anhydrides, N,N'-dialkylcarbodiimide, halogenated Halogenated lower aliphatic acid anhydrides, halogenated lower fatty acid anhydrides, arylphosphonic acid dihalides, thionyl halides) or mixtures thereof.

Among them, in terms of availability and cost reduction, aliphatic acid anhydrides, such as acetic acid anhydride, propionic acid anhydride, and lactic acid anhydride, or mixtures thereof, may be preferable of.

In the polyimide film composition, the dehydrating agent can be used in a ratio of about 0.5 mol to about 5 mol (for example, about 0.5 mol, about 1 mol, about 1.5 mol) relative to 1 mol of the amide acid group of the polyamide. , About 2 mol, about 2.5 mol, about 3 mol, about 3.5 mol, about 4 mol, about 4.5 mol, or about 5 mol). Within this range, the polyimide film composition can further improve the imidization efficiency through the dehydration of polyimide acid.

Polyimide Film preparation method

Another embodiment of the present invention relates to a method for preparing a polyimide film for thick graphite flakes. The method comprises: by heating at about 100°C to about 200°C (for example, about 100°C, About 110°C, about 120°C, about 130°C, about 140°C, about 150°C, about 160°C, about 170°C, about 180°C, about 190°C, or about 200°C ), the polyimide film composition is gelled, and the polyimide film composition containing the polyamide acid and the imidization catalyst is formed into a thickness of about 100 µm to about 200 µm (for example, about 100 µm). µm, about 110 µm, about 120 µm, about 130 µm, about 140 µm, about 150 µm, about 160 µm, about 170 µm, about 180 µm, about 190 µm, or about 200 µm) thin films; C to about 400°C (e.g., about 200°C, about 210°C, about 220°C, about 230°C, about 240°C, about 250°C, about 260°C, about 270°C, about 280°C, about 290°C, about 300°C, about 310°C, about 320°C, about 330°C, about 340°C, about 350°C, about 360°C, about 370°C, about 380°C, about 390°C, or about 400°C) the gelatinized polyimide film composition is initially imidized; and at about 300°C to about 500°C (for example, about 300°C, about 310°C, about 320°C, about 330°C, about 340°C, about 350°C, about 360°C, about 370°C, about 380°C, about 390°C, about 400°C, about 410°C, about 420°C, about 430°C, about 440°C, about 450°C, about 460°C, about 470°C, about 480°C, about 490°C, or At a temperature of about 500°C), the polyimide film composition that has been firstly imidized is secondarily imidized. The method according to the present invention allows a more economical and efficient preparation of polyimide films, which can be made into graphite sheets with both low brittleness and the required large thickness.

In addition, the polyimide film prepared according to the method of the present invention may have about 0% to about 0.004% (for example, about 0%, about 0.001%, about 0.002%, about 0.003%, or about 0.004%, for example, about 0.004%). 0% or about 0.001% to about 0.004%) of the first surface damage rate, the first surface damage rate is represented by Equation 1. Equation 1 is shown above.

In addition, the polyimide film composition, its components, specific examples of the components, and the amounts of the components are as described above.

Specifically, the amide acid group of the polyamide acid and the imidization catalyst can be about 1:0.15 to about 1:0.20 (for example, about 1:0.15, about 1:0.16, about 1:0.17, about 1 : 0.18, about 1:0.19, or about 1:0.20) in the polyimide film composition.

Specifically, the polyimide film composition may include: 100 parts by weight of polyamic acid; and about 17 parts by weight to about 36 parts by weight (for example, about 17 parts by weight, about 18 parts by weight, about 19 parts by weight) , About 20 parts by weight, about 21 parts by weight, about 22 parts by weight, about 23 parts by weight, about 24 parts by weight, about 25 parts by weight, about 26 parts by weight, about 27 parts by weight, about 28 parts by weight, about 29 parts by weight , About 30 parts by weight, about 31 parts by weight, about 32 parts by weight, about 33 parts by weight, about 34 parts by weight, about 35 parts by weight, or about 36 parts by weight) of the imidization catalyst.

In addition, the polyimide film composition may further include about 1,500 ppm to about 2,500 ppm (e.g., about 1,500 ppm, about 1,600 ppm, about 1,700 ppm, about 1,800 ppm, about 1,900 ppm, about 2,000 ppm, about 2,100 ppm, about 2,200 ppm, about 2,300 ppm, about 2,400 ppm, or about 2,500 ppm) inorganic fillers. The inorganic filler may include at least one selected from the group consisting of calcium carbonate, dicalcium phosphate, calcium hydrogen phosphate, barium sulfate, silicon oxide, titanium oxide, aluminum oxide, silicon nitride, and boron nitride.

The preparation method of the polyimide film according to the present invention may further include preparing polyimide acid before gelling the polyimide film composition. The preparation of polyamic acid herein can be performed by any suitable method known in the art, such as emulsion polymerization, solution polymerization, bulk polymerization, and suspension polymerization, but is not limited thereto.

If in the preparation method of the polyimide film, the polyimide film composition gels at a temperature lower than 100°C, it is difficult to form the polyimide film composition into polyimide film. If the polyimide film composition gels at a temperature higher than 200°C, the polyimide film composition may be excessively gelled, resulting in high brittleness of the graphite sheet prepared using the obtained polyimide film .

Specifically, the gelation of the polyimide film composition can be achieved through a process in which the polyimide film composition is provided in the form of a solution, and then the polyimide film composition is applied to the support, and then dried. To prepare a sheet-like gel. The support can be a glass plate, aluminum foil, endless stainless belt, or stainless drum, but it is not limited to this. The polyimide film composition can be coated by, for example, casting, but it is not limited to this. The sheet-like gel may be a self-supporting sheet-like gel prepared by drying and gelling at the aforementioned gelation temperature for about 10 to about 20 minutes.

Then, after being separated from the support, the sheet-like gel can permeate at about 200°C to about 400°C (for example, about 200°C, about 210°C, about 220°C, about 230°C, about 240°C). °C, about 250°C, about 260°C, about 270°C, about 280°C, about 290°C, about 300°C, about 310°C, about 320°C, about 330°C, about 340 °C, about 350 °C, about 360 °C, about 370 °C, about 380 °C, about 390 °C, or about 400 °C) the first imidization and at about 300 °C to about 500 °C (e.g., about 300°C, about 310°C, about 320°C, about 330°C, about 340°C, about 350°C, about 360°C, about 370°C, about 380°C, About 390°C, about 400°C, about 410°C, about 420°C, about 430°C, about 440°C, about 450°C, about 460°C, about 470°C, about 480°C, The temperature of about 490°C, or about 500°C) is secondary imidization to form a thin film. The primary and secondary imidization processes further imidize the unreacted amide groups, thereby further improving the quality of the obtained polyimide film. In addition, when the primary and secondary imidization are performed in the above-mentioned temperature range, the polyamide can be converted into polyimid with high efficiency.

The resulting polyimide film may have a thickness of about 100 µm to about 200 µm (for example, about 100 µm, about 110 µm, about 120 µm, about 130 µm, about 140 µm, about 150 µm, about 160 µm, about 170 µm , About 180 µm, about 190 µm, or about 200 µm). If the thickness of the polyimide film is less than about 100 µm, it is difficult to use the polyimide film to prepare thick graphite sheets. If the thickness of the polyimide film exceeds about 200 µm, the graphite flakes prepared with the polyimide film may be too brittle.

Graphite sheet

A further embodiment of the present invention relates to a thick graphite sheet. The graphite sheet according to the present invention has a thickness of about 50 µm to about 100 µm (for example, about 50 µm, about 60 µm, about 70 µm, about 80 µm, about 90 µm, or about 100 µm). Within this range, the graphite sheet can have a good heat capacity, and therefore has the characteristics of being more beneficially used as a heat sink of an electronic device.

In addition, the graphite sheet according to the present invention has about 0% to about 0.004% (for example, about 0%, about 0.001%, about 0.002%, about 0.003%, or about 0.004%, in another example, about 0% or about The second surface damage rate is 0.001% to about 0.004%), and the second surface damage rate is as shown in Equation 2, while having a thickness of about 50 µm to about 100 µm. Within the range of the second surface damage rate, the graphite sheet can have the characteristics of being more beneficially used as a heat dissipation material for electronic devices.

<Equation 2> Damage rate of the second surface (%)={(B ₁ /B ₀ )×100}, ---(2)

Where B ₀ is the area (in mm ² ) of the graphite flake sample measured using the graphite flake sample image under 10x magnification, and B _{1 is the graphite flake sample measured using the graphite flake sample image under 10x magnification} The area of the damaged area (in mm ² ).

Here, the second surface damage rate (%) can be measured in the same way as the first surface damage rate represented by Equation 1.

In one embodiment, the graphite sheet can be used with a thickness of about 100 µm to about 200 µm (for example, about 100 µm, about 110 µm, about 120 µm, about 130 µm, about 140 µm, about 150 µm, about 160 µm, About 170 µm, about 180 µm, about 190 µm, or about 200 µm) polyimide film. In another embodiment, the graphite sheet can be carbonized and the thickness of the graphitization is about 100 µm to about 200 µm (for example, about 100 µm, about 110 µm, about 120 µm, about 130 µm, about 140 µm, about 150 µm , About 160 µm, about 170 µm, about 180 µm, about 190 µm, or about 200 µm) polyimide film. In this case, the graphite sheet may have a thickness of about 50 µm to about 100 µm and may have a good heat capacity, and therefore has the characteristics of being more beneficially used as a heat sink of an electronic device.

In one embodiment, the graphite sheet may have an in-plane thermal conductivity of about 800 W/m·K or higher, particularly about 800 W/m·K to about 1,200 W/m·K (e.g., about 800 W/m·K). m·K, about 900 W/m·K, about 1,000 W/m·K, about 1,100 W/m·K, or about 1,200 W/m·K). Within this range, the graphite sheet may have the characteristics of being more beneficially used as a heat sink of an electronic device.

Preparation method of graphite sheet

Another embodiment of the present invention relates to a method for preparing thick graphite flakes, which has about 0% to about 0.004% (for example, about 0%, about 0.001%, about 0.002%, about 0.003%) as shown in Equation 2. , Or about 0.004%, in another example, about 0% or about 0.001% to about 0.004%) of the second surface damage rate.

The preparation method of the thick graphite sheet includes: preparing a carbonized sheet by heating a polyimide film from about 15°C to about 1,200°C; and by heating a polyimide film from about 1,200°C with a stepwise heating rate To about 2,800°C to graphitize the carbonized sheet to prepare a graphite sheet with a thickness of about 50 µm to about 100 µm.

The polyimide film may be the above-mentioned polyimide film. The polyimide film may be formed of a polyimide film composition containing polyimide acid and an imidization catalyst, and may have a thickness of about 100 µm to about 200 µm and a thickness of about 0% to about 0.004%. The surface damage rate and the first surface damage rate are represented by the above-mentioned equation 1 for the polyimide film.

Because the polyimide film used in the thick graphite sheet preparation method according to the present invention is the same as the above-mentioned polyimide film according to the present invention, and it is prepared by the polyimide film preparation method according to the present invention , So its detailed description will be omitted.

＜Carbonization step＞

In the preparation method of the thick graphite sheet, the preparation step of the carbonized sheet includes heating from about 15°C to about 1,200°C, particularly from about 20°C to about 1,200°C, more particularly from 50°C. To about 1,200°C to carbonize the polyimide film. In this carbonization temperature range, the polymer chains of the polyimide film can be thermally decomposed sufficiently to obtain carbonized sheets with amorphous carbon bodies, which can be graphitized into graphite sheets.

Specifically, the polyimide film can be introduced into a high temperature furnace such as an electric furnace, and then heated from about 15°C to about 1,200°C in a nitrogen/argon atmosphere in a process of about 12 to 14 hours. Carry out the carbonization of the polyimide film, thereby converting the polyimide film into a carbonized sheet.

In addition, it may be about 1°C/min to about 5°C/min (for example, about 1°C/min, about 2°C/min, about 3°C/min, about 4°C/min, or about 5°C/min. °C/min) heating rate to prepare the carbonized sheet. In this heating rate range, the polymer chains of the polyimide film can be sufficiently thermally decomposed, so as to obtain a carbonized sheet with an amorphous carbon body, which can be made into a graphite sheet through graphitization.

＜graphitization step＞

In the preparation method of thick graphite flakes, the preparation of graphite flakes involves graphitizing the carbonized flakes obtained in a carbonization step of heating from about 1,200°C to about 2,800°C at a stepwise heating rate to prepare a thickness of Graphite flakes from about 50 µm to about 100 µm. The graphitization process converts the carbonized flakes into graphite flakes through the redistribution of carbon in the amorphous carbon body of the carbonized flakes.

Specifically, the carbonized sheet can be introduced into a high-temperature furnace facility such as an electric furnace, and then gradually heated from about 1,200°C in a process of about 10 to 14 hours in a mixed gas environment of nitrogen, argon and a small amount of helium. To about 2,800°C to perform graphitization of the carbonized sheet, but not limited to this.

More specifically, the preparation of graphite flakes may include: performing primary graphitization of the carbonized flakes by heating from about 1,200°C to about 2,200°C; and performing heat treatment by heating from about 2,200°C to about 2,500°C. The secondary graphitization of the primary graphitized carbonized sheet; and the secondary graphitization of the secondary graphitized carbonized sheet by heating from about 2,500°C to about 2,800°C. In this way, the redistribution of carbon in the amorphous carbon body of the carbonized sheet can be achieved with higher efficiency, so as to obtain a graphite sheet with low brittleness and good surface quality while having the required large thickness.

More specifically, it can permeate from about 1.5 °C/min to about 5 °C/min (for example, about 1.5 °C/min, about 2 °C/min, about 2.5 °C/min, about 3 °C/min , About 3.5 °C/min, about 4 °C/min, about 4.5 °C/min, or about 5 °C/min) heating rate for the initial graphitization of the carbonized sheet, through about 0.4 °C/min To about 1.3 °C/min (for example, about 0.4 °C/min, about 0.5 °C/min, about 0.6 °C/min, about 0.7 °C/min, about 0.8 °C/min, about 0.9 °C/min min, about 1 °C/min, about 1.1 °C/min, about 1.2 °C/min, or about 1.3 °C/min) to perform the secondary graphitization of the primary graphitized carbonized sheet, and Permeable from about 8.5 °C/min to about 20 °C/min (for example, about 8.5 °C/min, about 9 °C/min, about 9.5 °C/min, about 10 °C/min, about 10.5 °C /min, about 11 °C/min, about 11.5 °C/min, about 12 °C/min, about 12.5 °C/min, about 13 °C/min, about 13.5 °C/min, about 14 °C/ min, about 14.5 °C/min, about 15 °C/min, about 15.5 °C/min, about 16 °C/min, about 16.5 °C/min, about 17 °C/min, about 17.5 °C/min , About 18 °C/min, about 18.5 °C/min, about 19 °C/min, about 19.5 °C/min, or about 20 °C/min) to carry out the secondary graphitized carbonized sheet The third graphitization. In this way, the redistribution of carbon in the amorphous carbon body of the carbonized sheet can be achieved with higher efficiency, so as to obtain a graphite sheet with low brittleness and good surface quality while having the required large thickness.

In addition, when the first to third graphitization processes are performed at the above heating rate within the above temperature range, the gas generated during the preparation of the graphite flakes can be stably discharged, thereby further preventing the surface of the graphite flakes from being damaged, and therefore, the equations 1 and 2 means that the surface damage rate has dropped to close to 0%.

The preparation method of thick graphite flakes may further comprise: after the graphite flakes are prepared, the temperature of about 5°C/min to about 10°C/min (for example, about 5°C/min, about 6°C/min, about 7°C /min, about 8°C/min, about 9°C/min, or about 10°C/min) to cool the prepared graphite sheet. In this way, the graphite flakes can have a further reduced brittleness and a further improved surface quality.

Instance

Next, the present invention will be described in more detail with reference to examples. However, it will be noted that these examples are provided for illustration only and should not be construed as limiting the present invention in any way.

Instance 1

After putting dimethylformamide (DMF) as an organic solvent in a 0.5 L reactor in a nitrogen environment, add oxydiphenylamine (ODA, 4, 4'-oxydianiline (4,4'-oxydianiline) and pyromellitic dianhydride (PMDA) as a dianhydride monomer, followed by polymerization to prepare a polyamide acid solution. Here, the weight ratio of the solid matter to the solvent in the reaction product is 20:80.

Then, 2,500 ppm of calcium phosphate with an average particle size of 3 µm was added as an inorganic filler to the polyamide acid solution, followed by stirring, to obtain a precursor composition.

Then, in an amount of 0.17 mol relative to 1 mol of the amide acid group, β-picoline (β-picoline) as an imidization catalyst was added, and then uniformly mixed and defoamed to prepare polyimide Film composition.

Then, the polyimide film composition was placed on a SUS plate (100SA, Sandvik) as a support and cast using a doctor blade with a gap of 500 µm, and then heated with hot air at a temperature of 100°C to 200°C Dry to prepare a sheet-like gel.

Then, the sheet-like gel was separated from the SUS plate, fixed on a pin frame, transferred to a hot tenter, and the first imidimide was performed at a temperature of 200°C to 400°C. For 10 minutes, the secondary imidization was performed at a temperature of 300°C to 500°C for 10 minutes. Then, the thin film product prepared through the primary and secondary imidization process was cooled to 25°C, and then separated from the pin frame to obtain a polyamide with a size of 20 cm×2.5 cm and a thickness of 125 µm. Imine film.

Instance 2 to 3 And a comparative example 1 to 4

Except that the molar amount of the imidization catalyst (β-picoline) was changed as shown in Table 1, a polyimide film with a thickness of 125 µm was obtained in the same manner as in Example 1.

Instance 4

The polyimide film prepared in Example 1 was carbonized by heating from about 50°C to about 1,200°C at a heating rate of about 1°C/min, thereby preparing a carbonized sheet.

Then, the carbonized sheet is subjected to the first to third graphitization processes, in which the carbonized sheet is baked by heating from about 1,200°C to about 2,800°C at a stepwise heating rate, thereby preparing a graphite sheet with a final thickness of 50 µm . Specifically, in the first graphitization process, the carbonized sheet is heated from about 1,200°C to about 2,200°C at a heating rate of 1.5 °C/min. The carbonized sheet is heated from about 2,200°C to about 2,500°C at a heating rate of 0.4°C/min. In the third graphitization process, the second graphitized carbonized sheet is heated at 8.5°C/min. The heating rate in min is from about 2,500°C to about 2,800°C.

Instance 5 to 6 And a comparative example 5 to 8

Except that the polyimide film prepared in Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, or Comparative Example 4 was used instead of the polyimide film prepared in Example 1, the same as in Example 4 Method to prepare graphite flakes with a final thickness of 50 µm.

Table 1 Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Polyamide acid (parts by weight) 100 100 100 100 100 100 100 Solvent 400 400 400 400 400 400 400 Imidation catalyst (molar amount) 0.17 0.20 0.15 0 0.28 0.25 0.24 Imidification catalyst (parts by weight) 27 29 25 0 36 33 32 Inorganic filler 2,500 ppm 2,500 ppm 2,500 ppm 2,500 ppm 2,500 ppm 2,500 ppm 2,500 ppm Thickness (µm) 125 125 125 125 125 125 125

Table 2 Example 4 Example 5 Example 6 Comparative example 5 Comparative example 6 Comparative example 7 Comparative example 8 Polyimide film Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Carbonization temperature (°C) 50 to 1,200 50 to 1,200 50 to 1,200 50 to 1,200 50 to 1,200 50 to 1,200 50 to 1,200 Initial graphitization temperature (°C) 1,200 to 2,200 1,200 to 2,200 1,200 to 2,200 1,200 to 2,200 1,200 to 2,200 1,200 to 2,200 1,200 to 2,200 Secondary graphitization temperature (°C) 2,200 to 2,500 2,200 to 2,500 2,200 to 2,500 2,200 to 2,500 2,200 to 2,500 2,200 to 2,500 2,200 to 2,500 Tertiary graphitization temperature (°C) 2,500 to 2,800 2,500 to 2,800 2,500 to 2,800 2,500 to 2,800 2,500 to 2,800 2,500 to 2,800 2,500 to 2800 Thickness (µm) 50 50 50 50 50 50 50

＜ characteristic Evaluation ＞

(1) Surface quality

The surface quality of each thick graphite sheet sample prepared in Examples 4 to 6 and Comparative Examples 5 to 8 was visually evaluated. Specifically, the surface quality was evaluated based on how many cracks were visually observed on the surface of each thick graphite sheet sample.

When no cracks are observed in the predetermined area (20 cm×2.5 cm (length×width)), the corresponding graphite sheet sample is rated as "good", and when 1 to 5 cracks are observed in the predetermined area, the corresponding The graphite flake sample of is rated as "normal", and when more than 5 cracks are observed in the predetermined area or graphitization is not achieved, the corresponding graphite flake sample is rated as "poor". The results are shown in Figures 1 to 3 and Table 3.

(2) Surface damage rate

The second surface damage rate represented by Equation 2 was measured on each of the thick graphite sheet samples prepared in Examples 4 to 6 and Comparative Examples 5 to 8. When the damage rate of the second surface exceeds 0.004%, the corresponding graphite flake sample is rated as "inferior quality". The results are shown in Table 3.

<Equation 2> Damage rate of the second surface (%)={(B ₁ /B ₀ )×100}, ---(2)

Where B ₀ is the area (in mm ² ) of the graphite flake sample measured using the graphite flake sample image under 10x magnification, and B _{1 is the graphite flake sample measured using the graphite flake sample image under 10x magnification} The area of the damaged area (in mm ² ).

(3) Thermal conductivity

Using a thermal diffusivity tester (LFA 467, Netsch Co.), the in-plane thermal diffusivity (in-plane thermal diffusivity) of each thick graphite sheet sample prepared in Examples 4 to 6 and Comparative Examples 5 to 8 was measured by the laser flash method. diffusivity), and then calculate the thermal conductivity by multiplying the measured value of the in-plane thermal diffusivity by the density (weight/volume) and the specific heat capacity (measured by DSC). Herein, samples with cracks or non-graphitization observed in the evaluation of (1) surface quality are marked as "unmeasurable". The results are shown in Table 3.

(4) Bright spots appear

The appearance of bright spots may cause surface defects of the graphite sheet. The number of protrusions with a size of 0.05 mm or more in each of the thick graphite sheet samples prepared in Examples 4 to 6 and Comparative Examples 5 to 8 was measured in a square of 50 mm×50 mm. Herein, samples with cracks or non-graphitization observed in the evaluation of (1) surface quality are marked as "unmeasurable". The results are shown in Table 3. table 3 Example 4 Example 5 Example 6 Comparative example 5 Comparative example 6 Comparative example 7 Comparative example 8 crack Not observed Not observed Not observed Have observed Have observed Have observed Have observed Surface quality good good good difference difference ordinary ordinary Damage rate of the second surface 0% 0% 0% Poor quality Poor quality Poor quality Poor quality In-plane thermal conductivity (W/m·K) 1,000 800 1,100 Can not be measured Can not be measured Can not be measured Can not be measured Number of highlights (EA) 1 2 0 Can not be measured Can not be measured Can not be measured Can not be measured Related schema Figure 1 - - Figure 3 - Picture 2 -

Although some embodiments have been described herein, it should be understood that those skilled in the art can make various changes, substitutions, substitutions, and equivalent embodiments of the present invention without departing from the spirit and scope of the present invention. .

no.

Figure 1 is an image showing the surface quality evaluation result of the polyimide film prepared in Example 1. Figure 2 is an image showing the results of surface quality evaluation of the polyimide film prepared in Comparative Example 7. Figure 3 is an image showing the surface quality evaluation result of the polyimide film prepared in Comparative Example 5. Figure 4 is a diagram illustrating the area measurement method in the first surface damage rate measurement step according to the present invention.

Claims (10)

A graphite sheet with a thickness of 50 µm to 100 µm and a second surface damage rate of 0% to 0.004%. The second surface damage rate is shown in Equation 2: The second surface damage rate (%)={(B ₁ / B ₀ )×100}, ---(2) Where B ₀ ^{is the area (in mm 2} ) of a graphite sheet sample measured using a graphite sheet sample image under 10x magnification, and B ₁ is used ^{The area of the damaged area (in mm 2} ) of the graphite sheet sample measured by the graphite sheet sample image at a magnification of 10 times. The graphite sheet according to claim 1, wherein the graphite sheet is formed of a polyimide film with a thickness of 100 µm to 200 µm. The graphite sheet according to claim 1, wherein the graphite sheet is obtained by carbonization and graphitization of a polyimide film with a thickness of 100 µm to 200 µm. The graphite sheet according to claim 1, wherein the graphite sheet has an in-plane thermal conductivity of 800 W/m·K to 1,200 W/m·K. A method for preparing graphite flakes includes: preparing a carbonized flake by heating a polyimide film from 15°C to 1,200°C; and heating from about 1,200°C to about 2,800°C at a stepwise heating rate , To graphitize the carbonized sheet to prepare a graphite sheet with a thickness of 50 µm to 100 µm, wherein the graphite sheet has a second surface damage rate of 0% to 0.004%, and the second surface damage rate is shown in Equation 2 ： The second surface damage rate (%)={(B ₁ /B ₀ )×100}, ---(2) Where B ₀ is a graphite sheet sample measured using a graphite sheet sample image under 10 times magnification The area (in mm ² as a unit), and B ₁ ^{is the damaged area (in mm 2} as a unit) of the graphite sheet sample measured using the graphite sheet sample image at a magnification of 10 times. The method for preparing a graphite sheet according to claim 5, wherein the preparation of the carbonized sheet includes thermally cracking the polyimide film by heating at a heating rate of 1°C/min to 5°C/min. The method for preparing a graphite sheet according to claim 5, wherein the preparation of the graphite sheet includes: performing the initial graphitization of the carbonized sheet by heating from 1,200°C to 2,200°C; and by heating from 2,200°C to 2,500°C C, to perform the secondary graphitization of the primary graphitized carbonized sheet; and by heating from 2,500°C to 2,800°C, to perform the tertiary graphitization of the secondary graphitized carbonized sheet. The graphite sheet preparation method according to claim 7, wherein: The initial graphitization of the carbonized sheet is carried out at a heating rate of 1.5 °C/min to 5 °C/min; The secondary graphitization of the carbonized sheet after the primary graphitization is performed at a heating rate of 0.4 °C/min to 1.3 °C/min; and The third graphitization of the second graphitized carbonized sheet is performed at a heating rate of 8.5 °C/min to 20 °C/min. The method for preparing a graphite sheet according to claim 5, wherein the polyimide film has a thickness of 100 µm to 200 µm. The method for preparing a graphite sheet according to claim 5, wherein the graphite sheet has an in-plane thermal conductivity of 800 W/m·K to 1,200 W/m·K.

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