TWI775102B - Polyimide film for graphite sheet and manufacturing method for the polyimide film - Google Patents

Abstract

Disclosed herein are a polyimide film for graphite sheets and a method of preparing the same. The polyimide film is formed of a polyimide film composition including a polyamic acid; and an imidization catalyst, and has a thickness of 100 µm to 200 µm and a first surface damage rate of 0% to 0.004%, as represented by Equation 1.

Description

Polyimide film for graphite sheet and method for producing the same

This application claims the benefit of Korean Patent Application No. 10-2019-0078274, filed with the Korea Intellectual Property Office on June 28, 2019, the entire contents of which are incorporated herein by reference in their entirety.

The present invention relates to a polyimide film for thick graphite sheets and a manufacturing method of the polyimide film for thick graphite sheets.

Graphite has good thermal conductivity and is highly favored as a means of dissipating heat. Specifically, the artificial graphite prepared in the form of flakes has a thermal conductivity of 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 in weight and size and the improvement in compactness and integration, the amount of heat generated 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 reduction in the operating speed of the semiconductor due to thermal load, a reduction in lifetime due to deterioration of the battery, or the like.

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

Artificial graphite flakes are usually prepared by carbonization and graphitization of polyimide films as precursors. Depending on the degree of thickness desired, thick polyimide films, eg, polyimide films having a thickness of 100 μm or more, can be used to prepare thick graphite flakes.

However, the use of such thick polyimide films to prepare graphite sheets has the problem of difficulty in obtaining high-quality graphite sheets with smooth surfaces and without damaging the graphite structure therein upon heat treatment, which will result in lower yield.

It is thought to be caused by, assuming that the carbonization and graphitization of the surface layer and the interior of the polyimide film are almost simultaneously carried out, the graphite structure that has been formed or is forming in the surface layer may be due to a large amount of sublimation in the thick polyimide film. gas and collapse or break. Another reason is that the graphitic structures that have formed or are forming in the inner portion in and near the middle of the film 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 technique capable of producing high-quality thick graphite flakes with good surface quality and intact graphite structure.

An object of the present invention is to provide a polyimide film that can prepare graphite flakes with low brittleness and good surface quality, and a desired large thickness, and a method for preparing the same.

Another object of the present invention is to provide a method for producing graphite flakes with low brittleness and good surface quality and thermal conductivity, while having a desired large thickness.

The above and other objects of the present invention will become apparent from the detailed description with reference to the following examples.

One embodiment of the present invention relates to a polyimide film for graphite sheets, which is formed from a polyimide film composition comprising: polyimide; and polyimide The above-mentioned polyimide film has a thickness of 100 µm to 200 µm and a first surface damage rate of 0% or 0.001% to 0.004%, and the first surface damage rate is represented by the following Equation 1: [Equation 1] First surface breakage rate (%)={(A ₁ /A ₀ )×100}, where A ₀ is the graphite flake sample area (mm ² ) measured using an image of the graphite flake sample at 10X magnification, and A ₁ is the damaged area area (mm ² ) of the graphite flake sample measured using an image of the graphite flake sample at 10X magnification, obtained by the following steps: Carbonization of polyimide film samples with dimensions of 200 mm x 25 mm by heating at a heating rate from 15°C to 1,200°C; C to 2,200°C for primary graphitization of carbonized polyimide film samples; by heating from 2,200°C to 2,500°C at a heating rate of 0.4°C/min to 1.3°C/min secondary graphitizing the primary graphitized polyimide film sample; and secondary graphitizing the secondary graphitization by heating from 2,500°C to 2,800°C at a heating rate of 8.5°C/min to 20°C/min The graphitized polyimide film samples were graphitized three times.

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

In an embodiment, the polyimide film composition may include: 100 parts by weight of polyimide; and 17 parts by weight to 36 parts by weight of an imidization catalyst.

In an embodiment, the polyimide film composition may further comprise 1,500 ppm to 2,500 ppm of an inorganic filler relative to 100 parts by weight of the polyimide, and the inorganic filler comprises calcium carbonate, dicalcium phosphate, calcium hydrogen phosphate, At least one of barium sulfate, silicon oxide, titanium oxide, aluminum oxide, silicon nitride, and boron nitride.

Another embodiment of the present invention relates to a method for preparing a polyimide film for graphite sheets, the method comprising: using a polyimide film composition comprising polyimide and an imidization catalyst , by gelling the polyimide film composition at a temperature of 100°C to 200°C to make a film with a thickness of 100 µm to 200 µm; at a temperature of 200°C to 400°C, the gelled The primary imidization of the polyimide film composition; and the secondary imidization of the primary imidized polyimide film composition at a temperature of 300°C to 500°C, wherein the polyimide The imine film has a first surface breakage rate of 0%, or 0.001% to 0.004%, which is represented by Equation 1.

A further embodiment of the present invention relates to a method for preparing a thick graphite sheet, comprising: preparing a carbonized sheet by heating the above-mentioned polyimide film from 15°C to 1,200°C; and by gradually changing the heating rate from 1,200°C °C to 2,800°C to graphitize the carbonized sheet to prepare a graphite sheet having a thickness of 50 µm to 100 µm, wherein the graphite sheet has a second surface breakage rate of 0% or 0.001% to 0.004%. The two-surface breakage rate is represented by the following equation 2: [Equation 2] The second-surface breakage rate (%)={(B ₁ /B ₀ )×100}, where B ₀ is the image of the graphite flake sample using 10x magnification Graphite flake sample area measured (mm ² ), and B ₁ is the broken area area (mm ² ) of the graphite flake sample measured using an image of the graphite flake sample at 10X magnification.

The step of preparing the carbonized sheet may comprise thermally cracking the polyimide film by heating at a heating rate of 1°C/min to 5°C/min.

The step of graphitizing the carbide sheet may include: performing primary graphitization of the carbide sheet by heating from 1,200°C to 2,200°C; performing secondary graphitization of the carbide sheet by heating from 2,200°C to 2,500°C ; and tertiary graphitization of the carbonized sheet by heating from 2,500°C to 2,800°C.

The step of primary graphitizing the carbonized sheet may be performed at a heating rate of 1.5 °C/min to 5 °C/min; the step of secondary graphitizing the carbonized sheet may be performed at a heating rate of 0.4 °C/min to 1.3 °C/min and the step of making the carbonized sheet tertiary graphitization can be carried out at a heating rate of 8.5 °C/min to 20 °C/min.

In the embodiment, the molar ratio of the amide group of the polyamide and the amide imidization catalyst in the polyimide film composition may be 1:0.15 to 1:0.20.

In an embodiment, the polyimide film composition may include: 100 parts by weight of polyimide; and 17 parts by weight to 36 parts by weight of an imidization catalyst.

In an embodiment, the polyimide film composition may further comprise 1,500 ppm to 2,500 ppm of an inorganic filler relative to 100 parts by weight of the polyimide, and the inorganic filler comprises calcium carbonate, dicalcium phosphate, calcium hydrogen phosphate, At least one of barium sulfate, silicon oxide, titanium oxide, aluminum oxide, silicon nitride and boron nitride.

The present invention provides a polyimide film that can be made into graphite flakes with low brittleness and good surface quality while having a desired large thickness, a preparation method thereof, and preparations using the same with low brittleness and good surface quality and thermal conductivity rate while having the required large thickness of graphite flakes.

Descriptions of known functions and constructions that may unnecessarily obscure the objects 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 refer specifically to the stated features The presence of components, integers, steps, operations, elements, components, and/or groups thereof, but does not preclude 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 (a)" and "an (an)" are used in this specification, they are also intended to include the plural forms unless the context clearly dictates otherwise.

Additionally, unless expressly stated otherwise, numerical values relating to a particular component should be construed as including a tolerance range in the interpretation of the component.

It will be understood that, although the terms "first", "second", etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, Layers and/or sections 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 denote a particular numerical range means "≥a and ≤b".

Polyimide film

One embodiment of the present invention relates to a polyimide film for graphite flakes. The polyimide film for graphite sheets according to the present invention is formed from a polyimide film composition, and the polyimide film composition includes: polyimide; and an imidization catalyst, which is a condensed Gelled and imidized polyimide membrane composition products.

The polyimide film for graphite sheets according to the present invention has 100 µm to 200 µm (eg, 100 µm, 110 µm, 120 µm, 130 µm, 140 µm, 150 µm, 160 µm, 170 µm, 180 µm, 190 µm µm, or 200 µm), which is larger than that of conventional polyimide films, and thus can be made through its carbonization and graphitization to have a thickness of 50 µm to 100 µm (eg, 50 µm, 60 µm, 70 µm, 80 µm, 90 µm, or 100 µm) graphite flakes.

In addition, the polyimide film for graphite sheets according to the present invention has 0% to 0.004% (eg, 0%, 0.001%, 0.002%, 0.003%, or 0.004%, in another example, 0% or 0.001% % to 0.004%) of the first surface breakage rate, as shown in Equation 1, and can therefore be made with both good surface quality and thicknesses of 50 µm to 100 µm (eg, 50 µm, 60 µm, 70 µm, 80 µm , 90 µm, or 100 µm) graphite flakes.

[Equation 1] First surface damage rate (%)={(A ₁ /A ₀ )×100},

where A ₀ is the area of the graphite flake sample (mm ² ) measured using an image of the graphite flake sample at 10X magnification, and A ₁ is the damaged area area of the graphite flake sample measured using an image of the graphite flake sample at 10X magnification (mm ² ), the graphite flake samples were obtained by the following steps: °C/min, or 5°C/min) heating rate from 15°C to 1,200°C to carbonize polyimide film samples with dimensions of 200 mm × 25 mm; by heating at 1.5 °C/min min to 5 °C/min (for example, 1.5 °C/min, 2 °C/min, 2.5 °C/min, 3 °C/min, 3.5 °C/min, 4 °C/min, 4.5 °C/min Min, or 5 °C/min) heating rate from 1,200 °C to 2,200 °C to primary graphitize carbonized polyimide film samples; min (for example, 0.4 °C/min, 0.5 °C/min, 0.6 °C/min, 0.7 °C/min, 0.8 °C/min, 0.9 °C/min, 1 °C/min, 1.1 °C/min min, 1.2 °C/min, or 1.3 °C/min) from 2,200°C to 2,500°C to secondary graphitize the primary graphitized polyimide film sample; and by heating with 8.5 °C/min to 20 °C/min (for example, 8.5 °C/min, 9 °C/min, 9.5 °C/min, 10 °C/min, 10.5 °C/min, 11 °C/min, 11.5 °C/min, 12 °C/min, 12.5 °C/min, 13 °C/min, 13.5 °C/min, 14 °C/min, 14.5 °C/min, 15 °C/min, 15.5 ° C/min, 16 °C/min, 16.5 °C/min, 17 °C/min, 17.5 °C/min, 18 °C/min, 18.5 °C/min, 19 °C/min, 19.5 °C/min min, or 20°C/min) heating rate from 2,500°C to 2,800°C to tertiarily graphitize the secondary graphitized polyimide film samples.

Specifically, the first surface breakage rate may represent a surface breakage rate measured on a graphite flake sample prepared by the following steps: by heating at a rate of 1°C/min to 5°C/min from Carbonization of polyimide film samples measuring 200 mm x 25 mm by heating from 15°C to 1,200°C; by heating from 1,200°C to 2,200°C for primary graphitization of carbonized polyimide film samples; primary graphitization by heating from 2,200°C to 2,500°C at a heating rate of 0.4°C/min to 1.3°C/min The graphitized polyimide film samples were re-graphitized; and the re-graphitized Polyimide film samples were graphitized three times.

More specifically, the first surface breakage rate may represent a surface breakage rate measured on a graphite flake sample prepared by the following steps: heating from 15°C by a heating rate of 1°C/min. to 1,200°C to carbonize a polyimide film sample with dimensions of 200 mm × 25 mm and a thickness of 125 µm; by heating from 1,200°C to 2,200°C at a heating rate of 1.5 °C/min. Primary graphitization of carbonized polyimide film samples; secondary graphitization of primary graphitized polyimide film samples by heating from 2,200°C to 2,500°C at a heating rate of 0.4 °C/min and tertiary graphitization of the secondary graphitized polyimide film samples by heating from 2,500°C to 2,800°C at a heating rate of 8.5°C/min.

In the first surface breakage rate, A ₀ is the area of the graphite flake sample (in mm _{) measured using an image of the graphite flake sample taken at 10x magnification using a digital camera and A 1} ^is the area of the graphite flake sample measured using a digital camera at 10 The area of the damaged area (in mm ² ) of the graphite flake sample measured by the image of the graphite flake sample taken at double magnification.

Here, it can be done by applying a filter with a grid of 1 mm × 1 mm square cells to a digital image of the graphite flake sample at 10x magnification, and then visually counting the square cells included in each area counts, whereby the measurement steps for each area are performed.

FIG. 4 is a diagram illustrating an area measurement method in the measurement step of the first surface damage ratio represented by Equation 1. FIG. Referring to FIG. 4, in the measurement step of the first surface breakage rate represented by Equation 1, a digital image of the prepared graphite sheet sample under 10 times magnification was obtained, and then a mesh with 1 mm × 1 mm square cells was A grid filter is used for the above digital image, as shown in Figure 4(a). Here, each cell grid has an area of 1 ^mm2 . In the first surface breakage rate, A ₀ is measured by counting cells in which the graphite sheet occupies 50% or more of the cell area, as shown in Fig. 4(b). Referring to Figure 4(b), A ₀ has a value of 200 mm ² because a total of 200 cells are contained in A ₀ . In the first surface breakage rate, A1 is measured by calculating, among the cells included in _A0 , cells in which 50% or more of the cell area occupied by the graphite flakes are visually confirmed to be broken, as shown in _Fig . 4 (c ) shown. Referring to Figure 4(c), since a total of 159 cells are contained in A1, A1 has _a value _of 159 ^mm2 . Putting the values of A ₀ and A ₁ into Equation 1, the first surface failure rate measured on the exemplary 20 mm x 10 mm graphite flake sample of Figure 4 was determined to be 79.5%.

Conventional polyimide films exhibit a high surface breakage rate when used to prepare thick graphite sheets with a thickness of 50 µm to 100 µm, and thus it is difficult to ensure that the graphite sheets have the required large thickness and good surface quality at the same time. In contrast, the polyimide films according to the present invention can be made into graphite sheets with low brittleness and good surface quality while having the desired large thickness.

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

＜Polyamic acid＞

The polyimide film composition of polyimide is used as a precursor for conversion to polyimide by an 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 the raw material of polyamide may include 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'- 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(3,4-dicarboxyphenyl)ethane dianhydride (1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride), bis(2,3-dicarboxyphenyl)methane dianhydride ( bis(2,3-dicarboxyphenyl)methane dianhydride), bis(3,4-dicarboxyphenyl)ethane dianhydride, oxydiphthalic anhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, p-phenylene-bis(trimellitic monoester) acid anhydride)), ethylene- Ethylene-bis(trimellitic monoester acid anhydride), bisphenol-A-bis(trimellitic monoester acid anhydride) , and at least one of its derivatives. The use of these exemplary dianhydride monomers results in polyamic acids having both improved imidization efficiency and improved uniformity. Additionally, these exemplary dianhydride monomers can be used alone or in mixtures thereof.

Examples of diamine monomers that can be used as raw materials for polyamides may include 4,4'-diaminodiphenylpropane (4,4'-diaminodiphenylpropane), 4,4'-diaminodiphenylmethane (4,4'-diaminodiphenylpropane) diaminodiphenylmethane), benzidine (benzidine), 3,3'-dichlorobenzidine (3,3'-dichlorobenzidine), 4,4'-diaminodiphenylsulfide (4,4'-diaminodiphenylsulfide), 3,3 '-Diaminodiphenylsulfone (3,3'-diaminodiphenylsulfone), 4,4'-diaminodiphenylsulfone (4,4'-diaminodiphenylsulfone), 4,4'-diaminodiphenylsulfone (4,4'-diaminodiphenylsulfone) -Oxydianiline)(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'-diaminodiphenylsilane (4,4'-diaminodiphenyldiethylsilane) -diaminodiphenylsilane), 4,4'-diaminodiphenylethylphosphine oxide (4,4'-diaminodiphenylethylphosphine oxide), 4,4'-diaminodiphenyl-N-methylamine (4,4'-diaminodiphenylethylphosphine oxide) diaminodiphenyl-N-methylamine), 4,4'-diaminodiphenyl-N-phenylamine (4,4'-diaminodiphenyl-N-phenylamine), 1,4-diaminobenzene (p-phenylenediamine) (1, At least one of 4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene (1,3-diaminobenzene), 1,2-diaminobenzene (1,2-diaminobenzene), and derivatives thereof. The use of these exemplary diamine monomers results in polyamic acids having both improved imidization efficiency and improved uniformity. Additionally, these exemplary diamine monomers can be used alone or in mixtures thereof.

For example, dianhydride monomers and diamine monomers that can be used as polyamide raw materials can be combined in a molar ratio of 1:0.9 to 1:1.1 (eg, 1:0.9, 1:1, or 1:1.1) For the polymerization of polyamide acid. Within this range, a polyamic acid having both improved imidization efficiency and improved uniformity can be obtained.

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

聚醯胺酸可具有90,000 cP至500,000 cP(例如， 90,000 cP、100,000 cP、110,000 cP、120,000 cP、130,000 cP、140,000 cP、150,000 cP、160,000 cP、170,000 cP、180,000 cP、190,000 cP、200,000 cP、 210,000 cP、220,000 cP、230,000 cP、240,000 cP、250,000 cP、260,000 cP、270,000 cP、280,000 cP、290,000 cP、300,000 cP、310,000 cP、320,000 cP、330,000 cP、340,000 cP、350,000 cP、360,000 cP、370,000 cP 380,000 CP, 390,000 CP, 400,000 CP, 410,000 CP, 420,000 CP, 430,000 CP, 440,000 CP, 450,000 CP, 460,000 CP, 470,000 CP, 480,000 CP, or 500,000 CP), especially 150,000 CP to 400,000 CP to 400,000 CP. More particularly, but not limited to, viscosities of 180,000 cP to 300,000 cP. Within this range, polyimide can further improve heat resistance and mechanical properties of the polyimide film according to the present invention.

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

The organic solvent may include any organic solvent capable of dissolving the polyamic 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'-dimethylacetamide (N,N'-dimethylformamide (N,N'-dimethylformamide) , 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 the organic solvent, an auxiliary solvent may be further used as necessary to adjust the solubility of the polyamic acid. Examples of the auxiliary solvent may include toluene, tetrahydrofuran, acetone, methyl ethyl ketone, methanol, ethanol and water.

When the polyamic acid is dissolved in an organic solvent and used in the form of a polyamic acid solution, the polyamic acid solution may contain 15 wt % to 20 wt % (for example, 15 wt %, 16 wt %, 17 wt %, 18 wt %, 19 wt %, or 20 wt %) of polyamic acid (solids) and 80 wt % to 85 wt % (eg, 80 wt %, 81 wt %, 82 wt %, 83 wt %, 84 wt % %, or 85 wt%) of organic solvents. 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 membrane composition is used to promote the conversion of polyimide to polyimide.

The imidization catalysts may include amine-based catalysts, such as aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines ( heterocyclic tertiary amines). Among them, heterocyclic tertiary amines may be preferred in terms of catalytic reactivity. Examples of heterocyclic tertiary amines include quinoline, isoquinoline, beta-picoline (BP), and pyridine. They can be used alone or in mixtures thereof.

In one embodiment, the imidization catalyst in the polyimide film composition may be in the range of 0.15 mol to 0.2 mol, for example, 0.15 mol, 0.16 mol, relative to 1 mol of the amide group of the polyimide acid. The amount of mol, 0.17 mol, 0.18 mol, 0.19 mol, or 0.20 mol is present. In 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 may be 17 parts by weight to 36 parts by weight (for example, 17 parts by weight, 18 parts by weight, 18 parts by weight) relative to 100 parts by weight of the polyimide acid. parts, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, 31 parts by weight, 32 parts by weight, 33 parts by weight, 34 parts by weight, 35 parts by weight, or 36 parts by weight) are present. Within this range, the imidization catalyst can make the polyimide film according to the present invention have a more regular matrix structure and further improve the crystallinity of the polyimide film.

＜Inorganic filler＞

In addition to the above components, the polyimide film composition may further contain an inorganic filler. The inorganic filler is dispersed in the matrix of the polyimide film and sublimes 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 gaps created by foaming can improve the bending resistance of graphite sheets prepared using polyimide films. In addition, since the inorganic filler is sublimated during the carbonization and/or graphitization of the polyimide film, and the polyimide is converted into graphite, it is possible to obtain graphite sheets with a highly regular and well-arranged structure. In addition, the inorganic filler can be used as a channel for releasing gas when it sublimates, thereby preventing surface defects and breakage caused by foaming.

The inorganic filler may include any inorganic filler that can be sublimated at a temperature of 1000° C. or higher, without limitation. In particular, the inorganic filler may include at least one of calcium carbonate, dicalcium phosphate, calcium hydrogen phosphate, barium sulfate, silicon oxide, titanium oxide, aluminum oxide, silicon nitride, and boron nitride. Thick graphite sheets with improved bending resistance and structural uniformity can be obtained using such inorganic fillers. Such exemplary inorganic fillers may be used alone or in mixtures thereof.

The inorganic filler in the polyimide film composition may be 1,500 ppm to 2,500 ppm, particularly 1,250 ppm to 2,250 ppm, more particularly 1,500 ppm to 2,000 ppm, relative to 100 parts by weight of the polyamide acid. amount exists. In this range, the sublimation gas generated in the polyimide film after 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 flakes prepared by the film, and at the same time, the polyimide structure can be converted into an artificial graphite structure with high efficiency.

The inorganic filler may have an average particle size of 1.5 µm to 4.5 µm (eg, 1.5 µm, 2 µm, 2.5 µm, 3 µm, 3.5 µm, 4 µm, or 4.5 µm), but not limited thereto. In this range, the inorganic filler can prevent the surface roughness of the polyimide film from being excessively reduced, and can further reduce the generation 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 by dehydration of the polyamide. In particular, the dehydrating agent may include aliphatic acid anhydrides, aromatic acid anhydrides, N,N'-dialkylcarbodiimide, halogenated Halogenated lower aliphatic acids, halogenated lower fatty acid anhydrides, arylphosphonic acid dihalides, thionyl halides or a mixture thereof.

Of these, aliphatic acid anhydrides such as acetic acid anhydride, propionic acid anhydride, and lactic acid anhydride, or mixtures thereof may be preferred in terms of availability and cost reduction of.

The dehydrating agent may be present in the polyimide film composition in an amount of 0.5 mol to 5 mol relative to 1 mol of the amide group of the polyamide. Within this range, the polyimide film composition can have a further improved imidization efficiency through the dehydration of the polyimide.

Preparation method of polyimide film

Another embodiment of the present invention relates to a method for preparing a polyimide film for thick graphite sheets, the method comprising: passing through a temperature of 100°C to 200°C (eg, 100°C, 110°C) , 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C), the gelled polyimide film is composed of material, the polyimide film composition comprising polyimide and imidization catalyst is formed into a thin film with a thickness of 100 μm to 200 μm; C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, initial imidization of the gelled polyimide film composition at a temperature of 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, or 400°C); and at 300°C to 500°C (for example, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C , 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, or 500°C), the The primary imidized polyimide membrane composition is secondary imidized. The method according to the present invention allows for a more economical and efficient production of polyimide films that can be made into graphite sheets with both low brittleness and the desired large thickness.

Additionally, polyimide films prepared according to the methods of the present invention may have 0% to 0.004% (eg, 0%, 0.001%, 0.002%, 0.003%, or 0.004%, eg, 0% or 0.001% to 0.004%) ), 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 group of the polyamide and the imidization catalyst can be 1:0.15 to 1:0.20 (eg, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19 , or a molar ratio of 1:0.20) in the polyimide film composition.

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

In addition, the polyimide film composition may further include 1,500 ppm to 2,500 ppm (eg, 1,500 ppm, 1,600 ppm, 1,700 ppm, 1,800 ppm, 1,900 ppm, 2,000 ppm, 2,100 ppm) relative to 100 parts by weight of the polyimide acid. ppm, 2,200 ppm, 2,300 ppm, 2,400 ppm, or 2,500 ppm) inorganic fillers. The inorganic filler may include at least one 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 comprise preparing polyimide before gelling the polyimide film composition. The preparation of the polyamic acid herein can be performed by any suitable method known in the art, such as, but not limited to, emulsion polymerization, solution polymerization, bulk polymerization, and suspension polymerization.

In the method for preparing the polyimide film, if the polyimide film composition is gelled at a temperature lower than 100° C., it is difficult to form the polyimide film composition into polyimide. membrane. If the polyimide film composition is gelled at a temperature higher than 200°C, the polyimide film composition may be excessively gelled, resulting in high brittleness of graphite sheets prepared using the resulting polyimide film .

Specifically, the gelation of the polyimide film composition can be achieved by a process in which the polyimide film composition is provided in a solution and then the polyimide film composition is applied to a support and then dried. to prepare a sheet-like gel. The support member may be a glass plate, an aluminum foil, an endless stainless belt, or a stainless drum, but not limited thereto. The polyimide film composition can be coated by casting, for example, but not limited thereto. Here, the polyimide film composition can be made into a self-supporting sheet-like gel by drying and gelling at the above-mentioned gelling temperature for about 10 to about 20 minutes.

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

The resulting polyimide films can have 100 µm to 200 µm (eg, 100 µm, 110 µm, 120 µm, 130 µm, 140 µm, 150 µm, 160 µm, 170 µm, 180 µm, 190 µm, or 200 µm )thickness of. If the thickness of the polyimide film is less than 100 µm, it is difficult to prepare thick graphite flakes with the polyimide film. If the thickness of the polyimide film exceeds 200 µm, the graphite flakes prepared using the polyimide film may be too brittle.

Graphite flakes

A further embodiment of the present invention relates to a method of making a thick graphite sheet having a second surface breakage rate of 0% or 0.001% to 0.004%, the second surface breakage rate being represented by Equation 2. For example, the graphite flakes may have a second surface failure rate of 0%, 0.001%, 0.002%, 0.003%, or 0.004%. In another example, the graphite flakes may have a second surface failure rate of 0% or 0.001% to 0.004%.

The method for preparing a thick graphite sheet comprises: preparing a carbonized sheet by heating a polyimide film from 15°C to 1,200°C; and carbonizing the above by heating from 1,200°C to 2,800°C at a stepwise heating rate flake graphitization to produce graphite flakes with thicknesses ranging from 50 µm to 100 µm.

[Equation 2] Second surface damage rate (%)={(B ₁ /B ₀ )×100},

where B ₀ is the area of the graphite flake sample (mm ² ) measured using an image of the graphite flake sample at 10X magnification, and B ₁ is the damaged area area of the graphite flake sample measured using an image of the graphite flake sample at 10X magnification (mm ² ).

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

The polyimide film may be the above-mentioned polyimide film. The polyimide film may be formed from a polyimide film composition comprising polyimide and an imidization catalyst, and may have a thickness of 100 µm to 200 µm and a first surface of 0% or 0.001% to 0.004% The breakage rate, the first surface breakage rate, is expressed as Equation 1 described above for the above-mentioned polyimide film.

Because the polyimide film used in the production method of the thick graphite sheet according to the present invention is the same as the above-mentioned polyimide film according to the present invention, and it is produced by the production method of the polyimide film according to the present invention , so a detailed description thereof will be omitted.

<Carbonization step>

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

Specifically, polyimide can be performed by introducing a polyimide film into a high temperature furnace such as an electric furnace, and then heating it from 15°C to 1,200°C in a nitrogen/argon atmosphere in a 12 to 14 hour process Carbonization of the imine film, thereby converting the polyimide film into a carbonized sheet.

Additionally, heating may be between 1°C/min to 5°C/min (eg, 1°C/min, 2°C/min, 3°C/min, 4°C/min, or 5°C/min) speed for the preparation of carbonized sheets. In this heating rate range, the polymer chains of the polyimide film can be sufficiently thermally decomposed to obtain carbonized sheets with amorphous carbon bodies, which can be made into graphite sheets through graphitization.

<Graphitization step>

In the preparation method of thick graphite flakes, the preparation of graphite flakes involves graphitizing the carbonized flakes obtained in the carbonization step by heating from 1,200°C to 2,800°C at a stepwise heating rate to prepare a thickness of 50 µm. to 100 µm graphite flakes. 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 carbide sheets can be introduced into a high-temperature furnace facility such as an electric furnace through which they are then gradually heated from 1,200°C to 2,800°C in a 10 to 14-hour process in a mixed gas atmosphere of nitrogen, argon and a small amount of helium. °C to perform the graphitization of the carbonized sheet, but not limited thereto.

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

More specifically, 1.5 °C/min to 5 °C/min (e.g., 1.5 °C/min, 2 °C/min, 2.5 °C/min, 3 °C/min, 3.5 °C/min) , 4 °C/min, 4.5 °C/min, or 5 °C/min) for the primary graphitization of the carbide sheet, which can pass through 0.4 °C/min to 1.3 °C/min (for example, 0.4 °C/min). C/min, 0.5 °C/min, 0.6 °C/min, 0.7 °C/min, 0.8 °C/min, 0.9 °C/min, 1 °C/min, 1.1 °C/min, 1.2 °C/min min, or 1.3 °C/min) heating rate for secondary graphitization of the primary graphitized carbide sheet, and can pass through 8.5 °C/min to 20 °C/min (for example, 8.5 °C/min, 9 °C/min, 9.5 °C/min, 10 °C/min, 10.5 °C/min, 11 °C/min, 11.5 °C/min, 12 °C/min, 12.5 °C/min, 13 ° C/min, 13.5 °C/min, 14 °C/min, 14.5 °C/min, 15 °C/min, 15.5 °C/min, 16 °C/min, 16.5 °C/min, 17 °C/min min, 17.5 °C/min, 18 °C/min, 18.5 °C/min, 19 °C/min, 19.5 °C/min, or 20 °C/min) heating rates for regraphitized Tertiary graphitization of carbonized sheets. In this way, the rearrangement of carbon in the amorphous carbon body of the carbonized sheet can be achieved with high 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 primary to tertiary graphitization processes are respectively performed at the above-mentioned heating rate within the above-mentioned temperature range, the gas generated during the preparation of the graphite sheet can be stably discharged, so as to further prevent the surface of the graphite sheet from being damaged, and thus further make the equation 1 and 2 indicates that the surface damage rate drops to close to 0%.

The method for preparing the thick graphite flakes may further include: after preparing the graphite flakes at 5°C/min to 10°C/min (for example, 5°C/min, 6°C/min, 7°C/min, 8°C/min) The prepared graphite flakes were cooled at a cooling rate of C/min, 9°C/min, or 10°C/min). In this way, the graphite flakes can have a further reduced brittleness and a further improved surface quality.

Yet another embodiment of the present invention relates to a thick graphite sheet prepared by the above-mentioned method for preparing a thick graphite sheet. The above-mentioned thick graphite sheet has a thickness of 50 µm to 100 µm. In this range, the graphite sheet can have good heat capacity, and thus has the characteristics of being used more favorably as a heat sink for electronic devices.

Thick graphite flakes are prepared using polyimide films with thicknesses ranging from 100 µm to about 200 µm. In addition, thick graphite flakes can be obtained by carbonizing and graphitizing polyimide films with thicknesses ranging from 100 µm to about 200 µm. In this example, the thick graphite sheet may have a thickness of 50 μm to 100 μm and may have a good heat capacity, and thus have characteristics more favorable for use as a heat sink for electronic devices.

The thick graphite sheet has a second surface breakage rate of 0%, or 0.001% to 0.004%, which is represented by Equation 2, and thus may have good surface quality. Within this range, the thick graphite sheet may have characteristics that are more advantageously used as a heat sink for electronic devices.

In addition, the thick graphite sheet may have an in-plane thermal conductivity of 800 W/m·K or higher, particularly 800 W/m·K to 1,200 W/m·K. Within this range, the graphite sheet may have characteristics that are more advantageously used as a heat sink for electronic devices.

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

Examples and Comparative Examples

Example 1

After putting dimethylformamide (DMF) as an organic solvent into a 0.5 L reactor in a nitrogen atmosphere, oxydiphenylamine (ODA, 3, 3'-oxydianiline (3,3'-oxydianiline) or 4,4'-oxydianiline (4,4'-oxydianiline) and pyromellitic dianhydride (PMDA) as dianhydride monomers ), followed by polymerization to prepare a polyamic acid solution. Here, the weight ratio of solid matter and 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 polyamic acid solution, followed by stirring to obtain a precursor composition.

Then, β-picoline as an imidization catalyst was added in an amount of 0.17 mol relative to 1 mol of the amide group, followed by uniform mixing and defoaming, thereby preparing polyimide membrane 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 500 µm gap, followed by hot air at a temperature of 100°C to 200°C drying, thereby preparing 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 subjected to primary imidization at a temperature of 200°C to 400°C For 10 minutes, and a 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 processes was cooled to 25°C, and then separated from the pin frame, so as to obtain a polyamide with a size of 20 cm × 2.5 cm and a thickness of 125 µm imine film.

Example 2 to 3

Except that the solvent amount in the polyimide solution and the molar amount of the imidization catalyst (β-picoline) in the polyimide film composition were changed as listed in Table 1, the same procedure as in Example 1 was used. A polyimide film with a thickness of 125 µm was obtained.

example 4

Carbonized sheets were prepared by carbonizing the polyimide film obtained in Example 1 by heating from 50°C to 1,200°C at a heating rate of about 1°C/min.

The carbonized sheet is then subjected to a primary to tertiary graphitization process in which the carbonized sheet is baked by heating from about 1,200°C to about 2,800°C at a step-by-step heating rate, thereby producing a graphite sheet with a final thickness of 50 µm . Specifically, in the primary graphitization process, the carbide 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 was heated from about 2,200°C to about 2,500°C at a heating rate of 0.4°C/min, and in the tertiary graphitization process, the secondary graphitized carbide sheet was heated by heating at 8.5°C/min. The heating rate for min is from about 2,500°C to about 2,800°C.

example 5

A graphite sheet having a final thickness of 50 µm was prepared in the same manner as in Example 4, except that the polyimide film prepared in Example 2 was used instead of the polyimide film prepared in Example 1.

example 6

A graphite sheet having a final thickness of 50 µm was prepared in the same manner as in Example 4, except that the polyimide film prepared in Example 3 was used instead of the polyimide film prepared in Example 1.

Comparative example 1( thermal method (thermal method))

After dimethylformamide (DMF) was put into a 0.5 L reactor as an organic solvent in a nitrogen atmosphere, oxydianiline (ODA, 3,3') was added as a diamine monomer in a weight ratio of 1:1. -oxydianiline) and pyromellitic dianhydride (PMDA) as a dianhydride monomer, followed by polymerization, whereby a polyamic acid solution was prepared. Here, the weight ratio of solid matter and 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 polyamic acid solution, followed by stirring to obtain a precursor composition.

Then, β-picoline as an imidization catalyst was added in an amount of 0.17 mol relative to 1 mol of the amide group, followed by uniform mixing and defoaming, thereby preparing a 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 500 µm gap, followed by hot air at a temperature of 100°C to 200°C drying, thereby preparing a sheet-like gel.

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

Comparative example 2( Catalytic method - General catalytic method (general catalytic method))

After dimethylformamide (DMF) was put into a 0.5 L reactor as an organic solvent in a nitrogen atmosphere, oxydianiline (ODA, 3,3') was added as a diamine monomer in a weight ratio of 1:1. -oxydianiline or 4,4'-oxydianiline) and pyromellitic dianhydride (PMDA) as a dianhydride monomer, followed by polymerization, thereby preparing a polyamic acid solution. Here, the weight ratio of solid matter and 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 polyamic acid solution, followed by stirring to obtain a precursor composition.

Then, β-picoline as an imidization catalyst was added in an amount of 0.17 mol relative to 1 mol of the amide group, followed by uniform mixing and defoaming, thereby preparing a 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 500 µm gap, followed by hot air at a temperature of 100°C to 200°C drying, thereby preparing 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 subjected to primary imidization at a temperature of 200°C to 400°C For 10 minutes, and a 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 processes was cooled to 25°C, and then separated from the pin frame, so as to obtain a polyamide with a size of 20 cm × 2.5 cm and a thickness of 125 µm imine film.

Comparative example 3 to 4

Except that the solvent amount in the polyimide solution and the molar amount of the imidization catalyst (β-picoline) in the polyimide film composition were changed as listed in Table 1, the same procedure as in Example 1 was used. A polyimide film with a thickness of 125 µm was obtained.

Comparative example 5

A carbonized sheet was prepared by carbonizing the polyimide film obtained in Comparative Example 1 by heating from 50°C to 1,200°C at a heating rate of about 1°C/min.

The carbonized sheet is then subjected to a primary to tertiary graphitization process in which the carbonized sheet is baked by heating from about 1,200°C to about 2,800°C at a step-by-step heating rate, thereby producing a graphite sheet with a final thickness of 50 µm . Specifically, in the primary graphitization process, the carbide sheet is heated from about 1,200°C to about 2,200°C at a heating rate of 1.5°C/min, and in the secondary graphitization process, the carbide sheet is heated by Heating from about 2,200°C to about 2,500°C at a heating rate of 0.4°C/min, and in the third graphitization process, the carbonized sheet was heated from about 2,500°C to about 2,500°C at a heating rate of 8.5°C/min. about 2,800°C.

Comparative example 6

A graphite sheet having a final thickness of 50 µm was prepared in the same manner as in Example 6, except that the polyimide film prepared in Comparative Example 2 was used instead of the polyimide film prepared in Comparative Example 5.

Comparative example 7

A graphite sheet having a final thickness of 50 µm was prepared in the same manner as in Example 6, except that the polyimide film prepared in Comparative Example 3 was used in place of the polyimide film prepared in Comparative Example 5.

Comparative example 8

A graphite sheet having a final thickness of 50 µm was prepared in the same manner as in Example 6, except that the polyimide film prepared in Comparative Example 4 was used in place of the polyimide film prepared in Comparative Example 5.

Table 1 Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Polyamide (parts by weight) 100 100 100 100 100 100 100 solvent 400 400 400 400 400 400 400 Imidization catalyst (molar amount) 0.17 0.20 0.15 0 0.28 0.25 0.24 Imidization catalyst (parts by weight) 27 29 25 0 36 33 32 Inorganic filler 2,500ppm 2,500ppm 2,500ppm 2,500ppm 2,500ppm 2,500ppm 2,500ppm 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 2,800 Thickness (µm) 50 50 50 50 50 50 50

< characteristic Evaluate >

(1) Surface quality

The surface quality of each of the thick graphite flake samples prepared in Examples 4 to 6 and Comparative Examples 5 to 8 was evaluated with the naked eye. Specifically, the evaluation of the surface quality was performed according to how many cracks were visually observed on the surface of each thick graphite sheet sample.

When no cracks were observed in the predetermined area (20 cm x 2.5 cm (length x width)), the corresponding graphite flake sample was rated as "good", and when 1 to 5 cracks were observed in the predetermined area, the corresponding Graphite flake samples of 100 were rated as "Fair", while the corresponding graphite flake samples were rated as "Poor" when more than 5 cracks were observed in a predetermined area or no graphitization was achieved. The results are shown in Figures 1 to 3 and Table 3.

(2) Surface damage rate

The second surface breakage 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 second surface breakage rate exceeded 0.004%, the corresponding graphite flake sample was rated as "inferior". The results are shown in Table 3.

[Equation 2] Second surface damage rate (%)={(B ₁ /B ₀ )×100},

where _B0 is the area of the graphite flake sample (in mm ⁾ measured using an image of the graphite flake sample at 10X magnification, and B1 is the area _of the graphite flake sample measured using an image of the graphite flake sample at 10X magnification Damaged area area (in ^mm2 ).

(3) Thermal conductivity

The in-plane thermal diffusivity (in-plane thermal) of each of the thick graphite sheet samples prepared in Examples 4 to 6 and Comparative Examples 5 to 8 was measured by a laser flash method using a thermal diffusivity tester (LFA 467, Netsch Co.). diffusivity), and thermal conductivity was then calculated by multiplying the measured in-plane thermal diffusivity by density (weight/volume) and specific heat capacity (measured by DSC). Here, samples that were observed to be cracked or not graphitized in the evaluation of (1) surface quality were marked as "unmeasurable". The results are shown in Table 3.

(4) Bright spots appear

The appearance of bright spots may lead to surface defects of the graphite flakes. The number of protrusions with a size of 0.05 mm or more in each of the thick graphite flake samples prepared in Examples 4 to 6 and Comparative Examples 5 to 8 was measured in a square of 50 mm×50 mm. Here, samples that were observed to be cracked or not graphitized in the evaluation of (1) surface quality were 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 observed observed observed observed surface quality good good good Difference Difference ordinary ordinary Second Surface Damage Rate 0% 0% 0% poor quality poor quality poor quality poor quality In-plane thermal conductivity (W/m·K) 1,000 800 1,100 not measurable not measurable not measurable not measurable Number of Highlights (EA) 1 2 0 not measurable not measurable not measurable not measurable Correlation schema Figure 1 - - Figure 3 - Figure 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 invention .

none.

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

Claims (8)

A polyimide film for graphite sheets, wherein the polyimide film is formed of a polyimide film composition comprising a polyimide acid and an imidization catalyst, and the polyimide film The amine film has a thickness of 100 µm to 200 µm and a first surface breakage rate of 0% or 0.001% to 0.004%, which is represented by Equation 1: [Equation 1] First surface breakage rate (%)={ (A ₁ /A ₀ )×100}, where A ₀ is the area (in mm ² ) of a graphite flake sample measured using an image of the graphite flake sample at 10X magnification, and A ₁ is the area of the graphite flake sample measured using 10 Image of the graphite flake sample at double magnification The area of the damaged region (in mm ⁾ of the graphite flake sample measured by the following steps: by 1 °C/min to 5 °C C/min heating rate from 15°C to 1,200°C to carbonize a polyimide film sample with dimensions of 200 mm × 25 mm; by heating at 1.5 °C/min to 5 °C/min The carbonized polyimide film samples were primary graphitized by heating at a heating rate from 1,200°C to 2,200°C; by heating from 2,200°C at a heating rate of 0.4°C/min to 1.3°C/min to 2,500°C for secondary graphitization of the primary graphitized polyimide film sample; and by heating from 2,500°C to 2,800° at a heating rate of 8.5°C/min to 20°C/min C, to tertiary graphitization of the second graphitized polyimide film sample. The polyimide film according to claim 1, wherein the molar ratio of the polyimide group of the polyimide and the imidization catalyst in the polyimide film composition is 1:0.15 to 1:0.20. The polyimide film of claim 1, wherein the polyimide film composition comprises: 100 parts by weight of the polyimide; and 17 parts by weight to 36 parts by weight of the imidization catalyst. The polyimide film according to claim 1, wherein the polyimide film composition further comprises an inorganic filler of 1,500 ppm to 2,500 ppm relative to 100 parts by weight of the polyimide, the inorganic filler The material includes at least one of calcium carbonate, dicalcium phosphate, calcium hydrogen phosphate, barium sulfate, silicon oxide, titanium oxide, aluminum oxide, silicon nitride, and boron nitride. A preparation method of a polyimide film for graphite sheets, wherein the method comprises: using a polyimide film composition comprising a polyimide and an imidization catalyst, passing through a polyimide film composition at a temperature of 100° C. to At a temperature of 200°C, the polyimide film composition is gelled to form a thin film with a thickness of 100 µm to 200 µm; at a temperature of 200°C to 400°C, the gelled polyimide film is amine film composition primary imidization; and secondary imidization of the primary imidized polyimide film composition at a temperature of 300°C to 500°C, wherein the polyimide The film has a first surface breakage rate of 0% or 0.001% to 0.004%, and the first surface breakage rate is represented by Equation 1: [Equation 1] First surface breakage rate (%)={(A ₁ /A ₀ )×100 }, where A ₀ is the area (in mm ⁾ of a graphite flake sample measured using an image of the graphite flake sample at 10X magnification, and A ₁ is the graphite flake sample using 10X magnification The damaged area area (in mm ⁾ of the graphite flake sample measured by the image of the graphite flake sample obtained by the following steps: C to 1,200°C to carbonize a polyimide film sample with dimensions of 200 mm x 25 mm; °C to primary graphitize the carbonized polyimide film samples; primary graphitization by heating from 2,200°C to 2,500°C at a heating rate of 0.4°C/min to 1.3°C/min The graphitized polyimide film sample was regraphitized; and the regraphitized by heating from 2,500°C to 2,800°C at a heating rate of 8.5°C/min to 20°C/min The polyimide film samples were graphitized three times. The preparation method according to claim 5, wherein the molar ratio of the amide group of the polyamide and the amide imidization catalyst in the polyimide film composition is 1:0.15 to 1:0.20 . The preparation method of claim 5, wherein the polyimide film composition comprises: 100 parts by weight of the polyimide; and 17 parts by weight to 36 parts by weight of the imidization catalyst. The preparation method of claim 5, wherein the polyimide film composition further comprises an inorganic filler of 1,500 ppm to 2,500 ppm relative to 100 parts by weight of the polyimide, the inorganic filler comprising carbonic acid At least one of calcium, dicalcium phosphate, calcium hydrogen phosphate, barium sulfate, silicon oxide, titanium oxide, aluminum oxide, silicon nitride, and boron nitride.

Images