Polyimide film for graphite sheets and graphite sheets manufactured from the same

Abstract

The present invention discloses a polyimide film for producing a graphite sheet, which contains a phosphorus-based compound having at least one alkyl group having 1 to 6 carbon atoms, and a graphite sheet produced from the polyimide film.

Description

[Technical Field]

[0001] The present invention relates to a polyimide film for graphite sheets and graphite sheets produced from the polyimide film. [Background technology]

[0002] Recently, electronic devices have become lighter, smaller, thinner, and more highly integrated, which causes a lot of heat to be generated. This heat can shorten the lifespan of the product and can lead to breakdowns and malfunctions. Therefore, thermal management for electronic devices has emerged as an important issue. Graphite sheets have a higher thermal conductivity than metal sheets such as copper and aluminum, and are attracting attention as heat dissipation materials for electronic devices. In particular, with the development of foldable devices, demand for graphite sheets used in hinges is on the rise. Therefore, research into graphite sheets with improved strength and flexibility is actively underway.

[0003] Graphite sheets can be produced by various methods, such as carbonizing and graphitizing a polymer film. In particular, polyimide films have attracted attention as polymer films for producing graphite sheets due to their excellent mechanical, thermal, dimensional, and chemical stability. A variety of additives can be used in polyimide films used in manufacturing graphite sheets, among which plasticizers are widely used to improve the physical properties of polyimide films. Adding a plasticizer during the manufacturing process of the film for graphite sheets can increase the foam thickness during baking. The strength, elongation, and elastic modulus of the polyimide film and the graphite sheet manufactured from it vary depending on the type, size, and molecular weight of the compound used as the plasticizer. Therefore, there is a growing need for research into the type and addition ratio of plasticizers to develop graphite sheets with properties tailored to specific applications. Furthermore, with the recent rapid development of foldable electronic products, there is a demand for the development of graphite sheets suitable for hinges. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Republic of Korea Patent Registration No. 10-1883434 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a polyimide film that can be used to produce a graphite sheet with improved flexibility and without a decrease in strength and elongation during the production of the graphite sheet. Another object of the present invention is to provide a high-quality graphite sheet produced from the polyimide film. [Means for solving the problem]

[0006] To achieve the above object, one embodiment of the present invention provides a polyimide film for producing a graphite sheet, which includes a phosphorus-based compound having at least one alkyl group having 1 to 6 carbon atoms. Another embodiment of the present invention provides a graphite sheet prepared by carbonizing, graphitizing, or carbonizing and graphitizing the polyimide film. [Effects of the Invention]

[0007] The present invention has the effect of providing a polyimide film containing a phosphorus-based compound and a graphite sheet produced from the polyimide film, which has excellent properties. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a stress-strain curve (SS curve) comparing the stress and strain of the polyimide film of Example 3 of the present application with the polyimide film of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments and examples of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be realized in various different forms and is not limited to the embodiments and examples described herein. Throughout this specification, when a part "comprises" a certain element, this does not mean that other elements are excluded, but that other elements can also be included, unless otherwise specified. In this specification, the singular expression includes the plural expression unless the context clearly indicates otherwise. When interpreting elements, they are interpreted as including a margin of error even if there is no explicit statement otherwise. In this specification, the "to" in "a to b" indicating a numerical range is defined as ≧a and ≦b.

[0010] The polyimide film according to one embodiment of the present application may include a phosphorus-based compound having at least one linear or branched alkyl group having 1 to 6 carbon atoms. For example, the phosphorus-based compound may be a phosphoric acid-based compound, and the alkyl group may be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a cyclopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a cyclobutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a cyclopentyl group, or the like. That is, the phosphorus-based compound may have 1 or more and 2 or less, 1 or more and 3 or less, 1 or more and 4 or less, 1 or more and 5 or less, or 1 or more and 6 or less carbon atoms.

[0011] The phosphorus-based compound may contain 1 to 4, 1 to 3, or 1 to 2 alkyl groups having 1 to 6 carbon atoms. On the other hand, the alkyl group having 1 to 6 carbon atoms may be directly bonded to the phosphorus (P) atom of the phosphorus-based compound. If the number of carbon atoms in the alkyl group of the phosphorus-based compound exceeds the above range, the molecular weight of the compound may increase and the phosphorus (P) content may decrease, which may result in a decrease in strength, elongation, and elastic modulus of the polyimide film containing the phosphorus-based compound. Meanwhile, the phosphorus-based compound may be a phosphate-based compound.

[0012] In one embodiment, the phosphorus-based compound contained in the polyimide film for producing a graphite sheet may be at least one selected from the group consisting of triethyl phosphate (TEP), trimethyl phosphate (TMP), tributyl phosphate (TBP), and tri-isobutyl phosphate (TiBP). In one embodiment, the polyimide film may contain 2 to 8 parts by weight of the phosphorus-based compound, based on 100 parts by weight of the total amount of imidization catalysts contained in the polyimide film. That is, when the total amount of imidization catalysts contained in the polyimide film is 100 parts by weight, the total amount of the phosphorus-based compound contained in the polyimide film may be 2 to 8 parts by weight.

[0013] For example, when the total content of the imidization catalyst contained in the polyimide film is 10 g, the total content of the phosphorus-based compound contained in the polyimide film may be 0.2 g or more and 0.8 g or less. For example, the phosphorus-based compound may be present in an amount of 2 to 8 parts by weight, 3 to 7 parts by weight, 3 to 6.5 parts by weight, or 3 to 6 parts by weight, based on 100 parts by weight of the total amount of the imidization catalyst contained in the polyimide film. If the content of the phosphorus-based compound exceeds the range of the present application, the gel film may shrink severely, preventing film formation and making it impossible to produce a polyimide film. If the content is below the range of the present application, the mechanical properties of the polyimide film may be reduced, such as a decrease in strength and elongation. In one embodiment, the polyimide film for producing a graphite sheet may have a strength in a machine direction (MD) of 265 MPa or more and 310 MPa or less and a strength in a transverse direction (TD) of 255 MPa or more and 320 MPa or less.

[0014] For example, the polyimide film for producing a graphite sheet may have a strength in the machine direction (MD) of 267 MPa or more and 309 MPa or less, 269 MPa or more and 307 MPa or less, 271 MPa or more and 305 MPa or less, 273 MPa or more and 300 MPa or less, 274 MPa or more and 295 MPa or less, 274.5 MPa or more and 293.6 MPa or less, 265 MPa or more and less than 270 MPa, 270 MPa or more and less than 275 MPa, 275 MPa or more and less than 280 MPa, 280 MPa or more and less than 285 MPa, 285 MPa or more and less than 290 MPa, 290 MPa or more and less than 295 MPa, 295 MPa or more and less than 300 MPa, 300 MPa or more and less than 305 MPa, or 305 MPa or more and less than 310 MPa. The strength in the transverse direction (TD) may be 261 MPa or more and 320 MPa or less, 267 MPa or more and 315 MPa or less, 273 MPa or more and 310 MPa or less, 279 MPa or more and 307 MPa or less, 281.9 MPa or more and 306.8 MPa or less, 255 MPa or more and less than 260 MPa, 260 MPa or more and less than 265 MPa, 265 MPa or more and less than 270 MPa, 270 MPa or more and less than 275 MPa, 275 MPa or more and less than 280 MPa, 280 MPa or more and less than 285 MPa, 285 MPa or more and less than 290 MPa, 290 MPa or more and less than 295 MPa, 295 MPa or more and less than 300 MPa, 300 MPa or more and less than 305 MPa, 305 MPa or more and less than 310 MPa, 310 MPa or more and less than 315 MPa, or 315 MPa or more and less than 320 MPa.

[0015] In one embodiment, the polyimide film for producing a graphite sheet may have an elongation in a machine direction (MD) of 128% or more and 135% or less, and an elongation in a transverse direction (TD) of 132% or more and 138% or less. For example, the polyimide film for producing a graphite sheet may have a machine direction (MD) elongation of 128.5% or more and 136% or less, 129% or more and 135.5% or less, 129% or more and 135% or less, 130% or more and 134.9% or less, 128% or more and less than 129%, 129% or more and less than 130%, 130% or more and less than 131%, 131% or more and less than 132%, 132% or more and less than 133%, 133% or more and less than 134%, or 134% or more and 135% or less. The elongation in the transverse direction (TD) is 130% or more and 139.5% or less, 130.5% or more and 139% or less, 131% or more and 138.5% or less, 131.5% or more and 138% or less, 132% or more and 137.5% or less, 132.1% or more and 137.1% or less, 132% or more and 133%, 133% or more and 134%, 134% or more and 135%, 135% or more and 136%, 136% or more and 137% or less, 137% or more and 138% or less. It may be 38% or less. In one embodiment, the polyimide film for producing a graphite sheet may have a modulus of elasticity in a machine direction (MD) of 1.8 GPa to 2.6 GPa and a modulus of elasticity in a transverse direction (TD) of 1.5 GPa to 2.5 GPa.

[0016] For example, the polyimide film for producing a graphite sheet may have a machine direction (MD) elastic modulus of 1.8 GPa or more and 2.58 GPa or less, 1.9 GPa or more and 2.51 GPa or less, 2.0 GPa or more and 2.44 GPa or less, 2.1 GPa or more and 2.37 GPa or less, 2.2 GPa or more and 2.3 GPa or less, 1.8 GPa or more and less than 1.9 GPa, 1.9 GPa or more and less than 2.0 GPa, 2.0 GPa or more and less than 2.1 GPa, 2.1 GPa or more and less than 2.2 GPa, 2.2 GPa or more and less than 2.3 GPa, 2.3 GPa or more and less than 2.4 GPa, 2.4 GPa or more and less than 2.5 GPa, or 2.5 GPa or more and less than 2.6 GPa. The elastic modulus in the transverse direction (TD) may be 1.6 GPa or more and 2.4 GPa or less, 1.7 GPa or more and 2.3 GPa or less, 1.8 GPa or more and 2.2 GPa or less, 1.9 GPa or more and 2.15 GPa or less, 2.0 GPa or more and 2.1 GPa or less, 1.5 GPa or more and less than 1.6 GPa, 1.6 GPa or more and less than 1.7 GPa, 1.7 GPa or more and less than 1.8 GPa, 1.8 GPa or more and less than 1.9 GPa, 1.9 GPa or more and less than 2.0 GPa, 2.0 GPa or more and less than 2.1 GPa, 2.1 GPa or more and less than 2.2 GPa, 2.2 GPa or more and less than 2.3 GPa, 2.3 GPa or more and less than 2.4 GPa, or 2.4 GPa or more and less than 2.5 GPa.

[0017] In one embodiment, the polyimide film for producing a graphite sheet may have an L* value of 50 or more and 70 or less as measured by a color difference meter. For example, the polyimide film for producing graphite sheet may have an L* value, measured with a color difference meter, of 51.4 or more and 68.2 or less, 52.8 or more and 66.4 or less, 54.2 or more and 64.6 or less, 55.6 or more and 62.8 or less, 57 or more and 61.5 or less, 57.1 or more and 61.2 or less, 50 or more and less than 55, 55 or more and less than 60, 60 or more and less than 65, or 65 or more and 70. Furthermore, the polyimide film for producing graphite sheet may have an a* value, measured with a color difference meter, of 12.5 or more and 18 or less. For example, the polyimide film for producing a graphite sheet may have an a* value measured with a color difference meter of 12.7 to 17.5, 12.8 to 17, 12.9 to 16.5, or 13.1 to 16.1.

[0018] The polyimide film for producing a graphite sheet may have a b* value of 70 or more and 100 or less as measured with a color difference meter. For example, the polyimide film for producing a graphite sheet may have a b* value measured with a color difference meter of 75 to 95, 80 to 93, 85 to 91, 86 to 90, or 87.5 to 89.3. In one embodiment, the polyimide film for producing a graphite sheet may have a transmittance of 25% or more and 40% or less as measured using a color difference meter (Ultra scan pro, Hunter Lab). For example, the polyimide film for producing a graphite sheet may have a transmittance measured using a color difference meter (Ultra scan pro, Hunter Lab) of 25.5% to 35%, 26% to 33%, 27% to 31%, or 27.4% to 30.9%.

[0019] The polyimide film for producing graphite sheets has a haze value of 6% or more and 17% or less as measured using a color difference meter (Ultra scan pro, Hunter Lab). It may be below. For example, the polyimide film for producing a graphite sheet may have a haze value measured using a color difference meter (Ultra scan pro, Hunter Lab) of 6.1% to 16%, 6.2% to 15%, 6.3% to 14%, 6.4% to 13%, 6.5% to 12%, or 6.6% to 11.1%. In one embodiment, the polyimide film for producing a graphite sheet may have a slope of a stress-strain curve calculated by the following Equation 1 at a strain of 0.2 mm / mm to 0.8 mm / mm, in the range of 50 to 100: [Number 1] Slope = (stress at strain 0.8 mm / mm - stress at strain 0.2 mm / mm) / (0.8 - 0.2)

[0020] In the above formula 1, (0.8-0.2) means the difference in strain between the point where the strain is 0.2 mm / mm and the point where the strain is 0.8 mm / mm. For example, the slope of the stress-strain curve may be 55 or more and 97 or less, 60 or more and 94 or less, 65 or more and 91 or less, 70 or more and 88 or less, 75 or more and 86 or less, 80 or more and 84 or less, 50 or more and less than 60, 60 or more and less than 70, 70 or more and less than 80, 80 or more and less than 90, or 90 or more and 100 or less in the section where the strain is 0.2 mm / mm or more. The slope is the slope after the yield point and may represent the modulus of elasticity or elastic coefficient of the polyimide film for the graphite sheet. In one embodiment, the polyimide film has a Young's modulus of 200 kgf / mm 2 More than 260kgf / mm 2 For example, the Young's modulus of the polyimide film may be 205 kgf / mm 2 More than 255kgf / mm 2 Below, 210kgf / mm 2 More than 250kgf / mm 2 Below, 220kgf / mm 2 Over 240kgf / mm 2 Below, 225kgf / mm 2 More than 232kgf / mm 2 It may be the following:

[0021] In one embodiment, the tensile strain of the polyimide film may be 94% or more and 127% or less. For example, the tensile strain of the polyimide film may be 95% or more and 120% or less, 96% or more and 113% or less, or 104% or more and 108% or less. In one embodiment, the polyimide film for manufacturing a graphite sheet is manufactured by imidizing a polyamic acid formed by reacting a dianhydride monomer with a diamine monomer, and the polyamic acid may have a weight average molecular weight of 100,000 to 500,000.

[0022] Within this range, graphitization may be easy during the production of a graphite sheet. Here, the "weight average molecular weight" can be measured using gel permeation chromatography (GPC) with polystyrene as a standard sample. The weight average molecular weight of the polyamic acid may be, for example, 150,000 to 500,000, another example, 200,000 to 400,000, and yet another example, 250,000 to 400,000, but is not limited thereto. As the dianhydride monomer and diamine monomer for forming the polyimide film for producing the graphite sheet, various monomers commonly used in the field of polyimide film production can be used.

[0023] For example, the dianhydride monomer of the polyimide film for producing a graphite sheet may be an aromatic dianhydride monomer, and the diamine monomer may be an aromatic diamine monomer. Examples of the dianhydride monomer include pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)sulfide dianhydride, and 2,2- Bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, p-phenylenebis(trimellitic acid monoester anhydride), p-biphenylenebis(trimellitic acid monoester anhydride), m-terphenyl-3,4,3',4'-tetracarboxylic acid dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic acid dianhydride Examples of suitable carboxylic acid dianhydrides include, but are not limited to, tetracarboxylic acid dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride, or combinations thereof. Examples of the diamine monomer include diamine monomers containing one benzene ring (e.g., 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid, etc.), diamine monomers containing two benzene rings (e.g., diaminodiphenyl ethers such as 4,4'-diaminodiphenyl ether and 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, and 3,3'-dimethyl-4,4'-diaminobiphenyl), , 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, bis(4-aminophenyl)sulfide, 4,4'-diaminobenzanilide, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 3,3'-Dimethoxybenzidine, 2,2'-Dimethoxybenzidine, 3,3'-Diaminodiphenyl ether, 3,4'-Diaminodiphenyl ether, 4,4'-Diaminodiphenyl ether, 3,3'-Diaminodiphenyl sulfide, 3,4'-Diaminodiphenyl sulfide, 4,4'-Diaminodiphenyl sulfide, 3,3'-Diaminodiphenyl sulfone, 3,4'-Diaminodiphenyl sulfone, 4,4'-Diaminodiphenyl sulfone, 3,3'-Diaminobenzophenone, 4,4'-Diaminobenzophenone, 3,3'-Diamino- 4,4'-Dichlorobenzophenone, 3,3'-Diamino-4,4'-dimethoxybenzophenone, 3,3'-Diaminodiphenylmethane, 3,4'-Diaminodiphenylmethane, 4,4'-Diaminodiphenylmethane, 2,2-Bis(3-aminophenyl)propane, 2,2-Bis(4-aminophenyl)propane, 2,2-Bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-Bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 3,3'-Diaminodiphenyl sulfoxide, 3 ,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, etc.), diamine monomers containing three benzene rings (e.g., 1,3-bis(3-aminophenyl)benzene, 1,3-bis(4-aminophenyl)benzene, 1,4-bis(3-aminophenyl)benzene, 1,4-bis(4-aminophenyl)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 3,3'-diamino-4-(4 -phenyl)phenoxybenzophenone, 3,3'-diamino-4,4'-di(4-phenylphenoxy)benzophenone, 1,3-bis(3-aminophenylsulfide)benzene, 1,3-bis(4-aminophenylsulfide)benzene, 1,4-bis(4-aminophenylsulfide)benzene, 1,3-bis(3-aminophenylsulfone)benzene, 1,3-bis(4-aminophenylsulfone)benzene, 1,4-bis(4-aminophenylsulfone)benzene, 1,3-bis[2-(4-aminophenyl)isopropyl]benzene, 1,4-bis[2-(3-aminophenyl, diamine monomers containing four benzene rings (e.g., 3,3'-bis(3-aminophenoxy)biphenyl, 3,3'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[3-(3-aminophenoxy)phenyl]ether, bis[3-(4-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl] ] ether, bis[4-(4-aminophenoxy)phenyl]ether, bis[3-(3-aminophenoxy)phenyl]ketone, bis[3-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[3-(3-aminophenoxy)phenyl]sulfide, bis[3-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide , bis[3-(3-aminophenoxy)phenyl]sulfone, bis[3-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[3-(3-aminophenoxy)phenyl]methane, bis[3-(4-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(4-aminophenoxy)phenyl]methane, 2,2-bis[3-(3-aminophenoxy)phenyl]propane, 2 ,2-bis[3-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[3-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, or combinations thereof can be used, but are not limited to these.

[0024] In particular, the dianhydride monomer may be pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4-biphenyltetracarboxylic dianhydride, oxydiphthalic anhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, or a combination thereof, and the diamine monomer may be 4,4'-oxydianiline, 3,4'-oxydianiline, p-phenylenediamine, m-phenylenediamine, 4,4'-methylenedianiline, 3,3'-methylenedianiline, or a combination thereof. For example, pyromellitic dianhydride may be used as the dianhydride monomer, and 4,4'-oxydianiline may be used as the diamine monomer.

[0025] The polyimide film for producing graphite sheets may have a thickness of 20 to 500 μm, for example, but is not limited to, 20 to 500 μm, more preferably 25 to 400 μm, even more preferably 30 to 300 μm, and still more preferably 35 to 200 μm. The polyimide film for producing graphite sheets can be produced by various methods commonly used in the field of polyimide film production. For example, the polyimide film for producing graphite sheets can be produced by polymerizing one or more dianhydride monomers and one or more diamine monomers in a solvent to produce a polyamic acid solution, adding an imidization catalyst, a dehydrating agent, and optionally a sublimable inorganic filler and a solvent to the polyamic acid solution to form a polyimide film composition, and then forming the composition into a film, but the method is not limited thereto.

[0026] The process of imidizing the polyamic acid solution may be carried out by a known imidization method such as a thermal imidization method, a chemical imidization method, or a hybrid imidization method that combines the thermal imidization method and the chemical imidization method. The average particle size (D 50 ) is 0.1 to 5.0 μm, and the total content of the sublimable inorganic filler may be 0.07 to 0.4% by weight based on 100% by weight of the total weight of the polyimide film. The sublimable inorganic filler can induce a predetermined foaming phenomenon by sublimating during carbonization and / or graphitization of the polyimide film. This foaming phenomenon facilitates the exhaust of sublimation gases generated during carbonization and / or graphitization, resulting in a high-quality graphite sheet. The predetermined voids formed by foaming can also improve the bending resistance ("flexibility") of the graphite sheet.

[0027] However, excessive foaming and the resulting large number of voids can significantly deteriorate the thermal conductivity and mechanical properties of the graphite sheet and can cause defects on the surface of the graphite sheet. Therefore, the type, content, and particle size of the sublimable inorganic filler must be carefully selected. "Average particle size (D 50 ) can be measured using a laser diffraction particle size analyzer (SALD-2201, Shimadzu) after ultrasonically dispersing the sublimable inorganic filler in a dimethylformamide solvent at 25°C for 5 minutes. The average particle size (D) of all sublimable inorganic fillers in polyimide film for graphite sheet production 50) may be, for example, 0.5 to 4.0 μm, for example, 1.0 to 5.0 μm, for example, 1.5 to 5.0 μm, for example, 1.5 to less than 2.5 μm, but is not limited thereto. The total content of the sublimable inorganic filler in the polyimide film may be, for example, 0.07 to 0.35 wt %, for example, 0.1 to 0.3 wt %, for example, 0.15 to 0.3 wt %, based on the total weight of the polyimide film, but is not limited thereto.

[0028] The sublimable inorganic filler has an average particle size (D 50 ) of 0.1 to 2.0 μm and a first sublimable inorganic filler having an average particle size (D 50 ) may contain a second sublimable inorganic filler having a particle size of more than 2.0 to 5.0 μm. The contents of the first sublimable inorganic filler and the second sublimable inorganic filler in the sublimable inorganic filler are not particularly limited, but for example, based on the total weight of the sublimable inorganic fillers, the first sublimable inorganic filler may be contained in an amount of 10 to 90 wt%, and the second sublimable inorganic filler may be contained in an amount of 10 to 90 wt%. For example, based on the total weight of the sublimable inorganic fillers, the content of the first sublimable inorganic filler may be, for example, 15 to 85 wt%, for example, 20 to 80 wt%, for example, 30 to 80 wt%, for example, and 50 to 80 wt%, and the content of the second sublimable inorganic filler may be, for example, 85 to 15 wt%, for example, 80 to 20 wt%, for example, 70 to 20 wt%, and for example, 50 to 20 wt%, but are not limited thereto.

[0029] Examples of the sublimable inorganic filler include calcium carbonate, dibasic calcium phosphate, barium sulfate, etc. More preferably, the sublimable inorganic filler may be dibasic calcium phosphate, but is not limited thereto. The solvent is not particularly limited as long as it can dissolve the polyamic acid, and may include, for example, an aprotic polar solvent.

[0030] In particular, sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide; formamide solvents such as N,N-dimethylformamide and N,N-diethylformamide; acetamide solvents such as N,N-dimethylacetamide and N,N-diethylacetamide; pyrrolidone solvents such as N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone; phenol solvents such as phenol, o-, m-, or p-cresol, xylenol, halogenated phenols, and catechol; and aprotic polar solvents such as hexamethylphosphoramide and γ-butyrolactone; and the like can be used alone or in combination, but are not limited to these. The dehydrating agent may be, but is not limited to, acetic anhydride, propionic anhydride, butyric anhydride, benzoic anhydride, or the like, which may be used alone or in combination of two or more.

[0031] The film formation may be performed by applying a polyamic acid solution onto a substrate in the form of a film, heating and drying the solution at a temperature of 30 to 200°C for 15 seconds to 30 minutes to produce a gel film, and then removing the substrate from the gel film and heat-treating the gel film at a temperature of 250 to 600°C for 15 seconds to 30 minutes, but is not limited to this. When a graphite sheet is manufactured using the polyimide film for manufacturing graphite sheet of the present invention, it is possible to manufacture a graphite sheet with excellent properties. A graphite sheet according to another embodiment of the present application can be produced by carbonizing, graphitizing, or carbonizing and graphitizing the polyimide film for producing a graphite sheet according to the present application.

[0032] The carbonization is a process of pyrolyzing the polymer chains of a polyimide film for producing a graphite sheet to form a preliminary graphite sheet containing amorphous carbon, non-crystalline carbon, and / or amorphous carbon. For example, the carbonization process may include, but is not limited to, heating the polyimide film from room temperature to a maximum temperature of 1,000°C to 1,500°C under reduced pressure or in an inert gas atmosphere for 10 to 30 hours and maintaining the temperature. Optionally, to achieve high carbon orientation, pressure may be applied to the polyimide film during carbonization using a hot press, for example, at a pressure of 5 kg / cm. 2 As another example, 15kg / cm 2 As another example, 25 kg / cm 2 It may be more than this, but is not limited to this. The graphitization is a process of rearranging carbon in an amorphous carbon body, non-crystalline carbon body, and / or amorphous carbon body to form a graphite sheet, and may include, but is not limited to, a step of raising and maintaining the temperature of a preliminary graphite sheet from room temperature to a maximum temperature in the range of 2,500°C to 3,000°C in an inert gas atmosphere for 2 hours to 30 hours. Optionally, to achieve high carbon orientation, pressure may be applied to the preliminary graphite sheet during graphitization using a hot press, for example, at a pressure of 100 kg / cm. 2 As another example, 200kg / cm 2 As another example, 300 kg / cm 2 It may be more than this, but is not limited to this.

[0033] The graphite sheet according to still another embodiment of the present application may have an elongation of 5.5% or more and 10% or less. For example, the elongation of the graphite sheet may be 5.5% or more and less than 6%, 6% or more and less than 7%, 7% or more and less than 8%, 8% or more and less than 9%, or 9% or more and less than 10%. In addition, the graphite sheet containing the phosphorus-based compound of the present invention can have an elongation that is increased by 250% or more compared to a graphite sheet containing no phosphorus-based compound. In particular, when the phosphorus-based compound is added in an amount exceeding 3%, the elongation can be increased by 400% or more. In one embodiment, the graphite sheet may have a strength of 63 MPa or more and 85 MPa or less and an elastic modulus of 1.0 GPa or more and 2.4 GPa or less.

[0034] For example, the strength of the graphite sheet is 63.1 MPa or more and 84 MPa or less, MPa or more and 83 MPa or less, 63.3 MPa or more and 82 MPa or less, 63.4 MPa or more and 81.5 MPa or less, 63.5 MPa or more and 1.2 MPa or less, 63 MPa or more and less than 65 MPa, 65 MPa or more and less than 70 MPa, 70 MPa or more and less than 75 MPa, 75 MPa or more and less than 80 MPa, or 80 MPa or more and 85 MPa or less.

[0035] For example, the elastic modulus of the graphite sheet may be 1.1 GPa or more and 2.3 GPa or less, 1.2 GPa or less and 2.2 GPa or less, 1.25 GPa or more and 2.15 GPa or less, 1.3 GPa or more and 2.1 GPa or less, 1.0 GPa or more and less than 1.5 GPa, 1.5 GPa or more and less than 2.0 GPa, or 2.0 GPa or more and 2.4 GPa or less. Meanwhile, the foaming thickness and rolling thickness of the graphite sheet may be 60 to 130 μm and 22 to 28 μm, respectively, and the thermal diffusion coefficient and thermal conductivity may be 550 to 620 mm. 2 / s and 850 to 990 W / (m*K). The density of the graphite sheet is 1.85 to 1.89 g / cm 3 may be. [Example]

[0036] The present invention will be described in more detail below with reference to examples, which are presented as preferred examples of the present invention and should not be construed as limiting the present invention in any way. Production Example 1 (Production of Polyimide Film) 250.0 g of dimethylformamide was placed in a reactor as a solvent and the temperature was adjusted to 20° C. 30.0 g of 4,4′-oxydianiline (ODA) as a diamine monomer was added thereto, followed by 30.0 g of pyromellitic dianhydride (PMDA) as a dianhydride monomer to prepare a polyamic acid solution with a viscosity of 230,000 cP. Next, the produced polyamic acid solution was mixed with 80.0 g of acetic anhydride as a dehydrating agent, 10.0 g of β-picoline as an imidization catalyst, and dibasic calcium phosphate (Ajinomoto Co., Inc., Top flow-K, average particle size (D 50 0.12 g of 2.5 μm cellulose acetate and 50.0 g of dimethylformamide were mixed. Furthermore, as shown in Table 1 below, appropriate amounts of phosphorus-based compounds were added to prepare polyimide film precursor solutions of Examples 1 to 4 and Comparative Examples 1 to 8. The prepared polyimide film precursor solution was cast onto a SUS plate (100SA, Sandvik) using a doctor blade to a thickness of 38 μm and dried at a temperature range of 100 °C to 200 °C to produce a self-supporting gel film. The gel film was then peeled off from the SUS plate, fixed to a pin frame, and transported to a high-temperature tenter where it was heated from 200 to 700°C, cooled to 25°C, and then separated from the pin frame to obtain a polyimide film.

[0037] Manufacturing Example 2 (Manufacturing of Graphite Sheet) The polyimide film produced in Production Example 1 was heated to 1,210°C at a rate of 3.3°C / min under nitrogen gas using a carbonization-capable electric furnace, and maintained at 1,210°C for approximately 2 hours (carbonization). Next, a first firing step was carried out by using a graphitizable electric furnace and increasing the temperature from 1,210°C to 2,200°C at a rate of 2.5°C / min under argon gas. After reaching 2,200°C, the temperature increase rate was changed to 1.25°C / min, and the temperature was continuously increased up to 2,500°C, whereupon the second firing step was carried out. After reaching 2,500°C, the heating rate was changed to 10°C / min and the temperature was continuously raised to 2,650°C, whereupon the third firing step was carried out. After leaving the mixture at 2,650°C for several minutes, graphitization was completed and graphite sheets were produced. Finally, the graphite sheet was cooled at a rate of 10°C / min. The contents of the phosphorus compounds in Examples 1 to 4 and Comparative Examples 1 to 8 are as shown in Table 1 below.

[0038] [Table 1] In Table 1, TEP is triethyl phosphate, and BDP is bisphenol A bisdiphenyl phosphate. bis(diphenyl phosphate), CDP is Cresyl diphenyl phosphate, and TCP is Tricresyl phosphate.

[0039] Example 1 A polyimide film was prepared by adding 3 parts by weight of triethyl phosphate (TEP) based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film according to Preparation Example 1. Then, a graphite sheet was prepared according to Preparation Example 2.

[0040] Example 2 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 3.5 parts by weight of triethyl phosphate (TEP) was added based on 100 parts by weight of the total amount of imidization catalysts contained in the entire polyimide film.

[0041] Example 3 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 4 parts by weight of triethyl phosphate (TEP) was added based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film.

[0042] Example 4 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 6 parts by weight of triethyl phosphate (TEP) was added based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film.

[0043] Comparative Example 1 A polyimide film and a graphite sheet were produced in the same manner as in Example 1, except that no phosphorus-based compound was added.

[0044] Comparative Example 2 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 9 parts by weight of triethyl phosphate (TEP) was added based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film.

[0045] Comparative Example 3 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 4 parts by weight of bisphenol A bis(diphenyl phosphate, BDP) was added instead of triethyl phosphate (TEP), based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film.

[0046] Comparative Example 4 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 6 parts by weight of bisphenol A bis(diphenyl phosphate, BDP) was added instead of triethyl phosphate (TEP), based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film.

[0047] Comparative Example 5 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 4 parts by weight of cresyl diphenyl phosphate (CDP) was added instead of triethyl phosphate (TEP), based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film.

[0048] Comparative Example 6 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 6 parts by weight of cresyl diphenyl phosphate (CDP) was added instead of triethyl phosphate (TEP), based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film.

[0049] Comparative Example 7 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 4 parts by weight of tricresyl phosphate (TCP) was added instead of triethyl phosphate (TEP), based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film.

[0050] Comparative Example 8 A polyimide film and a graphite sheet were prepared in the same manner as in Example 1, except that 6 parts by weight of tricresyl phosphate (TCP) was added instead of triethyl phosphate (TEP) based on 100 parts by weight of the total amount of imidization catalyst contained in the entire polyimide film. It was created. In Comparative Example 2, in which excessive TEP was used, and Comparative Example 8, in which excessive TCP was used, the gel film contracted severely and could not be formed into a film, so polyimide films could not be produced, and the strength, elastic modulus, elongation, L*a*b* value, transmittance, and haze could not be measured.

[0051] Evaluation example 1: Measurement of strength, elastic modulus and elongation of polyimide film The strength, modulus of elasticity and elongation of the polyimide films of Examples 1 to 4 and Comparative Examples 1 to 8 produced in Production Example 1 were measured. The strength and elongation were measured using Autograph Universal Testing Machines (Shimadzu, AG-IS) according to ASTM D882, and the elastic modulus was measured using an Instron 5564 model according to ASTM D882. The strength, modulus and elongation were measured in both the machine direction (MD) and the transverse direction (TD). The measurement results of Evaluation Example 1 are shown in Table 2 below. [Table 2] Compared with the polyimide film of Comparative Example 1, which did not contain a phosphorus-based compound, the polyimide films of Examples 1 to 4, which contained the phosphorus-based compound triethyl phosphate, had increased strength in both the machine direction and the width direction.

[0052] Furthermore, the strength of all of the polyimide films of Examples 1 to 4 containing triethyl phosphate was increased compared to the polyimide films of Comparative Examples 3 to 7 containing bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate, or tricresyl phosphate. Specifically, in Examples 1 to 4, the strength range was measured to be 216 MPa or more and 292 MPa or less in the machine direction, and 214 MPa or more and 307 MPa or less in the cross direction. In terms of elongation, the polyimide films of Examples 1 to 4 containing triethyl phosphate, a phosphorus-based compound, had similar or higher elongation than the polyimide film of Comparative Example 1, which did not contain a phosphorus-based compound. Specifically, in Examples 1 to 4, the range of elongation is 130% or more and 135% or less in the longitudinal direction. % or less, and in the cross direction it was measured to be 129% or more and 138% or less. Compared with the polyimide film of Comparative Example 1, which did not contain a phosphorus-based compound, the polyimide films of Examples 1 to 4, which contained the phosphorus-based compound triethyl phosphate, all had lower elastic moduli in both the machine direction and the width direction. Furthermore, the elastic modulus of the polyimide films of Examples 1 to 4, which contained triethyl phosphate, all decreased compared to the polyimide films of Comparative Examples 3 to 7, which contained bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate, or tricresyl phosphate. Specifically, in the case of Examples 1 to 4, the range of the elastic modulus measured was 2.2 GPa or more and 2.3 GPa or less in the machine direction, and 2.0 GPa or more and 2.1 GPa or less in the width direction.

[0053] Evaluation example 2: Measurement of color L*a*b* of polyimide film The color L*a*b* values ​​of the polyimide films of Examples 1 to 4 and Comparative Examples 1 to 8 produced in Production Example 1 were measured at room temperature using a color difference meter (Ultra scan pro, Hunter Lab). The measurement results of Evaluation Example 2 are shown in Table 3 below. [Table 3] Compared with the polyimide film of Comparative Example 1, which did not contain a phosphorus-based compound, and the polyimide films of Comparative Examples 3 to 7, which contained bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate, or tricresyl phosphate, the polyimide films of Examples 1 to 4, which contained the phosphorus-based compound triethyl phosphate, had reduced L* values ​​and therefore exhibited darker colors. Specifically, in the cases of Examples 1 to 4, the L* value was measured to be in the range of 57 or more and 62 or less.

[0054] Evaluation Example 3: Measurement of transmittance and haze of polyimide film The transmittance and haze of the polyimide films of Examples 1 to 4 and Comparative Examples 1 to 8 produced in Production Example 1 were measured. The transmittance and haze value were measured under illuminant A using a color difference meter (Ultra Scan Pro, Hunter Lab) based on the standard of ASTM D1003. The measurement results of Evaluation Example 3 are shown in Table 4 below. [Table 4] The transmittance of the polyimide films of Examples 1 to 4, which contained the phosphorus-based compound triethyl phosphate, was all reduced compared to the polyimide film of Comparative Example 1, which did not contain a phosphorus-based compound, and the polyimide films of Comparative Examples 3 to 7, which contained bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate, or tricresyl phosphate. Specifically, the transmittance range measured was 27% or more and 31% or less in the cases of Examples 1 to 4. Compared with the polyimide film of Comparative Example 1, which did not contain a phosphorus-based compound, and the polyimide films of Comparative Examples 3 to 7, which contained bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate, or tricresyl phosphate, the polyimide films of Examples 1 to 4, which contained the phosphorus-based compound triethyl phosphate, showed a tendency to have increased haze. In the case of Example 1, which contained 3 wt % triethyl phosphate, the haze was reduced compared to Comparative Examples 3 to 7, but in the cases of Examples 2 to 4, which contained 3.5, 4, and 6 wt % triethyl phosphate, respectively, the haze was increased compared to Comparative Examples 3 to 7.

[0055] Evaluation Example 4: Comparison of the slope of the stress-strain curve of polyimide film The Young's modulus and tensile strain of the polyimide films of Example 4 and Comparative Example 1 prepared according to Preparation Example 1 were measured. In addition, the stress and strain were measured, and a graph comparing the two values ​​(stress-strain curve) was drawn. The slope of the graph from 0.2 mm / mm or more to 0.8 mm / mm or less was calculated and compared. The Young's modulus, measured three times as an average, was 2.6 GPa for Comparative Example 1 and 2.2 GPa for Example 4. That is, the Young's modulus of the polyimide film of Example 4, which contained 6 wt % triethyl phosphate, was lower than that of the polyimide film of Comparative Example 1, which contained no phosphorus-based compound. In addition, the tensile strain was measured as an average of six measurements, and was 121.5% for Comparative Example 1 and 107.5% for Example 4. That is, the tensile strain was reduced in the polyimide film of Example 4, which contained 6 wt% triethyl phosphate, compared to the polyimide film of Comparative Example 1, which did not contain a phosphorus-based compound. As shown in Figure 1, the slope of the stress-strain curve was calculated from when the strain was 0.2 mm or more to 0.8 mm or less. The slope of the graph for Comparative Example 1 was 44.39, while the slope of the graph for Example 4 increased to 81.25. In other words, the stress after the yield point increased in the polyimide film of Example 3, which contained 6 wt% triethyl phosphate, compared to the polyimide film of Comparative Example 1, which did not contain a phosphorus-based compound.

[0056] Evaluation example 5: Measurement of thermal decomposition characteristics of polyimide film The thermal decomposition properties of the polyimide films of Example 3 and Comparative Examples 1, 3, 5 and 7 prepared according to Preparation Example 1 were measured. The thermal decomposition characteristics were measured using Thermogravimetric Analysis (TA Instruments, TGA5500) by increasing the temperature to 625°C at a rate of 10°C / min. Compared with the polyimide films of Comparative Example 1, which did not contain a phosphorus-based compound, and Comparative Examples 3, 5, and 7, which contained bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate, or tricresyl phosphate, the polyimide film of Example 3, which contained triethyl phosphate, all showed increased amounts of residues upon pyrolysis at 625°C. In the case of Example 3, the residual amount upon thermal decomposition at 625°C was measured to be 83 wt%. The residual amounts upon thermal decomposition at 625°C were measured to be 74 wt% in the case of Comparative Example 1, 77 wt% in the case of Comparative Example 3, 80 wt% in the case of Comparative Example 5, and 81 wt% in the case of Comparative Example 7, and therefore the residual amount upon thermal decomposition was measured to be larger in the case of Example 3 than in the cases of Comparative Examples 1, 3, 5, and 7. That is, it was determined that the polyimide film containing triethyl phosphate had a high residual amount and was therefore excellent in flame retardant properties.

[0057] Evaluation Example 6: Measurement of strength and elastic modulus of graphite sheet The strength and elastic modulus of the graphite sheets of Examples 1 to 4 and Comparative Examples 1 to 8 produced by Production Example 2 were measured. The strength was measured using Autograph Universal Testing Machines (Shimadzu, AG-IS) according to a method conforming to ASTM D882, and the elastic modulus was measured using an Instron 5564 model according to the ASTM D882 method. Additionally, strength and modulus were measured in the machine direction (MD). The measurement results of Evaluation Example 6 are shown in Table 5 below. [Table 5] The graphite sheets of Comparative Example 1, which did not contain any phosphorus-based compound, and Comparative Examples 3 to 7, which contained bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate, or tricresyl phosphate, contained the phosphorus-based compound triethylene phosphate. The graphite sheets of Examples 1 to 4 containing cellulose showed improved strength and reduced elastic modulus. Specifically, in the case of Examples 1 to 4, the strength range was measured to be 63.5 MPa to 81.2 MPa, and the elastic modulus range was measured to be 1.3 GPa to 2.1 GPa. That is, it was confirmed that Examples 1 to 4 had improved strength and flexibility compared to Comparative Examples 1 to 7.

[0058] Evaluation example 7: Measurement of elongation of graphite sheet The elongation of the graphite sheets of Examples 1 to 4 and Comparative Examples 1 to 8 produced in Production Example 2 was measured. The elongation was measured in the machine direction (MD) using Autograph Universal Testing Machines (Shimadzu, AG-IS) according to ASTM D882. The measurement results of Evaluation Example 7 are shown in Table 6 below. [Table 6] The graphite sheets of Examples 1 to 4, which contained the phosphorus-based compound triethyl phosphate, showed increased elongation compared to the graphite sheet of Comparative Example 1, which did not contain a phosphorus-based compound, and the graphite sheets of Comparative Examples 3 to 7, which contained bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate, or tricresyl phosphate. Specifically, in the cases of Examples 1 to 4, the range of elongation measured was 5.5% or more and 8% or less.

[0059] Evaluation Example 8: Measurement of foam thickness and rolled thickness of graphite sheet The foamed thickness and rolled thickness of the graphite sheets of Examples 1 to 4 and Comparative Examples 1 to 8 produced in Production Example 2 were measured. The foam thickness and rolled thickness were measured by a Digital Micrometer (Standard-type, Mitutoyo). The measurement results of Evaluation Example 8 are shown in Table 7 below. [Table 7] The graphite sheets of Examples 1 to 4, which contained the phosphorus-based compound triethyl phosphate, showed increased foam thickness compared to the graphite sheet of Comparative Example 1, which did not contain a phosphorus-based compound, and the graphite sheets of Comparative Examples 3 to 7, which contained bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate, or tricresyl phosphate. Specifically, in the cases of Examples 1 to 4, the foam thickness was measured to be 65 μm or more and 122 μm or less, and the rolled thickness was measured to be 22 μm or more and 25 μm or less. In the case of Examples 1 to 4, the application of TEP resulted in a smoother expansion phenomenon than in the graphite sheets of Comparative Examples 1 to 7, which is advantageous for obtaining graphite sheets. Furthermore, the voids formed by expansion are advantageous for the flexibility of the graphite sheet. Despite this expansion thickness, there was not much difference in the rolled thickness between Examples 1 to 4 and Comparative Examples 1 to 7. In other words, it was confirmed that both flexibility and thin rolled thickness were achieved due to the smooth expansion phenomenon.

[0060] Evaluation Example 9: Measurement of density, thermal diffusivity, and thermal conductivity of graphite sheet The density, thermal diffusion coefficient and thermal conductivity of the graphite sheets of Examples 1 to 4 produced by Production Example 2 were measured. The density was measured on test pieces cut into 15 mm x 300 mm (width x length) from the prepared polyimide film using a Pycnometer (AccuPyc1340, Micromeritics) at room temperature using helium gas. The thermal diffusion coefficient was measured by cutting a graphite sheet into a sample with a diameter of 1 inch and a thickness of 18 μm, and measuring the thermal diffusion coefficient in the planar direction by the Laser Flash method using a measuring device (Netsch, LFA467). The thermal conductivity was calculated by multiplying the measured thermal diffusivity values ​​(average values ​​of five measurements at 25°C) by the density (weight / volume) and specific heat (theoretical value: 0.85 kJ / (kg·K)). The measurement results of Evaluation Example 9 are shown in Table 8 below. [Table 8] The thermal diffusion coefficient of the graphite sheets of Examples 1 to 4 containing the phosphorus compound triethyl phosphate was 554 mm 2 / s or more 618mm 2 / s or less, and the thermal conductivity was measured to be between 816W / (m*K) and 965W / (m*K). In addition, in Examples 1 to 4, the density of the graphite sheet was 1.65 g / cm 3 More than 1.89g / cm 3 The following was measured: The examples of the manufacturing method of the present invention are merely preferred examples that will enable those skilled in the art to easily implement the present invention, and are not limited to the above examples, and therefore do not limit the scope of the present invention. Therefore, the true technical scope of protection of the present invention must be determined by the technical spirit of the appended claims. Furthermore, it is obvious to those skilled in the art that various substitutions, modifications, and changes are possible within the scope of the present invention, and it is obvious that parts that can be easily modified by those skilled in the art are also included in the scope of the present invention. [Industrial Applicability]

[0061] The present invention has the effect of providing a polyimide film containing a phosphorus-based compound and a graphite sheet produced from the polyimide film, which has excellent properties.

Claims

1. a phosphorus-based compound having at least one linear or branched alkyl group having 1 to 6 carbon atoms; Polyimide film for manufacturing graphite sheets.

2. The phosphorus-based compound is at least one selected from the group consisting of triethyl phosphate (TEP), trimethyl phosphate (TMP), tributyl phosphate (TBP), and triisobutyl phosphate (TiBP); 2. The polyimide film for producing a graphite sheet according to claim 1.

3. the phosphorus-based compound is contained in an amount of 2 parts by weight to 8 parts by weight based on 100 parts by weight of the total amount of the imidization catalyst contained in the polyimide film; 2. The polyimide film for producing a graphite sheet according to claim 1.

4. The strength in the machine direction (MD) is 265 MPa or more and 310 MPa or less, and the strength in the transverse direction (TD) is 255 MPa or more and 320 MPa or less; 2. The polyimide film for producing a graphite sheet according to claim 1.

5. The elongation in the machine direction (MD) is 128% or more and 135% or less, and the elongation in the transverse direction (TD) is 132% or more and 138% or less.

2. The polyimide film for producing a graphite sheet according to claim 1.

6. The elastic modulus in the machine direction (MD) is 1.8 GPa or more and 2.6 GPa or less, and the elastic modulus in the transverse direction (TD) is 1.5 GPa or more and 2.5 GPa or less, 2. The polyimide film for producing a graphite sheet according to claim 1.

7. The L* value measured by a color difference meter is 50 or more and 70 or less.

2. The polyimide film for producing a graphite sheet according to claim 1.

8. Strain is between 0.2 mm / mm and 0.8 mm / mm, The slope of the stress-strain curve calculated by the following formula 1 is 50 or more and 100 or less.

2. The polyimide film for producing a graphite sheet according to claim 1. [Equation 1] Slope = (stress at strain 0.8 mm / mm - stress at strain 0.2 mm / mm) / (0.8 - 0.2)

9. A graphite sheet produced by carbonizing, graphitizing, or carbonizing and graphitizing the polyimide film according to any one of claims 1 to 8.

10. 10. The graphite sheet according to claim 9, having an elongation of 5.5% or more and 10% or less.

11. 10. The graphite sheet according to claim 9, having a strength of 63 MPa or more and 85 MPa or less and an elastic modulus of 1.0 GPa or more and 2.4 GPa or less.

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