KR20240131021A - Polyimide film for graphite sheet and graphite sheet prepraed therefrom - Google Patents

Abstract

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

Description

Polyimide film for graphite sheet and graphite sheet prepared therefrom {POLYIMIDE FILM FOR GRAPHITE SHEET AND GRAPHITE SHEET PREPRAED THEREFROM}

The present invention relates to a polyimide film for a graphite sheet and a graphite sheet manufactured therefrom.

Recent electronic devices are becoming lighter, smaller, thinner, and more integrated, which causes them to generate a lot of heat. This heat can shorten the life of the product or cause it to malfunction or fail. Therefore, heat management for electronic devices is emerging as an important issue.

Graphite sheets have higher thermal conductivity than metal sheets such as copper or aluminum, and are attracting attention as heat dissipation materials for electronic devices. In particular, with the development of foldable devices, the demand for graphite sheets used in hinges is increasing. Accordingly, research on graphite sheets with improved strength and flexibility is actively being conducted.

Graphite sheets can be manufactured by various methods, for example, by carbonizing and graphitizing polymer films. In particular, polyimide films are attracting attention as polymer films for manufacturing graphite sheets due to their excellent mechanical, thermal, dimensional stability, and chemical stability.

Polyimide films used in the manufacture of graphite sheets can use various additives, among which plasticizers are widely used to improve the properties of polyimide films.

By adding a plasticizer in the manufacturing step of a film for graphite sheets, the foaming thickness can be increased during firing. At this time, the strength, elongation, elastic modulus, etc. of the polyimide film and the graphite sheet manufactured therefrom change depending on the type, size, and molecular weight of the compound used as the plasticizer. Accordingly, there is a growing demand for research on the type and addition ratio of plasticizers for the development of graphite sheets with properties suitable for the intended use.

In addition, as the pace of development of foldable electronic products has been accelerating recently, the development of graphite sheets for application to hinges is being demanded.

Republic of Korea Patent Publication No. 10-1883434

The purpose of the present invention is to provide a polyimide film capable of producing a graphite sheet having improved flexibility without deterioration in strength and elongation during the production of the graphite sheet.

Another object of the present invention is to provide a graphite sheet of excellent quality manufactured from the polyimide film.

One embodiment of the present invention to achieve the above-mentioned purpose provides a polyimide film for producing a graphite sheet, which includes a phosphorus compound having at least one alkyl group having 1 to 6 carbon atoms.

Another embodiment of the present invention provides a graphite sheet manufactured by carbonizing, graphitizing, or carbonizing and graphitizing the polyimide film.

The present invention has the effect of providing a polyimide film containing a phosphorus compound and a graphite sheet having excellent properties manufactured therefrom.

Figure 1 is a stress-strain curve (S-S Curve) comparing the stress and strain of the polyimide film of Example 3 of the present invention and the polyimide film of Comparative Example 1.

Hereinafter, embodiments and examples of the present invention will be described in detail so that those skilled in the art can easily practice the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments and examples described herein. Throughout this specification, when a part is said to “include” a certain component, this does not exclude other components unless specifically stated otherwise, but rather means that other components may be included.

In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

When interpreting a component, it is interpreted as including the error range even if there is no separate explicit description.

In this specification, “a to b” indicating a numerical range is defined as ≥a and ≤b.

A polyimide film according to one aspect of the present invention may include a phosphorus compound having at least one linear or branched alkyl group having 1 to 6 carbon atoms.

For example, the phosphorus compound may be a phosphoric acid 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, and the like.

That is, the carbon number of the above-mentioned phosphorus compound may be 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.

In addition, the above-mentioned compound may contain 1 to 4, 1 to 3, or 1 to 2 alkyl groups having 1 to 6 carbon atoms.

Meanwhile, the alkyl group having 1 to 6 carbon atoms can be directly bonded to the phosphorus (P) atom of the phosphorus compound.

If the number of carbon atoms in the alkyl group of the above-mentioned phosphorus compound is outside the above range, the molecular weight of the compound may increase and the phosphorus (P) content may decrease. In this case, the polyimide film containing the above-mentioned phosphorus compound may have reduced strength, elongation, and elastic modulus.

Meanwhile, the above-mentioned phosphorus compound may be a phosphate compound.

In one embodiment, the phosphorus compound included in the polyimide film for producing the graphite sheet may be at least one selected from the group consisting of triethyl phosphate (TEP), trimethyl phosphate (TMP), tributyl phosphate (TBP), and tri-iso-butyl phosphate (TiBP).

In one embodiment, the phosphorus compound may be included in an amount of 2 parts by weight or more and 8 parts by weight or less, based on 100 parts by weight of the total content of the imidization catalyst included in the polyimide film.

That is, when the total content of the imidization catalyst included in the polyimide film is considered to be 100 parts by weight, the total content of the phosphorus compound included in the polyimide film may be 2 parts by weight or more and 8 parts by weight or less.

For example, when the total content of the imidization catalyst included in the polyimide film is 10 g, the total content of the phosphorus compound included in the polyimide film may be 0.2 g or more and 0.8 g or less.

For example, the amount of the above-described phosphorus compound may be 2 parts by weight or more and 8 parts by weight or less, 3 parts by weight or more and 7 parts by weight or less, 3 parts by weight or more and 6.5 parts by weight or less, or 3 parts by weight or more and 6 parts by weight or less, based on 100 parts by weight of the total content of the imidization catalyst included in the polyimide film.

If the content of the above-mentioned phosphorus compound exceeds the content range of the present invention, severe shrinkage may occur in the gel film, preventing film formation and making it impossible to manufacture a polyimide film. If the content falls below the content range of the present invention, the mechanical properties of the polyimide film may deteriorate, such as a decrease in strength and elongation.

In one embodiment, the polyimide film for producing the graphite sheet may have a strength in the machine direction (MD) of 265 MPa or more and 310 MPa or less and a strength in the transverse direction (TD) of 255 MPa or more and 320 MPa or less.

For example, the polyimide film for producing the graphite sheet has 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, It can be 305 MPa or more and 310 MPa or less.

And, the strength in the transverse direction (TD) is 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 305 MPa Less than, 305 MPa or more but less than 310 MPa, 310 MPa or more but less than 315 MPa, 315 MPa or more but less than 320 MPa.

In one embodiment, the polyimide film for producing the graphite sheet may have an elongation in the machine direction (MD) of 128% or more and 135% or less and an elongation in the transverse direction (TD) of 132% or more and 138% or less.

For example, the polyimide film for manufacturing the graphite sheet may have an elongation in the machine direction (MD) 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.

And, the elongation in the transverse direction (TD) can be 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 less than 133%, 133% or more and less than 134%, 134% or more and less than 135%, 135% or more and less than 136%, 136% or more and 137% or less, 137% or more and 138% or less.

In one embodiment, the polyimide film for producing the graphite sheet may have an elastic modulus in the machine direction (MD) of 1.8 GPa or more and 2.6 GPa or less and an elastic modulus in the transverse direction (TD) of 1.5 GPa or more and 2.5 GPa or less.

For example, the polyimide film for manufacturing the graphite sheet may have an elastic modulus in the machine direction (MD) 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 2.6 GPa.

And, 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, 2.4 GPa or more and 2.5 GPa or less. there is.

In one embodiment, the polyimide film for producing the graphite sheet may have an L* value of 50 or more and 70 or less as measured by a colorimeter.

For example, the polyimide film for manufacturing the graphite sheet may have an L* value measured by a colorimeter 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 or less.

In addition, the polyimide film for manufacturing the graphite sheet may have an a* value of 12.5 or more and 18 or less as measured by a colorimeter.

For example, the polyimide film for manufacturing the above graphite sheet may have an a* value measured using a colorimeter of 12.7 or more and 17.5 or less, 12.8 or more and 17 or less, 12.9 or more and 16.5 or less, or 13.1 or more and 16.1 or less.

In addition, the polyimide film for manufacturing the graphite sheet may have a b* value of 70 or more and 100 or less as measured by a colorimeter.

For example, the polyimide film for manufacturing the above graphite sheet may have a b* value measured using a colorimeter of 75 or more and 95 or less, 80 or more and 93 or less, 85 or more and 91 or less, 86 or more and 90 or less, or 87.5 or more and 89.3 or less.

In one embodiment, the polyimide film for producing the graphite sheet may have a transmittance of 25% or more and 40% or less as measured using a colorimeter (Ultra scan pro, Hunter Lab).

For example, the polyimide film for manufacturing the above graphite sheet may have a transmittance of 25.5% or more and 35% or less, 26% or more and 33% or less, 27% or more and 31% or less, or 27.4% or more and 30.9% or less as measured using a colorimeter (Ultra scan pro, Hunter Lab Co.).

In addition, the polyimide film for manufacturing the graphite sheet may have a haze value of 6% or more and 17% or less as measured using a colorimeter (Ultra scan pro, Hunter Lab).

For example, the polyimide film for manufacturing the above graphite sheet may have a haze value measured using a colorimeter (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 the graphite sheet may have a slope of a stress-strain curve calculated by the following mathematical expression 1 of 50 or more and 100 or less at a strain of 0.2 mm/mm or more and 0.8 mm/mm or less.

[Mathematical Formula 1]

Slope = (Stress at strain 0.8 mm/mm - Stress at strain 0.2 mm/mm) / (0.8-0.2)

In the above mathematical expression 1, (0.8-0.2) means the strain difference at the strain points of 0.2 mm/mm and 0.8 mm/mm.

For example, the slope of the stress-strain curve may be, in the section of strain of 0.2 mm/mm or more, 55 to 97, 60 to 94, 65 to 91, 70 to 88, 75 to 86, 80 to 84, 50 to less than 60, 60 to less than 70, 70 to less than 80, 80 to less than 90, or 90 to 100.

The above slope is a slope after the yield point and may mean the elastic modulus or elastic coefficient of the polyimide film for the graphite sheet.

In one embodiment, the Young's modulus of the polyimide film may be 200 kgf/mm ² or more and 260 kgf/mm ² or less. For example, the Young's modulus of the polyimide film may be 205 kgf/mm ² or more and 255 kgf/mm ² or less, 210 kgf/mm ² or more and 250 kgf/mm ² or less, 220 kgf/mm ² or more and 240 kgf/mm ² or less, or 225 kgf/mm ² or more and 232 kgf/mm ² or less.

In addition, 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 producing the graphite sheet is produced by imidizing a polyamic acid formed by a reaction of a dianhydride monomer and a diamine monomer, and the polyamic acid may have a weight average molecular weight of 100,000 to 500,000.

In the above range, graphitization can be facilitated when manufacturing a graphite sheet. Here, the 'weight average molecular weight' can be measured using gel chromatography (GPC) and polystyrene as a standard sample. The weight average molecular weight of the polyamic acid can be, for example, 150,000 to 500,000, for another example, 200,000 to 400,000, for 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 manufacturing the above graphite sheet, various monomers commonly used in the field of polyimide film manufacturing can be used.

For example, the dianhydride monomer of the polyimide film for producing the graphite sheet may be an aromatic dianhydride monomer, and the diamine monomer may be an aromatic diamine monomer. The dianhydride monomers 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, 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, 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-dicarboxy phenoxy)phenyl]propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, Examples of suitable dianhydrides include, but are not limited to, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride, or combinations thereof. As diamine monomers, 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, 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'-Diaminodiphenylsulfone, 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'-Diaminodiphenylsulfoxide, 3,4'-Diaminodiphenylsulfoxide, 4,4'-diaminodiphenylsulfoxide, 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)isopropyl]benzene, 1,4-bis[2-(4-aminophenyl)isopropyl]benzene, etc.), 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[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, etc.), or combinations thereof can be used, but are not limited thereto.

In particular, as the dianhydride monomer, 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 can be used, and as the diamine monomer, 4,4'-oxydianiline, 3,4'-oxydianiline, p-phenylenediamine, m-phenylenediamine, 4,4'-methylenedianiline, 3,3'-methylenedianiline or a combination thereof can be used.

For example, pyromellitic dianhydride can be used as the dianhydride monomer, and 4,4'-oxydianiline can be used as the diamine monomer.

The thickness of the polyimide film for producing the above graphite sheet may be 20 to 500 ㎛. The thickness of the polyimide film for producing the graphite sheet may be, for example, 20 to 500 ㎛, more preferably 25 to 400 ㎛, even more preferably 30 to 300 ㎛, and even more preferably 35 to 200 ㎛, but is not limited thereto.

The polyimide film for producing the above graphite sheet can be produced by various methods commonly used in the field of polyimide film production. For example, the polyimide film for producing the graphite sheet can be produced by, but is not limited to, polymerizing one or more dianhydride monomers and one or more diamine monomers in a solvent to produce a polyamic acid solution, then adding an imidization catalyst, a dehydrating agent, and optionally a sublimable inorganic filler, a solvent, etc. to the polyamic acid solution to form a composition for a polyimide film, and then forming the composition into a film.

The process of imidizing the above polyamic acid solution can be performed using a known imidization method, such as a thermal imidization method, a chemical imidization method, or a composite imidization method using a combination of the thermal imidization method and the chemical imidization method.

The average particle size ( _D50 ) of the entire sublimable inorganic filler included in the polyimide film for manufacturing the above graphite sheet may be 0.1 to 5.0 ㎛, and the content of the entire sublimable inorganic filler may be 0.07 to 0.4 wt% based on 100 wt% of the total weight of the polyimide film.

The above-mentioned sublimable inorganic filler can induce a predetermined foaming phenomenon by sublimation during carbonization and/or graphitization of the polyimide film. This foaming phenomenon can facilitate the exhaust of sublimation gas generated during carbonization and/or graphitization, thereby enabling the acquisition of a high-quality graphite sheet, and the predetermined pores formed by the foaming can also improve the bending resistance ('flexibility') of the graphite sheet.

However, since excessive foaming and the resulting large number of voids can significantly deteriorate the thermal conductivity and mechanical properties of the graphite sheet and cause defects on the surface of the graphite sheet, the type, content, and particle size of the sublimable inorganic filler must be carefully selected.

The '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 ( _D50 ) of the entire sublimable inorganic filler in the polyimide film for producing a graphite sheet may be, for example, 0.5 to 4.0 ㎛, for example, 1.0 to 5.0 ㎛, for another example, 1.5 to 5.0 ㎛, for another example, 1.5 to less than 2.5 ㎛, but is not limited thereto. The content of the entire 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 another example, 0.15 to 0.3 wt%, based on the total weight of the polyimide film, but is not limited thereto.

The above sublimable inorganic filler may include a first sublimable inorganic filler having an average particle diameter (D ₅₀ ) of 0.1 to 2.0 ㎛ and a second sublimable inorganic filler having an average particle diameter (D ₅₀ ) of more than 2.0 to 5.0 ㎛.

The contents of the first sublimable inorganic filler and the second sublimable inorganic filler among the above sublimable inorganic fillers are not particularly limited, but for example, the first sublimable inorganic filler may be included in an amount of 10 to 90 wt% and the second sublimable inorganic filler may be included in an amount of 10 to 90 wt% based on the total weight of the sublimable inorganic filler. For example, the content of the first sublimable inorganic filler may be, for example, 15 to 85 wt%, for another example, 20 to 80 wt%, for another example, 30 to 80 wt%, or for another example, 50 to 80 wt%, and the content of the second sublimable inorganic filler may be, for example, 85 to 15 wt%, for another example, 80 to 20 wt%, for another example, 70 to 20 wt%, or for another example, 50 to 20 wt%, but is not limited thereto.

Examples of the above sublimable inorganic filler include calcium carbonate, dibasic calcium phosphate, barium sulfate, etc. The above sublimable inorganic filler may more preferably be dibasic calcium phosphate, but is not limited thereto.

The solvent is not particularly limited as long as it can dissolve polyamic acid. For example, the solvent may include an aprotic polar solvent.

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, catechol; aprotic polar solvents such as hexamethylphosphoramide and γ-butyrolactone; etc. can be used alone or in combination of two or more, but are not limited thereto.

The above dehydrating agent may be acetic anhydride, propionic anhydride, butyric anhydride, benzoic anhydride, etc., alone or in combination of two or more, but is not limited thereto.

The above film forming may be performed by applying a polyamic acid solution in a film shape on a substrate, heating and drying at a temperature of 30 to 200°C for 15 seconds to 30 minutes to produce a gel film, and then heat-treating the gel film from which the substrate has been removed at a temperature of 250 to 600°C for 15 seconds to 30 minutes, but is not limited thereto.

When manufacturing graphite sheets using the polyimide film of this invention, it is possible to manufacture graphite sheets with excellent properties.

A graphite sheet according to another aspect of the present invention can be manufactured by carbonizing, graphitizing, or carbonizing and graphitizing a polyimide film for manufacturing a graphite sheet of the present invention.

The above carbonization is a process for forming a preliminary graphite sheet including an amorphous carbon body, a non-crystalline carbon body and/or an amorphous carbon body by thermally decomposing the polymer chains of the polyimide film for producing a graphite sheet, and may include, for example, a step of heating and maintaining the polyimide film under reduced pressure or in an inert gas atmosphere from room temperature to a maximum temperature of 1,000° C. to 1,500° C. for 10 to 30 hours, but is not limited thereto. Optionally, pressure may be applied to the polyimide film using a hot press or the like during carbonization in order to achieve a high degree of orientation of the carbon, and the pressure at this time may be, for example, 5 kg/cm ² or more, for another example, 15 kg/cm ² or more, and for another example, 25 kg/cm ² or more, but is not limited thereto.

The above graphitization is a process of forming a graphite sheet by rearranging carbon in an amorphous carbon body, amorphous carbon body and/or an amorphous carbon body, and may include, for example, a step of heating and maintaining a preliminary graphite sheet, optionally in an inert gas atmosphere, from room temperature to a maximum temperature of 2,500° C. to 3,000° C. for 2 to 30 hours, but is not limited thereto. Optionally, in order to achieve a high orientation of carbon, pressure may be applied to the preliminary graphite sheet using a hot press or the like during graphitization, and the pressure at this time may be, for example, 100 kg/cm ² or more, for another example, 200 kg/cm ² or more, and for another example, 300 kg/cm ² or more, but is not limited thereto.

According to another aspect of the present invention, the graphite sheet 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 10% or less.

In addition, the graphite sheet with the phosphorus compound of the present invention added can have an elongation increase of 250% or more compared to a graphite sheet manufactured without adding the phosphorus compound.

In particular, when the above-mentioned phosphorus compound is added in an amount exceeding 3%, the elongation can increase by more than 400%.

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.

For example, the strength of the graphite sheet may be 63.1 MPa or more and 84 MPa or less, 63.2 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.

And, 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 ㎛ and 22 to 28 ㎛, respectively, and the thermal diffusivity and thermal conductivity may be 550 to 620 mm ² /s and 850 to 990 W/(m*K), respectively.

Additionally, the density of the graphite sheet may be 1.85 to 1.89 g/cm ³ .

Hereinafter, the present invention will be described in more detail by way of examples. However, these are presented as preferred examples of the present invention, and the present invention cannot be construed as being limited by these in any way.

Manufacturing Example 1 (Manufacture of polyimide film)

250.0 g of dimethylformamide was added as a solvent to the reactor and the temperature was adjusted to 20°C. 30.0 g of 4,4'-oxydianiline (ODA) as a diamine monomer was added, and then 30.0 g of pyromellitic dianhydride (PMDA) as a dianhydride monomer was added to produce a polyamic acid solution having a viscosity of 230,000 cP.

Next, 80.0 g of acetic anhydride as a dehydrating agent, 10.0 g of β-picoline as an imidization catalyst, 0.12 g of dibasic calcium phosphate (Ajinomoto Co., Ltd., Top flow-K, average particle size ( _D50 ): 2.5 μm) as a sublimable inorganic filler, and 50.0 g of dimethylformamide were mixed into the prepared polyamic acid solution.

In addition, polyimide film precursor solutions of Examples 1 to 4 and Comparative Examples 1 to 8 were prepared by adding an appropriate amount of a phosphorus compound as shown in Table 1 below.

The prepared polyimide film precursor solution was cast to 38 μm on a SUS plate (100SA, Sandvik) using a doctor blade and dried at a temperature range of 100°C to 200°C to produce a self-supporting gel film.

Next, the gel film was peeled off from the SUS plate, fixed to a pin frame, and transferred to a high-temperature tenter. The film was heated from 200°C to 700°C in the high-temperature tenter, cooled to 25°C, and then separated from the pin frame to obtain a polyimide film.

Manufacturing Example 2 (Manufacturing of graphite sheet)

The polyimide film manufactured by Manufacturing Example 1 was heated to 1,210°C at a rate of 3.3°C/min under nitrogen gas using an electric furnace capable of carbonization, and maintained at 1,210°C for about 2 hours (carbonization).

Next, the first calcination step was performed by heating from 1,210 ℃ to 2,200 ℃ at a heating rate of 2.5 ℃/min under argon gas using an electric furnace capable of graphitization.

After reaching 2,200 ℃, the heating rate was changed to 1.25 ℃/min and the temperature was continuously increased to 2,500 ℃ to perform the second firing step.

After reaching 2,500 ℃, the heating rate was changed to 10 ℃/min and the temperature was continuously increased to 2,650 ℃ to perform the third firing step, and after standing still at 2,650 ℃ for several minutes, graphitization was completed to manufacture a graphite sheet.

Finally, the graphite sheet was cooled at a rate of 10 ℃/min.

The contents of the compounds of Examples 1 to 4 and Comparative Examples 1 to 8 are as shown in Table 1 below.

Phosphorus compound type Content
^{(Based on 100 parts by weight of imidization catalyst)} Example 1 TEP 3 Example 2 TEP 3.5 Example 3 TEP 4 Example 4 TEP 6 Comparative Example 1 - - Comparative Example 2 TEP 9 Comparative Example 3 BDP 4 Comparative Example 4 BDP 6 Comparative Example 5 CDP 4 Comparative Example 6 CDP 6 Comparative Example 7 TCP 4 Comparative Example 8 TCP 6

In the above Table 1, TEP is triethyl phosphate, BDP is bisphenol A bis(diphenyl phosphate), CDP is cresyl diphenyl phosphate, and TCP is tricresyl phosphate.

Example 1

According to Manufacturing Example 1, a polyimide film was manufactured by adding 3 parts by weight of triethyl phosphate (TEP) based on 100 parts by weight of the total content of the imidization catalyst included in the entire polyimide film. Thereafter, a graphite sheet was manufactured according to Manufacturing Example 2.

Example 2

A polyimide film and a graphite sheet were manufactured 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 imidization catalyst content included in the entire polyimide film.

Example 3

A polyimide film and a graphite sheet were manufactured 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 imidization catalyst content included in the entire polyimide film.

Example 4

A polyimide film and a graphite sheet were manufactured 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 imidization catalyst content included in the entire polyimide film.

Comparative Example 1

Polyimide films and graphite sheets were manufactured in the same manner as in Example 1, except that no phosphorus compound was added.

Comparative Example 2

A polyimide film and a graphite sheet were manufactured 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 imidization catalyst content included in the entire polyimide film.

Comparative Example 3

A polyimide film and a graphite sheet were manufactured 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 imidization catalyst content contained in the entire polyimide film.

Comparative Example 4

A polyimide film and graphite sheet were manufactured 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 imidization catalyst content contained in the entire polyimide film.

Comparative Example 5

A polyimide film and a graphite sheet were manufactured 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 imidization catalyst content included in the entire polyimide film.

Comparative Example 6

A polyimide film and graphite sheet were manufactured 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 imidization catalyst content included in the entire polyimide film.

Comparative Example 7

A polyimide film and a graphite sheet were manufactured 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 imidization catalyst content included in the entire polyimide film.

Comparative Example 8

A polyimide film and graphite sheet were manufactured 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 imidization catalyst content included in the entire polyimide film.

In the case of Comparative Example 2 where TEP was used in excess and Comparative Example 8 where TCP was used in excess, severe shrinkage occurred in the gel film and the film could not be formed, so that the polyimide film could not be manufactured, and the strength, elastic modulus, elongation, L*a*b* value, transmittance, and haze could not be measured.

Evaluation Example 1: Measurement of strength, elastic modulus, and elongation of polyimide film

The strength, elastic modulus, and elongation of the polyimide films of Examples 1 to 4 and Comparative Examples 1 to 8 manufactured according to Manufacturing Example 1 were measured.

Strength and elongation were measured using Autograph Universal Testing Machines (SHIMADZU, AG-IS) according to ASTM D882. In addition, elastic modulus was measured using Instron 5564 model according to ASTM D882 method.

Additionally, strength, elastic modulus, and elongation were measured in both the machine direction (MD) and transverse direction (TD).

The measurement results according to Evaluation Example 1 are shown in Table 2 below.

polyimide film
(Manufacturing Example 1) Strength (MPa) Elastic modulus (GPa) Believers (%) MD TD MD TD MD TD Example 1 274.5 281.9 2.3 2.1 134.3 135.9 Example 2 286.6 294.1 2.2 2.0 134.9 137.1 Example 3 291.6 295.4 2.2 2.1 133.9 133.3 Example 4 293.6 306.8 2.2 2.1 130.0 132.1 Comparative Example 1 216.3 214.6 2.7 2.6 131.6 129.1 Comparative Example 2 - - - - - - Comparative Example 3 264.7 254.6 2.8 2.6 138.6 134.7 Comparative Example 4 247.7 248.3 3.1 2.9 126.4 133.7 Comparative Example 5 229.4 236.1 2.8 2.8 133.1 131.0 Comparative Example 6 231.2 234.6 2.9 2.8 137.3 137.2 Comparative Example 7 222.6 224.0 2.8 2.7 134.1 131.2 Comparative Example 8 - - - - - -

Compared to the polyimide film of Comparative Example 1 that did not include a phosphorus compound, the strength of the polyimide films of Examples 1 to 4 that included the phosphorus compound triethyl phosphate increased in both the machine direction and the width direction.

In addition, the strength of the polyimide films of Examples 1 to 4 containing triethyl phosphate all increased compared to the polyimide films of Comparative Examples 3 to 7 containing bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate or tricresyl phosphate.

Specifically, for 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 width direction.

In the case of the elongation, the elongation of the polyimide films of Examples 1 to 4 containing the phosphorus compound triethyl phosphate was similar to or higher than that of the polyimide film of Comparative Example 1 which did not contain the phosphorus compound.

Specifically, for Examples 1 to 4, the range of the ductility was measured to be 130% or more and 135% or less in the length direction, and 129% or more and 138% or less in the width direction.

Compared to the polyimide film of Comparative Example 1 that did not include a phosphorus compound, the elastic modulus of the polyimide films of Examples 1 to 4 that included the phosphorus compound triethyl phosphate decreased in both the machine direction and the width direction.

In addition, the elastic modulus of the polyimide films of Examples 1 to 4 containing triethyl phosphate all decreased compared to the polyimide films of Comparative Examples 3 to 7 containing bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate or tricresyl phosphate.

Specifically, for Examples 1 to 4, the elastic modulus was measured to be in the range of 2.2 GPa or more and 2.3 GPa or less in the machine direction and in the range of 2.0 GPa or more and 2.1 GPa or less in the width direction.

Evaluation Example 2: Color L*a*b* measurement of polyimide film

The color L*a*b* values of the polyimide films of Examples 1 to 4 and Comparative Examples 1 to 8 manufactured according to Manufacturing Example 1 were measured at room temperature using a colorimeter (Ultra scan pro, Hunter Lab Co., Ltd.).

The measurement results according to Evaluation Example 2 are shown in Table 3 below.

polyimide film
(Manufacturing Example 1) Color L* a* b* Example 1 61.2 13.1 89.3 Example 2 59.5 14.4 88.6 Example 3 58.3 15.5 88.0 Example 4 57.1 16.1 87.5 Comparative Example 1 81.3 1.7 101.1 Comparative Example 2 - - - Comparative Example 3 71.5 12.0 101.1 Comparative Example 4 75.3 12.0 106.7 Comparative Example 5 78.9 7.7 105.4 Comparative Example 6 78.0 10.5 107.5 Comparative Example 7 78.4 8.5 105.5 Comparative Example 8 - - -

Compared to the polyimide film of Comparative Example 1 that does not include a phosphorus compound and the polyimide films of Comparative Examples 3 to 7 that include bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate or tricresyl phosphate, the L* value of the polyimide films of Examples 1 to 4 that include the phosphorus compound triethyl phosphate decreased, and thus the color became darker.

Specifically, for Examples 1 to 4, the range of L* values was measured to be 57 or more and 62 or less.

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 manufactured according to Manufacturing Example 1 were measured.

Transmittance and haze values were measured under light source A using a colorimeter (UltraScan Pro, HunterLab) based on the ASTM D1003 standard.

The measurement results according to Evaluation Example 3 are shown in Table 4 below.

polyimide film
(Manufacturing Example 1) Transmittance (%) Haze(%) Example 1 30.9 6.6 Example 2 28.3 10.3 Example 3 28.0 10.2 Example 4 27.4 11.1 Comparative Example 1 63.1 9.0 Comparative Example 2 - - Comparative Example 3 44.8 9.8 Comparative Example 4 51.6 8.4 Comparative Example 5 58.2 9.1 Comparative Example 6 56.4 8.9 Comparative Example 7 57.4 9.6 Comparative Example 8 - -

Compared to the polyimide film of Comparative Example 1 not including a phosphorus compound and the polyimide films of Comparative Examples 3 to 7 including bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate or tricresyl phosphate, the transmittance of the polyimide films of Examples 1 to 4 including the phosphorus compound triethyl phosphate all decreased.

Specifically, for Examples 1 to 4, the range of transmittance was measured to be 27% or more and 31% or less.

Compared to the polyimide film of Comparative Example 1 not including a phosphorus compound and the polyimide films of Comparative Examples 3 to 7 including bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate or tricresyl phosphate, the haze of the polyimide films of Examples 1 to 4 including the phosphorus compound triethyl phosphate tended to increase.

In the case of Example 1 containing 3 wt% of triethyl phosphate, the haze decreased compared to Comparative Examples 3 to 7, but in the case of Examples 2 to 4 containing 3.5, 4, and 6 wt% of triethyl phosphate, respectively, the haze increased compared to Comparative Examples 3 to 7.

Evaluation Example 4: Comparison of the slope of stress-strain curves of polyimide films

The Young's modulus and tensile strain of the polyimide films of Example 4 and Comparative Example 1 manufactured according to Manufacturing Example 1 were measured. In addition, the stress and strain were measured, and a graph (stress-strain curve) comparing the two values was drawn, and the slope of the graph when the strain was 0.2 mm/mm or more and 0.8 mm/mm or less was calculated and compared.

When comparing the average values of the results measured three times, the Young's modulus was measured as 2.6 GPa for Comparative Example 1 and 2.2 GPa for Example 4. That is, the Young's modulus decreased in the case of the polyimide film of Example 4 containing 6 wt% of triethyl phosphate compared to the polyimide film of Comparative Example 1 not containing a phosphorus compound.

In addition, when comparing the average values of the results of six measurements, the tensile strain was measured as 121.5% for Comparative Example 1 and 107.5% for Example 4. That is, the tensile strain decreased in the case of the polyimide film of Example 4 containing 6 wt% of triethyl phosphate compared to the polyimide film of Comparative Example 1 not containing a phosphorus compound.

As shown in Fig. 1, in the stress-strain curve graph, when the slope of the graph was calculated from when the strain was 0.2 mm or more to 0.8 mm or less, the slope of the graph of Comparative Example 1 was 44.39, and the slope of the graph of Example 4 increased to 81.25. That is, the stress after the yield point increased in the case of the polyimide film of Example 3 containing 6 wt% of triethyl phosphate compared to the polyimide film of Comparative Example 1 not containing a phosphorus compound.

Evaluation Example 5: Measurement of thermal decomposition characteristics of polyimide film

The thermal decomposition characteristics of the polyimide films of Example 3 and Comparative Examples 1, 3, 5, and 7 manufactured according to Manufacturing Example 1 were measured.

Thermal decomposition characteristics were measured using Thermogravimetric Analysis (TA Instruments, TGA5500) at a heating rate of 10°C/min up to 625°C.

Compared to the polyimide films of Comparative Example 1 not including a phosphorus compound and Comparative Examples 3, 5 and 7 including bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate or tricresyl phosphate, the polyimide film of Example 3 including triethyl phosphate all showed an increase in the residual amount upon thermal decomposition 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 amount upon thermal decomposition at 625°C was measured to be 74 wt% for Comparative Example 1, 77 wt% for Comparative Example 3, 80 wt% for Comparative Example 5, and 81 wt% for Comparative Example 7, indicating that the residual amount upon thermal decomposition was measured to be greater in the case of Example 3 than in the cases of Comparative Examples 1, 3, 5, and 7.

That is, it was measured that the polyimide film containing triethyl phosphate had a high residual amount and thus was excellent in its effect as a flame retardant.

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 manufactured according to Manufacturing Example 2 were measured.

Strength was measured using Autograph Universal Testing Machines (SHIMADZU, AG-IS) according to ASTM D882. In addition, elastic modulus was measured using Instron 5564 model according to ASTM D882 method.

Additionally, strength and elastic modulus were measured in the machine direction (MD).

The measurement results according to Evaluation Example 6 are shown in Table 5 below.

Graphite Sheet
(Manufacturing example 2) Strength (MPa, MD) Elastic modulus (GPa, MD) Example 1 63.5 2.1 Example 2 81.2 2.0 Example 3 76.3 1.6 Example 4 67.4 1.3 Comparative Example 1 56.3 5.3 Comparative Example 2 - - Comparative Example 3 62.8 2.0 Comparative Example 4 50.1 1.3 Comparative Example 5 58.3 2.5 Comparative Example 6 63.1 2.8 Comparative Example 7 62.8 2.7 Comparative Example 8 - -

Compared to the graphite sheet of Comparative Example 1 not including a phosphorus compound and the graphite sheets of Comparative Examples 3 to 7 including bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate or tricresyl phosphate, the strength of the graphite sheets of Examples 1 to 4 including the phosphorus compound triethyl phosphate was improved and the elastic modulus was decreased.

Specifically, for Examples 1 to 4, the strength range was measured as 63.5 MPa to 81.2 MPa, and the elastic modulus range was measured as 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.

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 manufactured according to Manufacturing Example 2 was measured.

The test specimens were measured in the machine direction (MD) using Autograph Universal Testing Machines (SHIMADZU, AG-IS) according to ASTM D882.

The measurement results according to Evaluation Example 7 are shown in Table 6 below.

Graphite Sheet
(Manufacturing example 2) Believers (%, MD) Example 1 5.8 Example 2 7.5 Example 3 7.6 Example 4 7.4 Comparative Example 1 1.5 Comparative Example 2 - Comparative Example 3 5.4 Comparative Example 4 5.4 Comparative Example 5 4.3 Comparative Example 6 4.8 Comparative Example 7 4.6 Comparative Example 8 -

Compared to the graphite sheet of Comparative Example 1 which did not include a phosphorus compound and the graphite sheets of Comparative Examples 3 to 7 which included bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate or tricresyl phosphate, the elongation of the graphite sheets of Examples 1 to 4 which included the phosphorus compound triethyl phosphate increased.

Specifically, for Examples 1 to 4, the range of the degree of faith was measured to be 5.5% or more and 8% or less.

Evaluation Example 8: Measurement of foam thickness and rolling thickness of graphite sheet

The foaming thickness and rolling thickness of the graphite sheets of Examples 1 to 4 and Comparative Examples 1 to 8 manufactured according to Manufacturing Example 2 were measured.

The foam thickness and rolling thickness were measured by a Digital Micrometer (Standard-type, Mitutoyo).

The measurement results according to Evaluation Example 8 are shown in Table 7 below.

Graphite Sheet
(Manufacturing example 2) Foam thickness (㎛) Rolling thickness (㎛) Example 1 65 22 Example 2 85 25 Example 3 96 23 Example 4 122 23 Comparative Example 1 38 18 Comparative Example 2 - - Comparative Example 3 67 21 Comparative Example 4 76 22 Comparative Example 5 57 20 Comparative Example 6 58 21 Comparative Example 7 58 22 Comparative Example 8 - -

Compared to the graphite sheet of Comparative Example 1 not including a phosphorus compound and the graphite sheets of Comparative Examples 3 to 7 including bisphenol A bisdiphenyl phosphate, cresyl diphenyl phosphate or tricresyl phosphate, the foaming thickness of the graphite sheets of Examples 1 to 4 including the phosphorus compound triethyl phosphate increased.

Specifically, in the cases of Examples 1 to 4, the foaming thickness was measured to be 65 ㎛ or more and 122 ㎛ or less, and the rolling thickness was measured to be 22 ㎛ or more and 25 ㎛ or less.

In the case of Examples 1 to 4, since the foaming phenomenon is more smoothly achieved than in the graphite sheets of Comparative Examples 1 to 7 due to the application of TEP, the obtaining of the graphite sheet is advantageous. In addition, the pores formed by the foaming are also advantageous for the flexibility of the graphite sheet. Despite such a foaming thickness, in the case of Examples 1 to 4, there is no significant difference in the rolling thickness compared to the case of Comparative Examples 1 to 7. That is, it was confirmed that both flexibility and a thin rolling thickness were achieved through a smooth foaming phenomenon.

Evaluation Example 9: Measurement of density, thermal diffusivity and thermal conductivity of graphite sheets

The density, thermal diffusivity and thermal conductivity of the graphite sheets of Examples 1 to 4 manufactured according to Manufacturing Example 2 were measured.

The density was measured using a Pycnometer (AccuPyc 1340, Micromeritics) at room temperature in helium gas on specimens cut into 15 mm X 300 mm (width X length) sizes from the manufactured polyimide film.

The thermal diffusivity was measured by cutting a graphite sheet into a size of 1 inch in diameter and 18 ㎛ in thickness, preparing a sample, and measuring the thermal diffusivity in the plane direction by the Laser Flash method using a measuring device (Netsch, LFA 467).

The thermal conductivity was calculated by multiplying the thermal diffusivity values measured in this way (average values measured five times each at a temperature of 25℃) by the density (weight/volume) and specific heat (theoretical value: 0.85 kJ/(kg K)).

The measurement results according to Evaluation Example 9 are shown in Table 8 below.

Graphite Sheet
(Manufacturing example 2) Thermal diffusivity (mm ² /s) Density (g/cm ³ ) Thermal Conductivity (W/(m*K)) Example 1 618 1.84 965 Example 2 582 1.65 816 Example 3 554 1.85 873 Example 4 554 1.89 892

The thermal diffusivity of the graphite sheets of Examples 1 to 4 containing the phosphorus compound triethyl phosphate was measured to be 554 mm ² /s or more and 618 mm ² /s or less, and the thermal conductivity was measured to be 816 W/(m*K) or more and 965 W/(m*K) or less.

Additionally, in the cases of Examples 1 to 4, the density of the graphite sheet was measured to be 1.65 g/cm ³ or more and 1.89 g/cm ³ or less.

The embodiments of the manufacturing method of the present invention are only preferred embodiments that enable those skilled in the art with common knowledge in the technical field to which the present invention belongs to to easily carry out the present invention, and are not limited to the above-described embodiments, so that the scope of the rights of the present invention is not limited thereby. Therefore, the true technical protection scope of the present invention should be determined by the technical idea of the appended patent claims. In addition, it will be obvious to those skilled in the art that various substitutions, modifications, and changes are possible within the scope that does not depart from the technical idea of the present invention, and it is self-evident that parts that can be easily changed by those skilled in the art are also included in the scope of the rights of the present invention.

Claims (11)

Comprising a phosphorus compound having at least one linear or branched alkyl group having 1 to 6 carbon atoms,
Polyimide film for manufacturing graphite sheets.
In the first paragraph,
The above-mentioned phosphorus compound is at least one selected from the group consisting of triethyl phosphate (TEP), trimethyl phosphate (TMP), tributyl phosphate (TBP), and tri-iso-butyl phosphate (TiBP).
Polyimide film for manufacturing graphite sheets.
In the first paragraph,
Based on 100 parts by weight of the total content of the imidization catalyst included in the polyimide film, the phosphorus compound is included in an amount of 2 parts by weight or more and 8 parts by weight or less.
Polyimide film for manufacturing graphite sheets.
In the first paragraph,
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.
Polyimide film for manufacturing graphite sheets.
In the first paragraph,
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.
Polyimide film for manufacturing graphite sheets.
In the first paragraph,
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.
Polyimide film for manufacturing graphite sheets.
In the first paragraph,
The L* value measured by a colorimeter is 50 or more and 70 or less,
Polyimide film for manufacturing graphite sheets.
In the first paragraph,
Between strains of 0.2 mm/mm and 0.8 mm/mm,
The slope of the stress-strain curve calculated by the following mathematical expression 1 is 50 or more and 100 or less.
Polyimide film for manufacturing graphite sheets.

[Mathematical formula 1]
Slope = (Stress at strain 0.8 mm/mm - Stress at strain 0.2 mm/mm) / (0.8-0.2)
A graphite sheet manufactured by carbonizing, graphitizing, or carbonizing and graphitizing the polyimide film of any one of claims 1 to 8.
In Article 9,
Graphite sheet having a content of 5.5% or more and 10% or less.
In Article 9,
A graphite sheet 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.