Polyimide film for graphite sheet and graphite sheet produced from the same

Abstract

In the X-ray diffraction analysis in the plane direction, the full width at half maximum (FWHM) (deg., 2θ) of the (002) peak is 30° to 37°, and in the X-ray diffraction analysis in the thickness direction, the Herman's orientation index (f c ) is 0.06 to 0.20, and a graphite sheet produced from the polyimide film is disclosed.

Description

[Technical field]

[0001] The present invention relates to a polyimide film for graphite sheet and a graphite sheet produced therefrom, and more particularly to a polyimide film for graphite sheet having excellent thermal conductivity and a graphite sheet produced therefrom. [Background technology]

[0002] Recently, electronic devices have become lighter, smaller, thinner, and more highly integrated, which causes a lot of heat to be generated in the electronic devices. This heat can shorten the lifespan of the product and can cause breakdowns and malfunctions. Therefore, thermal management for electronic devices has emerged as an important issue.

[0003] Graphite sheets have a higher thermal conductivity than metal sheets such as copper and aluminum, and are therefore attracting attention as heat dissipation materials for electronic devices. Such graphite sheets can be manufactured in a variety of ways, for example, by carbonizing and graphitizing a polymer film. In particular, polyimide films have been in the spotlight as polymer films for manufacturing graphite sheets due to their excellent mechanical and thermal dimensional stability, chemical stability, and the like.

[0004] It is known that the physical properties of a graphite sheet produced from a polyimide film are affected by the physical properties of the polyimide film. Therefore, various polyimide films for graphite sheets have been developed, but there is still a need for a polyimide film that can produce a graphite sheet having higher thermal conductivity. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a polyimide film for a graphite sheet having excellent thermal conductivity. Another object of the present invention is to provide a graphite sheet produced from the polyimide film. [Means for solving the problem]

[0006] 1. According to one embodiment, there is provided a polyimide film for a graphite sheet. The polyimide film has a full width at half maximum (FWHM) (deg., 2θ) of a (002) peak of 30° to 37° in an X-ray diffraction analysis in a plane direction, and a Herman's orientation index (f) of the following formula 1 in an X-ray diffraction analysis in a thickness direction: c ) may be 0.06 to 0.20:

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[0007] The present invention has an effect of providing a polyimide film for a graphite sheet and a graphite sheet having excellent thermal conductivity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] In this specification, the singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, the terms including, having, etc., mean the presence of features or components described in the specification, but do not preclude the possibility that one or more other features or components may be added. When interpreting elements, they are interpreted as including error ranges unless otherwise expressly stated. In this specification, the "to" in the expression "a to b" indicating a numerical range is defined as ≧a and ≦b. In this specification, viscosity is measured at 23°C and a shear rate of 1 s -1This can be measured using the HAAKE Mars Rheometer. In this specification, the gel film can mean a film that is in an intermediate stage of curing from polyamic acid to polyimide and has self-supporting properties.

[0009] The polyimide film for graphite sheet according to one embodiment of the present invention has a (002) peak full width at half maximum (FWHM) (deg., 2θ) of 30° to 37° in an X-ray diffraction analysis in a plane direction, and a Herman's orientation index (f) of the following formula 1 in an X-ray diffraction analysis in a thickness direction: c ) may be 0.06 to 0.20:

number

[0010] For example, the polyimide film may have a (002) peak half-width of 30°, 31°, 32°, 33°, 34°, 35°, 36°, or 37° when analyzed by X-ray diffraction in the in-plane direction. According to one embodiment, the polyimide film may have a (002) peak half-width of 32° to 37° when analyzed by X-ray diffraction in the in-plane direction, 32° to 36° in another embodiment, 33° to 36° in yet another embodiment, and 33° to 34° in yet another embodiment, but is not limited thereto.

[0011] For example, when a polyimide film is analyzed by X-ray diffraction in the thickness direction, the Herman orientation degree (f c) may be 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.20. According to one embodiment, the polyimide film has a Hellman orientation (f) of Formula 1 when analyzed by X-ray diffraction in the thickness direction. c ) may be 0.06 to 0.16, according to another embodiment, 0.08 to 0.16, according to yet another embodiment, 0.08 to 0.11, and according to yet another embodiment, 0.10 to 0.12, but is not limited thereto.

[0012] According to one embodiment, the polyimide film may be derived from a gel film that is stretched from a polyamic acid solution. One method for improving the thermal conductivity of a graphite sheet is to increase the orientation of the polyimide film by stretching the gel film. Thus, a polyimide film derived from a stretched gel film may have a higher orientation than a polyimide film derived from an unstretched gel film, which may be more advantageous for producing a graphite sheet with excellent thermal conductivity.

[0013] According to one embodiment, the stretched gel film is formed by stretching the gel film in a MD (machine The film may be stretched in at least one of the TD (transverse direction) and TD (transverse direction).

[0014] According to one embodiment, the stretched gel film may be a gel film stretched at a ratio of 1.01 times to 1.5 times in MD (for example, 1.01 times, 1.05 times, 1.1 times, 1.15 times, 1.2 times, 1.25 times, 1.3 times, 1.35 times, 1.4 times, 1.45 times, or 1.5 times). This range may be advantageous for the production of a highly oriented polyimide film, and as a result, a graphite sheet produced therefrom may have excellent thermal conductivity. For example, the stretched gel film may be a gel film stretched at a ratio of 1.03 times to 1.5 times in MD, as another example, 1.05 times to 1.4 times, and as yet another example, 1.1 times to 1.4 times, but is not limited thereto.

[0015] According to one embodiment, the polyamic acid solution may be prepared by reacting a dianhydride monomer and a diamine monomer in a solvent.

[0016] The solvent is not particularly limited as long as it can dissolve the polyamic acid. For example, the solvent can include an aprotic polar solvent. Examples of aprotic polar solvents include amide solvents such as N,N'-dimethylformamide (DMF) and N,N'-dimethylacetamide (DMAc), phenol solvents such as p-chlorophenol and o-chlorophenol, N-methyl-pyrrolidone (NMP), gamma butyrolactone (GBL), and diglyme, which can be used alone or in combination of two or more. In some cases, the solubility of the polyamic acid may be adjusted using auxiliary solvents such as toluene, tetrahydrofuran (THF), acetone, methyl ethyl ketone (MEK), methanol, ethanol, and water.

[0017] As the diamine monomer, various diamine monomers known in the art may be used without limitation within the scope of the present invention. For example, the diamine monomer may include 4,4'-oxydianiline (ODA), p-phenyldiamine (PPD), or a combination thereof, in which case the polyimide film may have excellent orientation properties.

[0018] As the dianhydride monomer, various dianhydride monomers known in the art may be used without limitation within the scope of the present invention. For example, the dianhydride monomer may include pyromellitic dianhydride (PMDA), which may provide excellent alignment of the polyimide film.

[0019] The diamine monomer and the dianhydride monomer are reacted in a substantially equimolar amount in the solvent, and the term "substantially equimolar amount" means that the dianhydride monomer is contained in an amount of 99.8 mol% to 100.2 mol% based on the total number of moles of the diamine monomer. The reaction of the diamine monomer and the dianhydride monomer in substantially equimolar amounts can be carried out, for example, by (a) A method in which all of the diamine monomers (or dianhydride monomers) are added to a solvent, and then a dianhydride monomer (or diamine monomer) is added in a substantially equimolar amount to react the diamine monomers; (b) A method of adding a part of a diamine monomer (or a dianhydride monomer) to a solvent, adding a dianhydride monomer (or a diamine monomer) in a ratio of 95 mol % to 105 mol % relative to the diamine monomer (or the dianhydride monomer), and then adding and reacting the diamine monomer and / or the dianhydride monomer in substantially equimolar amounts; (c) A first composition is formed by adding a part of the diamine monomer (or dianhydride monomer) and a part of the dianhydride monomer (or diamine monomer) into a solvent so that one of them is in excess, and a second composition is formed by adding a part of the diamine monomer (or dianhydride monomer) and a part of the dianhydride monomer (or diamine monomer) into a separate solvent so that one of them is in excess, and the first composition and the second composition are mixed and reacted, and at this time, when the diamine monomer (or dianhydride monomer) is in excess in the first composition, the dianhydride monomer (or diamine monomer) is in excess in the second composition. In the above (a) to (c), the diamine monomer and the dianhydride monomer may mean one or more (for example, one or two) diamine monomers and dianhydride monomers.

[0020] According to one embodiment, the polyamic acid solution can satisfy the following formula 2:

number

[0021] According to one embodiment, in formula 2, η0 may be 50,000cps to 300,000cps (for example, 50,000cps, 100,000cps, 150,000cps, 200,000cps, 250,000cps, or 300,000cps). This range may be advantageous for producing a polyimide film with high orientation. For example, η0 may be 70,000cps to 300,000cps, another example is 70,000cps to 250,000cps, and yet another example is 100,000cps to 150,000cps, but is not limited thereto.

[0022] According to one embodiment, in formula 2, (s) may be 15% by weight to 30% by weight (for example, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight, or 30% by weight). This range may be advantageous for producing a polyimide film having high orientation. For example, % (s) is 17% to 25% by weight, another example is 17% to 23% by weight, and yet another example is 20% to 23% by weight. It may be, but is not limited to this.

[0023] According to one embodiment, the weight average molecular weight of the polyamic acid may be 100,000 g / mol to 170,000 g / mol (e.g., 100,000 g / mol, 110,000 g / mol, 120,000 g / mol, 130,000 g / mol, 140,000 g / mol, 150,000 g / mol, 160,000 g / mol, or 170,000 g / mol). A weight average molecular weight in this range may be advantageous for producing a polyimide film having high orientation. For example, the weight average molecular weight of the polyamic acid may be, but is not limited to, 100,000 g / mol to 160,000 g / mol, another example is 100,000 g / mol to 150,000 g / mol, yet another example is 120,000 g / mol to 150,000 g / mol, and yet another example is 130,000 g / mol to 150,000 g / mol.

[0024] According to one embodiment, the gel film, i.e., the gel film before being stretched, may be manufactured by forming a precursor composition by adding a catalyst composition to a polyamic acid solution, forming the precursor composition, and drying the precursor composition. Here, the "catalyst composition" may refer to a composition including an imidizing agent that promotes a ring-closing reaction of the polyamic acid, and / or a dehydrating agent that promotes the ring-closing reaction by dehydrating the polyamic acid.

[0025] As the imidizing agent, for example, aliphatic tertiary amines, aromatic tertiary amines, heterocyclic tertiary amines, etc. can be used. Among them, heterocyclic tertiary amines can be used from the viewpoint of reactivity as a catalyst. Examples of heterocyclic tertiary amines include quinoline, isoquinoline, β-picoline, pyridine, etc., which can be used alone or in combination of two or more. The imidizing agent is added in an amount of 0.05 mol to 3 mol (for example, 0.2 mol to 2 mol) per mol of amic acid group in the polyamic acid, and within the above range, sufficient imidization can be achieved and it can be advantageous for casting into a film, but it is not limited thereto.

[0026] Examples of the dehydrating agent include aliphatic acid anhydrides, aromatic acid anhydrides, N,N'-dialkylcarbodiimides, lower aliphatic halides, halogenated lower aliphatic acid anhydrides, arylphosphonic acid dihalides, and thionyl halides, which can be used alone or in combination of two or more. Among them, from the viewpoint of availability and cost, aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, and lactic anhydride can be used. The dehydrating agent is added in an amount of 0.5 mol to 5 mol (for example, 1 mol to 4 mol) per mol of amic acid group in the polyamic acid, and within the above range, sufficient imidization is possible and it may be advantageous to cast into a film, but it is not limited thereto.

[0027] According to an embodiment, the catalyst composition may further include a sublimable inorganic filler. Here, the term "sublimable inorganic filler" may refer to an inorganic filler that is sublimated by heat during the carbonization and / or graphitization process in the manufacture of a graphite sheet. When the polyimide film includes a sublimable inorganic filler, voids are formed in the graphite sheet by gas generated by sublimation of the sublimable inorganic filler in the manufacture of the graphite sheet, and thus, the sublimation gas generated in the manufacture of the graphite sheet can be smoothly exhausted to obtain a good quality graphite sheet, and the flexibility of the graphite sheet can be improved, ultimately improving the handleability and moldability of the graphite sheet. Examples of the sublimable inorganic filler include, but are not limited to, dibasic calcium phosphate, barium sulfate, calcium carbonate, and the like. The average particle size (D 50 The thickness of the sublimable inorganic filler may be 0.05 μm to 5.0 μm (for example, 0.1 μm to 4.0 μm), and a graphite sheet of good quality can be obtained within the above range, but is not limited thereto. The sublimable inorganic filler is contained in an amount of 0.01 parts by weight to 0.5 parts by weight (for example, 0.02 parts by weight to 0.2 parts by weight) based on 100 parts by weight of the polyamic acid, and a graphite sheet of good quality can be obtained within the above range. can be obtained, but is not limited to this.

[0028] According to one embodiment, the catalyst composition may further include a solvent. For the description of the solvent contained in the catalyst composition, refer to the description of the solvent contained in the polyamic acid solution.

[0029] According to one embodiment, the catalyst composition may include an imidizing agent, a dehydrating agent, a sublimable inorganic filler, and a solvent.

[0030] According to one embodiment, the catalyst composition may contain 3 wt% to 15 wt% of an imidizing agent, 30 wt% to 70 wt% of a dehydrating agent, 0.01 wt% to 0.5 wt% of the sublimable inorganic filler, and the remaining amount of a solvent, based on the total weight of the catalyst composition. In this case, it may be advantageous to produce a polyimide film having high orientation. For example, the catalyst composition may contain 5 wt% to 10 wt% of an imidizing agent, 40 wt% to 60 wt% of a dehydrating agent, 0.02 wt% to 0.2 wt% of a sublimable inorganic filler, and the remaining amount of a solvent, based on the total weight of the catalyst composition, but is not limited thereto.

[0031] According to one embodiment, the catalyst composition is added in an amount of 30 to 60 parts by weight per 100 parts by weight of the polyamic acid solution. This range may be advantageous for producing a polyimide film having high orientation. For example, the catalyst composition is added in an amount of 35 to 55 parts by weight, or another example, 37 to 52 parts by weight per 100 parts by weight of the polyamic acid solution, but is not limited thereto.

[0032] According to one embodiment, the precursor composition can satisfy Equation 3 below:

number

[0033] According to one embodiment, in formula 3, η1 may be 2,500 cps to 30,000 cps (e.g., 2,500 cps, 5,000 cps, 7,500 cps, 10,000 cps, 12,500 cps, 15,000 cps, 17,500 cps, 20,000 cps, 22,500 cps, 25,000 cps, 27,500 cps, or 30,000 cps). This range may be advantageous for producing a polyimide film having high orientation. For example, η1 may be 5,000 cps to 25,000 cps, or as another example, 7,500 cps to 15,000 cps, but is not limited to this.

[0034] According to one embodiment, in formula 3, t(η2) may be 100 seconds to 400 seconds (for example, 100 seconds, 150 seconds, 200 seconds, 250 seconds, 300 seconds, 350 seconds, or 400 seconds). This range may be advantageous for producing a polyimide film having high orientation. For example, t(η2) may be 100 seconds to 390 seconds, and as another example, t(η2) may be 100 seconds to 380 seconds, but is not limited thereto.

[0035] According to one embodiment, the film may be formed by casting the precursor composition onto a support, and the support may be a glass plate, an aluminum foil, an endless stainless steel belt, a stainless steel drum, or the like.

[0036] According to one embodiment, drying is performed at a temperature of 30° C. to 200° C. (e.g., 80° C. to 180° C.) for 15 seconds to 30 minutes (e.g., 2 minutes to 10 minutes). This range may be advantageous for producing a highly oriented polyimide film, but is not limited thereto.

[0037] The heat treatment is carried out to remove the solvent remaining in the stretched gel film and to imidize most of the remaining amic acid groups to obtain a polyimide film.

[0038] According to one embodiment, the heat treatment is carried out at a temperature of 250° C. to 600° C. (e.g., 260° C. to 550° C., as another example, 270° C. to 500° C.) for 30 seconds to 40 minutes (e.g., 2 minutes to 15 minutes). Sufficient imidization is achieved within the above range, but the present invention is not limited thereto.

[0039] The polyimide film described above has excellent orientation, and as a result, a graphite sheet manufactured from the polyimide film has excellent thermal conductivity.

[0040] According to another aspect, there is provided a graphite sheet produced from the above-mentioned polyimide film. The graphite sheet can be obtained by carbonizing and graphitizing the above-mentioned polyimide film.

[0041] "Carbonization" is a process of pyrolyzing the polymer chains of a polyimide film to form a preliminary graphite sheet containing an amorphous carbon body, a non-crystalline carbon body, and / or an amorphous carbon body, and is carried out, for example, by raising the temperature of a polyimide film from room temperature to a maximum temperature in the range of 1,000°C to 1,500°C at a rate of 0.3°C / min to 10°C / min under reduced pressure or in an inert gas atmosphere, and maintaining the temperature for 10 to 180 minutes, but is not limited thereto. Optionally, in order to achieve high carbon orientation, pressure may be applied to the polyimide film during carbonization using a hot press or the like, and the pressure at this time may be, for example, 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.

[0042] "Graphitization" is a process of forming a graphite sheet by rearranging carbon in an amorphous carbon body, non-crystalline carbon body, and / or amorphous carbon body, and is carried out, for example, by raising 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 at a rate of 0.5°C / min to 20°C / min under an inert gas atmosphere, and maintaining the temperature for 10 to 300 minutes, but is not limited thereto. Optionally, in order to achieve high carbon orientation, pressure may be applied to the preliminary graphite sheet during graphitization using a hot press or the like, and the pressure at this time may be, for example, 100 kg / cm. 2 As another example, 200 kg / cm 2 As another example, 300 kg / cm 2 It may be more than this, but is not limited to this.

[0043] According to one embodiment, the graphite sheet may have a thickness of 10 μm to 100 μm (e.g., 15 μm to 90 μm) and a thermal conductivity of 1,400 W / m·K or more (e.g., 1,400 W / m·K to 1,500 W / m·K). The graphite sheet according to one embodiment of the present invention is manufactured using a highly oriented polyimide film made from a gel film suitable for stretching, and therefore may have excellent thermal conductivity. EXAMPLES

[0044] The present invention will be described in more detail below with reference to examples. However, these are presented as preferred examples of the present invention and are not to be construed as limiting the present invention in any sense.

[0045] Working Example Examples 1 to 5 and Comparative Examples 1 to 4 341.5g of dimethylformamide was added as a solvent to the reactor, and the temperature was adjusted to 20°C. 51.5g of 4,4'-oxydianiline (ODA) was added thereto, and then 55.5g of pyromellitic dianhydride (PMDA) was added. After the temperature was raised to 40°C, pyromellitic dianhydride was further added little by little to produce a polyamic acid solution having the weight average molecular weight (Mw) value of Formula 1 in Tables 1 and 2.

[0046] The polyamic acid solution thus prepared was mixed with 57.7% by weight of acetic anhydride as a dehydrating agent, 7.1% by weight of β-picoline as an imidizing agent, and 2-calcium phosphate (average particle size (D 50 ):2.0μm) 0.1 wt% and the remaining amount of dimethylformamide were mixed to prepare a catalyst composition. The amount of the catalyst composition added was adjusted so that the polyimide film precursor composition had the value of Formula 2 in Tables 1 and 2.

[0047] The prepared precursor composition was cast on a SUS plate (100SA, Sandvik) using a doctor blade to form a film with a thickness of 250 μm, and dried at 130° C. for 4 minutes to prepare a gel film.

[0048] The gel film thus produced was separated from the SUS plate, and then stretched in the MD at the stretch ratios shown in Tables 1 and 2.

[0049] The stretched gel film was heat-treated at 420° C. for 5 minutes to produce a polyimide film having a thickness of 50 μm.

[0050] Evaluation example (1) Viscosity: Using a viscosity measuring device (Rheostress600, Haake), the viscosity (unit: cps) of the polyamic acid solution and the precursor composition was measured over time (unit: second) under conditions of a shear rate of 1 / s, a temperature of 23°C, and a plate gap of 1 mm. (2) Weight average molecular weight (Mw): The weight average molecular weight (unit: g / mol) of the polyamic acid in terms of polystyrene was determined using a molecular weight measuring device (Sykam GPC SYSTEM, Laser Chroma). (3) X-ray diffraction analysis: The detailed conditions related to the XRD analysis are as follows: -Light source: Bending magnet synchrotron radiation / 6D UNIST-PAL beamline (Pohang Light Source) -Energy used: 18.986keV (wavelength: 0.653Å) -Light source size: 100(H)×40(V)μm 2 -X-ray exposure time: 60~240 seconds -Detector: Rayonix MX225-HS (2880 x 2880 pixels, pi xel size:78μm) (4) Thermal conductivity (unit: W / m K): The polyimide films prepared in the examples and comparative examples were carbonized by heating to 1,200°C at a rate of 1°C / min under nitrogen gas using an electric furnace and maintaining the temperature for 2 hours. Thereafter, the polyimide films were carbonized by heating to 2,800°C at a rate of 10°C / min under argon gas and maintaining the temperature for 2 hours to produce graphite sheets having a thickness of 25 μm.

[0051] The graphite sheet thus produced was cut into a circular specimen with a diameter of 25.4 mm, and the thermal diffusivity of the specimen was measured by the laser flash method using a thermal diffusivity measuring device (LFA467, Netsch). The thermal conductivity was calculated by multiplying the measured thermal diffusivity by the density and specific heat (theoretical value: 0.85 kJ / kg K).

[0052] [Table 1]

[0053] [Table 2]

[0054] From Tables 1 and 2, in the X-ray diffraction analysis in the plane direction, the half-width of the (002) peak and in the X-ray diffraction analysis in the thickness direction, the Herman orientation (f c It can be seen that the graphite sheets made from the polyimides of Examples 1 to 5, whose thermal conductivity falls within the scope of the present invention, have superior thermal conductivity compared to the graphite sheets made from the polyimides of Comparative Examples 1 to 4, whose thermal conductivity falls within the scope of the present invention. The present invention has been described above with reference to the embodiments. Those skilled in the art will understand that the present invention can be realized in modified forms without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than restrictive manner. The scope of the present invention is defined in the claims, not in the above description, and all differences within the scope of the equivalents thereof should be interpreted as being included in the present invention. [Industrial Applicability]

[0055] The present invention has an effect of providing a polyimide film for a graphite sheet and a graphite sheet having excellent thermal conductivity.

Claims

1. A polyimide film for graphite sheet, comprising a polyimide having a dianhydride monomer and a diamine monomer as polymerization units, The dianhydride monomer includes pyromellitic dianhydride, and the diamine monomer includes 4,4'-oxydianiline; In the case of X-ray diffraction analysis in the plane direction, the full width at half maximum (FWHM) (deg., 2θ) of the (002) peak is 30° to 37°, and in the case of X-ray diffraction analysis in the thickness direction, the Herman's orientation (FWHM) of the following formula 1 is obtained: orientation index, f ｃ ) is 0.06 to 0.

20. [0010] (In the above formula 1, α is the half width (deg., 2θ) of the (002) peak.)

2. A method for producing the polyimide film for graphite sheet according to claim 1, The polyimide film is derived from a stretched gel film formed from a polyamic acid solution.

3. 3. The method for manufacturing a polyimide film for a graphite sheet according to claim 2, wherein the stretched gel film is stretched in a machine direction (MD) at a ratio of 1.01 to 1.5 times.

4. The weight average molecular weight of the polyamic acid is 100,000 g / mol to 170,000 g / mol; 3. The method for producing a polyimide film for graphite sheet according to claim 2, wherein the polyamic acid solution is produced by reacting a dianhydride monomer and a diamine monomer in a solvent and satisfies the following formula 2: [0025] (In the above formula 2, η ０ is the viscosity of the polyamic acid solution (23°C, unit: cps), % （ｓ） is the solids content of the polyamic acid solution, which is the weight percentage (unit: weight %) of the diamine monomer and the dianhydride monomer relative to the total weight of the diamine monomer, the dianhydride monomer, and the solvent, and e is the base of the natural logarithm.

5. In the above formula 2, η ０ is 50,000cps to 300,000cps, % （ｓ） The method for producing a polyimide film for a graphite sheet according to claim 4, wherein the content of the polyimide film is 15% by weight to 30% by weight.

6. The diamine monomer further includes p-phenyl diamine. The method for producing the polyimide film for graphite sheet according to claim 4.

7. 3. The method for producing a polyimide film for graphite sheet according to claim 2, wherein the gel film before being stretched is produced by forming a precursor composition by adding a catalyst composition to the polyamic acid solution to form a film, and drying the film, and the precursor composition satisfies the following formula 3: [0030] (In the above formula 3, η １ is the initial viscosity of the precursor composition (23° C., unit: cps), and t(η ２ ) is η １ From ２ is the time (in seconds) it takes to reach ２ is the final viscosity of the precursor composition (at 23° C. in cps).

8. In the above formula 3, η １ is 2,500cps to 30,000cps, and t(η ２ 8. The method for producing a polyimide film for graphite sheet according to claim 7, wherein the heating time is 100 seconds to 400 seconds.

9. 8. The method for producing a polyimide film for a graphite sheet according to claim 7, wherein the catalyst composition comprises an imidizing agent, a dehydrating agent, a sublimable inorganic filler, and a solvent.

10. The catalyst composition comprises: 3% to 15% by weight of said imidizing agent; 30% to 70% by weight of said dehydrating agent; 0.01% to 0.5% by weight of said sublimable inorganic filler; and 10. The method for producing a polyimide film for a graphite sheet according to claim 9, further comprising a residual amount of the solvent.

11. 8. The method for producing a polyimide film for graphite sheet according to claim 7, wherein the catalyst composition is added in an amount of 30 to 60 parts by weight per 100 parts by weight of the polyamic acid solution.

12. 8. The method for producing a polyimide film for graphite sheet according to claim 7, wherein the drying is carried out at a temperature of 30° C. to 200° C. for 15 seconds to 30 minutes.

13. 3. The method for producing a polyimide film for a graphite sheet according to claim 2, wherein the polyimide film is produced by heat treating a stretched gel film at a temperature of 250° C. to 600° C. for 30 seconds to 40 minutes.

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