TWI690487B - Method for manufacturing graphite sheet and polyimide film for graphite sheet - Google Patents

Abstract

The invention provides a method for manufacturing a graphite sheet for manufacturing a graphite sheet with good thermal diffusibility and flexibility, and a polyimide film for graphite sheets. The method for manufacturing a graphite sheet of the present invention includes the step of heat-treating a polyimide film having a phosphorus content of 0.025% by weight or more and 0.032% by weight or less to 2400°C or more.

Description

Method for manufacturing graphite sheet and polyimide film for graphite sheet

The invention relates to a method for manufacturing graphite sheets and a polyimide film for graphite sheets.

Graphite sheet has excellent heat dissipation characteristics, so it is used as a heat dissipation component for semiconductor components and other heat-generating components mounted on various electronic equipment or electrical equipment such as computers.

Such graphite flakes can be obtained by calcining polyimide film. For example, Patent Document 1 describes a technique for producing graphite sheets by calcining a polyimide film containing inorganic particles. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2014-136721

[Problems to be solved by the invention]

Previously, various graphite sheets have been known, but there is room for improvement in order to obtain graphite sheets having both thermal diffusibility and flexibility.

An object of one aspect of the present invention is to provide a method for manufacturing a graphite sheet for manufacturing a graphite sheet having good thermal diffusibility and flexibility, and a polyimide film for a graphite sheet. [Technical means to solve the problem]

The inventors of the present invention worked hard to solve the above-mentioned problems, and as a result, found that by using a polyimide film having a phosphorus content within a specific range as a raw material, a graphite sheet having both thermal diffusibility and flexibility can be manufactured, thereby The present invention has been completed. The present invention includes the following. [1] A method of manufacturing a graphite sheet, which includes the step of heat-treating a polyimide film having a phosphorus content of 0.025% by weight or more and 0.032% by weight or less to 2400°C or more. [2] A polyimide film for graphite sheets, wherein the phosphorus content is 0.025% by weight or more and 0.032% by weight or less. [Effect of invention]

According to one aspect of the present invention, a graphite sheet having good thermal diffusibility and flexibility can be obtained.

An embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to the configurations described below. Various changes can be made within the scope shown in the scope of the patent application, and the technical means disclosed in different embodiments or embodiments can be appropriately combined to obtain an embodiment or The embodiments are also included in the technical scope of the present invention. In addition, all the academic documents and patent documents described in this specification are cited as references in this specification. In this specification, unless otherwise specified, "A to B" indicating a numerical range means "A or more and B or less".

<1. Manufacturing method of graphite sheet> The method for manufacturing a graphite sheet according to one aspect of the present invention may include the step of heat-treating a polyimide film having a phosphorus content of 0.025% by weight or more and 0.032% by weight or less to 2400°C or more.

This manufacturing method is a so-called polymer thermal decomposition method in which the polyimide film is heat-treated in an inert gas atmosphere or under reduced pressure. Specifically, graphite sheets are obtained through the following steps: carbonization step, preheating the polyimide film to a temperature of about 1000°C to obtain a carbonaceous film; graphitization step, heating the carbonaceous film produced in the carbonization step to Graphitize at temperatures above 2400°C; and compress it in the compression step. Furthermore, the carbonization step and the graphitization step may be performed continuously, or the carbonization step may be ended, and then only the graphitization step is performed separately. In addition, in the manufacturing method of the graphite sheet according to an embodiment of the present invention, the compression step may be performed or not.

(Carbonization step) The carbonization step is a step of heat-treating the polyimide film to a temperature of about 1000°C to carbonize the polyimide film. For example, the maximum temperature is preferably 700°C to 1800°C, more preferably 800°C to 1500°C, further preferably 900°C to 1200°C, and particularly preferably 1000°C.

The heating rate of the carbonization step can be preferably exemplified by 0.01°C/min or more and less than 20°C/min, 0.1°C/min to 10°C/min, 0.2°C/min to less than 5.0°C/min, 0.5°C/min ~2.0℃/min. If the temperature increase rate is within the above range, a graphite sheet having good thermal diffusibility and flexibility can be obtained.

The retention time in the carbonization step (specifically, the retention time at the highest carbonization temperature) is preferably 1 minute to 1 hour, more preferably 5 minutes to 30 minutes, and still more preferably 8 minutes to 15 minutes. If the holding time is within the above range, a graphite sheet having good thermal diffusibility and flexibility can be obtained.

In the carbonization step, the laminated polyimide film obtained by stacking rectangular polyimide films can be carbonized, or the roll-shaped polyimide film can be directly carbonized in a roll shape, or can be self-rolled. The amide imide film is rolled out and carbonized.

(Graphitization step) The graphitization step is a step of heat-treating the carbonaceous film obtained in the carbonization step to a temperature above 2400°C to graphitize the carbonaceous film. For example, the maximum temperature may preferably be exemplified by 2400°C or higher, 2500°C or higher, 2600°C or higher, 2700°C or higher, 2800°C or higher, 2900°C or higher, or 3000°C or higher. The upper limit is not particularly limited, but it is preferably 3300°C or lower, and more preferably 3200°C or lower. Furthermore, the graphitization step is performed under reduced pressure or in an inert gas. As an inert gas, argon or helium is more suitable.

The heating rate in the graphitization step is preferably 0.01°C/min or more and less than 20°C/min, more preferably 0.1°C/min to 10°C/min, and further preferably 0.5°C/min to 5.0°C/min. If the heating rate is within the above range, a graphite sheet having good thermal diffusivity and flexibility can be obtained.

The retention time in the graphitization step (specifically, the retention time at the highest temperature for graphitization) is preferably 1 minute to 1 hour, more preferably 5 minutes to 30 minutes, and still more preferably 8 minutes to 15 minutes. If the holding time is within the above range, a graphite sheet having good thermal diffusibility and flexibility can be obtained.

In the graphitization step, the laminated carbide film obtained by laminating rectangular carbide films can be graphitized, or the roll-shaped carbide film can be directly graphitized in a roll shape, or the film can be rolled out from the roll-shaped carbide film. Graphitize.

(Compression step) A compression step can also be performed on the graphitized carbonaceous film. By performing the compression step, the obtained graphite sheet can be given flexibility. For the compression step, a method of compressing into a flat shape, or a method of rolling using a metal roller or the like can be used. The compression step can be performed at room temperature or in the graphitization step.

<2. Graphite sheet> The graphite sheet obtained by the above manufacturing method preferably has a thermal diffusivity of 8.0 cm ² /s or more, more preferably 8.3 cm ² /s or more, and even more preferably 8.5 cm ² /s or more.

In addition, the flexibility of the graphite sheet is preferably "C" or more, more preferably "B" or more, and even more preferably "A" or more in the softness evaluation of the following examples.

In addition, the thickness of the graphite sheet is preferably 5 μm to 60 μm, more preferably 10 μm to 50 μm, and still more preferably 15 μm to 40 μm.

The density of the graphite sheet is preferably 1.0 g/cm ³ to 2.26 g/cm ³ , more preferably 1.3 g/cm ³ to 2.2 g/cm ³ , and further preferably 1.6 g/cm ³ to 2.18 g/cm ³ .

<3. Polyimide film for graphite sheet> Hereinafter, a polyimide film that can be used in an embodiment of the present invention will be described in detail. The polyimide film for the graphite sheet used in the above manufacturing method is a polyimide film using an acid dianhydride component and a diamine component as raw materials, and contains a specific amount of phosphorus.

(phosphorus) The polyimide film preferably has a phosphorus content of 0.025% by weight to 0.032% by weight, and more preferably 0.027% by weight to 0.030% by weight. Within this range, the graphite sheet finally obtained has excellent thermal diffusivity and flexibility.

Phosphorus can be added to the polyimide film as inorganic particles (ie filler). Examples of the filler that can be used in one embodiment of the present invention include CaHPO ₄ , (NH ₄ ) ₂ HPO ₄ , and Ca ₂ P ₂ O ₇ . Among them, CaHPO ₄ and (NH ₄ ) ₂ HPO ₄ containing phosphoric acid expand well due to the gas generated during sublimation from the inside of the polyimide film, and obtain good graphite with excellent thermal conductivity, so it can be used preferably .

(Acid dianhydride component) Usable acid dianhydride components include pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 1,2,5,6-Naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid Dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 1,1-(3,4-dicarboxyphenyl ) Ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, bis (2, 3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, oxydiphthalic dianhydride, bis(3,4-dicarboxyphenyl) benzene dianhydride, P-phenylene bis (trimellitic acid monoester anhydride), ethyl bis (trimellitic acid monoester anhydride), bisphenol A bis (trimellitic acid monoester anhydride) and the like. These can be mixed in an arbitrary ratio. Among them, pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride is preferably used. By using this acid dianhydride component, the physical properties of the graphite sheet finally obtained become good.

(Diamine component) The diamine components that can be used include: 4,4'-diaminodiphenyl ether, p-phenylene diamine, 4,4'-diaminodiphenylmethane, benzidine, 3,3'-di Chlorobenzidine, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, 3,3'-diamine Diphenyl ether, 3,4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane, 4,4'-di Aminodiphenylsilane, 4,4'-diaminodiphenylethylphosphine oxide, 4,4'-diaminodiphenyl N-methylamine, 4,4'-diaminodiphenyl N-phenylamine, 1,3-diaminobenzene, 1,2-diaminobenzene and the like. These can be mixed in an arbitrary ratio. Among them, 4,4'-diaminodiphenyl ether or p-phenylene diamine is preferably used. By using this diamine component, the physical properties of the graphite sheet finally obtained become good.

(Thickness of Polyimide Film) The thickness of the polyimide film is 12.5 μm to 125 μm, preferably 25 μm to 100 μm, and more preferably 35 μm to 75 μm. Within the above range, the heat treatment is performed uniformly in the thickness direction, so the thermal diffusivity is improved.

(Method of imidization) Regarding the method of amidimation of polyimide, any one of the following methods can be used: a heat treatment method of heating the amidic acid as a precursor to convert the imide; or using an anhydride such as acetic anhydride Chemical dehydration agent or amide imidization accelerator represented by tertiary amines such as picoline, quinoline, isoquinoline, pyridine, etc., a chemical treatment method for amide imine conversion of polyamic acid as a precursor. As the amide imidization accelerator when the chemical treatment method is used, the tertiary amines listed above are preferable.

Especially for the obtained polyimide film, the coefficient of linear expansion is small, the elastic modulus is high, and the birefringence tends to become large. Furthermore, it can be rapidly graphitized at a relatively low temperature to obtain good quality graphite sheets. From a viewpoint, a chemical treatment method is preferable. In particular, the use of a dehydrating agent and an imidization accelerator together is preferred because the obtained polyimide film has a low linear expansion coefficient, a large elastic modulus, and a large birefringence. In addition, the chemical treatment method performs the amide imidization reaction more quickly. Therefore, the amide imidization reaction can be completed in a short time during the heat treatment, which is an industrially advantageous method with excellent productivity.

(Manufacturing method of polyamide) The method for producing polyamic acid is not particularly limited. For example, the aromatic acid dianhydride and diamine are dissolved in an organic solvent in substantially equal molar amounts, and the organic solution is stirred under controlled temperature conditions until aromatic The polymerization of the family acid dianhydride and the diamine is completed, whereby polyamic acid can be produced. The polymerization method is not particularly limited, and for example, any of the polymerization methods (1) to (5) described below is preferable. In addition, in (1)-(5), the case where an aromatic tetracarboxylic dianhydride is used as an aromatic acid dianhydride and an aromatic diamine compound is used as a diamine is exemplified.

(1) A method of dissolving an aromatic diamine compound in an organic polar solvent, and reacting the aromatic diamine compound with an aromatic tetracarboxylic dianhydride substantially equivalent to its molar equivalent to polymerize.

(2) The aromatic tetracarboxylic dianhydride is reacted with an aromatic diamine compound that is too small in molar amount relative thereto in an organic polar solvent to obtain a prepolymer having acid anhydride groups at both ends. Then, a method of polymerizing the prepolymer with an aromatic diamine compound that is substantially equal to the molar ratio of the aromatic tetracarboxylic dianhydride.

The specific example of the method of (2) above is the same as the following method: using diamine and acid dianhydride to synthesize a prepolymer having the above acid dianhydride at both ends, the same as the diamine used to synthesize the above prepolymer Diamine or different kinds of diamine react with the above prepolymer to synthesize polyamic acid. In the method of (2), the aromatic diamine compound that reacts with the prepolymer may be the same kind of aromatic diamine compound as the aromatic diamine compound used to synthesize the above prepolymer, or a different kind of aromatic Diamine compounds.

(3) The aromatic tetracarboxylic dianhydride and the aromatic diamine compound in excess molar amount relative thereto are reacted in an organic polar solvent to obtain a prepolymer having amine groups at both ends. Then, after adding an additional aromatic diamine compound to the prepolymer, the prepolymer and the aromatic tetracarboxylic acid are made in such a manner that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound become substantially equivalent. The method of dianhydride polymerization.

(4) After dissolving and/or dispersing the aromatic tetracarboxylic dianhydride in an organic polar solvent, the aromatic diamine compound is added in such a way that it becomes substantially equivalent to the acid dianhydride to make the aromatic Method for polymerizing tetracarboxylic dianhydride and aromatic diamine compound.

(5) A method of polymerizing a mixture of an aromatic tetracarboxylic dianhydride and an aromatic diamine compound that are substantially equal to moles in an organic polar solvent.

In addition, the present invention may be configured as described below. [1] A method of manufacturing a graphite sheet, which includes the step of heat-treating a polyimide film having a phosphorus content of 0.025% by weight or more and 0.032% by weight or less to 2400°C or more. [2] The method for manufacturing a graphite sheet according to [1], wherein the phosphorus content of the polyimide film is 0.027% by weight or more and 0.030% by weight or less. [3] A polyimide film for graphite sheets, wherein the phosphorus content is 0.025% by weight or more and 0.032% by weight or less. [4] The polyimide film for graphite sheets as in [3], wherein the phosphorus content is 0.027% by weight or more and 0.030% by weight or less.

Hereinafter, the present invention will be described in more detail by examples, but the present invention is not limited to the following examples. [Example]

<Phosphorus content of polyimide film> According to the ratio of the molecular weight of the phosphate used to the atomic weight of phosphorus, calculate and calculate the phosphorus content of the polyimide film.

14 mm。<Measurement of Bending Times in MIT Bending Resistance Test (Flexibility Evaluation)> The number of bending times in the MIT bending test of graphite sheets obtained by the following method was measured as an evaluation method of flexibility. The test method is shown below. In the MIT bending resistance test, the MIT Kneading Fatigue Test Model D manufactured by Toyo Seiki Co., Ltd. was used. The test conditions are set to R = 2 mm, left and right bending angle: 135°, spring:

14 mm.

The greater the number of bending times (MIT) in the bending resistance test, the more flexible the graphite sheet and the better the bending resistance. Therefore, even if a graphite sheet with a higher number of MITs is used for the bent portion, it is not easily damaged.

In addition, the evaluation criterion is set as follows. A: The number of bending times is more than 50000 times B: The number of bending times is more than 40,000 and less than 50,000 C: The number of bending times is more than 30,000 and less than 40,000 D: The number of bending times is more than 20,000 and less than 30,000 E: The number of bending times is less than 20,000 <Thermal diffusivity> The thermal diffusivity of the graphite sheet obtained by the following method was measured by the following method. Specifically, using a thermal diffusivity measuring device based on optical communication method ("LaserPit" of ULVAC Science and Technology Co., Ltd.), for a sample of graphite sheet cut into a shape of 4 mm × 40 mm, under an environment of 20°C Measured under AC conditions of 10 Hz.

<Method of making polyimide film> (Production Example 1) In a solution of 4,4'-diaminodiphenyl ether (ODA) in dimethylformamide, pyromellitic dianhydride (PMDA) is dissolved in such a way that ODA and PMDA become equivalent molar amounts, A solution of polyamic acid containing 18.5% by weight of polyamic acid was obtained. Calcium hydrogen phosphate was added to the obtained polyamic acid solution so that the concentration of calcium hydrogen phosphate was 0.11% by weight relative to the solid content of the polyamic acid. While cooling the solution, add an imidization catalyst containing 1 equivalent of acetic anhydride, 1 equivalent of isoquinoline, and dimethylformamide to the carboxylic acid group contained in the polyamic acid. Defoaming. Then, the mixed solution was coated on the aluminum foil so that the thickness after drying became 75 μm to obtain a mixed solution layer. The mixed solution layer on the aluminum foil is dried using a hot air oven and a far-infrared heater.

The drying conditions are as follows. First, the mixed solution layer on the aluminum foil was dried in a hot air oven at 120°C for 240 seconds to prepare a self-sustaining gel film. The gel film was peeled from the aluminum foil and fixed on the frame. Furthermore, the gel film was heated in a hot air oven at 120°C for 30 seconds, at 275°C for 40 seconds, at 400°C for 42 seconds, at 450°C for 50 seconds, and at 460°C using a far-infrared heater It was heated for 22 seconds and heated stepwise to dry. A polyimide film (A-1) having a phosphorus content of 0.025% by weight and a thickness of 75 μm was produced in the above manner.

(Production Example 2) To the obtained polyamic acid solution, calcium hydrogen phosphate was added in such a manner that the concentration of calcium hydrogen phosphate was 0.12% by weight relative to the solid content of the polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-2) with a phosphorus content of 0.027% by weight and a thickness of 75 μm was produced.

(Production Example 3) To the obtained polyamic acid solution, calcium hydrogen phosphate was added in such a manner that the concentration of calcium hydrogen phosphate was 0.13% by weight relative to the solid content of the polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-3) with a phosphorus content of 0.030% by weight and a thickness of 75 μm was produced.

(Production Example 4) To the obtained polyamic acid solution, calcium hydrogen phosphate was added in such a manner that the concentration of calcium hydrogen phosphate was 0.14% by weight relative to the solid content of the polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-4) with a phosphorus content of 0.032% by weight and a thickness of 75 μm was produced.

(Production Example 5) To the obtained polyamic acid solution, diammonium hydrogen phosphate was added so that the concentration of diammonium phosphate was 0.12% by weight relative to the solid content of polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-5) with a phosphorus content of 0.028% by weight and a thickness of 75 μm was prepared by the method.

(Production Example 6) To the obtained polyamic acid solution, calcium hydrogen phosphate was added in such a manner that the concentration of calcium hydrogen phosphate was 0.10% by weight relative to the solid content of the polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-6) with a phosphorus content of 0.023% by weight and a thickness of 75 μm was produced.

(Production Example 7) To the obtained polyamic acid solution, calcium hydrogen phosphate was added in such a manner that the concentration of calcium hydrogen phosphate was 0.15% by weight relative to the solid content of the polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-7) with a phosphorus content of 0.034% by weight and a thickness of 75 μm was produced.

(Production Example 8) To the obtained polyamic acid solution, calcium carbonate was added in place of calcium hydrogen phosphate so that the concentration of calcium carbonate was 0.15% by weight relative to the solid content of polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-8) with a phosphorus content of 0% by weight and a thickness of 75 μm was produced by the method.

<Manufacturing method of graphite sheet> (Example 1) Use a graphite sheet with a size of 220 mm × 220 mm to sandwich a polyimide film (A-1) with a size of 200 mm × 200 mm and a thickness of 75 μm (laminate 1 polyimide film and graphite sheet alternately), Under a nitrogen atmosphere, the temperature was raised to 1000°C at a heating rate of 0.5°C/min, followed by heat treatment at 1000°C for 10 minutes to carbonize.

After that, the temperature is increased to 2800°C (graphitization maximum temperature) at a temperature increase rate of 1°C/min under a reduced pressure in a temperature range of room temperature to 2200°C under a argon atmosphere in a temperature range above 2200°C. After that, it was kept at 2800°C for 10 minutes to produce graphite sheets. One obtained graphite sheet was sandwiched with a PET film with a size of 200 mm×200 mm×thickness of 400 μm, and compressed using a compression molding machine. The applied pressure is set to 10 MPa. The compressed graphite sheet has a thickness of 36 μm and a density of 1.87 g/cm ³ . For the graphite sheet after compression, the characteristics were studied by the above test.

(Example 2) A graphite sheet of Example 2 was produced in the same manner as in Example 1 except that the polyimide film (A-2) was used instead of the polyimide film (A-1). The compressed graphite sheet has a thickness of 36 μm and a density of 1.87 g/cm ³ . For the graphite sheet after compression, the characteristics were studied by the above test.

(Example 3) A graphite sheet of Example 3 was produced in the same manner as in Example 1 except that the polyimide film (A-3) was used instead of the polyimide film (A-1). The compressed graphite sheet has a thickness of 37 μm and a density of 1.92 g/cm ³ . For the graphite sheet after compression, the characteristics were studied by the above test.

(Example 4) A graphite sheet of Example 4 was produced in the same manner as Example 1 except that the polyimide film (A-4) was used instead of the polyimide film (A-1). The compressed graphite sheet has a thickness of 37 μm and a density of 1.92 g/cm ³ . For the graphite sheet after compression, the characteristics were studied by the above test.

(Example 5) A graphite sheet of Example 5 was produced in the same manner as in Example 1, except that the polyimide film (A-5) was used instead of the polyimide film (A-1). The compressed graphite sheet has a thickness of 36 μm and a density of 1.87 g/cm ³ . For the graphite sheet after compression, the characteristics were studied by the above test.

(Comparative Example 1) A graphite sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that the polyimide film (A-6) was used instead of the polyimide film (A-1). The thickness of the compressed graphite sheet is 35 μm, and the density is 1.97 g/cm ³ . For the graphite sheet after compression, the characteristics were studied by the above test.

(Comparative Example 2) A graphite sheet of Comparative Example 2 was produced in the same manner as in Example 1 except that the polyimide film (A-7) was used instead of the polyimide film (A-1). The compressed graphite sheet has a thickness of 38 μm and a density of 1.82 g/cm ³ . For the graphite sheet after compression, the characteristics were studied by the above test.

(Comparative Example 3) A graphite sheet of Comparative Example 3 was produced in the same manner as in Example 1 except that the polyimide film (A-8) was used instead of the polyimide film (A-1). The compressed graphite sheet has a thickness of 34 μm and a density of 2.03 g/cm ³ . For the graphite sheet after compression, the characteristics were studied by the above test.

Table 1 shows the production conditions and physical properties of the graphite sheets of Examples 1 to 5 and Comparative Examples 1 to 3.

[Table 1]

It can be seen from Examples 1 to 5 that the graphite sheet obtained from the polyimide film having a phosphorus content of 0.025% by weight or more and 0.032% by weight or less is excellent in both thermal diffusibility and flexibility. On the other hand, according to Comparative Example 1 and Comparative Example 3, it can be seen that although the graphite sheet obtained from the polyimide film having a phosphorus content of not more than 0.025% by weight is excellent in thermal diffusivity, it is inferior in flexibility. In addition, it is known from Comparative Example 2 that although the graphite sheet obtained from the polyimide film having a phosphorus content of more than 0.032% by weight is excellent in flexibility, it has poor thermal diffusivity. [Industry availability]

The graphite sheet obtained in the present invention has good thermal diffusivity and flexibility, for example, and therefore can be preferably used as a heat dissipation member of electronic equipment.

Claims (4)

A method for manufacturing graphite sheets, comprising the step of heat-treating a polyimide film with a phosphorus content of 0.025% by weight or more and 0.032% by weight or less to 2400°C or more. The method for manufacturing a graphite sheet according to claim 1, wherein the phosphorus content of the polyimide film is 0.027% by weight or more and 0.030% by weight or less. A polyimide film for graphite sheets, wherein the phosphorus content is 0.025% by weight or more and 0.032% by weight or less. Polyimide film for graphite sheet as claimed in claim 3, wherein the phosphorus content is 0.027% by weight or more and 0.030% by weight or less.