TW201942055A - Method for manufacturing graphite sheet and polyimide film for graphite sheet - Google Patents

Abstract

A method for manufacturing a graphite sheet and a polyimide film for a graphite sheet are provided for obtaining a graphite sheet having favorable heat diffusion properties and flexibility. This method for manufacturing a graphite sheet includes a step for heat-treating a polyimide film, with a phosphorus content of 0.025 to 0.032 wt%, to at least 2,400 DEG C.

Description

Method for manufacturing graphite sheet and polyimide film for graphite sheet

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

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

Such graphite flakes can be obtained by calcining a polyfluorene film. For example, Patent Document 1 describes a technique for producing a graphite sheet by firing a polyfluorene imide 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]

Various graphite sheets have been known in the past, but there is still room for improvement in order to obtain graphite sheets having both thermal diffusivity 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 diffusivity and flexibility, and a polyimide film for the graphite sheet.
[Technical means to solve the problem]

The present inventors have made intensive research in order to solve the above-mentioned problems, and as a result, it has been found that by using a polyimide film having a phosphorus content in a specific range as a raw material, a graphite sheet having both thermal diffusion and flexibility can be manufactured, The present invention has been completed. The present invention includes the following.
[1] A method for manufacturing a graphite sheet, which includes a 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 content of phosphorus is 0.025% by weight or more and 0.032% by weight or less.
[Effect of the invention]

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

One 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 respective structures described below. Various changes can be made within the scope shown in the scope of the patent application. The implementation forms or combinations obtained by appropriately combining the technical means disclosed in different implementation forms or embodiments can be obtained. Examples 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 addition, 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 a 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 higher.

This manufacturing method is a so-called polymer thermal decomposition method in which a polyimide film is heat-treated under an inert gas atmosphere or under reduced pressure. Specifically, a graphite sheet is obtained through the following steps: a carbonization step in which a polyimide film is preheated to a temperature of about 1000 ° C. to obtain a carbonaceous film; and a graphitization step in which the carbonaceous film produced in the carbonization step is heated to Graphitization is performed at a temperature above 2400 ° C; and a compression step is performed to compress it. In addition, 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. Furthermore, in the method for manufacturing a graphite sheet according to an embodiment of the present invention, it may be performed with or without a compression step.

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

For example, the heating rate of the carbonization step is preferably exemplified above 0.01 ° C / min 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, and 0.5 ° C / min. ~ 2.0 ° C / min. When the heating rate is within the above range, a graphite sheet having good thermal diffusivity and flexibility can be obtained.

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

In the carbonization step, a laminated polyimide film obtained by laminating a rectangular polyimide film may be carbonized, or a roll-shaped polyimide film may be directly carbonized in a roll shape, or may be self-rolled. The sulfonimide film is unrolled and carbonized.

(Graphitization step)
The graphitization step is a step of heat-treating the carbonaceous film obtained in the carbonization step to a temperature of 2400 ° C. or more, and graphitizing 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 is preferably 3300 ° C or lower, and more preferably 3200 ° C or lower. The graphitization step is performed under reduced pressure or in an inert gas. As the 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 still more preferably 0.5 ° C / min to 5.0 ° C / min. When 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 graphitization temperature) is preferably 1 minute to 1 hour, more preferably 5 minutes to 30 minutes, and still more preferably 8 minutes to 15 minutes. When the retention time is within the above range, a graphite sheet having good thermal diffusivity and flexibility can be obtained.

In the graphitization step, a laminated carbonized film obtained by laminating a rectangular carbonized film can be graphitized, a rolled carbonized film can be directly graphitized in a roll shape, or a rolled carbonized film can be rolled out of the film. Graphitized.

(Compression step)
The compression step may also be performed on the graphitized carbonaceous film. By performing the compression step, flexibility can be imparted to the obtained graphite sheet. As the compression step, a method of compressing into a flat shape, a method of rolling using a metal roll, or the like can be used. The compression step can be performed at room temperature or during the graphitization step.

＜ 2.Graphite sheet ＞
The thermal diffusivity of the graphite sheet obtained by the above manufacturing method is preferably 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.

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

The thickness of the graphite sheet is preferably 5 μm to 60 μm, more preferably 10 μm to 50 μm, and even 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 still more 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 one 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)
It is preferable that the polyimide film has a phosphorus content of 0.025% to 0.032% by weight, and more preferably 0.027% to 0.030% by weight. Within this range, the graphite sheet finally obtained is excellent in both thermal diffusibility and flexibility.

Phosphorus can be added to the polyimide film as inorganic particles (ie, fillers). 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 undergo good expansion by the gas generated during sublimation from the inside of the polyimide film, and obtain good graphite with excellent thermal conductivity, so it can be preferably used. .

(Acid dianhydride component)
Examples of 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-fluorenetetracarboxylic 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 acid dianhydride, bis (3,4-dicarboxyphenyl) fluorene dianhydride, Paraphenylene bis (trimellitic acid monoester anhydride), ethylidene bis (trimellitic acid monoester anhydride), bisphenol A bis (trimellitic acid monoester anhydride), and the like. These may be mixed at an arbitrary ratio. Among these, 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)
Examples of diamine components that can be used include: 4,4'-diaminodiphenyl ether, p-phenylene diamine, 4,4'-diaminodiphenylmethane, benzidine, 3,3'-di Chlorobenzidine, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylphosphonium, 4,4'-diaminodiphenylphosphonium, 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 may be mixed at an arbitrary ratio. Among them, 4,4'-diaminodiphenyl ether or p-phenylenediamine 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. If it is in the said range, since heat processing will be performed uniformly in the thickness direction, thermal diffusivity will improve.

(Imidization method)
Regarding the polyimide imidization method, any of the following methods may be used: a heat treatment method in which the polyimide acid as a precursor is heated to perform the imine conversion; or an acid anhydride such as acetic anhydride is used. Dehydrating agent or tertiary amines such as methylpyridine, quinoline, isoquinoline, pyridine and other amine imidization accelerators, the chemical treatment of the polyimide acid as a precursor to the imimine conversion. As the fluorene imidation accelerator in the case of using a chemical treatment method, the tertiary amines listed above are preferred.

Especially for the obtained polyimide film, the linear expansion coefficient is small, the elastic modulus is high, the birefringence is easy to increase, and rapid graphitization can be performed at relatively low temperature to obtain good quality graphite sheets. From a viewpoint, a chemical treatment method is preferable. In particular, the case where the dehydrating agent and the fluorene imidization accelerator are used in combination is preferable because the linear expansion coefficient of the obtained fluorene film is small, the elastic modulus is large, and the birefringence can be large, so it is preferable. In addition, the chemical treatment method advances the fluorene imidization reaction more quickly. Therefore, the fluorene imidization reaction can be ended in a short time during the heat treatment, which is an industrially advantageous method with excellent productivity.

(Manufacturing method of polyamic acid)
The method for producing polyamic acid is not particularly limited. For example, an aromatic acid dianhydride and a diamine are dissolved in an organic solvent in substantially equal molar amounts, and the organic solution is stirred under a controlled temperature until the aroma The polymerization of the family acid dianhydride and the diamine is completed, whereby a polyamino 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 preferred. 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 illustrated.

(1) A method in which an aromatic diamine compound is dissolved in an organic polar solvent, and an aromatic diamine compound is reacted with an aromatic tetracarboxylic dianhydride which is substantially equivalent to a molar amount thereof to polymerize.

(2) An aromatic tetracarboxylic dianhydride is reacted with an aromatic diamine compound in an excessively small molar amount in an organic polar solvent to obtain a prepolymer having acid anhydride groups at both ends. Next, a method for polymerizing an aromatic diamine compound that is substantially equal in mole relative to the aromatic tetracarboxylic dianhydride and the prepolymer.

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

(3) An aromatic tetracarboxylic dianhydride is reacted with an aromatic diamine compound which is an excessive molar amount relative to the organic disolvent to obtain a prepolymer having amine groups at both ends. Then, after adding an aromatic diamine compound to this prepolymer, the prepolymer and the aromatic tetracarboxylic acid are made so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound become substantially equal. Method for dianhydride polymerization.

(4) After the aromatic tetracarboxylic dianhydride is dissolved and / or dispersed in an organic polar solvent, an aromatic diamine compound is added so as to be substantially equal 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 substantially equal molar aromatic tetracarboxylic dianhydride and an aromatic diamine compound in an organic polar solvent.

The present invention may be configured as described below.
[1] A method for manufacturing a graphite sheet, comprising the steps 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 producing a graphite sheet according to [1], wherein the phosphorus content of the polyfluorene imine film is 0.027% by weight or more and 0.030% by weight or less.
[3] A polyimide film for graphite sheets, wherein the content of phosphorus is 0.025% by weight or more and 0.032% by weight or less.
[4] The polyimide film for a graphite sheet according to [3], wherein the content of phosphorus is 0.027% by weight or more and 0.030% by weight or less.

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

＜ Phosphorus content of polyimide film ＞
Based on the ratio of the molecular weight of the phosphate to the atomic weight of phosphorus, the phosphorus content of the polyimide film is calculated and calculated.

＜ Measurement of the number of bends in the MIT flexure resistance test (evaluation of flexibility) ＞
The number of bends in the MIT bending resistance test of the graphite sheet 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 rubbing 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 more the number of times of bending (MIT) in the bending resistance test means that the softer the graphite sheet is, the more excellent the bending resistance is. Therefore, even if a graphite sheet having a large number of times of MIT is used for a bent portion, it is not easy to be damaged.

The evaluation criteria are set as follows.
A: The number of bending times is 50,000 or more
B: The number of bending times is 40,000 times or more and less than 50,000 times
C: The number of bending times is more than 30,000 times and less than 40,000 times
D: The number of bending times is 20,000 times or more and less than 30,000 times
E: The number of bending times is less than 20,000 times. <Thermal diffusivity>
The thermal diffusivity of the graphite sheet obtained by the following method was measured by the following method. Specifically, a thermal diffusivity measuring device ("LaserPit" by ULVAC Polytechnic Co., Ltd.) based on the optical AC method was used to sample a graphite sheet cut into a shape of 4 mm × 40 mm in an environment of 20 ° C. Measured at 10 Hz AC.

＜ How to make polyimide film ＞
(Manufacturing example 1)
Dissolve pyromellitic dianhydride (PMDA) in a dimethylformamide solution in which 4,4'-diaminodiphenyl ether (ODA) is dissolved, so that ODA and PMDA become equal amounts. A polyamic acid solution containing 18.5% by weight of polyamic acid was obtained. To the obtained polyamic acid solution, calcium hydrogen phosphate was added so that the concentration of calcium hydrogen phosphate was 0.11% by weight based on the solid content of the polyamic acid. While cooling the solution, a hydrazone imidization catalyst containing 1 equivalent of acetic anhydride, 1 equivalent of isoquinoline, and dimethylformamide was added with respect to the carboxylic acid group contained in the polyamic acid. Defoaming. Then, this mixed solution was applied on an 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 described below. First, the mixed solution layer on the aluminum foil was dried at 120 ° C. for 240 seconds using a hot air oven to prepare a self-sustaining gel film. This gel film was peeled from the aluminum foil and fixed to a 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. Heating was performed for 22 seconds and drying was performed in steps. A polyimide film (A-1) having a phosphorus content of 0.025% by weight and a thickness of 75 μm was prepared in the above manner.

(Manufacturing example 2)
In 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 based on the solid content of the polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-2) having a phosphorus content of 0.027% by weight and a thickness of 75 μm was prepared.

(Manufacture example 3)
In 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 based on the solid content of the polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-3) having a phosphorus content of 0.030% by weight and a thickness of 75 μm was prepared.

(Manufacturing example 4)
In 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 based on the solid content of the polyamic acid, except that it was the same as in Production Example 1. A polyimide film (A-4) having a phosphorus content of 0.032% by weight and a thickness of 75 μm was prepared.

(Manufacturing example 5)
In the obtained polyamic acid solution, diammonium hydrogen phosphate was added in such a manner that the concentration of diammonium hydrogen phosphate was 0.12% by weight based on the solid content of the polyamic acid, except that it was the same as in Production Example 1. In this way, a polyimide film (A-5) having a phosphorus content of 0.028% by weight and a thickness of 75 μm was produced.

(Manufacturing example 6)
In 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, and was the same as in Production Example 1 except that the calcium hydrogen phosphate was added thereto. A polyimide film (A-6) having a phosphorus content of 0.023% by weight and a thickness of 75 μm was prepared.

(Manufacturing example 7)
In 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 based on the solid content of the polyamic acid, and was the same as that of Production Example 1 except that A polyimide film (A-7) having a phosphorus content of 0.034% by weight and a thickness of 75 μm was prepared.

(Manufacturing example 8)
The same procedure as in Production Example 1 was performed except that calcium carbonate was added to the obtained polyamic acid solution so that the concentration of calcium carbonate was 0.15% by weight based on the solid content of the polyamic acid, instead of calcium hydrogen phosphate. In this way, a polyimide film (A-8) having a phosphorus content of 0% by weight and a thickness of 75 μm was produced.

＜ 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 (alternately laminate a polyimide film and a graphite sheet). In a nitrogen atmosphere, the temperature was increased to 1000 ° C. at a temperature increase rate of 0.5 ° C./min, and then heat treatment was performed at 1000 ° C. for 10 minutes to carbonize.

Thereafter, in a temperature range from room temperature to 2200 ° C under reduced pressure, in a temperature range higher than 2200 ° C under an argon atmosphere, the temperature was raised to 2800 ° C at a temperature increase rate of 1 ° C / min (maximum graphitization temperature). Thereafter, it was held at 2800 ° C for 10 minutes to prepare a graphite sheet. One obtained graphite sheet was sandwiched by a PET film having a size of 200 mm × 200 mm × thickness of 400 μm, and compression processing was performed using a compression molding machine. The applied pressure was set to 10 MPa. The compressed graphite sheet had a thickness of 36 μm and a density of 1.87 g / cm ³ . For the compressed graphite sheet, the characteristics were studied by the above experiments.

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

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

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

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

(Comparative example 1)
A graphite sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that the polyfluorine film (A-6) was used instead of the polyfluorene film (A-1). The compressed graphite sheet had a thickness of 35 μm and a density of 1.97 g / cm ³ . For the compressed graphite sheet, the characteristics were studied by the above experiments.

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

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

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

[Table 1]

From Examples 1 to 5, it can be seen that the graphite sheet obtained from a 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, from Comparative Example 1 and Comparative Example 3, it was found that the graphite sheet obtained from a polyimide film having a phosphorus content of less than 0.025% by weight had poor thermal diffusibility, but poor flexibility. Further, it is understood from Comparative Example 2 that the graphite sheet obtained from a polyimide film having a phosphorus content of more than 0.032% by weight, although excellent in flexibility, has poor thermal diffusibility.
[Industrial availability]

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

Claims (4)

A method for manufacturing a graphite sheet, which comprises a 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. The method for manufacturing a graphite sheet according to claim 1, wherein the content of phosphorus in 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 content of phosphorus is 0.025% by weight or more and 0.032% by weight or less. For example, the polyimide film for the graphite sheet of claim 3, wherein the phosphorus content is 0.027% by weight or more and 0.030% by weight or less.