JPWO2019187620A1 - Graphite sheet and its manufacturing method - Google Patents

Abstract

Provided is a graphite sheet having good thermal diffusivity and flexibility, and a method for producing the same. A carbonization step of carbonizing a polyimide film having a phosphate content within a predetermined range to obtain a carbonaceous film, and heat treatment of the carbonaceous film at a predetermined temperature rise rate and a maximum temperature of 2600 ° C. or higher. A method for producing a graphite sheet, which comprises a graphitization step of obtaining a graphite sheet, wherein the phosphorus content is 0.01% by weight or more and 0.10% by weight or less.

Description

The present invention relates to a graphite sheet and a method for producing the same.

Since the graphite sheet has excellent heat dissipation characteristics, it is used as a heat dissipation component in semiconductor elements, other heat generating components, etc. mounted on various electronic devices such as computers or electric devices.

Such a graphite sheet can be obtained by firing a polyimide film. For example, Patent Document 1 describes a technique for producing a graphite sheet by firing a polyimide film containing inorganic particles.

Japanese Unexamined Patent Publication No. 2014-136721

Conventionally, various graphite sheets have been known, but there is still room for improvement in order to obtain a graphite sheet having both thermal diffusivity and flexibility.

One aspect of the present invention is to provide a graphite sheet having good thermal diffusivity and flexibility and a method for producing the same.

As a result of diligent studies to solve the above problems, the present inventors have found that a graphite sheet having a phosphorus content within a predetermined range is excellent in both thermal diffusivity and flexibility, and the present invention has been developed. It was completed. The present invention includes the following.
[1] A graphite sheet having a phosphorus content of 0.01% by weight or more and 0.10% by weight or less.
[2] A method for producing a graphite sheet having a phosphorus content of 0.01% by weight or more and 0.10% by weight or less.
A carbonization step of carbonizing a polyimide film having a phosphate content of 0.01% by weight or more and 0.49% by weight or less to obtain a carbonaceous film, and
A graphitization step in which the carbonaceous film is heat-treated at a heating rate of 0.01 ° C./min or more and less than 20 ° C./min and a maximum temperature of 2600 ° C. or higher to obtain a graphite sheet.
A method for manufacturing a graphite sheet including.

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

An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications can be made within the scope of the claims, and the technical means disclosed in different embodiments and examples can be used. Embodiments and examples obtained in appropriate combinations are also included in the technical scope of the present invention. In addition, all the academic documents and patent documents described in the present specification are incorporated as references in the present specification. Further, unless otherwise specified in the present specification, "A to B" representing a numerical range is intended to be "A or more and B or less".

<1. Graphite sheet manufacturing method>
The method for producing a graphite sheet according to one aspect of the present invention is a method for producing a graphite sheet having a phosphorus content of 0.01% by weight or more and 0.10% by weight or less, and a phosphate content of 0.01. A carbonization step of carbonizing a polyimide film having a weight% or more and 0.49% by weight or less to obtain a carbonic film, and a heating rate of the carbonic film at 0.01 ° C./min or more and less than 20 ° C./min. Anything may include a graphitization step of obtaining a graphite sheet by heat-treating the maximum temperature at 2600 ° C. or higher.

This production method is a so-called polymer pyrolysis method in which a polyimide film is heat-treated under an inert gas atmosphere or under reduced pressure. Specifically, the polyimide film is preheated to a temperature of about 1000 ° C. to obtain a carbonized film, and the carbonized film produced in the carbonization step is heated to a temperature of 2600 ° C. or higher to graphitize graphite. A graphite sheet is obtained through a carbonization step and a compression step of compressing the graphite sheet. The carbonization step and the graphitization step may be continuously performed, or the carbonization step may be completed and then only the graphitization step may be performed independently. Further, in the method for producing a graphite sheet according to an embodiment of the present invention, the compression step may or may not be performed.

(Carbonization process)
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 in the carbonization 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 0.5 ° C./min. It is more preferably less than ~ 5.0 ° C./min. When the heating rate is within the above range, phosphorus in the polyimide film remains to a preferable extent, and a graphite sheet having good thermal diffusivity and flexibility can be obtained.

The holding time in the carbonization step (specifically, the holding time at the maximum carbonization temperature) is preferably 1 minute to 1 hour, more preferably 5 minutes to 30 minutes, and 8 minutes to 15 minutes. Is more preferable. When the holding time is within the above range, phosphorus in the polyimide film remains to a preferable extent, and a graphite sheet having good thermal diffusivity and flexibility can be obtained.

In the carbonization step, the laminated polyimide film in which the rectangular polyimide film is laminated may be carbonized, the roll-shaped polyimide film may be carbonized in the roll shape, or the film is unwound from the roll-shaped polyimide film and carbonized. May be good.

(Graphitization process)
The graphitization step is a step of heat-treating the carbonaceous film obtained in the carbonization step to a temperature of 2600 ° C. or higher to graphitize the carbonic film. For example, the maximum temperature is preferably 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 carried out under reduced pressure or in an inert gas, and argon or helium is suitable as the inert gas.

The rate of temperature rise in the graphitization step is, for example, 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 5.0 ° C./min, A preferred example thereof is 0.5 ° C./min to 2.0 ° C./min. When the heating rate is within the above range, phosphorus in the polyimide film remains to a preferable extent, and a graphite sheet having good thermal diffusivity and flexibility can be obtained.

The holding time in the graphitization step (specifically, the holding time at the maximum graphitization temperature) is preferably 1 minute to 1 hour, more preferably 5 minutes to 30 minutes, and 8 minutes to 30 minutes. It is more preferably 15 minutes. When the holding time is within the above range, phosphorus in the polyimide film remains to a preferable extent, and a graphite sheet having good thermal diffusivity and flexibility can be obtained.

In the graphitization step, the laminated carbonized film in which the rectangular carbonized films are laminated may be graphitized, the roll-shaped carbonized film may be graphitized in the roll shape, or the film is unwound from the roll-shaped carbonized film to be graphitized. It may be carbonized.

(Compression process)
The carbonaceous film after graphitization may be subjected to a compression step. By applying the compression step, flexibility can be imparted to the obtained graphite sheet. As the compression step, a method of compressing in a planar shape, a method of rolling using a metal roll or the like can be used. The compression step may be carried out at room temperature or during the graphitization step.

<2. Graphite sheet ＞
The graphite sheet has a phosphorus content of 0.01% by weight to 0.10% by weight, more preferably 0.02% by weight to 0.08% by weight. Within such a range, the graphite sheet is excellent in both thermal diffusivity and flexibility.

The thermal diffusivity of the graphite sheet is preferably 7.0 cm ² / s or more, more preferably 7.3 cm ² / s or more, further preferably 8.0 cm ² / s or more ..

Further, 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 flexibility evaluation of Examples described later. ..

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 from ^{1.0g / cm 3 ~2.26g / cm 3} , more preferably from ^{1.3g / cm 3 ~2.2g / cm 3} , 1.6g / cm 3 ~2 It is more preferably .18 g / cm ³ .

<3. Polyimide film for graphite sheet>
Hereinafter, the polyimide film that can be used in one embodiment of the present invention will be described in detail. The polyimide film for a graphite sheet used in the production method is a polyimide film made from an acid dianhydride component and a diamine component as raw materials, and contains a predetermined amount of phosphate.

(Phosphate)
The polyimide film preferably has a phosphate content of 0.01% by weight to 0.49% by weight, more preferably 0.10% by weight to 0.40% by weight, and 0.12% by weight. It is more preferably% to 0.35% by weight. Within such a range, both the thermal diffusivity and the flexibility of the finally obtained graphite sheet are excellent.

Examples of the phosphate that can be used in one embodiment of the present invention include CaHPO ₄ , (NH ₄ ) ₂ HPO ₄ . Among them, CaHPO ₄ and (NH ₄ ) ₂ HPO ₄ can be preferably used because good swelling is generated by the gas generated when sublimating from the inside of the polyimide film and good graphite having excellent thermal conductivity can be obtained. .. Phosphate can be added to the polyimide film as inorganic particles (ie, fillers).

(Acid dianhydride component)
The acid dianhydride components that can be used are pyromellitic acid 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 Dihydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 1,1- (3,4-dicarboxyphenyl) Phenyl) 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) sulfonate dianhydride, p-phenylene bis (Trimeric acid monoesteric acid anhydride), ethylene bis (trimellitic acid monoesteric acid anhydride), bisphenol A bis (trimellitic acid monoesteric acid anhydride) and their analogs can be mentioned. These can be mixed in any proportion. Of these, it is preferable to use pyromellitic dianhydride or 3,3', 4,4'-biphenyltetracarboxylic dianhydride. By using such an acid dianhydride component, the physical properties of the finally obtained graphite sheet become good.

(Diamine component)
The diamine components that can be used are 4,4'-diaminodiphenyl ether, p-phenylenediamine, 4,4'-diaminodiphenylmethane, benzene, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenylsulfide, 3,3. ′ -Diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 1,5-diaminonaphthalene, 4,4′-diaminodiphenyldiphenylsilane, 4, 4'-diaminodiphenylsilane, 4,4'-diaminodiphenylethylphosphine oxide, 4,4'-diaminodiphenylN-methylamine, 4,4'-diaminodiphenylN-phenylamine, 1,3-diaminobenzene, 1 , 2-Diaminobenzene and their analogs can be mentioned. These can be mixed in any proportion. Of these, 4,4'-diaminodiphenyl ether and p-phenylenediamine are preferably used. By using such a diamine component, the physical properties of the finally obtained graphite sheet 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 within the above range, the heat treatment is uniformly performed in the thickness direction, so that the heat diffusibility is improved.

(Immidization method)
The imidization method of polyimide is a thermal cure method in which the precursor polyamic acid is heated to imidize, a dehydrating agent typified by an acid anhydride such as acetic anhydride, picolin, quinoline, isoquinolin, pyridine and the like. Any of the chemical cure method of imide-converting the polyimide polyamic acid as a precursor by using an imidization accelerator typified by the tertiary amines of the above may be used. As the imidization accelerator when the chemical cure method is used, the tertiary amines mentioned above are preferable.

In particular, from the viewpoint that the obtained polyimide film has a small coefficient of linear expansion, a high elastic modulus, birefringence tends to be large, and rapid graphitization is possible at a relatively low temperature, so that a high-quality graphite sheet can be obtained. Therefore, the chemical cure method is preferable. In particular, it is preferable to use a dehydrating agent and an imidization accelerator in combination because the linear expansion coefficient of the obtained polyimide film is small, the elastic modulus is large, and the birefringence can be large. Further, the chemical cure method is an industrially advantageous method having excellent productivity because the imidization reaction proceeds faster, so that the imidization reaction can be completed in a short time in the heat treatment.

(Manufacturing method of polyamic acid)
The method for producing the polyamic acid is not particularly limited, but for example, aromatic dianhydride and diamine are dissolved in an organic solvent in substantially equal molar amounts, and this organic solution is dissolved in the organic solvent to aromatic dianhydride and diamine. Polyamic acid can be produced by stirring under controlled temperature conditions until the polymerization with and is completed. The polymerization method is not particularly limited, but for example, any of the following polymerization methods (1)-(5) is preferable. In addition, in (1)-(5), the case where the aromatic tetracarboxylic dianhydride is used as the aromatic acid dianhydride and the aromatic diamine compound is used as the diamine is illustrated.

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

(2) Aromatic tetracarboxylic dianhydride is reacted with an aromatic diamine compound in a small molar amount in an organic polar solvent to obtain a prepolyma having an acid anhydride group at both ends. Subsequently, a method of polymerizing this prepolyma with an aromatic diamine compound which is substantially equimolar to the aromatic tetracarboxylic dianhydride.

In a specific example of the method (2) above, a prepolyamide having the acid dianhydride at both ends is synthesized using a diamine and an acid dianhydride, and the prepolyamide is the same as the diamine used for the synthesis of the prepolyma. It is the same as the method for synthesizing a polyamic acid by reacting the diamines of Also in the method (2), the aromatic diamine compound to be reacted with the prepolyma may be the same type of aromatic diamine compound as the aromatic diamine compound used in the synthesis of the prepolyma, or a different type of aromatic diamine compound.

(3) An aromatic tetracarboxylic dianhydride is reacted with an excess molar amount of an aromatic diamine compound in an organic polar solvent to obtain a prepolyma having amino groups at both ends. Subsequently, after the aromatic diamine compound is additionally added to this prepolyma, the prepolyma and the aromatic tetracarboxylic dianhydride so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound have substantially the same molar amount A method of polymerizing with.

(4) After dissolving and / or dispersing the aromatic tetracarboxylic dianhydride in an organic polar solvent, an aromatic diamine compound is added so as to be substantially equimolar to the acid dianhydride. , A method of polymerizing an aromatic tetracarboxylic dianhydride and an aromatic diamine compound.

(5) A method in which a mixture of a substantially equimolar aromatic tetracarboxylic dianhydride and an aromatic diamine compound is reacted in an organic polar solvent for polymerization.

The present invention can also have the following configuration.
[1] A graphite sheet having a phosphorus content of 0.01% by weight or more and 0.10% by weight or less.
[2] The graphite sheet according to [1], wherein the phosphorus content is 0.02% by weight or more and 0.08% by weight or less.
[3] A method for producing a graphite sheet having a phosphorus content of 0.01% by weight or more and 0.10% by weight or less.
A carbonization step of carbonizing a polyimide film having a phosphate content of 0.01% by weight or more and 0.49% by weight or less to obtain a carbonaceous film, and
A graphitization step in which the carbonaceous film is heat-treated at a heating rate of 0.01 ° C./min or more and less than 20 ° C./min and a maximum temperature of 2600 ° C. or higher to obtain a graphite sheet.
A method for manufacturing a graphite sheet including.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

<Phosphorus content of polyimide film>
The phosphorus content of the polyimide film was calculated from the ratio of the molecular weight of the phosphate used and the atomic weight of phosphorus.

<Phosphorus content of graphite sheet>
The phosphorus content of the graphite sheet was determined by using a fluorescent X-ray analyzer as a ratio between the phosphorus peak of the graphite film to be measured and the phosphorus peak of a substance having a known phosphorus concentration. Further, as a fluorescent X-ray analyzer, ZSX PrimusII manufactured by Rigaku Co., Ltd. was used, and as a substance having a known phosphorus concentration, a polyimide film having a phosphorus concentration of 0.034% by weight was used for measurement.

<Measurement of the number of bends in the MIT bending resistance test (flexibility evaluation)>
The number of times of bending of the graphite sheet obtained by the method described later in the MIT bending resistance test was measured and used as a method for evaluating flexibility. The test method is shown below. In the MIT bending resistance test, a MIT kneading fatigue resistance tester model D manufactured by Toyo Seiki Co., Ltd. was used. The test conditions were R = 2 mm, left and right bending angles: 135 °, and spring: φ14 mm.

The number of times of bending (MIT) in the bending resistance test means that the greater the number of times, the more flexible the graphite sheet is and the more excellent the bending resistance is. Therefore, even if a graphite sheet having a large number of MITs is used for the bent portion, it is less likely to be broken.

The evaluation criteria are as follows.
A: Number of bends is 100,000 or more B: Number of bends is 10,000 or more and less than 100,000 C: Number of bends is 1000 or more and less than 10,000 D: Number of bends is 100 or more and less than 1000 E: Number of bends is less than 100 Thermal diffusivity>
The thermal diffusivity of the graphite sheet obtained by the method described later was measured by the following method. Specifically, using a thermal diffusivity measuring device (“LaserPit” manufactured by ULVAC Riko Co., Ltd.) based on the optical AC method, a sample of a graphite sheet cut into a shape of 4 mm × 40 mm was subjected to an atmosphere of 20 ° C. Was measured under AC conditions of 10 Hz.

<Method of producing polyimide film>
(Manufacturing Example 1)
In a dimethylformamide solution in which 4,4'-diaminodiphenyl ether (ODA) was dissolved, pyromellitic dianhydride (PMDA) was dissolved so that the amount of ODA and PMDA was equivalent to that of 18. A polyacid solution containing 5% by weight was obtained. Calcium hydrogen phosphate was added to the obtained polyamic acid solution so that the concentration of calcium hydrogen phosphate was 0.15% by weight based on the solid content of the polyamic acid. While cooling this solution, an imidization catalyst containing 1 equivalent of acetic anhydride, 1 equivalent of isoquinoline, and dimethylformamide was added to the carboxylic acid group contained in the polyamic acid to defoam. Next, this mixed solution was applied onto an aluminum foil so as to have a thickness of 50 μm after drying to obtain a mixed solution layer. The mixed solution layer on the aluminum foil was 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 obtain a self-supporting gel film. The gel film was peeled off from the aluminum foil and fixed to the frame. Further, the gel film is heated stepwise in a hot air oven at 120 ° C. for 30 seconds, 275 ° C. for 40 seconds, 400 ° C. for 42 seconds, 450 ° C. for 50 seconds, and a far-infrared heater at 460 ° C. for 22 seconds. And dried. As described above, a polyimide film (A-1) having a phosphorus content of 0.034% by weight and a thickness of 50 μm was prepared.

(Manufacturing Example 2)
The same as in Production Example 1 except that calcium hydrogen phosphate was added to the obtained polyamic acid solution so that the concentration of calcium hydrogen phosphate was 0.05% by weight based on the solid content of the polyamic acid. A polyimide film (A-2) having a phosphorus content of 0.011% by weight and a thickness of 50 μm was prepared.

(Manufacturing Example 3)
The same as in Production Example 1 except that calcium hydrogen phosphate was added to the obtained polyamic acid solution so that the concentration of calcium hydrogen phosphate was 0.01% by weight based on the solid content of the polyamic acid. A polyimide film (A-3) having a phosphorus content of 0.002% by weight and a thickness of 50 μm was prepared.

(Manufacturing Example 4)
The same as in Production Example 1 was carried out except that calcium hydrogen phosphate was added to the obtained polyamic acid solution so that the concentration of calcium hydrogen phosphate was 0.30% by weight based on the solid content of the polyamic acid. A polyimide film (A-4) having a phosphorus content of 0.068% by weight and a thickness of 50 μm was prepared.

(Manufacturing Example 5)
The same procedure as in Production Example 1 was carried out except that diammonium hydrogen phosphate was added to the obtained polyamic acid solution so that the concentration of diammonium hydrogen phosphate was 0.15% by weight based on the solid content of the polyamic acid. A polyimide film (A-5) having a phosphorus content of 0.035% by weight and a thickness of 50 μm was prepared.

(Manufacturing Example 6)
A polyimide film (A-6) having a phosphorus content of 0% by weight and a thickness of 50 μm was produced in the same manner as in Production Example 1 except that no filler was added to the obtained polyamic acid solution.

(Manufacturing Example 7)
Similar to Production Example 1 except that calcium carbonate was added to the obtained polyamic acid solution instead of calcium hydrogen phosphate so that the concentration of calcium carbonate was 0.15% by weight based on the solid content of the polyamic acid. A polyimide film (A-7) having a phosphorus content of 0% by weight and a thickness of 50 μm was prepared.

(Manufacturing Example 8)
The phosphorus content was 0 in the same manner as in Production Example 1 except that calcium hydrogen phosphate was added to the obtained polyamic acid solution so that the concentration was 0.50% by weight based on the solid content of the polyamic acid. A polyimide film (A-8) having a thickness of .114% by weight and a thickness of 50 μm was prepared.

<Manufacturing method of graphite sheet>
(Example 1)
A polyimide film (A-1) having a size of 200 mm × 200 mm and a thickness of 50 μm is sandwiched between graphite sheets having a size of 220 mm × 220 mm (one polyimide film and a graphite sheet are alternately laminated), and 0.5 in a nitrogen atmosphere. After raising the temperature to 1000 ° C. at a heating rate of ° C./min, heat treatment was performed at 1000 ° C. for 10 minutes to carbonize.

After that, the temperature was raised to 2800 ° C. (maximum graphitization temperature) at a heating rate of 5.0 ° C./min under reduced pressure in the temperature range of room temperature to 2200 ° C. and in an argon atmosphere in the temperature range higher than 2200 ° C. A graphite sheet was prepared by holding at 2800 ° C. for 10 minutes. One of the obtained graphite sheets was sandwiched between PET films having a size of 200 mm × 200 mm × thickness of 400 μm, and compression treatment was carried out using a compression molding machine. The applied pressure was 10 MPa. The thickness of the graphite sheet after compression was 25 μm, and the density was 1.83 g / cm ³ .

(Example 2)
The graphite sheet of Example 2 was produced in the same manner as in Example 1 except that the temperature was raised to 2800 ° C. (maximum graphitization temperature) at a heating rate of 0.5 ° C./min. The thickness of the graphite sheet after compression was 24 μm, and the density was 1.9 g / cm ³ .

(Example 3)
The graphite sheet of Example 3 was produced in the same manner as in Example 1 except that the temperature was raised to 2800 ° C. (maximum graphitization temperature) at a heating rate of 0.1 ° C./min. The thickness of the graphite sheet after compression was 23 μm, and the density was 1.99 g / cm ³ .

(Example 4)
The graphite sheet of Example 4 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 thickness of the graphite sheet after compression was 23 μm, and the density was 1.99 g / cm ³ .

(Example 5)
The graphite sheet of Example 5 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 thickness of the graphite sheet after compression was 22 μm, and the density was 2.08 g / cm ³ .

(Example 6)
The graphite sheet of Example 6 was produced in the same manner as in Example 3 except that the polyimide film (A-4) was used instead of the polyimide film (A-1). The thickness of the graphite sheet after compression was 26 μm, and the density was 1.76 g / cm ³ .

(Example 7)
The graphite sheet of Example 7 was produced in the same manner as in Example 1 except that the temperature was raised to 2600 ° C. (maximum graphitization temperature) at a heating rate of 5.0 ° C./min. The thickness of the graphite sheet after compression was 27 μm, and the density was 1.69 g / cm ³ .

(Example 8)
The graphite sheet of Example 7 was produced in the same manner as in Example 1 except that the temperature was raised to 3000 ° C. (maximum graphitization temperature) at a heating rate of 5.0 ° C./min. The thickness of the graphite sheet after compression was 21 μm, and the density was 2.18 g / cm ³ .

(Example 9)
The graphite sheet of Example 9 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 thickness of the graphite sheet after compression was 25 μm, and the density was 1.83 g / cm ³ .

(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 graphite sheet after compression was 22 μm, and the density was 2.08 g / cm ³ .

(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 thickness of the graphite sheet after compression was 22 μm, and the density was 2.08 g / cm ³ .

(Comparative Example 3)
The graphite sheet of Comparative Example 3 was produced in the same manner as in Example 1 except that the temperature was raised to 2800 ° C. (maximum graphitization temperature) at a heating rate of 20 ° C./min. The thickness of the graphite sheet after compression was 29 μm, and the density was 1.58 g / cm ³ .

(Comparative Example 4)
A graphite sheet of Comparative Example 4 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 thickness of the graphite sheet after compression was 29 μm, and the density was 1.58 g / cm ³ .

(Comparative Example 5)
The graphite sheet of Comparative Example 5 was produced in the same manner as in Example 1 except that the temperature was raised to 2400 ° C. (maximum graphitization temperature) at a heating rate of 5.0 ° C./min. The thickness of the graphite sheet after compression was 31 μm, and the density was 1.47 g / cm ³ .

Table 1 shows the production conditions and physical properties of the graphite sheets of Examples 1 to 9 and Comparative Examples 1 to 5.

According to Examples 1 to 9, it can be seen that the graphite sheet having a phosphorus content of 0.01% by weight to 0.10% by weight is excellent in both thermal diffusivity and flexibility. On the other hand, according to Comparative Examples 1 and 2, it can be seen that the graphite sheet having a phosphorus content of less than 0.01% by weight is excellent in thermal diffusivity but inferior in flexibility. Further, from Comparative Examples 3 to 5, it can be seen that the graphite sheet having a phosphorus content of more than 0.10% by weight is excellent in flexibility but inferior in thermal diffusivity.

The graphite sheet obtained in the present invention has good heat diffusivity and flexibility, and can be suitably used as a heat radiating member for electronic devices.

Claims (3)

A graphite sheet having a phosphorus content of 0.01% by weight or more and 0.10% by weight or less. The graphite sheet according to claim 1, wherein the phosphorus content is 0.02% by weight or more and 0.08% by weight or less. A method for producing a graphite sheet having a phosphorus content of 0.01% by weight or more and 0.10% by weight or less.
A carbonization step of carbonizing a polyimide film having a phosphate content of 0.01% by weight or more and 0.49% by weight or less to obtain a carbonaceous film, and
A graphitization step in which the carbonaceous film is heat-treated at a heating rate of 0.01 ° C./min or more and less than 20 ° C./min and a maximum temperature of 2600 ° C. or higher to obtain a graphite sheet.
A method for manufacturing a graphite sheet including.