Film-like graphite, its manufacturing method, and battery using the same

Abstract

This film-like graphite satisfies condition (1) or condition (2).　Condition (1): A graphite crystal orientation degree P with respect to a film surface is 96% or greater.　Condition (2): The graphite crystal orientation degree P with respect to the film surface is 94% or greater, and the thickness is 42 μm or greater.

Description

[Technical Field]

[0001] The present invention relates to a thick film-like graphite that has high thermal conductivity, excellent heat dissipation performance, and excellent flexibility, a method for producing the same, and a battery using the same. This application claims priority based on Japanese Patent Application No. 2021-007441 filed in Japan on January 20, 2021, Japanese Patent Application No. 2021-024960 filed in Japan on February 19, 2021, Japanese Patent Application No. 2021-033870 filed in Japan on March 3, 2021, Japanese Patent Application No. 2021-194427 filed in Japan on November 30, 2021, Japanese Patent Application No. 2021-204228 filed in Japan on December 16, 2021, and Japanese Patent Application No. 2021-204500 filed in Japan on December 16, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] The data processing capabilities of electronic devices such as smartphones have improved dramatically, and the amount of heat generated has also increased significantly. Meanwhile, electronic devices are becoming smaller and thinner, and heat dissipators inside electronic devices are required to have higher performance and lighter weight. Film-like graphite is known as a flexible heat dissipator that is lighter than metals and has excellent heat dissipation performance (e.g., Patent Documents 1 to 6). Furthermore, it is desirable to quickly remove heat generated in lithium-ion batteries and all-solid-state batteries, particularly during rapid charging, to prevent overheating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2006-129632 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-114098 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-24571 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-189267 [Patent Document 5] Japanese Patent Application Laid-Open No. 2007-031237 [Patent Document 6] Japanese Patent Application Laid-Open No. 2016-153356 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the demand for thicker, more thermally conductive film-like graphite has increased due to the increasing demand for heat dissipation performance, but producing thick, highly thermally conductive film-like graphite is difficult.

[0005] Film-like graphite is typically obtained by heating a polymer film, typically a polyimide, to 2400°C or higher. However, when a thick polymer film is used, decomposition gases generated from the surface and interior of the film during heating can easily cause parts of the film surface to peel off, or foaming can occur within the film, destroying the film. As a result, film-like graphite may not be obtained, or even if it is obtained, its thermal conductivity is likely to be low. Even if the problems caused by decomposition gases are avoided by gradually increasing the temperature, the resulting film-like graphite tends to have low flexibility.

[0006] Therefore, to ensure the required heat dissipation performance, it was necessary to use multiple thin sheets of film-type graphite stacked together. However, when stacking multiple sheets of film-type graphite, materials with low thermal conductivity, such as adhesives, are used, which reduces the heat dissipation performance of the entire laminate. For this reason, it has become important to develop thick film-type graphite with high thermal conductivity that can provide sufficient heat dissipation performance on its own.

[0007] Patent Document 1 discloses that a graphite film having a maximum thickness of 57 μm was produced from a polymer film having a thickness of 125 μm using an electric current heating method. However, the thickness of the graphite film in Patent Document 1 is insufficient. Patent Document 2 discloses the production of film-like graphite up to 160 μm thick from a thick laminated film made by roughening the surface of a polyimide film and laminating two polyimide films together. However, in Patent Document 2, despite careful treatment in the graphitization step by setting the temperature rise rate at a relatively slow rate of 3°C / min, foaming could not be sufficiently reduced, and there is room for further improvement in thermal conductivity.

[0008] Patent Document 3 discloses that when a polymer film having a thickness of 80 μm or more and 300 μm or less is used, the temperature rise rate in the graphitization step is set to a slow rate of 2°C / min or less, thereby suppressing the amount of foaming gas per unit time and obtaining a thick film-like graphite. However, if the temperature rise rate in the graphitization step is slowed and the time required for the graphitization step is extended, the productivity of the film-like graphite decreases and the graphite structure grows excessively, making it impossible to ensure sufficient flexibility. As a result, when the film-like graphite is processed, such as by cutting it to the desired dimensions for use in devices such as smartphones or by laminating it with an adhesive, the handleability decreases, such as the film being more susceptible to breakage.

[0009] Patent Document 4 discloses that the foaming state of a graphite film can be determined by checking the number of boundary lines (wrinkles) on the surface of the graphite film from an SEM image, and that the flexibility of the film can be predicted from the determined foaming state. However, the graphite film disclosed in Patent Document 1 has insufficient thermal conductivity.

[0010] Patent Document 5 discloses that a graphite film having both high thermal conductivity and flexibility can be provided by forming a very high-density graphite layer near the film surface and forming an air-rich mixed layer of air and graphite layers inside. However, the thermal conductivity of the graphite film obtained by this method is also insufficient.

[0011] Patent Document 6 discloses that a thermal conductivity of 1,800 W / mK can be achieved by reducing the thickness of the graphite sheet to 9.6 μm or less. However, the amount of heat transport depends on both the thermal conductivity and the thickness, and a thin film reduces the amount of heat transport.

[0012] As described above, methods for obtaining film-like graphite with excellent thermal conductivity have been investigated in the past, but only films with low thermal conductivity have been obtained, particularly for thick films. Therefore, there has been a demand for film-like graphite that maintains high thermal conductivity regardless of film thickness.

[0013] Furthermore, while film-type graphite has high heat dissipation performance, it is more expensive than other heat dissipators. One reason for this is that the film shrinks during production, resulting in an area ratio of approximately 70 to 75% relative to the raw polymer film.

[0014] Lithium-ion secondary batteries and all-solid-state batteries generally use aluminum foil as the positive electrode current collector and copper foil as the negative electrode current collector. Although these metal foils have high electrical conductivity, materials with higher thermal conductivity are needed to quickly remove the heat generated during rapid charging and prevent overheating.

[0015] An object of one aspect of the present invention is to provide a thick filmy graphite having high thermal conductivity and excellent heat dissipation performance, as well as excellent flexibility, and at low cost, and a method for producing the filmy graphite. Another object of the present invention is to provide filmy graphite having high thermal conductivity and excellent heat dissipation performance, particularly filmy graphite having excellent thermal conductivity despite its thickness, and to provide a method for producing the filmy graphite.

[0016] Another aspect of the present invention aims to provide a thick filmy graphite that has high thermal conductivity, excellent heat dissipation performance, and high electrical conductivity, and to provide a lithium ion battery and an all-solid-state battery that use the same as a current collector. [Means for solving the problem]

[0017] The first aspect of the present invention has the following features. [1] Film-like graphite that satisfies the following condition (1) or (2): Condition (1): The degree of orientation P of graphite crystals relative to the film surface is 96% or more. Condition (2): The degree of graphite crystal orientation P relative to the film surface is 94% or more, and the thickness is 42 μm or more. [2] Film-like graphite that satisfies the following condition (3) or (4). Condition (3): The film thickness a (μm) is 58 μm or more, and the thermal conductivity b (W / mK) in the direction along the film surface is 800 W / mK or more. Condition (4): The film thickness a (μm) is 50 μm or more, the thermal conductivity b (W / mK) in the direction along the film surface is 1,350 W / mK or more, and a×b≧100,000. [3] Film-like graphite in which the product (a × b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is 88,000 or more. [4] The filmy graphite according to any one of [1] to [3], which satisfies the following conditions (5) and (6): Condition (5): When the thickness of the film is a (μm) and the thermal conductivity in the direction along the film surface is b (W / mK), the following formula 1a is satisfied. 2140≦12a+b...Formula 1a Condition (6): The minimum bending radius measured in a bending test is 16 mm or less. [5] Film-like graphite in which the number N of multiple bright areas obtained from a binarized image of bright and dark areas observed under a polarizing microscope in a cross section perpendicular to the film surface of the film-like graphite, the film thickness H (μm), and the film width W (μm) satisfy the following formula (7), or (8) and (9): N / H / W≦0.015 (7) N / H / W≦0.04 (8) H≧42 (9) [6] In a cross section perpendicular to the film surface of film-like graphite, the average area of multiple bright areas obtained from a binarized image of bright and dark areas observed under a polarizing microscope is 22 μm 2 or more, or the film thickness is 42 μm or more and the average area is 9 μm 2 This is the film-like graphite. [7] The filmy graphite according to any one of [1] and [3] to [6], which has a thickness of 58 μm or more. [8] The filmy graphite according to any one of [1] and [3] to [7], which has a thermal conductivity b (W / mK) of 800 W / mK or more in a direction along the film surface. [9] The filmy graphite according to any one of [1] and [3] to [7], which has a density of 1.7 g / cm 3 The filmy graphite according to any one of [1] to [8], wherein

[10] The filmy graphite according to any one of [1] to [9], which has an electrical conductivity of 9,000 S / cm or more in a direction along the film surface.

[11] The filmy graphite according to any one of [1] to

[10] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, the multilayer structure having a width of 40 μm or more and a thickness of 8 μm or more, and the direction of each layer of the multilayer structure forms an angle of 20° or less with the direction along the film surface.

[12] The filmy graphite according to

[11] , wherein each layer of the multilayer structure has numerous irregularities, and adjacent layers are in contact with each other at numerous locations.

[13] The filmy graphite according to

[11] or

[12] , wherein each layer of the multilayer structure has a flat surface or a smoothly curved surface, and adjacent layers are in close contact with each other.

[14] The minimum bending radius measured in the bending test is 16 mm or less. [1] The filmy graphite according to any one of [3] and [5] to

[13] .

[15] When a pressure of 100 MPa is applied to the entire surface of a film of graphite in an environment of 25°C, the film thickness before compression, T b Film thickness after compression vs. Ta The ratio (T a / T b ) is 0.7 or more.

[16] The filmy graphite according to any one of [1] to

[15] , which has a folding endurance of 10,000 or more folding cycles before breaking when measured in a planar body no-load U-shaped stretching test with a bending radius R of 2 mm and a bending angle of 180°.

[17] The filmy graphite according to any one of [1] to

[16] , which has a thermal conductivity in a direction perpendicular to the film surface of 1 W / mK or more and 20 W / mK or less.

[18] The filmy graphite according to any one of [1] to

[17] , which has a ratio of surface area to film area (surface area / film area) of 1.05 or more.

[19] The filmy graphite according to any one of [1] to

[18] , wherein the filmy graphite does not include a layer of adhesive or pressure-sensitive adhesive in the film thickness direction.

[20] The filmy graphite according to any one of [1], [2], and [4] to

[19] , wherein the product (a×b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is 88,000 or more.

[21] The filmy graphite according to any one of [1] to [4] and [6] to

[20] , wherein the number N of a plurality of bright area regions obtained from an image obtained by binarizing bright and dark areas observed in a polarizing microscope image in a cross section perpendicular to the film surface of the filmy graphite, the film thickness H (μm), and the film width W (μm) satisfy the following formula (7), or (8) and (9): N / H / W≦0.015 (7) N / H / W≦0.04 (8) H≧42 (9)

[22] In a cross section perpendicular to the film surface of film-like graphite, the average area of multiple bright areas obtained from a binarized image of bright and dark areas observed under a polarizing microscope is 9 μm 2 or more, or the film thickness is 42 μm or more and the average area is 9 μm 2The filmy graphite according to any one of [1] to [5] and [7] to

[21] above.

[23] A method for producing film-like graphite by heating a raw material film made of an organic polymer, wherein in the heating step, a laminated film formed by bonding two or more polymer films made of an organic polymer with a pressure-sensitive adhesive or adhesive is used as the raw material film.

[24] A method for producing filmy graphite, comprising: a carbonization step of carbonizing a raw material film made of an organic polymer to obtain a carbonized film; and a graphitization step of graphitizing the carbonized film to obtain a graphitized film, a method for producing filmy graphite, the method comprising the steps of: producing, from the raw material film having a thickness of 150 μm or more, filmy graphite having a thermal conductivity of 800 W / mK or more and a minimum bending radius of 16 mm or less in a bending test, from the raw material film having a thickness of 150 μm or more, by setting the maximum temperature rise width in any 30 minutes to 60° C. or more in a temperature rise pattern obtained by monotonically raising the temperature at 2000° C. or more in the graphitization step.

[25] A method for producing filmy graphite, comprising: a carbonization step of carbonizing a raw material film made of an organic polymer to obtain a carbonized film; and a graphitization step of graphitizing the carbonized film to obtain a graphitized film, The carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas.

[26] The method for producing filmy graphite according to

[25] , wherein the mixed gas contains a gaseous substance (A) consisting of at least one of acetylene and an acetylene derivative, and an inert gas.

[27] At least a part of the heating step in the mixed gas is f The method for producing filmy graphite according to

[25] or

[26] , wherein the method is carried out at the following temperature: T f(°C) is the highest temperature at which the observed weight loss rate of the measurement sample (weight loss per unit time) is 10% or more of the maximum weight loss rate in a thermogravimetric measurement in which a measurement sample made of the raw material film is heated to 1000°C at a temperature increase rate of 10°C / min while nitrogen gas is flowing at a rate of 200 mL / min and the temperature and weight of the measurement sample are recorded.

[28] The temperature rise history of the heating process in the mixed gas is monotonically increased by the following temperature rise pattern T s or more and the above T f The method for producing filmy graphite according to

[27] , comprising a period of 30 minutes or more in which the average heating rate is 5°C / min or less within the following temperature range: T s (°C) is the lowest temperature of 100°C or higher at which the weight loss rate of the measurement sample observed in the thermogravimetry is 0.8% or more of the maximum weight loss rate.

[29] The maximum heating temperature T in the graphitization process max The method for producing filmy graphite according to any one of

[23] to

[28] , wherein the temperature is 2400°C or higher and 2900°C or lower.

[30] The method for producing filmy graphite according to any one of

[24] to

[29] , wherein the raw material film is a laminated film formed by bonding two or more polymer films made of organic polymers with a pressure-sensitive adhesive or adhesive.

[31] A method for producing filmy graphite, comprising: a carbonization step of carbonizing a raw material film made of an organic polymer to obtain a carbonized film; and a graphitization step of graphitizing the carbonized film to obtain a graphitized film, wherein the raw material film has an area S m The area S of the graphitized film g The ratio (S g / S m ) is 0.8 or more.

[32] The graphitized film is compressed or rolled to a density of 1.7 g / cm 3 from said graphitized film having a density of less than 1.7 g / cm 3The method for producing filmy graphite according to

[31] , which produces the above filmy graphite.

[33] A battery, which is a lithium ion secondary battery or an all-solid-state battery, in which the filmy graphite according to any one of [1] to

[22] is used as a current collector or as a negative electrode active material and a negative electrode current collector.

[34] The film-like graphite according to any one of [1] to

[22] , wherein the thickness of the film is preferably from 42 μm to 250 μm, more preferably from 50 μm to 200 μm, even more preferably from 58 μm to 180 μm, still more preferably from 64 μm to 150 μm, even more preferably from 72 μm to 150 μm, particularly preferably from 75 μm to 150 μm, particularly more preferably from 80 μm to 130 μm, even particularly preferably from 85 μm to 130 μm, even particularly preferably from 100 μm to 130 μm, and most preferably from 102 μm to 120 μm.

[35] The filmy graphite according to any one of [1] to

[22] and

[34] , wherein the thermal conductivity in the direction along the film surface is preferably 800 W / mK or more and 2200 W / mK or less, more preferably 1000 W / mK or more and 2200 W / mK or less, even more preferably 1200 W / mK or more and 2200 W / mK or less, still more preferably 1350 W / mK or more and 2200 W / mK or less, even more preferably 1400 W / mK or more and 2200 W / mK or less, particularly preferably 1550 W / mK or more and 2200 W / mK or less, and most preferably 1600 W / mK or more and 2200 W / mK or less.

[36] The filmy graphite according to any one of [1] to

[22] ,

[34] , and

[35] , wherein the product (a×b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is preferably 88,000 or more and 500,000 or less, more preferably 110,000 or more and 500,000 or less, even more preferably 135,000 or more and 400,000 or less, particularly preferably 140,000 or more and 300,000 or less, and most preferably 160,000 or more and 270,000 or less.

[37] The filmy graphite according to any one of [1] to

[22] and

[34] to

[36] , wherein the thermal conductivity in the direction perpendicular to the film surface is preferably more than 0 W / mK and not more than 20 W / mK, more preferably 0.5 W / mK or more and 15 W / mK or less, even more preferably 1 W / mK or more and 10 W / mK or less, and particularly preferably 3 W / mK or more and 10 W / mK or less.

[38] The filmy graphite according to any one of [1] to

[22] and

[34] to

[37] , wherein the electrical conductivity in the direction along the film surface is preferably 9,000 S / cm or more and 30,000 S / cm or less, more preferably 10,000 S / cm or more and 20,000 S / cm or less, even more preferably 11,000 S / cm or more and 18,000 S / cm or less, particularly preferably 12,000 S / cm or more and 15,000 S / cm or less, and most preferably 13,500 S / cm or more and 15,000 S / cm or less.

[39] The filmy graphite according to any one of [4] to

[22] and

[34] to

[38] , wherein the value of 12a+b represented by formula 1a is preferably 2140 or more and 5000 or less, more preferably 2200 or more and 4500 or less, even more preferably 2250 or more and 4000 or less, still more preferably 2350 or more and 3800 or less, particularly preferably 2550 or more and 3800 or less, and most preferably 2750 or more and 3700 or less.

[40] The filmy graphite according to any one of [1] to

[22] and

[34] to

[39] , wherein the minimum bending radius is preferably more than 0 mm and not more than 16 mm, more preferably more than 0 mm and not more than 13 mm, even more preferably more than 0 mm and not more than 10 mm, particularly preferably 0 mm or more and not more than 8 mm, and most preferably more than 0 mm and not more than 6 mm.

[41] Density: 1.7 g / cm 3 More than 2.2g / cm 3 Preferably less than 1.8 g / cm 3 More than 2.1g / cm 3 Less than 1.9 g / cm is more preferable. 3 More than 2.0g / cm 3 The filmy graphite according to any one of [1] to

[22] and

[34] to

[40] , wherein the following is more preferable.

[42] The filmy graphite according to any one of [1] to

[22] and

[34] to

[41] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the width of the multilayer structure is preferably 40 μm or more and 100 μm or less, more preferably 45 μm or more and 80 μm or less, and even more preferably 50 μm or more and 70 μm or less.

[43] The filmy graphite according to any one of [1] to

[22] and

[34] to

[42] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the thickness of the multilayer structure is preferably 8 μm or more and 20 μm or less, and more preferably 10 μm or more and 15 μm or less.

[44] The filmy graphite according to any one of [1] to

[22] and

[34] to

[43] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the angle formed by each layer of the multilayer structure with the direction along the film surface is preferably greater than 0° and not greater than 20°, more preferably greater than 0° and not greater than 15°, and even more preferably greater than 0° and not greater than 10°.

[45] The filmy graphite according to any one of [1] to

[22] and

[34] to

[44] , comprising a multilayer structure in which a plurality of layers are superimposed on one another, adjacent layers being in close contact with one another, and in an image of a mode I crack propagation fracture surface of the filmy graphite observed with a scanning electron microscope (SEM), no voids are observed between adjacent layers even when observed at an accelerating voltage of 10 kV and a magnification of 1000 times.

[46] When a film of graphite is compressed under a pressure of 100 MPa across the entire surface of the film at 25°C, the film thickness before compression, T b Film thickness after compression vs. T a The ratio (T a / T b ) is preferably 0.7 or more and 1.0 or less, more preferably 0.8 or more and 1.0 or less, and even more preferably 0.9 or more and 1.0 or less. The filmy graphite according to any one of [1] to

[22] and

[34] to

[45] .

[47] The method for producing filmy graphite according to any one of

[23] to

[32] , wherein the thickness of the raw material film is preferably 75 μm or more and 550 μm or less, more preferably 125 μm or more and 500 μm or less, even more preferably 150 μm or more and 450 μm or less, still more preferably 175 μm or more and 400 μm or less, particularly preferably 200 μm or more and 375 μm or less, and most preferably 250 μm or more and 270 μm or less.

[48] The method for producing filmy graphite according to any one of

[23] to

[32] and

[47] , wherein the organic polymer is preferably a polymer having an aromatic ring, selected from the group consisting of polyimide, polyamide, polythiazole, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polybenzothiazole, polybenzobisthiazole, polybenzimidazole, polybenzobisimidazole, and polyparaphenylenevinylene, more preferably a polymer having an aromatic ring, and even more preferably a polyimide having an aromatic ring.

[49] The method for producing filmy graphite according to any one of

[23] to

[32] ,

[47] , and

[48] , wherein the carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas, and the concentration of the organic gas in the mixed gas is preferably 2 vol% or more and 95 vol% or less, more preferably 5 vol% or more and 50 vol% or less, even more preferably 10 vol% or more and 40 vol% or less, particularly preferably 20 vol% or more and 30 vol% or less, and most preferably 25 vol% or more and 30 vol% or less.

[50] The method for producing filmy graphite according to any one of

[23] to

[32] and

[47] to

[49] , wherein the carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas, and the maximum heating temperature in the organic gas heating step is preferably 400°C or higher and 1000°C or lower, more preferably 450°C or higher and 800°C or lower, and even more preferably 500°C or lower and 600°C or lower.

[51] The maximum heating temperature T in the graphitization process maxThe method for producing filmy graphite according to any one of

[23] to

[32] and

[47] to

[50] , wherein the temperature is preferably 2400°C or higher and 3000°C or lower, more preferably 2700°C or higher and 2900°C or lower, and even more preferably 2750°C or higher and 2800°C or lower.

[52] Area S of the raw material film m the area S of the graphitized film g The ratio (S g / S m ) is preferably 0.8 or more and 1.2 or less, more preferably 0.9 or more and 1.1 or less, and even more preferably 1.0 or more and 1.1 or less.

[53] The method for producing filmy graphite according to

[23] to

[32] and

[47] to

[52] , further comprising a pressing step of compressing or rolling the graphitized film.

[54] The density of the film-like graphite obtained in the pressing step is 1.6 g / cm 3 More than 2.2g / cm 3 Preferably less than 1.7 g / cm 3 More than 2.1g / cm 3 Less than 1.8 g / cm is more preferable. 3 More than 2.0g / cm 3 The method for producing filmy graphite according to

[53] is further preferably as follows:

[0018] The second aspect of the present invention has the following features. [1] Film-like graphite having a film thickness of 58 μm or more, a thermal conductivity in the direction along the film surface of 800 W / mK or more, and satisfying the following conditions (1) and (2): Condition (1): When the thickness of the film is a (μm) and the thermal conductivity in the direction along the film surface is b (W / mK), the following formula 1a is satisfied. 2140≦12a+b...Formula 1a Condition (2): The minimum bending radius measured in a bending test is 16 mm or less. [2] Density is 1.7g / cm 3The filmy graphite according to [1] above. [3] The filmy graphite according to [1] or [2], which includes a multilayer structure in which a plurality of layers are stacked on top of each other, the multilayer structure having a width of 40 μm or more and a thickness of 8 μm or more, and the orientation of each layer of the multilayer structure forms an angle of 20° or less with the direction along the film surface. [4] When a pressure of 100 MPa is applied to the entire surface of a film of graphite in an environment of 25°C, the film thickness before compression, T b Film thickness after compression vs. T a The ratio (T a / T b ) is 0.7 or more. [5] A method for producing filmy graphite, comprising: a carbonization step of carbonizing a raw material film made of an organic polymer to obtain a carbonized film; and a graphitization step of graphitizing the carbonized film to obtain a graphitized film, The method for producing filmy graphite, wherein the carbonization step includes a heating step in an organic gas in which the raw material film is heated in a mixed gas of an organic gas and an inert gas. [6] The method for producing filmy graphite according to [5], wherein the mixed gas contains a gaseous substance (A) consisting of at least one of acetylene and an acetylene derivative, and an inert gas. [7] At least a part of the heating step in an organic gas is carried out by the following T f The method for producing filmy graphite according to [5] or [6], which is carried out at the following temperature: T f (°C) is the highest temperature at which the observed weight loss rate of the measurement sample (weight loss per unit time) is 10% or more of the maximum weight loss rate in a thermogravimetric measurement in which a measurement sample made of the raw material film is heated to 1000°C at a temperature increase rate of 10°C / min while nitrogen gas is flowing at a rate of 200 mL / min and the temperature and weight of the measurement sample are recorded. [8] The temperature rise history of the heating process in the organic gas is monotonically increased by the following temperature rise pattern T s or more and the above Tf The method for producing filmy graphite according to [7], comprising a period of 30 minutes or more in which the average heating rate is 5°C / min or less within the following temperature range: T s (°C) is the lowest temperature of 100°C or higher at which the weight loss rate of the measurement sample observed in the thermogravimetry is 0.8% or more of the maximum weight loss rate. [9] The maximum heating temperature T in the graphitization process max The method for producing filmy graphite according to any one of [5] to [8], wherein the temperature is 2400°C or higher and 2900°C or lower.

[10] A method for producing filmy graphite, comprising: a carbonization step of carbonizing a raw material film made of an organic polymer to obtain a carbonized film; and a graphitization step of graphitizing the carbonized film to obtain a graphitized film, a method for producing filmy graphite, the method comprising the steps of: producing, from the raw material film having a thickness of 150 μm or more, filmy graphite having a thermal conductivity of 800 W / mK or more and a minimum bending radius of 16 mm or less in a bending test, from the raw material film having a thickness of 150 μm or more, by setting the maximum temperature rise width in any 30 minutes to 60° C. or more in a temperature rise pattern obtained by monotonically raising the temperature at 2000° C. or more in the graphitization step.

[11] The method for producing filmy graphite according to any one of [5] to

[10] , wherein the raw material film is a laminated film formed by bonding two or more polymer films made of organic polymers with a pressure-sensitive adhesive or adhesive.

[12] A method for producing filmy graphite, comprising: a carbonization step of carbonizing a raw material film made of an organic polymer to obtain a carbonized film; and a graphitization step of graphitizing the carbonized film to obtain a graphitized film, wherein the raw material film has an area S m The area S of the graphitized film g The ratio (S g / S m ) is 0.8 or more.

[13] A pressing process for compressing or rolling the graphitized film reduces the density to 1.7 g / cm 3 from said graphitized film having a density of less than 1.7 g / cm3 The method for producing filmy graphite according to

[12] , which produces the above filmy graphite.

[14] A film having a multilayer structure in which a plurality of layers are stacked on top of each other, the multilayer structure having a width of 40 μm or more and a thickness of 8 μm or more, the angle between the direction of each layer of the multilayer structure and the direction along the film surface being 20° or less, and a density of 1.7 g / cm 3 More film-like graphite.

[15] The filmy graphite according to

[14] , which has a thickness of 58 μm or more.

[16] The filmy graphite according to

[14] or

[15] , which has a minimum bending radius of 16 mm or less as measured in a bending test.

[17] The filmy graphite according to any one of

[14] to

[16] , wherein each layer constituting the multilayer structure has numerous irregularities, and adjacent layers are in contact with each other at numerous locations.

[18] The filmy graphite according to any one of

[14] to

[16] , wherein each layer of the multilayer structure has a flat surface or a smoothly curved surface, and adjacent layers are in close contact with each other.

[19] Film-like graphite having a film thickness a (μm) of 50 μm or more, a thermal conductivity b in the direction along the film surface of 1,350 W / mK or more, and the product of a and b of 100,000 or more.

[20] Film-like graphite in which the product (a × b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is 88,000 or more.

[21] Density is 1.7g / cm 3 The filmy graphite according to

[19] or

[20] , wherein

[22] The filmy graphite according to any one of

[19] to

[21] , which has a minimum bending radius measured in a bending test of 16 mm or less.

[23] The filmy graphite according to any one of [1] to [4] and

[14] to

[22] , which has a folding endurance of 10,000 or more times before breaking when measured in a planar body no-load U-shaped stretching test with a bending radius R of 2 mm and a bending angle of 180°.

[24] The filmy graphite according to any one of [1] to [4] and

[14] to

[23] , wherein the filmy graphite does not include a layer of adhesive or pressure-sensitive adhesive in the film thickness direction.

[25] The method for producing filmy graphite according to

[10] , characterized in that the number of folding cycles until fracture occurs is 10,000 or more when measured in a no-load U-shaped stretching test of a planar body with a bending radius R of 2 mm and a bending angle of 180°.

[26] The film-like graphite according to any one of [1] to [4] and

[14] to

[24] , wherein the thickness of the film is preferably from 42 μm to 250 μm, more preferably from 50 μm to 200 μm, even more preferably from 58 μm to 180 μm, still more preferably from 64 μm to 150 μm, even more preferably from 72 μm to 150 μm, particularly preferably from 75 μm to 150 μm, particularly more preferably from 80 μm to 130 μm, even particularly preferably from 85 μm to 130 μm, even particularly preferably from 100 μm to 130 μm, and most preferably from 102 μm to 120 μm.

[27] The filmy graphite according to any one of [1] to [4],

[14] to

[24] , and

[26] , wherein the thermal conductivity in the direction along the film surface is preferably 800 W / mK or more and 2200 W / mK or less, more preferably 1000 W / mK or more and 2200 W / mK or less, even more preferably 1200 W / mK or more and 2200 W / mK or less, still more preferably 1350 W / mK or more and 2200 W / mK or less, even more preferably 1400 W / mK or more and 2200 W / mK or less, particularly preferably 1550 W / mK or more and 2200 W / mK or less, and most preferably 1660 W / mK or more and 2200 W / mK or less.

[28] The filmy graphite according to any one of [1] to [4],

[14] to

[24] ,

[26] and

[27] , wherein the value of 12a+b represented by formula 1a is preferably 2140 or more and 5000 or less, more preferably 2200 or more and 4500 or less, even more preferably 2250 or more and 4000 or less, still more preferably 2350 or more and 3800 or less, particularly preferably 2550 or more and 3800 or less, and most preferably 2750 or more and 3700 or less.

[29] The filmy graphite according to any one of [1] to [4],

[14] to

[24] , and

[26] to

[28] , wherein the product (a×b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is preferably 88,000 or more and 500,000 or less, more preferably 110,000 or more and 500,000 or less, even more preferably 135,000 or more and 400,000 or less, particularly preferably 140,000 or more and 300,000 or less, and most preferably 160,000 or more and 270,000 or less.

[30] The filmy graphite according to any one of [1] to [4],

[14] to

[24] , and

[26] to

[29] , wherein the minimum bending radius is preferably greater than 0 mm and not greater than 16 mm, more preferably greater than 0 mm and not greater than 13 mm, even more preferably greater than 0 mm and not greater than 10 mm, particularly preferably greater than 0 mm and not greater than 8 mm, and most preferably greater than 0 mm and not greater than 6 mm.

[31] Density: 1.7 g / cm 3 More than 2.2g / cm 3 Preferably less than 1.8 g / cm 3 More than 2.1g / cm 3 Less than 1.9 g / cm is more preferable. 3 More than 2.0g / cm 3 The filmy graphite according to any one of [1] to [4],

[14] to

[24] , and

[26] to

[30] , wherein the following is more preferable.

[32] The filmy graphite according to any one of [1] to [4],

[14] to

[24] , and

[26] to

[31] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the width of the multilayer structure is preferably 40 μm or more and 100 μm or less, more preferably 45 μm or more and 80 μm or less, and even more preferably 50 μm or more and 70 μm or less.

[33] The filmy graphite according to any one of [1] to [4],

[14] to

[24] , and

[26] to

[32] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the thickness of the multilayer structure is preferably 8 μm or more and 20 μm or less, and more preferably 10 μm or more and 15 μm or less.

[34] The filmy graphite according to any one of [1] to [4],

[14] to

[24] , and

[26] to

[33] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and in which the angle formed by each layer of the multilayer structure with the direction along the film surface is preferably greater than 0° and not greater than 20°, more preferably greater than 0° and not greater than 15°, and even more preferably greater than 0° and not greater than 10°.

[35] The filmy graphite according to any one of [1] to [4],

[14] to

[24] , and

[26] to

[34] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, with adjacent layers in close contact with one another, and in an image of a mode I crack propagation fracture surface of the filmy graphite observed with a scanning electron microscope (SEM), no voids are observed between adjacent layers even when observed at an accelerating voltage of 10 kV and a magnification of 1000 times.

[36] When a pressure of 100 MPa is applied to the entire surface of a film of graphite in an environment of 25°C, the film thickness before compression, T b Film thickness after compression vs. T a The ratio (T a / T b ) is preferably 0.7 or more and 1.0 or less, more preferably 0.8 or more and 1.0 or less, and even more preferably 0.9 or more and 1.0 or less. The filmy graphite according to any one of [1] to [4],

[14] to

[24] , and

[26] to

[35] .

[37] The method for producing filmy graphite according to any one of [5] to

[13] and

[25] , wherein the thickness of the raw material film is preferably 75 μm or more and 550 μm or less, more preferably 125 μm or more and 500 μm or less, even more preferably 150 μm or more and 450 μm or less, still more preferably 175 μm or more and 400 μm or less, particularly preferably 200 μm or more and 375 μm or less, and most preferably 250 μm or more and 270 μm or less.

[38] The method for producing filmy graphite according to any one of [5] to

[13] ,

[25] and

[37] , wherein the organic polymer is preferably a polymer having an aromatic ring, selected from the group consisting of polyimide, polyamide, polythiazole, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polybenzothiazole, polybenzobisthiazole, polybenzimidazole, polybenzobisimidazole and polyparaphenylenevinylene, more preferably a polymer having an aromatic ring, and even more preferably a polyimide having an aromatic ring.

[39] The method for producing filmy graphite according to any one of [5] to

[13] ,

[25] ,

[37] and

[38] , wherein the carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas, and the concentration of the organic gas in the mixed gas is preferably 2 vol% or more and 95 vol% or less, more preferably 5 vol% or more and 50 vol% or less, even more preferably 10 vol% or more and 40 vol% or less, particularly preferably 20 vol% or more and 30 vol% or less, and most preferably 25 vol% or more and 30 vol% or less.

[40] The method for producing filmy graphite according to any one of [5] to

[13] ,

[25] and

[37] to

[39] , wherein the carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas, and the maximum heating temperature in the organic gas heating step is preferably 400°C or higher and 1000°C or lower, more preferably 450°C or higher and 800°C or lower, and even more preferably 500°C or lower and 600°C or lower.

[41] The maximum heating temperature T in the graphitization process maxThe method for producing filmy graphite according to any one of [5] to

[13] ,

[25] and

[37] to

[40] , wherein the temperature is preferably 2400°C or higher and 3000°C or lower, more preferably 2700°C or higher and 2900°C or lower, and even more preferably 2750°C or higher and 2800°C or lower.

[42] Area S of the raw material film m the area S of the graphitized film g The ratio (S g / S m ) is preferably 0.8 or more and 1.2 or less, more preferably 0.9 or more and 1.1 or less, and even more preferably 1.0 or more and 1.1 or less.

[0019] The third aspect of the present invention has the following features. [1] Film-like graphite having a film thickness of 58 μm or more, a thermal conductivity along the film surface of 800 W / mK or more, and a thermal conductivity perpendicular to the film surface of 1 W / mK or more and 20 W / mK or less, and satisfying the following condition (1): Condition (1): When the thickness of the film is a (μm) and the thermal conductivity in the direction along the film surface is b (W / mK), the following formula 1a is satisfied. 2140≦12a+b...Formula 1a [2] The filmy graphite according to [1], which has a minimum bending radius of 16 mm or less as measured in a bending test. [3] Density is 1.7g / cm 3 The filmy graphite according to [1] or [2], wherein [4] The filmy graphite according to [1], which includes a multilayer structure in which a plurality of layers are stacked on top of each other, the multilayer structure having a width of 40 μm or more and a thickness of 8 μm or more, and the direction of each layer of the multilayer structure forms an angle of 20° or less with the direction along the film surface. [5] When a pressure of 100 MPa is applied to the entire surface of a film of graphite in an environment of 25°C, the film thickness before compression, T b Film thickness after compression vs. T a The ratio (Ta / T b ) is 0.7 or more. [6] Film-like graphite in which the product (a × b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is 88,000 or more, and the thermal conductivity in the direction perpendicular to the film surface is 1 W / mK or more and 20 W / mK or less. [7] The filmy graphite according to [6], which has a minimum bending radius of 16 mm or less as measured in a bending test. [8] Density is 1.7g / cm 3 The filmy graphite according to [6] or [7] above. [9] The filmy graphite according to any one of [1] to [8], which has a folding endurance of 10,000 or more folding cycles before breaking when measured in a planar body no-load U-shaped stretching test with a bending radius R of 2 mm and a bending angle of 180°.

[10] The filmy graphite according to any one of [1] to [9], wherein the filmy graphite does not include a layer of adhesive or pressure-sensitive adhesive in the film thickness direction.

[11] The filmy graphite according to any one of [1] to

[10] , wherein the thickness of the film is preferably 42 μm or more and 250 μm or less, more preferably 50 μm or more and 200 μm or less, even more preferably 58 μm or more and 180 μm or less, still more preferably 64 μm or more and 150 μm or less, even more preferably 72 μm or more and 150 μm or less, particularly preferably 75 μm or more and 150 μm or less, particularly more preferably 80 μm or more and 130 μm or less, even particularly preferably 85 μm or more and 130 μm or less, even particularly preferably 100 μm or more and 130 μm or less, and most preferably 102 μm or more and 120 μm or less.

[12] The filmy graphite according to any one of [1] to

[11] , wherein the thermal conductivity in the direction along the film surface is preferably 800 W / mK or more and 2200 W / mK or less, more preferably 1000 W / mK or more and 2200 W / mK or less, even more preferably 1200 W / mK or more and 2200 W / mK or less, still more preferably 1350 W / mK or more and 2200 W / mK or less, even more preferably 1400 W / mK or more and 2200 W / mK or less, particularly preferably 1550 W / mK or more and 2200 W / mK or less, and most preferably 1660 W / mK or more and 2200 W / mK or less.

[13] The filmy graphite according to any one of [1] to

[12] , wherein the thermal conductivity in the direction perpendicular to the film surface is preferably more than 0 W / mK and not more than 20 W / mK, more preferably 0.5 W / mK or more and 15 W / mK or less, even more preferably 1 W / mK or more and 10 W / mK or less, and particularly preferably 3 W / mK or more and 10 W / mK or less.

[14] The filmy graphite according to any one of [1] to

[13] , wherein the value of 12a+b represented by formula 1a is preferably 2140 or more and 5000 or less, more preferably 2200 or more and 4500 or less, even more preferably 2250 or more and 4000 or less, still more preferably 2350 or more and 3800 or less, particularly preferably 2550 or more and 3800 or less, and most preferably 2750 or more and 3700 or less.

[15] The filmy graphite according to any one of [1] to

[14] , wherein the minimum bending radius measured in a bending test is preferably more than 0 mm and not more than 16 mm, more preferably more than 0 mm and not more than 13 mm, even more preferably more than 0 mm and not more than 10 mm, particularly preferably more than 0 mm and not more than 8 mm, and most preferably more than 0 mm and not more than 6 mm.

[16] Density is 1.7 g / cm 3 More than 2.2g / cm 3 Preferably less than 1.8 g / cm 3 More than 2.1g / cm 3 Less than 1.9 g / cm is more preferable. 3 More than 2.0g / cm 3 The filmy graphite according to any one of [1] to

[15] , wherein the following is more preferable.

[17] The filmy graphite according to any one of [1] to

[16] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the width of the multilayer structure is preferably from 40 μm to 100 μm, more preferably from 45 μm to 80 μm, and even more preferably from 50 μm to 70 μm.

[18] The filmy graphite according to any one of [1] to

[17] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the thickness of the multilayer structure is preferably from 8 μm to 20 μm, and more preferably from 10 μm to 15 μm.

[19] The filmy graphite according to any one of [1] to

[18] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and in which the angle formed by each layer of the multilayer structure with the direction along the film surface is preferably greater than 0° and not greater than 20°, more preferably greater than 0° and not greater than 15°, and even more preferably greater than 0° and not greater than 10°.

[20] The filmy graphite according to any one of [1] to

[19] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, with adjacent layers adhering to one another, and in an image of a mode I crack propagation fracture surface of the filmy graphite observed with a scanning electron microscope (SEM), no voids are observed between adjacent layers even when observed at an accelerating voltage of 10 kV and a magnification of 1000 times.

[21] When a pressure of 100 MPa is applied to the entire surface of a film of graphite in an environment of 25°C, the film thickness before compression, T b Film thickness after compression vs. T a The ratio (T a / T b ) is preferably 0.7 or more and 1.0 or less, more preferably 0.8 or more and 1.0 or less, and even more preferably 0.9 or more and 1.0 or less. The filmy graphite according to any one of [1] to

[20] .

[22] The filmy graphite according to any one of [1] to

[21] , wherein the product (a×b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is preferably 88,000 or more and 500,000 or less, more preferably 110,000 or more and 500,000 or less, even more preferably 135,000 or more and 400,000 or less, particularly preferably 140,000 or more and 300,000 or less, and most preferably 160,000 or more and 270,000 or less.

[0020] A fourth aspect of the present invention has the following features. [1] Film-like graphite having a film thickness of 58 μm or more, a thermal conductivity along the film surface of 800 W / mK or more, and an electrical conductivity along the film surface of 9000 S / cm or more. [2] The filmy graphite according to [1], wherein the electrical conductivity in the direction along the film surface is 10,000 S / cm or more. [3] The filmy graphite according to [1], wherein the electrical conductivity in the direction along the film surface is 11,000 S / cm or more. [4] The filmy graphite according to any one of [1] to [3], wherein the film has a thickness a (μm) and a thermal conductivity b (W / mK) in a direction along the film surface, and satisfies the following formula 1a: 2140≦12a+b...Formula 1a [5] The filmy graphite according to any one of [1] to [4], which has a minimum bending radius of 16 mm or less as measured in a bending test. [6] Density is 1.7g / cm 3 The filmy graphite according to any one of [1] to [5], wherein the filmy graphite is as described above. [7] The filmy graphite according to any one of [1] to [6], which comprises a multilayer structure in which a plurality of layers are superimposed on one another, the multilayer structure having a width of 40 μm or more and a thickness of 8 μm or more, and the direction of each layer of the multilayer structure forms an angle of 20° or less with the direction along the film surface. [8] When a pressure of 100 MPa is applied to the entire surface of a film of graphite in an environment of 25°C, the film thickness before compression, T b Film thickness after compression vs. T a The ratio (T a / T b ) is 0.7 or more. [9] Film-like graphite in which the product (a × b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is 88,000 or more, and the thermal conductivity in the direction perpendicular to the film surface is 1 W / mK or more and 20 W / mK or less.

[10] The filmy graphite according to [9], which has a minimum bending radius of 16 mm or less as measured in a bending test.

[11] Density is 1.7g / cm 3 The filmy graphite according to [9] or

[10] above.

[12] The filmy graphite according to any one of [1] to

[11] , which has a folding endurance of 10,000 or more folding cycles before breaking when measured in a no-load U-shaped stretch test for a planar body with a bending radius R of 2 mm and a bending angle of 180°.

[13] The filmy graphite according to any one of [1] to

[12] , wherein the filmy graphite does not include a layer of adhesive or pressure-sensitive adhesive in the film thickness direction.

[14] A lithium ion secondary battery or an all-solid-state battery using the filmy graphite according to any one of [1] to

[13] as a current collector.

[15] A lithium ion secondary battery or an all-solid-state battery using the filmy graphite according to any one of [1] to

[13] as a negative electrode active material and a negative electrode current collector.

[16] The film-like graphite according to any one of [1] to

[13] , wherein the thickness of the film is preferably from 42 μm to 250 μm, more preferably from 50 μm to 200 μm, even more preferably from 58 μm to 180 μm, still more preferably from 64 μm to 150 μm, even more preferably from 72 μm to 150 μm, particularly preferably from 75 μm to 150 μm, particularly more preferably from 80 μm to 130 μm, even particularly preferably from 85 μm to 130 μm, even particularly preferably from 100 μm to 130 μm, and most preferably from 102 μm to 120 μm.

[17] The filmy graphite according to any one of [1] to

[13] and

[16] , wherein the thermal conductivity in the direction along the film surface is preferably 800 W / mK or more and 2200 W / mK or less, more preferably 1000 W / mK or more and 2200 W / mK or less, even more preferably 1200 W / mK or more and 2200 W / mK or less, still more preferably 1350 W / mK or more and 2200 W / mK or less, even more preferably 1400 W / mK or more and 2200 W / mK or less, particularly preferably 1550 W / mK or more and 2200 W / mK or less, and most preferably 1660 W / mK or more and 2200 W / mK or less.

[18] The filmy graphite according to any one of [1] to

[13] ,

[16] , and

[17] , wherein the electrical conductivity in the direction along the film surface is preferably 9,000 S / cm or more and 30,000 S / cm or less, more preferably 10,000 S / cm or more and 20,000 S / cm or less, even more preferably 11,000 S / cm or more and 18,000 S / cm or less, particularly preferably 12,000 S / cm or more and 15,000 S / cm or less, and most preferably 13,500 S / cm or more and 15,000 S / cm or less.

[19] The filmy graphite according to any one of [1] to

[13] and

[16] to

[18] , wherein the value of 12a+b represented by formula 1a is preferably 2140 or more and 5000 or less, more preferably 2200 or more and 4500 or less, even more preferably 2250 or more and 4000 or less, still more preferably 2350 or more and 3800 or less, particularly preferably 2550 or more and 3800 or less, and most preferably 2750 or more and 3700 or less.

[20] The filmy graphite according to any one of [1] to

[13] and

[16] to

[19] , wherein the minimum bending radius is preferably greater than 0 mm and not greater than 16 mm, more preferably greater than 0 mm and not greater than 13 mm, even more preferably greater than 0 mm and not greater than 10 mm, particularly preferably greater than 0 mm and not greater than 8 mm, and most preferably greater than 0 mm and not greater than 6 mm.

[21] Density: 1.7 g / cm 3 More than 2.2g / cm 3 Preferably less than 1.8 g / cm 3 More than 2.1g / cm 3 Less than 1.9 g / cm is more preferable. 3 More than 2.0g / cm 3 The filmy graphite according to any one of [1] to

[13] and

[16] to

[20] , wherein the following is more preferable.

[22] The filmy graphite according to any one of [1] to

[13] and

[16] to

[21] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the width of the multilayer structure is preferably 40 μm or more and 100 μm or less, more preferably 45 μm or more and 80 μm or less, and even more preferably 50 μm or more and 70 μm or less.

[23] The filmy graphite according to any one of [1] to

[13] and

[16] to

[22] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the thickness of the multilayer structure is preferably 8 μm or more and 20 μm or less, and more preferably 10 μm or more and 15 μm or less.

[24] The filmy graphite according to any one of [1] to

[13] and

[16] to

[23] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, and the angle formed by each layer of the multilayer structure with the direction along the film surface is preferably greater than 0° and not greater than 20°, more preferably greater than 0° and not greater than 15°, and even more preferably greater than 0° and not greater than 10°.

[25] The filmy graphite according to any one of [1] to

[13] and

[16] to

[24] , which comprises a multilayer structure in which a plurality of layers are superimposed on one another, with adjacent layers in close contact with one another, and in an image of a mode I crack propagation fracture surface of the filmy graphite observed with a scanning electron microscope (SEM), no voids are observed between adjacent layers even when observed at an accelerating voltage of 10 kV and a magnification of 1000 times.

[26] When a pressure of 100 MPa is applied to the entire surface of a film of graphite in an environment of 25°C, the film thickness before compression, T b Film thickness after compression vs. T a The ratio (T a / T b ) is preferably 0.7 or more and 1.5 or less, more preferably 0.8 or more and 1.3 or less, and even more preferably 0.9 or more and 1.2 or less. The filmy graphite according to any one of [1] to

[13] and

[16] to

[25] .

[27] The filmy graphite according to any one of [1] to

[13] and

[16] to

[26] , wherein the product (a×b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is preferably 88,000 or more and 500,000 or less, more preferably 110,000 or more and 500,000 or less, even more preferably 135,000 or more and 400,000 or less, particularly preferably 140,000 or more and 300,000 or less, and most preferably 160,000 or more and 270,000 or less.

[0021] A fifth aspect of the present invention has the following features. [1] Film-like graphite having a degree of graphite crystal orientation P relative to the film plane direction of 96% or more, as calculated by the following formula 1 from the half-width W of a diffraction profile obtained by an ω scan of a diffraction peak of the (002) plane derived from hexagonal graphite crystals detected in the vicinity of 2θ=26° using a θ / 2θ scan method:

[0022]

number

[0023] [2] Film-like graphite having a degree of graphite crystal orientation P relative to the film plane direction, calculated from the half-width W of a diffraction profile obtained by an ω scan of a diffraction peak of the (002) plane derived from hexagonal graphite crystals detected in the vicinity of 2θ=26° using a θ / 2θ scan method, of 94% or more, and having a thickness of 42 μm or more.

[0024]

number

[0025] [3] The filmy graphite according to [1] or [2], which has a ratio of surface area to film area (surface area / film area) of 1.05 or more. [4] A method for producing film-like graphite by heating a raw material film made of an organic polymer, wherein in the heating step, a laminated film formed by bonding two or more polymer films made of an organic polymer with a pressure-sensitive adhesive or adhesive is used as the raw material film. [5] A method for producing film-like graphite by heating a raw material film made of an organic polymer, the heating step including a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas. [6] The method for producing filmy graphite according to [5], wherein the mixed gas contains a gaseous substance (A) consisting of at least one of acetylene and an acetylene derivative, and an inert gas. [7] At least a part of the heating step in the mixed gas is f The method for producing filmy graphite according to [5] or [6], which is carried out at the following temperature: T f(°C) is the highest temperature at which the weight loss rate (weight loss per unit time) of the measurement sample is 10% or more of the maximum value when the measurement sample is heated to 1000°C at a temperature increase rate of 10°C / min while nitrogen gas is flowing at a rate of 200 mL / min and the measurement sample is subjected to thermogravimetric measurement. [8] The temperature rise history of the heating process in the mixed gas is monotonically increased by the following temperature rise pattern T s or more and the above T f The method for producing filmy graphite according to [7], comprising a period of 30 minutes or more in which the average heating rate is 5°C / min or less within the following temperature range: T s (°C) is the lowest temperature among temperatures at or above 100°C that is 0.8% or more of the maximum weight loss rate of the measurement sample in the thermogravimetric measurement. [9] The method for producing filmy graphite according to any one of [5] to [8], wherein the raw material film is a laminated film formed by bonding two or more polymer films made of organic polymers with a pressure-sensitive adhesive or adhesive.

[10] The maximum temperature T max The method for producing filmy graphite according to any one of [4] to [9], wherein the temperature is 2400°C or higher and 2900°C or lower.

[11] A method for producing filmy graphite, comprising: a carbonization step of heating a raw material film made of an organic polymer in a mixed gas of an organic gas and an inert gas at 1500°C or less to obtain a carbonized film; and a graphitization step of heating the carbonized film in an inert gas at 2000°C or more to obtain a graphitized film, a method for producing filmy graphite, wherein the thickness of the raw material film is 150 μm or more, the maximum temperature rise in any 30-minute period in a temperature rise pattern obtained by monotonically raising the temperature to 2000° C. or higher in the graphitization step is 60° C. or more, and the method produces filmy graphite having a thermal conductivity of 800 W / mK or more and a minimum bending radius of 16 mm or less in a bending test.

[12] A method for producing filmy graphite, comprising: a carbonization step of heating a raw material film made of an organic polymer in a mixed gas of an organic gas and an inert gas at 1500°C or less to obtain a carbonized film; and a graphitization step of heating the carbonized film in an inert gas at 2000°C or more to obtain a graphitized film, wherein the raw material film has an area S m The area S of the graphitized film g The ratio (S g / S m ) is 0.8 or more.

[13] The graphitized film is compressed or rolled to a density of 1.7 g / cm 3 The method for producing the filmy graphite according to any one of [4] to

[12] , further comprising a pressing step for obtaining the filmy graphite.

[14] A method for producing filmy graphite, comprising: a carbonization step of heating a raw material film made of an organic polymer in a mixed gas of an organic gas and an inert gas at 1500°C or less to obtain a carbonized film; and a graphitization step of heating the carbonized film in an inert gas at 2000°C or more to obtain a graphitized film, a temperature rise pattern obtained by monotonically increasing the temperature at or above 2000°C in the graphitization step, in which the maximum temperature rise width in any 30 minutes is 60°C or more.

[15] The method for producing filmy graphite according to

[14] , which produces filmy graphite having a product of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface of 40,000 or more.

[16] The method for producing filmy graphite according to

[14] or

[15] , wherein the thickness a of the filmy graphite is 23 μm or less.

[17] The degree of graphite crystal orientation P in the film plane direction, calculated from the half-width W of the diffraction profile obtained by ω scanning of the diffraction peak of the (002) plane derived from hexagonal graphite detected at around 2θ=26° by the θ / 2θ scanning method, using the following formula 1, is 92% or more, the thickness is 58 μm or more, and the density is 1.6 g / cm 3This is the film-like graphite.

[0026]

number

[0027]

[18] The filmy graphite according to any one of [1] to [3] and

[17] , wherein the filmy graphite does not include a layer of adhesive or pressure-sensitive adhesive in the film thickness direction.

[19] The filmy graphite according to any one of [1] to [3],

[17] and

[18] , wherein the degree of graphite crystal orientation P is preferably 92% or more and less than 100%, more preferably 93% or more and 99% or less, even more preferably 94% or more and 99% or less, particularly preferably 95% or more and 99% or less, and most preferably 96% or more and 99% or less.

[20] The filmy graphite according to any one of [1] to [3] and

[17] to

[19] , wherein the thickness of the filmy graphite is preferably 15 μm or more and 250 μm or less, more preferably 30 μm or more and 200 μm or less, even more preferably 42 μm or more and 180 μm or less, even more preferably 50 μm or more and 150 μm or less, particularly preferably 58 μm or more and 130 μm or less, even particularly preferably 70 μm or more and 120 μm or less, and most preferably 80 μm or more and 120 μm or less.

[21] The filmy graphite according to any one of [1] to [3] and

[17] to

[20] , wherein the ratio of the surface area to the film area of the filmy graphite (surface area / film area) is preferably 1.05 or more and 1.5 or less, more preferably 1.06 or more and 1.5 or less, and even more preferably 1.07 or more and 1.3 or less.

[22] The method for producing filmy graphite according to any one of [4] to

[10] , wherein the heating step comprises a carbonization step of carbonizing the raw material film to obtain a carbonized film, and a graphitization step of graphitizing the carbonized film to obtain a graphitized film.

[23] The method for producing filmy graphite according to

[11] to

[16] and

[22] , further comprising a pressing step of compressing or rolling the graphitized film.

[24] The method for producing filmy graphite according to any one of [4] to

[16] ,

[22] , and

[23] , wherein the thickness of the raw material film is preferably 20 μm or more and 550 μm or less, more preferably 45 μm or more and 400 μm or less, even more preferably 70 μm or more and 270 μm or less, and particularly preferably 120 μm or more and 270 μm or less.

[25] The method for producing filmy graphite according to any one of [4] to

[16] and

[22] to

[24] , wherein the organic polymer is preferably a polymer having an aromatic ring, selected from the group consisting of polyimide, polyamide, polythiazole, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polybenzothiazole, polybenzobisthiazole, polybenzimidazole, polybenzobisimidazole, and polyparaphenylenevinylene, more preferably a polymer having an aromatic ring, and even more preferably a polyimide having an aromatic ring.

[26] The method for producing filmy graphite according to any one of [5] to

[16] and

[22] , wherein the carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas, and the concentration of the organic gas in the mixed gas is preferably 2 vol% or more and 95 vol% or less, more preferably 5 vol% or more and 50 vol% or less, even more preferably 10 vol% or more and 40 vol% or less, particularly preferably 20 vol% or more and 30 vol% or less, and most preferably 25 vol% or more and 30 vol% or less.

[27] The method for producing filmy graphite according to any one of [5] to

[16] ,

[22] , and

[26] , wherein the carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas, and the maximum heating temperature in the organic gas heating step is preferably 400°C or higher and 1000°C or lower, more preferably 450°C or higher and 800°C or lower, and even more preferably 500°C or lower and 600°C or lower.

[28] The maximum heating temperature T in the graphitization process maxThe method for producing filmy graphite according to any one of [5] to

[16] ,

[22] ,

[26] , and

[27] , wherein the temperature is preferably 2400°C or higher and 3000°C or lower, more preferably 2700°C or higher and 2900°C or lower, and even more preferably 2750°C or higher and 2800°C or lower.

[29] Area S of the raw material film m the area S of the graphitized film g The ratio (S g / S m ) is preferably 0.8 or more and 1.2 or less, more preferably 0.9 or more and 1.1 or less, and even more preferably 1.0 or more and 1.1 or less.

[30] The density of the film-like graphite obtained in the pressing step is 1.6 g / cm 3 More than 2.2g / cm 3 Preferably less than 1.7 g / cm 3 More than 2.1g / cm 3 Less than 1.8 g / cm is more preferable. 3 More than 2.0g / cm 3 The following are more preferred methods for producing filmy graphite according to

[11] to

[16] ,

[22] , and

[23] .

[0028] The sixth aspect of the present invention has the following features. [1] Film-like graphite in which the number N of multiple bright areas obtained from an image obtained by binarizing bright and dark areas observed under a polarizing microscope in a cross section perpendicular to the film surface of the film-like graphite, the film thickness H (μm), and the film width W (μm) satisfy the following formula 1b: N / H / W≦0.015...Formula 1b [2] Film-like graphite in which the number N of multiple bright areas obtained from an image obtained by binarizing bright and dark areas observed under a polarizing microscope in a cross section perpendicular to the film surface of film-like graphite, the film thickness H (μm), and the film width W (μm) satisfy the following formulas 2b and 3b: N / H / W≦0.04...Formula 2b H≧42...Formula 3b [3] In a cross section perpendicular to the film surface of film-like graphite, the average area of multiple bright areas obtained from a binarized image of bright and dark areas observed under a polarizing microscope is 22 μm 2 or more, or the film thickness is 42 μm or more and the average area is 9 μm 2 This is the film-like graphite. [4] The filmy graphite according to any one of [1] to [3], wherein the ratio of the film surface area to the film area (film surface area / film area) is 1.05 or more. [5] A method for producing film-like graphite by heating a raw material film, wherein the raw material film is a laminated film formed by bonding two or more films made of organic polymers with a pressure-sensitive adhesive or adhesive. [6] A production method for obtaining film-like graphite by heating a raw material film, the heating step including a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas. [7] The method for producing filmy graphite according to [6], wherein the organic gas is a gas consisting of at least one of acetylene and an acetylene derivative. [8] At least a part of the heating step in the mixed gas is f The method for producing filmy graphite according to [6] or [7], which is carried out at the following temperature: T f (°C) is the highest temperature at which the weight loss rate (weight loss per unit time) of the raw film is 10% or more of the maximum value when the raw film is heated to 1000°C at a temperature increase rate of 10°C / min while nitrogen gas is flowing at a rate of 200 mL / min and the raw film is subjected to thermogravimetry. [9] In the heating step in the mixed gas, the following T s or more and the above T f The method for producing filmy graphite according to [8], wherein the temperature range is as follows: Ts (°C) is the lowest temperature among temperatures above 100°C that is 0.8% or more of the maximum weight loss rate (weight loss per unit time) of the measurement sample in the thermogravimetric measurement.

[10] The method for producing filmy graphite according to any one of [6] to [9], wherein the raw material film is a laminated film formed by bonding two or more films made of organic polymers with a pressure-sensitive adhesive or adhesive.

[11] The maximum temperature T max The method for producing filmy graphite according to any one of [5] to

[10] , wherein the temperature is 2400°C or higher and 2900°C or lower.

[12] A method for producing filmy graphite, comprising: a carbonization step of heating a raw material film made of an organic polymer in a mixed gas of an organic gas and an inert gas at 1500°C or less to obtain a carbonized film; and a graphitization step of heating the carbonized film in an inert gas at 2000°C or more to obtain a graphitized film, a method for producing filmy graphite, wherein the thickness of the raw material film is 150 μm or more, the maximum temperature rise in any 30-minute period in a temperature rise pattern obtained by monotonically raising the temperature to 2000° C. or higher in the graphitization step is 60° C. or more, and the method produces filmy graphite having a thermal conductivity of 800 W / mK or more and a minimum bending radius of 16 mm or less in a bending test.

[13] A method for producing filmy graphite, comprising: a carbonization step of heating a raw material film made of an organic polymer in a mixed gas of an organic gas and an inert gas at 1500°C or less to obtain a carbonized film; and a graphitization step of heating the carbonized film in an inert gas at 2000°C or more to obtain a graphitized film, The area of the raw material film S m The area S of the graphitized film g The ratio (S g / S m ) is 0.8 or more.

[14] Density is 1.7g / cm 3 The graphitized film is compressed or rolled to a density of less than 1.7 g / cm3 The method for producing the filmy graphite according to any one of [5] to

[13] , which comprises a pressing step to obtain the filmy graphite.

[15] A method for producing filmy graphite, comprising: a carbonization step of heating a film made of an organic polymer in a mixed gas of an organic gas and an inert gas at 1500°C or less to obtain a carbonized film; and a graphitization step of heating the carbonized film in an inert gas at 2000°C or more to obtain a graphitized film, a temperature rise pattern obtained by monotonically increasing the temperature at or above 2000°C in the graphitization step, in which the maximum temperature rise width in any 30 minutes is 60°C or more.

[16] The method for producing filmy graphite according to

[15] , wherein the product of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface of the filmy graphite is 40,000 or more.

[17] The method for producing filmy graphite according to

[15] or

[16] , wherein the thickness a of the filmy graphite is 23 μm or less.

[18] The filmy graphite according to any one of [1] to [4], wherein the value of N / H / W represented by the formula (1a) is preferably 0.001 or more and 0.04 or less, more preferably 0.001 or more and 0.02 or less, and even more preferably 0.001 or more and 0.015 or less.

[19] In a cross section perpendicular to the film surface of film-like graphite, the average area of multiple bright areas obtained from a binarized image of bright and dark areas observed under a polarizing microscope is 9 μm 2 More than 100μm 2 Preferably, it is less than 10 μm 2 More than 90μm 2 Less than 12 μm is more preferable 2 More than 80μm 2 More preferably, 16 μm or less 2 More than 70μm 2 The following is particularly preferred: 22 μm 2 More than 60μm 2The filmy graphite according to any one of [1] to [4] and

[18] is most preferably as follows:

[20] The filmy graphite according to any one of [1] to [4],

[18] , and

[19] , wherein the thickness of the filmy graphite is preferably 15 μm or more and 250 μm or less, more preferably 30 μm or more and 200 μm or less, even more preferably 42 μm or more and 180 μm or less, even more preferably 50 μm or more and 150 μm or less, particularly preferably 58 μm or more and 130 μm or less, even particularly preferably 70 μm or more and 120 μm or less, and most preferably 80 μm or more and 120 μm or less.

[21] The filmy graphite according to any one of [1] to [4] and

[18] to

[20] , wherein the ratio of the surface area to the film area of the filmy graphite (surface area / film area) is preferably 1.05 or more and 1.5 or less, more preferably 1.06 or more and 1.5 or less, and even more preferably 1.07 or more and 1.3 or less.

[22] The filmy graphite according to any one of [5] to

[17] , wherein the thickness of the raw material film is preferably from 20 μm to 550 μm, more preferably from 45 μm to 400 μm, even more preferably from 70 μm to 270 μm, and particularly preferably from 120 μm to 270 μm.

[23] The method for producing filmy graphite according to any one of [5] to

[17] and

[22] , wherein the organic polymer is preferably a polymer having an aromatic ring, selected from the group consisting of polyimide, polyamide, polythiazole, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polybenzothiazole, polybenzobisthiazole, polybenzimidazole, polybenzobisimidazole, and polyparaphenylenevinylene, more preferably a polymer having an aromatic ring, and even more preferably a polyimide having an aromatic ring.

[24] The method for producing filmy graphite according to any one of [5] to

[17] ,

[22] , and

[23] , wherein the carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas, and the concentration of the organic gas in the mixed gas is preferably 2 vol% or more and 95 vol% or less, more preferably 5 vol% or more and 50 vol% or less, even more preferably 10 vol% or more and 40 vol% or less, particularly preferably 20 vol% or more and 30 vol% or less, and most preferably 25 vol% or more and 30 vol% or less.

[25] The method for producing filmy graphite according to any one of [5] to

[17] and

[22] to

[24] , wherein the carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas, and the maximum heating temperature in the organic gas heating step is preferably 400°C or higher and 1000°C or lower, more preferably 450°C or higher and 800°C or lower, and even more preferably 500°C or lower and 600°C or lower.

[26] A graphitization step is included in which the carbonized film is graphitized to obtain a graphitized film, and the maximum heating temperature T max The method for producing filmy graphite according to any one of [5] to

[17] and

[22] to

[25] , wherein the temperature is preferably 2400°C or higher and 3000°C or lower, more preferably 2700°C or higher and 2900°C or lower, and even more preferably 2750°C or higher and 2800°C or lower.

[27] Area S of the raw material film m the area S of the graphitized film g The ratio (S g / S m ) is preferably 0.8 or more and 1.2 or less, more preferably 0.9 or more and 1.1 or less, and even more preferably 1.0 or more and 1.1 or less.

[28] A method for producing filmy graphite according to any one of [5] to

[16] and

[22] to

[27] , comprising: a graphitization step of graphitizing the carbonized film to obtain a graphitized film; and a pressing step of compressing or rolling the graphitized film.

[29] The density of the film-like graphite obtained in the pressing step is 1.6 g / cm 3 More than 2.2g / cm 3 Preferably less than 1.7 g / cm 3 More than 2.1g / cm 3 Less than 1.8 g / cm is more preferable. 3 More than 2.0g / cm 3 The method for producing filmy graphite according to

[28] is further preferably as follows: [Effects of the Invention]

[0029] According to the present invention, it is possible to provide a thick filmy graphite having high thermal conductivity and excellent heat dissipation performance, as well as excellent flexibility, at low cost, and a method for producing the filmy graphite. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is an SEM image of a fracture surface of the filmy graphite of Example 5A. [Figure 2] FIG. 2 is a plot of the weight loss rate (weight loss per unit time) versus temperature for the raw material film used in the examples. [Figure 3] 1 is a photograph of the appearance of the graphitized film of Example 5A. [Figure 4] 1 is an SEM image of a fracture surface of the filmy graphite of Comparative Example 1A. [Figure 5] 1 is a photograph showing the appearance of the graphitized film of Comparative Example 2A. [Figure 6] 1 is a photograph showing the appearance of the graphitized film of Comparative Example 3A. [Figure 7] 1 is an SEM image of a fracture surface of filmy graphite (filmy graphite (EYGS121810) manufactured by Panasonic Corporation) of Comparative Example 4A. [Figure 8] FIG. 1 is a plot diagram of the thermal conductivity of film-like graphite of Examples 1A to 22A and Comparative Examples 1A and 4A against thickness. [Figure 9] 1 is a thermogram of the graphitization process of Example 5A. [Figure 10] 1 is a thermogram of the graphitization process of Example 19A. [Figure 11] This is an example of a diffraction profile obtained by ω scanning of the diffraction peak of the (002) plane derived from hexagonal graphite, detected near 2θ=26° in wide-angle X-ray diffraction measurement (reflection method, θ / 2θ scan method). [Figure 12] 1 is an example of an image obtained by observing the surface of the filmy graphite of Example 3B with a laser microscope. [Figure 13] 1 is a thermogram of the graphitization process of Example 3B. [Figure 14] 12B is a thermogram of the graphitization process of Example 12B. [Figure 15] 1 is a plot of the thermal conductivity of the film-like graphite of each Example and Comparative Example against the degree of graphite crystal orientation P. [Figure 16] 1 is an example of a simplified polarized image (PO image) observed with a polarizing microscope in a cross section perpendicular to the film surface of the filmy graphite of Example 10C. [Figure 17] 1 is an example of a simplified polarized image (PO image) observed with a polarizing microscope in a cross section perpendicular to the film surface of the filmy graphite of Comparative Example 2C. [Figure 18] 1 is an example of a bright-field image (BF image) observed with a microscope in a cross section perpendicular to the film surface of the filmy graphite of Example 10C. [Figure 19] 1 is a thermogram of the graphitization process of Example 2C. [Figure 20] 13C is a thermogram of the graphitization process of Example 13C. [Figure 21] The thermal conductivity of the filmy graphite of each example and comparative example is plotted against the number N of multiple bright regions / film thickness H (μm) / film width W (μm). [Figure 22] The thermal conductivity of the filmy graphite of each example and comparative example is plotted against the average area of a plurality of bright regions. [Figure 23]1 is an example of an image obtained by observing the surface of the filmy graphite of Example 2C with a laser microscope. [Figure 24] 1D is a thermogram of the graphitization process of Example 1D. [Figure 25] 1E is a thermogram of the graphitization process of Example 1E. DETAILED DESCRIPTION OF THE INVENTION

[0031] In this specification, the term "film-like graphite" refers to a film-like material that is mainly composed of graphite, is flexible, and consists essentially of carbon. "Thickness" refers to the thickness of polymer film, raw film, carbonized film, graphitized film, and film-like graphite measured using a standard outside micrometer, and is the average value of thicknesses measured at five randomly selected points.

[0032] [Film-type graphite] The filmy graphite of the present invention is a filmy graphite that satisfies the following condition (1) or condition (2). Condition (1): The degree of orientation P of graphite crystals relative to the film surface is 96% or more. Condition (2): The degree of graphite crystal orientation P relative to the film surface is 94% or more, and the thickness is 42 μm or more. The filmy graphite of the present invention has a film thickness of 58 μm or more and a thermal conductivity in the direction along the film surface of 800 W / mK or more.

[0033] The thickness of the filmy graphite of the present invention is preferably 42 μm or more, more preferably 50 μm or more, even more preferably 58 μm or more, even more preferably 64 μm or more, even more preferably 72 μm or more, particularly preferably 75 μm or more, particularly more preferably 80 μm or more, even particularly preferably 85 μm or more, even more particularly preferably 100 μm or more, and most preferably 102 μm or more. When the thickness is equal to or greater than the aforementioned lower limit, the heat dissipation performance per sheet of filmy graphite is improved, and the number of sheets of filmy graphite required for heat dissipation in electronic devices and the like can be reduced. Furthermore, the thickness of the filmy graphite of the present invention is preferably 250 μm or less, more preferably 200 μm or less, even more preferably 180 μm or less, even more preferably 150 μm or less, particularly preferably 130 μm or less, and most preferably 120 μm or less. When the thickness is equal to or less than the aforementioned upper limit, it becomes easier to reduce the thickness of electronic devices and the like. In addition, it becomes easier to ensure a certain degree of flexibility in the film-like graphite.

[0034] The thermal conductivity of the filmy graphite of the present invention in the direction along the film surface is preferably 800 W / mK or more, more preferably 1,000 W / mK or more, even more preferably 1,200 W / mK or more, even more preferably 1,350 W / mK or more, even more preferably 1,4000 W / mK or more, particularly preferably 1,550 W / mK or more, and particularly preferably 1,600 W / mK or more. If the thermal conductivity is equal to or greater than the above-mentioned lower limit, heat dissipation by the filmy graphite proceeds efficiently, and the number of sheets of filmy graphite required for heat dissipation in electronic devices and the like can be reduced. The higher the thermal conductivity of the filmy graphite of the present invention in the direction along the film surface, the better, with the practical upper limit being about 2,200 W / mK.

[0035] The thermal conductivity of filmy graphite in the direction along the film surface is calculated according to the following formula 2. b=α×d×c...Formula 2 However, the symbols in the formula 2 have the following meanings. b: Thermal conductivity of film-like graphite in the direction along the film surface (W / mK) α: Thermal diffusivity of film-like graphite in the direction along the film surface (mm 2 / s) d: Density of film-like graphite (g / cm 3 ) c: Specific heat of graphite (0.85 J / gK) The thermal diffusivity α of film-like graphite in the direction along the film surface is measured in an environment of 23°C using the cyclic heating method in accordance with JIS R 7240 (2018).

[0036] The filmy graphite of the present invention preferably satisfies the following condition (5), which improves the heat dissipation performance per sheet of filmy graphite and enables a reduction in the number of sheets of filmy graphite required for heat dissipation in electronic devices and the like.

[0037] Condition (5): When the thickness of the film is a (μm) and the thermal conductivity in the direction along the film surface is b (W / mK), the following formula 1a is satisfied. 2140≦12a+b...Formula 1a

[0038] The value of 12a+b is preferably 2140 or greater, more preferably 2200 or greater, even more preferably 2250 or greater, even more preferably 2350 or greater, particularly preferably 2550 or greater, and most preferably 2750 or greater. When the value of 12a+b is equal to or greater than the aforementioned lower limit, the thermal conductivity of the filmy graphite in the thickness direction and in the direction along the film surface is sufficiently high, and the filmy graphite can be said to have high heat dissipation performance. The higher the value of 12a+b, the better, and there is no particular upper limit, but it is substantially about 5000.

[0039] The filmy graphite of the present invention preferably further satisfies the following condition (6): This makes the filmy graphite highly flexible and less likely to break or crack during handling. Condition (2): The minimum bending radius measured in the bending test described below is 16 mm or less.

[0040] The minimum bending radius of the filmy graphite of the present invention is preferably 16 mm or less, more preferably 13 mm or less, even more preferably 10 mm or less, particularly preferably 8 mm or less, and most preferably 6 mm or less. The smaller the minimum bending radius, the better, and there is no particular lower limit, but it is substantially more than 0 mm.

[0041] (Bending test) In a 23°C environment, a Type 2 bending tester specified in JIS K5600-5-1 is fully unfolded, a film graphite test specimen and mandrel are attached, and the specimen is uniformly bent 180° over 1-2 seconds. The specimen is then inspected for the presence of creases or cracks. Mandrels with diameters of 32, 25, 20, 16, 12, 10, 8, 6, 5, 4, 3, and 2 mm are used, and the bending and visual inspection of the specimen is carried out in order, starting with the largest diameter mandrel. The position of the specimen is changed during each bending test to prevent distortions caused by bending the specimen once from affecting the next test. The minimum bending radius of the film-like graphite is then determined to be half the diameter of a mandrel one size larger in diameter than the mandrel on which a fold or crack was first observed in the test piece, i.e., half the diameter of the smallest mandrel among the mandrels on which no folds or cracks were observed in the test piece.

[0042] The number of folding cycles of the filmy graphite of the present invention when subjected to a planar body no-load U-shaped stretch test with a bending radius R of 2 mm and a bending angle of 180° is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 30,000 or more. If the number of folding cycles of the filmy graphite is equal to or greater than the above-mentioned lower limit, handling properties when attached to an electronic device are improved, and even when used in a folded portion of an electronic device or a portion that is subject to repeated bending, breaking or cracking is less likely to occur. The higher the number of folding cycles, the better, and there is no particular lower limit, but practically it is 1,000,000 or less.

[0043] (U-shaped expansion and contraction test of a planar body without load) For example, a desktop durability testing machine such as the DLDMLH-FS manufactured by Yuasa System Co., Ltd. can be used to test the sheet-like body in a U-shaped unloaded extension / contraction test. The bending angle, bending radius, and test speed can be selected to measure the number of folding cycles in the sheet-like body in a U-shaped unloaded extension / contraction test. The tilt clamp operation method used to deform the film can also be selected. After starting the test, the test specimen can be visually inspected at, for example, 1,000, 2,500, 5,000, 10,000, 20,000, 30,000, 40,000, and 50,000 folding cycles. The number of folding cycles until the test specimen breaks is defined as the number of folding cycles.

[0044] The density of the filmy graphite of the present invention is 1.7 g / cm 3 More than 1.8g / cm is preferable. 3 More preferably, 1.9 g / cm 3 If the density of the filmy graphite is equal to or greater than the lower limit, the amount of voids that hinder thermal conduction is reduced, and the thermal conductivity is increased. In addition, the density of the filmy graphite of the present invention is 2.2 g / cm or less. 3 Preferably less than 2.1 g / cm 3 Less than 2.0 g / cm is more preferable. 3 If the density of the filmy graphite is equal to or less than the upper limit, the flexibility of the filmy graphite is easily ensured by the presence of some voids.

[0045] The electrical conductivity of the filmy graphite of the present invention in the direction along the film surface is preferably 9,000 S / cm or higher. It is more preferably 10,000 S / cm or higher, even more preferably 11,000 S / cm or higher, particularly preferably 12,000 S / cm or higher, and most preferably 13,5000 S / cm or higher. When the electrical conductivity is equal to or higher than the lower limit, electrical conduction by the filmy graphite proceeds efficiently, significantly improving the performance of the filmy graphite when used as a current collector or a negative electrode active material / negative electrode current collector in batteries such as lithium ion batteries and all-solid-state batteries. The higher the electrical conductivity of the filmy graphite of the present invention in the direction along the film surface, the better, but the practical upper limit is about 30,000 S / cm.

[0046] The filmy graphite of the present invention preferably includes a multilayer structure in which a plurality of layers are superimposed on one another, the multilayer structure having a width of 40 μm or more and a thickness of 8 μm or more, and each layer of the multilayer structure preferably forms an angle of 20° or less with respect to the direction along the film surface. Here, "the width of the multilayer structure is XX μm or more and the thickness is Y μm or more" means "the region forming the multilayer structure can include a rectangle in which one adjacent side is XX μm long and the other side is Y μm long, and the direction of the XX μm long side coincides with the layer direction." However, the region forming the multilayer structure and the layer direction are obtained by observing the mode I crack propagation fracture surface of the filmy graphite with a scanning electron microscope (SEM). The filmy graphite of the present invention more preferably has a multilayer structure having a width of 50 μm or more and a thickness of 10 μm or more.

[0047] "The direction of each layer of the multilayer structure forms an angle of 20° or less with the direction along the film surface" means that the direction of the layers of the multilayer structure obtained by observing the mode I crack propagation fracture surface of the filmy graphite with a scanning electron microscope (SEM) forms an angle of 20° or less with the direction in the SEM image along the film surface of the filmy graphite. It is more preferable that the angle formed between the direction of the layers and the direction of the film surface is 10° or less. When the multilayer structure contained in the filmy graphite has a width of 40 μm or more and a thickness of 8 μm or more, and the angle between the direction of each layer of the multilayer structure and the direction along the film surface is 20° or less, the multilayer structure is sufficiently large and voids are unlikely to impede heat conduction, resulting in a high thermal conductivity along the film surface.

[0048] It should be noted that even when each layer has a small amplitude undulation with a short period, i.e., when there are many concaves and convexes, the structure in which adjacent layers are in contact with each other at many points is still considered to be included in the multilayer structure. The presence of the multilayer structure in the filmy graphite of the present invention increases the thermal conductivity in the direction along the film surface, improving the heat dissipation performance.

[0049] Preferably, each layer of the multilayer structure has a flat or smoothly curved surface, and adjacent layers are in close contact with each other. This further increases the thermal conductivity in the direction along the film surface, improving the heat dissipation performance of the filmy graphite. Here, "layers are in close contact with each other" refers to a state in which no voids are observed between adjacent layers in an image of the mode I crack propagation fracture surface of the filmy graphite observed with a scanning electron microscope (SEM) at an accelerating voltage of 10 kV and a magnification of 1000x.

[0050] When a pressure of 100 MPa is applied to the entire surface of a film of graphite in an environment of 25°C, the film thickness before compression, T b (μm) vs. film thickness after compression T a (μm) ratio (T a / T b ) is preferably 0.7 or more, more preferably 0.8 or more, and even more preferably 0.9 or more. a is the thickness measured 5 minutes after the compressive load is removed. a / T b The filmy graphite having a T of not less than the lower limit is a filmy graphite that has been sufficiently compressed, and has high thermal conductivity in the direction along the film surface.a / T b The higher the better, but the practical upper limit is 1.0.

[0051] Another example of the filmy graphite of the present invention is a filmy graphite having a multilayer structure in which a plurality of layers are stacked on top of each other, the multilayer structure having a width of 40 μm or more and a thickness of 8 μm or more, the direction of each layer of the multilayer structure forming an angle of 20° or less with the direction along the film surface, and a density of 1.7 g / cm 3 It is preferable that the width of the multilayer structure is 40 μm or more, the thickness is 8 μm or more, the angle between the direction of each layer constituting the multilayer structure and the direction along the film surface is 20° or less, and the density is 1.7 g / cm 3 If this is the case, the multilayer structure is sufficiently large and the proportion of voids is small, so that the thermal conductivity in the direction along the film surface is high.

[0052] In addition, the filmy graphite of the present invention preferably has a thickness of 58 μm or more, more preferably 64 μm or more, even more preferably 75 μm or more, particularly preferably 85 μm or more, and most preferably 100 μm or more. When the thickness is equal to or greater than the aforementioned lower limit, the heat dissipation performance per sheet of filmy graphite is improved, and the number of sheets of filmy graphite required for heat dissipation in electronic devices and the like can be reduced.

[0053] Furthermore, the filmy graphite of the present invention preferably has a minimum bending radius of 16 mm or less, more preferably 13 mm or less, even more preferably 10 mm or less, particularly preferably 8 mm or less, and most preferably 6 mm or less. When the minimum bending radius is equal to or less than the upper limit mentioned above, the filmy graphite has excellent flexibility and is less likely to break or crack during handling.

[0054] In the film-like graphite of the present invention, the product (a × b) of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is preferably 88,000 or more, more preferably 110,000 or more, even more preferably 135,000 or more, particularly preferably 140,000 or more, and most preferably 160,000 or more. When the product of a and b is equal to or greater than the above-mentioned lower limit, the heat dissipation performance per sheet of film-like graphite is improved, making it possible to reduce the number of sheets of film-like graphite required for heat dissipation in electronic devices and to use thinner films. In the present invention, "heat dissipation performance" refers to the ability of a material to transport heat per unit time. According to Fourier's law, the higher the thermal conductivity of a material and the larger the cross-sectional area of the material, the higher the heat dissipation performance. Note that the cross-sectional area here refers to the area of a cross section perpendicular to the direction of heat transfer, and the thicker the material, the higher the heat dissipation performance. In the case of film-like graphite, a × b serves as an indicator of heat dissipation performance. The higher the product (a×b) of the filmy graphite of the present invention, the better, but the practical upper limit is about 500,000.

[0055] The filmy graphite of the present invention preferably has a film thickness a (μm) of 50 μm or more, a thermal conductivity b in the direction along the film surface of 1,350 W / mK or more, and the product of a and b of 100,000 or more. The thickness a of the film is more preferably 58 μm or more, even more preferably 64 μm or more, even more preferably 75 μm or more, particularly preferably 85 μm or more, and most preferably 100 μm or more. If the thickness is 50 μm or more, the heat dissipation performance per sheet of film-like graphite increases, making it possible to reduce the number of sheets of film-like graphite required for heat dissipation in electronic devices and the like. The thermal conductivity b is more preferably 1,550 W / mK or more. If the thermal conductivity b is 1,550 W / mK or more, the heat dissipation performance per sheet of film-like graphite is improved, and the number of sheets of film-like graphite required for heat dissipation in electronic devices and the like can be reduced. From this viewpoint, the thermal conductivity b is more preferably 1650 W / mK or more, and most preferably 1750 W / mK or more.

[0056] The thermal conductivity of the filmy graphite of the present invention in a direction perpendicular to the film surface is preferably greater than 0 W / mK, more preferably 0.5 W / mK, even more preferably 1 W / mK or greater, and particularly preferably 3 W / mK or greater. When the thermal conductivity in the direction perpendicular to the film surface is equal to or greater than the aforementioned lower limit, heat dissipation from the filmy graphite in the perpendicular direction proceeds efficiently. There is no particular upper limit to the thermal conductivity of the filmy graphite of the present invention in a direction perpendicular to the film surface, but if the thermal conductivity in the perpendicular direction is too high, the film will have poor thermal conductivity in the film surface direction, so substantially, it is preferably 20 W / mK or less.

[0057] The filmy graphite of the present invention preferably consists of a single piece of filmy graphite and does not include a layer of adhesive or pressure-sensitive adhesive in the film thickness direction. To obtain thick filmy graphite, methods such as laminating multiple sheets of filmy graphite with an adhesive or pressure-sensitive adhesive, entirely covering multiple sheets of filmy graphite with a coating material, or fastening multiple sheets of filmy graphite with a metal jig are known. However, these methods have problems such as a reduced thermal conductivity due to the presence of an adhesive or pressure-sensitive adhesive layer with low thermal conductivity between the films, or air infiltration resulting in a large contact thermal resistance. Because the filmy graphite of the present invention consists of a single thick sheet of filmy graphite, it can have a higher thermal conductivity than other films of the same thickness.

[0058] The film-like graphite of the present invention described above is thick and has high thermal conductivity, resulting in excellent heat dissipation performance, and it also has flexibility. Therefore, there is no need to use multiple layers of conventional thin film-like graphite stacked on top of each other. This eliminates the need to include layers with low thermal conductivity, such as adhesives, and makes it possible to reduce the thickness of the entire heat dissipator without compromising the performance of the entire heat dissipator.

[0059] [Method for producing film-like graphite] The method for producing filmy graphite of the present invention is a method for obtaining filmy graphite by heating a raw material film, and the heating step for heating the raw material film preferably includes the following carbonization step and graphitization step. Also, the method for producing filmy graphite of the present invention preferably further includes the following pressing step. Carbonization process: A raw material film made of organic polymer is carbonized to obtain a carbonized film. Graphitization step: The carbonized film is graphitized to obtain a graphitized film. Pressing step: The graphitized film is compressed or rolled. In the present invention, "carbonization" means heating the organic polymer constituting the raw material film to vaporize volatile components from the organic polymer and convert it into a carbon-rich substance. In the present invention, "carbonized film" means a film containing a carbonaceous structure due to carbonization, from which elements other than carbon have been removed until the mass proportion of elements other than carbon in the film is 20% or less. In the present invention, "graphitization" means further heating the carbonized film at a high temperature to almost completely remove impurities other than carbon and promote a high degree of graphitization. "Graphitized film" means a film with an extremely high degree of graphitization and rich in graphite crystalline structure.

[0060] (raw film) The thickness of the raw material film is preferably 75 μm or more, more preferably 125 μm or more, even more preferably 150 μm or more, even more preferably 175 μm or more, particularly preferably 200 μm or more, and most preferably 250 μm or more. When the thickness of the raw material film is equal to or greater than the aforementioned lower limit, it is easy to obtain a thick film-like graphite with high heat dissipation performance per sheet, thereby reducing the number of sheets of film-like graphite required for heat dissipation in electronic devices and the like. Furthermore, the thickness of the raw material film is preferably 550 μm or less, more preferably 500 μm or less, even more preferably 450 μm or less, even more preferably 400 μm or less, particularly preferably 375 μm or less, and most preferably 270 μm or less. When the thickness of the raw material film is equal to or less than the aforementioned upper limit, the amount of foaming during heating is small and performance unevenness between the interior and surface of the film is unlikely to occur, making it easy to obtain a high-quality film-like graphite. Furthermore, it is easy to obtain a thick film-like graphite while maintaining a certain degree of flexibility.

[0061] The raw material film is a film made of an organic polymer. As the organic polymer, a polymer having an aromatic ring and a molecular chain with a certain degree of planarity, orientation, and rigidity is preferred. Examples include polymers having an aromatic ring, such as polyimide, polyamide, polythiazole, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polybenzothiazole, polybenzobisthiazole, polybenzimidazole, polybenzobisimidazole, and polyparaphenylenevinylene. Among these, polyimide is preferred from the viewpoint of availability. The organic polymer constituting the raw material film may be one type or two or more types.

[0062] The raw material film may be a laminated film formed by bonding two or more polymer films made of organic polymers with a pressure sensitive adhesive or adhesive. The pressure-sensitive adhesive or adhesive is not particularly limited, and preferably contains, as an adhesive component, a diamine or acid anhydride, which is a polyimide monomer, or a polyamic acid obtained by polymerizing them. Examples of diamines include oxydianiline. Examples of acid anhydrides include pyromellitic anhydride. Examples of polyamic acids include polyamic acids obtained by polymerizing oxydianiline and pyromellitic anhydride. The pressure-sensitive adhesive or adhesive is preferably one in which the above-mentioned adhesive component is dissolved in a low-volatility organic solvent. Adhesives containing tackifiers, phenolic resin-based adhesives, acrylic adhesives, melamine-based adhesives, silicone-based adhesives, etc. may also be used.

[0063] There are no particular limitations on the means for applying the adhesive or glue to the polymer film, as long as it can be applied uniformly. After laminating the polymer films, it is preferable to pass them through a pressure roll to remove excess adhesive or glue, thereby making the adhesive or glue between the polymer films as thin as possible. The thickness of the adhesive or glue between the polymer films is not particularly limited, but is preferably 1 μm or less. By making the adhesive or glue thin, it becomes easier to suppress foaming during the carbonization process. Alternatively, the polymer film may be laminated and then heated to remove the organic solvent before the carbonization step. The heating temperature for removing the organic solvent is preferably 350° C. or higher.

[0064] (carbonization process) In the carbonization process, for example, the raw film is heated to 1500°C or less in an inert gas or a mixed gas of an organic gas and an inert gas, and elements other than carbon are removed until the mass proportion of elements other than carbon in the raw film is 20% or less. In the carbonization process, the temperature may be raised continuously, or may be raised stepwise with a period during which the temperature is maintained constant. Alternatively, the temperature may be raised, lowered, and then raised again. The carbonization process may be performed using a batch heating method or a continuous supply heating method in which the raw film is continuously supplied.

[0065] The carbonization step preferably includes a mixed gas heating step in which the raw material film is heated in a mixed gas of an organic gas and an inert gas. In a production method that does not include a mixed gas heating step, rapid heating in the graphitization step can easily cause delamination within the film or damage to the film due to the pressure of the gas generated by decomposition of the carbonized film, resulting in a decrease in the thermal conductivity of the film-like graphite. However, by including a mixed gas heating step in the carbonization step, film damage caused by the gas generated by decomposition of the carbonized film can be suppressed even when the temperature rise rate in the graphitization step is high, thereby easily producing film-like graphite with high thermal conductivity. Heating the raw material film in a mixed gas of an organic gas and an inert gas not only helps to suppress carbon loss due to decomposition, but also allows the carbon in the organic gas to be incorporated into the raw material film. This makes it easier to obtain a carbonized film with a large area, thereby ultimately producing a film-like graphite with a large area.

[0066] In the carbonization process including the heating in a mixed gas step, the heating in a mixed gas step may be followed by further heating in an inert gas, or the raw material film may be heated in an inert gas and then the heating in a mixed gas step may be carried out. Alternatively, the entire carbonization process may be the heating in a mixed gas step.

[0067] The inert gas may be any gas that does not react with the raw material film, and examples thereof include nitrogen gas, argon gas, and a mixture thereof. Of these, nitrogen gas is preferred from the viewpoint of economical efficiency. The inert gas used in the carbonization step may be one type or two or more types.

[0068] The organic gas is an organic compound that becomes gaseous at the heating temperature in the carbonization step. The organic gas is not particularly limited, and examples thereof include hydrocarbons that are gaseous at 23°C and 1 atmosphere, such as methane, ethane, ethylene, and acetylene. Even organic compounds that are liquid or solid at 23°C and 1 atmosphere can be used as the organic gas as long as they become gaseous at the heating temperature in the carbonization step. As the organic gas, a gaseous substance (A) consisting of at least one of acetylene and an acetylene derivative is preferred, from the viewpoint of easily suppressing carbon loss due to decomposition. The organic gas used in the carbonization step may be one type or two or more types.

[0069] The concentration of the organic gas in the mixed gas varies depending on the type of organic gas. For example, in the case of acetylene gas, it is preferably 2% by volume or more, more preferably 5% by volume or more, even more preferably 10% by volume or more, particularly preferably 20% by volume or more, and most preferably 25% by volume or more, relative to the total volume of the mixed gas. When the concentration of the organic gas is equal to or greater than the lower limit, carbon loss due to decomposition is easily suppressed, and the carbon in the organic gas is efficiently incorporated into the raw material film, ultimately facilitating the production of a large-area film-like graphite, thereby improving productivity. Furthermore, when the organic gas is acetylene gas, the concentration of the organic gas in the mixed gas is preferably 95% by volume or less, more preferably 50% by volume or less, even more preferably 40% by volume or less, and particularly preferably 30% by volume or less, relative to the total volume of the mixed gas. When the concentration of the organic gas is equal to or less than the upper limit, the organic gas is not used more than necessary, which leads to cost reduction and is industrially stable.

[0070] The temperature rise pattern obtained by monotonically increasing the temperature history of the mixed gas heating process preferably includes a period of 30 minutes or more during which the average temperature rise rate is 5°C / min or less (hereinafter referred to as the "slow temperature rise period"). This facilitates efficient incorporation of carbon in the organic gas into the raw material film and also helps to suppress carbon loss due to thermal decomposition. Here, the "temperature rise pattern obtained by monotonically increasing the temperature history" is obtained by replacing the temperature at each point in the temperature rise history (temperature per hour) from the start of the temperature rise to the point at which the maximum temperature of the heating process is reached (temperature rise period) with the maximum temperature from the start of the temperature rise to that point. The "temperature rise pattern obtained by monotonically increasing the temperature history" is a monotonically increasing function of temperature with time, consisting only of curves with positive slopes and straight lines with zero slope.

[0071] While nitrogen gas was flowing at a flow rate of 200 mL / min, the measurement sample made of the raw material film was heated to 1000°C at a temperature increase rate of 10°C / min, and the temperature and weight of the measurement sample during heating were recorded by thermogravimetry. p , T s , T f Define T p (°C) is the temperature at which the weight loss rate (weight loss per unit time) observed in thermogravimetry is at its maximum. T s (°C) is the lowest temperature above 100°C at which the rate of weight loss of the measurement sample observed in thermogravimetry is 0.8% or more of the maximum rate of weight loss. T f (°C) is the highest temperature at which the rate of weight loss of the measurement sample observed in thermogravimetry is 10% or more of the maximum rate of weight loss.

[0072] In the carbonization step, at least a part of the heating step in the mixed gas is carried out by T f It is preferably carried out at the following temperatures: The temperature during the slow temperature rise period included in the mixed gas heating process is T f The following is preferred: T p On the other hand, the temperature during the slow temperature rise period is preferably T sIf the temperature during the slow temperature rise period is within this range, carbon can be efficiently taken up from the organic gas into the raw material film that is being heated and decomposed, and loss of carbon due to decomposition can be easily suppressed.

[0073] In the mixed gas heating process, when the temperature reaches T s More than T f The average heating rate during the slow heating period described below is preferably 5° C. / min or less, more preferably 3° C. / min or less, and even more preferably 1° C. / min or less. When the average heating rate is equal to or less than the upper limit mentioned above, the orientation of the graphite crystals can be ensured to a certain extent, and a high-quality film-like graphite can be more easily obtained even if the subsequent graphitization step is performed at a higher speed. Also, when the temperature is T s More than T f The length of the slow temperature rise period is preferably 30 minutes or more, more preferably 60 minutes or more, and even more preferably 90 minutes or more. s More than T f By including the period in the following, it is possible to supply a sufficient amount of organic gas, which makes it easier to efficiently take in carbon from the organic gas and also makes it easier to suppress the loss of carbon due to decomposition.

[0074] The maximum heating temperature in the mixed gas heating step depends on the raw material film and the organic gas used, but is preferably 1000°C or less, more preferably 800°C or less, and even more preferably 600°C or less. If the maximum heating temperature is below the upper limit, the organic gas can be handled stably. The maximum heating temperature in the mixed gas heating step is T s When the maximum heating temperature is equal to or higher than the lower limit, the raw material film can be reacted with the organic gas at a temperature at which thermal decomposition of the raw material film is likely to occur, and therefore carbon in the organic gas is easily incorporated, making it easier to obtain a carbonized film with a large area.

[0075] (Graphitization process) In the graphitization step, for example, the carbonized film is heated in a graphitization furnace under an inert gas atmosphere while increasing the temperature to 2000°C or higher, and graphite crystals are grown to obtain a graphitized film. For example, the carbonized film in the carbonization furnace after the carbonization step may be cooled to a temperature where it is not affected by oxygen, removed from the carbonization furnace, and transferred to a graphitization furnace where it is heated again to perform the graphitization step, or the carbonization step may be performed by continuously heating the film without cooling it after the carbonization step.

[0076] In the graphitization step, the temperature may be increased continuously, or may be increased stepwise by providing a period during which the temperature is maintained constant. Alternatively, the temperature may be increased, then decreased, and then increased again. The graphitization step may be carried out by a batch heating method, or a continuous supply heating method in which a carbonized film is continuously supplied and graphitized. Alternatively, a carbonized film produced by a batch heating method may be graphitized in a continuous heating graphitization furnace.

[0077] Maximum heating temperature T in the graphitization process max The temperature is preferably 3000°C or less, more preferably 2900°C or less, and even more preferably 2800°C or less. max When T is equal to or less than the upper limit, the consumption of the heating element and heat insulating material of the graphitization furnace is slow, thereby reducing the frequency of maintenance. In addition, excessive growth of graphite crystals can be suppressed, ensuring appropriate voids between the graphite crystals, making it easier to obtain a flexible film-like graphite. Here, the voids between the graphite crystals refer to micro- or macro-voids observed in carbon materials. max is preferably 2400°C or higher, more preferably 2700°C or higher, and even more preferably 2750°C or higher. max When is equal to or greater than the lower limit, the carbon network planes of the graphite crystals in the filmy graphite are likely to be oriented parallel to the film surface, and high thermal conductivity is likely to be exhibited.

[0078] The graphitization process is carried out at temperatures from 2000°C to T maxIn a temperature rise pattern obtained by monotonically raising the temperature from the temperature rise history up to 100°C, the maximum value of the temperature rise width in any 30 minutes (hereinafter referred to as the "maximum temperature rise width in 30 minutes") is preferably 60°C or higher. The maximum temperature rise width in 30 minutes is more preferably 90°C or higher, and even more preferably 210°C or higher. By setting the maximum temperature rise width in 30 minutes to 90°C or higher, it is possible to generate appropriate foaming within the carbonized film during the graphitization process, making it easier to obtain appropriate flexibility. In addition, it is possible to reduce the consumption of heat insulating materials in the graphitization furnace and the total amount of electricity used in the graphitization process.

[0079] The graphitization process is carried out at temperatures from 2000°C to T max In a temperature rise pattern obtained by monotonically raising the temperature from the temperature rise history up to 100°C, the maximum value of the temperature rise width in any 60 minutes (hereinafter referred to as the "60-minute maximum temperature rise width") is preferably 120°C or more. The 60-minute maximum temperature rise width is more preferably 180°C or more, and even more preferably 420°C or more. By setting the 60-minute maximum temperature rise width to 120°C or more, it is possible to generate appropriate foaming within the carbonized film during the graphitization process, and to ensure appropriate flexibility. The graphitization process is carried out at temperatures from 2000°C to T max In the temperature rise pattern obtained by monotonically raising the temperature up to the temperature rise history, the maximum temperature rise width in any 90 minutes (hereinafter referred to as "maximum temperature rise width in 90 minutes") is preferably 180°C or more.

[0080] The graphitization process is carried out at temperatures from 2000°C to T max The temperature rise pattern, which is a monotonically rising temperature history up to T max The time required to reach this state is preferably 40 minutes or more, more preferably 60 minutes or more, and even more preferably 90 minutes or more. The maximum temperature rise rate within 60 minutes in the graphitization step is preferably not more than 900° C., more preferably not more than 720° C. When the maximum temperature rise rate within 60 minutes is not more than the aforementioned upper limit, the amount of gas generated per unit time from within the film during the graphitization step is reduced, making it easier to obtain a thick film-like graphite with excellent thermal conductivity properties. The maximum temperature rise rate within 30 minutes in the graphitization step is preferably not more than 540° C., more preferably not more than 450° C., and most preferably not more than 360° C. When the maximum temperature rise rate within 30 minutes is not more than the aforementioned upper limit, the amount of gas generated per unit time from inside the film during the graphitization step is further reduced, making it easier to obtain a thick film-like graphite with excellent thermal conductivity properties.

[0081] In the present invention, it is preferable to produce filmy graphite having a thermal conductivity of 800 W / mK or more and a minimum bending radius of 16 mm or less in a bending test by using a raw material film having a thickness of 150 μm or more, with a temperature rise pattern in which the temperature rise history of the graphitization step is monotonically increased to 2000° C. or more, with a maximum temperature rise of 60° C. or more in any 30-minute period. The bending test will be described in detail in the Examples below.

[0082] Area of raw film S m The area of the graphitized film obtained in the graphitization process, S g The ratio (S g / S m ) is preferably 0.8 or more, more preferably 0.9 or more, and even more preferably 1 or more. g / S m The larger the S, the larger the area of the film-like graphite obtained, which improves productivity and reduces costs. g / S m There is no particular lower limit to the ratio, but it is practically about 1.2.

[0083] (pressing process) In the pressing step, the graphitized film obtained in the graphitization step is compressed or rolled. By performing the pressing step, the graphite crystal layers tend to be oriented in the direction along the film surface, voids within the graphitized film are crushed, increasing the density, and also eliminating any warping or waviness that may have occurred in the graphitized film. When compressing or rolling, it is preferable to sandwich the material between two polyimide films, as this prevents contamination of the pressure rolls. In the present invention, in the pressing step, a graphitized film having a density of 1.6 g / cm3 It is preferable to obtain a film-like graphite of 1.7 g / cm or more. 3 It is more preferable to obtain a film-like graphite of 1.8 g / cm or more. 3 It is more preferable to obtain the above film-like graphite.

[0084] A preferred method of compressing or rolling is to pass the graphitized film between pressure rolls made of a hard material such as metal. In this case, the film may be passed through the same pressure roll repeatedly, or may be passed through multiple pressure rolls in sequence. The method of compressing or rolling is not particularly limited to the above methods, and may also be, for example, a method in which the graphitized film is sandwiched between metal plates and pressure is applied with a hydraulic cylinder or the like.

[0085] In the method for producing filmy graphite of the present invention described above, by carrying out the heating step in a mixed gas, the amount of foaming gas is reduced even if the temperature rise rate in the graphitization step is high, and peeling of the film surface and film destruction are suppressed. In addition, the time for the graphitization step can be shortened, thereby suppressing excessive growth of the graphite structure and producing filmy graphite with flexibility. Furthermore, since shrinkage of the film during production is also suppressed, filmy graphite with a large area is easily obtained, resulting in excellent productivity and low cost.

[0086] In this specification, the term "filmy graphite" refers to a flexible filmy material that is made up of an aggregate of graphite crystallites and is composed substantially of carbon alone.

[0087] [Film-type graphite] The filmy graphite of one example of the embodiment of the present invention has a graphite crystal orientation degree P in the film plane direction of 96% or more. The filmy graphite of another example of the embodiment has a graphite crystal orientation degree P in the film plane direction of 94% or more and a thickness of 42 μm or more. The filmy graphite of yet another example of the embodiment has a graphite crystal orientation degree P in the film plane direction of 92% or more, a thickness of 58 μm or more, and a density of 1.6 g / cm3 That's all.

[0088] The degree of graphite crystal orientation P in the film-like graphite of the present invention in the film plane direction is preferably 92% or more, more preferably 93% or more, even more preferably 94% or more, particularly preferably 95% or more, and most preferably 96% or more. The higher the degree of graphite crystal orientation P, the higher the thermal conductivity of the filmy graphite in the film plane direction. There is no particular upper limit to the graphite crystal orientation degree P, but if the crystal orientation degree is too high, the film will have poor flexibility, so the upper limit is practically about 99%.

[0089] The degree of graphite crystal orientation P with respect to the film surface direction of filmy graphite can be determined using wide-angle X-ray diffraction measurement (reflection method, θ / 2θ scan method) as follows. (Method for evaluating the degree of graphite crystal orientation P) The measurement device used is an X-ray diffractometer using CuKα radiation as a radiation source. A fully automated multipurpose X-ray diffractometer such as the SmartLab, manufactured by Rigaku Corporation, can be used. The film-like graphite is fixed to a sample stage without warping, so that the angle of incidence of the incident X-rays and the angle of reflection of the reflected X-rays are equal to the normal to the film surface of the film-like graphite. One-dimensional X-ray diffraction spectra of the film-like graphite in the 2θ direction are measured using the θ / 2θ scan method. The position of the reflection diffraction peak of the (002) plane derived from the hexagonal crystal structure of graphite, detected near 2θ = 26°, is read from the spectrum obtained in this measurement. The detector is fixed at this peak position, and the X-ray diffraction spectrum of the film-like graphite is measured using the ω scan method. This produces a diffraction profile, such as that shown in Figure 11. The half-width W (°) of the diffraction peak is read from the diffraction profile, and the degree of graphite crystal orientation P [%] is calculated using the following equation 1:

[0090]

number

[0091] The thickness of the filmy graphite of the present invention is not particularly limited, but the greater the thickness, the greater the heat transport capacity. Therefore, it is preferably 15 μm or more, more preferably 30 μm or more, even more preferably 42 μm or more, even more preferably 50 μm or more, particularly preferably 58 μm or more, even particularly preferably 70 μm or more, and most preferably 80 μm or more. Furthermore, the thickness of the filmy graphite of the present invention is preferably 250 μm or less, more preferably 180 μm or less, even more preferably 150 μm or less, and particularly preferably 120 μm or less. When the thickness is equal to or less than the upper limit, it becomes easy to reduce the thickness of electronic devices, etc. Also, it becomes easy to ensure a certain degree of flexibility in the film-like graphite. The "thickness" referred to here is the thickness measured using a standard outside micrometer for polymer film, raw film, carbonized film, graphitized film, and film-like graphite, and is the average value of thicknesses measured at five randomly selected points.

[0092] The ratio of the surface area to the film area of the filmy graphite of the present invention (surface area / film area) is preferably 1.05 or more, more preferably 1.06 or more, and even more preferably 1.07 or more. The higher the surface area / film area, the greater the degree of foaming that occurs in the graphitization process of the filmy graphite, and the more voids are inserted into the film, resulting in a filmy graphite with excellent flexibility. There is no particular upper limit to the surface area / film area, but the lower the surface area / film area, the more the interfacial thermal resistance caused by unevenness on the film surface is reduced. Therefore, the ratio is preferably 1.5 or less, and more preferably 1.3 or less.

[0093] (Surface area / film area evaluation method) Here, "surface area / film area" is defined as the ratio of the surface area calculated from the surface shape observed with a laser microscope to the film area of the observed range. A laser microscope is used as the measurement device. A laser microscope with sufficient performance, such as the Keyence Corporation VK-X100 shape measurement laser microscope, can be used. A 5 x 5 cm piece of film-like graphite is placed on the sample stage, ensuring that the film does not warp and with the film surface facing upward. The objective lens is set to 50x magnification and 2048 x 1536 pixels, and the objective lens is moved in 0.12 μm increments along the Z axis (height direction) to obtain surface shape data for the sample. The surface area is calculated from the obtained surface shape data of the sample, and the ratio of the surface area to the film area (surface area / film area) is calculated.

[0094] The filmy graphite of the present invention described above has high thermal conductivity in the film plane direction and excellent heat dissipation performance. Moreover, this property is true regardless of the film thickness, even for thick filmy graphite. Furthermore, when the ratio (surface area / film area) is 1.05 or more, excellent flexibility is obtained.

[0095] (Mechanism of flexibility) The mechanism by which a flexible, flexible film-like graphite with excellent flex resistance is obtained is believed to be as follows: During the graphitization process in production, pyrolysis gas is generated inside the film, causing voids between the graphite crystallites. These voids allow the graphite crystallites to slide easily between each other, allowing the entire film to bend without being destroyed by the stress generated when bending. When pyrolysis gas is generated inside the film, it causes cracks on the film surface as the gas is released to the outside of the film. Alternatively, voids are generated inside the film, which disrupt the orientation of the graphite crystals and are observed as irregularities on the film surface. The inventors used the ratio (surface area / film area) as an index of the shape of such a film surface, and found that when this ratio is 1.05 or higher, the filmy graphite also has excellent flexibility.

[0096] The raw material film preferably contains an appropriate amount of inorganic or organic fine particles so that foaming occurs during the graphitization process. Examples include inorganic acid salts, oxides, polyesters, stearic acid, trimellitic acid, organic tin, lead, azo compounds, and nitrone compounds. Among these, inorganic acid salts such as phosphate esters and calcium phosphate are preferred, as they can generate an appropriate amount of voids in the film-like graphite by the gas generated during the graphitization process. The fine particles may be of one type or two or more types.

[0097] In the present invention, it is preferable to use a raw material film having a thickness of 150 μm or more, and to use a temperature rise pattern in which the temperature is raised monotonically to 2000° C. or higher in the graphitization step, with a maximum temperature rise of 60° C. or more in any 30-minute period, to obtain a filmy graphite having a thermal conductivity of 800 W / mK or more and a minimum bending radius of 16 mm or less in a bending test. The bending test will be described in detail in the Examples below.

[0098] In the present invention, it is preferable to produce filmy graphite in which the product of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is 40,000 or more. Such filmy graphite has a large heat transport capacity. Furthermore, from the viewpoint of facilitating the thinning of electronic devices and the like, it is more preferable to produce filmy graphite in which the film thickness a is 23 μm or less.

[0099] In the present invention, it is preferable that the film-like graphite does not include a layer composed of an adhesive or pressure-sensitive adhesive in the thickness direction of the film-like graphite, and is composed of a single sheet of film-like graphite. A method for obtaining multilayered film-like graphite by bonding pieces of film-like graphite together with an adhesive or pressure-sensitive adhesive to improve heat transport capacity is known, but this method results in the inclusion of an adhesive layer with low thermal conductivity in the film-like graphite, resulting in insufficient heat transport capacity. Since the present invention does not include such an adhesive layer, the heat transport capacity is greater when compared at the same thickness.

[0100] [Film-type graphite] In one example of the embodiment of the filmy graphite of the present invention, the number N of multiple bright regions obtained from an image obtained by binarizing bright and dark regions observed in a polarizing microscope image of a cross section perpendicular to the film surface of the filmy graphite, divided by film thickness H (μm) and film width W (μm) (hereinafter referred to as CN), is 0.015 or less. In another example of the filmy graphite of the embodiment, CN is 0.04 or less and the thickness is 42 μm or more. In yet another example of the filmy graphite of another embodiment, the average area (hereinafter referred to as AS) of the multiple bright regions is 22 μm 2 In addition, in another example of filmy graphite according to still another embodiment, the average area (hereinafter, referred to as AS) of the plurality of bright regions is 9 μm 2 or more, and the thickness is 42 μm or more.

[0101] The CN of the filmy graphite of the present invention is preferably 0.04 or less, more preferably 0.02 or less, and even more preferably 0.015 or less. The lower the CN, the higher the thermal conductivity of the film-like graphite in the film plane direction. There is no particular lower limit for CN, but if CN is too low, the film will have poor flexibility, or will have no crystalline structure and low thermal conductivity, so the lower limit is essentially around 0.001. The AS of the filmy graphite of the present invention is 9 μm 2 More than 10 μm is preferable. 2 More preferably, 12 μm or more 2 is more preferable, and 16 μm 2 is particularly preferred, and 22 μm 2 is most preferred. The larger the AS, the higher the thermal conductivity of the film-like graphite in the film plane direction. There is no particular lower limit for AS, but if AS is too low, the film will have poor flexibility, so it is practically 100 μm 2 The degree is at the lower limit.

[0102] The CN and AS of filmy graphite can be determined using a polarizing microscope as follows. (Evaluation method for the number of multiple bright areas N / film thickness H (μm) / film width W (μm), and the average area of multiple bright areas) Film-like graphite is cut into strips using a cutter (or ultrasonic cutter) and embedded in resin to create a sample. Next, the sample is polished with a handy wrap or similar to completely remove the epoxy resin covering the observation surface (cross section) of the sample, and then a flat sample cross section is prepared using a cross-section polisher that uses an argon ion beam. A bright-field image (BF image) and a simple polarized image (PO image) are obtained using a digital microscope or similar. Note that the simple polarized image (PO image) is observed in a crossed Nicol (crossed Nicol) position, and the angle of the sample stage on which the sample is placed is adjusted to maximize the brightness of the bright areas in the sample. Using image analysis software, etc., the obtained PO image is binarized to obtain an image of the bright and dark areas observed in a cross section perpendicular to the film surface of the film-like graphite. The number of bright areas obtained by binarization is counted and taken as the number of bright areas, N. The film thickness H is determined by using image analysis software or the like to remove voids observed inside the filmy graphite from the BF image obtained above, and measuring the total length of the solid portion observed perpendicular to the film surface of the filmy graphite. The film width W is defined as the width of the film-like graphite in the film surface direction when the count number is measured from the PO image. CN is calculated from the count number obtained by the above method, film thickness, and film width. The average area of the plurality of bright regions is obtained by calculating the average area of the plurality of bright regions obtained by the above method using image analysis software or the like.

[0103] [Mechanism of thermal conductivity] The mechanism by which film-like graphite with excellent thermal conductivity in the film plane direction is obtained is as follows: Thermal conductivity in graphite occurs mainly through lattice vibrations, i.e., the conduction of phonons. Thermal conduction by phonons depends on the perfection of the solid crystal, and the larger the crystallite size of the graphite, the higher the phonon thermal conductivity. Phonon propagation in graphite occurs along the basal plane (ab axis) of the graphite. Therefore, in film-like graphite, the more the basal plane of graphite crystals with large crystallite size is oriented in the film plane direction, the higher the thermal conductivity of the film-like graphite in the film plane direction. Polarizing microscopy is one of the evaluation methods that can evaluate the crystallinity and crystal orientation of graphite and polymer materials. Graphite is an optically uniaxial crystal and therefore exhibits optical anisotropy. When observed under crossed Nicols with a polarizing microscope, areas containing graphite crystals oriented in a specific direction (i.e., the two vibration directions of the graphite crystals do not coincide with the vibration directions of both Nicols, i.e., the orientation does not coincide with the depolarization) appear bright. Figures 16 and 17 show examples of cross-sectional polarizing microscopy images of film-type graphite taken perpendicular to the film surface. Continuously bright regions (bright areas) are thought to reflect the orientation of graphite crystals in a specific direction. Therefore, analyzing these bright regions in the observed image allows us to evaluate the crystallinity and orientation of film-type graphite. After extensive investigation, the authors found that the number of bright areas in an observed image (count / film thickness (μm) / film width (μm) (CN)) correlates well with the thermal conductivity of film-like graphite. In other words, the smaller the CN, the higher the thermal conductivity of film-like graphite in the film plane direction. This is because when individual graphite crystallites are small and numerous crystallites are dispersed throughout the film, numerous bright areas are observed, resulting in a large CN. On the other hand, as graphite crystallites coalesce and their size increases, the CN decreases. In other words, the smaller the CN, the fewer the interfaces between graphite crystallites, which makes it difficult for phonons to disperse, resulting in higher thermal conductivity. In another example of the embodiment, it was found that the average area of the plurality of bright regions also correlates with thermal conductivity. That is, it was found that the larger the average area, the higher the thermal conductivity of the filmy graphite in the film plane direction. This is thought to be because the larger the average area of the bright regions, the larger the size of the graphite crystallites, and the higher the thermal conductivity due to phonons.

[0104] The filmy graphite of the present invention described above has high thermal conductivity in the film plane direction and excellent heat dissipation performance. Moreover, this property is true regardless of the film thickness, even for thick filmy graphite. Furthermore, when the ratio (surface area / film area) is 1.05 or more, excellent flexibility is obtained.

[0105] In the present invention, it is preferable to produce filmy graphite in which the product of the film thickness a (μm) and the thermal conductivity b (W / mK) in the direction along the film surface is 40,000 or more. Such filmy graphite has a large heat transport capacity. Furthermore, from the viewpoint of facilitating the thinning of electronic devices and the like, it is more preferable to produce filmy graphite in which the film thickness a is 23 μm or less. [Example]

[0106] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following descriptions.

[0107] [Raw film] In all of the following examples, a polyimide film (Kapton (registered trademark) H type (hereinafter referred to as "polyimide film KH") manufactured by DuPont-Toray Co., Ltd.) was used as the raw material film. Thermogravimetry was carried out on this polyimide film KH (raw material film). Figure 2 shows the plot of the weight loss rate (weight loss per unit time) versus temperature when the raw material film was heated at 10°C / min in a nitrogen atmosphere. p , T s , T f were 595°C, 475°C, and 675°C, respectively.

[0108] [Thermogravimetry] Thermogravimetry (TG) was carried out using a simultaneous differential thermal and thermogravimetry analyzer (STA7300, manufactured by Hitachi High-Tech Science Corporation) according to the following procedure. The raw film was cut into approximately 3 mm squares and stacked in a platinum container to form a measurement sample weighing approximately 3 mg. While nitrogen gas was flowing at a rate of 200 mL / min, the sample was heated to 1000°C at a rate of 10°C / min, and the temperature and weight of the measurement sample were recorded every second.

[0109] [Thermal diffusivity in the film surface direction] The thermal diffusivity α of the film-like graphite in the direction along the film surface was measured in an environment of 23°C using a BETHEL Thermowave Analyzer TA33 in accordance with JIS R 7240 (2018) using the cyclic heating method (distance change method). Five measurement frequencies were used: 60 Hz, 70 Hz, 75 Hz, 80 Hz, and 90 Hz. The average of the thermal diffusivities measured at each of the five frequencies was taken as the thermal diffusivity α of the film-like graphite in the direction along the film surface. The sample size for the measurement was 4 cm to 10 cm in length in the measurement direction and 1.5 cm to 10 cm in length in the direction perpendicular to the measurement direction on the film surface. The thickness of the cut sample was measured.

[0110] [Thermal diffusivity in the direction perpendicular to the film] The thermal diffusivity α' of the film-like graphite in the direction perpendicular to the film surface was measured using a cyclic heating method (frequency change method) in an environment of 23°C using a Thermowave Analyzer TA33 manufactured by BETHEL Corporation. Ten measurement frequencies were selected so that the phase was in the range of -3 rad to -1 rad, and the phase was measured. In this case, the ten frequency points were selected so that the frequency intervals were equal. The thermal diffusivity α' was calculated from the slope of the square root of the obtained phase and frequency. For the measurement, the sample size was 5 cm square, and the thickness was measured using a cut sample.

[0111] [Thermal conductivity in the film surface direction] The thermal conductivity of the film-like graphite in the direction along the film surface was calculated according to the following formula 2. b=α×d×c...Formula 2 However, the symbols in the formula 2 have the following meanings. b: Thermal conductivity of film-like graphite in the direction along the film surface (W / mK) α: Thermal diffusivity of film-like graphite in the direction along the film surface (mm 2 / s) d: Density of film-like graphite (g / cm 3 ) c: Specific heat of graphite (0.85 J / gK)

[0112] [Thermal conductivity in the direction perpendicular to the film] The thermal conductivity of the film-like graphite in the direction perpendicular to the film surface was calculated according to the following formula 2-b. b'= α'×d×c...Equation 2-b However, the symbols in the formula 2-b have the following meanings. b': Thermal conductivity of film-like graphite in the direction perpendicular to the film surface (W / mK) α': Thermal diffusivity of film-like graphite in the direction perpendicular to the film surface (mm 2 / s) d: Density of film-like graphite (g / cm 3 ) c: Specific heat of graphite (0.85 J / gK)

[0113] [density] The density d of the filmy graphite was calculated from the following formula 3 by measuring the weight of the filmy graphite in air and in ethanol. d=ρs×Wa / (Wa-Ws) Equation 3 However, the symbols in the formula 3 have the following meanings. d: Density of film-like graphite (g / cm 3 ) ρs: Density of ethanol (g / cm 3 ) Wa: Weight of film-like graphite in air (g) Ws: Weight of film-like graphite in ethanol (g)

[0114] [Fracture surface observation] Information on the internal structure of film-like graphite was obtained by observing the fracture surface of the film-like graphite during mode I crack propagation using a scanning electron microscope (SEM). Specifically, a rectangular specimen with a short side of 10 mm or more was cut from the film-like graphite. A 3 mm deep notch was made with a razor along a line connecting the centers of the two long sides of the specimen, from each long side. Tension was applied in the long-side direction, causing the crack to propagate and tear the specimen. The fracture surface of the torn specimen was observed with an SEM at an accelerating voltage of 10 kV, providing a contrast that allowed distinction between the specimen cross section and the background. The fracture surface was observed multiple times, changing the observation location so that a continuous stretch of 1 mm or more could be observed in the film plane direction.

[0115] [Compression test] In an environment of 25°C, a pressure of 100 MPa was applied to the entire film surface of the film-like graphite to compress it. The film thickness T of the film-like graphite before compression b (μm) and the film thickness after compression, T a (μm), respectively, and T a / T b was calculated.

[0116] [Unloaded U-shaped expansion and contraction test of a planar object] The no-load U-shaped stretch test for the film-like graphite sheet was performed using a desktop durability tester DLDMLH-FS manufactured by Yuasa System Co., Ltd., according to the following procedure. A test specimen measuring 50 mm in width and 150 mm in length was cut and attached to the tester using double-sided tape. The test was performed at a bending angle of 180°, a bending radius of 2 mm, and a test speed of 60 Hz. The tilt clamp was used in a bending test mode, which alternated between a straight and bent state according to the bending state of the test specimen. After the test began, the test specimen was visually inspected at 1,000, 2,500, 5,000, 10,000, 20,000, 30,000, 40,000, and 50,000 bending cycles. The number of bending cycles until the specimen broke was recorded as the number of folding cycles.

[0117] The pressing process in each of the following examples was carried out using a hydraulic calender-embosser manufactured by Yuri Roll Co., Ltd., according to the following procedure. The graphitized film was sandwiched between commercially available polyimide films and compressed under conditions of a linear pressure of 900 kg / cm to 2700 kg / cm and a roll rotation speed of 0.5 m / min. Compression was repeated until the difference in film thickness before and after compression was within 1 μm. The linear pressure was defined as the value obtained by dividing the load on the roll by the length of the graphitized film inserted into the roll in the roll width direction.

[0118] [Method for measuring electrical conductivity] The electrical conductivity of the film-like graphite in the direction along the film surface was measured at 23°C using a Hioki RM3545 resistance meter in accordance with JIS K 7194 (1994) using the four-probe method. The four-probe was pressed against the film-like graphite to measure the electrical resistance. The electrical resistivity (R × RCF × t) was calculated from the product of the electrical resistance value R obtained by the measurement, the resistivity correction factor RCF, which is calculated from the sample shape, size, measurement position, etc. based on the Poisson equation described in JIS K 7194 (1994), and the thickness t of the film-like graphite. The electrical conductivity was then calculated as the reciprocal of the electrical resistivity. The sample size was 5 cm square, and the thickness was measured using a cut sample.

[0119] Example 1A A 125 μm-thick polyimide film from PIKH was used as the raw film. The raw film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450 °C at an average heating rate of 10 °C / min in an acetylene-containing nitrogen gas atmosphere (acetylene gas concentration: 25% by volume), and then increased from 450 °C to 550 °C at a heating rate of approximately 0.2 °C / min (heating process in mixed gas). After the temperature was increased to 550 °C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000 °C at a heating rate of approximately 10 °C / min and held at that temperature for 1 hour. After the carbonization process, the film was allowed to cool and then transferred to a graphitization furnace for the graphitization process. In the graphitization furnace, the temperature was increased to 2800 °C at a heating rate of approximately 10 °C / min in an argon atmosphere, held at 2800 °C for 1 hour, and then cooled to obtain a graphitized film. The graphitized film obtained showed no surface peeling or damage due to foaming. The obtained graphitized film was sandwiched between two polyimide films and compressed seven times under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min to obtain a graphite film.

[0120] Example 2A A filmy graphite was obtained in the same manner as in Example 1A, except that in the step of heating in the mixed gas, the temperature was increased at a rate of about 0.6°C / min.

[0121] Example 3A A film-like graphite was obtained in the same manner as in Example 1A, except that in the graphitization step, the temperature increase rate was changed to be maintained at about 5°C / min.

[0122] Example 4A A film-like graphite was obtained in the same manner as in Example 1A, except that in the graphitization step, the temperature increase rate was changed to be maintained at about 2°C / min.

[0123] Example 5A A film-like graphite was obtained in the same manner as in Example 1A, except that in the graphitization step, the power output value of the graphitization furnace was kept constant and the temperature was increased to the temperature record shown in Fig. 9. According to the temperature record shown in Fig. 9, the temperature was 2062°C 30 minutes after reaching 2000°C, 2120°C 60 minutes later, and 2176°C 90 minutes later. An SEM image of the fracture surface of the obtained film-like graphite is shown in Fig. 1. A photograph of the appearance of the graphitized film before compression is shown in Fig. 3. In FIG. 1, the portion indicated by "B" is a multilayer structure, and the portion indicated by "C" is a gap.

[0124] Example 6A One side of a 75 μm-thick polyimide film made of PIKH was coated with an N-methyl-2-pyrrolidone solution containing 20% by weight of polyamic acid obtained by polymerizing oxydianiline and pyromellitic anhydride. Another 75 μm-thick polyimide film made of PIKH was then bonded to the coated side of the polyimide film. The pressure roll used in Example 1A was then used as a mangle to remove excess solution. The bonded film was placed under a nitrogen atmosphere at atmospheric pressure, heated to 350°C at an average heating rate of 2°C / min, held for 1 hour, and then allowed to cool. A 150 μm-thick laminated film was obtained, consisting of two 75 μm-thick polyimide films firmly bonded together. Film-like graphite was obtained in the same manner as in Example 5A, except that this laminated film was used as the raw material film.

[0125] Example 7A A filmy graphite was obtained in the same manner as in Example 5A, except that a 175 μm thick laminate film prepared by laminating a 50 μm thick polyimide film of PIKH to a 125 μm thick polyimide film of PIKH was used as the raw material film.

[0126] Example 8A Film-like graphite was obtained in the same manner as in Example 5A, except that a 200 μm-thick laminated film prepared by laminating a 75 μm-thick polyimide film of PIKH to a 125 μm-thick polyimide film of PIKH was used as the raw material film in the same manner as in Example 6A.

[0127] Example 9A A filmy graphite was obtained in the same manner as in Example 5A, except that a 250 μm thick laminate film obtained by laminating a 125 μm thick polyimide film of PIKH to a 125 μm thick polyimide film of PIKH was used as a raw material film in the same manner as in Example 6A.

[0128] Example 10A A film-like graphite was obtained in the same manner as in Example 9A, except that the temperature increase rate in the graphitization step was maintained at about 15°C / min.

[0129] Example 11A T in the graphitization process max A film-like graphite was obtained in the same manner as in Example 9A, except that the temperature was kept at 2700°C and the heating rate was kept at about 2°C / min.

[0130] Example 12A Film-like graphite was obtained in the same manner as in Example 6A, except that a 200 μm-thick laminated film prepared by laminating a 75 μm-thick polyimide film of PIKH to a 125 μm-thick polyimide film of PIKH was used as the raw material film, in the same manner as in Example 11A.

[0131] Example 13A Film-like graphite was obtained in the same manner as in Example 11A, except that a 175 μm-thick laminated film prepared by laminating a 50 μm-thick polyimide film of PIKH to a 125 μm-thick polyimide film of PIKH was used as the raw material film in the same manner as in Example 6A.

[0132] Example 14A A filmy graphite was obtained in the same manner as in Example 1A, except that a 75 μm thick polyimide film of PIKH was used as the raw material film.

[0133] Example 15A The temperature rise rate in the graphitization process was kept at about 1°C / min. max A filmy graphite was obtained in the same manner as in Example 1A, except that the heating temperature was set to 2900°C.

[0134] Example 16A A film-like graphite was obtained in the same manner as in Example 1A, except that the temperature increase rate in the graphitization step was maintained at about 20°C / min.

[0135] Example 17A Film-like graphite was obtained in the same manner as in Example 1A, except that a 150 μm-thick laminated film obtained by laminating a 75 μm-thick polyimide film of PIKH to a 75 μm-thick polyimide film of PIKH was used as a raw material film in the same manner as in Example 6A.

[0136] Example 18A Film-like graphite was obtained in the same manner as in Example 1A, except that a 175 μm-thick laminated film prepared by laminating a 50 μm-thick polyimide film of PIKH to a 125 μm-thick polyimide film of PIKH was used as a raw material film in the same manner as in Example 6A.

[0137] Example 19A A 200 μm thick laminated film was used as the raw material film, consisting of a 125 μm thick polyimide film of PIKH laminated to a 75 μm thick polyimide film of PIKH laminated in the same manner as in Example 6A. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450°C at an average heating rate of 10°C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume), and then the heating rate was maintained at approximately 0.2°C / min from 450°C to 550°C (heating process in mixed gas). After the temperature was increased to 550°C, the atmosphere was switched to nitrogen gas, and the heating rate was maintained at approximately 10°C / min to 800°C. After the carbonization process, the film was allowed to cool and then transferred to a graphitization furnace, where the graphitization process was carried out. A film-like graphite was obtained in the same manner as in Example 1A, except that in the graphitization step, the power output value of the graphitization furnace was kept constant and the temperature was increased to the temperature record shown in Fig. 10. According to the temperature record shown in Fig. 10, the temperature was 2096°C 30 minutes after reaching 2000°C, 2185°C 60 minutes later, and 2270°C 90 minutes later.

[0138] Example 20A A filmy graphite was obtained in the same manner as in Example 19A, except that a 250 μm thick laminate film prepared by laminating a 125 μm thick polyimide film of PIKH to a 125 μm thick polyimide film of PIKH was used as a raw material film in the same manner as in Example 6A.

[0139] Example 21A A 200 μm thick laminate film was used as the raw material film, obtained by laminating a 75 μm thick polyimide film of PIKH to a 125 μm thick polyimide film of PIKH in the same manner as in Example 6A. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 500 °C at an average heating rate of 10 °C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume) and maintained at this temperature for 3 hours. Film-like graphite was obtained in the same manner as in Example 19A, except that the atmosphere was then switched to nitrogen gas and the temperature was increased to 800 °C at a heating rate of approximately 10 °C / min.

[0140] Example 22A Film-like graphite was obtained in the same manner as in Example 21A, except that a 250 μm-thick laminated film obtained by laminating a 125 μm-thick polyimide film of PIKH to a 125 μm-thick polyimide film of PIKH was used as the raw material film in the same manner as in Example 6A.

[0141] [Comparative Example 1A] A film-like graphite was obtained in the same manner as in Example 5A, except that the heating step in a mixed gas was not performed, and that in the carbonization step, the temperature was raised to 1,000°C at a rate of about 10°C / min in a nitrogen gas atmosphere and held at that temperature for 1 hour. An SEM image of the fracture surface of the obtained film-like graphite is shown in Fig. 4. The portion indicated by "D" in FIG. 4 has a multi-layer structure.

[0142] [Comparative example 2A] A graphitized film was obtained in the same manner as in Example 7A, except that the heating step in a mixed gas was not performed, and in the carbonization step, the temperature was raised to 1,000°C at a rate of approximately 10°C / min in a nitrogen gas atmosphere and maintained at that temperature for 1 hour. The obtained graphitized film was quite hard and was destroyed in the subsequent pressing step. A photograph of the appearance of the graphitized film before compression is shown in Figure 5.

[0143] [Comparative example 3A] A graphitized film was obtained in the same manner as in Example 10A, except that a 125 μm-thick polyimide film of PIKH was used as the raw material film, the heating step in a mixed gas was not performed, and the temperature was increased to 1000°C in a nitrogen gas atmosphere at a heating rate of approximately 10°C / min and maintained at that temperature for 1 hour in the carbonization step. Foaming occurred during the graphitization process, and the graphitized film was partially destroyed. Furthermore, the graphitized film was hard and destroyed during the subsequent pressing step. A photograph of the appearance of the graphitized film before compression is shown in FIG. 6.

[0144] [Comparative example 4A] Film-like graphite (EYGS121810, thickness 100 μm) manufactured by Panasonic Corporation was used as a comparison. Figure 7 shows an SEM image of the fracture surface of the film-like graphite before compression.

[0145] [Comparative example 5A] A laminated film-type graphite consisting of one sheet of film-type graphite (EYGS121803, thickness 25 μm) manufactured by Panasonic Corporation and three sheets of film-type graphite (EYGA121802F, PGS thickness 17 μm, double-sided tape thickness 6 μm) manufactured by Panasonic Corporation was used for comparison.

[0146] The manufacturing conditions for each example are shown in Table 1, and the test results are shown in Table 2. In Table 2, among the rectangles that can be included in the region forming the multilayer structure, one adjacent side is XX μm long and the other side is Y μm long, and the direction of the XX μm long side coincides with the layer direction, the XX μm and Y μm of the largest rectangle are shown as the width and thickness of the multilayer structure, respectively. The thermal conductivity of the filmy graphite of each example and comparative example is plotted against thickness in Figure 8. For the plot of Comparative Example 4A in Figure 8, the catalog value of the commercially available product is used.

[0147] [Table 1]

[0148] [Table 2]

[0149] As shown in Tables 1 and 2, Example 14A, which used a raw material film with a thickness of 75 μm, only produced a thin film-like graphite with a thickness of 39 μm, while Example 1A, which used a raw material film with a thickness of 125 μm, produced a thick film-like graphite with a thickness of 58 μm. This result indicates that in order to produce thick film-like graphite with a thickness of 58 μm or more and high heat dissipation performance, it is better to use a thick raw material film.

[0150] Comparing Examples 1A, 3A, 4A, 5A, and 15A, each of which had a raw material film thickness of 125 μm, the faster the heating rate in the graphitization step, the smaller the minimum radius of curvature of the resulting filmy graphite, resulting in superior flexibility. Example 15A had a minimum bending radius exceeding 16 mm, resulting in insufficient flexibility. These results are believed to be due to the fact that excessive growth of the graphite structure was suppressed by increasing the heating rate in the graphitization step. Furthermore, the filmy graphites of Examples 1A, 3A, 4A, and 5A had higher thermal conductivities b than Example 16A, which used an equivalent raw material film but had a particularly high heating rate in the graphitization step. These results demonstrate that a higher heating rate in the graphitization step is better in terms of flexibility of the filmy graphite, while a lower heating rate in the graphitization step is better in terms of heat dissipation performance (thermal conductivity).

[0151] Comparing Examples 5A to 9A, which were heated under the same conditions in the carbonization and graphitization steps, thicker and more flexible film-like graphite was obtained as the thickness of the raw material film was increased. Furthermore, comparing Examples 5A to 9A, the thinner the film-like graphite, the smaller the minimum bending radius and the more flexible it became. This is thought to be because the thinner the film-like graphite, the smaller the compressive stress on the inner surface and the tensile stress on the outer surface when the film is bent. Furthermore, comparing Examples 5A to 9A, the thermal conductivity and S g / S m This indicates that the effect of the heating process in mixed gas is fully exerted even if the raw material film is thick.

[0152] Comparing Example 10A with Example 9A, by increasing the rate of temperature rise in the graphitization step, the minimum bending radius of the filmy graphite became smaller and flexibility improved. On the other hand, comparing Example 10A with Example 9A, the filmy graphite with a lower rate of temperature rise in the graphitization step had a higher thermal conductivity. T in the graphitization process max In comparison with Examples 11A to 13A, in which the temperature was 2700°C, the thinner the film-like graphite, the smaller the minimum bending radius and the more flexible it was, as in the case of Examples 5A to 9A. max When comparing Example 7A with Example 13A, Example 8A with Example 12A, and Example 9A with Example 11A when the temperature is 2800°C and 2700°C, T max By increasing the temperature to 2700°C, the minimum bending radius of the film-like graphite became smaller, improving its flexibility. From these results, it can be seen that in terms of flexibility of film-like graphite, the higher the heating rate in the graphitization process, the better. max By optimizing the heating conditions in the graphitization process, it is possible to obtain a film-like graphite that combines heat dissipation performance (thermal conductivity) and flexibility.

[0153] Comparing Examples 1A, 17A, and 18A, which were all heated under the same conditions in the carbonization and graphitization steps, it was found that as the thickness of the raw material film was increased, thicker film-like graphite with higher heat dissipation performance (thermal conductivity) was obtained.

[0154] In Comparative Example 1, in which the heating step in a mixed gas was not performed in the carbonization step, the thermal conductivity of the filmy graphite was lower than that of Example 5A, which used a raw material film of the same thickness. Comparing the SEM photograph of the fracture surface of Example 5A shown in Fig. 1 with the SEM photograph of the fracture surface of Comparative Example 1 shown in Fig. 4, differences in the cross-sectional structure were observed. In Comparative Example 1, foaming during the production process was not suppressed, and the layered structure of the graphite was not smooth but had a wavy shape, with many voids being observed. This is thought to be the cause of the lower thermal conductivity of the filmy graphite of Comparative Example 1 in the direction along the film surface.

[0155] In Comparative Example 2, in which the heating step in a mixed gas was not performed in the carbonization step, the graphitized film obtained was extremely hard and broke in the pressing step, compared to Example 7A, which used a raw material film of the same thickness. These results confirmed that by performing the heating step in a mixed gas, a flexible graphitized film can be obtained even when a thicker raw material film than that used in the prior art is used, and that a thick film-like graphite can be produced.

[0156] 6, in Comparative Example 3, in which the heating step in a mixed gas was not carried out, the graphitized film was partially destroyed by foaming during decomposition, and was destroyed in the pressing step, even though the thickness of the raw material film was 125 μm, which was thinner than the raw material film of Example 10A. Even when the raw material film was thick as in Example 10A, the decomposition of the film was suppressed by carrying out the heating step in a mixed gas, and the amount of decomposed gas was reduced, so that even if the temperature rise rate in the graphitization step was increased, film destruction due to excessive foaming was suppressed, and high-quality film-like graphite was obtained.

[0157] The commercially available film-like graphite of Comparative Example 4 has a low thermal conductivity of 700 W / mK and a density of 0.85 g / cm 3 and low, and even T a / T b The thermal conductivity was also low at 0.64%. Furthermore, as shown in Figure 7, the SEM image showed numerous voids, indicating poor orientation of the graphite crystal layers, and no multilayer structure with a thickness of 8 μm or more was observed. From these results, it is believed that the thickness of the film-like graphite of Comparative Example 4 was ensured by insufficient compression or rolling during the manufacturing process, resulting in low density and many voids, which resulted in poor thermal conductivity.

[0158] In Examples 1A to 16A and 19A to 22A in which the heating step in a mixed gas was performed, S g / S mIn addition, when comparing Example 1A with Example 2A, it can be seen that the temperature increase rate in the heating step in the mixed gas is reduced and the time during which the organic gas acts is extended, which results in a decrease in the S g / S m In this way, the area S of the graphitized film increased by performing the heating process in the mixed gas. g It was confirmed that the effect of increasing the amount of organic gas acting on the substrate was greater, and that the effect was further increased by increasing the time that the organic gas was acting on the substrate.

[0159] [Method for evaluating graphite crystal orientation degree P] The measurement equipment used was a fully automated multipurpose X-ray diffractometer, SmartLab, manufactured by Rigaku Corporation, using CuKα radiation as a radiation source. The film-like graphite was fixed on a sample stage so that the incident angle of the incident X-rays and the reflection angle of the reflected X-rays were equal to the normal to the film surface, and the film-like graphite was prevented from warping. One-dimensional X-ray diffraction spectra in the 2θ direction of the film-like graphite were measured using the θ / 2θ scan method. The measurement conditions were a tube voltage of 45 kV, a tube current of 200 mA, a scan range (2θ) of 25–28°, a scan step of 0.01°, a scan rate of 4.0° / min, and a continuous scan mode. The position of the reflection diffraction peak of the (002) plane, derived from the hexagonal crystal structure of graphite, detected near 2θ = 26°, was read, and the detector was fixed at this peak position. The X-ray diffraction spectrum of the film-like graphite was measured using the ω scan method. The measurement conditions were: tube voltage 45 kV, tube current 200 mA, scan range (ω) -5.8 to 31.4°, scan step 0.02°, scan speed 20.0° / min, and scan mode CONTINUOUS. The half-width W (°) of the diffraction peak obtained from this spectrum was read, and the degree of graphite crystal orientation P [%] was calculated using the following equation 1.

[0160]

number

[0161] [Surface area / film area evaluation method] The measurement device used was a Keyence Corporation VK-X100 profile measurement laser microscope. A 5 × 5 cm sample cut from film-type graphite was placed on the sample stage, ensuring the film was not warped and facing upward. The measurement mode was surface profile mode, and the objective lens was set to 50x magnification with 2048 × 1536 pixels. The objective lens was moved in 0.12 μm increments along the Z axis (height direction) to obtain surface profile data. The upper and lower limits of the objective lens movement along the Z axis were set to the positions where the laser image of the sample (film-type graphite) became completely black. The laser brightness was adjusted so that the reflected laser light intensity did not saturate at heights between the upper and lower limits along the Z axis. Specifically, the laser brightness and lighting filter were adjusted so that the light intensity did not exceed the saturation line (65,535 counts). The film area of the film observation range of the obtained image and the surface area were calculated from the surface shape data of the sample, and the ratio (surface area / film area) was calculated.

[0162] [Thermal Conductivity] The thermal conductivity of the film-like graphite in the direction along the film surface was calculated according to the following formula 2. b=α×d×c...Formula 2 However, the symbols in the formula 2 have the following meanings. b: Thermal conductivity of film-like graphite in the direction along the film surface (W / mK) α: Thermal diffusivity of film-like graphite in the direction along the film surface (mm 2 / s) d: Density of film-like graphite (g / cm 3 ) c: Specific heat of graphite (0.85 J / gK)

[0163] [Flexibility (bending test)] The minimum bending radius was evaluated as an index of the flexibility of film-like graphite. In a 23°C environment, a Type 2 bending tester specified in JIS K5600-5-1 was fully unfolded, a film-like graphite test specimen and mandrel were attached, and the specimen was uniformly bent 180° over 1-2 seconds. The specimen was then inspected for the presence of creases or cracks. Mandrels with diameters of 32, 25, 20, 16, 12, 10, 8, 6, 5, 4, 3, and 2 mm were used, and the specimen was bent and visually inspected, starting with the largest diameter mandrel. The specimen was repositioned during each mandrel bending test to prevent distortions or other effects from bending the specimen. The minimum bending radius of the film-like graphite was determined to be half the diameter of a mandrel one size larger in diameter than the mandrel on which a fold or crack was first observed in the test piece, i.e., half the diameter of the smallest mandrel among the mandrels on which no folds or cracks were observed in the test piece.

[0164] The pressing process in each of the following examples was carried out using a hydraulic calender / embossing machine (manufactured by Yuri Roll Co., Ltd.) according to the following procedure. The graphitized film was sandwiched between commercially available polyimide films and compressed under conditions of a linear pressure of 900 kg / cm to 2700 kg / cm and a roll rotation speed of 0.5 m / min. Compression was repeated until the difference in film thickness before and after compression was within 1 μm. The linear pressure was defined as the value obtained by dividing the load on the roll by the length of the graphitized film inserted into the roll in the roll width direction.

[0165] Example 1B A 50 μm-thick polyimide film (KH) was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 500°C at an average heating rate of 10°C / min in an acetylene-containing nitrogen gas atmosphere (acetylene gas concentration: 25% by volume), and then the film was isothermally maintained at 500°C for 3 hours (heating process in mixed gas). After isothermal maintenance at 500°C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000°C at a heating rate of approximately 10°C / min and maintained at this temperature for 1 hour. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace for the graphitization process. In the graphitization furnace, the temperature was increased to 2800°C at a heating rate of approximately 20°C / min in an argon atmosphere, and the film was maintained at 2800°C for 1 hour, after which it was cooled to obtain a graphitized film. The resulting graphitized film was sandwiched between two polyimide films and compressed under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min to obtain a graphite film.

[0166] Example 2B One side of a 75 μm-thick polyimide film KH was coated with an N-methyl-2-pyrrolidone solution containing 20% by mass of polyamic acid obtained by polymerizing oxydianiline and pyromellitic anhydride. Another 75 μm-thick polyimide film KH was then bonded to the coated side of the polyimide film KH, and the excess solution was removed using the pressure roll used in Comparative Example 1 as a mangle. The bonded film was placed under atmospheric pressure in a nitrogen atmosphere, heated to 350°C at an average heating rate of 2°C / min, held for 1 hour, and then allowed to cool, resulting in a 150 μm-thick laminated film in which two 75 μm-thick polyimide films were firmly bonded together. The laminated film was used as a raw material film and carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450°C at an average heating rate of 10°C / min in an acetylene-containing nitrogen gas atmosphere (acetylene gas concentration: 25% by volume), and then increased from 450°C to 550°C at a heating rate of approximately 0.6°C / min (heating process in mixed gas). After the temperature was increased to 550°C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000°C at a heating rate of approximately 10°C / min and held there for 1 hour. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace, where the graphitization process was carried out. In the graphitization furnace, the temperature was increased to 2800°C at a heating rate of approximately 5°C / min in an argon atmosphere, held at 2800°C for 1 hour, and then cooled to obtain a graphitized film. The obtained graphitized film was sandwiched between two polyimide films and compressed under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min, and the two sandwiched polyimide films were removed to obtain a film-like graphite.

[0167] Example 3B A 125 μm thick polyimide film KH was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450 °C at an average heating rate of 10 °C / min in an acetylene-containing nitrogen gas atmosphere (acetylene gas concentration: 25% by volume), and then increased from 450 °C to 550 °C at a heating rate of approximately 0.2 °C / min (heating process in mixed gas). After the temperature was increased to 550 °C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000 °C at a heating rate of approximately 10 °C / min and held there for 1 hour. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace for the graphitization process. In the graphitization process, the power output of the graphitization furnace was kept constant in an argon atmosphere, and the temperature was increased according to the temperature profile shown in Figure 13. 13, the temperature 30 minutes after reaching 2000°C is 2062°C, the temperature 60 minutes after is 2120°C, and the temperature 90 minutes after is 2176°C. In the graphitization furnace, the temperature was held at 2800°C for 1 hour, and then cooled to obtain a graphitized film. The resulting graphitized film was sandwiched between two polyimide films and compressed under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min to obtain a graphite film. FIG. 12 shows a part of an image obtained by observing the surface of the obtained film-like graphite with a laser microscope.

[0168] Example 4B A 175 μm thick laminated film was obtained in the same manner as in Example 2B, except that a 125 μm thick polyimide film KH and a 50 μm thick polyimide film KH were used. The laminated film was used as a raw material film, and a carbonization process was carried out on the raw material film in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450°C at an average heating rate of 10°C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume), and then the heating rate was maintained at approximately 0.2°C / min from 450°C to 550°C (heating process in mixed gas). After the temperature was increased to 550°C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000°C at a heating rate maintained at approximately 10°C / min and held there for 1 hour. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace, where the graphitization process was carried out. In the graphitization furnace, the temperature was increased to 2800°C in an argon atmosphere at a heating rate of approximately 2°C / min, held at 2800°C for 1 hour, and then cooled to obtain a graphitized film. The resulting graphitized film was sandwiched between two polyimide films and compressed under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min to obtain a graphite film.

[0169] Example 5B A film-like graphite was obtained in the same manner as in Example 4B, except that a 200 μm-thick laminated film obtained in the same manner as in Example 2B was used, except that a 125 μm-thick polyimide film KH and a 75 μm-thick polyimide film KH were used as the raw material film.

[0170] Example 6B Filmy graphite was obtained in the same manner as in Example 3B, except that a 200 μm thick laminate film similar to that in Example 5B was used as the raw material film.

[0171] Example 7B A film-like graphite was obtained in the same manner as in Example 3B, except that a 250 μm-thick laminated film obtained in the same manner as in Example 2B was used as the raw material film, except that two sheets of 125 μm-thick polyimide film KH were used.

[0172] Example 8B A 50 μm-thick polyimide film KH was used as a raw material film, and a carbonization step of the raw material film was carried out in a carbonization furnace. In the carbonization furnace, the temperature was raised to 1,000°C at a heating rate of about 10°C / min in a nitrogen gas atmosphere, and then held at that temperature for 1 hour, in the same manner as in Example 3B, except that the temperature was raised to 1,000°C and held at that temperature for 1 hour.

[0173] Example 9B A graphite film was obtained in the same manner as in Example 8B, except that a 75 μm thick polyimide film KH was used as the raw material film.

[0174] Example 10B A 50 μm thick polyimide film KH was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 1000°C at an average heating rate of 5°C / min under a nitrogen gas atmosphere, and then maintained at 1000°C for 1 hour. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace for the graphitization process. In the graphitization furnace, the temperature was increased to 2600°C under an argon atmosphere at a heating rate of approximately 1°C / min. After reaching 2600°C, the temperature was increased to 2900°C at a heating rate of approximately 0.8°C / min. The film was then maintained at 2900°C for 1 hour, and then cooled to obtain a graphitized film. The resulting graphitized film was sandwiched between two polyimide films and compressed under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min to obtain a graphite film.

[0175] Example 11B A graphite film was obtained in the same manner as in Example 10B, except that a polyimide film KH having a thickness of 125 μm was used as the raw material film.

[0176] Example 12B A 125 μm thick polyimide film KH was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450°C at an average heating rate of 10°C / min in an acetylene gas-containing nitrogen gas atmosphere (acetylene gas concentration: 25% by volume), and then the heating rate was maintained at approximately 0.2°C / min from 450°C to 550°C (heating process in mixed gas). After the temperature was increased to 550°C, the atmosphere was switched to nitrogen gas, and the heating rate was maintained at approximately 10°C / min to 800°C. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace for the graphitization process. A film-like graphite was obtained in the same manner as in Example 1B, except that the graphitization process was performed in an argon atmosphere, with the power output of the graphitization furnace kept constant, and the temperature was increased to the temperature record shown in FIG. 14. According to the temperature record shown in FIG. 14, the temperature was 2096°C 30 minutes after reaching 2000°C, 2185°C 60 minutes later, and 2270°C 90 minutes later.

[0177] Example 13B A 175 μm thick laminate film was obtained in the same manner as in Example 2B, except that a 125 μm thick polyimide film KH and a 50 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 12B, except that this 175 μm thick laminate film was used as the raw material film.

[0178] Example 14B A 200 μm thick laminate film was obtained in the same manner as in Example 2B, except that a 125 μm thick polyimide film KH and a 75 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 12B, except that this 200 μm thick laminate film was used as the raw material film.

[0179] Example 15B A 250 μm thick laminate film was obtained in the same manner as in Example 2B, except that a 125 μm thick polyimide film KH and a 125 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 12B, except that this 250 μm thick laminate film was used as the raw material film.

[0180] Example 16B A 125 μm thick polyimide film KH was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 500°C at an average heating rate of 10°C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume), and then the temperature was maintained at 500°C for 3 hours (heating step in mixed gas). The atmosphere was switched to nitrogen gas, and the temperature was increased to 800°C while maintaining a heating rate of approximately 10°C / min. Otherwise, a film-like graphite was obtained in the same manner as in Example 12B.

[0181] Example 17B A 175 μm thick laminate film was obtained in the same manner as in Example 2B, except that a 125 μm thick polyimide film KH and a 50 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 16B, except that this 175 μm thick laminate film was used as the raw material film.

[0182] Example 18B A 200 μm thick laminate film was obtained in the same manner as in Example 2B, except that a 125 μm thick polyimide film KH and a 75 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 16B, except that this 200 μm thick laminate film was used as the raw material film.

[0183] Example 19B A 250 μm thick laminate film was obtained in the same manner as in Example 2B, except that a 125 μm thick polyimide film KH and a 125 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 16B, except that this 250 μm thick laminate film was used as the raw material film.

[0184] Example 20B A 75 μm thick polyimide film KH was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450 °C at an average heating rate of 10 °C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume), and then the heating rate was maintained at approximately 0.2 °C / min from 450 °C to 550 °C (heating process in mixed gas). After the temperature was increased to 550 °C, the atmosphere was switched to nitrogen gas, and the heating rate was maintained at approximately 10 °C / min to 800 °C. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace, where the graphitization process was carried out. A film-like graphite was obtained in the same manner as in Example 1B, except that in a graphitization furnace, the temperature was increased to 2800°C at a rate of about 10°C / min in an argon atmosphere, held at 2800°C for 1 hour, and then cooled to obtain a graphitized film.

[0185] [Comparative example 1B] Film-like graphite (EYGS121803, thickness 25 μm) manufactured by Panasonic Corporation was used as a comparison.

[0186] [Comparative Example 2B] Film-like graphite (EYGS121805, thickness 50 μm) manufactured by Panasonic Corporation was used as a comparison.

[0187] [Comparative example 3B] Film-like graphite (EYGS121810, thickness 100 μm) manufactured by Panasonic Corporation was used as a comparison.

[0188] [Comparative example 4B] Film-type graphite (Graphinity, thickness 40 μm) manufactured by Kaneka Corporation was used as a comparison.

[0189] [Comparative Example 5B] Film-like graphite (SDK, 40 μm) manufactured by Jiangsu Sidike New Material Technology Co., Ltd. was used for comparison.

[0190] [Comparative Example 6B] Film-like graphite (SDK, 70 μm) manufactured by Jiangsu Sidike New Material Technology Co., Ltd. was used for comparison.

[0191] The test results of the filmy graphite obtained in each of the Examples and Comparative Examples are shown in Table 1. Moreover, the thermal conductivity of the filmy graphite of each of the Examples and Comparative Examples is plotted against the degree of graphite crystal orientation P in Fig. 15.

[0192] [Table 3]

[0193] 15, the thermal conductivity of the filmy graphite tends to increase as the graphite crystal orientation degree P increases, and a stable high thermal conductivity is exhibited. The filmy graphite of Examples 3B, 6B to 11B, and 20B, which had a graphite crystal orientation degree P of 96% or more, had particularly high thermal conductivity and particularly excellent heat dissipation performance. Furthermore, the filmy graphite of Examples 1B to 9B, 12B to 16B, 18B, and 19B, which had a (surface area / film area) ratio of 1.05 or more, had a small minimum bending radius and excellent flexibility. As shown in Figure 12, cracks and irregularities were observed on the surface of the filmy graphite of Example 3B, which suggests that pyrolysis gas was generated inside the film during the graphitization process, creating voids between the graphite crystallites, thereby improving flexibility.

[0194] [CN, AS evaluation method] The specimens were cut into strips approximately 5 mm x 8 mm using a cutter (or ultrasonic cutter). They were embedded in epoxy resin (product name: Epoxy Resin (G-2), a two-component thermosetting resin, manufactured by GATAN) at 40 °C under reduced pressure and then molded into plates at 100 °C. The specimens were then polished with a HandyLap (manufactured by JEOL Ltd.) to completely remove the epoxy resin covering the observation surface (cross section). A smooth cross section was then prepared using a cross-section polisher (SM-09010, manufactured by JEOL Ltd.) with an argon ion beam. Bright-field (BF) and simple polarized (PO) images were obtained using a digital microscope (DSX510, manufactured by Olympus) with a 20x objective lens (MPLFN20XBDP, manufactured by Olympus) at a 5x zoom. To check whether the sample had been damaged by this pretreatment, a separate plasma FIB-SEM was used to deposit tungsten as a protective film, and then an area of the sample that was not at the end was drilled with an argon ion beam and observed with the SEM. By comparing this with the image obtained, the validity of the sample cross-section preparation was confirmed. Using image analysis software (Image-J), the obtained PO image was converted to 8-bit and normalized so that the pixel value distribution range of the image was 0 to 255. The area to be analyzed was selected, and within that area, a binarized image of the bright and dark areas observed in the polarized microscope image of a cross section perpendicular to the film surface of the film-like graphite was obtained. The binarization threshold was set to 128, and areas with a value of 128 or higher were considered bright areas. The number of multiple bright areas obtained by this binarization was counted across the entire image using image analysis software. Similarly, the average area of the multiple bright areas obtained using this method was calculated and used as the AS. The film thickness was determined by using the same image analysis software (Image-J) to remove voids observed inside the filmy graphite from the BF image obtained by the same observation method as above, measuring the total length of the solid part observed perpendicular to the film surface of the filmy graphite, and averaging the total length of 10 points in the image. When the number N of the plurality of bright regions was measured from the PO image, the film width was defined as the width of the film-like graphite measured in the film surface direction. CN was calculated from the number N of multiple bright areas obtained by the above method, the film thickness H, and the film width W.

[0195] The pressing process in each of the following examples was carried out using a hydraulic calender / embossing machine (manufactured by Yuri Roll Co., Ltd.) according to the following procedure. The graphitized film was sandwiched between commercially available polyimide films and compressed under conditions of a linear pressure of 900 kg / cm to 2700 kg / cm and a roll rotation speed of 0.5 m / min. Compression was repeated until the difference in film thickness before and after compression was within 1 μm. The linear pressure was defined as the value obtained by dividing the load on the roll by the length of the graphitized film inserted into the roll in the roll width direction.

[0196] Example 1C One side of a 75 μm-thick polyimide film (KH) was coated with an N-methyl-2-pyrrolidone solution containing 20% by weight of polyamic acid obtained by polymerizing oxydianiline and pyromellitic anhydride. Another 75 μm-thick polyimide film (KH) was then bonded to the coated side of the polyimide film. The pressure roll used in Example 1C was then used as a mangle to remove excess solution. The bonded film was placed under a nitrogen atmosphere at atmospheric pressure, heated to 350°C at an average heating rate of 2°C / min, held for 1 hour, and then allowed to cool, resulting in a 150 μm-thick laminated film in which two 75 μm-thick polyimide films were firmly bonded. The laminated film was used as a raw material film and carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450°C at an average heating rate of 10°C / min in an acetylene-containing nitrogen gas atmosphere (acetylene gas concentration: 25% by volume), and then increased from 450°C to 550°C at a heating rate of approximately 0.6°C / min (heating process in mixed gas). After the temperature was increased to 550°C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000°C at a heating rate of approximately 10°C / min and held there for 1 hour. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace, where the graphitization process was carried out. In the graphitization furnace, the temperature was increased to 2800°C at a heating rate of approximately 5°C / min in an argon atmosphere, held at 2800°C for 1 hour, and then cooled to obtain a graphitized film. The obtained graphitized film was sandwiched between two polyimide films and compressed under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min, and the two sandwiched polyimide films were removed to obtain a film-like graphite.

[0197] Example 2C A 125 μm thick polyimide film KH was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450 °C at an average heating rate of 10 °C / min in an acetylene gas-containing nitrogen gas atmosphere (acetylene gas concentration: 25% by volume), and then increased from 450 °C to 550 °C at a heating rate of approximately 0.2 °C / min (heating process in mixed gas). After the temperature was increased to 550 °C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000 °C at a heating rate of approximately 10 °C / min and held there for 1 hour. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace for the graphitization process. In the graphitization process, the power output of the graphitization furnace was kept constant in an argon atmosphere, and the temperature was increased according to the temperature profile shown in Figure 19. 19, the temperature 30 minutes after reaching 2000°C is 2062°C, the temperature 60 minutes after is 2120°C, and the temperature 90 minutes after is 2176°C. In the graphitization furnace, the temperature was held at 2800°C for 1 hour, and then cooled to obtain a graphitized film. The resulting graphitized film was sandwiched between two polyimide films and compressed under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min to obtain a graphite film. FIG. 23 shows a part of an image obtained by observing the surface of the obtained film-like graphite with a laser microscope.

[0198] Example 3C A 175 μm thick laminated film was obtained in the same manner as in Example 2C, except that a 125 μm thick polyimide film KH and a 50 μm thick polyimide film KH were used. The laminated film was used as a raw material film, and a carbonization process was carried out on the raw material film in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450°C at an average heating rate of 10°C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume), and then the heating rate was maintained at approximately 0.2°C / min from 450°C to 550°C (heating process in mixed gas). After the temperature was increased to 550°C, the atmosphere was switched to nitrogen gas, and the heating rate was maintained at approximately 10°C / min to 1000°C, where it was maintained for 1 hour. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace, where the graphitization process was carried out. In the graphitization furnace, the temperature was increased to 2700°C in an argon atmosphere at a heating rate of approximately 2°C / min, maintained at 2700°C for 1 hour, and then cooled to obtain a graphitized film. The resulting graphitized film was sandwiched between two polyimide films and compressed under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min to obtain a graphite film.

[0199] Example 4C A film-like graphite was obtained in the same manner as in Example 4C, except that a 200 μm-thick laminate film obtained in the same manner as in Example 2C was used, except that a 125 μm-thick polyimide film KH and a 75 μm-thick polyimide film KH were used as the raw material film.

[0200] Example 5C Filmy graphite was obtained in the same manner as in Example 3C, except that a 200 μm thick laminate film similar to that in Example 5C was used as the raw material film.

[0201] Example 6C A 125 μm thick polyimide film KH was used as the raw material film, and a 250 μm thick laminate film obtained in the same manner as in Example 2C, except that a graphitization furnace was used, was used as the raw material film, and film-like graphite was obtained in the same manner as in Example 3C.

[0202] Example 7C A 50 μm thick polyimide film KH was used as the raw material film. In a carbonization furnace, the temperature was increased from room temperature to 450°C at an average heating rate of 10°C / min in an acetylene gas-containing nitrogen gas atmosphere (acetylene gas concentration: 25% by volume), and then the temperature was increased from 450°C to 550°C at a heating rate of approximately 0.6°C / min (heating process in mixed gas). After the temperature was increased to 550°C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000°C at a heating rate of approximately 10°C / min and held there for 1 hour. In a carbonization furnace, the temperature was increased to 2800°C in an argon atmosphere at a heating rate of approximately 2°C / min, and then held at 2800°C for 1 hour, after which the temperature was held there for 1 hour. A film-like graphite was obtained in the same manner as in Example 4C.

[0203] Example 8C A film-like graphite was obtained in the same manner as in Example 8C, except that a 150 μm-thick laminated film obtained in the same manner as in Example 2C was used as the raw material film, except that two sheets of 75 μm-thick polyimide film KH were used.

[0204] Example 9C A film-like graphite was obtained in the same manner as in Example 3C, except that the temperature was raised to 2800°C in an argon atmosphere at a rate of about 2°C / min, and then held at 2800°C for 1 hour, and then held there for another 1 hour.

[0205] Example 10C A film-like graphite was obtained in the same manner as in Example 3C, except that the temperature was increased to 2800°C in an argon atmosphere at a heating rate of about 10°C / min, and then held at 2800°C for 1 hour, and then held there for another 1 hour. Example 11C A 50 μm-thick polyimide film KH was used as the raw material film. In a carbonization furnace, the temperature was increased from room temperature to 1,000°C at an average heating rate of 10°C / min under a nitrogen gas atmosphere, and then the temperature was maintained for 1 hour. In the same manner as in Example 2C, a graphite film was obtained.

[0206] Example 12C A 75 μm-thick polyimide film KH was used as the raw material film. In a carbonization furnace, the temperature was increased from room temperature to 1,000°C at an average heating rate of 10°C / min under a nitrogen gas atmosphere, and then the temperature was maintained for 1 hour. In the same manner as in Example 2C, a graphite film was obtained.

[0207] Example 13C A 125 μm-thick polyimide film KH was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450°C at an average heating rate of 10°C / min in an acetylene gas-containing nitrogen gas atmosphere (acetylene gas concentration: 25% by volume), and then the heating rate was maintained at approximately 0.2°C / min from 450°C to 550°C (heating process in mixed gas). After the temperature was increased to 550°C, the atmosphere was switched to nitrogen gas, and the heating rate was maintained at approximately 10°C / min to 800°C. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace for the graphitization process. A film-like graphite was obtained in the same manner as in Example 1C, except that the graphitization process was performed in an argon atmosphere, with the power output of the graphitization furnace kept constant, and the temperature was increased to the temperature record shown in Figure 20. According to the temperature record shown in FIG. 20, the temperature was 2096°C 30 minutes after reaching 2000°C, 2185°C 60 minutes later, and 2270°C 90 minutes later.

[0208] Example 14C A 175 μm thick laminate film was obtained in the same manner as in Example 1C, except that a 125 μm thick polyimide film KH and a 50 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 13C, except that this 175 μm thick laminate film was used as the raw material film.

[0209] Example 15C A 200 μm thick laminate film was obtained in the same manner as in Example 1C, except that a 125 μm thick polyimide film KH and a 75 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 13C, except that this 200 μm thick laminate film was used as the raw material film.

[0210] Example 16C A 250 μm thick laminate film was obtained in the same manner as in Example 1C, except that a 125 μm thick polyimide film KH and a 125 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 13C, except that this 250 μm thick laminate film was used as the raw material film.

[0211] Example 17C A 125 μm thick polyimide film KH was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 500°C at an average heating rate of 10°C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume), and then the temperature was maintained at 500°C for 3 hours (heating step in mixed gas). The atmosphere was switched to nitrogen gas, and the temperature was increased to 800°C while maintaining a heating rate of approximately 10°C / min. Otherwise, a film-like graphite was obtained in the same manner as in Example 13C.

[0212] Example 18C A 175 μm thick laminate film was obtained in the same manner as in Example 1C, except that a 125 μm thick polyimide film KH and a 50 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 17C, except that this 175 μm thick laminate film was used as the raw material film.

[0213] Example 19C A 200 μm thick laminate film was obtained in the same manner as in Example 1C, except that a 125 μm thick polyimide film KH and a 75 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 17C, except that this 200 μm thick laminate film was used as the raw material film.

[0214] Example 20C A 250 μm thick laminate film was obtained in the same manner as in Example 1C, except that a 125 μm thick polyimide film KH and a 125 μm thick polyimide film KH were used. A filmy graphite was obtained in the same manner as in Example 17C, except that this 250 μm thick laminate film was used as the raw material film.

[0215] [Example 21C] A 50 μm thick polyimide film KH was used as the raw material film. The raw material film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450 °C at an average heating rate of 10 °C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume), and then the heating rate was maintained at approximately 0.2 °C / min from 450 °C to 550 °C (heating process in mixed gas). After the temperature was increased to 550 °C, the atmosphere was switched to nitrogen gas, and the heating rate was maintained at approximately 10 °C / min to 800 °C. After the carbonization process, the carbonized film was allowed to cool and then transferred to a graphitization furnace, where the graphitization process was carried out. A film-like graphite was obtained in the same manner as in Example 1C, except that in a graphitization furnace, the temperature was increased to 2800°C at a rate of about 10°C / min in an argon atmosphere, held at 2800°C for 1 hour, and then cooled to obtain a graphitized film.

[0216] [Example 22C] A filmy graphite was obtained in the same manner as in Example 21C, except that a 75 μm thick polyimide film KH was used as the raw material film.

[0217] [Example 23C] A 50 μm thick polyimide film KH was used as the raw material film. In a carbonization furnace, the temperature was increased from room temperature to 1000°C at an average heating rate of 5°C / min under a nitrogen gas atmosphere, and then maintained at that temperature for 1 hour. After the carbonization step, the carbonized film was allowed to cool and then transferred to a graphitization furnace, where the graphitization step was carried out. In the graphitization furnace, the temperature was increased to 2900°C under an argon atmosphere at a heating rate of approximately 1°C / min, maintained at 2900°C for 1 hour, and then cooled to obtain a graphitized film. A film-like graphite was obtained in the same manner as in Example 1C.

[0218] [Example 24C] A graphite film was obtained in the same manner as in Example 23C, except that a 125 μm thick polyimide film KH was used as the raw material film.

[0219] [Comparative example 1C] Film-like graphite (EYGS121803, thickness 25 μm) manufactured by Panasonic Corporation was used as a comparison.

[0220] [Comparative Example 2C] Film-like graphite (EYGS121805, thickness 50 μm) manufactured by Panasonic Corporation was used as a comparison.

[0221] [Comparative example 3C] Film-like graphite (EYGS121810, thickness 100 μm) manufactured by Panasonic Corporation was used as a comparison.

[0222] [Comparative Example 4C] Film-type graphite (Graphinity, thickness 40 μm) manufactured by Kaneka Corporation was used as a comparison.

[0223] [Comparative Example 5C] Film-like graphite (SDK, 40 μm) manufactured by Jiangsu Sidike New Material Technology Co., Ltd. was used for comparison.

[0224] [Comparative Example 6C] Film-like graphite (SDK, 70 μm) manufactured by Jiangsu Sidike New Material Technology Co., Ltd. was used for comparison.

[0225] The test results for the filmy graphite obtained in each of the Examples and Comparative Examples are shown in Table 4. Furthermore, the thermal conductivity of the filmy graphite of each of the Examples and Comparative Examples is plotted against the number N of multiple bright regions / film thickness H (μm) / film width W (μm) (CN) in Fig. 21, and the thermal conductivity of the filmy graphite of each of the Examples and Comparative Examples is plotted against the average area (AS) of multiple bright regions in Fig. 22.

[0226] [Table 4]

[0227] As shown in Table 4 and FIG. 21, the smaller the ratio (number of multiple bright regions N / film thickness H (μm) / film width W (μm) (CN)), the higher the thermal conductivity of the filmy graphite tends to be. The filmy graphite of Examples 1C, 2C, 5C, 8C, 9C, 13C, and 15C to 24C, in which CN was 0.015 or less, had high thermal conductivity and particularly excellent heat dissipation performance. Similarly, as shown in Figure 22, the larger the average area (AS) of multiple bright regions, the higher the thermal conductivity of the film-like graphite tends to be. 2 The film-like graphite of Examples 2C, 7C to 9C, and 13C to 22C had high thermal conductivity and particularly excellent heat dissipation performance. Furthermore, the filmy graphite of Examples 1C to 6C, 10 to 17C, and 19 to 22C, which had a (surface area / film area) ratio of 1.05 or more, had a small minimum bending radius and excellent flexibility. As shown in Figure 23, cracks and irregularities were observed on the surface of the filmy graphite of Example 3C, which suggests that pyrolysis gas was generated inside the film during the graphitization process, creating voids between the graphite crystallites, thereby improving flexibility.

[0228] [Raw film] In all of the following examples, Kapton (registered trademark) H type (hereinafter referred to as "PIKH") polyimide film manufactured by DuPont-Toray Co., Ltd. was used as the raw material film.

[0229] [Thermal diffusivity] The thermal diffusivity α of the film-like graphite in the direction along the film surface was measured in an environment of 23°C using a BETHEL Thermowave Analyzer TA33 in accordance with JIS R 7240 (2018) using the cyclic heating method. Five measurement frequencies were used: 60 Hz, 70 Hz, 75 Hz, 80 Hz, and 90 Hz. The average of the thermal diffusivities measured at each of the five frequencies was taken as the thermal diffusivity α of the film-like graphite in the direction along the film surface. The sample size for the measurement was 4 cm to 10 cm in length in the measurement direction and 1.5 cm to 10 cm in length in the direction perpendicular to the measurement direction on the film surface. The thickness of the cut sample was measured.

[0230] [density] The density d of the filmy graphite was calculated from the following formula 3 by measuring the weight of the filmy graphite in air and in ethanol. d=ρs×Wa / (Wa-Ws) Equation 3 However, the symbols in the formula 3 have the following meanings. d: Density of film-like graphite (g / cm 3 ) ρs: Density of ethanol (g / cm 3 ) Wa: Weight of film-like graphite in air (g) Ws: Weight of film-like graphite in ethanol (g)

[0231] [Fracture surface observation] Information on the internal structure of film-like graphite was obtained by observing the fracture surface of the film-like graphite during mode I crack propagation using a scanning electron microscope (SEM). Specifically, a rectangular specimen with a short side of 10 mm or more was cut from the film-like graphite. A 3 mm deep notch was made with a razor along a line connecting the centers of the two long sides of the specimen, from each long side. Tension was applied in the long-side direction, causing the crack to propagate and tear the specimen. The fracture surface of the torn specimen was observed with an SEM at an accelerating voltage of 10 kV, providing a contrast that allowed distinction between the specimen cross section and the background. The fracture surface was observed multiple times, changing the observation location so that a continuous stretch of 1 mm or more could be observed in the film plane direction.

[0232] [Compression test] In an environment of 25°C, a pressure of 100 MPa was applied to the entire film surface of the film-like graphite to compress it. The film thickness T of the film-like graphite before compression b (μm) and the film thickness after compression T a (μm), respectively, and T a / T b was calculated.

[0233] The pressing process in each of the following examples was carried out using a hydraulic calender-embosser manufactured by Yuri Roll Co., Ltd., according to the following procedure. The graphitized film was sandwiched between commercially available polyimide films and compressed under conditions of a linear pressure of 900 kg / cm to 2700 kg / cm and a roll rotation speed of 0.5 m / min. Compression was repeated until the difference in film thickness before and after compression was within 1 μm. The linear pressure was defined as the value obtained by dividing the load on the roll by the length of the graphitized film inserted into the roll in the roll width direction.

[0234] Example 1D One side of a 75 μm-thick polyimide film made of PIKH was coated with an N-methyl-2-pyrrolidone solution containing 20% by weight of polyamic acid, a polymer of oxydianiline and pyromellitic anhydride. Another 75 μm-thick polyimide film made of PIKH was then bonded to the coated side of the polyimide film, and excess solution was removed using a mangle. The bonded film was placed under a nitrogen atmosphere at atmospheric pressure and heated to 350°C at an average heating rate of 2°C / min. After holding for 1 hour, it was allowed to cool, resulting in a 150 μm-thick laminated film in which two 75 μm-thick polyimide films were firmly bonded. This laminated film was used as the raw film. The raw film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450°C at an average rate of 10°C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume), and then increased from 450°C to 550°C at a rate of approximately 0.2°C / min (heating process in organic gas). After increasing the temperature to 550°C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000°C at a rate of approximately 10°C / min and held there for 1 hour. After the carbonization process, the film was allowed to cool and then transferred to a graphitization furnace for the graphitization process. The graphitization furnace was heated to the temperature record shown in Figure 24 at a constant power output, and then cooled to obtain a graphitized film. The obtained graphitized film was sandwiched between two polyimide films and compressed seven times under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min to obtain a graphite film.

[0235] [Raw film] In all of the following examples, Kapton (registered trademark) H type (hereinafter referred to as "PIKH") polyimide film manufactured by DuPont-Toray Co., Ltd. was used as the raw material film.

[0236] [Thermal diffusivity] The thermal diffusivity α of the film-like graphite in the direction along the film surface was measured in an environment of 23°C using a BETHEL Thermowave Analyzer TA33 in accordance with JIS R 7240 (2018) using the cyclic heating method. Five measurement frequencies were used: 60 Hz, 70 Hz, 75 Hz, 80 Hz, and 90 Hz. The average of the thermal diffusivities measured at each of the five frequencies was taken as the thermal diffusivity α of the film-like graphite in the direction along the film surface. The sample size for the measurement was 4 cm to 10 cm in length in the measurement direction and 1.5 cm to 10 cm in length in the direction perpendicular to the measurement direction on the film surface. The thickness of the cut sample was measured.

[0237] [density] The density d of the filmy graphite was calculated from the following formula 3 by measuring the weight of the filmy graphite in air and in ethanol. d=ρs×Wa / (Wa-Ws) Equation 3 However, the symbols in the formula 3 have the following meanings. d: Density of film-like graphite (g / cm 3 ) ρs: Density of ethanol (g / cm 3 ) Wa: Weight of film-like graphite in air (g) Ws: Weight of film-like graphite in ethanol (g)

[0238] [Fracture surface observation] Information on the internal structure of film-like graphite was obtained by observing the fracture surface of the film-like graphite during mode I crack propagation using a scanning electron microscope (SEM). Specifically, a rectangular specimen with a short side of 10 mm or more was cut from the film-like graphite. A 3 mm deep notch was made with a razor along a line connecting the centers of the two long sides of the specimen, from each long side. Tension was applied in the long-side direction, causing the crack to propagate and tear the specimen. The fracture surface of the torn specimen was observed with an SEM at an accelerating voltage of 10 kV, providing a contrast that allowed distinction between the specimen cross section and the background. The fracture surface was observed multiple times, changing the observation location so that a continuous stretch of 1 mm or more could be observed in the film plane direction.

[0239] [Compression test] In an environment of 25°C, a pressure of 100 MPa was applied to the entire film surface of the film-like graphite to compress it. The film thickness T of the film-like graphite before compression b (μm) and the film thickness after compression, T a (μm), respectively, and T a / T b was calculated.

[0240] The pressing process in each of the following examples was carried out using a hydraulic calender-embosser manufactured by Yuri Roll Co., Ltd., according to the following procedure. The graphitized film was sandwiched between commercially available polyimide films and compressed under conditions of a linear pressure of 900 kg / cm to 2700 kg / cm and a roll rotation speed of 0.5 m / min. Compression was repeated until the difference in film thickness before and after compression was within 1 μm. The linear pressure was defined as the value obtained by dividing the load on the roll by the length of the graphitized film inserted into the roll in the roll width direction.

[0241] Example 1E One side of a 75 μm-thick polyimide film made of PIKH was coated with an N-methyl-2-pyrrolidone solution containing 20% by weight of polyamic acid, a polymer of oxydianiline and pyromellitic anhydride. Another 75 μm-thick polyimide film made of PIKH was then bonded to the coated side of the polyimide film, and excess solution was removed using a mangle. The bonded film was placed under a nitrogen atmosphere at atmospheric pressure and heated to 350°C at an average heating rate of 2°C / min. After holding for 1 hour, it was allowed to cool, resulting in a 150 μm-thick laminated film in which two 75 μm-thick polyimide films were firmly bonded. This laminated film was used as the raw film. The raw film was carbonized in a carbonization furnace. In the carbonization furnace, the temperature was increased from room temperature to 450°C at an average rate of 10°C / min in an atmosphere of nitrogen gas containing acetylene gas (acetylene gas concentration: 25% by volume), and then increased from 450°C to 550°C at a rate of approximately 0.2°C / min (heating process in organic gas). After increasing the temperature to 550°C, the atmosphere was switched to nitrogen gas, and the temperature was increased to 1000°C at a rate of approximately 10°C / min and held there for 1 hour. After the carbonization process, the film was allowed to cool and then transferred to a graphitization furnace for the graphitization process. The graphitization furnace was heated to the temperature record shown in Figure 25 with a constant power output, and then cooled to obtain a graphitized film. The obtained graphitized film was sandwiched between two polyimide films and compressed seven times under conditions of a linear pressure of 900 kgf / cm and a roll rotation speed of 0.5 m / min to obtain a graphite film. [Industrial Applicability]

[0242] According to the present invention, it is possible to provide a thick filmy graphite having high thermal conductivity and excellent heat dissipation performance, as well as excellent flexibility, at low cost, and a method for producing the filmy graphite. [Explanation of symbols]

[0243] 1: Light area 2: Film thickness measurement direction 3: Solid part 4: Void part

Claims

1. A filmy graphite that satisfies the following condition (1) or (2): Condition (1): The degree of graphite crystal orientation P relative to the film surface is 96% or more, and the thickness is 64 μm or more. Condition (2): The degree of graphite crystal orientation P relative to the film surface is 94% or more, and the thickness is 102 μm or more.

2. A filmy graphite that satisfies the following condition (3) or (4): Condition (3): The thickness a (μm) of the film is 102 μm or more and 200 μm or less, and the thermal conductivity b (W / mK) in the direction along the film surface is 1,550 W / mK or more. Condition (4): The film thickness a (μm) is 50 μm or more, the thermal conductivity b (W / mK) in the direction along the film surface is 1,350 W / mK or more, and a×b≧160,000.

3. A film-like graphite having a product (a×b) of a film thickness (a) (μm) and a thermal conductivity (b) (W / mK) in a direction along the film surface of 160,000 or more, and a film thickness (a) (μm) of 15 μm or more.

4. The filmy graphite according to any one of claims 1 to 3, which satisfies the following conditions (5) and (6): Condition (5): When the thickness of the film is a (μm) and the thermal conductivity in the direction along the film surface is b (W / mK), the following formula 1a is satisfied. 2750≦12a+b...Formula 1a Condition (6): The minimum bending radius measured in a bending test is 16 mm or less.

5. A film-like graphite, wherein the number N of a plurality of bright region areas obtained from an image obtained by binarizing bright and dark regions observed in a polarizing microscope image in a cross section perpendicular to the film surface of the film-like graphite, the film thickness H (μm), and the film width W (μm) satisfy the following formulas (8) and (9), the film has a multilayer structure in which a plurality of layers are superimposed on each other, the multilayer structure has a width of 40 μm or more and a thickness of 8 μm or more, and the direction of each layer of the multilayer structure forms an angle of 20° or less with the direction along the film surface: N / H / W≦0.04...(8) H≧102 (9)

6. In a cross section perpendicular to the film surface of film-like graphite, the average area of multiple bright areas obtained from an image obtained by binarizing bright and dark areas observed under a polarizing microscope is 9 μm ２ or greater, and has a film thickness of 102 μm or greater, includes a multilayer structure in which a plurality of layers are superposed on one another, the multilayer structure having a width of 40 μm or greater and a thickness of 8 μm or greater, and the direction of each layer of the multilayer structure forms an angle of 20° or less with the direction along the film surface.

7. The filmy graphite according to any one of claims 2 to 4, having a thickness of 58 µm or more.

8. 8. The filmy graphite according to any one of claims 1 and 3 to 7, which has a thermal conductivity b (W / mK) in a direction along the film surface of 800 W / mK or more.

9. Density is 1.7 g / cm ３ The filmy graphite according to any one of claims 1 to 8, wherein

10. 10. The filmy graphite according to claim 1, which has an electrical conductivity of 9,000 S / cm or more in a direction along the film surface.

11. 11. The filmy graphite according to any one of claims 1 to 4 and 7 to 10, comprising a multilayer structure in which a plurality of layers are superimposed on one another, the multilayer structure having a width of 40 μm or more and a thickness of 8 μm or more, and the direction of each layer of the multilayer structure forms an angle of 20° or less with the direction along the film surface.

12. 12. The filmy graphite according to claim 11, wherein each layer of the multilayer structure has a large number of projections and recesses, and adjacent layers are in contact with each other at a large number of locations.

13. 13. The filmy graphite according to claim 11 or 12, wherein each layer forming the multilayer structure has a flat surface or a smoothly curved surface, and adjacent layers are in close contact with each other.

14. 14. The filmy graphite according to any one of claims 1 to 3 and 5 to 13, which has a minimum bending radius of 16 mm or less as measured in a bending test.

15. The filmy graphite according to any one of claims 1 to 14, wherein, when compressed by applying a pressure of 100 MPa to the entire film surface of the filmy graphite in an environment of 25°C, the ratio (Ta / Tb) of the film thickness Ta after compression to the film thickness Tb before compression is 0.7 or more.

16. The filmy graphite according to any one of claims 1 to 15, which has a folding endurance of 10,000 or more folding cycles before fracture when measured in an unloaded U-shaped stretch test for a sheet body with a bending radius R of 2 mm and a bending angle of 180°.

17. 17. The filmy graphite according to any one of claims 1 to 16, which has a thermal conductivity in a direction perpendicular to the film surface of 1 W / mK or more and 20 W / mK or less.

18. 18. The filmy graphite according to any one of claims 1 to 17, wherein the ratio of the surface area to the film area (surface area / film area) is 1.05 or more.

19. The filmy graphite according to any one of claims 1 to 18, wherein the filmy graphite does not include a layer of an adhesive or pressure-sensitive adhesive in the film thickness direction.

20. 20. The filmy graphite according to any one of claims 1, 2, and 4 to 19, wherein the product (a × b) of the film thickness a (µm) and the thermal conductivity b (W / mK) in the direction along the film surface is 88,000 or greater.

21. The filmy graphite according to any one of claims 1 to 4 and 6 to 20, wherein the number N of a plurality of bright region areas obtained from an image obtained by binarizing bright and dark regions observed in a polarizing microscope image in a cross section perpendicular to the film surface of the filmy graphite, the film thickness H (µm), and the film width W (µm) satisfy the following formula (7), or (8) and (9): N / H / W≦0.015...(7) N / H / W≦0.04...(8) H≧102 (9)

22. In a cross section perpendicular to the film surface of the film-like graphite, the average area of multiple bright areas obtained from an image obtained by binarizing bright and dark areas observed under a polarizing microscope is 22 μm ２ or more, or the film thickness is 42 μm or more and the average area is 9 μm ２ The filmy graphite according to any one of claims 1 to 5 and 7 to 21, wherein

23. A method for producing filmy graphite, comprising: a carbonization step of carbonizing a raw material film made of an organic polymer to obtain a carbonized film; and a graphitization step of graphitizing the carbonized film to obtain a graphitized film, the carbonization step includes a mixed gas heating step of heating the raw material film in a mixed gas of an organic gas and an inert gas, A method for producing filmy graphite, wherein the thickness of the filmy graphite is 15 μm or more.

24. 24. The method for producing filmy graphite according to claim 23, wherein the mixed gas contains a gaseous substance (A) consisting of at least one of acetylene and an acetylene derivative, and an inert gas.

25. 25. The method for producing filmy graphite according to claim 23 or 24, wherein at least a part of the heating step in the mixed gas is carried out at a temperature equal to or lower than Tf as described below. Tf (°C) is the highest temperature at which the observed weight loss rate (weight loss per unit time) of the measurement sample is 10% or more of the maximum weight loss rate in a thermogravimetric measurement in which a measurement sample made of the raw material film is heated to 1000°C at a temperature increase rate of 10°C / min while nitrogen gas is flowing at a flow rate of 200 mL / min and the temperature and weight of the measurement sample are recorded.

26. 26. The method for producing filmy graphite according to claim 25, wherein the temperature rise pattern obtained by monotonically raising the temperature in the heating step in the mixed gas includes a period of 30 minutes or more in which an average temperature rise rate is 5° C. / min or less in a temperature region of not less than Ts and not more than Tf as follows: Ts (°C) is the lowest temperature among temperatures of 100°C or higher at which the weight loss rate of the measurement sample observed in the thermogravimetry is 0.8% or more of the maximum weight loss rate.

27. The method for producing filmy graphite according to any one of claims 23 to 26, wherein a maximum heating temperature Tmax in the graphitization step is 2400°C or higher and 2900°C or lower.

28. The method for producing filmy graphite according to any one of claims 23 to 27, wherein the raw material film is a laminated film formed by bonding two or more polymer films made of organic polymers together with a pressure-sensitive adhesive or adhesive.

29. A battery which is a lithium ion secondary battery or an all-solid-state battery, in which the filmy graphite according to any one of claims 1 to 22 is used as a current collector or as a negative electrode active material and a negative electrode current collector.

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