Film-like graphite

Abstract

To provide a film-like graphite having high thermal conductivity, especially, to provide a film-like graphite having excellent thermal conductivity while the film is thick.SOLUTION: Disclosed is a film-like graphite satisfying the following condition (1) or the condition (2). The condition (1): in the X-ray diffraction (XRD) measurement, an integral width B of a diffraction peak of a (100) plane derived from a graphite crystal detected neighboring 2θ=42.4° measured by a θ / 2θ scanning method is 0.235°or under. The condition (2): the integral width B is 0.255°or under and a film thickness H of the film-like graphite is 39 μm or over.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to film-like graphite.

Background Art

[0002] Electronic devices such as smartphones have significantly improved data processing capabilities, and accordingly, the amount of heat generated has also increased significantly. On the other hand, electronic devices have become smaller and thinner, and there is a demand for higher performance and lighter weight for heat dissipation members inside the electronic devices. Film-like graphite is known as a heat dissipation member that is lighter than metals, has excellent heat dissipation performance, and is flexible (for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, due to the increasing required heat dissipation performance, the demand for film-like graphite with a higher thermal conductivity than before has been increasing. However, the conventional technology has insufficient heat dissipation performance, and it has been difficult to obtain a film-like graphite with a particularly thick film and a high thermal conductivity.

[0005] Patent Document 1 discloses that the foaming state of a graphite film can be known by checking the amount of boundary lines (wrinkles) from the SEM image of the graphite film surface, and the superiority or inferiority of the bending resistance can be predicted therefrom. However, the graphite film of Patent Document 1 has insufficient thermal conductivity, and its thermal conductivity only reaches about 1,400 W / mK.

[0006] Patent Document 2 discloses that by forming a very high-density graphite layer near the film surface and forming a mixed layer of an air layer / graphite layer rich in an air layer inside, a graphite film having both high thermal conductivity and flexibility can be provided. However, even with this method, the thermal conductivity only reaches about 1,320 W / mK.

[0007] Patent Document 3 discloses that a thermal conductivity of 1,800 W / mK can be achieved by making the thickness of the graphite sheet 9.6 μm or less. However, the heat transport amount depends on both the thermal conductivity and the thickness, and when the film thickness is small, the heat transport amount also decreases.

[0008] As described above, methods for obtaining film-like graphite with excellent thermal conductivity have been studied in the past. However, especially for thick films, only those with low thermal conductivity have been obtained, and film-like graphite that maintains a high thermal conductivity regardless of the film thickness is required.

[0009] An object of the present invention is to provide film-like graphite having high thermal conductivity. In particular, it provides film-like graphite having excellent thermal conductivity despite the film being thick.

Means for Solving the Problems

[0010] The present invention has the following aspects. [1] Film-like graphite that satisfies the following condition (1) or condition (2). Condition (1): In X-ray diffraction (XRD) measurements, the integral width B of the diffraction peak of the (100) plane originating from the graphite crystal detected near 2θ = 42.4° by the θ / 2θ scan method is 0.235° or less. Condition (2): The integral width B is 0.255° or less, and the film thickness H of the film-like graphite is 39 μm or more. [2] The film-like graphite according to [1], wherein the integral width B of condition (2) is 0.245° or less. [3] The film-like graphite according to [1] or [2], wherein the film thickness H of the above condition (2) is 55 μm or more. [4] A film-like graphite according to any one of [1] to [3], wherein the degree of graphite crystal orientation P with respect to the film surface is 94% or more. [5] The film-like graphite according to [1] to [4], wherein, in condition (1) above, the integral width B is 0.235° or less and the film thickness H of the film-like graphite is 42 μm or more. [6] A film-like graphite in which the product (B × F) of the integral width B of the diffraction peak of the (100) plane originating from the graphite crystal detected near 2θ = 42.3° by the θ / 2θ scan method in X-ray diffraction (XRD) measurements and the half-width F(°) of the diffraction profile obtained from the ω scan of the diffraction peak of the (002) plane originating from the hexagonal graphite crystal detected near 2θ = 26.5° by the θ / 2θ scan method in X-ray diffraction (XRD) measurements is 3.0 or less. [7] A film-like graphite according to any one of [1] to [5], wherein the product (B × F) of the integral width B of the diffraction peak of the (100) plane originating from the graphite crystal detected near 2θ = 42.3° by the θ / 2θ scan method in X-ray diffraction (XRD) measurement and the half-width F(°) of the diffraction profile obtained from the ω scan of the diffraction peak of the (002) plane originating from the hexagonal graphite crystal detected near 2θ = 26.5° by the θ / 2θ scan method in X-ray diffraction (XRD) measurement is 3.0 or less. [8] A film-like graphite according to any of [1] to [7], wherein the thermal conductivity b in the film plane direction is 1,500 W / mK or more. [9] A film-like graphite as described in any of [1] to [8], having an electrical conductivity of 6,000 S / cm or more.

[10] A film-like graphite as described in any of [1] to [9], wherein the minimum bending radius is 16 mm or less.

[11] Density is 1.7 g / cm³ 3 The above describes the film-like graphite described in any of [1] to

[10] .

[12] A film-like graphite according to any of [1] to

[11] , wherein the ratio of surface area to film area (surface area / film area) is 1.05 or greater.

[13] A film-like graphite according to any of [1] to

[12] , wherein the number of multiple bright areas N obtained from an image obtained by binarizing the bright and dark areas observed by polarizing microscope images 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). N / H / W ≤ 0.011···(7)

[14] A film-like graphite according to any of [1] to

[13] , wherein the number N of multiple bright areas obtained from an image obtained by binarizing the bright and dark areas observed by polarizing microscope images 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) of the film-like graphite satisfy the following formulas (8) and (9). N / H / W ≤ 0.04 ···(8) H≧42···(9)

[15] In a cross section perpendicular to the film surface of a film-like graphite, the average area AS of multiple bright regions obtained from a binarized image of bright and dark regions observed by polarized light microscopy is 22 μm². 2 The film-like graphite described in any of the above [1] to

[14] .

[16] In a cross section perpendicular to the film surface of a film-like graphite, the average area AS of multiple bright regions obtained from a binarized image of bright and dark regions observed by polarized light microscopy is 9 μm². 2A film-like graphite as described above and having a film thickness of 42 μm or more, as described in any of [1] to

[15] .

[17] A film-like graphite as described in [1] to

[16] , having a thickness of 39 μm or more.

[18] A film-like graphite according to any one of [1] to

[17] , wherein the full width at half maximum of the (002) diffraction peak is 10.8° or less in X-ray diffraction (XRD) measurements.

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

[18] , wherein the integral width B of the diffraction peak is 0.231° or less.

[20] A film-like graphite as described in any of [1] to

[19] , wherein, in a planar no-load U-shaped stretch test, the number of folds before fracture is 10,000 or more when measured with a bending radius R of 2 mm and a bending angle of 180°.

[21] A film-like graphite that does not contain an adhesive or tack in the film thickness direction, as described in any of [1] to

[21] . [Effects of the Invention]

[0011] The film-like graphite of the present invention exhibits excellent thermal conductivity in the planar direction. [Brief explanation of the drawing]

[0012] [Figure 1] This is an example of a diffraction profile of the (100) plane originating from the hexagonal graphite crystal, detected near 2θ = 42.3° in a wide-angle X-ray diffraction measurement (transmission method, θ / 2θ scan method) of the film-like graphite of Example 1. [Figure 2] This is an example of a diffraction profile obtained by ω scanning of the diffraction peak of the (002) plane originating from the hexagonal graphite crystal detected near 2θ = 26.5° in a wide-angle X-ray diffraction measurement method (reflection method, θ / 2θ scan method) of the film-like graphite of Example 1. [Figure 3] This is an example of an image obtained by observing the surface of the film-like graphite of Example 1 with a laser microscope. [Figure 4]This is an example of a simple polarized image (PO image) observed with a polarizing microscope in a cross-section perpendicular to the film surface of the film-like graphite of Example 3. [Figure 5] This is an example of a simple polarized image (PO image) observed with a polarizing microscope in a cross-section perpendicular to the film surface of the film-like graphite of Comparative Example 2. [Figure 6] This is a plot of the weight loss rate (weight loss per unit time) against temperature for the raw material film used in the example. [Figure 7] This is the temperature record of the graphitization process in Example 1. [Figure 8] This is the temperature record of the graphitization process in Example 2. [Figure 9] This is the temperature record of the graphitization process in Example 5. [Figure 10] This is a schematic diagram showing the heat dissipation test. [Figure 11] The thermal conductivity of the film-like graphite of each example and comparative example is plotted against the integral width B of the diffraction peak of the (100) plane derived from the graphite crystal. [Modes for carrying out the invention]

[0013] In this specification, "film-like graphite" means a flexible, film-like material that is primarily composed of graphite and consists substantially only of carbon.

[0014] The film-like graphite of the present invention satisfies either condition (1) or condition (2) below. Condition (1): In X-ray diffraction (XRD) measurements, the integral width B of the diffraction peak of the (100) plane originating from the graphite crystal detected near 2θ = 42.3° by the θ / 2θ scan method is 0.235° or less. Condition (2): The integral width B is 0.255° or less, and the film thickness H of the film-like graphite is 39 μm or more.

[0015] The film-like graphite of the present invention preferably has an integrated width B of the diffraction peak of the (100) plane originating from the graphite crystal of 0.255° or less, more preferably 0.235° or less, even more preferably 0.231° or less, and particularly preferably 0.227° or less. A lower value of the integration width B indicates a larger crystallite size in the a-axis direction of the graphite crystal, and the thermal conductivity of the film-like graphite increases in the direction in which this a-axis is oriented. There is no particular lower limit to the integration width B, but if the integration width B is too low, the resulting film tends to be less flexible, so in practice, a value of 0.100° or higher is preferable.

[0016] The integral width B of the diffraction peak of the (100) plane originating from the graphite crystal in film-like graphite can be determined using wide-angle X-ray diffraction measurement methods (transmission method, θ / 2θ scan method) as follows. (Method for evaluating the integral width B of the diffraction peak of the (100) plane originating from graphite crystals) As the measuring device, an X-ray diffractometer using CuKα rays as the source is used. A fully automated multi-purpose X-ray diffractometer such as the SmartLab manufactured by Rigaku Corporation can be used. The film-like graphite is fixed to the sample stage so that the angle of incidence of the incident X-rays and the angle of reflection of the reflected X-rays are equal in the direction perpendicular to the film surface of the film-like graphite, and the one-dimensional X-ray diffraction spectrum of the film-like graphite in the 2θ direction is measured using the θ / 2θ scanning method (transmission method). This yields a diffraction profile such as that shown in Figure 1. The integral width B(°) of the reflection diffraction peak of the (100) plane originating from the hexagonal graphite, detected near 2θ = 42.3°, is read from the measurement.

[0017] The thickness of the film-like 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 39 μm or more, even more preferably 42 μm or more, even more preferably 55 μm or more, particularly preferably 58 μm or more, and most preferably 72 μm or more. Furthermore, there is no particular upper limit to the thickness of the film-like graphite of the present invention, but if it is too thick, it will have poor flexibility, so a thickness of 1,000 μm or less is preferred, 500 μm or less is more preferred, and 250 μm or less is even more preferred. If the thickness is below the aforementioned upper limit, it becomes easier to make electronic devices and other devices thinner. Furthermore, it becomes easier to ensure a certain degree of flexibility in the graphite film. The "thickness" referred to here is the average of the thickness measured using a standard outside micrometer at five randomly selected locations for each of the polymer film, raw material film, carbonized film, graphitized film, and film-like graphite.

[0018] The degree of graphite crystal orientation P of the film-like graphite of the present invention with respect to the film plane direction is preferably 94.0% or more, more preferably 94.5% or more, and even more preferably 95.0% or more. The higher the degree of crystal orientation P of the graphite, the higher the thermal conductivity of the film-like graphite in the direction of the film surface. There is no particular upper limit to the graphite crystal orientation P, but if the crystal orientation is too high, the resulting film will have poor flexibility, so it is practically preferable to have an orientation of 99% or less.

[0019] The degree of graphite crystal orientation P in the film plane direction of a film-like graphite can be determined using wide-angle X-ray diffraction measurement (reflection method, θ / 2θ scan method), as described later in the examples. (Method for evaluating the degree of orientation P of graphite crystals) As the measuring device, an X-ray diffractometer using CuKα rays as the radiation source is used. A fully automated multi-purpose X-ray diffractometer such as the SmartLab manufactured by Rigaku Corporation can be used. The film-like graphite is fixed to the sample stage so that the angle of incidence of the incident X-rays and the angle of reflection of the reflected X-rays are equal in the direction perpendicular to the film surface of the film-like graphite, and the one-dimensional X-ray diffraction spectrum of the film-like graphite in the 2θ direction is measured using the θ / 2θ scan method (reflection method). In the spectrum obtained from this measurement, the position of the reflection diffraction peak of the (002) plane originating from the hexagonal graphite, detected near 2θ = 26.5°, is read. 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 yields a diffraction profile, for example, as shown in Figure 2. The full width at half maximum F(°) 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.

[0020]

number

[0021] The product (B×F) of the integral width B(°) and the half-width F(°) of the film-like graphite of the present invention is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. A smaller product (B×F) means that the crystallite size in the a-axis direction of the graphite crystal is larger and the a-axis is oriented toward the film plane of the film-like graphite, resulting in a higher thermal conductivity of the film-like graphite in the film plane direction. There is no particular lower limit to the product (B×F), but if the product (B×F) is too small, the film tends to have poor flexibility, so it is substantially preferable to have a product of 0.1 or more.

[0022] The film-like graphite of the present invention preferably has a thermal conductivity b in the film plane direction of 1,500 W / mK or more. If the thermal conductivity is 1,500 W / mK or more, good heat dissipation performance is likely to be obtained. From this perspective, the thermal conductivity is more preferably 1,600 W / mK or more, and even more preferably 1,700 W / mK or more. There is no particular limit on the upper limit, but 2,500 W / mK or less is preferable, 2,300 W / mK or less is even more preferable, and 2,100 W / mK or less is even more preferable.

[0023] The film-like graphite of the present invention preferably has an electric conductivity of 6,000 S / cm or more. If the electric conductivity is 6,000 S / cm or more, electric conduction by the film-like graphite proceeds efficiently and it can be used as a conductive material, which is preferable. The higher the electric conductivity in the direction along the film surface of the film-like graphite of the invention, the better, more preferably 7,000 S / cm or more, and even more preferably 8,000 S / cm or more. The substantial upper limit is preferably 30,000 S / cm or less.

[0024] The density of the film-like graphite of the present invention is preferably 1.7 g / cm 3 or more, more preferably 1.8 g / cm 3 or more, and even more preferably 1.9 g / cm 3 or more. If the density of the film-like graphite is at least the lower limit value, the amount of voids that is a factor inhibiting heat conduction decreases, and the thermal conductivity increases. Also, the density of the film-like graphite of the present invention is preferably 2.2 g / cm 3 or less, more preferably 2.1 g / cm 3 or less, and even more preferably 2.0 g / cm 3 or less. If the density of the film-like graphite is at most the upper limit value, it is easy to ensure the flexibility of the film-like graphite due to the presence of some voids.

[0025] The ratio of surface area to film area (surface area / film area) of the film-like graphite of the present invention is preferably 1.05 or higher, more preferably 1.06 or higher, and even more preferably 1.07 or higher. The higher the surface area / film area, the greater the degree of foaming that occurs in the graphitization process of the film-like graphite, resulting in the insertion of a moderate amount of voids into the film and a film-like 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 lower the thermal resistance at the interface caused by the irregularities on the film surface. For this reason, it is preferably 1.5 or lower, and more preferably 1.3 or lower.

[0026] (Method for evaluating surface area / film area) Here, "surface area / film area" is defined as the ratio of the surface area, calculated from the surface shape observed by a laser microscope, to the film area of ​​that observed range. A laser microscope is used as the measuring device. A laser microscope with sufficient performance, such as the VK-X100 shape measuring laser microscope manufactured by Keyence Corporation, can be used. A 5×5cm piece of film-like graphite is placed on the sample stage so that the film does not curl and the film surface faces upwards. The objective lens is set to 50x magnification with 2048×1536 pixels, and the objective lens is moved in the Z-axis direction (height direction) in increments of 0.12 μm to obtain surface shape data of the sample. This yields an image like the one shown in Figure 3. The surface area is calculated from the surface shape data of the obtained sample, and its ratio to the film area (surface area / film area) is calculated.

[0027] (Mechanism of Flexibility Development) The film-like graphite of the present invention is flexible and has excellent bending resistance. The mechanism is thought to be as follows: During the graphitization process in manufacturing, thermal decomposition gas is generated inside the film, creating voids between the graphite crystallites. These voids make it easier for the graphite crystallites to slide, and the entire film can be bent without the graphite crystallites being destroyed by the stress generated when bending. When thermal decomposition gas is generated inside the film, the release of the gas to the outside of the film causes cracks to form on the film surface. Furthermore, the formation of voids inside the film disrupts the orientation of the graphite crystals, which is observed as unevenness on the film surface. The inventors have used a ratio (surface area / film area) as an indicator of such film surface shape and have found that when this value is 1.05 or higher, the film-like graphite also possesses excellent flexibility.

[0028] The film-like graphite of the present invention preferably has a minimum bending radius of 16 mm or less. If the minimum bending radius is 16 mm or less, it has sufficient flexibility and is easy to handle. From these viewpoints, the minimum bending radius is more preferably 10 mm or less, even more preferably 5 mm or less, and particularly preferably 3 mm or less.

[0029] In the present invention, the film-like graphite preferably has a resistance to 10,000 or more folds before breaking when measured in a planar unloaded U-shaped stretch test with a bending radius R of 2 mm and a bending angle of 180°.

[0030] In the planar U-shaped stretch test of the film-like graphite of the present invention, when the bending radius R is 2 mm and the bending angle is 180°, the number of times it can withstand bending is preferably 10,000 times or more, more preferably 20,000 times or more, and even more preferably 30,000 times or more. If the number of times the film-like graphite can withstand bending is equal to or greater than the lower limit, the handling when attached to electronic devices will be improved, and even when used in bending parts or parts that are repeatedly bent in electronic devices, breakage and cracking will be less likely to occur. The more times the number of times it can withstand bending, the better, and there is no particular lower limit, but in practice it is 1,000,000 times or less.

[0031] The film-like graphite of the present invention has a ratio of 0.011 or less for the number of multiple bright areas N / film thickness H (μm) / film width W (μm) (hereinafter, N / H / W is denoted as CN) obtained from a binarized image of bright and dark areas observed by a polarized microscope image of a cross-section perpendicular to the film surface of the film-like graphite. Furthermore, in another example of the embodiment, the film-like graphite has a CN value of 0.04 or less and a film thickness H of 42 μm or more. In addition, in another example of the embodiment, the film-like graphite has an average area (hereinafter referred to as AS) of 22 μm 2 That concludes the explanation. Furthermore, in yet another embodiment, the film-like graphite has an average area AS of 9 μm². 2 The above conditions are met, and the film thickness H is 42 μm or more.

[0032] The CN value of the film-like 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 value, the higher the thermal conductivity of the graphite film in the direction of the film surface. There is no particular lower limit for the CN value, but if the CN value is too low, the film will have poor flexibility or, in fact, a film that does not have a crystalline structure and therefore has low thermal conductivity. In practice, the lower limit is around 0.001. Furthermore, the average area AS of the film-like graphite of the present invention is 9 μm². 2 The above is preferable, and 10 μm 2 The above is more preferable, 12 μm 2 More preferably, 16 μm 2 This is particularly preferred, and 22 μm 2 Most preferable. The larger the average area AS, the higher the thermal conductivity of the film-like graphite in the film plane direction. There is no particular lower limit to AS, but if the average area AS is too low, the film will have poor flexibility, so it is practically 100 μm. 2 The degree is the lower limit.

[0033] The CN value of the film-like graphite and the average area AS can be determined using a polarizing microscope as follows. (Method for evaluating the number of bright areas N / film thickness H (μm) / film width W (μm), and the average area AS of the multiple bright areas) The graphite film is cut into strips using a cutter (or ultrasonic cutter), embedded in resin, and prepared as a sample. Next, the sample is polished with a handy wrap to completely remove the epoxy resin covering the observation surface (cross-section), and then a flat sample cross-section is prepared using a cross-section polisher with an argon ion beam. Bright-field images (BF images) and simple polarized images (PO images) are obtained using a digital microscope. The simple polarized image (PO image) is observed at the crossed nicols (orthogonal nicols) position, and the angle of the sample stage on which the sample is placed is adjusted so that the brightness of the bright areas in the sample is maximized. Using image analysis software, a binarized image is obtained from the acquired PO image, showing 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 after binarization is measured and defined as the number of bright areas N. The film thickness H is determined by using image analysis software to remove the voids observed inside the film-like graphite from the BF image obtained above, and then measuring the total length of the solid portion observed perpendicular to the film surface of the film-like graphite. The film width W is defined as the width of the film-like graphite in the direction of the film surface when measuring the count from the PO image described above. The CN value is calculated from the count, film thickness, and film width obtained using the above method. The average area AS of multiple bright areas is obtained by calculating the average area AS of multiple bright areas obtained by the above method using image analysis software or the like.

[0034] [Mechanism of thermal conductivity] The mechanism by which a film-like graphite with excellent thermal conductivity in the film plane direction can be obtained is as follows. Thermal conductivity in graphite is primarily due to lattice vibrations, i.e., phonon conduction. Phonon-mediated thermal conductivity depends on the crystal integrity of the solid; the larger the crystallite size of the graphite, the higher the phonon-mediated thermal conductivity. Phonon propagation in graphite occurs along the basal plane (ab-axis) of the graphite. Therefore, in a graphite film, the more the basal plane of the larger crystallite size graphite crystals is oriented relative to the film plane, the higher the thermal conductivity of the graphite film in the direction of the film plane. Polarizing microscopes are one evaluation method that can assess the crystallinity and crystal orientation of graphite and polymer materials. Graphite exhibits optical anisotropy because it is an optically uniaxial crystal. When observed under crossed nicols with a polarizing microscope, areas where graphite crystals are oriented in a specific direction (where the two vibration directions of the graphite crystal do not coincide with the vibration directions of both nicols, i.e., oriented in a direction that does not coincide with the extinction position) appear bright. Figures 4 and 5 show examples of images observed with a cross-sectional polarizing microscope perpendicular to the film surface of a graphite film. The continuously bright areas (bright regions) are thought to reflect the orientation of the graphite crystals in a certain direction. Therefore, by analyzing these bright areas in the observed image, it is possible to evaluate the crystallinity and orientation of the graphite film. As a result of diligent research, the inventors have found that the number of multiple bright regions N / film thickness H (μm) / film width W (μm) (hereinafter, N / H / W will be referred to as CN) obtained from a binarized image of bright and dark regions observed in a polarized microscope image of a cross-section perpendicular to the film surface of film-like graphite correlates well with the thermal conductivity of film-like graphite. Specifically, they found that the smaller the value of CN, the higher the thermal conductivity of film-like graphite in the direction of the film surface. This is because when individual graphite crystallites are small and many crystallites are dispersed in the film, the bright regions are separated and observed in large numbers, resulting in a larger value of CN. Conversely, as graphite crystallites coalesce and the crystallite size increases, the value of CN decreases. In other words, it is thought that the smaller the value of CN, the fewer the interfaces between graphite crystallites, the less likely phonons are to disperse, and the higher the thermal conductivity. Furthermore, in another embodiment, it was found that the average area AS of multiple bright regions also correlates with the thermal conductivity. Specifically, it was found that the larger the average area AS, the higher the thermal conductivity of the film-like graphite in the direction of the film plane. This is thought to be because the larger the average area AS of the bright regions, the larger the size of the graphite crystallites, and thus the higher the thermal conductivity due to phonons.

[0035] The film-like graphite of the present invention, as described above, has high thermal conductivity in the direction of the film surface and excellent heat dissipation performance. Moreover, this characteristic holds true regardless of the film thickness, even for thick film-like graphite. Furthermore, a ratio (surface area / film area) of 1.05 or higher results in excellent flexibility.

[0036] The film-like graphite of the present invention preferably consists of a single film-like graphite and does not contain any adhesive or bonding agent layers in the film thickness direction. Methods for obtaining thick film-like graphite include laminating multiple film-like graphite sheets with adhesive or bonding agents, covering multiple film-like graphite sheets with a coating material, or fixing multiple film-like graphite sheets with a metal jig. However, such methods have problems: the presence of adhesive or bonding layers with low thermal conductivity between the films reduces thermal conductivity, or air can enter, creating high contact thermal resistance. The film-like graphite of the present invention consists of a single thick film-like graphite sheet, thus achieving higher thermal conductivity when compared at the same thickness.

[0037] The film-like graphite of the present invention, as described above, is thick and has high thermal conductivity, giving it excellent heat dissipation performance, and it is also flexible. Therefore, there is no need to use multiple layers of conventional thin film-like graphite. This eliminates the need to include layers with low thermal conductivity, such as adhesives, and makes it possible to make the heat sink thinner without compromising the overall performance of the heat sink.

[0038] [Method for manufacturing film-like graphite] The present invention relates to a method for producing film-like graphite, wherein the heating step for heating the raw material film preferably includes the carbonization step and the graphitization step described below. Furthermore, the present invention relates to a method for producing film-like graphite, wherein the method for producing film-like graphite further preferably includes the pressing step described below. Carbonization process: A carbonized film is obtained by carbonizing a raw material film made of organic polymer. Graphitization process: The carbonized film is graphitized to obtain a graphitized film. Pressing process: The graphitized film is compressed or rolled. In this invention, "carbonization" means heating the organic polymer constituting the raw material film to vaporize volatile components from the organic polymer and transform it into a carbon-rich substance. In this invention, "carbonized film" means a film containing a carbonaceous structure due to carbonization, in which elements other than carbon have been removed until the mass percentage of elements other than carbon in the film is 20% or less. In this invention, "graphitization" means further heating the carbonized film at a high temperature to almost completely remove impurities other than carbon and to highly advance graphitization. "Graphitized film" means a film with an extremely high degree of graphitization and rich in graphite crystal structure.

[0039] (Raw material 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. If the thickness of the raw material film is above the lower limit, it is easier to obtain a thick film-like graphite with high heat dissipation performance per sheet, thus reducing the number of film-like graphite sheets required for heat dissipation in electronic devices, etc. Furthermore, the thickness of the raw material film is preferably 2,000 μm or less, more preferably 1,000 μm or less, and even more preferably 500 μm or less. If the thickness of the raw material film is below the upper limit, the amount of foaming during heating is small, and there is less variation in performance between the inside and surface of the film, making it easier to obtain a high-quality film-like graphite. In addition, it becomes easier to ensure a certain degree of flexibility while making the resulting film-like graphite thick.

[0040] The raw material film is a film made of organic polymers. As organic polymers, those having aromatic rings and molecular chains with a certain degree of planarity, orientation, and rigidity are preferred. Examples of polymers having aromatic rings include polyimide, polyamide, polythiazole, polyoxadiazole, polybenzoxazole, polybenzobisoxazole, polybenzothiazole, polybenzobisthiazole, polybenzimidazole, polybenzobisimidazole, and poly(p-phenylenevinylene). 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.

[0041] As the raw material film, a laminated film may be used, which is made by bonding two or more polymer films made of organic polymers together with an adhesive or bonding agent. The adhesive is not particularly limited, but it is preferable to include diamines or acid anhydrides, which are monomers of polyimide, or polyamic acids obtained by polymerizing them, as adhesive components. 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 adhesive is preferably prepared by dissolving the adhesive components in a low-volatility organic solvent. Adhesives containing tackifiers, phenolic resin adhesives, acrylic adhesives, melamine adhesives, silicone adhesives, etc., may also be used.

[0042] There are no particular restrictions on the means of applying the adhesive to the polymer film, as long as it can be applied uniformly. It is preferable to remove excess adhesive by passing the polymer films through a pressure roll after lamination, thereby making the adhesive between the polymer films as thin as possible. The thickness of the adhesive between the polymer films is not particularly limited, but 1 μm or less is preferred. Making the adhesive thin makes it easier to suppress foaming during the carbonization process. Alternatively, the polymer film may be bonded together, heated to remove the organic solvent, and then the carbonization process may be carried out. The heating temperature for removing the organic solvent is preferably 350°C or higher.

[0043] (carbonization process) In the carbonization process, for example, the raw material film is heated to 1,500°C or less in an inert gas or a mixed gas of organic and inert gases, and elements other than carbon are removed until the mass percentage of elements other than carbon in the raw material film is 20% or less. In the carbonization process, the temperature may be raised continuously, or it may be raised in stages with a period of holding the temperature constant. Alternatively, the temperature may be lowered after raising and then raised again. The carbonization process may be a batch heating method or a continuous supply heating method in which the raw material film is continuously supplied.

[0044] The carbonization process preferably includes a mixed gas heating step in which the raw material film is heated in a mixed gas mixture of an organic gas and an inert gas. In manufacturing methods that do not include a mixed gas heating step, if the film is heated rapidly in the graphitization process, the pressure of the gas generated by the decomposition of the carbonized film can easily cause delamination or breakage within the film, thus reducing the thermal conductivity of the film-like graphite. However, by including a mixed gas heating step in the carbonization process, even if the heating rate in the graphitization process is high, film breakage caused by the gas generated by the decomposition of the carbonized film can be suppressed, making it easy to obtain film-like graphite with high thermal conductivity. Heating the raw material film in a mixed gas mixture of an organic gas and an inert gas not only suppresses the loss of carbon due to decomposition, but also allows 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 surface area, and ultimately, a film-like graphite with a large surface area can be obtained.

[0045] In a carbonization process that includes a heating step in a mixed gas, further heating in an inert gas may be performed after the heating step in the mixed gas, or the heating step in the mixed gas may be performed after heating the raw material film in an inert gas. Alternatively, the entire carbonization process may be considered as a heating step in a mixed gas.

[0046] Any inert gas that does not react with the raw material film can be used, and examples include nitrogen gas, argon gas, or a mixture thereof. Among these, nitrogen gas is preferred due to its economic advantages. The inert gas used in the carbonization process may be one type or two or more types.

[0047] The organic gas is an organic compound that becomes a gas at the heating temperature of the carbonization process. The organic gas is not particularly limited, and examples include hydrocarbons that are gaseous at 23°C and 1 atm, such as methane, ethane, ethylene, and acetylene. Even organic compounds that are liquid or solid at 23°C and 1 atm can be used as organic gases if they become gaseous at the heating temperature of the carbonization process. As for 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 the loss of carbon due to decomposition. The organic gas used in the carbonization process may be one type or two or more types.

[0048] The concentration of organic gas in the mixed gas depends on the type of organic gas, but 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. If the concentration of organic gas is above the lower limit, the loss of carbon due to decomposition is easily suppressed, and the carbon in the organic gas is efficiently incorporated into the raw material film, making it easier to obtain a film-like graphite with a large surface area, thus improving productivity. Furthermore, in the case of acetylene gas, the concentration of 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. If the concentration of organic gas is below the upper limit, the use of organic gas beyond what is necessary is avoided, leading to cost reduction and industrial stability.

[0049] In the heating process in the mixed gas heating step, it is preferable to include a period of 30 minutes or more (hereinafter referred to as the "slow heating period") in the heating pattern with a monotonic heating history. This makes it easier for carbon in the organic gas to be efficiently incorporated into the raw material film, and also helps to suppress the loss of carbon due to thermal decomposition. Here, the "heating pattern with a monotonic heating history" is obtained by replacing the temperature at each point in the heating history (temperature at each time) from the start of heating to the point where the maximum temperature of the heating process is reached (heating period) with the maximum temperature from the start of heating to that point. The "heating pattern with a monotonic heating history" is a monotonically increasing function of temperature with respect to time, consisting only of curves with a positive slope and straight lines with a slope of 0.

[0050] While flowing nitrogen gas at a flow rate of 200 mL / min, the measurement sample, consisting of the raw material film, is heated to 1000°C at a heating rate of 10°C / min. Thermogravimetric analysis, which records the temperature and weight of the measurement sample during heating, is used to determine the following temperature T p , T s , T f Define. T p (°C) is defined as the temperature at which the observed rate of weight loss (weight loss per unit time) in thermogravimetric measurements reaches its maximum value. T s (°C) is defined as the lowest temperature above 100°C at which the observed weight loss rate of the sample measured in thermogravimetric analysis is 0.8% or more of the maximum weight loss rate. T f (°C) is defined as the highest temperature at which the observed weight loss rate of the sample measured in thermogravimetric analysis is 10% or more of the maximum weight loss rate.

[0051] In the carbonization process, at least a portion of the heating process in the mixed gas is T f It is preferable to carry out the procedure at the following temperatures. The temperature during the slow heating period included in the mixed gas heating process is T f The following is preferable: T p The following is more preferable. On the other hand, the temperature during the slow heating period is T sThe above is preferable. If the temperature during the slow heating period is within this range, carbon can be efficiently incorporated from the organic gas into the raw material film that is being heated and decomposing, and the loss of carbon due to decomposition can be suppressed.

[0052] In the mixed gas heating process, the temperature is T s More than T f The average heating rate during the following slow heating period is preferably 5°C / min or less, more preferably 3°C / min or less, and even more preferably 1°C / min or less. If the average heating rate is below the above upper limit, the orientation of the graphite crystals can be ensured to some extent, and even if the subsequent graphitization process is accelerated, it becomes easier to obtain high-quality film-like graphite. Also, the temperature is T s More than T f The length of the following slow heating period is preferably 30 minutes or more, more preferably 60 minutes or more, and even more preferably 90 minutes or more. The slow heating period is 30 minutes or longer, and the temperature of the heating pattern obtained by monotonically increasing the heating history is T s More than T f Including the following periods ensures a sufficient supply of organic gases, facilitates efficient carbon uptake from the organic gases, and suppresses carbon loss through decomposition.

[0053] The maximum heating temperature in the mixed gas heating process depends on the raw material film and the organic gas used, but is preferably 1000°C or lower, more preferably 800°C or lower, and even more preferably 600°C or lower. If the maximum heating temperature is below the above upper limit, the organic gas can be handled stably. The maximum heating temperature in the mixed gas heating process is T s The above is preferable. If the maximum heating temperature is above the lower limit, the raw material film can be reacted with the organic gas at a temperature at which thermal decomposition is likely to occur, so carbon in the organic gas is easily incorporated, and a carbonized film with a large surface area is more likely to be obtained.

[0054] (Graphitization process) In the graphitization process, 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 to grow graphite crystals and obtain a graphitized film. For example, the carbonized film in the carbonization furnace after the carbonization process may be cooled to a temperature unaffected by oxygen, removed from the carbonization furnace, transferred to a graphitization furnace, and heated again to carry out the graphitization process, or the graphitization process may be carried out by continuously heating the film without cooling it down after the carbonization process.

[0055] In the graphitization process, the temperature may be increased continuously, or it may be increased in stages with a period of maintaining a constant temperature. Alternatively, the temperature may be lowered after heating and then increased again. The graphitization process may be carried out using a batch heating method, a continuous supply heating method in which the carbonized film is graphitized while being continuously supplied, or a carbonized film produced by the batch heating method may be graphitized in a graphitization furnace using a continuous heating method.

[0056] Maximum heating temperature T in the graphitization process max The temperature is preferably 3,000°C or lower, more preferably 2,900°C or lower, and even more preferably 2,800°C or lower. max If the value is below the aforementioned upper limit, the consumption of the heating element and insulation material of the graphitization furnace will be slower, thus reducing the frequency of maintenance. Furthermore, excessive growth of graphite crystals can be suppressed, ensuring adequate voids between the graphite crystals, making it easier to obtain flexible, film-like graphite. Here, the voids between graphite crystals refer to micro or macro voids observed in the carbon material. max The temperature is preferably 2,400°C or higher, more preferably 2,700°C or higher, and even more preferably 2,750°C or higher. max If the value is above the aforementioned lower limit, the carbon network plane of the graphite crystals in the film-like graphite is more likely to be oriented parallel to the film surface, and high thermal conductivity is more likely to be exhibited.

[0057] The graphitization process starts at 2,000°C. maxIn a heating pattern where the heating history up to a certain point is monotonically increased, it is preferable that the maximum value of the heating range over any 30 minutes (hereinafter referred to as the "30-minute maximum heating range") be 60°C or higher. It is more preferable that the 30-minute maximum heating range be 90°C or higher, and even more preferable that be 210°C or higher. By setting the 30-minute maximum heating range 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 the insulation material of the graphitization furnace and the total power consumption in the graphitization process.

[0058] The graphitization process starts at 2,000°C. max In a heating pattern where the heating history up to a certain point is monotonically increased, it is preferable that the maximum value of the heating range over any 60 minutes (hereinafter referred to as the "60-minute maximum heating range") be 120°C or higher. It is more preferable that the 60-minute maximum heating range be 180°C or higher, and even more preferable that be 420°C or higher. By setting the 60-minute maximum heating range to 120°C or higher, it is possible to generate appropriate foaming within the carbonized film during the graphitization process, thereby ensuring appropriate flexibility. The graphitization process starts at 2,000°C. max It is preferable that the maximum value of the temperature increase over any 90-minute period (hereinafter referred to as the "90-minute maximum temperature increase") in a temperature increase pattern obtained by monotonically increasing the temperature history up to that point be 180°C or higher.

[0059] The graphitization process starts at 2,000°C. max The heating pattern obtained by monotonically increasing the heating history up to this point is: max It is preferable that the time to reach the destination be 40 minutes or more, more preferably 60 minutes or more, and even more preferably 90 minutes or more. The maximum temperature increase over 60 minutes in the graphitization process is preferably 900°C or less, and more preferably 720°C or less. If the maximum temperature increase over 60 minutes is below the above upper limit, the amount of gas generated per unit time from inside the film during the graphitization process is reduced, making it easier to obtain a thick film-like graphite with excellent thermal conductivity. The maximum 30-minute heating range in the graphitization process is preferably 540°C or less, more preferably 450°C or less, and most preferably 360°C or less. If the maximum 30-minute heating range is below the above upper limit, the amount of gas generated per unit time from inside the film during the graphitization process is further reduced, making it easier to obtain a thicker film-like graphite with excellent thermal conductivity.

[0060] In the present invention, it is preferable to produce a film-like graphite having a thermal conductivity of 800 W / mK or higher and a minimum bending radius of 16 mm or less in a bending test, using a raw material film with a thickness of 150 μm or more, by monotonically increasing the heating history of the graphitization process to 2000°C or higher, and setting the maximum value of the heating range over any 30 minutes to 60°C or higher. The bending test will be described in detail in the examples below.

[0061] Area S of the raw material film m The area S of the graphitized film obtained in the graphitization process is relative to the area S of the graphitized film. g The ratio (S g / S m ) is preferably 0.8 or higher, more preferably 0.9 or higher, and even more preferably 1 or higher. g / S m The larger the value, the larger the area of ​​the resulting film-like graphite, which improves productivity and reduces costs. g / S m There is no specific lower limit, but in practice it is around 1.2.

[0062] (Pressing process) In the pressing process, the graphitized film obtained in the graphitization process is compressed or rolled. The pressing process makes it easier for the layers of graphite crystals to orient along the film surface, the voids within the graphitized film are compressed, increasing its density, and any warping or undulation that may have occurred in the graphitized film is eliminated. When compressing or rolling, it is preferable to sandwich the material between two polyimide films. This helps prevent soiling of the pressure rolls. In this invention, during the pressing process, a graphitized film with a density of 1.6 g / cm³ is obtained.3 It is preferable to obtain the above-mentioned film-like graphite, at 1.7 g / cm³. 3 It is more preferable to obtain the above-mentioned film-like graphite, 1.8 g / cm³ 3 It is even more preferable to obtain the above-described film-like graphite.

[0063] A preferred method of compression 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 repeatedly through the same pressure rolls, or sequentially through multiple stages of pressure rolls. The method of compression or rolling is not particularly limited to the above method; for example, a method of pressing the graphitized film between metal plates using a hydraulic cylinder or the like may also be used.

[0064] In the method for producing film-like graphite according to the present invention described above, by performing a heating step in a mixed gas, the amount of foaming gas is reduced even if the heating rate of the graphitization step is high, thereby suppressing peeling and film breakage of the film surface. Furthermore, since the time of the graphitization step can be shortened, excessive growth of the graphite structure is suppressed, and flexible film-like graphite can be obtained. In addition, since shrinkage of the film during manufacturing is also suppressed, it is easier to obtain film-like graphite with a large surface area, resulting in excellent productivity and low cost. [Examples]

[0065] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description. Examples 1, 2, 5, and 6 are for reference only.

[0066] [Raw material film] In the following embodiments, polyimide film (manufactured by Toray DuPont Ltd., Kapton® H type (hereinafter referred to as "polyimide film KH")) was used as the raw material film. Thermogravimetric analysis was performed on this polyimide film KH (raw material film). Figure 6 shows the plot of the weight loss rate (weight loss per unit time) against temperature when the raw material film was heated in a nitrogen atmosphere at 10°C / min.p , T s , T f The temperatures were 595°C, 475°C, and 675°C, respectively.

[0067] [Method for evaluating the integral width B of diffraction peaks of the (100) plane originating from graphite crystals] As the measurement device, a fully automated multi-purpose X-ray diffractometer manufactured by Rigaku Corporation, the SmartLab, which uses CuKα rays as a radiation source, was used. The film-like graphite was fixed to the sample stage so that the angle of incidence of the incident X-rays and the angle of reflection of the reflected X-rays were equal in the direction perpendicular to the film surface of the film-like graphite, and so as not to bend. The one-dimensional X-ray diffraction spectrum of the film-like graphite in the 2θ direction was measured using the θ / 2θ scanning method (transmission method). The measurement conditions were: tube voltage 45kV, tube current 200mA, scanning range (2θ) 20~50°, scanning step 0.01°, scanning speed 4.0° / min, and scanning mode CONTINUOUS. The integral width B(°) of the reflection diffraction peak position of the (100) plane originating from the hexagonal graphite, detected near 2θ=42.3° in this measurement was read. The integral width B was calculated using the analysis software Smart Lab Studio II.

[0068] [Method for evaluating the degree of orientation P of graphite crystals] As the measurement device, a fully automated multi-purpose X-ray diffractometer, SmartLab, manufactured by Rigaku Corporation, which uses CuKα rays as a radiation source, was used. The film-like graphite was fixed to the sample stage so that the angle of incidence of the incident X-rays and the angle of reflection of the reflected X-rays were equal in the direction perpendicular to the film surface of the film-like graphite, and so as not to bend. The one-dimensional X-ray diffraction spectrum of the film-like graphite in the 2θ direction was measured using the θ / 2θ scanning method. The measurement conditions were: tube voltage 45kV, tube current 200mA, scanning range (2θ) 25~28°, scanning step 0.01°, scanning speed 4.0° / min, and scanning mode CONTINUOUS. The position of the reflection diffraction peak of the (002) plane originating from the hexagonal graphite, detected near 2θ=26.5° obtained from this measurement, was read, and the detector was fixed at this peak position, and the X-ray diffraction spectrum of the film-like graphite was measured using the ω scanning method. The measurement conditions were: tube voltage 45kV, tube current 200mA, scanning range (ω)-5.8~31.4°, scanning step 0.02°, scanning speed 20.0° / min, and scanning mode CONTINUOUS. The full width at half maximum F(°) of the diffraction peak obtained from this spectrum was read, and the degree of graphite crystal orientation P[%] was calculated using Equation 1 below.

[0069]

number

[0070] [Thermogravimetry] Thermogravimetric analysis (TG) was performed using a differential thermogravimetric simultaneous thermometer (STA7300, manufactured by Hitachi High-Tech Science Corporation) according to the following procedure. The raw material film was cut into approximately 3 mm squares, and multiple pieces were stacked in a platinum container to create a sample weighing approximately 3 mg. The sample was heated to 1,000°C at a heating rate of 10°C / min while nitrogen gas was flowed through it at a flow rate of 200 mL / min, and the temperature and weight of the sample were recorded every second.

[0071] [Thermal diffusivity in the direction of the film surface] The thermal diffusivity α in the direction along the film surface of film-like graphite was measured at 23°C using a BETHEL TA33 thermowave analyzer in accordance with JIS R 7240 (2018) using the periodic heating method (distance variation method). Measurement frequencies were set to 60Hz, 70Hz, 75Hz, 80Hz, and 90Hz. The average value of the thermal diffusivity measured at each of the five frequencies was defined as the thermal diffusivity α in the direction along the film surface of the film-like graphite. For the measurement, the sample size was set to a length of 4cm to 10cm in the measurement direction and a length of 1.5cm to 10cm in the direction perpendicular to the measurement direction of the film surface. The film thickness was measured from the cut-out sample.

[0072] [Thermal conductivity in the direction of the film surface] The thermal conductivity of the film-like graphite in the direction along the film surface was calculated according to Equation 2 below. b=α×d×c...Equation 2 However, each symbol in Formula 2 above has the following meaning: b: Thermal conductivity (W / mK) in the direction along the film surface of film-like graphite. α: Thermal diffusivity (mm²) in the direction along the film surface of film-like graphite. 2 / s) d: Density of film-like graphite (g / cm³) 3 ) c: Specific heat of graphite (0.85 J / gK)

[0073] [density] The density d of the film-like graphite was determined by measuring the weight of the film-like graphite in air and ethanol, and using the following formula 3. d = ρs × Wa / (Wa - Ws) ... Equation 3 However, each symbol in formula 3 above has the following meaning: d: Density of film-like graphite (g / cm³) 3 ) ρs: Density of ethanol (g / cm³) 3 ) Wa: Weight of film-like graphite in air (g) Ws: Weight (g) of film-like graphite in ethanol

[0074] [Evaluation of minimum bending radius] As an indicator of the flexibility of film-like graphite, a method was used to evaluate the minimum bending radius. In an environment of 23°C, a Type 2 bending test apparatus specified in JIS K5600-5-1 was fully extended, a film-like graphite test specimen and mandrel were mounted, and the specimen was bent evenly 180° over 1-2 seconds. After bending, the specimen was inspected to check 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 bending and visual inspection of the test specimens were performed in order from the mandrel with the largest diameter. During the bending process using each mandrel, the position of the test specimen was changed to prevent the effects of strain and other factors caused by bending the specimen once from affecting subsequent tests. Then, the minimum bending radius of the film-like graphite was defined as half the diameter of a mandrel that was one size larger in diameter than the mandrel in which the first fold or crack was observed in the test specimen, or half the diameter of the smallest mandrel among the mandrels in which no fold or crack was observed in the test specimen.

[0075] [Unloaded U-shaped stretching test of a planar body] The unloaded U-shaped stretch test of a planar graphite film was performed using a tabletop durability tester DLDMLH-FS manufactured by Yuasa System Equipment Co., Ltd., following the procedure below. A test specimen was cut to a width of 50 mm and a length of 150 mm, and the specimen was fixed to the tester using double-sided tape. The test was performed with a bending angle of 180°, a bending radius of 2 mm, and a test speed of 60 Hz. The tilt clamp was set to a bending test mode that alternated between a straight and bent state according to the bending state of the test specimen. Visual inspection of the test specimen was performed at 1,000, 2,500, 5,000, 10,000, 20,000, 30,000, 40,000, and 50,000 bending cycles after the start of the test, and the number of bending cycles until the test specimen broke was defined as the number of bending cycles to withstand.

[0076] [Heat dissipation test] A test specimen was cut from the film-like graphite to a width of 50 mm and a length of 200 mm and placed on an insulating board. A 10 mm x 15 mm micro ceramic heater (manufactured by Kashima Co., Ltd., Micro Ceramic Heater SCP15 x 10) was placed in one corner of the surface of the placed test specimen, and the heater was heated at 3 W under a constant current and voltage. In this case, the micro ceramic heater had been pre-coated with a blackbody spray with an emissivity of 0.94 (manufactured by Ichinen TASCO Co., Ltd., Blackbody Spray TA410KS), and grease (manufactured by Shin-Etsu Chemical Co., Ltd., Thermal Conductive Grease G-776) was applied to the back of the micro ceramic heater and attached to the test specimen. The test procedure is shown in Figure 10. Once the heater temperature reached a constant level, the maximum temperature of the heater was read using a thermal imaging camera (manufactured by FLIR, A6700SC). Emissivity correction was performed using the analysis software ResearchIR. Furthermore, the above tests were conducted in a temperature and humidity controlled environment at a room temperature of 23°C and a humidity of 50%RH.

[0077] The pressing process in each of the following examples was carried out using a hydraulic calender / embossing machine manufactured by Yuri Roll Co., Ltd., following the procedure below. The graphitized film was sandwiched between commercially available polyimide films and compressed under conditions of a linear pressure of 900 kg / cm to 2,700 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.

[0078] [Example 1] 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, under a nitrogen gas atmosphere containing acetylene gas (acetylene gas concentration: 25 vol%), the temperature was raised from room temperature to 450°C at an average heating rate of 10°C / min, and then from 450°C to 550°C the temperature was raised while maintaining a heating rate of approximately 0.2°C / min (heating process in mixed gas). After raising the temperature to 550°C, the atmosphere was switched to nitrogen gas, and the temperature was raised to 1,000°C while maintaining a heating rate of approximately 10°C / min, and held 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, under an argon atmosphere, the power output of the graphitization furnace was kept constant, and the temperature was raised according to the temperature profile shown in Figure 7. In the temperature profile shown in Figure 7, the temperature 30 minutes after reaching 2,000°C was 2,062°C, 60 minutes later it was 2,120°C, and 90 minutes later it was 2,176°C. In the graphitization furnace, the temperature was held at 2,800°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 film-like graphite. Figure 3 shows a portion of the images obtained by observing the surface of the resulting film-like graphite with a laser microscope.

[0079] [Example 2] 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, under a nitrogen gas atmosphere containing acetylene gas (acetylene gas concentration: 25 vol%), the temperature was raised from room temperature to 450°C at an average heating rate of 10°C / min, and then from 450°C to 550°C the temperature was raised while maintaining a heating rate of approximately 0.2°C / min (heating process in mixed gas). After raising the temperature to 550°C, the atmosphere was switched to nitrogen gas, and the temperature was raised to 800°C while maintaining a heating rate of approximately 10°C / min, and held for 1 hour. After the carbonized film was allowed to cool after the carbonization process, it was transferred to a graphitization furnace and the graphitization process was carried out. In the graphitization process, film-like graphite was obtained in the same manner as in Example 1, except that the power output value of the graphitization furnace was kept constant under an argon atmosphere and the temperature was raised according to the temperature profile shown in Figure 8. In the temperature profile shown in Figure 8, the temperature 30 minutes after reaching 2,000°C was 2,096°C, 60 minutes later it was 2,185°C, and 90 minutes later it was 2,270°C.

[0080] [Example 3] A 75 μm thick polyimide film KH was coated on one side with an N-methyl-2-pyrrolidone solution containing 20% ​​by mass of polyamic acid, which is a polymer of oxydianiline and pyromellitic anhydride. Another 75 μm thick polyimide film KH was bonded to the coated surface of the first polyimide film, and the excess solution was removed using the pressure roll used in Example 1 as a mangle. The bonded film was placed under atmospheric pressure and 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 to obtain a 150 μm thick laminated film in which two 75 μm thick polyimide films were firmly bonded together. A film-like graphite was obtained in the same manner as in Example 2, except that this laminated film was used as the raw material film.

[0081] [Example 4] In the same manner as in Example 3, a film-like graphite was obtained in the same manner as in Example 2, except that a laminated film with a thickness of 250 μm was used as the raw material film, which was made by laminating a 125 μm thick polyimide film KH to a 125 μm thick polyimide film KH.

[0082] [Example 5] A polyimide film KH with a thickness of 75 μm was used as the raw material film, and a film-like graphite was obtained in the same manner as in Example 2, except that the temperature was raised according to the temperature profile shown in Figure 9. In the temperature profile shown in Figure 9, the temperature 30 minutes after reaching 2,000°C was 2,083°C, the temperature 60 minutes later was 2,160°C, and the temperature 90 minutes later was 2,229°C.

[0083] [Example 6] A film-like graphite was obtained in the same manner as in Example 5, except that a 125 μm thick polyimide film KH was used as the raw material film.

[0084] [Example 7] A film-like graphite was obtained in the same manner as in Example 5, except that a laminated film with a thickness of 200 μm was used as the raw material film, which was made by laminating a 125 μm thick polyimide film KH to a 75 μm thick polyimide film KH in the same manner as in Example 3.

[0085] [Example 8] A film-like graphite was obtained in the same manner as in Example 5, except that a laminated film with a thickness of 250 μm was used as the raw material film, which was made by laminating a 125 μm thick polyimide film KH to a 125 μm thick polyimide film KH in the same manner as in Example 3.

[0086] [Example 9] In the same manner as in Example 3, a film-like graphite was obtained in the same manner as in Example 5, except that a laminated film with a thickness of 375 μm was used as the raw material film, which was made by laminating a 125 μm thick polyimide film KH to a 125 μm thick polyimide film KH, and then laminating another 125 μm thick polyimide film KH to that film.

[0087] [Example 10] In the same manner as in Example 3, a 500 μm thick laminated film was obtained as the raw material film, except that a 125 μm thick polyimide film KH was laminated to a 125 μm thick polyimide film KH, then another 125 μm thick polyimide film KH was laminated to it, and then another 125 μm thick polyimide film KH was laminated to it.

[0088] [Comparative Example 1] A film-type graphite (EYGS182303, 25 μm thick) manufactured by Panasonic Corporation was used as a comparison sample.

[0089] [Comparative Example 2] A film-type graphite (EYGS182305, 50 μm thick) manufactured by Panasonic Corporation was used as a comparison.

[0090] [Comparative Example 3] Kaneka Corporation's film-type graphite (Graphity TM A thickness of 36 μm was used as a comparison target.

[0091] The test results for each example are shown in Table 1. Furthermore, Figure 11 shows the thermal conductivity of the film-like graphite for each example and comparative example plotted against the integral width B of the diffraction peak of the (100) plane derived from the graphite crystal.

[0092] As shown in Table 1 and Figure 11, the narrower the integral width B of the diffraction peak of the (100) plane derived from the graphite crystal, the higher the thermal conductivity of the film-like graphite tended to be, and a consistently high thermal conductivity was observed. The thermal conductivity of the film-like graphite in Examples 3, 4, and 6-10, where the integral width B was 0.231° or less, was particularly high, and the heat dissipation performance was particularly excellent. Furthermore, the film-like graphites of Examples 1 to 10, which had a (surface area / film area) ratio of 1.05 or higher, exhibited a small minimum bending radius and excellent flexibility. As shown in Figure 3, cracks and irregularities were observed on the surface of the film-like graphite of Example 1. This suggests that thermal decomposition gases were generated inside the film during the graphitization process, creating voids between the graphite crystallites, which improved flexibility.

[0093] [Table 1] [Industrial applicability]

[0094] According to the present invention, it is possible to provide a film-like graphite that is thick, has high thermal conductivity and heat dissipation performance, and is also excellent in flexibility and electrical conductivity. [Explanation of Symbols]

[0095] 1. Test specimen of film-like graphite 2. Micro ceramic heater 3. Insulation board

Claims

1. A film-like graphite that meets the following conditions. Conditions: In X-ray diffraction (XRD) measurements, the integral width B of the diffraction peak of the (100) plane originating from the graphite crystal detected near 2θ = 42.3° by the θ / 2θ scan method is 0.255° or less, and the film thickness H of the film-like graphite is 72 μm or more.

2. The film-like graphite according to claim 1, wherein the integral width B of the above condition is 0.245° or less.

3. The film-like graphite according to claim 1, wherein the degree of graphite crystal orientation P relative to the film surface is 94% or more.

4. The film-like graphite according to claim 1, wherein the product (B × F) of the integral width B of the diffraction peak of the (100) plane originating from the graphite crystal detected near 2θ = 42.3° by the θ / 2θ scan method in X-ray diffraction (XRD) measurement and the half-width F (°) of the diffraction profile obtained from the ω scan of the diffraction peak of the (002) plane originating from the hexagonal graphite crystal detected near 2θ = 26.5° by the θ / 2θ scan method in X-ray diffraction (XRD) measurement is 3.0 or less.

5. The film-like graphite according to claim 1, wherein the thermal conductivity b in the film surface direction is 1500 W / mK or more.

6. The film-like graphite according to claim 1, wherein the electrical conductivity is 6,000 S / cm or more.

7. The film-like graphite according to claim 1, wherein the minimum bending radius is 16 mm or less.

8. Density is 1.7 g / cm³ ３ The above is the film-like graphite according to claim 1.

9. The film-like graphite according to claim 1, wherein the ratio of surface area to film area (surface area / film area) is 1.05 or more.

10. The film-like graphite according to claim 1, wherein, in a cross section perpendicular to the film surface of the film-like graphite, the number N of multiple bright areas obtained from an image obtained by binarizing the bright and dark areas observed by polarizing microscope images, the film thickness H (μm), and the film width W (μm) satisfy the following formula (1). N / H / W≦0.011...(1)

11. The film-like graphite according to claim 1, wherein, in a cross section perpendicular to the film surface of the film-like graphite, the number N of multiple bright areas obtained from an image obtained by binarizing the bright and dark areas observed by a polarizing microscope image, the film thickness H (μm), and the film width W (μm) of the film-like graphite satisfy the following formulas (2) and (3). N / H / W≦0.04...(2) H ≥ 42 ... (3)

12. In a cross-section perpendicular to the film surface of a film-like graphite, the average area AS of multiple bright regions obtained from a binarized image of bright and dark areas observed by polarized light microscopy is 22 μm². ２ The above is the film-like graphite according to claim 1.

13. The film-like graphite according to claim 1, wherein in X-ray diffraction (XRD) measurement, (002) the full width at half maximum of the diffraction peak is 10.8° or less.

14. The film-like graphite according to claim 1, wherein the integral width B of the diffraction peak is 0.231° or less.

15. The film-like graphite according to claim 1, wherein, in a planar body unloaded U-shaped stretch test, the number of folds before fracture is 10,000 or more when measured with a bending radius R of 2 mm and a bending angle of 180°.

16. The film-like graphite according to claim 1, wherein no adhesive or tack is contained in the film thickness direction of the film-like graphite.

Images