JP5799051B2 - Method for producing graphite film - Google Patents

Description

  The present invention relates to a heat radiating film for electronic equipment, precision equipment and the like, and a graphite film used as a heat spreader material, and more particularly to a method for producing a graphite film having excellent bending resistance and heat diffusibility and less surface thickness variation.

  The problem of cooling semiconductor elements mounted on various electronic and electrical devices such as computers and other heat-generating parts has attracted attention. As a cooling method for such a component to be cooled, a fan is attached to the device housing on which the component is mounted, and the device housing is cooled, or the cooling component includes a heat pipe, a heat spreader, a heat sink, a fin, etc. In general, a method of cooling by attaching a heat conductor and transporting heat from the element to the outside is generally used. Examples of the heat conductive material attached to the component to be cooled include an aluminum plate and a copper plate. In this case, a heat generating component is attached to a part of the aluminum or copper plate or the heat pipe, and the other part of the plate is radiated to the outside using fins or a fan.

By the way, in recent years, each device on which a heat-generating component such as a semiconductor element is mounted tends to be downsized, and the amount of heat generated by the member tends to increase. However, since the housing is downsized, the space for inserting components such as fins, heat sinks and fans has been limited. Therefore, in recent years, a graphite film excellent in thermal diffusibility is regarded as a promising thermal conductor (heat conductor). The graphite film is a material in which carbon has a layered structure, the in-plane thermal conductivity of the graphite film is very high, the density is as light as about 1 to 2 g / cm ^3, and the electric conductivity is high. . In addition, since the thickness of the sheet can be reduced and it is flexible, it is expected as a heat conductor material or heat spreader material in a narrow place or a place where a gap needs to be routed.

  Currently, there is a graphite film produced by a polymer pyrolysis method or an expanding method as a generally available graphite film. As described in Patent Document 1, the polymer pyrolysis method uses a polymer film such as polyoxadiazole, polyimide, polyphenylene vinylene, polybenzimidazole, polybenzoxazole, polythiazole, or polyamide in an inert atmosphere such as argon or helium. This is a method of obtaining a graphite film by heat treatment under pressure or under reduced pressure.

  In addition, as a method for producing film-like graphite having good quality and high flexibility and toughness, a polymer film having a thickness capable of obtaining a graphite film can be obtained at 2400 ° C. or higher by generating gas from the film by heating at normal pressure. A method for producing filmy graphite (Patent Document 2) is known, which comprises rolling a graphite film obtained by heat treatment at a temperature.

  Furthermore, JP 2000-178016 (Patent Document 3) proposes a method for producing a graphite film that exhibits the same physical properties as single crystal graphite, has high quality, is flexible and tough, and has excellent thermal diffusivity. . This manufacturing method uses a polyimide film as a raw material, a first heat treatment step in which heat treatment is performed in an inert gas at a maximum temperature range of 1000 ° C. to 1600 ° C., and further a heat treatment is performed at a maximum temperature range of 2500 ° C. to 3100 ° C. A second heat treatment step to be performed, and a method for producing a graphite film having appropriate characteristics by controlling heat treatment conditions such as a heating rate and a constant temperature, and further comprising a rolling step. It is a method of expressing flexibility by applying. Further, as described in claim 7 of Patent Document 3, the density of the graphite film is in the range of 0.3 to 0.7 g / cc, or the film thickness of the graphite film is 10 to 10 times the film thickness of the raw material film. If it is within the range, a graphite film having excellent flexibility and toughness can be obtained by performing a post-treatment rolling step. As described in claim 8 of Patent Document 3, the density of the graphite film obtained by the rolling step is obtained. Has disclosed a method for producing a graphite film such that the flexibility and toughness of the obtained graphite sheet are excellent when the ratio is in the range of 0.7 to 1.5 g / cc.

JP 61-275116 A Patent Publication No. 2976481 In the method for producing a graphite film as described in JP-A-2000-178016, the points for contributing flexibility and flex resistance to the film are “foaming of the film during graphitization” and “graphitization”. It is “compression processing of the film after processing”. The mechanism that can impart flex resistance to the film is as follows.

In the final stage of graphitization (2600 ° C. or higher), N ₂ that does not form a graphite skeleton, and internal gas (hereinafter referred to as foaming gas) such as filler (phosphoric acid) is generated, and the graphite layer is lifted to foam the film. By compressing a foamed graphite film after the graphitization treatment (hereinafter referred to as a film after the graphite treatment), a graphite film having excellent bending resistance is obtained. The reason why the bending resistance is excellent by compressing the foamed graphitized film is that there is a slight space between the graphite layers after compression, so that the distortion of the graphite layer during folding can be released This is because it can.

  However, not all foamed graphite films are excellent in bending resistance. The magnitude of foaming in the thickness direction of the graphite film (hereinafter referred to as the degree of foaming) varies depending on the conditions for graphitization, and this degree of foaming is one factor that determines the superiority or inferiority of the bending resistance. If the degree of foaming is too small, the amount of air layer present between the graphite layers is insufficient, and the distortion of the graphite layer cannot be released at the time of folding, resulting in a hard and inferior bending resistance film. Moreover, when the degree of foaming is too large, the graphite layer may be damaged by the foaming gas, resulting in a graphite film with poor flex resistance.

  The structure of current electronic devices is becoming more and more complex, and the size is becoming smaller. How to efficiently release heat in a narrow space is an important issue. There are several attempts to fold and use a graphite film, which is characterized by having flexibility in the space-saving part. For example, an idea has been devised in which heat from a heat generating part of a folding mobile phone or notebook computer is released to the liquid crystal side through the bent part.

  However, the graphite film is brittle in material, and in particular, when bending with a small radius of curvature or when the bending angle is large, cracks often occur at the bent portion.

  In addition, bending resistance and thermal diffusivity are contradictory properties, and conventional graphite films have pursued bending resistance, and thus thermal diffusivity may not be sufficient.

  Although the graphite films obtained from Patent Documents 1 to 3 have a certain degree of bending resistance and thermal diffusivity, they have not had sufficient characteristics as heat dissipation materials for recent electronic devices that have become smaller and more complicated.

● Reason why the graphite films of Patent Documents 1 to 3 are not sufficiently flexible ●
(1) Since the density of the film after graphitization is small (the degree of foaming is too large)
As for the conventional graphite film, the density of the film after graphitization treatment is in the range of 0.3 to 0.7 g / cc as in Patent Document 3, or the film thickness of the graphitization treatment film is 2 of the film thickness of the raw material film. When it is in the range of 10 to 10 times, a graphite film having excellent flexibility and toughness is obtained when a post-treatment rolling step is performed.

However, the graphite film expanded to such a density may have poor bending resistance. A large degree of foaming means that the graphite layer is greatly lifted by the foaming gas, and in such a graphite film, the growth of the graphite layer in the surface direction is inhibited by the foaming gas.
(2) Insufficient compression of the film after graphitization treatment The compression of the expanded graphite film as much as possible can contribute to flexibility. This is because a thinner thickness is less susceptible to bending stress. As described in claim 8 of Patent Document 3, the conventional graphite film has a film density obtained by a rolling process in the range of 0.7 to 1.5 g / cc, and the film after graphitization is sufficiently compressed. It was not. The reason why the film after the graphitization treatment could not be sufficiently compressed is that the degree of foaming of the film after the graphitization treatment is large (the density is large), and the film is compressed in the post-rolling step.
(3) There is uneven compression.

Since the post-graphitization film described in Patent Documents 2 and 3 has a large degree of foaming, the thickness variation in the film plane is large. Even in this way, since the film after the graphitization treatment having a large thickness variation is rolled with a metal roller, a uniform compression treatment cannot be performed, and the thickness variation of the finished film is large. For this reason, the bending resistance is poor because stress for bending is concentrated on the thick portion.
(4) The graphite film is destroyed in the rolling process.

  In the post-rolling process, the graphite film may be stretched by applying linear pressure at the contact portion with the roller during the rolling process, and the flat graphite layer may be destroyed and the bending resistance may be reduced. there were. Further, when the graphite film is rolled using a high strength material such as a metal roller, there is a problem in that scratches and wrinkles are easily formed on the surface, and dents and vertical stripes are generated.

● Reason for thermal diffusivity of graphite films of Patent Documents 1 to 3 ●
(1) Since the density of the film after graphitization is small (the degree of foaming is too large)
As described above, bending resistance and thermal diffusivity are contradictory characteristics. The graphite films of Patent Documents 1 to 3 pursue too much to improve the bending resistance and excessively foam the film in the process of graphitization. Therefore, for the same reason as the poor bending resistance, the growth of the graphite layer in the surface direction is not sufficient and the thermal diffusivity is poor.
(2) The graphite film is destroyed in the rolling process.

  In the post-rolling process, the graphite film is stretched by applying linear pressure at the contact portion with the roller during the rolling process, and the planarly formed graphite layer may be destroyed and thermal diffusivity may be reduced. there were.

  Thus, although some attempts have been made to improve the flex resistance of graphite films, sufficient characteristics for mounting in recent electronic devices have not been achieved, and further improvements in flex resistance and thermal diffusibility have been achieved. There is a need for the development of excellent graphite films.

(1) A first aspect of the present invention is a method for producing a graphite film comprising a graphitization step of heat-treating a polymer film having a thickness of 5 μm or more and 250 μm or less at a temperature of 2400 ° C. or more, and a post-treatment step. The post-processing step is a post-surface pressing step of pressing the post-graphitizing film into a surface shape. The density of the film is 0.7 g / cm ³ or more and 1.68 g / cm ³ or less. It is a manufacturing method of a graphite film.
(2) the second invention, the density of the graphite film obtained by subjecting the rear surface pressing step, characterized in that at most 1.5 g / cm ³ or more 2.20 g / cm ³ (1 The method for producing a graphite film as described in 1).
(3) According to a third aspect of the present invention, in the method for producing a graphite film, comprising a graphitization step of heat-treating a polymer film having a thickness of 5 μm or more and 250 μm or less at a temperature of 2400 ° C. or more, and a post-treatment step, The graphite film has a density of 0.7 g / cm ³ or more and 1.68 g / cm ³ or less, and the post-treatment step is a post-rolling step of rolling the post-graphitizing film. It is.
(4) a fourth aspect of the present invention, the density of the graphite film obtained by subjecting the rear rolling step, claims, characterized in that at most 1.5 g / cm ³ or more 2.20 g / cm ³ (3 The method for producing a graphite film as described in 1).
(5) The fifth aspect of the present invention is as described in (1) or (2) above, wherein in the rear surface pressurizing step, the film after graphitization is pressed into a planar shape at a pressure of 2 MPa or more and 40 MPa or less. This is a method for producing a graphite film.
(6) A sixth aspect of the present invention is characterized in that, in the rear surface pressurizing step, the post-graphitization-treated film has a planar shape and has a pressure of 4 MPa or more and 20 MPa or less (1), (2), ( 5. A method for producing a graphite film according to any one of 5).
(7) A seventh aspect of the present invention is any one of (1) to (6), wherein the thermal diffusivity in the surface direction of the graphite film is 7.0 × 10 ⁻⁴ m ² / s or more. It is a manufacturing method of the graphite film as described in above.

  A graphite film having excellent bending resistance and thermal diffusibility and less surface thickness variation can be produced.

The cross-sectional schematic diagram of a graphitization process film. The cross-sectional schematic diagram of the graphite film after a compression process. Thickness measurement point.

In the method for producing a graphite film comprising a graphitization step of heat-treating a polymer film having a thickness of 5 μm or more and 250 μm or less at a temperature of 2400 ° C. or more, and a post-treatment step, the density of the film after the graphitization treatment is 0.7 g / cm ^3. 1.60 g / cm ³ or less, and the post-treatment step is (1) a post-surface pressure step of pressing the post-graphitization film into a surface, or (2) after rolling the post-graphitization film A method for producing a graphite film, which is a rolling process.

<Graphite film>
As a countermeasure against an increase in heat generation density of electronic devices in recent years, a graphite film having an excellent thermal diffusibility has attracted attention. Currently, there is a graphite film produced by a polymer pyrolysis method or an expanding method as a generally available graphite film.

<Outline of production method of graphite film of the present invention>
The method for producing a graphite film of the present invention is a graphite film obtained by heat-treating a polymer film at a temperature of 2400 ° C. or higher.

  In general, a first heat treatment step (carbonization step) in which a polymer film is heat-treated in an inert gas at a maximum temperature range of 1000 ° C. to 1600 ° C., and further a heat treatment at a maximum temperature range of 2500 ° C. to 3100 ° C. And a second heat treatment step (graphitization step). The inert gas used is implemented with argon, helium, or the like.

  In addition, as described above, the film can be foamed in the graphitization step, and the foamed graphitized film can be subjected to compression treatment to impart bending resistance.

<Polymer film>
The polymer film that can be used in the present invention is not particularly limited, but polyimide (PI), polyamide (PA), polyoxadiazole (POD), polybenzoxazole (PBO), polybenzobisoxazal (PBBO) ), Polythiazole (PT), polybenzothiazole (PBT), polybenzobisthiazole (PBBT), polyparaphenylene vinylene (PPV), polybenzimidazole (PBI), and polybenzobisimidazole (PBBI). Of these, a heat-resistant aromatic polymer film containing at least one selected from the above is preferable because the finally obtained graphite has high bending resistance and thermal diffusivity. What is necessary is just to manufacture these films with a well-known manufacturing method. Among these, polyimide is preferable because various materials and structures can be obtained by selecting various raw material monomers. In addition, the polyimide film is more likely to be graphite having good crystallinity and excellent bending resistance and heat diffusibility because the film is more easily carbonized and graphitized than polymer films made of other organic materials.

<Thickness of polymer film>
The thickness of the polymer film that can be used in the present invention is 5 μm to 250 μm, preferably 10 μm to 180 μm, and more preferably 20 μm to 130 μm. When the thickness of the polymer film is less than 5 μm, since the film is thin, the foaming gas easily escapes and does not foam in the graphitization step. In addition, if the thickness of the polymer film is greater than 250 μm, the foaming gas is difficult to escape from the film because the film is too thick. A foamed graphitized film cannot be obtained.

<Carbonization process>
The carbonization step of the present invention is preferably a method in which a polymer film as a starting material is heat-treated under reduced pressure or in an inert gas. This heating is usually performed at a temperature of about 1000 ° C. For example, when the temperature is increased at a rate of 10 ° C./minute, it is desirable to hold the temperature for about 30 minutes in the temperature range of 1000 ° C. More specifically, the carbonization temperature for carbonizing the polymer film is preferably 600 ° C. or more and less than 2000 ° C.

  Also, as a method of holding a polymer film during heat treatment, for example, a method of holding a polymer film between two graphite plates or a graphite sheet and holding it in a graphite square container is known. It has been.

<Graphitization process>
The graphitization step of the present invention is preferably a method in which the carbonized film obtained in the carbonization step is heat-treated under reduced pressure or in an inert gas. This heating is usually performed at a temperature of 2400 ° C. or higher, and it is desirable to hold the temperature for about 60 minutes in the maximum temperature range.

  Also, as a method of holding a polymer film during heat treatment, for example, a method of holding a polymer film between two graphite plates or a graphite sheet and holding it in a graphite square container is known. It has been.

  Further, the graphitization step of the present invention may be performed after the polymer film carbonized by the carbonization step (carbonized film) is once taken out from the furnace for carbonization step and then transferred to the graphitization furnace, The carbonization step and the graphitization step may be performed continuously in the same furnace.

<Film-treated film>
A polymer film subjected to a carbonization step and a graphitization step is a post-graphitization film. The post-graphitization film of the present invention exhibits a foamed state after the graphitization step. As described above, the mechanism that exhibits the foamed state is that the graphite layer is lifted with the generation of a foaming gas such as nitrogen that does not form a graphite skeleton in the graphitization step.

<Density of film after graphitization>
The film after the graphitization treatment is in a foamed state. As described above, the degree of foaming is one factor that determines the flex resistance and thermal diffusivity of the graphite film. The density of the post-graphitizing film having a large degree of foaming is small because it has many spaces between graphite layers. On the contrary, the density of the post-graphitizing film having a small degree of foaming is large.

Density of graphitization treatment after film of the present invention, 0.70 g / cm ³ or more · 1.68 g / cm ³ or less, preferably 0.70 g / cm ³ or more 1.50 g / cm ³ or less, more preferably 0. It is 75 g / cm ³ or more and 1.30 g / cm ³ or less. When the density of the film after the graphitization treatment is less than 0.70 g / cm ³ , the degree of foaming is too large and the graphite layer is destroyed, so that the graphite film has poor bending resistance and thermal diffusibility. On the other hand, when the density of the film after the graphitization treatment is larger than 1.68 g / cm ³ , the degree of foaming is too small and the bending resistance is deteriorated.

<(Density of film after graphitization treatment) and (Weight per unit area of graphite film / Thickness of polymer film)>
There is a correlation between the density of the graphitized film and the weight per unit area of the graphite film / the thickness of the polymer film. As described above, the density of the post-graphitized film decreases when the degree of foaming is large, and increases when the degree of foaming is small. When the degree of foaming is large, that is, when the density is small, the film expands in the thickness direction and the crystal growth in the plane direction is hindered, so the weight per unit area of the graphite film increases. On the other hand, when the degree of foaming is small, that is, when the density is high, the film does not expand greatly in the thickness direction, and crystals grow in the plane direction, so the weight per unit area of the graphite film is small.

The weight per unit area of the graphite film of the present invention / the thickness of the polymer film is 0.86 or more and 1.08 g / cm ³ or less, preferably 0.88 or more and 1.06 or less, more preferably 0.91. Above and below 1.04. When the weight per unit area of the graphite film / the thickness of the polymer film is smaller than 0.86, the degree of foaming is too small, there are few voids between the graphite layers, and the bending resistance is poor. On the other hand, when the weight per unit area of the graphite film / the thickness of the polymer film is larger than 1.08, the degree of foaming is too large, and the graphite layer is destroyed. It becomes a graphite film with poor diffusibility.

  The weight per unit area / the thickness of the polymer film is calculated by the following formula.

Weight per unit area of graphite film (g / cm ² ) / thickness of polymer film (μm)
The weight per unit area of the graphite film / the thickness of the polymer film correlates with the degree of foaming of the post-graphitizing film (after foaming), and is an index to know the degree of foaming of the post-graphitizing film. .

<Factors determining the density of the film after graphitization>
The degree of foaming of the film after graphitization treatment, that is, the density, is one factor that determines the bending resistance and thermal diffusivity of the graphite film after compression. Therefore, it is important to optimize this foaming state. As a factor that controls the foamed state (density) of the film after graphitization,
(1) Carbonization heating rate,
(2) Graphitization heating rate,
(3) Maximum graphitization temperature,
(4) pressure applied to the film during graphitization,
(5) molecular orientation of the raw film,
And so on. For optimization of the foaming state, the balance of each factor is important, and the above conditions must be changed as appropriate. By combining the above five factors in a well-balanced manner and optimizing the degree of foaming (the density of the graphitized film), a graphite film having extremely excellent bending resistance and thermal diffusivity can be obtained. The relationship between each factor and the density after graphitization is shown below.

<Carbonization heating rate and density of film after graphitization>
Carbonization temperature rising rate is one of the major factors that determine the degree of foaming of the graphitized film. If the carbonization temperature rise rate is slow, the degree of foaming of the film after graphitization is large (small density), and if the carbonization temperature rise rate is high, the degree of foaming is small (density is large). The mechanism will be described below.

  When the carbonization temperature rising rate is slow, the molecular orientation of the carbonized film after the carbonization process becomes dense. As a result, there are few escape paths of the foaming gas generated in the graphitization step, the foaming gas is difficult to escape, and the degree of foaming is increased because the graphite layer is lifted greatly. On the other hand, if the carbonization temperature rising rate is high, the molecular orientation of the carbonized film becomes coarse and the foaming gas is easily released, so the degree of foaming of the film after graphitization is small.

  The carbonization temperature rising rate of the present invention is 0.1 ° C./min to 15 ° C./min, preferably 0.3 ° C./min to 10 ° C./min, more preferably 0.5 ° C./min to 7 ° C./min. It is as follows. When the carbonization temperature rise rate is slower than 0.1 ° C./min, the heat treatment time becomes longer, so the production efficiency becomes worse. On the other hand, if the carbonization temperature rise rate is too slow, the degree of foaming of the post-graphitizing film becomes too large, resulting in a graphite film with poor flex resistance and thermal diffusivity. On the other hand, when the carbonization heating rate is faster than 15 ° C./min, soot is likely to be generated during the heat treatment. In addition, since the temperature rising rate is too high, the molecular orientation of the film is lost during carbonization, and the carbonized film is difficult to be graphitized.

  The carbonization temperature increase rate of the present invention may not always be increased at a constant temperature increase rate during the carbonization process. For example, the temperature may be increased at 1 ° C./min only in the region from 450 ° C. to 900 ° C. where the molecular structure of the film changes greatly, and the temperature may be increased at 5 ° C./min in other regions.

<Graphitization heating rate and density of film after graphitization>
The graphitization temperature increase rate is also one of the major factors that determine the degree of foaming of the film after graphitization. When the graphitization temperature rise rate is slow, the degree of foaming of the film after graphitization is small (the density is large), and when the graphitization temperature rise rate is fast, the degree of foaming is large (the density is small). The mechanism will be described below.

  If the graphitization temperature increase rate is slow, the amount of foaming gas generated during the graphitization process per unit time is small, so that the graphite layer cannot be lifted so much. On the other hand, when the graphitization temperature rising rate is high, the amount of foaming gas generated during the graphitization process per unit time is large, so the degree of foaming becomes large.

  The graphitization temperature increase rate of the present invention is 0.1 ° C./min to 15 ° C./min, preferably 0.3 ° C./min to 10 ° C./min, more preferably 0.5 ° C./min to 7 ° C./min. It is below min. When the graphitization temperature increase rate is slower than 0.1 ° C./min, the heat treatment time becomes long, so that the production efficiency is deteriorated. Also, if the graphitization heating rate is too slow, the amount of foaming gas generated per unit time will be small, and the degree of foaming of the film after graphitization will be too small. It becomes a poor graphite film. On the other hand, when the graphitization temperature rising rate is faster than 15 ° C./min, soot is likely to be generated during the heat treatment. In addition, since the rate of temperature rise is too fast, the amount of foaming gas generated per unit time during the graphitization treatment increases, which is not good because the graphite layer peels off and becomes a tattered film.

  In addition, the graphitization temperature increase rate of the present invention does not always have to be increased at a constant temperature increase rate during the graphitization process, as in the carbonization step.

<Maximum temperature for graphitization and density of film after graphitization>
When the maximum graphitization temperature is low, the degree of progress of graphitization is small and the degree of foaming is also small.

  In the method for producing a graphite film of the present invention, the heat treatment temperature is required to be at least 2400 ° C., finally 2800 ° C. or more, more preferably 2900 ° C. or more, and further preferably 3000 ° C. or more. By setting such a heat treatment temperature, the graphite layer grows in the surface direction, and a graphite film having excellent bending resistance and thermal diffusivity is obtained. On the other hand, when the maximum graphitization temperature is lower than 2400 ° C., the progress of graphitization may not be sufficient for a part of the film. If the graphitization is not sufficiently advanced, the degree of foaming is not sufficient and the film becomes very hard, resulting in a graphite film with poor flex resistance and thermal diffusivity.

  The higher the heat treatment temperature is, the higher the quality can be converted to graphite, but it is preferable that the temperature is as low as possible from the viewpoint of economy. In the method for producing a graphite film of the present invention, the heat treatment temperature is at most 3500 ° C. or less, more preferably 3200 ° C. or less, further preferably 3100 ° C. or less. In an industrial furnace that is generally available at present, the maximum temperature at which heat treatment is possible is limited to 3000 ° C.

<Density and thermal diffusivity of graphitized film>
There is a correlation between the density of the film after the graphitization treatment and the thermal diffusivity. Generally, the higher the density, the higher the thermal diffusivity because the film has a graphite layer grown in the plane direction. On the other hand, when the density is small, the thermal diffusivity is often small because the graphite layer is destroyed by the foaming gas.

The thermal diffusivity in the plane direction of the graphite film of the present invention is 7.0 × 10 ⁻⁴ m ² / s or more, preferably 7.5 × 10 ⁻⁴ m ² / s or more, and more preferably 8.0 × 10. ^-4 m ² / s or better. If it is 7.0 × 10 ⁻⁴ m ² / s or more, the heat diffusibility is high, so that heat is easily released from the heat generating device, and the temperature rise of the heat generating device can be suppressed. On the other hand, if it is less than 7.0 × 10 ⁻⁴ m ² / s, the heat diffusibility is inferior, so that heat cannot be released from the heat generating device, and the temperature rise of the heat generating device may not be suppressed.

  Usually, the bending resistance and thermal diffusivity of a graphite film obtained by the polymer decomposition method are contradictory properties, and the thermal diffusivity often deteriorates when the flex resistance is obtained. However, since the graphite film of the present invention suppresses the degree of foaming and has both high thermal diffusibility and bending resistance, it is used for electronic devices that have recently increased in calorific value and are becoming smaller. If you are very good.

<Compression of film after graphitization>
By compressing the post-graphitized film exhibiting a foamed state, a graphite film having extremely excellent bending resistance is obtained. The mechanism for increasing the bending resistance is as follows.

  The graphite layer lifted by the foaming gas in the graphitization step is greatly inclined (extruded) from the surface direction as shown in FIG. Since the graphite layer that is greatly inclined in this way inhibits the bending operation, the film after graphitization treatment has poor bending resistance. Since the graphite layer protruding from the surface direction can be aligned in the surface direction by physical pressurization by the compression treatment (FIG. 2), the bending resistance is improved. Basically, the greater the compression pressure, the thinner the graphite film and the higher the bending resistance.

  The method for compressing the post-graphitizing film of the present invention may be any method as long as it is a method capable of compressing the post-graphitizing film in a foamed state. In particular, the post-rolling step and the rear surface pressing step are particularly excellent methods because the film can be uniformly compressed.

<Post-rolling process>
As a method for compressing the film after the graphitization treatment, there is a post-rolling step as described in Patent Document 2. Specifically, a method of passing two ceramic or stainless steel rollers is described.

  However, in the post-rolling process using the conventional post-graphitized film, the graphite film is stretched by applying linear pressure at the contact portion with the roller during the rolling process, and is formed into a planar shape. In some cases, the layer was broken and the bending resistance and thermal diffusivity were lowered. In addition, there is a problem of bending resistance and thermal diffusibility variation due to partial density variations and low density, and deterioration of flex resistance and thermal diffusivity due to containing many air layers. . Further, when the graphite film is rolled using a high strength material such as a metal roller, there is a problem in that scratches and wrinkles are easily formed on the surface, and dents and vertical stripes are generated. Furthermore, particularly when rolling with a strong force to increase the degree of compression, there is a case where the film is compressed while wrinkling the film after the graphitization treatment and generating creases (entrainment creases).

The film after the graphitization treatment of the present invention has a density of 0.70 g / cm ³ or more and 1.68 g / cm ³ or less, which suppresses the degree of foaming more than usual, and has less waviness and thickness variation. It is easier to carry out the post-rolling step than the post-treatment film. Therefore, the post-graphite-treated film subjected to the post-rolling process becomes a graphite film with little wrinkles, broken wrinkles (rolling wrinkles), and thickness variations.

<Rear surface pressure process>
In the post-rolling process described above, when the density of the film after the graphitization treatment is high, a graphite film with little wrinkles, creases (rolling wrinkles), and thickness variations can be produced to some extent, but it may not be sufficient.

  Therefore, as a compression method for producing a higher quality graphite film, there is a rear surface pressurizing step in which the graphitized film is pressed into a planar shape. Since the back surface pressing step can uniformly press in the surface direction, it is superior in bending resistance compared to the rolling step, and it is possible to produce a high quality graphite film with very little thickness variation and wrinkles.

  The rear surface pressing step is superior to the post-rolling step for the following reasons 1 to 4.

  (Reason 1) Since the film after the graphitization treatment having a small density has many undulations, it may generate creases (entrainment creases) during the post-rolling process. However, in the rear surface pressurizing step, such folded wrinkles (entrainment wrinkles) are unlikely to occur because the surface pressure is applied.

(Reason 2) Since the film after the graphitization treatment having a small density has a large thickness variation, it is difficult to press uniformly in the post-rolling process. However, in the rear surface pressurizing step, the film can be uniformly pressed regardless of the thickness variation because of pressurization in the surface state (reason 3). A large compression pressure is required. However, it is difficult to increase the compression pressure in the post-rolling process. Increasing the pressure tends to damage the graphite. In addition, many folds (entrainment folds) occur. In the rear surface pressurizing step, it is difficult to damage the graphite even if the pressure is increased, and creases (entrainment creases) do not occur.

  (Reason 4) In the post-rolling process, the compression pressure is difficult to adjust because the nip width is fixed. On the other hand, the rear surface pressurization can adjust the compression pressure, and the pressure can be adjusted according to the state of the film after the graphitization treatment. In addition, the pressure can be gradually increased or decreased, and compression suitable for the state of the film after graphitization is possible.

  In the method for producing a graphite film according to the present invention, the polymer film graphitized through the graphitization step, that is, the film after the graphitization treatment, further includes pressing in a planar shape (rear surface pressing step). It is preferable to obtain a graphite film with excellent bending resistance, thermal diffusivity, scratches and dents on the surface, no wrinkles, and excellent flatness. is there. Such a (rear surface pressing step) can be performed even at room temperature. In such a (rear surface pressurizing step), it is preferable to press in a planar shape together with the film-like medium other than the post-graphitized film.

  In addition, it is preferable to press the sheet in a state where a plurality of the graphite films are laminated and arranged, and the graphite film itself plays a role as a cushioning material, so that the graphite having excellent flatness without scratching the surface. A film can be obtained.

  Such (rear surface pressing) can be performed by a single plate press, a vacuum press or the like. More specifically, a graphite film is sandwiched between a plastic plate, a ceramic plate, and a metal plate with a bolt by using a press that can press the graphite film in a plane, such as a press, a hot press, or a single plate press. There is a method of tightening. By using these methods, it becomes possible to pressurize uniformly in a planar shape, the graphite layer is compressed without breakage, does not cause a decrease in thermal diffusivity, high thermal diffusivity, high density, A graphite film having no flaws and no wrinkles on the surface can be obtained.

  In addition, the pressurization process can be carried out in several stages. Especially for a film after a graphitization treatment with large undulations, if it is pressurized with a large pressure from the beginning, it causes wrinkles and folds (entrainment wrinkles). In such a case, it is better to first pressurize with a weak pressure first and then pressurize with a higher pressure after the prepressurization. Furthermore, compression unevenness may occur due to thickness tolerance of single plate press, film-like media, etc.In such a case, press once, change the position of the film after graphitization, and press again A graphite film with little thickness variation can be obtained.

<Film medium>
Examples of the film-like medium other than the post-graphitized film include a graphite film obtained from natural graphite, a resin film, a metal plate, and a metal foil. Specific examples include graphite films obtained from natural graphite, buffer rubber materials, iron plates, Teflon (registered trademark) films, polyimide films, and PET films.

  Examples of the “with film-like medium” include the following modes. For example, (a medium other than the film after the graphitization treatment / one piece of the graphite film / a medium other than the graphite film / one piece of the graphite film / a medium other than the film after the graphite treatment /...) (Non-graphite treated film / multiple sheets of post-graphitized film / medium other than post-graphitized film / multiple sheets of post-graphitized film / non-graphitized film) In the case of sandwiching like a medium / ...).

<Bending resistance of graphite film (MIT)>
The number of bendings (R is 2 mm, left and right bending angle 135 °, spring φ14 mm) in the MIT bending resistance test of the graphite film produced by the method for producing a graphite film of the present invention is 500 times or more, preferably 1000 times or more, and Preferably 5000 times or more is good. When the MIT bending resistance test is 500 times or more, it is flexible and easy to handle. On the other hand, a graphite film of less than 500 times is difficult to handle and may be destroyed when attached to equipment.

  Moreover, in the use used especially in a bending part, it is 10,000 times or more, Preferably it is 50000 times or more, More preferably, 100,000 times or more is good. If it is 10,000 times or more, since it is excellent in bending resistance, it is difficult to break even if it is used in a bent portion. Specifically, even when it is used at a hinge of a mobile phone or a bent portion of a small electronic device, it can be used without reducing its function. Moreover, since it is excellent in bending resistance, handling property at the time of attachment to an electronic device is also improved.

<Bending radius and bending angle of MIT bending test>
The MIT bending resistance test of the graphite film can be measured using an MIT fatigue resistance tester model D manufactured by Toyo Seiki Co., Ltd. In the measurement, the bending radius R and the bending angle can be selected, and R can be selected to be 2 mm, 1 mm, or the like. Usually, the smaller the bending radius R and the larger the bending angle, the more severe the test. In particular, in electronic devices such as mobile phones, game machines, liquid crystal TVs, and PDPs, which have a small space, it is very important that the device has a small folding radius and a large folding angle, which enables space-saving design of the device. is there. The details of the MIT test method are described in the Examples column.

<Pressure in rear surface pressurization process>
The pressure for pressurizing the film after graphitization treatment in the rear surface pressurizing step of the present invention into a planar shape is 2 MPa to 40 MPa, preferably 4 MPa to 20 MPa, more preferably 8 MPa to 15 MPa. When the pressure for pressurizing the film after the graphitization treatment is less than 2 MPa, the pressure is too small to sufficiently compress the film, resulting in a graphite film with poor bending resistance. On the other hand, if the pressure for pressurizing the film after graphitization treatment is larger than 40 MPa, the pressure is too large and the graphite film is destroyed during the compression treatment, and the graphite film having poor bending resistance, thermal diffusibility, and poor appearance Become.

<Density of graphite film after back surface pressurization process>
The density of the graphite film after after planar pressurization step of the present invention, 1.50 g / cm ³ or more 2.20 g / cm ³ or less, preferably 1.60 g / cm ³ or more 2.15 g / cm ³ or less, more preferably 1.75 g / cm ³ or more and 2.10 g / cm ³ or less. When the density of the graphite film after the back surface pressurizing step is smaller than 1.0 g / cm ³ , the graphite film is insufficient in compression and has poor bending resistance. On the other hand, if the density of the graphite film after the back surface pressurization step is larger than 2.40 g / cm ³ , the compression is too large and the graphite film is destroyed during the compression treatment, resulting in bending resistance, thermal diffusibility, and appearance. Bad graphite film.

<Thickness unevenness of the graphite film after the rear surface pressing step>
When the thickness of the graphite film is uneven, the bending resistance may be deteriorated because stress for bending is concentrated on the thick portion. In addition, excellent properties of the graphite film such as thermal diffusivity, electrical conductivity, and tensile strength are impaired.

  Since the film after the graphitization treatment with a small density has a large thickness variation, it is difficult to press uniformly in the post-rolling process. However, in the rear surface pressurizing step, since the surface is pressed, it can be uniformly applied regardless of the thickness variation.

<Folding wrinkles (rolling wrinkles) of the graphite film after the rear surface pressurizing step>
If the graphite film has a crease (entrainment crease), the bending resistance may be deteriorated because stress to the fold is concentrated on the crease. In addition, excellent properties of the graphite film such as thermal diffusivity, electrical conductivity, and tensile strength are impaired.

  Since the film after the graphitization treatment with a small density has many undulations, it may generate creases (entrainment creases) during the post-rolling process. However, in the rear surface pressurizing step, such folded wrinkles (entrainment wrinkles) are unlikely to occur because the surface pressure is applied.

<Applications>
Since it is excellent in flexibility and electrical conductivity, it is particularly suitable for applications utilizing this feature. The characteristics of graphite film that excel in heat conduction are that it is necessary for applications that need to transfer heat, escape heat, spread heat, make heat uniform, make heat response faster, warm faster, cool faster. Is suitable. By spreading the heat instantaneously, it is possible to prevent and mitigate sudden temperature changes, or to avoid local heat concentration. On the other hand, it can be used for applications that cause sudden changes or detect slight changes in heat. By relaxing the heat, strength and adhesiveness can be ensured even in a high temperature environment. In addition, by transferring heat uniformly and accurately, characteristics such as high accuracy, high quality, and high image quality can be improved. When used in manufacturing equipment, it is possible to improve productivity by shortening tact time, improving heating / cooling efficiency, improving drying efficiency, speeding up, and shortening waiting time by taking advantage of the ability to transport heat quickly and in large quantities. . In addition, it is possible to reduce defects and enhance the heat retaining function by uniformizing heat and quick transportation. In addition, by adopting it in various devices, it is possible to save space, thin film, reduce weight, simplify the mechanism, improve the degree of freedom of installation, and eliminate unnecessary parts to save power and reduce noise. It becomes possible. In addition, since heat can be released, there is no deterioration in characteristics even in heat cycle environmental tests and annealing treatments, solder heat resistance, adhesive layer adhesion, heat resistance, reliability, durability can be improved, and heat insulation can be improved. It can also be increased and protected from heat-sensitive parts. As a result, maintenance can be reduced, cost can be reduced, and safety can be improved.

  Specific applications include the following. For example, electronic devices such as servers, server personal computers, desktop personal computers, word processors, keyboards, and games, portable electronic devices such as notebook computers, electronic dictionaries, PDAs, mobile phones, portable game devices, and portable music players. Liquid crystal display, transmissive liquid crystal display device, reflective LCD panel, plasma display, SED, LED, organic EL, inorganic EL, liquid crystal projector, rear projector, liquid crystal panel, backlight device (variation prevention, temperature unevenness improvement), TFT substrate , Electron emission devices, electron source substrates and face plates (weight reduction), display panel frame composites, light emitting devices, charge injection light emitting devices, optical and display devices such as watches, and parts thereof. Light emitting / illuminating devices such as lasers, semiconductor lasers, light emitting diodes, fluorescent lamps, incandescent bulbs, light emitting dots, issuing element arrays, lighting units, flat light emitting devices, and document lighting devices. Single or multiple recording heads (heater, heat insulating material, heat storage layer, etc.) for inkjet (spreading ink using thermal energy), line heads, long ink heads, solid ink jet devices, heat dissipation for ink jet heads Ink jet printer (ink head) devices such as plates, ink cartridges, ink jet head silicon substrates, ink jet drive drivers, and heating sources (halogen lamp heaters) for heating ink jet recording paper, and parts thereof. Toner cartridge, device having laser light source, scanning optical device (light emitting unit, deflection scanning polygon mirror, polygon mirror rotation driving motor, optical component leading to photosensitive drum), exposure device, developing device (photosensitive drum, light receiving member, Development roller, development sleeve, cleaning device), transfer device (transfer roll, transfer belt, intermediate transfer belt, etc.), fixing device (fixing roll (core, outer peripheral member, halogen heater, etc.), surf heater, electromagnetic induction heater, ceramic Electrophotographic equipment consisting of heater, fixing film, film heating device, heating roller, pressure roller / heating body, pressure member, belt nip), sheet cooling device, sheet loading device, sheet discharge device, sheet processing device, etc. Image forming apparatus and parts thereof. In the fixing device, the effect of improving the thermal characteristics due to the use of graphite film is remarkable, including uneven image quality in the width direction, image quality defects, image quality variation in continuous paper feeding, rise / fall time, real-time support, high temperature followability, paper feeding The temperature difference, wrinkle, strength, power saving, on-demand heating, high temperature offset and low temperature offset, overheating of the heater peripheral member, and heater cracking can be greatly improved. Other recording devices such as thermal transfer recording devices (ribbons), dot printers, sublimation printers. Semiconductor-related parts such as semiconductor elements, semiconductor packages, semiconductor sealing cases, semiconductor die bonding, liquid crystal display element driving semiconductor chips, CPUs, MPUs, memories, power transistors, and power transistor cases. Printed circuit board, rigid wiring board, flexible wiring board, ceramic wiring board, build-up wiring board, mounting board, high-density mounting printed circuit board, (tape carrier package), TAB, hinge mechanism, sliding mechanism, through hole, resin packaging Wiring boards such as sealing materials, multilayer resin moldings, and multilayer boards. CD, DVD (optical pickup, laser generator, laser receiver), Blu-ray disc, DRAM, flash memory, hard disk drive, optical recording / reproducing device, magnetic recording / reproducing device, magneto-optical recording / reproducing device, information recording medium, optical recording disc , Magneto-optical recording medium (translucent substrate, optical interference layer, domain wall motion layer, intermediate layer, recording layer, protective layer, heat dissipation layer, information track), light receiving element, light detecting element, optical pickup device, magnetic head, light Magnetic recording magnetic heads, semiconductor laser chips, laser diodes, laser drive ICs and other recording devices, recording / reproducing devices, and parts thereof. Digital camera, analog camera, digital single-lens reflex camera, analog single-lens reflex camera, digital camera, digital video camera, camera-integrated VTR, camera-integrated VTR IC, video camera light, electronic flash device, imaging device, imaging tube cooling Apparatus, imaging apparatus, imaging element, CCD element, lens barrel, image sensor and information processing apparatus using the same, X-ray absorber pattern, X-ray mask structure, X-ray imaging apparatus, X-ray exposure apparatus, X-ray Flat detector, X-ray digital imaging device, X-ray area sensor substrate, electron microscope sample cooling holder, electron beam drawing device (electron gun, electron gun, electron beam drawing device), radiation detection device and radiation imaging system, scanner, Image reading device, moving image pickup device and still image pickup device, image recording device such as a microscope, and parts thereof. Primary batteries such as alkaline batteries and manganese batteries, secondary batteries such as lithium ion batteries, nickel metal hydride and lead storage batteries, electric double layer capacitors, electrolytic capacitors, assembled batteries, solar cells, solar cell module installation structures, photoelectric conversion substrates, Heat dissipation materials for battery devices such as photovoltaic element arrays, power generation elements, and fuel cells (power generation cells, outside the housing, inside the fuel tank). Power supplies (rectifier diodes, transformers), DC / DC converters, switching power supply devices (forward type), current leads, superconducting device systems, etc. and their components. Motors and parts such as motors, linear motors, planar motors, vibration wave motors, motor coils, circuit units for rotational control drive, motor drivers, inner rotor motors, vibration wave actuators, etc. Vacuum processing equipment, semiconductor manufacturing equipment, vapor deposition equipment, thin film single crystal semiconductor layer manufacturing equipment, plasma CVD, microwave plasma CVD, sputtering equipment, vacuum chambers, vacuum pumps, vacuum pumps, cryotraps, cryopumps, etc., electrostatic chucks , Vacuum vacuum chucks, pin chuck type wafer chucks, sputtering targets, semiconductor exposure devices, lens holding devices and projection exposure devices, photomasks, and other deposited film manufacturing devices (temperature constant, quality stable) and parts thereof. Heat treatment equipment by resistance heating / induction heating / infrared heating, dryer, annealing equipment, laminating equipment, reflow equipment, heat bonding (crimping) equipment, injection molding equipment (nozzles / heating section), resin molding dies, LIM molding, rollers Molding equipment reformed gas production (reforming part, catalyst part, heating part, etc.) stamper, (film, roll, recording medium), bonding tool, catalyst reactor, chiller, color filter substrate coloring device, resist Various manufacturing devices such as heating / cooling devices, welding equipment, magnetic induction heating films, anti-condensation glass, liquid remaining amount detection devices, heat exchange devices, and parts thereof. Heat insulation devices such as heat insulation materials, vacuum heat insulation materials, and radiation heat insulation materials. Chassis, housing, and exterior cover for various electronic and electrical equipment and manufacturing equipment. Heat dissipation components such as radiators, openings, heat pipes, heat sinks, fins, fans, and heat dissipation connectors. Cooling parts such as Peltier elements, electrothermal conversion elements, and water-cooled parts. Temperature control device, temperature control device, temperature detection device and parts. Heating element-related parts such as thermistors, thermoswitches, thermostats, thermal fuses, overvoltage protection elements, thermoprotectors, ceramic heaters, flexible heaters, composites of heaters, heat conduction plates and insulation, heater connectors and electrode terminal parts. Suitable for radiating parts with high emissivity, electromagnetic shielding parts such as electromagnetic shielding and electromagnetic wave absorbers, composites with metals such as aluminum, copper and silicon, and composites with ceramics such as silicon nitride, boron nitride and alumina is there.

  In the following, various embodiments of the present invention will be described along with some comparative examples.

[Production Method of Polyimide Film A]
In a DMF (dimethylformamide) solution in which 1 equivalent of 4,4′-oxydianiline was dissolved, 1 equivalent of pyromellitic dianhydride was dissolved to obtain a polyamic acid solution (18.5 wt%).

  While this solution was cooled, an imidation catalyst containing 1 equivalent of acetic anhydride, 1 equivalent of isoquinoline, and DMF was added to the carboxylic acid group contained in the polyamic acid to degas. Next, this mixed solution was applied onto an aluminum foil so as to have a predetermined thickness after drying. The mixed solution layer on the aluminum foil was dried using a hot air oven and a far infrared heater.

  The drying conditions for film production when the finished thickness is 75 μm are shown below. The mixed solution layer on the aluminum foil was dried in a hot air oven at 120 ° C. for 240 seconds to form a self-supporting gel film. The gel film was peeled off from the aluminum foil and fixed to the frame. Further, the gel film was heated stepwise in a hot air oven at 120 ° C. for 30 seconds, 275 ° C. for 40 seconds, 400 ° C. for 43 seconds, 450 ° C. for 50 seconds, and a far infrared heater at 460 ° C. for 23 seconds. And dried.

  In addition, when producing films with other thicknesses, the firing time was adjusted in proportion to the thickness. For example, in the case of a film having a thickness of 50 μm, the baking time was set to 2/3 times that in the case of 75 μm, and in the case of a film having a thickness of 125 μm, it was set to 5/3 times. When the thickness is large, it is necessary to take a sufficient baking time at a low temperature in order to prevent foaming due to evaporation of the solvent or imidization catalyst of the polyimide film.

<Various physical property measurement conditions>
<Measurement of film thickness after graphitization>
As a method for measuring the thickness of the film after the graphitization treatment, a 10 cm × 10 cm film was measured in a thermostatic chamber at room temperature of 25 ° C. using a thickness gauge (Heidenhain Co., Ltd., HEIDENHAIN-CERTO). When the lower left end of the graphite film is (0, 0), the measurement location is (1, 1), (1, 5), (1, 9), (5, 1), (5, 5), Nine points (5, 9), (9, 1), (9, 5), (9, 9) were measured and averaged to obtain a measured value (FIG. 3).

<Density measurement of film after graphitization treatment>
The density of the film after the graphitization treatment was calculated by multiplying the weight (g) of the 10 cm square film after the graphitization treatment by the product of the length (10 cm), the width (10 cm), and the thickness of the film after the graphitization treatment (cm ³ ). It was calculated by dividing.

<Measurement of thermal diffusivity in the surface direction of the film after graphitization>
The thermal diffusivity in the surface direction of the film after the graphitization treatment was measured using a thermal diffusivity measuring device (“LaserPit” available from ULVAC-RIKO Co., Ltd.) by an optical alternating current method. Samples were cut and measured at 10 Hz in a 20 ° C. atmosphere.

<Thickness measurement of graphite film>
As a method for measuring the thickness of the graphite film, a 10 cm × 10 cm film was measured in a thermostatic chamber at room temperature of 25 ° C. using a thickness gauge (Heidenhain Co., Ltd., HEIDENHAIN-CERTO). When the lower left end of the graphite film is (0, 0), the measurement location is (1, 1), (1, 5), (1, 9), (5, 1), (5, 5), Nine points (5, 9), (9, 1), (9, 5), and (9, 9) were measured and averaged to obtain a measured value. <Density measurement of graphite film>
The density of the graphite film was calculated by dividing the weight (g) of the 10 cm square graphite film by the volume (cm ³ ) calculated by the product of the vertical (10 cm), horizontal (10 cm), and thickness of the graphite film.

<MIT bending resistance test of graphite film>
The conditions of the MIT bending resistance test of the graphite film using the raw film having a thickness of 50 μm and 75 μm are as follows. A graphite film is cut to 1.5 × 10 cm, and a test load of 100 gf (0.98 N), a speed of 90 times / minute, a bending clamp curvature is used, using a model D of Toyo Seiki Co., Ltd. The radius R was 2 mm. The bending angle was measured at 135 ° to the left and right. A spring with a diameter of 14 mm was used.

  The conditions of the MIT bending resistance test of the graphite film using the raw film having a thickness of 25 μm and 125 μm were the same as the above conditions except that the bending angle was measured at 90 ° to the left and right.

<Thickness unevenness of graphite film>
The thickness unevenness of the graphite film was evaluated by the difference between the maximum value and the minimum value of 9 points measured by measuring the thickness of the graphite film. When the difference in thickness was 0 to 3 μm, ◎, 3 to 5 μm was ◯, 5 to 7 μm was Δ, and x was larger than 7 μm.

<Folding folds of graphite film (rolling folds)>
The crease (entrainment crease) of the graphite film was visually observed. A case where no folds were confirmed, a case where folds of less than 5 cm were confirmed, and a case where folds of 5 cm or more were confirmed were rated as x.

Example 1
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. A carbonized film obtained by carbonization is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 2 ° C./min using a graphitization furnace to perform a graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Example 2)
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Example 3)
A polyimide film A (PI-A) having a thickness of 50 μm (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 5 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

Example 4
A polyimide film A (PI-A) having a thickness of 50 μm (length: 200 mm × width: 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 10 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Example 5)
A 75 μm-thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. A carbonized film obtained by carbonization is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 2 ° C./min using a graphitization furnace to perform a graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Example 6)
A 75 μm-thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Example 7)
A 75 μm thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 5 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Example 8)
A 75 μm thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 10 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

Example 9
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a post-rolling step was performed using a rolling roller.

(Example 10)
A 75 μm-thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a post-rolling step was performed using a rolling roller.

(Example 11)
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 2 MPa.

(Example 12)
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 5 MPa.

(Example 13)
A 75 μm-thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 5 MPa.

(Example 14)
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 20 MPa.

(Example 15)
A 75 μm-thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 20 MPa.

(Example 16)
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 40 MPa.

(Example 17)
A 25 μm-thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 0.5 ° C./min using an electric furnace. . A carbonized film obtained by carbonization is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and is graphitized by raising the temperature to 2900 ° C. at 10 ° C./min using a graphitization furnace. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Example 18)
A 125 μm thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 5 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 1 ° C./min using a graphitization furnace to perform the graphitization treatment. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Comparative Example 1)
A polyimide film A (PI-A) (length: 200 mm × width: 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 1 ° C./min using an electric furnace. A carbonized film obtained by carbonization is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and is graphitized by raising the temperature to 2900 ° C. at 5 ° C./min using a graphitization furnace. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Comparative Example 2)
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. A carbonized film obtained by carbonization is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and is graphitized by raising the temperature to 2900 ° C. at 5 ° C./min using a graphitization furnace. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Comparative Example 3)
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 15 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 0.5 ° C./min using a graphitization furnace. I did it. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Comparative Example 4)
A 75 μm thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 1 ° C./min using an electric furnace. A carbonized film obtained by carbonization is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and is graphitized by raising the temperature to 2900 ° C. at 5 ° C./min using a graphitization furnace. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Comparative Example 5)
A 75 μm-thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. A carbonized film obtained by carbonization is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and is graphitized by raising the temperature to 2900 ° C. at 5 ° C./min using a graphitization furnace. It was. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Comparative Example 6)
A 75 μm-thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 15 ° C./min using an electric furnace. The carbonized film obtained by the carbonization treatment is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and the temperature is raised to 2900 ° C. at 0.5 ° C./min using a graphitization furnace. I did it. After cooling to room temperature, the graphitized film after the heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a back surface pressing step was performed using a compression molding machine. The applied pressure was 10 MPa.

(Comparative Example 7)
A polyimide film A (PI-A) (length 200 mm × width 200 mm) having a thickness of 50 μm was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. A carbonized film obtained by carbonization is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and is graphitized by raising the temperature to 2900 ° C. at 5 ° C./min using a graphitization furnace. It was. After cooling to room temperature, the graphitized film after heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a post-rolling step was performed using a rolling roller.

(Comparative Example 8)
A 75 μm-thick polyimide film A (PI-A) (length 200 mm × width 200 mm) was sandwiched between graphite plates, and carbonized by heating to 1000 ° C. at 2 ° C./min using an electric furnace. A carbonized film obtained by carbonization is sandwiched from above and below by an expanded graphite sheet having a length of 250 mm, a width of 250 mm, and a thickness of 250 μm, and is graphitized by raising the temperature to 2900 ° C. at 5 ° C./min using a graphitization furnace. It was. After cooling to room temperature, the graphitized film after heat treatment was sandwiched from above and below by a polyimide film having a length of 250 mm × width of 250 mm × thickness of 125 μm, and a post-rolling step was performed using a rolling roller.

  Table 1 summarizes various physical properties of the graphitized film and the compressed graphite film used in Examples and Comparative Examples measured by the inventor / applicant.

<MIT bending resistance test of graphite film>
As a result of the MIT bending resistance test, Examples 1 to 18 were bent 1000 times or more, and Comparative Examples 1 to 8 were less than 500 times, and the density was 0.70 g / cm ³ or more. For a post-graphitized film of 68 g / cm ³ or less, (1) a post-surface pressurizing step of pressing the post-graphitized film into a surface, or (2) a post-rolling step of rolling the post-graphitized film As a result, a graphite film exhibiting excellent bending resistance was obtained.

● Density and flex resistance of film after graphitization treatment ・ Polyimide film with a raw material thickness of 50 μm When comparing Examples 1 to 4 and Comparative Examples 1 to 3, the density after graphitization treatment is 0.70 g / cm ³ or more. When it is in the range of 1.68 g / cm ³ or less, the number of bending is 1000 times or more. Further the density is in the range of 0.70 g / cm ³ or more 1.50 g / cm ^3, it can be seen that the bending resistance number 10000 or more times and that excellent bending. The graphitized film prepared so as to have such a density exhibits very excellent bending resistance when subjected to compression treatment because the growth in the plane direction of the graphite layer is very excellent. .

On the other hand, when the density of the film after the graphitization treatment is smaller than 0.70 g / cm ³ , the degree of foaming is too large as in Comparative Examples 1 and 2, and the graphite layer is broken, so Bad graphite film. If the density of the film after graphitization is greater than 1.68 g / cm ³ , the degree of foaming is too small as in Comparative Example 3, resulting in poor flex resistance.

-Polyimide film whose raw material thickness is 75 micrometers Even if Examples 5-8 and Comparative Examples 4-6 are compared, it turns out that it exists in the same tendency as the case of the polyimide film whose raw material thickness is 50 micrometers.

-In the case of a post-rolling process Even if it compares the Examples 9-10 which performed the post-rolling process, and Comparative Examples 7-8, the density of the film after a graphitization process is 0.70 g / cm < ³ > or more. It can be seen that the bending resistance is high when it is in the range of cm ³ or less.

● Post-rolling step and rear surface pressing step and bending resistance ・ Polyimide film with a raw material thickness of 50 μm Graphitization with the same density as Example 2 in which a post-graphitizing film obtained by heat treatment was subjected to a rear surface pressing step When Example 9 which carried out the post-rolling process of the process film is compared, it turns out that the direction which performed the back surface pressure process has many frequency | counts of bending.

  This is because, in the post-rolling process, the graphitized film is passed through two stainless steel rollers, so that the graphite film is stretched by applying linear pressure at the contact portion with the rollers, and formed into a flat shape. It seems that the graphite layer is broken and the bending resistance is lowered.

  In addition, the post-rolled graphite film has many creases (rolling creases) and thickness variations, and the bending resistance is thought to have deteriorated due to the concentration of bending stresses in non-uniform areas such as creases and thickness variations. It is.

  In addition, since it is difficult to increase the compression pressure in the post-rolling process, it is considered that the reason why the bending resistance is poor is that the compression cannot be sufficiently performed.

-Polyimide film with a raw material thickness of 75 [mu] m Even when Example 6 and Example 10 are compared, it can be seen that there is a tendency similar to the case of a polyimide film with a raw material thickness of 50 [mu] m.

-Compression pressure and bending resistance in the rear surface pressing step-Polyimide film with a raw material thickness of 50 µm When comparing Examples 2, 11, 12, 14, and 16, the pressure in the rear surface pressing step is 2 MPa or more. The number of bending is 1000 times or more. Further, it can be seen that when the pressure is 4 MPa or more, the bending frequency is 5000 times or more, and when the pressure is 8 MPa or more, 10,000 or more is shown, which shows very excellent bending resistance. Thus, the bending resistance improves as the compression pressure in the rear surface pressurizing step increases.

-Polyimide film with a raw material thickness of 75 μm Even when Examples 6, 13, and 15 are compared, it can be seen that the same tendency as in the case of a polyimide film with a raw material thickness of 50 μm is observed.

<Measurement of thermal diffusivity of graphite film>
Density and thermal diffusivity of film after graphitization treatment ・ Polyimide film with a raw material thickness of 50 μm When comparing Examples 1 to 4 and Comparative Examples 1 to 3, the density of the film after graphitization treatment is small (the degree of foaming is large) ), The thermal diffusivity becomes worse. Conventionally, the thermal diffusivity of the graphite film can be improved by suppressing the degree of foaming of the post-graphitized film as in the present invention (by preparing the graphitized film so as to increase the density).

-Polyimide film whose raw material thickness is 75 micrometers Even if Examples 5-8 and Comparative Examples 4-6 are compared, it turns out that it exists in the same tendency as the case of the polyimide film whose raw material thickness is 50 micrometers.

<Thickness unevenness of graphite film>
● Density and thickness unevenness of graphitized film ・ Polyimide film having a raw material thickness of 50 μm Comparing Examples 1 to 4 and Comparative Examples 1 to 3, the density after graphitizing was 0.7 g / cm ³ or more. When it is in the range of 68 g / cm ³ or less, the thickness of the film after graphitization is small, so that the compression treatment is very easy, and the thickness of the graphite film after compression is very small. When the density of the film after the graphitization treatment is reduced (when the degree of foaming is increased), the thickness variation of the film after the graphitization treatment is increased, so that the thickness unevenness of the graphite film after the compression is also increased. Moreover, when the density of the film after a graphitization process is too large, since the film is hard and is hard to compress, the thickness nonuniformity of the graphite film after compression increases.

-Polyimide film whose raw material thickness is 75 micrometers Even if Examples 5-8 and Comparative Examples 4-6 are compared, it turns out that it exists in the same tendency as the case of the polyimide film whose raw material thickness is 50 micrometers.

● Post-rolling step and rear surface pressing step and thickness unevenness ・ Polyimide film with a raw material thickness of 50 μm Graphitization treatment with the same density as Example 2 in which a post-graphitizing film obtained by heat treatment was subjected to a rear surface pressing step Comparing Example 9 in which the film was post-rolled, it can be seen that there was more thickness unevenness when the post-rolling process was performed.

  This is because, in the post-rolling step, the film after graphitization treatment is passed through two stainless steel rollers, so that pressure is applied uniformly in order to compress the film while applying linear pressure at the contact portion with the rollers. Because it is difficult.

-Polyimide film whose raw material thickness is 75 micrometers Even if Example 6 and Comparative Example 10 are compared, it turns out that it exists in the same tendency as the case of the polyimide film whose raw material thickness is 50 micrometers.

● Compression pressure and thickness unevenness in the rear surface pressurizing process ・ Polyimide film having a raw material thickness of 50 μm When comparing Examples 2, 11, 12, 14, and 16, the thickness unevenness decreases as the pressure in the rear surface pressurizing process increases. I understand that.

-Polyimide film with a raw material thickness of 75 [mu] m Even when Examples 10, 13, and 15 are compared, it can be seen that there is a tendency similar to the case of a polyimide film with a raw material thickness of 50 [mu] m.

<Folding folds of graphite film (rolling folds)>
● Post-rolling step and rear surface pressing step and crack • Polyimide film with a raw material thickness of 50 μm Graphitization treatment with the same density as Example 2 in which a post-graphitizing film obtained by heat treatment was subjected to a rear surface pressing step When Example 9 in which the film was post-rolled was compared, the film subjected to the back surface pressurizing process did not generate creases (rolling wrinkles), but the film subjected to the post-rolling treatment was particularly graphitized. The smaller the density of the rear film, the more folds (entrainment wrinkles) occurred.

  This is because, in the post-rolling step, the film after the graphitization treatment is passed through two stainless steel rollers, so that the wrinkle of the film after the graphitization treatment is involved and large creases are generated.

-Polyimide film whose raw material thickness is 75 micrometers Even if Example 6 and 10 are compared, it turns out that it exists in the same tendency as the case of the polyimide film whose raw material thickness is 50 micrometers.

  As described above, it can be seen that the graphite film of the present invention has both excellent bending resistance that can withstand use at a bent portion and excellent thermal diffusibility that can quickly diffuse heat from a heat generating portion. In particular, Examples 1 to 3, 5 to 7, and 14 to 16 have excellent bending resistance and thermal diffusibility.

11 Graphite layer 12 Graphite film surface direction 31 Measurement points 32 Reference point (0, 0)

Claims (4)

In a method for producing a graphite film including a graphitization step of heat-treating a polymer film having a thickness of 5 μm or more and 250 μm or less at a temperature of 2400 ° C. or more, and a post-treatment step,
The density of the film after graphitization treatment is 0.7 g / cm ³ or more and 1.68 g / cm ³ or less, and the post-treatment step is a post-rolling step of rolling the film after graphitization treatment,
Graphite film obtained by subjecting the rear rolling step has a density, 1.5 g / cm ³ or more 2.20 g / cm ³ or less and the number bent at MIT bending test is more than 5000 times A method for producing a graphite film. The method for producing a graphite film according to claim 1, wherein a thermal diffusivity in a plane direction of the graphite film is 7.0 × 10 ⁻⁴ m ² / s or more.   3. The method for producing a graphite film according to claim 1, wherein a graphitization temperature rising rate in the graphitization step is 0.1 ° C./min or more and 15 ° C./min or less.   The method for producing a graphite film according to any one of claims 1 to 3, wherein, in the post-rolling step, the post-graphitizing film is sandwiched from above and below by the film and rolled.

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