JP5642990B2 - Method for producing graphite film - Google Patents

Description

  The present invention relates to a method for producing a scroll-like graphite film.

  The heat dissipating parts are used for semiconductor elements and other heat generating parts mounted on various electronic / electrical devices such as computers. When heat dissipation parts are used for large products, graphite films are long and large-area graphite films made from polymer films wound in rolls. Has been done.

  For example, there has been proposed a method in which a polymer film having a width of 250 mm and a length of 30 m is wound around a carbonaceous cylindrical core having an outer diameter of 150 mm (Patent Document 1). In this method, the shape of the obtained graphite film is proposed. There was a problem that quality variations such as collapse and tearing as shown in FIG.

JP 2006-327907 A

  The present invention is to solve the problem that the shape of a graphite film is broken and tearing easily occurs when the graphite film is rewinded.

That is, the present invention
The present invention relates to a method for producing a graphite film, characterized in that heat treatment is performed at a temperature of 2000 ° C. or higher in a state where the first surface of the polymer film is wound inward (Claim 1).
The method for producing a graphite film according to claim 1, wherein the amount of warpage of the polymer film is 0.5 mm or more and 16 mm or less (claim 2).
3. The method according to claim 1 or 2, further comprising a step of selecting the surface that was the first surface of the polymer film so as to be wound inside the roll, and performing a graphitization step after the step of selecting. The method for producing a graphite film according to claim 3 (claim 3),
Is.

  According to the method for producing a graphite film of the present invention, shape collapse is unlikely to occur. In addition, according to the method for producing a graphite film of the present invention, it is difficult for a tear failure to occur when the graphite film is rolled up.

Collapse of cylindrical shape of graphite film after graphitization process. A tear when a graphite film is stretched. Polymer film warpage. The curvature of the edge of the graphite film that has collapsed the cylindrical shape. Rewind test. Film tear during rewind test. The carbonization jig used at the time of the graphite preparation of this invention. The state set in the furnace of the graphitization process of the present invention. A container for performing the graphitization process in landscape orientation. Measurement of warpage of polymer film. Schematic of center slack and end slack. Schematic of the manufacturing apparatus of a polyimide film. Direction of warping of polyimide film, sampling place for warping amount measurement sample. Collection place for graphite film thermal diffusivity measurement sample.

  The present invention relates to a method for producing a graphite film in which a heat treatment is performed at a temperature of 2000 ° C. or higher in a state where a polymer film is wound in a cylindrical shape (hereinafter also referred to as a roll).

  By winding so that the 1st surface of a polymer film may become the inner side of a roll, the collapse of the cylindrical shape after heat processing and the crack defect at the time of rewinding a film can be suppressed.

<Polymer film warping direction, warping amount>
The polymer film used in the present invention has warpage. The warpage can be confirmed by a sag measurement in film winding property evaluation according to JIS C2151. Details are described in the Examples section. The direction of warping can be understood by checking the film edge as indicated by 31 and 32 in FIG. 31 is warped on the upper surface side, and 32 is warped on the lower surface side.

  The amount of warpage of the polymer film can be measured by a sag measurement in the film winding property evaluation according to JIS C2151. A test piece having a width of 100 mm (TD direction) and a length of 3000 mm (MD direction) is used. Details are described in the Examples section.

  The warpage amount of the polymer film used in the present invention is 1 mm or more and 16 mm or less, preferably 1.5 mm or more and 10 mm or less, and more preferably 2 mm or more and 8 mm or less. If it is 1 mm or more and 16 mm or less, the cylindrical shape of the fired graphite film does not collapse by heat treatment in a state where the first surface is wound inwardly, and there is little tearing from the end even if it is stretched, In addition, a graphite film that does not cause tearing failure even if it is rolled up is obtained.

<Definition of first surface and second surface of polymer film>
In this invention, a 2nd surface means the surface of the side where a film warps like FIG. The surface opposite to the second surface is defined as the first surface. By heat-treating the first surface of the polymer film so that it is wound inward, the cylindrical shape of the graphite film after firing does not collapse, and even if it is stretched, there is little tearing from the end, and rewinding Even in this case, a graphite film that does not cause poor tearing can be obtained.

<Method for producing graphite film>
The method for producing a graphite film of the present invention is a method for producing a graphite film by heat-treating a polymer film, and may include 1) a preparation step, 2) a carbonization step, and 3) a graphitization step. In order to suppress the shape of the film from collapsing and torn defects during rewinding, it is preferable to perform the graphitization step with the surface that was the first surface of the polymer film being inside the roll.

  1) In the preparation process, a polymer film such as a polyimide film is cut into a sheet shape and held between plates or sheets in a square jig, or a long polymer film is wound around an inner jig. There are ways to keep it. The jig used at this time is preferably a heat-resistant tool such as a graphite material. The inner core around which the polymer film is wound is preferably cylindrical.

  The method for producing a graphite film according to the present invention is characterized in that the first surface of the polymer film is heat-treated in a state of being wound inwardly. Therefore, if it prepares so that the 1st surface of a polymer film may become an internal winding in the step of a preparation process, it can manufacture, without performing rewinding etc. in a carbonization process and a graphitization process.

  2) The carbonization step is a step of preheating the polymer film held on the jig to a temperature of at least about 800 ° C., and is a step of thermally decomposing the polymer film to obtain a carbonized film. The obtained carbonized film weighs about 60% of the polymer film and is a glassy film.

  3) The graphitization step is a step of graphitizing by heating the carbonized film or polymer film prepared in the carbonization step at a temperature of 2000 ° C. or higher. The maximum graphitization temperature is 2000 ° C. or higher, preferably 2700 ° C. or higher, more preferably 2800 ° C. or higher, still more preferably 2900 ° C. or higher. When the temperature is 2000 ° C. or higher, graphitization proceeds and the film can be converted into a high-quality graphite film which is difficult to tear.

  The continuous body of the polymer film may be conveyed while being rolled, and may be continuously carbonized by passing through the furnace in the middle. When winding, the graphitization can be performed as it is by winding so that the first surface of the original polymer film is an inner winding.

  In the graphitization step, it is not necessary to hold the film on a jig, but in order to prevent the shape of the film from collapsing, it is preferable to heat-treat in a state where the first surface of the polymer film is wound inside. . Therefore, it is preferable from the viewpoint of workability to wind the polymer film so that the first surface of the polymer film is on the inner side in the preparation step. However, the carbonized film has the first surface of the polymer film on the inner side. The graphitization may be carried out by rewinding as described above.

  Further, the carbonization step and the graphitization step may be performed continuously, or the carbonization step may be terminated, and then only the graphitization step may be performed alone.

<Process to sort>
The step of sorting according to the present invention is a step of sorting and preparing the surface so that the surface that was the first surface of the polymer film is wound inside the scroll in the graphitization step.

  As long as the screening is prior to the graphitization process, the polymer film stage and the carbonized film stage are not limited.

<Polymer film of the present invention>
The polymer film used in the present invention is not particularly limited. For example, polyimide (PI), polyamide (PA), polyoxadiazole (POD), polybenzoxazole (PBO), polybenzobisoxazal (PBBO), Selected from the group consisting of polythiazole (PT), polybenzothiazole (PBT), polybenzobisthiazole (PBBT), polyparaphenylene vinylene (PPV), polybenzimidazole (PBI), polybenzobisimidazole (PBBI) A polymer film may be mentioned. By using at least one of these, it is easy to obtain a graphite film having excellent crystallinity and excellent thermal diffusivity and thermal conductivity.

<Thickness of polymer film>
The thickness of the polymer film of the present invention is not particularly limited, but is preferably 10 μm to 130 μm, more preferably 18 μm to 80 μm, and still more preferably 22 μm to 60 μm. When the thickness is 10 μm or more and 130 μm or less, the cylindrical shape of the fired graphite film is not collapsed and the cylindrical curl is stretched by performing heat treatment in a state where the first surface of the polymer film is wound inward. It is possible to obtain a graphite film that is difficult to tear even if it is rolled.

<Width and length of polymer film>
When the width of the polymer film of the present invention is 100 mm or more, further 200 mm or more, and particularly 400 mm or more, the shape of the resulting graphite film is likely to collapse, but the first surface of the polymer film of the present invention is internally wound. By performing the heat treatment in a state of being wound around, the cylindrical shape of the fired graphite film is not collapsed, the cylindrical curl can be stretched, and a graphite film that is difficult to tear even if it is rolled can be obtained.

  Further, when the length of the polymer film of the present invention is 10 m or more, further 20 m or more, particularly 40 m or more, the shape of the resulting graphite film is likely to be collapsed. By performing the heat treatment in a state of being wound, the cylindrical shape of the graphite film after firing is not collapsed, and the cylindrical curl can be stretched, and a graphite film that is difficult to tear even after rewinding can be obtained.

<Polyimide film>
As the polymer film of the present invention, a polyimide film is most suitable for the following reasons. (1) It is easy to obtain a graphite film having good crystallinity and good thermal diffusibility due to the progress of carbonization and graphitization of the film. (2) Molecules related to various structures and properties by selecting various raw material monomers. Easy to design. A polyimide film obtained by using a chemical cure method in which polyamic acid as a precursor is converted into an imide by using a dehydrating agent and amines in combination is more preferable.

  The polyimide film is likely to be warped because it is formed by the casting method, but by heat treatment in a state where the first surface of the present invention is wound inward, the shape collapse after firing is less likely to occur, A graphite film that is less prone to tear during rewinding is obtained.

<Method for forming polyimide film>
The collapse of the shape after firing of the graphite film, the cracking failure that occurs when the cylindrical shape is stretched, and the cracking failure that occurs during the rewinding operation are affected by the warping of the polyimide film that is the raw material. This warp of the polyimide film occurs in the film forming process.

  The manufacturing equipment for imidizing the polyimide precursor and finally making it a polyimide film product is largely divided into a drum chamber or belt chamber having a heating means for casting and chemical curing, and a tenter chamber for performing thermal curing. Divided.

  FIG. 12 shows an example of the production process of the polyimide film according to the present invention. First, the process in the belt chamber 1210 is a process in which a polyimide precursor mixed by a mixer is extruded into a film shape by a T-die 1212, and reaction hardening is performed. In the chamber, a film-like polyimide precursor extruded from a T-die is formed into a film on an endless belt or casting drum 1214. The precursor formed in the form of a film is imidized by being heated by a heating means while being moved by the rotation of a belt or a drum. In this belt chamber, products generated by the reaction, mainly combustible volatile components such as acetic acid and organic solvents evaporate.

  The temperature conditions in the belt chamber are exemplified. The belt 1 chamber is 100 ° C., the belt 2 chamber 120 ° C., the belt 3 chamber 130 ° C., and the cooling pulley 1226 is self-supported by the cast film according to the temperature conditions such as 80 ° C. Sex is imparted. Although the details of the mechanism are not known, the temperature condition of the belt chamber, the temperature condition of the cooling pulley, and the rotation speed of the belt influence the warpage of the polyimide film.

  Through these steps, while the polyimide precursor film is imidized, the film becomes a gel film having self-supporting properties and is peeled off from the endless belt.

  The gel film 1216 is fixed at the end and is heated in the tenter chamber 1218. For example, the tenter chamber 1218 includes a heating furnace 1220 and a slow cooling furnace 1222. In FIG. 12, the film moves in the tenter chamber by moving a pin sheet having a film fixed with pins by rotational driving of a pin conveyor. The gel film is further imidized by gradually heating in a heating furnace 1220 that performs thermal curing.

  For example, using a hot air furnace or a far-infrared heater as the heating furnace 1220, the temperature in the heating furnace 1220 is gradually raised to complete imidization to polyimide.

  The temperature of the heat treatment varies depending on the initial set temperature, the film thickness, the type of organic solvent used for the reaction of the polyimide precursor, and the like. Specifically, for example, the initial set temperature is preferably 200 ° C. to 250 ° C. for a film having a final film thickness of 25 μm, and 150 ° C. to 200 ° C. for a film having a final film thickness of 125 μm. At this stage, it is considered that the gel film is effectively dried and the imidization reaction proceeds at the same time.

  After that, it is preferable to gradually heat to a maximum temperature of 500 ° C. or more and 630 ° C. or less. More preferably, a range of 540 ° C. or higher and 580 ° C. or lower is preferable. The temperature gradient reaching the maximum temperature is not particularly limited as long as the heat treatment is performed in the above temperature range. The heat treatment time is several seconds to several tens of minutes, preferably 1 minute to 5 minutes, and is appropriately set in relation to the heat treatment temperature.

  The temperature gradient is set according to the state of the film such as the film thickness and the degree of drying, and is not particularly limited. Specifically, in the case of a film having a film thickness of 25 μm, it is 30 seconds at a temperature range of 200 ° C. to 250 ° C., 30 seconds at a temperature range of 300 ° C. to 350 ° C., and 400 ° C. to 450 ° C. 30 seconds in the following temperature range, and 60 seconds in the temperature range from 500 ° C. to 580 ° C.

  In the heat curing step in the heating furnace 1220, the completely imidized polyimide film is gradually cooled in the cooling furnace 1222.

<Belt surface, air surface>
In the present invention, when the polymer film is formed by the casting method, the surface on which the gel film is in contact with the endless belt is referred to as a belt surface, and the opposite surface is referred to as an air surface.

<Surface roughness Ra>
When a polymer film is formed by a casting method, the surface roughness of the belt surface tends to be larger than that of the air surface. This is because irregularities occur on the surface when the gel film is peeled off from the endless belt.

  The graphite film surface roughness Ra can be evaluated based on a light wave interference type surface roughness measurement method measured based on JIS B0652. Details of the measurement are shown in the Examples section.

<Cylindrical shape collapse and rewindability of the fired graphite film>
If the shape of the film collapses as indicated by 12 in FIG. 1, the cylindrical curl cannot be stretched. The reason is that the edge of the film is warped inward as shown in FIG. 4, so that if it is forcibly spread, tearing will occur from there as shown in FIG. In order to suppress such defects, it is preferable to perform heat treatment in a state where the first surface of the polymer film is wound inside.

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

<Various physical property measurement conditions>
<Confirmation of warping direction of polymer film and measurement of warping amount>
The confirmation of the direction of warping of the polymer film and the evaluation of the amount of warping are sag measurement based on the evaluation of the winding property of the film described in JIS C2151, and the degree of warping of the film end is measured at room temperature (23 ° C.) It was measured.
(Method for preparing test piece) 1) A new length of about 3 m is drawn from the roll of the polymer film. 2) A test knife having a width of 100 mm (TD direction) and a length of 2000 mm (MD direction) is cut out from the vicinity of the center. The place where the width of 100 mm is cut out is from the center of the original roll as shown in FIG. For example, if the width of the roll of the original polymer film is 400 mm, the width of 100 mm is cut out from around 150 mm from the end. At this time, care is taken that the TD direction and MD direction of the original roll coincide with the TD direction and MD direction of the test piece.
In the same manner, steps 1) and 2) are performed to prepare three test pieces.

  (Regarding Apparatus) The apparatus will be described next (FIG. 10).

a) Mounting base with rolls It has two metal rolls that rotate freely, and a solid mounting base that supports the two rolls in parallel. Each roll is prepared with a diameter of 100 mm ± 10 mm on which the maximum width of the film to be tested can be sufficiently placed. The axes of the two rolls are on the same horizontal plane and are fixed in parallel within 0.1 degrees (ie, within 1.8 mm for a roll length of 1 m) with a spacing of 1500 mm ± 15 mm from each other. The roll shall have a cylindrical shape with a cylindricity of 0.1 mm or less, and the surface shall have a suitable finish (not a polished finish). As shown at 106 in FIG. 10, a device for attaching the film roll to be tested (desorption shaft) is attached to the gantry just below one roll (first roll). This device is as follows.

  1) The desorption axis for placing the film is parallel to the axis of the first roll within 1 degree.

  2) The position of the side of the film can be adjusted freely.

b) Device for applying tension to the film At the opposite end of the gantry, a weight or spring clamp can be fixed to the film freely hanging from the second roll (second roll). The weight or spring load is 50 g per 1 cm width of the film and can be adjusted so that tension can be applied as uniformly as possible in the width direction of the film. Alternatively, it may be wound around a tension roll to apply a uniform tension of 50 g per 1 cm width.

c) Dimensional measuring instrument An instrument is provided for measuring the distance between the plane between the two rolls and the film that has been lowered along the line parallel to the rolls at the center between the two rolls. The instrument used for the measurement is a steel ruler with a length of 1525 mm or more and a steel ruler with a length of 1 mm and a length of 150 mm. Alternatively, a complicated instrument that automatically or semi-automatically indicates the position of the film may be used.

  (Measurement Procedure) As shown in FIG. 10, test pieces are placed in the length direction on two rolls of the apparatus. Tension (50 g per cm above) is applied to the free end of the film. The final position of passing the second roll of film is adjusted so that the film is approximately horizontal in the middle of the two rolls.

  Using a steel ruler and a steel ruler with a scale, check the film along the width direction at the center of the two rolls.

  (Method of confirming the direction of warping) When the upper surface is warped as shown by 111 in FIG. 11, the upper surface is the second surface, and when the upper surface is warped like 112, the lower surface is the second surface. .

  (Measurement method of warpage amount) When the upper surface is the second surface as indicated by 111 in FIG. 11, the film is turned over, and the second surface is disposed on the lower surface as indicated by 112 and measured. As shown at 114 in FIG. 11, the sag from the catenary line at the shortest part is measured. The left and right sag is measured and the average value is reported as the amount of warpage of the specimen.

  (Result) The amount of warpage is the median of the three measured values.

<Measurement of surface roughness Ra of polymer film>
The surface roughness Ra of the polymer film was evaluated by the light wave interference type surface roughness measured based on JIS B0652. This measurement is a method of measuring the surface roughness by enlarging the light wave interference fringes generated by the standard reflecting surface and the surface to be measured with a microscope. Measurement was performed in the range of 1.44 × 1.08 mm using a model number (ZYGO NEW VIEW 5030 system) manufactured by Zygo Corporation. The objective lens used was 2.5 × Michelson, and the first and second surfaces were measured at room temperature (23 ° C.). Ten arbitrary points per side were measured at 10 mm intervals in the MD direction, and the average value was taken as the measured value.

<Measurement of thermal diffusivity in the surface direction of graphite film>
The thermal diffusivity in the surface direction of the graphite film is a sample obtained by cutting the graphite film into a 4 × 40 mm shape using a thermal diffusivity measuring device (“LaserPit” manufactured by ULVAC-RIKO Co., Ltd.) by an optical alternating current method. Measurement was performed at 10 Hz in an atmosphere of 23 ° C. Three test pieces were extracted from points 1, 2, and 3 in FIG. 1 is near the center of 50 mm from the inside of the graphite roll, 3 is near the center of 50 mm from the outside, and 2 is between 1 and 3. The vicinity of the center indicates the vicinity of a width of 100 mm if the roll has a TD width of 200 mm. Table 1 shows the average value of thermal diffusivity measured using three test pieces.
<Cylindrical film collapsed cylindrical shape>
When the graphitized film is taken out from the furnace, the cylindrical shape of the graphitized film is greatly collapsed as shown by 12 in FIG. 1, B is slightly broken, and A is not collapsed as shown in 11 of FIG. It was.

<Rewind test>
A rewinding test was performed as shown in FIG. Place a 1 inch diameter paper tube into the space of the central part of the graphitized cylindrical graphite film roll, set it sideways, and place it in parallel on the 3 inch diameter winding side paper tube Rewinded. The roll of graphite film and the 1-inch paper tube were not fixed, and the 1-inch paper tube was a free roller, and the paper tube on the winding side was driven to perform rewinding. The rewinding speed was 1 m / min and room temperature (23 ° C.). The tear of the graphite film was evaluated.

  The evaluation method of the tear of the graphite film in the rewinding test will be described. Over the entire length of the roll, as shown in FIG. 2, the number of cracks with a length of 5 mm or more generated within 30 mm (TD direction) from both ends was counted and converted as the number of cracks per unit length (1 m). The crack failure per 1 m is less than 0.05 / m, A is 0.05 / m or more and less than 0.2 / m, B, 0.2 / m or more to less than 1 / m is C, 1 / m or more to less than 2 / m is D, and 2 / m or more is E.

<Manufacturing method of polyimide film>
[Production Method of Polyimide Film A]
One equivalent of pyromellitic dianhydride was dissolved in a DMF (dimethylformamide) solution in which one equivalent of 4,4′-oxydianiline was dissolved to obtain a polyamic acid solution (18.5% by weight).

  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.

  The DMF solution of polyamic acid produced in the polymerization process is mixed with a curing agent (acetic anhydride, isoquinoline) at a constant ratio by a mixer, and continuously from a T die to an endless belt (surface roughness Ra is 10 μm). The film was cast-coated at a thickness of 600 μm and dried with hot air while rotating the belt. At this time, the temperature conditions of the belt chamber were a belt temperature of 120 ° C. × 4 minutes and a cooling pulley temperature of 70 ° C. When this mixed varnish was heated, dehydration within the molecule occurred and the imidization reaction proceeded. Also, the self-supporting film (gel film) whose residual solvent amount at the belt chamber outlet is about 46% due to the evaporation of the solvent is peeled off from the belt, fixed to the pin frame, and 300 ° C. in the tenter chamber. Heat treatment was performed at ˜580 ° C. for a total of 4 minutes. Thereafter, the temperature was lowered to room temperature in the cooling chamber, and the film was peeled off from the pin and wound up. A polyimide film A having a thickness of 50 μm was produced. The warp amount of the obtained polyimide film A was 5 mm, the first surface was a belt surface during film formation, and the second surface was an air surface. The surface roughness Ra of the first surface was 43 μm, and the second surface was 36 μm.

[Production Method of Polyimide Film B]
Continuously casted from T-die onto endless belt at a thickness of about 850 μm, belt chamber temperature conditions were belt temperature 115 ° C. × 7 minutes, cooling pulley temperature 60 ° C., tenter chamber A polyimide film B having a thickness of 75 μm was produced in the same manner as the polyimide film A, except that heat treatment was performed at 300 ° C. to 580 ° C. for a total of 8 minutes. The amount of warpage of the obtained polyimide film B was 3 mm, the first surface was a belt surface during film formation, and the second surface was an air surface. The surface roughness Ra of the first surface was 43 μm, and the second surface was 38 μm.

[Production Method of Polyimide Film C]
A polyimide film C having a thickness of 50 μm was produced in the same manner as the polyimide film A, except that the belt chamber temperature was 110 ° C. × 8 minutes and the cooling pulley temperature was 60 ° C. The warpage amount of the obtained polyimide film C was 0.5 mm.

[Production Method of Polyimide Film D]
A polyimide film D having a thickness of 50 μm was produced in the same manner as the polyimide film A, except that the belt chamber temperature was set to a belt temperature of 135 ° C. × 4 minutes and a cooling pulley temperature of 80 ° C. The warpage amount of the obtained polyimide film D was 16 mm.

[Production Method of Polyimide Film E]
A polyimide film E having a thickness of 50 μm was produced in the same manner as the polyimide film A, except that an endless belt having a surface roughness Ra of 30 μm was used. The amount of warpage of the obtained polyimide film E was 4 mm, the surface roughness Ra of the first surface was 51 μm, and the second surface was 27 μm.

Example 1
A polyimide film A having a thickness of 50 μm, a width of 250 mm, and a length of 50 m is wound around a cylindrical graphite inner core having an outer diameter of 100 mm and a length of 300 mm, as shown in FIG. An outer cylinder having an inner diameter of 130 mm was covered. The container has several holes, such as 74, for providing air permeability. This container was set sideways in the electric furnace. Carbonization was performed under a temperature rising condition of 2 ° C./min up to 1400 ° C. Next, the obtained roll-shaped carbonized film was set on an inner core having an outer diameter of 100 mm as shown in FIG. 8, and this container was set in a vertical orientation on a frame in a graphitization furnace. Graphitization was performed at a temperature rising condition of 5 ° C./min up to 2900 ° C. The degree of collapse of the cylindrical shape of the obtained graphite film, the rewinding test, and the thermal diffusivity were measured.

(Example 2)
The same operation as in Example 1 was performed except that the polyimide film B was used.

Example 3
The same procedure as in Example 1 was performed except that 71 cylindrical core was not used during the graphitization treatment.

Example 4
Example 1 except that a polyimide film A having a width of 500 mm was used, and that it was set in the graphitization furnace sideways (in a state where the inner core was lifted by a support) as shown in FIG. It carried out like.

(Example 5)
The same operation as in Example 1 was performed except that the polyimide film C was used.

(Example 6)
The same operation as in Example 1 was performed except that the polyimide film D was used.

(Example 7)
The same operation as in Example 1 was performed except that the polyimide film E was used.

(Example 8)
A polyimide film A having a thickness of 50 μm, a width of 250 mm, and a length of 2 m is sandwiched and held in a rectangular container by an expanded graphite sheet having a thickness of 250 μm (trade name: PERMA-FOIL, manufactured by Toyo Tanso Co., Ltd.). Carbonization treatment was performed under the temperature rising condition of 2 ° C./min up to 1400 ° C. in the same manner as in Example 1 except that the weight was applied so that the pressure of 6 g / cm ² was applied uniformly.

  Further, the obtained carbonized film was wound around a cylindrical graphite inner core having an outer diameter of 30 mm and a length of 300 mm with the surface that was the first surface of the polyimide film as an inner winding, and was the same as in Example 1. In addition, the graphitization treatment was performed under the temperature rising condition of 5 ° C./min up to 2900 ° C. The degree of collapse of the cylindrical shape of the obtained graphite film, the rewinding test, and the thermal diffusivity were measured. Then, graphitization was performed.

(Comparative Example 1)
It implemented like Example 1 except having wound so that a 2nd surface might become an inner side.

(Comparative Example 2)
It implemented like Example 2 except having wound so that a 2nd surface might become an inner side.

(Comparative Example 3)
It implemented like Example 3 except having wound so that a 2nd surface might become an inner side.

(Comparative Example 4)
It implemented like Example 4 except having wound so that a 2nd surface might become an inner side.

(Comparative Example 5)
It implemented like Example 5 except having wound so that a 2nd surface might become an inner side.

(Comparative Example 6)
It implemented like Example 6 except having wound so that a 2nd surface might become an inner side.

(Comparative Example 7)
It implemented like Example 7 except having wound so that a 2nd surface might become an inner side.

(Comparative Example 8)
The obtained carbonized film was carried out in the same manner as in Example 8 except that the surface which was the second surface of the polyimide film was wound so as to be inward and graphitized.

<Result>
<Effect of inner winding of first surface of polymer film>
As shown in Table 1, the cylindrical shape of the graphite film after the heat treatment did not collapse in Examples 1 to 8 where the heat treatment was performed with the first surface of the polymer film wound inward. In the rewinding test, almost no tear failure occurred. On the other hand, in Comparative Examples 1 to 8 where the heat treatment was performed so that the second surface of the polymer film was on the inside, the cylindrical shape after the heat treatment was greatly collapsed as shown in 12 of FIG. A tear occurred from the edge. In the rewinding test, tearing failures frequently occurred and the handling property was very poor.

<About the amount of warpage>
When Examples 1, 5, and 6 were compared, in Example 5 where the amount of warping was small, the cylindrical shape did not collapse, but a tear failure occurred in Example 1 during the rewinding test. Moreover, in Example 6 with a large amount of warpage, the cylindrical shape after the heat treatment collapsed as compared with Example 1.

<Presence / absence of core during graphitization process>
Examples 1 and 3 and Comparative Examples 1 and 3 are compared. In Example 3, even when there was no inner core during graphitization, the polymer film was wound and heat-treated so that the first surface of the polymer film was on the inside, so that the cylindrical shape did not collapse. Since there is no core, the weight put into the furnace is reduced, and consumption of electric power and the like can be suppressed.

<About the method of carrying out carbonization treatment in sheet form>
Even if Example 8 and Comparative Example 8 in which the carbonization treatment was performed in a sheet form were compared and graphitized with the inner surface of the surface that was the first surface of the polyimide film, the cylindrical shape of the graphite film after the heat treatment was It did not collapse. In the rewinding test, almost no tear failure occurred.

11 Graphite film whose cylindrical shape has not collapsed 12 Graphite film 21 whose cylindrical shape has collapsed 21 Failure to tear 31 Warpage to the upper surface 32 Warpage to the lower surface 41 Warpage to the outside of the winding 42 Warping to the inside of the winding 51 Graphite film 52 2 inches Unwinding free roll 53 3-inch winding drive roll 54 Distance between rolls 71 Cylindrical graphite cylindrical core 72 Outer cylinder 73 Polyimide film 74 wound around the cylindrical core Opening 81 for giving air permeability Carbonized Film 82 Base 91 Support 101 Roll 1
102 Roll 2
103 Polymer film 104 Suspension line 105 Slack 106 Desorption shaft 111 on which the film is placed When the center sag 112 When the end sag 113 When the end sag 114 Center sag 114 10 Belt sag 1210 T-die 1214 Endless belt 1216 Gel film 1218 Tenter chamber 1220 Heating furnace 1222 Cooling furnace 1224 Polyimide film 1226 Cooling pulley 141 Winding inside 142 Winding outside

Claims (3)

The first surface of the polymer film is the surface opposite to the surface on which the film warps,
A method for producing a graphite film, wherein heat treatment is performed at a temperature of 2000 ° C. or higher in a state where the first surface of the polymer film is wound in an inner winding. The method for producing a graphite film according to claim 1, wherein the amount of warpage of the polymer film is 0.5 mm or more and 16 mm or less :
The amount of warpage of the polymer film is a sag measurement based on the evaluation of the winding property of the film described in JIS C2151, and the size of the warp of the film end is measured at 23 ° C. Wherein the step of providing as the first surface is a surface of the polymer film is wound on the inside of the scroll, to claim 1 or claim 2, characterized in that the graphitization step after the step of the preparation The manufacturing method of the graphite film of description.