JP2000247619A - Production of flexible graphite sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a thickness after baking with good efficiency and to produce a sheet which is strong to bending and is highly flexible with a good reproducibility by baking a polyimide film at a specific temperature or above in inert gas and holding the film for a specified time at a specified temperature in a specific temperature range. SOLUTION: In a heat treatment process for producing the graphite sheet by baking the polyimide film of a film thickness of 50 to 300 μm at >=2500 deg.C by heating up the film with a combination of a heating up rate from room temperature to a heating up rate of <=30 deg.C/minute in the inert gas, the film is held for: the specified time at the specified temperature between 1800 and 2500 deg.C, by which the thickness after the baking is controlled and the graphite sheet is obtained. The thickness of the graphite sheet after the baking is larger than the thickness of the polyimide film of starting raw material and the thickness of the sheet is larger as the holding time at the specified temperature is shorter. Further, the graphite sheet after the baking is subjected to a rolling treatment, by which the flexibility and homogeneity, such as uniformity, may be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a flexible graphite sheet used as a heat radiating material or a heat equalizing material as an electric conductor or a heat conductor.

[0002]

2. Description of the Related Art A method for directly obtaining a flexible graphite sheet by heat treatment and rolling treatment of a polyimide film is already known from Japanese Patent Publication No. 1-49642. The properties of this sheet are the same as those of single-crystal graphite, with no problems such as scale-like exfoliation and residual acid, high quality, high bending resistance, excellent flexibility, and excellent thermal conductivity. Is obtained.

[0003] A method for producing a graphite sheet is to select an aromatic polyimide polymer film among condensed aromatic polymer films capable of a graphitization reaction as a raw material, and to perform the reaction in an atmosphere of an inert gas such as nitrogen or Ar. , And then a high-temperature heat treatment is performed at a certain rate in an inert gas atmosphere.

By controlling the firing conditions such as the rate of temperature rise during the preliminary heat treatment and the high-temperature heat treatment at this time, a graphite sheet having a controlled thickness after firing can be produced. By being thicker than the polyimide film, a graphite sheet which is strong in bending and highly flexible can be obtained.

[0005]

According to these inventions,
By controlling the firing conditions such as the rate of temperature increase during the preliminary heat treatment and the high-temperature heat treatment, a graphite sheet having a controlled thickness after firing can be produced. However, since there are many parameters in the firing conditions, it is necessary to control them.If the firing conditions are not properly controlled, the graphite after firing will be ragged and will not have a sheet shape, or will be sufficiently thick. However, it is difficult to provide flexibility.

The present invention has been made to solve these problems. In a heat treatment step of producing a graphite sheet by heating a polyimide film from room temperature in an inert gas and firing at a temperature of 2500 ° C. or more. , 1800
The purpose of the present invention is to control the thickness after sintering by maintaining the temperature at a constant temperature between ℃ and 2500 ℃ for a certain time.

[0007]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention relates to a method of raising the temperature of a polyimide film from room temperature to a maximum firing temperature of 2500 ° C. or more in an inert gas at a certain heating rate, and firing the graphite film. In the heat treatment process for producing the sheet, by maintaining the temperature at a constant temperature between 1800 ° C. and 2500 ° C. for a certain period of time, the thickness after firing can be controlled efficiently, and a graphite sheet which is strong in bending and highly flexible can be reproduced. Can be manufactured well.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a polyimide film is heated from room temperature in an inert gas to a temperature of 250.degree.
In a heat treatment step of producing a graphite sheet by firing at a temperature of 0 ° C. or more, the thickness after firing is controlled by maintaining the temperature at a constant temperature of 1800 ° C. to 2500 ° C. for a certain time. This is a method for producing a graphite sheet having flexibility. With such a configuration, the thickness after firing can be controlled, so that a graphite sheet having excellent flexibility, toughness, and excellent thermal conductivity can be obtained.

According to a second aspect of the present invention, the heating rate is 30
It is desirable to use a combination of any of the heating rates of not more than ° C / min.

The thickness after firing can be controlled by setting the holding time at a constant temperature between 1800 ° C. and 2500 ° C. to 20 hours or less.

[0011] As described in claim 4, it is also possible to hold at two or more constant temperatures between 1800 ° C and 2500 ° C for a fixed time.

[0012] Further, as described in claim 5, 1800
It is also possible to raise a part or all of the temperature range between ℃ and 2500 ° C. at a heating rate between 0.1 ° C./min and 1 ° C./min.

[0013] According to a sixth aspect of the present invention, the temperature of 25
By setting the holding time of the maximum heat treatment temperature at 00 ° C. or more to 20 hours or less, the thickness after firing can be controlled.

A preliminary heat treatment step in which the temperature is raised from room temperature and baked from 1000 ° C. to 1600 ° C., and then further from room temperature to 250 ° C.
It is also possible to use a combination with a high-temperature heat treatment step of firing at a maximum firing temperature of 0 ° C. or more.

As described in claim 8, the thickness of the graphite sheet after firing is desirably greater than the thickness of the starting polyimide film. Such a sheet becomes a sheet excellent in flexibility and toughness.

It is preferable that the thickness of the polyimide film, which is a starting material, is 50 μm or more and 300 μm or less.

Further, as described in claim 10, the flexibility and homogeneity of the graphite sheet may be improved by rolling the fired graphite sheet.

(Example 1) An experiment was conducted using a polyimide film as a starting material having a thickness of 125 µm manufactured by Toray DuPont (trade name: Kapton). As a preliminary heat treatment, the maximum treatment temperature was increased to 1200 ° C. at a rate of 5 ° C./min in a nitrogen atmosphere, and the temperature was kept at 1200 ° C. for 2 hours. Further, as a high-temperature heat treatment, the temperature is raised at a rate of 5 ° C. /
min to 2200 ° C and 1 at 2200 ° C
After holding for a period of time, the temperature was further increased at a rate of 5 ° C./min to a maximum processing temperature of 2700 ° C.
, And the temperature was lowered to room temperature to perform a heat treatment.

The thickness of the graphite sheet fired and heat-treated in this manner was about 500 μm, which was larger than the thickness of the starting polyimide film. This graphite sheet was foldable and flexible. Furthermore, by rolling this graphite sheet, flexibility was improved and homogeneity such as thickness was improved as compared to before rolling.

Example 2 In this example, a graphite sheet was produced by the same heat treatment process as in Example 1 except that the holding time at 2200 ° C. in the high-temperature heat treatment was omitted. The graphite thus heat-treated and fired was tattered and did not have a sheet shape.

Example 3 In this example, a graphite sheet was produced by the same heat treatment process as in Example 1 except that the holding time at 2200 ° C. in the high-temperature heat treatment was set to 4 and 8 hours. The thickness of the graphite sheet fired and baked in this manner is about 350 μm, 220 μm for the graphite sheet held at 2200 ° C. for 4 hours.
About 250 for graphite sheet held at 0 ° C for 8 hours
The thickness after firing was able to be controlled by controlling the holding time at 2200 ° C. Each of these graphite sheets was in a state thicker than the thickness of the polyimide film as a starting material, and could be bent and had flexibility. Furthermore, by rolling this graphite sheet, flexibility was improved and homogeneity of thickness and the like was improved as compared with before the rolling.

(Embodiment 4) In this embodiment, the rate of temperature increase in the preliminary heat treatment and the high-temperature heat treatment up to 2200 ° C. is 10 ° C. /
A graphite sheet was produced by the same heat treatment as in Example 1 except that the temperature was changed to min. The thickness of the graphite sheet thus heat-treated and fired is about 200.
μm. Although there was flexibility, the flexibility was poor as compared with Example 1.

Example 5 In this example, a graphite sheet was produced in the same manner as in Example 4, except that the maximum heat treatment temperature in the high-temperature treatment was 2900 ° C. The thickness of the graphite sheet that had been heat-treated and fired in this manner was about 500 μm, which was thicker than the thickness of the starting polyimide film, and was foldable and flexible. Furthermore, by rolling this graphite sheet, flexibility was improved and homogeneity such as thickness was improved as compared to before rolling.

(Example 6) In this example, a graphite sheet was produced in the same manner as in Example 1, except that the holding temperature during the high-temperature heat treatment step was set at 2000 ° C and 2400 ° C. The thickness of the graphite sheet thus heat-treated and fired is about 550 μm at a holding temperature of 2000 ° C.
m and about 450 μm at 2400 ° C., which was thicker than the thickness of the starting polyimide film, and could be bent and had flexibility. Furthermore, by rolling this graphite sheet, flexibility was improved and homogeneity such as thickness was improved as compared to before rolling.

(Embodiment 7) In this embodiment, a temperature between 2150 ° C. and 2250 ° C. is set to 0.5 ° C./m instead of holding at 2200 ° C. for one hour during the high-temperature heat treatment step.
A graphite sheet was prepared in the same manner as in Example 1 except that the temperature was raised at a rate of temperature increase of in. The heat-treated and fired graphite sheet has a thickness of about 45.
The thickness was 0 μm, which was thicker than the thickness of the polyimide film as the starting material. Furthermore, by rolling this graphite sheet, flexibility was improved and homogeneity such as thickness was improved as compared to before rolling.

Example 8 In this example, a graphite sheet was produced in the same manner as in Example 5 except that a 75 μm-thick product made by Toray DuPont (Kapton) was used as a starting material polyimide film. Was prepared. The thickness of the graphite sheet thus heat-treated and fired was about 150 μm, which was larger than the thickness of the starting polyimide film, and was foldable and flexible. Furthermore, by rolling this graphite sheet, flexibility was improved and homogeneity of thickness and the like was improved as compared with before the rolling.

[0027]

As described above, according to the present invention, the temperature of the polyimide film is raised from room temperature to 2500 ° C. in an inert gas.
In the heat treatment step of baking at the above temperature to produce a graphite sheet, the thickness after baking can be controlled by maintaining the baking at a certain temperature between 1800 ° C. and 2500 ° C. for a certain period of time. It is possible to obtain a graphite sheet with good reproducibility, flexibility, toughness, and excellent thermal conductivity without becoming a sheet shape or having a sufficient thickness without flexibility. .

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshimasa Oki 3-10-1 Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa Prefecture Inside Matsushita Giken Co., Ltd. (72) Inventor Souji Tsuchiya 3 Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa No.10-1 Matsushita Giken Co., Ltd. F-term (reference) 4G046 EA03 EB02 EB04 EC03 EC05

Claims (10)

[Claims] In a heat treatment step of heating a polyimide film from room temperature in an inert gas to a temperature of 2500 ° C. or more to produce a graphite sheet, 1800
A method for producing a flexible graphite sheet, characterized in that the thickness after firing is controlled by maintaining the film at a constant temperature of between 2500C and 2500C for a fixed time. 2. The method for producing a flexible graphite sheet according to claim 1, wherein the heating rate comprises a combination of any one of heating rates of 30 ° C./min or less. 3. The method for producing a flexible graphite sheet according to claim 1, wherein the holding time at a constant temperature between 1800 ° C. and 2500 ° C. is 20 hours or less. 4. The method according to claim 1, further comprising maintaining the temperature at two or more constant temperatures between 1800 ° C. and 2500 ° C. for a certain time.
4. The method for producing a flexible graphite sheet according to any one of items 1 to 3. 5. A part or all of a temperature range between 1800 ° C. and 2500 ° C. is changed from 0.1 ° C./min to 1 ° C./mi.
2. The method according to claim 1, wherein the temperature is increased at a rate of n.
5. The method for producing a flexible graphite sheet according to any one of items 1 to 4. 6. The method for producing a flexible graphite sheet according to claim 1, wherein the holding time of the maximum heat treatment temperature at a temperature of 2500 ° C. or more is 20 hours or less. 7. A polyimide film in an inert gas for 2 hours.
A heat treatment step of producing a graphite sheet by firing at a temperature of 500 ° C. or higher is performed by raising the temperature from room temperature to a temperature of 1000 ° C.
A flexible heat treatment process according to any one of claims 1 to 6, comprising a preliminary heat treatment process of sintering to a temperature of from 1600C to 1600C, and a high temperature heat treatment process of further raising the temperature from room temperature to a maximum heat treatment temperature of 2500C or more. Method for producing highly durable graphite sheets. 8. The graphite sheet after firing has a thickness of:
The method for producing a flexible graphite sheet according to any one of claims 1 to 7, wherein the thickness is larger than the thickness of the starting polyimide film. 9. The film thickness of a polyimide film as a starting material is 50 μm or more and 300 μm or less.
The method for producing a flexible graphite sheet according to any one of the above. 10. The method for producing a flexible graphite sheet according to claim 1, further comprising a step of rolling the fired graphite sheet.