JP2000178016A - Production of graphite sheet and thermal conductive material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high quality graphite sheet having high flexibility and toughness and excellent in thermal conductivity. SOLUTION: This method for producing the graphite sheet in foamed state comprises a first heat treatment step of heat treating a polyimide film as a raw material at upper limit temperature of 1,000-1,600 deg.C under an inert atmosphere and, after heat treating in the first heat treatment step, a second heat treating step of heat treating at the upper limit temperature of 2,500-3,100 deg.C under an inert atmosphere. The graphite sheet can be obtained by the process mentioned above.

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 graphite sheet and a heat conductor using the same, and more particularly to a technique for producing a graphite sheet.

[0002]

2. Description of the Related Art Conventionally, graphite sheets occupy an important position as industrial materials due to their heat resistance, chemical resistance, high electrical conductivity, etc., and are widely used as heat conductive materials, heat resistant seals, electrodes, and the like. Have been.

[0003] For example, as an artificially produced one,
New Carbon Industry (Toshiyuki Ishikawa, published in October 1980,
On page 118, etc. of Kindai Kyoikusha Co., Ltd.).

[0004] Specifically, scaly natural graphite is
After being treated with a mixture of sulfuric acid and nitric acid, the mixture is rapidly heated to a high temperature of about 1000 ° C., greatly expanded along the interlayer (in the C-axis direction), and compression molded together with a binder to form a graphite sheet. Here, it is disclosed that the apparent thickness expands tens to hundreds of times of the starting sample graphite. This is a so-called expanding method for producing a graphite sheet.

[0005] The graphite sheet thus obtained is formed by molding powder into a sheet.
Exhibits compression reduction and stress relaxation.

[0006]

However, in such a method for manufacturing a graphite sheet, since sulfuric acid or nitric acid is used to spread the interlayer, even if the acid is washed off by washing with water or the like. It cannot be completely removed, and a trace amount of acids remains in the expanded graphite. For example, when used as a gasket material for a long time, there is a problem that the metal gradually corrodes and corrodes metals.

[0007] In addition, since a binder or the like is used, the contact property between the scale-like graphite is deteriorated, and the heat conduction property and electric conduction property peculiar to graphite cannot be sufficiently exhibited.
Since the bonding degree is also weak, there are also problems such as flake-like peeling and lack of flexibility.

The present invention has been made to solve these problems, and a polymer film, particularly a polyimide film, is obtained by heat treatment to obtain a graphite sheet, exhibiting the same physical properties as a single crystal graphite, and having high quality and flexibility. sex,
An object of the present invention is to realize a graphite sheet that is rich in toughness and excellent in thermal conductivity.

[0009]

In order to solve this problem, the present invention provides a first heat treatment step in which a polyimide film is used as a raw material and a heat treatment is performed in an inert gas at a maximum temperature of 1000 ° C. to 1600 ° C. , And the maximum temperature is 250
A second heat treatment step of performing a heat treatment at a temperature in the range of 0 ° C. to 3100 ° C., and further, a graphite exhibiting an appropriate foaming state by controlling heat treatment conditions such as a heating rate and a constant temperature. This is a method for producing a sheet, and is a method for expressing flexibility by further performing a rolling process. By bringing the graphite sheet obtained by such a manufacturing method into contact with a heat source, a heat conductor having a heat radiating and soaking action is realized.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention according to claim 1 includes a first heat treatment step of performing heat treatment in an inert gas at a maximum temperature of 1000 ° C. to 1600 ° C. using a polyimide film as a raw material; A second heat treatment step of performing a heat treatment in an inert gas at a maximum temperature in the range of 2500 ° C. to 3100 ° C. after the first heat treatment step. Unnecessary component atoms in the graphite sheet contained in the polyimide film are thermally decomposed and gasified to be removed, thereby reliably forming a foamable graphite sheet.

Further, as set forth in claim 2, the upper limit temperature in the first heat treatment step is set to 1200 ° C. to 1600 ° C., whereby a graphite sheet having favorable foamability is obtained by the method of manufacturing a graphite sheet according to claim 1. Can be

Here, the temperature rise rate in the first and second heat treatment steps is 1 to 20 ° C./m.
By producing a graphite sheet in the range of in, a suitable expandable graphite sheet can be obtained.

According to a fourth aspect of the present invention, in the first heat treatment step, the heat treatment is performed at a constant temperature in a temperature range of 400 to 700 ° C. for a constant time. By the production of the graphite sheet, a suitable expandable graphite sheet can be obtained.

Further, as set forth in claim 5, in the second heat treatment step, heat treatment is performed in a temperature range of 1800 to 2300 ° C. at a fixed temperature for a fixed time.
According to the method for producing a graphite sheet described in any one of the items 1 to 4, a suitable expandable graphite sheet can be obtained.

Further, the present invention further comprises a rolling step of rolling the graphite sheet.
The graphite sheet having suitable flexibility can be obtained by the method for producing a graphite sheet according to any one of (1) to (5).

Further, as described in claim 7, a graphite sheet obtained by the method for producing a graphite sheet according to any one of claims 1 to 5, wherein the density of the sheet is 0.3 to 0.7 g. / Cc or a range of 2 to 10 times the thickness of the raw material film, thereby obtaining a graphite sheet and a suitable foamable graphite sheet.

Further, as described in claim 8, a graphite sheet obtained by the method for producing a graphite sheet according to any one of claims 1 to 5, wherein the density is 0.7 to 1. A graphite sheet having a suitable flexibility can be obtained from a graphite sheet characterized by being in the range of 5 g / cc.

The present invention described in claim 9 is the same as claim 8.
The described graphite sheet is used as a heat conductor which is used in contact with a heat source to be a high quality and flexible heat conductor.

The graphite sheet having such a structure is as follows.
The graphite sheet surely has a foamed state, exhibits the same physical properties as single-crystal graphite, and is further rolled to provide a graphite sheet having high quality, high flexibility, and excellent thermal conductivity.

More specifically, the present invention provides an aromatic polyimide polymer film in an inert gas,
Starting from pyrolysis, through a carbon precursor, within a temperature range of almost 100% carbonized material, preferably from 1000 ° C. to 1600
The first heat treatment step (preliminary calcination) is performed by first raising the temperature from a suitable starting temperature, for example, room temperature, up to a temperature of up to 400 ° C. Performing heat treatment for a certain time may be effective for the purpose. Thereafter, the temperature is once lowered to near the starting temperature, and then raised again to a temperature range in which the graphitization is completed, preferably, to any temperature in the range of 2500 ° C. to 3100 ° C. to perform the second heat treatment step. (Main firing).

On the way, from 1800 ° C. to 230
Performing heat treatment at a constant temperature in a temperature range of 0 ° C. may be effective for the purpose. By performing such processing and controlling the thickness and density values as the properties of the sheet, the obtained graphite sheet is surely formed into a foamed state that becomes a suitable sheet.

This polyimide film is known to provide the highest quality graphite structure among those using an aromatic condensed polymer known to have a graphite structure by thermal baking. .

The thickness of the starting polyimide film is preferably in the range of 25 to 300 μm in view of the simplicity that a commercially available polyimide film can be used. Looking at the film thickness,
The thickness is in the range of 2 to 10 times the film thickness of the raw material.

An embodiment will be described below. (Example 1) In the present embodiment, a polyimide film having a film thickness of 75 μm (trade name: Kapton, manufactured by Dupont Toray) is typically used.

Here, in order to effectively and surely extract the foaming property by the heat treatment, it is preferable to use a film which has not been subjected to any special treatment such as adding a special additive to the film.

First, as a first heat treatment, in an inert gas atmosphere, the temperature is raised at a rate of 1 ° C./min and 5 ° C./min.
And the temperature is raised from room temperature at 20 ° C./min.
After setting the temperature to 00 ° C. and maintaining the temperature at 1600 ° C. for 1 hour, the temperature was lowered to room temperature, and the preliminary firing was completed.

After completion of the preliminary firing, high-temperature firing was performed. In this high-temperature sintering, the temperature is increased from room temperature at a rate of 3 ° C./min from room temperature in an inert gas atmosphere.
After maintaining at 0 ° C. for 1 hour, the temperature was lowered to room temperature, and the high-temperature firing was completed.

The graphite sheet fired in this manner is in a uniform foamed state, and the thickness of the sheet is 100 to 1
It was 80 μm and had flexibility.

Next, a rolling treatment was performed by passing the fired graphite sheet between rolling rollers. The rolling process made the graphite sheet more flexible and increased the thickness uniformity. Film thickness after rolling is 50-150μ
m.

The thickness of the starting polyimide film is not limited to 75 μm, but is
As a result of confirming the results within the range of 0 μm, similar results were obtained. Of course, this range is not an essential limitation on the development of the foaming state and is not limited.

(Embodiment 2) In the present embodiment, in the high-temperature firing, the heating rate is set to 10 ° C./min, and
After holding at 00 ° C. for 2 hours, a graphite sheet was prepared in the same manner as in Embodiment 1, except that the temperature was raised to 2700 ° C. The graphite sheet fired in this manner was in a uniform foamed state, had flexibility, and had a thickness of 90 to 180 μm.

(Embodiment 3) In the present embodiment, in the first heat treatment, the temperature is raised at a rate of 1 ° C./min and 5 ° C./m
A graphite sheet was produced in the same manner as in Embodiment 1 except that the temperature was raised from room temperature at in and 20 ° C./min, the maximum temperature was set to 1300 ° C., the temperature was kept at 1300 ° C. for 1 hour, and then the temperature was lowered to room temperature. The graphite sheet fired in this manner was in a uniform foamed state, had flexibility, and had a thickness of 90 to 200 μm.

(Embodiment 4) In the present embodiment, in high-temperature baking, the temperature was raised at a rate of 20 ° C./min to 2800 ° C.
A graphite sheet was produced in the same manner as in Embodiment 3, except that the temperature was raised to the maximum. The graphite sheet fired in this manner was in a uniform foamed state, had flexibility, and had a thickness of 80 to 180 μm.

(Embodiment 5) In the present embodiment, in the preliminary firing, the heating rate is 1 ° C./min and 5 ° C./min.
And at 20 ° C./min from room temperature to a maximum temperature of 12
A graphite sheet was produced in the same manner as in Embodiment 1, except that the temperature was set to 00 ° C., and the temperature was kept at 1200 ° C. for 1 hour, and then the temperature was lowered to room temperature. The graphite sheet fired in this manner was in a uniform foamed state, had flexibility, and had a thickness of 100 to 220 μm.

(Embodiment 6) In the present embodiment, in the high-temperature sintering, the temperature was raised at a rate of 20 ° C./min to 2700 ° C.
A graphite sheet was produced in the same manner as in Embodiment 5, except that the temperature was raised to the maximum. The graphite sheet fired in this manner was in a uniform foamed state, had flexibility, and had a thickness of 90 to 230 μm.

(Embodiment 7) In the present embodiment, in the first heat treatment, the heating rate is 1 ° C./min, 5 ° C./m
A graphite sheet was produced in the same manner as in Embodiment 1 except that the temperature was raised from room temperature at in and 20 ° C./min, the maximum temperature was set to 1000 ° C., and the temperature was lowered to room temperature after holding at 1000 ° C. for 1 hour. The graphite sheet fired in this manner was in a uniform foamed state, had flexibility, and had a thickness of 100 to 240 μm.

(Embodiment 8) In the present embodiment, in the high-temperature firing, the temperature was raised at a rate of 20 ° C./min to 2700 ° C.
A graphite sheet was produced in the same manner as in Embodiment 7, except that the temperature was raised to the maximum. The graphite sheet fired in this manner was in a uniform foamed state, had flexibility, and had a thickness of 90 to 250 μm.

(Embodiment 9) In the present embodiment, in the first heat treatment, the heating rate is 1 ° C./min, 5 ° C./m
In and 20 ° C / min, the temperature was raised from room temperature to 800 ° C, held at 800 ° C for 1 hour, cooled to room temperature, and then fired at a high temperature in an inert gas atmosphere in an inert gas atmosphere. The temperature is increased at a rate of 1 ° C./min, and the maximum temperature is set to 2700 ° C., which is a graphitized region.
After maintaining at 2700 ° C. for 1 hour, the temperature was lowered to room temperature, and the high-temperature firing was completed. The graphite sheet fired in this manner has a heating rate of 1 ° C./min and 5 ° C./min.
In the case of min, foaming occurred excessively, so that the sheet was partially peeled or tattered. When the temperature was raised at a rate of 20 ° C./min, the foam was in a uniform foaming state, had flexibility, and had a thickness of 90 to 180 μm.

Embodiment 10 In this embodiment, in the first heat treatment, the temperature is raised from room temperature at a rate of 5 ° C./min, the maximum temperature is set to 800 ° C., and the temperature is maintained at 800 ° C. for 1 hour. After cooling to room temperature,
In an inert gas atmosphere, the temperature was raised from room temperature at a rate of 5 ° C /
The temperature is raised at a rate of 2700 ° C., which is a graphitized region, at 2700 ° C.
After maintaining at ℃ for 1 hour, the temperature was lowered to room temperature, and the high-temperature firing was completed. The graphite sheet fired in this manner was excessively foamed at a temperature rising rate of 5 ° C./min, so that the sheet was partially peeled or tattered. When the heating rate was 10 ° C./min, the foam was in a uniform foaming state, had flexibility, and had a thickness of 100 to 190 μm.

(Embodiment 11) In the present embodiment, in the first heat treatment, the temperature is raised from room temperature at a rate of 5 ° C./min to a maximum temperature of 800 ° C. and held at 800 ° C. for 1 hour. After cooling to room temperature,
In an inert gas atmosphere, the temperature was raised from room temperature at a rate of 5 ° C /
The maximum temperature was set to 2700 ° C., which is a graphitized region, at 2700 ° C. for 10 minutes and 30 minutes.
After maintaining the temperature for a minute, the temperature was lowered to room temperature, and the high-temperature firing was completed.
In each case, the graphite sheet fired in such a manner was excessively foamed, so that the sheet was partially peeled or tattered.

The maximum temperature of the first heat treatment is set at 800 ° C. to 10 ° C.
By performing the experiment while changing the temperature between 00 ° C., if the maximum temperature of the first heat treatment is less than 1000 ° C., excessive foaming is apt to occur at the time of high-temperature sintering, and the graphite does not exhibit a sheet shape and is likely to be tattered. Therefore, it can be seen that it is necessary to control the foaming state by controlling the rate of temperature rise during pre-firing, the rate of temperature rise during high-temperature firing, and the holding time at the highest temperature.

The reason that foaming is likely to occur during high-temperature baking and graphite is not likely to take the form of a sheet and tends to be tattered is that a large amount of residual gas remains in the polyimide film after pre-baking. This is considered to be caused by breaking the shape of the film when is released from the inside of the film.

That is, in the present embodiment, by setting the maximum temperature of the first heat treatment to 1000 ° C. or more, the residual gas in the raw material polyimide film can be reduced, and the graphite does not take a sheet shape. It is possible to control the degree of foaming at the time of high temperature firing without being tattered, and to ensure a flexible graphite sheet,
It can be understood that it can be created efficiently.

(Embodiment 12) In this embodiment, 50c
Raw polyimide film with a size of mx 50 cm
The pieces are simultaneously placed in an electric furnace, and the preheating is performed at a heating rate of 1 ° C./min, 5 ° C./min, and 20 ° C./m
in to raise the maximum temperature to 1300 ° C.
After maintaining at 300 ° C. for 1 hour, the temperature was lowered to room temperature, and the preliminary firing was completed.

Then, after the completion of the preliminary firing, high-temperature firing was performed. In this high-temperature firing, the temperature is increased from room temperature at a rate of 1 ° C./min from room temperature in an inert gas atmosphere.
After maintaining at 0 ° C. for 1 hour, the temperature was lowered to room temperature, and the high-temperature firing was completed.

Each of the graphite sheets fired in this manner is in a uniform foamed state, and the thickness of the sheet is 1
It was 00 to 200 μm, and had flexibility.

(Embodiment 13) In the present embodiment, 50c
Raw polyimide film with a size of mx 50 cm
The pieces are simultaneously placed in an electric furnace, and the preheating is performed at a heating rate of 1 ° C./min, 5 ° C./min, and 20 ° C./m
in to raise the temperature from room temperature to 1000 ° C.
A graphite sheet was produced in the same manner as in Embodiment 12, except that the temperature was kept at 000 ° C. for 1 hour.

In the graphite sheet fired in this manner, foaming occurred excessively at a temperature rising rate of 1 ° C./min and 5 ° C./min, so that the sheet was partially peeled or tattered. In addition, the heating rate is 20 ° C /
At min, the sheet was in a uniform foamed state, had flexibility, and had a thickness of 90 to 180 μm.

The maximum temperature in the preliminary firing is 1000 ° C.
When a large number of raw material polyimide films are fired by performing experiments by changing the temperature between 1200 ° C., if the maximum temperature of the preliminary firing is less than 1200 ° C., foaming tends to occur excessively during high-temperature firing, and 1200 ° C. or less. It can be seen that graphite does not exhibit a sheet shape and is likely to be ragged.

Example 14 In the present embodiment, a graphite sheet was produced in the same manner as in Embodiment 1, except that the first heat treatment was performed at 600 ° C. for 1 hour. The graphite sheet fired in this manner is in a uniform foamed state, has flexibility, and has a sheet thickness of 90 to
It was 180 μm.

(Embodiment 15) In the present embodiment, except for holding at 2000 ° C. for 1 hour during the high temperature firing step,
A graphite sheet was produced in the same manner as in the first embodiment.
The graphite sheet fired in this manner is in a uniform foamed state, has flexibility, and has a thickness of 8 sheets.
It was 0 to 160 μm.

(Example 16) In this embodiment, the foamable and flexible graphite sheet obtained in the above embodiment is connected to a heat source such as electric equipment, and the like.
It was used as a heat conductor for heat dissipation.

Since the heat conductor in the present embodiment has a graphite structure, it exhibits good heat conductivity in the direction of the bonding surface between its carbon atoms, so that the heat from the heat source is actually transferred to the outside efficiently. It was able to transmit heat and radiate heat.

The heat conductor had sufficient flexibility due to foaming properties, and the heat conductor could be handled very freely. Furthermore, because of this flexibility, the degree of freedom of attachment to the heat source is high, and it is possible to sufficiently cope with an electric device having a complicated heat source.

[0055]

As described above, according to the present invention, when a graphite sheet is obtained by heat-treating a polymer film, particularly a polyimide film, no residual acid, flake-like peeling, etc. occurs, and the same as single-crystal graphite. Thus, a graphite sheet with high quality, high flexibility, high toughness, and excellent thermal conductivity was obtained.

The graphite sheet can be suitably applied as a heat conductor for radiating heat from a heat source.

Continuation of front page (72) Inventor Akira Taomoto 3-10-1 Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa F-term in Matsushita Giken Co., Ltd. 4G046 EA03 EA05 EB04 EC01 EC06 EC08

Claims (9)

[Claims] 1. A first heat treatment step in which a polyimide film is used as a raw material and heat treatment is performed in an inert gas at an upper limit temperature in a range of 1000 ° C. to 1600 ° C., and after the first heat treatment step, further heat treatment is performed in an inert gas. Maximum temperature 2500 ℃ -3100
A second heat treatment step of performing a heat treatment at a temperature in the range of ° C. to produce a graphite sheet exhibiting a foamed state. 2. An upper limit temperature in the first heat treatment step is set to 1
The method for producing a graphite sheet according to claim 1, wherein the temperature is from 200C to 1600C. 3. The heating rate in the first and second heat treatment steps is in the range of 1 to 20 ° C./min.
3. The method for producing a graphite sheet according to 2. 4. The method according to claim 1, wherein in the first heat treatment step, 400 to 700
The method for producing a graphite sheet according to any one of claims 1 to 3, wherein the heat treatment is performed at a constant temperature for a fixed time in a temperature range of ° C. 5. The method according to claim 5, wherein in the second heat treatment step, 1800 to 23
The method for producing a graphite sheet according to any one of claims 1 to 4, wherein the heat treatment is performed at a fixed temperature for a fixed time in a temperature range of 00C. 6. The method for producing a graphite sheet according to claim 1, further comprising a rolling treatment step of rolling the graphite sheet. 7. A graphite sheet obtained by the method for producing a graphite sheet according to claim 1, wherein the density of the sheet is 0.3 to 0.7 g / cc.
Characterized in that the thickness is in the range of 2 to 10 times the thickness of the raw material film. 8. A graphite sheet obtained by the method for producing a graphite sheet according to claim 1, wherein the density is 0.7 to 1.5 g by a rolling process.
/ Cc in the range of / cc. 9. The graphite sheet according to claim 8,
Thermal conductor used in contact with the heat source.