JPH1121117A - Production of graphite film and graphite film and heat conductive body using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a graphite film having the same physical properties as a single- crystal graphite and improved in quality, flexibility, toughness, etc., by preparing a polyimide film, burning the film to a specified upper limit temp. respectively at the first and second heat treating steps and setting the condition at which the film exhibits a foaming state between the first temp. raising rate and the second temp. raising rate. SOLUTION: There are the step at which the polyimide film is prepared, the first heat treating step at which the film is burned by raising the temp. from the first starting temp. to the upper limit temp. of 1000-1200 deg.C at the first temp. raising rate in an inert gas, and the second heat treating step at which the film is moreover burned thereafter by raising the temp. from the second starting temp. to the upper limit temp. of more than 2500 deg.C at the second temp. raising rate in the inert gas. The first and second temp. raising rates are preferably in a range of 1-20 deg.C/min and 5-20 deg.C/min respectively. The second temp. raising rate is enable to set more than or less than the first temp. raising rate, and the first and second starting temps. are room temp. preferably. Uniformity and the flexibility can be improved at the step at which the resultant graphite film is subjected to rolling treatment.

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 film, a graphite film, and a heat conductor using the same, and more particularly, to a graphite film which can be suitably used as a heat conductor such as a heat radiating material or a soaking material. Related to the manufacturing technology of

[0002]

2. Description of the Related Art Conventionally, graphite films occupy an important position as industrial materials because of 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 (C-axis direction), and compression-molded with a binder to form a graphite film. 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 film.

[0005] The graphite film thus obtained is formed by molding powder into a film, and thus exhibits compression-reducing properties and stress relaxation properties.

[0006]

However, in such a method of manufacturing a graphite film, since sulfuric acid or nitric acid is used to spread the interlayer, even if the acid is washed out 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.
There is also a problem in that the degree of bonding is weak, so that peeling is likely to occur in a scale-like manner.

SUMMARY OF THE INVENTION 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 film, which exhibits the same physical properties as a single crystal graphite, and has high quality and flexibility. ,
An object of the present invention is to realize a graphite film that is rich in toughness and excellent in thermal conductivity.

[0009]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention comprises a step of preparing a polyimide film and a step of raising a temperature from a first starting temperature in an inert gas at a first heating rate. A first heat treatment step of firing to a first upper limit temperature in a carbonization temperature range, and a graphitization temperature range after the first heat treatment step in an inert gas at a second temperature rising rate from a second starting temperature. A second heat treatment step of firing to a temperature equal to or higher than a certain upper limit temperature, wherein the graphite film exhibits a foamed state between the first heating rate and the second heating rate. A method for producing a graphite film having a condition setting step of setting sufficient conditions, a graphite film obtained by such a production method, and a heat conductor using such a graphite film. .

With such a configuration, a polymer film,
In particular, a graphite film is obtained by heat-treating a polyimide film, and exhibits the same physical properties as single-crystal graphite, and realizes a high-quality, flexible, tough, and excellent thermal conductive graphite film.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention according to claim 1 includes a step of preparing a polyimide film and a step of preparing a polyimide film in an inert gas.
From the starting temperature at the first heating rate to the upper limit temperature of 10
A first heat treatment step of firing to 00 ° C to 1200 ° C;
A second heat treatment step in which the first heat treatment step is followed by baking in an inert gas from a second starting temperature at a second temperature raising rate to an upper limit temperature of 2500 ° C. or more, further comprising a second heat treatment step. And a condition setting step of setting conditions sufficient for the graphite film to exhibit a foamed state between the first temperature rising rate and the second temperature rising rate.

[0012] With such a configuration, unnecessary component atoms in the graphite film are thermally decomposed and gasified to be removed, thereby reliably forming an expandable graphite film.

Here, it is preferable that the first heating rate is in a range of 1 to 20 ° C./min.

On the other hand, it is preferable that the second heating rate be in the range of 5 to 20 ° C./min.

More specifically, as described in claim 4,
In the condition setting step, the second heating rate may be set to be higher than or equal to the first heating rate.

On the other hand, in the condition setting step, the second heating rate may be set to be lower than the first heating rate.

Further, as described in claim 6, it is convenient and preferable that the first starting temperature is room temperature and the second starting temperature is also room temperature.

Further, as described in claim 7, the first heat treatment step may include a step of temporarily stopping the temperature raising operation and maintaining the temperature.

Furthermore, the present invention may further include a rolling step of rolling the graphite film to improve the homogeneity and flexibility of the film.

It is preferable that the polyimide film does not substantially contain an additive material.

According to a tenth aspect of the present invention, there is provided a graphite film obtained by the method for producing a graphite film according to any one of the first to ninth aspects, wherein the thickness of the graphite film is greater than that of the starting polyimide film. Is a thick graphite film.

The graphite film having such a configuration has a foamed state without fail, exhibits the same physical properties as single-crystal graphite, and is a graphite film having high quality, flexibility, toughness, and excellent heat conductivity. .

The present invention according to claim 11 is a thermal conductor which uses the graphite film according to claim 10 in contact with a heat source, and is a high-quality, flexible and tough thermal conductor. Becomes

More specifically, the present invention provides an aromatic polyimide polymer film in an inert gas, wherein the polymer is
Starting from thermal decomposition, through a carbon precursor, within a temperature range of almost 100% carbonized material, preferably from 1000 ° C to 1200 ° C
To an appropriate starting temperature, for example, room temperature, and then heat-treated (preliminary sintering), and then temporarily lowered to near the starting temperature, and then heated again to complete the graphitization. If a configuration is adopted in which the temperature is raised to 2500 ° C. or higher and heat treatment is performed (final baking), the obtained graphite film is compared with a graphite film that does not employ such a configuration, for example, a film that only performs main baking. Obtaining the knowledge that a foamed state can be reliably formed, and furthermore, between those of the maximum temperature and the rate of temperature rise of these preliminary firing and those of the final firing,
It has been completed with the knowledge that optimum conditions can be set in consideration of the production time and the quality of the obtained expandable graphite film such as the film thickness, density, and surface condition.

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 polyimide film as a starting material is preferably in the range of 25 to 300 μm in view of the simplicity that a commercially available polyimide film can be used. The film thickness is about 1 mm or less.

(Embodiment 1) In the present embodiment, a polyimide film having a film thickness of 50 μm (trade name: Kapton, manufactured by Dupont Toray) is typically used.

Here, in order to effectively and surely draw out 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 preliminary firing, the temperature was raised from room temperature in an inert gas atmosphere, the maximum temperature was set to 1000 ° C. in the carbonization region, and when the maximum temperature was reached, the preliminary firing was terminated. In this case, the heating rate is 1
° C / min, 2 ° C / min, 5 ° C / min, 10 ° C / m
in, 15 ° C./min, and 20 ° C./min, respectively, and preliminary firing was performed.

Then, after the completion of the preliminary firing, the main firing was performed. In this firing, the temperature is raised from room temperature in an inert gas atmosphere, and the maximum temperature is set to the graphitized region 27.
The temperature was set to 00 ° C., and when the maximum temperature was reached, the main firing was completed. In this case, the heating rate was 5 ° C./min.
10 ° C / min, 15 ° C / min and 20 ° C / min
The main firing was performed in combination with each of the preheating rates.

The results are shown in Table 1 below as the quality of foamability.

[0032]

[Table 1]

The evaluation of the foamability in Table 1 was carried out by observing the surface and cross-sectional shape of the resulting product.

First, whether or not the desired flexibility, that is, the foamable graphite sheet has been formed can be basically determined by visual observation of the surface state of the resultant product after the main firing.

This is because if the conditions are not good, the sheet will not be formed, but will be a collection of powders or lumps. I went.

Next, as to whether or not the foam is foamable, if the surface of the resulting product has metallic luster, an ordinary graphite sheet is formed and the foamed state is obtained. And there is no flexibility,
Observe the surface condition of the resulting product in sheet form,
A pass / fail decision is made secondarily.

Finally, the cross-sectional shape of the surface having no metallic luster was confirmed, and the quality of the foamability was judged.

The result of the rejection judgment made in this way is
It is shown by ○, Δ, and × in (Table 1).は indicates good foaming property, △ indicates practical foaming property, and ×
Indicates that no foamability was exhibited.

According to the results, when the temperature rise rate of the preliminary firing is low, good foamability cannot be obtained even if the temperature rise rate of the final firing is increased, When the heating rate is increased, the foaming property starts to be obtained when the heating rate in the main firing is increased about 3 to 10 times. Then, when the temperature rise rate of the pre-firing reaches a certain value, good foaming property is expressed at a temperature rise rate of the main firing equal to or more than that, and when the temperature rising rate of the pre-firing exceeds that value, It can be understood that a good foaming property is exhibited even at a lower heating rate of the main firing.

Accordingly, it can be understood that there is a certain correlation between the rate of temperature rise in the structure in which the heat treatment is performed in two stages of pre-firing and main firing to improve the foamability, and the required foaming state It can be seen that conditions considered to be optimal can be set according to the characteristics of the above and the efficiency such as the production time.

That is, in the present embodiment, in a configuration in which the heat treatment in two stages of pre-firing and main firing is performed to improve the foaming state of the graphite sheet to be produced, the foaming property is required. According to the degree of demand,
It can be understood that optimal conditions are set in advance in consideration of the production efficiency and the like, and a graphite film having a foaming property can be produced more reliably and efficiently by such heat treatment.

The heating rate during pre-firing or main firing is within the range described in the present embodiment. However, if the rate is lower than the rate shown in the present embodiment, the graphite sheet cannot have sufficient foaming properties. If the speed is higher than the speed shown in the embodiment, the quality of the graphite sheet may be problematic, which is not practical.

The starting temperatures in the pre-firing and the main firing do not always have to be the same at room temperature, and can be individually set as long as each temperature is equal to or lower than the temperature at which carbonization starts.

The thickness of the polyimide film as a starting material is not limited to 50 μm. When the thickness of the commercially available polyimide film is in the range of 25 to 300 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.

Further, after the main firing in the present embodiment, a step of rolling the graphite film may be added. By adding such a step, the homogeneity of the graphite film such as the film thickness was improved, and the flexibility itself was also improved. Also,
The film thickness increases when a rate of temperature increase is large, so that it is also effective when it is desired to limit the film thickness within a certain limit.

(Embodiment 2) In this embodiment, the maximum temperature of pre-firing is the same, but graphite is the same as in Embodiment 1 except that the maximum temperature of main firing is 2900 ° C. in the graphitized region. A film was prepared and the foaming state was evaluated.

The results are shown in Table 2 below as the quality of foamability.

[0048]

[Table 2]

The evaluation of foaming properties in Table 2 was performed in the same manner as in the first embodiment. The results of the determination made in this manner are indicated by ○, Δ, and × in Table 2. ○ indicates that the foaming property was good, Δ indicates that the foaming property appeared and could be put to practical use, and x indicates that the foaming property did not appear at all.

According to the result, the overall tendency of development of foaming property is the same as that of the first embodiment, but no foaming property was developed in the first embodiment as compared with the first embodiment. Even when the rate of temperature rise in pre-firing is low, if the rate of temperature rise in main firing is high, foaming properties begin to be obtained. When the temperature rise rate of the pre-firing reaches a certain value, the temperature rise rate of the pre-firing in which good foaming properties are exhibited at the same or higher temperature rate of the main firing is also higher than that of the first embodiment. You can see that it is lower.

(Embodiment 3) In the present embodiment, the maximum temperature of the pre-firing is the same, but the maximum temperature of the main firing is set to 10 ° C.
A graphite film was prepared in the same manner as in Embodiment 1 except that the temperature was gradually changed every 0 ° C., and the foaming state was evaluated in the same manner.

According to this result, the tendency confirmed by comparing the first embodiment with the second embodiment is maintained.
It was also confirmed that the higher the maximum temperature of the main firing, the higher the foaming property was obtained even when the rate of temperature rise in the preliminary firing in which the foaming property did not appear was small.

However, in terms of the degree of graphitization of the graphite sheet, the maximum temperature during the firing is 2500 ° C.
It is preferable that it is the above. This is because, at a temperature lower than that, a case occurs where the graphite structure is not sufficiently developed.

(Embodiment 4) In the present embodiment, the maximum temperature of pre-firing is set to 1000
A graphite film was produced in the same manner as in Embodiment 3 except that the temperature was gradually changed every 100 ° C. within the range of from 2000 ° C. to 2000 ° C., and the foaming state was evaluated in the same manner.

According to these results, the tendency of comparison between the first embodiment and the second embodiment is maintained. The higher the maximum temperature of the main firing, the higher the temperature increase rate of the preliminary firing in which the foaming property did not appear. It was also confirmed that foaming properties could be obtained even when was small.

However, from the viewpoint of suitable carbonization at the time of pre-firing, the maximum temperature at the time of pre-firing is 1000 ° C to 1 ° C.
Preferably it is in the range of 200 ° C. At a lower temperature, carbonization is not sufficient, and there is a problem in the graphite structure of the graphite sheet obtained at a large heating rate during the main firing, or the graphite sheet obtained at a higher temperature may have a problem. This is because no substantial difference was found in the foamability and the graphite structure.

(Fifth Embodiment) This embodiment is different from the first embodiment in that the quality of the obtained graphite sheet is improved by maintaining the same at a certain temperature for a certain time during the preliminary firing. The effect of performing a so-called keep process will be discussed.

More specifically, the results obtained when a pre-baking treatment was carried out at 500 ° C. for 1 hour at 500 ° C. are shown in Table 3 below.

[0059]

[Table 3]

According to this result, a higher heating rate at which the foaming property is developed is required.
And the tendency of comparing Embodiment 2 with Embodiment 2 was maintained.

Further, the keeping temperature and time are set at 500 ° C.
The same tendency was confirmed when the temperature was checked up to 1000 ° C. in a combination of 30 minutes to 2 hours.

(Embodiment 6) In this embodiment, among the graphite films obtained in the above embodiment, those having evaluations of "O" and "B" are communicated to a heat source such as electric equipment, and the like.
Used as thermal conductor.

Since the heat conductor of the present embodiment has a graphite structure and exhibits good heat conductivity in the direction of the bonding surface between its carbon atoms, 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.

[0065]

As described above, according to the present invention, a graphite film is obtained by heat-treating a polymer film, in particular, a polyimide film, and is free from residual acid and flake-like peeling, and has the same physical properties as single-crystal graphite. Thus, a graphite film having high quality, flexibility, toughness, and excellent thermal conductivity was surely obtained.

Then, such a graphite film is
It can be suitably applied as a heat conductor for radiating heat from a heat source.

Claims (11)

[Claims] 1. A process for preparing a polyimide film,
A first heat treatment step in which the temperature is raised from a first starting temperature at a first temperature rising rate in an inert gas to a maximum temperature of 1000 ° C. to 1200 ° C., and an inert gas is further added after the first heat treatment step A second heat treatment step of firing at a second heating rate from a second starting temperature to an upper limit temperature of 2500 ° C. or more, wherein the first heating rate and the second heating rate are further increased. A method for producing a graphite film, comprising a condition setting step of setting conditions sufficient for the graphite film to exhibit a foamed state between the second temperature rising rate and the second temperature increasing rate. 2. The first heating rate is 1 to 20 ° C./min.
The method for producing a graphite film according to claim 1, wherein 3. The second heating rate is 5 to 20 ° C./min.
The method for producing a graphite film according to claim 1, wherein 4. In the condition setting step, the second heating rate is set to be higher than or equal to the first heating rate.
Or a method for producing a graphite film according to item 3. 5. The method according to claim 2, wherein in the condition setting step, the second heating rate is set to be lower than the first heating rate.
Or a method for producing a graphite film according to item 3. 6. The method for producing a graphite film according to claim 1, wherein the first starting temperature is room temperature, and the second starting temperature is also room temperature. 7. The method for producing a graphite film according to claim 1, further comprising a step of temporarily stopping the temperature raising operation and maintaining the temperature in the first heat treatment step. 8. The method for producing a graphite film according to claim 1, further comprising a rolling treatment step of rolling the graphite film. 9. The method for producing a graphite film according to claim 1, wherein the polyimide film contains substantially no additive. 10. A graphite film obtained by the method for producing a graphite film according to claim 1, wherein the thickness of the graphite film is larger than a thickness of a polyimide film as a starting material. 11. A heat conductor which uses the graphite film according to claim 10 in contact with a heat source.