JP3065896B2 - Manufacturing method of highly oriented graphite - Google Patents

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 highly oriented graphite body. The highly oriented graphite body according to the present invention can be industrially used as a monochromator for X-ray diffraction and neutron diffraction, an electrode for a fuel cell, a high-temperature heating element, and a high-temperature structural component.

[0002]

2. Description of the Related Art Conventionally, a highly oriented graphite body has been known in which a hydrocarbon-containing gas is guided on a substrate directly heated to a specific temperature, and pyrolytic carbon formed is peeled off. 2500 ° C to 3000 ° C under pressure perpendicular to
It has been manufactured by processing at the above ultra-high temperature. The highly oriented graphite body produced by this method has many variations in quality due to the production method, and has a problem that stable supply is not always sufficient and the product itself becomes very expensive.

It is well known that graphitization is promoted by heat treatment with a boron compound added to carbons. It is considered that this is because boron forms a solid solution with carbon on the hexagonal mesh surface and diffuses and moves in the mesh surface, thereby eliminating the distortion of the mesh surface.

[0004] A method of producing a graphite body in which graphite crystals are remarkably developed by utilizing the boron solid solution and a high density carbon by utilizing the boron solid solution and the sintering accelerating action which occurs at the time of structural change of carbon. Methods for making the material are already known.

That is, as an example of the former, Japanese Patent Application Laid-Open No. 47-56
A method of heating the amorphous carbon fiber obtained from the polyacrylonitrile fiber shown in 2 above at 2000 ° C. or more, and introducing a gasified alkyl borate into the mixture to graphitize it. Adding a boron compound to a pitch coke or petroleum coke powder described in JP-A-52-106395 in an amount of 5 to 12% by weight;
There is a method of producing graphite powder having a structure similar to natural graphite by heating to about 2000 ° C. or more.

An example of the latter is disclosed in Japanese Patent Publication No. 53-31.
Boric acid is added to the carbon fiber denoted by
A method of obtaining a molded body by applying pressure and heat treatment at a temperature of at least 1000 ° C. under a pressure of about 500 kg / cm ² ,
Boron oxide was added to the pyrolytic graphite powder indicated by 0, and 1
1800 under unidirectional pressurization of 100 to 400 kg / cm ²
A method of obtaining a pyrolytic graphite molded body by treating at 2200 ° C., by adding boric acid to an amorphous carbon powder or an artificial graphite powder shown in JP-B-54-3681, and applying a direct current or an alternating current to form a high-density graphite. Boric acid is added to the amorphous carbon powder shown in JP-B-54-3682, and the pressure is increased to 2,000 kg under a pressure of several hundred kg / cm ^2.
There is a method of firing at a temperature of not less than ℃ to obtain a high-density graphite molded body.

[0007] However, these conventional methods all involve a heat treatment by adding a boron compound to carbon to produce a carbon body in which graphite crystals have been developed by the action of boron. It is difficult to get.

Recently, a plurality of aromatic polymer films are laminated and carbonized, or after carbonization, a plurality of films are laminated, and further subjected to high temperature treatment under mechanical pressure and graphitized to obtain highly oriented graphite. Japanese Patent Application Laid-Open No. 01-203208,
Open 01-105199, JP 05-17115, JP 0
5-17116, JP-A-05-17117, JP-A-05-1
7118, JP 04-202052, JP 05-974
18 .

A thermosetting polymer resin such as polyimide is
Generally, it is difficult to graphitize, and a good graphite body having an orientation cannot be obtained. This is because the disorder of the molecular orientation and the existence of the cross-linking between the molecules in the carbon precursor inhibit the graphitization and the transition to the molecular orientation.

However, recently, when these kinds of thermosetting resins are formed into a film, the molecular orientation in the film becomes extremely good, and this film is transformed into high-quality graphite by high-temperature treatment. Was known. Each of the above patents is intended to produce a highly oriented graphite body by laminating these aromatic polymer films having a good molecular orientation or a carbonized film thereof, and heat-treating the resultant into a carbonized graphite.

According to this method, a laminate of highly oriented graphite thin films can be obtained, but there are the following problems. One is that in order to increase the degree of graphitization, that is, the degree of crystallinity, it is necessary to perform a heat treatment at a high temperature of at least 2,000 and several hundred degrees Celsius or more. The higher the heat treatment temperature, the higher the price of the product. Therefore, a production method with a low heat treatment temperature is desired.

The second problem is the adhesion between the laminated graphite films. That is, sufficient mechanical adhesion between layers cannot be obtained only by mechanical pressing under a high temperature state, and peeling may occur during use as a component.

[0013] Third, it is desirable that the thermal expansion or contraction of the film during the heat treatment process be low. In particular, the graphitization treatment is performed in a carbon mold, and since the periphery is constrained, if the dimensional change due to heating is large, internal thermal distortion occurs, wrinkles are likely to occur, and as a result, the alignment property decreases. Will bring.

[0014]

[Means for Solving the Problems] The present invention is to deposit or apply a very small amount of a rare earth element such as boron or lanthanum or a compound thereof on a thermosetting resin film such as polyimide or its carbonized film on the film surface. Then, a plurality of sheets are laminated in a carbon mold, and a high-temperature treatment is performed while pressing in a direction perpendicular to the film surface. The method can solve the above problem. .

As a raw material, a thermosetting resin film such as an aromatic polyimide film or the like is used.
A carbonized film heat-treated at 00 ° C. is used. Not all aromatic polyimides or thermosetting resin films give high degree of graphitization and high degree of orientation of the graphite layer surface.The degree of flatness is high and rigid, and aromatic molecules are well oriented in the film in advance. It is necessary. Particularly preferred is the chemical formula

An aromatic polyimide film or a carbonized aromatic polyimide film containing

It is also known that the thickness of a film as a starting material has an effect on the degree of graphitization of a film after a high-temperature heat treatment, and a thinner film generally yields a higher degree of graphitization. After cutting these films into a predetermined size, boron or a rare earth element is vacuum-deposited on the film surface.

Alternatively, it is applied on the film surface by a coating method. In the case of using a coating method, for example, in the case of boron, boric acid (H ₃ BO ₃ ) is used by dissolving it in ethanol, and a compound such as a salt or a chloride is dissolved in a suitable solvent and applied as a liquid.

In the case of an uncarbonized film, a film coated with these elements or compounds thereof is cut into a desired size, and heat-treated at about 1000 ° C. in an inert atmosphere to obtain a carbonized film. In this case, dimensional contraction is caused by carbonization, so it is desirable to predict in advance.

Next, a plurality of these films are laminated and heat-treated at a high temperature of 2000 ° C. or more using a graphite mold while applying a mechanical pressure in a direction perpendicular to the film surface. Graphitization and orientation progress due to the heat treatment under pressure, and at the same time, bonding between the films accompanying diffusion of the deposited different elements proceeds, and a highly oriented graphite body is obtained.

In the case of a polyimide film, the interplanar spacing d (002) sharply decreases with an increase in the graphitizing temperature, and finally, at a graphitizing temperature of 3000 ° C., d
The value of (002) is 3.354 ° which is close to the theoretical value of graphite crystals.
Approaching. In the graphitization, if a rare earth element such as boron or lanthanum is present, the graphitization is promoted more than in the case of no addition. Table 1 shows an example in which graphitization is promoted by the presence of the additional element.

[Table 1]

By heat treatment at a high temperature of 2000 ° C. or more, boron or a rare earth element diffuses into the carbon structure to promote regularization of the crystal structure.
A graphitization degree which cannot be obtained unless the processing temperature is around 000 ° C. is obtained at a lower temperature. In addition, due to the diffusion of boron or the rare earth element, the strong bonding between the films is promoted, so that a graphite body having a high orientation and a thickness can be obtained, and the films are separated during use. Can no longer be seen.

The thickness of the graphite body can be adjusted by adjusting the number of films to be laminated. When laminating films, it is desirable that the deposition surface or the coating surface is always aligned in one direction. Pressing during firing is performed by unidirectional pressing at 100 to 400 kg / cm ² , and a higher pressing force produces a highly oriented graphite body. The thinner the film, the better the orientation of the graphite body is obtained by laminating the films. When a thin film is used, it is necessary to stack as many sheets as possible in order to obtain a thick graphite body.

The raw material film undergoes dimensional shrinkage due to heat treatment in the carbonization stage. Without surface modification by boron or rare earth elements, shrinkage of about 23% occurs in the plane parallel direction, but with surface modification, dimensional shrinkage of about 20%. On the other hand, at the stage where the carbonized film is subjected to a higher temperature treatment at 1000 ° C., expansion occurs in the plane parallel direction.

For example, when the carbonized film is treated at 2500 ° C., the expansion is about 15% when there is no surface modification, and about 12% when the surface modification is performed with boron or a rare earth element. The small dimensional change results in a small thermal stress generated during the heat treatment process, and therefore a highly oriented graphite body with little deformation can be obtained.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to embodiments.

[0026]

Example 1 A plurality of 3 cm × 3 cm pieces of film were cut out of a commercially available 25 μm thick polyimide film, and each piece was placed in a vacuum deposition apparatus, and metallic boron was deposited on one side of the film. Next, about 30 pieces of boron-deposited film were laminated so that the deposition surface was in one direction,
Installed in graphite mold, 20MPa perpendicular to film surface
Hot pressing was performed at 2200 ° C. for 1 hour in an inert atmosphere while pressing.

As a result, a highly oriented graphite body having a thickness of about 1 mm and having a crystal structure with a crystal plane size of about 500 ° in the c-axis direction with a layer spacing was obtained. FIG. 1 shows an SEM photograph of the orientation state of the graphite crystal. The whole had an orientation close to that of a single crystal, the bonding between the films was strong, and no peeling phenomenon was exhibited.

[0028]

Example 2 A plurality of 3 cm × 3 cm pieces of film were cut out from a commercially available 25 μm thick polyimide film, and each was placed in a vacuum deposition apparatus, and metallic boron was deposited on one side of the film. Next, about 30 pieces of boron-deposited film were laminated so that the deposition surface was in one direction,
Installed in graphite mold, 20MPa perpendicular to film surface
Hot pressing was performed at 2200 ° C. for 1 hour while applying pressure.

After that, at 2800 ° C. in an inert atmosphere
As a result of the heat treatment, a thickness of about 1 mm having a crystal structure with a crystallite size of 1000 ° or more in the c-axis direction and a layer plane interval
A highly oriented graphite body in which no exfoliation phenomenon was observed was obtained.

[0030]

Example 3 A plurality of 3 cm × 3 cm pieces of film were cut out from a commercially available 25 μm thick polyimide film, and each was placed in a vacuum deposition apparatus, and metal lanthanum was deposited on one side of the film. Next, about 30 lanthanum-deposited film pieces were laminated so that the vapor-deposited surface was in one direction, and placed in a graphite mold.
Hot pressing was performed at 2200 ° C. for 1 hour while applying a pressure of Pa.

Thereafter, in an inert atmosphere at 2500 ° C.
As a result of the heat treatment, a thickness of about 1 mm having a crystal structure with a crystallite size of 1000 ° or more in the c-axis direction and a layer plane interval
Was obtained.

[0032]

Example 4 A plurality of 3 cm × 3 cm pieces of film were cut out from a commercially available 25 μm-thick polyimide film, and each was placed in a vacuum deposition apparatus, and metallic boron was deposited on one side of the film. Next, about 30 pieces of boron-deposited film were laminated so that the deposition surface was in one direction,
Installed in graphite mold, 20MPa perpendicular to film surface
Hot pressing was performed at 2200 ° C. for 1 hour while applying pressure.

After that, at 2800 ° C. in an inert atmosphere
As a result of the heat treatment, a thickness of about 1 mm having a crystal structure with a crystallite size of 1000 ° or more in the c-axis direction and a layer plane interval
A highly oriented graphite body in which no exfoliation phenomenon was observed was obtained.

[0034]

Comparative Example 1 A plurality of film pieces of 3 cm × 3 cm size were cut out from a commercially available 25 μm-thick polyimide film, and about 30 film pieces were laminated without vapor deposition of metal boron or a rare earth element, and placed in a graphite mold. While applying a pressure of 20 MPa in the direction perpendicular to the film surface, 22
Hot pressing was performed at 00 ° C. for 1 hour. And then
As a result of heat treatment at 2500 ° C. in an inert atmosphere, a highly oriented graphite body having a thickness of about 1 mm and having a crystal structure with a crystal plane size of 960 ° in a c-axis direction and a layer spacing was obtained. However, the degree of graphitization was lower than when a film on which boron or a rare earth element was vapor-deposited was used, and the obtained graphite body was not easily sintered between laminated films and was easily peeled.

[Brief description of the drawings]

FIG. 1 is a SEM photograph of a cross-sectional structure of a highly oriented graphite body according to the present method.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takehiko Tsukui 1-14 Bunkyo-cho, Nagasaki City, Nagasaki Prefecture Examiner, Nagasaki University Faculty of Engineering Misako Anzai (56) References JP-A-5-339079 (JP, A) 2-44020 (JP, A) JP-A-64-51383 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/52 C01B 31/04 101

Claims (4)

(57) [Claims] 1. A polyimide film or a carbonized polyimide film, on which boron or a rare earth element or a compound thereof is vapor-deposited or coated, and a plurality of the films are laminated. A method for producing a highly oriented graphite body, characterized in that it is fired while being pressed in the vertical direction. 2. The method according to claim 1, wherein the boron or the rare earth element is an oxide, a hydroxide, or a carbide of the boron or the rare earth element. 3. A polyimide film or a carbonized polyimide film having the following chemical formula: The method for producing a highly oriented graphite body according to claim 1, wherein the method is an aromatic polymer film or a carbonized aromatic polymer film containing: 4. A high-orientation film, characterized in that a polyimide film or a carbonized polyimide film is subjected to the production method according to claim 1, and further subjected to a high-temperature treatment at 2500 ° C. or more in an inert atmosphere under normal pressure. Method for producing graphite.