JPH01203208A - Production of highly oriented graphite - Google Patents

Abstract

PURPOSE:To obtain highly oriented graphite having good quality for industrial use, with industrial advantage, by carbonizing aromatic polymer film after laminating or by laminating it after carbonizing, and further by graphitizing under mechanical pressure. CONSTITUTION:Films of one or more kinds of aromatic polymers such as polyimide, polyoxadiazole are carbonized. The laminated films after carbonizing are graphitized under mechanical pressure, especially under pressure in the direction of laminated layer, to adhere the films each other. That is, the laminated films above-mentioned are heated above the graphitizing temp., especially at 3,100-3,700 deg.C under >=5kg/cm<2>, especially at 100-500kg/cm<2>, in a non-oxidative atmosphere with a machine capable of simultaneously pressing and heating. Thereby, the highly oriented and firmly integrated graphite of good quality is obtd. without destruction or consumption of the laminated material.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention applies to some electrical appliances, heating elements and structural materials, high temperature and high pressure gaskets, heat insulating materials, corrosion resistant seals, brushes for electrical appliances, X-ray monochromators, and speakers. The present invention relates to a method for producing highly oriented graphite used for vibration elements such as cones and substrates for producing graphite intercalation compounds.

(Prior art) Conventionally, natural graphite has been used as highly oriented graphite for applications that utilize the crystalline properties of graphite as described above, and there have been other problems such as limited production and low purity. As an alternative to natural graphite with dots, chirashi graphite and hydrocarbons produced by precipitation from a Fe+Ni/C system melt, decomposition of carbides such as Sr HA1, or precipitation from a carbon melt under high temperature and high pressure can be used. Highly oriented pyrographite is produced by pyrolytic deposition and hot working. Another known method is to heat-treat an aromatic polymer film to obtain a graphite film.

(Problems to be Solved by the Invention) However, Quiche graphite is usually in the form of flakes, and producing bulk Quiche graphite requires a great deal of labor, and the production method for highly oriented pyrographite is complicated. In addition, in the method of heat-treating aromatic polymer films, the thinner the film used as the material, the higher the graphite orientation tends to be, so in principle only thin films can be obtained.
Both of the above methods have drawbacks that limit their industrial application.

As a result of intensive studies to solve these drawbacks, the present inventors have discovered that in a method for heat-treating aromatic polymer films, if a plurality of films or carbonized products thereof are laminated and heat-treated under mechanical pressure, the material It was discovered that multiple films used as a material can be strongly bonded and integrated with each other, and from the thinnest possible high-quality aromatic polymer films to the thicker than the film and in some cases rigid highly oriented graphite. The present invention was conceived based on the idea that it can be easily manufactured.

That is, an object of the present invention is to industrially advantageously produce high-quality, highly oriented graphite suitable for industrial use.

(Means for Solving the Problems) Therefore, the object of the present invention is to laminate and carbonize a plurality of aromatic polymer films, or laminate a plurality of aromatic polymer films after carbonization, and then apply graphite under mechanical pressure. This can be easily achieved by

(for production) The present invention will be explained in detail below.

Graphite is made up of a regular collection and arrangement of fine crystallites consisting of graphite layer planes, which are a laminate of carbon network planes.
Graphite whose crystallites are well oriented is called highly oriented graphite.

Furthermore, although the boundaries between the terms carbonization and graphitization are not necessarily clear, the former usually refers to a reaction in which organic matter is thermally decomposed to release different elements and a carbon network plane is produced, and the latter refers to a reaction in which organic matter is thermally decomposed to release different elements and a carbon network plane is generated. This means that carbon network planes are stacked to form graphite microcrystals, and the microcrystals grow and align. However, in the present invention, carbonization is a term used to include a state in which carbonization in the above-mentioned normal sense has been completed, but graphitization has not yet been completed and is in progress.

X-ray diffraction is often used to evaluate graphite crystals, and in particular, the lattice constant Co of graphite in the C-axis direction, calculated from the position of the OOJ diffraction line, that is, the direction perpendicular to the graphite layer plane,
and <001) The size Lc of the crystallite in the C-axis direction and the size La of the crystallite in the a-axis direction, which are determined from the half-width of the diffraction line, are often used. Co corresponds to the interlayer spacing between the graphite layer surfaces, and the smaller it is, the more graphitization is progressing within the crystallites,
On the other hand, the smaller the half width of the (007) diffraction line, the larger Lc and La calculated from it. To evaluate the degree of orientation of graphite crystallites, a quantity called mosaic spread is used, which represents the variation in the angles formed by the normal lines of the graphite layer planes of countless crystallites.

This mosaic spread occurs when the graphite sample and X-ray detector are set at the position where the (θ0-2) diffraction line is observed, and only the graphite sampler is slightly rotated in the normal crystal X-ray diffraction method. It is expressed by the size of the range of rotation angles of the graphite sample in which the (00,2) diffraction line can be observed.

That is, t, where co is the minimum value of natural graphite, is 70? It can be said that the closer to A, the larger Lc and La, and the smaller the mosaic splay, the smaller the mosaic splay, the higher the graphite structure is and the higher the quality of the highly oriented graphite.

There are other methods of evaluating graphite based on its electrical and magnetic properties, including magnetic resistance, residual resistance ratio, etc. as indicators. When magnetic resistance is expressed as electrical resistivity as a function ρ(B) of magnetic field B, residual resistance ratio is the electrical resistivity ρ7 at a temperature T near room temperature and the electrical resistivity ρa at an extremely low temperature To. The ratio ρT/ρTo. The larger the maximum value of magnetic resistance for a graphite sample (the larger the residual resistance ratio is, the more developed the graphite structure is in the graphite sample, the more integrated the graphite crystallites are, and the closer it is to a perfect graphite crystal). I can say that.

The method of the present invention is characterized by laminating such high-quality, highly oriented layers and further graphitizing them under mechanical pressure. As the film used as the material, a polymer film containing an aromatic ring in the monomer can be used, and among them, a heat-resistant aromatic polymer that is easily graphitized, specifically, polyimide, polyamide, polyamideimide, polyoxaneazole. , polybenzimidazole, polyphenylenehynylene, polyhelinaphthalene, polybismaleimide triazine, and polybismaleimide.

In the method of the present invention, a plurality of aromatic polymer films may be stacked and carbonized, seven films may be carbonized at a time, and no other special measures are required for carbonization, but after carbonization, graphite The lattice constant Co in the C-axis direction of the film to be subjected to the oxidation process is 1, . 7! It is preferable to adjust the carbonization conditions, that is, mainly the firing temperature, in the range of 2000° C. or higher depending on the type of aromatic polymer of the film material so as to obtain -6.9OA. This is because carbon exceeding CO2 or QO2 is hardly graphitized and has poor flexibility, so it easily breaks when pressurized.On the other hand, if CO is less than 6.2λ, the graphite of each film This is because the film laminate has progressed too much, and even if the film laminate is heated again under pressure, the individual films may not be properly bonded and integrated, and there is a risk of peeling cracks occurring on the film laminate surface. Further, the carbonization process may be carried out under pressure, but if the pressure is too strong, there is a risk that the gas containing foreign elements released during carbonization will have no place to escape and remain as bubbles, and the film hardened by carbonization may In order to prevent cracking, it is sufficient to apply a weak pressure that does not shift the position of the film to be carbonized.

The graphitization step in the method of the present invention needs to be carried out under mechanical pressure, especially under pressure in the direction of lamination of the films, in order to bond the laminated films together. It is common to use a machine that simultaneously applies pressure and heat to the film laminate! Rotation
By applying a pressure of more than 100° C., preferably 100-j00 cape/crtl, and heating in a non-oxidizing atmosphere to a temperature higher than the graphitization temperature, preferably about 3,700 to 3,200° C., there is no risk of destroying or wasting the laminate. This is suitable because it allows the production of highly oriented graphite of high quality that is strongly integrated.

In addition, when using a method of heating and pressurizing the heated object without directly applying electricity, such as when using an induction heating type hot press, for example, when using a method of heating and pressurizing the heated object without directly applying electricity, multiple layers of polymeric films are laminated from the beginning in seven successive steps. It can be graphitized and integrated by just using it. In addition, when applying mechanical pressure, if a laminate of aromatic polymer films or a carbonized product thereof is sandwiched between a male mold and a female mold, and the pressure and heat are applied, highly oriented graphite of irregular shape, which has been difficult to obtain in the past, can be produced. Easy to manufacture. Further, in the carbonization and/or graphitization step, if the material to be carbonized or the material to be graphitized is heated while being pulled from the surroundings by forces acting on the film surface and balanced against each other, highly oriented graphite can be obtained.

In addition, in the method of the present invention, there is no restriction in principle on the number of carbonized aromatic polymer films laminated, and the number of carbonized aromatic polymer films is sufficient to firmly bond and integrate each film in the graphitization step. Any number of laminated graphite sheets may be used as long as the number of graphite sheets can be stacked to the extent that uniform pressure and heating can be performed, and even when using a normal electrically heated hot press, it is possible to produce highly oriented graphite having a thickness of about /θ. Further, by considering the shrinkage rate of the aromatic polymer film accompanying carbonization and graphitization, highly oriented graphite having a desired thickness and size can be produced within the capability of hot pressing.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example: Aromatic polyimide film (Kapton manufactured by DuPont) with a thickness of 508 m was cut into rectangular shapes in the order of 0 x 3 θ, and 70 θ sheets were stacked, sandwiched between graphite plates from above and below, and heated at room temperature in a furnace with a nitrogen stream passed through them. Ito at a heating rate of 1 min/θ℃ from
The temperature was raised to θ°C, held for 7 hours, allowed to cool naturally to room temperature in a furnace, then placed in a graphite Tamman furnace with a nitrogen stream passed through it, and heated at a heating rate of θ°C per minute for 2 hours. When the temperature was raised to θ0°C, held for 7 hours, and allowed to cool naturally to room temperature, a carbon fired body was obtained whose lattice constant in the C-axis direction was 6.7A as calculated from an X-ray diffraction image. The carbon fired body was set in a graphite die, and was pressurized from above and below with a pressure of 0θL&-.
Heat with electric current for 30 minutes, cool to room temperature, and apply heat resistance x 2
Evening X-? A plate-like graphite of a was obtained. The properties of the plate graphite are shown in Table Vc.

Table: The bulk specific gravity of the plate graphite is equal to the theoretical value of ideal graphite, the lattice constant in the C-axis direction is the same as that of the highest quality natural graphite, and the mosaic spread by X-ray diffraction shows that it is of high quality and highly oriented. It is similar to pyrographite. In addition, the maximum value of magnetic resistance (Δρ) when a magnetic field of /ρ4, 2K and /T is applied at the liquid nitrogen temperature is /ρ) 771(, I T , max
indicates that the plate graphite is of good quality.

(Effects) According to the method of the present invention, highly oriented graphite with a highly developed graphite structure and properties equivalent to or better than conventional highest quality graphite can be easily obtained, providing great industrial benefits. It is.

Applicant: Toyo Carbon Co., Ltd. Representative patent attorney - (7 others)

Claims (2)

[Claims] (1) A method for producing highly oriented graphite, which comprises laminating a plurality of aromatic polymer films and carbonizing them, or laminating a plurality of aromatic polymer films after carbonization, and further graphitizing them under mechanical pressure. (2) The aromatic polymer is one or more selected from the group consisting of polyimide, polyamide, polyamideimide, polyoxaneazole, polybenzimidazole, polyphenylene vinylene, polyberinaphthalene, polybismaleimide triazine, and polybismaleimide. The method for producing highly oriented graphite according to claim 1, wherein the highly oriented graphite is an aromatic polymer.