JPH05222620A - Heat-conductive material - Google Patents

Abstract

PURPOSE:To increase the thermal conductivity of a material containing carbon fiber or carbon film. CONSTITUTION:The cross section of carbon fiber or carbon film is modified and is allowed to have a leaflet-oriented structure to increase the thermal conductivity. The conductivity of heatconductive materials are over 500W/m.K. The carbon fiber and film is graphitized. In a heat-conductive material, the carbon fiber or film may be composited with resins, carbonaceous binders, ceramics, metals and other matrixes. The pitch carbon fiber and film are produced by melt-extruding an optically anisotropic pitch containing more than 95wt.% of optically anisotropic phase and having 200 to 320 deg.C softening point through slit nozzles, making the fiber or film of a modified cross section infusible and graphitizing the infusible product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat conductive material containing pitch-based carbon fiber and the like.

[0002]

2. Description of the Related Art Polyacrylonitrile-based carbon fibers and pitch-based carbon fibers made from coal or petroleum-based pitches are widely used as carbon fibers. Among them, pitch-based carbon fiber is excellent in economic efficiency. In particular, pitch-based carbon fiber made from optically anisotropic pitch has high strength and high elastic modulus, and is excellent in mechanical properties as well as in thermal conductivity and conductivity, which is superior to polyacrylonitrile-based carbon fiber. There is.

As a sectional structure of the pitch-based carbon fiber,
Radial type, random type, onion type and the like are known. For example, carbon fibers having a radial structure are apt to crack, and physical properties are likely to deteriorate due to macro defects. JP-A-59
Japanese Patent Publication No. 53717 discloses a high-strength, high-modulus pitch-based carbon fiber having a microstructure with a specific orientation angle, crystal size and layer spacing. This prior document also discloses a pitch-based carbon fiber having a cross-sectional structure arranged in the circumferential direction in the surface layer portion and arranged in a radial or mosaic shape in the central portion.

Factors affecting such a cross-sectional structure include, for example, the structure of the nozzle when the Bitch raw material is melted and extruded, the spinning temperature, the viscosity during spinning, and the like.

Japanese Patent Laid-Open No. 61-108725 discloses a pitch-based carbon fiber having a leaf-shaped lamella arrangement in which the pitch is melt-spun, infusibilized and fired using a spinneret having a specific spinneret. Is disclosed.
The carbon fiber having an elliptical cross section obtained by this method has high tensile strength.

[0006] The applicant of the present invention is also disclosed in JP-A-62-1705.
In Japanese Patent Publication No. 26, a method for producing a carbon fiber having an elliptical cross section is disclosed. The carbon fiber having an elliptical cross section obtained by this method has a large surface area per unit area and is therefore excellent as a composite material with other materials.

However, these prior arts do not disclose thermal conductivity.

On the other hand, in order to improve the heat energy efficiency, various heat exchange materials, for example, metals having high thermal conductivity such as copper, aluminum and iron are used in the heat exchanger. Where corrosion resistance is required, nickel,
Stainless steel is used. Among these metals, copper has the highest thermal conductivity and its value is 400
It is about W / m · K. However, copper has small mechanical properties and cannot be effectively used as a heat exchange material. Furthermore, when used in a harsh environment, it is hard to say that it does not have sufficient corrosion resistance and the like, and still has sufficient properties as a heat exchange material.

Therefore, it is conceivable to use the above-mentioned carbon fiber which is chemically inert, and is excellent in heat resistance and mechanical properties as the heat exchange material. But carbon fiber
The thermal conductivity is small and the characteristics as a heat exchange material are not sufficient. In particular, when a resin, a carbonaceous binder, a matrix such as metal or ceramics, and the carbon fiber are combined to form a composite, the thermal conductivity is further reduced.

Therefore, it is an object of the present invention to provide a heat conductive material having a high heat conductivity despite containing a carbonaceous material.

[0011]

In order to achieve the above object, the present inventors have
As a result of diligent studies, it was found that pitch-based carbon fibers having a deformed cross section and a leaflet orientation structure exhibit remarkably high thermal conductivity, and the present invention was completed.

That is, according to the present invention, the cross section is irregular, the leaflet orientation structure is provided, and the thermal conductivity is 500 W / m.
Provided is a thermally conductive material composed of a pitch-based carbon fiber or film having a K or more.

The preferred carbon fibers or films are graphitized. The heat conductive material may include the carbon fiber or film and a matrix.

In the present specification, the "leaflet oriented structure" means a structure radially oriented with an axis extending from the center point of the cross-section irregular shape to the apex as the central axis and a structure similar thereto.

"Carbon fiber" refers to carbonized or graphitized fiber. “Carbonization” refers to firing a carbonizable component at a temperature of, for example, about 1000 to 2000 ° C. in an atmosphere of an inert gas such as nitrogen gas, carbon dioxide, or argon, or under vacuum. The “graphitization” means, for example, in the inert gas atmosphere or in the vacuum, for example, 2000
It means that the above components are calcined at a temperature of about 3,000 ° C., and they are included in the concept of graphitization even when they do not have the crystal structure of graphite.

The term "film" is used to include a substantially two-dimensional structure sometimes called a sheet or tape.

The carbon fiber and film of the present invention may be pitch-based carbonaceous matter and have a different cross section. Examples of the cross-sectional shape of the carbon fiber include a triangular shape, a hollow triangular shape, a rectangular shape, a hollow quadrangular shape, an elliptical shape, a cross shape, and a star shape. A preferable cross-sectional shape is a rectangular shape or an elliptical shape.

The cross sections of the carbon fiber and the film have a leaflet-oriented structure. As shown in FIG. 1, in the leaflet oriented structure, the pitch-based carbon fiber 1 having an elliptical cross section has a radially oriented structure with the major axis as the central axis and a similar structure. Also,
Carbon fibers having a triangular cross section, a star shape, and the like have a structure in which an axis extending from the center point of the cross section to the apex is the center axis, and the axis is radially oriented from this center axis, and a structure similar to such a structure. Fibers with such a leaflet orientation structure,
Compared with conventional radial orientation and random orientation fibers,
Remarkably high thermal conductivity. Further, the fibers having the above-mentioned structure have high mechanical properties such as tensile strength and elastic modulus, as well as electrical conductivity, like conventional carbon fibers.

Further, the carbon fiber and the film are
Although it may be carbonized, it is preferably graphitized in order to enhance thermal conductivity. The thermal conductivity exponentially increases remarkably as the degree of graphitization increases.

Such carbon fibers and films have a thermal conductivity of 500 W / mK or more, preferably 900 W / m.
It is more than m · K and is higher than the thermal conductivity of copper 400 W / m · K.

The average diameter of the pitch-based carbon fibers is, for example, 1 to 40 μm, preferably 5 to 30 μm. The carbon fibers may be long fibers or short fibers. The thickness of the film is, for example, 5 to 100.
μm, preferably about 10 to 50 μm. If the film is tape-shaped, the aspect ratio (width / thickness) is 1
It is 0 to 1000, more preferably about 30 to 300.

The carbon fiber or film may be subjected to a conventional surface treatment such as oxidation treatment in order to enhance the wettability with the matrix. Depending on the type of the matrix, a film forming treatment such as an oxidation treatment may be performed. Treatment such as titanium, titanium nitride, titanium carbide, silicon carbide, boron, boron nitride, or aluminum may be performed by a CVD method or the like.

The heat conductive material of the present invention may contain the above-mentioned carbon fiber and / or film and a matrix. Examples of the matrix include binders such as resins, carbonaceous binders, metals and ceramics.

As the resin, a thermosetting resin, a thermoplastic resin or a mixture thereof can be used. Examples of the thermosetting resin include, for example, epoxy resin, vinyl ester resin, phenol resin, unsaturated polyester, polyimide, polyurethane, diallyl phthalate, and the like. The conventional curing agent is used in combination.

Examples of the thermoplastic resin include polypropylene, acrylic resin, polyesters such as polyethylene terephthalate and polybutylene terephthalate, styrene polymers such as polyacrylonitrile, acrylonitrile-butadiene-styrene copolymer, polyacetal, polycarbonate, nylon 6, and the like. Examples thereof include nylon such as nylon 66, polyamide, polyphenylene oxide, polyphenylene sulfide, polyarylate, polysulfone, polyether sulfone, polyether ether ketone, polyoxybenzylene, polyamide imide, and polyether imide.

Examples of the carbonaceous binder include carbonizable or graphitizable binders such as furan resins such as phenol resin and furfural resin, polyacrylonitrile, pitch, and mesocarbon microbeads.

As the ceramic raw material, for example, oxide-based inorganic powder such as alumina, carbide-based inorganic powder, nitride-based inorganic powder, boride-based inorganic powder, natural or synthetic ceramic raw material, etc. can be used. ..

Examples of the metal include aluminum, titanium, iron, magnesium, copper, nickel, cobalt and alloys containing these metals.

The ratio of the carbon fiber or film to the matrix can be selected within a range in which the thermal conductivity is not lowered, but the content of the carbon fiber or film is usually 10 to 85% by volume, preferably 25 to 75% by volume, Preferably 30 to 7
It is about 5% by volume. Carbon fiber or film content is 1
If it is less than 0% by volume, the thermal conductivity of the composite material is lowered,
If it exceeds 5% by volume, the integrity of the composite material may deteriorate.

The heat conductive material of the present invention is useful for producing a composite material having high heat conductivity.

The composite of the carbon fiber and / or film and the matrix can be carried out by a conventional method. For example, when the matrix is a resin, it can be composited and molded by a filament winding method, a pultrusion method, a prepreg method, a pellet injection molding method, a foam reservoir method, a stamping method or the like. When the matrix is a carbonaceous binder, a molded article molded in the same manner as the case of the resin can be carbonized or fired to form a composite. Further, when the matrix is ceramics, it can be made into a composite by molding by compression molding, extrusion molding, wet molding or the like and sintering. When the matrix is a metal, it can be formed into a preform by a molten metal infiltration method, an ion plating method, a thermal spraying method, or the like, and can be compounded and molded by a hot pressing method, a hot roll method, or the like.

When the carbon fibers and the film are composited, the carbon fibers and the film are oriented in one direction when conducting heat in one direction, and the carbon fibers and the film are oriented in two directions when conducting heat in two directions. It should be compounded. Further, in the case of conducting heat evenly, the carbon fibers or films may be oriented in three directions or randomly to form a composite. The carbon fiber and the film may be used in combination when the composite is formed.

The composite material in which the carbon fiber or film and the matrix are composited has a small decrease in thermal conductivity and exhibits high thermal conductivity.

The carbon fiber or film can be manufactured by the following method. That is, subjecting the spinning step of melt spinning the optically anisotropic pitch from the nozzle, the obtained pitch-based fiber or film having an irregular cross-section, the infusibilizing step of making it infusible, and the firing step of baking the infusibilized fiber or film. Can be manufactured by

The optically anisotropic pitch may be either coal-based or petroleum-based. The preferred optically anisotropic pitch is
It is a mesophase pitch containing 95% by weight or more, preferably 97% by weight or more of an optically anisotropic phase. The softening point of the pitch is, for example, about 180 to 330 ° C., preferably 200.
It is about 320 ° C. The use of such a mesophase pitch facilitates the production of fibers having a leaflet oriented structure. The benzene insoluble content of the pitch is, for example, 85
~ 90% by weight, quinoline insoluble content is 35 to 50% by weight
It is a degree.

In the spinning step, a nozzle or a slit-shaped spinning nozzle (spout) for forming fibers having an irregular cross section is used. The shape of the nozzle may be any shape as long as the fiber or film having the irregular cross section can be obtained, and can be appropriately selected according to the cross sectional shape of the fiber. A preferable nozzle shape is a slit-shaped nozzle capable of obtaining a fiber or film having a rectangular cross section or an elliptical cross section. In the slit-shaped nozzle, the slit width (length) and the slit height (diameter) are not particularly limited, but when producing fibers, the slit width W is 0.2 to 2
mm, preferably about 0.4 to 1.5 mm, the height H of the slit is 0.04 to 0.2 mm, preferably 0.06 to
It is about 0.15 mm. When the height H of the slit is less than 0.04 mm, the spinnability tends to deteriorate. Further, when a nozzle having a circular spinning hole is used, fibers having radial orientation and random orientation are obtained depending on the melting temperature and the spinning method, but carbon fibers obtained by carbonizing or graphitizing such fibers have low thermal conductivity.

In the slit nozzle, the ratio W / H between the slit width W and the slit height H can be appropriately selected, but is preferably 1.5 <W / H <20, more preferably 2.5 <W. / H <10.

In the case of producing carbon fiber, the spinning method is not particularly limited, and a conventional melt spinning method, air sucker method, vortex method or the like can be adopted. Further, when a film is manufactured using pitch as a raw material, neck-down, that is, a phenomenon that the width of the film is narrowed during molding is likely to occur. In such a case, it is preferable to melt spin the film by adopting the method previously proposed by the applicant (Japanese Patent Laid-Open No. 3-936).
13 publication). That is, the pitch is extruded from a slit-shaped nozzle, and the extruded sheet-shaped pitch is pulled by a winding device and wound up. At that time, in order to prevent neck-down of the sheet-like pitch, before the sheet-like pitch is sufficiently solidified, the width of the sheet-like pitch is being reduced by traction, near the widthwise end faces of the sheet-like pitch, air currents such as nitrogen. In the direction of expanding the width of the sheet-like pitch, for example, 50 to 100 m /
A pitch film is produced by spraying at a speed of about a second (speed at the outlet of the airflow outlet).

In the infusibilizing step, the melt-spun pitch-based fiber or film is subjected to, for example, 200 to 500 ° C. in the presence of oxygen, air or an oxygen-containing substance (for example, an oxidizing agent such as nitric acid or carbon dioxide). Preferably 200-400 ° C
Heat treatment to some extent. The infusibilization can prevent fusion between fibers and films.

In the firing step, the infusibilized fiber or film is carbonized or graphitized. In the firing step, the thermal conductivity improves as the firing temperature increases. Therefore, the firing temperature is a temperature at which graphitization is possible, preferably 2500
It is preferable to calcine and graphitize at a temperature of not lower than 0 ° C, more preferably not lower than 2700 ° C. In particular, when firing at a temperature of 2500 ° C. or higher, the thermal conductivity exponentially improves remarkably. The graphitization temperature may be 3000 ° C or higher. In particular, in the case of having a leaflet orientation structure having an irregular cross section, the rate of increase in thermal conductivity is remarkable as compared with fibers such as circular radial type and circular random type fibers.

The heat conductive material of the present invention can be used for various purposes, but is useful as a heat exchange material for a heat exchanger.
Examples of heat exchangers include waste heat exchangers, engine parts such as Stirling engine heat pumps and direct drive heat pumps, heat exchangers for solar energy such as LNG vaporizers and solar water heaters, and low-quality energy such as low-temperature waste heat. Examples include a heat exchanger for recovery. Also,
The natural gas cylinder itself, which generates heat during pressure filling, may be formed of the above material.

When it is used as a heat exchange material, it has high thermal conductivity, is chemically inert, and has excellent mechanical properties. Therefore, heat exchange efficiency can be improved, and the heat exchanger can be miniaturized. It can be used even in the environment.

[0043]

EFFECTS OF THE INVENTION The heat conductive material of the present invention has a specific cross-sectional structure and is composed of pitch-based carbon fiber or film having high heat conductivity. The rate is high.

[0044]

EXAMPLES The present invention will be described in more detail based on the following examples.

In the following Examples and Comparative Examples, the thermal conductivity was measured by a laser flash method [Vacuum Riko Co., Ltd., TC-7000, laser output:
[Ruby laser]. The thermal conductivity was measured at room temperature (25 ° C.), the thermal diffusivity of the back surface of the sample was measured using an infrared detector (InSb sensor), and the specific heat of the back surface of the sample was measured using a PR thermocouple.

Example 1 A coal-based mesophase pitch having an optically anisotropic phase content of 100% by weight and a softening point of 300 ° C. was used and a slit width of 0.53 m.
Melt spinning was performed at a nozzle temperature of 345 ° C. using a slit-shaped nozzle (W / H = 7.5) having a slit height of m and a slit height of 0.07 mm. The spinning viscosity of the mesophase pitch was 1000 poise. Further, nitrogen gas was blown at a position 25 cm below the nozzle under the condition of 2 L / min to rapidly cool the pitch fiber.

The pitch fiber obtained was mixed at 3 ° C. under the condition of 2 ° C./min.
The infusibilization treatment was performed by raising the temperature to 10 ° C. and holding it for 15 minutes. The infusible fiber is then placed in an inert gas, 1
1200 ° C, 2500 ° C, 280 at a heating rate of 5 ° C / min
The temperature was raised to 0 ° C. and 3000 ° C. to carbonize or graphitize. The cross section of the fiber was elliptical and had a leaflet oriented structure. The relationship between the firing temperature and the thermal conductivity of the pitch-based carbon fiber is shown by a circle in the graph of FIG.

Comparative Example 1 A perfect circular nozzle (hole diameter 0.2 mm) was used, and the nozzle temperature was 35.
Carbon fibers were obtained by infusibilizing, carbonizing or graphitizing in the same manner as in Example 1 except that melt spinning was performed at 0 ° C. to a yarn diameter of 12 μm. The cross section of the fiber was circular and had a radial orientation structure. The relationship between the firing temperature and the thermal conductivity of the pitch-based carbon fiber is shown by Δ in the graph of FIG.

Comparative Example 2 A perfect circular nozzle (hole diameter 0.2 mm) was used, and the nozzle temperature was 35.
Carbonization or graphitization was performed in the same manner as in Example 1 except that the pitch fiber obtained was melt-spun at 5 ° C. to a diameter of 12 μm, the temperature of the obtained pitch fiber was raised to 305 ° C. under the condition of 2 ° C./minute, and was held for 15 minutes.
Carbon fiber was obtained. The cross section of the fiber was circular and had a randomly oriented structure. The relationship between the firing temperature and the thermal conductivity of the pitch-based carbon fiber is shown by □ in the graph of FIG.

As shown in FIG. 2, the pitch-based carbon fiber (Example) having a modified cross-section and a leaflet orientation structure was obtained in Comparative Example 1.
Also, the thermal conductivity is superior to that of the pitch-based carbon fiber of Comparative Example 2. In particular, a marked difference is observed in the thermal conductivity at high temperatures.

Example 2 Carbon fiber having a leaflet orientation structure obtained by firing at 2800 ° C. in Example 1 was used as a base material, pitch was impregnated, and the temperature was raised to 1500 ° C. at a heating rate of 5 ° C./min. After firing, pitch was further impregnated and fired in the same manner as above to produce a carbon / carbon composite material. When the thermal conductivity of the obtained composite material was measured, it was 660 W / m · K.

Example 3 Carbon fiber having a leaflet orientation structure obtained by firing at 2800 ° C. in Example 1 was used as a base material, and copper was melted to obtain carbon fiber / copper = 60/40% by volume. A composite material was prepared. When the thermal conductivity of the obtained composite material was measured, it was 780 W / m · K.

Comparative Example 3 Carbon fiber / copper = 60 was carried out in the same manner as in Example 3 except that the carbon fiber of Example 3 was replaced by the carbon fiber having the random orientation structure obtained in Comparative Example 2. A composite material of / 40% by volume was prepared. When the thermal conductivity of the obtained composite material was measured, it was 300 W / m · K.

Example 4 Carbon fiber having a leaflet orientation structure obtained by firing at 2800 ° C. in Example 1 was used as a base material, and aluminum was melted to obtain carbon fiber / aluminum = 60/40% by volume. A composite material was prepared. When the thermal conductivity of the obtained composite material was measured, it was 680 W / m.
It was K.

Comparative Example 4 Carbon fiber / aluminum = 60/40% by volume was used in the same manner as in Example 4 except that the carbon fiber obtained in Comparative Example 2 was used.
A composite material of When the thermal conductivity of the obtained composite material was measured, it was 210 W / m · K.

Comparative Example 5 The thermal conductivity of copper alone was measured and found to be 386 W / m · K.
Met.

Comparative Example 6 The thermal conductivity of aluminum alone was measured and found to be 228.
It was W / m · K.

Comparative Example 7 The thermal conductivity of iron alone was measured and found to be 76 W / m · K.

As described above, the carbon fiber having a cross-section irregular shape and a leaflet orientation structure, or the composite material of the carbon fiber and carbon or metal is a carbon fiber having a circular section and a random orientation structure or a radial orientation structure, or A marked difference in thermal conductivity is recognized as compared with the composite material of the carbon fiber and the metal and also as compared with the metal carrier.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a pitch-based carbon fiber constituting a heat conductive material.

FIG. 2 is a graph showing the results of Example 1 and Comparative Examples 1 and 2.

[Explanation of symbols]

 1 ... Pitch-based carbon fiber

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location D01D 5/253 7199-3B

Claims (3)

[Claims] 1. A heat-conductive material having a cross-sectional shape, a leaflet-oriented structure, and a pitch-based carbon fiber or film having a heat conductivity of 500 W / m · K or more. 2. The heat conductive material according to claim 1, wherein the carbon fiber or film is graphitized. 3. The heat conductive material according to claim 1, comprising a carbon fiber or film and a matrix.