WO2006057458A1

WO2006057458A1 - Composition for heat-conducting composite material containing carbon material and use thereof

Info

Publication number: WO2006057458A1
Application number: PCT/JP2005/022239
Authority: WO
Inventors: Satoshi Miyake; Yukihiko Takahashi; Tsutomu Masuko
Original assignee: Showa Denko K.K.
Priority date: 2004-11-29
Filing date: 2005-11-28
Publication date: 2006-06-01

Abstract

The invention provides a material for producing a heat radiation fan or a heat radiation sheet to be used for local heat radiation in electronic devices or parts, which is particularly light in weight and has an excellent high thermal conductivity. Specifically, the invention provides a composition for composite material containing a composition containing carbon material and ceramic material, a composite material obtained by dispersing the composition in polymer material or oil and a molded product obtained by molding the composite material, which is light in weight and excellent in thermal conductivity. The carbon material is preferably a vapor grown carbon fiber having an average filament diameter of 50 to 500 nm and an aspect ratio of 5 to 100. The blending amount of the carbon material is from 0.1 to 20 mass % based on the ceramic amount.

Description

DESCRIPTION

Composition for Heat-Conducting Composite Material Containing Carbon Material and Use Thereof

CROSS-REFERENCE TO RELATED APPLICATIONS

This is an application filed pursuant to 35 U.S.C. Section 111(a) with claiming the benefit of U.S. provisional application Serial No. 60/633,174 filed December 6, 2004, U.S. provisional application Serial No. 60/671,530 filed April 15, 2005 and U.S. provisional application Serial No. 60/671,531 filed April 15, 2005 under the provision of 35 U.S.C. Ill (b) , pursuant to 35 U.S.C. Section 119(e) (l).

TECHNICAL FIELD

The present invention relates to a composition for producing a composite material, containing a carbon material and a ceramic material; to a composite material containing the composition and a polymer material or an oil; to a method for producing the composite material; and to a molded product which is produced through molding of the composite material and is light in weight and excellent in thermal conductivity.

BACKGROUND ART

In recent years, continued efforts have been devoted to miniaturization of LSIs (large-scale integrated circuits) to meet the demand for electronic devices of higher performance. Therefore, leakage of electric power in LSIs affects full attainment of performance thereof. A problem caused by such electric power leakage is heating of LSIs. When the temperature rise due to such LSI heating is not suppressed, the amount of electrical leakage may be further increased, and in the worst case, thermal runaway may occur.

In order to cope with such a problem, heat radiation fans or heat radiation sheets have been employed for local cooling or heat release. However, recent downsizing of electronic devices does not allow mounting of a heat radiation fan. In addition, a conventional heat radiation sheet fails to attain sufficient heat release, due to an increase in the amount of heat generation associated with development of high-packing-density electronic devices. In view of the foregoing, demand has arisen for a heat radiation sheet exhibiting improved heat radiation property. Conventionally, there has been known, as a heat radiation sheet, a sheet formed by dispersing a thermally conductive filler in a matrix resin. Examples of filler for use therein include those which have a functional group on the surface and can be incorporated into the resin in a desired amount, such as aluminum oxide, boron nitride, silicon nitride and aluminum nitride.

However, such a filler per se exhibits low thermal conductivity, and thus enhancement of the thermal conductivity of a heat radiation sheet requires incorporation of a large amount of the filler, leading to an increase in the mass of the heat radiation sheet. Therefore, attempts have been made to develop a heat radiation sheet incorporating, as a filler, fine graphite powder or carbon fiber, which is light in weight and exhibits excellent thermal conductivity, for the purpose of reducing the mass of the heat radiation sheet. By addition of fine graphite powder, a heat radiation sheet produced having an enhanced thermal conductivity as compared with a ceramic material can be obtained. However, fine graphite powder, which does not have a functional group on its surface, exhibits poor adhesion with resin and therefore, strength of the sheet decreases. Further, when carbon fiber or vapor grown carbon fiber is added to a resin, flowability of the resultant composition considerably decreases. Therefore, such carbon fiber cannot be incorporated into resin in a large amount, which leads to difficulty in production of a heat radiation sheet having sufficient thermal conductivity.

Japanese Patent Application Laid-Open {kokai) No. 11-279406 discloses a method for dispersing pitch-based carbon fiber in a silicone rubber base, thereby enhancing the thermal conductivity of the resultant product. However, this method involves a problem, in that attaining a practically sufficient thermal conductivity requires incorporation of a large amount of pitch- based carbon fiber. Japanese Patent Application Laid-Open (kokai) No. 2002-020179 discloses a composite material of high thermal conductivity prepared by incorporating fine graphite powder and vapor grown carbon fiber into a furan resin, etc.

However, graphite cannot be incorporated into such resin in a large amount, since graphite has substantially no functional groups on its surface. Thus, when graphite is used, the weight of the obtained composite material can be decreased, but sufficient thermal conductivity is difficult to attain. In addition, when a ceramic material and vapor grown carbon fiber are mixed in a dry manner, filaments of the vapor grown carbon fiber tend to form fluffy aggregates. Thus, such carbon fiber is difficult to be dispersed in a ceramic material and over the matrix.

There is another problem that when vapor grown carbon fiber having high aspect ratio is added to a resin, flowability of the resultant composition considerably decreases. Therefore, since such carbon fiber cannot be incorporated into resin in a large amount, sufficient thermal conductivity cannot be attained.

Japanese Patent Application Laid-Open (kokai) No. 2003-

119019 discloses that a ceramic material is surface treated with a coupling agent or a surfactant, whereby flowability of a matrix containing the ceramic material is enhanced. Although the flowability is enhanced through employment of surface-treated ceramic material, when a heat radiation material is produced from a surface-treated ceramic material per se having a low thermal conductivity is used, contact resistance between the particles increases, and thermal conductivity decreases. Thus, sufficient thermal conductivity is difficult to attain.

Therefore, strong demand has arisen for development of a material for providing a molded product used for a heat radiation fan or heat radiation sheet which is light in weight and has high thermal conductivity.

DISCLOSURE OP THE INVENTION

An object of the present invention is to provide a material for molded product to be used for producing a heat radiation fan or a heat radiation sheet, which is light in weight and has high thermal conductivity.

The present invention is directed to a composition for composite material, a composite material containing the composition, a production method thereof, and a molded product prepared therefrom, as follows.

[1] A composition for composite material comprising a carbon material and a ceramic material. [2] The composition for composite material as described in 1 above, wherein the carbon material is at least one species selected from the group consisting of carbon fiber, coke powder and graphite powder. [3] The composition for composite material as described in 2 above, wherein the carbon fiber is vapor grown carbon fiber or carbon nanotube.

[4] The composition for composite material as described in 3 above, wherein the vapor grown carbon fiber has an average fiber diameter of 50 to 500 nm and an aspect ratio of 5 to 1,000. [5] The composition for composite material as described in 4 above, wherein a vapor grown carbon fiber having an average fiber diameter of 50 to 500 nm and an aspect ratio not less than 5 and less than 40 is dispersed in the ceramic material powder. [6] The composition for composite material as described in any one of 1 to 5 above, wherein the ceramic material is at least one compound selected from the group consisting of aluminum oxide, magnesium oxide, zinc oxide, silicon dioxide and boron nitride. [7] The composition for composite material as described in any one of 1 to 6 above, wherein the ceramic material is in the form of ceramic particles having an average particle size of 0.3 to 80 μm and a specific surface area of 0.01 to 15 m²/g. [8] The composition for.composite material as described in any one of 1 to 7 above, wherein the carbon material is vapor grown carbon fiber and the ceramic material is aluminum oxide or boron nitride.

[9] The composition for composite material as described in any one of 4 to 8 above, comprising a vapor grown carbon fiber having an average fiber diameter of 10 to 500 nm and an aspect ratio of 5 to 1,000 and ceramic material particles, wherein filaments of the vapor grown carbon fiber are deposited on at least part of a surface of the ceramic material particle via a polymer compound which is adherent to both the vapor grown carbon fiber and the ceramic particles. [10] The composition for composite material as described in 9 above, wherein the polymer compound is at least one compound selected from the group consisting of a phenolic resin, a polyvinyl alcohol resin, a furan resin, a cellulose resin, a polystyrene resin, a polyimide resin and an epoxy resin. [11] The composition for composite material as described in 9 above, wherein the blending amount of the polymer compound is 0.1 to 30 mass % with respect to the total amount of the ceramic material and the vapor grown carbon fiber. [12] The composition for composite material as described in any one of 1 to 11 above, wherein the blending amount of the carbon material is 0.1 to 20 mass % that of the ceramic material. [13] A composite material prepared from the composition as described in any one of 1 to 12 above, wherein a polymer material or an oil is blended in. [14] The composite material as described in 13 above, wherein a polymer material or an oil material is blended into a composition in which a vapor grown carbon fiber having an average fiber diameter of 10 to 500 nm and an aspect ratio of 5 to 1,000 and ceramic material particles are contained and filaments of the vapor grown carbon fiber are deposited on at least part of a surface of the ceramic material particle via a polymer compound adherent to both the vapor grown carbon fiber and the ceramic particles. [15] The composite material as described in 13 or 14 above, wherein the polymer material or the oil is at least one species selected from the group consisting of an aliphatic resin, an ^• unsaturated polyester resin, an acrylic resin, a methacrylic resin, a vinyl ester resin, an epoxy resin, a silicone resin, a silicone oil, a petroleum-based oil and a fluorine-based oil.

[16] The composite material as described in any one of 13 to 15 above, wherein the blending amount of the polymer material or the oil is 1 to 35 mass % the total amount of the carbon material and the ceramic material. [17] A molded product formed of the composite material as described in any one of 13 to 16 above.

[18] The molded product as described in 17 above, which is in the form of a sheet or a film.

[19] A heat radiation sheet using the molded product as described in 17 above.

[20] A personal computer using the heat radiation sheet as described in 18 above.

[21] A game machine using the heat radiation sheet as described in 18 above. [22] A digital video camera using the heat radiation sheet as described in 18 above.

[23] A digital camera using the heat radiation sheet as described in 18 above.

[24] A television set using the heat radiation sheet as described in 18 above

[25] A mobile phone using the heat radiation sheet as described in 18 above.

[26] A method for producing the composite material as described in 13 above, comprising subjecting a carbon material and a ceramic material to shear-stirring under dry conditions and dispersing the resultant composition in a polymer material or an oil. [27] A method for producing the composite material as described in 14 above, comprising depositing a vapor grown carbon fiber having an average fiber diameter of 10 to 500 nm and an aspect ratio of 5 to 1,000 on ceramic material particles by use of a polymer compound which is adherent to both the vapor grown carbon fiber and the ceramic material particles, thereby forming a composition containing composite particles, and dispersing the composition in a polymer material or an oil.

The composition for composite material of the present invention contains a ceramic material having a functional group on the surface and a carbon material having a lighter weight and higher thermal conductivity as compared with the ceramic material. Accordingly, in a case where the composition of the present invention is used, the amount required for attaining a certain thermal conductivity in the resultant composite material can be smaller than the amount in a case where a filler which contains ceramic material only is used, so that the composite material of the present invention can be light in weight. On the other hand, as compared with a case where a filler containing only a carbon material is blended in, the composition of the present invention, which contains a ceramic material having a functional group on its surface, can be blended in in a larger amount, whereby a higher thermal conductivity can be obtained in the resultant composite material.

Addition of an appropriately selected ceramic material of low density enables further reduction in weight of the composite material while maintaining a desired thermal conductivity. Meanwhile, addition of an appropriately selected carbon material of high thermal conductivity enables further enhancement of the thermal conductivity of the composite material while maintaining a desired weight.

The composite material of the present invention, which contains the aforementioned composition and a polymer material or an oil, is light in weight and has a high thermal conductivity conventional composite materials cannot achieve. The molded product of the present invention, which is formed through molding of the composite material, also is light in weight, has a high thermal conductivity and an excellent heat radiation property. Therefore, the molded product is suitable for use as a heat radiation sheet or a heat radiation film that can suppress temperature rise due to LSI heating which is a problem pending in attempts for improvement on performances of electronic devices or electronic components.

BRIEF DESCRIPTION OF DRAWINGS Fig.l is a graph showing relationship between the blending amount of the vapor grown carbon fiber and the thermal conductivity ratio of the composite material containing the carbon material against the thermal conductivity of the composite material where ceramic material only is added without carbon material, in Examples 1, 2, 4, 6, 7 and 8 and Comparative Example 1. ^λΛX" represents a blending amount of ceramic material and Y represents a blending amount of vapor grown carbon fiber.

Fig.2 is an electron micrograph at a magnification of 1,000 of the composite material obtained in Example 15.

Fig.3 is an electron micrograph at a magnification of 3,500 of the composite material obtained in Example 15.

Fig.4 is an electron micrograph at a magnification of 1,000 of the composite material obtained in Example 16. Fig.5 is an electron micrograph at a magnification of 3,500 of the composite material obtained in Example 16.

Fig.6 is an electron micrograph at a magnification of 1,000 of the composite material obtained in Example 17.

Fig.7 is an electron micrograph at a magnification of 3,500 of the composite material obtained in Example 17.

BEST MODE FOR CARRYING OUT THE INVENTION

The composition for composite material of the present invention contains a carbon material and a ceramic material. The carbon material may be at least one species selected from the group consisting of carbon fibers, such as vapor grown carbon fiber (thermal conductivity: 400 to 1,200 w/(m-k)), carbon nanotube (thermal conductivity: 400 to 1,200 w/(m-k)) and pitch- or PAN-based carbon fiber (thermal conductivity: 200 to 1,000 w/(m-k)); coke powder (thermal conductivity: 100 to 200 w/(m-k)); and graphite powder (thermal conductivity: 100 to 200 w/(m-k)).

Preferred among the aforementioned carbon materials is carbon fiber, which has a high thermal conductivity. More preferred is vapor grown carbon fiber or carbon nanotube, which has a higher thermal conductivity. Even more preferred from the viewpoint of uniform dispersibility in a polymer material or an oil when preparing a composite material is a vapor grown carbon fiber having a smaller specific surface area (specific surface area of vapor grown carbon fiber: 10 to 20 m²/g, specific surface area of carbon nanotube: 200 to 300 m²/g) .

When the carbon material to be employed is vapor grown carbon fiber, the average fiber diameter of the carbon fiber is preferably 50 to 500 nm, more preferably 70 to 300 run, much more preferably 80 to 200 nm, particularly preferably 100 to 150 nm.

If a vapor grown carbon fiber having an average fiber diameter of less than 50 nm is used, handling property decreases, whereas if a vapor grown carbon fiber having an average fiber diameter exceeding 500 nm is used, the aspect ratio decreases and thermal conductivity is lowered.

The vapor grown carbon fiber to be employed preferably has an aspect ratio of 5 to 1,000, more preferably 10 to 500, much more preferably 15 to 150, particularly preferably 20 to 120. A vapor grown carbon fiber having an aspect ratio of 5 or higher exhibits a significant effect of thermal conductivity enhancement, whereas a vapor grown carbon fiber having an aspect ratio of 1,000 or less provides good handling property.

By using a vapor grown carbon fiber having an a aspect ratio of 5 or more but less than 40, flowability of the composition for composite material in the composite material is enhanced, and the thermal conductivity is not so lowered and the viscosity can be lowered, as compared with a case using a vapor grown carbon fiber having an aspect ratio of 40 or more. Specifically, the thermal conductivity of the composite material of the present invention in a case where alumina is used as a ceramic material is 1.6 (W/(m-K)) or more, and the viscosity is 20 (Pa-s) or less at 10 rpm and 30(Pa-s) or less at 100 rpm. In a case where boron nitride is used as a ceramic material, the thermal conductivity is 2.0 (W/(m-K)) or more, preferably 2.5 (W/(m-K)) or more, even more preferably 2.8 (W/(m-K)) or more, and the viscosity is 30 (Pa-s) or less at 10 rpm and 40(Pa-s) or less at 100 rpm.

More preferred aspect ratio is from 10 to 39, still more preferably 15 to 38, particularly preferably 20 to 38. As the aforementioned carbon materials, those commercially available may be used. Alternatively, the carbon materials may be produced through known production methods described in various documents.

A vapor grown carbon fiber can be produced by introducing an organic compound (e.g., benzene) serving as a raw material and an .organo-transition metallic compound (e.g., ferrocene) serving as a catalyst into a high-temperature reaction furnace by use of a carrier gas to thereby thermally decompose the organic compound in a vapor phase. Examples of production methods for vapor grown carbon fiber include a method in which carbon fiber is formed on a substrate through thermal decomposition (Japanese Patent Application Laid-Open (kokai) No. 60-27700); a method in which carbon fiber is formed through thermal decomposition in a dispersed and floating state (Japanese Patent Application Laid- Open (kokai) No. 60-54998); and a method in which carbon fiber is grown on a reaction furnace wall through thermal decomposition (Japanese Patent No. 2778434). The carbon fiber employed in the present invention can be produced through any of these methods. The thus-produced vapor grown carbon fiber as is may be employed as a raw material. However, the as-produced vapor grown carbon fiber may have thermal decomposition products derived from the raw material organic compound serving on its surface, or the fiber structure constituting the carbon fiber may exhibit insufficient crystallinity. Therefore, the as-produced vapor grown carbon fiber may be subjected to thermal treatment in an inert gas atmosphere, in order to remove impurities such as thermal decomposition products from the carbon fiber, or to improve crystallinity of the carbon fiber structure. For the purpose of removing impurities such as thermal decomposition products derived from raw materials, thermal treatment at about 800 to about 1,500 ⁰C in an inert gas such as argon is preferable. Further, for the purpose of improving crystallinity of the carbon fiber structure, thermal treatment at about 2,000 to about 3,000 ⁰C in an inert gas such as argon is preferable. The thus-treated vapor grown carbon fiber is commercially available as, for example, VGCF (registered trademark; product of Showa Denko K.K.),

In a case where carbon nanotύbe is used as carbon material, the average fiber diameter is preferably 3 to 50 nm, more preferably 3 to 40 nm, even more preferably 3 to 30 nm, particularly preferably 3 to 20 nm. The filament length is preferably 2 to 20 urn, more preferably 5 to 15 μm, even more preferably 6 to 13 μm, particularly preferably 8 to 12 μm. The carbon nanotube used in the present invention may be commercially available product, or can be easily prepared by one of ordinary skill in the art according to production methods as described in many documents.

The ceramic material employed in the present invention, which is uniformly dispersed in a polymer material or an oil, serving as a matrix of the composite material, is preferably at least one species selected from the group consisting of aluminum oxide, magnesium oxide, silicon nitride, boron nitride, and aluminum nitride. Of these, boron nitride, aluminum oxide and/or magnesium oxide are more preferred, since such an oxide exhibits good compatibility with a polymer material or an oil, enables the composite material to be readily molded, and tends to prevent air bubbles or the like from entering the composite material during molding. Boron nitride, aluminum oxide and magnesium oxide have thermal expansion coefficients of 1 x 10^"6/°C, 6 x 10^~6/°C, and 14 x 10~⁶/°C, respectively. Thus, under application of heat, boron nitride and aluminum oxide exhibit a smaller change in volume, as compared with other fillers, and, at the interface between such a ceramic material and a polymer material or an oil, separation can be reduced. Therefore, the ceramic material employed in the present invention is particularly preferably aluminum oxide.

The ceramic material employed in the present invention is preferably in the form of particles having an average particle size of 0.3 to 80 μm, more preferably 0.5 to 70 μm. Ceramic particles having an average particle size of 0.3 μm or more provide good handling property, whereas ceramic particles having an average particle size of 80 μm or less can prevent strength reduction and maintain surface smoothness. The ceramic material preferably has a specific surface area of 0.01 to 15 m²/g, more preferably 0.01 to 10 m²/g, as measured through the nitrogen adsorption method (BET method) . When the specific surface area is 0.01 m²/g or more, strength reduction can be suppressed, whereas when the specific surface area is 15 m²/g or less, reduction in the amount of the ceramic material to be incorporated can be suppressed.

In the composition of the present invention, the amount of the carbon material is preferably 0.1 to 20 mass %, more preferably 0.5 to 10 mass %, particularly preferably 0.8 to 8 mass %, based on the amount of the ceramic material. When the amount of the carbon material is 0.1 mass % or more, a heat conduction effect is obtained, whereas when the carbon material amount is 20 mass % or less, the composition provides good handling property. No particular limitation is imposed on the method of mixing the carbon material with the ceramic material. However, when carbon fiber, in particular, vapor grown carbon fiber, is used as carbon material, mixing is preferably carried out within a short period of time under application of shear force by use of a Henschel mixer, a ball mill, a jet mill, or a similar apparatus. Through mixing under application of shear force, the whole or a part of vapor grown carbon fiber filaments having a three- dimensional structure is raveled out, whereby the resultant composition can be highly dispersed in a polymer material or an oil material at the time of mixing.

The polymer compound employed in the present invention is adherent to both vapor grown carbon fiber filaments and ceramic particles. The adherent polymer compound is a substance which stands between ceramic particles and vapor grown carbon fiber to thereby allow them in firm contact and in an integrated state through chemical bonding such as covalent bonding, van der Waals bonding, or hydrogen bonding. Any polymer that exhibits a resistance against compression, bending, peeling, impact, tension, tear, etc. during treatments such as mixing, stirring, removing of solvent, heat treatment and the like may be employed as the adherent polymer compound, so long as no peeling-off or falling- off of the vapor grown carbon fiber filaments occurs.

For example, the polymer is preferably at least one species selected from the group consisting of phenolic resins, polyvinyl alcohol resins, furan resins, cellulose resins, polystyrene resins, polyimide resins and epoxy resins. Of these, phenolic resins and polyvinyl alcohol resins are preferred, phenolic resins being more preferred. Particularly when a phenolic resin prepared by blending in a drying oil or a fatty acid thereof is used, a dense composite material in which the matrix and filers are tightly bonded can be produced. Assumably, the mechanism for this is that phenolic resin reacts with unsaturated bonds contained in the drying oil, to thereby form so-called drying- oil-modified phenolic resin, which mitigates decomposition during curing process and prevents foaming. In addition, not only unsaturated bonds but also considerably long alkyl chain and an ester bond, which are present in a drying oil, are assumed to play some role in facilitating removal of gas during the curing process.

Examples of the phenolic resin to be employed, produced by reaction of a phenol with an aldehyde, include non-modified phenolic resins such as novolak resins and resol resins, and partially modified phenolic resins. In addition, rubber such as nitrile rubber may be added to the phenolic resin in accordance with needs. Examples of the phenol serving as a starting material include phenol, cresol, xylenol, and alkylphenols having 20 or less carbon atoms. A phenolic resin where a drying oil or a fatty acid thereof is mixed in may be produced by subjecting phenol compound to addition-reaction with a drying oil in advance in the presence of a strong acid catalyst and then causing addition-reaction with formalin with addition of a base catalyst to thereby adjust the reaction system to be basic or by reacting a phenol compound with formalin and then adding a drying oil to the reaction product.

The drying oil is a vegetable oil which, when formed into thin film and exposed to air, is dried up and solidified in a relatively short period of time. Examples of the drying oil include generally known oil species such as tung oil, linseed oil, dehydrated castor oil, soybean oil, and cashew nut oil, and a fatty acid contained in the oils. The amount of the drying oil or a fatty acid thereof with respect the phenolic resin is preferably 5 to 50 parts by mass based on 100 parts by mass of the phenolic resin (e.g., a phenol-formalin condensate). When the amount of drying oil or fatty acid thereof is in excess of 50 parts by mass, bonding property decreases, resulting in lowering the density of vapor grown carbon fiber, whereas when the amount is less than 5 parts by mass, dense composite material cannot be produced.

In the case where vapor grown carbon fiber filaments are bonded to ceramic particles by use of the above polymer compound, the polymer compound may be diluted with acetone, ethanol, toluene, or a similar solvent so as to adjust the viscosity of the polymer, whereby bonding is facilitated.

The polymer compound may be adhered at least partially on the outer surfaces of ceramic particles, preferably completely on the outer surfaces, uniformly or non-uniformly, so long as the polymer is virtually adhered on the surfaces. No particular limitation is imposed on the atmosphere where bonding is performed, and any of the atmospheric conditions (normal pressure) , pressurized conditions and reduced-pressure conditions may be employed. However, bonding is preferably performed under reduced-pressure conditions, since affinity of the polymer to ceramic particles or vapor grown carbon fiber filaments is enhanced.

No particular limitation is imposed on the mixing/stirring method, and an apparatus such as a ribbon mixer, a screw kneader, a Spartan ryuzer, a Lodige mixer, a planetary mixer, or a general-purpose mixer may be employed.

The stirring time and temperature are appropriately determined in accordance with components, viscosity and the like of the ceramic material, vapor grown carbon fiber, and polymer compound. Generally, the temperature is about 0⁰C to about 50 ⁰C, preferably about 10⁰C to about 30°C. Alternatively, the mixing time is controlled and the composition is diluted with a solvent, such that the mixture has a viscosity 500 Pa-s or less at a given mixing temperature. In such a case, any solvent may be employed so long as the solvent has excellent affinity to the ceramic material, vapor grown carbon fiber, and polymer compound. Examples of the solvent include alcohols, ketones, aromatic hydrocarbons and esters. Of these, methanol, ethanol, butanol, acetone, methyl ethyl ketone, toluene, ethyl acetate, butyl acetate, etc. are preferred.

After completion of stirring, the solvent is preferably removed partially or completely. Any known method such as hot air blow drying or vacuum drying may be employed. The drying temperature, which varies in accordance with the boiling point, vapor pressure, etc. of the solvent used, for example, is 50 °C or higher, preferably 100 to 1,000 °C, more preferably 150 to 500 ⁰C.

Curing by heat may be performed by means of a known heating apparatus. From the viewpoint of productivity in the production process, a rotary kiln, a continuous furnace with a belt conveyer, or a similar apparatus, which allows continuous processing, is preferred.

The blending amount of the polymer compound (e.g., phenolic resin) to be added with respect to the total amount of ceramic material and vapor grown carbon fiber is preferably 0.1 mass % to 30 mass %, more preferably 0.1 to 20 mass %, particularly preferably 0.1 to 15 mass %. When the polymer is added in a amount of 0.1 mass % or more, ceramic particles are completely covered with the polymer, and when the amount is controlled to 30 mass % or less, contact resistance between particles can be suppressed.

Through formation of a composite of a ceramic material and vapor grown carbon fiber by using a binder, tribological property among the particles is enhanced, and contact resistance between particles which is the most detrimental factor to lowering in flowability of a matrix containing a large amount of filler particle can be reduced. Thus, flowability higher than that of a conventional composite material can be attained. By using the composition for composite material of the present invention, a composite material having a high thermal conductivity and a high flowability can be obtained. Thermal conductivity ratio of the composite material of the present invention is always more than 80 % as compared with the thermal conductivity ratio of a composite material where no polymer adherent to ceramic material surface is used and no vapor grown carbon fiber is deposited on the surface, and further, viscosity of the material of the invention is 25 (Pa-s) or less at 10 rpm and 20 (Pa-s) or less at 100 rpm, preferably 10 (Pa-s) or less at 100 rpm, more preferably 5 (Pa-s) or less at 100 rpm.

The composite material of the present invention is prepared by sufficiently dispersing the aforementioned composition in a polymer material or an oil. The polymer material or oil to be employed may be a known one. Preferred examples of polymer material include an aliphatic resin, an unsaturated polyester resin, an acrylic resin, a methacrylic resin, a vinyl ester resin, an epoxy resin and a silicone resin. Preferred examples of oil include a silicone oil, a petroleum-based oil and a fluorine-based oil. These materials are generally employed singly, but may be employed in combination of two or more species. Of these, an epoxy resin and a silicone resin are preferred, since the resin can be formed into a thin coating film, and exhibits excellent thermal conductivity among various resins.

The thermal conductivity ratio of the composite material of the present invention, containing a carbon material, preferably a vapor grown carbon fiber or a carbon nanotube, more preferably a vapor grown carbon fiber, is 1.0 or more against the thermal conductivity of a composite material containing ceramic material only without containing vapor grown carbon fiber. That is, the composite material according to the present invention is a composite material having a thermal conductivity ratio of 1.0 or more against such a ceramic-containing composite material without vapor grown carbon fiber .

As the experimental results of Examples 1, 2, 4, 6, 7 and 8 and Comparative Example 1, Fig.l shows a graph where the ratio of the vapor grown carbon fiber amount (Y) to the sum amount of the ceramic amount (X) and the vapor grown carbon fiber amount (Y), i.e., the substitution ratio of the vapor grown carbon fiber (%) is plotted on the horizontal axis and the thermal conductivity ratio of the composite material containing vapor grown carbon fiber against the thermal conductivity of the ceramic-containing composite material without vapor grown carbon fiber is plotted on the vertical axis.

In the composite material of the present invention, the amount of the polymer material or the oil is preferably 1 to 35 mass %, more preferably 1 to 25 mass %, based on the total amount of the carbon material and the ceramic material. When the amount of the polymer material or the oil is 1 mass % or more, the composite material exhibits good flowability, whereas when the amount is 35 mass % or less, the composite material is provided with high thermal conductivity. No particular limitation is imposed on the method of dispersing the aforementioned composition in the polymer material or the oil. When the carbon material to be employed is carbon fiber, which has a small fiber diameter and filaments of the fiber tend to aggregate together, it is preferable that the composition be subjected to mixing/stirring under dry conditions by use of a stirring apparatus such as a Henschel mixer before being incorporated into the polymer material or the oil. When the polymer material or the oil is added to the thus-stirred composition, and weak shear force is applied to the resultant mixture, the composition can be well dispersed in the polymer material or the oil.

After completion of dispersion, the resultant composite material can be subjected to defoaming treatment by use of a centrifugal defoaming apparatus, to thereby provide the composite material with reliably high thermal conductivity. Further, it is preferable that the rotation speed during kneading be regulated to 50 rpm or less in some cases where a certain type of carbon material such as vapor grown carbon fiber is used, since filaments of such a carbon material may be broken by shear stress, which leads to reduction in thermal conductivity.

The molded product of the present invention is produced through molding of the aforementioned composite material. Examples of the molding technique which may be employed include compression molding techniques such as FRP molding and transfer molding; casting techniques such as cast molding and embedding; rolling techniques such as calendaring; injection molding techniques such as RIM molding and injection foam molding; foaming techniques such as extrusion foaming;, and extrusion techniques such as inflation film molding and T-die film molding. Such a molding technique is selected in accordance with the intended form of the molded product. When a sheet-like or film- like molded product is to be produced, preferably, a rolling technique or an extrusion technique is employed. In a molded product produced from the composite material of the present invention, weight reduction and thermal conductivity enhancement are highly achieved in a well-balanced manner. Therefore, the molded product can be employed as a heat radiation member of, for example, an electronic device or an electronic component. Particularly, a sheet-like or film-like molded product exhibits excellent heat radiation property, and thus the molded product can be employed as a heat radiation sheet that can suppress temperature rise due to LSI heating which is a problem pending in attempts for improvement on performances of electronic devices or electronic components.

Electronic devices and electronic parts using the heat radiation sheet of the present invention may be used in a variety of applications such as personal computers, game machines, digital video cameras, digital cameras, television sets and mobile phones. Particularly, the heat radiation sheet of the present invention, which is excellent in radiation performance, can be mounted in a small electronic product.

EXAMPLES

The present invention will next be described in detail with reference to the Examples and the Comparative Examples, which should not be construed as limiting the invention thereto. In the Examples and the Comparative Examples, thermal conductivity of molded product samples and viscosity were measured through the following methods. ^•Thermal conductivity:

Thermal conductivity was determined through the nonstationary hot wire method by use of a quick thermal conductivity meter (model: QTM-500, product of Kyoto Electronics Manufacturing Co., Ltd.), after the samples was maintained at 23 ⁰C in a thermostatic chamber. ^•Viscosity:

Viscosity was determined by use of a B-type viscometer (product of Brookfields Engineering) , after the each sample was stirred for one minute at a rotation speed of 10 rpm and 100 rpm.

Varnish A, employed in the Examples 15 to 17 and the Comparative Examples 7 to 8, was produced through the following procedure.

Tung oil (100 parts by mass) , phenol (150 parts by mass) , and nonylphenol (150 parts by mass) were mixed, and the mixture was maintained at 50 °C. To the mixture, sulfur (0.5 parts by mass) was added, followed by stirring. The mixture was gradually heated and maintained at 120 ⁰C for one hour, whereby addition reaction between the tung oil and the phenols was carried out. Subsequently, the reaction mixture was cooled to 60 °C or lower, and hexamethylenetetramine (6 parts by mass) and 37-mass % formalin (100 parts by mass) were added to the mixture. The resultant mixture was allowed to react at 90 ⁰C for about 2 hours, and dehydrated under vacuum. The dehydrated product was diluted with methanol (100 parts by mass) and acetone (100 parts by mass) , to thereby produce a varnish having a viscosity of 20 mPa-s (20⁰C) (hereinafter referred to as "varnish A") .

Example 1:

Aluminum oxide (AS-10, product of Showa Denko K.K., average particle size: 39 μm, BET specific surface area: 0.5 m²/g) (396 g) and vapor grown carbon fiber (VGCF, product of Showa Denko K.K._r average fiber diameter: 150 nm, aspect ratio: 70) (4 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition containing the aluminum oxide and the vapor grown carbon fiber was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.), Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Example 2: Aluminum oxide (AS-10, product of Showa Denko K.K., average particle size: 39 μm, BET specific surface area: 0.5 m²/g) (380 g) and vapor grown carbon fiber (VGCF, product of Showa Denko K.K., average fiber diameter: 150 nm, aspect ratio: 70) (20 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition containing the aluminum oxide and the vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Example 3:

Aluminum oxide (AS-IO, product of Showa Denko K.K., average particle size: 39 μm, BET specific surface area: 0.5 m²/g) (594 g) and vapor grown carbon fiber (VGCF, product of Showa Denko K.K., average fiber diameter: 150 nm, aspect ratio: 70) (6 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition containing the aluminum oxide and the vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut piece was measured.

Example 4: Aluminum oxide (AS-IO, product of Showa Denko K.K., average particle size: 39 μm, BET specific surface area: 0.5 m²/g) (380 g) and vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 nm, aspect ratio: 30) (20 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition containing the aluminum oxide and the vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 °C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into a piece measuring 100 mm in width, 50 mm in length, and 20 mm in height, and the thermal conductivity of the cut piece was measured.

Example 5:

Aluminum oxide (AS-10, product of Showa Denko K.K., average particle size: 39 μm, BET specific surface area: 0.5 m²/g) (588 g) and vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 nm, aspect ratio: 30) (12 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition containing the aluminum oxide and the vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into a piece measuring 100 mm in width, 50 mm in length, and 20 mm in height, and the thermal conductivity of the cut piece was measured.

Example 6:

Aluminum oxide (AS-10, product of Showa Denko K.K., average particle size: 39 μm, BET specific surface area: 0.5 m²/g) (396 g) and vapor grown carbon fiber (VGCF-S, product of Showa Denko K.K., average fiber diameter: 100 nm, aspect ratio: 100) (4 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition containing the aluminum oxide and the vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 °C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into a piece measuring 100 mm in width, 50 mm in length, and 20 mm in height, and the thermal conductivity of the cut piece was measured.

Example 7:

Aluminum oxide (AS-10, product of Showa Denko K.K., average particle size: 39 um, BET specific surface area: 0.5 m²/g) (392 g) and vapor grown carbon fiber (VGCF-S, product of Showa Denko K.K., average fiber diameter: 100 nm, aspect ratio: 100) (8 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition containing the aluminum oxide and the vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 °C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into a piece measuring 100 mm in width, 50 mm in length, and 20 mm in height, and the thermal conductivity of the cut piece was measured. Example 8 :

Aluminum oxide (AS-IO, product of Showa Denko K.K., average particle size: 39 μm, BET specific surface area: 0.5 m²/g) (376 g) and vapor grown carbon fiber (VGCF-S, product of Showa Denko K.K., average fiber diameter: 150 nm, aspect ratio: 30) (24 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition containing the aluminum oxide and the vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into a piece measuring 100 mm in width, 50 mm in length, and 20 mm in height, and the thermal conductivity of the cut piece was measured.

Comparative Example 1:

Aluminum oxide (AS-10, product of Showa Denko K.K., average particle size: 39 μm, BET specific surface area: 0.5 m²/g) (400 g) was treated for 10 seconds by means of a Henschel mixer. Subsequently, the resultant aluminum oxide was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) . Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 °C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into a piece measuring 100 mm in width, 50 mm in length, and 20 mm in height, and the thermal conductivity of the cut piece was measured.

Comparative Example 2:

Aluminum oxide (AS-10, product of Showa Denko K.K., average particle size: 39 μm, BET specific surface area: 0.5 m²/g) (600 g) was treated for 10 seconds by means of a Henschel mixer. Subsequently, the resultant aluminum oxide was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into a piece measuring 100 mm in width, 50 mm in length, and 20 mm in height, and the thermal conductivity of the cut piece was measured.

Comparative Example 3:

Vapor grown carbon fiber (VGCF-S, product of Showa Denko K.K., average fiber diameter: 100 nm, aspect ratio: 100) (4 g) was treated for 10 seconds by means of a Henschel mixer. The resultant vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into a piece measuring 100 mm in width, 50 mm in length, and 20 mm in height, and the thermal conductivity of the cut piece was measured.

Comparative Example 4:

Vapor grown carbon fiber (VGCF-S, product of Showa Denko K.K., average fiber diameter: 100 nm, aspect ratio: 100) (8 g) was treated for 10 seconds by means of a Henschel mixer. The resultant vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into a piece measuring 100 mm in width, 50 mm in length, and 20 mm in height, and the thermal conductivity of the cut piece was measured.

As is clear from Table 1, when the total filler content is the same between molded products, a molded product containing a ceramic material and only a small amount of vapor grown carbon fiber exhibits more excellent heat radiation property as compared with a molded product containing a ceramic material only. As is also clear from Table 1, a molded product containing no ceramic material exhibits low thermal conductivity.

As compared with Comparative Examples 1 and 2 where the total filler content required for attaining a thermal conductivity of 10 w/(m-k) exceeds 3 kg, in all of Examples 1 to 8, the total filler required is 3 kg or less. The results indicate that incorporation of vapor grown carbon fiber together with a ceramic material can reduce the total amount of the filler required for attaining a predetermined thermal conductivity, thereby reducing the weight of the resultant molded product. Therefore, the present invention has a very high industrial value.

Example 9:

Vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 ran, aspect ratio: 40) was pulverized by use of a ball mill for one minute, to thereby produce vapor grown carbon fiber (A) (average fiber diameter: 150 ran, aspect ratio: 38) . The thus-produced vapor grown carbon fiber (A) (12 g) and alumina (AS-10, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX/ product of Tokushu Kika Kogyo Co., Ltd.) Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Separately, vapor grown carbon fiber (A) (12 g) and alumina (AS-IO, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Viscosity of the kneaded product was measured by use of a B-type viscometer.

Example 10:

Vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 ran, aspect ratio: 40) was pulverized by use of a ball mill for 5 minutes, to thereby produce vapor grown carbon fiber (B) (average fiber diameter: 150 run, aspect ratio: 33) . The thus-produced vapor grown carbon fiber (B) (12 g) and alumina (AS-10, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 °C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Separately, vapor grown carbon fiber (B) (12 g) and alumina (AS-IO, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Viscosity of the kneaded product was measured by use of a B-type viscometer.

Example 11:

Vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 ran, aspect ratio: 40) was pulverized by use of a ball mill for 10 minutes, to thereby produce vapor grown carbon fiber (C) (average fiber diameter: 150 nm, aspect ratio: 28) . The thus-produced vapor grown carbon fiber (C) (12 g) and alumina (AS-10, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Separately, vapor grown carbon fiber (C) (12 g) and alumina (AS-10, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) . Viscosity of the kneaded product was measured by use of a B-type viscometer.

Example 12:

Vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 run, aspect ratio: 40) was pulverized by use of a ball mill for 30 minutes, to thereby produce vapor grown carbon fiber (D) (average fiber diameter: 150 nm, aspect ratio: 24) . The thus-produced vapor grown carbon fiber (D) (12 g) and alumina (AS-10, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE

Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 °C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Separately, vapor grown carbon fiber (D) (12 g) and alumina (AS-10, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) . Viscosity of the kneaded product was measured by use of a B-type viscometer.

Example 13: Vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 nm, aspect ratio: 40) was pulverized by use of a ball mill for 60 minutes, to thereby produce vapor grown carbon fiber (E) (average fiber diameter: 150 nm, aspect ratio: 20) . The thus-produced vapor grown carbon fiber (E) (12 g) and alumina (AS-10, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Separately, vapor grown carbon fiber (E) (12 g) and alumina (AS-10, product of Showa Denko K.K.) (288 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) . Viscosity of the kneaded product was measured by use of a B-type viscometer.

Example 14:

Vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 ran, aspect ratio: 40) was pulverized by use of a ball mill for 60 minutes, to thereby produce vapor grown carbon fiber (E) (average fiber diameter: 150 nm, aspect ratio: 20) . The thus-produced vapor grown carbon fiber (E) (8 g) and boron nitride (EX, product of Showa Denko K.K.) (192 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 °C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus- obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured. Separately, vapor grown carbon fiber (E) (8 g) and boron nitride (EX, product of Showa Denko K.K.) (192 g) were mixed together for 10 seconds by means of a Henschel mixer. The mixture was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Viscosity of the kneaded product was measured by use of a B-type viscometer.

Comparative Example 5:

Alumina (AS-10, product of Showa Denko K.K.) (288 g) and vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 run, aspect ratio: 40) (12 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition (D) containing the aluminum oxide and the vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) . Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Separately, alumina (AS-10, product of Showa Denko K.K.) (288 g) and vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 ran, aspect ratio: 40) (12 g) were incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Viscosity of the kneaded product was measured by use of a B-type viscometer.

Comparative Example 6:

Boron nitride (EX, product of Showa Denko K.K.) (192 g) and vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 run, aspect ratio: 40) (8 g) were mixed together for 10 seconds by means of a Henschel mixer. The resultant composition (E) containing the boron nitride and the vapor grown carbon fiber was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Separately, boron nitride (EX, product of Showa Denko K.K.) (192 g) and vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 run, aspect ratio: 40) (8 g) were incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) . Viscosity of the kneaded product was measured by use of a B-type viscometer. Table 2

As is clear from Table 2, in comparison between Examples 9 to 13 where VGCF with a reduced aspect ratio and alumina were mixed together and Comparative Example 5 where VGCF with an aspect ratio of 40 and alumina were mixed together, the results show that flowability could be remarkably improved without reducing thermal conductivity in Examples 9 to 13. Further, in comparison between Example 14 where VGCF with a reduced aspect ratio and boron nitride were mixed together and Comparative

Example 6 where VGCF with an aspect ratio of 40 and boron nitride were mixed together, the results show that flowability could be remarkably improved without reducing thermal conductivity in Example 14. Thus, through employment of the composite material composition of the present invention, the amount of filler employed in heat radiation material can be increased, as compared with conventional composite material compositions, and heat radiation material having excellent heat radiation performance can be produced. Therefore, the present invention has a very high industrial value. Example 15 :

Varnish A (5.4 parts by mass, as resin solid content) was dissolved in ethanol (12.6 parts by mass) under stirring, to thereby prepare a well-dissolved solution. The solution was added to alumina (AS-IO, product of Showa Denko K.K.) (96 parts by mass) such that the modified phenolic resin solid content was adjusted to 4 mass %. The mixture was kneaded by use of a planetary mixer for 30 minutes. To the kneaded product, a vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 nm, aspect ratio: 40, graphitized at 2,800

⁰C) (4 parts by mass) was added, and the mixture was kneaded. The product was dried at 80 °C for 2 hours by means of a vacuum drier, to thereby remove ethanol. The thus-dried product was maintained in a vacuum drier at 180 ⁰C for 10 minutes, then 150 °C for 2 hours, to thereby cure the product. The thus-produced alumina- vapor grown carbon fiber composite composition (A) (300 g) was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) . Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured. The images observed by electron microscope are shown in Figs. 2 and 3.

Separately, alumina-vapor grown carbon fiber composite composition (A) (300 g) was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Viscosity of the kneaded product was measured by use of a B-type viscometer.

Example 16:

Varnish A (5.4 parts by mass, as resin solid content) was dissolved in ethanol (12.6 parts by mass) under stirring, to thereby prepare a well-dissolved solution. The solution was added to alumina (AS-10, product of Showa Denko K.K.) (96 parts by mass) such that the modified phenolic resin solid content was adjusted to 7 mass %. The mixture was kneaded by use of a planetary mixer for 30 minutes. To the kneaded product, a vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 run, aspect ratio: 40, graphitized at 2,800⁰C) (4 parts by mass) was added, and the mixture was kneaded. The product was dried at 80 ⁰C for 2 hours by means of a vacuum drier, to thereby remove ethanol. The thus-dried product was maintained in a vacuum drier at 180°C for 10 minutes, then 150 ⁰C for 2 hours, to thereby cure the product. The thus-produced alumina-vapor grown carbon fiber composite composition (B) (300 g) was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 °C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured. The images observed by electron microscope are shown in Figs. 4 and 5.

Separately, alumina-vapor grown carbon fiber composite composition (B) (300 g) was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Viscosity of the kneaded product was measured by use of a B-type viscometer.

Example 17:

Varnish A (5.4 parts by mass, as resin solid content) was dissolved in ethanol (12.6 parts by mass) under stirring, to thereby prepare a well-dissolved solution. The solution was added to alumina (AS-10, product of Showa Denko K.K.) (96 parts by mass) such that the modified phenolic resin solid content was adjusted to 10 mass %. The mixture was kneaded by use of a planetary mixer for 30 minutes. To the kneaded product, a vapor grown carbon fiber (VGCF-H, product of Showa Denko K.K., average fiber diameter: 150 nm, aspect ratio: 40, graphitized at 2,800°C) (4 parts by mass) was added, and the mixture was kneaded. The product was dried at 80 °C for 2 hours by means of a vacuum drier, to thereby remove ethanol. The thus-dried product was maintained in a vacuum drier at 180 °C for 10 minutes, then 150 °C for 2 hours, to thereby cure the product. The thus-produced alumina- vapor grown carbon fiber composite composition (C) (300 g) was incorporated into a commercially available two-component silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) . Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 ⁰C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured. The images observed by electron microscope are shown in Figs. 6 and 7. Separately, alumina-vapor grown carbon fiber composite composition (C) (300 g) was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) . Viscosity of the kneaded product was measured by use of a B-type viscometer.

Comparative Example 7:

Aluminum oxide (AS-IO, product of Showa Denko K.K.) (300 g) was mixed by means of a Henschel mixer for 10 seconds. The mixed product was incorporated into a commercially available silicone oil (TSE3070, product of GE Toshiba Silicones) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.). Subsequently, the thus-kneaded material was subjected to treatment at a rotation speed of 450 rpm for 5 minutes in a centrifugal defoaming apparatus, and the thus-treated material was charged into a mold. Thereafter, the thus-charged material was allowed to stand and cured at 120 °C for 2 hours in a vacuum dryer, to thereby yield a rubber-like molded product. The thus-obtained molded product was cut into pieces each measuring 100 mm in width, 50 mm in length, and 20 mm in height, and thermal conductivity of the cut pieces was measured.

Separately, aluminum oxide (AS-10, product of Showa Denko K.K.) (300 g) which had been mixed by means of a Henschel mixer for 10 seconds was incorporated into a commercially available polyethylene glycol (PEG-200, product of Sanyo Chemical

Industries, Ltd.) (100 g) , and the resultant mixture was kneaded at a rotation speed of 50 rpm for 10 minutes by means of a kneader (T.K. HIVIS MIX, product of Tokushu Kika Kogyo Co., Ltd.) Viscosity of the kneaded product was measured by use of a B-type viscometer .

Table 3

As is clear from Table 3, in Examples 15 to 17 where vapor grown carbon fiber was added, the thermal conductivity of the molded product was enhanced as compared with the Comparative Example 7 where no vapor grown carbon fiber was added. In addition, in the compositions of Examples 15 to 17 where the vapor grown carbon fiber formed a composite with alumina by the mediation of phenolic resin, viscosity was remarkably reduced as compared with Comparative Example 5 where the vapor grown carbon fiber was simply mixed by use of a Henschel mixer. Further, in all of the electron microscopic images, the vapor grown carbon fiber was highly dispersed to cover the alumina surface and no aggregates consisting only of carbon filaments were observed. Therefore, according to the present invention, remarkable enhancement in thermal conductivity and reduction of viscosity, which has been a long-standing technical challenge in the field of filler for heat radiation material, can be realized. Thus, the present invention has a very high industrial value.

Claims

CIAIMS

1. A composition for composite material comprising a carbon material and a ceramic material.

2. The composition for composite material as claimed in claim 1, wherein the carbon material is at least one species selected from the group consisting of carbon fiber, coke powder and graphite powder.

3. The composition for composite material as claimed in claim 2, wherein the carbon fiber is vapor grown carbon fiber or carbon nanotube.

4. The composition for composite material as claimed in claim 3, wherein the vapor grown carbon fiber has an average fiber diameter of 50 to 500 nm and an aspect ratio of 5 to 1,000.

5. The composition for composite material as claimed in claim 4, wherein a vapor grown carbon fiber having an average fiber diameter of 50 to 500 nm and an aspect ratio not less than 5 and less than 40 is dispersed in the ceramic material powder.

6. The composition for composite material as claimed in any one of claims 1 to 5, wherein the ceramic material is at least one compound selected from the group consisting of aluminum oxide, magnesium oxide, zinc oxide, silicon dioxide and boron nitride.

7. The composition for composite material as claimed in any one of claims 1 to 6, wherein the ceramic material is in the form of ceramic particles having an average particle size of 0.3 to 80 μm and a specific surface area of 0.01 to 15 m²/g.

8. The composition for composite material as claimed in any one of claims 1 to 7, wherein the carbon material is vapor grown carbon fiber and the ceramic material is aluminum oxide or boron nitride.

9. The composition for composite material as claimed in any one of claims 4 to 8, comprising a vapor grown carbon fiber having an average fiber diameter of 10 to 500 nm and an aspect ratio of 5 to 1,000 and ceramic material particles, wherein filaments of the vapor grown carbon fiber are deposited on at least part of a surface of the ceramic material particle via a polymer compound which is adherent to both the vapor grown carbon fiber and the ceramic particles.

10. The composition for composite material as claimed in claim 9, wherein the polymer compound is at least one compound selected from the group consisting of a phenolic resin, a polyvinyl alcohol resin, a furan resin, a cellulose resin, a polystyrene resin, a polyimide resin and an epoxy resin.

11. The composition for composite material as claimed in claim 9, wherein the blending amount of the polymer compound is 0.1 to 30 mass % with respect to the total amount of the ceramic material and the vapor grown carbon fiber.

12. The composition for composite material as claimed in any one claims 1 to 11, wherein the blending amount of the carbon material is 0.1 to 20 mass % that of the ceramic material.

13. A composite material prepared from the composition as described in any one of claims 1 to 12, wherein a polymer material or an oil is blended in.

14. The composite material as claimed in claim 13, wherein a polymer material or an oil material is blended into a composition in which a vapor grown carbon fiber having an average fiber diameter of 10 to 500 nm and an aspect ratio of 5 to 1,000 and ceramic material particles are contained and filaments of the vapor grown carbon fiber are deposited on at least part of a surface of the ceramic material particle via a polymer compound adherent to both the vapor grown carbon fiber and the ceramic particles.

15. The composite material as claimed in claim 13 or 14, wherein the polymer material or the oil is at least one species selected from the group consisting of an aliphatic resin, an unsaturated polyester resin, an acrylic resin, a methacrylic resin, a vinyl ester resin, an epoxy resin, a silicone resin, a silicone oil, a petroleum-based oil and a fluorine-based oil.

16. The composite material as claimed in any one of claims 13 to 15, wherein the blending amount of the polymer material or the oil is.1 to 35 mass % the total amount of the carbon material and the ceramic material.

17. The molded product formed of the composite material as described in any one of claims 13 to 16.

18. The molded product as claimed in claim 17, which is in the form of a sheet or a film.

19. A heat radiation sheet using the molded product as described in claim 17.

20. A personal computer using the heat radiation sheet as described in claim 18.

21. A game machine using the heat radiation sheet as described in claim 18.

22. A digital video camera using the heat radiation sheet as described in claim 18.

23. A digital camera using the heat radiation sheet as claimed in claim 18.

24. A television set using the heat radiation sheet as described in claim 18.

25. A mobile phone using the heat radiation sheet as described in claim 18.

26. A method for producing the composite material as described in claim 13, comprising subjecting a carbon material and a ceramic material to shear-stirring under dry conditions and dispersing the resultant composition in a polymer material or an oil.

27. A method for producing the composite material as described in claim 14, comprising depositing a vapor grown carbon fiber having an average fiber diameter of 10 to 500 nm and an aspect ratio of 5 to 1,000 on ceramic material particles by use of a polymer compound which is adherent to both the vapor grown carbon fiber and the ceramic material particles, thereby forming a composition containing composite particles, and dispersing the composition in a polymer material or an oil.