Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
  • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
  • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
  • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
  • D01F9/32—Apparatus therefor
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/20—Graphite
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/20—Graphite
  • C01B32/205—Preparation
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/20—Graphite
  • C01B32/21—After-treatment
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
  • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
  • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
  • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
  • D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
  • D01F9/24—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds

Definitions

• This invention relates to carbon fiber powder that has excellent thermal conductivity and filling capability, a method of making the same, and a thermally conductive composition containing the powder.
• a molded article and a liquid composition such as a sheet material made of a thermally conductive polymer composition, polymer grease and adhesive, are placed between a radiator and one of the followings: a printed circuit board; a semiconductor package; and a heat radiator.
• the heat radiator is, for example, a radiation plate or a heat sink.
• thermally conductive compositions include a matrix, such as resin and rubber, and a filler that has high thermal conductivity in the matrix.
• Possible fillers include metal oxide, metal nitride, metal carbide, and metal hydroxide. Examples of such possible fillers include aluminum oxide, boron nitride, silicon nitride, magnesium oxide, zinc oxide, silicon carbide, quartz, and aluminum hydroxide.
• such compositions do not necessarily have sufficient thermal conductivity.
• compositions that include highly thermally conductive graphite powders or carbon fibers as filler in the matrix.
• Japanese Laid-Open Patent Publication No.62-131033 discloses a molded body made of thermally conductive resin in which the resin is filled with graphite powders.
• Japanese Laid-Open Patent Publication No.4-246456 discloses a composition of polyester resin containing carbon black or graphite.
• Japanese Laid-Open Patent Publication No.5-17593 discloses a thermally conductive molded body of great mechanical strength in which the carbon fibers are arranged in a certain direction and are impregnated with graphite powder and thermosetting resin.
• Japanese Laid-Open Patent Publication No.5-222620 discloses a thermally conductive material using pitch-based carbon fibers that have a specific cross section.
• Japanese Laid-Open Patent Publication No.5-247268 discloses a rubber composition in which is mixed synthetic graphite having a particle size of 1 to 20 ⁇ m.
• Japanese Laid-Open Patent Publication No.9-283955 discloses a thermally conductive sheet in which the graphitized carbon fibers of specific aspect ratio are dispersed in polymer, such as silicone rubber.
• Japanese Laid-Open Patent Publication No.10-298433 discloses a composition and a radiation sheet in which silicone rubber has, mixed within it, spherical graphite powders having an interplanar spacing of crystals from 0. 330 to 0. 340 nm.
• Japanese Laid-Open Patent Publication No.2-242919 and Japanese Laid-Open Patent Publication No.7-48181 disclose certain pitch-based carbon fibers as highly thermally conductive carbon fibers.
• pitch-based carbon fiber has been known for highly thermally conductive carbon fiber used as thermally conductive filler. More particularly, isotropic pitch-based carbon fiber and mesophase pitch-based carbon fiber have been known for that purpose. Such pitch-based carbon fiber is obtained by spinning raw pitch, infusibilizing the resulting pitch fiber, and graphitizing it by heating. On the other hand, highly thermally conductive fiber cannot be obtained from PAN-type carbon fibers and rayon-type carbon fibers produced by graphitizing polyacrylonitrile fiber and rayon fiber by heating, since the graphitization upon heating is hard to achieve. To this end, a pitch-based carbon fiber is advantageous.
• Japanese Laid-Open Patent Publication No.9-324127 discloses highly thermally conductive powdery graphite, die bond adhesive for a semiconductor element, and a semiconductor device in which the powdery graphite is blended in thermosetting adhesive resin.
• the powdery graphite is obtained by graphitizing a polymeric film by heating and pulverizing or cutting the resultant graphitized film.
• pitch fiber used as a raw material has poor heat resistance. Therefore, to prevent pitch fiber from melting at high temperature, infusibilizing for several hours below 400 degree C. with oxygen-containing gas such as air, placing in oxidative water solution such as nitric acid and chromic acid, or polymerizing with light or gamma ray, are required before the graphitization process by heating. This leads to low productivity of the fiber.
• the powdery graphite proposed in Japanese Laid-Open Patent Publication No.9-324127 has an advantage that the infusibilization process is eliminated.
• a planar polymeric film is used as a raw material of the powdery graphite, cumbersome pulverization or cutting of the film is needed after heat treatment.
• the resultant pulverized products or cut products have non-uniform shape or size. In other words, fine powders and coarse powders are present in the products. Thus, it is difficult to contain such powdery graphite filler in a matrix at high concentration.
• the objective of the present invention is to provide carbon fiber powder that has excellent thermal conductivity, as well as is filled in a matrix at high concentration; a simple method of making the carbon fiber powder; and a thermally conductive composition including the carbon fiber powder.
• a carbon fiber is produced by graphitizing a polymeric fiber having an aromatic ring on its main chain by heating.
• the carbon fiber may be in the powder form.
• the carbon fiber powder is a pulverized or cut product of the carbon fiber that is obtained by graphitizing by heating a polymeric fiber having an aromatic ring on its main chain.
• an aromatic ring generally refers to a ring that belongs to an aromatic group and means a group of organic compounds including aromatic hydrocarbons, such as benzene ring, naphthalene ring, and anthracene ring, and derivatives thereof.
• the polymeric fiber of the present invention is not particularly limited to, but includes, polybenzazole fiber, aromatic polyamide fiber, aromatic polyimide fiber, polyphenylene sulfide fiber, wholly aromatic polyester fiber, polyphenylene benzoimidazole fiber, polyparaphenylene fiber, and polyparaphenylene vinylene fiber.
• polymeric fiber of the present invention As a raw material is that such polymeric fiber has so high heat resistance that it is hard to melt but often keeps its shape upon heating, and thus the above-mentioned infusibilization process is not necessarily needed. Thus, productivity at a manufacturing step is improved.
• a further reason for using the polymeric fiber of the present invention as a raw material is that pulverization or cutting is easier when using such fiber rather than using the planar graphite film as a raw material. Besides, fine and uniform carbon fiber powders having a limited bulk can be easily obtained.
• the polymeric fiber of the present invention is more preferably at least one fiber selected from the group consisting of polybenzazole fiber, aromatic polyamide fiber, aromatic polyimide fiber, polyphenylene sulfide fiber, and wholly aromatic polyester fiber.
• the polymeric fiber is at least one fiber selected from the group consisting of polybenzazole fiber, aromatic polyimide fiber, and aromatic polyamide fiber.
• the polymeric fiber having an aromatic ring on its main chain tends to be graphitized easier upon heating as it has more aromatic rings.
• carbon fiber or carbon fiber powder that has extremely excellent thermal conductivity is obtained by using such preferred polymeric fibers.
• the diameter, profile of cross section, and length of the polymeric fiber of the present invention is not limited.
• polybenzazole fiber refers to a polymeric fiber that is formed of polybenzazole polymer.
• the polybenzazole fiber is generally excellent in strength, modulus of elasticity, heat resistance, flame resistance, and electric insulation.
• the polybenzazole polymer (PBZ) refers to polybenzooxazole homopolymer (PBO), polybenzothiazole homopolymer (PBT); or random copolymer, sequential copolymer, block copolymer, or graft copolymer of PBO and PBT.
• PBO polybenzooxazole homopolymer
• PBT polybenzothiazole homopolymer
• random copolymer sequential copolymer, block copolymer, or graft copolymer of PBO and PBT.
• PBZ may be synthesized by a known method.
• An example of commercially available PBZ is ZYLONTM from Toyobo Co., Ltd.
• the aromatic polyamide fiber includes poly(paraphenylene isophthalic amide) and poly(metaphenylene isophthalic amide).
• aromatic polyamide fiber examples include, for poly(paraphenylene isophthalic amide), KEVLARTM from Du Pont-Toray Co., Ltd., TechnoraTM from Teijin Limited, and TwaronTM from Akzo; and for poly(metaphenylene isophthalic amide), NOMEXTM from Du Pont-Toray Co., Ltd., CONEXTM from Teijin Limited, and ApyeilTM from Unitika Ltd.
• the aromatic ring of these products may include a substituent such as halogen group, alkyl group, cyano group, acetyl group, and nitro group.
• aromatic polyimide fiber from Inspec Fibres GmbH
• polyphenylene sulfide fiber PROCONTM from Toyobo Co., Ltd.
• wholly aromatic polyester fiber VECTRANTM from Unitika Ltd.
• ECONOLTM from Sumitomo Chemical Company Limited
• polybenzoimidazole fiber from Hoechst Celanse
• the carbon fiber powders are produced by graphitizing the above-mentioned polymeric fiber of the present invention by heating, and pulverizing or cutting the resultant carbon fiber.
• the heating temperature should be at least 2500 degree C. When the temperature is lower than 2500 degree C., graphitization of the fiber becomes insufficient and carbon fiber that has high thermal conductivity can not be obtained.
• the heating is conducted under vacuum or in an inert gas, such as argon gas or nitrogen gas.
• the fiber is not heated under vacuum or in an inert gas, the polymeric fiber may be undesirably degenerated by oxidation.
• the fiber is preferably heated for a given time at a high temperature from 2800 to 3200 degree C. in argon gas. This actively promotes graphitization of the fiber to produce highly thermally conductive carbon fiber in which graphite structure highly develops.
• the process is not particularly limited to specific rates of heating temperature or to a specific treating period.
• polymeric fibers are preferably bundled.
• Such bundle of the fibers allows a large amount of the fibers to be placed in a certain volume of the heating reactor.
• the heating treatment is conducted efficiently and the productivity is improved.
• pressurizing the bundled polymeric fibers an even larger amount of the fibers can be placed in a certain volume of the heating reactor, thereby improving productivity.
• pulverizing machines such as a Victory mill, a jet mill, and a high-speed rotation mill or cutters for chopping fibers.
• a rotor of each machine that has blades that rotate at high speed to cut the fibers in a direction perpendicular to the fibers.
• the average length of the pulverized or cut fibers is changed by adjusting the rotation number of the rotor or an angle of the blades.
• Grinding machines such as a ball mill could be used for pulverizing the fibers.
• Such machines are undesirable in that they apply perpendicular pressure to fibers, which generates cracks in the axial direction of the fibers. This pulverization or cutting process may be conducted either before or during the heating of the fiber.
• the graphitized carbon fiber powders specifically take the form of fiber (including a pulverized product or a cut product that keeps the fibrous form), a scale, a whisker, a micro coil, or a nanotube.
• fiber including a pulverized product or a cut product that keeps the fibrous form
• scale including a pulverized product or a cut product that keeps the fibrous form
• whisker including a whisker, a micro coil, or a nanotube.
• nanotube a nanotube
• the diameter of the graphitized carbon fiber powders is not particularly limited but is preferably 5-20 ⁇ m.
• the fiber powders that have a diameter of 5-20 ⁇ m are easily produced industrially.
• the fiber diameters smaller than 5 ⁇ m or larger than 20 ⁇ m decrease the productivity of the fiber powders.
• the average particle size or length of the graphitized carbon fiber powders is not particularly limited but is preferably 5-500 ⁇ m.
• the average particle size of each fiber powder is smaller than 5 ⁇ m, the contact of the fiber powders in the matrix is reduced and a heat transfer becomes insufficient. This reduces the thermal conductivity of the resultant thermally conductive composition.
• the average particle size is larger than 500 ⁇ m, the fiber powders are too bulky to be mixed in the matrix at a high concentration.
• the average particle size can be calculated from the particle size distribution by laser diffractometry model.
• the graphitized carbon fiber powders have an interplanar spacing (d002) of graphite planes of less than 0.3370 nm.
• interplanar spacing (d002) is less than 0.3370 nm, carbon fiber powders and a thermally conductive composition that have higher thermal conductivity can be achieved.
• the interplanar spacing (d002) is 0.3370 nm or greater, the thermal conductivity is inadequate. Accordingly, a composition that has high thermal conductivity can not be obtained by using such carbon fiber powders as thermally conductive filler.
• the lower limit of the interplanar spacing (d002) is a theoretical value of 0.3354 nm.
• a diffractometry pattern of the carbon fibers is measured by using CuK alpha as a X-ray source and highly purified silicon as a standard material.
• the interplanar spacing (d002) is calculated from the peak position and half-value width of the (002) diffractometry pattern. This calculation is based on a method pursuant to Japan Society for the Promotion of Science.
• the thermal conductivity is not particularly limited but preferably at least 400W/(m ⁇ K), more preferably at least 800W/(m ⁇ K), and most preferably at least 1000W/(m ⁇ K).
• a thermally conductive composition includes the above-mentioned carbon fiber powders in a matrix as thermally conductive filler.
• the matrix is preferably selected according to required characteristics or applications such as a shape, hardness, mechanical properties, thermal properties, electrical properties, durability, and reliability of the resultant sheet.
• Matrix is preferably a polymeric material if molding capability is taken into consideration.
• the polymeric material is preferably selected from thermoplastic resin, thermoplastic elastomer, thermosetting resin, and vulcanized rubber according to required characteristics.
• preferred thermally conductive adhesives include adhesive polymeric materials such as epoxy resin, polyimide, and acrylic resin.
• Preferred molding materials include thermoplastic resin, thermoplastic elastomer, thermosetting resin, and vulcanized rubber.
• the thermoplastic resin includes polyethylene, polypropylene, ethylene- ⁇ -olefin copolymer such as ethylene-propylene copolymer, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene vinyl acetate copolymer, polyvinyl alcohol, polyacetal, fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene acrylonitrile copolymer, ABS resin, polyphenylene ether (PPE) resin and modified PPE resin, aliphatic and aromatic polyamides, polyimide, polyamide imide, polymethacrylic acid and polymethacrylates such as polymethyl methacrylate, polyacrylic acids, polycarbonate, polyphenylene sulfide, poly
• the thermoplastic elastomer includes repeatedly moldable and recyclable thermoplastic elastomers such as styrene-butadiene or styrene-isoprene block copolymers and hydrogenated polymer thereof, styrenic thermoplastic elastomer, olefinic thermoplastic elastomer, vinyl chloride thermoplastic elastomer, polyester thermoplastic elastomer, polyurethane thermoplastic elastomer, and polyamide thermoplastic elastomer.
• thermoplastic elastomers such as styrene-butadiene or styrene-isoprene block copolymers and hydrogenated polymer thereof, styrenic thermoplastic elastomer, olefinic thermoplastic elastomer, vinyl chloride thermoplastic elastomer, polyester thermoplastic elastomer, polyurethane thermoplastic elastomer, and polyamide thermoplastic elastomer.
• thermosetting resin includes epoxy resin, polyimide, bis-maleimide resin, benzocyclobutene, phenol resin, unsaturated polyester, diallyl phthalate, silicone resin, polyurethane, polyimide silicone, thermosetting polyphenylene ether resin and modified PPE resin.
• the vulcanized rubber and analogues thereof include natural rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene rubber, chlorinated polyethylene, chlorosulfonated polyethylene, butyl rubber and halide butyl rubber, fluorine rubber, urethane rubber, and silicone rubber.
• the matrix polymer is preferably at least one material selected from the group consisting of silicone rubber, epoxy resin, polyurethane, unsaturated polyester, polyimide, bis-maleimide, benzocyclobutene, fluororesin, polyphenylene ether resin and thermoplastic elastomer. More preferably, the matrix polymer is at least one material selected from the group consisting of silicone rubber, epoxy resin, unsaturated polyester resin, polyimide, polyurethane and thermoplastic elastomer.
• fluororesin In an application for a wiring board where permittivity and dielectric loss tangent are small and frequency characteristic is required, fluororesin, thermosetting polyphenylene ether resin, modified PPE resin, and polyolefin resin are desired.
• a polymer matrix such as low-hardness vulcanized rubber and low-hardness thermoplastic elastomer may be used.
• thermosetting resin or vulcanized rubber are not limited to thermosetting but include known methods such as light setting and moisture setting.
• the intended thermally conductive composition is obtained by mixing the above-mentioned carbon fiber powders with the matrix and degassing it if necessary.
• known mixing machines such as a blender, a mixer, a roller, an extruder may be used.
• the content of the carbon fiber powders is preferably 1 to 800 parts by weight, more preferably 5 to 500 parts by weight, and most preferably 20 to 300 parts by weight relative to 100 parts by weight of the matrix.
• the content is less than 1 part by weight, the thermal conductivity of the resultant composition is lowered and radiating property is decreased.
• the content is more than 800 parts by weight, the viscosity of the composition is increased, which makes it difficult to disperse the carbon fiber powders in the matrix uniformly. Also, gas bubbles are inevitably included in the matrix.
• the surface of the powders may be previously oxidized by electrolytic oxidation or treated with a known coupling agent or a known sizing agent.
• the surface of the carbon fiber powders may also be coated with metal or ceramics by various methods such as electroless plating; electroplating; physical vapor evaporation such as vacuum evaporation, sputtering and ion plating; chemical vapor deposition, spraying; coating; immersion; and mechanochemical method in which fine particles are mechanically fixed on the surface of the fibers.
• the thermally conductive polymer composition may also include other thermally conductive materials, an incombustible agent, a softening agent, a colorant, and a stabilizer as required.
• the other thermally conductive materials include the following:
• metal and ceramic such as silver, copper, gold, aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, and aluminum hydroxide
• the carbon fibers, graphites, and beads may be in the form of, for example, spherical powder, powder, fiber, needle, a scale, a whisker, a microcoil, single-wall, or multi-wall nanotube.
• the composition preferably includes at least one electrical insulative thermally conductive filler selected from the group consisting of aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide and aluminum hydroxide.
• the thermally conductive composition may be processed by, for example, compression molding, extrusion molding, injection molding, casting molding, blow molding, blade molding, and calendering molding.
• the composition When the composition is liquid, it may be processed by painting, printing, dispensing, and potting other than the above methods.
• a thermally conductive molded article that has excellent thermally conductive property may be produced by processing the composition into a predetermined shape by the above molding methods.
• a thermally conductive sheet which has excellent thermal conductivity may be obtained by using vulcanized rubber or thermoplastic elastomer which has low hardness as a matrix and molding the composition into a sheet by the above molding methods.
• the thermally conductive composition may be used as a material for liquid articles such as thermally conductive grease and thermally conductive adhesive, for both of which a high heat radiation property is required.
• the composition may be used as a material for molded articles such as printed circuit boards, semiconductor packages, heat radiation members including radiation plates and heat sink, a housing, and a thermally conductive sheet.
• the conductive composition may be used to form thermally conductive grease and thermally conductive adhesive placed between the heating element and the heat transfer member or to form heat radiation members, such as a radiator, a cooler, a heat sink, a heat spreader, a die pad, a printed circuit board, a cooling fan, a heat pipe, and a housing.
• a heat-dissipating measure is possible.
• the polymeric fiber having an aromatic ring on its main chain is used, preferably, at least one polymeric fiber selected from the group consisting of polybenzazole fiber, aromatic polyamide fiber, aromatic polyimide fiber, polyphenylene sulfide fiber, and wholly aromatic polyester fiber. Therefore, a highly thermally conductive carbon fiber can be produced in which graphite structure highly develops.
• the carbon fiber or carbon fiber powder can be produced in which graphite planes highly develop in the running direction of the linear polymers or in the direction of the fiber axis. Consequently, the carbon fiber or carbon fiber powder has excellent thermal conductivity, particularly in the direction parallel to the graphite planes.
• the polymeric fiber having an aromatic ring on its main chain preferably, at least one polymeric fiber selected from the group consisting of polybenzazole fiber, aromatic polyamide fiber, aromatic polyimide fiber, polyphenylene sulfide fiber, and wholly aromatic polyester fiber, is heated at least 2500 degree under vacuum or inert gas to graphitize.
• the carbon fiber powders are mixed in the matrix. Therefore, a thermally conductive complex material can be obtained in which the content of the carbon fiber powders is larger and thermal conductivity is greater than conventional ones, or a thermally conductive complex material can be obtained in which the content of the carbon fiber powders is smaller but thermal conductivity is similar.
• the interplanar spacing (d002) of graphite planes by X-ray diffractometry is less than 0.3370 nm, the thermal conductivity of the thermally conductive composition is greatly improved.
• the reason is still unclear why the thermal conductivity is improved like this, it is supposed that it is ascribable to the very strong correlation between the microstructure of the carbon fibers and thermal passages when the carbon fibers are dispersed in the matrix.
• thermoly conductive composition As a matrix of the thermally conductive composition, at least one polymeric material is used selected from the group consisting of vulcanized rubber, thermoplastic elastomer, thermoplastic resin, and thermosetting resin that has molding capability. Thus, a thermally conductive composition can be obtained that is applicable depending on various applications or required characteristics.
• the content of the carbon fiber powders in the composition is 1 to 800 parts by weight relative to 100 parts by weight matrix. This prevents an increase in the viscosity of the composition and prevents inclusion of bubbles.
• a thermally conductive composition is obtained in which the carbon fiber powders are uniformly dispersed in the matrix and which has improved thermal conductivity.
• polybenzazole fiber As a polymeric fiber having an aromatic ring on its main chain, polybenzazole fiber (Toyobo Co., Ltd., a tradename ZYLONTM HM: polybenzooxazole fiber) was used. After being bundled, the polymeric fibers were placed in a heating reactor and heated at 3000 degree C. in an argon gas for two hours to be graphitized to produce carbon fibers. The resultant carbon fibers were pulverized with a high-speed rotation mill to form carbon fiber powders (Sample 1). The carbon fiber powders had a fiber diameter of 9 ⁇ m, an average particle size of 50 ⁇ m, and an interplanar spacing (d002) between the graphite planes of 0.3360 nm by X-ray diffractometry.
• d002 interplanar spacing
• polybenzazole fiber As a polymeric fiber having an aromatic ring on its main chain, polybenzazole fiber (Toyobo Co., Ltd., a tradename ZYLONTM HM: polybenzooxazole fiber) was used. After being bundled, the polymeric fibers were cut to an average length of 5 mm, placed in a heating reactor, and heated at 3200 degree C. in an argon gas for two hours to be graphitized to produce carbon fibers. The resultant carbon fibers were further pulverized with a high-speed rotation mill to form carbon fiber powders (Sample 2). The carbon fiber powders had a fiber diameter of 9 ⁇ m, an average particle size of 25 ⁇ m, and an interplanar spacing (d002) between the graphite planes of 0.3358 nm by X-ray diffractometry.
• d002 interplanar spacing
• aromatic polyimide fiber (Inspec Fibres, a tradename P84) was used as a polymeric fiber having an aromatic ring on its main chain. After being bundled, the polymeric fibers were placed in a heating reactor and heated at 3000 degree C. in an argon gas for two hours to be graphitized to produce carbon fibers. The resultant carbon fibers were pulverized with a high-speed rotation mill to form carbon fiber powders (Sample 3). The carbon fiber powders had a fiber diameter of 9 ⁇ m, an average particle size of 50 82 m, and an interplanar spacing (d002) between the graphite planes of 0.3364 nm by X-ray diffractometry.
• d002 interplanar spacing
• an aromatic polyimide film (Du Pont-Toray Co., Ltd., a tradename KAPTONTM a thickness of 25 ⁇ m) was used.
• the polymeric film was placed in a heating reactor and heated at 3000 degree C. in an argon gas for 2 hours to be graphitized to produce a graphite film.
• the resultant graphite film was pulverized with a high-speed rotation mill to form carbon powders (Sample 4). Although the carbon powders had an average particle size of 45 ⁇ m, the shape and size of each particle is unequal and fine powders of the size of less than 5 ⁇ m and coarse powders of the size of more than 500 ⁇ m were mixed considerably.
• the interplanar spacing (d002) between the graphite planes by X-ray diffractometry was 0.3368 nm.
• Examples 1 to 7 and Comparative examples 1 and 2 are the examples of a soft thermally conductive sheet formed of silicone rubber.
• Examples 8 to 12 and Comparative example 3 are the example of a thermally conductive sheet in which recyclable thermoplastic elastomer is used.
• Examples 13 to 17 and Comparative example 4 are example of a thermally conductive molded article that is capable of injection molding.
• Examples 18 to 22 and Comparative example 5 is a thermally conductive adhesive of epoxy resin.
• a thermally conductive composition was prepared as in Example 1, except that the carbon fiber powders of Sample 2 were used as thermally conductive filler.
• a thermally conductive sheet having a thickness of 2 mm was formed.
• the resultant sheet had an Asker C hardness of 15.
• the thermal conductivity in the thickness direction of the sheet was 3.0W/(m ⁇ K).
• a thermally conductive composition was prepared as in Example 1, except that the carbon fiber powders of Sample 3 were used as thermally conductive filler.
• a thermally conductive sheet having a thickness of 2 mm was formed.
• the resultant sheet had an Asker C hardness of 15.
• the thermal conductivity in the thickness direction of the sheet was 2.7W/(m ⁇ K).
• a thermally conductive composition was prepared as in Example 1, except that the powders of Sample 4 were used as thermally conductive filler.
• a thermally conductive sheet having a thickness of 2 mm was formed.
• the carbon powders of Sample 4 were unequal so that the carbon powders are difficult to mix in the matrix and gas bubbles could not be removed.
• the resultant sheet had an Asker C hardness of 13.
• the thermal conductivity in the thickness direction of the sheet was 1.0W/(m ⁇ K).
• a thermally conductive composition was prepared as in Example 1, except that commercially available pitch-based carbon fiber powder (Petoca materials Ltd., milled Melblon) was used as thermally conductive filler.
• a thermally conductive sheet having a thickness of 2 mm was formed.
• the resultant sheet had an Asker C hardness of 15.
• the thermal conductivity in the thickness direction of the sheet was 2.3W/(m ⁇ K).
• a thermally conductive composition was prepared as in Example 1, except that the content of the carbon fiber powders was varied to 5, 20, 300, and 500 parts by weight, respectively.
• a thermally conductive sheet having a thickness of 2 mm was formed.
• the thermal conductivity in the thickness of the resultant sheets was 1.6W/(m ⁇ K), 199W/(m ⁇ K), 3.6W/(m ⁇ K), and 4.2W/(m ⁇ K), respectively.
• thermally conductive filler type
• a pellet-like thermally conductive composition was prepared as in Example 8, except that the content of the carbon fiber powders was varied to 5, 20, 300, 500 parts by weight, respectively.
• a thermally conductive sheet having a thickness of 3 mm was formed.
• the thermal conductivity in the thickness of the resultant sheets was 1.3W/(m ⁇ K), 1.6W/(m ⁇ K), 2.9W/(m ⁇ K), and 3.6W/(m ⁇ K), respectively.
• a pellet-like thermally conductive composition was prepared as in Example 8, except that commercially available pitch-based carbon fiber powder (Petoca materials Ltd., milled Melblon) was used as thermally conductive filler.
• a thermally conductive sheet having a thickness of 3 mm was formed.
• the resultant sheet had a Shore A hardness of 68.
• the thermal conductivity in the thickness of the sheet was 1.4W/(m ⁇ K).
• thermally conductive filler type
• a pellet-like thermally conductive composition was prepared as in Example 13, except that the content of the carbon fiber powders was varied to 5, 20, 300, 500 parts by weight, respectively.
• a thermally conductive molded article was formed having a thickness of 3 mm.
• the thermal conductivity in the thickness of the resultant molded articles was 1.1W/(m ⁇ K), 1.3W/(m ⁇ K), 2.8W/(m ⁇ K), and 3.5W/(m ⁇ K), respectively.
• a pellet-like thermally conductive composition was prepared as in Example 13, except that the carbon powders of Sample 4 were used as thermally conductive filler.
• a thermally conductive molded article was formed having a thickness of 3 mm. As described previously, the carbon powders of Sample 4 were unequal so that the carbon powders are difficult to mix in the matrix and gas bubbles could not be removed.
• the thermal conductivity in the thickness of the resultant molded article was 0.8W/(m ⁇ K).
• thermally conductive filler type
• a thermally conductive composition which is a thermally conductive adhesive, was prepared as in Example 18, except that the content of the carbon fiber powders was varied to 5, 20, 300, 500 parts by weight, respectively.
• a plate specimen of thickness of 1 mm was formed.
• the thermal conductivity in the thickness of the resultant plate specimen 1.2W/(m ⁇ K), 1.8W/(m ⁇ K), 3.4W/(m ⁇ K), and 4.1W/(m ⁇ K), respectively.
• a thermally conductive composition which is a thermally conductive adhesive, was prepared as in Example 18, except that commercially available pitch-based carbon fiber powder (Petoca materials Ltd., milled Melblon) was used as thermally conductive filler. A plate specimen of thickness of 1 mm was formed. The thermal conductivity of the resultant plate specimen was 2.3W/(m ⁇ K).
• thermally conductive compositions of Examples 1 to 22 include, in the matrix, the carbon fiber powders of the present invention (Sample 1 to 3) that are obtained by graphitizing the polymeric fiber having an aromatic ring on its main chain by heating.
• the thermally conductive compositions of Comparative example 1 and Comparative example 4 include, in the matrix, the conventional carbon powders (Sample 4) that are obtained by graphitizing the aromatic polyimide film by heating and pulverizing it.
• the thermally conductive compositions of Comparative example 2, Comparative example 3 and Comparative example 5 also include, in the matrix, the conventional pitch-based graphitized carbon fiber powders that are produced by treating raw pitch by several processes such as spinning, infusibilization, graphitization, and pulverization.
• compositions of Examples 1 to 3 had higher thermal conductivity compared with those of Comparative example 1 and Comparative example 2.
• the compositions of Example 8 had a higher thermal conductivity than that of Comparative example 3.
• the compositions of Example 13 had a higher thermal conductivity than that of Comparative example 4.
• the composition of Example 18 had a higher thermal conductivity than that of Comparative example 5. Accordingly, is was confirmed that the carbon fiber powders of the present invention of Samples 1 to 3 had a higher thermal conductivity than that of the conventional carbon powders of Sample 4 or the conventional pitch-based carbon fiber powders.
• the fiber is heated, graphitized, and pulverized or cut. This eliminates the need of an infusibilization process. In addition, by using carbon fibers rather than a film, the pulverization or cutting process is simplified. Therefore, in this method, high-performance carbon fiber powders that have two characters of high thermal conductivity and high filling capability can be manufactured easily.

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