JP2009108118A - Pitch-based carbon short fiber filler and molded product using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pitch-based carbon short fiber filler with high thermal conductivity and high moldability and a composite molding material. <P>SOLUTION: In the pitch-based carbon short fiber filler, a graphene sheet is closed at a filler end face when observed by a transmission electron microscope, while a surface observed by a scanning electron microscope is substantially flat, and the number average fiber length is 80 to 500 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermally conductive filler using pitch-based carbon short fibers as a raw material. More specifically, it relates to pitch-based carbon short fiber fillers whose average fiber diameter and distribution, average fiber length and distribution, and surface and end face shapes are controlled. It is suitably used for heat dissipation members, heat exchangers, and electromagnetic wave shielding.

  High-performance carbon fibers can be classified into PAN-based carbon fibers made from polyacrylonitrile (PAN) and pitch-based carbon fibers made from a series of pitches. Carbon fibers are widely used in aerospace applications, construction / civil engineering applications, sports / leisure applications, etc., taking advantage of their extremely high strength and elastic modulus compared to ordinary synthetic polymers.

  In recent years, while an efficient use method of energy typified by energy saving has been attracting attention, heat generation due to Joule heat in high-speed CPUs and electronic circuits has become a problem. In order to solve these problems, it is necessary to achieve so-called thermal management in which heat is efficiently processed.

  Carbon fibers are said to have higher thermal conductivity and better heat dissipation than ordinary synthetic polymers. Carbon materials such as carbon fibers are said to achieve high thermal conductivity by phonon movement. This phonon is transmitted well in materials where the crystal lattice is developed. Actually, the thermal conductivity of commercially available PAN-based carbon fibers is usually smaller than 200 W / (m · K), and is not necessarily suitable from the viewpoint of thermal management. On the other hand, it is recognized that pitch-based carbon fibers have high graphitization properties, so that the crystal lattice is well developed, and it is easy to achieve high thermal conductivity compared to PAN-based carbon fibers.

  In addition to carbon fiber, materials with excellent thermal conductivity include metal oxides such as aluminum oxide, boron nitride, aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, silica, aluminum hydroxide, metal nitride, metal carbide, metal Hydroxides are known. However, many of the metal-based fillers have a high specific gravity and become heavy when used as a composite material. When carbon fiber is added in the same volume as the metallic material filler with a small specific gravity, it not only has the advantage of reducing the weight of the composite material, but also uses carbon black because its shape is fibrous. There is also an advantage that the powder fall-off is unlikely to occur, and the composite material is reinforced and hardened.

  Next, the characteristics of the composite material used for thermal management are discussed. In order for the composite material to achieve sufficient heat conduction, the filler mainly responsible for heat conduction needs to form a three-dimensional network. For example, in the case of spherical fillers of uniform size, the filler network in the molded body depends on the dispersion state, but if uniform dispersion is assumed, it becomes a percolation behavior. Accordingly, in order to obtain sufficient thermal conductivity and electrical conductivity, it is necessary to add a certain amount of filler. However, in the method of forming a molded body, it is often very difficult to disperse the medium and the filler at a certain concentration or more.

  Under such circumstances, in order to effectively transfer heat, studies have been made to give a filler three-dimensional crosslinking. For example, Patent Document 1 discloses an attempt to transport a heat flow by forming a metal network. However, it is considered that a very high level of technology is required for dispersion into the matrix. Patent Document 2 discloses that alloying causes the matrix and filler to melt simultaneously, and as a result, high thermal conductivity is achieved while maintaining formability.

Japanese Patent Laid-Open No. 6-196684 International Publication No. 03/029352 Pamphlet

  As mentioned above, in order to create a resin composition that is lightweight and has high thermal conductivity, a material with high thermal conductivity and low specific gravity is required, and the maximum thermal conductivity is exhibited in the final use state. Such filler control has been strongly desired.

  In order to improve the thermal conductivity and reduce the specific gravity in the final molded body, the present inventors have used pitch-based carbon short fibers having high thermal conductivity as the thermal conductive material, the average fiber diameter and The inventors have found that this can be achieved by paying attention to the dispersion, the average fiber length and distribution thereof, the surface shape, and the fine structure, appropriately controlling the dispersion, and the present invention.

  That is, an object of the present invention is a pitch-based carbon short fiber filler in which a graphene sheet is closed in observation of a filler end surface with a transmission electron microscope, a surface observed with a scanning electron microscope is substantially flat, and an average fiber length Is 80 μm or more and 500 μm or less can be achieved by the pitch-based carbon short fiber filler.

Furthermore, the objective of this invention provides the composition which consists of the said pitch-type carbon short fiber filler, a thermoplastic resin, and / or a thermosetting resin, and contains 3-200 said filler with respect to 100 volume parts of resin. There is.
Furthermore, the object of the present invention is to provide a heat radiating material for electronic parts, a radio wave shielding material, or a heat exchanger, the main component of which is the molded body.

  The pitch-based carbon short fiber filler of the present invention has a specific shape and is controlled in size, so that it has a high heat and moisture resistance, suppresses an increase in the viscosity of the matrix, and combines a high thermal conductivity. It can be applied to a molded body, and a composite molding material having good moldability and high thermal conductivity can be obtained. The composite molded body can increase the efficiency of the heat sink for electronic parts and the heat exchanger. Furthermore, since the pitch-based carbon short fibers are excellent in radio wave shielding in a frequency band of several GHz, it is possible to supply a radio wave shielding plate.

Hereinafter, embodiments of the present invention will be sequentially described.
The pitch-based carbon short fiber filler of the present invention is characterized in that the graphene sheet has a closed structure when the shape of the filler end face is observed with a transmission electron microscope. When the end face of the filler is closed as a graphene sheet, generation of extra functional groups and localization of electrons due to shape do not occur, so the concentration of impurities such as water can be reduced, For example, it is preferable from the viewpoint that hydrolysis resistance is improved when it is combined with a resin that is affected by hydrolysis, such as a condensation polymer. In addition, when the graphitization is performed, vertical cracking is likely to occur due to the shrinkage of the carbon fibers. However, when the end face is closed, this is suppressed, so that a reduction in mechanical strength when the composite molded body is obtained is suppressed. In particular, in the filler having a fiber length shorter than 1 mm as in the present invention, the structure in which the graphene sheet is closed is particularly preferable because the ratio of the end face to the filler surface area is high.

  Note that the graphene sheet is closed means that the end of the graphene sheet itself constituting the carbon fiber is not exposed at the end of the carbon fiber, the graphite layer is curved in a substantially U shape, and the curved portion is the end of the carbon fiber. It is in the state exposed to the part.

  In addition, the pitch-based carbon short fiber filler of the present invention is characterized in that the observation surface with a scanning electron microscope is substantially flat. Here, “substantially flat” means that the surface does not have severe unevenness like a fibril structure, and when there is intense unevenness on the surface of the filler, the surface area of the filler is reduced during kneading with the matrix resin. It causes an increase in viscosity accompanying the increase and deteriorates moldability. Therefore, it is desirable that the surface unevenness is as small as possible. Although there is no particular limitation on defining it as being substantially smooth, specifically, in observation with a scanning electron microscope, it is included if there are 10 or less irregularities in the field of view (magnification 1000). Means good.

  The pitch-based carbon short fiber filler having a smooth observation surface can be obtained by graphitizing the carbon fiber filler after pulverization, as will be described in detail later. When pulverized after graphite, the pitch-based carbon short fiber filler has more irregularities, and the irregularities are observed on the observation surface with a scanning electron microscope.

  The pitch-based carbon short fiber filler of the present invention has an average fiber length of 80 μm or more and 500 μm or less. When the average fiber length is less than 80 μm, a network of pitch-based carbon fiber fillers inside the composite material cannot be sufficiently formed, and it is necessary to increase the filler filling amount in order to exhibit high thermal conductivity. On the other hand, when the average fiber length exceeds 500 mm, the entanglement of the fibers remarkably increases, and when mixed with the resin, the viscosity becomes very large and handling becomes difficult. Here, the average fiber length is a number average fiber length, and a predetermined number is measured in a plurality of fields of view using a length measuring device under an optical microscope, and can be obtained from the average value.

  The average fiber diameter of the pitch-based carbon fiber filler of the present invention observed with an optical microscope is preferably 2 to 20 μm. When the thickness is less than 2 μm, the number of carbon fibers per unit weight increases and the specific surface area increases. As a result, the viscosity when mixed with the matrix becomes high, and it becomes difficult to add a large amount of pitch-based carbon fiber filler. When the average fiber diameter exceeds 20 μm, unevenness in the infusibilization process becomes large, and a portion where fusion occurs partially occurs. More preferably, it is 5-15 micrometers, More preferably, it is 6-12 micrometers.

  In addition, it is preferable that the CV value calculated | required as a percentage of fiber diameter dispersion | distribution with respect to an average fiber diameter is 5-20. It is impossible in the process that the CV value is less than 5. On the other hand, when the CV value exceeds 20, there is a high possibility that fibers having a diameter of 20 μm or more causing troubles due to infusibilization will increase, which is not preferable from the viewpoint of productivity.

  When the pitch-based carbon short fiber filler of the present invention is classified with a sieve having a mesh size of 53 μm, the proportion remaining on the sieve is 30 to 60%, and when classified with a sieve having a mesh size of 100 μm, The remaining ratio is preferably 10 to 29%. The carbon short fiber filler remaining on the mesh sieve having a mesh size of 53 μm suitably forms a matrix and effectively acts on heat conduction. Moreover, since the carbon fiber remaining on the 100 μm mesh sieve has a high bulk density, it is entangled in the matrix to form voids. When the short carbon fibers remaining under the 53 μm mesh enter the voids, the filling state of the carbon fibers in the matrix becomes suitable. This condition is preferably satisfied when the classification is performed with a 53 μm mesh sieve and the ratio remaining on the sieve is 30 to 60%. When the classification is performed with a mesh sieve having an opening of 100 μm, the ratio remaining on the sieve Is 10 to 29%. The average fiber length and the ratio remaining on the mesh can be controlled by controlling the pulverization conditions and the classification conditions.

  A specific control method is to remove a short fiber length or a pitch-based carbon short fiber filler having a long fiber length using a sieve or a mesh after pulverization. The fiber length distribution can be controlled by controlling the crushing strength, for example, the rotation speed of the cutter blade, the rotation speed of the ball mill, etc. It can be controlled precisely.

  In the present invention, the true density of the pitch-based carbon short fiber filler strongly depends on the graphitization temperature, but is preferably in the range of 1.8 to 2.3 g / cc. More preferably, it is 1.9 to 2.3 g / cc. Further, the thermal conductivity in the fiber axis direction of the pitch-based carbon short fiber filler is 300 W / (m · K) or more, and more preferably 400 W / (m · K) or more.

  The pitch-based carbon short fiber filler preferably has a crystallite size derived from the thickness direction of the hexagonal network surface of 10 nm or more, and a crystallite size derived from the growth direction of the hexagonal network surface of 20 nm or more.

  The crystallite size corresponds to graphitization in both the thickness direction of the hexagonal network surface and the growth direction of the hexagonal network surface, and a certain size or more is necessary to exhibit thermophysical properties. The crystallite size derived from the thickness direction of the hexagonal mesh surface and the crystallite size in the growth direction of the hexagonal mesh surface can be obtained by an X-ray diffraction method. The measurement method was the concentration method, and the Gakushin method was used as the analysis method. The crystallite size in the thickness direction of the hexagonal mesh plane is obtained using a diffraction line from the (002) plane, and the crystallite size in the growth direction of the hexagonal mesh plane is obtained using a diffraction line from the (110) plane, respectively. It was. The reason why the crystallite size is important is that heat conduction is mainly performed by phonons, and it is the crystals that generate phonons.

  Hereinafter, a preferred method for producing the pitch-based carbon short fiber filler of the present invention will be described. Examples of the raw material for the pitch-based carbon fiber filler used in the present invention include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, and condensed heterocyclic compounds such as petroleum-based pitch and coal-based pitch. Among them, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferable, and optically anisotropic pitch, that is, mesophase pitch is particularly preferable. This is because the mesophase pitch is particularly preferable for improving the thermal conductivity of the carbon fiber because the degree of graphitization is easily improved when the graphitization treatment is performed.

  The softening point of the optically anisotropic pitch serving as the raw material pitch can be determined by the Mettler method, and is preferably 250 ° C. or higher and 350 ° C. or lower. When the softening point is lower than 250 ° C., fusion between fibers and large heat shrinkage occur during infusibilization. On the other hand, when the temperature is higher than 350 ° C., thermal decomposition of the pitch occurs and it becomes difficult to form a yarn.

  The optically anisotropic pitch can be fiberized by melt spinning after being melted and discharged from a nozzle and cooled. Specific examples of the spinning method include a normal spinning method in which a pitch discharged from a die is drawn by a winder, a melt blow method using hot air as an atomizing source, and a centrifugal spinning method in which a pitch is drawn using centrifugal force. Among these, the melt blow method is preferably used for reasons such as control of the radius of curvature and high productivity.

  The optically anisotropic pitch is melt-spun, then infusibilized, fired, pulverized as necessary, and finally graphitized to obtain a pitch-based carbon fiber filler. The raw material pitch is spun by a melt blow method, and then becomes pitch-based carbon short fibers by infusibilization, firing, milling, and graphitization. In some cases, a sieving step may be included after milling. The pitch-based carbon short fiber filler of the present invention is characterized in that the graphene sheet observed by a transmission electron microscope is closed. Such pitch-based carbon short fiber filler is subjected to graphitization after milling. It can preferably be obtained by carrying out. Hereinafter, preferred embodiments of the respective steps will be described by taking the melt blow method as an example.

  The spinning temperature is preferably such that the viscosity of the optically anisotropic pitch is in the range of 3 to 25 Pa · S (30 to 250 poise). The temperature is more preferably in the range of 5 to 20 Pa · S (50 to 200 poise). As the spinning nozzle, a nozzle having an introduction angle α of 10 to 90 ° and a ratio L / D of the discharge port length L to the discharge port diameter D of 6 to 20 is preferably used. When the spinning conditions are within this range, the shearing force applied to the optically anisotropic pitch can arrange the aromatic rings to some extent. When the spinning condition deviates from this condition, for example, when the shearing force is stronger, such as when the viscosity is larger, the introduction angle is smaller, or the L / D is larger, the alignment is too advanced and graphitization occurs. In addition, the carbon fiber is easily broken. On the contrary, under conditions where the shearing force is small, such as the viscosity is smaller, the introduction angle is larger, or the L / D is smaller, and the shearing force is small, the aromatic rings are not arranged so much. The degree of graphitization does not improve so much and high thermal conductivity cannot be obtained.

  The pitch fibers drawn out from the nozzle holes are shortened by blowing a gas having a linear velocity of 100 to 10,000 m per minute heated to 100 to 350 ° C. in the vicinity of the thinning point. As the gas to be blown, air, nitrogen, or argon can be used, but air is preferable from the viewpoint of cost performance.

Pitch fibers are collected on a wire mesh belt to form a continuous mat, and further cross-wrapped to form a three-dimensional random mat.
The three-dimensional random mat refers to a mat in which pitch fibers are entangled three-dimensionally in addition to being cross-wrapped. This entanglement is achieved in a cylinder called chimney while reaching the wire mesh belt from the nozzle. Since the linear fibers are entangled three-dimensionally, the characteristics of the fibers that normally exhibit only one-dimensional behavior are reflected in the three-dimensional.

  The three-dimensional random mat made of pitch fibers thus obtained is infusible by a known method. Infusibilization is achieved at 200 to 350 ° C. using air or a gas obtained by adding ozone, nitrogen dioxide, nitrogen, oxygen, iodine, bromine to air. Considering safety and convenience, it is preferable to carry out in the air. The infusibilized pitch fiber is fired at 600-1500 ° C. in vacuum or in an inert gas such as nitrogen, argon, krypton, and then graphitized at 2000-3500 ° C. In many cases, the graphitization is performed in low-cost nitrogen, and graphitization is generally performed by changing the type of the inert gas according to the type of furnace used.

  After infusibilization or firing, the obtained fiber is pulverized as necessary. The pulverization can be performed by a known method. Specifically, a cutter, a ball mill, a jet mill, a crusher, or the like can be used. In order to perform milling efficiently, a method of cutting fibers in a direction perpendicular to the fiber axis by rotating a rotor to which blades are attached at high speed is appropriate.

  As described above, the specific control of the pulverization conditions and the classification conditions can be performed by removing the short fiber length or the long fiber length pitch-based carbon short fiber filler using a sieve or a mesh after the pulverization. The fiber length distribution can be controlled by controlling the crushing strength, for example, the rotation speed of the cutter blade, the rotation speed of the ball mill, etc. It can be controlled precisely.

  The above-mentioned milled and sieved fibers are heated to 2300-3500 ° C. and graphitized to obtain the final pitch-based carbon short fibers. Graphitization is carried out in an atmosphere capable of blocking external physical and chemical effects in an Atchison furnace or the like. The graphitization temperature is preferably 2000 to 3500 ° C. in order to increase the thermal conductivity of the carbon fiber. More preferably, it is 2300-3500 degreeC. It is preferable to put it in a graphite crucible at the time of graphitization because the physical and chemical action from the outside can be blocked. The graphite crucible is not limited in size and shape as long as the above-described carbon fiber can be put in a desired amount, but the oxidizing gas in the furnace during graphitization or cooling, or In order to prevent damage to the carbon fiber due to reaction with water vapor, a highly airtight one with a lid can be suitably used.

  In the present invention, the pitch-based carbon short fiber filler may be subjected to a surface treatment, and then a sizing agent may be added to 0.01 to 10 parts by weight, preferably 0.1 to 2.5 parts by weight with respect to 100 parts by weight of the filler. As the sizing agent, any commonly used sizing agent can be used. Specifically, an epoxy compound, a water-soluble polyamide compound, a saturated polyester, an unsaturated polyester, vinyl acetate, water, alcohol, glycol are used alone or in a mixture thereof. Can do. Such surface treatment is effective in view of increasing the bulk density. However, since the excessive sizing agent is added to the heat resistance, it can be carried out according to the required physical properties.

  A composition in which a pitch-based carbon short fiber filler and a thermoplastic resin and / or a thermosetting resin are mixed is also included. At this time, the pitch-based carbon short fiber filler is added in an amount of 3 to 200 parts by volume with respect to 100 parts by volume of the resin. When the addition amount is less than 3 parts by volume, it is difficult to ensure sufficient thermal conductivity. On the other hand, it is often difficult to add more than 200 volume parts of pitch-based carbon short fiber filler to the resin.

  The resin contains any one or more of a thermoplastic resin and a thermosetting resin, and a thermoplastic resin and a thermosetting resin may be appropriately mixed and used in order to develop desired physical properties in the composite molded body. it can.

  Examples of thermoplastic resins that can be used in the matrix include ethylene-α-olefin copolymers such as polyethylene, polypropylene, and ethylene-propylene copolymers, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, and ethylene-acetic acid. Vinyl copolymer, polyvinyl alcohol, polyacetal, fluororesin (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6 naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, ABS Resins, polyphenylene ether (PPE) resins, modified PPE resins, aliphatic polyamides, aromatic polyamides, polyimides, polyamideimides, polymethacrylic acids ( Polymethacrylates such as methyl methacrylate), polyacrylic acids, polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone, polyetheretherketone, polyketone, liquid crystal polymer, ionomer, etc. It is done.

  Among these, as thermoplastic resins, polycarbonates, polyethylene terephthalates, polybutylene terephthalates, polyethylene 2,6 naphthalates, nylons, polypropylenes, polyethylenes, polyether ketones, polyphenylene sulfides, and acrylonitrile-butadiene-styrene Preferred is at least one resin selected from the group consisting of system copolymer resins.

  In addition, examples of the thermosetting resin include epoxies, acrylics, urethanes, silicones, phenols, imides, thermosetting modified PPEs, thermosetting PPEs, and the like. Even if it uses, you may use in combination of 2 or more types as appropriate.

  The composite material and composite molded body of the present invention are prepared by mixing a pitch-based carbon short fiber filler and a resin. When mixing, a kneader, a mixer, a blender, a roll, an extruder, a milling machine, a self-revolution A mixing device or a kneading device such as an agitator of the type is preferably used. The composite molded body can be molded by a molding method such as an injection molding method, a press molding method, a calendar molding method, a roll molding method, an extrusion molding method, a casting molding method, or a blow molding method. The molding conditions strongly depend on the method and the matrix. In the case of a thermoplastic resin, the molding is performed in a state where the temperature is higher than the melt viscosity of the resin. In the case where the matrix is a thermosetting resin, a method of applying a curing temperature of the resin in an appropriate mold can be exemplified.

  Further, in the composite material and composite molded body of the present invention, a heat conductive filler other than carbon fibers can be used as necessary. Specifically, metal oxides such as silica, aluminum oxide, magnesium oxide and zinc oxide, metal hydroxides such as aluminum hydroxide and magnesium hydroxide, metal nitrides such as boron nitride and aluminum nitride, silver, gold and copper And metals or alloys such as aluminum, carbon materials such as graphite, expanded graphite, and diamond.

  In the composition of the present invention, glass fiber, potassium titanate whisker, zinc oxide whisker, aluminum borate whisker, aramid fiber, alumina fiber, silicon carbide fiber, ceramic fiber, asbestos fiber, as long as the effects of the present invention are not impaired. Fibrous filler such as stone fiber, metal fiber, wollastonite, zeolite, sericite, kaolin, mica, clay, pyrophyllite, bentonite, asbestos, talc, alumina silicate, etc., calcium carbonate, magnesium carbonate, Non-fibrous fillers such as carbonates such as dolomite, sulfates such as calcium sulfate and barium sulfate, glass beads, glass flakes, ceramic beads, silicon carbide and silica, which may be hollow, Can use two or more of these together It is a function.

  When the composition of the present invention is formed into a flat plate and the thermal conductivity is measured, it shows a thermal conductivity of 2 W / (m · K) or more. The thermal conductivity of 2 W / (m · K) is about one digit higher than that of the resin used as the matrix.

  The composition of the present invention can be used as a heat sink for electronic components by utilizing its high thermal conductivity. In addition, since high thermal conductivity can be obtained by increasing the amount of pitch-based carbon short fiber filler added, even in electronic parts, automobiles that require relatively high heat resistance and industrial power that requires large currents It can be suitably used for a connector of a module. More specifically, it can be used for a heat sink, a semiconductor package component, a heat sink, a heat spreader, a die pad, a printed wiring board, a cooling fan component, a housing, and the like. It can also be used as a part of a heat exchanger. Can be used for heat pipes. Furthermore, the radio wave shielding property of the pitch-based carbon short fiber filler can be utilized, and can be suitably used particularly as a radio wave shielding member in the GHz band.

Examples are shown below, but the present invention is not limited thereto.
(1) The average fiber diameter and fiber diameter dispersion of the pitch-based carbon short fiber filler were determined by measuring 60 graphitized pitch-based carbon fiber fillers using a scale under an optical microscope according to JIS R7607. I asked for it.
(2) Average fiber length of pitch-based carbon short fiber filler:
The average fiber length is the number average fiber length. The pitch-based carbon short fiber filler that has undergone graphitization is measured with an optical microscope with a length measuring instrument (measured by 10 fields and 200 lines each), and obtained from the average value. It was. The magnification was appropriately adjusted according to the yarn length.
(3) The proportion of the pitch-based carbon short fiber filler remaining on the mesh is 100 g of carbon fiber, sieved with a mesh having an opening of 100 μm and an opening of 53 μm with a shaker (manufactured by Tanaka Tech, R-1). It calculated | required by measuring the mass of the carbon fiber obtained afterwards.
(4) The true density of the pitch-based carbon short fiber filler was measured by a density gradient tube method described in JIS R7601.
(5) The crystal size is determined by X-ray diffraction, and the crystallite size derived from the thickness direction of the hexagonal network surface is determined using diffraction lines from the (002) plane, and the crystal derived from the growth direction of the hexagonal network surface. The child size was determined using diffraction lines from the (110) plane. In addition, the request was made in accordance with the Gakushin Law.
(6) The thermal conductivity of the pitch-based carbon fiber was fixed using silver paste so that the distance between both ends of the pitch-based carbon fiber after graphitization was 1 cm, which was produced under the same conditions except for the electrical resistivity. Then, 20 electrical resistances at both ends were measured with a tester, calculated using the radius of the pitch-based carbon fiber, and calculated from the following relational expression (refer to Japanese Patent No. 3648865) of thermal conductivity and electrical resistance. .
K = 1272.4 / ER-49.4
(K is the thermal conductivity of carbon fiber W / (m · K), ER is the electrical resistivity of carbon fiber μΩm)
(7) The end face of the pitch-based carbon short fiber filler was observed with a transmission electron microscope at a magnification of 1,000,000 times, magnified on a photograph at 4 million times, and a graphene sheet was confirmed.
(8) The surface of the pitch-based carbon short fiber filler was observed with a scanning electron microscope at a magnification of 1000 times, and irregularities were confirmed.
(9) The thermal conductivity of the flat molded body was measured with QTM-500 manufactured by Kyoto Electronics.

[Example 1]
A pitch made of a condensed polycyclic hydrocarbon compound was used as a main raw material. The optical anisotropy ratio was 100%, and the softening point was 283 ° C. Using a hole cap having a diameter of 0.2 mmφ, heated air was ejected from the slit at a linear velocity of 5000 m / min, and the melt pitch was pulled to produce pitch-based short fibers having an average fiber diameter of 14.5 μm. The spinning temperature at this time was 325 ° C., and the melt viscosity was 18.5 Pa · S (185 poise). The spun short fibers were collected on a belt to form a mat, and then a web made of pitch-based short fibers having a basis weight of 320 g / m ^{2 by} cross wrapping.

  The web was infusibilized by raising the temperature from 175 ° C. to 310 ° C. in air at an average temperature increase rate of 4 ° C./min. The infusible web was fired at 800 ° C. in a nitrogen atmosphere, milled, pulverized with a cutter (manufactured by Turbo Kogyo) at 800 rpm, and classified with a sieve having an opening of 1 mm and graphitized at 3000 ° C. The average fiber diameter of the pitch-based carbon short fiber filler after graphitization was 9.7 μm, and the percentage of the fiber diameter dispersion to the average fiber diameter was 10%. The average fiber length is 150 μm on average. When classified with a sieve having a mesh size of 53 μm, the ratio remaining on the sieve is 45%. When classified with a sieve having a mesh size of 100 μm, the ratio remaining on the sieve Was 24%. The true density was 2.15 g / cc.

It was confirmed that the graphene sheet was closed on the end face of the pitch-based carbon short fiber filler by observation with a transmission microscope. Moreover, the surface was substantially smooth with one unevenness | corrugation by observation with the scanning electron microscope.
The crystallite size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 38 nm. The crystallite size in the growth direction of the hexagonal network surface was 77 nm.
The electric resistance of the pitch-based carbon fiber was 1.6 μΩm, and the thermal conductivity was 750 W / (m · K).

[Example 2]
A pitch made of a condensed polycyclic hydrocarbon compound was used as a main raw material. The optical anisotropy ratio was 100%, and the softening point was 283 ° C. Using a hole cap with a diameter of 0.2 mmφ, heated air was ejected from the slit at a linear velocity of 6000 m / min, and the melt pitch was pulled to produce pitch short fibers having an average fiber diameter of 11 μm. The spinning temperature at this time was 320 ° C., and the melt viscosity was 21.0 Pa · S (210 poise). The spun short fibers were collected on a belt to form a mat, and then a web made of pitch-based short fibers having a basis weight of 280 g / m ^{2 by} cross wrapping.

  The web was infusibilized by raising the temperature in the air from 175 ° C. to 280 ° C. at an average heating rate of 3 ° C./min. The infusibilized web was fired at 800 ° C. in a nitrogen atmosphere, milled, pulverized with a cutter (manufactured by Turbo Kogyo) at 700 rpm, and classified with a sieve having an opening of 1 mm and graphitized at 3000 ° C. The average fiber diameter of the pitch-based carbon short fiber filler after graphitization was 8.1 μm, and the percentage of the fiber diameter dispersion to the average fiber diameter was 13%. The average fiber length is 135 μm on average. When classified with a sieve having a mesh size of 53 μm, the ratio remaining on the sieve is 37%. When classified with a sieve having a mesh size of 100 μm, the ratio remaining on the sieve Was 16%. The true density was 2.15 g / cc.

It was confirmed that the graphene sheet was closed on the end face of the pitch-based carbon short fiber filler by observation with a transmission microscope. Moreover, the surface was substantially smooth with one unevenness | corrugation by observation with the scanning electron microscope.
The crystallite size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 39 nm. The crystallite size in the growth direction of the hexagonal network surface was 84 nm.
The electric resistance of the pitch-based carbon fiber was 1.6 μΩm, and the thermal conductivity was 750 W / (m · K).

[Example 3]
In Example 1, a pitch-based carbon short fiber filler was prepared in the same manner except that the rotation speed of the cutter was changed to 900 rpm.
The average fiber diameter of the pitch-based carbon short fiber filler after graphitization was 9.7 μm, and the percentage of the fiber diameter dispersion to the average fiber diameter was 11%. The average fiber length is 130 μm on average, the proportion remaining on the sieve is 35% when classified with a sieve having a mesh size of 53 μm, and the ratio remaining on the sieve when classified with a mesh sieve having an aperture of 100 μm Was 18%. The true density was 2.15 g / cc.

It was confirmed that the graphene sheet was closed on the end face of the pitch-based carbon short fiber filler by observation with a transmission microscope. Moreover, the surface was substantially smooth with one unevenness | corrugation by observation with the scanning electron microscope.
The crystallite size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 37 nm. The crystallite size in the growth direction of the hexagonal network surface was 77 nm.
The electric resistance of the pitch-based carbon fiber was 1.6 μΩm, and the thermal conductivity was 750 W / (m · K).

[Comparative Example 1]
A pitch-based carbon fiber filler was prepared in the same manner as in Example 1 except that the pulverization step was changed after firing to graphitization.
The average fiber diameter of the pitch-based carbon short fiber filler after graphitization was 9.7 μm, and the percentage of the fiber diameter dispersion to the average fiber diameter was 11%. The average fiber length is 140 μm on average. When classified with a sieve having a mesh size of 53 μm, the percentage remaining on the sieve is 41%, and when classified with a sieve having a mesh size of 100 μm, the ratio remaining on the sieve Was 19%. The true density was 2.15 g / cc.

  The obtained pitch-based carbon short fiber filler was observed with a transmission electron microscope at a magnification of 1,000,000 times and magnified on a photograph to 4,000,000 times. It was confirmed that there was a portion where the graphene sheet on the end face of the pitch-based carbon short fiber filler was open. Further, the surface was 16 uneven as observed by a scanning electron microscope, and was not substantially smooth.

The crystallite size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 37 nm. The crystallite size in the growth direction of the hexagonal network surface was 77 nm.
The electric resistance of the pitch-based carbon fiber was 1.6 μΩm, and the thermal conductivity was 750 W / (m · K).

[Example 4]
For 100 parts by volume of polycarbonate resin (Teijin Kasei L-1225WP), 60 parts by volume of the pitch-based carbon short fiber filler prepared in Example 1 was kneaded with a biaxial kneader (manufactured by Kurimoto Iron Works), did. This chip was obtained by an injection molding machine (M-50B manufactured by Meiki Seisakusho) to obtain a 2 mm-thick flat plate composite molded body. When the thermal conductivity of this composite molded body was measured, it was 2.5 W / (m · K). When kept at a temperature of 80 ° C. and a humidity of 90% for 500 hours, the composite material could not be folded by hand.

[Example 5]
Kneading with 100 parts by volume of polybutylene terephthalate resin (202 made of polyplastics) with 80 parts by volume of the pitch-based carbon short fiber filler prepared in Example 1 using a biaxial kneader (manufactured by Kurimoto Iron Works), a master chip It was. This chip was obtained by an injection molding machine (M-50B manufactured by Meiki Seisakusho) to obtain a 2 mm-thick flat plate composite molded body. The thermal conductivity of this composite molded body was measured and found to be 3.2 W / (m · K). When kept at a temperature of 80 ° C. and a humidity of 90% for 500 hours, the composite material could not be folded by hand.

[Example 6]
100 parts by volume of a polyphenylene sulfide resin (polyplastics 0220A9) was kneaded with 60 parts by volume of the pitch-based carbon short fiber filler prepared in Example 1 with a biaxial kneader (manufactured by Kurimoto Iron Works), did. This chip was obtained by an injection molding machine (M-50B manufactured by Meiki Seisakusho) to obtain a 2 mm-thick flat plate composite molded body. The thermal conductivity of the composite molded body was measured and found to be 2.9 W / (m · K). When kept at a temperature of 80 ° C. and a humidity of 90% for 500 hours, the composite material could not be folded by hand.

[Example 7]
A master chip was prepared by kneading 100 parts by volume of polypropylene resin (PM900A manufactured by Sun Allomer) with 80 parts by volume of the pitch-based carbon short fiber filler prepared in Example 1 using a biaxial kneader (manufactured by Kurimoto Iron Works). This chip was obtained by an injection molding machine (M-50B manufactured by Meiki Seisakusho) to obtain a 2 mm-thick flat plate composite molded body. The thermal conductivity of the composite molded body was measured and found to be 3.3 W / (m · K). When kept at a temperature of 80 ° C. and a humidity of 90% for 500 hours, the composite material could not be folded by hand.

[Example 8]
With 100 volume parts of silicone resin (Toray Dow Silicone SE-1740) by 100 volume parts of pitch-based carbon short fiber filler prepared in Example 3, with a revolving stirrer (Shinky Awatori Rentaro AR-250). It knead | mixed and it was set as the composite slurry. This slurry was placed in a square metal frame with a side of 300 mm, and was pressed with a vacuum press (manufactured by Kitagawa Seiki) to obtain a flat plate-like composite molded body having a thickness of 0.5 mm. The thermal conductivity of the composite molded body was measured and found to be 11.2 W / (m · K).

[Example 9]
With respect to 150 parts by volume of epoxy resin (Japan Epoxy Resin Epicoat 871, EpiCure 307), 100 revolutions of pitch-based carbon short fiber filler prepared in Example 3 was used as a self-revolving stirrer (Shinky Awatori Rentaro AR-250). Kneaded to obtain a composite slurry. This slurry was placed in a square metal frame with a side of 300 mm, and was pressed with a vacuum press (manufactured by Kitagawa Seiki) to obtain a flat plate-like composite molded body having a thickness of 0.5 mm. It was 14.1 W / (m * K) when the heat conductivity of this composite molded object was measured.

[Comparative Example 2]
100 parts by volume of polycarbonate resin (L-1225WP manufactured by Teijin Kasei) is kneaded with a biaxial kneader (manufactured by Kurimoto Iron Works) with 60 parts by volume of the pitch-based carbon short fiber filler prepared in Comparative Example 1, did. This chip was obtained by an injection molding machine (M-50B manufactured by Meiki Seisakusho) to obtain a 2 mm-thick flat plate composite molded body. The thermal conductivity of the composite molded body was measured and found to be 1.3 W / (m · K). When kept at a temperature of 80 ° C. and a humidity of 90% for 500 hours, it was confirmed that the composite material could be folded in half by hand and inferior in hydrolysis resistance.

  The pitch-based carbon short fiber filler of the present invention is classified by the surface state of the filler, the average fiber length and its dispersion, the proportion remaining on the sieve when classified with a mesh sieve having an opening of 53 μm, and the mesh sieve having an opening of 100 μm. In this case, by controlling the ratio remaining on the sieve by classification with a sieve or a mesh, the composite material using the same expresses high thermal conductivity and makes it possible to have high moldability. As a result, it can be used in places where high heat dissipation characteristics are required, and thermal management is ensured.

Claims (12)

  A graphene sheet is closed in a filler end face observation with a transmission electron microscope, and is a pitch-based carbon short fiber filler having a substantially flat observation surface with a scanning electron microscope, and has an average fiber length of 80 μm or more and 500 μm or less. That the pitch-based carbon short fiber filler.   When the average fiber diameter observed with an optical microscope is in the range of 2 to 20 μm, the percentage of fiber diameter dispersion (CV) with respect to the average fiber diameter is in the range of 3 to 20, and classification is performed with a mesh sieve having an opening of 53 μm. 2. The pitch system according to claim 1, wherein the proportion remaining on the sieve is 30 to 60%, and the proportion remaining on the sieve is 10 to 29% when classified with a mesh sieve having an opening of 100 μm. Carbon short fiber filler.   The pitch-based carbon short fiber filler according to claim 1 or 2, wherein a true density is in a range of 1.8 to 2.3 g / cc, and a thermal conductivity in a fiber axis direction is 300 W / (m · K) or more. .   4. The pitch-based carbon short according to claim 1, wherein the crystallite size derived from the thickness direction of the hexagonal network surface is 10 nm or more, and the crystallite size derived from the growth direction of the hexagonal network surface is 20 nm or more. Fiber filler.   It consists of the pitch type | system | group short carbon fiber filler of any one of Claims 1-4, and a thermoplastic resin and / or a thermosetting resin, The said filler of 3-200 volume parts with respect to 100 volume parts of resin. A composition containing   Thermoplastic resins are polycarbonates, polyethylene terephthalates, polybutylene terephthalates, polyethylene 2,6 naphthalates, nylons, polypropylenes, polyethylenes, polyether ketones, polyphenylene sulfides, and acrylonitrile-butadiene-styrene copolymers. The composition according to claim 5, which is at least one resin selected from the group consisting of polymerized resins.   The thermosetting resin is at least one resin selected from the group consisting of epoxies, acrylics, urethanes, silicones, phenols, imides, thermosetting modified PPEs, and thermosetting PPEs Item 6. The composition according to Item 5.   The composition in any one of Claims 5-7 whose heat conductivity in the state shape | molded in flat form is 2 W / (m * K) or more.   The composition according to any one of claims 5 to 8 is selected from the group consisting of an injection molding method, a press molding method, a calender molding method, a roll molding method, an extrusion molding method, a cast molding method, and a blow molding method. A molded body obtained by molding by at least one method.   A heat dissipating material for electronic parts, the main component of which is the molded body according to claim 9.   A radio wave shielding material comprising the molded article according to claim 9 as a main material.   The heat exchanger which uses the molded object of Claim 9 as a main material.