JP2009108119A - Thermal conductive filler and molded body using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pitch-based carbon short fiber filler and a composite molded material, which have high thermal conductance and high moldability. <P>SOLUTION: The pitch-based carbon short fiber filler has a mean fiber length (L1) of 40 μm or more but less than 80 μm observed with an optical microscope, a closed graphene sheet by filler end face observation with a transmission electron microscope, and a substantially flat surface observed with a scanning electron microscope. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermally conductive filler, a composition comprising the same and a resin, and a molded body obtained by molding the composition. More specifically, the present invention relates to a heat conductive filler using a pitch-based carbon short fiber filler as a raw material and a heat countermeasure material using the same.

  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 fiber is widely used for aerospace applications, construction / civil engineering applications, industrial robots, sports / leisure applications, etc., taking advantage of its significantly higher strength and elastic modulus than ordinary synthetic polymers. . In addition, PAN-based carbon fibers are often used mainly in the field of utilizing the strength, and pitch-based carbon fibers are used in the field of utilizing the elastic modulus.

  In recent years, an efficient method of using energy typified by energy saving has attracted attention, while heat generation due to Joule heat in a CPU and an electronic circuit that have been speeded up has been recognized as a serious problem. In order to solve these problems, it is necessary to achieve so-called thermal management in which heat is efficiently processed.

  In order to realize thermal management, inorganic materials having high thermal conductivity such as metal, metal oxide, metal nitride, metal oxynitride, and alloy are often used. Metal die casting can be considered a typical example. However, in order to manufacture a housing for an electric component having a complicated shape, it is desirable from the viewpoint of cost effectiveness to use the above-mentioned material as a composite material mixed with some matrix as a filler. However, the thermal conductivity of the synthetic resin often used for the matrix is about 1/100 or less that of the filler, and a large amount of filler needs to be mixed. However, the addition of a large amount of filler causes deterioration of moldability and impairs practicality. Therefore, there has been a demand for a highly thermally conductive filler that takes into consideration a shape that can efficiently exhibit thermal conductivity.

  In general, carbon fibers are said to have higher thermal conductivity than other synthetic polymers, but further improvements in thermal conductivity are being studied for thermal management applications. However, the thermal conductivity of commercially available PAN-based carbon fibers is usually smaller than 200 W / (m · K). This is because the PAN-based carbon fiber is a so-called non-graphitizable carbon fiber, and it is very difficult to improve the graphitization property that bears heat conduction. On the other hand, pitch-based carbon fibers are called graphitizable carbon fibers, and can be made more graphitic than PAN-based carbon fibers, and are recognized to easily achieve high thermal conductivity. Therefore, there is a possibility that a highly thermally conductive filler in which consideration is given to a shape capable of efficiently expressing thermal conductivity can be obtained.

  However, it is difficult to process a carbon fiber alone into a heat conductive member, and it is necessary to use a very special method. Therefore, like a metallic filler or the like, it is required to form a composite material of some matrix and carbon fiber, to form a molded body, and to improve the thermal conductivity of the molded body.

  And in order for a molded object to achieve sufficient heat conduction, it is necessary for the filler mainly responsible for heat conduction 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.

In view of such a background, studies have been made to give fillers 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.
However, the addition of a metal material having a specific gravity greater than that of the resin also increases the specific gravity of the resin composition, and must be considered disadvantageous for applications in which weight reduction is discussed on the order of 1 g.

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 addition, high cost performance was also desired.

  The inventors of the present invention aim to improve the thermal conductivity and reduce the specific gravity in the final molded body, and the pitch-based carbon short fibers having high thermal conductivity as the thermal conductive material are sized and dispersed. The inventors have found that this can be achieved by paying attention to the surface shape and fine structure, appropriately controlling, and further dispersing in a matrix. In addition, the inventors have found that a specific fiber diameter can be used to increase productivity and supply a material with high cost performance, and the present invention has been achieved.

  That is, the object of the present invention is that the average fiber length (L1) observed with an optical microscope is 40 μm or more and less than 80 μm, and the graphene sheet is closed in the filler end face observation with a transmission electron microscope. It is to provide a pitch-based carbon short fiber filler having a substantially flat observation surface.

A further object of the present invention is to provide a composition comprising the above pitch-based carbon short fiber filler and a thermoplastic resin and / or a thermosetting resin, and containing 10 to 300 parts by volume of the filler with respect to 100 parts by volume of the resin. It is to provide.
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.

  In the pitch-based carbon short fiber filler of the present invention, the graphene sheet is closed in the filler end face observation with the transmission electron microscope, the observation surface with the scanning electron microscope is substantially flat, and the size is further controlled. This makes it possible to impart a high thermal conductivity to the composite molded body while suppressing an increase in viscosity when it is made into a composition with a resin, and a composite molding material with good moldability and high thermal conductivity. It is possible to The molded body obtained from the composition of the pitch-based carbon short fiber filler resin of the present invention 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. Moreover, it is excellent in productivity and can improve cost performance.

Next, embodiments of the present invention will be described sequentially.
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 the shape do not occur, so the concentration due to adsorption and adhesion of impurities such as water is reduced. Furthermore, for example, it is possible to further increase the affinity with a different kind of filler such as expanded graphite, which is preferable. Moreover, when the graphene sheet is closed, vertical cracking of the pitch-based carbon short fiber filler is suppressed. In particular, in the pitch-based carbon short fiber filler having an average fiber length shorter than 1 mm as in the present invention, the graphene sheet is closed because the ratio of the end face to the pitch-based carbon short fiber filler surface area is high. Is particularly preferred. Such a structure has an effect of suppressing vertical cracking of the pitch-based carbon short fiber filler. Moreover, since the affinity with water is secondarily poor, the wet heat durability performance is improved.

  Note that the graphene sheet is closed when the end of the graphene sheet itself constituting the pitch-based carbon short fiber filler is not exposed at the end of the pitch-based carbon short fiber filler, and the graphite layer is curved in a substantially U shape. The curved portion is exposed at the end of the pitch-based carbon short fiber filler.

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 of the pitch-based carbon short fiber filler does not have severe unevenness like a fibril structure. When defects such as severe irregularities are present on the surface of the pitch-based carbon short fiber filler, an increase in the viscosity accompanying an increase in the surface area is caused at the time of kneading with the matrix resin, and the moldability is deteriorated. Therefore, it is desirable that defects such as surface irregularities be as small as possible. More specifically, it is assumed that there are 10 or less defects such as irregularities in the observation visual field in an image observed at 1000 times with a scanning electron microscope.

  The pitch-based carbon short fiber filler in which the observation surface of the present invention is smooth and the graphene sheet is closed in the filler end face observation with a transmission electron microscope will be described in detail later, and is obtained by graphitizing the carbon fiber filler after pulverization. be able to.

  The pitch-based carbon short fiber filler of the present invention has an average fiber length (L1) of 40 μm or more and less than 80 μm. More preferably, in the average fiber length (L1) observed with an optical microscope, the ratio of the fiber length of 100 μm or less is 70% by weight or more. Here, the average fiber length is a number average fiber length, and is obtained from an average value obtained by measuring a predetermined number in a plurality of visual fields using a length measuring device under an optical microscope. L1 has an optimum value depending on the purpose, but when the filler is used for heat transfer path preparation, that is, as a heat dissipation aid, L1 is preferably in the range of 30 to 70 μm. In this case, the resin viscosity at the time of resin filling becomes low, and handling properties are improved. Furthermore, the short carbon fiber filler can increase the filling amount at the time of resin filling. As a result, the effect as a heat dissipation aid is enhanced. L1 exhibits an effect as a heat dissipation aid by being almost equal to the average particle size of inorganic fillers such as alumina and boron nitride, metal fillers such as inorganic particles and copper, and metal particles, which are other heat dissipation aids. When it is shorter than 40 μm, it is difficult to develop a network effect that links other heat dissipation aids. When L1 is 80 μm or more, the bulk density becomes small and mixing with the matrix component becomes difficult.

  It is preferable that the percentage (CV value) with respect to D1 of fiber diameter dispersion | distribution (S1) which is dispersion | distribution of a fiber diameter in the pitch-type carbon short fiber filler observed with the optical microscope is 3 to 20% of range. The CV value is preferably 3 to 15%. It can be considered that the smaller the CV value is, the higher the process stability is, and the variation in the product is reduced. However, it is difficult to achieve a reduction from 3% at present. On the other hand, when the value is larger than 20%, the product has a large variation in average fiber diameter and a large unevenness. The ratio of L1 to D1 (L1 / D1) is preferably in the range of 1-40. When L1 / D1 is smaller than 1, powder falling in the final molded product becomes remarkable. On the other hand, when L1 / D1 exceeds 40, the viscosity increases during kneading with the matrix resin, and the handling property is lowered.

  The average fiber diameter (D1) of the pitch-based carbon short fiber filler of the present invention observed with an optical microscope is preferably 7 to 12 μm. More preferably, it is 8-11 micrometers. When D1 is larger than 12 μm, it is easy to cause fusion with adjacent yarns in the infusibilization process. When D1 is smaller than 7 μm, the surface area per weight of the pitch-based short carbon fiber filler is increased, and the fiber surface is substantially Even if it is flat, the moldability is deteriorated in the same manner as the fiber having irregularities on the surface, which is not preferable for practical use.

  The true density of the pitch-based carbon short fiber filler of the present invention strongly depends on the graphitization temperature, but is preferably in the range of 1.5 to 2.3 g / cc. More preferably, it is 2.0-2.2 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 of the present invention has a crystallite size derived from the thickness direction of the hexagonal network surface of 10 nm or more, and further a crystallite size derived from the growth direction of the hexagonal network surface of 20 nm or more. preferable.

  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 diffraction lines from the (002) plane, and the crystallite size in the growth direction of the hexagonal mesh plane is obtained using diffraction lines from the (110) plane. be able to.

Hereinafter, the preferable manufacturing method of the pitch type | system | group carbon short fiber filler of this invention is described.
Examples of the raw material for pitch-based carbon short fibers 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. These may be used singly or in combination of two or more, but it is particularly desirable to use mesophase pitch alone in order to improve the thermal conductivity of the short carbon fiber.

  The softening point of the raw material pitch can be determined by the Mettler method, and is preferably 230 ° C. or higher and 340 ° C. or lower. If the softening point is lower than 230 ° C., fusion between fibers or large heat shrinkage occurs during infusibilization. On the other hand, when the temperature is higher than 340 ° C., thermal decomposition of the pitch occurs and it becomes difficult to form a yarn. Furthermore, a gas component is generated, bubbles are generated in the yarn, and the strength is deteriorated.

  The raw material pitch is spun by a melt blow method, and then infusibilized, fired, milled, graphitized, and optionally screened to form pitch-based carbon short fibers. The pitch-based carbon short fiber filler of the present invention is characterized in that the graphene sheet is closed in the filler end face observation with a transmission electron microscope. Such pitch-based carbon short fiber filler is graphitized after milling. It can obtain preferably by implementing a process. Hereinafter, more preferred embodiments of the respective steps will be described.

  In the present invention, there are no particular restrictions on the shape of the spinning nozzle for pitch fibers used as a raw material for pitch-based carbon short fibers, but the ratio L / D of the nozzle hole diameter D to the nozzle hole length L is 1-20. Is preferably used, and more preferably 8 or more and 15 or less. The temperature of the nozzle at the time of spinning is not particularly limited, and may be a temperature at which a stable spinning state can be maintained, that is, a temperature at which the viscosity of the spinning pitch is 1 to 100 Pa · S, preferably 10 to 40 Pa · S.

The pitch fibers drawn out from the nozzle holes are shortened by blowing a gas having a linear velocity of 100 to 10000 m per minute heated to 100 to 370 ° 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 are further cross-wrapped to form a web with a constant basis weight.

  The web made of pitch fibers thus obtained is infusible by a known method and fired at 700 to 900 ° C. Infusibilization is performed under air or an oxidizing gas using a gas obtained by adding ozone, nitrogen dioxide, nitrogen, oxygen, iodine, or bromine to air. The infusibilization temperature is achieved by applying a heat treatment for a predetermined time at a temperature of 170 to 340 ° C. More preferably, it is 190-300 degreeC, More preferably, it is the range of 200-280 degreeC. In view of safety and convenience, it is desirable to carry out in air. The heating rate is suitably 1 to 10 ° C./min. Productivity is poor at 1 ° C. or lower, and unevenness occurs at 10 ° C. or higher, causing troubles such as fusion. In addition, there is a close relationship with the basis weight of the web, and when the basis weight is larger than 750 g / m 2, the unevenness of the oxygen adsorption amount due to infusibilization increases, resulting in process troubles such as unevenness of the product and fusion to the belt.

  And the infusible pitch fiber is fired in a non-oxidizing atmosphere using an inert gas such as nitrogen, argon, or krypton in the range of 400 to 1000 ° C., but at normal pressure, And it is carried out in low-cost nitrogen.

  The web made of infusibilized and fired pitch fibers is further milled and sieved in order to further shorten the fibers and make them a certain length. For milling, a pulverizer such as a Victory mill, a jet mill, a high-speed rotary mill, or a cutting machine is 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.

  The average fiber length of the fibers produced by milling is controlled by adjusting the rotational speed of the rotor, the angle of the blade, and the like. Furthermore, it is also possible to use a sieve, and the average fiber length is 40 μm or more and less than 80 μm, more preferably 30 to 70 μm. Such adjustment of the average fiber length can be achieved by combining the coarseness of the sieve.

  The pitch-based short fibers prepared by using the above milling treatment and, in some cases, sieving together, are heated to 2300-3500 ° C. and graphitized to obtain the final pitch-based carbon short fiber filler. Graphitization is performed in a non-oxidizing atmosphere in an Atchison furnace, an electric furnace or the like.

  In the present invention, the pitch-based carbon short fiber filler may be surface-treated and then a sizing agent may be added to the filler in an amount of 0.01 to 10% by weight, preferably 0.1 to 2.5% by weight. 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.

  In the present invention, a composition obtained by mixing a pitch-based carbon short fiber filler with a thermoplastic resin and / or a thermosetting resin is also included. At this time, 10 to 300 parts by volume of the pitch-based carbon short fiber filler is added to 100 parts by volume of the resin. If the addition amount is less than 10 parts by volume, it is difficult to ensure sufficient thermal conductivity. On the other hand, it is often difficult to add more than 300 parts by volume of pitch-based carbon short fiber filler to the matrix.

  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.

  Examples of the thermosetting resin include epoxies, acrylics, urethanes, silicones, phenols, imides, thermosetting modified PPEs, thermosetting PPEs, and the like. Or two or more types may be used in appropriate combination.

  The composition of the present invention is 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-revolving stirrer For example, a mixing device or a kneading device is preferably used. The composite material and / or the composite molded body is molded by a molding method such as an injection molding method, a press molding method, a calender molding method, a roll molding method, an extrusion molding method, a casting molding method, or a blow molding method. Is possible. 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.

  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.

  In order to further improve the thermal conductivity, moldability, and mechanical properties of the composition of the present invention, a filler other than the pitch-based carbon short fiber filler may be added as necessary. Specifically, metal oxides such as aluminum oxide, magnesium oxide, silicon oxide, and zinc oxide, metal hydroxides such as aluminum hydroxide and magnesium hydroxide, metal nitrides such as boron nitride and aluminum nitride, oxynitride Examples thereof include metal oxynitrides such as aluminum, metal carbides such as silicon carbide, metals or metal alloys such as gold, silver, copper, and aluminum, and carbon materials such as natural graphite, artificial graphite, expanded graphite, and diamond. Furthermore, for functions that require fibrous fillers such as glass fiber, potassium titanate whisker, zinc oxide whisker, aluminum boride whisker, boron nitride whisker, aramid fiber, alumina fiber, silicon carbide fiber, asbestos fiber, gypsum fiber, metal fiber, etc. You may add suitably according to it. Wollastonite, zeolite, sericite, kaolin, mica, clay, pyrophyllite, bentonite, asbestos, talc, alumina silicate and other silicates, calcium carbonate, magnesium carbonate, dolomite and other carbonates, calcium sulfate, barium sulfate, etc. Non-fibrous fillers such as sulfate, glass beads, glass flakes, and ceramic beads can be added as necessary. These may be hollow, and two or more of these may be used in combination. However, many of the above compounds have a density higher than that of the pitch-based carbon short fiber filler, and when the purpose is to reduce the weight, it is necessary to pay attention to the addition amount and the addition ratio.

  The molded body obtained by molding 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) Average fiber diameter and fiber diameter dispersion of pitch-based carbon short fiber filler:
The pitch-based carbon fiber filler that had undergone graphitization was obtained by photographing 10 fields of view at 400 × under an optical microscope.
(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) Fiber length ratio of pitch-based carbon short fiber filler:
The pitch-based carbon short fiber filler that had undergone graphitization was sieved, and after weight measurement, the ratio was determined.
(4) True density of pitch-based carbon short fiber filler:
It calculated | required using the specific gravity method.
(5) Crystal size:
Obtained by X-ray diffraction, the crystallite size derived from the thickness direction of the hexagonal mesh surface is obtained using diffraction lines from the (002) plane, and the crystallite size derived from the growth direction of the hexagonal mesh surface is the (110) plane. It was determined using the diffraction line from. In addition, the request was made in accordance with the Gakushin Law.
(6) Thermal conductivity of pitch-based carbon short fiber filler:
The resistivity of pitch-based short carbon fibers after graphitization prepared under the same conditions except for the pulverization step is measured, and the relationship between the thermal conductivity and electrical resistivity disclosed in JP-A-11-117143 is expressed. It calculated | required from following formula (1).
[Equation 1]
K = 1272.4 / ER-49.4 (1)
Here, K represents the thermal conductivity W / (m · K) of the pitch-based short carbon fiber after graphitization, and ER represents the electrical specific resistance μΩm of the same pitch-based short carbon fiber.
(7) Thermal conductivity of the flat molded body:
Measured with QTM-500 manufactured by Kyoto Electronics.
(8) Confirmation of a substantially flat surface:
The number of defects such as irregularities was counted in an image obtained by observing the pitch-based carbon short fiber filler with a scanning electron microscope at 1000 times.

[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 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 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 170 ° C. to 290 ° C. in air at an average heating rate of 7 ° C./min. The infusible web was fired at 800 ° C. in a nitrogen atmosphere and then milled, and sieved to a short fiber filler having an average fiber length of 55 μm. The fiber length ratio of 100 μm or less was 83%. Then, it graphitized by heat-processing at 3000 degreeC with the electric furnace made into the non-oxidizing atmosphere, and it was set as the pitch-type carbon short fiber filler. The average fiber diameter was 8.4 μm. The percentage of the fiber diameter dispersion to the average fiber diameter was 14%. The true density was 2.15 g / cc.

  The image was observed with a transmission electron microscope at a magnification of 1,000,000 times and magnified on a photograph at 4 million times. It was confirmed that the graphene sheet was closed at the end face of the pitch-based carbon short fiber filler. Further, the surface of the pitch-based carbon short fiber filler observed with a scanning electron microscope at a magnification of 4000 times was smooth and free from defects such as large irregularities.

The crystallite size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 36 nm. The crystallite size in the growth direction of the hexagonal network surface was 80 nm.
A single yarn was extracted from a graphitized web prepared by the same process up to firing and not milled, and heat-treated at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere, and the electrical resistivity was measured. 2.1 μΩm. The thermal conductivity obtained using the following formula (1) was 550 W / (m · K).
[Equation 2]
K = 1272.4 / ER-49.4 (1)

[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 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 short fibers having an average fiber diameter of 15 μm. The spun short fibers were collected on a belt to form a mat, and further a web made of pitch-based short fibers having a basis weight of 400 g / m ^{2 by} cross wrapping.

  The web was infusibilized by raising the temperature from 170 ° C. to 320 ° C. in air at an average heating rate of 7 ° C./min. The infusible web was fired at 800 ° C. in a nitrogen atmosphere and then milled, and sieved to a short fiber filler having an average fiber length of 50 μm. The fiber length ratio of 100 μm or less was 83%. Then, it graphitized by heat-processing at 3000 degreeC with the electric furnace made into the non-oxidizing atmosphere, and it was set as the pitch-type carbon short fiber filler. The average fiber diameter was 10.1 μm. The percentage of the fiber diameter dispersion to the average fiber diameter was 12%. The true density was 2.15 g / cc. The image was observed with a transmission electron microscope at a magnification of 1,000,000 times and magnified on a photograph at 4 million times. The graphene sheet was closed on the end face of the pitch-based carbon short fiber filler. Further, the surface of the pitch-based carbon short fiber filler observed with a scanning electron microscope at a magnification of 4000 times was smooth and free from defects such as large irregularities.

The crystallite size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 36 nm. The crystallite size in the growth direction of the hexagonal network surface was 80 nm.
A single yarn was extracted from a graphitized web prepared by the same process up to firing and not milled, and heat-treated at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere, and the electrical resistivity was measured. 2.2 μΩm. The thermal conductivity obtained using the above formula (1) was 530 W / (m · K).

[Example 3]
The process up to milling was the same as in Example 1, and graphitized at 2300 ° C. in an electric furnace in a non-oxidizing atmosphere to obtain a pitch-based carbon short fiber filler. The average fiber length was 55 μm. The fiber length ratio of 100 μm or less was 83%. The average fiber diameter was 8.4 μm. The percentage of the fiber diameter dispersion to the average fiber diameter was 14%. The true density was 1.8 g / cc. The image was observed with a transmission electron microscope at a magnification of 1,000,000 times and magnified on a photograph at 4 million times. The graphene sheet was closed on the end face of the pitch-based carbon short fiber filler. Further, the surface of the pitch-based carbon short fiber filler observed with a scanning electron microscope at a magnification of 4000 times was smooth and free from defects such as large irregularities.

The crystallite size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 11 nm. The crystallite size in the growth direction of the hexagonal network surface was 10 nm.
A single yarn was extracted from a graphitized web prepared by the same process up to firing and not milled, and heat-treated at 2300 ° C. in an electric furnace in a non-oxidizing atmosphere, and the electrical resistivity was measured. It was 3.4 μΩm. The thermal conductivity obtained using the above formula (1) was 320 W / (m · K).

[Comparative Example 1]
Example 1 A web was produced by the same method and heat-treated at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere, and then milled. The average fiber diameter (D1) was 8.3 μm. The average fiber length (L1) was 45 μm. The fiber length ratio of 100 μm or less was 85%. 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 of the pitch-based carbon short fiber filler observed with a scanning electron microscope at a magnification of 1000 times had 18 defects such as large irregularities, and was not smooth.

[Example 4]
A polycarbonate resin (L-1225WP manufactured by Teijin Chemicals Ltd.) is selected as the thermoplastic resin, and the pitch-based carbon short fiber filler prepared in Example 1 is 250 parts by volume with respect to 100 parts by volume of the polycarbonate. And compounded into a composite material. This chip was processed into a 2 mm thick flat plate with an injection molding machine manufactured by Meiki Seisakusho to obtain a composite molded body. When the thermal conductivity of this composite molded body was measured, it was 2.0 W / (m · K).

[Example 5]
A polycarbonate resin (L-1225WP manufactured by Teijin Chemicals Ltd.) is selected as the thermoplastic resin, and the pitch-based carbon short fiber filler prepared in Example 2 is 250 parts by volume with respect to 100 parts by volume of the polycarbonate. And compounded into a composite material. This chip was processed into a 2 mm thick flat plate with an injection molding machine manufactured by Meiki Seisakusho to obtain a composite molded body. When the thermal conductivity of this composite molded body was measured, it was 2.5 W / (m · K).

[Example 6]
Polyphenylene sulfide resin (polyplastics 0220A9) was selected as the thermoplastic resin, and the pitch-based carbon short fiber filler prepared in Example 2 was 250 parts by volume with respect to 100 parts by volume of polyphenylene sulfide, and biaxial kneading made by Kurimoto. Compounded in a machine to make a composite material. This chip was processed into a 2 mm thick flat plate with an injection molding machine manufactured by Meiki Seisakusho to obtain a composite molded body. When the thermal conductivity of this composite molded body was measured, it was 3.5 W / (m · K).

[Example 7]
A polypropylene resin (PM900A manufactured by Sun Allomer) was selected as the thermoplastic resin, and the pitch-based carbon short fiber filler prepared in Example 2 was 235 parts by volume with respect to 100 parts by volume of polypropylene. Compounded into composite material. This chip was processed into a 2 mm thick flat plate with an injection molding machine manufactured by Meiki Seisakusho to obtain a composite molded body. When the thermal conductivity of this composite molded body was measured, it was 2.0 W / (m · K).

[Example 8]
A silicone resin (SE-1740 manufactured by Toray Dow Silicone) was selected as the thermosetting resin, and the pitch-based carbon short fiber filler produced in Example 1 was 250 parts by volume with respect to 100 parts by volume of silicone. Mixing was performed with a kneader, and the mixture was placed in a square metal frame with a side of 300 mm, and pressed with a vacuum press to obtain a flat plate-like composite molded body with a thickness of 0.5 mm. The thermal conductivity of this composite molded body was measured and found to be 3.1 W / (m · K).

[Example 9]
A silicone resin (SE-1740 manufactured by Toray Dow Silicone) was selected as the thermosetting resin, and the pitch-based carbon short fiber filler prepared in Example 2 was 250 parts by volume with respect to 100 parts by volume of silicone. Mixing was performed with a kneader, and the mixture was placed in a square metal frame with a side of 300 mm, and pressed with a vacuum press to obtain a flat plate-like composite molded body with a thickness of 0.5 mm. The thermal conductivity of this composite molded body was measured and found to be 3.7 W / (m · K).

[Comparative Example 2]
A flat plate was produced from a polycarbonate resin (L-1225WP manufactured by Teijin Chemicals) to which no pitch-based carbon short fiber filler was added. The thermal conductivity was 0.2 W / (m · K).

[Comparative Example 3]
A flat plate was prepared from a polyphenylene sulfide resin (0220A9 manufactured by Polyplastics), to which no pitch-based carbon short fiber filler was added. The thermal conductivity was 0.2 W / (m · K).

[Comparative Example 4]
A flat plate was prepared from a silicone resin (SE-1740 manufactured by Toray Dow Silicone), to which no pitch-based carbon short fiber filler was added. The thermal conductivity was 0.3 W / (m · K).

[Comparative Example 5]
A composite material was obtained under the same conditions as in Example 4 except that the pitch-based carbon short fiber filler prepared in Comparative Example 1 was used. However, the viscosity of the composite material was higher than that in Example 4. This composite material was processed into a flat plate having a thickness of 2 mm using an injection molding machine manufactured by Meiki Seisakusho to obtain a composite molded body. The composite molded body had a thermal conductivity of 2.0 W / (m · K).
When this composite molded body was subjected to a wet heat durability test at 60 ° C. and 90% RH, deterioration progressed after 1000 hours, and the composite molded body was broken.

[Example 10]
A weight heated to 70 ° C. was placed on the flat composite molded body produced in Example 4 to obtain a heat conductive sheet. The thermal conductivity was higher than that of Comparative Example 2. It was found that it functions as a heat dissipation member.

[Example 11]
A weight heated to 70 ° C. was placed on the flat composite molded body produced in Example 8 to obtain a heat conductive sheet. The thermal conductivity was higher than that of Comparative Example 4. It was found that it functions as a heat dissipation member.

Claims (12)

  The average fiber length (L1) observed with an optical microscope is 40 μm or more and less than 80 μm, the graphene sheet is closed in the filler end face observation with the transmission electron microscope, and the observation surface with the scanning electron microscope is substantially flat A pitch-based carbon short fiber filler.   In the average fiber length (L1) observed with an optical microscope, the ratio of 100 μm or less accounts for 70% by weight or more, the average fiber diameter (D1) observed with an optical microscope is in the range of 2 μm or more and 20 μm or less, and the average fiber diameter ( The pitch-based carbon short fiber filler according to claim 1, wherein the fiber diameter dispersion (S1) to D1) has a 100-percent fraction in the range of 3 to 20, and the ratio of L1 to D1 is 1 to 40.   The pitch-based carbon short fiber filler according to claim 1 or 2, wherein a true density is in a range of 1.5 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 carbon short fiber filler in any one of Claims 1-4, a thermoplastic resin, and / or a thermosetting resin, and contains the said filler of 10-300 volume parts with respect to 100 volume parts of resin. Composition.   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, The composition according to claim 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.