JP2011184827A - Pitch-based graphitized short fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat transfer agent that has an excellent filling property to resin and supplies a molded product with high thermal conductivity and surface designability. <P>SOLUTION: The pitch-based graphitized short fiber includes an average fiber diameter of 5-15 μm, a volume-based average fiber length of 20-30 μm, a maximum fiber length of ≤100 μm and a ratio of short fibers having fiber length of ≤50 μm of ≥95%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to pitch-based graphitized short fibers that are excellent in resin filling properties and can impart high thermal conductivity, and thermal conductive compositions therefrom.

  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. Similarly, an electroluminescent element that uses electron injection as a light emission principle is also manifesting as a serious problem. On the other hand, when considering the process of forming various elements, an environmentally conscious process is demanded, and as a countermeasure against this, switching to so-called lead-free solder to which lead is not added has been made. Since lead-free solder has a higher melting point than ordinary lead-containing solder, efficient use of process heat is required. And in order to solve the problem originating in the heat which such a product and process includes, it is necessary to achieve the efficient process (thermal management) of heat.

  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.

  Next, the characteristics of the molded body used for thermal management are considered. In general, in order to impart high thermal conductivity to a molded article, it is preferable to highly fill a thermal conductive agent having excellent thermal conductivity. A heat conductive agent with a high aspect ratio is in contact with each other to form a network, so that high thermal conductivity is easily exhibited, while a thickening effect increases when kneading with a resin, resulting in high filling. It becomes difficult to do. Thus, various carbon fibers with controlled fiber lengths have been proposed in order to achieve efficient thermal conductivity (Patent Documents 1 to 4).

JP 2008-214819 A JP 2009-108119 A JP 2009-108424 A International Publication No. 2008/108482 Pamphlet

  An object of the present invention is to provide pitch-based graphitized short fibers that are excellent in resin filling properties and can impart high thermal conductivity. Another object of the present invention is a thermally conductive composition comprising pitch-based graphitized short fibers and at least one matrix component selected from the group consisting of thermoplastic resins, thermosetting resins, aramid resins, and rubbers, Furthermore, it is providing the molded object excellent in the thermal conductivity and surface property from it.

  As a result of intensive studies to obtain a heat conductive agent for producing a heat dissipation material excellent in thermal conductivity, the present inventors have controlled this by controlling the fiber length of pitch-based graphitized short fibers. The present inventors have found that it is possible to provide a thermally conductive composition and a molded article excellent in thermal conductivity and surface property, and have reached the present invention.

  In the present invention, the average fiber diameter is 5 to 15 μm, the volume conversion average fiber length is 20 to 30 μm, the maximum fiber length is 100 μm or less, and the proportion of short fibers having a fiber length of 50 μm or less is 95% or more. It is a pitch-based graphitized short fiber characterized by being.

  The pitch-based graphitized short fibers of the present invention have a high filling property, which makes it possible for the heat conductive composition and the molded body to obtain high heat conductivity. The pitch-based graphitized short fibers of the present invention can be used as a paint or paste by mixing with a matrix and adding a solvent as necessary. Since the pitch-based graphitized short fiber of the present invention does not contain a long fiber length component, a molded product or a coating film excellent in surface properties and design properties can be obtained. The paint or paste obtained from the pitch-based graphitized short fiber of the present invention can be used as an electrode or the like.

Hereinafter, embodiments of the present invention will be sequentially described.
The pitch-based graphitized short fiber of the present invention has an average fiber diameter of 5 to 15 μm, a volume-converted average fiber length of 20 to 30 μm, a maximum fiber length of 100 μm or less, and a fiber length of 50 μm or less. The ratio is 95% or more.

  The thermal conductivity of the molded body greatly depends on the filling amount of the thermal conductive agent as long as the interaction between the thermal conductive agents to be filled is not large. In addition, even when the heat conductive agent has a large interaction such as a fiber shape, it generally shows an interaction only in the orientation direction of the heat conductive agent and hardly shows any other interaction. . Therefore, for example, in the case of a flat plate shape, the thermal conductivity in the thickness direction of the flat plate greatly depends on the filler of the thermal conductive agent.

  The filling amount of the heat conductive agent is determined by the viscosity when kneading the matrix and the heat conductive agent. This viscosity is influenced by the interaction between the heat conducting agents, but the interaction is affected by the aspect ratio and surface shape of the heat conducting agent. Furthermore, if a small amount of a heat conductive agent with a high aspect ratio is included, the viscosity tends to increase rapidly, so that the long fiber component in the heat conductive agent with a high aspect ratio, that is, pitch-based graphitized short fibers is removed as much as possible. It is preferable to do this.

  As a range satisfying this condition, the average fiber diameter is 5 to 15 μm, the volume conversion average fiber length is 20 to 30 μm, the maximum fiber length is 100 μm or less, and the ratio of short fibers having a fiber length of 50 μm or less is 95. % Or more.

  The pitch-based graphitized short fibers of the present invention have an average fiber diameter of 5 to 15 μm observed with an optical microscope. When the average fiber diameter is less than 5 μm, the aspect ratio becomes high, and the viscosity of the matrix / short fiber mixture becomes high when combined with the matrix, and the filling property is lowered. Conversely, if the average fiber diameter exceeds 15 μm, fine powder is likely to be generated during pulverization, and the fine powder increases the viscosity of the matrix / short fiber mixture and lowers the filling property. More preferably, it is 7-13 micrometers.

  The pitch-based graphitized short fibers of the present invention have a volume-converted average fiber length of 20 to 30 μm. When the volume-converted average fiber length is less than 20 μm, the proportion containing fine powder substantially increases, the viscosity of the trix / short fiber mixture increases, and the fillability decreases. On the other hand, if the average fiber length in terms of volume exceeds 30 μm, the long fiber component increases the viscosity of the matrix / short fiber mixture and lowers the fillability. More preferably, it is 20-25 micrometers. The volume-converted average fiber length is obtained by measuring the fiber length for a specific number of fibers, obtaining an average value of square values of the respective fiber lengths, and obtaining the square root of the average value.

  The pitch-based graphitized short fiber of the present invention has a maximum fiber length of 100 μm or less. If the maximum fiber length exceeds 100 μm, the long fiber component increases the viscosity of the matrix / short fiber mixture and lowers the fillability. More preferably, the maximum fiber length is 90 μm or less.

  The pitch-based graphitized short fiber of the present invention has a fiber length of 50 μm or less and a ratio of 95% or more. When the ratio of the fiber length of 50 μm or less is less than 95%, the long fiber component increases the viscosity of the matrix / short fiber mixture and lowers the filling property. More preferably, the ratio of the fiber length of 50 μm or less is 97% or more. Here, the ratio of short fibers having a fiber length of 50 μm or less is calculated using the number of short fibers having a length of 1 μm or more as the denominator, and the number of short fibers having a fiber length of 50 μm or less as a numerator.

  The pitch-based graphitized short fibers of the present invention can be obtained by classifying the pitch-based carbon short fibers or pitch-based graphitized short fibers after milling with a mesh having a screen diameter of 50 μm or less a plurality of times. At this time, in general, when the fiber diameter is large, classification is performed efficiently because the ratio of long fibers passing in the vertical direction with respect to the mesh decreases. When the pitch-based carbon short fibers are graphitized to obtain the pitch-based graphitized short fibers, since the fiber diameter tends to be small, it is preferable to classify in the state of the pitch-based carbon short fibers before graphitization.

  In the pitch-based graphitized short fibers of the present invention, the percentage (CV value) with respect to the average fiber diameter of the fiber diameter dispersion in the pitch-based graphitized short fibers observed with an optical microscope is preferably 3 to 15%. The CV value is an index of fiber diameter variation, and the smaller the value, the higher the process stability and the smaller the product variation. When the CV value is less than 3%, the fiber diameters are extremely uniform, so the amount of small short fibers entering the gaps between the pitch-based graphitized short fibers decreases, and the pitch-based graphitized short fibers are packed more densely. It can be difficult to achieve and, as a result, it can be difficult to obtain high performance composites. On the other hand, when the CV value is larger than 15%, dispersibility deteriorates when composited with a matrix, and it may be difficult to obtain a composite material having uniform performance. The CV value is preferably 5 to 13%. The CV value is adjusted by adjusting the viscosity of the melted mesophase pitch at the time of spinning. Specifically, when spinning by the melt blow method, the melt viscosity at the nozzle hole at the time of spinning is 5.0-25.0 Pa · S. It can be realized by adjusting to.

  The pitch-based graphitized short fibers of the present invention are preferably composed of graphite crystals, and the crystallite size derived from the growth direction of the hexagonal network surface is preferably 30 nm or more. The crystallite size corresponds to the degree of graphitization in any of the growth directions of the hexagonal network surface, and a certain size or more is necessary to exhibit thermophysical properties. The crystallite size in the growth direction of the hexagonal network surface can be obtained by an X-ray diffraction method. The measurement method is a concentration method, and the Gakushin method is preferably used as an analysis method. The crystallite size in the growth direction of the hexagonal mesh plane can be obtained using diffraction lines from the (110) plane.

  In the pitch-based graphitized short fiber of the present invention, it is preferable that the end face of the graphene sheet is closed in the fiber end observation with a transmission electron microscope. When the end face of the graphene sheet is closed, generation of extra functional groups and localization of electrons due to the shape are difficult to occur. For this reason, active points do not occur in the pitch-based graphitized short fibers, and curing by reducing the catalytic active point can be suppressed by kneading with a thermosetting resin such as a silicone resin or an epoxy resin. In addition, since the end face of the graphene sheet is closed, adsorption of water and the like can be reduced, and for example, in the case of kneading with a resin that involves hydrolysis such as polyester, a remarkable improvement in wet heat durability can be achieved.

  The pitch-based graphitized short fibers of the present invention are preferably within a visual field range of a transmission electron microscope magnified 500,000 to 4 million times, and the end face of the graphene sheet is preferably 80% closed. If the graphene sheet end face closing rate is 80% or less, generation of extra functional groups and localization of electrons due to the shape may be caused, and the reaction with other materials may be promoted. The closing rate of the graphene sheet end face is preferably 90% or more, and more preferably 95% or more.

  The graphene sheet end face structure varies greatly depending on whether pulverization is performed before graphitization or pulverization is performed after graphitization. That is, when a pulverization process is performed after graphitization, the graphene sheet grown by graphitization is cut and broken, and the graphene sheet end face tends to be open. On the other hand, when graphitization is performed after pulverization, the graphene sheet end face is curved in a U-shape during the graphite growth process, and the curved portion is likely to be exposed at the pitch-based graphitized short fiber end. For this reason, in order to obtain a pitch-based graphitized short fiber having a graphene sheet end face closing rate exceeding 80%, it is preferable to perform graphitization after pulverization.

  The pitch-based graphitized short fibers of the present invention preferably have a substantially flat side observation surface with a scanning electron microscope. Here, “substantially flat” means that the pitch-based graphitized short fibers do not have severe unevenness like a fibril structure. When defects such as severe irregularities are present on the surface of the pitch-based graphitized short fibers, the viscosity increases with the increase of the surface area when kneading with the matrix, 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 an observation field in an image observed at 800 to 1000 times with a scanning electron microscope. A technique for obtaining such pitch-based graphitized short fibers can be preferably obtained by performing graphitization after milling.

Hereinafter, a preferred method for producing the pitch-based carbon short fibers of the present invention will be described.
Examples of the raw material for the pitch-based graphitized short fibers of the present invention include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, condensed heterocyclic compounds such as petroleum pitch and coal pitch, and the like. Of these, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferred.

  Mesophase pitch is used as a raw material for the pitch-based graphitized short fibers of the present invention. The mesophase ratio of the mesophase pitch is at least 90% or more, more preferably 95% or more, and further preferably 99% or more. The mesophase ratio of the mesophase pitch can be confirmed by observing the pitch in the molten state with a polarizing microscope.

  Furthermore, the softening point of the raw material pitch is preferably 230 ° C to 340 ° C. The infusibilization treatment needs to be performed at a temperature lower than the softening point. For this reason, when the softening point is lower than 230 ° C., it is necessary to perform the infusibilization treatment at a temperature lower than at least the softening point, and as a result, it takes a long time for infusibilization. On the other hand, if the softening point exceeds 340 ° C., a high temperature exceeding 340 ° C. is required for spinning, which causes thermal decomposition of the pitch and causes problems such as generation of bubbles in the yarn due to the generated gas. A more preferable range of the softening point is 250 ° C to 320 ° C, more preferably 260 ° C to 310 ° C. The softening point of the raw material pitch can be obtained by the Mettler method. Two or more raw material pitches may be used in appropriate combination. The mesophase ratio of the raw material pitch to be combined is preferably at least 90% or more, and the softening point is preferably 230 ° C to 340 ° C.

  The mesophase pitch is spun by a melting method and then converted into pitch-based graphitized short fibers by infusibilization, carbonization, pulverization, and graphitization. In the present invention, a classification step is added after pulverization or graphitization, but a classification step is preferably added after pulverization.

Hereinafter, preferred embodiments of each step will be described.
The spinning method is not particularly limited, but a so-called melt spinning method can be applied. Specific examples include a normal spinning drawing method in which a mesophase pitch discharged from a die is drawn with a winder, a melt blow method using hot air as an atomizing source, and a centrifugal spinning method in which a mesophase pitch is drawn using centrifugal force. Among these, it is desirable to use the melt blow method for reasons such as control of the form of the pitch-based carbon fiber precursor and high productivity. For this reason, the melt blow method will be described below with respect to the method for producing pitch-based graphitized short fibers of the present invention.

  The spinning nozzle for forming the pitch-based carbon fiber precursor may have any shape. Normally, a perfect circle is used, but there is no problem even if a nozzle having an irregular shape such as an ellipse is used in a timely manner. The ratio of the nozzle hole length (LN) to the hole diameter (DN) (LN / DN) is preferably in the range of 2-20. When LN / DN exceeds 20, a strong shearing force is imparted to the mesophase pitch passing through the nozzle, and a radial structure appears in the fiber cross section. The expression of the radial structure is not preferable because it may cause a crack in the fiber cross-section during the graphitization process and may cause a decrease in mechanical properties. On the other hand, if LN / DN is less than 2, shearing cannot be imparted to the raw material pitch, resulting in a pitch-based carbon fiber precursor having a low orientation of graphite. For this reason, even when graphitized, the degree of graphitization cannot be sufficiently increased, and it is difficult to improve the thermal conductivity. In order to achieve both mechanical strength and thermal conductivity, it is necessary to apply appropriate shear to the mesophase pitch. For this reason, the ratio (LN / DN) of the nozzle hole length (LN) to the hole diameter (DN) is preferably in the range of 2 to 20, and more preferably in the range of 3 to 12.

  There are no particular restrictions on the temperature of the nozzle during spinning, the shear rate when the mesophase pitch passes through the nozzle, the amount of air blown from the nozzle, the temperature of the wind, etc., and the conditions under which a stable spinning state can be maintained, that is, the mesophase pitch The melt viscosity at the nozzle holes is preferably in the range of 1 to 100 Pa · s.

  When the melt viscosity of the mesophase pitch passing through the nozzle is less than 1 Pa · s, the melt viscosity is too low to maintain the yarn shape, which is not preferable. On the other hand, when the melt viscosity of the mesophase pitch exceeds 100 Pa · s, a strong shearing force is applied to the mesophase pitch and a radial structure is formed in the fiber cross section, which is not preferable. In order to keep the shearing force applied to the mesophase pitch within an appropriate range and maintain the fiber shape, it is necessary to control the melt viscosity of the mesophase pitch passing through the nozzle. Therefore, the melt viscosity of the mesophase pitch is preferably in the range of 1 to 100 Pa · s, more preferably in the range of 3 to 30 Pa · s, and further preferably in the range of 5 to 25 Pa · s. .

The shear rate when the mesophase pitch passes through the nozzle is preferably 5000 to 15000 s ⁻¹ .

  The direction of the blow airflow is not particularly limited, but is preferably 20 to 70 degrees with respect to the spinning direction, and more preferably 30 to 60 degrees.

  The amount of air blown from the nozzle is preferably a linear speed of 5000 to 20000 m / min. More preferably, the linear velocity is 8000 to 15000 m / min.

  The speed of the airflow blown from the nozzle is preferably 330 to 370 ° C, more preferably 340 to 360 ° C.

  The pitch-based graphitized short fiber of the present invention has an average fiber diameter of 5 to 15 μm or less. However, the control of the average fiber diameter of the pitch-based graphitized short fiber can be performed by changing the hole diameter of the nozzle or changing the raw material pitch from the nozzle. Adjustment is possible by changing the discharge amount or changing the draft ratio. The change of the draft ratio can be achieved by blowing a gas having a linear velocity of 5000 to 20000 m / min heated to 100 to 400 ° C. in the vicinity of the refinement point. There is no particular restriction on the gas to be blown, but air is desirable from the viewpoint of cost performance and safety.

The pitch-based carbon fiber precursor is collected on a belt such as a wire mesh to form a pitch-based carbon fiber precursor web. At that time, the weight per unit area can be adjusted according to the belt conveyance speed, but if necessary, it may be laminated by a method such as cross wrapping. The basis weight of the pitch-based carbon fiber precursor web is preferably 150 to 1000 g / m ^{2 in} consideration of productivity and process stability.

  The pitch-based carbon fiber precursor web thus obtained is infusibilized to form a pitch-based infusible fiber web. Infusibilization can be performed in air or in an oxidizing atmosphere using a gas in which ozone, nitrogen dioxide, nitrogen, oxygen, iodine, or bromine is added to air, but in consideration of safety and convenience, it is performed in air. It is desirable. Further, both batch processing and continuous processing can be performed, but continuous processing is desirable in consideration of productivity. The infusibilization treatment is achieved by applying a heat treatment for a predetermined time at a temperature of 150 to 350 ° C. A more preferable temperature range is 160 to 340 ° C. A heating rate of 1 to 10 ° C./min is preferably used. In the case of continuous treatment, the above heating rate can be achieved by sequentially passing through a plurality of reaction chambers set at arbitrary temperatures. A more preferable range of the heating rate is 3 to 9 ° C./min in consideration of productivity and process stability.

  The pitch-based infusible fiber web is carbonized at a temperature of 600 to 2000 ° C. in a vacuum or in a non-oxidizing atmosphere using an inert gas such as nitrogen, argon, or krypton, to become a pitch-based carbon fiber web. . Carbonization treatment is preferably performed at normal pressure and in a nitrogen atmosphere in consideration of cost. Further, both batch processing and continuous processing can be performed, but continuous processing is desirable in consideration of productivity.

  The carbonized pitch-based carbon fiber web is subjected to processing such as cutting, crushing and pulverization in order to obtain a desired fiber length. The treatment method is selected according to the desired fiber length, but when the volume-converted average fiber length is 20 to 30 μm, a high-speed rotational impact type pulverizer using impact force such as a hammer, blade and pin, high-speed air flow An air-flow type pulverizer that uses kinetic energy possessed by, a shear friction type pulverizer that uses shear friction under a compressive force, a medium-type pulverizer that uses a pulverizing medium such as balls and beads, and the like are preferably used. Further, in order to efficiently pulverize, as a pretreatment for the pulverization, using a guillotine-type, uniaxial, biaxial and multi-axial rotary cutter, a roll-type pulverizer, and the like, cutting to several tens μm to several mm and It can also be coarsely pulverized. In order to obtain a desired fiber length, a plurality of pulverizers may be used, and the treatment atmosphere may be either dry or wet. Furthermore, it can be obtained not only by selecting the model of the pulverizer, but also by controlling the rotational speed of the rotor / rotating blade, the air flow pressure, the supply amount, the clearance between the blades, the residence time in the pulverizer, and the like.

  When the maximum fiber length is 100 μm or less and the ratio of the fiber length of 50 μm or less is 95% or more, classification treatment is performed after pulverization or graphitization. As described above, it is preferably performed before graphitization after pulverization. As the treatment method, classifiers such as a stirring sieve type, a vibration sieve type, a centrifugal separation type, a gravity type, an inertial force type and a filtration type are used, but the maximum fiber length is 100 μm or less and the fiber length is 50 μm or less. When the content is 95% or more, a stirring sieve method is preferably used. The fiber length can be controlled by the screen diameter of the stirring sieve classifier. When the maximum fiber length is 100 μm or less and the ratio of the fiber length is 50 μm or less is 95% or more, the screen diameter is 50 μm or less. It is desirable to carry out once. In addition, fibers having an undesired fiber length generated by the classification treatment can be circulated to a pulverizer in order to improve productivity.

  The pitch-based carbon short fibers prepared by using the above-described cutting / crushing / pulverizing treatment and classification treatment are heated to 2000 to 3500 ° C. and graphitized to obtain final pitch-based graphitized short fibers. Graphitization is performed in an Atchison furnace, an electric furnace, or the like, and is performed in a vacuum or in a non-oxidizing atmosphere using an inert gas such as nitrogen, argon, or krypton.

  The pitch-based graphitized short fibers of the present invention can be combined with a matrix to obtain a heat conductive composition such as a compound, sheet, grease, adhesive, or a molded product. At this time, the surface-treated pitch-based graphitized short fibers are added in an amount of 3 to 500 parts by weight with respect to 100 parts by weight of the matrix. When the addition amount is less than 3 parts by weight, it is difficult to ensure sufficient thermal conductivity. On the other hand, it is often difficult to add more than 500 parts by weight of pitch-based graphitized short fibers to the matrix.

  The matrix is at least one selected from the group consisting of a thermoplastic resin, a thermosetting resin, an aramid resin, and rubber. A thermoplastic resin and a thermosetting resin can be appropriately mixed and used in order to develop desired physical properties in the molded body. That is, the present invention comprises pitch-based graphitized short fibers and at least one matrix component selected from the group consisting of thermoplastic resins, thermosetting resins, aramid resins, and rubbers. The heat conductive composition containing 3 to 300 parts by weight of surface-treated pitch-based graphitized short fibers is included.

  Polyolefin and its copolymer (polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, ethylene- Ethylene-α-olefin copolymers such as propylene copolymers), polymethacrylic acid and copolymers thereof (polymethacrylates such as polymethyl methacrylate), polyacrylic acid and copolymers thereof, polyacetal and Its copolymer, fluororesin and its copolymer (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyester and its copolymer (polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6 naphthalate, liquid crystal Polymers), polystyrene and copolymers thereof (styrene-acrylonitrile copolymers, ABS resins, etc.), polyacrylonitrile and copolymers thereof, polyphenylene ether (PPE) and copolymers thereof (including modified PPE resins, etc.), Aliphatic polyamide and its copolymer, polycarbonate and its copolymer, polyphenylene sulfide and its copolymer, polysulfone and its copolymer, polyethersulfone and its copolymer, polyether nitrile and its copolymer, Examples include polyether ketone and its copolymer, polyether ether ketone and its copolymer, polyketone and its copolymer, elastomer, acrylic and its copolymer, liquid crystal polymer and the like.

  Above all, from the group consisting of polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, aliphatic polyamide, polypropylene, polyethylene, polyetherketone, polyphenylene sulfide, and acrylonitrile-butadiene-styrene copolymer resin, acrylic At least one resin selected is preferred. One of these may be used alone, or two or more may be used in appropriate combination.

  In addition, as the thermosetting resin, epoxy resin, acrylic resin, urethane resin, silicone resin, phenol resin, thermosetting modified PPE resin and thermosetting PPE resin, polyimide resin and its copolymer, aromatic polyamideimide resin And copolymers thereof, etc., and one of these may be used alone, or two or more thereof may be used in appropriate combination.

  As an aramid resin, an aromatic dicarboxylic acid component composed of terephthalic acid and / or isophthalic acid, 1,4-phenylenediamine, 1,3-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, and Examples include wholly aromatic polyamides derived from at least one aromatic diamine component selected from the group consisting of 1,3-bis (3-aminophenoxy) benzene.

  The rubber is not particularly limited, but natural rubber (NR), acrylic rubber, acrylonitrile butadiene rubber (NBR rubber), isoprene rubber (IR), urethane rubber, ethylene propylene rubber (EPM), epichlorohydrin rubber, chloroprene rubber (CR), Examples include silicone rubber and copolymers thereof, styrene butadiene rubber (SBR), butadiene rubber (BR), and butyl rubber.

  The heat conductive composition of the present invention is prepared by mixing pitch-based graphitized short fibers and a matrix. During mixing, kneaders, various mixers, blenders, rolls, extruders, milling machines, self-revolving A mixing device or a kneading device such as an agitator of the type is preferably used.

  In order to further increase the thermal conductivity of the composition of the present invention, fillers other than pitch-based graphitized short fibers 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, and aluminum oxynitride Examples thereof include metal oxynitrides such as silicon carbide, metal carbides such as silicon carbide, metals or metal alloys such as gold, silver, copper, aluminum, and metal silicon, and carbon materials such as natural graphite, artificial graphite, expanded graphite, and diamond. You may add these suitably according to a function. Two or more types can be used in combination. However, many of the above compounds have a density higher than that of pitch-based graphitized short fibers, and when the purpose is to reduce the weight, it is necessary to pay attention to the addition amount and addition ratio. In addition, depending on the shape of the above compound, the viscosity increases when kneading with the matrix and the filling property decreases, so it is necessary to pay attention to the shape and the addition ratio.

  Furthermore, glass fibers, potassium titanate whiskers, zinc oxide whiskers, aluminum boride whiskers, boron nitride whiskers, aramid fibers, alumina fibers, silicon carbide fibers, asbestos fibers are used to enhance other properties such as moldability and mechanical properties. In addition, a fibrous filler such as gypsum fiber or metal fiber may be appropriately added depending on a required function and within a range not impairing the filling property. Two or more of these can be used in combination. 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 sulfates, glass beads, glass flakes, and ceramic beads can be added as needed as long as they do not impair the filling properties. 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 pitch-based graphitized short fibers, and when the purpose is to reduce the weight, it is necessary to pay attention to the addition amount and addition ratio.

  Moreover, you may add two or more other additives to a composition as needed. Examples of other additives include mold release agents, flame retardants, emulsifiers, softeners, plasticizers, and surfactants.

  More specifically, the use of the composition will be described. The composition can be used as a heat radiating member, a heat transfer member, or a constituent material thereof for effectively radiating heat generated by electronic components such as a semiconductor element, a power source, and a light source in an electronic device or the like. .

  When the matrix is a thermally conductive composition made of a thermoplastic resin, it is selected from the group consisting of injection molding, press molding, calendar molding, roll molding, extrusion molding, cast molding, and blow molding. It can shape | mold by the at least 1 type of method which can be obtained. And a sheet-like molded object can be shape | molded by extrusion molding methods, such as extrusion by a roll and extrusion by die | dye. The molding conditions depend on the molding method and the matrix, and the molding is performed in a state where the temperature is higher than the melt viscosity of the resin.

  When the matrix is a thermally conductive composition made of a thermosetting resin, at least one selected from the group consisting of an injection molding method, a press molding method, a calendar molding method, a roll molding method, an extrusion molding method, and a casting molding method. It can shape | mold by a method and a molded object can be obtained. The molding conditions depend on the molding method and the matrix, and examples thereof include a method of imparting the curing temperature of the resin in an appropriate mold.

  In the case where the matrix is a thermally conductive composition made of an aramid resin, the aramid resin can be dissolved in a solvent, pitch-based graphitized short fibers can be mixed therein, and molded using a casting method. The solvent is not particularly limited as long as the aramid resin can be dissolved. Amide solvents such as N-dimethylacetamide and N-methylpyrrolidone can be used.

  When the matrix is a thermally conductive composition made of rubber, it can be molded by at least one method selected from the group consisting of a press molding method, a calendar molding method, and a roll molding method to obtain a molded body. The molding conditions depend on the molding technique and the matrix, and can include a method of imparting the vulcanization temperature of the rubber.

The present invention includes a molded body obtained by molding the above heat conductive composition in this way.
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 graphitized short fibers 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. Further, the radio wave shielding property of pitch-based graphitized short fibers can be used, and it can be suitably used particularly as a radio wave shielding member in the GHz band.

  The pitch-based graphitized short fibers of the present invention can be used as a paint or paste by mixing with the matrix described above and adding a solvent as necessary. Furthermore, it can be used as an electrode or the like using a paint or paste obtained from the pitch-based graphitized short fibers of the present invention.

Examples are shown below, but the present invention is not limited thereto.
In addition, each value in a present Example was calculated | required according to the following method.
(1) The average fiber diameter of pitch-based graphitized short fibers was measured from 60 averages using a scale under an optical microscope in accordance with JIS R7607 and obtained from the average value.
(2) Pitch-based graphitized short fiber volume-converted average fiber length, maximum fiber length, and ratio of fiber length of 50 μm or less were measured with 3000 fibers having a fiber length of 1 μm or more using PITA1 manufactured by Seishin Corporation. An average value of square values was obtained, and a volume-converted average fiber length was obtained from the square root of the average value. Further, the maximum fiber length was determined from the length of the longest short fiber among 3000 fibers, and the ratio of the fiber length of 50 μm or less was determined from the number of the fiber length of 50 μm or less among 3000 fibers.
(3) The crystallite size of the pitch-based graphitized short fibers was determined by the Gakushin method by measuring reflection from the (110) plane appearing in X-ray diffraction.
(4) The end faces of the pitch-based graphitized short fibers were observed with a transmission electron microscope at a magnification of 1,000,000 times and magnified on a photograph at 4 million times to confirm a graphene sheet.
(5) The surface of the pitch-based graphitized short fibers was observed with a scanning electron microscope at a magnification of 1000 times, and irregularities were confirmed.
(6) The thermal conductivity of the thermally conductive molded body was measured by LFA-447 (laser flash method) manufactured by NETZSCH.
(7) The surface property of the thermally conductive molded body was visually observed on the surface of the obtained molded body to confirm the presence or absence of bubbles.

[Example 1]
A pitch mainly composed of a condensed polycyclic hydrocarbon compound was used as a main raw material. The raw material pitch had an optical anisotropy ratio of 100% and a softening point of 283 ° C. Using a cap with a hole with a diameter of 0.2 mmφ, heated air was ejected from the slit at a linear velocity of 5500 m / min, and the pitch was melted to produce pitch-based short fibers having an average diameter of 11.2 μm. The spinning temperature at this time was 325 ° C., and the melt viscosity was 17.5 Pa · S (175 poise). The spun fibers were collected on a belt to form a mat, and then a pitch-based carbon fiber precursor web made of a pitch-based carbon fiber precursor having a basis weight of 350 g / m ^{2 by} cross wrapping.
This pitch-based carbon fiber precursor web was heated from 170 ° C. to 300 ° C. at an average heating rate of 5 ° C./min to be infusible, and further fired at 800 ° C. The pitch-based carbon fiber web was pulverized at 1000 rpm using a cutter (manufactured by Turbo Kogyo Co., Ltd.), passed through a mesh with a screen diameter of 30 μm and classified three times, and the components under the sieve were graphitized at 3000 ° C.
The average fiber diameter of the pitch-based graphitized short fibers was 8.1 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter (CV value) was 11%. The volume conversion average fiber length was 23 μm, the maximum fiber length was 90 μm, and the ratio of the fiber length of 50 μm or less was 97%. The crystal size derived from the growth direction of the hexagonal network surface was 80 nm.
It was confirmed by observation with a transmission microscope that the graphene sheet was closed on the end face of the pitch-based graphitized short fiber. Moreover, the surface was substantially smooth with one unevenness | corrugation by observation with the scanning electron microscope.

[Example 2]
The pitch-based graphitized short fiber obtained in Example 1 was added to 100 parts by weight of a two-part curable silicone resin (trade name “SE1740A & B” made by Toray Dow Silicone), and a vacuum revolving mixer (Sinky Awatori Netaro ARV-310) was mixed and added until the matrix / pitch graphitized short fibers lost their fluidity. The amount added at this time was 410 parts by weight. This mixture was cured at 130 ° C. for 2 hours to prepare a thermally conductive molded body. The thermal conductivity of the thermally conductive molded body was 3.2 W / (m · K). Further, molding defects such as bubbles were not observed on the surface of the obtained molded body.

[Comparative Example 1]
Pitch-based graphitized short fibers were obtained in the same manner as in Example 1 except that a mesh having a screen diameter of 100 μm was used during classification.
The average fiber diameter of the pitch-based graphitized short fibers was 8.1 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter (CV value) was 11%. The volume conversion average fiber length was 28 μm, the maximum fiber length was 140 μm, and the ratio of the fiber length of 50 μm or less was 85%. The crystal size derived from the growth direction of the hexagonal network surface was 80 nm.
It was confirmed by observation with a transmission microscope that the graphene sheet was closed on the end face of the pitch-based graphitized short fiber. Moreover, the surface was substantially smooth with one unevenness | corrugation by observation with the scanning electron microscope.

[Comparative Example 2]
Pitch-based graphitized short fibers were obtained in the same manner as in Example 1 except that the number of times of classification was one.
The average fiber diameter of the pitch-based graphitized short fibers was 8.1 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter (CV value) was 11%. The volume conversion average fiber length was 24 μm, the maximum fiber length was 110 μm, and the ratio of the fiber length of 50 μm or less was 81%. The crystal size derived from the growth direction of the hexagonal network surface was 80 nm.
It was confirmed by observation with a transmission microscope that the graphene sheet was closed on the end face of the pitch-based graphitized short fiber. Moreover, the surface was substantially smooth with one unevenness | corrugation by observation with the scanning electron microscope.

[Comparative Example 3]
A pitch mainly composed of a condensed polycyclic hydrocarbon compound was used as a main raw material. The raw material pitch had an optical anisotropy ratio of 100% and a softening point of 283 ° C. Using a cap with a hole with a diameter of 0.2 mmφ, heated air was ejected from the slit at a linear velocity of 5500 m / min, and the melt pitch was pulled to produce pitch-based short fibers with an average diameter of 14.5 μm. The spinning temperature at this time was 337 ° C., and the melt viscosity was 8.0 Pa · s (80 poise). The spun fibers were collected on a belt to form a mat, and a pitch-based carbon fiber precursor web made of a pitch-based carbon fiber precursor having a basis weight of 320 g / m ^{2 by} cross-wrapping.
This pitch-based carbon fiber precursor web was heated from 170 ° C. to 300 ° C. at an average heating rate of 5 ° C./min to be infusible, and further fired at 800 ° C. The pitch-based carbon fiber web was pulverized at 800 rpm using a cutter (manufactured by Turbo Kogyo), classified through a mesh having a screen diameter of 100 μm, and the components on the sieve were graphitized at 3000 ° C.
The average fiber diameter of the pitch-based graphitized short fibers was 8.8 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter (CV value) was 12%. The volume conversion average fiber length was 240 μm, the maximum fiber length was 1200 μm, and the ratio of the fiber length of 50 μm or less was 48%. The crystal size derived from the growth direction of the hexagonal network surface was 70 nm.
It was confirmed by observation with a transmission microscope that the graphene sheet was closed on the end face of the pitch-based graphitized short fiber. Moreover, the surface was substantially smooth with one unevenness | corrugation by observation with the scanning electron microscope.

[Comparative Example 4]
The pitch-based graphitized short fiber obtained in Comparative Example 1 was added to 100 parts by weight of a two-part curable silicone resin (trade name “SE1740A & B” manufactured by Toray Dow Silicone), and a vacuum revolving mixer (Sinky Awatori Netaro ARV-310) was mixed and added until the matrix / pitch graphitized short fibers lost their fluidity. The amount added at this time was 330 parts by weight. This mixture was cured at 130 ° C. for 2 hours to prepare a thermally conductive molded body. The thermal conductivity of the thermally conductive molded body was 2.2 W / (m · K). Three bubbles of about 1 mm per 5 cm × 5 cm were observed on the surface of the obtained molded body.

[Comparative Example 5]
The pitch-based graphitized short fiber obtained in Comparative Example 2 was added to 100 parts by weight of a two-part curable silicone resin (trade name “SE1740A & B” manufactured by Toray Dow Silicone), and a vacuum revolving mixer (Sinky Awatori Netaro ARV-310) was mixed and added until the matrix / pitch graphitized short fibers lost their fluidity. The amount added at this time was 310 parts by weight. This mixture was cured at 130 ° C. for 2 hours to prepare a thermally conductive molded body. The thermal conductivity of the thermally conductive molded body was 1.9 W / (m · K). Five bubbles of about 1 mm per 5 cm × 5 cm were observed on the surface of the obtained molded body.

[Comparative Example 6]
The pitch-based graphitized short fiber obtained in Comparative Example 3 was added to 100 parts by weight of a two-part curable silicone resin (trade name “SE1740A & B” manufactured by Toray Dow Silicone), and a vacuum revolving mixer (Sinky Awatori Netaro ARV-310) was mixed and added until the matrix / pitch graphitized short fibers lost their fluidity. The amount added at this time was 100 parts by weight. This mixture was cured at 130 ° C. for 2 hours to prepare a thermally conductive molded body. The thermal conductivity of the thermally conductive molded body was 2.0 W / (m · K). Eight bubbles of about 3 mm per 5 cm × 5 cm were observed on the surface of the obtained molded body.

  The pitch-based graphitized short fiber of the present invention improves the filling property of the pitch-based graphitized short fiber by controlling the fiber length of the pitch-based graphitized short fiber having excellent thermal conductivity, and has high heat conductivity in the molded body. And imparting excellent surface properties. As a result, it can be widely used in electronic devices that require high heat dissipation characteristics and design properties, and thermal management is ensured.

Claims (7)

  The average fiber diameter is 5 to 15 μm, the volume-converted average fiber length is 20 to 30 μm, the maximum fiber length is 100 μm or less, and the proportion of short fibers having a fiber length of 50 μm or less is 95% or more. Pitch-based graphitized short fiber.   The pitch-based graphitized short fiber has a fiber diameter dispersion percentage (CV value) of 3 to 15% with respect to the average fiber diameter, a crystallite size derived from the growth direction of the hexagonal mesh surface is 30 nm or more, and a transmission type The pitch-based graphitized short fibers according to claim 1, wherein the graphene sheet is closed in the filler end face observation with an electron microscope, and the observation surface with a scanning electron microscope is substantially flat.   From the pitch-based graphitized short fibers according to any one of claims 1 to 2, and at least one matrix component selected from the group consisting of thermoplastic resins, thermosetting resins, aramid resins, and rubbers. A heat conductive composition containing 3 to 500 parts by weight of pitch-based graphitized short fibers with respect to 100 parts by weight of the matrix component.   The thermoplastic resin is polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2, 6-naphthalate, aliphatic polyamide, polypropylene, polyethylene, polyetherketone, polyphenylene sulfide, acrylic and acrylonitrile-butadiene-styrene copolymer resin. The thermally conductive composition according to claim 3, which is at least one resin selected from the group consisting of:   The thermosetting resin is an epoxy resin, acrylic resin, urethane resin, silicone resin, phenol resin, thermosetting modified PPE resin, thermosetting PPE, polyimide resin and copolymer thereof, aromatic polyamideimide resin and The thermally conductive composition according to claim 3, which is at least one resin selected from the group consisting of copolymers.   The rubber is at least one selected from the group consisting of natural rubber, acrylic rubber, acrylonitrile butadiene rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, epichlorohydrin rubber, chloroprene rubber, silicone rubber, styrene butadiene rubber, butadiene rubber, and butyl rubber. The thermally conductive composition according to claim 3.   The heat conductive molded object formed by shape | molding the heat conductive composition of any one of Claims 3-6.