JP2011089216A - Insulated pitch-based graphitized short fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally conductive material which has insulating properties and excellent thermal conductivity at the same time. <P>SOLUTION: Insulated pitch-based graphitized short fibers have a silicon carbide layer on its surface, and have a crystallized size in the growing direction of a carbon hexagonal plane of 60 nm or more. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an insulated pitch-based graphitized short fiber having silicon carbide on the surface, and is suitably used for a heat dissipation member of an electronic component.

  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 contains, 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, carbon fibers exhibit electrical conductivity. Therefore, a composition in which carbon fibers are combined with a matrix exhibits conductivity. However, the CPU and electronic circuit described above are often attached to an insulating substrate. Therefore, it is difficult to use a composition using carbon fiber for an electronic substrate.

  Patent Documents 1 and 2 propose a method of coating an insulating layer on a thermally conductive composition. However, it is difficult to cope with a complicated shape by such a method. Patent Document 3 discloses an insulating layer made of silicon oxide, Patent Document 4 shows an insulating layer made of silica or silicon carbide, and Patent Document 5 shows an insulating layer made of silicon carbide. A method of coating has been proposed. The technique of integrating silicon carbide and carbon fiber is an effective means for obtaining a strong insulating layer. In Patent Documents 3 and 4, the sol-gel method is used as a means for coating with silicon carbide, but the sol-gel method including solution treatment, drying, filtration, and heat treatment is difficult to uniformly coat all fillers, It is not preferable for an insulating process that requires a uniform coating of all fillers. In Patent Document 5, heat treatment using silicon chloride gas after electrolytic treatment is used, but this technique is for the purpose of improving oxidation resistance, and the structure of the carbon fiber is disturbed due to the electrolytic treatment. It is expected that the graphitization degree is lowered and the thermal conductivity is lowered. Moreover, in this technique, the surface treatment of carbon fiber is performed twice or more, and it cannot be said that it is a manufacturing process suitable for mass production.

JP 2008-208316 A JP 2008-205453 A JP 2007-128986 A JP 2007-107151 A JP-A-6-65859

  An object of the present invention is to provide an insulated pitch-based graphitized short fiber having excellent network forming ability in a matrix and having both high thermal conductivity and insulating properties. Another object of the present invention is a thermally conductive composition comprising an insulated pitch-based graphitized short fiber and at least one matrix component selected from the group consisting of a thermoplastic resin, a thermosetting resin, and rubber, and The object is to provide a molded body from that.

As a result of intensive investigations to obtain a heat conductive agent exhibiting high thermal conductivity and insulating properties, the inventors of the present invention have used pitch-based graphitized short fibers having excellent thermal conductivity as a core, and pitch-based graphite. The present inventors have found that it is possible to obtain a thermal conductive agent having both high thermal conductivity and insulating property by coating the surface of the short fiber with a silicon carbide layer, and have reached the present invention.
The present invention is an insulated pitch-based graphitized short fiber having a silicon carbide layer on the surface and a crystallite size derived from the growth direction of the carbon hexagonal network surface of 60 nm or more.

  Insulated pitch-based graphitized short fibers of the present invention have high thermal conductivity and insulating properties by changing the surface of pitch-based graphitized short fibers excellent in thermal conductivity to silicon carbide treatment, which is an insulating material. It is possible to obtain an insulated pitch-based graphitized short fiber.

Hereinafter, embodiments of the present invention will be sequentially described.
The insulated pitch-based graphitized short fiber of the present invention is a pitch-based graphitized short fiber having a silicon carbide layer on the surface. For the purpose of insulating the graphitized short fibers, it is preferable that the surface of the graphitized short fibers is almost completely covered with a silicon carbide layer.

The specific resistance of pitch-based graphitized short fibers is usually on the order of 10 ⁻⁴ Ω · cm and exhibits conductivity. Also, when a molded product is mixed with a resin, the molded product exhibits conductivity. Therefore, it is difficult to use it as a heat countermeasure for a part where electrical conductivity is not desired, such as an electronic board sealant. In contrast, the specific resistance of inorganic compounds such as metal oxides, metal nitrides, and metal halides is on the order of 10 ¹⁴ Ω · cm, indicating high insulation. Therefore, the pitch-based graphitized short fibers can be insulated by converting the surface of each pitch-based graphitized short fiber into these inorganic compounds. However, when coating with an inorganic compound, the insulating inorganic compound may be peeled off from the pitch-based graphitized short fiber when the pitch-type graphitized short fiber insulated by coating and the matrix are mixed to form a molded body. Yes, it is not always possible to maintain the insulation of the molded body. On the other hand, when the surface of the pitch-based graphitized short fibers is changed to an insulating material such as an inorganic compound, the insulating layer does not peel even when kneaded with the resin, and the insulating property can be maintained.

  Most inorganic compounds except carbon compounds are inferior in thermal conductivity to pitch-based graphitized short fibers. Therefore, when insulating the pitch-based graphitized short fibers with an inorganic compound, it is necessary to coat with an inorganic compound having as high a thermal conductivity as possible in order to suppress a decrease in thermal conductivity. Further, when insulating the pitch-based graphitized short fibers with an inorganic compound, it is necessary to form an insulating surface with a small amount of the inorganic compound. Therefore, it is preferable to use a material that can easily control reaction conditions such as temperature when forming an insulating surface.

  As a substance capable of forming an insulating surface excellent in thermal conductivity by reaction with these requirements and pitch-based graphitized short fibers, siliconization of pitch-based graphitized short fibers by silicon monoxide gas treatment can be mentioned.

  There are no particular limitations on the conditions for silicon carbide, but the reaction proceeds more as the temperature increases. Silicon monoxide gas is obtained by sublimation by heating silicon monoxide, sublimation by heating silicon monoxide obtained from the reaction between silicon dioxide and pitch-based graphitized short fibers, or by reaction between silicon and silicon dioxide. Although it is obtained from sublimation by heating of the obtained silicon monoxide, the vapor pressure by sublimation is usually higher as the temperature is higher, so that the reaction proceeds more by increasing the treatment temperature. Although there is no limitation in particular in the temperature of heat processing, Preferably it is 1300-2500 degreeC. Although there is no particular limitation on the silicon carbide conversion method, pitch-based graphitized short fibers are placed in a pressure vessel in an electric furnace, and silicon monoxide gas generated elsewhere in the furnace is introduced, or pitch-based graphite This can be achieved by mixing and heating silicon monoxide, silicon, or a mixture of silicon and silicon dioxide in the short fiber.

  The carbon portion of the insulated pitch-based graphitized short fiber in the present invention is composed of graphite crystals, and the crystallite size derived from the growth direction of the hexagonal network surface of the graphite crystals is 60 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. There is no particular limitation on the method for controlling the crystallite size derived from the growth direction of the hexagonal mesh surface of the graphite crystal. Controlling the crystallite size derived from the growth direction of the surface and not disturbing the orientation of the graphite crystal by treatment.

  The insulated pitch-based graphitized short fibers of the present invention preferably have a silicon content of 1 to 20 parts by weight with respect to 100 parts by weight of the pitch-based graphitized short fibers. If the silicon content is 1 part by weight or less, the entire surface of the pitch-based graphitized short fibers cannot be made of silicon carbide, and insulation cannot be expected. On the other hand, if the silicon content is 20 parts by weight or more, the silicon carbide layer is too much, and it tends to be difficult to obtain high thermal conductivity when forming a molded product. Preferably it is 3-15 weight part.

  The insulated pitch-based graphitized short fibers in the present invention preferably have an average fiber diameter of 2 to 20 μm observed with an optical microscope. When the average fiber diameter is less than 2 μm, the number of the short fibers increases when compounded with the resin, so that the viscosity of the resin / short fiber mixture becomes high and molding may be difficult. Conversely, if the average fiber diameter exceeds 20 μm, the number of short fibers decreases when combined with the resin, so that the short fibers are less likely to contact each other, making it difficult to exhibit effective heat conduction when used as a composite material. May be. A preferable range of the average fiber diameter is 5 to 15 μm, and more preferably 7 to 13 μm. The method for controlling the average fiber diameter is not particularly limited, but it is preferable to control the average fiber diameter of the pitch-based graphitized short fibers used as a raw material for the insulated pitch-based graphitized short fibers.

  In the insulated pitch-based graphitized short fibers in the present invention, the percentage (CV value) with respect to the average fiber diameter of the fiber diameter dispersion in the insulated 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 is deteriorated when composited with a resin, and it may be difficult to obtain a composite material having uniform performance. The CV value is preferably 5 to 13%. For the CV value, use a gas to control the CV value of the pitch-based graphitized short fiber that is the raw material of the insulated pitch-based graphitized short fiber and to make the surface treatment amount uniform during siliconization. There is.

  There are generally two types of pitch-based graphitized short fibers: milled fibers having an average fiber length of less than 1 mm and cut fibers having an average fiber length of 1 mm or more and less than 10 mm. Since the appearance of the milled fiber is powdery, it is excellent in dispersibility, and the appearance of the cut fiber is close to the fiber shape.

  The insulated pitch-based graphitized short fiber in the present invention corresponds to a milled fiber, and the average fiber length is preferably 20 to 500 μm. Here, the average fiber length is a number average fiber length, using a length measuring device under an optical microscope, measuring a predetermined number in a plurality of fields of view, if the average fiber length that can be determined from the average value is less than 20 μm, It becomes difficult for the short fibers to come into contact with each other, and it is difficult to expect effective heat conduction. On the other hand, when the average fiber length is greater than 500 μm, the viscosity of the matrix / short fiber mixture increases when mixed with the resin, and the moldability tends to decrease. More preferably, it is the range of 20-300 micrometers. There is no particular limitation on the method for obtaining such insulated pitch-based graphitized short fibers, but it can be achieved by controlling the average fiber industry of pitch-based graphitized short fibers that are the raw materials for insulated pitch-based graphitized short fibers. .

  Insulated pitch-based graphitized short fibers in the present invention preferably have a substantially flat side observation surface with a scanning electron microscope. Here, “substantially flat” means that the insulated 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 insulated pitch-based graphitized short fibers, the viscosity increases as the surface area increases during kneading with the matrix resin, and the moldability deteriorates. 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. As a method for obtaining such pitch-based graphitized short fibers, the surface of pitch-based graphitized short fibers as a raw material is substantially flat, and the surface treatment amount becomes uniform during silicon carbide treatment. Gas may be used.

[Pitch-based graphitized short fiber]
The pitch-based graphitized short fiber in the present invention is specified from the viewpoint of having a preferable shape and surface property for obtaining the above-mentioned insulated pitch-based graphitized short fiber, and sufficient thermal conductivity as a thermally conductive filler. It is preferable to use the pitch-based graphitized short fibers.

  The pitch-based graphitized short fibers in the present invention preferably have an average fiber diameter of 2 to 20 μm observed with an optical microscope. This is because the preferred average fiber diameter of the insulated pitch-based graphitized short fibers is 2 to 20 μm, and in order to achieve this, the average fiber diameter of the pitch-based graphitized short fibers used as the raw material is preferably 2 to 20 μm.

  In the pitch-based graphitized short fibers in 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 preferable CV value of the insulated pitch-based graphitized short fiber is 3 to 15%, and in order to achieve this, the CV value of the pitch-based graphitized short fiber used as the raw material is preferably 3 to 15%. . The CV value of the pitch-based graphitized short fiber adjusts 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. This can be realized by adjusting to 0 to 25.0 Pa · S.

  The pitch-based graphitized short fibers in the present invention correspond to milled fibers, and the average fiber length is preferably 20 to 500 μm. The preferable average fiber length of the insulating pitch-based graphitized short fibers is 20 to 500 μm, and in order to achieve this, the average fiber length of the pitch-based graphitized short fibers as a raw material is preferably 20 to 500 μm. There is no particular limitation on the method for obtaining such pitch-based graphitized short fibers, but when milling with a cutter, etc., the rotation speed of the cutter, the rotation speed of the ball mill, the air velocity of the jet mill, the collision of the crusher The average fiber length can be controlled by adjusting the number of times and the residence time in the milling apparatus. Moreover, it can adjust by performing classification operation, such as a sieve, from pitch-type carbon short fiber after milling, and removing pitch-type carbon short fiber of short fiber length or long fiber length.

  The pitch-based graphitized short fibers in the present invention are composed of graphite crystals, and the crystallite size derived from the growth direction of the hexagonal network surface is 60 nm or more. The crystallite size of the insulated pitch-based graphitized short fiber derived from the growth direction of the hexagonal network surface of the graphite crystal is 60 nm or more. To achieve this, the graphite of the pitch-based graphitized short fiber that is the raw material is used. The crystallite size derived from the growth direction of the hexagonal network surface of the crystal is 60 nm or more.

  In the pitch-based graphitized short fiber in 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, no active sites are generated in the pitch-based graphitized short fibers, and when the silicon monoxide gas treatment is performed, the activity of the entire surface of the pitch-based graphitized short fibers can be suppressed, and the silicon carbide content can be easily controlled. Tend to be. Moreover, adsorption | suction of water etc. can also be reduced, for example, also in kneading | mixing with resin accompanying hydrolysis like polyester, the remarkable heat-and-heat durability performance improvement can be brought about. It is preferable that the end face of the graphene sheet is 80% closed within the field of view by a transmission electron microscope magnified 500,000 to 4,000,000 times. If it 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 the pulverization treatment is performed before graphitization, 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 in 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. The surface of the insulated pitch-based graphitized short fiber is preferably substantially flat, and in order to achieve this, the surface of the pitch-based graphitized short fiber is also preferably substantially flat. A technique for obtaining such pitch-based graphitized short fibers can be preferably obtained by performing graphitization after milling.

[Method for producing pitch-based graphitized short fibers]
A preferred method for producing pitch-based graphitized short fibers used in the present invention will be described below.
Examples of the raw material for pitch-based graphitized short fibers used in the present invention include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, condensed heterocyclic compounds such as petroleum-based pitch and coal-based pitch, and the like. Among these, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferable, and mesophase pitch is particularly preferable. 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. or higher and 340 ° C. or lower. 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 low temperature at least lower than the softening point. 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. or higher and 320 ° C. or lower, more preferably 260 ° C. or higher and 310 ° C. or lower. 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. or higher and 340 ° C. or lower.

  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 some cases, a classification step may be added after the pulverization.

Hereinafter, preferred embodiments of each step of producing pitch-based graphitized short fibers used for insulating pitch-based graphitized short fibers 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 for the method for producing pitch-based graphitized short fibers in 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 hole may be 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 pitch-based graphitized short fiber used for the insulated pitch-based graphitized short fiber of the present invention preferably has an average fiber diameter (D1) of 2 to 20 μm or less. This control can be adjusted by changing the nozzle hole diameter, changing the discharge amount of the raw material pitch from the nozzle, or changing the draft ratio. The draft ratio can be changed by blowing a gas having a linear velocity of 100 to 20000 m / minute heated to 100 to 400 ° C. in the vicinity of the thinning 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 spun 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 by a known method 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. In some cases, classification processing is performed. The treatment method is selected according to the desired fiber length, but a guillotine type, one-axis, two-axis, and multi-axis rotary type cutters are preferably used for cutting, and an impact action is used for crushing and crushing. Hammer type, pin type, ball type, bead type and rod type, high speed rotary type using collision between particles, roll type using compression / tearing action, cone type and screw type etc. Preferably used. In order to obtain a desired fiber length, cutting, crushing and pulverizing may be performed by a plurality of machines. The treatment atmosphere may be either wet or dry. For the classification treatment, a classification device such as a vibration sieve type, a centrifugal separation type, an inertial force type, or a filtration type is preferably used. The desired fiber length can be obtained not only by selecting a model, but also by controlling the number of revolutions of the rotor / rotating blade, supply amount, clearance between blades, residence time in the system, and the like. In the case of using classification treatment, the desired fiber length can also be obtained by adjusting the sieve mesh pore diameter and the like.

  The pitch-based carbon short fibers prepared by using the above-described cutting, crushing / pulverizing treatment, and, in some cases, classification treatment, are heated to 2000-3500 ° C. and graphitized to obtain the 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.

[Thermal conductive composition]
A thermally conductive composition is obtained by combining the insulating pitch-based graphitized short fibers of the present invention and a matrix component. The present invention includes this thermally conductive composition. Molding materials such as compounds, sheets, greases, adhesives and the like and heat conductive molded articles can be obtained from the heat conductive composition of the present invention.

  At this time, the insulated pitch-based graphitized short fiber is added in an amount of 3 to 300 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 300 parts by weight of insulating 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. In order to express desired physical properties in the composite molded body, a thermoplastic resin and a thermosetting resin can be appropriately mixed and used.

  Polyolefins and their copolymers (polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, ethylene as thermoplastic resins that can be used in the matrix -Ethylene-α-olefin copolymer such as propylene copolymer), polymethacrylic acid and its copolymer (polymethacrylic acid ester such as polymethyl methacrylate), polyacrylic acid and its copolymer, polyacetal And copolymers thereof, fluororesins and copolymers thereof (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyesters and copolymers thereof (polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6 naphtha) Liquid crystal polymers), polystyrenes and copolymers thereof (styrene-acrylonitrile copolymers, ABS resins, etc.), polyacrylonitriles and copolymers thereof, polyphenylene ethers (PPE) and copolymers thereof ( Modified PPE resins, etc.), aliphatic polyamides and copolymers thereof, polycarbonates and copolymers thereof, polyphenylene sulfides and copolymers thereof, polysulfones and copolymers thereof, polyether sulfones and their Copolymers, polyether nitriles and copolymers thereof, polyether ketones and copolymers thereof, polyether ether ketones and copolymers thereof, polyketones and copolymers thereof, elastomers, liquid crystalline polymers, polyimides And copolymers thereof. One of these may be used alone, or two or more may be used in appropriate combination.

  Examples of the thermosetting resins include epoxy resins, acrylic resins, urethane resins, silicone resins, phenol resins, thermosetting polyimides, thermosetting modified PPEs, and thermosetting PPEs. One kind may be used alone, or two or more kinds 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, aromatic polyamideimides and copolymers thereof.

  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 composition of the present invention is prepared by mixing insulating pitch-based graphitized short fibers and a matrix, and at the time of mixing, a kneader, various mixers, a blender, a roll, an extruder, a milling machine, a self-revolving type A mixing device such as a stirrer or a kneading device is preferably used.

  In order to further increase the thermal conductivity of the heat conductive composition of the present invention, fillers other than silicon carbide-coated 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, oxynitride Examples thereof include metal oxynitrides such as aluminum, metal carbides such as silicon carbide, and carbon materials such as 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, when a conductive filler is added, maintenance of insulation cannot be achieved, so care must be taken.

  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. A fibrous filler such as gypsum fiber may be appropriately added depending on the required function. 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 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 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.

  When 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. Here, the solvent is not particularly limited as long as the aramid resin can be dissolved, but specifically, amide solvents such as N, 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.

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 diameters of the insulating pitch-based graphitized short fibers and the pitch-based graphitized short fibers were measured from the average value by measuring 60 fibers using a scale under an optical microscope according to JIS R7607.
(2) The average fiber length of the insulating pitch-based graphitized short fibers and the pitch-based graphitized short fibers was measured from 1500 using PITA1 manufactured by Seishin Enterprise, and obtained from the average value.
(3) The surfaces of the insulating pitch-based graphitized short fibers and the pitch-based graphitized short fibers were observed with a scanning electron microscope at a magnification of 1000 times, and irregularities were confirmed.
(4) The silicon content of the insulating pitch-based graphitized short fiber was calculated from the weight difference before and after silicon carbide.
(5) Confirmation of silicon carbide layer The surface of insulated pitch-based graphitized short fibers was subjected to infrared spectroscopic analysis using Magna 750 manufactured by Thermo Nicole, and a peak near 700 cm ⁻¹ derived from Si—C bonds was observed. It was confirmed by detecting.
(6) The specific resistance of the insulated pitch-based graphitized short fiber was determined using MCP-PD51 manufactured by Mitsubishi Chemical Analytech.
(7) The crystallite size of the insulated pitch-based graphitized short fibers and pitch-based graphitized short fibers was determined by the Gakushin method by measuring the reflection from the (110) plane appearing in X-ray diffraction.
(8) The end face of the pitch-based graphitized short fiber was observed with a transmission electron microscope at a magnification of 1,000,000 times, magnified on a photograph at 4 million times, and a graphene sheet was confirmed.
(9) The specific resistance of the thermally conductive composition was determined using Hiresta UP manufactured by Mitsubishi Chemical Analytech.
(10) The thermal conductivity of the thermally conductive composition was determined using QTM-500 manufactured by Kyoto Electronics Industry.

[Reference 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. This pitch-based carbon fiber web was pulverized at 900 rpm using a cutter (manufactured by Turbo Kogyo) and 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 number average fiber length was 100 μm, and 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.
The specific resistance of the pitch-based graphitized short fibers was 2.5 × 10 ⁻⁴ Ω · cm.

[Example 1]
100 parts by weight of pitch-based graphitized short fibers prepared in Reference Example 1 were mixed with 300 parts by weight of silicon (manufactured by Wako Pure Chemical Industries) and 300 parts by weight of silicon dioxide (manufactured by Wako Pure Chemical Industries), and placed in a graphite crucible. This was treated in an Atchison furnace at 1500 ° C. for 3 hours in an argon atmosphere. The obtained mixture was heated and filtered in an aqueous sodium hydroxide solution to obtain insulated pitch-based graphitized short fibers. The presence of the surface silicon carbide layer was confirmed by infrared spectroscopy. As a result of observation with a scanning electron microscope, there was one unevenness and the surface was substantially smooth.

The silicon content was 10 parts by weight with respect to 100 parts by weight of pitch-based graphitized short fibers. The specific resistance of the insulated pitch-based graphitized short fiber was 5.0 × 10 ⁸ Ω · cm.
The average fiber diameter of the insulated pitch-based graphitized short fibers was 8.2 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter (CV value) was 12%. The number average fiber length was 100 μm, and the crystal size derived from the growth direction of the hexagonal network surface was 80 nm.

[Example 2]
100 parts by weight of pitch-based graphitized short fibers prepared in Reference Example 1 were mixed with 500 parts by weight of silicon monoxide (manufactured by Osaka Titanium Technology), and placed in a graphite crucible. This was treated in an Atchison furnace at 1500 ° C. for 3 hours in an argon atmosphere. The obtained mixture was heated and filtered in an aqueous sodium hydroxide solution to obtain insulated pitch-based graphitized short fibers. The presence of the surface silicon carbide layer was confirmed by infrared spectroscopy. As a result of observation with a scanning electron microscope, there was one unevenness and the surface was substantially smooth.

The silicon content was 13 parts by weight with respect to 100 parts by weight of pitch-based graphitized short fibers. The specific resistance of the insulated pitch-based graphitized short fiber was 8.0 × 10 ⁸ Ω · cm.
The average fiber diameter of the insulated pitch-based graphitized short fibers was 8.2 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter (CV value) was 12%. The number average fiber length was 100 μm, and the crystal size derived from the growth direction of the hexagonal network surface was 80 nm.

[Example 3]
45 parts by weight of the insulated pitch-based graphitized short fibers obtained in Example 1 and 100 parts by weight of a silicone resin (SE1740 manufactured by Toray Dow Corning) were mixed with a vacuum self-revolving mixer (Shinky Awatori Kentaro ARV-310). ) For 3 minutes to obtain a composite slurry. The slurry was pressed with a vacuum press (manufactured by Kitagawa Seiki) to obtain a plate-like composite molded body having a thickness of 0.5 mm, and cured at 130 ° C. for 2 hours to prepare a heat conductive composition. The specific resistance of the heat conductive composition was 3.5 × 10 ⁹ Ω · cm. The heat conductivity of the heat conductive composition was 6.2 W / (m · K).

[Example 4]
45 parts by weight of insulated pitch-based graphitized short fibers obtained in Example 2 and 100 parts by weight of silicone resin (manufactured by Dow Corning Toray, SE1740) were mixed with a vacuum self-revolving mixer (Shinky Awatori Kentaro ARV-310) ) For 3 minutes to obtain a composite slurry. The slurry was pressed with a vacuum press (manufactured by Kitagawa Seiki) to obtain a plate-like composite molded body having a thickness of 0.5 mm, and cured at 130 ° C. for 2 hours to prepare a heat conductive composition. The specific resistance of the heat conductive composition was 4.8 × 10 ⁹ Ω · cm. The heat conductivity of the heat conductive composition was 6.1 W / (m · K).

[Comparative Example 1]
45 parts by weight of the pitch-based graphitized short fibers obtained in Reference Example 1 and 100 parts by weight of a silicone resin (SE1740 manufactured by Toray Dow Corning Co., Ltd.) were subjected to a vacuum revolving mixer (Shinky Awatori Nertaro ARV-310). And mixed for 3 minutes to form a composite slurry. The slurry was pressed with a vacuum press (manufactured by Kitagawa Seiki) to obtain a plate-like composite molded body having a thickness of 0.5 mm, and cured at 130 ° C. for 2 hours to prepare a heat conductive composition. The specific resistance of the heat conductive composition was 5.0 × 10 ² Ω · cm. The heat conductivity of the heat conductive composition was 5.4 W / (m · K).

  The insulated pitch-based graphitized short fiber of the present invention can provide insulation while exhibiting high thermal conductivity by making the surface of the pitch-based graphitized short fiber excellent in thermal conductivity silicon carbide. I'm coughing. As a result, it can be widely used in electronic devices that require high heat dissipation characteristics, and thermal management is ensured.

Claims (10)

  An insulated pitch-based graphitized short fiber having a silicon carbide layer on the surface of a pitch-based graphitized short fiber and having a crystallite size derived from the growth direction of the carbon hexagonal network surface of 60 nm or more.   The insulated pitch-based graphitized short fiber according to claim 1, wherein 1 to 20 parts by weight of silicon is contained with respect to 100 parts by weight of the pitch-based graphitized short fiber.   The insulated pitch-based graphitized fiber has an average fiber diameter of 2 to 20 μm, a fiber diameter dispersion percentage (CV value) with respect to the average fiber diameter of 3 to 15%, and a number average fiber length of 20 to 500 μm. 3. The insulated pitch-based graphitized short fiber according to claim 1, which has a substantially flat observation surface with a scanning electron microscope.   The pitch-based graphitized short fibers are made from mesophase pitch, the average fiber diameter is 2 to 20 μm, the percentage of fiber diameter dispersion (CV value) with respect to the average fiber diameter is 3 to 15, and the number average fiber length is 4. The method according to claim 1, wherein the graphene sheet is 20 to 500 μm, the graphene sheet is closed in the filler end face observation with a transmission electron microscope, and the observation surface with a scanning electron microscope is substantially flat. Insulated pitch-based graphitized short fiber.   5. The insulated pitch-based graphitized short fiber according to claim 1, wherein the pitch-based graphitized short fiber is treated with silicon monoxide gas under a condition of 1300 to 2500 ° C. 6. Manufacturing method.   The at least 1 sort (s) of matrix selected from the group which consists of the insulated pitch type | system | group graphitized short fiber of any one of Claims 1-4, a thermoplastic resin, a thermosetting resin, an aramid resin, and rubber | gum. A thermally conductive composition comprising 3 to 300 parts by weight of pitch-based graphitized short fibers with respect to 100 parts by weight of a matrix component.   The thermoplastic resins are polycarbonates, polyethylene terephthalates, polybutylene terephthalates, polyethylene-2, 6-naphthalates, aliphatic polyamides, polypropylenes, polyethylenes, polyether ketones, polyphenylene sulfides, and acrylonitrile- The thermally conductive composition according to claim 6, which is at least one resin selected from the group consisting of butadiene-styrene copolymer resins and polyimides.   The thermosetting resin is at least one selected from the group consisting of epoxy resins, acrylic resins, urethane resins, silicone resins, phenol resins, thermosetting polyimides, thermosetting modified PPEs, and thermosetting PPEs. The thermally conductive composition according to claim 6, which is a resin.   The rubber component is natural rubber (NR), acrylic rubber, acrylonitrile butadiene rubber (NBR rubber), isoprene rubber (IR), urethane rubber, ethylene propylene rubber (EPM), epichlorohydrin rubber, chloroprene rubber (CR), silicone rubber, The thermally conductive composition according to claim 6, which is at least one selected from the group consisting of styrene butadiene rubber (SBR), butadiene rubber (BR), and butyl rubber.   The heat conductive molded object formed by shape | molding the heat conductive composition in any one of Claims 7-9.