JP2009215403A - Sheet-like heat-conductive molded body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-conductive molded body having excellent heat conductivity. <P>SOLUTION: In the sheet-like heat-conductive molded body containing 90 to 100 wt.% composition composed of a resin, pitch type graphite short fibers having an aspect ratio of 3 or more and an inorganic compound having an aspect ratio of 3 or below, when such a content of the pitch type graphite short fibers that heat conductivity of the sheet is made double or more if the content is increased by 5 wt.% is defined as Wf<SB>A</SB>wt.% in a relation between the heat conductivity of a sheet composed of the resin and pitch type graphite short fibers having an aspect ratio of 3 or more and a content of the pitch type graphite short fibers and such a content of the inorganic compound that the heat conductivity is made double or more if the content is increased by 5 wt.% is defined as Wf<SB>B</SB>wt.% in a relation between the heat conductivity of a sheet composed of the resin and the inorganic compound having the aspect ratio of 3 or below and a content of the inorganic compound in the sheet, a content (Wf<SB>C</SB>wt.%) of the pitch type graphite short fibers and a content (Wf<SB>D</SB>wt.%) of the inorganic compound in the composition satisfy a relation of Wf<SB>C</SB>/Wf<SB>A</SB>+Wf<SB>D</SB>/Wf<SB>B</SB>>1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sheet-like thermally conductive molded article containing pitch-based graphitized short fibers. More specifically, it is a thermally conductive molded body in which the ratio of the content of pitch-based graphitized short fibers and inorganic filler in the thermally conductive molded body is controlled, and is suitably used for heat dissipation members and heat exchangers of electronic components. .

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

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

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

  Next, the characteristics of the molded body used for thermal management are considered. In general, since a molded body using carbon fibers has an aspect ratio, it tends to have a high viscosity when mixed with a resin, and it is often difficult to perform high filling. For this reason, it is often the case that a molded body is obtained by combining with a compound having a lower aspect ratio, particularly a thermally conductive inorganic compound, than when using carbon fiber alone. However, most of the inorganic compounds have a lower thermal conductivity than carbon fibers except for some of them, and it is difficult to efficiently increase the thermal conductivity compared to carbon fibers. Patent Documents 1 and 2 report a molded body in which carbon fiber and an inorganic compound are combined. However, the composition is not necessarily appropriate, and it is difficult to say that the performance is sufficiently extracted.

JP-A-8-283456 JP 2001-156227 A

As described above, development of thermal management applications is progressing from the viewpoint of high thermal conductivity of carbon fibers, particularly pitch-based carbon fibers. However, from the viewpoint of thermal management, it is required that the thermal conductivity as a molded body is further increased.
Therefore, there has been a strong demand for a thermally conductive molded body having high thermal conductivity due to high filling of the thermally conductive filler.

  In view of improving the thermal conductivity of the sheet-like molded body, the present inventors have focused attention on the filling state of the carbon fiber, and the pitch-based graphitized short fiber having an aspect ratio of 3 or more and an aspect ratio of 3 When the content and mixing ratio of the following compounds are within a certain range, it is found that the thermal conductivity of the thermally conductive molded body is remarkably improved, and a thermally conductive molded body having excellent thermal conductivity is obtained. I reached that.

The present invention is a sheet containing 90 to 100% by weight of a composition comprising a resin, pitch-based graphitized short fibers having an aspect ratio of 3 or more, and an inorganic compound having an aspect ratio of 3 or less, and the aspect ratio of the resin is In the relationship between the thermal conductivity of a sheet comprising three or more pitch-based graphitized short fibers and the content of pitch-based graphitized short fibers in the sheet, the thermal conductivity is increased when the content is increased by 5% by weight. The content of the pitch-based graphitized short fiber that is twice or more is Wf _A wt%, and the thermal conductivity of the sheet composed of a resin and an inorganic compound having an aspect ratio of 3 or less and the content of the inorganic compound in the sheet When the content of the inorganic compound that increases the thermal conductivity by 2 times or more when the content is increased by 5 wt% is Wf _B wt%, the content of pitch-based graphitized short fibers (Wf _C % By weight) and the inorganic compound It is a sheet-like thermally conductive molded body containing pitch-based graphitized short fibers and an inorganic compound so that the content (Wf _D wt%) has a relationship of Wf _C / Wf _A + Wf _D / Wf _B > 1 .

By containing the pitch-based graphitized short fibers and the inorganic compound at a ratio such that Wf _C / Wf _A + Wf _D / Wf _B > 1 is satisfied, the resin is composed of the resin and the inorganic compound. It becomes possible to provide a sheet-like thermally conductive molded body having a thermal conductivity of 3 times or more with respect to the thermal conductivity of the sheet whose amount is (Wf _C + Wf _D ) wt%.

  The sheet-like thermally conductive molded article of the present invention has high thermal conductivity by controlling the content and mixing ratio of pitch-based graphitized short fibers having an aspect ratio of 3 or more and inorganic compounds having an aspect ratio of 3 or less. It can be expressed in the molded body.

Hereinafter, embodiments of the present invention will be sequentially described.
The sheet-like thermally conductive molded body of the present invention is a sheet containing 90 to 100% by weight of a composition comprising a resin, pitch-based graphitized short fibers having an aspect ratio of 3 or more, and an inorganic compound having an aspect ratio of 3 or less. In the relationship between the thermal conductivity of the sheet comprising the resin and the pitch-based graphitized short fibers having an aspect ratio of 3 or more and the content of the pitch-based graphitized short fibers in the sheet, the content is 5% by weight. The thermal conductivity and sheet of a sheet comprising a resin and an inorganic compound having an aspect ratio of 3 or less, wherein the content of the pitch-based graphitized short fibers whose thermal conductivity increases by a factor of 2 or more when increased is Wf _A wt% In relation to the content with the inorganic compound in the composition, when the content of the inorganic compound that increases the thermal conductivity by 2 times or more when the content is increased by 5 wt% is Wf _B wt%, the pitch graphitization Short fiber content (Wf _C %) And the content of the inorganic compound (Wf _D wt%), the sheet containing pitch-based graphitized short fibers and the inorganic compound so as to have a relationship of Wf _C / Wf _A + Wf _D / Wf _B > 1 It is a heat conductive molded article.

By containing the pitch-based graphitized short fibers and the inorganic compound at a ratio such that Wf _C / Wf _A + Wf _D / Wf _B > 1 is satisfied, the resin is composed of the resin and the inorganic compound. It becomes possible to provide a sheet-like thermally conductive molded body having a thermal conductivity of 3 times or more with respect to the thermal conductivity of the sheet whose amount is (Wf _C + Wf _D ) wt%.

  The sheet-like thermally conductive molded body of the present invention can have a thermal conductivity of 5 W / (m · K) or more, more preferably 10 W / (m · K) or more in a state of being formed into a flat plate shape. It is.

The value of Wf _C / Wf _A + Wf _D / Wf _B is preferably 1.05 or more, more preferably 1.1 or more. In particular, the value of Wf _C / Wf _A is preferably 0.25 or more, more preferably 0.3 or more, depending on the use. The value of Wf _D / Wf _B depends on the use, but is preferably 0.75 or more, more preferably 0.8 or more.

  When the content of pitch-based graphitized short fibers or inorganic compounds is increased by 5% by weight, the state where the thermal conductivity is doubled or more means that the connection between the fillers has developed rapidly, and the network of the thermal conductive material Is fully formed. Such a state is sometimes called percolation.

In the pitch-based graphitized short fibers having an aspect ratio of 3 or more in the present invention, fillers can be efficiently connected to each other to easily form a network of a heat conductive material, and even if the content in the resin is small, the percolation Can be achieved. Percolation occurs even with an inorganic compound having an aspect ratio of 3 or less, but Wf _A wt% <Wf _B wt%. In particular, when the inorganic compound is spherical, percolation appears when a body-centered cubic, face-centered cubic, hexagonal close-packed structure, etc. can be formed, but in order to develop percolation, it is often necessary to contain 70% by weight or more. However, by adding pitch-based graphitized carbon fiber that can achieve percolation at a low concentration to the inorganic compound, the percolation concentration can be lowered compared to when the inorganic compound is used alone, and the thermal conductivity can be reduced by adding a smaller amount. Making it easier to achieve significant improvements. Furthermore, by using an inorganic compound having an aspect ratio of 3 or less, it is possible to suppress a rapid increase in viscosity when mixed with a resin, compared to when using pitch-based graphitized short fibers alone, which is favorable. Formability can be obtained.

  The sheet-like thermally conductive molded body of the present invention preferably has a pitch-based graphitized short fiber content of 3 to 50% by weight. When the content of pitch-based graphitized short fibers is 3% by weight or less, there are few heat conductive materials, and heat conductivity cannot be expected. On the other hand, when the content of the pitch-based graphitized short fibers is 50% by weight or more, it is difficult to disperse the pitch-based graphitized short fibers in the resin and process the sheet-shaped molded body. Preferably it is 5-30 weight part.

  The pitch-based graphitized short fibers in the present invention preferably have an average fiber diameter (D1) of 2 to 20 μm observed with an optical microscope. When D1 is less than 2 μm, the number of the short fibers increases when compounding with the resin, so that the viscosity of the resin / short fiber mixture becomes high and molding becomes difficult. On the other hand, when D1 exceeds 20 μm, the number of short fibers decreases when combined with the resin, so that the short fibers do not easily come into contact with each other, and it is difficult to exhibit effective heat conduction when used as a composite material. A preferable range of D1 is 5 to 15 μm, and more preferably 7 to 13 μm.

  In the pitch-based graphitized short fibers in the present invention, the percentage (CV value) to the average fiber diameter (D1) of the fiber diameter dispersion (S1) in the pitch-based graphitized short fibers observed with an optical microscope is preferably 3-15. 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 very uniform, so the amount of small fibers with a small size entering the gaps between pitch-based graphitized short fibers is reduced, and a denser packing state is formed when compounded with resin. 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, the dispersibility is deteriorated when compounding with the resin, and it may be difficult to obtain a composite material having uniform performance. The CV value is preferably 5-13. 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.

  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 pitch-based graphitized short fibers in the present invention correspond to milled fibers, and the average fiber length (L1) is preferably 20 to 300 μm. Here, the average fiber length is a number average fiber length, and a predetermined number is measured in a plurality of fields of view using a length measuring device under an optical microscope, and can be obtained from the average value. When L1 is smaller than 20 μm, it becomes difficult for the short fibers to come into contact with each other, and it becomes difficult to expect effective heat conduction. On the other hand, when it is larger than 300 μm, the viscosity of the matrix / short fiber mixture tends to be high when mixing with the resin, and the moldability tends to be low. More preferably, it is the range of 20-250 micrometers. 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 preferably made 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 mesh 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 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, 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. 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. When defects such as severe irregularities are present on the surface of pitch-based graphitized short fibers, an increase in viscosity accompanying an increase in surface area is caused at the time of kneading with the matrix resin, and the moldability is deteriorated. Therefore, it is desirable that defects such as surface irregularities be as small as possible. More specifically, it is assumed that there are 10 or less defects such as irregularities in the observation visual field in an image observed at 1000 times with a scanning electron microscope. As a method for obtaining such pitch-based graphitized short fibers, it can be preferably obtained by performing graphitization after milling.

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

  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 air volume blown from the nozzle, the temperature of the wind, etc. 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 in the present invention preferably has an average fiber diameter (D1) of 2 to 20 μm or less, but the control of the average fiber diameter of the pitch-based graphitized short fiber changes the hole diameter of the nozzle. Or it can adjust by changing the discharge amount of the raw material pitch from a nozzle, or changing a 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 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 rotation type using collision of 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 pulverization may be configured 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, and 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. Moreover, when using a classification process, desired fiber length can be obtained also by adjusting a sieve mesh hole diameter.

  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.

  In the present invention, the pitch-based graphitized short fibers may be subjected to a surface treatment or a sizing treatment for the purpose of further improving the affinity of the matrix, improving the moldability, and improving the mechanical strength when used as a composite material. Further, sizing treatment may be performed after surface treatment as necessary. The surface treatment method is not particularly limited, and specific examples include electrodeposition treatment, plating treatment, ozone treatment, plasma treatment, and acid treatment. There is no particular limitation on the sizing agent used for the sizing treatment, but specifically, an epoxy compound, a water-soluble polyamide compound, a saturated polyester, an unsaturated polyester, vinyl acetate, water, alcohol, glycol may be used alone or in a mixture thereof. it can. The sizing agent may be attached in an amount of 0.01 to 10% by weight based on the filler. However, since the sizing agent-attached pitch-based carbon fiber filler may have active sites, it is preferable that the sizing treatment is as little as possible. A preferable adhesion amount is 0.1 to 2.5% by weight. It is desirable to use the sizing agent in consideration of the purpose and the matrix to be combined.

  In the present invention, an inorganic compound having an aspect ratio of 3 or less is used. Specifically, metal oxides such as aluminum oxide, magnesium oxide, silicon oxide, and zinc oxide, metal hydroxides such as aluminum hydroxide and magnesium hydroxide, metal nitrides such as boron nitride and aluminum nitride, oxynitride Examples thereof include metal oxynitrides such as aluminum, metal carbides such as silicon carbide, metals or metal alloys such as gold, silver, copper, and aluminum, and carbon materials such as natural graphite, artificial graphite, expanded graphite, and diamond. Two or more types can be used in combination.

  The sheet-like thermally conductive molded body of the present invention preferably has an inorganic compound content of 20 to 90% by weight. When the content of the inorganic compound is 20% by weight or less, the ratio of pitch-based graphitized short fibers increases relatively, and it is difficult to disperse the pitch-based graphitized short fibers in the resin and process it into a sheet-like molded body. It is easy to become. Conversely, when the content of the inorganic compound is 90% by weight or more, the amount of the resin is relatively small, and it is difficult to disperse the inorganic compound and the pitch-based graphitized fiber and process it into a sheet-like molded body. . Preferably it is 30-80 weight part.

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

  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), aliphatic polyamides and copolymers thereof, aromatic polyamides and copolymers thereof, polyimides and copolymers thereof, polyamideimides and copolymers thereof, polycarbonates and copolymers thereof Polymers, polyphenylene sulfides and copolymers thereof, polysulfones and copolymers thereof, polyether sulfones and copolymers thereof, polyether nitriles and copolymers thereof, polyether ketones and copolymers thereof , Polyether ether ketones and copolymers thereof, polyketones and And copolymers, elastomers, liquid crystalline polymers, silicone oils, and the like. One of these may be used alone, or two or more may be used in appropriate combination.

  Examples of the thermosetting resin include epoxies, acrylics, urethanes, silicones, phenols, imides, thermosetting modified PPEs, thermosetting PPEs, polybutadiene rubbers and copolymers thereof, Examples thereof include acrylic rubber and copolymers thereof, silicone rubber and copolymers thereof, natural rubber, and the like. One of these may be used alone, or two or more may be used in appropriate combination.

  The composition constituting the sheet-like thermally conductive molded body of the present invention is prepared by mixing pitch-based graphitized short fibers and inorganic compounds with a resin. At this time, the pitch-based graphitized short fibers, the inorganic compound, and the resin may be kneaded at the same time, or the remaining fillers may be kneaded after the pitch-based graphitized short fibers or the inorganic compound are kneaded with the resin. In mixing, a mixing device or a kneading device such as a kneader, various mixers, a blender, a roll, an extruder, a milling machine, or a self-revolving stirrer is preferably used.

  The sheet-like thermally conductive molded body of the present invention is molded by a molding method such as an injection molding method, a press molding method, a calendar molding method, a roll molding method, an extrusion molding method, a casting molding method, or a blow molding method. It is possible. The molding conditions depend on the molding method and the matrix. In the case of a thermoplastic resin, the molding is performed in a state where the temperature is higher than the melt viscosity of the resin. In the case where the matrix is a thermosetting resin, a method of applying a curing temperature of the resin in an appropriate mold can be exemplified.

  The sheet-like thermally conductive molded body of the present invention is a sheet containing 90 to 100% by weight of a composition comprising a resin, pitch-based graphitized short fibers having an aspect ratio of 3 or more, and an inorganic compound having an aspect ratio of 3 or less. However, examples of components other than the composition constituting the sheet include various functional fillers such as inorganic compounds having an aspect ratio of more than 3 and various additives.

Examples of various functional fillers include fibrous fillers such as glass fibers and alumina fibers for improving mechanical strength, non-fibrous fillers such as mica and calcium carbonate for improving moldability.
A plurality of additives may be used as necessary. Examples of the additive include a release agent, a flame retardant, an emulsifier, a softener, a plasticizer, and a surfactant.

  The sheet-like thermally conductive molded body obtained in this way can be used by being attached to a heating element. The molded body 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. .

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) The number average fiber length of the pitch-based graphitized short fibers was determined from the average value of 2000 (10 fields of view, 200) measured with a length measuring device under an optical microscope.
(3) The ratio between the in-plane direction and the thickness direction of the pitch-based graphitized short fibers in the molded body is the number of cross sections of the molded body observed in a scanning electron microscope at a magnification of 100 times and aligned in the in-plane direction. And the number in the thickness direction was counted, and the ratio was obtained.
(4) The crystallite size of the pitch-based graphitized short fibers was determined by the Gakushin method by measuring the reflection from the (110) plane appearing in X-ray diffraction.
(5) 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 a magnification of 4 million times, and a graphene sheet was confirmed.
(6) The surface of the pitch-based graphitized short fiber was observed with a scanning electron microscope at a magnification of 1000 times, and irregularities were confirmed.
(7) The thermal conductivity in the in-plane direction of the sheet-like thermally conductive molded body was determined by the probe method using QTM-500 manufactured by Kyoto Electronics.

[Reference Example 1]
A pitch made of a condensed polycyclic hydrocarbon compound was used as a main raw material. The optical anisotropy ratio was 100%, and the softening point was 283 ° C. Using a 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 325 ° C., and the melt viscosity was 18.5 Pa · S (185 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.
The pitch-based carbon fiber precursor web was heated from 170 ° C. to 320 ° 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) and graphitized at 3000 ° C.

The average fiber diameter of the pitch-based graphitized short fibers was 9.8 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter (CV value) was 11%. The number average fiber length was 150 μm, and 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.
Pitch-based graphitized short fibers and two-component curable silicone resin (trade name “SE1740” manufactured by Toray Dow Silicone Co., Ltd.) are used 3 by using a revolving mixer (trade name “Shinky Co., Ltd. product name“ Awatori Kentaro ARV310 ”). After mixing for a minute, it is pressed by a vacuum press machine (manufactured by Kitagawa Seiki) to obtain a flat composite molded body having a thickness of 0.5 mm, and cured at 130 ° C. for 2 hours. Created. Percolation Wf _A % was 36% by weight.

[Reference Example 2]
Alumina (trade name AX10-32 manufactured by Micron) and a two-part curable silicone resin (trade name “SE1740” manufactured by Toray Dow Silicone Co., Ltd.) are mixed with a revolving mixer (trade name “Awatori Neraro ARV310” manufactured by Shinky Corporation). ) Using a vacuum press machine (manufactured by Kitagawa Seiki) to obtain a flat composite molded body having a thickness of 1 mm and cured at 130 ° C. for 2 hours, whereby a sheet-like thermal conductivity is obtained. A molded body was prepared. Percolation Wf _A % was 88% by weight.

[Example 1]
Pitch-based graphitized short fibers were produced in the same manner as in Reference Example 1.
Pitch-based graphitized short fibers Wf _C 10% by weight, alumina (trade name AX10-32 manufactured by Micron) 70% by weight Wf _D and two-part curable silicone resin (trade name “SE1740” manufactured by Toray Dow Silicone) 20% by weight % Is mixed for 3 minutes using a revolutionary mixing machine (trade name “Awatori Nertaro ARV310” manufactured by Shinky Corporation), and then pressed with a vacuum press (made by Kitagawa Seiki) to form a flat plate with a thickness of 0.5 mm. Was obtained, and cured at 130 ° C. for 2 hours to prepare a sheet-like thermally conductive molded body. Was _{Wf C / Wf A + Wf D} / Wf B = 1.07.
When Wf _C + Wf _D = 80% by weight, the thermal conductivity of the sheet-like thermally conductive molded body made of alumina and the two-part curable silicone resin was 1.0 W / m · K.
The sheet-like heat conductive molded body thus prepared has a heat conductivity of 6.5 W / m · K, and Wf _C + Wf _D = 80 wt% sheet-like heat composed of alumina and a two-part curable silicone resin. The thermal conductivity was 6.5 times that of the conductive molded body.

[Example 2]
Pitch-based graphitized short fibers were produced in the same manner as in Reference Example 1.
20% by weight of pitch-based graphitized short fibers Wf _C , alumina (trade name AX10-32 manufactured by Micron), 60% by weight of Wf _D, and 20 parts by weight of two-part curable silicone resin (trade name “SE1740” manufactured by Toray Dow Silicone) % Is mixed for 3 minutes using a revolutionary mixing machine (trade name “Awatori Nertaro ARV310” manufactured by Sinky Corporation) and then pressed with a vacuum press (made by Kitagawa Seiki) to form a flat plate with a thickness of 0.5 mm. Was obtained, and cured at 130 ° C. for 2 hours to prepare a sheet-like thermally conductive molded body. Wf _C / Wf _A + Wf _D / Wf _B = 1.24.
The sheet-like heat conductive molded body thus produced has a thermal conductivity of 15.1 W / m · K, and Wf _C + Wf _D = 80 wt% sheet-like heat composed of alumina and a two-part curable silicone resin. The thermal conductivity was 15.1 times that of the conductive molded body.

[Comparative Example 1]
Pitch-based graphitized short fibers were produced in the same manner as in Reference Example 1.
Pitch-based graphitized short fiber Wf _C 5% by weight, alumina Wf _D 60% by weight, two-component curable silicone resin (trade name “SE1740” manufactured by Toray Dow Silicone Co., Ltd.) 35% by weight Product name “Awatori Nerita ARV310”) for 3 minutes, and then pressed with a vacuum press (made by Kitagawa Seiki Co., Ltd.) to obtain a flat composite molded product having a thickness of 0.5 mm at 130 ° C. By curing for 2 hours, a sheet-like thermally conductive molded body was prepared. Was _{Wf C / Wf A + Wf D} / Wf B = 0.82.
When Wf _C + Wf _D = 65% by weight, the thermal conductivity of the sheet-like thermally conductive molded body made of alumina and the two-part curable silicone resin was 0.8 W / m · K.
The sheet-like heat conductive molded body thus prepared has a thermal conductivity of 1.5 W / m · K, and Wf _C + Wf _D = 65 wt% sheet-like heat composed of alumina and a two-part curable silicone resin. The thermal conductivity was 1.9 times that of the conductive molded body.

  The sheet-like thermally conductive molded article of the present invention has a high heat resistance by controlling the content and mixing ratio of pitch-based graphitized short fibers in the sheet-like thermally conductive molded article and an inorganic compound having an aspect ratio of 3 or less. It is possible to develop conductivity. As a result, it can be used in places where high heat dissipation characteristics are required, and thermal management is ensured.

Claims (9)

A sheet containing 90-100% by weight of a resin, a pitch-based graphitized short fiber having an aspect ratio of 3 or more, and an inorganic compound having an aspect ratio of 3 or less,
When the content is increased by 5% by weight in the relationship between the thermal conductivity of a sheet composed of a resin and pitch-based graphitized short fibers having an aspect ratio of 3 or more and the content of pitch-based graphitized short fibers in the sheet The content of the pitch-based graphitized short fiber having a thermal conductivity of 2 times or more is Wf _A wt%,
In the relationship between the thermal conductivity of a sheet composed of a resin and an inorganic compound having an aspect ratio of 3 or less and the content of the inorganic compound in the sheet, the thermal conductivity is more than doubled when the content is increased by 5% by weight. When the content of the inorganic compound becomes Wf _B wt%,
The pitch-based graphitized short fiber content (Wf _C wt%) and the inorganic compound content (Wf _D wt%) in the composition are in a relationship of Wf _C / Wf _A + Wf _D / Wf _B > 1. Sheet-like thermally conductive molded body. 2. The sheet according to claim 1, wherein the sheet has a thermal conductivity that is at least three times the thermal conductivity of the sheet comprising the resin and the inorganic compound and the content of the inorganic compound is (Wf _C + Wf _D ) wt%. -Like thermally conductive molded body.   The sheet-like thermally conductive molded article according to claim 1 or 2, wherein the content of the pitch-based graphitized short fibers is 3 to 50% by weight.   Content of this inorganic compound is 20 to 90 weight%, The sheet-like heat conductive molded object of any one of Claims 1-3.   The pitch-based graphitized short fibers used as the raw material of the sheet-like thermally conductive molded body are made of mesophase pitch as a raw material, have an average fiber diameter of 2 to 20 μm, and have a fiber diameter dispersion percentage (CV value) of 3 with respect to the average fiber diameter. -15, the number average fiber length is 20-300 μm, the crystallite size derived from the growth direction of the hexagonal network surface is 30 nm or more, and the graphene sheet is closed in the filler end face observation by a transmission electron microscope, The sheet-like thermally conductive molded article according to any one of claims 1 to 4, wherein an observation surface with a scanning electron microscope is substantially flat.   The resins are polycarbonates, polyethylene terephthalates, polybutylene terephthalates, polyethylene 2,6 naphthalates, nylons, polypropylenes, polyethylenes, polyether ketones, polyphenylene sulfides, and acrylonitrile-butadiene-styrene copolymer resins. The sheet-like thermally conductive molded article according to any one of claims 1 to 5, which is at least one kind of resin selected from the group consisting of the above.   The resin is at least one resin selected from the group consisting of epoxies, acrylics, urethanes, silicones, phenols, imides, thermosetting modified PPEs, and thermosetting PPEs. The sheet-like thermally conductive molded article according to any one of 5.   The sheet-like thermally conductive molded body according to any one of claims 1 to 7, wherein the thermal conductivity in a state of being formed into a flat plate is 5 W / (m · K) or more.   The molding method is 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, a cast molding method, and a blow molding method. The sheet-like thermally conductive molded article according to item 1.