JP2010065123A - Heat-conductive molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-conductive molding having high heat-conductivity along the thickness direction. <P>SOLUTION: The heat-conductive molding includes a pitch-based graphitized staple fiber, an inorganic compound having three-dimensional needle-like conformation, and a matrix component. The pitch-based graphitized staple fiber has tendency to be aligned along a direction of the matrix flow when molding, while the formulated inorganic compound having three-dimensional needle-like conformation prevents aligning of the pitch-based graphitized staple fiber along the direction of the matrix flow, so that a portion of the pitch-based graphitized staple fiber is aligned along the thickness of the heat-conductive molding, increasing the heat-conductivity along the thickness direction of the heat-conductive molding. The matrix component is, for example, a thermoplastic resin, a thermoset resin, a rubber component, or the like. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a thermally conductive molded article comprising pitch-based graphitized short fibers, an inorganic compound having a three-dimensional acicular structure, and a matrix 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 attention is paid to the process of forming various elements, an environmentally conscious process is required, and as a countermeasure, 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, carbon fibers that are heat conductive materials come into contact with each other, and the possibility of forming a network increases. Therefore, it is easy to exhibit a higher thermal conductivity than a molded body using a spherical heat conductive material such as many inorganic compounds. However, since it has an aspect ratio, when it is formed into a sheet-like molded body or the like, the carbon fibers are likely to be arranged in the plane of the sheet-like molded body and a network in the plane grows. For this reason, the thermal conductivity in the in-plane direction of the sheet-like molded body is likely to be high, but the thermal conductivity in the thickness direction of the sheet-like molded body is difficult to increase. Therefore, a method of arranging carbon fibers in the thickness direction of the sheet-like molded body by a method as shown in Patent Documents 1 to 3 has been proposed.

  However, the method described above can be achieved relatively easily in an environment where the carbon fibers are relatively mobile, such as in a liquid resin, but is difficult to achieve by a technique such as injection molding or press molding. In addition, the apparatus tends to be large, and it is difficult to say that the method can be easily achieved.

JP 2000-191987 Japanese Unexamined Patent Publication No. 2000-195998 JP 2000-281995 A

  As described above, from the viewpoint that a heat conductive molded body excellent in heat conductivity in the thickness direction is required, the heat conductive material is preferably a fibrous material excellent in forming a network in the matrix. Moreover, it is preferable that the heat conductive material shown here exhibits the network forming ability also in the thickness direction of the molded body.

  An object of the present invention is to provide a thermally conductive molded body having high thermal conductivity not only in the in-plane direction but also in the thickness direction.

  In view of providing a heat dissipating material excellent in thermal conductivity in the thickness direction and in-plane direction of the molded body, the present inventors changed the pitch-based graphitized short fiber excellent in thermal conductivity into a three-dimensional acicular structure. The present invention finds that a thermally conductive molded article having good thermal conductivity in the thickness direction and in-plane direction can be provided by dispersing the inorganic compound in the matrix and forming a network in the thickness direction and in-plane direction. Reached.

The object of the present invention is further 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 casting molding method, and a blow molding method. This can be achieved by a molded body obtained by molding by at least one method.

  The thermally conductive molded body of the present invention uses a pitch-based graphitized short fiber, an inorganic compound having a three-dimensional needle-like structure, and a matrix component to form a network of pitch-based graphitized short fibers in the matrix. By forming not only in the plane but also in the thickness direction, high thermal conductivity can be imparted in the thickness direction and the in-plane direction of the thermally conductive molded body.

Hereinafter, embodiments of the present invention will be sequentially described.
The thermally conductive molded article of the present invention is characterized by comprising pitch-based graphitized short fibers, an inorganic compound having a three-dimensional acicular structure, and a matrix component. When a thermally conductive molded body is made from pitch-based graphitized short fibers and a matrix component, the pitch-based graphitized short fibers tend to be arranged in the plane of the thermally conductive molded body. This is because compounds having an aspect ratio tend to line up in the direction in which the matrix flows in, for example, an injection molding method, a calendar molding method, or a roll molding method. In such a case, the thermal conductivity of the thermally conductive molded body is excellent in the arrangement direction of the pitch-based graphitized short fibers, that is, the in-plane direction, but the thickness direction is not so excellent.

  However, when an inorganic compound having a three-dimensional acicular structure is mixed with pitch-based graphitized short fibers and a matrix component, the pitch-based graphitized short fibers have a three-dimensional acicular structure along the matrix flow direction. The inorganic compound inhibits, and the direction in which the pitch-based graphitized short fibers are arranged becomes random. As a result, a part of the pitch-based graphitized short fibers are arranged in the thickness direction of the thermally conductive molded body, and the thermal conductivity in the thickness direction of the thermally conductive molded body is improved.

  The heat conductive molded body of the present invention can have a heat conductivity in the thickness direction of 1 W / (m · K) or more, more preferably 2 W / (m · K). That's it. Although there is no restriction | limiting in particular in the measuring method of the heat conductivity of the thickness direction of a heat conductive molded object, Specifically, the laser flash method as described in ASTM E 1461, the method as described in ASTM D5470, etc. can be used.

  It is preferable that content of the inorganic compound which has a three-dimensional acicular structure is 5-250 volume parts with respect to 100 volume parts of pitch type | system | group graphitized short fibers, in the heat conductive molded object of this invention. If the content of the inorganic compound having a three-dimensional acicular structure is smaller than 5 parts by volume, the amount is not sufficient to inhibit the arrangement of pitch-based graphitized short fibers, and thermal conductivity in the thickness direction cannot be expected. Conversely, if the content of the inorganic compound having a three-dimensional needle-like structure is larger than 250 parts by volume, the inorganic compound having a three-dimensional needle-like structure works in the direction of inhibiting the dispersion of pitch-based graphitized short fibers into the matrix, It becomes difficult to obtain a uniform thermally conductive molded body. More preferably, the content of the inorganic compound is 10 to 80 parts by volume with respect to 100 parts by volume of the pitch-based graphitized short fibers.

  The heat conductive molded body of the present invention preferably has a pitch-based graphitized short fiber content of 3 to 200 parts by volume with respect to 100 parts by volume of the matrix component. If the pitch-based graphitized short fiber content is less than 3 parts by volume, it is difficult to ensure sufficient thermal conductivity. On the other hand, when the content of pitch-based graphitized short fibers is more than 200 parts by volume, it is often difficult to uniformly disperse pitch-based graphitized short fibers in the matrix.

  The pitch-based graphitized short fibers preferably have a ratio of short fibers having a radius of curvature in all the fibers and in the range of the radius of curvature of 10 to 60 cm in the range of 60% to 99%. When the radius of curvature exceeds 60 cm or when the graphitized short fibers are straight, they exist in one dimension, and thus the network of graphitized short fibers tends to be difficult to form. On the other hand, in the case of the graphitized short fibers having the curvature described above, since the graphitized short fibers exist in two dimensions, it tends to easily form a network of graphitized short fibers. When the radius of curvature is smaller than 10 cm, the curvature is too large, so that the two-dimensional spread of graphitized short fibers is small, and a network of graphitized short fibers is not easily formed. When more networks of graphitized short fibers are formed, a heat conduction path is formed, so that heat conduction is increased. The curvature can be obtained by observing the fiber with an optical microscope and observing the fiber length and the bending method.

  It is advantageous that the ratio of fibers having a radius of curvature in the entire pitch-based graphitized short fiber of the present invention and having a radius of curvature in the range of 10 to 60 cm is preferably 70% to 99%. Particularly preferred pitch-based graphitized short fibers are those having a radius of curvature of all the fibers and a ratio of fibers having a radius of curvature in the range of 10 to 50 cm of 60% to 99%, preferably 70% to 99%. It is. The ratio of the fibers having a radius of curvature of 10 to 60 cm is determined by observing pitch-based graphitized short fibers 50 times under an optical microscope, measuring a predetermined number using a scale, and the radius of curvature is 10 to 60 cm. The ratio is calculated from the number of certain fibers.

A melt blow method is preferably used to give the carbon fiber curvature. When spinning by the melt blow method, air is blown to the raw material pitch, and the blown air can apply force from a direction different from the spinning direction. Furthermore, a force can be applied three-dimensionally by the turbulent flow formed by the blown air.

  The method for controlling the radius of curvature is not particularly limited. Specifically, there are a method for controlling the spinning time by the air to be blown, a method for controlling turbulence, and the like. Specific examples of the method for controlling the spinning time by the air to be blown include the temperature and viscosity of the raw material pitch and the temperature of the blown air. The higher the temperature of the raw material pitch, the lower the viscosity of the raw material pitch, making it difficult to spin for a long time. Therefore, the curvature becomes small. Further, the higher the temperature of the blow air, the longer the time until the raw material pitch is solidified and the larger the curvature. There are no particular restrictions on the method of controlling the turbulent flow and the radius of curvature, but more specifically, controlling the angle at which blown air is applied to the spinning direction and installing a cylinder called chimney at the bottom of the melt-blow base it can.

  In addition, although the method of twisting a fiber is reported to patent 2838140 gazette, when a fiber is twisted, when combining with a matrix, a matrix is held in the twisted part of carbon fiber, and it is composite. The amount of the matrix required for the conversion becomes large, and it becomes difficult to highly fill the carbon fiber, which is not preferable for heat conduction.

  In the pitch-based graphitized short fibers of the present invention, the proportion of short fibers whose surface observed by a scanning electron microscope is cleaved is preferably 30% to 99%. When the surface of the pitch-based graphitized short fibers is cleaved, the space occupied by the graphitized short fibers becomes larger, and a network of short fibers is easily formed. Here, the surface is cleaved means that the short fiber side surface is opened and the inside can be observed, or that a linear crack is confirmed on the short fiber side surface. In order for the network of short fibers to function effectively, the ratio of the short fibers whose surface is cleaved may be 30% to 99% of the total fibers. More preferably, it is 40% to 99%.

  In order to cleave the surface of the pitch-based graphitized short fibers, a melt blow method is preferably used. The melt blow method is a spinning method in which air is blown into a melted mesophase pitch. When the melted mesophase pitch comes out from the nozzle tip, the fiber cross section takes a radial structure due to the ballast effect. By blowing air here, the radial structure of the fiber cross section collapses and changes to a Pannam structure. The Pannam structure is defined in Carbon 38 (2000) P741-747. Since the pannum structure is a structure that bisects the fiber, the surface is cleaved when the fiber contracts in the firing and graphitization steps after spinning.

  There is no particular limitation on the method for controlling the surface cleavage, that is, the method for making the pannum structure easy. Specifically, the method is to increase the amount of blown air, or to reduce the shearing force applied by the melted mesophase pitch when leaving the nozzle. That is, there is a method of increasing the viscosity of the melted mesophase pitch.

  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. When the average fiber diameter is less than 2 μm, the number of the short fibers increases when they are combined with the resin, so that the viscosity of the resin / short fiber mixture tends to be high and molding tends to 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. Become. A preferable range of the average fiber diameter is 5 to 15 μm, and more preferably 7 to 13 μm.

  In the pitch-based graphitized short fibers of the present invention, the percentage (CV value) of the average fiber diameter of the fiber diameter dispersion in the pitch-based graphitized short fibers observed with an optical microscope is preferably 5-15. The CV value is an index of fiber diameter variation, and the smaller the value, the higher the process stability and the smaller the fiber diameter variation. When the CV value is less than 5, the fiber diameters are extremely uniform, so the amount of short fibers with a small fiber diameter entering the gaps between the pitch-based graphitized short fibers is reduced, and a denser packing state is formed when compounding with the resin. It tends to be difficult to form. As a result, it becomes difficult to highly fill the pitch-based graphitized fibers, making it difficult to obtain a high-performance composite material. On the other hand, when the CV value is larger than 15, dispersibility is deteriorated when compounded with a resin, the viscosity at the time of molding increases, and it may be difficult to obtain a composite material having uniform performance. The CV value is preferably 5-13. The CV value is obtained by adjusting the viscosity of the melt mesophase pitch during spinning. Specifically, when spinning by the melt blow method, the melt viscosity at the nozzle hole during 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 is preferably 20 to 500 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 the average fiber length is smaller than 20 μm, it becomes difficult for the short fibers to contact each other, and it becomes difficult to expect effective heat conduction. On the other hand, when it exceeds 500 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 20-300 micrometers. There is no particular limitation on the method for obtaining such pitch-based graphitized short fibers, but the milling conditions, that is, when pulverizing with a cutter, 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.

  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. A technique for obtaining such pitch-based graphitized short fibers can be preferably obtained by performing graphitization after milling.

The pitch-based graphitized short fibers in the present invention are preferably composed of graphite crystals, and the crystallite size derived from the growth direction of the hexagonal network surface is preferably 20 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.
The true density of the pitch-based graphitized short fibers is preferably 1.8 to 2.3 g / cc. When it is within this range, the degree of graphitization is sufficiently increased and sufficient thermal conductivity can be exhibited, and the energy cost for graphitization is also commensurate with the characteristics of the obtained fiber filler. More preferably, it is 1.9 to 2.3 g / cc.

The thermal conductivity in the fiber axis direction of the pitch-based graphitized short fibers is also preferably 600 W / m · K or more. In the case of 600 W / m · K or more, sufficient heat conductivity can be obtained when a heat conductive molded body is produced by mixing with a matrix. The thermal conductivity shown here can be obtained by calculation from the following relational expression (refer to Japanese Patent No. 3648865) of the thermal conductivity and the electrical resistance from the electrical specific resistance, and K = 1272.4 / ER-49.4.
(K is the thermal conductivity of carbon fiber, ER is the electrical resistivity of carbon fiber)
Substantially synonymous with electrical resistivity.

Hereinafter, a preferred method for producing pitch-based graphitized short fibers in the present invention will be described.
Examples of raw materials for pitch-based graphitized short fibers include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, condensed heterocyclic compounds such as petroleum pitch and coal 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 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 them, in order to give the pitch-based carbon fiber precursor of the present invention curvature and surface cleavage, it is desirable to use a melt blow method using hot air. Hereinafter, the melt blow method will be described 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 thermal conductivity, which is not preferable. 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 at the time of 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 conditions for obtaining a stable spinning state and the desired curvature, The melt viscosity at the nozzle holes of the mesophase pitch may be in the range of 5.0 to 25.0 Pa · s.

  When the melt viscosity of the mesophase pitch passing through the nozzle is less than 5 Pa · s, the spinning time is shortened, the curvature is decreased, and the curvature radius tends to be increased. On the other hand, when the melt viscosity of the mesophase pitch exceeds 25.0 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 having a curvature, it is necessary to control the melt viscosity of the mesophase pitch passing through the nozzle. For this reason, it is preferable to make the melt viscosity of mesophase pitch into the range of 5.0-25.0 Pa.s.

  The pitch-based graphitized short fibers in the present invention have an average fiber diameter of 2 to 20 μm or less, but the average fiber diameter of the pitch-based graphitized short fibers can be controlled by changing the nozzle hole diameter or by using the raw material pitch from the nozzles. It is possible to adjust by changing the discharge amount or changing the draft ratio. The draft ratio can be changed by blowing a gas having a linear velocity of 5000 to 20000 m per minute heated to 100 to 400 ° C. in the vicinity of the refinement point. There is no particular restriction on the gas to be blown, but air is desirable from the viewpoint of cost performance and safety.

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

  The pitch-based carbon fiber precursor web thus obtained is infusibilized 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 graphitized short fibers. However, since the sizing agent-attached pitch-based graphitized short fibers 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.

  The heat conductive molded object of this invention contains the inorganic compound which has a three-dimensional acicular structure. The three-dimensional needle-like structure refers to a structure in which needle-like substances come out from the center in three or more directions in different directions not in the same plane. Specifically, a shape like a tetrapot is mentioned.

  The size of the needle-shaped substance is intended to inhibit the movement of the pitch-based graphitized short fibers, and is therefore preferably equal to or slightly smaller than the size of the pitch-based graphitized short fibers, that is, the diameter is 0. It is preferable that the length is 2 to 20 μm and the length is 1 to 600 μm.

  Furthermore, since the purpose is to inhibit the movement of the pitch-based graphitized short fibers, it is preferable that a three-dimensional needle-like structure can be maintained during blending with the matrix. Although there is no restriction | limiting in particular in the inorganic compound which has a three-dimensional acicular structure, Specifically, a zinc oxide is mentioned, The product manufactured by Amtec, such as Panatetra by Amtec, is mentioned.

  The matrix which comprises the heat conductive molded object of this invention is at least 1 sort (s) selected from the group which consists of a thermoplastic resin, a thermosetting resin, and rubber | gum. 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 naphtho) Rate, liquid crystalline polymer, etc.), polystyrenes and copolymers thereof (styrene-acrylonitrile copolymers, ABS resins, etc.), polyacrylonitriles and copolymers thereof, polyphenylene ethers (PPE) and copolymers thereof (modified) Including PPE resin), 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 Examples thereof include copolymers, elastomers, liquid crystalline polymers, and silicone oils. One of these may be used alone, or two or more may be used in appropriate combination.

In addition, examples of the thermosetting resin include epoxies, acrylics, urethanes, silicones, phenols, imides, thermosetting modified PPEs, thermosetting PPEs, and the like. Or two or more types may be used in appropriate combination.
The 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, styrene butadiene rubber (SBR), butadiene rubber (BR), and butyl rubber.

The heat conductive molded body of the present invention can be molded by a molding method such as an injection molding method, a press molding method, a calender molding method, a roll molding method, an extrusion molding method, a cast molding method, or a blow molding method. It is. 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 obtained by molding by these methods of the present invention is included.

  In order to further increase the thermal conductivity of the composition of the present invention, fillers other than pitch-based graphitized short fibers may be added as necessary. Specifically, metal oxides such as aluminum oxide, magnesium oxide and silicon oxide, metal hydroxides such as aluminum hydroxide and magnesium hydroxide, metal nitrides such as boron nitride and aluminum nitride, metals such as aluminum oxynitride Examples thereof include metal carbides such as oxynitride and 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. You may add these suitably according to a function. Two or more types can be used in combination.

  Furthermore, in order to further improve other characteristics such as moldability and mechanical properties, glass fiber, potassium titanate whisker, aluminum boride whisker, boron nitride whisker, aramid fiber, alumina fiber, silicon carbide fiber, asbestos fiber, gypsum fiber, A fibrous filler such as a metal fiber may be appropriately added depending on a 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.

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

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 curvature of pitch-based graphitized short fibers is magnified 4 times under an optical microscope, measured 2000 using a scale, the number of radii of curvature of 10 to 60 cm is observed, and the ratio to 2000 is determined. Asked.
(2) The average fiber diameter and the fiber diameter dispersion of the pitch-based graphitized short fibers were measured from 60 averages using a scale under an optical microscope in accordance with JIS R7607 and obtained from the average values.
(3) The number-average fiber length of pitch-based graphitized short fibers was magnified 4 times under an optical microscope, and 2000 fibers were measured on a scale, and the average value was obtained from the average value.
(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 true density of the pitch-based carbon short fibers was measured by a gas replacement method described in JIS M8717.
(6) The thermal conductivity of the pitch-based graphitized short fibers was fixed using silver paste so that the distance between both ends of the pitch-based graphitized fibers was 1 cm, which was produced under the same conditions except for the electrical resistivity. Then, 20 electrical resistances at both ends were measured with a tester, calculated using the radius of the pitch-based carbon fiber, and calculated from the following relational expression (refer to Japanese Patent No. 3648865) of thermal conductivity and electrical resistance.
K = 1272.4 / ER-49.4
(K is the thermal conductivity of carbon fiber W / (m · K), ER is the electrical resistivity of carbon fiber μΩm)
(7) The end face of the pitch-based 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.
(8) Cleavage and surface shape of the pitch-based graphitized short fibers were observed with a scanning electron microscope at a magnification of 800 times. The number of observations was 50.
(9) The thermal conductivity in the thickness direction of the thermally conductive molded body was measured by Netch LFA447 (laser flash method).

[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 285 ° C. Using a hole cap with a diameter of 0.2 mmφ, heated air is ejected from the slit at 45 degrees with respect to the spinning direction at a linear velocity of 6000 m / min, pulling the melt pitch, and a pitch system with an average diameter of 11.3 μm Short fibers were produced. The spinning temperature at this time was 320 ° C., and the melt viscosity was 19.5 Pa · S (195 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 300 g / m ² was obtained 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 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 8.2 μm, and the ratio of the fiber diameter dispersion to the average fiber diameter (CV value) was 10%. The number average fiber length was 150 μm. The ratio of the radius of curvature of all fibers in the range of 10 to 60 cm was 80%. Moreover, the ratio of the fiber with surface cleavage by observation with a scanning electron microscope was 40%.
The crystal size derived from the growth direction of the hexagonal network surface of the pitch-based graphitized short fibers was 70 nm, the true density was 2.2 g / cc, and the thermal conductivity was 700 W / m · K.
It was confirmed by observation with a transmission microscope that the graphene sheet was closed on the end face of the pitch-based graphitized short fiber. Moreover, the surface was substantially smooth with one unevenness | corrugation by observation with the scanning electron microscope.

[Example 1]
30 parts by volume of the pitch-based graphitized short fibers obtained in Reference Example 1, 5 parts by volume of zinc oxide whisker having a three-dimensional needle-like structure (manufactured by Amtec, trade name Panatetra), silicone resin (manufactured by Toray Dow Silicone, SE1740) 65 parts by volume was mixed for 3 minutes using a vacuum self-revolving mixer (Shinky Awatori Nertaro ARV-310) to obtain a composite slurry. This slurry was pressed by 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 thermally conductive molded body. It was 3.8 W / (m * K) when the heat conductivity of the heat conductive molded object was measured.

[Example 2]
30 parts by volume of the pitch-based graphitized short fibers obtained in Reference Example 1, 15 parts by volume of zinc oxide whisker having a three-dimensional needle-like structure (manufactured by Amtec, trade name Panatetra), silicone resin (manufactured by Toray Dow Silicone, SE1740) 55 parts by volume was mixed for 3 minutes using a vacuum self-revolving mixer (Shinky Awatori Nertaro ARV-310) to obtain a composite slurry. This slurry was pressed by 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 thermally conductive molded body. It was 4.7 W / (m * K) when the heat conductivity of the heat conductive molded object was measured.

[Example 3]
30 parts by volume of pitch-based graphitized short fibers obtained in Reference Example 1, 5 parts by volume of zinc oxide whisker having a three-dimensional needle-like structure (manufactured by Amtec, Panatetra), 65 volumes of polycarbonate resin (manufactured by Teijin Chemicals, L-1225WP) The part was kneaded with a biaxial kneader (manufactured by Kurimoto Iron Works) to obtain a master chip. This chip was mixed with an injection molding machine (M-50B manufactured by Meiki Seisakusho Co., Ltd.) to obtain a flat composite molded body having a thickness of 2 mm to obtain a thermally conductive molded body. It was 2.1 W / (m * K) when the heat conductivity of heat conductivity was measured.

[Example 4]
30 parts by volume of pitch-based graphitized short fibers obtained in Reference Example 1, 5 parts by volume of zinc oxide whisker having a three-dimensional needle structure (Amtech, Panatetra), 65 volumes of polyphenylene sulfide resin (manufactured by Polyplastics, 0220A9) The part was kneaded with a biaxial kneader (manufactured by Kurimoto Iron Works) to obtain a master chip. This chip was mixed with an injection molding machine (M-50B manufactured by Meiki Seisakusho Co., Ltd.) to obtain a flat composite molded body having a thickness of 2 mm to obtain a thermally conductive molded body. It was 2.5 W / (m * K) when the heat conductivity of heat conductivity was measured.

[Comparative Example 1]
30 parts by volume of the pitch-based graphitized short fibers obtained in Reference Example 1 and 70 parts by volume of a silicone resin (made by Toray Dow Silicone, SE1740) were mixed with a vacuum revolving mixer (Shinky Awatori Nertaro ARV-310). And mixed for 3 minutes to form a composite slurry. This slurry was pressed by 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 thermally conductive molded body. It was 2.3 W / (m * K) when the heat conductivity of the heat conductive molded object was measured.

[Comparative Example 2]
30 parts by volume of pitch-based graphitized short fibers described in Comparative Example 1 and 70 parts by volume of polycarbonate resin (manufactured by Teijin Chemicals, L-1225WP) were kneaded with a biaxial kneader (manufactured by Kurimoto Iron Works) to form a master chip. . This chip was mixed with an injection molding machine (M-50B manufactured by Meiki Seisakusho Co., Ltd.) to obtain a flat composite molded body having a thickness of 2 mm to obtain a thermally conductive molded body. It was 1.0 W / (m * K) when the heat conductivity of heat conductivity was measured.

[Comparative Example 3]
30 parts by volume of pitch-based graphitized short fibers described in Comparative Example 1 and 70 parts by volume of polyphenylene sulfide resin (polyplastics, 0220A9) were kneaded with a biaxial kneader (manufactured by Kurimoto Iron Works) to obtain a master chip. . This chip was mixed with an injection molding machine (M-50B manufactured by Meiki Seisakusho Co., Ltd.) to obtain a flat composite molded body having a thickness of 2 mm to obtain a thermally conductive molded body. It was 1.4 W / (m * K) when the heat conductivity of heat conductivity was measured.

  The heat conductive molded body of the present invention comprises pitch-based graphitized short fibers, an inorganic compound having a three-dimensional needle-like structure, and a matrix component, thereby making it possible to express high heat conductivity in the thickness direction. Yes. As a result, it can be used in places where high heat dissipation characteristics are required, and thermal management is ensured.

Claims (14)

  A thermally conductive molded article comprising pitch-based graphitized short fibers, an inorganic compound having a three-dimensional acicular structure, and a matrix component.   The thermally conductive molded article according to claim 1, comprising 5 to 250 parts by volume of the inorganic compound with respect to 100 parts by volume of the pitch-based graphitized short fibers.   The thermally conductive molded article according to any one of claims 1 to 2, comprising 3 to 200 parts by volume of the pitch-based graphitized short fibers with respect to 100 parts by volume of the matrix component.   The pitch-based graphitized short fiber has a radius of curvature in all the fibers, and the ratio of the short fibers whose radius of curvature is in the range of 10 to 60 cm is 60% to 99%, and is an observation surface with a scanning electron microscope The thermally conductive molded body according to any one of claims 1 to 3, wherein a ratio of short fibers in which the slab is cleaved is 30% to 99%.   5. The pitch-based graphitized short fibers have an average fiber diameter of 2 to 20 μm, a fiber diameter dispersion percentage with respect to the average fiber diameter (CV value) of 5 to 15, and a number average fiber length of 5 to 600 μm. The heat conductive molded object of any one of Claims.   The graphene sheet is closed in observing the end face of the graphitized short fiber with a transmission electron microscope of the pitch-based graphitized short fiber, and the observation surface with a scanning electron microscope is substantially flat. The heat conductive molded object of 1 item | term.   The crystallite size derived from the growth direction of the hexagonal network surface of the pitch-based graphitized short fiber is 20 nm or more, the true density is in the range of 1.8 to 2.3 g / cc, and the thermal conductivity in the fiber axis direction. Is 600 W / (mK) or more, The heat conductive molded object of any one of Claims 1-6 characterized by the above-mentioned.   The thermally conductive molded article according to any one of claims 1 to 7, wherein the inorganic compound is at least one selected from the group consisting of zinc oxide.   The thermally conductive molded article according to any one of claims 1 to 8, wherein the matrix is at least one selected from the group consisting of a thermoplastic resin, a thermosetting resin, and a rubber component.   The thermoplastic resins are polycarbonates, polyethylene terephthalates, polybutylene terephthalates, polyethylene 2,6 naphthalates, nylons, polypropylenes, polyethylenes, polyether ketones, polyphenylene sulfides, and acrylonitrile-butadiene-styrene series. The thermally conductive molded article according to any one of claims 1 to 9, which is at least one resin selected from the group consisting of copolymer resins.   The thermosetting resin is at least one resin selected from the group consisting of epoxies, acrylics, urethanes, silicones, phenols, imides, thermosetting modified PPEs, and thermosetting PPEs. The heat conductive molded object of any one of Claims 1-9.   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 molded article according to any one of claims 1 to 9, 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 in any one of Claims 1-12 whose heat conductivity of the thickness direction in the state shape | molded in flat form is 1 W / (m * K) or more.   A group comprising the thermally conductive molded body according to any one of claims 1 to 13, comprising an injection molding method, a press molding method, a calendar molding method, a roll molding method, an extrusion molding method, a casting molding method, and a blow molding method. A sheet-like thermally conductive molded body obtained by molding by at least one method selected from the above.