JP2008208159A - Heat-resistant heat-conductive composite sheet and heat-resistant heat-conductive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop a heat-dissipating material having heat-conductance and heat-resistance. <P>SOLUTION: The composite material having heat-conductivity and heat-resistance at the same time is produced by compounding a thermoplastic resin composed mainly of a fluororesin and having a melting point of ≥250°C with a highly heat-conductive carbon fiber containing remarkably developed graphite crystals and produced by using mesophase pitch as a raw material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a composite material having both heat resistance and heat conductivity, and a heat conductive sheet formed by molding. More specifically, the present invention relates to a heat-resistant heat-conducting composite material and a heat-conducting material that are provided in contact with or near a high-temperature heat source and used for the purpose of efficient transmission, transportation, dissipation, etc. of heat. Regarding the sheet.

  In electrical elements and devices (hereinafter, collectively referred to as “devices”) that generate a large amount of heat, such as CPUs, MPUs, power transistors, LEDs, and laser diodes, the heat dissipation technology of devices has become a major issue. For these heat dissipation, for example, a cooling source such as a heat sink or a heat pipe is used (for example, Patent Documents 1 to 3), but a heat dissipation sheet is used for the purpose of increasing the thermal conductivity of these devices and the cooling source. There are many.

  Conventionally, a rubber-like elastic sheet filled with a thermally conductive filler or the like has been proposed as a heat dissipation sheet. The rubber elastically deforms and enters the surface of the contacted object (device, heat sink, etc.) with minute irregularities, and by expelling the air there, the substantial contact area between the contacted objects is increased. Designed to improve heat transfer efficiency.

  However, in these conventional heat conductive sheets, a matrix resin that exhibits rubber-like elasticity at room temperature is used. For example, in an environment where the heating element temperature exceeds 150 ° C., the heat resistance is inferior. It has been difficult to use stably due to problems such as deterioration of the mechanical strength and insufficient mechanical strength.

  In view of such circumstances, the present inventor has eagerly searched for a material having both heat resistance and excellent thermal conductivity that can withstand use under these high-temperature environments. It has been found that a composite material composed of specific carbon fibers can be suitably used, and the present invention has been achieved.

Here, many proposals have already been made for the use of sliding materials for composite materials obtained by mixing fluororesin and carbon fibers. (For example, patent documents 4-8). However, in these proposals, carbon fibers are mixed for the purpose of mechanical reinforcement of composite materials, improvement of friction resistance, etc., so carbon fibers are PAN having excellent mechanical strength and wear resistance. Carbon fibers using isotropic pitch as a raw material have been selected. Since these carbon fibers do not have high thermal conductivity, those having high thermal conductivity of composite materials have not been obtained. (For example, in Examples of Patent Documents 4 and 5, the thermal conductivity of the composite material is described, but the thermal conductivity of the fluororesin itself is 0.2 to 0.3 W / m · K. Although a slightly higher value is exemplified, it cannot be said that it has excellent thermal conductivity). In addition, the reason why the thermal conductivity of these carbon fibers is not high is that the development of graphite crystals, which are the main component of thermal conduction in the carbon fibers, is insufficient.
That is, the function as a high heat conductive material cannot be expected for a general composite material including a fluororesin and carbon fiber, which has been conventionally proposed for use as a sliding material.

JP 2003-273300 A JP 2004-071643 A JP 2005-259794 A JP-A-5-320455 JP 2001-131372 A JP-A-9-132691 JP 61-037842 A JP-A-62-2223255

Conventionally proposed heat dissipation sheet / heat transfer member is intended to suppress / increase the decrease in effective contact area due to surface irregularities in the contacted body (device, heat sink, etc.) that is the cause of heat conduction inhibition by applying elastic body As described above, it is used in. In addition, a layered body having rubber elasticity has been proposed for the purpose of relaxing mechanical stress due to direct contact between the device and a heat sink or the like. In the prior art, since the heat radiating sheet and the heat transfer member use a rubber elastic body, there is a problem in that the heat resistance and mechanical characteristics are inferior, and stable use is not possible.
An object of the present invention is to provide a heat-resistant and heat-conductive composite material that solves the problems related to heat resistance that the prior art has, and combines heat resistance and heat conductivity.

That is, the heat-radiating sheet that satisfies the problems of the present invention basically requires thermal conductivity, but firstly it is required to have heat resistance, and secondly, it is flexible enough to be in close contact with the contacted body. Must be satisfied. It is an object of the present invention to develop a heat-dissipating material having such performance.
The present inventors have found that a composition (composite material) obtained by blending an appropriate amount of graphitized carbon fiber in a heat-resistant resin with flexibility as a matrix can solve the above-mentioned problems, and has achieved the present invention. did.

That is, the present invention is as follows.
1. It is composed of at least a thermoplastic resin having a melting point of 250 ° C. or higher and a carbon fiber having an aspect ratio of 2 or higher, satisfies the following requirements (A) to (E), and has a thermal conductivity of 0.7 W / m · K or higher. Is a heat-resistant heat conductive composite material.
(A) At least 50% by weight or more of the thermoplastic resin is made of a fluororesin,
(B) The carbon fiber is a graphitized carbon fiber using mesophase pitch as a starting material,
(C) The true density of the carbon fiber is 1.7 to 2.5 g / cc,
(D) The crystallite size in the c-axis direction and ab-axis direction of the graphite crystal contained in the carbon fiber is both 20 nm or more,
(E) Carbon fiber is mixed in the composite material in a proportion of 5 to 50% by weight. The heat-resistant heat-conductive composite material according to 1 above, wherein the carbon fiber has a heat conductivity of at least 200 W / m · K or more.
3. The heat-resisting heat conductive composite material according to any one of 1 and 2, wherein the fluororesin contains at least tetrafluoroethylene or a copolymer thereof.
4). A heat-resistant heat conductive sheet obtained by molding the heat-resistant heat-conductive composite material of any one of 1 to 3 into a sheet having a thickness of 20 to 5000 μm.

  ADVANTAGE OF THE INVENTION According to this invention, the heat resistant heat conductive composite material which makes heat resistance and heat conductivity compatible, and does not damage a device surface can be provided. This member is disposed so as to cover the device as a heat-dissipating sheet / heat transfer member, or to join the heat conduction / heat-dissipating member such as a heat sink and a heat pipe to the device, thereby improving the heat conduction efficiency.

In the following, the present invention will be described in more detail.
The carbon fiber used in the present invention preferably has a thermal conductivity in the fiber axis direction of at least 200 W / (m · K) or more, more preferably 300 W / (m · K) or more, and still more preferably 400 W / (M · K) or more, most preferably 500 W / (m · K) or more.

In order to develop such a high thermal conductivity in the carbon fiber, it is preferable that the content of graphite crystals in the carbon fiber (hereinafter referred to as graphitization rate) is high, and that the crystallite size is large. It is preferable to realize conduction. This is due to the fact that the heat conduction in the carbon fiber is mainly carried by the phonon conduction.
Regarding the graphitization rate, it is preferable that the true density of the pitch-based graphitized carbon fiber is in the range of 1.7 to 2.5 g / cc as a reflection value.

Regarding the crystallite size, the crystallite size (Lc) in the c-axis direction of the graphite crystal (hexagonal network surface) in the carbon material is preferably at least 20 nm or more, more preferably 30 nm or more, still more preferably 40 nm or more. It is.
Still more preferably, the crystallite size (La) in the ab axis direction of the graphite crystal (hexagonal network surface) in the carbon material is preferably at least 20 nm or more, more preferably 30 nm or more, still more preferably 50 nm or more, most preferably Preferably it is 70 nm or more.
These crystallite sizes can be obtained by the X-ray diffraction method. The Gakushin method is used as an analysis method, and the crystallite size is obtained by using diffraction lines from the (002) plane and the (110) plane of the graphite crystal. Can do.

  Thus, in order to obtain a carbon material with a very high graphitization rate, raw materials such as PAN and rayon are not so preferable as described above, and cyclic hydrocarbons having condensed heterocyclic rings, that is, pitch-based raw materials are used. It is preferable to use a liquid crystal mesophase pitch among them.

As for the form of the carbon material, a spherical or indefinite shape can be used. Especially when a mesophase pitch is used, the growth surface of the graphite crystal is oriented almost in one direction to obtain extremely high thermal conductivity. It is more preferable that it is a fibrous shape that enables the above.
From these things, the pitch-based graphitized carbon fiber using the pitch as a raw material is optimal as the carbon material used in the present invention.

  Examples of raw materials for such pitch-based carbon fibers include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, condensed heterocyclic compounds such as petroleum-based pitch and coal-based pitch, and the like. In particular, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferred.

  In particular, an optically anisotropic pitch, that is, a mesophase pitch is preferable. These may be used singly or in appropriate combination of two or more, but the use of mesophase pitch alone can increase the graphitization rate in the graphitization treatment, and consequently The thermal conductivity of the carbon fiber can be improved, which is a preferred embodiment.

The softening point of the raw material pitch can be determined by the Mettler method, and is preferably in the range of 230 ° C. or higher and 340 ° C. or lower. If the softening point is lower than 230 ° C., fusion between fibers or large heat shrinkage occurs during infusibilization. If the temperature is higher than 340 ° C., the pitch is thermally decomposed in the spinning process, which tends to make the spinning molding difficult. Furthermore, under high temperature spinning conditions, gas components are generated, bubbles are generated inside the spun fibers, leading to strength deterioration, and yarn breakage is likely to occur.
The raw material pitch is spun by a known melt spinning method or melt blowing method, and then graphitized carbon fibers can be obtained by various processes such as infusibilization, carbonization firing, and graphitization.

  In addition, when a short fiber is used as the filler-like heat conductive material, it is necessary to perform fiber cutting and milling. Cutting and milling can be carried out after the graphitization step, but more preferably after the carbonization and firing step, and if necessary, sieving is performed to form a short fiber-like pitch suitable as a filler. Graphitized carbon fiber can be obtained.

In the following, as an example, the steps related to the production of pitch-based graphitized carbon fiber using the melt blow method will be described.
First, the shape of the spinning nozzle is not particularly limited, but those having a ratio of the nozzle hole length to the hole diameter of less than 3 are preferably used, and more preferably about 1.5.

  There are no particular restrictions on the nozzle temperature during spinning, and there is no problem as long as the temperature can maintain a stable spinning state. If the viscosity of the raw material pitch is in an appropriate range, the spinning state is stabilized, that is, the pitch viscosity during spinning is 0.1 to 20 Pa · S, preferably 8 to 16 Pa · S, more preferably 10 to 14 Pa · S. The temperature may be S.

  The pitch fibers drawn out from the nozzle holes are shortened by blowing a gas having a linear velocity of 100 to 10000 m per minute heated to 100 to 370 ° C. in the vicinity of the thinning point. As the gas to be blown, air, nitrogen, argon or the like can be used, but air is preferable from the viewpoint of cost performance.

The pitch fibers are collected on a wire mesh belt, become a continuous mat, and are further cross-wrapped to form a web having a predetermined basis weight (weight per unit area).
The web made of pitch fibers thus obtained has a three-dimensional randomness due to the interlace of the fibers. These webs can be infusibilized by known methods.

  Infusibilization is achieved by applying heat treatment for a certain time at a temperature of about 200 to 300 ° C., for example, using air or a mixed gas obtained by adding ozone, nitrogen dioxide, nitrogen, oxygen, iodine or bromine to air. . Considering safety and convenience, it is desirable to carry out in air.

The infusible pitch fiber is then fired in a temperature range of 700 to 900 ° C. in a vacuum or in an inert gas such as nitrogen, argon or krypton. Usually, the calcination is performed at low pressure using nitrogen at low cost.
A random mat-like web made of infusibilized and fired pitch fibers can be subjected to a graphitization step to produce a random mat-like graphitized carbon fiber aggregate.

  Moreover, when producing short fiber-like carbon fiber, it is preferable to perform a graphitization process after implementing cutting, milling, and sieving as needed. In the cutting and milling processes, a pulverizer or cutting machine such as a Victory mill, a jet mill, or a high-speed rotary mill is used. In order to perform milling efficiently, a method of cutting fibers in a direction perpendicular to the fiber axis by rotating a rotor to which blades are attached at high speed is appropriate.

  The average fiber length of the fibers is controlled by adjusting the number of rotations of the rotor, the angle of the blade, etc., but it is preferable to perform sieving for the purpose of adjusting the fiber length more finely. The sieving can be classified by, for example, passing through a sieve and combining the coarseness of the sieve.

  The graphitization step is performed by heating the carbon fiber to 2300 to 3500 ° C. in a non-oxidizing atmosphere using an Atchison furnace or the like, and a short fiber pitch-based graphitized carbon fiber can be created.

  In addition, it is preferable that the short fiber-like pitch-based graphitized carbon fiber has a structure in which the graphene sheet is closed by observing the shape of the fiber end face with a transmission electron microscope. When the end surface of the filler is closed as a graphene sheet, generation of extra functional groups and localization of electrons due to the shape do not occur, so that the concentration of impurities such as water can be reduced.

  Note that the graphene sheet is closed means that the end of the graphene sheet itself constituting the carbon fiber is not exposed at the end of the carbon fiber, the graphite layer is curved in a substantially U shape, and the curved portion is the end of the carbon fiber. It is in the state exposed to the part.

  The pitch-based graphitized carbon fiber preferably has a substantially flat observation surface with a scanning electron microscope. Here, “substantially flat” means that the surface does not have severe unevenness like a fibril structure, and when there is intense unevenness on the surface of the fiber, the surface area increases upon kneading with the matrix resin. It is desirable that the surface irregularities be as small as possible, since this causes an increase in the viscosity accompanying this and lowers the moldability.

  The fiber diameter of the pitch-based graphitized carbon fiber thus obtained is 1 to 30 μm as an average fiber diameter (D1) observed with an optical microscope, more preferably 3 to 20 μm, and further preferably 5 to 15 μm. When the fiber diameter is larger than 30 μm, adjacent fibers are likely to be fused in the infusibilization step. When the fiber diameter is less than 1 μm, the surface area per weight of the pitch-based carbon fiber filler is increased, and the fiber surface is substantially Even if it is flat, the formability may be lowered in the same manner as a fiber having irregularities on the surface, which may be inappropriate in practice. The percentage of the fiber diameter dispersion (S1), which is the dispersion of the fiber diameter with respect to the average fiber diameter (D1) observed with an optical microscope, is preferably in the range of 5 to 18%. More preferably, it is 5 to 15% of range.

  In addition to pitch-based graphitized carbon fibers using the melt blow spinning method described so far, pitch-based graphitized carbon fibers usable in the present invention include pitch-based graphitized carbon fibers obtained by melt spinning. . However, it is more preferable to use the pitch-based graphitized carbon fiber of this method because the melt blow spinning method is more excellent in the productivity and quality (surface properties, appearance, etc.) of the pitch-based graphitized carbon fiber.

  On the other hand, as a pitch-based graphitized carbon fiber whose fiber diameter is smaller and finer than the pitch-based graphitized carbon fiber described so far, for example, in WO 04/031461 pamphlet, a carbon material as a core material, A composite fiber is prepared by a blend spinning method (or conjugate spinning method) using an olefin-based material or the like as a matrix material, and the matrix material is dissolved and removed as a post-treatment, so that a final fiber of about 0.1 to 1 μm is obtained. A technique for obtaining fine graphitized pitch-based carbon fibers having a diameter with high productivity is disclosed, and these can also be suitably used.

Overall, the average fiber diameter of the pitch-based graphitized carbon fibers preferably used in the present invention is in the range of about 0.1 to 30 μm.
The aspect ratio expressed by the ratio of average fiber length / average fiber diameter is preferably at least 2 or more. This is because when the aspect ratio is less than 2, the characteristics of the fiber shape cannot be exhibited so much that it is difficult to form an efficient heat conduction path.
The aspect ratio is more preferably 5 or more, further preferably 10 or more, and most preferably 20 or more.

  In the case where a composite material is prepared by dispersing and mixing a carbon material in a fluororesin, the aspect ratio is about 10,000 or less, more preferably 1000 or less, and even more preferably 100 or less, from the viewpoint of handleability during dispersion mixing. It is often preferable to use short fiber carbon fibers.

  The fiber length is preferably at least 0.2 μm or more, more preferably 20 μm or more, still more preferably 100 μm or more, and most preferably 200 μm or more.

  When a composite material is prepared by dispersing and mixing a carbon material in a fluororesin, the fiber length is about 100 mm or less, more preferably 10 mm or less, and even more preferably 1 mm or less from the viewpoint of handleability during dispersion mixing. It is often preferable to use short fiber carbon fibers.

  These pitch-based graphitized carbon fibers are preferably mixed in the composite material of the present invention in a range of approximately 5 to 50% by weight, more preferably 10 to 40% by weight, and still more preferably 15 to 30% by weight. It is. Less than 5% by weight is not preferable because the effect of increasing the thermal conductivity of the composite material becomes insufficient, and more than 50% by weight is preferable because the moldability of the composite material is greatly reduced and it becomes difficult to obtain a good molded product. Absent.

  As the thermoplastic resin used in the composite material of the present invention, those having high heat resistance and being thermally stable are preferable, and those having at least a melting point of 250 ° C. or more are preferably used. Among them, fluorine resins excellent in chemical stability and chemical resistance are preferable, for example, tetrafluoroethylene, trifluoroethylene and the like are representatively exemplified, and among them, tetrafluoroethylene or a copolymer thereof is particularly preferable. Preferably mentioned.

  More specifically, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer Preferred examples include coalescence (ETFE).

In addition, as a thermoplastic resin, not only these fluororesins but what blended these heat resistant thermoplastic resins other than a fluororesin and fluororesins can also be used. As these thermoplastic resins, for example, heat-resistant thermoplastic resins having a glass transition temperature of at least 150 ° C. or more are preferably used, and polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyimide, polyamideimide and the like are preferably exemplified. Is done.
These thermoplastic resins can be used in various shapes such as powder, pellets, irregular shapes, fibers, and fibrils, and can also be used in a state dispersed in water or other solvents.

In addition to the pitch-based graphitized carbon fiber and thermoplastic resin as the main components, the composite material of the present invention requires other types of carbon fibers, carbon fine particles, various inorganic fillers, metal fillers, and the like. You may mix according to it. Further, a binder resin, a dispersant, a release agent, a plasticizer and other various additives can be mixed as necessary.
The composite material of the present invention preferably has a thermal conductivity of at least 0.7 W / m · K, more preferably 1.0 W / m · in order to exhibit excellent thermal conductivity and heat dissipation. K or more, more preferably 1.3 W / m · K or more.

  Moreover, the various moldings using the composite material of the present invention are suitably used as heat-conductive or heat-radiating moldings having heat resistance. Molding is possible in various forms such as block, solid, sheet, non-woven fabric, woven fabric, and fiber. Here, the sheet-like molded product is particularly useful as a heat conductive sheet or a heat radiating sheet. The thickness of the sheet depends on the application, but a range of approximately 20 to 5000 μm is appropriate in view of mechanical properties and handling properties.

  The sheet can be molded by various methods as described in the examples described later. Mixing of the thermoplastic resin and pitch-based graphitized carbon fiber can be performed by either a dry method or a wet method. In the latter case, it is also preferable to use an appropriate dispersant or binder together. For those that are not melt-moldable, molding by powder compression, rolling, or the like is preferably used. For those that can be melt-molded, injection molding or extrusion is used. Further, when a fibrous or fibrillar thermoplastic resin is used, a papermaking method is also applicable. Further, when the thermoplastic resin is soluble in a solvent, sheet molding by a casting method is also possible.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention does not receive any limitation by this. In addition, each value in an Example was calculated | required according to the following method.
(1) Average fiber diameter of carbon fiber:
The graphitized pitch-based carbon fiber was photographed with 10 fields of view under an optical microscope at a magnification of 400 times, and the dimensions were determined from the enlarged photograph image.
(2) Average fiber length of carbon fiber:
The graphitic carbon fiber pitch was obtained by photographing 10 visual fields under an optical microscope. The magnification was appropriately adjusted according to the fiber length.
(3) True density of carbon fiber:
It calculated | required using the specific gravity method.
(4) Crystal size:
Obtained by X-ray diffraction, the crystal size in the thickness direction of the hexagonal mesh surface is obtained using diffraction lines from the (002) plane, and the crystal size in the growth direction of the hexagonal mesh surface is obtained by using diffraction lines from the (110) plane. Asked. In addition, the request was made in accordance with the Gakushin Law.
(5) Thermal conductivity of carbon fiber:
The resistivity of the fiber after graphitization treatment prepared under the same conditions except for the pulverization step was measured, and the relationship between the thermal conductivity and the electrical resistivity disclosed in JP-A-11-117143 is represented by the following formula (1 )
[Equation 1]
C = 1272.4 / ER-49.4 (1)
Here, C represents the thermal conductivity (W / m · K) of the fiber after graphitization, and ER represents the electrical specific resistance μΩm of the same fiber.
(6) Thermal conductivity:
Measurement was performed by a probe method using a thermal conductivity measuring device “QTM-500” manufactured by Kyoto Electronics.
(7) Electrical resistivity:
The measurement was performed using an electrical resistance measuring device “Loresta EP” manufactured by Dia Instruments.

[Experimental example] (Production of thermally conductive carbon fiber)
The main raw material was mesophase pitch composed of condensed polycyclic hydrocarbon compounds. The optical anisotropy ratio was 100%, and the softening point was 283 ° C. Using a spinneret having a diameter of 0.2 mm, heated air was ejected from the slit at a linear velocity of 5000 m / min, and the pitch pitch carbon fibers having an average fiber diameter of 15 μm were drawn by pulling the melt pitch. The spun fibers were collected on a belt to form a mat, and a web made of pitch-based carbon fibers having a basis weight of 320 g / m ² by cross-wrapping.

  The web was infusibilized by increasing the temperature from 175 ° C. to 280 ° C. in air at an average temperature increase rate of 7 ° C./min. After firing the infusible web at 800 ° C. in a nitrogen atmosphere, the carbon fiber having an average fiber length of about 400 μm (hereinafter referred to as carbon fiber A) and the carbon fiber having an average fiber length of about 50 μm are obtained by milling, sieving, etc. (Hereinafter referred to as carbon fiber B).

These fibers were then graphitized by heat treatment at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere. The average fiber diameter was 9.7 μm. The percentage of the fiber diameter dispersion to the average fiber diameter was 14%. The true density was 2.18 g / cc.
Using a transmission electron microscope, the pitch-based graphitized carbon fiber was observed at a magnification of 1,000,000 times and magnified on a photograph at 4 million times. It was confirmed that the graphene sheet was closed on the end face of the pitch-based graphitized carbon fiber. Further, the surface of the pitch-based graphitized carbon fiber observed with a scanning electron microscope at a magnification of 4000 times was smooth with no large irregularities.

The crystallite size in the c-axis direction of the graphite crystal obtained by the X-ray diffraction method of the pitch-based graphitized carbon fiber was 33 nm. The crystallite size in the ab axis direction was 57 nm.
Moreover, the single yarn was extracted from the graphitized web heat-treated at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere, and the electrical specific resistance was measured. However, it was 2.2 μΩ · m. The thermal conductivity obtained using the following formula (1) was 530 W / m · K.

[Example 1]
It is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, and PFA resin having a melting point of about 310 ° C. (“NEOFRON PFA” manufactured by Daikin Industries) and 20% by weight of carbon fiber A prepared in the experimental example are mixed with a mixer. After uniformly mixing, the mixture was melt-mixed at 320 ° C. by a single screw extruder and pelletized.
Next, using this pellet, injection molding was performed to prepare a test piece. The cylinder temperature was 390 ° C. and the mold temperature was 200 ° C.
The thermal conductivity of this test piece was 1.4 W / m · K.

[Example 2]
In Example 1, a test piece was prepared in exactly the same manner as in Example 1 except that carbon fiber B was used instead of carbon fiber A. The thermal conductivity of this test piece was 0.9 W / m · K.

[Comparative Example 1]
In Example 1, instead of carbon fiber A, a test piece was prepared in exactly the same manner as in Example except that carbon fiber made from isotropic pitch (“Kureka Chop M-207S” manufactured by Kureha) was used. As a result, the thermal conductivity of this test piece was 0.4 W / m · K.

[Comparative Example 2]
In Example 1, instead of the thermally conductive carbon fiber created in the experimental example, carbon fiber made from polyacrylonitrile (PAN) (“Tenax HTA-C6” manufactured by Toho Tenax) was used, and When a test piece was prepared in exactly the same manner, the thermal conductivity of this test piece was 0.5 W / m · K.

[Example 3]
A carbon fiber dispersion prepared by dispersing carbon fiber A prepared in the experimental example in water in the presence of a dispersant and an aqueous dispersion of polytetrafluoroethylene having a melting point of about 327 ° C. in a solid content ratio. The fibers and polytetrafluoroethylene were mixed so as to have a mixing ratio of 2: 8, then heated to 40 ° C., stirred, and co-coagulated. The co-coagulated product was dried to obtain a composite material composition.
The composition was molded into a plate shape through two rolls, and then pelletized using a pelletizer.
The pellets were filled into a cylindrical mold, compression-pressed at 250 ° C. to prepare a preformed article, and then heated at 370 ° C. for 24 hours to obtain a cylindrical sintered body.
Next, this sintered body was cut in a thickness of 0.4 mm in the circumferential direction in the same manner as peeling, and a film-like test piece was obtained. The thermal conductivity of this test piece was 1.1 W. / M · K.

[Example 4]
In Example 2, a test piece was prepared in exactly the same manner as in Example 1 except that carbon fiber B was used instead of carbon fiber A. The thermal conductivity of this test piece was 0.8 W / m · K.

[Comparative Example 3]
In Example 2, instead of the carbon fiber created in the experimental example, carbon fiber (made by Kureha “Kureka Chop M-201”) using isotropic pitch as a raw material was used in exactly the same manner as in the example. When the test piece was prepared, the thermal conductivity of this test piece was 0.4 W / m · K.

  The composite material of the present invention is suitable as a heat radiating sheet (heat conductive sheet) provided in contact with or near a high-temperature heat source, and is disposed at a joint portion between a device such as a CPU, LED, or laser diode and a heat sink. It can be suitably used as a heat conductive sheet or a heat radiating sheet that enables efficient heat transfer around a heating source such as various heaters.

Claims (4)

It is composed of at least a thermoplastic resin having a melting point of 250 ° C. or higher and a carbon fiber having an aspect ratio of 2 or higher, satisfies the following requirements (A) to (E), and has a thermal conductivity of 0.7 W / m · K or higher. A heat-resistant heat-conducting composite material characterized by
(A) At least 50% by weight or more of the thermoplastic resin is made of a fluororesin,
(B) The carbon fiber is a graphitized carbon fiber using mesophase pitch as a starting material,
(C) The true density of the carbon fiber is 1.7 to 2.5 g / cc,
(D) The crystallite size in the c-axis direction and ab-axis direction of the graphite crystal contained in the carbon fiber is both 20 nm or more,
(E) Carbon fiber is mixed in the composite material at a ratio of 5 to 50% by weight.   The heat-resistant heat conductive composite material according to claim 1, wherein the carbon fiber has a heat conductivity of at least 200 W / m · K.   The heat-resistant thermally conductive composite material according to claim 1 or 2, wherein the fluororesin contains at least tetrafluoroethylene or a copolymer thereof.   A heat-resistant heat conductive sheet obtained by molding the heat-resistant heat conductive composite material according to claim 1 into a sheet having a thickness of 20 to 5000 µm.