JP2007291267A - Thermally conductive molding material and molded sheet using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally conductive molding material which has a high thermal conductivity and is easily processed into a thin layer. <P>SOLUTION: The thermally conductive molding material consists of a pitch-based carbon fiber staple A having a specified aspect ratio in addition to a specified average fiber diameter and an average fiber length and an expansion graphite B. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermally conductive molding material and a molded sheet using the same. More specifically, the present invention relates to a thermally conductive molding material containing pitch-based short carbon fibers of a certain size and expanded graphite, and a molded sheet using the same.

  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. In order to solve these problems, it is necessary to achieve so-called thermal management in which heat is efficiently processed.

  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 also called graphitizable carbon fibers and can be made more graphitic than PAN-based carbon fibers, and it is recognized that high thermal conductivity is easily achieved.

  By the way, in order for carbon fiber to actually act as a heat conducting member, it is difficult to form a carbon fiber alone, and it is necessary to use a very special technique. Therefore, it is necessary to make some matrix and carbon fiber into a composite material, to make it into a molded body, and to improve the thermal conductivity of the molded body. In order to achieve sufficient heat conduction, carbon fibers as fillers mainly responsible for heat conduction must form a three-dimensional network. For example, in the case of spherical fillers of uniform size, the filler network in the molded body depends on the dispersion state, but when uniform dispersion occurs, the behavior becomes percolation. Therefore, in order to obtain sufficient thermal conductivity and electrical conductivity, it is necessary to add a certain amount or more of spherical filler. However, in the method of forming a molded body, it is often very difficult to disperse the medium and the filler at a certain concentration or more.

In addition, as a thermally conductive carbon material, there is a material obtained by processing natural graphite into a scaly shape and rolling expanded graphite that has been subjected to high-temperature treatment under a strong acid. In comparison, a high degree of freedom in molding and a point that light weight can be achieved are merits. A method of using a rolled product of expanded graphite as a heat dissipation material (see Patent Document 1), a resin and expanded graphite are mixed. A method for obtaining a heat dissipation material (see Patent Document 2) is disclosed.
However, from the viewpoint of thermal management, it is becoming necessary that the thermal conductivity as a molded body is extremely high. Therefore, it has been strongly desired to suppress the thermal resistance when the expanded graphite is processed and molded.

JP 2005-252190 A JP 2001-31880 A

  An object of the present invention is to provide a heat dissipating material having reduced thermal resistance without deteriorating the problems of the prior art and degrading moldability.

  In view of improving the thermal conductivity in the final molded body, the inventors of the present invention appropriately use, as a thermal conductive molding material, pitch-based carbon short fibers having high thermal conductivity as a thermal conduction aid for expanded graphite. It has been found that by mixing, a heat dissipation material with reduced thermal resistance can be obtained without degrading moldability, and the present invention has been achieved.

That is, the object of the present invention is to
A pitch-based carbon short fiber A having an average fiber diameter (D1) in the range of 5 μm to 12 μm, an average fiber length (L1) in the range of 10 μm to 60 μm, and a ratio of L1 to D1 of 1 to 10; The expanded graphite B is contained so that the ratio of the weight W (A) of A to the weight (B) of B, W (A): W (B) is in the range of 1: 1 to 1:99. It can be achieved by a thermally conductive molding material.

  Further, in the present invention, the pitch-based carbon short fibers A and the expanded graphite B are uniformly dispersed and mixed, and the true density of the pitch-based carbon short fibers A is in the range of 1.5 to 2.2 g / cc. Yes, the thermal conductivity in the fiber axis direction is 300 W / (m · K) or more, the graphene sheet on the fiber end face of the pitch-based carbon short fiber A is closed, and the expanded graphite B is in the form of particles, It is included that the particle size is in the range of 5 μm to 2000 μm.

  Furthermore, another object of the present invention is achieved by a heat conductive molding sheet obtained by laminating the heat conductive molding material according to claim 1, and the heat conductive molding material according to claim 1 is further heated. Add a plastic resin and mix to make it into a thin layer. The thermoplastic resin is polycarbonate, polyethylene terephthalate, polyethylene 2,6 naphthalate, nylon, polypropylene, polyethylene, polyether ketone, polyphenylene sulfide. The process of forming at least one kind of resin consisting of a group of silicones and the heat conductive molding material into a thin layer may be performed by any one of a hot press method, a cold press method, and a roll rolling method. Is included.

  The further another objective of this invention is achieved by the heat sink produced using the heat conductive molded sheet in any one of Claims 6-9.

  The heat conductive molding material of the present invention is produced by appropriately mixing expanded graphite and pitch-based carbon short fibers having a defined size and structure to reduce thermal resistance and processing the heat conductive molding material. High thermal conductivity can be expressed in the heat conductive sheet. Furthermore, a heat radiating plate can be produced by the thermal conductive sheet, and can be used very effectively for Joule heat countermeasures.

Next, embodiments of the present invention will be described sequentially.
Examples of the raw material of the pitch-based carbon short fiber A used in the present invention include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, and condensed heterocyclic compounds such as petroleum-based pitch and coal-based pitch. Among them, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferable, and optically anisotropic pitch, that is, mesophase pitch is particularly preferable. These may be used alone or in combination of two or more, but it is particularly desirable to use mesophase pitch alone in order to improve the thermal conductivity of the obtained short carbon fiber.

The softening point of the raw material pitch can be obtained by the Mettler method, and it is preferable to use a pitch having a softening point of 240 ° C. or higher and 360 ° C. or lower. When the softening point is lower than 240 ° C., there is a concern that the fibers may be fused or large heat shrinkage occurs during infusibilization. When the softening point is higher than 360 ° C., the thermal decomposition of the pitch occurs and it becomes difficult to form the fibers. Concerns arise.
The raw material pitch is spun by a melt blow method, and then becomes pitch-based short carbon fibers A by infusibilization, firing, milling, sieving, and graphitization. Each step will be described below.

  In the present invention, there is no particular limitation on the nozzle shape of the discharge die for spinning the pitch fiber that is the raw material of the pitch-based carbon short fiber A, but it is preferable that the ratio of the nozzle hole length to the hole diameter is smaller than 3. More preferably, those smaller than 1.5 are used. The temperature of the nozzle at the time of spinning is not particularly limited, and may be a temperature at which a stable spinning state can be maintained, that is, a temperature at which the viscosity of the spinning pitch is 1 to 100 Pa · S, preferably 5 to 30 Pa · S.

  The pitch fibers discharged 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 or argon can be used, but air is desirable from the viewpoint of cost performance.

Pitch fibers are collected on a wire mesh belt to form a continuous mat, and are further cross-wrapped to form a web with a constant basis weight.
The web made of pitch fibers thus obtained is infusible by a known method and fired at 700 to 900 ° C. Infusibilization is achieved at 200 to 350 ° C. using air or a gas obtained by adding ozone, nitrogen dioxide, nitrogen, oxygen, iodine, bromine to air. Considering safety and convenience, it is desirable to carry out in air. The infusibilized pitch fiber is fired in vacuum or in an inert gas such as nitrogen, argon or krypton, but is generally carried out under normal pressure and in low-cost nitrogen.

  The web made of pitch fibers that has been fired is an aggregate of carbon fibers, but milling and sieving are performed in order to further shorten the carbon fibers and to keep the fiber length constant. . For milling, a pulverizer such as a Victory mill, a jet mill, a high-speed rotary mill, or a cutting machine 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 short carbon fibers produced by milling is controlled by adjusting the rotational speed of the rotor, the angle of the blade, and the like. Furthermore, the fiber length is divided into 10 to 60 μm, more preferably 15 to 50 μm by the sieve. Such size adjustment can be achieved by combining the coarseness of the sieve.

  The pitch-based carbon short fiber A of the present invention is heated to 2300 to 3500 ° C. and graphitized to obtain the final pitch-based carbon short fiber A. Graphitization is performed in a non-oxidizing atmosphere.

  Next, the shape of the pitch-based carbon short fiber A in the present invention will be described. The fiber length of the pitch-based carbon short fibers A is determined by the above-described sieving and is 10 to 60 μm, and the average fiber diameter is almost uniquely determined by the spinning process. The average fiber diameter of the pitch-based carbon short fibers A is a value smaller by 1 to 2 μm than the average fiber diameter of the raw yarn when it is spun. In the present invention, the average fiber diameter of the pitch-based carbon short fibers A is in the range of 5 μm to 12 μm. 7 to 11 μm is particularly preferable.

  When the average fiber diameter is smaller than 5 μm, the specific surface area of the pitch-based short carbon fibers A increases and mixing with the expanded graphite B becomes difficult. On the other hand, if it is larger than 12 μm, infusibility becomes particularly difficult in processing from the raw yarn, and there is a concern that the productivity will deteriorate and the price will become extremely high.

  Thus, it is necessary to further define the ratio between the average fiber diameter and the average fiber length within an appropriate range of the average fiber diameter and the average fiber length. This is because the size of the fiber diameter and the size of the fiber length are not reversed, and as a result, the surface area of the pitch-based carbon short fibers A can be suppressed within a certain range.

  In the present invention, the ratio of the average fiber length to the average fiber diameter is desirably 1 to 10, and more desirably 2 to 5. When the ratio is smaller than 1, the ratio of short carbon fibers in which the range of fiber diameter and fiber length is reversed increases and the specific surface area is increased, so that the dispersibility between the short carbon fibers and the expanded graphite B is deteriorated. On the other hand, when it is larger than 10, although the reinforcing effect when the heat conductive molding material is formed into a molded body such as a heat conductive sheet can be expected, the number of short carbon fibers in the unit volume decreases, the thermal resistance This reduces the effect of reducing.

  In the present invention, the mixing ratio of the pitch-based carbon short fibers A and the expanded graphite B is 1: 1 to 1:99 by weight. When the weight ratio of the pitch-based carbon short fibers A is larger than that of the expanded graphite B, the moldability is deteriorated. On the other hand, unless the pitch-based carbon short fibers A having a weight ratio of at least 1% are added, the effect of reducing the thermal resistance is not sufficiently manifested.

  Furthermore, it is preferable that the pitch-based carbon short fibers A and the expanded graphite B are uniformly dispersed and mixed. Specifically, the pitch-based carbon short fibers A and the expanded graphite B are mixed with a mixer, a blender, a roll, and an extrusion. It can carry out by processing by mixing apparatuses, such as a machine, or a kneading apparatus.

The true density of the pitch-based carbon short fibers A strongly depends on the graphitization temperature, but is preferably in the range of 1.5 to 2.2 g / cc. More preferably, it is 1.6-2.0 g / cc. The thermal conductivity in the fiber axis direction of the pitch-based carbon short fibers A is preferably 300 W / (m · K) or more, and more preferably 400 W / (m · K) or more.
The pitch-based short carbon fiber A fiber is particularly excellent in thermal conductivity and handling properties by satisfying all the above-mentioned ranges.

Furthermore, it is preferable that the graphene sheet of the fiber end surface of the pitch-based carbon short fiber A in the present invention is closed. Whether or not the graphene sheet is closed can be easily confirmed by observation with a transmission electron microscope.
That is, the state in which the graphene sheet is closed means that the end of the graphene sheet itself is not exposed to the end of the pitch-based carbon short fiber A, and the graphene sheet is curved substantially U-shaped, and the curved portion is pitch-based. The state exposed to the carbon short fiber A edge part is pointed out.

  When the graphene sheet is closed, 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. This is preferable because the affinity can be further increased. In particular, in the pitch-based carbon short fibers A having a short fiber length as in the present invention, it is particularly preferable that the graphene sheet is closed because the ratio of the end faces in the surface area of the pitch-based carbon short fibers A is high. .

  In addition, the pitch-based carbon short fiber A filler may be surface-treated, and then a sizing agent may be added to the filler in an amount of 0.01 to 10% by weight, preferably 0.1 to 2.5% by weight. As the sizing agent, any commonly used sizing agent can be used. Specifically, an epoxy compound, a water-soluble polyamide compound, a saturated polyester, an unsaturated polyester, vinyl acetate, water, alcohol, glycol are used alone or in a mixture thereof. Can do. However, in the present invention, since the reinforcing effect is not so important, there is little need to actively carry out sizing that becomes thermal resistance.

  The graphite that is the raw material of the expanded graphite B in the present invention is preferably graphite with high crystallinity such as natural graphite, quiche graphite, and pyrolytic graphite. However, natural graphite is more preferable in terms of price. There is no restriction | limiting as natural graphite, A commercial item can be used. The expanded graphite B is immersed in a solution containing an acidic substance and an oxidizing agent to generate a graphite intercalation compound, and the graphite intercalation compound is heated to expand the C-axis direction of the graphite crystal to obtain expanded graphite B. If necessary, it can be obtained by including a washing step and a drying step. As the acidic substance used for the treatment of graphite, sulfuric acid or a mixed solution of sulfuric acid and nitric acid is preferably used. Furthermore, hydrogen peroxide and hydrochloric acid are preferably used as the oxidizing agent in order to obtain good expanded graphite B.

  There is no limitation on the method of converting graphite into expanded graphite B, but as a known method, graphite is immersed in an acidic substance which is sulfuric acid or a mixed solution of sulfuric acid and nitric acid, and an oxidizing agent such as hydrogen peroxide or hydrochloric acid is further added. There is a method in which a graphite intercalation compound is formed by adding and treating, followed by washing with water and then rapid heating to expand the C-axis direction of the graphite crystal. Alternatively, commercially available expanded graphite B may be used.

  The expanded graphite B in the present invention is preferably in the form of particles and having a particle size in the range of 5 to 2000 μm. When the size is less than 5 μm, the surface area increases remarkably when mixed with short carbon fibers. When a particle having a particle diameter of 2000 μm or more is used, there is no problem with mixing with short carbon fibers, but the moldability is deteriorated. More preferably, it is 10-1000 micrometers, More preferably, it is 30-500 micrometers.

  The heat conductive molding material of the present invention can be processed into a thin layer to form a heat conductive molding sheet. Although the thickness is in the range of 0.1 to 5 mm, the range of 0.1 to 1 mm is particularly preferable in order to improve the thermal conductivity.

  Further, a thermoplastic resin can be added to the heat conductive molding material, mixed and kneaded by a known method, and then processed into a thin layer to obtain a heat conductive sheet. Examples of the thermoplastic resin added to the heat conductive molding material include polycarbonates, polyethylene terephthalates, polyethylene 2,6 naphthalates, nylons, polypropylenes, polyethylenes, polyether ketones, polyphenylene sulfides, and silicones. Two or more polymer resin compositions can be used. More specifically, ethylene-α-olefin copolymers such as polyethylene, polypropylene, ethylene-propylene copolymer, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymer , Polyvinyl alcohol, polyacetal, fluorine resin (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, ABS resin, polyphenylene ether (PPE) ) Resin, modified PPE resin, aliphatic polyamide, aromatic polyamide, polyimide, polyamideimide, polymethacrylic acid (polymethacrylate such as polymethylmethacrylate) Ester), polyacrylic acids, polycarbonate, polyphenylene sulfide, polysulfone, polyether sulfone, polyether nitrile, polyether ketone, polyketone, liquid crystal polymer, ionomer and the like. And a high molecular resin composition may be used individually by 1 type, may be used in combination of 2 or more types suitably, and may use the polymer alloy which consists of 2 or more types of polymeric materials. Examples of the thermosetting resin include an epoxy resin, a phenol resin, a silicone resin, a polyurethane resin, a polyimide resin, a thermosetting modified PPE resin, and a thermosetting PPE resin. And these may be used by 1 type, may be used in combination of 2 or more types suitably, and may use the polymer alloy which consists of 2 or more types of polymeric materials. Furthermore, as the matrix resin, a thermoplastic resin and a thermosetting resin can be appropriately mixed and used in order to develop desired physical properties in the carbon fiber reinforced plastic molded body.

  The mixing amount of the heat conductive molding material and the thermoplastic resin can be changed greatly depending on the performance of the heat conductive sheet. However, when the thermoplastic resin is not added and up to about 50% by weight of the thermoplastic resin is added. Defined as a range. If it exceeds 50% by weight, the moldability is good, but the thermoplastic resin composition becomes thermal resistance.

  In the present invention, thin-layer processing can be performed by any one of a hot press method, a cold press method, and a roll rolling method, and the heat conductive molding material can be processed into a heat conductive sheet. In particular, a roll rolling method is preferably used. Moreover, it is possible to process into a sheet form, returning the C axis | shaft by which the expanded graphite B was extended by using a heating roll in the case of roll rolling. Moreover, when a heating roll is used, the elongation derived from a thermoplastic resin can be provided to a heat conductive sheet by melt | dissolving and resolidifying a thermoplastic resin composition.

  Since the heat conductive sheet of the present invention can be punched or cut, it can be used as a flat heat sink. This heat radiating plate prevents heat storage of electronic components and motors, and can quickly release generated heat to the outside of the system.

Examples are shown below, but the present invention is not limited thereto.
(1) The average fiber length and the fiber diameter dispersion of the pitch-based carbon short fibers A were determined by photographing the graphitic graphitized pitch-based carbon short fibers A at 400 times under an optical microscope at 10Ox.
(2) The thermal conductivity of the carbon fiber is determined by measuring the resistivity of the yarn after firing, and expressing the relationship between the thermal conductivity and electrical resistivity disclosed in JP-A-11-117143 (1) )
[Equation 1]
K = 1272.4 / ER-49.4 (1)
Here, K represents the thermal conductivity W / (m · K) of the carbon fiber, and ER represents the electrical specific resistance μΩm of the carbon fiber.
(3) The true density of the pitch-based carbon short fibers A was determined using a specific gravity method.
(4) The heat dissipation was evaluated at a temperature after 30 seconds by placing the weight heated to 75 ° C. on the thermally conductive molded sheet for 3 minutes, then removing the weight. Evaluations were made assuming that the temperature after 30 seconds was lower than the temperature of Comparative Example 1, and that the higher one was worse. Evaluation was carried out using a thermoviewer.

[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 287 ° C. Using a melt blow method, a hole cap having a diameter of 0.2 mmφ was used, heated air was ejected from the slit at a linear velocity of 4800 m / min, and the pitch was melted to produce pitch-based short fibers having an average fiber diameter of 15 μm. . The spun fibers were collected on a belt to form a mat, and then a web made of pitch-based short fibers having a basis weight of 320 g / m ^{2 by} cross wrapping.

  The web was infusibilized by raising the temperature from 175 ° C. to 285 ° C. in air at an average heating rate of 7 ° C./min. The infusible web was fired at 800 ° C. in a nitrogen atmosphere, and then milled and sieved so that the average fiber length was 30 μm. Then, it graphitized by heating to 3000 degreeC with the Atchison furnace made into non-oxidizing atmosphere. The average fiber diameter was 10.1 μm. This was designated as pitch-based carbon short fiber A. The thermal conductivity was 480 W / (m · K). The true density was 1.95 g / cc. The graphene sheet was closed on the end face of the pitch-based short carbon fiber A observed with a transmission electron microscope.

Pitch-based short carbon fibers A and expanded graphite B (expanded graphite B) made by Nishimura Graphite having an average particle size of 100 μm were mixed at a weight ratio of 25:75 to obtain a heat conductive molding material.
The produced heat conductive molding material was made into a 0.3 mm thick heat conductive molding sheet by roll rolling. Roll rolling was performed at a roll temperature of 200 ° C. and a pressure of 7.35 MPa.
The temperature 30 seconds after removing the weight was 33 ° C., and the heat dissipation was good.

[Example 2]
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 287 ° C. Using a melt blow method, a hole cap having a diameter of 0.2 mmφ was used, heated air was ejected from the slit at a linear velocity of 4800 m / min, and the melt pitch was pulled to produce pitch-based short fibers having an average diameter of 15 μm. The spun fibers were collected on a belt to form a mat, and then a web made of pitch-based short fibers having a basis weight of 320 g / m ^{2 by} cross wrapping.

  The web was infusibilized by raising the temperature from 175 ° C. to 285 ° C. in air at an average heating rate of 7 ° C./min. The infusibilized web was fired at 800 ° C. in a nitrogen atmosphere, and then milled and sieved to an average fiber length of 30 μm. Then, it graphitized by heating to 3000 degreeC with the Atchison furnace made into non-oxidizing atmosphere. The average fiber diameter was 10.1 μm. This was designated as pitch-based carbon short fiber A. The thermal conductivity was 480 W / (m · K). The true density was 1.95 g / cc. The graphene sheet was closed on the end face of the pitch-based short carbon fiber A observed with a transmission electron microscope.

Pitch-based short carbon fibers A and expanded graphite B (expanded graphite B) made of Nishimura Graphite having an average particle size of 100 μm were mixed at a weight ratio of 1: 1 to obtain a heat conductive molding material.
The produced heat conductive molding material was made into a 0.3 mm thick heat conductive molding sheet by roll rolling. Roll rolling was performed at a roll temperature of 200 ° C. and a pressure of 7.35 MPa.
After removing the weight, the temperature after 30 seconds was 30 ° C., and the heat dissipation was good.

[Example 3]
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 287 ° C. Using a melt blow method, a hole cap having a diameter of 0.2 mmφ was used, heated air was ejected from the slit at a linear velocity of 4800 m / min, and the melt pitch was pulled to produce pitch-based short fibers having an average diameter of 15 μm. The spun fibers were collected on a belt to form a mat, and then a web made of pitch-based short fibers having a basis weight of 320 g / m ^{2 by} cross wrapping.

  The web was infusibilized by raising the temperature from 175 ° C. to 285 ° C. in air at an average heating rate of 7 ° C./min. The infusible web was fired at 800 ° C. in a nitrogen atmosphere, and then milled, and sieved to an average fiber length of 30 μm. Then, it graphitized by heating to 3000 degreeC with the Atchison furnace made into non-oxidizing atmosphere. The average fiber diameter was 10.1 μm. This was designated as pitch-based carbon short fiber A. The thermal conductivity was 480 W / (m · K). The true density was 1.95 g / cc. The graphene sheet was closed on the end face of the pitch-based short carbon fiber A observed with a transmission electron microscope.

Pitch-based short carbon fibers A and expanded graphite B (expanded graphite B) made by Nishimura Graphite having an average particle size of 100 μm were mixed at a weight ratio of 5:95 to obtain a heat conductive molding material.
The produced heat conductive molding material was made into a 0.3 mm thick heat conductive molding sheet by roll rolling. Roll rolling was performed at a roll temperature of 200 ° C. and a pressure of 7.35 MPa.
After removing the weight, the temperature after 30 seconds was 40 ° C., and the heat dissipation was good.

[Comparative Example 1]
Only the expanded graphite B (expanded graphite B) made by Nishimura Graphite having an average particle diameter of 100 μm without using the pitch-based carbon short fibers A was formed into a thermally conductive molded sheet having a thickness of 0.3 mm by roll rolling. Roll rolling was performed at a roll temperature of 200 ° C. and a pressure of 7.35 MPa.
After removing the weight, the temperature after 30 seconds was 43 ° C., and the heat dissipation was normal.

[Example 4]
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 287 ° C. Using a hole cap with a diameter of 0.2 mmφ, heated air was ejected from the slit at a linear velocity of 4800 m / min, and the melt pitch was pulled to produce pitch-based short fibers having an average diameter of 15 μm. The spun fibers were collected on a belt to form a mat, and then a web made of pitch-based short fibers having a basis weight of 320 g / m ^{2 by} cross wrapping.

  The web was infusibilized by raising the temperature from 175 ° C. to 285 ° C. in air at an average heating rate of 7 ° C./min. The infusible web was fired at 800 ° C. in a nitrogen atmosphere, and then milled, and sieved to an average fiber length of 30 μm. Then, it graphitized by heating to 3000 degreeC with the Atchison furnace made into non-oxidizing atmosphere. The average fiber diameter was 10.1 μm. This was designated as pitch-based carbon short fiber A. The thermal conductivity was 480 W / (m · K). The true density was 1.95 g / cc. The graphene sheet was closed on the end face of the pitch-based short carbon fiber A observed with a transmission electron microscope.

The pitch-based carbon short fibers A and the expanded graphite B (expanded graphite B) made by Nishimura Graphite with an average particle size of 100 μm are mixed at a weight ratio of 1: 1, and polyethylene is used as the thermoplastic resin for the pitch-based carbon short fibers A. And 10% by weight based on the total weight of the expanded graphite B and a thermally conductive molding material.
The produced heat conductive molding material was made into a 0.3 mm thick heat conductive molding sheet by roll rolling. Roll rolling was performed at a roll temperature of 200 ° C. and a pressure of 7.35 MPa.
After removing the weight, the temperature after 30 seconds was 39 ° C., and the heat dissipation was slightly good. However, elasticity was imparted to the heat conductive molded sheet.

[Example 5]
The heat conductive molded sheet produced in Example 2 was cut into a U shape to produce a model heat sink. Production (processing) was easy. When a heated weight was placed, it was observed that heat was diffusing in a U shape, and the heat dissipation was good.

Claims (10)

A pitch-based carbon short fiber A having an average fiber diameter (D1) in the range of 5 μm to 12 μm, an average fiber length (L1) in the range of 10 μm to 60 μm, and a ratio of L1 to D1 of 1 to 10; , Expanded graphite B,
A thermally conductive molding material, which is contained such that the ratio of the weight W (A) of A to the weight (B) of B, W (A): W (B) is in the range of 1: 1 to 1:99.   The heat conductive molding material according to claim 1, wherein the pitch-based carbon short fibers A and the expanded graphite B are uniformly dispersed and mixed.   The true density of the pitch-based carbon short fibers A is in the range of 1.5 to 2.2 g / cc, and the thermal conductivity in the fiber axis direction is 300 W / (m · K) or more. Thermally conductive molding material.   The heat conductive molding material in any one of Claims 1-3 with which the graphene sheet of the fiber end surface of the pitch-type carbon short fiber A is closed.   The thermally conductive molding material according to any one of claims 1 to 4, wherein the expanded graphite B is in the form of particles and has a particle size in the range of 5 µm to 2000 µm.   A heat conductive molding sheet obtained by forming the heat conductive molding material according to claim 1 into a thin layer.   A heat conductive molding sheet according to claim 1, wherein a thermoplastic resin is further added to the heat conductive molding material according to claim 1 and mixed to form a thin layer.   The thermoplastic resin is at least one resin comprising the group of polycarbonates, polyethylene terephthalates, polyethylene 2,6 naphthalates, nylons, polypropylenes, polyethylenes, polyether ketones, polyphenylene sulfides, and silicones. The thermally conductive sheet according to claim 7.   The thermally conductive molded sheet according to any one of claims 6 to 8, wherein the treatment for forming the thermally conductive molding material into a thin layer is performed by any one of a hot press method, a cold press method, and a roll rolling method.   The heat sink produced using the heat conductive molded sheet in any one of Claims 6-9.