JP2018031098A - Pitch-based carbon fiber milled, thermally conductive molded body, and method for producing pitch-based carbon fiber milled - Google Patents

Abstract

Disclosed is a pitch-based carbon fiber mill that is excellent in thermal conductivity and has little inhibition of curing of a matrix such as a resin. An anisotropic pitch is used as a raw material, an average fiber diameter is 5 to 15 μm, a volume-converted average fiber length is 300 μm or less, a fiber cross section has an onion structure or a random structure, and a fiber end surface by a transmission electron microscope In observation, a pitch-based carbon fiber milled with an open graphene sheet. The fiber length of 10% (L10) cumulative fiber length converted to volume average fiber length is 40% or more. The fiber length of 90% (L90) cumulative fiber length is 250% or less with respect to the volume-converted average fiber length. [Selection] Figure 3

Description

  The present invention relates to a heat conductive filler for a heat radiating member, a pitch-based carbon fiber mill used as a reinforcing material for resin and rubber, and the like.

  In recent years, with the increase in the density of heat-generating electronic components and the reduction in size, thickness, and weight of electronic devices, further improvement in heat dissipation characteristics for heat dissipation members used for them has been demanded. Conventionally, metals such as aluminum and copper with high thermal conductivity have been used as the heat radiating member, but further high thermal conductivity and light weight are required, and from a cured product filled with a thermal conductive filler. A heat conductive sheet, a fluid heat conductive paste in which a liquid matrix is filled with a heat conductive filler, a heat conductive paint, a heat conductive adhesive, and the like have been proposed. As a material for realizing these, a pitch-based carbon fiber having a light weight, a high heat dissipation property, and a low expansion property has attracted attention.

  Carbon fibers can be classified into PAN-based carbon fibers using polyacrylonitrile (PAN) as a raw material and pitch-based carbon fibers using pitches as a raw material. Carbon fiber is widely used for aerospace applications, construction / civil engineering applications, sports / leisure applications, etc., utilizing the characteristics of high strength and elastic modulus. Carbon fiber is said to have high thermal conductivity and excellent heat dissipation. The thermal conductivity of the PAN-based carbon fiber is usually lower than 200 W / (m / K). This is because the PAN-based carbon fiber is a non-graphitizable carbon fiber and it is difficult to increase the growth of graphite crystals that are responsible for heat conduction. On the other hand, the pitch-based carbon fiber using anisotropic pitch as a raw material tends to form a large graphite crystal and easily exhibits a large thermal conductivity. For this reason, the pitch-type carbon fiber which uses a mesophase pitch as a raw material is anticipated as a highly heat conductive filler.

  Processing of carbon fiber into a heat conductive member is mainly performed by combining it with a matrix to form a resin composition. And the molded object which is a resin composition is used in the state stuck on the surface of the heat generating body, or the state inserted | pinched between a heat generating body and a heat radiator. Therefore, it is desired to impart flexibility to the resin composition, and a rubber composition filled with a heat conductive filler has been proposed. However, when the heat conductive filler is filled in a high amount, the viscosity becomes high, and further, the rubber curing reaction may be inhibited.

  Therefore, in Patent Document 1 and Patent Document 2, by making pitch-based graphitized short fibers having a specific fiber end face shape and fiber surface structure, an increase in viscosity accompanying an increase in surface area when a composition with rubber is obtained. It has been proposed that the rubber can be highly filled with pitch-based graphitized short fibers without preventing or inhibiting the curing. However, in order to suppress curing inhibition, it is difficult to sufficiently develop the heat conduction characteristics of the heat conductive filler itself by using a specific fiber end face shape.

  Also, in Patent Document 3, when graphitized and then pulverized, vertical cracks are likely to occur in the fiber axis direction, and the ratio of the fracture surface area to the total surface area of the pulverized carbon fiber increases, resulting in heat transfer efficiency. Has been pointed out. Therefore, in Patent Document 3, the occurrence of vertical cracks in the fiber axis direction is suppressed by performing pulverization after spinning, infusibilization, and carbonization and then performing graphitization.

  However, as proposed in Patent Document 1, Patent Document 2, and Patent Document 3, it is considered that most graphene sheets are closed at the fiber end face by graphitizing after pulverization, and the heat conduction characteristics are sufficiently It is thought that it is difficult to express it. For this reason, there has been a demand for a carbon fiber mill with high thermal conductivity that minimizes the inhibition of curing of the matrix resin and the rubber composition and suppresses vertical cracks in the fiber axis direction during pulverization.

  Patent Document 4 relates to a method for producing a carbon fiber having a high tensile elastic modulus and a high compressive strength in a pitch-based carbon fiber. When producing a carbon fiber, the structure is controlled at the inlet hole inlet portion and melt spinning is performed. There has been proposed a carbon fiber manufacturing method characterized by the above. Patent Document 5 explains that the production of a carbon fiber precursor used as a material for a heat-dissipating sheet explains that the domain size in the fiber cross section has a great influence on the thermal conductivity. Proposed. In this invention, the knowledge of patent document 4 and patent document 5 was newly optimized with respect to manufacture of pitch-type carbon fiber milled.

W02010 / 087371 JP 2007-291576 A Japanese Patent No. 4759122 Japanese Patent Laid-Open No. 7-42025 JP 2014-188129 A

  In order to improve the thermal conductivity of the thermally conductive molded body, when carbon fiber milled is filled in resin or rubber at high density, the curing reaction of the resin or rubber is often hindered. It was difficult.

  Moreover, when suppressing hardening inhibition, it is difficult to fully express the heat conductive property of heat conductive filler itself by making it into the state where a specific fiber end surface shape, ie, most graphene sheets, is closed.

  Therefore, the object of the present invention is to minimize the resin or rubber curing inhibition while having higher thermal conductivity than conventional products, and when the matrix is rubber, it is packed in a high density as long as the flexibility is not impaired. Thus, it is an object to provide a pitch-based carbon fiber mill capable of producing a molded body having high thermal conductivity.

The present invention as means for solving the problems is as follows.
(1) Using an anisotropic pitch as a raw material, the average fiber diameter is 5 to 15 μm, the volume-converted average fiber length is 300 μm or less, the fiber cross section is an onion structure or a random structure, and the fiber end face is observed with a transmission electron microscope And pitch-based carbon fiber milled, wherein the graphene sheet is open.
(2) The fiber length of 10% (L10) cumulative fiber length is 40% or more, and the fiber length of 90% (L90) cumulative fiber length is 250% with respect to the volume average fiber length. The pitch-based carbon fiber milled as described in (1), wherein:
(3) The pitch-based carbon fiber mill according to (1) or (2), wherein the thermal conductivity in the fiber direction is 500 to 1400 W / mK.
(4) The pitch-based carbon fiber milled according to any one of (1) to (3) and at least one matrix component selected from a thermoplastic resin, a thermosetting resin, and a rubber component. Thermally conductive molded body.
(5) First step of melt spinning an optically anisotropic mesophase pitch to obtain a pitch-based carbon fiber precursor having an onion structure or a random structure in the fiber cross section, and the pitch system obtained in the first step After the carbon fiber precursor is heat-treated in the infusibilization step and the carbonization step, the carbon fiber precursor is obtained in the second step and the second step in which the carbon fiber precursor is fired at a firing temperature of 2800 ° C. to 3200 ° C. A pitch-based carbon fiber milled production method for producing a pitch-based carbon fiber milled product according to (1) by adjusting the size of the fired pitch-based carbon fiber product from the pulverizing / classifying step.

  The pitch-based carbon fiber mill of the present invention has higher thermal conductivity than conventional products, and can be filled with high density within a range that does not impair flexibility by minimizing the inhibition of resin matrix hardening. Therefore, it is possible to provide a thermally conductive molded body having high thermal conductivity.

Graph for explaining that fiber length of 10% (L10) cumulative fiber length is 40% or more with respect to volume average fiber length Graph for explaining that fiber length of accumulated 90% (L10) of converted fiber length is 250% or less with respect to volume converted average fiber length Pitch-based carbon fiber milled flow chart It is an enlarged view of the spinning nozzle part for making the cross section of anisotropic pitch-type carbon fiber into a random structure. It is an enlarged view of the spinning nozzle part for making the cross section of an anisotropic pitch-type carbon fiber into an onion structure. It is a whole photograph of pitch type carbon fiber milled (random structure). It is a photograph of the section and surface of pitch system carbon fiber mill. It is the photograph of the fiber end surface observed with the transmission electron microscope, and shows a state in which the graphene sheet is opened. It is the photograph of the fiber end surface observed with the transmission electron microscope, and shows the state where the graphene sheet is closed.

  A pitch-based carbon fiber mill that is an embodiment of the present invention will be described. The pitch-based carbon fiber milled of this embodiment is mixed with a matrix material and used as a thermally conductive molded body. As the matrix material, at least one selected from the group consisting of a thermoplastic resin, a thermosetting resin, and a rubber component can be used. Since the pitch-based carbon fiber milled of the present embodiment is excellent in thermal conductivity, it is not necessary to fill with high density so that the flexibility of the thermally conductive molded body is impaired. Therefore, a thermally conductive molded body having both thermal conductivity and flexibility can be obtained.

  The pitch-based carbon fiber milled of the present embodiment uses anisotropic pitch as a raw material, the average fiber diameter is 5 to 15 μm, the volume-converted average fiber length is 300 μm or less, and the fiber cross section is configured with an onion structure or a random structure. The graphene sheet is open in the fiber end face observation with a transmission electron microscope. Hereinafter, the reasons for limitation will be described with reference to each component.

(About anisotropic pitch)
An anisotropic pitch is obtained by generating a mesophase with respect to a predetermined pitch and modifying it to a pitch rich in spinnability. Distillation, solvent extraction, hydrogenation, etc. are performed if necessary, and further impurities are removed by filtration, etc., and reforming is performed by thermal polymerization. As the predetermined pitch, coal-based pitches such as coal tar and coal-tar pitch, coal-liquefied pitch, ethylene tar pitch, petroleum-based pitches such as decant oil pitch obtained from fluid catalytic catalytic cracking residue oil, catalysts from naphthalene, etc. A synthetic pitch generated by using can be used. When the total anisotropic pitch is 100% by volume, the mesophase content is preferably 60% by volume or more, more preferably 90% or more. By increasing the mesophase content, the conversion to graphite crystals is facilitated in the graphitization step described later, and the heat conduction characteristics are improved.

(Onion structure and random structure)
As a structure seen in the cross section of the anisotropic pitch-based carbon fiber, a radial structure, an onion structure, and a random structure are known. The radial structure is a structure in which the carbon fiber graphite crystal molecules (the carbon hexagonal network plane) are radial with respect to the central axis of the fiber. However, an actual anisotropic pitch-based carbon fiber is not formed in a radial shape in which all the cross sections are neatly arranged, and often includes an onion-like structure and a random-like structure. Therefore, when about 80% or more of the cross section of the anisotropic pitch-based carbon fiber is radial, it is regarded as a radial structure.

  The onion structure refers to a structure in which the carbon fiber graphite crystal molecules (the carbon hexagonal network plane) are concentric with the central axis of the fiber. However, the actual anisotropic pitch-based carbon fiber is not formed in a concentric circle in which all the cross-sections are neatly arranged and often includes a partially radial-like structure or a random-like structure. . Therefore, when about 80% or more of the cross section of the anisotropic pitch-based carbon fiber is concentric, it is regarded as an onion structure.

  The random structure refers to a structure in which the carbon fiber graphite crystal molecules (the carbon hexagonal network plane) have neither a radial structure part nor a concentric structure part with respect to the central axis of the fiber. When the cross-section of the anisotropic pitch-based carbon fiber is neither the radial structure described above nor the onion structure, it is regarded as a random structure.

    It is known that anisotropic pitch-based carbon fibers are greatly changed in fiber characteristics and structure by controlling spinning conditions in the melt spinning process. The structure of the cross section of the anisotropic pitch-based carbon fiber can be controlled by the shape of the spinning nozzle in the spinning process, the way the pitch flows immediately above the nozzle, and the like.

  Here, when an anisotropic pitch-based carbon fiber is used as a thermally conductive filler, when the fiber surface is observed with a scanning electron microscope, there may be no defects (hereinafter referred to as uneven defects) consisting of severe unevenness. is important. In the case where there are uneven defects on the fiber surface, the viscosity increases during kneading with the matrix material, and further causes the inhibition of curing of the matrix material.

  When the fiber cross section has a radial structure, irregularities are easily generated on the fiber surface, and further, the frequency of occurrence of vertical cracks in the fiber axis direction is increased in the pulverization step. Therefore, it is important to control the fiber cross section so as to have an onion structure or a random structure in which unevenness defects are less likely to occur. The present inventors have found that the effect of inhibiting the hardening of the matrix material by anisotropic pitch-based carbon fibers can be greatly reduced by configuring the structure of the fiber cross section with an onion structure or a random structure.

  In addition, by using an onion structure or a random structure, vertical cracks in the fiber axis direction are less likely to occur in the pulverization step after the graphitization step (details of these steps will be described later), and the thermal conductivity can be increased. . The structure of the cross section of the pitch-based carbon fiber mill can be specified by observing with a scanning microscope or a polarizing microscope.

(About the average fiber diameter of pitch-based carbon fiber milled)
The average fiber diameter of the pitch-based carbon fiber milled is 5 μm or more and 15 μm or less, preferably 10 μm or more and 13 μm or less. When the average fiber diameter is less than 5 μm, the thermal conductivity decreases. When the average fiber diameter exceeds 15 μm, vertical cracks are likely to occur in the fiber axis direction, and the surface area of the fibers increases, which causes poor curing of the matrix material when mixed with the matrix material.

  As the average fiber diameter, an arithmetic average value of the fiber diameters of each fiber measured using a scanning electron microscope can be used.

(For volume converted average fiber length of 300 μm or less)
The volume-converted average fiber length of the pitch-based carbon fiber milled is 300 μm or less. When the volume-converted average fiber length exceeds 300 μm, the pitch-based carbon fiber milled bulk increases, which may cause poor curing of the matrix material. Therefore, it is necessary to reduce the amount of pitch-based carbon fiber milled mixed with the matrix material, and as a result, the thermal conductivity is greatly reduced. The lower limit of the volume-converted average fiber length of the pitch-based carbon fiber milled is not particularly limited, but is preferably 100 μm. When the volume-converted average fiber length is shorter than 100 μm, the thermal conductivity of the heat conductive molded body is lowered.

(About the graphene sheet is open)
In the fiber end face observation with a transmission electron microscope, the graphene sheet of anisotropic pitch-based carbon fiber must be open. The graphene sheet is a sheet-like material having a lattice structure in which carbon atoms are bonded in a hexagonal shape on a plane. That the graphene sheet is open means that the end of the graphene sheet constituting the carbon fiber is exposed at the end of the carbon fiber. On the other hand, the graphene sheet being closed means that the graphite layer is curved in a U shape and the curved portion is exposed at the end of the carbon fiber.

  By making the graphene sheet open, graphite crystals are arranged over the entire length of the short fibers, so that the heat conduction efficiency can be increased. In addition, an electrically insulating film or the like is easily formed.

  In order to make the graphene sheet open, as described later, the pitch-based carbon fibers need to be infusible and carbonized, then graphitized in a chopped state or a long fiber state, and pulverized after the graphitization treatment. . On the other hand, in Patent Document 3, as described in the background art, since graphitization is performed after pulverization, the graphene sheet is closed and the heat conduction characteristics cannot be sufficiently exhibited.

  Here, when the graphene sheet is open, the functional groups and active sites in the fiber cross section are increased and the reaction with the catalyst is promoted more easily than when the graphene sheet is closed. However, in this embodiment, since the cross-sectional structure of the anisotropic pitch-based carbon fiber has a random structure or an onion structure, the inhibition of curing is less likely to occur. The inhibitory effect can be lowered.

(The fiber length of 10% (L10) cumulative fiber length is preferably 40% or more with respect to the volume average fiber length)
As a preferable condition, in the anisotropic pitch-based carbon fiber of the present embodiment, the fiber length of the volume-converted fiber length cumulative 10% (L10) is 40% or more with respect to the volume-converted average fiber length. The volume conversion fiber length accumulation will be described with reference to the graph of FIG. In FIG. 1, the horizontal axis is the fiber length, and the vertical axis is the ratio of each fiber length. The volume-converted average fiber length is X (μm) (hereinafter the same).

  The fiber length of 10% (L10) in terms of the volume converted fiber length is 40%. The fiber length in the 10% cumulative from the short side of the fiber length distribution is 40% of the volume converted average fiber length (that is, 0.4X (μm )). That is, in the fiber length distribution of FIG. 1, the portion indicated by hatching is a short group in which the short side accumulation is 10%, and the maximum fiber length of this short group is 0.4X (μm).

  When the fiber length of 10% (L10) cumulative fiber length is less than 40% of the volume average fiber length, the proportion of the small fiber length increases, so it is mixed with the matrix material and thermally conductive molded. When manufacturing the body, the contact between the graphitized carbon fibers decreases, and the thermal conductivity decreases. It may also cause matrix hardening inhibition.

  The volume-converted average fiber length can be measured using a particle size / shape distribution measuring instrument (for example, manufactured by Seishin Enterprise) having an image analysis function. Specifically, “1500 fibers were measured using PITA1 manufactured by Seishin Co., Ltd., and the average value of the squares of each fiber length was determined, and the volume-converted average fiber length was determined from the square root of this average value.

(The fiber length of 90% (L90) cumulative fiber length is preferably 250% or less with respect to the volume average fiber length)
As a preferable condition, in the anisotropic pitch-based carbon fiber of this embodiment, the fiber length of the volume converted fiber length 90% (L90) is 250% or less with respect to the volume converted average fiber length. Referring to FIG. 2, the volume length of 90% (L90) cumulative fiber length is 250%, and the 90% cumulative fiber length from the short side of the fiber length distribution is 250% of the volume average fiber length ( That is, it means 2.5X (μm)). That is, the portion indicated by hatching in the fiber length distribution of FIG. 2 is a long group in which the long side accumulation is 10%, and the minimum fiber length of this long group is 2.5 × (μm).

  When the fiber length of 90% (L90) cumulative fiber length with respect to the volume-converted average fiber length exceeds 250%, the proportion of the large fiber length increases, and the graphitized carbon fiber becomes bulky, and the matrix becomes bulky. It becomes difficult to fill with high density. Therefore, it is necessary to reduce the amount of pitch-based carbon fiber milled mixed with the matrix material, resulting in a decrease in thermal conductivity.

  Next, a method for manufacturing a pitch-based carbon fiber mill that is an embodiment of the present invention will be described with reference to FIGS. However, the manufacturing method demonstrated here is an illustration of this invention, and is not limited to this. FIG. 3 is a process diagram of pitch-based carbon fiber milling. FIG. 4 is an enlarged view of a spinning nozzle portion for making the cross section of the anisotropic pitch-based carbon fiber a random structure. FIG. 5 is an enlarged view of a spinning nozzle portion for making the cross-section of the anisotropic pitch-based carbon fiber into an onion structure.

  Spinning step: In S1, an anisotropic pitch is melt-spun under predetermined spinning conditions. Referring to FIG. 4, the spinning nozzle unit 10 includes a contraction part hole 1, an introduction hole 2, an approach part 3, a flat part 4, and a discharge hole 5 from the upstream side to the downstream side in the discharge direction of the anisotropic pitch. Are provided in this order. Two flow-reducing portion holes 1 are formed at the inlet for feeding the anisotropic pitch toward the spinning nozzle portion 10. However, the number of the contraction part holes 1 may be one.

  The cross-sectional shape when each of the flow-reducing portion holes 1 is cut in a direction perpendicular to the discharge direction is an ellipse, and when the major axis of the ellipse is D1 and the minor axis is D1 ′, D1 ≧ 8D1 ′. Preferably, 30D1 ′ ≧ D1 ≧ 10D1 ′.

  The long diameter D1 can be set to 0.5 to 3.0 mm, for example. The short diameter D1 ′ can be set to 0.05 to 0.25 mm, for example.

  The anisotropic pitch that has entered the contracted portion hole 1 is once contracted, then expanded by the introduction hole 2, and again contracted by the tapered approach portion 3. The diameter of the introduction hole 2 can be set to 2.0 to 3.0 mm, for example. The approach portion 3 is formed in a tapered shape having a smaller diameter on the downstream side than the upstream side, and a preferable angle thereof is 130 to 140 degrees.

A flat portion 4 is formed at the lower end of the approach portion 3, and a discharge hole 5 having a circular cross-sectional shape is formed in the flat portion 4. The anisotropic pitch shrunk in the approach part 3 is pushed out from the discharge hole 5 at a predetermined pressure and drawn at a predetermined take-up speed, whereby pitch fibers having a predetermined fiber diameter are obtained. A preferable temperature of the pitch fiber is a temperature showing 100 to 1500 poise of clay, and a more preferable temperature is a temperature showing 200 to 800 poise. A preferable diameter of the discharge hole 5 is 0.05 mm to 0.5 mm. The predetermined pressure is preferably 1 to 200 kg / cm ² . The take-up speed is preferably 100 to 2000 m / min. The fiber diameter after stretching is preferably 5 to 20 μm.

  According to the above-described spinning nozzle, by increasing the aspect ratio of the reduced-flow portion hole 1, the cross-sectional shape of the reduced-flow portion hole 1 is further flattened, and the cross-section of the anisotropic pitch-based carbon fiber is made a random structure. Can do. That is, by setting the aspect ratio to D1 ≧ 8D1 ′, the cross section of the anisotropic pitch-based carbon fiber can have a random structure. Thereby, the uneven | corrugated defect in the fiber surface of an anisotropic pitch type carbon fiber reduces, and the hardening inhibition of the matrix material by an anisotropic pitch type carbon fiber can be reduced significantly. When the aspect ratio is D1 <8D1 ′, a radial structure is obtained.

  Referring to FIG. 5, the anisotropic pitch 21 in the spinning nozzle unit 20 is agitated at a position above the capillary 23 using the agitation rod 22, thereby causing a flow toward the capillary 23 with the anisotropic pitch 21. Disturb or create a new flow (circumferential vortex flow at the top of the capillary 23). By discharging the anisotropic pitch 21 under these conditions, the cross section of the anisotropic pitch-based carbon fiber can have an onion structure. The temperature and viscosity of the anisotropic pitch 21 and the pressure during discharge can be made the same as in the case of the random structure.

  While controlling the structure of the anisotropic pitch by the above method, it is extruded from the discharge holes at a predetermined pressure and stretched at a predetermined take-up speed to obtain a pitch-based carbon fiber precursor having a predetermined fiber diameter.

  Infusibilization step: In S2, an infusibilization process is performed. The infusibilization treatment is a heat treatment in an oxidizing gas atmosphere to add oxygen to the pitch-based carbon fiber precursor. The heating temperature is preferably 100 to 350 ° C, more preferably 130 to 320 ° C. The heating time is preferably 10 minutes to 10 hours, more preferably 1 to 6 hours. As the oxidizing gas, oxygen, air, or a gas in which nitrogen dioxide, chlorine, or the like is mixed can be used.

  Carbonization step: In S3, the infusible pitch-based carbon fiber precursor is carbonized. The carbonization treatment is performed by performing a heat treatment in an inert gas atmosphere. Nitrogen, argon, or the like can be used as the inert gas. The heating temperature is preferably 900 to 1500 ° C. Here, it is known that the pitch-based carbon fiber precursor subjected to carbonization has a correlation between the heat treatment temperature after the infusibilization treatment and the value of the elastic modulus after the heat treatment, and the elasticity can be obtained by adjusting the heat treatment temperature. The rate can be adjusted in the range of 10 GPa to 1000 GPa.

  Chop treatment step: In S4, the carbon fiber precursor that has been finished up to the carbonization step is cut into 2 mm to 200 mm and processed into a chop shape. Thereby, while handling property improves, the bulk density of a pitch-type carbon fiber precursor becomes high in the graphitization process mentioned later, and it can raise baking efficiency. However, the chop treatment process: S4 may be omitted, and the process may proceed to the graphitization process process: S5.

  Graphitization treatment step: In S5, the chopped pitch-based carbon fiber precursor is heat-treated at a high temperature in an inert gas. Thereby, a pitch-based carbon fiber fired product excellent in thermal conductivity is obtained. A batch type electric furnace is usually used for graphitization. This electric furnace is equipped with a graphitic heater, heated in an inert gas atmosphere such as nitrogen or argon, held at a maximum temperature for a certain time, cooled, cooled, and graphitized. As another heating furnace, an Atchison furnace capable of performing graphitization at a relatively large volume of around 3000 ° C. can also be used. This is because the coke and carbon beads are filled around the heated member, and the coke and carbon beads generate heat due to Joule heat by supplying a larger current than the electrodes arranged before and after the furnace, and oxygen in the atmosphere The oxidizing gas is consumed by coke and carbon beads, and the periphery of the object to be heated is in an inert gas atmosphere.

  The heating temperature in the graphitization treatment must be 2800-3200 ° C. When the heating temperature is 2800 ° C. or lower, the thermal conductivity cannot be sufficiently increased. When the heating temperature exceeds 3200 ° C., the graphite sublimation temperature is reached. Therefore, it is industrially difficult to improve graphitization even if the temperature is increased further. Moreover, the lower limit of the heating temperature is preferably 2900 ° C. or higher, more preferably 2950 ° C. or higher. Thereby, the heat conductivity of the length direction of the obtained graphitized pitch-type carbon fiber can be raised to 500-1400 W / m * K. If the thermal conductivity is lower than 500 W / m · K, it is insufficient to improve the thermal conductivity, while it is industrially difficult to adjust so that the thermal conductivity exceeds 1400 W / m · K. It requires temperature and time and is not suitable for the present invention.

  The graphitized and fired pitch-based carbon fiber fired product is subjected to treatments such as cutting, pulverization, and classification in order to obtain a predetermined fiber length. For cutting, a guillotine-type cutter, a multi-axis rotary cutter, or the like is suitable. For grinding, a type of grinding such as a cutter mill, jet mill, turbo mill, hammer mill, or the like that cuts in a direction perpendicular to the fiber axis is suitable. Although there are methods using a grinder such as a ball mill, these methods are not desirable because vertical cracks in the fiber axis direction increase.

  For classification, a classifier such as a vibration sieve type or a centrifugal type can be used. Classification is performed, the amount of fine powder and coarse powder is controlled, and the fiber length distribution is adjusted. In order to obtain a predetermined fiber length, a production line constituted by a plurality of machines for cutting, crushing, and classification may be used. Control methods other than model selection can be adjusted to a predetermined fiber length distribution by combining raw material input speed, mill rotation speed of pulverizer, sieve device mesh, screener screen type, and the like. The fiber length distribution can be calculated by a laser diffraction method or an image analysis method.

  FIG. 6 is an overall photograph of the pitch-based carbon fiber milled (random structure) manufactured by the above-described manufacturing process, and FIG. 7 is a cross-sectional and surface photograph of the pitch-based carbon fiber milled. As shown in these photographs and the like, the average fiber diameter is 5 to 15 μm, the volume conversion average fiber length is 300 μm or less, the graphene sheet is open, and the volume conversion fiber length accumulation is 10% with respect to the volume conversion average fiber length. (L10) has a fiber length distribution with a fiber length of 40% or more, a volume converted fiber length of 90% (L90) and a fiber length of 250% or less, and a thermal conductivity in the length direction of 500 to 1400 W / m · K. A pitch-based carbon fiber milled can be obtained.

  In addition, the pitch-based carbon fiber has an onion structure or a random structure in the fiber cross section, has few occurrences of vertical cracks in the fiber axis direction, has few irregularities on the fiber surface, and maintains the fiber shape.

  Here, for the purpose of surface treatment of the pitch-based carbon fiber milled, the surface of the carbon fiber is previously oxidized by means such as electrolytic oxidation, or treated with a coupling agent or a sizing agent to form a matrix polymer material. It is possible to improve wettability and filling property, and to improve the peel strength between the polymer material and the powder interface.

  Also, metal or ceramics on the surface of graphitized carbon fiber, physical vapor deposition method such as electroless plating method, electrolytic plating method, vacuum vapor deposition method, sputtering method, ion plating method, chemical vapor deposition method, coating method, immersion It can also be coated by a method such as a method.

  The pitch-based carbon fiber milled according to this embodiment is mixed with the matrix material as described above and used as a thermally conductive molded body. In the thermally conductive molded body, when the matrix material is 100 parts by weight, the preferred mixing amount of the pitch-based carbon fiber milled is 10 to 350 parts by weight.

  The thermoplastic resin used for the matrix material is polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polyvinyl acetal, polyvinylidene fluoride, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene. , Polyacrylonitrile, styrene-acrylonitrile copolymer, polyphenylene-ether copolymer (PPE) resin, polyimide, polyamideimide, polymethacrylic acid, polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone , Polyketone, liquid crystal polymer, silicone resin, ionomer and the like.

  Thermosetting resins used for the matrix material include epoxies, acrylics, urethanes, silicones, phenols, imides, thermosetting modified PPEs, thermosetting PPEs, polybutadiene rubbers and the like Examples thereof include copolymers, acrylic rubbers and copolymers thereof, silicone rubbers and copolymers thereof, and natural rubber. Moreover, what combined 2 or more types of these may be used.

  In addition to the matrix material and the pitch-based carbon fiber mill, the heat conductive molded body may be mixed with powdered or fibrous metal or ceramics. As the metal, silver, copper, gold, aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, aluminum hydroxide, or the like can be used. In addition, a filler having a large thermal conductivity used in a conventional thermally conductive molded body such as a metal-coated resin can also be used.

  As the ceramic, conventional graphitized carbon fiber, non-graphitized carbon fiber, natural graphite, artificial graphite, whisker-like, or nanotube-like carbon can be used.

  In applications where electrical insulation is particularly required as the final product, an electrically insulating thermally conductive filler comprising aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide and aluminum hydroxide is used. It is preferable to use together.

  Since the pitch-based carbon fiber milled of this embodiment does not inhibit the curing of the rubber composition and can be highly filled, the effect of the present invention is more manifested when the matrix material is a rubber component. From this viewpoint, the thermally conductive molded article of the present invention is suitable when the matrix component is a rubber component.

  As the rubber component, natural rubber, acrylic rubber, acrylonitrile butadiene rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, epichlorohydrin rubber, chloroprene rubber, silicone rubber, styrene butadiene rubber, butadiene rubber, butyl rubber and the like can be used.

The thermally conductive molded body can be molded by a compression molding method, a press molding method, a calendar molding method, a roll molding method, or an extrusion molding method. The heat conductive molded body thus obtained can be incorporated into a heating element by processing as necessary. Moreover, it is good also as a heat conductive sheet using a heat conductive molded object. By processing into a sheet shape, it can be used as a heat radiating member, heat transfer member, or a constituent material for effectively radiating the heat generated by electronic components such as semiconductor elements, power supplies, light sources, etc. in electronic devices etc. it can.
(Example)
Examples are shown below, but the present invention is not limited thereto.
Example 1
A coal tar pitch having a softening point of 80 ° C. from which quinoline-insoluble components had been removed was hydrogenated at a pressure of 13 MPa and a temperature of 340 ° C. in the presence of a Ni—Mo catalyst to obtain a hydrogenated coal tar pitch. This hydrogenated coal tar pitch was heat-treated at 480 ° C. under normal pressure and then reduced in pressure to remove low-boiling components to obtain mesophase pitch. This pitch was further filtered at a temperature of 340 ° C. using a filter to remove foreign matters in the pitch, and a purified mesophase pitch was obtained. This pitch had a softening point of 304 ° C., a toluene insoluble content of 85% by weight, a pyridine insoluble content of 42% by weight, and a mesophase content of 97%.

  Melt spinning was performed using this pitch. The number of inlet holes at the inlet is one, and once the current is reduced by an elliptical current-reducing portion having a long side of 2.6 mm and a short side of 0.1 mm, the diameter is expanded by an introduction hole having a diameter of 2.8 mm. The shape from the hole to the discharge hole is shrunk at the approach part that forms an angle of 135 degrees, once at the end of the approach to a flat part, passing through the discharge hole having a circular cross-sectional shape provided in the flat part, Spinning was performed. Spinning was performed at a mesophase pitch viscosity of 400 poise and a pitch fiber take-up speed of 400 m / min to obtain pitch fibers having a single yarn diameter of 14 μm, and 6000 pitch fibers were bundled to produce pitch fibers. This pitch fiber was infusibilized at 130 to 320 ° C. in an oxidizing gas atmosphere.

  Next, the infusibilized pitch fiber that had been infusibilized in the carbonization step was carbonized at a heating temperature of 1200 ° C. in a nitrogen gas atmosphere. A carbon fiber precursor that has been carbonized is cut to a size of 5 mm with a guillotine cutting machine, processed into a chop shape, then heated and fired at 3000 ° C. in an Atchison furnace, and graphitized and fired pitch-based carbon fiber chop Got.

  The graphitized and fired pitch-based carbon fiber chop was pulverized by a cutter mill (manufactured by Turbo Industry) and a turbo mill (manufactured by Turbo Industry), and classified by a turbo screener (manufactured by Turbo Industry). A screen having an aperture of 74 μm was used as a turbo screener under operating conditions of a cutter mill frequency of 30 Hz and a turbo mill frequency of 36 Hz. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter was 11.6 μm, the volume-converted average fiber length was 100 μm, and the volume-converted fiber length. The fiber length of 10% (L10) is 50 μm, the fiber length of 90% (L90) is 90 μm, and the fiber length is 10% (L10). The fiber length of 90% (L90) cumulative fiber length converted to volume average fiber length of 50% was 190%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, there are no defects such as severe irregularities. The fiber cross section was a random structure. FIG. 8 is a photograph of the fiber end face observed with a transmission electron microscope, confirming that the graphene sheet is open.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of the above pitch-based carbon fiber milled with an average fiber length of 100 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 21 W / mK.

(Example 2)
Production is performed in the same manner as in Example 1 until a graphitized and fired pitch-based carbon fiber chop is obtained, and a screen having an opening of 100 μm is formed in the turbo screener under the operating conditions of a cutter mill frequency of 32 Hz and a turbo mill frequency of 34 Hz in the pulverization process. used. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 11.4 μm, the volume-converted average fiber length is 150 μm, and the volume-converted fiber length. Cumulative 10% (L10) fiber length is 85 μm, Volume converted fiber length 90% (L90) is 295 μm, Volume converted average fiber length is 10% (L10). The fiber length of the volume converted fiber length cumulative 90% (L90) was 197% with respect to the volume converted average fiber length of 57%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction as in Example 1, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, it appears that there are severe irregularities. No defects were present, and the fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of pitch-based carbon fiber milled with an average fiber length of 150 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm. Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 27 W / mK.

(Example 3)
Production was performed in the same manner as in Example 1 until a purified mesophase pitch was obtained, and melt spinning was performed using this pitch. The number of inlet holes at the inlet is two, an elliptical constricted part with a long side of 1.0 mm and a short side of 0.1 mm. All shapes were contracted at an approach portion that formed an angle of 135 degrees, once formed as a flat portion at the end of the approach, and passed through a discharge hole having a circular cross-sectional shape provided in the flat portion, and spinning was performed. Spinning was performed at a mesophase pitch viscosity of 400 poise and a pitch fiber take-up speed of 400 m / min to obtain pitch fibers having a single yarn diameter of 14 μm, and 6000 pitch fibers were bundled to produce pitch fibers. This pitch fiber was infusibilized at 130 to 320 ° C. in an oxidizing gas atmosphere. Next, the infusibilized pitch fiber that had been infusibilized in the carbonization step was carbonized at a heating temperature of 1200 ° C. in a nitrogen gas atmosphere. A carbon fiber precursor that has been carbonized is cut to a size of 5 mm with a guillotine cutting machine, processed into a chop shape, then heated and fired at 3000 ° C. in an Atchison furnace, and graphitized and fired pitch-based carbon fiber chop Got.

  The graphitized and fired pitch-based carbon fiber chop was pulverized by a cutter mill (manufactured by Turbo Industry) and a turbo mill (manufactured by Turbo Industry), and classified by a turbo screener (manufactured by Turbo Industry). A screen having an aperture of 74 μm was used as a turbo screener under operating conditions of a cutter mill frequency of 30 Hz and a turbo mill frequency of 36 Hz. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 11.5 μm, the volume-converted average fiber length is 100 μm, and the volume-converted fiber length. Cumulative 10% (L10) fiber length is 48 μm, Volume converted fiber length cumulative 90% (L90) fiber length is 194 μm, Volume converted fiber length cumulative fiber length is 10% (L10) The fiber length of the volume converted fiber length 90% (L90) was 194% with respect to the volume converted average fiber length of 48%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, there are no defects such as severe irregularities. The fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of the above pitch-based carbon fiber milled with an average fiber length of 100 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 20 W / mK.

Example 4
Production is performed in the same manner as in Example 3 until a graphitized and fired pitch-based carbon fiber chop is obtained, and a screen having an opening of 100 μm is formed on the turbo screener under operating conditions of a cutter mill frequency of 32 Hz and a turbo mill frequency of 35 Hz in the pulverization process. used. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 11.3 μm, the volume-converted average fiber length is 150 μm, and the volume-converted fiber length. The cumulative fiber length of 10% (L10) is 84 μm, the cumulative fiber length of 90% (L90) is 297 μm, the average fiber length of the volume is 10% (L10). The fiber length of the volume converted fiber length 90% (L90) was 198% with respect to the volume converted average fiber length of 56%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, there are no defects such as severe irregularities. The fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of pitch-based carbon fiber milled with an average fiber length of 150 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm. Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 25 W / mK.

(Example 5)
Until the refined mesophase pitch was obtained, the same production as in Example 1 was carried out, and melt spinning was carried out using this pitch under the same conditions as in Example 1 to obtain a pitch fiber having a single yarn diameter of 11 μm. Pitch fibers were produced by bundling 6000 fibers. It is manufactured in the same manner as in Example 1 until the subsequent graphitized and fired pitch-based carbon fiber chop is obtained. In the pulverization step, the operating conditions are a cutter mill frequency of 29 Hz and a turbo mill frequency of 35 Hz. Using the screen. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 7 μm, the volume-converted average fiber length is 100 μm, and the volume-converted fiber length cumulative 10 % (L10) fiber length is 50 μm, volume-converted fiber length cumulative 90% (L90) fiber length is 190 μm, and volume-converted fiber length cumulative 10% (L10) fiber length is 50%. In addition, the fiber length of 90% (L90) cumulative fiber length was 190% with respect to the volume-average fiber length.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction as in Example 1, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, it appears that there are severe irregularities. No defects were present, and the fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of the above pitch-based carbon fiber milled with an average fiber length of 100 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 19 W / mK. Since the average fiber diameter is smaller than that of Example 1, it is considered that the thermal conductivity was lowered.

(Example 6)
Until the refined mesophase pitch was obtained, it was produced in the same manner as in Example 1. Using this pitch, melt spinning was carried out under the same conditions as in Example 3 to obtain a pitch fiber having a single yarn diameter of 11 μm. Pitch fibers were produced by bundling 6000 fibers. It is manufactured in the same manner as in Example 3 until the subsequent graphitized and fired pitch-based carbon fiber chop is obtained. In the pulverization step, the operating conditions are a cutter mill frequency of 29 Hz and a turbo mill frequency of 34 Hz. Using the screen. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 7 μm, the volume-converted average fiber length is 100 μm, and the volume-converted fiber length cumulative 10 % (L10) fiber length is 48 μm, volume-converted fiber length cumulative 90% (L90) fiber length is 194 μm, volume-converted fiber length cumulative 10% (L10) fiber length is 48% with respect to volume-converted average fiber length The fiber length of the volume converted fiber length cumulative 90% (L90) with respect to the volume converted average fiber length was 194%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, there are no defects such as severe irregularities. The fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of the above pitch-based carbon fiber milled with an average fiber length of 100 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 18 W / mK.

(Example 7)
Production is performed in the same manner as in Example 1 until a graphitized and fired pitch-based carbon fiber chop is obtained, and a screen having an opening of 150 μm is formed on the turbo screener under the operating conditions of a cutter mill frequency of 22 Hz and a turbo mill frequency of 28 Hz in the pulverization process. used. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter was 11.6 μm, the volume-converted average fiber length was 280 μm, and the volume-converted fiber length. Cumulative 10% (L10) fiber length is 132 μm, Volumetric fiber length cumulative 90% (L90) is 525 μm, Volumetric mean fiber length is 10% (L10). The fiber length of the volume converted fiber length cumulative 90% (L90) was 188% with respect to the volume converted average fiber length of 47%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction as in Example 1, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, it appears that there are severe irregularities. No defects were present, and the fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 12% by weight of the above pitch-based carbon fiber milled with an average fiber length of 280 μm and 68% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. Since the volume-converted average fiber length is large and resin curing failure is likely to occur, the amount of pitch-based carbon fiber milled added is less than in other examples. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 18 W / mK.

(Example 8)
Production was performed in the same manner as in Example 1 until a purified mesophase pitch was obtained. By rotating the stirring rod using the apparatus of FIG. 5, a circumferential spiral flow was created, and melt spinning was performed under these conditions. The spinning conditions were the same as in Example 1. A pitch fiber having a single yarn diameter of 14 μm was obtained, and 6000 pitch fibers were bundled to produce a pitch fiber.

  This pitch fiber was infusibilized at 130 to 320 ° C. in an oxidizing gas atmosphere. It is manufactured in the same manner as in Example 1 until the subsequent graphitized and fired pitch-based carbon fiber chop is obtained. In the pulverization process, the operating conditions are a cutter mill frequency of 30 Hz and a turbo mill frequency of 35 Hz. Using the screen. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 11.3 μm, the volume-converted average fiber length is 99 μm, and the volume-converted fiber length. Cumulative 10% (L10) fiber length is 48 μm, Volume converted fiber length cumulative 90% (L90) fiber length is 191 μm, Volume converted fiber length cumulative fiber length is 10% (L10) The fiber length of the volume converted fiber length 90% (L90) was 193% with respect to the volume converted average fiber length of 48%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, there are no defects such as severe irregularities. The fiber cross section had an onion structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of pitch-based carbon fiber milled with an average fiber length of 99 μm in terms of volume, and 65% by weight of alumina particles having an average particle diameter of 3 μm. Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 20 W / mK.

Example 9
Production is performed in the same manner as in Example 8 until a graphitized and fired pitch-based carbon fiber chop is obtained, and a screen having an opening of 100 μm is formed on the turbo screener under the operating conditions of a cutter mill frequency of 31 Hz and a turbo mill frequency of 33 Hz. used. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter was 11.3 μm, the volume-converted average fiber length was 149 μm, and the volume-converted fiber length. Cumulative 10% (L10) fiber length is 84 μm, Volume converted fiber length 90% (L90) is 294 μm, Volume converted fiber length is 10% (L10). The fiber length of the cumulative 90% (L90) volume converted fiber length was 197% with respect to the average fiber length converted to volume of 56%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction as in Example 8, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, it appears that there are severe irregularities. There were no defects and the fiber cross section was an onion structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of the pitch-based carbon fiber milled with the above-mentioned volume conversion average fiber length of 149 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 26 W / mK.

(Example 10)
It was manufactured in the same manner as in Example 1 until a graphitized and fired pitch-based carbon fiber chop was obtained, and was pulverized in a pulverization process using only a cutter mill under an operating condition of a frequency of 40 Hz. As a result of measuring the obtained pitch-based carbon fiber mill with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 11.3 μm, the volume-converted average fiber length is 100 μm, and the volume-converted fiber length. Cumulative 10% (L10) fiber length is 31 μm, Volume converted fiber length 90% (L90) is 275 μm, Volume converted fiber length is 10% (L10), The fiber length of the volume converted fiber length 90% (L90) was 275% with respect to the volume converted average fiber length of 31%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, there are no defects such as severe irregularities. The fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 10% by weight of pitch-based carbon fiber milled with an average fiber length of 100 μm in terms of volume, and 70% by weight of alumina particles with an average particle diameter of 3 μm. Were mixed and dispersed to obtain a silicone resin composition. Since the fiber length of 10% (L10) of accumulated volume-converted fiber lengths relative to the volume-converted average fiber length is low and the resin is liable to cause poor curing of the resin, the amount of pitch-based carbon fiber milled added is less than in other examples. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 17 W / mK.

(Comparative Example 1)
Production was performed in the same manner as in Example 1 until a purified mesophase pitch was obtained, and melt spinning was performed using this pitch. The number of inlet holes at the inlet is one, an elliptical constricted portion with a long side of 1.8 mm and a short side of 0.3 mm. The diameter of the inlet hole is 2.0 mm. Spinning was carried out by passing the discharge hole having a round cross-sectional shape provided in the flat part and a flat part having an angle of 180 degrees. Spinning was performed at a mesophase pitch viscosity of 400 poise and a pitch fiber take-up speed of 400 m / min to obtain pitch fibers having a single yarn diameter of 14 μm, and 6000 pitch fibers were bundled to produce pitch fibers. This pitch fiber was infusibilized at 130 to 320 ° C. in an oxidizing gas atmosphere.

  Next, the infusibilized pitch fiber that had been infusibilized in the carbonization step was carbonized at a heating temperature of 1200 ° C. in a nitrogen gas atmosphere. The carbon fiber precursor that has been carbonized is cut to a size of 5 mm with a guillotine cutting machine, processed into a chopped shape, heated and fired at 3000 ° C. in an Atchison furnace, and graphitized and fired pitch-based carbon A fiber chop was obtained.

  The graphitized and fired pitch-based carbon fiber chop was pulverized by a cutter mill (manufactured by Turbo Industry) and a turbo mill (manufactured by Turbo Industry), and classified by a turbo screener (manufactured by Turbo Industry). A screen having an aperture of 74 μm was used as a turbo screener under operating conditions of a cutter mill frequency of 30 Hz and a turbo mill frequency of 36 Hz. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 11.5 μm, the volume-converted average fiber length is 100 μm, and the volume-converted fiber length. The fiber length of 10% (L10) is 41 μm, the fiber length of 90% (L90) is equivalent to 235 μm, and the fiber length is 10% (L10). The fiber length of the volume conversion fiber length accumulation 90% (L90) was 235% with respect to the volume conversion average fiber length of 41%.

  The obtained pitch-based carbon fiber milled had many vertical cracks in the fiber axis direction, and as a result of observing the fiber surface with a scanning electron microscope, irregularities were confirmed. The fiber cross section was a radial structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of the above pitch-based carbon fiber milled with an average fiber length of 100 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press cured at 80 ° C. for 1 hour with a hot press molding machine to form a silicone molded plate having a thickness of 3.0 mm. However, the silicone resin was not sufficiently cured, and a completely cured silicone product was obtained. Could not get. This is probably because pitch carbon carbon fiber mills had many vertical cracks in the fiber axis direction, and there were many irregularities on the fiber surface, which increased the surface area and caused inhibition of curing. In addition, when mixing and dispersing with the silicone resin, an increase in viscosity accompanying an increase in surface area was caused, and sufficient mixing and dispersion could not be achieved.

(Comparative Example 2)
Until a graphitized and fired pitch-based carbon fiber chop is obtained, it is manufactured in the same manner as in Comparative Example 1, and a screen with an opening of 100 μm is formed on the turbo screener under the operating conditions of a cutter mill frequency of 32 Hz and a turbo mill frequency of 35 Hz. used. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter was 11.3 μm, the volume-converted average fiber length was 149 μm, and the volume-converted fiber length. Cumulative 10% (L10) fiber length is 69 μm, Volumetric fiber length cumulative 90% (L90) fiber length is 320 μm, Volumetric mean fiber length is 10% (L10) cumulative fiber length is 10% (L10). The fiber length of the volume converted fiber length cumulative 90% (L90) was 218% with respect to the volume converted average fiber length of 46%.

  The obtained pitch-based carbon fiber milled had many vertical cracks in the fiber axis direction, and as a result of observing the fiber surface with a scanning electron microscope, irregularities were confirmed. The fiber cross section was a radial structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 12% by weight of the pitch-based carbon fiber milled with the above-mentioned volume conversion average fiber length of 149 μm, and 68% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. Since there are many vertical cracks in the fiber axis direction and the resin tends to be hard to cure, the amount of pitch-based carbon fiber milled added was less than in Example 1. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 12 W / mK. Furthermore, it is considered that the thermal conductivity is deteriorated because the domain size in the fiber cross section is smaller than that in Example 2.

(Comparative Example 3)
Until the carbon fiber precursor finished up to the carbonization step is obtained, it is manufactured in the same manner as in Example 1, and the carbon fiber precursor is subjected to a turbo screener under the operating conditions of a cutter mill frequency of 34 Hz and a turbo mill frequency of 36 Hz in the pulverization step. A carbon fiber precursor milled was obtained using a screen having an opening of 100 μm. The carbon fiber precursor mill was heated and fired at 3000 ° C. in an Atchison furnace to obtain a graphitized and fired pitch-based carbon fiber mill. As a result of measuring the obtained pitch-based carbon fiber mill with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter was 11.2 μm, the volume-converted average fiber length was 149 μm, and the volume-converted fiber length. Cumulative 10% (L10) fiber length is 82 μm, Volume converted fiber length 90% (L90) is 293 μm, Volume converted average fiber length is 10% (L10). The fiber length of the cumulative 90% (L90) volume converted fiber length was 197% with respect to the average fiber length converted to 55%.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, there are no defects such as severe irregularities. The fiber cross section was a random structure. FIG. 9 is a photograph of the fiber end face observed with a transmission electron microscope, and it was confirmed that the graphene sheet was closed.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of pitch-based carbon fiber milled with an average fiber length of 140 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm. Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 16 W / mK.

  In Comparative Example 3, since the thermally conductive sheet is configured using pitch-based carbon fiber milled with the graphene sheet closed, it is considered that the thermal conductivity is reduced as compared with the Example.

(Comparative Example 4)
Production is performed in the same manner as in Example 1 until a graphitized and fired pitch-based carbon fiber chop is obtained, and a screen having an aperture of 74 μm is formed on the turbo screener under the operating conditions of a cutter mill frequency of 27 Hz and a turbo mill frequency of 34 Hz in the pulverization step. used. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 4 μm, the volume-converted average fiber length is 100 μm, and the volume-converted fiber length cumulative 10 % (L10) fiber length is 50 μm, volume-converted fiber length cumulative 90% (L90) fiber length is 190 μm, and volume-converted fiber length cumulative 10% (L10) fiber length is 50%. In addition, the fiber length of 90% (L90) cumulative fiber length was 190% with respect to the volume-average fiber length.

  The obtained pitch-based carbon fiber milled has little occurrence of longitudinal cracks in the fiber axis direction as in Example 1, and the fiber shape is maintained. As a result of observing the fiber surface with a scanning electron microscope, it appears that there are severe irregularities. No defects were present, and the fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 15% by weight of the above pitch-based carbon fiber milled with an average fiber length of 100 μm, and 65% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 12 W / mK. Since the average fiber diameter is less than 5 μm, it is considered that the thermal conductivity was lowered as compared with the examples.

(Comparative Example 5)
Production is performed in the same manner as in Example 1 until a graphitized and fired pitch-based carbon fiber chop is obtained, and a screen having an opening of 74 μm is formed on the turbo screener under the operating conditions of a cutter mill frequency of 31 Hz and a turbo mill frequency of 37 Hz. used. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 16 μm, the volume-converted average fiber length is 100 μm, and the volume-converted fiber length cumulative 10 % (L10) fiber length is 50 μm, volume-converted fiber length cumulative 90% (L90) fiber length is 190 μm, and volume-converted fiber length cumulative 10% (L10) fiber length is 50%. In addition, the fiber length of 90% (L90) cumulative fiber length was 190% with respect to the volume-average fiber length.

  The obtained pitch-based carbon fiber milled had many vertical cracks in the fiber axis direction, and as a result of observing the fiber surface with a scanning electron microscope, irregularities were confirmed. The fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of a two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 12% by weight of the above pitch-based carbon fiber milled with an average fiber length of 100 μm, and 68% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. Since the average fiber diameter is more than 15 μm and the resin tends to be hard to cure, the amount of pitch-based carbon fiber milled added is less than that of Example 1 and the like. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 15 W / mK.

(Comparative Example 6)
Production is performed in the same manner as in Example 1 until a graphitized and fired pitch-based carbon fiber chop is obtained, and a screen with an opening of 250 μm is formed on the turbo screener under the operating conditions of a cutter mill frequency of 22 Hz and a turbo mill frequency of 25 Hz in the pulverization process. used. As a result of measuring the obtained pitch-based carbon fiber milled with a particle size / shape distribution measuring instrument which is an image analysis method manufactured by Seishin Enterprise, the average fiber diameter is 11.6 μm, the volume-converted average fiber length is 350 μm, and the volume-converted fiber length. Cumulative 10% (L10) fiber length is 158 μm, Volume converted fiber length cumulative 90% (L90) fiber length is 652 μm, Volume converted fiber length cumulative fiber length is 10% (L10). The fiber length of 90% (L90) cumulative fiber length in volume conversion was 186% with respect to 45% and volume conversion average fiber length.

  The obtained pitch-based carbon fiber milled had many vertical cracks in the fiber axis direction, and as a result of observing the fiber surface with a scanning electron microscope, irregularities were confirmed. The fiber cross section was a random structure. Moreover, it was confirmed that the graphene sheet was opened by observing the fiber end face with a transmission electron microscope.

  20% by weight of two-component addition reaction type silicone resin (SE1885) manufactured by Toray Dow Corning Co., Ltd., 5% by weight of the above pitch-based carbon fiber milled with a volume-converted average fiber length of 350 μm, and 75% by weight of alumina particles with an average particle diameter of 3 μm Were mixed and dispersed to obtain a silicone resin composition. Since the volume-converted average fiber length is more than 300 μm and the resin tends to be poorly cured, the amount of pitch-based carbon fiber milled added is significantly less than in Example 1 and the like. This silicone resin composition was press-cured at 80 ° C. for 1 hour with a hot press molding machine to mold a silicone molded plate having a thickness of 3.0 mm. The obtained silicone molded plate was cut to obtain a thermally conductive molded plate having a thickness of 3.0 mm, a vertical length of 20 mm, and a horizontal length of 20 mm. When the thermal conductivity in the in-plane direction of the thermally conductive molded plate was measured by a laser flash method, the thermal conductivity was 9 W / mK.

DESCRIPTION OF SYMBOLS 1 Constriction part hole 2 Introduction hole 3 Approach part 4 Flat part 5 Discharge hole 10 Spinning nozzle part

Claims (5)

  An anisotropic pitch is used as a raw material, an average fiber diameter is 5 to 15 μm, a volume-converted average fiber length is 300 μm or less, a fiber cross section is an onion structure or a random structure, and graphene is observed in a fiber end face observation with a transmission electron microscope. Pitch-based carbon fiber milled, characterized in that the sheet is open.   With respect to the volume-converted average fiber length, the fiber length of the volume-converted fiber length 10% (L10) is 40% or more, and the fiber length of the volume-converted fiber length 90% (L90) is 250% or less. The pitch-based carbon fiber milled according to claim 1.   The pitch-based carbon fiber milled according to claim 1 or 2, wherein the thermal conductivity in the fiber direction is 500 to 1400 W / mK.   A thermally conductive molded article comprising the pitch-based carbon fiber mill according to any one of claims 1 to 3 and at least one matrix component selected from a thermoplastic resin, a thermosetting resin, and a rubber component. . A first step of melt spinning an optically anisotropic mesophase pitch to obtain a pitch-based carbon fiber precursor having a fiber cross-section with an onion structure or a random structure;
A second heat treatment is performed on the pitch-based carbon fiber precursor obtained in the first step in the infusibilization step and the carbonization step, followed by firing at a firing temperature of 2800 ° C. to 3200 ° C. in a chopped state or a long fiber state. Process,
The pitch-based carbon fiber milled method for producing the pitch-based carbon fiber milled according to claim 1, wherein the pitch-based carbon fiber fired product obtained in the second step is size-adjusted by a pulverizing / classifying step.