JP2009275323A - Pitch-based graphitized staple fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pitch-based graphitized staple fiber slight in the possibility of causing the setting inhibition of a thermosetting resin even if kneaded with the resin. <P>SOLUTION: The pitch-based graphitized staple fiber has the following characteristics: (i) The average fiber diameter observed by optical microscope is larger than 2 μm but not larger than 20 μm, and the fiber diameter distribution percentage based on the average fiber diameter is 3-20%. (ii) The fiber surface observed by scanning electron microscope is substantially flat. (iii) When the five fibers' ends, whose graphene sheet edge faces have the whole length of longer than 50 nm but shorter than 300 nm, are observed by transmission electron microscope, the average value of the closure percentage represented by formula (1), closure percentage (%)=B/A×100 (A is the whole length (nm) of the graphene sheet edge face of the fiber end; and B is the length (nm) of portion where the edge face is curved U-shaped fashion), is greater than 80% but less than 100%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pitch-based graphitized short fiber excellent in thermal conductivity. More specifically, the present invention relates to pitch-based graphitized short fibers that have fewer reactive sites than conventional carbon fibers and are excellent in thermal conductivity.

In order to improve the thermal conductivity of housings such as electrical parts, the use of carbon fibers that exhibit excellent thermal conductivity with a small amount of addition has been studied. Carbon fibers include PAN-based carbon fibers and pitch-based carbon fibers. PAN-based carbon fibers are non-graphitizable carbon, and it is very difficult to improve the graphitization property that bears heat conduction. On the other hand, pitch-based carbon fibers are called graphitizable carbon fibers, and can be made highly graphitizable, so that high thermal conductivity is easily achieved.
However, pitch-based carbon fibers with exposed graphite end faces at the end of the fiber have very high reactivity at the graphite end faces, and when kneaded with thermosetting resins such as silicone resins and epoxy resins, they cause resin hardening inhibition and hardening. Has the disadvantage of requiring a lot of time. For this reason, it has been difficult to efficiently produce a molded product from pitch-based carbon fibers and a thermosetting resin.

Structure control of the graphite end face at the fiber end has been reported for carbon fibers having a tube structure typified by carbon nanotubes (Patent Documents 1, 2, and 3). The carbon fiber having such a tube structure is an ultrafine carbon fiber having a fiber diameter of several to several tens of nanometers, the fiber cross section has an onion structure, and the control of the structure of the graphite end surface of the fiber end is easy. is there.
However, the carbon fiber produced by ordinary melt spinning has a very large fiber diameter of several to several tens of μm, and the fiber cross section is significantly different from that of the carbon nanotube. For this reason, it has been very difficult to control the structure of the graphite end face at the end of the fiber as in the case of carbon nanotubes, but recently, pitch-based carbon fibers in which the end of the fiber is closed have been proposed (Patent Document 4). ). This carbon fiber has the advantage that there is little possibility of causing the curing inhibition of the resin.
JP 2000-327317 A JP 2003-049329 A JP 2002-146634 A JP 2007-291576 A

  Therefore, an object of the present invention is to provide a pitch-based graphitized short fiber having a closing rate of the graphene sheet end face in a predetermined range and less likely to cause inhibition of resin curing even when kneaded with a thermosetting resin. is there. Another object of the present invention is to provide a pitch-based graphitized short fiber having a closing rate of the end face of the graphene sheet in a predetermined range and capable of forming a so-called intercalation compound. Moreover, the objective of this invention is providing the pitch-type carbon fiber excellent in thermal conductivity.

  Moreover, this invention is providing the composition containing this pitch-type carbon fiber. Furthermore, this invention is providing the molded object, such as a heat sink for electronic components, a radio wave shielding board, a heat exchanger, which consists of a composition.

  When the present inventors produce pitch-based graphitized short fibers, after applying a predetermined stress to the pitch passing through the spinning nozzle and pulverizing the carbon fibers instead of pulverizing the graphitized carbon fibers It has been found that, when graphitized, carbon fibers having a closing rate of the end face of the graphene sheet in a predetermined range can be obtained. Further, the obtained carbon fiber has been found that a composite molded product can be obtained in a short time without causing inhibition of resin curing even when kneaded with a thermosetting resin, thereby completing the present invention.

That is, according to the present invention, (i) the average fiber diameter (D1) observed with an optical microscope is greater than 2 μm and less than or equal to 20 μm, and the percentage of fiber diameter dispersion (S1) with respect to the average fiber diameter (D1) is 3 to 20%. Range,
(Ii) The surface of the observation with a scanning electron microscope is substantially flat, and (iii) The total length of the end surface of the graphene sheet at the end of the fiber by a transmission electron microscope is more than 50 nm and less than 300 nm. When observed, equation (1)
Closure rate (%) = B / A × 100 (1)
(A represents the total length (nm) of the end surface of the graphene sheet at the fiber end, and B represents the length (nm) of the portion where the end surface is curved in a U-shape)
Is a pitch-based graphitized short fiber having an average value (average closing rate) of more than 80% and less than 100%.

  Moreover, this invention is a composition which contains this pitch-type graphitized short fiber and a matrix, and the content rate of a short fiber is 3-60 volume%.

  Furthermore, this invention includes molded objects, such as a flat plate, the heat sink for electronic components, a radio wave shielding board, a heat exchanger, which consist of this composition.

  Since the pitch-based graphitized short fibers of the present invention have a high ratio of the end face of the graphene sheet being closed, there are few reactive sites. Therefore, the pitch-based graphitized short fibers of the present invention hardly cause inhibition of resin curing even when kneaded with a thermosetting resin, and a composite can be obtained in a short time. In addition, the pitch-based graphitized short fibers of the present invention have a graphene sheet end face closing rate in a predetermined range, and can produce so-called interlayer compounds. The pitch-based graphitized short fibers of the present invention have high thermal conductivity, and can exhibit excellent thermal conductivity even when added in a small amount to the resin.

<Pitch-based graphitized short fibers>
(Average fiber diameter: D1)
The average fiber diameter (D1) observed with an optical microscope of the pitch-based graphitized short fibers of the present invention is greater than 2 μm and not greater than 20 μm, preferably 5 to 15 μm, more preferably 7 to 13 μm. When D1 is less than 2 μm, the number of fillers increases when they are combined with the matrix, so that the viscosity of the matrix / filler mixture becomes high and molding becomes difficult, which is not preferable. On the other hand, when D1 exceeds 20 μm, the number of fillers is reduced when they are combined with the matrix, so that the fillers are less likely to come into contact with each other, and effective heat conduction is less likely to occur when a composite material is obtained.

(CV value)
The percentage (CV value) of the fiber diameter dispersion (S1) to the average fiber diameter (D1) observed with an optical microscope of the pitch-based graphitized short fibers of the present invention is 3 to 20%, preferably 5 to 15%. The CV value is an index of fiber diameter variation, and the smaller the value, the higher the process stability and the smaller the product variation. When the CV value is less than 3%, the fiber diameters are very uniform. For this reason, the amount of small-sized fibers entering the gaps between the fibers is reduced, and it becomes difficult to form a denser packed state when compounding with the matrix, resulting in difficulty in obtaining a high-performance composite material. This is not preferable. On the other hand, when the CV value is larger than 20%, dispersibility deteriorates when it is combined with a matrix, and it may be difficult to obtain a composite material having uniform performance. The CV value can be adjusted by controlling the viscosity of the melted mesophase pitch during spinning.

(Surface unevenness)
The pitch-based graphitized short fiber of the present invention is characterized in that the observation surface on the side surface with a scanning electron microscope is substantially flat. Here, “substantially flat” means that the side surface does not have severe unevenness like a fibril structure. In the case where defects such as severe irregularities are present on the surface, an increase in the viscosity accompanying an increase in the surface area is caused at the time of kneading with the matrix resin, and the moldability is deteriorated. For this reason, it is desirable that defects such as surface irregularities be as small as possible. More specifically, it is preferable that there are 10 or less defects such as irregularities in the observation field of view in an image observed at 1000 times with a scanning electron microscope. Such pitch-based graphitized short fibers can be obtained, for example, by performing a graphitization process after a pulverization process.

(End face of graphene sheet)
The pitch-based graphitized short fiber of the present invention is represented by the formula (1) when the total length of the end surface of the graphene sheet at the end of the fiber is more than 50 nm and less than 300 nm by a transmission electron microscope. The average closing rate (average closing rate) exceeds 80% and is less than 100%.
Closure rate (%) = B / A × 100 (1)
(A represents the total length (nm) of the end surface of the graphene sheet at the fiber end, and B represents the length (nm) of the portion where the end surface is curved in a U-shape)
The closing rate is represented by the ratio of the length (nm) of the portion where the end surface is curved in a U shape to the total length (nm) of the end surface of the graphene sheet at the fiber end. FIG. 1 shows a schematic diagram of the graphitized short fiber ends. A shows the total length of the end surface of the graphene sheet at the fiber end, and B shows the length of the portion where the end surface is curved in a U shape, that is, the length of the portion excluding the portion where the end surface is open and not curved in the U shape It shows.

When the average closing rate of the end face of the graphene sheet exceeds 80%, generation of extra functional groups and localization of electrons due to the shape are difficult to occur. For this reason, active sites do not occur in the pitch-based graphitized short fibers, and inhibition of curing due to a decrease in the catalytic activity points can be suppressed by kneading with a thermosetting resin such as a silicone resin or an epoxy resin. Moreover, adsorption | suction of water etc. can also be reduced, for example, also in kneading | mixing with resin accompanying hydrolysis like polyester, the remarkable heat-and-heat durability performance improvement can be brought about. An average closing rate of 80% or less is not preferable because it may cause generation of extra functional groups and localization of electrons due to the shape and promote reaction with other materials. The average closing rate of the graphene sheet end face is preferably 90% or more and less than 100%, more preferably 95% or more and less than 100%.
When the average closing rate of the end face of the graphene sheet is 100%, for example, it becomes impossible to put a compound between the layers of the graphene sheet, and so-called an interlayer compound cannot be made. For this reason, for example, specification as a lithium ion battery or a hydrogen storage material becomes difficult, and the use of carbon fiber is limited, which is not preferable.

The closing rate can be suitably obtained when the total length of the end face of the graphene sheet at the fiber end is more than 50 nm and less than 300 nm. If the total length of the end face is less than 50 nm, it is necessary to enlarge the end face image of the graphene sheet at the end of the fiber to 4 million times or more, which is not preferable because it becomes a partial data interpretation and makes it difficult to grasp the entire image. On the other hand, when the total length of the end face exceeds 300 nm, it is difficult to visually recognize the U-shaped curved structure on the end face of the graphene sheet, and it is not preferable because the closing rate of the end face of the graphene sheet cannot be derived. A more preferable range of the total length is 60 nm or more and 200 nm or less.
The graphene sheet end face structure varies greatly depending on whether pulverization is performed before graphitization or pulverization is performed after graphitization. That is, when a pulverization process is performed after graphitization, the graphene sheet grown by graphitization is cut and broken, and the graphene sheet end face tends to be open. On the other hand, when the pulverization treatment is performed before graphitization, the graphene sheet end face tends to be curved in a U shape during the growth process of graphite. For this reason, in order to obtain a pitch-based graphitized short fiber having an average closing rate of the graphene sheet end face exceeding 80%, it is preferable to perform graphitization after pulverization.
Pitch-based graphitized short fibers having an average closing rate of more than 80% and less than 100% can be preferably obtained by applying a specific stress to the pitch passing through the spinning nozzle and graphitizing after grinding. I can do it.

(Average fiber length: L1)
There are generally two types of pitch-based graphitized short fibers: milled fibers having an average fiber length of less than 1 mm and cut fibers having an average fiber length of 1 mm or more and less than 10 mm. Since the appearance of the milled fiber is powdery, it is excellent in dispersibility, and the appearance of the cut fiber is close to the fiber shape.
The pitch-based graphitized short fibers of the present invention correspond to milled fibers, and the average fiber length (L1) is preferably 10 μm or more and 700 μm or less. Here, the average fiber length is a number average fiber length, and can be obtained from an average value obtained by measuring a predetermined number in a plurality of fields of view using a length measuring device under an optical microscope. L1 is preferably controlled to a value suitable for the purpose, but when the short fiber is used as a heat conductive material, L1 is preferably in the range of 10 to 700 μm. When L1 is smaller than 10 μm, the short fibers are hardly brought into contact with each other, and it is difficult to expect effective heat conduction. On the other hand, if it exceeds 700 μm, the viscosity of the matrix / short fiber mixture increases when mixed with the matrix, and the moldability tends to be remarkably lowered, which is not preferable. A more preferable range is 20 to 300 μm, and a more preferable range is 20 to 250 μm.

There is no particular limitation on the method for obtaining such pitch-based graphitized short fibers, but when pulverizing, that is, when pulverizing with a cutter, the rotational speed of the cutter, the rotational speed of the ball mill, the air velocity of the jet mill, The average fiber length can be controlled by adjusting the number of collisions, the residence time in the pulverizer, and the like. Moreover, it can also adjust by performing classification operation, such as a sieve, from the pitch-based carbon short fibers after pulverization to remove pitch-based carbon short fibers having a short fiber length or a long fiber length.
The ratio (L1 / D1) of the average fiber length (L1) to the average fiber diameter (D1) is preferably in the range of 1-50. L1 / D1 also depends on the average fiber length, but when L1 / D1 is smaller than 1, it is difficult to expect an effect derived from the fiber shape, that is, heat conduction derived from the ease of contact between the short fibers. It is not preferable. On the other hand, if L1 / D1 exceeds 50, the viscosity of the matrix / short fiber mixture becomes remarkably high when mixed with the matrix, which makes it difficult to mold. More preferably, it is 1.5 to 20 when the average fiber length is 20 to 150 μm, and 10 to 50 when the average fiber length is 150 to 500 μm.

(True density)
The true density of the pitch-based graphitized short fibers of the present invention is preferably in the range of 2.15 to 2.30 g / cc. The true density of pitch-based graphitized short fibers increases as the degree of graphitization increases. More preferably, it is 2.18-2.30 g / cc.

(Thermal conductivity)
The thermal conductivity in the fiber axis direction of the pitch-based graphitized short fibers is preferably 400 W / (m · K) or more. More preferably, it is 500 W / (m · K) or more. The method for obtaining such pitch-based graphitized short fibers is not particularly limited, but specifically, it can be achieved by increasing the graphitization temperature or increasing the graphitization time.

(Crystal size)
The pitch-based graphitized short fibers of the present invention are composed of graphite crystals, the crystal size derived from the thickness direction of the hexagonal network surface is 30 nm or more, and the crystal size derived from the growth direction of the hexagonal network surface is 80 nm. The above is preferable. The crystal size corresponds to the degree of graphitization in both the thickness direction of the hexagonal mesh surface and the growth direction of the hexagonal mesh surface, and a certain size or more is required to exhibit thermophysical properties. is there. The crystal size derived from the thickness direction of the hexagonal mesh surface and the crystal size in the growth direction of the hexagonal mesh surface can be determined by an X-ray diffraction method. The measurement method is a concentration method, and the Gakushin method is preferably used as an analysis method. The size of the crystal in the thickness direction of the hexagonal mesh plane is obtained using a diffraction line from the (002) plane, and the size of the crystal in the growth direction of the hexagonal mesh plane is obtained using a diffraction line from the (110) plane. Each can be requested. The method for obtaining such pitch-based graphitized short fibers is not particularly limited, but specifically, it can be achieved by increasing the graphitization temperature or increasing the graphitization time.

<Manufacture of pitch-based graphitized short fibers>
Next, the manufacturing method of the pitch-based graphitized short fiber of the present invention will be described. Examples of the raw material for pitch-based graphitized short fibers used in the present invention include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, condensed heterocyclic compounds such as petroleum-based pitch and coal-based pitch, and the like. Among these, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferable, and mesophase pitch is particularly preferable. The mesophase ratio of the mesophase pitch is at least 90% or more, more preferably 95% or more, and further preferably 99% or more. The mesophase ratio of the mesophase pitch can be confirmed by observing the pitch in the molten state with a polarizing microscope.

  The softening point of the raw material pitch is preferably 230 ° C. or higher and 340 ° C. or lower. The infusibilization treatment needs to be performed at a temperature lower than the softening point. For this reason, when the softening point is lower than 230 ° C., it is necessary to perform the infusibilization treatment at a temperature at least lower than the softening point. On the other hand, if the softening point exceeds 340 ° C., the pitch is liable to cause thermal decomposition, and the generated gas causes problems such as generation of bubbles in the yarn. A more preferable range of the softening point is 250 ° C. or higher and 320 ° C. or lower, and more preferably 260 ° C. or higher and 310 ° C. or lower. The softening point of the raw material pitch can be obtained by the Mettler method. Two or more raw material pitches may be used in appropriate combination. The mesophase ratio of the raw material pitch to be combined is preferably at least 90% or more, and the softening point is preferably 230 ° C. or higher and 340 ° C. or lower.

The mesophase pitch is spun by a melting method, and then becomes a pitch-based graphitized short fiber by infusibilization, carbonization, pulverization, and graphitization. In some cases, a classification step may be added after the pulverization. The pitch-based graphitized short fibers of the present invention are characterized in that the closing rate of the end face of the graphene sheet is more than 80% and less than 100% in fiber end observation with a transmission electron microscope. As described above, such pitch-based graphitized short fibers can be preferably obtained by applying a specific stress to the pitch passing through the spinning nozzle and by performing graphitization after pulverization. If a specific stress cannot be applied to the pitch passing through the spinning nozzle, or if pulverization is performed after graphitization, the graphene sheet grown by graphitization is cut and broken, and the graphene sheet end face opens. . On the other hand, when the pulverization treatment is performed before graphitization, a desired graphitized short fiber in which the end face of the graphene sheet is curved in a U shape is more than 80% and less than 100% in the entire length of the end face.
Hereinafter, preferred embodiments of each step will be described.

(spinning)
Spinning can be performed by a so-called melt spinning method. Specific examples include a normal spinning drawing method in which a mesophase pitch discharged from a die is drawn with a winder, a melt blow method using hot air as an atomizing source, and a centrifugal spinning method in which a mesophase pitch is drawn using centrifugal force. Among them, it is desirable to use the melt blow method for reasons such as high productivity. For this reason, the melt blow method will be described below.

  The spinning nozzle for forming the pitch-based carbon fiber precursor may have any shape. Usually, a perfect circle is used, but there is no problem even if a nozzle having an irregular shape such as an ellipse is used at appropriate times. The ratio of the nozzle hole length (LN) to the hole diameter (DN) (LN / DN) is preferably in the range of 3.1 to 20. When LN / DN exceeds 20, a strong shearing force is imparted to the mesophase pitch passing through the nozzle, and a radial structure appears in the fiber cross section. The expression of the radial structure is not preferable because it may cause a crack in the fiber cross-section during the graphitization process and may cause a decrease in mechanical properties. On the other hand, if LN / DN is less than 3.1, shearing cannot be imparted to the raw material pitch, resulting in a pitch-based carbon fiber precursor with low graphite orientation. For this reason, even when graphitized, the degree of graphitization cannot be sufficiently increased, and it is difficult to improve the thermal conductivity. In order to achieve both mechanical strength and thermal conductivity, it is necessary to apply appropriate shear to the mesophase pitch. For this reason, the ratio (LN / DN) of the nozzle hole length (LN) to the hole diameter (DN) is preferably in the range of 3.1 to 20, and more preferably in the range of 3.5 to 12.

There are no particular restrictions on the temperature of the nozzle during spinning, the shear rate when the mesophase pitch passes through the nozzle, the amount of air blown from the nozzle, the temperature of the wind, etc., and the conditions under which a stable spinning state can be maintained, that is, the mesophase pitch The melt viscosity at the nozzle holes is preferably in the range of 2 to 40 Pa · s.
When the melt viscosity of the mesophase pitch passing through the nozzle is less than 2 Pa · s, the melt viscosity is too low to maintain the yarn shape, which is not preferable. On the other hand, when the melt viscosity of the mesophase pitch exceeds 40 Pa · s, a strong shearing force is applied to the mesophase pitch and a radial structure is formed in the fiber cross section, which is not preferable. In order to keep the shearing force applied to the mesophase pitch within an appropriate range and maintain the fiber shape, it is necessary to control the melt viscosity of the mesophase pitch passing through the nozzle. Therefore, the melt viscosity of the mesophase pitch is preferably in the range of 2 to 40 Pa · s, more preferably in the range of 3 to 30 Pa · s, and further preferably in the range of 5 to 25 Pa · s. .

The stress applied to the pitch passing through the spinning nozzle is determined by the product of the melt viscosity of the pitch passing through the spinning nozzle and the shear rate of the pitch passing through the nozzle.
The melt viscosity of the pitch passing through the spinning nozzle can be determined by a viscosity measuring device such as a capillary rheometer.
The pitch shear rate can be calculated by the following equation from the flow velocity of the pitch passing through the spinning nozzle and the hole diameter of the nozzle hole.
γ = 8 × V / DN
(Γ: shear rate, V: flow velocity of pitch in capillary (m / s), DN: pore diameter of capillary (m))
In order to obtain pitch-based graphitized short fibers having an average closing rate of more than 80% and less than 100% according to the present invention, a method of controlling the stress of the pitch passing through the spinning nozzle to a predetermined value as described above is preferable. A preferable range of stress is 30 to 200 kPa, and a more preferable range is 50 to 150 kPa.

As a method for controlling the stress of the pitch passing through the spinning nozzle to a predetermined value, the melt viscosity of the pitch passing through the spinning nozzle is in the range of 2 to 40 Pa · s, and the shear rate of the pitch passing through the nozzle is 3000 to 3000 It is preferable to select conditions that are in the range of 20000 s ⁻¹ .
If the shear rate of the pitch passing through the nozzle is less than 3000 s ⁻¹ , sufficient stress cannot be applied to the pitch passing through the spinning nozzle, resulting in a pitch-based carbon fiber precursor with low orientation. For this reason, even when graphitized, the degree of graphitization cannot be sufficiently increased, and it is difficult to improve thermal conductivity, which is not preferable. In addition, pitch-based carbon fiber precursors with low orientation cannot achieve high graphitization, and no graphene sheet is observed at the fiber ends, resulting in difficulty in closing the graphene sheet end face. The average closing rate of the obtained pitch-based graphitized short fibers is less than 80%.

On the other hand, when the shear rate exceeds 20000 s ⁻¹ , a strong shear force is applied to the mesophase pitch passing through the nozzle, and a pitch-based carbon fiber precursor with high orientation is obtained. For this reason, the graphene sheet expression at the end of the fiber becomes remarkable, and as a result, the end face of the graphene sheet becomes easy to close, and the average closing rate of the obtained pitch-based graphitized short fibers becomes 100%. When the shear rate exceeds 20000 s ⁻¹ and a highly oriented pitch-based carbon fiber precursor is used, a radial structure appears in the fiber cross section, which may cause cracks in the fiber cross section during the graphitization process. Since it may cause deterioration of characteristics, it is not preferable. A more preferable range of the shear rate of the pitch passing through the nozzle is a range of 5000 to 13000 s ⁻¹ .

The pitch-based graphitized short fibers of the present invention are characterized in that the average fiber diameter (D1) is greater than 2 μm and not more than 20 μm. Adjustment is possible by changing, changing the discharge amount of the raw material pitch from the nozzle, or changing the draft ratio. The draft ratio can be changed by blowing a gas having a linear velocity of 100 to 20000 m / minute heated to 100 to 400 ° C. in the vicinity of the refinement point. There is no particular restriction on the gas to be blown, but air is desirable from the viewpoint of cost performance and safety. The pitch-based carbon fiber precursor may be collected on a wire mesh belt, formed into a continuous mat, and then cross-wrapped to obtain a constant basis weight web. At that time, the weight per unit area can be adjusted according to the belt conveyance speed, but if necessary, it may be laminated by a method such as cross wrapping. The basis weight of the pitch-based carbon fiber precursor web is preferably 150 to 1000 g / m ^{2 in} consideration of productivity and process stability.

(Infusibilization)
The pitch-based carbon fiber precursor web obtained by the above method is infusibilized by a known method to form a pitch-based infusible fiber web. Infusibilization can be performed in air or in an oxidizing atmosphere using a gas in which ozone, nitrogen dioxide, nitrogen, oxygen, iodine, or bromine is added to air, but in consideration of safety and convenience, it is performed in air. It is desirable. Further, both batch processing and continuous processing can be performed, but continuous processing is desirable in consideration of productivity. The infusibilization treatment is achieved by applying a heat treatment for a predetermined time at a temperature of 150 to 350 ° C. A more preferable temperature range is 160 to 340 ° C. A heating rate of 1 to 10 ° C./min is preferably used. In the case of continuous treatment, the above heating rate can be achieved by sequentially passing through a plurality of reaction chambers set at arbitrary temperatures. A more preferable range of the heating rate is 3 to 9 ° C./min in consideration of productivity and process stability.

(Carbonization treatment)
The pitch-based infusible fiber web obtained by the above method is carbonized at a temperature of 600 to 2000 ° C. in a vacuum or in a non-oxidizing atmosphere using an inert gas such as nitrogen, argon or krypton. Become a carbon fiber web. Carbonization treatment is preferably performed at normal pressure and in a nitrogen atmosphere in consideration of cost. Further, both batch processing and continuous processing can be performed, but continuous processing is desirable in consideration of productivity.

(Pulverization)
In the production of pitch-based graphitized short fibers, the most important point is to pulverize the pitch-based carbon fiber web after carbonization. The carbonized pitch-based carbon fiber web is subjected to processing such as cutting, crushing and pulverization in order to obtain a desired fiber length. In some cases, classification processing is performed. The treatment method is selected according to the desired fiber length, but a guillotine type, uniaxial, biaxial, and multiaxial rotary type cutter is preferably used for cutting. Hammer type, pin type, ball type, bead type and rod type using impact action for crushing and crushing, high speed rotation type using collision between particles, roll type using compression / tearing action, cone type and screw A crusher, a pulverizer, or the like of a formula is preferably used. In order to obtain a desired fiber length, cutting, crushing and pulverization may be configured by a plurality of machines. The treatment atmosphere may be either wet or dry. For the classification treatment, a classification device such as a vibration sieve type, a centrifugal separation type, an inertial force type, and a filtration type is preferably used. The desired fiber length can be obtained not only by selecting a model, but also by controlling the number of revolutions of the rotor / rotating blade, supply amount, clearance between blades, residence time in the system, and the like. Moreover, when using a classification process, desired fiber length can be obtained also by adjusting a sieve mesh hole diameter.

(Graphitization)
The pitch-based carbon short fibers prepared by using the above-described cutting, crushing / pulverizing treatment, and, in some cases, classification treatment, are heated to 2000-3500 ° C. and graphitized to obtain the final pitch-based graphitized short fibers. Graphitization is performed in an Atchison furnace, an electric furnace, or the like, and is performed in a vacuum or in a non-oxidizing atmosphere using an inert gas such as nitrogen, argon, or krypton. In the present invention, surface treatment such as sizing may be performed in any of a series of manufacturing processes.

<Composition>
The present invention includes a composition comprising the pitch-based graphitized short fibers of the present invention and a matrix, wherein the content of the pitch-based graphitized short fibers is 3 to 60% by volume, preferably 10 to 50% by volume. . When the content of pitch-based graphitized short fibers is less than 3% by volume, it is difficult to ensure sufficient thermal conductivity. On the other hand, it is difficult to add more than 60% by volume.
The matrix is preferably a thermoplastic resin and / or a thermosetting resin. Furthermore, a thermoplastic resin and a thermosetting resin can be appropriately mixed and used in order to develop desired physical properties in the composite molded body.

  Polyolefins and their copolymers (polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, ethylene as thermoplastic resins that can be used in the matrix -Ethylene-α-olefin copolymer such as propylene copolymer), polymethacrylic acid and its copolymer (polymethacrylic acid ester such as polymethyl methacrylate), polyacrylic acid and its copolymer, polyacetal And copolymers thereof, fluororesins and copolymers thereof (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyesters and copolymers thereof (polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6 naphtha) Liquid crystal polymers), polystyrenes and copolymers thereof (styrene-acrylonitrile copolymers, ABS resins, etc.), polyacrylonitriles and copolymers thereof, polyphenylene ethers (PPE) and copolymers thereof ( Modified PPE resins), aliphatic polyamides and copolymers thereof, aromatic polyamides and copolymers thereof, polyimides and copolymers thereof, polyamideimides and copolymers thereof, polycarbonates and copolymers thereof Polymers, polyphenylene sulfides and copolymers thereof, polysulfones and copolymers thereof, polyether sulfones and copolymers thereof, polyether nitriles and copolymers thereof, polyether ketones and copolymers thereof , Polyether ether ketones and copolymers thereof, polyketones and These copolymers, silicone oils and the like.

Among these, as thermoplastic resins, polycarbonates and copolymers thereof, polyesters and copolymers thereof, polyamides and copolymers thereof, polyolefins and copolymers thereof, polyether ketones and copolymers thereof, polyphenylene Preferable examples include at least one resin selected from the group consisting of sulfides and copolymers thereof, ABS resins, and silicone oil. One of these may be used alone, or two or more may be used in appropriate combination. Moreover, an additive such as a flame retardant or other functional filler may be mixed in these thermoplastic resins.
Examples of the thermosetting resin include epoxies, acrylics, urethanes, silicones, phenols, imides, thermosetting modified PPEs, thermosetting PPEs, polybutadiene rubbers and copolymers thereof, Examples thereof include acrylic rubber and copolymers thereof, silicone rubber and copolymers thereof, natural rubber, and the like. One of these may be used alone, or two or more may be used in appropriate combination. Further, an additive such as a flame retardant or a functional filler may be mixed in these thermosetting resins.

  The composition of the present invention is prepared by mixing pitch-based graphitized short fibers and a matrix. During mixing, kneaders, various mixers, blenders, rolls, extruders, milling machines, self-revolving stirring A mixing device such as a machine or a kneading device is preferably used. Then, the composite material and / or the composite molded body is subjected to molding methods such as injection molding, press molding, calendar molding, roll molding, extrusion molding, powder molding, cast molding, and blow molding. And can be molded. The molding conditions depend on the molding method and the matrix. In the case of a thermoplastic resin, the molding is performed in a state where the temperature is higher than the melt viscosity of the resin. In the case where the matrix is a thermosetting resin, a method of applying a curing temperature of the resin in an appropriate mold can be exemplified.

<Molded body>
The molded body obtained by molding the composition of the present invention into a flat plate shape preferably has a thermal conductivity of 2 W / (m · K) or more. That is, this invention includes the flat plate which consists of this composition and whose heat conductivity is 2 W / (m * K) or more. The thermal conductivity of 2 W / (m · K) is about one digit higher than that of the polymer material used as the matrix. The composition of the present invention can be used, for example, as a molded body for a heat sink for electronic parts, a radio wave shielding plate, a heat exchanger, and the like. Therefore, this invention includes the heat sink for electronic components which consists of this composition. An electromagnetic wave shielding plate made of the composition is included. The present invention includes a heat exchanger comprising the composition.

Examples are shown below, but the present invention is not limited thereto.
(1) Average fiber diameter and fiber diameter dispersion of pitch-based graphitized short fibers:
The average fiber diameter and fiber diameter dispersion were determined from the average value of 60 pitch-based graphitized short fibers measured under an optical microscope using a scale according to JIS R7607. Moreover, CV value was determined by following formula (2) as a ratio of the obtained average fiber diameter (Ave) and the deviation (S) of a fiber diameter.
CV = S / Ave × 100 (2)
here,

Where X is the observed value and n is the number of observations.
(2) Average fiber length of pitch-based graphitized short fibers:
The average fiber length is a number average fiber length, and 2000 pitch-graphitized short fibers subjected to graphitization were measured under an optical microscope with a length measuring instrument, and obtained from the average value. The magnification was appropriately adjusted according to the fiber length.
(3) True density of pitch-based graphitized short fibers:
The true density of the pitch-based graphitized short fibers was measured by the float / sink method. That is, a mixed solution of dibromoethane having a specific gravity of 2.17 (g / cm ³ ) and bromoform having a specific gravity of 2.89 (g / cm ³ ) is prepared in a cylinder and controlled at a temperature of 25 ± 0.2 ° C. Pitch-based graphitized short fibers are infiltrated into the above mixed solution, held at 1.3 kPa for 3 minutes, and then stirred until the pitch-based graphitized carbon fibers come to the center of the mixed solution. After 10 minutes, dibromoethane is added if the pitch-based graphitized carbon fiber emerges, and bromoform is added dropwise if it sinks. This operation is repeated until the pitch-based graphitized carbon fiber is stationary. After the pitch-based graphitized carbon fiber was stationary, the density of the mixed liquid was measured with a specific gravity float to obtain the density of the pitch-based graphitized carbon fiber.
(4) Crystal size:
The size of the crystallite derived from the thickness direction of the hexagonal mesh surface obtained by X-ray diffraction method is obtained using the diffraction line from the (002) plane, and the size of the crystallite derived from the growth direction of the hexagonal mesh surface. Was determined using diffraction lines from the (110) plane. In addition, the request was made in accordance with the Gakushin Law.
(5) Thermal conductivity of pitch-based graphitized short fibers:
A yarn was extracted from a pitch-based graphitized fiber web produced under the same conditions except for the pulverization step, and the resistivity was measured to represent the relationship between the thermal conductivity and the electrical resistivity disclosed in JP-A-11-117143. It calculated | required from following formula (3).
K = 1272.4 / ER-49.4 (3)
Here, K represents the thermal conductivity W / (m · K) of the pitch-based graphitized fiber, and ER represents the electrical specific resistance μΩm of the same pitch-based graphitized fiber.
(6) Confirmation of a substantially flat surface:
The number of defects such as irregularities was counted in an image obtained by observing the pitch-based graphitized short fibers with a scanning electron microscope at 1000 times. In the case of 10 places or less, it was smooth.
(7) Fine structure of the end face of the graphene sheet of pitch-based graphitized short fibers:
In the fiber end observation with a transmission electron microscope of pitch-based graphitized short fibers, 5 graphene sheet end face images of 500 to 2.5 million times the fiber end were observed, and the total length A (nm) and end face of the graphene sheet end face at the fiber end The length B (nm) of the portion curved in a U-shape was measured, and the closing rate was determined by the closing rate (%) = B / A × 100.
(8) Thermal conductivity of flat molded body:
Measured with QTM-500 manufactured by Kyoto Electronics.

[Example 1]
A mesophase pitch composed of a condensed polycyclic hydrocarbon compound having an optical anisotropy ratio of 100% and a softening point of 288 ° C. was used as a raw material. A pitch of melt viscosity of 15 Pa · s is obtained by using a base having a 0.2 mmφ diameter hole and a 2 mm long capillary for the raw material melted at 335 ° C., and blowing heated air from the slit at a linear velocity of 5500 m / min. Is pulled at a flow rate of 0.0002 (m) and a shear rate of 7500 s ⁻¹ to give a stress of 112.5 kPa, and then collected on a wire mesh belt to form a continuous mat, and further weighted by cross wrapping. A pitch-based carbon fiber precursor web of 350 g / m ² was obtained. In addition, the average fiber diameter of the pitch-type carbon fiber precursor which comprises this web was 11.3 micrometers.
This pitch-based carbon fiber precursor web was heated and infusible from 175 ° C. to 280 ° C. at an average heating rate of 4 ° C./min to prepare a pitch-based infusible fiber web. Next, the pitch-based infusible fiber web was fired at 800 ° C. in a nitrogen atmosphere, and then pulverized with a jet mill pulverizer (SK Jet Oh Mill) manufactured by Seishin Corporation to obtain pitch-based carbon short fibers. Pitch-based graphitized short fibers were obtained by heat-treating the pitch-based carbon short fibers at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere.

The average fiber diameter (D1) of the pitch-based graphitized short fibers is 8.2 μm, the ratio of L1 to D1 is 8.5, the percentage of the fiber diameter dispersion to the average fiber diameter (CV value) is 13%, and the true density is 2. It was 193 g / cc. Further, in the observation of five fiber ends with a transmission electron microscope of pitch-based graphitized short fibers, the graphene sheet end face closing rates determined from the 1.7 million times graphene sheet end face images were 89%, 94%, and 94%, respectively. 92% and 90%, and the average closing rate of the end face of the graphene sheet was 91.8%.
Further, the surface of the pitch-based graphitized short fiber observed with a scanning electron microscope at a magnification of 1000 was smooth and free from defects such as large irregularities. The crystal size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 55 nm. The crystal size in the growth direction of the hexagonal network surface was 125 nm.

From the pitch-based graphitized fiber web that was heat-treated at 3000 ° C. in a non-oxidizing atmosphere in a pitch-based carbon fiber web that was produced in the same process until firing and was not pulverized, The electrical resistivity was extracted and measured to be 1.6 μΩm. The thermal conductivity was 750 W / (m · K). Further, when the characteristics of the LIB negative electrode agent were examined, the capacity was 345 mAh / g, which was close to the theoretical value of graphite (375 mAh / g).
10 ml of Toray Dow silicone thermosetting resin (SE1740A) and 10 g of pitch-based graphitized short fibers were kneaded for 3 minutes with a vacuum planetary mixer (Sinky ARV-310), and Toray Dow silicone thermosetting resin (SE1740B). 10 ml of the mixture was added, and the mixture was further vacuum-kneaded for 3 minutes to prepare 20 ml of slurry. The slurry was heat-treated at 130 ° C., and the curing time of the resin was measured.

[Comparative Example 1]
The pitch-based infusible fiber web was graphitized at 3000 ° C. to produce a pitch-based graphitized fiber web and then pulverized to produce pitch-based graphitized short fibers.
The average fiber diameter (D1) of the pitch-based graphitized short fibers is 7.4 μm, the ratio of L1 to D1 is 6.8, the percentage of the fiber diameter dispersion to the average fiber diameter is 17%, and the true density is 2.185 g / cc. there were. Further, in the observation of five fiber ends with a transmission electron microscope of pitch-based graphitized short fibers, the graphene sheet end face closing rates obtained from the 1.7 million times graphene sheet end face images were 11%, 7%, and 10%, respectively. The average closing rate of the graphene sheet end face was 8.2%. Further, 20 or more defects such as large irregularities were observed in the observation field on the surface of the pitch-based graphitized short fibers observed with a scanning electron microscope at a magnification of 1000 times. The crystal size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 30 nm. The crystal size in the growth direction of the hexagonal network surface was 61 nm. The pitch-based carbon fiber web was extracted from a pitch-based graphitized fiber web heat-treated at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere, and the electrical resistivity was measured to be 1.6 μΩm. It was. The thermal conductivity was 750 W / (m · K).
10 ml of Toray Dow silicone thermosetting resin (SE1740A) and 10 g of pitch-based graphitized short fibers were kneaded for 3 minutes with a vacuum planetary mixer (Sinky ARV-310), and Toray Dow silicone thermosetting resin (SE1740B). 10 ml of the mixture was added, and the mixture was further vacuum-kneaded for 3 minutes to prepare 20 ml of slurry. When the slurry was heat-treated at 130 ° C. and the time for curing of the resin was measured, it was not cured even after 90 minutes.

[Comparative Example 2]
Pitch-based graphitized short fibers were obtained by heat-treating the pitch-based carbon short fibers at 2000 ° C. in an electric furnace in a non-oxidizing atmosphere. The average fiber diameter (D1) of pitch-based graphitized short fibers is 8.2 μm, the ratio of L1 to D1 is 8.5, the percentage of the fiber diameter dispersion to the average fiber diameter is 13%, and the true density is 2.103 g / cc. there were. Further, in the observation of five fiber ends with a transmission electron microscope of pitch-based graphitized short fibers, the graphene sheet end face closing rates obtained from the 1.7 million times graphene sheet end face images were 21%, 28%, and 20%, respectively. 27% and 24%, and the average closing rate of the end face of the graphene sheet was 24%. Further, the surface of the pitch-based graphitized short fiber observed with a scanning electron microscope at a magnification of 1000 was smooth and free from defects such as large irregularities. The crystal size in the thickness direction of the hexagonal network surface determined by the X-ray diffraction method was 5 nm. The crystal size in the growth direction of the hexagonal network surface was 10 nm.
10 ml of Toray Dow silicone thermosetting resin (SE1740A) and 10 g of pitch-based graphitized short fibers were kneaded for 3 minutes with a vacuum planetary mixer (Sinky ARV-310), and Toray Dow silicone thermosetting resin (SE1740B). 10 ml of the mixture was added, and the mixture was further vacuum-kneaded for 3 minutes to prepare 20 ml of slurry. When the slurry was heat-treated at 130 ° C. and the time for curing of the resin was measured, it was not cured even after 90 minutes.

[Comparative Example 3]
In the observation of the end of five fibers with a transmission electron microscope of carbon fiber (K223QM) manufactured by Mitsubishi Chemical Corporation, the closing rate of the graphene sheet end face obtained from the 1.7 million magnification graphene sheet end face image is all 0%. The average closing rate of the end face of the graphene sheet was 0%. Further, the surface of the pitch-based graphitized short fiber observed with a scanning electron microscope at a magnification of 1000 was smooth and free from defects such as large irregularities.
10 ml of Toray Dow silicone thermosetting resin (SE1740A) and 10 g of the above-mentioned carbon fiber are kneaded for 3 minutes with a vacuum type planetary mixer (ARV-310 made by Sinky), and 10 ml of Toray Dow silicone thermosetting resin (SE1740B). Addition and further vacuum kneading for 3 minutes to prepare 20 ml of slurry. When the slurry was heat-treated at 130 ° C. and the time for curing of the resin was measured, it was not cured even after 90 minutes.

[Comparative 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 283 ° C. Using a hole with a diameter of 0.2 mmφ and a cap with a length of 0.6 mm, heated air is ejected from the slit at a linear velocity of 5000 m / min, and a pitch with a melt viscosity of 55 Pa · s is pulled at a shear rate of 7500 s ⁻¹ . Thus, a stress of 412.5 kpa was applied to the pitch, and pitch-based short fibers having an average fiber diameter of 15 μm were produced. The spun short fibers were collected on a belt to form a mat, and further a pitch-based carbon short fiber web having a basis weight of 320 g / m ^{2 by} cross wrapping.
The web was infusibilized by increasing the temperature from 175 ° C. to 280 ° C. in air at an average temperature increase rate of 7 ° C./min. The infusible web was fired at 800 ° C. in a nitrogen atmosphere and then pulverized to obtain pitch-based carbon short fibers having an average fiber length of 28 μm. Then, it graphitized by heat-processing at 3000 degreeC with the electric furnace made into the non-oxidizing atmosphere, and it was set as the pitch-type graphitized short fiber. The average fiber diameter was 10.1 μm, the percentage of the fiber diameter dispersion to the average fiber diameter was 13%, and the true density was 2.17 g / cc.

When observed with a transmission electron microscope at a magnification of 1,000,000 and enlarged on a photograph at a magnification of 4 million, the closing rates of the end faces of the five graphene sheets were all 100%. Further, the surface of the pitch-based carbon short fiber filler, which was observed with a scanning electron microscope at a magnification of 4000 times, was smooth with no large irregularities. When the LIB negative electrode agent characteristics of the pitch-based graphitized short fibers described above were examined, the capacity was 285 mAh / g, which was far from the theoretical value of graphite (375 mAh / g).
The above results are summarized and shown in Table 1 below.

[Example 2]
As a thermoplastic resin, polyphenylene sulfide (polyplastic, Fortron, 0220A9) is selected, and the pitch-based graphitized short fiber prepared in Example 1 is used at a volume ratio of 70:30 in a Kurimoto biaxial kneader. A composition was prepared. This composition was molded into a flat plate having a thickness of 2 mm using an injection molding machine manufactured by Meiki Seisakusho. The thermal conductivity of this flat plate was measured and found to be 4.1 W / (m · K).

[Comparative Example 5]
A plate of polyphenylene sulfide without the addition of pitch-based graphitized short fibers was prepared. The thermal conductivity was 0.4 W / (m · K).

  The pitch-based graphitized short fibers of the present invention can be used for electronic parts and the like.

The schematic diagram of the terminal of pitch system graphitized short fiber is shown.

Explanation of symbols

A Total length of graphene sheet end face at fiber end B Length of end face curved in U shape

Claims (11)

(I) The average fiber diameter (D1) observed with an optical microscope is greater than 2 μm and not greater than 20 μm, and the percentage of the fiber diameter dispersion (S1) relative to the average fiber diameter (D1) is in the range of 3 to 20%.
(Ii) The surface of the observation with a scanning electron microscope is substantially flat, and (iii) The total length of the end surface of the graphene sheet at the end of the fiber by a transmission electron microscope is more than 50 nm and less than 300 nm. A pitch-based graphitized short fiber having an average closing rate (average closing rate) represented by the formula (1) of more than 80% and less than 100% when observed.
Closure rate (%) = B / A × 100 (1)
(A represents the total length (nm) of the end surface of the graphene sheet at the fiber end, and B represents the length (nm) of the portion where the end surface is curved in a U-shape) The pitch-based graphitized short fiber according to claim 1, having an average closing rate of more than 95% and less than 100. The pitch-based graphitized short fibers according to claim 1 or 2, wherein the average fiber length (L1) is in the range of 10 µm to 700 µm, and the ratio of L1 to the average fiber diameter (D1) is 1 to 50. The pitch according to any one of claims 1 to 3, wherein the true density is in the range of 2.15 to 2.30 g / cc, and the thermal conductivity in the fiber axis direction is 400 W / (m · K) or more. Graphitized short fiber. The size of the crystallite derived from the thickness direction of the hexagonal network surface is 30 nm or more, and the size of the crystallite derived from the growth direction of the hexagonal network surface is 80 nm or more. The pitch-based graphitized short fiber described. The composition which contains the pitch-type graphitized short fiber as described in any one of Claims 1-5, and a matrix, and the content rate of a short fiber is 3-60 volume%. The composition according to claim 6, wherein the matrix is a thermoplastic resin and / or a thermosetting resin. A flat plate comprising the composition according to claim 6 and having a thermal conductivity of 2 W / (m · K) or more. A heat sink for electronic parts, comprising the composition according to claim 6. A radio wave shielding plate comprising the composition according to claim 6. A heat exchanger comprising the composition according to claim 6.

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