WO2010084856A1

WO2010084856A1 - Pitch-based carbon fiber web, pitch-based carbon staple fiber, and processes for production of same

Info

Publication number: WO2010084856A1
Application number: PCT/JP2010/050554
Authority: WO
Inventors: 博志櫻井; 寛原; 幸夫中本; 正一高木
Original assignee: 帝人株式会社
Priority date: 2009-01-20
Filing date: 2010-01-19
Publication date: 2010-07-29
Also published as: TW201042105A; JPWO2010084856A1

Abstract

Provided is a pitch-based carbon fiber which has a smaller mean -fiber-diameter distribution and more excellent mechanical strengths as compared with those of a pitch-based carbon fiber produced by melt blowing. Disclosed is a pitch-based carbon fiber web composed of pitch-based carbon fibers which have a mean fiber diameter of 5 to 20µm, a CV value of mean fiber diameter of 3 to 8%, a tensile modulus of 150 to 1000GPa, and a tensile strength of 2.5 to 5GPa. The carbon fiber web can be suitably produced by spinning which is accompanied with drawing by air jet parallel to the direction of the spinning.

Description

Pitch-based carbon fiber web, pitch-based carbon short fibers, and manufacturing method thereof

The present invention relates to a pitch-based carbon fiber web, a pitch-based carbon short fiber that can be suitably used as a heat-dissipating material and a resin reinforcing material, and methods for producing them. More specifically, the pitch-based carbon has a significantly smaller average fiber diameter distribution than pitch-based carbon fiber webs or short pitch-based carbon fibers manufactured by a conventional melt-blowing method, and has both strength and elastic modulus. The present invention relates to a pitch-based carbon fiber web composed of fibers, pitch-based carbon short fibers, and a method for producing the same.

Spinning methods for pitch-based carbon fibers include the usual spinning and drawing method in which the mesophase pitch discharged from the die is drawn by a winder, the melt blow method using hot air as an atomizing source, and the centrifugal spinning method that draws mesophase pitch using centrifugal force. Is mentioned. Among them, the melt blow method is preferably used for reasons such as control of the form of the pitch-based carbon fiber precursor and high productivity (for example,

Patent Documents

1, 2, and 3). These pitch-based carbon fibers are blown by high-speed air to the mesophase pitch melt-spun in the vicinity of the die, and the stretched filaments are accumulated in a nonwoven fabric on a screen conveyor or perforated drum, and then the nonwoven fabric is infusible. Manufactured by firing. Conventionally, the air blown from the base of the melt blow method is a method in which the air is blown at a certain angle, not parallel to the fiber axis direction.

The pitch-based carbon fiber obtained by the melt-blowing method has a wider yarn diameter distribution than a normal spinning drawing method in which the mesophase pitch discharged from the die is stretched with air and is pulled by a winder. For this reason, there has been a problem that the amount of oxygen attached to each fiber is different in the infusibilization process of the production, and the physical properties of the finally obtained carbon fiber become non-uniform. Further, when the mesophase pitch is stretched with air, pitch molecules that are extremely oriented when passing through the capillary are disturbed by the air, so that the mechanical properties of the finally obtained carbon fiber deteriorate. It was.

Japanese Patent Laid-Open No. 4-108150 JP 2008-285797 A JP 2008-285795 A

In the conventional melt blow method, the yarn diameter varies. Further, since the orientation of pitch molecules constituting the pitch-based carbon fiber precursor is disturbed by air, there is a problem that the mechanical properties of the finally obtained carbon fiber are deteriorated.

Therefore, pitch-based carbon fiber webs, pitch-based carbon short fibers composed of pitch-based carbon fibers with small variations in thread diameter and excellent mechanical strength compared to carbon fibers obtained by conventional melt-blowing methods, and production thereof It is an object of the present invention to provide a method.

The present invention relates to a pitch-based carbon fiber having an average fiber diameter of 5 to 20 μm, an average fiber diameter CV value of 3 to 8%, a tensile elastic modulus of 150 to 1000 GPa, and a tensile strength of 2.5 to 5 GPa. It is related with the pitch-type carbon fiber web comprised.

The present invention also relates to pitch-based carbon short fibers obtained by further pulverizing and firing the pitch-based carbon fiber web.

The pitch-based carbon fiber web of the present invention has (1) a mesophase pitch having a melt viscosity in the spinning hole of greater than 5 Pa · s and less than 100 Pa · s (greater than 50 poise and less than 1000 poise) by an air jet parallel to the spinning direction. A step of producing a pitch-based carbon fiber precursor web composed of long fibers by spinning while pulling; (2) the pitch-based carbon fiber precursor web is infusible in an oxidizing gas atmosphere, and the pitch-based infusible fiber web And (3) a method for producing a pitch-based carbon fiber web comprising a step of firing a pitch-based infusible fiber web.

Further, after the steps (1) to (3) for obtaining a pitch-based carbon fiber web, the pitch-based carbon short fibers of the present invention can be preferably obtained by (4) grinding and (5) firing.

The pitch-based carbon fiber web and the pitch-based carbon short fiber of the present invention have a significantly smaller variation in the diameter of the pitch-based carbon fiber constituting the web than the pitch-based carbon fiber produced by the conventional melt-blowing method, and the machine It has excellent strength and can provide various physical properties such as mechanical properties, thermal properties, and electrical properties.

Schematic of spinning apparatus of Examples 1 and 3 Schematic of spinning device of Comparative Example 1

In the pitch-based carbon fiber web of the present invention, the pitch-based carbon fiber constituting the pitch-based carbon fiber has less variation in yarn diameter and superior mechanical strength as compared to pitch-based carbon fiber produced by a conventional melt-blowing method. Various physical properties such as properties, thermal properties, and electrical properties can be provided uniformly.

[Pitch-based carbon fiber web]
The pitch-based carbon fibers constituting the pitch-based carbon fiber web of the present invention have an average fiber diameter of 5 to 20 μm observed with an optical microscope. When the average fiber diameter is less than 5 μm, for example, the number of fillers increases when pulverized and combined with the matrix as pitch-based carbon short fibers, so that the viscosity of the matrix / filler mixture increases and molding becomes difficult. On the other hand, when the average fiber diameter exceeds 20 μm, the number of fillers decreases when they are combined with the matrix, so that the fillers are less likely to come into contact with each other, and it is difficult to exhibit effective heat conduction when used as a composite material. A more preferable range of the average fiber diameter is 7 to 15 μm.

In addition, the pitch-based carbon fiber constituting the pitch-based carbon fiber web of the present invention has a percentage (CV value) of 3 to 8% of the average fiber diameter of the fiber diameter dispersion of the pitch-based carbon fiber observed with an optical microscope. When the CV value is 3 to 8%, in the infusibilization of the production process, a uniform oxygen adhesion amount is achieved in each fiber, and the physical properties of the finally obtained carbon fiber become uniform, and the performance is uniform. A composite material can be obtained. When the CV value is smaller than 3%, the fiber diameters are extremely uniform, so the amount of small-sized filler entering the gap between the fillers is reduced, and it becomes difficult to form a denser packed state when compounding with the matrix. As a result, it may be difficult to obtain a high-performance composite material. When the CV value is larger than 8%, the oxygen adhesion amount in infusibilization is difficult to be uniform. The CV value is preferably 4-7%.

The tensile elastic modulus of the pitch-based carbon fiber constituting the pitch-based carbon fiber web of the present invention is in the range of 150 to 1000 GPa. When it is less than 150 GPa, since the crystallinity of the pitch-based carbon fiber is low, the durability of the web is also lowered, which is not preferable. On the other hand, when it exceeds 1000 GPa, the elongation of the pitch-based carbon fiber becomes small, and the handling property of the web is lowered, which is not preferable. A more preferable range of the tensile modulus of the pitch-based carbon fiber constituting the web is 200 to 800 GPa, and a more preferable range is 300 to 700 GPa. Further, the tensile strength of the pitch-based carbon fibers constituting the web of the present invention is in the range of 2.5 to 5 GPa. If it is less than 2.5 GPa, the elongation of the pitch-based carbon fiber is low, and the handling property of the web is lowered, which is not preferable. On the other hand, if it exceeds 5 GPa, the crystallinity of the pitch-based carbon fibers is reduced, and the crystallinity of the pitch-based carbon fibers is low, which is not preferable because the durability of the web also decreases. A more preferable range of the tensile strength is 2.7 to 4.8 GPa.

The pitch-based carbon fiber web of the present invention is formed by randomly entangling a bundle of pitch-based carbon fibers gathered at least five or more. For this reason, the pitch-based carbon fiber web of the present invention has a feature that a bundle of pitch-based carbon fibers is easily applied to the needle when the needle punching process is performed. Therefore, when the web is cross-wrapped, the delamination strength of the felt obtained after the needle punching is improved as compared with the web manufactured by the conventional melt blow method.

[Pitch-based carbon fiber web manufacturing method]
Next, each process is demonstrated sequentially about the preferable manufacturing method of the pitch-type carbon fiber web of this invention.

[Mesophase pitch of raw material]
As a raw material of the pitch-based carbon fiber, mesophase pitch is preferable, and the mesophase pitch 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. Examples of the raw material for mesophase pitch include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, and condensed heterocyclic compounds such as petroleum pitch and coal pitch. Of these, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferred.

Furthermore, the softening point of the raw material pitch is preferably 230 ° C. or higher and 340 ° C. or lower. The infusibilization treatment of the pitch-based carbon fiber precursor 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, when the softening point exceeds 340 ° C., the pitch is liable to cause thermal decomposition, and the generated gas causes problems such as the generation of bubbles in the yarn, which is not preferable. 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.

[(1) Process for producing pitch-based carbon fiber precursor web]
The spinning method in the production method of the present invention is a so-called melt spinning method, and is characterized by spinning while pulling a mesophase pitch with an air jet parallel to the spinning direction. Mesophase pitch, which is a raw material for pitch-based carbon fibers, is an aggregate of polycyclic aromatic molecules having different molecular weights, and the carbon fiber precursor immediately after spinning is very brittle. For this reason, in the melt-blowing method, the spun carbon fiber precursor is cut by wind force and accumulated in a non-woven shape in a short fiber state. In contrast, in the method of the present invention, the mesophase pitch is spun while being pulled by an air jet parallel to the spinning direction. For this reason, there is no application of stress by air in the fiber cross-sectional direction, and the substantially pitch-based carbon fiber precursor forms a web as long fibers. The air jet may be substantially parallel to the spinning direction. The long fiber referred to in the present invention refers to a fiber having a fiber length of 1 m or more, and the web refers to a non-woven fabric.

The melt viscosity in the spinning hole is preferably greater than 5 Pa · s and less than 100 Pa · s (greater than 50 poise and less than 1000 poise). When the melt viscosity in the spinning hole is less than 5 Pa · s, when the mesophase pitch is pulled with an air jet parallel to the spinning direction, the mesophase pitch is not viscous, and thus the yarn is broken by the pulling. Further, once the yarn breakage occurs, the yarn diameter increases until the mesophase pitch pushed out in a rod shape from the spinneret is pulled by the air jet, and the CV value serving as an index indicating variation in the yarn diameter increases, which is not preferable. . On the other hand, when the viscosity exceeds 100 Pa · s, the viscosity of the mesophase pitch is high, so that the mesophase pitch pushed out in a rod shape from the spinneret cannot be sufficiently pulled, and the yarn diameter increases. For this reason, it takes a lot of time in the infusibilization process in the next step, which causes a decrease in productivity, which is not preferable. A more preferable range of the melt viscosity in the spinning hole is greater than 10 Pa · s and less than 50 Pa · s (greater than 100 poise and less than 500 poise).

The shape of the spinning nozzle for forming the pitch-based carbon fiber precursor may be any. Normally, a perfect circle is used, but there is no problem even if an irregularly shaped nozzle such as an ellipse is appropriately used. The ratio of the nozzle hole length (LN) to the hole diameter (DN) (LN / DN) is preferably in the range of 2-20. When LN / DN exceeds 20, a strong shearing force is applied to the mesophase pitch passing through the nozzle, and a radial structure is developed in the fiber cross section. The expression of the radial structure is not preferable because it may cause a crack in the fiber cross-section during the graphitization process and may cause a decrease in mechanical properties. On the other hand, if LN / DN is less than 2, shearing cannot be imparted to the raw material pitch, resulting in a pitch-based carbon fiber precursor with low orientation of pitch molecules. 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 of the nozzle hole length (LN) to the hole diameter (DN) (LN / DN) is preferably in the range of 2 to 20, more preferably in the range of 3 to 12. A jig that disturbs the flow of the mesophase pitch may be inserted immediately above the nozzle.

A conventional melt-blow base has a flow passage for blowing air from the vicinity of the nozzle hole, which reduces the pressure resistance of the base and reduces the degree of freedom in the design of the base, making it impossible to install many nozzle holes. There was a problem. However, in this method, there is no need to provide a flow passage for blowing air in the vicinity of the nozzle hole, and the degree of freedom in designing the die can be increased. For this reason, the number of nozzle holes can be increased as compared with the melt blow die, and as a result, it can be expected to improve productivity. There are no particular restrictions on the way in which the nozzle holes are arranged, but examples include a method in which nozzle holes are concentrically arranged, and a method in which nozzle holes are arranged in multiple rows in a straight line.

In the present invention, it is preferable shear rate of mesophase pitch passing through the spinning holes is greater 30000s less than ^-1 from 6000 s ^-1. If the shear rate of the mesophase pitch passing through the spinning hole is less than 6000 s ⁻¹ , the productivity may be significantly reduced. On the other hand, if it exceeds 30000 s ⁻¹ , a large shear is generated in the mesophase pitch passing through the capillary, and it tends to easily develop a radial structure that causes the carbon fiber to crack. A more preferable range of the shear rate of the mesophase pitch passing through the spinning hole is in the range of 7000 to 20000 s ⁻¹ .

In the present invention, it is preferable to pull the melt-spun mesophase pitch with an air jet of 300 to 10000 m / min. When the air jet speed is less than 300 m / min, the yarn diameter of the carbon fiber precursor becomes large, and it takes a lot of time for the infusibilization treatment in the next step, which is not preferable. On the other hand, when it exceeds 10,000 m / min, the yarn diameter of the carbon fiber precursor becomes too thin, and the yarn may be broken in the process of extending the mesophase pitch. The air flow rate is a value measured by a flow meter, and the wind speed is calculated by dividing the flow rate by the sectional area of the suction gun.

The more preferable range of the wind speed is 500 to 6000 m / min, and more preferably 700 to 3000 m / min. There is no particular limitation on the gas used for the air jet, but air is desirable from the viewpoint of cost performance and safety. The temperature of the gas used for the air jet may be equal to or lower than the softening point of the mesophase pitch in order to suppress the yarn breakage of the carbon fiber precursor, but room temperature is preferable from the viewpoint of cost performance and safety.

When the mesophase pitch is spun while being pulled by an air jet parallel to the spinning direction to form a pitch-based carbon fiber precursor web composed of long fibers, it may be passed through a spinning cylinder. The shape of the spinning cylinder is not particularly limited, but it may be easily charged with static electricity, and is preferably a cylinder with countermeasures against static electricity. Furthermore, it is preferable to collect a pitch-based carbon fiber precursor web by installing a collector equipped with a suction machine.

In step (1), the mesophase pitch is spun while being pulled by an air jet parallel to the spinning direction to form a pitch-based carbon fiber precursor web composed of long fibers. In the long fibers before the web is formed, The orientation degree of the pitch-based carbon fiber precursor evaluated by X-ray is preferably 84.5% or more. Conventionally, the air blown from the base of the melt blow method is blown out at a certain angle, not parallel to the fiber axis direction. For this reason, the pitch molecules that are extremely oriented in the fiber axis direction in the die are subjected to stress applied in the fiber cross-sectional direction by air, and the orientation of the pitch molecules is disturbed. In the method of the present invention, since the mesophase pitch is pulled by an air jet parallel to the spinning direction, almost no stress is applied in the fiber cross-sectional direction by air. For this reason, the degree of orientation of the pitch molecules is higher than that of the pitch-based carbon fiber precursor prepared by the melt blow method. When the degree of orientation of the pitch-based carbon fiber precursor evaluated by X-ray is less than 84.5%, it is difficult to increase the thermal conductivity of the fired pitch-based carbon fiber, which is not preferable. The reason for this is presumed that if the orientation degree of the pitch-based carbon fiber precursor is low, the end faces of the hexagonal network layer cannot be well connected in the carbonization process and cannot grow into a large crystal. A more preferable range of the degree of orientation of the pitch-based carbon fiber precursor evaluated by X-ray is 85% or more, more preferably 85.5% or more.

Note that the pitch-based carbon fiber precursors aligned in the fiber axis direction before the web is formed can be collected by, for example, providing a sampling point in a spinning cylinder and performing sampling.

The mesophase pitch is spun while being pulled by an air jet parallel to the spinning direction to form a long fiber composed of a pitch-based carbon fiber precursor. This pitch-based carbon fiber precursor is collected by a belt such as a wire mesh and is pitch-based. It becomes a carbon fiber precursor web. At that time, the weight per unit area can be adjusted according to the belt conveyance speed, but if necessary, it may be laminated by a method such as cross wrapping. The basis weight of the pitch-based carbon fiber precursor web is preferably 150 to 1000 g / m ² in consideration of productivity and process stability. Since the pitch-based carbon fiber precursor web is spun while pulling the mesophase pitch with an air jet parallel to the spinning direction, a bundle of at least five pitch-based carbon fiber precursors is randomly entangled with the nonwoven fabric. Become.

[(2) Process for producing pitch-based infusible fiber web]
The pitch-based carbon fiber precursor web thus obtained is infusibilized by a known method to form a pitch-based infusible fiber web. The infusibilization of the pitch-based infusible fiber web is performed in an oxidizing gas atmosphere, where the oxidizing gas is air or a gas and air that can extract electrons from the pitch-based carbon fiber precursor. Refers to mixed gas. Examples of the gas that can extract electrons from the pitch-based carbon fiber precursor include ozone, iodine, bromine, and oxygen. However, in view of safety, convenience, and cost performance, it is particularly desirable to infusibilize the pitch-based carbon fiber precursor web in the air. 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 certain time at a temperature of 150 to 350 ° C. A more preferable temperature range is 160 to 340 ° C. A temperature increase rate of 1 to 10 ° C./min is preferably used. In the case of continuous treatment, the above temperature increase 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.

In the method of the present invention, it is preferable to attach oxygen in the range of 6.2 to 7.8 wt% to the pitch-based infusible fiber web by the above-described operation. When the oxygen adhesion amount to the pitch-based infusible fiber web is less than 6.2 wt%, fusion may occur between the fibers in the next carbonization step. On the other hand, when the oxygen adhesion amount exceeds 7.8 wt%, the graphitizable property of the pitch-based carbon fiber finally obtained may be lowered, and the thermal conductivity may be lowered. A more preferable range of the amount of oxygen attached to the pitch-based infusible fiber web is in the range of 6.5 to 7.5 wt%. The amount of oxygen attached to the pitch-based infusible fiber web can be determined by elemental analysis.

[(3) Process for producing pitch-based carbon fiber web]
The infusible fiber web is then fired to obtain a pitch-based carbon fiber web. Firing the pitch-based infusible fiber at less than 2000 ° C. is preferably performed in a vacuum or in a non-oxidizing atmosphere using an inert gas such as nitrogen, argon, or krypton. The pitch-based infusible fiber can be fired at a temperature of less than 2000 ° C. by either batch processing or continuous processing, but continuous processing is desirable in consideration of productivity. In firing exceeding 2000 ° C., the atmosphere gas causes ionization, and therefore it is preferable to use an inert gas such as argon or krypton. In addition, the more preferable baking temperature for obtaining the pitch-type carbon fiber web of this invention is 1000 degreeC or more, More preferably, it is 1300 degreeC or more, More preferably, it is 1500 degreeC or more.

[Pitch-based short carbon fiber]
Pitch-based carbon short fibers can be obtained by grinding the pitch-based carbon fiber web of the present invention to a desired fiber length. More preferably, the pitch-based carbon short fiber of the present invention can be obtained by pulverizing the pitch-based carbon fiber web of the present invention to a desired fiber length and firing at 1000 ° C. to 3400 ° C. That is, after the steps (1) to (3) for obtaining the pitch-based carbon fiber web of the present invention, the pitch-based carbon short fibers of the present invention can be obtained by (4) grinding and (5) firing.

That is, the present invention is (1) pitch-based carbon composed of long fibers by spinning a mesophase pitch having a melt viscosity in the spinning hole of greater than 5 Pa · s and less than 100 Pa · s while being pulled by an air jet parallel to the spinning direction. A step of producing a fiber precursor web, (2) a step of infusifying the pitch-based carbon fiber precursor web in an oxidizing gas atmosphere to produce a pitch-based infusible fiber web, and (3) a pitch-based infusible fiber web. And (4) the obtained pitch-based carbon fiber web is pulverized, and (5) a method for producing pitch-based carbon short fibers that is fired at 1000 ° C. to 3400 ° C.

In the method for producing pitch-based carbon short fibers, the firing temperature in (3) is preferably 600 to 1200 ° C. When the firing temperature of the pitch-based infusible fiber web is less than 600 ° C., the mechanical strength of the pitch-based infusible fiber constituting the pitch-based infusible fiber web is remarkably low. It is not preferable because it cannot be done. On the other hand, if the firing temperature of the pitch-based infusible fiber web exceeds 1200 ° C., the fibers tend to longitudinally crack along the fiber axis direction by the next pulverization treatment. A more preferable range of the firing temperature of the pitch-based infusible fiber web before pulverization is 650 to 950 ° C.

After firing the infusible fiber web, treatments such as cutting, crushing and pulverization are carried out. In some cases, classification treatment may be carried out. The treatment method is selected according to the desired fiber length, but a guillotine type, one-axis, two-axis, and multi-axis rotary type cutters are preferably used for cutting, and an impact action is used for crushing and crushing. Hammer type, pin type, ball type, bead type and rod type, high speed rotation type using collision of particles, roll type using compression / tearing action, cone type and screw type etc. Preferably used. In order to obtain a desired fiber length, cutting, crushing and pulverization may be configured by a plurality of machines. The treatment atmosphere may be either wet or dry. For the classification treatment, a classification device such as a vibration sieve type, a centrifugal separation type, an inertial force type, and a filtration type is preferably used. The desired fiber length can be obtained not only by selecting a model, but also by controlling the number of revolutions of the rotor / rotating blade, supply amount, clearance between blades, residence time in the system, and the like. Moreover, when using a classification process, desired fiber length can be obtained also by adjusting a sieve mesh hole diameter.

The pitch-based carbon short fibers can be produced by firing the obtained pulverized product at 1000 ° C. to 3400 ° C. The firing temperature is preferably 2500-3200 ° C.

The pitch-based carbon short fibers of the present invention have an average fiber diameter of 5 to 20 μm, an average fiber diameter of 3 to 8%, and a number average fiber length of 10 to 1000 μm. A more preferable range of the average fiber diameter is 7 to 15 μm. The CV value is preferably 4-7%. A preferred range of the number average fiber length is 30 to 350 μm.

Further, it is preferable that the interplanar spacing (d002 value) of the graphite layer determined by the X-ray diffraction method is 0.3366 nm or less and the crystallite size (Lc) derived from the thickness direction is 20 nm or more. The d002 value indicates the interplanar spacing of the graphite layer constituting the graphite, and the theoretical value of graphite is 0.3354 nm. This is the practical lower limit, and the closer to the theoretical value of 0.3354 nm, the higher the graphitization property. It is extremely difficult to artificially produce such highly graphitizable carbon fibers.

As the interplanar spacing (d002 value) of the graphite layer determined by the X-ray diffraction method is closer to 0.3354 nm, graphitization is higher, heat conduction is more likely to occur, and pitch-based carbon fibers with higher heat conductivity are obtained. A preferable value of the d002 value obtained by the X-ray diffraction method is 0.3362 nm or less, more preferably 0.3360 nm or less. The more preferable range of the crystallite size (Lc) derived from the thickness direction of the graphite crystal of the pitch-based carbon fiber is 40 nm or more, more preferably 70 nm or more, and the upper limit is substantially 200 nm or less. The pitch-based carbon short fibers of the present invention can be used for resin reinforcing agents, heat conductive fillers, and the like.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention does not receive any limitation by this. In addition, each value in an Example was calculated | required according to the following method.
(1) The average fiber diameter of pitch-based carbon fibers and 60 fiber diameter-dispersed pitch-based carbon fibers were measured using a scale under an optical microscope and obtained from the average value. Further, the CV value was determined by the following formula as a ratio between the obtained average fiber diameter (Ave) and fiber diameter deviation (S).
CV = S / Ave × 100
Here, S = √ ((ΣX−Ave) ² / n), X is an observed value, and n is the number of observations.
(2) Oxygen adhesion amount of pitch-based infusible fiber web The oxygen adhesion amount of the pitch-based infusible fiber web was evaluated by CHNS-O Analyzer (FLASH EA 1112 Series manufactured by Thermo ELECTRON CORPRATION).
(3) Evaluation of d002, Lc, La d002 and the crystallite size derived from the thickness direction of the hexagonal network surface are determined using diffraction lines from the (002) plane, and the crystallite size derived from the growth direction of the hexagonal network surface Was determined using diffraction lines from the (110) plane. In addition, the request was made in accordance with the Gakushin Law.
(4) Measurement of melt viscosity The viscosity of the pitch passing through the capillary was determined using a capillary rheometer CAPILOGRAPH 1D (Toyo Seiki Seisakusho Co., Ltd.). In addition, the shear rate of the pitch which passes a capillary was calculated | required by following formula (a).
(A) γ = 8V / D
(Where γ is the shear rate (s ⁻¹ ) of the mesophase pitch in the capillary, D is the pore diameter (m) of the capillary, and V is the flow velocity (m / s) of the mesophase pitch in the capillary. .)
The flow rate of the mesophase pitch in the capillary was determined by calculating the resin speed passing through the capillary from the amount of liquid fed per time fed from the gear pump.
The resin temperature was determined by monitoring a thermocouple-equipped resin pressure sensor NP463-1 / 2-10MPA-15 / 45-K (manufactured by Nippon Dainisco Co., Ltd.) attached to the top of the capillary.
(5) Softening point The softening point was calculated | required by heating up from 260 degreeC to 1 degree-C / min in nitrogen atmosphere using METTLER FP90 (made by METTLER TOLEDO).
(6) Degree of orientation of pitch-based carbon fiber precursor After collecting the pitch-based carbon fiber precursor in a state of being aligned in the fiber axis direction just below the die, the sample is placed on a fiber sample table, and a wide-angle X-ray diffraction method ( (β scan). The X-ray diffractometer is 4036A2 type manufactured by Rigaku Corporation, and the goniometer which is an apparatus for measuring the crystal plane angle is 2155D type manufactured by Rigaku Corporation. . The degree of orientation was calculated by the following formula (b) from the half width of the intensity distribution obtained by scanning the diffraction peak in the circumferential direction (β scan).
(B) Degree of orientation = (180−H) / 180
(Here, H indicates half-value width [deg.])
(7) Air wind speed The air speed was calculated by measuring the air volume with an acrylic taper tube flow meter (manufactured by Fluid Industries Co., Ltd.) and dividing the flow rate by the sectional area of the suction gun.
(8) Tensile strength and tensile elastic modulus of pitch-based carbon fiber The tensile strength and tensile elastic modulus of pitch-based carbon fiber are determined by measuring 120 carbon fibers and measuring each fiber diameter. The strength was measured with a Tensilon measuring device (ORIENTEC RTC-1150A), and the total number average value of tensile strength and tensile modulus was determined.
(9) Evaluation of d002, Lc, and La by X-ray diffraction method The interplanar spacing (d002) of the graphite layer constituting the graphite, and the crystallite size (Lc) derived from the thickness direction of the hexagonal mesh surface are from the (002) plane. The crystallite size (La) derived from the growth direction of the hexagonal network surface was determined using the diffraction lines from the (110) plane. In addition, the request was made in accordance with the Gakushin Law.
(10) Measurement of fiber length of pitch-based carbon short fibers The average fiber length of pitch-based carbon short fibers is the number-average fiber length, and was measured from an average value by measuring 2000 or more with a length measuring device under an optical microscope. . The magnification was appropriately adjusted according to the fiber length.

[Example 1]
A mesophase pitch composed of aromatic hydrocarbons with a mesophase rate of 100% and a softening temperature of 277 ° C., using a die with a diameter of 0.2 mmφ, a length of 2 mm, and a spinning hole of 41 holes at 328 ° C., and a flow velocity in the capillary of 0.185 m / s. (Shear rate γ: 7400 s ⁻¹ ), and a suction gun was installed at a position 40 cm below the base, and an average diameter of 10 was obtained by pulling the melt mesophase pitch with an air jet parallel to the spinning direction at a wind speed of 740 m / min. A pitch-based carbon fiber precursor web made of long fibers having a diameter of 2 μm and a yarn diameter CV of 4.5% was prepared. The melt viscosity at 328 ° C. and a shear rate of 7400 s ⁻¹ evaluated with a capillary rheometer was 17.5 (Pa · s). Further, the degree of orientation of the pitch-based carbon fiber precursor sampled from the middle of the spinning cylinder was 85.1%. No thread breakage occurred while pulling the melt mesophase pitch under the conditions described above. A schematic diagram of the spinning device of the present invention is shown in FIG. A sample for measuring the degree of orientation of the pitch-based carbon fiber precursor was collected by providing a sampling location on the spinning cylinder of FIG. 1 and collecting the sample.

Next, the carbon fiber precursor web was heated from 200 ° C. to 320 ° C. in an air atmosphere in 30 minutes to obtain a pitch-based infusible fiber web. The oxygen adhesion amount of the pitch-based infusible fiber web was 7.2 wt%. Next, the pitch-based infusible fiber web was fired at 3000 ° C. over 5 hours from room temperature in an argon gas atmosphere to form a pitch-based carbon fiber web. The average fiber diameter of the pitch-based carbon fibers constituting the pitch-based carbon fiber web was 8.1 μm, and the CV value of the fiber diameter was 4.7%. D002 determined by the X-ray diffraction method was 0.3364 (nm), Lc was 44 (nm), and La was 116 (nm). The pitch-based carbon fiber had a tensile strength of 4.5 GPa and a tensile modulus of 780 GPa.

[Example 2]
The pitch-based infusible fiber web of Example 1 was fired from room temperature to 1500 ° C. in an argon gas atmosphere over 2 hours to prepare a pitch-based carbon fiber web. The pitch-based carbon fiber had a tensile strength of 3.9 GPa and a tensile modulus of 235 GPa.

[Example 3]
The pitch-based infusible fiber web prepared by the method of Example 1 was fired at 800 ° C. in a nitrogen gas atmosphere to obtain a pitch-based carbon fiber web, and then pulverized by a turbo mill to obtain a pulverized product. Subsequently, it was baked at 3000 ° C. over 5 hours from room temperature under an argon gas atmosphere, thereby producing pitch-based carbon short fibers. The average fiber diameter of the pitch-based carbon short fibers was 8.3 μm, and the CV value of the fiber diameter was 4.8%. Further, d002 obtained by an X-ray diffraction method was 0.3365 (nm), Lc was 42 (nm), and La was 111 (nm). The number average fiber length of the pitch-based carbon short fibers was 55 μm.

[Example 4]
A mesophase pitch composed of aromatic hydrocarbons with a mesophase rate of 100% and a softening temperature of 276 ° C., a diameter of 0.2 mmφ, a length of 2 mm, and a spin hole 41 hole at 330 ° C., and a capillary flow velocity of 0.313 m / s. (Shear rate γ: 12500 s ⁻¹ ), and a suction gun was installed at a position 40 cm below the base, and an average diameter of 14 was obtained by pulling the melt mesophase pitch with an air jet parallel to the spinning direction at a wind speed of 670 m / min. A pitch-based carbon fiber precursor web made of long fibers having a diameter of 2 μm and a yarn diameter CV of 4.5% was prepared. The melt viscosity at 330 ° C. and a shear rate of 12500 s ⁻¹ evaluated with a capillary rheometer was 12.5 (Pa · s). Further, the degree of orientation of the pitch-based carbon fiber precursor sampled from the middle of the spinning cylinder was 84.7%. In addition, yarn breakage did not occur while pulling the melted mesophase pitch under the above conditions.

Next, the carbon fiber precursor web was heated from 200 ° C. to 330 ° C. in an air atmosphere in 30 minutes to obtain a pitch-based infusible fiber web. The oxygen adhesion amount of the pitch-based infusible fiber web was 7.1 wt%. Next, the pitch-based infusible fiber web was fired at 3000 ° C. over 5 hours from room temperature in an argon gas atmosphere to form a pitch-based carbon fiber web. The average fiber diameter of the pitch-based carbon fibers constituting the pitch-based carbon fiber web was 11.1 μm, and the CV value of the fiber diameter was 4.2%. Further, d002 obtained by an X-ray diffraction method was 0.3362 (nm), Lc was 52 (nm), and La was 146 (nm). The pitch-based carbon fiber had a tensile strength of 4.5 GPa and a tensile modulus of 820 GPa.

[Example 5]
The pitch-based infusible fiber web of Example 4 was fired from room temperature to 1500 ° C. in an argon gas atmosphere over 2 hours to prepare a pitch-based carbon fiber web. The tensile strength of the pitch-based carbon fiber was 4.0 GPa and the tensile elastic modulus was 240 GPa.

[Example 6]
The pitch-based infusible fiber web prepared by the method of Example 4 was fired at 800 ° C. in a nitrogen gas atmosphere to obtain a pitch-based carbon fiber web, and then pulverized by a turbo mill to obtain a pulverized product. Subsequently, it was baked at 3000 ° C. over 5 hours from room temperature under an argon gas atmosphere, thereby producing pitch-based carbon short fibers. The average fiber diameter of the pitch-based carbon short fibers was 11.3 μm, and the CV value of the fiber diameter was 5.1%. Further, d002 determined by X-ray diffraction method was 0.3363 (nm), Lc was 48 (nm), and La was 137 (nm). The number average fiber length of the pitch-based carbon short fibers was 230 μm.

[Comparative Example 1]
A mesophase pitch consisting of aromatic hydrocarbons with a mesophase rate of 100% and a softening temperature of 276 ° C. was used at a pressure of 0.223 m in a capillary using a spinneret of a perfect circle with a diameter of 0.2 mmφ and a length of 2 mm at 338 ° C. / S (shear rate γ: 8920 s ⁻¹ ), and air at 343 ° C. is blown from the slit next to the spinning hole at an angle of 35 ° to the fiber axis at 10800 m / min to pull the molten mesophase pitch. Thus, a carbon fiber precursor web having an average diameter of 15.3 μm was prepared. The melt viscosity at 338 ° C. and a shear rate of 8920 s ⁻¹ evaluated with a capillary rheometer was 8.2 (Pa · s). While spinning the melted mesophase pitch under the above conditions, breakage of the yarn was noticeable. Further, the degree of orientation of the pitch-based carbon fiber precursor collected directly under the base was 83.2%. Next, the web made of the carbon fiber precursor was heated from 200 ° C. to 320 ° C. in an air atmosphere in 30 minutes to obtain a web made of infusible carbon fibers. The oxygen adhesion amount of the infusible carbon fiber was 7.6 wt%. Subsequently, the web made of the pitch-based infusible fiber was fired at 3000 ° C. in an argon gas atmosphere from room temperature for 5 hours to produce a web made of pitch-based carbon fiber. The average fiber diameter of the pitch-based carbon fibers was 10.3 μm, and the CV value of the fiber diameter was 10.8%. The pitch-based carbon fiber had a tensile strength of 2.2 GPa and a tensile modulus of 740 GPa. A schematic diagram of the spinning device of Comparative Example 1 is shown in FIG.

[Comparative Example 2]
The pitch-based infusible fiber web of Comparative Example 1 was fired from room temperature to 1500 ° C. in an argon gas atmosphere over 2 hours to prepare a pitch-based carbon fiber web. The tensile strength of the pitch-based carbon fiber was 1.6 GPa, and the tensile modulus was 225 GPa.

[Comparative Example 3]
A mesophase pitch composed of aromatic hydrocarbons with a mesophase rate of 100% and a softening temperature of 276 ° C., using a die with a diameter of 0.2 mmφ, a length of 2 mm, and a spinning hole of 41 holes at 338 ° C., and a flow velocity in the capillary of 0.223 m / s. (Shear rate γ: 8920 s ⁻¹ ) and a suction gun was installed at a position 40 cm below the base, and an attempt was made to pull the molten mesophase pitch with an air jet parallel to the spinning direction at a wind speed of 670 m / min. Thread breaks occurred frequently. The melt viscosity at 338 ° C. and a shear rate of 8920 s ⁻¹ evaluated with a capillary rheometer was 6.2 (Pa · s). The CV value of the yarn diameter of the carbon fiber precursor constituting the carbon fiber precursor web was 32%.

1. Base 2. 2. Suction gun 3. Carbon fiber precursor 4. Spinning cylinder Collector 6 Wind flow 7. Carbon fiber precursor web Aspirator 9. Sampling port 10. Flow meter 11. Air ejection part 12. Base 13. Spinning cylinder 14. Collector 15. Carbon fiber precursor web 16. Carbon fiber precursor

Claims

Pitch composed of pitch-based carbon fibers having an average fiber diameter of 5-20 μm, an average fiber diameter CV value of 3-8%, a tensile modulus of 150-1000 GPa, and a tensile strength of 2.5-5 GPa Carbon fiber web.
(1) A mesophase pitch having a melt viscosity in the spinning hole of greater than 5 Pa · s and less than 100 Pa · s is spun while being pulled by an air jet parallel to the spinning direction, thereby producing a pitch-based carbon fiber precursor web composed of long fibers. A step of manufacturing, (2) a step of infusifying the pitch-based carbon fiber precursor web in an oxidizing gas atmosphere to manufacture a pitch-based infusible fiber web, and (3) a step of firing the pitch-based infusible fiber web. The method for producing a pitch-based carbon fiber web according to claim 1.
The method for producing a pitch-based carbon fiber web according to claim 2, wherein in the step (1) of producing the pitch-based carbon fiber precursor web, the melt viscosity in the spinning hole is greater than 10 Pa · s and less than 50 Pa · s.
The long fiber before the pitch-based carbon fiber precursor web of step (1) is formed has an orientation degree of the pitch-based carbon fiber precursor evaluated by X-ray of 84.5% or more. A method for producing a pitch-based carbon fiber web.
The pitch-based carbon fiber web production according to claim 2, wherein the oxygen adhesion amount of the pitch-based infusible fiber web in the step (2) of producing the pitch-based infusible fiber web is 6.0 wt% or more and less than 8.0 wt%. Method.
A pitch-based carbon short fiber obtained by pulverizing the pitch-based carbon fiber web according to claim 1 and further firing at 1000 ° C to 3400 ° C.