JP3406696B2 - Method for producing high thermal conductivity carbon fiber - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an average fiber diameter of 4 to 8 .mu.m.
Is a method for producing high thermal conductivity carbon fibers. The carbon fiber obtained by the present invention is widely used as a material for space, a material for aircraft, a material for brake of an automobile, and the like, which require thermal shock resistance and dimensional stability. 2. Description of the Related Art At present, PAN-based carbon fibers made from polyacrylonitrile (PAN) and pitch-based carbon fibers made from pitch are manufactured as carbon fibers. PAN-based carbon fibers are mainly used. However, since the thermal conductivity of commercially available PAN-based carbon fibers is smaller than 100 W / mK,
Use in fields where thermal shock resistance and dimensional stability are required is limited. [0004] On the other hand, pitch-based carbon fibers using mesoface pitch as a raw material are generally said to exhibit higher thermal conductivity than PAN-based carbon fibers. THORNELP-12
0 indicates high thermal conductivity, but less than 700 W / mK. [0005] Japanese Patent Application Laid-Open No. Hei 5-163609 discloses 30
Disclosed is a method for producing a carbon fiber having a lamination of graphite crystallite in the layer plane direction of more than 1000 °, an electric resistivity of less than 1.1 μΩm, and a thermal conductivity of more than 1100 W / mK by firing at 00 ° C. or more. Have been. However, pitch-based carbon fibers having a thermal conductivity of more than 1100 W / mK have extremely high elasticity, so that the fiber yarns become rigid, causing the fiber yarns to break during handling of the fibers or to generate a large amount of fluff. There's a problem. [0007] For this reason, a small diameter high thermal conductivity carbon fiber which can easily handle the fiber is required, but no production method has been reported. Japanese Patent Application Laid-Open No. 4-163319 discloses that pitch fibers are made infusible, subjected to drawing heat treatment and drawing preliminary carbonization treatment in an oxygen-containing atmosphere, and carbonized while being drawn in an inert gas atmosphere to conduct heat. A method for producing a carbon fiber having high modulus and compressive strength is disclosed. However, even if the stretching process is performed, the PAN
There is no report on a method for producing a thin high-thermal-conductivity carbon fiber having a fiber diameter of less than 8 μm, which is easy to handle comparable to that of the base carbon fiber. [0010] Also, J.I. Mater. Res. , Vol.
5, No. 3, P570-577, Mar 1990, "Structure and Electrical Properties of Pitch-Based Carbon Fibers Fired at Various Temperatures", the fiber diameter of the pitch fibers is changed to carry out infusibilization and carbonization. As a result of firing at a temperature, the carbon fibers obtained from the pitch fibers having a large fiber diameter have a larger graphitic property when graphitized because the average size of the mesoface domains in the pitch fibers is larger than those having a smaller fiber diameter. Therefore, it is inferred that it is difficult to obtain carbon fibers having high thermal conductivity from thin carbon fibers. As described above, it is inferred from the prior art that it is difficult to obtain carbon fibers having high thermal conductivity from thin carbon fibers. As a result of intensive studies to produce carbon fibers with a high diameter, thin carbon fibers produced by a specific method have a higher graphitization property than carbon fibers The inventors have found that carbon fibers can be obtained, and have reached the present invention. An object of the present invention is to provide a method for producing high thermal conductivity carbon fiber having a fiber diameter of 4 to 8 μm. According to the present invention, a mesoface pitch having an optical anisotropy is melt-spun, and is infused and graphitized to produce a carbon fiber. A) The shape from the introduction hole to the discharge hole contracts at the approach portion at an angle of 90 to 150 degrees. B) The flat portion is temporarily formed at the end of the approach portion. C) The diameter of the capillary provided in the flat portion is 50 to 110 μm.
Is passed through a spinning nozzle having a discharge hole having a circular cross section to perform spinning, obtain a fine pitch fiber having a fiber diameter of 5 to 11 μm, carbonize, and then graphitize in an inert gas atmosphere. A high thermal conductivity carbon fiber having a fiber diameter of 4 to 8 μm. Hereinafter, the contents of the present invention will be described in detail. The pitch which is the starting material of the carbon fiber of the present invention includes coal-based pitch such as coal tar, coal tar pitch, coal liquefied pitch, ethylene tar pitch, and decant oil pitch obtained from fluid catalytic cracking residue. Various pitches such as a petroleum pitch or a synthetic pitch made from naphthalene or the like using a catalyst or the like are included. The optically anisotropic mesoface pitch of the present invention is obtained by generating a mesoface at the pitch by a conventionally known method. It is desirable that the mesoface pitch has a high orientation of the pitch fiber when spun, so that the mesoface content is 60% or more, preferably 80% or more, more preferably 90% or more. . If the content of the mesophase is less than 60%, the amount of optical anisotropy is small, so that the tensile strength is undesirably low. The mesoface pitch used in the present invention has a softening point of 200 to 400 ° C., preferably 250 to 35 ° C.
0 ° C is preferred. It is difficult to adjust a pitch having a softening point of less than 200 ° C. If a pitch having a softening point of more than 400 ° C. is used, it is necessary to set a high spinning temperature, so that stable spinning cannot be performed. If solid matter of 3 μm or more is present in the pitch, yarn breakage frequently occurs during spinning. Therefore, the pitch obtained before the spinning is a filter having an absolute filtration accuracy of 3 μm or less, or a filter equivalent to or equivalent to this filter. It is desirable to remove foreign matter in the pitch by a filtration method having the above filtration accuracy. As a result of various studies for producing high thermal conductivity pitch-based carbon fibers, in order to obtain high thermal conductivity by increasing the graphitization property, the orientation of molecules in the pitch fiber state in the fiber axis direction must be improved. It has been found that spinning good ones is effective. In the present invention, when spinning the pitch fiber from the pitch described above, the shape (θ1) from the introduction hole to the discharge hole is contracted at an approach portion having an angle of 90 to 150 degrees as shown in FIG. At the end, make a flat part (θ2)
The liquid is passed through the discharge hole having a circular cross section provided in the flat portion, the capillary diameter (D3) is 50 to 110 μm, and the discharge port length (L)
2) using a spinning nozzle having a diameter of 0.07 to 0.17 mm, the pitch viscosity of the discharge port is 100 to 1000 poise,
By producing pitch fibers having a small diameter of 5 to 11 μm, preferably 200 to 800 poise, more preferably 400 to 800 poise, pitch fibers having a high orientation in the fiber axis direction can be obtained, and a high tensile modulus,
A high thermal conductivity carbon fiber having high tensile strength is obtained. However, in the carbon fiber, the radial component leads to a crack in the axial direction, and this crack is a place where tensile damage is likely to occur. At the end of the conventional approach, a pitch fiber is obtained using a spinning nozzle having a circular cross section having no flat portion at the end of a flat section, and the cross section of the carbon fiber obtained by infusibilizing, carbonizing and graphitizing is scanned. When observed with an electron microscope, the fiber surface layer has a radial structure of at least 1.5 μm to 2.5 μm, the inside of the fiber has a random or onion structure, and has a plurality of structures, and can maintain a certain high strength. However, the nozzle structure used in the present invention, that is, the shape from the introduction hole to the discharge hole contracts at the approach portion at an angle of 90 to 150 degrees, and once becomes flat at the end of the approach, the discharge hole has a circular cross section. Is used, the radial component of the fiber surface layer becomes 1.5 μm or less, preferably 1.0 μm or less, and the radial component decreases. As described above, the nozzle used in the present invention has a smaller radial component in the surface layer portion, so that a higher tensile strength can be maintained. If the approach angle θ1 is less than 90 degrees, the length of the inlet becomes long and inappropriate, and if it exceeds 150 degrees, the effect of providing a flat portion at the end of the approach becomes difficult to obtain. Since the approach angle θ1 is determined in this manner, and in order to obtain excellent tensile strength, the length L1 of the inlet is preferably 3 to 10 mm, preferably 4 to 6 mm, and the inlet diameter D1 is 0.5 to 10 mm, preferably 1.2 to 5 mm, and the residence time at the inlet is 1 to
It is preferably 400 seconds, preferably 4 to 200 seconds. The inlet diameter is less than 0.5 mm or 10 m
If the retention time is longer than 1 m or more than 400 seconds, a fiber having excellent strength cannot be obtained. The diameter D2 of the flat portion is desirably 0.8 times or less the introduction diameter D1 and 1.5 times or more the discharge diameter D3. At this time, the effect of the present invention can be obtained most.
The cross section of the discharge hole is most effective when a circular one is used to improve the tensile strength. If the capillary diameter is less than 50 μm, it becomes extremely difficult to process the capillary or the maintenance of the nozzle becomes complicated. If it exceeds 110 μm, spinning of fine pitch fibers becomes unstable, which is not preferable. If the discharge port length is less than 0.07 mm, stable spinning cannot be performed. If the discharge port length is more than 0.17 mm, it is presumed that the radial portion of the fiber surface layer increases, so that high strength cannot be maintained. Therefore, it is desirable that the ratio of the capillary diameter to the discharge port length is in the range of 1.5 to 2. When the pitch viscosity is less than 100 poise,
Since the viscosity is extremely low, yarn breakage increases and spinning becomes almost impossible, and if it exceeds 1000 poise, if yarn breakage occurs during spinning, it will adhere to other yarns or nozzle surfaces,
Unstable spinning is not preferred. Further, in order to obtain a fine carbon fiber having an excellent handling surface of 4 to 8 μm, the fiber diameter of the pitch fiber is reduced by infusing, carbonizing and graphitizing the pitch fiber. 5 to 11 μm
Must be. Next, the pitch fiber is usually heated in an oxidizing gas atmosphere at 100 to 350 ° C., preferably 130 to 320 ° C.
C, usually 10 minutes to 10 hours, preferably 1 to 6 hours,
Perform infusibilization treatment. As the oxidizing gas, oxygen, air or a mixture of these gases with nitrogen dioxide, chlorine or the like is used. If the infusibilizing temperature is less than 100 ° C., the reactivity of the pitch will be low, and if it exceeds 350 ° C., excessive oxidation will occur, and the tensile strength will decrease. If the infusibilization time is less than 10 minutes, the reaction is not reached, and if it exceeds 10 hours, the infusibilization is excessively unfavorable. The infusibilized fiber is carbonized and graphitized in an atmosphere of an inert gas such as nitrogen or argon for 1 second to 1 second.
0 hours, preferably for 10 seconds to 6 hours, and a tensile elastic modulus of 1
00 GPa-1000 GPa, tensile strength 2.0 GPa-
By obtaining 5.0 GPa carbon fiber and graphitizing it,
A fine pitch system having a high fiber elasticity and a high tensile strength, and having a thermal conductivity of more than 1100 W / mK when graphitized at 3000 ° C. or higher, and having a fiber diameter of 4 to 8 μm and excellent handling properties. A high thermal conductivity carbon fiber is obtained. The degree of progress of the graphitization of the graphitized fiber was evaluated based on the lamination thickness Lc002, crystallite size La110, and layer interval d002 determined by wide-angle X-ray diffraction. The lamination thickness Lc002 is 002 in the carbon crystal.
La110 indicates the crystallite size, La002 indicates the layer spacing on the 002 plane of the crystal, and Lc0 indicates the layer thickness of the crystal.
02 is 50-500Å, La110 is 100-1000
As described above, d002 indicates a value of 3.352 to 3.450 °. It can be determined that the larger the values of Lc002 and La110 and the smaller the value of d002, the higher the graphitization property. Thus, scattering of conduction electrons due to lattice defects is suppressed, and high thermal conductivity is exhibited. Lamination thickness Lc002, crystallite size La
110, the layer interval d002 is obtained by powdering a fiber, mixing it with standard silicon, and using a powder method as a sample.
It was determined by the Gakushin method “method for measuring lattice constant and crystallite size of artificial graphite” from the diffraction lines on the 110 and 110 planes. The thermal conductivity of the carbon fiber was 10 m in diameter.
m, a cylindrical unidirectional carbon fiber reinforced plastic having a thickness of 3 mm to 6 mm, and a specific heat and a thermal diffusivity were measured using a laser flash method thermal constant measuring apparatus model PS-7 manufactured by Rigaku Denki Co., Ltd. Was calculated by Λ = Cp × α × ρ / Vf where λ is the thermal conductivity of the carbon fiber, α is the thermal diffusivity of the carbon fiber, and Cp is the absolute specific heat of the unidirectional carbon fiber reinforced plastic. , Ρ is the density, and Vf is the volume fraction of carbon fibers contained in the unidirectional carbon fiber reinforced plastic. Since the thermal conductivity of the matrix resin is so small as to be negligible with respect to the thermal conductivity of the carbon fiber, the thermal conductivity of the carbon fiber is determined by λ. The measurement was performed at room temperature (25
C). Hereinafter, in order to further clarify the present invention,
An example and a comparative example will be described. EXAMPLE 1 Coal tar pitch was used as a raw material, and hydrogenation was carried out directly in the presence of a catalyst. The hydrogenated pitch was heat-treated at a reduced pressure of 500 ° C., and then a low-boiling component was obtained. Except that a mesoface pitch was obtained. This pitch had a softening point of 304 ° C., a toluene-insoluble content of 80% by weight, and a mesophase content of 94%. Using this mesoface pitch, the shape from the introduction hole to the discharge hole as shown in FIG. 1 contracts at the approach portion at an angle of 120 degrees, and once becomes a flat portion at the end of the approach,
Capillary diameter 0.10mm, discharge port length 0.15m
m, using a nozzle having a flat part length of 0.8 mm, spinning so that the pitch viscosity of the discharge port becomes 450 poise, and a fiber diameter of 1
A 0 μm pitch fiber was obtained. The pitch fiber was heated from 150 ° C. to 310 ° C. at a rate of 1 ° C./min in an oxidizing atmosphere in which nitrogen dioxide gas was added to air at 5% by volume and oxygen gas at 10% by volume to obtain infusible fiber. Was. The infusible fiber was heated to 390 ° C. and carbonized for 50 minutes to obtain a carbonized fiber. Next, the carbonized fiber was graphitized at a temperature of 3200 ° C. for 3 hours to obtain a carbon fiber. The carbon fiber had a fiber diameter of 7.4 μm, a tensile modulus of 900 GPa, a tensile strength of 3.3 GPa, and an X-ray structural parameter Lc002 of 450 ° and La110 of 9
10 °, d002 is 3.364 °, thermal conductivity 1180W
/ MK, and generation of fluff was extremely small. Example 2 Using the pitch of Example 1, a nozzle having an introduction angle of 135 degrees, a capillary diameter of 0.09 mm, and a discharge port length of 0.14 mm as shown in FIG. Is spun to 600 poise, and the fiber diameter is 9.5μ.
m pitch fibers were obtained. Using this pitch fiber, infusibilization, carbonization and graphitization were performed under the same conditions as in Example 1 to obtain a carbon fiber. This carbon fiber had a fiber diameter of 6.8 μm, a tensile modulus of 980 GPa, a tensile strength of 4.0 GPa, and X-ray structural parameters Lc002 of 480 ° and La110 of 9
70 °, d002 is 3.359 °, thermal conductivity 1230W
/ MK, and generation of fluff was extremely small. Comparative Example 1 Using the pitch of Example 1, a nozzle having an introduction angle of 120 degrees, a capillary diameter of 0.10 mm, and a discharge port length of 0.15 mm as shown in FIG. Is spun so as to be 450 poise, and the fiber diameter is 10 μm.
Was obtained. Using this pitch fiber, infusibilization, carbonization and graphitization were performed under the same conditions as in Example 1 to obtain a carbon fiber. The carbon fiber had a fiber diameter of 7.4 μm, a tensile modulus of 900 GPa, a tensile strength of 2.8 GPa, and X-ray structural parameters Lc002 of 420 ° and La110 of 7
60 °, d002 3.365 °, thermal conductivity 1070W
/ MK, and the generation of fluff was large. Comparative Example 2 Using the pitch of Example 1, a nozzle having an introduction angle of 120 °, a capillary diameter of 0.10 mm, and a discharge port length of 0.15 mm as shown in FIG. Is spun to 600 poise, fiber diameter 13μm
Was obtained. Using this pitch fiber, infusibilization, carbonization and graphitization were performed under the same conditions as in Example 1 to obtain a carbon fiber. This carbon fiber has a fiber diameter of 9.0 μm, a tensile modulus of elasticity of 900 GPa, a tensile strength of 2.5 GPa, an X-ray structural parameter Lc002 of 350 °, and La110 of 5
90 °, d002 is 3.370 °, thermal conductivity 600 W /
mK and fluff was generated frequently. Comparative Example 3 Using the pitch of Example 1, a nozzle having an introduction angle of 120 degrees, a capillary diameter of 0.10 mm, and a discharge port length of 0.15 mm as shown in FIG. Spin to 700 poise, fiber diameter 13μm
Was obtained. Using this pitch fiber, infusibilization, carbonization and graphitization were performed under the same conditions as in Example 1 to obtain a carbon fiber. The carbon fiber had a fiber diameter of 9.3 μm, a tensile modulus of 900 GPa, a tensile strength of 2.3 GPa, and X-ray structural parameters Lc002 of 360 ° and La110 of 6
50 °, d002 is 3.369 °, thermal conductivity 700 W /
mK and fluff was generated frequently. Comparative Example 4 Using the pitch of Example 1, using a nozzle having an introduction angle of 120 degrees, a capillary diameter of 0.12 mm, and a discharge port length of 0.20 mm as shown in FIG. Is spun to 600 poise, fiber diameter 10μm
Was obtained. Using this pitch fiber, infusibilization, carbonization and graphitization were carried out under the same conditions as in Example 1 to obtain a carbon fiber. The carbon fiber had a fiber diameter of 7.3 μm, a tensile modulus of 900 GPa, a tensile strength of 2.7 GPa, and X-ray structural parameters Lc002 of 290 ° and La110 of 4
90 °, d002 is 3.379 °, thermal conductivity 530 W /
mK and fluff was generated frequently. The carbon fiber of the present invention is a technology which is easy to apply industrially, and has a very large thermal conductivity as compared with a conventional carbon fiber carbonized or graphitized under the same conditions.
Space materials and aircraft that generate very little fluff and have few problems of fiber thread breakage, that is, can produce fine-diameter carbon fiber with excellent handling properties, and are required to have thermal shock resistance and dimensional stability. It is possible to provide carbon fibers suitable for use in fields such as materials for automobiles and materials for automobiles.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic partial cross-sectional view of a spinning nozzle used in the present invention. FIG. 2 is a schematic partial cross-sectional view of a conventional spinning nozzle used in a comparative example. [Description of Signs] D1 Inlet diameter D2 Flat part diameter D3 Capillary diameter L1 Inlet length L2 Discharge port length θ1 Approach part angle θ2 Flat part angle

Continuation of front page (56) References JP-A-63-105116 (JP, A) JP-A-2-229219 (JP, A) JP-A-6-65813 (JP, A) JP-A-5-117918 (JP) JP-A-6-146119 (JP, A) JP-A-5-1663619 (JP, A) JP-A-60-252723 (JP, A) JP-A-60-194120 (JP, A) JP-A-60-194120 59-168127 (JP, A) JP-A-7-42025 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D01F 9/14-9/155

Claims (1)

(57) [Claims 1] When producing a carbon fiber by melt-spinning an optically anisotropic mesoface pitch and performing infusibilization, carbonization and graphitization, the mesoface pitch is reduced. A) the shape from the introduction hole to the discharge hole contracts at the approach portion at an angle of 90 to 150 degrees; B) a flat portion is temporarily formed at the end of the approach portion; C) the diameter of the capillary provided in the flat portion is 50 to 110 μm.
Spinning by passing through a spinning nozzle having a discharge hole having a circular cross-section, obtaining a fine pitch fiber having a fiber diameter of 5 to 11 μm, infusible and carbonized, and then graphitized in an inert gas atmosphere. A method for producing a high thermal conductivity carbon fiber having a fiber diameter of 4 to 8 μm.