JP3265693B2 - Carbon fiber production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing carbon fibers. The carbon fiber produced according to the present invention exhibits a very high thermal conductivity by itself, or gives a very high thermal conductivity carbon fiber by firing at an extremely high temperature. The fiber is suitably used as a structural material for space which requires high dimensional stability and thermal shock resistance, a heat radiation material for high energy density electronic devices, and the like.

[0002]

2. Description of the Related Art High-performance carbon fibers are roughly classified into PAN-based carbon fibers made from polyacrylonitrile (PAN) and pitch-based carbon fibers made from pitches, and have high specific strength and high specific elastic modulus, respectively. Taking advantage of this feature, it is widely used as a material for aircraft, a material for sporting goods, a material for construction, and the like.

However, in applications such as space materials that require dimensional stability under a large temperature distribution and thermal shock resistance, and heat radiation materials for electronic devices in which high energy densities continue to increase, the above-described machines are used. High thermal conductivity is required in addition to the mechanical properties, and many studies have been made to improve the thermal conductivity of carbon fibers. However, the thermal conductivity of commercially available PAN-based carbon fibers is usually 200
It is smaller than W / m · K, and the electric resistivity is larger than 6 μΩm.

On the other hand, pitch-based carbon fibers are generally
Although it is recognized that high thermal conductivity and low electrical resistivity can be easily achieved as compared with the system carbon fiber, the thermal conductivity of a commercially available pitch system carbon fiber is usually smaller than 700 W / m · K. Recently, a method of producing a carbon fiber having a low electrical resistivity by defining a softening point of the pitch, a spinning temperature, and a firing temperature has been proposed (Japanese Patent Laid-Open No. 2-242919). However, spinning at a high temperature was not sufficient for industrial production.

[0005]

As described above, although carbon fibers with high thermal conductivity are being developed, the spinning state is unstable, so that carbon fibers with high thermal conductivity are produced in a stable spinning state. A way was desired.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have been found to have an optical heterogeneity having a narrow molecular weight distribution and a homogeneous property containing almost no heavy components. By spinning an isotropic pitch under special conditions such that the domain size of the pitch liquid crystal (the size of the liquid crystal structure) increases, it has been found that carbon fibers with high thermal conductivity can be obtained in a stable spinning state. The present invention has been reached.

That is, the gist of the present invention is that the glass transition temperature width determined by a differential scanning calorimeter is 40 ° C. or less, the content of the optically anisotropic phase is 10% by volume or more, and quinoline A pitch having an insoluble content of 5% by weight or less is used as a spinning material pitch, and an introduction angle α is larger than 100 °,
Production of carbon fiber characterized by being made infusible, carbonized and / or graphitized after spinning using a spinning nozzle having a ratio L / D of a discharge port length L and a discharge port diameter D smaller than 2. Be in the way.

Hereinafter, the present invention will be described in more detail. As a starting material of the spinning material pitch used in the present invention, coal-based coal tar, coal tar pitch, hydride of coal tar pitch, coal liquefaction, petroleum heavy oil, thermal polycondensation reaction product of petroleum resin And carbonaceous raw materials such as polymerization reaction products obtained by the catalytic reaction of condensed polycyclic hydrocarbons such as naphthalene and anthracene.

[0009] These carbonaceous materials contain impurities such as free carbon, undissolved coal, ash, and catalysts. These impurities are filtered, centrifuged, or separated by settling using a solvent. It is desirable to remove in advance by a known method such as Further, the carbonaceous raw material may be preliminarily treated by, for example, a method of extracting a soluble component with a specific solvent after heat treatment, or a method of hydrogenating in the presence of a hydrogen-donating solvent or hydrogen gas. . In particular, as a starting material of the raw material pitch used in the present invention, it is preferable to use condensed polycyclic hydrocarbons from the viewpoint of removing impurities, and particularly preferable are naphthalene, anthracene, phenanthrene, acenaphthene, pyrene, and acenaphthylene. And its alkyl-substituted compounds. These may be used alone or as a mixture of two or more, but it is preferable to use substantially alone. This is because, for example, the form of the obtained polycondensation reaction product differs between naphthalene and anthracene. Of these starting materials, naphthalene is particularly preferably used.

When the starting material of the carbonaceous raw material is a condensed polycyclic hydrocarbon, it is subjected to polycondensation in the presence of a Lewis acid catalyst, preferably at room temperature to 400 ° C., followed by further treatment as required. To produce pitches with physical properties. The Lewis acid catalyst includes SO ₃ , BF ₃ , AlCl ₃ , AlB
r ₃ , SnCl ₄ , FeCl ₃ , ZnCl ₂ , SO ₂ ,
Li ⁺ , Na ⁺ , Ag ⁺ , Fe ³⁺ , Al ³⁺ , Cu ²⁺ , H
g ⁺ , H ⁺ , NO ₂ ⁺ , HF.BF _{3 and the} like, among which HF.BF ₃ , AlCl ₃ , and BF ₃ are particularly preferable.

The spinning material pitch in the present invention is a homogeneous optically anisotropic pitch having a particularly narrow molecular weight distribution and containing almost no heavy components such as quinoline insolubles. Specifically, pitches in which the glass transition temperature width determined by a differential scanning calorimeter is 40 ° C. or less, the content of the optically anisotropic phase is 10% by volume or more, and the quinoline insoluble content is 5% by weight or less. Is used.

The method for producing the raw material pitch is not particularly limited as long as a pitch satisfying these properties can be obtained. However, when the above-mentioned carbonaceous raw material is optically homogeneous, it is necessary to convert it to optically anisotropic material.
To 500 ° C., preferably 350 to 450 ° C., for 2 minutes to 50 hours, preferably 5 minutes to 5 hours, under an atmosphere of an inert gas such as nitrogen, argon, water vapor, or under blowing, and further, if necessary. Processing is performed to produce a pitch having desired physical properties.

Next, the spinning material pitch in the present invention will be described. The spinning material pitch of the present invention has a glass transition temperature width (ΔT _g ) of 4 as determined by a differential scanning calorimeter.
It is necessary that the temperature be 0 ° C. or less. Originally, the glass transition point is a temperature unique to a substance, and refers to a temperature at which physical properties such as specific heat of a substance change discontinuously. However, in the case of a substance having various molecular structures, such as a pitch for spinning, and having a wide molecular weight distribution from a low softening point component to a high softening point component, since the substance is a mixture, it has a low glass transition temperature. Will exist. In other words, in the case of a spinning material pitch having many molecular species from low softening point components to high softening point components and a molecular weight distribution, the glass transition temperature width is undesirably large. Therefore, a raw material pitch having a narrow molecular weight distribution having a glass transition temperature width of 40 ° C. or less is suitably used.

Second, the pitch for the spinning raw material of the present invention is:
It is essential that the content ratio of the optically anisotropic phase is 10% by volume or more. When the optically anisotropic phase is less than 10% by volume, the crystallinity of the carbon fiber is reduced, and the carbon fiber tends to have poor performance. The content volume ratio of the optically anisotropic phase is preferably 70% by volume or more, more preferably 90% by volume or more,
It is preferable from the viewpoint of easy development of the elastic modulus due to the development of crystallinity of the carbon fiber.

Third, the pitch for the spinning material of the present invention is:
It is an essential requirement that the quinoline insoluble content is 5% by weight or less. This is because if a heavy component such as a quinoline-insoluble component is contained in an amount of more than 5% by weight, the homogeneity and spinnability of the carbon fiber spinning pitch are impaired, and the arrangement of graphite crystals required for the high thermal conductivity carbon fiber is impaired. It is. In the present invention, the shape of the spinning nozzle when spinning pitch fibers from the above-mentioned raw material pitch is such that the nozzle introduction angle α is larger than 100 ° as shown in FIG. A nozzle having an L / D smaller than 2 is used, and a nozzle having an L / D smaller than 1.0 is preferable.

By using such a nozzle, the shear force acting on the pitch liquid crystal from the inner wall of the nozzle can be suppressed, and the domain size (the size of the liquid crystal structure) of the pitch liquid crystal in the process of drawing into the pitch fiber can be reduced. It can be prepared so that it is not divided more than necessary and does not become smaller. Usually, at the time of spinning pitch fibers, in order to treat or remove impurities and gel-like heavy substances contained in the raw material pitch, a mesh filter, a glass bead,
Metal powder, sintered metal filter, etc. are installed.
However, if such a filter is in the flow path of the pitch liquid crystal, the pitch liquid crystal is divided by the shear stress, and the size of the pitch liquid crystal is undesirably reduced.

That is, the pitch residence time immediately above the nozzle hole and on the pitch supply side from the tip of the nozzle is within one hour,
In the pitch liquid crystal flow path located preferably within 20 minutes, more preferably within 10 minutes, it is preferable that a filter or the like having a structure for dividing the pitch liquid crystal is not provided. The spinning temperature is not particularly limited, and is a temperature at which a stable spinning state can be maintained, that is, the pitch viscosity is 10 to 800 poise, preferably 100 to 300 poise.
Any temperature is acceptable as long as the temperature becomes poise.

The pitch fiber thus obtained is infusibilized in a conventional manner and carbonized and / or graphitized at a desired temperature, so that the graphite crystallites are large and the electrical conductivity and the thermal conductivity are low. Large carbon fibers can be obtained. At this time, the higher the temperature of carbonization and graphitization, and the longer the time of carbonization and graphitization, the larger the graphite crystallite grows, and carbon fibers having high electrical conductivity and thermal conductivity are obtained.

It is also possible to first produce a material fired at a low carbonization temperature, to form a composite material, and then fire it at a higher temperature. Generally, the physical properties and characteristics of carbon materials are 10
The crystallite structure evaluated at a size of about {1000} and a structure in which the crystallites are aggregated, that is, 0.1 μm
It is known that it is governed by the organizational structure evaluated at a size of about m to 100 μm (Suguro Otani, Yuzo Sanada, Basics of Carbonization Engineering Ohmsha (1980) 13
0).

The carbon fiber obtained according to the present invention has a cross section of 4 to 90%, preferably 30 to 90% of the cross section from the center to the outer periphery of the fiber cross section in order to spin the pitch liquid crystal without giving shearing. It is made of graphite with a large organizational structure. The tissue structure at the center of this tissue has a length of 0.4
Is a textured structure in which a laminated structure of の 2 μm or more is bent or folded, and the size of the textured structure is, on average, 2 or more in the length or thickness of the laminated portion compared to the size of the textured structure at the outer periphery of the fiber. More than double. In addition, these texture structures can be confirmed by observing the cross section perpendicular to the fiber length direction with a scanning electron microscope at a magnification of 4000 to 10000 times according to the fiber diameter.

[0021]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In addition, in the following examples, each measurement was performed by the following method.

(1) Glass Transition Temperature Width (ΔT _g ) Using a differential scanning calorimeter, JIS K7121-19
87 Plastic transition temperature measurement method ”. The glass transition temperature width (ΔT _g ) was determined according to“ JIS K7121-19 ”from the DSC curve obtained by this method.
87 9.3 Determination of Glass Transition Temperature ”, ie, the difference between T _ig and T _eg described in FIG. 2. That is, a straight line obtained by extending each baseline before and after the glass transition, and a step-like change in the glass transition. The temperatures at the intersections with the tangents drawn at the point where the slope of the curve of the portion becomes the maximum are T _ig and T _eg (corresponding to the low-temperature side baseline and the high-temperature side baseline, respectively), and T _ig and T _eg Was calculated as ΔT _g .Measurement was usually performed three or more times on the same sample,
The average value was taken as ΔT _g .

(2) Content Ratio of Optically Anisotropic Phase A pitch sample obtained by pulverizing a pitch sample into several mm squares is embedded with a sample piece over almost the entire surface of a resin having a diameter of 2 cm according to a conventional method. It was determined by observing the entire surface under a polarizing microscope (100 to 600 times) and measuring the ratio of the area of the optically anisotropic portion to the total surface area of the sample.

(3) Amount of quinoline-insoluble matter The measurement was carried out according to Japanese Industrial Standards "JIS K2421". (4) Thermal conductivity Carbon fiber is a disc-shaped unidirectional carbon fiber reinforced plastic (CFRP) having a diameter of 10 mm and a thickness of 3 to 6 mm, and a laser flash method thermal constant measuring device TC- manufactured by Vacuum Riko Co., Ltd.
The specific heat and thermal diffusivity of the CFRP were measured according to 3000, and calculated by the following equation.

[0025]

## EQU1 ## K = Cp · α · ρ / Vf

Where K is the thermal conductivity of the carbon fiber, Cp is the specific heat of CFRP, α is the thermal diffusivity of CFRP, and ρ is the CFR.
The density of P and Vf represent the volume fraction of carbon fibers contained in CFRP. The thickness of the CFRP was changed according to the thermal conductivity of the carbon fiber, and a sample having a large thermal conductivity was made thick and a sample having a small thermal conductivity was made thin. Specifically, after laser irradiation, the temperature on the back surface of the sample increases, and it takes several tens of msec to reach the maximum temperature.
However, the thickness of the CFRP was adjusted so that the time t1 / 2 until the temperature rises by 1/2 of the temperature rise ΔTm at that time was 10 msec or more (up to 15 msec) (see FIG. 3).

The specific heat was determined by attaching glassy carbon as a light receiving plate to the front surface of the sample and measuring the temperature rise after laser irradiation using an R thermocouple bonded to the center of the back surface of the sample. The measured values were calibrated using sapphire as a standard sample. The thermal diffusivity was determined by applying a film to both surfaces of the sample by carbon spray until the surface was no longer visible and measuring the temperature change on the back surface of the sample after laser irradiation with an infrared detector. The thermal conductivity of the carbon fiber can also be estimated from the electrical conductivity using a very good correlation between the thermal conductivity and the electrical conductivity of the carbon fiber.

Example 1 Naphthalene was prepared in the presence of an HF / BF ₃ catalyst in the range of 200 to 30.
Polymerization is carried out at 0 ° C., after the reaction, the catalyst is recovered in a gaseous state and low boiling components are removed. The content of the optically anisotropic phase is 2% by volume, the softening point is 176 ° C., and the quinoline insoluble matter is 1. A pitch of 6% by weight and a toluene-insoluble content of 34% by weight was obtained.

Next, nitrogen gas was blown into the pitch 50 g at a rate of 450 Nl / hour at 400 ° C.
For 3 hours to obtain a spinning material pitch. This raw material pitch had an optically anisotropic phase content of 100% by volume, a glass transition temperature width of 25 ° C., and a quinoline insoluble content of 3.0% by weight. The obtained optically anisotropic pitch is changed to an introduction angle of 1
A nozzle having a nozzle pitch of 50 ° and L / D = 0.5 was used, and the inside of the nozzle hole and the pitch introduction side were not filled with a filter, a filter aid, etc. which are usually used for pitch spinning.
Prepared and spun to give a tissue diameter of 12μ
m pitch fibers were obtained.

The spinning state was very stable, and no breakage phenomenon during spinning was observed at 2 hours. Then
This pitch fiber is heated from room temperature to 140 ° C. in air for 24 hours.
After raising the temperature over a period of 10 minutes, the temperature was raised to 310 ° C. at a rate of 10 ° C./min, followed by a heat treatment for 30 minutes.
An infusible fiber was obtained. This infusibilized fiber is put in nitrogen gas 140
As a result of firing at 0 ° C. and further graphitizing at 2500 ° C. in argon gas, carbon fibers having a thermal conductivity of 480 W / m · K were obtained. Observation of the cross section of the carbon fiber with a scanning electron microscope revealed a structure of a graphite structure greatly folded from the center to the outer periphery of the fiber. This scanning electron micrograph (× 4000) is shown in FIG.

Example 2 A carbon fiber was produced in exactly the same manner as in Example 1 except that the graphitization temperature was 3000 ° C. When the thermal conductivity of the obtained carbon fiber was measured, it was 860 W / m · K.

Comparative Example 1 Naphthalene was prepared in the presence of an HB.BF ₃ catalyst in the range of 200 to 40.
Polymerized at 0 ° C., the content of optically anisotropic phase is 100% by volume
Was prepared. The optically anisotropic structure of this pitch has a “coarse flow-like” structure and a glass transition temperature width of 52 ° C.
The quinoline insoluble content was 18.5% by weight. When this was spun using the same spinning nozzle as in Example 1,
Breaks during spinning were observed twice an hour. This pitch fiber was infusibilized, fired, and graphitized in exactly the same manner as in Example 1, and the thermal conductivity of the obtained carbon fiber was 350 W / m · K.

Comparative Example 2 An optically anisotropic pitch prepared in the same manner as in Comparative Example 1 was spun using a nozzle having an introduction angle of 90 ° and L / D = 4. Could not be obtained. When a small amount of the obtained pitch fiber was treated in the same manner as in Comparative Example 1 and graphitized at 2500 ° C.,
Although carbon fibers were obtained, both strength and handleability were low, and CFRP for measuring thermal conductivity could not be produced.

[0034]

From the carbon fiber spinning material pitch of the present invention, a carbon fiber having a high thermal conductivity can be produced in a stable spinning state, and is also suitable for a C / C composite which requires a high thermal conductivity. Materials can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view of a spinning nozzle used in the method for producing carbon fiber of the present invention.

FIG. 2 is an explanatory diagram of how to determine a glass transition temperature width (ΔT _g ).

FIG. 3 is an explanatory diagram of a method of obtaining a thermal conductivity.

FIG. 4 is a scanning electron micrograph showing a shape of a fiber in a cross section of a carbon fiber obtained in Example 2 of the present invention.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuo Shirasaki 1000 Kamoshita-cho, Midori-ku, Yokohama-shi, Kanagawa Prefecture Inside the Mitsubishi Chemical Research Institute (72) Inventor Osamu Kajiwara 1st-province town of Sakaide-shi, Kagawa Prefecture Mitsubishi Chemical Corporation Inside the Sakaide Factory (56) References JP-A-4-2804 (JP, A) JP-A-59-168127 (JP, A) JP-A-5-1663619 (JP, A) JP-A-5-222621 (JP, A A) (58) Field surveyed (Int. Cl. ⁷ , DB name) D01D 4/02 D01F 9/14-9/155

Claims (4)

(57) [Claims] 1. A glass transition temperature width determined by a differential scanning calorimeter of 40 ° C. or less, an optically anisotropic phase content of 10% by volume or more,
A pitch having a quinoline insoluble content of 5% by weight or less is used as a spinning material pitch, and an introduction angle α is larger than 100 °, and a ratio L / D of a discharge port length L and a discharge port diameter D is smaller than 2. A method for producing carbon fiber, comprising spinning using a nozzle, infusing, carbonizing and / or graphitizing. 2. In a pitch flow path immediately above a nozzle hole,
2. The method for producing carbon fibers according to claim 1, wherein the raw material pitch is introduced into the nozzle hole without spinning the pitch liquid crystal, and spinning is performed. 3. A carbon fiber having a structure in which a structure in which a graphite net surface is laminated at a center portion is bent or folded, and has a structure structure larger than that of an outer peripheral portion. The method for producing a carbon fiber according to claim 1. 4. The method according to claim 1, wherein the spinning material pitch is obtained by polycondensing a condensed polycyclic hydrocarbon using a Lewis acid catalyst.