JPS6141325A - Manufacture of carbon fiber - Google Patents

Abstract

PURPOSE:To produce a carbon fiber having anisotropic structure, by using a pitch having latent anisotropy as a raw material, melt-spinning the pitch, and infusibilizing and carbonizing the fiber. CONSTITUTION:A pitch having latent anisotropy is melted by heating usually at 200-300 deg.C, and the molten liquid is extruded through a nozzle and cooled to obtain a spun pitch fiber. The pitch fiber is infusibilizd by heating in an oxygen- containing atmosphere, and carbonized by heating in an inert gas at 800-1,500 deg.C (preferably at a heating rate of 5-20 deg.C/min). When the heating is continued to >=2,000 deg.C, a graphitized fiber can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing carbon fibers (including graphite fibers) having an anisotropic structure using potentially anisotropic pitch as a raw material.

In general, pitch has been used as a binder, impregnation pitch, coke raw material, artificial graphite raw material, etc.
Recently, in addition to these uses, attention has been paid to its use as a raw material for carbon fibers.

Regarding pitch as a raw material for carbon fiber, optically isotropic pitch (hereinafter simply referred to as isotropic pitch) was initially used industrially, but in recent years, optically anisotropic pitch (hereinafter simply referred to as anisotropic pitch) has been adopted industrially. The use of pitch (referred to as carbon fiber) as an industrial carbon fiber raw material is being considered. Isotropic carbon fibers obtained from isotropic pitch correspond to so-called low elastic modulus and low strength products from the viewpoint of mechanical properties, etc., but on the other hand, isotropic carbon fibers obtained from anisotropic pitch Anisotropic carbon fibers are high-modulus, high-strength products, and exhibit properties comparable to high-performance carbon fibers obtained by heat-treating polyacrylonitrile or rayon under tension. Therefore, in the future, it is thought that the proportion of anisotropic pitch as a raw material pitch for carbon fiber production will increase, and much research is being directed to its production.

Anisotropic pitch is generated in the process of heat treating isotropic pitch. That is, when isotropic pitch is heated to 350-450°C, reactions such as cyclization, aromatization, and polycondensation proceed in the pitch, forming anisotropic small spheres ( Spherulites) begin to appear. These anisotropic microspheres are composed of relatively high molecular weight hydrocarbons with a polycyclic and polynuclear skeleton, are composed of components with a high aromatic content, and are a type of liquid crystal with a nematic structure. Also this/J%
The i-form mainly consists of quinolinated components and gradually grows by increasing the temperature or prolonging the treatment time.
Coalescence of the spherules then occurs. Through this process, the entire pitch comes to have an anisotropic structure, and the viscosity of the entire system increases significantly, eventually turning into coke. A small sphere or a phase of small spheres exhibiting this anisotropy is called a mesoface, and a pitch that includes a mesoface or has a large pot that is a mesoface is called a mesoface pitch. Conventional carbon fibers having an anisotropic structure are manufactured by spinning the mesoface pitch described above, making it infusible, and carbonizing it (Japanese Patent Publication No. 49-8634, Japanese Patent Application Laid-open No. 49-1912).
No. 7, JP-A-53-65425, JP-A-53-119
No. 326, JP-A-54-160427).

There are several difficult problems when producing carbon fiber using mesoface pitch as a raw material, but the fundamental problem is that the melting temperature and melt viscosity of the mesoface component generally differ from those of the isotropic component forming the matrix. This is due to the fact that it is higher than

In other words, when a pitch containing mesophase is melted at a relatively low temperature such that the matrix component exhibits a liquid state, the mesophase behaves in-phase and the entire system exhibits thixotropic behavior, making its spinning difficult. many. On the other hand, when melted at a relatively high temperature where mesophase pitch also melts, mesophase pitch gradually increases its viscosity and eventually becomes coke, as it is thermally unstable at such high temperatures. Ru. Particularly in pitches with a high mesophase content, the rate of coking is high. This coking phenomenon makes continuous spinning difficult. In this way, when producing carbon fibers using mesoface pitch as a raw material, the resulting carbon fibers exhibit anisotropy, and although their performance is superior to that of carbon fibers obtained from isotropic pitches, There is a fundamental problem that melt spinning is difficult, and no method to solve this problem has been proposed yet.

The present invention was made in order to fundamentally solve the above-mentioned problems encountered in the production of carbon fiber using mesoface pitch. ) low melting temperature and low melt viscosity,
Therefore, carbon fibers can be spun at low temperatures below 300°C, and C) carbon fibers can be produced using a special pitch that does not contain mesophase and is suitable as a raw material for carbon fibers with an anisotropic structure, that is, potentially anisotropic pitch. The present invention provides a method for manufacturing.

The potentially anisotropic pitch used in the present invention has an H/C (hydrogen/carbon atomic ratio) of 0 obtained from petroleum-based or coal-based raw materials.
．． 43 to 0.75, a substantially quinoline-soluble polycyclic and polynuclear skeleton with a structure in which polycyclic and polynuclear hydrocarbons such as those present in aromatic pitches generally referred to as mesophase pitches are partially hydrogenated. contains hydrocarbons as potential anisotropy-forming components, does not substantially form mesophase in the molten state, and forms a homogeneous and optically isotropic single phase as a whole, and when external force is applied, Indicates the orientation in that direction, H
/C is defined as a pitch of 0.55 to 1.2.

This potential anisotropic pitch is clearly distinguished from conventional isotropic pitch and anisotropic pitch, and is a completely new type of pitch discovered by the present inventor.

The potentially anisotropic pitch used as a carbon fiber raw material in the present invention can be regarded as an isotropic pitch as a whole, but it contains a polycyclic polynuclear skeleton with a carbon skeleton that can be a mesophase component. Contains hydrocarbons and therefore has latent orientation, and when external forces such as shearing force or stretching force are applied, optical anisotropy is observed indicating that the molecules are oriented in that direction, and carbonization It is a pitch that has the property of exhibiting anisotropy during the graphitization process. The hydrocarbon component with a polycyclic polynuclear skeleton having a carbon skeleton that can be a mesophase constituent component is one whose 11/C is 0.43 to 0.75, preferably 0.45, obtained from petroleum, coal, etc.
The polycyclic polynuclear hydrocarbons present in aromatic pitches with a molecular weight of ~0.65 have a partially hydrogenated structure and constitute mesophases included in conventional anisotropic pitches. Although it is similar to hydrocarbons in that it has a polycyclic and polynuclear skeleton, it is clearly different in that it is substantially soluble in quinoline and exists without forming mesophase or phase separation in the molten state. Therefore, unlike anisotropic pitches containing so-called mesophases, potential anisotropic pitches containing this type of pitch exhibit optical isotropy, are homogeneous, form a single phase, have a low melting temperature, and have a low melt viscosity. small.

In addition, since this potentially anisotropic pitch has the aforementioned potential anisotropy, it has the characteristic that by melt-spinning it as a raw material and carbonizing it, a carbon fiber with an anisotropic structure can be obtained. have

Further, the potentially anisotropic pitch used as a carbon fiber raw material in the present invention usually has a melting temperature of about 150 to 350°C, often 300°C or less, is viscously homogeneous, non-thixotropic, and has Newtonian flow. . In addition, it has excellent thermal stability in the molten state, does not form coke even when heated at about 350°C, and has a low melt viscosity, usually 200 to 300°C.
The temperature is 100 poise or less in °C. Since the latent anisotropic pitch has such melting characteristics, it has extremely excellent melt spinnability when producing carbon fibers.

The content of partially hydrogenated polycyclic polynuclear skeleton hydrocarbons, soluble in quinoline, in the potentially anisotropic pitch, with a carbon skeleton that can be a mesophase component, is usually 1 to 90% by weight, preferably 5 to 90% by weight. It is 70% by weight.

The potentially anisotropic pitch used in the present invention is obtained by using, for example, a mesophase pitch previously produced by a conventional method as a raw material, in which the mesophase contained therein substantially disappears and the entire pitch becomes substantially It can be produced by hydrogenating until a single phase is formed, followed by heat treatment. In this case, the mesophase content in the mesophase pitch used as a raw material is 1 to 90% by weight, preferably 5 to 70% by weight.

Hydrogenation treatment is carried out for the purpose of partial hydrogenation of polycyclic polynuclear hydrocarbons, and various conventionally known methods employed for hydrogenation of aromatic nuclei and the like are employed. For example, reduction methods using alkali metals, alkaline earth metals and their compounds, electrolytic reduction methods, homogeneous catalytic hydrogenation methods using complex catalysts, etc., and heterogeneous catalytic hydrogenation methods using solid catalysts. etc. Furthermore, we have developed a non-catalytic hydrogenation method under hydrogen pressure and hydrogen donors such as tetralin (H
A method of hydrogenation using Hydrogen Donor is also possible. Hydrogenation conditions vary depending on the method used, but a temperature of 400°C or less and a pressure of normal pressure to 200 atmospheres can be employed. Furthermore, when hydrogenating the raw material pitch, it can be carried out in the form of powder, dispersion or melt, or a suitable solvent can also be used.

The hydrogenation treatment is carried out until the mesophase contained in the raw material pitch is substantially changed into a quinoline-soluble component and the mesophase disappears. The hydrocarbons of the quinoline-soluble polycyclic polynuclear skeleton that form the mesophase become quinoline-soluble by being partially hydrogenated, and the mesophase that existed in the pitch before the hydrogenation treatment disappears.

To obtain the potentially anisotropic pitch of the present invention, the hydrotreated pitch as described above is then heated and held in the molten state for a certain period of time. Normally, pitch that has been hydrogenated until the mesophase disappears as described above is isotropic, but inevitably an excessive amount of hydrogen enters the aromatic nuclei, etc.
The hydrogenated pitch usually does not exhibit orientation even when an external force is applied thereto, and in order to form a potentially anisotropic pitch, the hydrogenated pitch needs to be heat-treated. What is the heating temperature in this case?

Generally, the temperature is higher than the melting humidity and lower than 450°C, preferably 280 to 430°C. Of course, during heating in this case, care must be taken to ensure that mesophases are not formed again. Additionally, the entire process can be carried out under normal pressure or under pressure-controlled conditions. Due to this heat treatment.

The light boiling point components remaining in the pitch resulting from hydrogenation are volatilized, and the hydrogen that has excessively entered aromatic nuclei is dehydrogenated, resulting in a pitch with latent anisotropy and increased thermal stability. can get. . Therefore, by combining the above hydrogenation treatment step and this heat treatment step to treat the raw pitch, a potentially anisotropic pitch with a controlled hydrocarbon content in a polycyclic polynuclear skeleton can be obtained.

The raw material pitch used for potential anisotropic pitch is:
Both petroleum-based and coal-based pitches are applicable, and generally, the conventionally called mesophase pitch or anisotropic pitch, or a specific pitch component separated from these pitches can also be arbitrarily adopted. can. In general,
The raw material pitch used in the present invention can be used as long as it has an H/C (hydrogen/carbon atomic ratio) in the range of 0.43 to 0.75, and according to the present invention, such raw material pitch can be used. Pitch is converted to H/(1, o by hydrogenation and heat treatment)
, to a potential anisotropic pitch ranging from 55 to 1.2. The inclusion of partial hydrides of polycyclic and polynuclear hydrocarbons, such as those contained in the mesophase phase in aromatic pitches with H/C in the range of 0.43 to 0.75, increases the potential of anisotropic pitches. It is a special feature.

The following table shows a comparison of the physical properties of potential anisotropic pitch and conventionally known mesophase pitch and isotropic pitch for spinning.

Table 1 Now, whether or not the pitch obtained by the method described above has potential anisotropy can be determined as follows. A sample is prepared by embedding a portion of the pitch in resin in a conventional manner and then polishing it, and applying an external force in one direction to its surface (for example, by rubbing the surface in one direction using a mouthpiece, etc.).

When the surface is viewed with a polarizing microscope, the determination is made based on whether or not weakly polarized light is seen due to the orientation of the molecules in the direction of the external force. In particular, if two parts rubbed in directions orthogonal to each other are placed within the same field of view, it can be determined very clearly.

The potentially anisotropic pitch described above has extremely advantageous characteristics as a raw material pitch for carbon fiber production. That is, as mentioned above, this pitch is 350°C or less, usually 180°C.
It has a low melting temperature of ~300°C and a melt viscosity that allows spinning, and has excellent thermal stability.
There are no difficulties in melt spinning, which are encountered when producing carbon fiber using conventional mesoface pitch as a raw material. Note that all melting temperatures in this specification mean softening points measured by the Koka flow tester method.

The production of carbon fibers from potentially anisotropic pitch will now be detailed below.

To produce carbon fiber from potentially anisotropic pitch, raw pitch is heated and melted above its melting point, usually at 200 to 300°C, the melt is extruded through a nozzle, cooled while spinning, and then this spun material is The pitch is heated in an oxygen-containing atmosphere to make it infusible, and then further heated to a high temperature in an inert gas to carbonize it. The carbonization temperature in this case is 800-15
00°C, and by setting the temperature increase rate during heating to about 2-b5-b°C or higher, graphitized fibers can be obtained. In the case of the present invention, when observing the cross section of pitch fibers immediately after spinning using an optical microscope, potential anisotropic pitch orientation in the fiber axis direction is often not observed because the surface is not disturbed by polishing. However, due to the stretching effect during spinning, a latent selective orientation of molecules in the fiber axis direction is formed, so that an anisotropic structure is clearly expressed in the subsequent carbonization and graphitization stages. Carbon fibers with a natural structure are formed.

Next, the present invention will be explained in more detail with reference to Examples. In the examples, 0 means a quinolinated component, and QS
means a quinoline soluble component, BI means a benzene insoluble component, and BS means a benzene soluble component.

Example I Isotropic pitch produced from decant oil obtained from the FCC method (fluid catalytic cracking of petroleum fractions) was heat treated at 420° C. to obtain mesoface pitch.

The H/C (atomic ratio) of this pitch is 0.57, and according to the solvent fractionation method, QI is 32.8%, 05-BI is 48.3%, B
It was 518.9%. Under a polarizing microscope, many optically anisotropic small spheres were observed at this pitch, as shown in FIG. 1, and it was a so-called mesoface pitch. This pitch has poor thermal stability at spinning temperatures and poor spinnability.

It was difficult to spin into long fibers at a speed of 100 m/n1 m or more. This pitch was powdered and hydrogenated by Birch reduction method at a temperature of 95°C. Hydrogenated pitch QI<0.4%, 05-Bl36.5%, B563
%, it was a single-phase pitch containing substantially no QI. Moreover, H/C (atomic ratio) in this hydrogenated pitch increased to 1.01. This hydrogenated pitch did not become oriented even when an external force was applied to it, and did not exhibit potential anisotropy.

Next, this hydrogenated pitch was heated to 400° C. in an inert gas stream and then held under reduced pressure to remove trace amounts of low molecular components.

The pitch thus obtained had a QI<0.3%, substantially no QI acid component, and an H/C atomic ratio of 0.98.

Under a polarizing microscope, as shown in Figure 2, no mesophase structure was observed at all, but by rubbing in one direction, weak but clear polarized light could be seen along that direction, as shown in Figure 3. , it was confirmed that it has potential anisotropy. Figures 3 (a), (b) and (c) are polarized light micrographs of the pitch surface after rubbing in the directions of the arrows perpendicular to each other; In view,
This is a case where the microscope stage is rotated by 45@ and 90', respectively. The melting temperature of this pitch is approximately 240℃,
It has excellent thermal stability and no structural change was observed even after heating at 350°C for 3 hours.

This pitch was melt-spun under the following conditions.

Spinning diameter: 0.6mm Spinning pressure (water column)
35cm spinning temperature
270-280℃ Spinning speed 350m
Next, the obtained pitch fibers were heated to 280° C. in air to make them infusible, and then heated to 1000° C. at a temperature increase rate of 5° C./min in an argon stream to carbonize them.

When the cross section of this carbon fiber was observed with a polarizing microscope, it was confirmed that the vertical cross section and the horizontal cross section had an anisotropic structure as shown in FIGS. 4 and 5, respectively. This carbon fiber was further graphitized at 2500°C, and its degree of orientation was measured by X-ray diffraction. The results are shown by curve 1 in FIG.

In this graph, the horizontal axis represents the angle (θ) between the fiber axis and the C-axis direction of the carbon crystallite, and the vertical axis represents the relative diffraction intensity (RI) of the (002) diffraction line. In the case of completely isotropic carbon or graphite fibers, the relative diffraction intensity (RI) of the diffraction lines
is horizontal as shown in curve 2, but in the case of the graphite fiber according to the present invention, the RI changes significantly with θ, and it is clearly understood that the graphite fiber according to the present invention is oriented.

Table 2 shows the tensile strength and elastic modulus of the carbon fibers and graphite fibers thus obtained.

Table 2

[Brief explanation of the drawing]

Figure 1 shows a polarized light micrograph (magnification: 400x) of the surface of the mesophase pit used as a raw material, Figure 2 shows the potential anisotropic pitch, and Figure 3 shows the surface of the mesophase pit used as a raw material. This is a polarized light micrograph of the pitch surface after it has been removed. Third
In the figure, the arrow indicates the direction of rubbing. Figure 3(b)
, (c) are the same field of view as in (a) when the microscope stage is rotated by 45° and 90'', respectively. Figures 4 and 5 show the carbon fibers obtained from the potential anisotropic pitch. Polarized light micrographs (magnification: 800x) of longitudinal and transverse sections are shown, respectively. Fig. 6 is a graph showing the results of measuring the degree of orientation by X-ray diffraction method. Applicant's agent, patent attorney Toshiaki Ikeura No. 10 Figure 5 Figure 6 Figure θ (angle)

Claims (1)

[Claims] (1) A method for producing carbon fibers, which comprises using potentially anisotropic pitch as a raw material, melt-spinning it, making it infusible, and carbonizing it.