JPS62162022A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To obtain a carbon fiber having high strength and elastic modulus, by heat-treating a carbonaceous raw material, treating the obtained mesophase pitch with a centrifugal separator furnished with a light medium-heavy medium separation weir, melt-spinning collected heavier component and subjecting the spun fiber to infusibilization, carbonization, etc. CONSTITUTION:A carbonaceous raw material (e.g. coal-based pitch) is heat- treated and the treated material is supplied through a feed pipe 6 to a centrifugal separator preferably in a state of <=430 deg.C and a viscosity of 0.1-10ps. The material is separated in layers at the inner wall of a rotary cylinder 1 into a heavy medium layer having high anisotropy and a light medium layer in which development of anisotropy is not sufficient. The heavy medium is passed through a gap between a heavy medium over flow weir 3 and a light medium-heavy medium separation weir 5 and taken out through a heavy medium discharging port 8. The heavy component composed of a mesophase pitch having a softening point of preferably 220-320 deg.C (e.g. having a softening point of 305 deg.C and anisotropic ratio of 93% at a spinning temperature) is spun under molten state and the fiber is successively subjected to infusibilization, carbonization and, if necessary, graphitization to obtain the objective fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing carbon fibers, and more particularly, using a spinning pitch that provides high-performance carbon fibers with high strength and high modulus. The present invention relates to a method for manufacturing carbon fiber.

[Conventional technology]

Carbon fiber is a material with high specific strength and specific modulus, and is attracting the most attention as a filler fiber for high-performance composite materials.In particular, pitch-based carbon fiber has abundant raw materials and has a large amount of waste during the carbonization process. It has various advantages compared to polyacrylonitrile carbon fiber, such as high fiber elastic modulus.

As is well known, carbonaceous raw materials such as heavy oil, tar, pitch, etc. are processed at 160-. When heated to 100° C., small spheres with particle sizes ranging from several microns to several hundred microns and exhibiting optical anisotropy under polarized light become biotropic. This anisotropic structure is composed of layered and oriented planar polymeric aromatic hydrocarbons produced by thermal polycondensation reactions of carbonaceous raw materials, and is considered to be a precursor of graphite crystal structure. bl.

A heat-treated product containing such an anisotropic structure is generally called mesophase pitch.

As a method for using such mesophase pitch as a spinning pitch, for example, petroleum-based pitch is heat-treated at about A method has been proposed in which the pitch is obtained and used as the spinning pitch (JP-A-4T9-/?
/ Koku issue).

However, since it takes a long time to meso-form an isotropic carbonaceous raw material by this method, the carbonaceous raw material is treated with a sufficient amount of solvent in advance to obtain its insoluble matter, and then the insoluble matter is g0
Heat treatment for a short time of 7θ minutes or less at a temperature of 0°C results in a highly oriented, optically anisotropic portion with a weight ratio of 75 or more, and a quinoline soluble fraction! A method has been proposed in which a so-called neo-mesophase pitch having a weight of S or less is formed and this is used as a spinning pitch (Japanese Patent Application Laid-open No. Sho! Darit, o4I Koku).

In addition, as a spinning pitch with good orientation for producing high-performance carbon fibers, for example, an optical fiber obtained by subjecting coal tar pitch to intensive hydrogenation treatment in the presence of tetrahydroquinoline, and then heating it for a short time at about ago°C. isotropically at 100℃
Pitch that has the property of becoming anisotropic when heated to a higher temperature, so-called brimesophase pitch (4I Kaisho Z)
g-it Dako No. 1 Publication), or a pitch that is optically isotropic and exhibits orientation in that direction when an external force is applied, which is obtained by hydrogenating mesophasic pitch by Birch reduction method, etc. The so-called dormant mesophase (JP-A-Sho, t
No. 7-100/l&) etc. have been proposed.

Pitch fibers can be obtained by melt spinning such spinning pitch through a nozzle. Next, by making the pitch fiber infusible, carbonizing it, and optionally graphitizing it, a pitch-based high-performance carbon fiber can be obtained.

(Problems to be Solved by the Invention) Jin's pitch-based high-performance carbon fibers have various advantages over polyacrylonitrile-based carbon fibers, such as a high yield in the carbonization process and a high fiber elastic modulus. However, pitch-based carbon fibers produced from Tamesophase pitch obtained by conventionally known methods generally have the disadvantage that they are slightly inferior in strength to polyacrylonitrile-based carbon fibers.

Therefore, in the production of pitch-based carbon fibers, attempts have been made to produce high-performance carbon fibers, and various proposals have been made so far. However, it has not yet been possible to stably obtain carbon fibers with high performance comparable to that of PAN-based carbon fibers.

Generally, in order to improve the performance of pitch-based carbon fibers, the presence of highly oriented molecules within the fiber is essential. , it was very difficult to spin.

For example, when the optical anisotropy ratio measured at room temperature reaches 100%, the softening point also reaches szo"crlc.

Melt spinning of pitch is usually performed at the softening point of pitch) lθ~&
Since spinning is carried out at a temperature 0°C higher, the spinning temperature is as high as 50°C, which is a pitch with a softening point of sago°C], and the generation of pyrolysis gas and coking are significant, making it difficult to stabilize the spinning operation. become unable to do so.

Therefore, conventionally, the anisotropy of the spinning pitch is /ρOX'! By stopping the heat treatment until the meso phase forms a continuous phase without allowing the meso phase to develop, a spinning pitch that maintains spinnability was obtained. However, high-performance carbon fibers cannot be obtained with such a spinning pitch, and pitch with a low degree of orientation (mesophase content -〇~'yo%) is fed to a centrifuge in a molten state to produce 1aooo-group. Simultaneously separate one layer of the solid slurry and the optically anisotropic phase by applying an acceleration of o, oooa, or
Alternatively, a centrifugal separation method has been proposed which separates the slurry into 3 layers: an optically isotropic phase, an optically anisotropic phase, and a solid slurry (Japanese Patent Application Laid-open No. 6/9). However, separation of the optically anisotropic phase using such a centrifugal separator is performed from the upper layer of the optically anisotropic phase (a portion close to the optically isotropic phase), and in such a method, one-dimensional Separation between the orthotropic phase and the anisotropic phase was insufficient and high performance carbon fibers could not be obtained.

(Means for Solving the Problems) Therefore, in order to solve the above problems, the present inventors have conducted extensive studies on a method for producing mesophase pitch that provides high-performance carbon fibers, and have found that Show your gender,
In addition, noting that mesophase pitch with a low softening point is heavier than pitch whose anisotropy is not sufficiently developed, a centrifugal separator equipped with a liquid-liquid separation layer was used to remove the layer.
By centrifuging each to separate the heavy liquid layer from the heavy liquid layer and obtaining them separately), heat-treated pitch (
It was discovered that the isotropic phase pitch (@liquid part) could be substantially removed from the heavy liquid part, and the present invention was completed based on this knowledge.

That is, the purpose of the present invention is to obtain a spinning pitch for carbon fiber that provides a pitch-based carbon fiber having high strength and high modulus of elasticity by removing components that form an isotropic phase at the spinning temperature, A method of manufacturing carbon fiber is provided.

The purpose is to produce carbon fibers by melt-spinning menphase pitch obtained by heat-treating carbonaceous raw materials, making the pitch fibers infusible, carbonizing them, and graphitizing them if necessary. In the method of
The heavy liquid and light liquid were separated into a heavy liquid layer and a light liquid layer, and the heavy liquid and light liquid were obtained separately through the separation weir so that the heavy liquid was obtained from the part of the heavy liquid layer that was farthest from the light liquid layer. This can be easily achieved by a carbon fiber manufacturing method characterized in that the heavy liquid layer is then melt-spun.

In the following, the present invention will be described in detail. The spinning pitch of the present invention is not particularly limited as long as molecular species that are easily oriented are formed and an optically anisotropic pitch is provided. You can use a conventional one such as .

The carbonaceous raw material for obtaining these spinning pitches is 1
For example, coal-based coal tar, coal tar pitch,
Examples include liquefied coal, heavy petroleum oil, tar, and pitch. These carbonaceous raw materials usually contain free carbon,
Although it contains impurities such as undissolved coal and ash, it is desirable to remove these impurities in advance by well-known methods such as filtration, centrifugation, or static sedimentation using a solvent.

In addition, the carbonaceous raw material may be pre-treated by, for example, heat-treated and then extracted with a specific solvent, or hydrogenated in the presence of a hydrogen-donating solvent or hydrogen gas. It's okay.

In the present invention, such a spinning pitch is used as a light liquid in a molten state.
It is introduced into a rotating cylinder of a centrifugal separator having a heavy liquid separation weir.

In a centrifugal separation operation, the lower the viscosity, the smaller the centrifugal force and the faster the separation will be completed. However, if you try to lower the viscosity at too high a temperature, it will cause thermal deterioration of the spinning pitch. Viscosity 100 voids or less, preferably o,
It is preferable to operate at a temperature of i to 10 poise. 100
Although it is possible to perform centrifugal separation even when the viscosity is higher than that, the time required for separation or the required centrifugal force increases in proportion to the viscosity, so it is not a good idea because the cost of the equipment is large.

For example, it is preferable that the pitch leaving the heat treatment reactor be centrifuged for a short time at the same temperature as the heat treatment temperature without passing through a heat exchanger or the like.

In addition, it is preferable to maintain the inside of the centrifugal separator in an inert atmosphere, and the inert atmosphere is not particularly limited as long as it does not react with the spinning pitch, but rare gases such as nitrogen and argon can be used. Nitrogen is preferably used for ease of use.

Note that depending on the amount of inert gas contained in the spinning pitch already introduced in the heat treatment step, there is no need to further forcefully ventilate the inert gas.

Next, the present invention will be explained based on FIGS. FIGS. 1 and 1 are schematic configuration diagrams of a centrifugal separator for separating and removing light liquids such as gas components and isotropic phase pitch from heavy liquids. In the figure, l is a rotating cylinder, c is a light liquid overflow weir, 3 is a heavy liquid overflow weir, and da is a gas-liquid separation weir. is a heavy liquid separation weir, ru is a feed pipe, and /da is a liquid overflow weir.

In Fig. 1, the rotating cylinder / is the rotating shaft /, 7, a light liquid overflow weir is provided at one end of the rotating cylinder in contact with its periphery, and a heavy liquid overflow weir is provided in contact with its periphery at the other end. 3 is provided.

The gas-liquid separation weir is for separating gas components from liquid, and has a cylindrical structure with a mouth-shaped cross section, and the wedge-shaped part is designed to handle the small diameter end of the light liquid overflow weir. It is installed concentrically with the rotating cylinder. It is better to insert one end of the mouth part deeper than the small diameter end of the light liquid overflow weir. However, if it is inserted too deeply, it will disturb the interface between the light liquid and heavy liquid, but it will be fixed in place. It can also be fixed to

The light liquid-heavy liquid separation weir J is designed to prevent the mixing of light liquid and to extract only the heavy liquid from the part farthest from the light liquid layer.
Heavy liquid overflow weir 3 with truncated conical cylinder structure
It is installed with a predetermined gap 1111 between the two. One end of the tip 11 of the light liquid-heavy liquid separation weir S needs to be inserted deeply, at least as far as the light liquid-heavy liquid interface. It is best to insert it deep enough not to obstruct the outflow of the heavy liquid when removing it from the heavy liquid. The light liquid-heavy liquid separation weir S does not necessarily have to be fixed to the rotating cylinder, but as mentioned above, there are many embellishments that narrow the clearance with the rotating cylinder. It is safer to fix it to a rotating cylinder to prevent contact with the rotating cylinder.

Feed pipe 6 is provided from above to increase separation efficiency.

It is preferable to install the rotary cylinder at a position as far away as possible from the light liquid overflow weir 3 and the heavy liquid overflow weir 3 at the center position.

In the centrifugal separator having such a structure, the mesophase pitch supplied into the rotating inner cylinder through the feed pipe 6 forms a heavy liquid layer with high anisotropy on the inner wall of the rotating inner cylinder due to centrifugal force. The liquid layer is separated into a light liquid layer whose anisotropy is not sufficiently developed.

12 The light liquid separated in a single layer is led out from the multi-rotation inner cylinder/by the light liquid overflow weir, flows down the inner wall of the outer cylinder 10, and is taken out of the light liquid outflow system through the light liquid outflow mechanism provided in the outer cylinder 10. It will be served.

In addition, the heavy liquid flows through the gap between the heavy liquid overflow weir 3 and the light liquid-heavy liquid separation weir 5, passes through a slit provided at the meeting part of the painting platform, flows down the inner wall of the outer cylinder 10, and the heavy liquid flows. It is led out of the system through exit t. Further, the gas components contained in the mesophase pitch are removed from the surface of the light liquid layer into the gas phase due to the difference in gravity, and the gas components are removed to the outside of the weft thread at the gas outlet 9.

The average residence time of the liquid is determined by the height of the low weir and the heavy liquid overflow weir 3 and the liquid feed rate, but in order to adjust the separation ratio of light liquid and heavy liquid, the height of both overflow weirs should be the same, and the light liquid , a method of draining almost the same amount of heavy liquid and recycling the amount of light liquid into feed liquid according to the desired degree of separation;
For example b, as shown in FIG. 2, it is preferable to provide a plurality of light liquid overflows and adjust them by appropriately selecting the ratio of their opening areas.

The degree of separation of gas components and light liquid-heavy liquid is preferably controlled based on three conditions: viscosity of the liquid, strength of centrifugal force, and residence time.

The required centrifugal force and residence time differ depending on the viscosity of the liquid, but for example, when the liquid viscosity is S voice, the centrifugal force is 3.
00 to g 000 G and residence time/~60 minutes.

Since the stress becomes high, it is better to select the operating viscosity (operating temperature), centrifugal force and residence time in consideration of the cost of the equipment and the properties of the spinning pitch.

There is no problem if the axis of rotation of the rotating cylinder is vertical as well as horizontal, but if the axis of rotation is vertical, it may be necessary to take measures to remove the light liquid and heavy liquid discharged from the rotating cylinder. Melt.

In addition, the light liquid-heavy liquid separation weir S in FIG. It can also be installed in a location where Further, the gas-liquid separation layer q may be omitted if bubbles may remain in the separated light liquid.

The spinning pitch, which is a heavy liquid from which gas components and light liquid components with insufficiently developed anisotropy such as isotropic phase pitch have been removed, is supplied to a spinning device and melt-spun to form pitch fibers. Pitch-based carbon fibers with high properties are produced by subjecting the fibers to cine melting treatment and carbonization treatment using known methods, and further graphitization treatment as required).

(Effects) According to the present invention, gas components remaining in the pitch after heat treatment and light liquids such as isotropic phase pitch can be sufficiently and efficiently removed.
High-performance carbon fibers with high strength and high modulus of elasticity can be obtained from the resulting spinning pitch, which is a heavy liquid with high anisotropy.

Surprisingly, according to the method of the present invention, there is almost no light boiling during spinning, unlike in the case of mesophase pitch obtained by static separation method or conventional centrifugation method, and stable spinning is achieved. It was easy to use, and the strength and modulus of elasticity were substantially the same or higher than those obtained by heat treatment, which resulted in substantially only the meso phase, and by centrifugal degassing.

In addition, the softening point of pitch in the present invention is a value measured by the Metgy method. The anisotropy ratio under 1+ spinning temperature is
Using a Rhine hot stage, a sample of 4tO-Arθ■ was placed in an aluminum cup with a diameter of φ x 2, and the temperature was raised at a rate of q°C/min while flowing nitrogen at a rate of q°C/min under a polarizing microscope. It was determined by observing at a lower magnification (100x magnification) and measuring the ratio of the area of optical anisotropy to a constant surface area of the sample.

EXAMPLES The present invention will be specifically explained below with reference to examples, but the present invention is not limited to the following examples as long as it does not go beyond the gist of the invention.

Example - Coal-based pitch was heat-treated at 1130°C for 7 hours under nitrogen gas ventilation to achieve a softening point of 2go°C and anisotropy ratio of 30% at room temperature.
I got the pitch.

This pitch was collected under a nitrogen atmosphere at 3'70°C (viscosity O, cocoise) using a centrifugal separator with the structure shown in Figs. The outer diameter of the light liquid-heavy liquid separation weir j is 4t, the inner diameter of the rotating cylinder is 2! rOw
m, number of revolutions/3! Orpm (centrifugal force zooG))
It was continuously supplied to the feed tube B and processed with an average residence time of 3 minutes.

The softening point of the heavy liquid that flows out from the heavy liquid outlet is 3Q! The anisotropy ratio at the spinning temperature of °C was 93 (100% at room temperature).

When the pitch of the grain was melt-spun at 3 degrees θ℃, the winding speed/
000 rn/- and the pitch fiber diameter was gμ or more, stable spinning could be performed for more than 1 hour without breakage.

Pitch fiber (thread diameter/μ) The carbon fiber with a thread diameter of 9.5μ obtained by infusible at 310℃ in an air atmosphere and then carbonized at 7400℃ under a nitrogen atmosphere has a tensile strength of J/0.
KJ, tensile modulus Koku T/, J.

When the heat-treated pitch obtained in Comparative Example-/Example-/ was spun as it was, volatilization at a low boiling point and severe pulsation immediately below the spinning nozzle were observed, and the winding speed was 4io.

Stable spinning could not be achieved even at m/■ pitch fiber diameter/μ.

A carbon fiber with a thread diameter of 10.7μ obtained in the same manner as in Example/from a small amount of pitch fiber has a tensile strength of 70 kg/sJ.
, tensile modulus/3T/-.

Comparative Example-11 Example-/Heat treatment pitch fjlθ℃ obtained at 60
The mixture was allowed to stand still for several minutes, and the pitch of the lower layer was sampled and subjected to melt spinning in the same manner as in Example.

The pitch of the lower layer at this time had an anisotropy ratio of about 30% at the spinning temperature.

The spinnability of the lower layer pitch obtained by static separation was similar to Comparative Example -/, and stable spinning was difficult. In addition, the pitch fiber obtained in a small amount was used in the same manner as in Example 1.
0. The characteristic of carbon fiber of θμ is tensile strength! r! r#
/wJ, tensile modulus co0. It was kT/-.

Example - Coal-based pitch under nitrogen gas aeration at 30°C/hour QQ
After heat treatment, the softening point is 93℃, and the anisotropy ratio at room temperature is 93℃.
(anisotropy ratio go 5A at aaO°C).

This pitch was measured at a temperature of 3go using the same equipment as in Example/.
°C (viscosity S poise) rotation speed 3go.

rpm (,7360G) and an average residence time of 30 minutes.

The pitch flowing out of the heavy liquid outlet has a softening point of 310C and an anisotropy ratio of 9g96 or more at the spinning temperature (1O at room temperature).
OX).

This pitch was melt-spun at 3° C. for 3 days in the same manner as in Example 1. When the winding speed was 1000 m/min and the pitch fiber diameter was g μ, stable spinning was possible without breakage for over 1 hour.

Carbon fibers with a thread diameter of 9.3μ obtained from pitch fibers (thread diameter 1 μμ) in the same manner as in Example / have a tensile strength of 3 daq ”9 /
-1 tensile modulus of elasticity was t'r7'-.

Comparative Example-3 The heat-treated pitch obtained in Example-1 was subjected to equipment treatment at 31θ°C for one hour.

However, the meso phase (heavy liquid layer) and the isotropic phase (light liquid layer) did not separate at all.

Comparative Example 4 The heat-treated pitch obtained in Example 1 was introduced into a centrifugal separator with a heavy liquid outlet in the middle of the liquid overflow weir after removing the light liquid-heavy liquid separation weir. As a result of treatment in the same manner as in Example 1, the pitch that flowed out from the heavy liquid outlet had a softening point of 301°C and an anisotropic ratio gzN (9 t N at room temperature) and an isotropic pitch under the spinning temperature. Separation was insufficient.

This pitch was spun at 337°C, and the same sK infusible carbonization as in Example-C was performed to obtain a large carbon fiber with a yarn diameter of 9, dμ, tensile strength, qrkg/-1, and elastic modulus of 13T/-. It was worse than anything else.

[Brief explanation of drawings]

1 and 1 are schematic configuration diagrams of an example of an apparatus used in an embodiment of the present invention. /: Rotating tube Koni light liquid overflow 4-weir 3: Heavy liquid overflow weir mite gas-liquid separation weir 3: Light liquid-heavy liquid separation weir ≦: Feed pipe 7: Light liquid outflow t: Heavy liquid outflow port 9: Gas outlet 10: Outer cylinder //: Outflow volume adjustment notch/Koni light liquid-heavy liquid interface/3: Rotating shaft

Claims (5)

[Claims] (1) A method for producing carbon fibers by melt-spinning mesophase pitch obtained by heat-treating a carbonaceous raw material, and subjecting the resulting pitch fibers to infusible, carbonized, and, if necessary, graphitized treatments, comprising: The mesophase pitch is fed to a centrifugal separator equipped with a light liquid-heavy liquid separation weir to separate it into a heavy liquid layer and a light liquid layer. A method for producing carbon fibers, which comprises obtaining a heavy liquid and a light liquid separately, and then melt-spinning the heavy liquid. (2) The method according to claim 1, characterized in that the light liquid and/or heavy liquid extraction section of the centrifugal separator has a notch or opening for adjusting the outflow amount. (3) The method according to claim 1, wherein the centrifugal force of the centrifugal separator is 300 to 8000G. (4) Softening point of mesophase pitch is 220-320℃
The method according to claim 1, characterized in that: (5) The method according to claim 1, wherein the anisotropy ratio of the heavy liquid layer is 90% or more at the spinning temperature.