JPH0681220A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To stably and quickly produce a large amount of carbon fiber from mesophase pitch without causing end breakage. CONSTITUTION:A mesophase pitch fiber is infusibilized in an oxidizing gas atmosphere containing NO2 and O2 and carbonized in two stages. The primary carbonization is carried out at 350-400 deg.C for >=10min by loading the fiber in a can, etc., in a deliverable state. The secondary carbonization is performed at 800-1300 deg.C for 5sec to 2min while continuously transferring the fiber in linear state. As necessary, the carbonized fiber is graphitized.

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, and more particularly to a method for producing carbon fibers from various pitches in a stable manner without yarn breakage, and in large quantities and rapidly.

[0002]

2. Description of the Related Art Carbon fiber is a material having a high specific strength and a high specific elastic modulus, and has recently attracted attention as a strong and light material in the aerospace field, the automobile industry and other industrial fields.

In such fields, inexpensive materials having high strength and high elastic modulus are desired.

Currently, PAN-based carbon fibers made from polyacrylonitrile (PAN) and pitch-based carbon fibers made from pitches are manufactured as carbon fibers, but at present, they have high strength and high elastic modulus. Performance carbon fiber is mainly P
AN-based carbon fiber is used.

However, the PAN-based carbon fiber has a limit to further increase the elastic modulus, the PAN as a raw material thereof is expensive, and the yield of the carbon fiber obtained from the PAN is low. There is a problem that the price of carbon fiber is inevitably high.

[0006] Therefore, in recent years, various studies have been conducted to improve the performance of pitch-based carbon fibers made of mesophase pitch, which has a high yield of carbon fibers and is easily made to have a high elastic modulus.

However, pitch fibers are fragile,
The infusible fiber, which is an intermediate process product, has a strength of 5 to 10 kg.
To significantly brittle and / mm ^2, the fibers 100 to 10
The infusible fiber yarns, which are aggregated in 10,000 fibers, are difficult to handle, and there is a problem that the yarns are easily broken and it is difficult to produce long fibers, and there is a lot of fuzz.

Further, when the infusible fiber yarn is drawn out linearly and carbonized or graphitized, it is disclosed in JP-A-4-9122.
As disclosed in Japanese Patent Publication No. 9, there is a problem that the single yarn in the fiber yarn is fused at the time of carbonization or graphitization, and the yarn becomes rigid, so that the product quality is significantly deteriorated.

Regarding such a problem, Japanese Patent Publication No. 62-202
Japanese Patent No. 81 discloses a method in which after infusibilization, initial carbonization is performed in the range of 400 to 650 ° C, and the initial carbonized fiber is handled.

Generally, when pitch fibers are infusibilized and carbonized, as shown in Japanese Patent Publication No. 62-20281, the breaking elongation of the fibers is remarkably improved at a carbonization temperature of 500 to 600 ° C. There is a point to do.

It is known that carbonization is performed in this temperature range to handle the yarn by utilizing the fact that the breaking elongation is large.

On the other hand, a method of using nitrogen dioxide as an infusibilizing gas has been proposed as a method for improving productivity such as shortening the infusibilizing treatment time or improving the physical properties of carbon fiber.
No. 29, or a method of mixing nitrogen dioxide and steam is described in JP-A No. 2-6618.

By using a gas in which nitrogen dioxide gas is mixed with the infusible gas, the infusibilization time can be remarkably shortened as compared with the conventional infusibilization by air.

However, when nitrogen dioxide is used as the infusible gas, it is generally known to be 400 to 650.
Even if initial carbonization is performed in the range of ℃, although the breaking elongation of the fiber is improved, there is a problem that the handling strength of the yarn is not improved in such a range that the breaking strength is low and yarn breakage occurs (Fig. 1).

[0015]

DISCLOSURE OF THE INVENTION The present invention, when the infusible fiber obtained by using nitrogen dioxide gas is further carbonized or graphitized, the yarn is broken or fused without using an oil agent or the like. It is to provide a method for improving the handling property such as eliminating the problem, and further improving the productivity such as shortening the processing time.

[0016]

The present invention provides (1) mesophase
Winding pitch fiber yarn made from ace pitch on bobbin
Either take it off or deposit it so that it can be delivered as it is,
As they are, nitrogen dioxide (NO ₂) And oxygen (O₂)
Oxidation infusible treatment in an oxidizing gas atmosphere containing
Baked in an inert atmosphere for 10 min or more at temperatures above ℃ and below 400 ℃
Formed and primary carbonized, and then the yarn is drawn out linearly
Secondary carbonization is carried out while continuing conveyance, and then as necessary.
A method for producing a carbon fiber characterized by performing graphitization,

(2) At a temperature of 800 to 1300 ° C. for 5 seconds to
The method according to claim 1, wherein secondary carbonization is performed while the yarn is continuously conveyed linearly for 2 minutes, and then graphitization is performed if necessary.

The details of the present invention will be described below.

The pitch which is the starting material for the carbon fiber of the present invention includes coal-based pitch such as coal tar and coal tar pitch, coal liquefied pitch, ethylene tar pitch, decant oil pitch obtained from fluid catalytic cracking residual oil, and the like. Various pitches such as petroleum-based pitches described above, or synthetic pitches made from naphthalene using a catalyst or the like can be used.

The mesophase pitch used in the carbon fiber of the present invention is the above-mentioned pitch in which the mesophase is generated by a conventionally known method.

It is desirable that the mesophase pitch has a high orientation of pitch fibers when spun, and therefore the mesophase content is desirably 40% or more, more preferably 70% or more.

The mesophase pitch used in the present invention has a softening point of 200 to 400 ° C., more preferably 250 to 400 ° C.
A temperature of 350 ° C is preferable.

Pitch fibers are obtained by melt spinning the mesophase pitch by a method known so far.

For example, the mesophase pitch has a viscosity of 1
A caliber of 0.1 at a temperature of 00 poise to 2000 poise
mm ~ 0.5mm capillary, pressure 0.1 ~ 1
100 to 200 while extruding at about 00 kg / cm ^2.
Stretched at a take-up speed of 0 m / min and a fiber diameter of 5 to 2
A pitch fiber of 0 μm is obtained.

Next, the pitch fiber has a nitrogen dioxide concentration of 2 to 10% by volume and an oxygen concentration of 2 to 2 as a yarn (fiber bundle).
0% by volume, optionally containing 2-10% by volume of steam,
In an oxidizing gas atmosphere in which the remaining gas is an inert gas such as nitrogen, the temperature is 100 to 320 ° C., and the processing time is 30 to 300 m.
in, preferably infusible under the condition of 40 to 200 min.

It is important that the infusible yarn is first carbonized (primary carbonization) at a temperature of 350 ° C. or higher and lower than 400 ° C. for 10 min or longer in an inert atmosphere such as nitrogen gas.

In FIG. 1, the infusible fiber is changed to 30 at different carbonization temperatures.
The results of measuring the breaking elongation of the single fiber and the breaking strength of the carbonized fiber yarn when carbonized for a minute are shown.

The average value of elongation at break of single fiber is 400 to 6
It shows the maximum value at the carbonization temperature of about 50 ° C., which is the result as the conventional knowledge.

However, at a carbonization temperature of 400 ° C. or higher, the fiber length shrinks about 3.2% at the carbonization process, and at 500 ° C., it shrinks 4.5%.

Therefore, it is considered that the length of the single fiber in the yarn becomes non-uniform due to shrinkage during carbonization, the fiber alignment is disturbed, and the breaking strength of the carbonized fiber yarn is significantly reduced.

On the other hand, as seen in FIG. 1, the breaking strength of the fiber yarn shows a high value at 350 to 390 ° C.

It is considered that when the temperature is 400 ° C. or higher, the variation in the strength of the single fiber becomes large, whereas when the temperature is less than 400 ° C., the variation becomes small, and the strength development rate of the yarn becomes high.

The present inventor pays attention to this point, divides the carbonization into two stages, and performs the primary carbonization at 350 ° C. or higher and lower than 400 ° C. for 10 minutes or longer, preferably for 20 to 60 minutes, and linearly feeding it out to some extent. After imparting strength that does not cause yarn breakage even when continuously conveyed, secondary carbonization is performed by continuously conveying the yarn linearly for a short time of 5 seconds to 2 minutes at a high temperature of 800 to 1300 ° C. It has made it possible to stably and rapidly mass-produce fibers.

As described above, at 350 to 390 ° C., there is an advantage that fibers having high strength can be obtained. On the other hand, when the carbonization temperature is lower than 350 ° C., a yarn having a temperature of 800 to 1300 ° C. for 5 seconds to 2 minutes is formed. When carbonization is carried out continuously (secondary carbonization), a decomposition product generated during carbonization causes a problem such as fusion of fibers or rigidity.

Therefore, it is necessary to temporarily carbonize the infusible fiber at least at a temperature of 350 ° C. or more for 10 minutes or more.

As shown in FIG. 2, when the change of the Nls orbital by XPS (photoelectron spectroscopy analyzer) was observed, the infusible fiber just obtained had a peak near 405 eV indicating NO ₂ content (carbonization at 300 ° C. for 30 min). ) Exists, and it is shown in FIG. 3 that this peak disappears and becomes stable by carbonization at 350 ° C. or higher and 10 min or higher (carbonization at 380 ° C. for 30 min).

Therefore, 405e generated by infusibilization
The nitrogen compound in the vicinity of V needs to be carbonized over a certain temperature and time as in the primary carbonization in the present invention,
If this is not the case, fusion and stiffening of the fibers will be observed due to rapid carbonization.

When the temperature of the secondary carbonization is lower than 800 ° C., the strength of the secondary carbonized yarn is low and it is difficult to handle it in the next graphitizing step, and when it exceeds 1300 ° C., the secondary carbonized fiber Has a large elastic modulus and causes a problem such as fluffing when the secondary carbonized yarn is wound around the bobbin.

After that, graphitization is performed if necessary.

[0040]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. In the present invention, various physical property values used to express the characteristics of the pitch-based carbon fiber and the raw material pitch were measured by the following methods.

(1) Softening point The softening point is the temperature at which the apparent viscosity calculated from the Hagen-Poiseuille equation using a flow tester becomes 20,000 poise.

(2) Toluene insoluble matter, pyridine insoluble matter Toluene insoluble matter and pyridine insoluble matter are JIS-K-242.
5 (1978).

(3) Single yarn breaking elongation The single yarn breaking elongation was measured according to the method described in JIS-R-7601 (1986).

(4) Breaking strength of fiber thread The breaking strength of the fiber thread is a sample in which tabs are fixed to both ends of the fiber thread with an adhesive so that the measured length of the thread is 3000 m. Create a large number of and pull it at a pulling speed of 50 m
Tensile breaking load was determined by pulling at a speed of m / min.

Coal tar pitch having a softening point of 80 ° C. from which quinoline insoluble matter was removed as a raw material was directly hydrogenated using a catalyst.

This hydrotreated pitch was heat-treated at 480 ° C. under normal pressure and then the low boiling point was removed to obtain mesophase pitch. This pitch had a softening point of 304 ° C., a toluene insoluble content of 85% by weight, a pyridine insoluble content of 40% by weight, and a mesophase content of 95%.

A pitch fiber having a diameter of 13 μm and a mesophase pitch viscosity of 800 poise was spun by a conventionally known method using this pitch and a spinning machine having a nozzle pack having a capillary diameter of 0.14 mm and a number of nozzle holes of 3000. Then, the pitch fibers were stored in a can while being bundled with an air sucker without using an oil agent.

With the pitch fiber stored in the can,
Nitrogen dioxide gas was added to the air in an amount of 5% by volume and steam was added in an amount of 5% by volume, and the temperature was raised from 150 ° C. to 300 ° C. at 1 ° C./min while blowing in an oxidizing gas from the bottom of the can.
The infusible fiber was obtained by maintaining the temperature at 300 ° C for 30 minutes.

The can containing the infusible fiber is left as it is under nitrogen gas atmosphere to remove the infusible fiber at 10 ° C./min.
Then, the temperature was raised to 300 ° C. to 600 ° C., the temperature was maintained for 30 minutes to carry out primary carbonization.

FIG. 1 shows the results obtained by measuring the elongation at break of the single yarn of the obtained fiber and the breaking strength of the fiber yarn at a length of 1 m.

The primary carbonized yarn was passed through a furnace having an inlet temperature of 500 ° C., an outlet temperature of 1100 ° C. and a length of 2 m while linearly feeding the fiber yarn from the can at a speed of 4 m / min, The obtained secondary carbonized fiber was wound on a bobbin.

Next, the secondary carbonized fiber was graphitized at a temperature of 2300 ° C. while rewinding the yarn from the bobbin to obtain a graphitized fiber.

If the primary carbonization temperature is less than 350 ° C., 2
During the subsequent carbonization, the yarn became rigid and fractured.

On the other hand, when the primary carbonization temperature is 350 ° C. or higher, the yarn is not rigid, but when the primary carbonization temperature is 400 ° C. or higher, graphitized fibers with a lot of fuzz are obtained, and the primary carbonization temperature is 350 ° C. Those having a temperature of up to 390 ° C. were free of fiber fluff, and beautiful graphitized fibers could be obtained.

[0055]

INDUSTRIAL APPLICABILITY According to the present invention, carbon fibers can be produced with good productivity, and the obtained fibers are beautiful with no fluff.

[Brief description of drawings]

FIG. 1 is a relationship diagram of a treatment (firing) temperature in a carbonization treatment, strength, and elongation.

FIG. 2 is a spectroscopic analysis diagram before carbonization of infusible fibers.

FIG. 3 is a spectroscopic analysis diagram after carbonization of infusible fibers.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihisa Nishikawa 1 Fuji-machi, Hirohata-ku, Himeji City Nippon Steel Corporation Hirohata Works

Claims (2)

[Claims] 1. A pitch made from mesophase pitch as a raw material
Wrap the fiber thread around the bobbin, or
It is deposited so that it can be discharged, and these are directly added to nitrogen dioxide (N
O ₂) And oxygen (O₂) Insoluble in an oxidizing gas atmosphere containing
Treatment, then 10 mi above 350 ° C and below 400 ° C
firing in an inert atmosphere for n or more to primary carbonize, then thread
Secondary carbonization is carried out while continuously feeding the strips in a linear fashion.
And then graphitize if necessary.
Carbon fiber manufacturing method. 2. The secondary carbonization is carried out while the yarn is continuously conveyed linearly at a temperature of 800 to 1300 ° C. for 5 seconds to 2 minutes, and then graphitization is carried out if necessary. The method described.