JPH0681221A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To provide a process for improving the productivity of the graphitization process for a pitch-based carbon fiber and the quality of the product. CONSTITUTION:A pitch fiber produced by using a mesophase pitch as a raw material is oxidized in an oxidizing atmosphere containing nitrogen dioxide and oxygen, baked in an inert gas atmosphere at 350-400 deg.C for >=10min and continuously carbonized at 800-1300 deg.C. In this processed, the baking of the fiber is carried out while applying a tension of 50-2,500g/mm<2> to the fiber. The yarn is cut at a broken part of the yarn before winding the carbon fiber on a bobbin or receiving in a receptor.

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, the pitch fiber is fragile and the strength of the infusible fiber which is an intermediate step product is 5 to 10 kg /
Since the fiber is extremely brittle at mm ² , the fiber is 100 to 10
The infusible fiber yarns, which are aggregated into 30,000 fibers, are difficult to handle, and there are problems that the yarns are easily broken and long fibers are difficult to produce, and fuzz is often generated.

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.

Further, in Japanese Patent Application Laid-Open No. 60-126324, the fiber is heated to a breaking elongation of more than 2.5% for carbonization, and then the fiber yarn is carbonized under tension at higher temperature and atmosphere. A method for producing a carbon fiber bundle having good filament alignment by graphitization is described.

On the other hand, there is a method of using nitrogen dioxide as an infusibilizing gas to improve productivity such as shortening the infusibilizing treatment time or to improve physical properties of carbon fiber.
No. 9 or Japanese Patent Laid-Open No. 2-6618 discloses a method of mixing nitrogen dioxide and steam.

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).

Further, due to the shrinkage of the fibers, the uniformity of the fibers is poor and the development of the physical properties is unstable, and the yarn breaks in the graphitization process, which causes a decrease in the productivity.

In the graphitization process, the temperature is 2000 to 3000 ° C.
Generally, the yarn is conveyed linearly for a very short time of several seconds to several minutes.

At this time, in order to improve the productivity, it is common to pass several to several hundred yarns through one graphitizing furnace, and these yarns were installed before and after the graphitizing furnace. Driven by rollers.

The drive roller is provided in order to simplify the equipment.
A single roller conveys a plurality of yarns, and if even one of the plurality of yarns breaks, the conveyance of all yarns is stopped and the broken yarns are restored.

Therefore, the fiber once stopped in the furnace cannot be made into a product, and the productivity is remarkably reduced.

Therefore, it is desired to develop a technique for preventing breakage of the yarn in the graphitization process.

[0022]

DISCLOSURE OF THE INVENTION The present invention is directed to handling such as eliminating yarn breakage and fusion of yarn when carbonizing and graphitizing infusible fibers obtained by using nitrogen dioxide gas. The object of the present invention is to provide a method of improving the productivity and further improving the productivity and quality of the carbonization and graphitization treatment steps.

[0023]

According to the present invention, pitch fibers made from mesophase pitch as a raw material are oxidized in an oxidizing gas atmosphere containing nitrogen dioxide and oxygen, and the oxidized fibers are heated to 350 ° C.
Firing at ~ 400 ° C for 10 min or more in an inert atmosphere,
After that, when continuously carbonizing at a temperature of 800 to 1300 ° C., a method for producing a carbon fiber, which comprises firing while applying a tension of 50 to 2500 g / mm ² to the yarn, and 800 to 1300 ° C. When the fiber is continuously carbonized at the temperature of, and the fiber is continuously received by the bobbin or the receiver, the yarn is forced to be rigid or partially broken before it is received by the bobbin or the receiver. It is a method for producing a carbon fiber, which is characterized by cutting.

The contents of the present invention will be described in detail below.

The pitch which is the starting material of 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.

The mesophase pitch is preferably such that the pitch fibers are highly oriented when spun, and therefore the mesophase content is preferably 40% or more, more preferably 70% or more.

The softening point of the mesophase pitch used in the present invention is 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).
20% by volume, 2 to 10% by volume of water vapor as needed, and an oxidizing gas atmosphere in which the remaining gas is an inert gas such as nitrogen, temperature 100 to 320 ° C., treatment time 30 to 3
It is infusibilized under the condition of 00 min, preferably 40 to 200 min.

It is essential 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.

FIG. 1 shows the infusible fiber at 30 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
Although it shows the maximum value at the carbonization temperature of about 50 ° C., it is understood that the breaking strength of the carbonized fiber yarn gradually increases from the infusibilized yarn at the firing temperature of 390 ° C., and sharply decreases at 400 ° C. or higher.

Although the cause is not clear, although the average strength and the elongation at break of the single fiber are improved as the carbonization temperature is increased, the variations are increased.

At a carbonization temperature of less than 400 ° C., both the strength and the elongation at break of the single fiber are smaller than those of the carbonized yarn of about 400 to 500 ° C., but there is little variation, and it is considered that the strength development rate when formed into a yarn is high.

Moreover, at a carbonization temperature of 400 ° C. or higher, the fiber length is about 3.2% during the carbonization process, and at 500 ° C., it is 4.5%.
Shrinks about%.

Therefore, the length of the monofilament in the yarn becomes non-uniform due to shrinkage during carbonization, the alignment of the fibers is disturbed, the strength of the carbonized fiber yarn is remarkably reduced, and the final product carbon fiber or graphitized. It significantly reduces the quality of the fiber.

Therefore, when carbonization (secondary carbonization) is performed at a temperature of 800 to 1300 ° C., 50 to 2500 g /
By performing the firing while applying a tension of mm ² , more preferably 60 to 1000 g / mm ² , it becomes possible for the first time to make uniform shrinkage in the fiber length direction that occurs at a carbonization temperature of 400 ° C. or higher, so that the yarn alignment An improved yarn can be obtained.

The tension when carrying out the secondary carbonization is 50 g / mm.
^If it is less than ² , the alignment of the fiber threads is not improved, and it is 2500
If it exceeds g / mm ² , the yarn is likely to break during secondary carbonization.

On the other hand, when the primary carbonization temperature is lower than 350 ° C., when the yarn is continuously carbonized (secondary carbonization) at a temperature of 800 to 1300 ° C. for 5 seconds to 2 minutes, decomposition occurs during carbonization. Depending on the object, problems such as fusion of fibers or rigidity occur.

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

The infusibilized fiber obtained by the infusibilization containing nitrogen dioxide gas contains a certain amount of nitrogen compound and needs to be carbonized at a certain temperature and for a certain period of time. Fusion of fibers by carbonization,
Rigidity can be seen.

When the temperature of the secondary carbonization is lower than 800 ° C.,
The strength of the secondary carbonized yarn is low, it is difficult to handle in the next graphitization process, and when it exceeds 1300 ° C., the elastic modulus of the secondary carbonized fiber becomes large, and the secondary carbonized yarn was wound on the bobbin. In this case, problems such as fuzzing occur.

By obtaining the secondary carbonized yarn by setting the production conditions as described above, the productivity in the next graphitization step is extremely improved.

However, in the case of pitch-based carbon fibers, since fragile pitch fibers are used as a starting material, defects in carbonized yarns are inevitable, for example, fusion between fibers or stiffness occurs, or fiber yarns are produced. It is extremely difficult to get rid of the part that is partially damaged and partially broken.

Therefore, before winding the secondary carbonized yarn on a container such as a can or a bobbin, the yarn is detected visually or by an optical detection device to detect a partial defect in the fiber yarn. By forcibly cutting the filaments and removing the defective parts, it becomes possible to supply carbonized filament yarns that do not contain any defects in the next step, the graphitization step, further improving the productivity of the graphitization step. As a result, the productivity of carbon fiber products can be significantly improved.

[0048]

EXAMPLES Various physical properties obtained in the examples 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 and pyridine-insoluble matter Toluene-insoluble matter and pyridine-insoluble matter are JIS-K-242.
5 (1978).

(3) Single yarn breaking elongation, graphitized yarn strength and elastic modulus It 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 measurement length of the thread consisting of 3000 fibers is 1 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 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%.

Using this pitch, the capillary diameter of 0.
Using a spinning machine having a nozzle pack with 14 mm and 3000 nozzle holes, the viscosity of the mesophase pitch is 800.
A pitch fiber having a yarn diameter of 13 μm was spun by poise, and the pitch fiber was stored in a can while being focused with an air sucker without using an oil agent.

While the pitch fiber was stored in a can (container), an oxidizing gas obtained by adding 5% by volume of nitrogen dioxide gas and 5% by volume of steam to the air was blown from the lower part of the can to 150 ° C. to 300 ° C. The temperature was raised at 1 ° C./min, and the temperature was kept at 300 ° C. for 30 minutes to obtain infusible fibers.

The can containing the infusible fiber is left as it is under a nitrogen gas atmosphere to remove the infusible fiber at 10 ° C./min.
At 300 ° C to 600 ° C at that temperature for 3
It was held for 0 min to carry out primary carbonization.

The breaking elongation of the single yarn of the obtained fiber and the breaking strength of the fiber yarn at a length of 1 m were measured and the results are shown in FIG.

The primary carbonized yarn was introduced into a furnace having an inlet temperature of 500 ° C., an outlet temperature of 1100 ° C., and a length of 2 m in a nitrogen gas atmosphere.
Secondary carbonization was carried out while passing through at a speed of 00 g / mm ² and a speed of 4 m / min, and the obtained secondary carbonized fiber was wound on a bobbin.

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, the yarns having a primary carbonization temperature of 350 ° C. or higher were not stiff, but the ones having a primary carbonization temperature of 400 ° C. or higher were secondary carbonized yarns with much fuzz.

Next, secondary carbonization was carried out with the primary carbonization temperature of 390 ° C. while changing the tension.

As shown in FIG. 2, the primary carbonized yarn 2 fed from the can 1 was given tension by the dancer roller 3 and passed through the secondary carbonization furnace 4.

Between the outlet of the furnace and the winding machine 2 for winding the yarn around the bobbin, the yarn is wound around a roll 7 having a diameter of 20 mm at an angle of about 90 degrees, and as shown in FIG. A yarn flaw detector 8 for detecting a partial breakage of a yarn or a rigid portion on the upper surface by a laser beam was installed, and after passing through two places, a secondary carbonized fiber was wound on a bobbin 9.

After that, the secondary carbonized fiber was wound around the bobbin and the tension was 300 g / m at a temperature of 2300.degree.
Graphitized fiber was obtained by performing graphitization in an argon atmosphere for 30 seconds while giving m ² .

The results are shown in Tables 1 and 2.

[0067]

[Table 1]

[0068]

[Table 2]

[0069]

EFFECTS OF THE INVENTION According to the present invention, it is possible to continuously pass a yarn for a long time by applying a tension at the time of the secondary carbonization, or by eliminating a yarn scratched portion after the secondary carbonization. In addition to being able to produce carbon fiber well, the obtained fiber was beautiful without fluffing.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a treatment temperature and strength / elongation in carbonization treatment.

FIG. 2 is a diagram showing an example of a production process of the present invention.

FIG. 3 is an explanatory diagram of yarn flaw detection according to the present invention.

[Explanation of symbols] 1 cans 2 primary carbonized yarn 3 dancer roller 4 secondary carbonization furnace 5 feed roller 6 secondary carbonized yarn 7 roll 8 yarn flaw detector 9 bobbin 10 yarn wound portion 11 laser beam

 ─────────────────────────────────────────────────── ─── 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 fiber thread made of mesophase pitch as a raw material is wound around a bobbin or is deposited so that the thread can be fed out as it is, and these are directly oxidized in an oxidizing gas atmosphere containing nitrogen dioxide and oxygen. Fusion treatment, and 35
It is fired in an inert atmosphere at 0 to less than 400 ° C. for 10 minutes or more to perform primary carbonization, and then the filament is fed out in a linear shape to 80
When secondary carbonization is carried out while continuously conveying at a temperature of 0 to 1300 ° C. for 5 seconds to 2 minutes, 50 to 2500 g /
A method for producing a carbon fiber, which comprises secondary carbonizing while applying a tension of mm ² . 2. Continuously at a temperature of 800 to 1300 ° C.
When the subsequent carbonization is performed and the fibers are continuously received by the bobbin or the receiver, the rigid or partially broken part of the yarn is detected before the fiber is received by the bobbin or the receiver, and the yarn is forced at that position. The method for producing a carbon fiber according to claim 1, wherein the carbon fiber is cut into pieces.