JPH09143823A - Production of carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carbon fiber having a high performance at a low cost by stably executing the flame resistant treatment of an acrylic precursor fiber for a carbon fiber in a heated air under a specific condition in a short time without using any special device. SOLUTION: This method for producing a carbon fiber is to treat an acrylic precursor fiber for the carbon fiber to make it flame resistant in a heated air by adding an elongation so as to give 50-200g/d tension until attaining 1.22g/cm<3> fiber density. It is possible to conduct the treatment to make the fiber flame resistant is a short time as approximately 25min while preventing the fiber from a cutting by melting or a winding to a roll.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for efficiently and stably producing carbon fibers.

[0002]

BACKGROUND OF THE INVENTION Carbon fiber is widely used for sports / leisure applications because it is lightweight and has excellent strength and elastic modulus. In recent years, its performance has been further improved, and primary structural materials for space / aircraft, etc. It is starting to be used as well. However, since it is still more expensive than the conventionally used metal materials and the like, its development to the general industry / industrial field has been delayed, and is currently limited to special applications.

The basic factor of the high cost of carbon fibers is their poor productivity, and above all, the fact that the flame resistance treatment of acrylic precursor fibers is inefficient. The flameproofing treatment of the acrylic precursor fiber is an exothermic reaction and is accompanied by a large amount of heat generation. For this reason, when a rapid flameproofing treatment is performed, a runaway reaction is induced by heat storage, and the fiber may be melted and cut or, in an extreme case, ignited. In order to avoid such a runaway reaction, it is usually short for about 1 hour, and if long,
It is usual to perform the flameproofing treatment for several hours, which causes the productivity to be remarkably reduced.

As a method for shortening the flameproofing treatment time, Japanese Patent Publication No. 53-21396 discloses a method of intermittently and repeatedly contacting acrylic precursor fibers with the surface of a heating body. According to this method, The acrylic precursor fiber is apt to cause fusion, and even if the obtained flame-resistant fiber is carbonized, it is not possible to obtain a carbon fiber that can be practically used.

Japanese Unexamined Patent Publication (Kokai) No. 58-214525 discloses a method of treating an acrylic precursor fiber in a heating and oxidizing atmosphere while intermittently contacting it with a cooling roller. Since the temperature of the fiber is high, the fiber is not cooled quickly on the roller, and the staying time in the flameproofing treatment chamber is not specified, so depending on the conditions, fusion of the fiber is likely to occur and stable treatment is possible. Can't do.

JP-B-51-9410 discloses that the zone where the fiber is subjected to heat treatment is separated from the zone where the fiber is accommodated, and the ambient temperature of the zone where the fiber is subjected to the heat treatment is separated from the zone where the fiber is heat treated. Although a method of treating the fiber while keeping the temperature lower than the temperature is disclosed, even in this method, since the residence time in the heat treatment chamber is not specified,
Stable processing cannot be performed.

Japanese Laid-Open Patent Publication No. 3-220321 discloses a flame resistance in which an area including a roller group and a heat treatment area are separated from each other, a time for passing through the heat treatment area is defined, and a temperature of an area including the roller and the roller group is specified. A chemical reactor is disclosed. According to this method, the flame-resistant fiber for carbon fiber can be certainly obtained in a short time, but the apparatus is complicated and expensive.

Japanese Unexamined Patent Publications No. 5-175523 and No. 4-163322 disclose a flameproofing method and apparatus using a fluidized bed. However, in this method, the apparatus is complicated and expensive. Instead, a step of removing the fluidized bed is required.

Further, JP-A-60-88128, JP-A-60-246821 and JP-A-62-257.
Japanese Patent No. 422 discloses that when a flame-proofing treatment is carried out in a hot-air circulation flame-proofing furnace which is industrially used and has a simple furnace structure, the acrylic precursor fiber is stretched to obtain high strength and high elasticity carbon. Although a method for obtaining fibers has been disclosed, stable flame-resistant fibers for carbon fibers cannot be obtained by this method unless the flame-proofing treatment time is long. When the flameproofing treatment temperature is increased to shorten the flameproofing treatment time and the flameproofing treatment is carried out in a short time, excessive tension is applied to the acrylic precursor fiber, and fluffing or cutting occurs.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a method for inexpensively obtaining a high-performance carbon fiber which is stably flame-proofed in a short time without using a special device. The challenge is to provide.

[0011]

According to the present invention, when the acrylic precursor fiber for carbon fiber is flame-resistant in heated air, the tension is 50 until the fiber density reaches 1.22 g / cm ^3.
The above problem is solved by a method for producing carbon fiber, which is characterized in that flame resistance treatment is performed by adding elongation so as to be 200 mg / d.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In order to finish the flameproofing treatment of the acrylic precursor fiber in a short time, it is necessary to treat it at a high temperature, but as described above, the flameproofing treatment of the acrylic precursor fiber is an exothermic reaction. However, since a large amount of heat is generated, a rapid flameproofing treatment may induce a runaway reaction due to heat storage, and the fiber may be melted and cut or, in an extreme case, ignited. Therefore, it is necessary to set the preset temperature of the flameproofing treatment furnace within a range that does not induce a runaway reaction of the acrylic precursor fiber to be treated.

Particularly, in the initial stage of the flameproofing treatment, if elongation is applied so that the tension of the acrylic precursor fiber exceeds 200 mg / d, the temperature at which the fiber is cut becomes low and the treatment cannot be performed at a high temperature. In addition, when the tension of the acrylic precursor fiber is extended so as to be less than 50 mg / d and subjected to the flameproofing treatment, the orientation of the fiber is relaxed, and it is not possible to obtain a high-performance carbon fiber. Since the fibers are easily wrapped around the roll for flameproofing, stable treatment cannot be performed.

Therefore, in order to perform the flameproofing treatment stably in a short time, the tension is 50 to 20 at the beginning of the flameproofing treatment, that is, until the fiber density reaches 1.22 g / cm ^3.
It is necessary to add elongation so as to obtain 0 mg / d and perform flameproofing treatment.

[0015]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

(Example 1) Using a hot air circulation type flameproofing furnace having four temperature zones, the first zone, the second zone, the third zone, and the fourth zone are arranged in the order in which the fibers pass through each temperature zone. Call. The density of the fibers exiting each zone was 1.22 g / cm ³ in the first zone and 1.27 g / c in the second zone.
m ^3, 1.32 g / cm ³ in the third zone, made to be 1.36 g / cm ³ in the fourth zone, and, the temperature was set so that the furnace residence time of the fiber in total 25 minutes.

A drive roll for continuously feeding the acrylic precursor fibers was provided before the flameproofing step, and a drive roll was provided between the first zone and the second zone and also after the flameproofing step. Each of the drive rolls was configured so that the front and rear tension could be divided.

The tension in the first zone of the fiber is 100 mg /
d, the tension of the second zone and the third zone is 250 mg / d
And subjected to flameproofing treatment under the above conditions.
Subsequently, preliminary carbonization was performed in an inert atmosphere at 300 ° C to 600 ° C, and carbonization treatment was performed in an inert atmosphere at a maximum of 1400 ° C. The carbon fiber obtained has a strength of 460 kg /
mm ^2, has high performance and modulus 25t / mm ^2, it was not at all fluff generation.

Example 2 The tension of the first zone of the fiber is 2
The flameproofing treatment and the carbonization treatment were performed in the same manner as in Example 1 except that the elongation was set to be 00 mg / d. Generation of fluff was slightly observed, but the carbon fiber obtained had a strength of 44.
It had a high performance of 5 kg / mm ² and an elastic modulus of 25 t / mm ² .

(Comparative Example 1) The tension of the first zone of the fiber was 2
When the flameproofing treatment was performed in the same manner as in Example 1 except that the fiber was stretched to 50 mg / d, the fiber was cut in the first zone.

Example 3 The tension of the first zone of the fiber is 5
The flameproofing treatment and the carbonization treatment were performed in the same manner as in Example 1 except that the elongation was set to 0 mg / d. Generation of fluff was slightly observed, but the carbon fiber obtained had a strength of 440.
It had high performance of kg / mm ² and elastic modulus of 25 t / mm ² .

(Comparative Example 2) The tension of the first zone of the fiber was 4
When the flameproofing treatment was performed in the same manner as in Example 1 except that the fiber was wound so as to be 0 mg / d, the fiber was wrapped around the roll in the first zone and could not be flameproofed.

[0023]

EFFECTS OF THE INVENTION According to the present invention, by only defining the tension at the initial stage of flame resistance to a specific range, stable flame resistance treatment can be performed in a short time of 25 minutes, and a high performance and high quality carbon fiber can be obtained. It can be obtained at low cost.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Hayashi 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory

Claims (1)

[Claims] 1. When the acrylic precursor fiber for carbon fiber is flame-resistant in heated air, the density of the fiber is 1.22 g / cm ^3.
Until reaching, the method for producing a carbon fiber is characterized in that elongation is applied so that the tension becomes 50 to 200 mg / d, and flameproofing treatment is performed.