JPH0796725B2 - Pitch-based carbon fiber manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a pitch-based carbon fiber, and more particularly, to a method for stably producing a pitch-based carbon fiber exhibiting improved physical properties. Is.

Conventional technology Carbon fiber was originally manufactured from rayon,
In terms of its characteristics and economy, it is currently occupied by PAN-based carbon fibers made from polyacrylonitrile (PAN) fiber and pitch-based carbon fibers made from coal or petroleum pitch. Among them, the technology for producing high-performance grade carbon fiber using pitch as a raw material is attracting attention because it is excellent in economic efficiency.For example, pitch fiber obtained by melt spinning of optically anisotropic pitch is made infusible. -It is known that the fired carbon fiber has higher strength and higher elastic modulus than the conventional pitch-based carbon fiber (Japanese Patent Publication No. 54-1).
No. 810).

Such a pitch-based carbon fiber manufacturing process generally includes a pitch preparation step, a pitch melt-spinning step, a pitch fiber infusibilization treatment step, and carbonization or graphitization by heating the infusible fiber at a higher temperature to form carbon fibers. It consists of a firing process.

Among these, the infusibilizing step is an indispensable step for carbonizing the pitch fiber without melting it, and a method of heating for a long time in high temperature air is generally adopted.
This infusibilization by air or oxygen basically utilizes the oxidation reaction of the pitch fiber, but if this is insufficient, fusion between fibers occurs, and if it is excessive, carbonization of the fiber after carbonization occurs. Strength and Young's modulus decrease. Therefore, the infusibilizing step is an important step that affects the physical properties of fibers in the industrial production of pitch-based carbon fibers. However, the optimum conditions for infusibilization by air have not been clarified yet,
In addition, there are still problems with the reproducibility of the physical properties of the fiber, and it can be said that this is technically incomplete.

As the infusibilized yarn that replaces air, for example, one using ozone (Carbon.vol 3,31 (1965)), one using air containing NO ₂ (JP-A-55-98914), and a mixed gas of chlorine and air are used. What is used (JP-A-49-75828), one that is soaked in saturated chlorine water and then air-oxidized (JP-A-49-72828), treated with fine powder of activated carbon impregnated with sulfuric acid and bromine gas, and then air-oxidized (Japanese Patent Application Laid-Open No. 49-72828), one that is treated with fine powder of activated carbon impregnated with sulfuric acid and bromine gas, and then air-oxidized (13th Conference on Carbon, p94 (1977)). This method is also intended to substantially shorten the infusibilizing treatment time and does not have the effect of improving the physical properties of the fiber after carbonization.

The main object of the present invention is to stably and efficiently improve the physical properties of carbon fiber after firing by adopting a novel infusibilizing method in the production of pitch-based carbon fiber. It is to provide a method to do.

Means for Solving the Problems According to the present invention, when the pitch fiber obtained by melt-spinning the pitch containing 50% or more of the optically anisotropic region is fired to produce a carbon fiber. , 100 to 400 ° C. (preferably 200 ° C. to 350 ° C.) in an atmosphere in which iodine and oxygen coexist in the pitch fiber and iodine is 0.01 mol% or more
Infusibilized at the temperature of 1000 ℃, then 1000 ℃ in an inert atmosphere
This is achieved by the method of firing at the above temperature, and thus it becomes possible to produce a pitch-based carbon fiber having a high strength of about 600 kg / mm ² or more.

As the spinning pitch, which is the raw material of the pitch fiber used in the method of the present invention, petroleum-based or coal-based pitch is used.
The method of the present invention has the effect of shortening the infusibilizing treatment time regardless of the composition of the pitch, and improving the physical properties of the carbon fiber after the firing treatment. It is preferable to use a pitch having an anisotropic region of 50% or more, preferably 80% or more. The method for measuring the ratio of the optically anisotropic region referred to here is described in US Pat. No. 4,628,001.

The melting point of the spinning pitch according to the Mettler method is preferably 280 to 340 ° C, more preferably 290 to 330 ° C. Further, the proportion of the quinoline-soluble portion of the spinning pitch is preferably 30% by weight or more, and particularly preferably 50% by weight or more. The larger the ratio of the optically anisotropic region of the spinning pitch that is preferably used in the present invention (hereinafter referred to as the amount of optical anisotropy), the better. Such a pitch has a homogeneous system and is excellent in spinnability.

Raw materials for such spinning pitch include, for example, coal-based heavy oil such as coal tar pitch and coal liquefaction, atmospheric residual oil of petroleum, vacuum distillation residual oil, and by-products of heat treatment of these residual oils. Using refined petroleum heavy oil such as tar, pitch, oil sand, bitumen,
By subjecting this to a combination of heat treatment, solvent extraction, hydrogenation, etc., a spinning pitch can be obtained.

When melt-spinning the pitch, as the hole shape of the preferred spinning nozzle, the centerline distance of the wetting edge in the spinning hole of the spinning nozzle as described in U.S. Pat.No. 4,628,001 is Ln, and when the wetting edge width Wn is at least Ln, It is preferable to use a non-circular one, more preferably a slit-shaped one, which simultaneously satisfies the following two equations Ln <10 mm 1.0 <Ln / Wn ≦ 20.

By spinning using the above method, the generation of cracks in the cross section of the carbon fiber can be suppressed.

In melt spinning, the spinning temperature is preferably lower than 360 ° C. The spinning draft rate is 30 or more, especially 50.
The spinning speed is preferably 100% to 1500 m / min.

According to the method of the present invention, the pitch fiber thus obtained is subjected to an infusibilizing treatment in a state where iodine and oxygen coexist, and then heated in an inert atmosphere to be fired to obtain a high-performance pitch-based carbon fiber. However, it has a feature.

This method substantially eliminates the infusibilizing step with air, which has been considered as an essential step in the conventional pitch-based carbon fiber manufacturing method.

The concentrations of iodine and oxygen in the mixed gas used in this method are not particularly limited. However, in order to efficiently carry out the present invention, it is preferable that the iodine concentration in the mixed gas is 0.01 (mol)% or more and the oxygen concentration is 1 (mol)% or more. However, when the iodine concentration is 0.01 (mol)% or less, or the oxygen concentration is 1 (mol)% or less,
It is industrially unfavorable because it takes a long time to process. Further, it is economically advantageous to use air instead of oxygen gas.

The mixed gas used in the present invention includes components other than iodine, oxygen or air, such as carbon monoxide, carbon dioxide, nitrogen,
It can contain nitrogen oxides, noble gases, hydrocarbon gases and the like.

In the method of the present invention, the pitch fiber is treated with a mixed gas containing iodine and oxygen at a temperature of 100 ° C to 400 ° C as described above. Ten
If the temperature is lower than 0 ° C, the time required for the treatment becomes extremely long, which is unsuitable for industrial production. At temperatures above 400 ° C, the suitable processing time is extremely short, and strict management of the processing time is required.

Further, the more preferable range of the treatment temperature is 200 ° C to 350 ° C.

Here, the treatment temperature is the maximum heat history temperature received in the mixed gas when the pitch fiber is treated with the mixed gas containing iodine and oxygen, before reaching that temperature, or
The pattern of the temperature history thereafter is not limited at all.

Further, the atmospheric pressure at the time of processing is not limited, either,
The higher the pressure, the more efficiently the effect can be exhibited.

The infusibilizing treatment time in the method of the present invention is not particularly limited, but it is preferable to satisfy the range of the following formula.

Here, T (° C) is the infusibilizing temperature, and t (min) is the processing time at T ° C.

Thus, the pitch fibers treated with a mixed gas containing iodine and oxygen are fired at a temperature of 1000 ° C. or higher in an inert atmosphere to carbonize them, and if necessary, further graphitized to obtain excellent physical properties. It is possible to produce a pitch-based carbon fiber having

Action / Effect The carbon fiber obtained by the above method has higher elongation and higher strength than those obtained by infusibilizing pitch fiber spun in the conventional manner with air, and has excellent reproducibility of physical properties. It becomes a thing. Further, when compared at the same temperature and the same pressure, the time required for the infusibilizing treatment is drastically shortened as compared with the case of the above conventional method.

Although the mechanism by which the above-mentioned effects are exhibited by the method of the present invention has not been completely clarified, it can be explained as follows. That is, iodine alone reacts with the pitch,
The molecules in the pitch are made to have a high molecular weight, the aromaticity of each molecule is improved, and the viscosity of the pitch is rapidly increased. This fact can be proved quantitatively because it is possible to observe a decrease in the amount of aliphatic hydrogen in the pitch by infrared absorption measurement after the reaction of iodine pitch.
Also, at this time, iodine itself is extremely unlikely to bond to the pitch molecule by a chemical reaction. By combining the effect of iodine with the effect of oxygen, the infusibilizing treatment can be completed in a state where the degree of oxidation by oxygen is extremely low, that is, the oxygen content in the pitch fiber after the treatment is low.
Generally, the oxygen introduced into the pitch fiber by infusibilization with air is gasified and desorbed as a low molecular weight carbon oxide in the initial stage of the subsequent carbonization treatment. The generation of this gas causes defects on the surface and inside of the fiber, disturbs the crystal structure in the fiber, and further lowers the yield of the carbonization reaction. According to the method of the present invention, it is possible to minimize the above-mentioned adverse effects due to oxygen introduced into the fiber, and therefore it is possible to produce a high performance pitch-based carbon fiber with extremely few defects.

As a method of treating pitch fibers in the coexistence of iodine and oxygen, a method of doping pitch fibers with a very small amount of iodine and then treating them in air is known. However, in this method, the iodine that is doped during the treatment in air volatilizes from the fiber, and the elimination and reaction of iodine occur competitively. According to the method of the present invention, since the fibers can always be treated in a state close to equilibrium with respect to the iodine concentration in the atmosphere, the treated state can be reproduced exactly, and as a result, it is possible to carry out a suitable infusibilizing treatment in a wider temperature range. is there.

Further, the method of the present invention has a process advantage that the infusibilization can be performed in a single step, as compared with the above-mentioned method which requires two steps of doping and air treatment.

In the case of chlorine, which is the same halogen group, the infusibilizing effect may exist, but chlorine has an excessive oxidizing power than iodine, and an excessive excessive oxidation reaction occurs locally to improve the physical properties of carbon fiber after firing. Have difficulty. In the case of iodine, the oxidizing power is relatively weak, but iodine and the pitch molecule form a charge transfer complex, so that iodine is absorbed by the pitch fiber and distributed uniformly in an extremely short time. As a result, the reaction progresses uniformly and mildly from the surface layer of the fiber to the central part. Therefore,
Among the halogen group, iodine can be said to have a specific effect on the infusibilization of the pitch fiber with respect to its reactivity and diffusivity.

Thus, in the method of the present invention, by treating the pitch fiber with a mixed gas containing iodine and oxygen, it is possible to significantly improve the physical properties of the carbon fiber after firing, and as shown in Examples described later, strength and elongation.・ The modulus is comparable to or superior to the physical properties of PAN-based carbon fiber, and at the same time, the infusibilization step by air, which has been an essential step of the conventional pitch-based carbon fiber manufacturing method, is substantially unnecessary. is there.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.
The strength, elongation, Young's modulus, etc. of the fibers shown in this example are
It is the value measured according to JIS R7601.

Example 1 Using commercially available coal tar as a raw material and having an optical anisotropy amount of 92%, a quinoline-soluble portion of 95.4% and a melting point of 305 ° C. according to the Mettler method according to the method described in JP-A-59-53717. A spinning pitch was prepared.

The spinning pitch was charged into a fixed-quantity feeder equipped with a heater, and after melting and defoaming, slit width was 60 microns, center line distance was 54
Melt spinning was performed on a spinneret with a 0 micron single slit spin hole.

In this case, the feeder discharge rate was set to 0.032 ml / min / hole, the die temperature was 335 ° C, and the winding speed was 600 m / min.

The pitch fiber was heated from room temperature to 225 ° C. at a heating rate of 2.5 ° C./min in an iodine-air mixed gas containing 0.5 (mol) iodine, and kept at 225 ° C. for 2 hours.

Then, at a heating rate of 500 ° C / min in a nitrogen atmosphere, 1300 ° C.
It was heated up to and heated (carbonized). As a result of measuring physical properties, this carbon fiber has a strength of 620 kg / mm ² , an elongation of 2.4% and a Young's modulus.
It showed an excellent value of 26 T / mm ² .

Examples 2 to 4 Carbon fibers were produced in the same manner as in Example 1 except for the iodine concentration in the air-iodine mixed gas and the treatment temperature and time with the mixed gas. The results of measuring the physical properties of the obtained carbon fiber are shown in Table 1.

Comparative Example 1 Pitch fibers were prepared by spinning in exactly the same manner as in Example 1. This pitch fiber was heated to 350 ° C. in air at a temperature rising rate of 2.5 ° C./min and held at 350 ° C. for 30 minutes.

Then, in a nitrogen atmosphere, the temperature was raised to 1300 ° C. at a temperature rising rate of 500 ° C./minute to perform firing treatment. As a result of measuring physical properties, the carbon fiber had a strength of 405 kg / mm ² , an elongation of 1.87% and a Young's modulus of 21.7 T / mm ² .

Comparative Example 2 Pitch fibers were obtained by spinning in exactly the same manner as in Example 1. This pitch fiber was heated in air from room temperature to 225 ° C. at a heating rate of 2.5 ° C./min and held at 225 ° C. for 2 hours.

Next, when the temperature was raised to 1300 ° C. at a temperature rising rate of 500 ° C./min in a nitrogen atmosphere, the fibers were fused during the temperature rise.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-28019 (JP, A) JP-A-62-191518 (JP, A) European Patent Publication 169023 (EP, A)

Claims (2)

[Claims] 1. A pitch fiber obtained by melt-spinning a pitch containing 50% or more of an optically anisotropic region is fired to produce a carbon fiber, wherein iodine and oxygen coexist in the pitch fiber, And 100 in an atmosphere containing 0.01 mol% or more of iodine.
A method for producing pitch-based carbon fibers, which comprises infusibilizing treatment at a temperature of up to 400 ° C and then firing treatment at a temperature of 1000 ° C or higher in an inert atmosphere. 2. As a melt-spun pitch fiber, where Ln is the centerline distance of the wetting edge in the spinning hole and Wn is the wetting edge width, the following two equations Ln <10 mm 1.0 <Ln / Wn ≦ 20 are satisfied. The method for producing a pitch-based carbon fiber according to claim 1, wherein a fiber spun from a slit-shaped spinning hole that is simultaneously satisfied is used.