JPH11229232A - Method for producing acrylonitrile-based precursor fiber for carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acrylonitrile-based precursor for carbon fiber which can easily exhibit high strength and high modulus even when formed into carbon fiber by densifying and homogenizing the fiber structure. It is an object of the present invention to provide a fiber and a production method excellent in economy. SOLUTION: As a monomer component, acrylonitrile is contained in an amount of 98% by weight or more and a carboxylic acid group is 5.0 × 10 ^-5 to
An acrylonitrile-based precursor fiber for carbon fiber, which is spun by using a dimethylformamide or dimethylsulfoxide solution containing 2.0 × 10 ⁻⁴ equivalents / g of acrylonitrile-based polymer and ammonia as a stock solution for spinning. Manufacturing method.

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 acrylonitrile-based precursor fibers for producing carbon fibers or graphite fibers, and more particularly, to a highly dense acrylonitrile-based fiber suitable for producing carbon fibers having high strength and high elasticity. The present invention relates to a method for producing a precursor fiber and an acrylonitrile-based precursor fiber for carbon fiber obtained by the method.

[0002]

2. Description of the Related Art Conventionally, carbon fibers and graphite fibers (hereinafter collectively referred to as carbon fibers) having an acrylic fiber as a precursor have been used for aerospace applications, sports, It is widely used as a reinforcing fiber material for high performance composites for leisure use. further,
Quality of carbon fiber for high performance of these composite materials,
Further improvement in performance is required, and further reduction in manufacturing cost is expected to spread to industrial materials.

[0003] Acrylonitrile fiber as a precursor of carbon fiber is an intermediate product for producing carbon fiber, which is a final product, unlike acrylic fiber for clothing. Therefore, what is required is to provide a carbon fiber having excellent quality and performance, and at the same time, it is possible to provide a precursor having excellent stability at the time of spinning the precursor, and having a high productivity in the firing step of forming the carbon fiber at a low cost. It is extremely important that they be things.

[0004] When producing high-performance carbon fibers, it is essential that the acrylonitrile-based precursor fibers, which are precursors thereof, be of high quality without defects, and have a more dense and homogeneous fiber structure. Is a necessary condition. Many proposals have been made from such a viewpoint. Among them, there are proposals such as increasing the degree of polymerization of a raw material polymer and reducing the content of a copolymer component other than acrylonitrile.

[0005] When the degree of polymerization of the raw material polymer is increased or the content of copolymerization components other than acrylonitrile is reduced, the solubility of the raw material polymer in the solvent generally decreases. For example, a highly soluble solvent such as dimethylformamide or dimethylsulfoxide is used. However, during coagulation, the precipitation coagulation property of the polymer becomes extremely high, and there is a problem that a devitrified coagulated yarn, that is, a coagulated yarn having a porous fiber structure is formed.

In order to suppress the devitrification, Japanese Patent Publication No.
JP 23588 proposes blending ammonia, an amine compound and the like into an organic solvent solution of an acrylonitrile copolymer. However, it is essential that the acrylonitrile copolymer described in this publication contains a sulfonic acid group-containing vinyl compound in addition to a carboxylic acid group-containing vinyl compound which is a starting point of a flame-resistant reaction. The inclusion of such a comonomer increases the number of defects at the time of firing, and is not preferable as a precursor fiber for carbon fiber.

Further, in the acrylonitrile-based polymer which is a raw material of the acrylonitrile-based precursor fiber, it is necessary to sufficiently consider not only the shaping property to the fiber but also the complicated thermochemical reaction in the firing step.

That is, in order to obtain a carbon fiber excellent in both performance and quality at a lower production cost, fusing (fusing) occurs and carbon fiber performance is reduced when a carbon structure is obtained by firing heat treatment. Desirably, the thermal reaction characteristics are such that the generation of a thermal decomposition product is small and the calcination can be performed in a short time.

[0009] Conversion from acrylonitrile fiber to carbon fiber involves significant physical and chemical changes, and the causal relationship between the two is extremely unclear. Various studies have been made on theoretical elucidation, but the present situation still includes many unsolved problems.

[0010] From an industrial point of view, few have quantitatively indicated which polymerization composition is suitable as the basic acrylonitrile-based polymer constituting the acrylonitrile-based precursor fiber.

Summarizing the findings from the conventionally proposed ones, acrylonitrile-based polymers for carbon fiber precursors include those containing acrylonitrile in a polymerization composition of at least a certain amount (about 90% by weight or more). Is preferable, and it is effective to introduce a suitable reaction-initiating group for passing the calcination process in a short time, that is, a functional group (for example, a carboxyl group) that promotes a cyclization condensation reaction of a nitrile group. While taking these conditions into consideration, a method of adding other comonomers to facilitate the shaping of the precursor fiber may be mentioned.

Heretofore, for example, when a polymer having a high acrylonitrile content in a polymer composition is used, the solubility in a solvent is reduced, and the production of precursor fibers must rely on a very limited method. Also, the concentration of the stock solution becomes dilute, and thus the carbon fiber performance and the spinning shape are not sufficiently satisfactory.

[0013] Further, the one in which the content of the copolymer component is increased in order to increase the degree of freedom in the spinning and shaping, is obtained by fusing (fusing) in the firing heat treatment of the precursor fiber using the same.
, And the carbonization yield is lowered, and the passability of the firing step and the quality and performance of the carbon fiber are still insufficient.

The following proposals have been made to overcome such various problems and at the same time suggest a composition of a raw material polymer which can be calcined in a shorter time, or which is advantageous for this.

For example, a method of improving the calcination rate and the carbonization yield by preparing a polymer composition having high cyclization and oxidation reactivity in flame resistance at the initial stage of calcination (Japanese Patent Publication No. 47-33)
No. 019), an attempt was made to shorten the calcination time while considering the stability in the polymer production and spinning process by limiting the polymer composition by using a vinyl carboxylate monomer (Japanese Patent Application Laid-Open No. 51-7209). Publication).

However, each of them merely presents a wide range of constitutions regarding the polymer composition, that is, the types and contents of the copolymerized monomers, and sufficiently satisfies the characteristics required for the precursor fiber such as the firing characteristics. It is not at all possible to disclose an appropriate composition. Furthermore, although it is thought that the reaction promotion itself by flame resistance enables high-speed sintering, the performance of the obtained carbon fiber tends to be rather impaired, and both the productivity and performance of the carbon fiber are improved. Has not been achieved.

Under these circumstances, Japanese Patent Laid-Open Publication No. 52-34027
Japanese Patent Laid-Open Publication No. H11-15064 discloses a method for economically and stably producing high-performance carbon fibers by limiting the polymer composition and further devising firing conditions. In particular, it is noteworthy that the combined use of (meth) acrylamide and the carboxyl group-containing monomer has a specific effect in promoting the flame-resistant reaction.

JP-A-5-339813 proposes to control the copolymerization composition of acrylonitrile and acrylamide methacrylic acid to carry out hot spinning to obtain a highly dense acrylonitrile-based precursor fiber. I have. Although this proposal has made it possible to compensate for the drawbacks of the conventional wet spinning method, it is insufficient as an acrylonitrile-based precursor fiber for obtaining higher performance carbon fibers.

As described above, although many methods have been proposed, acrylonitrile-based precursor fibers having high productivity and providing high-performance carbon fibers are used as precursor fibers for carbon fibers. Not yet obtained. In particular, while many proposals have been made regarding the acrylonitrile-based polymer composition in order to efficiently carry out the flame-resistant reaction in the firing step, the fiber structure is controlled in the coagulation step that governs the fiber structure, At present, there are no proposals for attempts to obtain precursor fibers for high-performance carbon fibers.

[0020]

DISCLOSURE OF THE INVENTION In view of such problems of the prior art, the present inventors have made intensive studies on densification and homogenization of the precursor fiber structure, and as a result, have reached the present invention. is there. That is, the present invention provides an acrylonitrile-based precursor fiber for carbon fiber that can easily exhibit high strength and high elastic modulus even when formed into carbon fiber by densifying and homogenizing the fiber structure, and is excellent in economical efficiency. To provide a manufacturing method.

[0021]

According to the present invention, there is provided an acrylonitrile-based polymer containing 98% by weight or more of acrylonitrile as a monomer component and containing 5.0 × 10 ^{−5 to} 2.0 × 10 ⁻⁴ equivalents / g of carboxylic acid groups. The present invention relates to a method for producing an acrylonitrile-based precursor fiber for a carbon fiber (hereinafter, also simply referred to as a precursor fiber), which is spun using a dimethylformamide or dimethylsulfoxide solution in which the coalesced and ammonia are dissolved as a spinning solution. .

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The acrylonitrile polymer used in the present invention contains 9% of acrylonitrile as a monomer component.
Contains 8% by weight or more. If the content is less than 98% by weight, the copolymer other than acrylonitrile becomes a defect point when carbon fiber is formed, which impairs the quality and performance of the carbon fiber.

The carboxylic acid group contained in the polymer plays a role of enhancing the oxidization resistance in the firing step, but also serves as a defect point of the carbon fiber. It is. That is, when the content of the carboxylic acid group is less than 5.0 × 10 ⁻⁵ eq / g, the thermal reactivity is low and the treatment at a higher temperature is required. If the treatment is performed at a high temperature, a runaway reaction is likely to occur, and it is difficult to obtain a stable firing process passage property. Conversely, firing at a low speed is required to suppress the runaway reaction, which is not economical.

The carboxylic acid group content is 2.0 × 1
When the amount exceeds 0 ^-4 equivalent / g, the ring-closing reaction of the nitrile group of the polymer is accelerated, so that the oxidation reaction does not proceed to the inside of the fiber, and the flame-resistant structure proceeds only in the portion near the fiber surface layer. However, in such a structure, in the next higher temperature carbonization step, the decomposition of the undeveloped portion of the flame resistant structure at the center of the fiber cannot be suppressed, so that the performance of the carbon fiber, particularly the tensile modulus, is remarkably reduced.

In the present invention, as a method for introducing a carboxylic acid group into an acrylonitrile-based polymer, a vinyl-based monomer having a carboxyl group such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid or the like may be used. And by copolymerizing with other monomer components. Among them, acrylic acid, methacrylic acid and itaconic acid are preferred.

The acrylonitrile polymer used in the present invention may be acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, in addition to acrylonitrile and the above-mentioned carboxylic acid group-containing vinyl monomer, as long as the requirements of the present invention are satisfied. And small amounts of monomers such as vinyl group-containing carboxylic acid esters such as crotonic acid, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, diacetone acrylamide, maleic anhydride, methacrylonitrile, styrene and α-methylstyrene. You can go out. Of these, acrylamide is particularly preferred as the copolymer component. The rate of the thermal cyclization reaction is dominated by the content of the carboxylic acid group, but rapidly increases due to the coexistence of a small amount of acrylamide.

In order to produce an acrylonitrile polymer using such a monomer, any of known polymerization methods such as solution polymerization and suspension polymerization can be used.

It is preferable to remove unreacted monomers, polymerization catalyst residues, and other impurities from the polymerized polymer as much as possible. Further, from the viewpoint of elongation in precursor fiber spinning and performance development of carbon fiber, the polymerization degree of the polymer is preferably such that the intrinsic viscosity [η] is 1.0 or more, particularly 1.4 or more. Further, those having an intrinsic viscosity [η] of 2.0 or less are usually used.

The solvent of the spinning solution is a solvent for dissolving the acrylonitrile-based polymer, and in the present invention, dimethylformamide or dimethylsulfoxide is used. Usually, dimethylacetamide or the like can be considered as a solvent for the acrylonitrile-based polymer, but the polymer used in the present invention has a high acrylonitrile content of 98% by weight or more, so that dimethylformamide or dimethylsulfoxide is used. It is essential to use a good solvent.

In order to obtain a dense coagulated yarn upon spinning, it is preferable to use a polymer solution having a polymer concentration of a certain level or more as a spinning solution, and the concentration of the acrylonitrile-based polymer is 17% by weight, more preferably It is at least 19% by weight. Further, it is usually preferably 25% by weight or less.

By the way, acrylonitrile is 98% by weight.
A coagulated yarn obtained by spinning a spinning dope obtained by dissolving the polymer contained in dimethylformamide or dimethyl sulfoxide is generally devitrified or contains macrovoids. Here, the macrovoid is a general term for voids having a spherical shape, a spindle shape, and a cylindrical shape having a maximum diameter of 0.1 to several μm. For the purpose of densification and improvement of homogeneity of the precursor fiber, it is preferable not to include devitrification and macrovoids.

In the present invention, a polymer solution containing ammonia is used as a stock solution in order to solve the problems of devitrification and macrovoids. At this time, 20% of the carboxylic acid groups in the polymer
It is considered that the above forms an ammonium salt, and the presence of ammonia in the stock solution reduces the rate of diffusion of water into the stock solution, resulting in a transparent, coagulated yarn without macrovoids.
It is preferable that the pH at this time is 8 or more, preferably 9 or more. On the other hand, if too much ammonia is added, the change over time in the viscosity of the stock solution becomes large.

The method of adding ammonia is not particularly limited, but it can be easily adjusted to an appropriate pH by, for example, bubbling ammonia into the polymer solution.

In order to improve the performance of the carbon fiber, the denseness and homogeneity of the precursor fiber are important factors. If the fiber structure of the precursor fiber is insufficient in density or homogeneity, it becomes a defect point during firing and impairs the performance of the carbon fiber. In order to obtain a dense and homogeneous precursor fiber, the properties of the coagulated yarn are extremely important. In the production method of the present invention, it is preferable to further manufacture the coagulated yarn so that the porosity is 50% or less.

The porosity is an index of the denseness and homogeneity of the coagulated yarn. When the porosity is 50% or less, the pores present in the coagulated yarn are sufficiently uniform. As a result of the study by the present inventors, the porosity of the coagulated yarn targeted by the present invention is 50%.
In the following range, the porosity and the average pore radius show a good correlation. Conversely, if the porosity exceeds 55%, there is no correlation between the porosity and the average pore radius, and only the average pore radius increases. This indicates that as the porosity increases, the number of pores having a large radius increases, which is considered to indicate that the coagulated yarn is not homogeneous.

In the present invention, a coagulated yarn having a porosity of 50% or less can be easily obtained by including the above polymer composition and ammonia in the spinning dope. As the coagulation bath at this time, an aqueous solution containing the solvent used in the spinning solution is preferably used, and the concentration of the contained solvent is adjusted so that the porosity of the coagulated yarn is set to 50% or less. The concentration of the solvent is 40 to 80% by weight, preferably 50 to 70% by weight.

The temperature of the coagulation bath is preferably low,
Usually, it is 60 ° C. or lower, more preferably 50 ° C. or lower.
If the temperature of the coagulation bath is lowered, a denser coagulated yarn can be obtained. However, if the temperature is too low, the take-up speed of the coagulated yarn is reduced and productivity is reduced. Therefore, it is desirable to set the temperature in an appropriate range.

In the spinning, the spinning solution is discharged from a nozzle hole having a circular cross section into a coagulation bath (wet spinning), or once discharged into the air and then guided to the coagulation bath (dry-wet spinning) to form a coagulated yarn. And Spinning draft is based on polymer concentration,
An appropriate setting is made according to the draw ratio so that a desired denier fiber is obtained.

Next, the coagulated yarn is washed and stretched prior to dry densification. There is no particular limitation on the washing and stretching, and stretching after washing, washing after stretching, or simultaneous washing can be performed. As a stretching method, stretching in a bath is usually used. At this time, in the bath stretching, the coagulated yarn may be stretched directly in the coagulation bath or in the stretching bath, or may be stretched in the bath after partially stretching in the air. Stretching in the bath is usually performed in a stretching bath at 50 to 98 ° C. once or in two or more steps, and may be washed before, after, or simultaneously.

The fiber after drawing and washing is subjected to an oil treatment by a known method. The type of the oil agent is not particularly limited, but an amino silicon-based surfactant is preferably used.

After the oil treatment, the mixture is dried and densified to obtain a precursor fiber. The temperature of the dry densification needs to be higher than the glass transition temperature of the fiber. However, the temperature may be substantially different from the water-containing state to the dry state.
A method using a heating roller at about 00 ° C. is preferable.

After the drying and densification, dry stretching with a high-temperature heating roller or the like, or steam stretching with pressurized steam may be performed as necessary.

[0043]

The present invention will be described in detail with reference to the following examples. In the following description, "%" represents% by weight.

(A) "Copolymer composition" The content of each monomer such as acrylamide and carboxylic acid-containing monomer in the copolymer was determined by ¹ H-NMR method (JEOL GSZ-400 type superconducting FT-NMR). Measured and determined.

(B) "Intrinsic viscosity [η] of copolymer" Measured with a dimethylformamide solution at 25 ° C.

(C) "Porosity and average pore radius of the coagulated yarn" The yarns from the coagulation bath and the drawing bath are collected, washed with water, and the structure is fixed by freeze drying with liquid nitrogen. .
About 0.2 g of the dried sample is precisely weighed and placed in a dilatometer. Next, a vacuum (0.0
5 Torr or less), and then filled with mercury. Then, the measurement is performed using a porosimeter. The pore volume is determined from the mercury intrusion amount. The pressure is applied up to 3000 bar. The porosity was determined using the following equation. Porosity = V / (V + M) Here, M is the volume of the sample, and V is the pore volume.

[0047] (d) Determination of carboxylic acid "Determination of carboxylic acid groups" was quantified by ¹ H-NMR of the above (b).

(E) “Strand strength and elastic modulus of carbon fiber” Measured according to the method described in JIS-7601.

Example 1 Acrylonitrile (hereinafter abbreviated as AN), methacrylic acid (hereinafter abbreviated as MAA), distilled water and dimethylacetamide, and azobisisobutyronitrile as a polymerization initiator were placed in an overflow polymerization vessel. A constant amount per minute and continue stirring while maintaining at 65 ° C.
The acrylonitrile polymer was obtained from the overflowed polymer slurry through washing and drying. Composition is AN / M
AA = 98.7 / 1.3 (%), that is, the amount of carboxylic acid groups was 1.5 × 10 ⁻⁴ equivalent / g. The intrinsic viscosity [η] of the copolymer was 1.7.

The acrylonitrile copolymer was dissolved in dimethylformamide to prepare a polymer solution, and ammonia was bubbled until the pH reached 9 to obtain a spinning stock solution (polymer concentration 21%, stock solution temperature 70 ° C.). Prepared.

This spinning stock solution was discharged into an aqueous solution of dimethylformamide having a concentration of 70% and a bath temperature of 35 ° C. using a die having a diameter of 0.075 mm and a number of holes of 3,000, to obtain a transparent coagulated yarn free of macrovoids. . The porosity at this time is 32%
Met. Further, the coagulated yarn is washed and desolvated while being stretched 1.5 times in air and 3.4 times in warm water, then immersed in a silicone oil solution, and dried and densified with a 140 ° C heating roller. It has become. Subsequently, the film was stretched 1.5 times on a hot plate at 180 ° C., and 1.1 times at a winding speed of 77 m / min.
A denier precursor fiber was obtained.

This fiber was treated in a hot air circulating type flame stabilizing furnace at 230 to 260 ° C. in the air for 50 minutes while giving an elongation of 5% to form a flame resistant fiber. Low-temperature heat treatment for 1.5 minutes at a temperature of 5 ° C. and an elongation of 5%.
For about 1.5 minutes under -4% elongation. The strand strength of the obtained carbon fiber is 521 kg.
/ Mm ² , and the strand elastic modulus was 26.3 ton / mm ² .

Example 2 Polymerization was carried out by the same polymerization method as in Example 1 while changing the charged monomer composition, to obtain a polymer having an intrinsic viscosity of 1.8 with the composition shown in Table 1. This polymer was dissolved in dimethylsulfoxide, and ammonia was bubbled until the pH reached 8 to obtain a spinning stock solution (polymer concentration 21%).
%, Stock solution temperature 70 ° C.).

Using this undiluted spinning solution and an aqueous dimethyl sulfoxide solution having a concentration of 50% and a bath temperature of 35 ° C. as a coagulation bath, a coagulated yarn was obtained in the same manner as in Example 1, and further processed similarly to 1.1 denier. Was obtained. This precursor fiber was fired in the same manner as in Example 1 to obtain a carbon fiber.

When the coagulated yarn was observed with an optical microscope, it was a transparent and macrovoid-free fiber. Further, the porosity of the coagulated yarn and the strand performance of the obtained carbon fiber were as shown in Table 2.

Example 3 AN, MAA, distilled water and ammonium persulfate, ammonium bisulfite and sulfuric acid as polymerization initiators were supplied to an overflow type polymerization vessel at a constant rate per minute, and stirring was continued while maintaining the temperature at 50 ° C. An acrylonitrile polymer was obtained from the overflowing polymer slurry through washing and drying. Table 1 shows the composition and carboxylic acid group content of this copolymer. The intrinsic viscosity [η] of this polymer was 1.7.

A transparent coagulated yarn free of macrovoids was obtained in the same manner as in Example 1 except that this polymer was used, and further subjected to post-treatment in the same manner as in Example 1 to obtain 1.1 denier. A precursor fiber was obtained.

Further, firing was carried out in the same manner as in Example 1 to obtain carbon fibers. The porosity of the coagulated yarn and the strand performance of the carbon fiber were as shown in Table 2.

Example 4 Polymerization was carried out by the same polymerization method as in Example 3 while changing the charged monomer composition to obtain a polymer having the composition shown in Table 1. A carbon fiber was obtained in the same manner as in Example 2 except that this polymer was used.

The coagulated yarn at this time was transparent and free of macrovoids as in Example 3. The porosity of the coagulated yarn and the strand performance of the obtained carbon fiber were as shown in Table 2.

Example 5 The acrylonitrile polymer used in Example 3 was dissolved in dimethylformamide, and ammonia was bubbled until pH 9 to obtain a spinning stock solution (polymer concentration 22%, stock solution temperature 70 ° C.). Prepared.

The undiluted spinning solution was 0.15 mm in diameter and 3 holes.
Dry-wet spinning was performed using a 2,000 nozzle. The air gap was set to 5 mm, and the mixture was discharged into an aqueous dimethylformamide solution having a concentration of 70% and a bath temperature of 20 ° C. to form a coagulated yarn. The coagulated yarn was transparent and homogeneous without macrovoids, and the porosity at this time was 28%.

Further, the coagulated yarn was washed and desolvated while being stretched 1.2 times in air and 4 times in boiling water, immersed in a silicone oil solution, and dried and densified with a heating roller at 140 ° C. It has become. Subsequently, after stretching 1.70 times between the drying rolls at 180 ° C., at a winding speed of 160 m / min,
A 1.1 denier precursor fiber was obtained.

This fiber was treated in a hot-air circulation type flame stabilizing furnace at 230 to 260 ° C. in the air for 50 minutes while giving an elongation of 5% to obtain a flame resistant fiber having a fiber density of 1.36 g / cm ^3. The fiber is heated at a maximum temperature of 600 under a nitrogen atmosphere.
℃, low-temperature heat treatment at an elongation of 5% for 1.5 minutes, and in the same atmosphere in a high-temperature heat treatment furnace with a maximum temperature of 1400 ℃
Treated for about 1.5 minutes under 5% elongation.

The strand strength of the obtained carbon fiber was 55
2 kg / mm ² , strand elastic modulus is 27.1 ton /
mm ² .

Example 6 Using the same spinning dope as in Example 3, spinning, washing, stretching, oil treatment, and dry densification were performed in the same manner as in Example 3. 1. Dry and densified fibers
The film was stretched 3.3 times in pressurized steam of 5 kg / cm ² G, dried again, and spun at 110 m / min. Winding up with 1.
One denier precursor fiber was obtained.

This fiber was fired in the same manner as in Example 3 to obtain a carbon fiber. The porosity of the coagulated yarn and the strand performance of the obtained carbon fiber were as shown in Table 2.

Example 7 Polymerization was carried out in the same manner as in Example 1 except that the charged monomer composition was changed to obtain a polymer having an intrinsic viscosity of 1.7 having the composition shown in Table 1. This polymer was dissolved in dimethyl sulfoxide, and ammonia was bubbled until the pH reached 8. A spinning stock solution (polymer concentration 21%, stock solution temperature 70%)
° C).

Using this spinning stock solution and a dimethyl sulfoxide aqueous solution having a concentration of 50% and a bath temperature of 35 ° C. as a coagulation bath, a coagulated yarn was obtained in the same manner as in Example 1, and further processed similarly to 1.1 denier. Was obtained. This precursor fiber was fired in the same manner as in Example 1 to obtain a carbon fiber.

When the coagulated yarn was observed with an optical microscope, it was a transparent fiber without macrovoids. Further, the porosity of the coagulated yarn and the strand performance of the obtained carbon fiber were as shown in Table 2.

[0071]

[Table 1] In the table, AN represents acrylonitrile, AAm represents acrylamide, MAA represents methacrylic acid, and IA represents itaconic acid.

[0072]

[Table 2]

Comparative Example 1 A solution obtained by dissolving the copolymer obtained by polymerization in Example 1 in dimethylformamide was mixed with a spinning solution (polymer concentration of 2) without bubbling ammonia.
Example 1 except that 1%, stock solution temperature 7, 0 ° C.) was used.
A coagulated yarn was obtained in the same manner as described above, and further processed in the same manner to obtain a precursor fiber. This precursor fiber was fired in the same manner as in Example 1 to obtain a carbon fiber. The coagulated yarn at this time is devitrified,
Many voids were found inside the coagulated yarn.

Comparative Example 2 A solution obtained by dissolving a copolymer obtained by polymerization in Example 7 in dimethyl sulfoxide was added to a spinning stock solution (polymer concentration 2) without bubbling ammonia.
(1%, stock solution temperature: 70 ° C.) except that the mixture was fired in the same manner as in Example 7 to obtain carbon fibers. At this time, the coagulated yarn was devitrified, and many voids were found inside the coagulated yarn.

Comparative Example 3 Polymerization was carried out in the same manner as in Example 1 except that the charged monomer composition was changed to obtain a copolymer having a composition shown in Table 3 and having an intrinsic viscosity [η] of 1.7.

A coagulated yarn was obtained by wet spinning using this copolymer obtained by adding ammonia in the same manner as in Example 1 as an undiluted spinning solution, and further processed to obtain a 1.1 denier precursor fiber. Was. This precursor fiber was fired in the same manner as in Example 1 to obtain a carbon fiber.

The porosity of the coagulated yarn and the strand performance of the obtained carbon fiber were as shown in Table 4.

Comparative Example 4 Polymerization was carried out in the same manner as in Example 3 except that the charged monomer composition was changed, to obtain a copolymer having a composition shown in Table 3 and an intrinsic viscosity [η] of 1.7.

This copolymer was subjected to wet spinning using an ammonia-added material as a spinning dope in the same manner as in Example 1 to obtain a transparent coagulated yarn without macrovoids. Further, the same treatment was performed to obtain a 1.1-denier precursor fiber, which was fired in the same manner as in Example 1 to obtain a carbon fiber.

The porosity of the coagulated yarn and the strand performance of the obtained carbon fiber were as shown in Table 4.

Comparative Example 5 Polymerization was carried out in the same manner as in Comparative Example 4 except that the charged monomer composition was changed to obtain a polymer having an intrinsic viscosity of 1.7 as shown in Table 3.

A copolymer obtained by adding ammonia to the copolymer in the same manner as in Example 1 was used as a spinning dope to obtain a transparent coagulated yarn free of macrovoids by wet spinning. Further, the same treatment was performed to obtain a 1.1-denier precursor fiber, which was fired in the same manner as in Example 1 to obtain a carbon fiber.

The porosity of the coagulated yarn and the strand performance of the obtained carbon fiber were as shown in Table 4.

[Comparative Example 6] The copolymer obtained by polymerization in Example 1 was added to dimethylacetamide so as to have a polymer concentration of 21%, heated and dissolved, but undissolved residue was formed. No uniform stock solution was obtained.

[0085]

[Table 3] In the table, AN represents acrylonitrile, AAm represents acrylamide, and MAA represents methacrylic acid.

[0086]

[Table 4]

[0087]

According to the present invention, an acrylonitrile-based precursor fiber for carbon fiber which can easily exhibit high strength and high elastic modulus even when formed into carbon fiber by densifying and homogenizing the fiber structure, And a production method that is economical.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ryoji Shimizu 20-1 Miyukicho, Otake City, Hiroshima Prefecture Inside Mitsubishi Rayon Co., Ltd. Central Research Laboratory

Claims (5)

[Claims] 1. A monomer component containing acrylonitrile in an amount of 98% by weight or more and a carboxylic acid group of 5.0 × 10 ⁻⁵ or more.
An acrylonitrile-based precursor fiber for carbon fiber, which is spun by using a dimethylformamide or dimethylsulfoxide solution containing 2.0 × 10 ⁻⁴ equivalents / g of acrylonitrile-based polymer and ammonia as a stock solution for spinning. Manufacturing method. 2. The method for producing an acrylonitrile-based precursor fiber for carbon fibers according to claim 1, wherein the porosity of the coagulated yarn obtained by spinning the acrylonitrile-based polymer is 50% or less. 3. The method for producing an acrylonitrile-based precursor fiber for carbon fiber according to claim 1, wherein the pH of the spinning solution is 8 to 11. 4. An acrylonitrile-based precursor fiber for carbon fiber produced by the production method according to claim 1. Description: 5. A carbon fiber obtained by firing the acrylonitrile-based precursor fiber for carbon fiber according to claim 4.