JP3002614B2 - Acrylonitrile fiber and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylonitrile fiber suitable for producing carbon fiber or graphite fiber and a method for producing the same.

[0002]

2. Description of the Related Art Carbon fibers and graphite fibers having acrylonitrile fibers as precursors (hereinafter collectively referred to as "carbon fibers")
) Is commercially produced and sold as a reinforcing fiber material for high-performance composite materials such as aerospace applications, sports and leisure applications due to its excellent mechanical properties. In the market, high-quality and inexpensive carbon fibers are required for improving the performance of these composite materials.

[0003] Many proposals have been made on the composition and spinning method of a copolymer as a raw material of acrylonitrile fiber (hereinafter sometimes referred to as "precursor fiber") as a precursor of carbon fiber. For example, with respect to the composition of the copolymer, one having a high content of an acrylonitrile component has been proposed for the purpose of improving the performance of carbon fibers. As spinning methods, dry-wet spinning and wet spinning have been proposed. Dry-wet spinning has a higher production cost than the wet spinning method, and the wet spinning method is adopted in consideration of the production cost. However, fibers obtained by wet spinning have low structural denseness and many fluffs, so that the mechanical performance of carbon fibers obtained by firing them is generally insufficient. There is also a problem that there are many single fiber breaks during spinning.

When producing carbon fibers from precursor fibers,
The precursor fiber is subjected to a flame-proof treatment and then to a carbonization treatment. Therefore, when selecting an acrylonitrile-based copolymer as a raw material of precursor fiber, not only the shapeability to the fiber, but also the thermochemical reaction characteristics and the performance of the carbon fiber in the flame-proofing / carbonization process should be sufficiently evaluated. It needs to be considered. That is, the copolymer composition of the precursor fiber, smoothing of the cyclization reaction in the oxidization treatment step, prevention of fusion of the fiber, shortening of the processing time, and the carbon fiber to the precursor fiber after the carbonization treatment The optimum range should be determined in consideration of the yield, strength, elastic modulus, elongation, etc. of the carbon fiber. However, there are very few examples of quantitatively showing that any composition is suitable as an industrially valuable universal.

[0005] Summarizing the findings from conventionally proposed acrylonitrile-based polymers for carbon fiber precursors, acrylonitrile contains at least a certain amount (about 90% by weight or more) in the polymer composition. And a suitable reaction-initiating group for passing through the baking process in a short time, that is, a functional group that promotes the cyclization condensation reaction of the nitrile group (for example, a carboxyl group)
In order to facilitate the shaping of the precursor fiber, it is effective to introduce
The addition of other comonomers leads to a final polymer composition, etc., and is only a little qualitative knowledge.

Heretofore, when acrylonitrile occupies a high proportion in a polymer composition, its solubility in a solvent is reduced, so that the production of precursor fibers must be performed by a very limited method, and the concentration of a stock solution is also low. Because
The carbon fiber performance and spin shapeability are not sufficiently satisfactory.

In the case where the content of the comonomer is increased in order to increase the degree of freedom in spinning and shaping, fusing (fusing) is liable to occur in the firing heat treatment of the precursor fiber using the same, and at the same time, the carbonization yield decreases. However, it is still insufficient in terms of the passing property of the firing step and the quality and performance of the carbon fiber. Further, there are very few proposals which can overcome the above-mentioned various problems and which can be calcined in a shorter time, or suggest a composition of a raw material polymer which is advantageous for this.

[0008] For example, a method of improving a calcination rate and a carbonization yield by making a polymer composition having high cyclization and oxidation reactivity in flame resistance at the initial stage of calcination (Japanese Patent Publication No. 47-33019). Attempts to shorten the baking time while considering the stability of the polymer production and spinning process by limiting the polymer composition such as using a vinyl carboxylate monomer (Japanese Patent Publication No. 51-7209); A method of adding an amine or a peroxide to the polymer (Japanese Patent Publication No. 51-7209)
JP-A-48-87120).

However, these methods all have a wide range of limitations on the polymer composition, that is, the type and content of the comonomer, and it cannot be said that the firing characteristics and the like of the precursor fibers are selected appropriately. Further, it is thought that the promotion of reaction itself by flame resistance itself enables high-speed firing, but the performance of the obtained carbon fiber tends to be rather impaired, and both carbon fiber productivity and performance are satisfied. Has not been obtained. Additives such as amines and peroxides to the polymer,
It is not an industrially superior method because it has various adverse effects on the stability of the spinning dope and the precursor fiber.

Under these circumstances, a precursor fiber having a ternary copolymer of acrylonitrile / acrylamide / methacrylic acid as a polymer composition has been proposed in JP-A-48-87120 and JP-A-52-34027. Have been. That is, in the former, a precursor fiber of acrylonitrile / acrylamide / methacrylic acid = 96/3/1 (wt%), and in the latter, their ratio is 95.5 / 3.0 /.
A 1.5 (mol%) or 93.7 / 3.9 / 2.4 (wt%) precursor fiber is disclosed.

However, in the polymer composition of the precursor fibers disclosed in these publications, the total composition ratio of acrylamide and methacrylic acid is excessive. When these precursor fibers are subjected to flameproofing treatment, the flameproofing reaction of the surface layer portion proceeds rapidly, and the flameproofing reaction of the central portion is delayed. The thus obtained oxidized fiber has a double cross section. This trend is
This is noticeable when the flameproofing treatment is to be performed in a short time.
And it is difficult to obtain a carbon fiber having a high elastic modulus from the oxidized fiber having a double cross section structure.

On the other hand, JP-A-63-35821 discloses a precursor fiber having a small iodine adsorption amount,
This precursor fiber is substantially a two-component system of acrylonitrile / itaconic acid and has a different copolymerization component from the precursor fiber of the present invention. Further, the content of acrylonitrile in the precursor fiber is more than that of the present invention and substantially 99% by weight or more.

[0013]

According to the method described in Japanese Patent Application Laid-Open No. 52-34027, the obtained carbon fiber has a high strength despite the fact that the oxidization treatment time is as long as 50 to 100 minutes. Is 300 kg / mm ² or less. Also, in the method described in JP-A-48-87120, the flame-proofing treatment time is as long as 40 minutes, and the obtained carbon fiber has a strength of 400 kg / mm ² or less. That is, although a precursor fiber of a ternary copolymer of acrylonitrile / acrylamide / methacrylic acid has been conventionally proposed, a fiber capable of producing a high-performance carbon fiber by a short-time flame-resistant treatment has not been known. .

Further, no technique has been known for wet spinning precursor fibers having less fluff without breaking yarn for a long time using such a ternary copolymer as a spinning raw material.

An object of the present invention is to provide an acrylonitrile-based fiber capable of producing a carbon fiber having a high strength and a high elastic modulus by firing in a shorter time. Another object of the present invention is to provide a method for wet-spinning precursor fibers having less fluff without breaking the yarn for a long time.

[0016]

The gist of the present invention is that acrylonitrile 96.0 to 98.5% by weight, acrylamide 1.0 to 3.5% by weight, and methacrylic acid 0.5% by weight or more are used as constituents. Acrylonitrile-based copolymer, wherein the weight% A of acrylamide and the weight% M of methacrylic acid in the copolymer are represented by the following formulas (I) and (I).
An acrylonitrile fiber which is a fiber comprising a copolymer satisfying I) and has an iodine adsorption amount of 1% by weight or less per fiber weight. X = 0.21 to 0.23 (I) M + A ^X = 1.82 to 2.18 (II) The gist of the present invention is to provide a method for producing a fiber by wet spinning a copolymer having the above composition. Wherein the tensile modulus of the coagulated fiber is about 2.0 to 3.0 g / d (d = denier is based on the weight of the polymer in the coagulated fiber). .

The copolymer constituting the precursor fiber of the present invention contains 96.0 to 98.5% by weight of acrylonitrile and the total amount of acrylamide and methacrylic acid is 4.0 to 1.5.
An acrylonitrile copolymer in the range of weight%, wherein the amounts of acrylamide and methacrylic acid in the copolymer are in a specific range. The present inventors have found that the flame retardant reactivity of the precursor fiber containing acrylonitrile and methacrylic acid is sharply increased due to the coexistence of a small amount (content of the copolymer of about 1.0% by weight or more) of acrylamide. To do,
In addition, the inventors have found that when the composition of acrylamide and methacrylic acid is in a specific range, the oxidization resistance is remarkably excellent, and the present invention has been completed.

Acrylonitrile in the copolymer is 96.0
When the amount is less than the weight percentage, heat fusion of the fibers is caused in the firing step, and the quality and performance of the carbon fibers are impaired. Also,
Due to the low heat resistance of the polymer itself, adhesion between the single fibers is likely to occur during spinning of the precursor fiber in a process such as drying the fiber or drawing with a heated roller. When the content of acrylonitrile in the copolymer exceeds 98.5% by weight, the content of acrylamide and methacrylic acid in the copolymer becomes less than a predetermined amount, as will be described in detail later. Cannot be achieved, which is not preferable.

When the content of acrylamide is less than 1.0% by weight, the structure of the precursor fiber cannot be sufficiently dense (that is, the amount of iodine adsorbed is 1% by weight or less). It cannot be outstanding. Further, in this region, a slight change in the composition greatly affects the oxidization resistance, and it is difficult to stably produce carbon fibers. On the other hand, if the acrylamide content in the copolymer exceeds 3.5% by weight, the acrylonitrile content in the copolymer decreases, and as described above, the heat resistance of the copolymer decreases, which is not preferable. .

When the content of methacrylic acid is less than 0.5% by weight or the value of the above formula (II) is less than 1.82, the carbon fiber having a high performance can be obtained by firing for a short time because of a slow oxidization resistance reaction. Can not get. When the flame-proofing treatment is performed in a short time, the flame-proofing temperature must be increased, which causes a runaway reaction, which causes a problem in process passability and safety. On the other hand, when the value of the above formula (II) is larger than 2.18, the oxidation resistance becomes high, so that the vicinity of the surface layer of the fiber reacts rapidly during the oxidation treatment, while the reaction in the central portion is delayed. The oxidized fiber forms a double cross-section structure. This tendency becomes conspicuous as the flameproofing treatment time is shortened, and the carbon fiber performance, particularly the elastic modulus, is sharply reduced.

The amount of methacrylic acid may be within the above range, but the lower the content of methacrylic acid, the better, as long as proper flame retarding reactivity can be ensured. This is because methacrylic acid easily enters the polymer chain in a block manner in the copolymerization with acrylonitrile, so that it is difficult for the methacrylic acid to be efficiently incorporated into the ring structure in the firing step.

On the other hand, acrylamide has high random copolymerizability with acrylonitrile, and is considered to form a ring structure in a form very similar to acrylonitrile by heat treatment. Particularly, thermal decomposition in an oxidizing atmosphere is very small. It can be contained in a large amount as compared with methacrylic acid.

The iodine adsorption amount of the precursor fiber of the present invention is 1% by weight or less per fiber weight. If the iodine adsorption amount of the precursor fiber exceeds 1% by weight, the fineness / density of the fiber structure is impaired and the fiber structure becomes inhomogeneous, and defect points of the fiber are formed. Therefore, the carbon fiber obtained by firing using a precursor fiber having an iodine adsorption amount exceeding 1% by weight has a reduced denseness and has structural defects, so that it can exhibit excellent tensile strength and tensile modulus. Can not.

Incidentally, in the present invention, the iodine adsorption amount means a value measured by the following method. 2g precursor fiber
And collected in a 100 ml Erlenmeyer flask.
Add iodine solution (potassium iodide 100 g, acetic acid 90)
g, 2,4-dichlorophenol 10 g, iodine 50
g in distilled water to make a 1000 ml solution)
Add 0 ml, shake at 60 ° C. for 50 minutes, and perform iodine adsorption treatment. Thereafter, the adsorption-treated yarn is washed with ion-exchanged water for 30 minutes, further washed with distilled water, and then centrifugally dehydrated.
The dehydrated yarn is put in a 300 ml beaker, 200 ml of dimethyl sulfoxide is added and dissolved at 60 ° C. This solution is
Potentiometric titration with an aqueous solution of / 100 silver nitrate to determine the iodine adsorption amount.

The precursor fiber of the present invention has a surface roughness coefficient of 2.
It is preferably in the range of 0 to 4.0. Those having a surface roughness coefficient in this range can be obtained by a wet spinning method. When the degree of unevenness of the surface is at this level, the fusion between the fibers during the oxidization treatment is suppressed, so that the process passability during the oxidization treatment is improved. Further, when the obtained carbon fiber is formed into a composite such as a prepreg, the impregnation property of the matrix resin between the carbon fibers is improved.

The surface roughness coefficient is a value measured by the following method. At the time of measurement, the contrast condition of the scanning electron microscope is adjusted using a magnetic tape as a standard sample. That is, a high-performance magnetic tape was used as a standard sample, and a secondary electron curve was imaged under the conditions of an acceleration voltage of 13 KV, a magnification of 1000 times, and a scanning speed of 3.6 cm / sec. The contrast condition is adjusted to be 40 mm. Then, after such adjustment, the direction perpendicular to the fiber axis of the test precursor (fiber diameter direction)
First, primary electrons are scanned, and a secondary (reflected) electron curve reflected from the fiber surface is imaged on a cathode ray tube using a line profile device, and this is photographed on a film at a magnification of 10,000 times. The acceleration voltage at this time is 13 KV, and the scanning speed is 0.18 cm / sec. The secondary electron curve photograph obtained in this way is further stretched by a factor of two at the time of printing, that is, the magnification is set to 20000 times as a total to make a secondary electron curve diagram (photograph). A typical example is shown in FIG. In the figure, d is the fiber diameter, d 'is the area in which the right and left ends of the fiber diameter are removed by 20%, that is, 60% of the center of the fiber diameter in the diameter direction, and d' =
0.6d. Also, 1 is the total length (linear conversion length) of the secondary electron curve in the range of d '. The surface roughness coefficient is represented by l / d '.

Next, a method for producing the precursor fiber of the present invention will be described. The polymerization method of the acrylonitrile polymer used in the present invention is not limited to any of known methods such as solution polymerization and slurry polymerization, but it is preferable to remove unreacted monomers, residues of polymerization catalyst, and other impurities as much as possible. Further, from the viewpoints of drawing by spinning the precursor fiber and exhibiting carbon fiber performance, the degree of polymerization of the polymer is preferably one having an intrinsic viscosity [η] of 0.8 or more. As the solvent used for spinning and shaping, known organic and inorganic solvents can be used.

The precursor fiber of the present invention can be produced by either a wet spinning method or a dry-wet spinning method, but the wet spinning method is advantageous in terms of cost. Wet spinning basically consists of the steps of spinning, coagulation, drawing (in bath or in air and bath) and dry densification.

The present inventors have investigated the tensile modulus of the coagulated fiber, which is a process yarn in wet spinning, and the final precursor fiber obtained by post-processing this fiber as a precursor fiber such as a single fiber cut or a fluff. We found a relationship with phenomena that impair quality. That is, the tensile modulus of the coagulated fiber is about 2.0 to 3.0 g / d.
(Where d = denier is based on the weight of the polymer in the coagulated fiber), the precursor fiber obtained by further post-treatment such as drawing, washing and drying of the coagulated fiber has a single fiber breakage.
It has very little fluff and has stable and high quality despite being obtained by a wet spinning method.

The tensile modulus of the coagulated fiber is controlled within the above range in consideration of the following points. For example, when the tensile modulus is less than 2.0 g / d when the composition of the copolymer, the solvent, the concentration of the stock solution, the concentration of the coagulating solution, the nozzle, and the discharge amount are set to certain values, the conditions for increasing the tensile modulus are as follows: Increasing stock solution concentration, increasing coagulating solution concentration, increasing coagulating solution temperature, increasing spinning draft. Conversely, the tensile modulus is 3.0 g.
If it is greater than / d, the opposite condition is set. Suitable conditions include an intrinsic viscosity [η] of 1.5 to
When a copolymer of about 2.0 is used, the concentration of the copolymer in the spinning solution is about 15 to 30% by weight, and the concentration of the coagulating liquid is 65%.
It is preferably about 75% by weight.

When the tensile modulus of the coagulated fiber is less than about 2.0 g / d, uneven elongation is caused in the initial stage of the spinning process such as in a coagulating solution, and the fineness of the obtained fiber bundle is extremely uneven. Become. Further, fluctuations in stretchability in each spinning step become remarkable, and stable continuous spinning becomes difficult. On the other hand, when the tensile modulus exceeds about 3.0 g / d, breakage of a single fiber in a coagulation bath and a decrease in stretchability in a subsequent step are caused, and all of the mechanical properties, quality and production stability can be satisfied. It becomes difficult to obtain a precursor fiber. If the tensile modulus of the coagulated fiber is out of the range of the present invention, it is difficult to obtain a carbon fiber having a high strength and a high modulus from the precursor fiber.

In the present invention, the stretching method is not particularly limited, but usually a bath stretching method is employed. In the in-bath drawing step, the coagulated fiber may be drawn directly, or the coagulated fiber may be drawn in the air and then drawn in the bath. Stretching in the bath is usually performed in a stretching bath at 50 to 98 ° C. once or twice or more in multiple stages, and washing may be performed before, after, or in the middle. By these operations, it is preferable that the coagulated fiber is stretched about 6 times or more by the time when the stretching in the bath is completed.

The fiber after drawing and washing in a bath can be treated with an oil agent and dried and densified by any known method.
In consideration of the drying speed, the facility of the facility, the effect of densifying the fiber, and the like, a method using a heating roller at about 100 to 200 ° C. is preferable. Further, if necessary, before or after dry densification, the fiber may be further stretched by a high-temperature heating roller or pressure steam.

The precursor fiber thus obtained is subjected to a flame-proofing treatment and a carbonization treatment by a known method.

[0035]

The present invention will be described in detail with reference to the following examples. In Examples and Comparative Examples, “%” represents “% by weight”. (A) “Copolymer composition”: ¹ H-NMR method (JEOL G
SX-400 type superconducting FT-NMR). (B) "Tensile modulus of coagulated fiber": After collecting a coagulated fiber bundle, immediately pull it with a tensilon at a sample length (gripping interval) of 10 cm and a pulling speed of 10 cm / min in an atmosphere of a temperature of 23 ° C and a humidity of 50%. Perform the test. The modulus of elasticity is expressed by the following formula: denier (d; coagulated fiber bundle 900) of the coagulated fiber bundle.
The weight occupied by the polymer per 0 m) was obtained and shown in g / d. d = 9000 × f × Qp / V f: number of filaments, Qp: discharge amount of polymer per one nozzle hole (g / min), V: coagulated fiber take-off speed (m
/ Min) (c) “Intrinsic viscosity of polymer [η]”: Measured with a dimethylformamide solution at 25 ° C. (D) "Strand strength and elastic modulus of carbon fiber": JIS
It measured according to -7601.

Example 1 97.1% of acrylonitrile, 2.0 of acrylamide
%, A copolymer consisting of 0.9% methacrylic acid and having an intrinsic viscosity [η] of 1.7 was dissolved in dimethylformamide at a copolymer concentration of 23% to obtain a spinning dope. Using a 12000 hole nozzle, the spinning stock solution was concentrated at a concentration of 70% at a temperature of 3
The wet spinning was performed in an aqueous solution of dimethylformamide at 5 ° C.
The tensile modulus of the obtained coagulated fiber was 2.3 g / d. This coagulated fiber is washed and desolvated while being stretched 7 times in boiling water, then immersed in a silicon-based oil solution, and heated at 140 ° C.
The precursor fibers were obtained by carrying out dry densification with a heating roller of No. 1. During the spinning process, almost no breakage of single fiber and fluff was observed, and the stability was good. The iodine adsorption amount of this fiber is 0.8%, and the surface roughness coefficient is 3.1.
Met. This fiber was subjected to heat treatment for 30 minutes while giving 5% elongation in a hot-air circulation type flame stabilizing furnace at 230 to 260 ° C. in the air to form a fiber having a fiber density of 1.368 g / cm ^3. The maximum temperature is 600 under 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 obtained carbon fiber had a strand strength of 476 kg / mm ² and a strand elastic modulus of 26.8 ton / mm ² . The precursor fiber had a fiber density of 1.36 in 50 minutes of oxidization treatment.
When the steel is subjected to a flameproofing treatment so as to be 0 g / cm ³ and then carbonized under the same conditions, the strand strength is 480 kg.
/ Mm ² , and the strand elastic modulus was 27.4 ton / mm ² . It was found that the carbon fiber performance was hardly improved, and that the oxidization treatment time of 30 minutes was sufficient.

Comparative Examples 1 to 3 The conditions of the coagulation bath were respectively 60% concentration and 35 ° C.
Ruformamide aqueous solution (Comparative Example 1), concentration 73%, temperature
35 ° C. aqueous dimethylformamide solution (Comparative Example 2) or
Is a 70% aqueous solution of dimethylformamide at a temperature of 50 ° C
Liquid (Comparative Example 3), and the flameproofing treatment time was set to 50 minutes. Except for that, the precursor fiber was obtained in the same manner as in Example 1.
Fired. Table 1 shows the tensile modulus of the coagulated fiber, the degree of single fiber breakage, the degree of fluff, the amount of iodine adsorbed, and the strand characteristics of the carbon fiber of the precursor fiber. In addition, the performance of the carbon fiber was further reduced when the oxidation treatment time was 30 minutes.

Example 2 Using the same acrylonitrile copolymer as in Example 1,
A dimethylacetamide solution having a copolymer concentration of 21% was used as a spinning stock solution, and a concentration of 70% was obtained using a 12000 hole nozzle.
% And wet spinning in an aqueous dimethylacetamide solution at a temperature of 35 ° C. Subsequently, the coagulated fiber was stretched 1.5 times in the air, washed and desolvated while being stretched in boiling water. Thereafter, a precursor fiber was obtained and fired in the same manner as in Example 1. Table 1 shows the iodine adsorption amount of the precursor fiber, the strand characteristics of the carbon fiber, and the like.

Comparative Examples 4 to 8 Precursor fibers were obtained and baked in the same manner as in Example 2 except that the composition of the acrylonitrile copolymer was set to the values shown in Table 2. Table 2 shows the iodine adsorption amount of the precursor fiber, the strand characteristics of the carbon fiber, and the like. In addition, in the case of Comparative Example 4, combustion and fuming occurred in the flameproofing step.

Examples 3 to 5 As the acrylonitrile copolymer, those having an intrinsic viscosity [η] of 1.7 shown in Table 1 were used, and a dimethylacetamide solution having a copolymer concentration of 21% was used as a spinning dope to prepare 12,000 holes. Using a nozzle, wet spinning was performed in an aqueous solution of dimethylacetamide having a concentration of 71% and a temperature of 38 ° C. Subsequently, the coagulated fiber is washed and desolvated while being stretched 6 times in boiling water, then immersed in a silicone oil solution, dried and densified with a 140 ° C. heating roller, and further heated with a high-temperature heating roll. The fiber was stretched 1.4 times to obtain a precursor fiber. During the spinning process, almost no breakage of single fiber and fluff was observed, and the stability was good. Table 1 shows the tensile modulus of the coagulated fiber and the iodine adsorption amount of the obtained precursor fiber. The fiber was fired under the same conditions as in Example 1 to obtain a carbon fiber. Table 1 shows the strand properties of the obtained carbon fibers.

Comparative Example 9 A precursor fiber was obtained in the same manner as in Example 5, except that the coagulation bath conditions were an aqueous dimethylacetamide solution having a concentration of 65% and a temperature of 38 ° C. At this time, the tensile modulus of the coagulated fiber was 3.3 g.
/ D, the iodine adsorption amount of the obtained precursor fiber was 1.9%. During the spinning step, the fiber was wound around the roller immediately after the coagulation bath, immediately after the hot water drawing, and the drying roller, and the obtained precursor fiber had many fluffs and pills.
Further, the fiber was made to have a flame resistance of 30 under the same conditions as in Example 1.
The carbon fiber was obtained by firing in a minute treatment. The strand characteristics of the obtained carbon fiber were as follows: strength 460 kg / mm ² , elastic modulus 2
Although it was 7.2 ton / mm ^2, it was low quality with many fluff and single fiber breakage.

Comparative Examples 10 to 15 As the acrylonitrile copolymer, those having an intrinsic viscosity of 1.7 shown in Table 3 were used.
The fiber was spun and fired in the same manner as described above. In the case of Comparative Example 15, fluff was generated in the flame-proofing treatment step, and the fiber was frequently wound around the roll.

Example 6 A copolymer having an intrinsic viscosity [η] of 1.7 having the composition shown in Table 1 was dissolved in dimethylacetamide at a copolymer concentration of 23% to prepare a stock solution for spinning. This spinning stock solution was wet-spun into a dimethylacetamide aqueous solution having a concentration of 70% and a temperature of 35 ° C using a 2000-hole nozzle. This coagulated fiber was stretched 1.5 times in air at room temperature, and then washed and desolvated while stretching 4.7 times in boiling water. Next, this was immersed in a silicon-based oil solution and dried and densified with a heating roller at 140 ° C. to obtain a 1.5-denier precursor fiber. During the spinning process, almost no breakage of single fiber and fluff was observed, and the stability was good. Next, the fiber was fired under the same conditions as in Example 1. Table 1 shows the iodine adsorption amount of the precursor fiber, the strand characteristics of the carbon fiber, and the like.

Comparative Example 16 A precursor fiber was obtained and calcined in the same manner as in Example 6 except that the composition of the acrylonitrile copolymer was set to the values shown in Table 3. Table 3 shows the iodine adsorption amount of the precursor fiber, the strand characteristics of the carbon fiber, and the like.

Comparative Example 17 A precursor fiber was obtained and baked in the same manner as in Example 6 except that the composition of the acrylonitrile copolymer was set to the values shown in Table 3 and the solidification concentration was changed to 72.5%. Table 3 shows the iodine adsorption amount of the precursor fiber, the strand characteristics of the carbon fiber, and the like.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

As described above, the precursor fiber of the present invention can be subjected to a rapid flame-proofing treatment, and the production cost of carbon fiber can be remarkably reduced as compared with the conventional product. Further, the carbon fiber obtained therefrom has excellent quality and performance. Further, according to the method for producing the precursor fiber of the present invention, the precursor fiber having less fluff can be wet-spun without breaking the yarn for a long time.

[Brief description of the drawings]

FIG. 1 is an example of a secondary electron curve diagram for measuring a surface roughness coefficient.

 ──────────────────────────────────────────────────続 き Continuing from the front page Judge Masami Kobayashi Judge, Yumiko Niki Judge, Katsuhiko Ishii (56) References JP-A-48-87120 (JP, A) JP-A-63-85168 (JP, A)

Claims (2)

(57) [Claims] 1. An acrylonitrile copolymer comprising 96.0 to 98.5% by weight of acrylonitrile, 1.0 to 3.5% by weight of acrylamide, and 0.5% by weight or more of methacrylic acid, A fiber comprising a copolymer in which the weight% A of acrylamide and the weight% M of methacrylic acid in the copolymer satisfy the following formulas (I) and (II), and the amount of adsorbed iodine is 1 per fiber weight. Acrylonitrile-based fibers that are less than or equal to% by weight. X = 0.21 to 0.23 (I) M + A ^X = 1.82 to 2.18 (II) 2. A method for producing a fiber by wet spinning an acrylonitrile-based copolymer, wherein the tensile modulus of the coagulated fiber is about 2.0 to 3.0 g / d (where d = denier is the polymer in the coagulated fiber). 2. The method for producing acrylonitrile-based fibers according to claim 1, wherein