JP2005113296A - Carbon yarn, acrylonitrile-based precursor yarn and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thick acrylonitrile-based precursor yarn having a high grade, a high quality, and especially an excellent strength-developing property in a state little causing the breakage of the fibers and fuzzing at a low production cost and in excellent productivity, to provide a thick carbon yarn, and to provide a method for producing the same. <P>SOLUTION: This method for producing the acrylonitrile-based precursor yarn is characterized by extruding the organic solvent solution of an acrylonitrile-based polymer from 30, 000 or more spinning nozzles each having a nozzle aperture of 45 to 75μm into a dimethylacetamide aqueous solution at a coagulated yarn takeoff speed/extrusion linear speed of ≤0.8, washing/drawing the extruded swollen yarn, guiding the yarn into the first oiling tank to impart the first oil to the yarn, once squeezing the yarn with guides, imparting the second oil to the yarn in the second oiling tank, drying the yarn to compact the yarn, and then subjecting the yarn to the second drawing treatment in a draw ratio of 5 to 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a thick carbon fiber and a thick acrylonitrile-based precursor fiber that are low in production cost, excellent in productivity, low in yarn breakage and fluff generation, high quality, high quality, and particularly excellent in strength development. It relates to the manufacturing method.

  Conventionally, as an acrylonitrile-based precursor fiber for carbon fiber, in order to obtain a carbon fiber having high strength and high elastic modulus, it has a quality of 3,000 to 20,000 filaments, which is less likely to cause yarn breakage and fluff and has excellent quality. , So-called small tows are mainly produced, and carbon fibers produced in the future have been used in many fields such as aerospace, sports, and sports.

  On the other hand, the use of carbon fiber is being expanded to general industrial fields such as automobiles, civil engineering, architecture, and energy. For this reason, there is a demand for supply of thick carbon fibers with high strength, high elastic modulus, lower cost and excellent productivity. For example, Patent Documents 1 to 3 disclose a method for producing a thick carbon fiber or an acrylonitrile-based precursor fiber, but the carbon fiber disclosed in any of them is not sufficiently strong in strength, and the number of conventional filaments is The current situation is that the strand strength and elastic modulus of 12,000 or less small tows are not reached.

JP-A-10-121325 Japanese Patent Laid-Open No. 11-189913 JP 2001-181925 A

  Accordingly, the present invention provides a thick carbon fiber and a thick acrylonitrile-based precursor that are low in production cost, excellent in productivity, low in yarn breakage and fluff generation, high quality, high quality, and particularly excellent in strength development. It is an object to provide a fiber and a method for manufacturing the fiber.

The first gist of the present invention is a strand strength (JIS R7601-1986) obtained by firing an acrylonitrile-based precursor fiber having a single fiber fineness of 0.7 to 1.3 dtex and a filament number of 30,000 or more. Is a carbon fiber of 500 kg / mm ² or more.

The second gist is that the number of bonds between single fibers is 5 / 30,000 or less, and the crystal region size perpendicular to the fiber axis is 1.1 × 10 ⁻⁸ m or more. It is a body fiber.

  The third gist is that an organic solvent solution of an acrylonitrile-based polymer is mixed with a dimethylacetamide aqueous solution with a nozzle diameter of 45 to 75 μm, a spinning nozzle having a pore number of 30,000 or more and a solidified yarn take-off speed / discharge linear velocity. After washing / stretching the swollen yarn discharged at 0.8 or less, guide it to the first oil bath, apply the first oil agent, squeeze it once with the guide, and then apply the second oil agent in the second oil bath. And a total drawing ratio of 5 to 10 times by dry densification secondary drawing, which is a method for producing an acrylonitrile-based precursor fiber.

  According to the present invention, a thick carbon fiber and a thick acrylonitrile-based precursor that are low in production cost, excellent in productivity, low in yarn breakage, fuzz generation, high quality, high quality, and particularly excellent in strength development. Fiber and its manufacturing method can be supplied.

Hereinafter, the present invention will be described in detail.
"Acrylonitrile precursor fiber"
The acrylonitrile-based precursor fiber of the present invention is a tow obtained by bundling a plurality of single fibers of an acrylonitrile-based polymer.

(Acrylonitrile polymer)
The acrylonitrile-based polymer is preferably a polymer containing 95% by mass or more of acrylonitrile units in terms of strength development of carbon fibers obtained by firing acrylonitrile-based precursor fibers.
An acrylonitrile polymer is a polymer of acrylonitrile and a monomer that can be copolymerized with it by redox polymerization in an aqueous solution, suspension polymerization in a heterogeneous system, emulsion polymerization using a dispersing agent, or the like. Can be obtained.
Examples of monomers that can be copolymerized with acrylonitrile include (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth) acrylate. Esters; vinyl halides such as vinyl chloride, vinyl bromide, vinylidene chloride; acids such as (meth) acrylic acid, itaconic acid, crotonic acid and their salts; maleic imide, phenylmaleimide, (meth) acrylamide, Styrene, α-methylstyrene, vinyl acetate; polymerizable unsaturated monomer containing a sulfo group such as sodium styrene sulfonate, sodium allyl sulfonate, sodium β-styrene sulfonate, sodium methallyl sulfonate; 2-vinylpyridine , 2-methyl-5-vinylpyridine and the like Examples thereof include a polymerizable unsaturated monomer containing a lysine group.

(Single fineness)
The fineness of the single fiber constituting the acrylonitrile-based precursor fiber needs to be 0.7 to 1.3 dtex. If the fineness of the single fiber is less than 0.7 dtex, it will be difficult to stably spin the acrylic fiber yarn. Conversely, if the fineness exceeds 1.3 dtex, the cross-sectional double structure becomes remarkable, and a high-performance carbon fiber is obtained. It ’s hard to be.

(Number of filaments)
The number of filaments constituting the acrylonitrile-based precursor fiber needs to be 30,000 or more. Within this range, the most preferable number of filaments may be selected from the production conditions of acrylonitrile-based precursor fiber and carbon fiber. In consideration of handling of acrylonitrile-based precursor fiber, production cost, productivity, and further uniform heat treatment in the flameproofing process and the carbonization process, the number is preferably 100,000 or less.

(Number of bonds between single fibers)
The number of bonds between single fibers constituting the acrylonitrile-based precursor fiber is 5 pieces / 30,000 or less, and the crystal region size perpendicular to the fiber axis is 1.1 × 10 ⁻⁸ m or more. preferable. The adhesion of single fibers not only causes generation of fuzz and bundle breakage in the subsequent flameproofing process and carbonization process, but also significantly reduces the strand strength. Therefore, it is preferable that the number of adhesions be as small as possible.

Here, the number of bonded single fibers is measured as follows.
To determine the adhesion between single yarns, the wound precursor fiber is cut to about 5 mm, dispersed in 100 mL of acetone, stirred for 1 minute at 100 rpm (rotation / minute), filtered through black filter paper, and single yarn Measure the number of bonded fibers.

(Crystal region size perpendicular to fiber axis)
In the present invention, the crystal region size perpendicular to the fiber axis is preferably 1.1 × 10 ⁻⁸ m or more.

  The crystal region size is measured by the following method. The acrylonitrile-based precursor fiber is cut to a length of 50 mm, 30 mg of this is precisely collected, and aligned so that the sample fiber axes are exactly parallel, and then a thickness of 1 mm using a sample adjusting jig. Arranges into a uniform fiber sample bundle. The fiber sample bundle is impregnated with a vinyl acetate / methanol solution and fixed so as not to collapse, and then fixed to a wide-angle X-ray diffraction sample stage. As an X-ray source, a CuKα ray (using Ni filter) X-ray generator manufactured by Rigaku Corporation was used, and 2θ = 17 corresponding to the surface index (100) of graphite by a transmission method using a Goniometer manufactured by Rigaku Corporation. A diffraction peak near ° is detected by a scintillation counter. At this time, the output is 40 kV-100 mA. The crystal region size La is determined from the half width at the diffraction peak using the following formula.

La = Kλ / (β ₀ cos θ)
[Wherein K is the Scherrer constant of 0.9, λ is the wavelength of the X-ray used (here, Cu418 radiation is used, 1.5418 × 10 ⁻² m), θ is the Bragg diffraction angle, β ₀ Is the true half-value width, β ₀ = β _E −β ₁ (β _E is the apparent half-value width, β ₁ is the device constant, here 1.05 × 10 ⁻² rad). ]

(Strength of single fiber of acrylonitrile precursor fiber)
The strength of the single fiber of the acrylonitrile-based precursor fiber is preferably 5 cN / dtex or more, more preferably 6.5 cN / dtex or more, and further preferably 7 cN / dtex or more. If the strength of the single fiber is less than 5 cN / dtex, the occurrence of fluff due to the breakage of the single yarn in the firing process increases and the passing through the firing process becomes worse. The strength of the carbon fiber obtained is also significantly reduced.

  Here, the strength of the single fiber of the acrylonitrile-based precursor fiber is determined by using a single fiber automatic tensile strength / elongation measuring instrument (UTM II-20 manufactured by Orientec Co., Ltd.), and using the single fiber stuck on the mount as a load cell chuck. It is calculated | required by carrying out a tension test at a speed | rate of 20.0 mm / min, and measuring a strong elongation.

(Fineness of single fiber of acrylonitrile precursor fiber)
Furthermore, the fineness unevenness (CV value) of the single fiber constituting the acrylonitrile-based precursor fiber is 10% or less, preferably 7% or less, more preferably 5% or less. If it exceeds 10%, yarn breakage and winding troubles are likely to occur in the spinning process and firing process.

Here, the fineness unevenness of the single fiber is determined as follows.
After passing an acrylonitrile polymer fiber for measurement through a tube made of vinyl chloride resin having an inner diameter of 1 mm, the sample is prepared by cutting it with a knife. Next, the sample was adhered to the SEM sample stage so that the fiber cross section of the acrylonitrile polymer was facing upward, and Au was further sputtered to a thickness of about 10 nm, and then with a XL20 scanning electron microscope manufactured by PHILIPS, The fiber cross-section is observed under the conditions of an acceleration voltage of 7.00 kV and a working distance of 31 mm, and the fiber cross-sectional area of a single fiber is measured at about 300 randomly to calculate the fineness.

(Oil agent adhesion spots on acrylonitrile-based precursor fiber)
Further, the adhesion spot (CV value) of the oil agent in the length direction of the acrylonitrile-based precursor fiber is also 10% or less, preferably less than 5%.
If the adhesion of the oil agent in the length direction of the acrylonitrile-based precursor fiber is large, adhesion or fusion occurs in the spinning process, resulting in trouble such as single yarn breakage or bundle breakage.
The obtained carbon fiber is not so preferable in terms of quality and performance (particularly strand strength). In order to obtain high-quality, high-performance acrylonitrile-based precursor yarns and carbon fibers, the point of production is how oil can be uniformly applied regardless of the total fineness of small tow and large tow. is there.

  In addition, the adhesion spots due to the length direction of the oil agent are sampled continuously at N = 10 in the length direction of the precursor yarn, and the wavelength dispersion type fluorescent X-ray analyzer (desktop fluorescence) of Rigaku Corporation. Measurement is performed using an X-ray analyzer ZSXmini) to measure oil adhesion spots.

"Method for producing acrylonitrile-based precursor fiber"
As a method for producing the acrylonitrile-based precursor fiber of the present invention, a spinning stock solution composed of an acrylonitrile-based polymer and an organic solvent is placed in a first coagulation bath composed of an organic aqueous solution having a concentration of 50 to 70% by mass and a temperature of 30 to 50 ° C. A swollen yarn is discharged from a spinning nozzle with a nozzle diameter of 45 to 75 μm and a hole number of 30,000 or more to obtain a swollen yarn at a solidified yarn take-off speed / discharge linear velocity of 0.8 or less. Remove the moisture content as much as possible with the blow bar and give it to the first oil bath, apply the first oil agent, and once squeeze with two or more guides, then apply the second oil agent in the second oil bath, Acrylonitrile-based precursor fibers can be obtained by performing a total draw ratio of 5 to 10 times by dry densification secondary drawing.

(Spinning stock solution)
Examples of the organic solvent used for the spinning dope include dimethylacetamide, dimethylsulfoxide, dimethylformamide, and the like. Among them, dimethylacetamide is preferably used because it is less deteriorated due to hydrolysis of the solvent and gives good spinnability.

(Spinneret)
The spinneret for extruding the spinning dope has nozzle holes with a hole diameter of about 0.7 to 1.3 dtex as the single fiber fineness of the acrylonitrile precursor fiber, that is, a hole diameter of 45 to 75 μm. A spinneret can be used.
By using a small-bore nozzle, the “spinning speed of the coagulated yarn / the discharge linear speed of the spinning solution from the nozzle” becomes small (0.8 times or less), so that good spinnability can be maintained.

(Wet heat stretching for swollen yarn)
The swollen yarn taken from the coagulation bath further enhances the fiber orientation by subsequent wet heat drawing. This wet heat stretching is performed by stretching the swollen fibers in a swollen state while being washed with water, or by stretching in hot water. Among them, it is preferable to perform stretching in hot water from the viewpoint of high productivity.

(Swelling degree of swollen fiber)
Moreover, it is preferable that the swelling degree of the swollen fiber before drying after the wet heat stretching is 100% by mass or less. A fiber in which the swelling degree of the swollen fiber after drying after wet heat stretching is 100% by mass or less means that the surface layer part and the fiber interior are uniformly oriented. After uniformizing the coagulation of the coagulated yarn in the coagulation bath by lowering the “coagulated yarn take-off speed / discharge line speed of the spinning dope from the nozzle” during the production of the coagulated yarn in the coagulation bath The film can be uniformly oriented up to the inside by being wet-heat-stretched. Thereby, the swelling degree of the swollen fiber before drying can be set to 100% by mass or less.

Here, the swelling degree of the swelling fiber is determined as follows.
After removing the adhering solution of the fiber in the swollen state with a centrifuge [3,000 rpm (rotation / min), 15 minutes], and drying this with a hot air dryer (105 ° C. × 2 hours) With the mass w ₀ of
Swelling degree (mass%) = (w−w ₀ ) × 100 / w ₀
Can be obtained.

"Carbon fiber"
The carbon fiber of the present invention is a carbon fiber obtained by firing an acrylonitrile-based precursor fiber having a single fiber fineness of 0.7 to 1.3 dtex and a filament number of 30,000 or more, and has a strand strength (JIS R7601). -1986) is a carbon fiber of 500 kg / mm ² or more.

The carbon fiber of the present invention can be obtained by firing the aforementioned acrylonitrile-based precursor fiber by a known method. Among them, the acrylonitrile-based precursor fiber is 220 to 250 for each zone from a low temperature to a high temperature. Flame-proofing is performed continuously in a flame-proofing furnace adjusted to 0 ° C. while restricting shrinkage to obtain a flame-resistant fiber yarn having a density of about 1.36 g / cm ³ , and then has a temperature distribution of 300 to 700 ° C. In a carbonization furnace comprising a nitrogen atmosphere having a temperature distribution of 1,000 to 1,300 ° C., followed by carbonization treatment for 1 to 5 minutes while restricting shrinkage in the carbonization furnace in a nitrogen atmosphere Then, a method of carbonizing for 1 to 5 minutes while limiting shrinkage is preferable.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, although the Example described below is an example of the best embodiment in this invention, this invention is not limited by these Examples.

Acrylonitrile, acrylamide and methacrylic acid are copolymerized by aqueous suspension polymerization in the presence of ammonium persulfate-ammonium hydrogen sulfite and iron sulfate, and consist of acrylonitrile units / acrylamide / methacrylic acid units = 96/3/1 (mass ratio). Acrylonitrile polymer was obtained. This acrylonitrile-based polymer was dissolved in dimethylacetamide to prepare a 21% by mass spinning solution.
This spinning dope is passed through a spinneret having a pore size of 50,000 and a pore diameter of 45 μm and discharged into a coagulation bath composed of an aqueous dimethylacetamide solution having a concentration of 60% by mass and a temperature of 35 ° C. to obtain a coagulated yarn. It was taken up at a take-up speed of 45 times.

Next, this fiber was stretched 3 times simultaneously with water washing, led to the first oil bath of aminosilicone oil prepared to 1.5% by mass, and the first oil was applied, and once squeezed with several guides Then, the second oil was applied in the second oil bath of aminosilicone oil prepared to 1.5% by mass. This fiber was dried using a hot roll, and dry heat secondary stretching between hot rolls was performed 2.0 times. Thereafter, the moisture content of the fiber was adjusted with a touch roll and wound with a winder to obtain an acrylonitrile-based precursor fiber having a single fiber fineness of 1.2 dtex.
The obtained acrylonitrile-based precursor fibers were measured for adhesion number, crystal region size, single fiber strength, single fiber fineness spots, oil agent adhesion spots, and swelling degree and are shown in Table 1.

The acrylonitrile-based precursor fiber was subjected to flameproofing treatment continuously at a flameproofing treatment temperature of 226, 229, 234, 239, and 244 ° C. for 12 minutes each for a total of 60 minutes, and a flame resistant fiber yarn having a density of 1.36 g / cm ^3. Got. The process tension at the time of the flameproofing treatment at this time was set to 136 × 10 ⁻³ cN / dTex, and the shrinkage of the fiber was restricted. Subsequently, in a carbonization furnace composed of a nitrogen atmosphere having a temperature distribution of 300 to 700 ° C. With a tension of 68 × 10 ⁻³ cN / dTex and with a 1.5 minute carbonization treatment followed by a temperature distribution of 1,000 to 1,300 ° C. while limiting fiber shrinkage. Manufacture carbon fiber by applying a carbonization treatment for 1.5 minutes while applying a tension of 68 × 10 ⁻³ cN / dTex in a carbonization furnace comprising a nitrogen atmosphere and restricting the shrinkage of the fiber. did.

  An acrylonitrile-based precursor fiber was obtained in the same manner as in Example 1 except that the single fiber fineness was changed to 0.78 dtex, and the single fiber fineness was taken up at a take-up speed of 0.7 times the discharge linear speed of the spinning dope. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.

  Except that the wet heat draw ratio was changed to 4.5 times, the secondary drawing after drying and densification was changed to 2 times, and the take-up speed was 0.3 times the discharge linear speed of the spinning dope, and the same as in Example 1. Thus, an acrylonitrile-based precursor fiber having a single fiber fineness of 1.2 dtex was obtained. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.

  The acrylonitrile-based precursor fiber having a single fiber fineness of 1.2 dtex was used in the same manner as in Example 1 except that the nozzle diameter of the spinneret was changed to 75 μm and the take-up speed was 0.79 times the discharge linear speed of the spinning solution. Got. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.

  An acrylonitrile-based precursor fiber having a single fiber fineness of 1.2 dtex was obtained in the same manner as in Example 1 except that the spinneret was changed to a spinneret having a hole number of 30,000 and a nozzle hole diameter of 45 μm. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.

The spinneret was changed to a spinneret having a number of holes of 30,000 and a nozzle hole diameter of 45 μm, and was discharged into a coagulation bath to obtain a coagulated yarn, which was taken up at a take-up speed 0.44 times the discharge linear speed of the spinning dope. The acrylonitrile system having a single fiber fineness of 0.78 dtex was used in the same manner as in Example 1 except that the fiber was washed with water and simultaneously stretched 4.75 times and dry heat secondary stretched between hot rolls was 2.0 times. Precursor fibers were obtained. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.
[Comparative Example 1]

A single fiber fineness of 1.2 dtex was obtained in the same manner as in Example 1 except that the spinneret was changed to a spinneret having a hole number of 50,000 and a nozzle hole diameter of 90 μm, and the take-up speed was 1.79 times the discharge linear speed of the spinning solution. An acrylonitrile-based precursor fiber was obtained. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.
The coagulated yarn taken up at a take-up speed of 1.79 times the discharge linear speed of the spinning dope broke out of drawing in the coagulation bath, and stable spinning was difficult. Moreover, the strand strength of the carbon fiber obtained by baking was also low.
[Comparative Example 2]

Example 1 except that the wet heat draw ratio was changed to 6.0 times, the secondary drawing after drying and densification was changed to 2.0 times, and the drawing speed was 0.23 times the discharge linear speed of the spinning dope. In the same manner as above, an acrylonitrile-based precursor fiber having a single fiber fineness of 1.2 dtex was obtained. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.
The acrylonitrile-based precursor fiber having a total draw ratio exceeding 10 times increased the number of single-fiber adhesion, and the fineness unevenness of the single fiber exceeded 10%, and the carbon fiber obtained therefrom had low strand strength.
[Comparative Example 3]

Example 1 except that the wet heat draw ratio was changed to 2.0 times, the secondary drawing after drying and densification was changed to 2.0 times, and the take-up speed was 0.67 times the discharge linear speed of the spinning dope. In the same manner as above, an acrylonitrile-based precursor fiber having a single fiber fineness of 1.2 dtex was obtained. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.
The acrylonitrile-based precursor fiber having a total draw ratio of 5 times or less had a swelling degree of the swollen yarn before drying exceeding 100%, and the carbon fiber obtained therefrom had low strand strength.
[Comparative Example 4]

A single fiber fineness of 1.2 dtex was obtained in the same manner as in Example 1, except that the spinneret was changed to a spinneret having a hole number of 50,000 and a nozzle hole diameter of 30 μm, and the take-up speed was 0.14 times the discharge linear speed of the spinning dope. An acrylonitrile-based precursor fiber was obtained. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.
Acrylonitrile precursor fibers spun with a spinneret with a nozzle hole diameter of 30 μm at a rate of 0.14 times the discharge linear velocity of the spinning dope have an increased number of single fiber bonds, and further, yarn breakage and bundle breakage in the dry heat secondary stretching process And stable spinning was difficult. Moreover, the strand strength of the carbon fiber obtained by baking was also low.
[Comparative Example 5]

A single fiber fineness of 1.2 dtex was obtained in the same manner as in Example 1 except that only the first oil agent was given to the first oil bath of the aminosilicon-based oil agent prepared to 1.5% by mass and the second oil bath was bypassed. Acrylonitrile-based precursor fiber was obtained. This acrylonitrile-based precursor fiber was fired in the same manner as in Example 1 to obtain carbon fibers.
In the acrylonitrile-based precursor fiber spun in one stage of the oil bath adhesion treatment, the number of adhesions between single fibers increased, and the adhesion spots of the oil agent also increased. Moreover, the strand strength of the carbon fiber obtained by baking was also low.

  According to the present invention, a thick carbon fiber and a thick acrylonitrile-based precursor that are low in production cost, excellent in productivity, low in yarn breakage, fuzz generation, high quality, high quality, and particularly excellent in strength development. Fiber and its manufacturing method can be supplied.

Claims (7)

Carbon fiber having a strand strength (JIS R7601-1986) of 500 kg / mm ² or more obtained by firing an acrylonitrile-based precursor fiber having a single fiber fineness of 0.7 to 1.3 dtex and a filament number of 30,000 or more. . An acrylonitrile-based precursor fiber having a number of bonds between single fibers of 5 / 30,000 or less and a crystal region size perpendicular to the fiber axis of 1.1 × 10 ⁻⁸ m or more.   The acrylonitrile-based precursor fiber according to claim 2, wherein the strength of the single fiber is 5.0 cN / dtex or more, and the fineness unevenness (CV value) of the single fiber is 10% or less.   The acrylonitrile-based precursor fiber according to claim 2 or 3, wherein an oil agent adhesion spot (CV value) in a length direction is 10% or less.   The acrylonitrile-based precursor fiber according to any one of claims 2 to 4, wherein the swelling degree of the swollen yarn before drying is 100% by mass or less.   Swelling of an organic solvent solution of acrylonitrile polymer discharged into a dimethylacetamide aqueous solution from a spinning nozzle having a nozzle diameter of 45 to 75 μm and a pore number of 30,000 or more at a coagulated yarn take-off rate / discharge linear velocity of 0.8 or less After the yarn is washed / stretched, it is guided to the first oil bath, the first oil agent is applied, and after first squeezing with a guide, the second oil agent is subsequently applied in the second oil bath, followed by dry densification secondary stretching. A method for producing an acrylonitrile-based precursor fiber, wherein the total draw ratio is 5 to 10 times.   The method for producing an acrylonitrile-based precursor fiber according to claim 6, wherein the organic solvent is dimethylacetamide.