阅读说明：本技术 聚缩醛纤维的制造方法 (Method for producing polyacetal fiber ) 是由 伊东显 须长大辅 三上素直 于 2018-06-08 设计创作，主要内容包括：本发明提供改善了白色色泽不均的聚缩醛纤维的制造方法。根据一个实施方式提供一种聚缩醛纤维的制造方法,该制造方法包括吐出工序、收取工序、拉伸工序和卷绕工序,并且连续地进行这些工序,作为聚缩醛纤维的原料使用氧亚甲基共聚物,该氧亚甲基共聚物具有氧亚甲基单元和氧亚乙基单元,相对于氧亚甲基单元100摩尔,氧亚乙基单元的含量为0.5～7.0摩尔,用于拉伸工序的拉伸部的辊温度为130～155℃,以满足规定的数学式的方式设置运转参数。(The invention provides a method for producing a polyacetal fiber improved in white color unevenness. According to one embodiment, a method for producing a polyacetal fiber is provided, which comprises a discharge step, a collection step, a drawing step, and a winding step, and these steps are continuously performed, wherein an oxymethylene copolymer having oxymethylene units and oxyethylene units is used as a raw material of the polyacetal fiber, the content of the oxyethylene units is 0.5 to 7.0 moles per 100 moles of the oxymethylene units, the roll temperature of a drawing section used in the drawing step is 130 to 155 ℃, and operating parameters are set so as to satisfy a predetermined mathematical formula.)

1. A method for producing a polyacetal fiber, characterized in that:

comprising a discharge step, a take-up step, a drawing step and a winding step, and these steps are continuously performed,

an oxymethylene copolymer having oxymethylene units and oxyethylene units, the oxyethylene units being contained in an amount of 0.5 to 7.0 mol per 100 mol of the oxymethylene units, is used as a raw material for the polyacetal fibers,

the roll temperature of the stretching section used in the stretching step is 130 to 155 ℃,

a value obtained by dividing a speed difference between a speed at which the oxymethylene copolymer is discharged from a discharge port in the discharge step and a speed at which the fiber is taken up by a take-up roll in the take-up step by a distance between the discharge port and the take-up roll is defined as a speed difference x (1/sec) per unit distance, as formula (A),

the speed difference per unit distance (x) is (take-up roll speed (m/sec) — discharge speed of resin at the discharge port (m/sec))/distance (m) · (a)),

the ratio of the area of the discharge port to the cross-sectional area of the polyacetal fiber after the winding step is defined as an area ratio y (dimensionless unit) as formula (B),

area ratio (y) being the area (mm) of the discharge opening²) Cross-sectional area (mm) of polyacetal fiber after winding step²)···(B)，

At this time, formula (C) is satisfied:

y＞1600/x···(C)，

wherein x is more than 1.5 and less than 15.

2. The manufacturing method according to claim 1, wherein:

1400 < y < 2500 is satisfied in said formula (C).

3. The manufacturing method according to claim 1 or 2, characterized in that:

satisfies formula (D):

y＞8000/x ···(D)，

wherein x is more than 1.5 and less than 15.

Technical Field

The present invention relates to a method for producing polyacetal fibers.

Background

Polyacetal is a polymer having a polymer skeleton mainly composed of repeating units of oxymethylene units, and is used mainly as an injection molding material in a wide range of fields including automobiles and electric appliances because of its characteristics such as mechanical strength, chemical resistance and solvent resistance.

As a method for producing polyacetal fibers, a method for producing high-strength and high-elastic-modulus fibers (patent document 1), a method for producing high-strength fibers having heat resistance, abrasion resistance, and chemical resistance (patent document 2), and the like have been disclosed.

Disclosure of Invention

Technical problem to be solved by the invention

As described above, although polyacetal is a resin material having excellent physical properties, when a fiber is spun by a conventional method, the color of the obtained polyacetal fiber may be partially white. When the fiber has such unevenness in color, there is a possibility that the unevenness in fiber thickness becomes large, or that the processability in the subsequent preliminary twisting, weaving and knitting processes becomes unstable.

The present inventors have found that polyacetal fibers are more likely to cause white color unevenness than general resin fibers such as polyester fibers. Accordingly, an object of the present invention is to provide a method for producing a polyacetal fiber having improved white color unevenness.

Technical solution for solving technical problem

The present inventors have intensively studied to solve the above problems, and as a result, they have found that the above problems can be solved by a production method using an oxymethylene copolymer containing an oxymethylene unit and an oxyethylene unit in a predetermined ratio as a raw material and setting an operating parameter so as to satisfy a certain formula, and have reached the present invention.

The present invention is as follows, for example.

[1] A method for producing a polyacetal fiber,

the manufacturing method comprises a discharge step, a take-up step, a drawing step and a winding step, and these steps are continuously performed,

an oxymethylene copolymer having oxymethylene units and oxyethylene units, the oxyethylene units being contained in an amount of 0.5 to 7.0 mol per 100 mol of the oxymethylene units, is used as a raw material for the polyacetal fibers,

the roll temperature of the stretching section used in the stretching step is 130 to 155 ℃,

a value obtained by dividing a speed difference between a speed at which the oxymethylene copolymer is discharged from the discharge port in the discharge step and a speed at which the fiber is taken up by the take-up roll in the take-up step by a distance between the discharge port and the take-up roll is defined as a speed difference x (1/sec) per unit distance, which is represented by formula (A),

the speed difference per unit distance (x) is (take-up roller speed (m/sec) — discharge speed of resin at the discharge port (m/sec))/distance (m) … (a),

the ratio of the area of the discharge port to the cross-sectional area of the polyacetal fiber after the winding step is defined as an area ratio y (dimensionless unit) as formula (B),

area ratio (y) being the area (mm) of the discharge opening²) Cross-sectional area (mm) of polyacetal fiber after winding step²)…(B)，

At this time, the formula (C) is satisfied,

y＞1600/x…(C)，

(wherein, x is more than 1.5 and less than 15).

[2] The production process according to [1], wherein 1400 < y < 2500 is satisfied in the above formula (C).

[3] The production process according to [1] or [2], wherein the formula (D) is satisfied,

y＞8000/x…(D)，

(wherein, x is more than 1.5 and less than 15).

Drawings

FIG. 1 is a schematic view of an apparatus for producing polyacetal fibers.

Fig. 2 is a graph showing a relationship of a velocity difference per unit distance to an area ratio.

Detailed Description

The present invention will be described in detail below by way of examples of manufacturing examples, and the like, but the present invention is not limited to the examples of manufacturing examples, and the like, and can be carried out by changing the method to any method without departing from the scope of the present invention.

< method for producing polyacetal fiber >

The method for producing a polyacetal fiber of the present invention is a method for obtaining a polyacetal fiber by using an oxymethylene copolymer containing an oxymethylene unit and an oxyethylene unit at a predetermined ratio as a raw material. The manufacturing method comprises the following steps: a discharge step of discharging the polyacetal fibers from a discharge port of a spinning machine; a collecting step of collecting the discharged polyacetal fibers; a drawing step of drawing the collected polyacetal fibers; and a winding step of winding the drawn polyacetal fiber, and these steps are continuously performed. In the method for producing polyacetal fibers of the present invention, the roll temperature of the stretching section used in the stretching step is 130 to 155 ℃, and the difference between the speed at which the oxymethylene copolymer is discharged from the discharge port in the discharging step and the speed at which the polyoxymethylene copolymer is collected by the collection roll in the collection step is divided by the distance between the discharge port and the collection roll, and the resultant difference is defined as the speed difference x (1/sec) per unit distance as formula (A),

the speed difference per unit distance (x) is (take-up roller speed (m/sec) — discharge speed of resin at the discharge port (m/sec))/distance (m) … (a),

the ratio of the area of the discharge port to the cross-sectional area of the polyacetal fiber after the winding step is defined as an area ratio y (dimensionless unit) as formula (B),

the area ratio (y) being that of the discharge openingArea (mm)²) Cross-sectional area (mm) of polyacetal fiber after winding step²)…(B)，

At this time, the formula (C) is satisfied,

y＞1600/x…(C)，

(wherein, x is more than 1.5 and less than 15).

As described above, the present inventors have found that white color unevenness can be unexpectedly improved by a production method using an oxymethylene copolymer containing an oxymethylene unit and an oxyethylene unit in a predetermined ratio as a raw material and setting operating parameters so as to satisfy the above-mentioned numerical expression. The inventors of the present invention have also found that, according to one embodiment of the present invention, not only the white unevenness but also the spinnability of the fiber can be improved.

One embodiment of the method for producing polyacetal fibers of the present invention will be described with reference to the schematic diagram of fig. 1. In one embodiment of the present invention, a polyacetal fiber is produced by collecting a plurality of fibrous materials (filaments) discharged from a discharge port of a spinning machine with a collecting roller to produce fibers, and then drawing the fibers with a pre-drawing roller and a drawing roller, and after the drawing step, the drawn fibers are wound with a winding roller. The discharge step, the take-up step, the drawing step, and the winding step are continuously performed. In the present specification, "continuously performed" means that: each step is not performed as a separate step, but is performed as a series of steps. For example, the drawing step is a step of drawing the fiber collected in the collecting step directly in the drawing step. The method for producing polyacetal fibers of the present invention can be used not only for the method of spinning multifilament as shown in fig. 1 but also for the method of spinning monofilament.

The structure of the spinning machine used in the production method of the present invention is not particularly limited, and any spinning machine may be used as long as it can melt the oxymethylene copolymer as a raw material and discharge the polyacetal fibers from the discharge port. If necessary, the oxymethylene copolymer as a raw material may be melt-kneaded in a spinning machine equipped with an extruder or the like. Examples of the spinning machine include a common melt spinning device for multifilament or monofilament, which is composed of a single-shaft extruder, a gear pump, a screen, and a die. The barrel temperature of the extruder, the gear pump temperature, the number of orifices of the discharge nozzle, and the like may be appropriately adjusted as necessary. The fineness (fiber thickness) of the drawn fiber can be appropriately adjusted by the feed amount of the raw material and the speed of the take-up roll.

The filament discharged from the discharge port of the spinning machine was collected as polyacetal fiber by a collecting roller, then sent to a pre-drawing roller, and then drawn by 1 or more drawing rollers. By drawing, the tensile strength of the fiber can be improved. In the present specification, "pre-drawing roll" means a roll positioned between a drawing roll and a take-up roll, and is generally a roll in which a fiber is not drawn between the pre-drawing roll and the take-up roll or is slightly drawn to ensure spinning stability. The "stretching roll" is a roll disposed after the pre-stretching roll, and the fiber is stretched between the pre-stretching roll and the stretching roll, and/or between a plurality of stretching rolls. In the method for producing polyacetal fibers of the present invention, at least 1 drawing roll, preferably 2 or more drawing rolls are used. It is preferable to use 2 or more stretching rollers because the polyacetal fiber can be stretched in a plurality of stages.

In the production method of the present invention, the roll temperature of the stretching section is 130 to 155 ℃. In the present specification, "the roll of the stretching section" means any 1 or more of the roll before stretching and the 1 or more stretching rolls. Therefore, any 1 or more of the pre-stretching roll and the 1 or more stretching rolls may be 130 to 155 ℃, and is not particularly limited. The temperature of 1 or more stretching rolls is preferably 130 to 155 ℃, and the temperature of both of 1 or more stretching rolls and rolls before stretching is more preferably 130 to 155 ℃. When the roll temperature is 130 ℃ or higher, the resin can be sufficiently softened, and the occurrence of yarn breakage before fiber elongation in the drawing step can be effectively suppressed. Further, if the roll temperature is 155 ℃ or lower, the melting point of the resin is sufficiently kept away, and the phenomenon that the fibers stick to the roll can be suppressed, so that fiber breakage can be effectively suppressed.

As described above, in the production method of the present invention, the polyacetal fibers having improved white color unevenness can be obtained by satisfying the above formula (C) with the velocity difference (x) per unit distance and the area ratio (y) obtained from the formulas (a) and (B). The respective equations are explained below.

The following formula (a) is a formula in which a velocity difference (x) per unit distance is defined.

The speed difference per unit distance (x) is (take-up roller speed (m/sec) — discharge speed of resin at discharge port (m/sec))/distance (m) … (a)

That is, the velocity difference x (1/sec) per unit distance is defined as the velocity difference between the velocity at which the oxymethylene copolymer is discharged from the discharge port in the discharge step and the take-up velocity of the fiber by the take-up roller in the take-up step, divided by the distance between the discharge port and the take-up roller. In the present specification, "the discharge rate of the oxymethylene copolymer from the discharge port in the discharge step" means: the linear velocity (m/sec) of the resin (oxymethylene copolymer) discharged from the discharge port of the spinning machine at the discharge port. In the present specification, the "distance between the discharge port and the collecting roller" refers to a distance (m) from the discharge port of the spinning machine to the center of the collecting roller as shown in fig. 1. When the fiber extruded from the discharge port of the extruder during spinning is collected by the collecting roller, the condition until the extruded resin is solidified by contacting with the outside air while being collected is considered to be important, and therefore the above formula (a) is set as a parameter.

The following formula (B) is a formula in which the area ratio (y) is defined.

Area ratio (y) being the area (mm) of the discharge opening²) Cross-sectional area (mm) of polyacetal fiber after winding step²)…(B)

That is, the ratio of the area of the discharge port to the cross-sectional area of the polyacetal fiber after the winding step is defined as an area ratio y (dimensionless unit). In the present specification, the area (mm) of the discharge port²) The term "means the area of each discharge port of a spinning machine that discharges resin. By passing the cross-sectional area (mm) of each polyacetal fiber after the winding step²) The area ratio (y) in the formula B can be obtained by dividing the area of the discharge port. It is considered that whether or not the finally obtained fiber is excellent with little white color unevenness is extruded in the whole spinning stepSince it is important what state the fiber extruded from the discharge port of the extruder reaches the take-up roll through the take-up roll and the draw roll and finally becomes, the above formula (B) is set as a parameter.

The following expression (C) is an expression defining a relationship between the velocity difference (x) per unit distance and the area ratio (y).

y＞1600/x…(C)

(wherein, 1.5 < x < 15)

That is, the polyacetal fibers having improved white color unevenness can be obtained by satisfying the above formula (C) with the velocity difference (x) per unit distance and the area ratio (y) obtained from the above formulae (a) and (B). In a preferred embodiment of the present invention, 1400 < y < 2500 is satisfied in the above formula (C).

In a preferred embodiment of the present invention, the production method satisfies the following formula (D).

y＞8000/x…(D)

(wherein, 1.5 < x < 15)

By satisfying the above formula (D), a polyacetal fiber having less white unevenness can be obtained.

The take-up speed (m/min) of the take-up roll and the take-up speed (m/min) of the take-up roll are not particularly limited as long as they satisfy the above formula (C), but the take-up speed (m/min) of the take-up roll and the take-up speed (m/min) of the roll before stretching are preferably 300 to 6000m/min, and particularly preferably 400 to 3000m/min, for example. The winding speed (m/min) of the drawing roll and the winding roll is preferably 1000 to 6000m/min, and particularly preferably 2000 to 6000 m/min. The rotational speed of the rollers prior to stretching is preferably substantially the same as the take-up speed of the take-up roller. The winding speed of the winding roll is substantially the same as the rotation speed of the drawing roll, but in consideration of shrinkage of the polyacetal fiber, the winding speed is preferably slightly slower than the rotation speed of the drawing roll.

According to a preferred embodiment of the present invention, the stretching can be performed in multiple stages using a pre-stretching roll and 2 or more stretching rolls in the stretching step. By performing the drawing in multiple stages, the spinning stability and the processability 2 times can be further improved.

According to a preferred embodiment of the present invention, the drawing step is performed using a pre-drawing roll and 2 or more drawing rolls, and in the drawing step, the polyacetal fibers pass through the 2 or more drawing rolls after passing through the pre-drawing roll, and the temperature of at least 1 roll of the 2 or more drawing rolls is 3 to 20 ℃ higher than the temperature of the pre-drawing roll, more preferably 5 to 20 ℃ higher. The drawing step is carried out using a pre-drawing roller and 2 or more drawing rollers, and in the configuration in which the polyacetal fibers pass through the 2 or more drawing rollers after passing through the pre-drawing roller in the drawing step, the spinning stability is improved by adjusting the temperatures of the pre-drawing roller and the drawing rollers. According to a further preferred embodiment of the present invention, in the stretching step, the temperature of the pre-stretching roll and the temperature of at least 1 roll of the 2 or more stretching rolls are 130 to 155 ℃. By adjusting the temperature of the pre-drawing roll and the drawing roll as described above, a polyacetal fiber having good spinning properties can be obtained.

The discharge amount of the resin spun from 1 hole of the extruder nozzle is not particularly limited as long as the resin satisfies the above formula (C), and is preferably 0.001 to 0.5 kg/hr, more preferably 0.01 to 0.10 kg/hr, and further preferably 0.05 to 0.09 kg/hr.

The size of the hole of the extruder nozzle is not particularly limited as long as the above formula (C) is satisfied, but is preferably 0.1 to 1.0mm, and more preferably 0.2 to 0.6 mm.

The diameter of the filament thickness of the polyacetal fiber after the winding step is not particularly limited, but is preferably 0.001 to 0.10mm, more preferably 0.01 to 0.03mm, and still more preferably 0.01 to 0.02 mm.

< polyacetal fiber >

The polyacetal fiber of the present invention is a fiber of a polymer having an oxymethylene structure in a unit structure, and can be obtained by spinning an oxymethylene copolymer by the production method of the present invention. The polyacetal fibers of the present invention are excellent in white color unevenness, and the fibers as a whole are uniform and have a transparent white color. In a preferred embodiment of the present invention, the polyacetal fibers of the present invention are also excellent in spinnability. In the present specification, "spinnability" is an index indicating whether or not the operation can be stopped without breaking the fiber during spinning and the fiber can be stably obtained. The criteria of the index are specifically shown in the examples of the present specification.

In the production method of the present invention, the oxymethylene copolymer used as a raw material for the polyacetal fiber has oxymethylene units and oxyethylene units, and the content of the oxyethylene units is 0.5 to 7.0 mol, preferably 1.0 to 4.0 mol, and more preferably 1.0 to 2.5 mol, based on 100 mol of the oxymethylene units. The content of the oxymethylene unit and the oxyethylene unit in the oxymethylene copolymer can be determined by a Nuclear Magnetic Resonance (NMR) method.

The oxymethylene copolymer used as a raw material for the polyacetal fibers in the production method of the present invention may contain, in addition to the oxymethylene copolymer containing polyoxymethylene units and polyoxyethylene units, another oxymethylene copolymer. As such an oxymethylene copolymer, a copolymer containing an oxyalkylene unit represented by the following formula (1) in addition to an oxymethylene unit in the molecule can be used.

(in the formula, R₀And R₀' may be the same or different and is a hydrogen atom, an alkyl group, a phenyl group or an alkyl group interrupted by 1 or more ether bonds, and m is an integer of 2 to 6)

The alkyl group is an unsubstituted or substituted C1-20 linear or branched alkyl group, preferably a C1-4 linear or branched alkyl group. Examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, decyl, dodecyl, and octadecyl groups.

As substituents, mention may be made of hydroxyl, amino, alkoxy, alkenyloxymethyl and halogen. Among them, examples of the alkoxy group include a methoxy group, an ethoxy group, and a propoxy group. Examples of the alkenyloxymethyl group include allyloxymethyl groups.

The phenyl group is a phenyl group which is unsubstituted or substituted with an unsubstituted or substituted alkyl group, an unsubstituted or substituted aryl group, or a halogen. Among them, examples of the aryl group include a phenyl group, a naphthyl group, and an anthryl group.

Examples of the alkyl group interrupted by 1 or more ether bonds include groups represented by the following formula (2).

－CH₂－O－(R₁－O)_p－R₂(2)

(in the formula, R₁Is alkylene, p represents an integer of 0 to 20, R₂Is a hydrogen atom, an alkyl group, a phenyl group or a glycidyl group, wherein each (R)₁-O) units which may be identical or different)

The alkylene group is a linear or branched, unsubstituted or substituted alkylene group having 2 to 20 carbon atoms, and examples thereof include an ethylene group, a propylene group, a butylene group, and a 2-ethylhexyl group. As R₁The alkylene group of (a) is preferably ethylene and propylene.

R₀And R₀' are preferably the same and are hydrogen atoms.

Examples of the oxyalkylene unit represented by the formula (1) include an oxyethylene unit, an oxypropylene unit, an oxybutylene unit, an oxypentylene unit and an oxyhexylene unit, preferably an oxyethylene unit, an oxypropylene unit and an oxybutylene unit, and more preferably an oxyethylene unit.

The oxymethylene copolymer may further have a unit represented by the following formula (3).

－CH(CH₃)－CHR₃－ (3)

(in the formula, R₃Is a group represented by the following formula (4)

－O－(R₁－O)_p－R₄(4)

(in the formula, R₄Is a hydrogen atom, an alkyl group, an alkenyl group, a phenyl group or a phenylalkyl group, R₁And p is the same as defined in formula (2)

The alkenyl group is a straight-chain or branched, unsubstituted or substituted alkenyl group having 2 to 20 carbon atoms, a vinyl group, an allyl group, a 3-butenyl group, or the like.

Examples of the alkyl moiety and the phenyl moiety in phenylalkyl groups include the alkyl groups and phenyl groups described above. Examples of the phenylalkyl group include a benzyl group, a phenylethyl group, a phenylbutyl group, a 2-methoxybenzyl group, a 4-methoxybenzyl group, and a 4- (allyloxymethyl) benzyl group.

In the present invention, when a crosslinked structure is present, the alkenyl group and the glycidyl group in the group represented by formula (2) or the alkenyl group in the group represented by formula (4) can become a crosslinking point at the time of further polymerization reaction, and thus a crosslinked structure can be formed.

The method for producing the oxymethylene copolymer is not particularly limited, and examples thereof include: a method of bulk polymerizing trioxane as a 3-mer of formaldehyde and a comonomer using a cationic polymerization catalyst such as boron trifluoride, perchloric acid, or a heteropoly-acid. Examples of comonomers include: cyclic ether with 2-8 carbon atoms such as ethylene oxide, 1, 3-dioxolane, 1,3, 5-trioxepane, 1,3, 6-trioxacyclooctane and the like; cyclic formals having 2 to 8 carbon atoms such as cyclic formals of ethylene glycol and cyclic formals of diethylene glycol. By these comonomers, R is formed₀And R₀' the oxyalkylene unit represented by the formula (1) which is the same and is a hydrogen atom.

In the present invention, other oxymethylene copolymers include 2-membered copolymers and multipolymers. Therefore, as the oxymethylene copolymer used in the production method of the present invention, an oxymethylene copolymer having an oxymethylene unit and an oxyalkylene unit represented by the above formula (1), an oxymethylene copolymer having an oxymethylene unit, an oxyalkylene unit represented by the above formula (1) and a unit represented by the above formula (3), an oxymethylene copolymer further having a crosslinked structure, and the like can be widely used. In the present invention, R₀And R₀The unit represented by the formula (1) which is not simultaneously a hydrogen atom can be formed by copolymerizing a glycidyl ether compound and/or an epoxy compound, and the unit represented by the formula (3) can be formed by copolymerizing an allyl ether compound, for example.

The glycidyl ether and the epoxy compound are not particularly limited, and there may be mentioned: epichlorohydrin; alkyl glycidyl formals such as methyl glycidyl formal, ethyl glycidyl formal, propyl glycidyl formal and butyl glycidyl formal; diglycidyl ethers such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1, 4-butanediol diglycidyl ether, hexamethylene glycol diglycidyl ether, resorcinol diglycidyl ether, bisphenol a diglycidyl ether, hydroquinone diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polybutylene glycol diglycidyl ether; triglycidyl ethers such as glycerol triglycidyl ether and trimethylolpropane triglycidyl ether; tetraglycidyl ethers such as pentaerythritol tetraglycidyl ether.

As the allyl ether compound, there may be mentioned polyethylene glycol allyl ether, methoxypolyethylene glycol allyl ether, polyethylene glycol-polypropylene glycol allyl ether, butoxypolyethylene glycol-polypropylene glycol allyl ether, polypropylene glycol diallyl ether, phenylethyl allyl ether, phenylbutyl allyl ether, 4-methoxybenzyl allyl ether, 2-methoxybenzyl allyl ether and 1, 4-diallyloxymethylbenzene.

Examples of the chain transfer agent include carboxylic acids, carboxylic acid anhydrides, esters, amides, imides, phenols, and acetal compounds. Among them, phenol, 2, 6-dimethylphenol, methylal and polyacetal dimethoxy compound are preferable, and methylal is more preferable. Examples of the solvent include aliphatic hydrocarbons such as hexane, heptane and cyclohexane, aromatic hydrocarbons such as benzene, toluene and xylene, and halogenated hydrocarbons such as methylene chloride and dichloroethane. The chain transfer agent may be used alone or in the form of a solution dissolved in a solvent. When the chain transfer agent is methylal, the amount of the chain transfer agent added may be usually less than 2X 10 relative to trioxane^－1The range of wt%.

Examples of commercially available oxymethylene copolymers include "IUPITAL (registered trademark)," F20-03 "," IUPITAL (registered trademark), "F40-03" (manufactured by Mitsubishi engineering plastics Co., Ltd.).

The oxymethylene copolymer may contain known additives and/or fillers within a range not to impair the object of the present invention. Examples of the additives include a crystal nucleating agent, an antioxidant, a plasticizer, a delustering agent, a foaming agent, a lubricant, a mold release agent, an antistatic agent, an ultraviolet absorber, a light stabilizer, a heat stabilizer, a deodorant, a flame retardant, a sliding agent, a perfume, an antibacterial agent, and the like. Examples of the filler include glass fiber, talc, mica, calcium carbonate, and potassium titanate whisker. In addition, pigments and dyes may be added to make a desired color tone. Further, the resin composition may be modified by adding a transesterification catalyst, various monomers, a coupling agent (for example, other polyfunctional isocyanate compounds, epoxy compounds, glycidyl compounds, diaryl carbonates, etc.), a terminal treating agent, other resins, wood flour, and a natural organic filler represented by starch. The timing of adding the above-mentioned additives, fillers and the like is not limited at all, and they may be added at the stage of producing the oxymethylene copolymer, or may be added to the extruder together with the oxymethylene copolymer at the time of producing the polyacetal fiber.

The polyacetal fiber obtained by the production method of one embodiment of the present invention includes a plurality of filaments. That is, the polyacetal fibers are obtained by collecting a plurality of filaments discharged from a plurality of discharge ports.