JPS60209013A - Preparation of polyester yarn - Google Patents

Abstract

PURPOSE:To draw polyester yarn while controlling properly non-crystalline orientation, by cooling once polyester yarn obtained by melt spinning to <=the glass transition temperature, drawing it successively in a heating zone under heating, setting winding conditions in a specific range. CONSTITUTION:Yarn Y obtained by melt spinning is cooled and solidified, introduced into the heating zone 3, drawn by the drawing rollers 6 and 7 at >=4,000m/ min, and wound by the winder 10 at >=4,000m/min into a pirn shape. The winder 10 is a spindle drive type, and winding tension is controlled constant. The spindle itself is reciprocated at Tcm/sec velocity [V/2,400<=T<=V/180; V is winding velocity (m/min)], and yarn having 1.7-2.8g/d yield point stress, and the variation width DELTAT of stretch tension value measured in the fiber axis direction at 4% stretch of <=0.13g/d is wound as yarn having 3-40m per cm in the direction of bobbin axis.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for producing polyester fiber, and more particularly, it has excellent post-processing passability and weavability at high speed, and when developed into a highly twisted textured fabric. The present invention relates to a method for producing polyester fibers that has good crimp performance and can produce a woven fabric with uniform grain quality.

[Prior art]

Conventionally, polyester fibers have been supplied to the market in the form of cheese-wound or paan-wound packages. These polyester fibers are obtained mainly by drawing amorphous undrawn yarn spun at low speed in a separate step, or by directly drawing the yarn after spinning without winding it. Such polyester fibers are woven in a post-processing process, and in recent years, in order to reduce costs in this post-processing process, the speed of the weaving preparation process and the weaving speed have been increased.

However, when conventional polyester fibers are passed through higher-level processes at high speeds, they often break due to fluff, and even when woven at high speeds, the fabrics often have defects such as sink marks and streaks, which is a big problem. It has become. Furthermore, when developed as a textured fabric, not only the high-order passability is poor, but also the uniformity of the wrinkles that appear is poor, and the wrinkle performance varies widely within the fabric, making it difficult to obtain a desirable textured fabric.

After conducting various investigations into the causes of these two major problems in the use of conventional polyester fibers, it was discovered that the two problems mentioned above, which seemed to be caused by completely different devices, were actually caused by the same cause. .

In other words, the above-mentioned problems during high-speed weaving, as well as performance problems, are fundamental problems that are closely related to the internal structural characteristics of conventional drawn yarn, especially the structure of the amorphous part. requires fundamental improvements in the internal structural properties of the fibers.

In other words, conventional drawn yarns have a strong structure by stretching the molecular chains close to their limits and increasing their amorphous orientation, but loosening this structure and appropriately controlling the amorphous orientation solves the above problems. It turned out to be effective. However, in the conventional stretching method in which the yarn is held between rollers, it is not possible to uniformly stretch the yarn while appropriately loosening the amorphous orientation.

In addition, although threads with a relaxed amorphous orientation are very effective in solving the two problems mentioned above, they also have a new problem due to their weak mechanical properties due to their low amorphous orientation. The conventional winding method was not able to obtain a homogeneous package, as distortion was applied to the film during winding, causing problems such as warpage.

[Purpose of the invention]

An object of the present invention is to provide a method for producing polyester fibers that can be stretched uniformly while appropriately controlling the amorphous orientation, have uniform and good crimp performance, and can follow high-speed weaving. .

[Structure of the invention]

The present invention achieves the above object by cooling the polyester yarn discharged from the spinneret once to below the glass transition temperature, then introducing it into the heating zone again, heating and stretching it, and then using a spindle with a winding speed of 4000 m7 minutes or more. Using a drive-type winder, the spindle itself is reciprocated at a speed TcIrL/sec that satisfies the following formula without contacting the package being wound with other items, and the yield point stress is 1.7~
The fluctuation width ΔT of the stretch tension value measured in the fiber axis direction at 2.8 g/d and 4% stretch is 0.13 g/d.
This method is characterized in that the yarn length is 3 to 40% per unit length (1 cm) in the axial direction of the bobbin, and is wound as a package with substantially no real twist.

2400≦T≦5T (in the formula, V is the winding speed m7 minutes) First, in the present invention, a polyester polymer is melted and discharged from a nozzle to form a yarn at a temperature below the glass transition temperature. After cooling once, it is introduced into the heating zone again and heated and stretched.

As mentioned above, conventional drawn yarns have a high amorphous orientation and are excellent in S-shaped properties. In this case, the value is as high as 3 g/d or more.

Although such strong properties generally improve the mechanical properties of textiles and are desirable properties, they act as a negative factor when applied to highly twisted textiles or high-speed weaving applications.

That is, firstly, if the amorphous orientation is too high, it is difficult to set the twist, which causes wrinkle unevenness in the woven fabric when it is made into a woven fabric, reducing the quality of the woven fabric.

Secondly, due to the high amorphous orientation, high stress is generated in response to a certain strain (elongation) applied to the yarn during high-speed weaving, and this is left behind as a large strain inside the yarn, which causes stress during dyeing. Distortion develops and staining spots occur.

As a result of research by the present inventors, it has been found that in order to solve this problem, it is necessary to improve the physical properties so as to reduce the amorphous orientation of the fibers. Specifically, the yield point stress is 1.7 to 2.8 g.
The amorphous orientation may be controlled to such an extent that /d is satisfied.

However, when using the conventional stretching method in which the yarn is gripped between rollers and the stretching ratio is set low to reduce the amorphous orientation, uniform stretching cannot be achieved, resulting in uneven fiber internal structure and thickness, resulting in poor product quality. It becomes unusable.

There is also a method of high-speed spinning at a spinning speed of 5,000 m for 7 minutes or more in order to lower the amorphous orientation, but in the darning method, the amorphous orientation is too low, the grain development is reduced, and the weaving method 1. A new problem arises in that it becomes easier to stretch due to the instantaneous impact force applied at the moment of impact.

Therefore, in order to uniformly draw fibers with a controlled amorphous orientation with a yield point stress of 1.7 to 2.8 g/d, it is necessary to use both conventional drawing methods and high-speed spinning methods. Not applicable.

Therefore, in the present invention, after the yarn is solidified in the spinning process, it is reintroduced into the heating zone, re-stretched, and then taken off at a take-up speed of 4000 m/min or more, which is characterized by a yield point stress of 1.7 to 2.8 g/d. A yarn with a desired degree of amorphous orientation can be obtained under uniform stretching.

By controlling the degree of amorphous orientation in this way, the wrinkle performance in high-twist applications is improved and it becomes possible to handle high-speed weaving, but such fibers are difficult to handle due to their low amorphous orientation. is extremely difficult.

For example, since the amorphous orientation is low, strain is likely to be applied to the inside of the fiber during winding due to impact force or external force that would not cause problems with conventional yarns. To explain this with a specific example, when winding with the conventional cheese method, high-speed traverse is used, but the winding tension is substantially higher at both ends of the traverse than in the center, causing excessive internal strain in the yarn. to be internalized.

In addition, a large impact force is applied to the yarn due to the sudden turn of the traverse guide, and yarn clumps are likely to occur at both end surfaces, making it easy for large distortions to occur. Therefore, both end faces are in a state of large internal strain from the time the winding is started.

This tendency is amplified because as the winding speed increases, the traverse speed also increases. Such internal distortions are characteristically manifested in fabrics and dyed fabrics, resulting in stripes and degrading the quality of the fabric.

Therefore, the fibers with controlled amorphous orientation of the present invention are
It is important to wind the film in such a way that strain is not applied as much as possible during winding, and that the amount of strain applied does not vary depending on the winding position.

Therefore, in the present invention, a spindle drive type winder is used as the winder, and the package being wound must be wound in a completely non-contact state with other objects. Even in a spindle drive type winder, it is not advisable to use roller bales that come into contact with the package to control the winding speed. Even for other purposes, if there is a roller-like object that comes into contact with the package, it will press down on the package with a certain amount of surface pressure, which will press the wound yarn against each other and cause extra strain during winding. Since the threads overlap excessively, the unwinding property becomes poor. In the present invention, it is important that the package during winding does not come into contact with any other object. For this purpose, in order to control the winding speed, it is necessary to detect the winding tension and reduce the spindle rotation speed according to the amount of winding to maintain a constant tension, or to memorize the decreasing pattern of the spindle rotation speed in advance. , program control or the like is applied to reduce the number of rotations according to the winding time.

In the present invention, a package must be formed by using such a spindle drive type winding machine and reciprocating the spindle body with a bobbin attached thereto at a speed of 2400 to 18 G'' seconds. However, V is the winding speed (?7 L/min). In this way, the thread to be wound on the bobbin is forced to perform a reciprocating motion on the spindle itself, so that the thread to be wound on the bobbin always travels at a substantially constant position without having to move along the thread path as in a traverse motion.

Therefore, there is almost no variation in the winding tension depending on the winding position of the package, and there is extremely little strain imparted to the yarn, so that a uniform package can be obtained. If the reciprocating speed T of the spindle is faster than + (cIIL/sec), the inertial force of the spindle when folding both end faces of the package is too large, resulting in the package itself having the disadvantage of chattering, buckling, etc. . Especially as the volume increases,
This phenomenon becomes noticeable.

In addition, when it is less than 24oo (CrIL/sec), the deviation due to traverse between the previously wound yarn and the next wound yarn on the package surface is small, and the yarns are too close to each other. For this reason, tension fluctuations during unwinding are large, causing problems in higher-order processes. It is preferable to control within the range of ≦T≦4 (α7 seconds).

By sequentially decreasing the winding width as the winding diameter of the yarn increases, a preferable taper angle can be imparted to the package, and a stable package form can be formed. Furthermore, if a real twist is applied to the yarn to be wound to improve unwinding property, extra strain will be added to the yarn, which will later appear as unevenness, so the yarn will be wound without adding any real twist. need to take it.

As described above, the yield point stress is specified to be 1.7 to 2.8 g/d by the drawing method in which the yarn is immediately introduced into a heating zone after solidification and taken off at a drawing speed of 4000 m/min μ. Uniform stretching is performed while controlling the amorphous orientation,
By specifying the winding method so as to minimize strain on the yarn, polyester fibers with good crimp performance and applicable to high-speed weaving can be obtained.

In addition, this polyester fiber has a ΔT of 0.13 g/d or less, preferably 0.1 Vd during the variation of the stretch tension value during 4-way stretching, measured in the fiber axis direction.
It is as follows.

This limit on the stretch tension value is a measure of the strain inherent in the system, and polyester fiber packages that do not satisfy the above-mentioned specifications will develop sink marks and streaks when made into a knitted fabric.

Furthermore, in order to prevent strain distribution from occurring in the package, the unit length of the package in the bobbin axis direction is 1 c.
It is necessary to control the length of the yarn wound on the package to a length of 3 to 40 tn regardless of the winding layer of the package, and preferably 5 to 30 m.

A package with a yarn length of less than 3 m means that the traverse speed of the yarn during winding is high, and the actual winding tension at both ends of the package increases and the impact force at the time of folding is too large. Sometimes, a large strain is applied at this end face, resulting in a strain distribution that is so large that it becomes a defect in the knitted fabric as a package.

When the yarn length is longer than 40 m, the yarns are too closely spaced, causing fluctuations in unwinding tension and generation of fuzz when unwinding from the package, causing problems in higher-order processes.

In order to form such a package, it is necessary to form the package so that the end face of the package has a taper angle of 25° or less.

Therefore, the traverse width of the yarn must be gradually reduced depending on the amount of winding. If the taper angle is greater than 25°, the shoulders tend to sag from the tapered part of the package, and it is not possible to form a package with good unwinding properties.

Note that the heating zone in the present invention only needs to be a heated space through which the yarn passes, and for example, a tube having a cylindrical shape or a rectangular cross section is used.

In order to perform uniform stretching in such a heating zone, a flow rate of 10 to 66 Nl for 7 minutes and a temperature of 10
A preferred method is to heat the heating zone atmosphere from around the heating zone to 100 to 300°C while introducing heating gas at 0 to 300°C.

Furthermore, when introducing the heating gas into the heating zone, if it is introduced from the top of the heating zone so as to be approximately perpendicular to the running direction of the yarn, and then allowed to run along the running direction of the yarn, the uniformity is further improved. Further, if a rectifying filter is arranged to surround the yarn path and the heated gas is introduced while being rectified through the rectifying filter, the uniformity is further improved.

Further, it is preferable that the yarns are not completely concentrated when they enter the heating zone after solidification, since the heat treatment efficiency is better and the uniformity is also better.

Furthermore, it is preferable to subject the yarn to an interlacing treatment to improve the cohesiveness of the yarn before winding it. This is because by performing the interlacing treatment, it is possible to prevent abnormally high strain or stress from being applied to each single yarn during winding. The degree of entanglement is achieved by providing a disturbance that slightly disturbs the parallelism so that the filaments are not completely parallel. Preferably, the number of entanglements on water is about 1/m to 70/m. The position where the interlacing process is performed can be arbitrarily selected depending on the purpose, such as in front of the first godet roller, between the first godet roller and the second godet roller, or between the second godet roller and the winder.

In particular, when installed between the final take-up godet roller (second godet roller in the above case) and the winder, the yarn path is constant and the winding tension is constant, so the entangling tension is constant and uniform entangling is achieved. This is preferable because it allows processing. Furthermore, even when the yarn is installed in front of the first godet roller or between the first and second godet rollers, the yarn is intertwined and bundled at the exit of the final take-up godet roller, so the yarn is easily separated, and in addition, the winding tension is always constant. Therefore, it is preferable that the package can be formed with extremely low winding tension.

In order to make the polyester fibers wound around the package more uniform, it is effective to take into consideration the tension at the time of winding and the bobbin diameter. That is, since the relaxation of strain after the package is made depends on the tightening force, it is preferable to reduce the tightening force as much as possible. Generally, when tightening a package, the force P is the distance 1 from the center of the package.
It is expressed as T (r): winding tension], but it is preferable to decrease the value of P. Specifically, lowering the winding tension T (r) , the radius of the innermost layer portion may be increased, that is, the bobbin diameter may be increased.

The winding tension T (r) is 0.5 g/d, more preferably 0.3 g7. Do the following. The bobbin diameter is preferably 2 inches or more from the viewpoint of production efficiency.

Note that the surface drive type winder, which is widely used as a spinning winder, winds the package by contacting it with the drive roll, and the cheese winder, which winds the package into a cheese shape, have a drive roll. It is also necessary to make reciprocating movements, and this cannot be applied to the present invention.

In the present invention, polyester means polyester having ethylene terephthalate units as the main repeating unit, and polyethylene terephthalate is the main target, but
A copolyester copolymerized with a third component may be used as long as it contains 80 molti or more of polyethylene terephthalate. Moreover, the cross-sectional shape of the polyester fiber can be applied to various known irregular cross-sections from a round cross-section.

Furthermore, the method for producing polyester fibers of the present invention will be explained based on the drawings.

FIG. 1 is a schematic diagram showing an example of the spinning and winding process of the present invention.

The polyester yarn Y melt-spun from the spinneret 1 is cooled and solidified by the cooling device 2, and then introduced into the heating zone 6.

A predetermined amount of oil is applied to Y by the oil supply device 4, and while being entangled by the interlaced nozzle 5, it is passed to the take-up roller 6.
7, the material can be removed at a removal speed of 4000 m1 minute or more.

The yarn leaving the second godet roller 7 passes through a yarn path guide 9 and is wound up into a pirn shape by a winding device 10 at a speed of 4000 m/min or more.

The winding device 10 is of a spindle drive type and has a drive motor 11.
It is independently driven by. The drive motor 11 is controlled via a tension detector 8 for detecting winding tension and a control panel 14. The drive motor 11 is controlled by a control panel 14 consisting of a power controller 16 and a tension setting device 12 so that the winding tension is constant, and the winding speed is always controlled to be constant.

The winding device (spindle) 10 is connected to a hydraulic cylinder 15, and the movement of the hydraulic cylinder causes the winding device 10, that is, the package 160, to reciprocate. Therefore, the thread does not move reciprocatingly, but is wound around the windshield. Rotating - The package 16 is rotated without contacting anything.

Note that the meaning of "running in substantially the same position" includes cases where the yarn sways slightly due to entanglement treatment, fluctuations in spinning tension, etc., and cases such as those shown in FIG.

That is, FIG. 2 shows the state at the beginning of winding onto the bobbin 17 (the second state).
Figure A) and a somewhat thickened state (Figure 2 B) are shown.
When the yarn path guide 9 is fixed, depending on the amount of winding, the yarn path may be sequentially moved as indicated by θ as shown in FIG. 2B.

Naturally, the thread guide 9 and the winding device 10 are
A more preferable method is to move θ little by little according to the amount of winding so that θ=0° at all times.

Moreover, FIG. 3 is a longitudinal sectional view of a heating cylinder showing an example of the heating zone of the present invention. The cooled and solidified polyester yarn Y runs into the heating cylinder 18 without contacting the heating cylinder and is heated.

A rectifying filter 20 is provided above the heating cylinder 18, a heated gas supply section 21 is provided to surround the filter, and heated gas is introduced from the heated gas supply section 22 through the filter 20.

Regarding the method of introducing the heated gas, although a filter type was illustrated, the method is not limited to this.

〔Effect of the invention〕

As described above, according to the method for producing polyester fiber of the present invention, the melt-spun polyester yarn is once cooled to below the glass transition temperature, and then heated and stretched in a heating zone, so that uniform stretching can be achieved. It is possible to control the amorphous content, improving the performance of high-twist yarns, and making it possible to handle high-speed weaving.

Further, according to the present invention, a spindle drive type winder is used as the winder, and the package being wound is not in contact with other things, and the spindle itself with the bobbin attached is moved according to the formula V.
Speed TcIIL that satisfies /2400≦T≦V/180
Since the yarn is wound while being reciprocated at a speed of 1/sec (V is the winding speed per minute), there is almost no variation in the winding tension depending on the winding position of the package, and a yarn with extremely little distortion can be obtained.

〔Example〕

Examples of the present invention will be described below.

In addition, the physical property values in Examples were measured by the following method.

(1) Yield Point Stress Using a Tensilon tensile tester manufactured by Toyo Baldwin Co., Ltd., a strength and elongation curve was drawn under conditions of a sample length of 200 mm and a tensile speed of 100 mm/min. The model chart is shown in Figure 4. From the chart, the strength of the intersection C between the tangent A passing through the origin and the tangent B of the straight line after the curve yields is defined as Y, and Y is divided by the denier d of the multifilament. Let the value be the yield point stress.

(2) Uniformity (Worcester's mottling) Yarn speed 25
m/min, range ±12.5%, chart speed 5 cm/min, and measure the uneven thickness in the fiber axis direction. As shown in the figure.

The yarn to be tested 24 unwound from the package 26 passes through the guide 25 and is adjusted to a primary tension of 0.1 g/g by the tension adjustment device 26.
d, and between the constant speed rows 227 and 29, the dancer roller 28 and the load 28' are applied! After applying a load of 70.2 g/d and adjusting the tension to a constant tension, it is stretched by 4% between the rows 229 and 31 arranged at intervals of 1501111, and is then continuously run at a surface speed of 80 m/min of the roller 61. At this time, the tension fluctuation of the extension part is detected by the pickup 60,
Record at a chart speed of 601 m1/min.

In the figure, f represents a frictionless roller, S represents a separate roller, and 62 represents a winder.

FIG. 6 shows an example of a chart obtained by measurement using the apparatus shown in FIG. Chart length of any part 15c
Large JL I-J /? during the fluctuation of tension in IrL? %J
,? e/-IMl f(JA A〒-01, A〒-
<Example 1> - Polyethylene terephthalate fibers were obtained by different manufacturing methods shown below.

Manufacturing method 1> Polyethylene terephthalate was melted at 290°C and discharged from a nozzle with a hole diameter of 0.2 mm and a diameter of 36 mm. Spinning speed 50
00m/min, 6ooom/min, 75D-36
A yarn of F was obtained. The winding device shown in FIG. 1 was used. The spindle reciprocating speed was 10 CIrL/sec, and the taper angle was 20°. These samples are designated as 41.2.

<Production method 2> Polyethylene terephthalate is melted at 290°C and the pore size is 0.
．． It was discharged at a rate of 29.2 g per minute from a mouthpiece with 211+1φ36 holes, and after applying an oil agent, it was taken up at a speed of 1000 m7 with a pair of Nelson-type heating rollers heated to 85°C, and then it was rolled at 160°. After stretching 3.5 times with a pair of Nelson-type heating rollers heated to C, the same spindle dry-type winder as in manufacturing method 1 was used at a spindle reciprocating speed of IO/sec, a speed of 3500 m7 min, and a taper angle of 20
Winded at °. Let this sample be /163.

<Manufacturing method 3> Polyethylene terephthalate was melted at 290°C and discharged from a mouthpiece with 36 holes and a hole diameter of 0.2WIWLφ.

The cooled and solidified yarn was introduced into a heating cylinder with an inner diameter of 15 mm and a length of 1 m, as shown in Fig. 3, which was placed 2 m below the mouthpiece.

The heating cylinder is electrically heated from around the cylinder, and its set temperature is 20
The temperature was set to 0°C. Also, inside the heating cylinder is 200°C925Nl.
/min of heated gas was introduced through a sintered metal filter with an opening of 20μ.

By changing the take-up speed of the yarn that had passed through the heating zone in this way, samples with take-off speeds of /16.4 to /168 were obtained. Note that the discharge amount was changed according to the take-up speed so that the total denier was 75D. The winding device was the same as that used in manufacturing method 1, and the traverse reciprocating speed was 10 (-m) 17 seconds, and the taper angle was 20°.

Table 1 shows the physical property values of Samples/161 to 8 obtained by the above-mentioned manufacturing methods 1 to 3. Table 1 also shows the results of high-speed weaving when embossed fabrics were produced using these fibers.

(Margins below this page) As is clear from Table 1, the yield point stress of the yarn produced by manufacturing method 3 of the present invention and taken at a take-up speed of 4000 m for 7 minutes or more is 1.7.
~2.8 g/d, and it can be seen that the katsushi has good weaving performance, and no sink spots occur even during high-speed weaving.

<Example-2> Polyethylene terephthalate was melted at 290°C and
．． 2. Spinning from 36 IIφ nozzles, take-up speed 130
It was withdrawn at m/min.

The thus obtained undrawn yarn was stretched at various draw ratios to obtain yarn having a yield point stress of 1.7 to 2.8 g/a.

The US values of these yarns were all distributed between 0.90 and 1.40, and the uniformity was poor. Furthermore, when such threads were dyed into fabrics, dyeing spots occurred frequently.

<Example 3> Regarding samples of /%6 and 7 of Example-1 Example-1
Winding was carried out under the same conditions as above, with the spindle reciprocating speed changed as shown in Table 2.

The stretch tension ΔT of the wound yarn is also shown in Table 2.

<Table-2> As is clear from Table-2, the rotor 9-11°l615-17 satisfies the range of traverse reciprocating motion in the present invention.
It can be seen that the package is homogeneous and has a good quality.

<Example-4> The 46 in Example-1 was prepared in the same manner as in Example 1 except for the winding machine.
．． 7 yarns are supplied. The winder was a TW-601 cheese winder manufactured by Toshi Engineering Co., Ltd., and the traverse speed was 850 reciprocations/min.

The ΔT of the obtained package was as large as 0.24 at a winding speed of 4000 m7 minutes and 0.27 at a winding speed of 5000 m7 minutes.
I can understand that cheese indian is not desirable.

<Example-1> A 75-denier, 36-filament package was prepared under the same conditions as Example-1, except that the flow rate of heated gas introduced into the heating zone for the sump light of Examples-1 and 47 was changed as shown in Table-3. I got it. The US values of the obtained yarns are also shown in Table 3.

<Table 3> As is clear from Table 3, 420 to 23 with a flow rate of 10 to so Nt/min are preferable because they have a small US value and good uniformity.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the spinning process of the present invention, FIGS. 2A and 2B are side schematic diagrams illustrating the winding position in the present invention, and FIG. 3 is a heating zone in the present invention. A vertical section schematic diagram showing an example, FIG. 4 is a model diagram of a strong elongation curve showing a method for measuring yield point stress, and FIG. 5 is a model diagram of a measuring device for measuring ΔT during fluctuations in stretch tension. FIG. 6 shows a chart of stretch tension measured by the apparatus of FIG. 5 for calculating ΔT. 6... Heating tube, 10... Winding device, 16... Package. Agent: Patent Attorney Shin Ogawa − Patent Attorney Ken Noguchi Teru Patent Attorney Kazuhiko Saishita

Claims (1)

[Scope of Claims] After the polyester yarn discharged from the spinneret is once cooled to below the glass transition temperature, it is introduced into the heating zone again to be heated and stretched, and then the spindle drive has a winding speed of 4000 m for 7 minutes or more. The package being wound by the mold winding machine is moved in a reciprocating manner at a speed of TcIIL/sec that satisfies the following formula, with the spindle itself reciprocating in a state where the package being wound is not in contact with other objects, and the yield point stress is 1.7 to 2.8. g/d, the variation width ΔT of the stretch tension value measured in the fiber axis direction during 4-inch stretching is 0
．． 1 unit length of yarn in the bobbin axis direction of 13g/d or less
1. A method for producing polyester fiber, characterized in that the yarn length per crrL) is 3 to 40 fi, and the fiber is wound as a package with substantially no real twist. 1≦T≦cypress■ 400 (In the formula, V is the winding speed m7 minutes)