JP2001011733A - Polyester for melt-spinning, partially oriented undrawn fiber of polyester and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyester which is used for melt spinning, has excellent fiber formability and excellent productivity and can give partially oriented undrawn fibers having excellent drawability, process passableness and draw fiber physical properties, by copolymerizing trimellitic acid, trimesic acid or one of their derivatives so as to satisfy specific conditions. SOLUTION: This polyester copolymerized with trimellitic acid, trimesic acid or one of their derivatives so as to satisfy the conditions of the inequalities: 0.08<=c<=0.28, and 1.48<=c+2×(IV)<=1.60 [c(mol.%) is the copolymerization amount of the trimelliic acid, the trimesic acid or one of their derivatives; IV (dVg) is the intrinsic viscosity of the polyester]. The main repeating units preferably comprise ethylene terephthalate units. The polyester is preferably melt-spun at a taking speed of 3,000 to 5,000 m/min to obtain the polyester partially oriented undrawn fiber preferably having a birefringence of 0.020 to 0.060.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester for melt spinning, an undrawn polyester partially oriented yarn, and a method for producing the same. More specifically, the present invention relates to a method for producing a polyester for melt spinning and a partially oriented polyester non-oriented yarn excellent in spinning properties and productivity, and a partially oriented polyester non-oriented yarn excellent in stretchability, processability, and physical properties of a stretched yarn.

[0002]

2. Description of the Related Art Polyester fibers such as polyethylene terephthalate are used in large quantities and in a wide range of fields because of their excellent properties. Above all, a partially oriented undrawn yarn having a take-up speed of 2000 to 4000 m / min (hereinafter abbreviated as POY) has an advantage that it can be used not only for drawing but also for drawing false twisting as it is. Therefore, it occupies an important industrial position. On the other hand, with regard to false twisted yarns, by adopting the draw false twisting process in which drawing and false twisting are simultaneously performed using this POY, the productivity is greatly improved compared to the conventional method of false twisting drawn yarns. Was achieved.

In recent years, there has been an increasing demand for further improvement in productivity, and attempts have been made to increase productivity per unit time by increasing the spinning speed of undrawn yarn. In the case of a fiber, there is a problem that orientation crystallization proceeds with an increase in spinning speed, and the mechanical properties of the fiber change. For the purpose of solving this problem and obtaining fibers having the same characteristics even when the spinning speed is increased, many means have been studied to suppress the molecular orientation of polyester which increases as the spinning speed increases. Among them, a method of incorporating a polyfunctional branching agent into polyester is known.

Japanese Patent Application Laid-Open No. 63-75112 discloses a technique capable of increasing the yarn processing speed by introducing trimesic acid, trimellitic acid or their esters into polyester. Although this technique certainly improves the process passability at the time of processing, it does not consider the improvement of productivity due to the suppression of orientation at all. Examples of trimethyl trimellitate copolymers mentioned in this technology include about 6 meq (corresponding to about 0.12 mol%), a relative viscosity (LRV) of about 21 (about 20.5 for the reference standard polymer), The productivity improvement is small with this polymer. Further, in this technique, it is described that an increase in the relative viscosity hinders the transport of the polymer, particularly spinning, sharply increases defects during spinning, and significantly increases the number of spinning cuts. There is a description that there is no.

JP-A-53-292 discloses a method for improving the draw ratio by copolymerizing a polyester with a chain branching agent. In this technique, although the draw ratio is improved by increasing the elongation, that is, the effect of suppressing the orientation during spinning is recognized, pentaerythritol, which is described as a preferred example of the branching agent, is volatile and has a drawback that it is difficult to handle. . Further, although it is described that the trimer acid is effective, it is necessary to increase the amount of addition.
For this reason, there is a concern of gelation, and in addition to an increase in filtration pressure, spinning properties, particularly high-speed spinning properties, are poor, and stable production is difficult, so that improvement in productivity cannot be expected. Further, the POY obtained has poor drawability and process passability, and further has a problem that the drawn yarn properties, particularly the strength, are reduced.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, to suppress the orientation during spinning, and to improve the productivity of partially oriented undrawn polyester yarn having excellent spinning properties. Providing a polyester, and providing a method for stably and efficiently producing the polyester partially oriented undrawn yarn without any process problems,
It is still another object of the present invention to provide a polyester partially oriented undrawn yarn which is excellent in drawability, process passability, and drawn yarn properties.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been studied in order to suppress the molecular orientation, which increases with an increase in the spinning speed, and to obtain a partially oriented polyester unoriented yarn having good spinnability, stretchability and stretched yarn properties. The inventors have found that it is possible to eliminate the drawbacks of the prior art by maintaining a specific relationship between the content of trimellitic acid, trimesic acid or a derivative thereof and the intrinsic viscosity (IV) of the polyester, and arrived at the present invention. Things.

[0008] That is, the present invention provides a polyester for melt spinning, characterized in that trimellitic acid, trimesic acid or a derivative thereof is contained so as to satisfy the following conditions.

[0009]

(Equation 2)

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester referred to in the present invention is
Preferred are polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, and more preferred is polyethylene terephthalate.

The polyester used in the present invention may have other components copolymerized within a range not to impair the gist of the present invention. Further, the polyester of the present invention may contain a small amount of additives such as a matting agent, a flame retardant, and a lubricant. As the copolymerization component, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, 5-sodium sulfoisophthalic acid, and 5-tetrabutylphosphonium isophthalic acid Aromatic, aliphatic, alicyclic dicarboxylic acids and their derivatives such as acids, and propylene glycol;
Butylene glycol, tetramethylene glycol, 1,
Examples thereof include aromatic, aliphatic, and alicyclic diol compounds such as 4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol, polyalkylene glycol, bisphenol A, and bisphenol S.

In the polyester for melt spinning in the present invention, trimellitic acid, trimesic acid or a derivative thereof is copolymerized. Polyfunctional compounds other than these have problems in reactivity with polyester, affinity and ease of handling. The derivative is not particularly limited, and examples thereof include an alkyl ester.

In the present invention, the copolymerization amount of trimellitic acid, trimesic acid or a derivative thereof is 0.08 to 0.28 mol% based on the acid component of the polyester. When the copolymerization amount is less than 0.08 mol%, the effect of suppressing the orientation is insufficient. As the copolymerization amount is increased, the effect of suppressing the orientation is increased, but if it is more than 0.28 mol%, the spinning property and the stretchability are deteriorated.

The polyester for melt-spinning in the present invention must have the intrinsic viscosity (IV) and the copolymerization amount of trimellitic acid, trimesic acid or a derivative thereof satisfying the following conditions.

[0015]

(Equation 3) It is more preferable that the following condition is satisfied.

[0016]

(Equation 4) Kagaku Doujin (Chemical Special Edition No. 39, p113 (1969))
It is generally known that in melt spinning, when the IV of a polymer, that is, the degree of polymerization, is increased, the orientation of fibers obtained at the same spinning speed is promoted, as described in Japanese Patent Application Laid-Open No. H11-163,028. However, as a result of diligent studies by the inventors, when trimellitic acid, trimesic acid or a derivative thereof is copolymerized, if the IV of the polymer is increased, the orientation of the fiber, which is obtained at the same spinning speed, is suppressed. The effect was found.

By increasing the IV according to the present invention, it becomes possible to sufficiently increase the alignment suppressing effect without excessively increasing the copolymerization amount of trimellitic acid, trimesic acid or a derivative thereof. In addition, it is possible to simultaneously improve the deterioration of the spinning property and the productivity by causing a large amount of trimesic acid or a derivative thereof to be copolymerized. In addition, the drawn yarn properties can be improved by a synergistic effect of an increase in IV and a decrease in the copolymerization amount of trimellitic acid, trimesic acid or a derivative thereof.

The proper range of IV in the present invention varies depending on the copolymerization amount of trimellitic acid, trimesic acid or a derivative thereof. However, when the IV is smaller than the above conditions, the effect of suppressing the alignment becomes insufficient. The larger the IV, the greater the orientation suppression effect. However, if the IV is larger than the above condition, the orientation suppression effect gradually decreases, and in addition, the spinnability deteriorates.

When trimellitic acid, trimesic acid or a derivative thereof is copolymerized, it is not clear why the orientation of the fiber obtained at the same spinning speed is suppressed when the IV of the polymer is increased. Can be considered.

Since the molecular orientation in polyester melt spinning is affected by the spinning tension, to obtain a fiber in which the molecular orientation is suppressed even if the spinning speed is increased in the spinning process,
It is considered effective to form a portion having a high elongational viscosity in the polyester by a branching / crosslinking component or the like.
As the elongational viscosity of this portion is larger, the effect of suppressing the orientation becomes larger, so that the effect of suppressing the orientation is increased by increasing the copolymerization amount of the branching / crosslinking component. Many exist.

On the other hand, when IV is increased, even if the copolymerization amount of the branching / crosslinking component is the same, the elongational viscosity increases because the molecular weight of the branching / crosslinking component increases. At this time, the elongational viscosity of the non-branched / crosslinked polyester part also increases, but it is considered that the elongational viscosity of the branched / crosslinked part is more dominant when the orientation suppression effect appears in the thinning behavior in melt spinning. Therefore, it is presumed that, as a result, increasing the IV suppresses the orientation of the obtained fiber.

PO formed from the polyester of the present invention
Y shows a lower degree of orientation when melt-spinning is performed under the same spinning conditions as compared with POY formed from a polyester not copolymerized with trimellitic acid, trimesic acid or a derivative thereof. Therefore, when the yarn is drawn at the same spinning speed, the draw ratio at the time of drawing and drawing false twisting can be made larger, so that the fineness of POY necessary to obtain a drawn polyester yarn and processed yarn having a desired fineness is increased. It is possible to improve the POY production amount per unit time (increase the spinning discharge amount).

Further, in order to obtain the same degree of orientation from the polyester of the present invention as that of POY formed from a polyester not copolymerized with trimellitic acid, trimesic acid or a derivative thereof, it can be realized by increasing the spinning speed of POY. . In this case, the fineness of the POY required to obtain a drawn polyester yarn and a processed yarn having a desired fineness is almost the same as that of the POY made of the polyester of the present invention and the POY made of the polyester which does not copolymerize trimellitic acid, trimesic acid or a derivative thereof. Equivalent to the POY of the present invention
Can be obtained at a higher spinning speed, so that the POY production amount per unit time can be further improved (the spinning discharge amount can be increased).

PO formed from the polyester of the present invention
Since Y has an orientation suppressing effect, it has various favorable properties when performing stretching or stretch false twisting, and in addition to the advantage that the POY production amount per unit time can be increased, stretching and stretching can be performed. It has favorable characteristics such as improved processability during false twisting, improved physical properties of drawn yarn, and higher crimp characteristics when processed yarn is used.

The partially oriented polyester yarn of the present invention has a birefringence of 0.020 which is an index indicating the degree of molecular orientation.
It is preferable to be 0.060. Birefringence is 0.0
When the ratio is 20 to 0.060, an appropriate heating temperature and stretching ratio can be obtained in stretching and false twisting, and stable stretching and processing can be performed.

The partially oriented undrawn polyester yarn of the present invention comprises a polyester for melt spinning, wherein trimellitic acid, trimesic acid or a derivative thereof is copolymerized so as to satisfy the following conditions: 3000 to 5000 m / m.
It can be produced by melt spinning at a take-off speed of a minute.

[0027]

(Equation 5) The copolymerization of trimellitic acid, trimesic acid or a derivative thereof into the polyester can be carried out during the polycondensation reaction of the polyester or at any stage after the reaction. Alternatively, a master chip for copolymerizing trimellitic acid, trimesic acid or a derivative thereof at a high concentration may be separately prepared, and this may be mixed during melt spinning.

By using the polyester of the present invention, melt spinning, which has a large effect of suppressing orientation and is excellent in spinnability, in particular, melt spinning of POY becomes possible, and an improvement in productivity can be achieved. Further, the polyester of the present invention is obtained by a simple method of copolymerizing the polyester with trimellitic acid, trimesic acid or a derivative thereof, and adjusting the copolymerization amount and the intrinsic viscosity to satisfy specific conditions. POY has favorable properties such as stretchability, processability, and the properties of drawn yarn, and is considered to be particularly significant from an industrial viewpoint.

Hereinafter, the present invention will be described specifically and in more detail with reference to examples. However, the present invention is not limited to the following examples. The physical properties in the examples were measured by the following methods.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Intrinsic viscosity (IV) Measured in orthochlorophenol at 25 ° C.

B. Strength and elongation Using Orientec Tensilon tensile tester, PO
In the case of Y, the initial sample length is 50 mm and the pulling speed is 400 mm
Per minute, and in the case of a drawn yarn, the initial sample length was 200 mm and the tensile speed was 200 mm / min.

C. Birefringence (Δn) Using a BH-2 polarizing microscope compensator manufactured by OLYMPUS, the birefringence was determined from the retardation and the fiber diameter by an ordinary interference fringe method.

D. Fineness spot (U%) Using a Worcester spot tester manufactured by Chelbegar Worcester,
Yarn speed 100m / min, measured with measurement type normal, U%
The value was determined.

E. POY productivity (W ₇₅ ) The fineness of the drawn yarn obtained in the example and the spinning discharge amount required to obtain a 75D drawn yarn from the spinning discharge amount at that time are calculated from the following formula, and the POY productivity is calculated. Index.

[0035]

(Equation 6) Example 1 When performing a general polycondensation reaction using terephthalic acid and ethylene glycol, trimethyl trimellitate (hereinafter referred to as TMT)
(Abbreviated as M) was copolymerized with terephthalic acid at 0.16 mol%, and the conditions were adjusted so that the IV became 0.68 to obtain a polyester.

Using a single-screw extruder, the spinning temperature was
Spinneret with a hole diameter of 0.23 mmφ and 36 holes at 295 ° C
Spinning speed of 50.0 g / min and 4000 m / min
To obtain a polyester POY. Thread cutting during spinning
This did not occur, and the spinnability was excellent. This POY fiber
Table 1 shows the degree, elongation, Δn, and U%. Δn is 31 × 10
^-3From POY (Comparative Example 2) obtained at the same spinning speed as
And TMTM is copolymerized with polyester.
That the orientation during spinning is suppressed by
You.

This POY was stretched at a stretching speed of 800 m / min, a hot roller temperature of 90 ° C. and a draw roller temperature of 120 ° C. so that the residual elongation was 38%. No yarn breakage occurred during stretching, no fluff was seen on the wound yarn, and the stretchability and process passability were excellent. Table 1 shows the fineness and strength of the drawn yarn. The strength was 5.2 g / d, indicating that the yarn had sufficient strength as a drawn yarn.

The POY productivity was 56.7 g / min, which is higher than that of POY (Comparative Example 2) obtained at the same spinning speed.

As can be seen from Table 1, by using a polyester obtained by copolymerizing TMTM and having an IV of 0.68, the orientation is suppressed even if the spinning speed of POY is increased. In addition to being able to improve POY productivity (increase in spinning discharge), the obtained POY has characteristics that it has excellent drawability, process passability, and excellent drawn yarn physical properties. Understand.

[0040]

[Table 1] Comparative Example 1 A polyester was obtained in the same manner as in Example 1 except that TMTM was not copolymerized. The IV of this polyester is 0.6
It was 4.

Spinning was carried out in the same manner as in Example 1 except that the spinning speed was changed to 3000 m / min.
Y was obtained. No yarn breakage occurred during spinning, and the spinning properties were excellent. Table 1 shows the fineness, elongation, Δn, and U% of this POY.

This POY does not break during drawing,
No fluff was seen in the wound yarn, and the stretchability and process passability were excellent. Table 1 shows the fineness and strength of the drawn yarn. The POY productivity was 40.3 g / min.

As can be seen from Table 1, the polyester which does not copolymerize TMTM has sufficient spinning properties, stretchability and stretched yarn properties, but has the same spinning speed as that of Example 1 even though the POY properties are equivalent. , The POY productivity is reduced (the spinning discharge amount is reduced). Comparative Example 2 Using the polyester polymerized in Comparative Example 1, spinning was performed in the same manner as in Example 1 to obtain a polyester POY. Single yarn breakage occurred once during spinning, but the spinnability was generally good. Table 1 shows the fineness, elongation, and Δn of this POY. Δn increases to 50 × 10 ^{−3 as the} spinning speed increases.

In this POY, no yarn breakage occurred during stretching, but a single fluff was observed in the wound yarn. Table 1 shows the fineness and strength of the drawn yarn. POY productivity is 4
1.7 g / min.

As can be seen from Table 1, when the spinning speed of POY is increased, the POY elongation is decreased and the draw ratio is decreased, so that the POY productivity (spinning discharge) is hardly improved. Comparative Example 3 A polyester was obtained in the same manner as in Example 1 except that the IV was changed to 0.64, and spun in the same manner as in Example 1 to obtain a polyester POY. Since the IV is too low relative to the TMTM copolymerization amount, thread breakage occurs several times during spinning,
The spinnability was poor. The fineness and elongation of this POY, Δn,
Table 1 shows U%.

In this POY, yarn breakage occurred several times during drawing, and several wounds were found on the wound yarn. Table 1 shows the fineness and strength of the drawn yarn. The strength is as low as 3.9 g / d, which indicates that the strength is not sufficient as a drawn yarn. POY productivity was 45.7 g / min, and TMT
It can be seen that it is larger than the case where M is not copolymerized (Comparative Example 2), but smaller than that of Example 1.

As can be seen from Table 1, although the orientation is suppressed by copolymerizing TMTM, the effect of suppressing the orientation is small due to the low IV, and the degree of improvement in POY productivity (increase in spinning discharge) is small. It can be seen that, in addition to poor yarn-making properties, the obtained POY also has problems in stretchability, process passability, and stretched yarn properties. Example 2 The copolymerization amount of TMTM was 0.24 mol%, and the IV was 0.6.
A polyester was obtained in the same manner as in Example 1 except that the value was changed to 4, and spun in the same manner as in Example 1 to obtain a polyester POY. No yarn breakage occurred during spinning, and the spinning properties were excellent. Table 1 shows the fineness, elongation, Δn, and U% of this POY.

This POY does not break during drawing,
No fluff was seen in the wound yarn, and the stretchability and process passability were excellent. Table 1 shows the fineness and strength of the drawn yarn. The POY productivity was 57.3 g / min.

As can be seen from Table 1, even when the IV is 0.64, by increasing the TMTM copolymerization amount, the orientation is suppressed, so that the draw ratio can be increased and the POY productivity is improved (spinning discharge). It can be seen that, in addition to being able to increase the amount, the obtained POY is excellent in stretchability and process passability, and has sufficient drawn yarn properties. Example 3 The copolymerization amount of TMTM was 0.28 mol%, and the IV was 0.6.
The polyester was obtained by spinning in the same manner as in Example 1 except that the polyester was obtained in the same manner as in Example 1 except that the spinning speed was set at 4, and the spinning speed was 5000 m / min.
Y was obtained. Single yarn breakage occurred at the start of spinning, but the spinning properties were generally good. The fineness and elongation of this POY, Δn,
Table 2 shows U%.

In this POY, one fluff was observed in the wound yarn after stretching, but no yarn breakage occurred during stretching, and the stretchability and process passability were good. Table 2 shows the fineness and strength of the drawn yarn. The POY productivity was 57.9 g / min.

As can be seen from Table 2, even when the IV was 0.60, the spinning speed was increased to 5000 by increasing the TMTM copolymerization amount.
Since the orientation is suppressed even at m / min, the draw ratio can be increased, and the POY productivity can be improved (the spinning discharge amount can be increased).
Has sufficient drawn yarn properties. Example 4 The copolymerization amount of TMTM was 0.28 mol%, and the IV was 0.6.
A polyester was obtained in the same manner as in Example 1 except that the number was changed to 6, and spun in the same manner as in Example 1 to obtain a polyester POY. Single yarn breakage occurred at the start of spinning, but the spinning properties were generally good. Table 2 shows the fineness, elongation, Δn, and U% of this POY.

In this POY, one fluff was observed in the wound yarn after stretching, but no yarn breakage occurred during stretching, and the stretchability and process passability were good. Table 2 shows the fineness and strength of the drawn yarn. The POY productivity was 60.0 g / min.

As can be seen from Table 2, by increasing the TMTM copolymerization amount, the orientation is suppressed, so that the draw ratio can be increased, and the POY productivity can be greatly improved (the spinning discharge amount can be increased). It can be seen that, in addition to this, the obtained POY has sufficient drawn yarn properties. Comparative Example 4 The copolymerization amount of TMTM was 0.32 mol%, and the IV was 0.6.
A polyester was obtained in the same manner as in Example 1 except that the number was changed to 6, and spun in the same manner as in Example 1 to obtain a polyester POY. Thread breakage occurred several times during spinning, and the spinnability was poor. Fineness, elongation, Δn, U% of this POY
Are shown in Table 2.

In this POY, yarn breakage frequently occurred during stretching, and a large number of fluffs were also observed in the wound yarn. The fineness of this drawn yarn,
The strength is shown in Table 2. The strength is as small as 3.6 g / d, which indicates that the strength is not sufficient as a drawn yarn. In addition,
POY productivity was 60.3 g / min.

As can be seen from Table 2, by increasing the TMTM copolymerization amount, the orientation is further suppressed, and the POY productivity can be greatly improved (increase in spinning discharge amount), but the spinnability is poor.
Further, it can be seen that the obtained POY also has problems in stretchability, process passability, and stretched yarn physical properties. Example 5 A polyester was obtained in the same manner as in Example 1 except that the copolymer species was trimethyl trimesate, the amount of copolymerization was 0.08 mol%, and the IV was 0.70, and the same procedure as in Example 1 was carried out. Spinning was performed by the method to obtain a polyester POY. No yarn breakage occurred during spinning, and the spinning properties were excellent. This P
Table 2 shows the fineness, elongation, Δn, and U% of OY.

This POY does not cause yarn breakage during stretching,
No fluff was seen in the wound yarn, and the stretchability and process passability were excellent. Table 2 shows the fineness and strength of the drawn yarn. The strength was 5.3 g / d, which is almost the same as that of Comparative Example 1. The POY productivity was 50.0 g / min.

As can be seen from Table 2, even when the TMTM copolymerization amount is 0.08 mol%, by increasing the IV, the orientation is suppressed, so that the draw ratio can be increased and the POY productivity is improved (spinning). It can be seen that, in addition to being able to increase the discharge amount, the obtained POY has characteristics that are excellent in stretchability, process passability, and stretched yarn properties. Example 6 A polyester was obtained in the same manner as in Example 1 except that the copolymer species was trimethyl trimesate, the copolymerization amount was 0.08 mol%, and the IV was 0.76, and a spinning speed of 3 was obtained.
Spinning was performed in the same manner as in Example 1 except that the speed was set to 000 m / min, to obtain a polyester POY. No yarn breakage occurred during spinning, and the spinning properties were excellent. Table 2 shows the fineness, elongation, Δn, and U% of this POY.

This POY does not break during drawing,
No fluff was seen in the wound yarn, and the stretchability and process passability were excellent. Table 2 shows the fineness and strength of the drawn yarn. The strength was 5.5 g / d, which is equal to or higher than that of Comparative Example 1. The POY productivity was 50.3 g / min.

As can be seen from Table 2, even if the TMTM copolymerization amount is 0.08 mol%, by increasing the IV, the orientation is suppressed, so that the stretching ratio can be further increased.
It can be seen that, in addition to being able to improve the POY productivity (increase in spinning discharge amount), the obtained POY has characteristics excellent in stretchability, process passability, and stretched yarn properties.

[0060]

[Table 2]

[0061]

By using the polyester of the present invention,
Melt spinning, which has a large orientation suppression effect and is excellent in spinnability, in particular, melt spinning of POY becomes possible, and an improvement in productivity can be achieved. The polyester of the present invention can be obtained by a simple method in which trimellitic acid, trimesic acid or a derivative thereof is copolymerized in the polyester, and the copolymerization amount and the intrinsic viscosity are adjusted to satisfy specific conditions. further,
The POY formed from the polyester of the present invention has preferable properties such as stretchability, processability, and improved physical properties of the drawn yarn.

[Brief description of the drawings]

FIG. 1 shows the relationship between IV and the copolymerization amount of trimellitic acid, trimesic acid or a derivative thereof satisfied by the polyester of the present invention.

Claims (4)

[Claims] 1. A polyester for melt spinning wherein trimellitic acid, trimesic acid or a derivative thereof is copolymerized so as to satisfy the following conditions. (Equation 1) 2. The polyester for melt spinning according to claim 1, wherein the main repeating unit is ethylene terephthalate. 3. A polyester partially oriented undrawn yarn formed from the polyester according to claim 1 and having a birefringence of 0.020 to 0.060. 4. The polyester according to claim 1 or 2,
A method for producing a polyester partially oriented unstretched yarn, comprising melt-spinning at a take-up speed of 3000 to 5000 m / min.