JP5151029B2 - Polyester composition and fibers comprising the same - Google Patents

Description

  The present invention relates to a polyester composition whose main repeating unit is propylene terephthalate. More specifically, the present invention relates to a polyester composition that is excellent in yarn-making property and can obtain high-strength fibers, and fibers made thereof.

  Polyesters typified by polyethylene terephthalate (hereinafter referred to as PET) are excellent in mechanical strength, chemical resistance, etc., and are therefore widely used for fibers, films or resin applications. For example, in the case of fibers, PET fibers are widely used regardless of whether they are used for clothing or industrial materials. However, since the PET fiber has a low stretch elastic recovery rate and refractive recovery rate, it has not been suitably used for applications that require stretch properties, such as innerwear for sportswear, sports clothing, pantyhose, and the like. Various proposals have been made to improve the properties of such PET fibers. One example is polypropylene terephthalate (common name) using 1,3-propanediol (hereinafter referred to as PG) instead of ethylene glycol. It has been proposed to obtain a fiber having a high elastic recovery rate and a high refractive recovery rate by using polytrimethylene terephthalate (hereinafter referred to as PTT).

In recent years, as inexpensive PG production methods have been developed, PTT has been manufactured at a low cost, but PTT is known to be inferior in thermal stability to PET due to its molecular structure. Yes. In particular, when a titanium compound is used as a catalyst, not only the PTT polymer is markedly yellowish, but also side reactions are likely to occur during the polymerization reaction, and the decomposition reaction is accelerated (deterioration of heat stability of the melt) and the polymerization reaction rate. Therefore, it is difficult to produce a high molecular weight PTT polymer due to its low speed, so a low molecular weight prepolymer is produced by melt polymerization, and the resulting polymer is once cooled and solidified, and then at a temperature below the melting point. A method of increasing the molecular weight by performing polycondensation (solid phase polymerization method) is known (Patent Documents 1 and 2). However, the solid phase polymerization property of PTT is not sufficient by the method simply by changing the solid phase polymerization conditions, etc., and it takes a long time to obtain a high molecular weight polymer, so that it is difficult to produce on an industrial scale. In addition, even when yarn is produced using high molecular weight PTT pellets obtained by solid phase polymerization, yarn breakage frequently occurs due to a decrease in molecular weight due to decomposition reaction during spinning and unstable spinnability. Also, the obtained fiber properties are not satisfactory in strength, and there is a problem that only those having poor practical performance can be obtained.
Republished WO2003 / 033564 JP 2000-159875 A

  An object of the present invention is to provide a polyester composition that overcomes the problems of the prior art, is excellent in yarn forming properties, and can obtain high-strength fibers.

The above-mentioned problem is that the main repeating unit is composed of propylene terephthalate, (1) contains 0.1 to 30 ppm of antimony compound in terms of antimony atom, (2) contains 0.5 to 20 ppm of alkali metal compound in terms of metal atom, and A polyester containing an amount satisfying the following formula, wherein the antimony compound of (1) and the alkali metal compound of (2) are reacted from the initial stage of esterification or transesterification of the polyester, and / or Alternatively , the polyester composition is added at the beginning of the polycondensation reaction and has an intrinsic viscosity of 0.75 to 2 dl / g and a dipropylene glycol content of 5 mol% or less. it can.

0.01 ≦ Sb / M ≦ 10
(In the formula, Sb and M represent the number of moles of antimony atoms and metal atoms of the alkali metal compound contained in 10 ⁶ g of polyester, respectively.)

  The polyester composition of the present invention can provide a polyester composition that can solve the conventional problems, is excellent in yarn-making property, and can obtain high-strength fibers.

  The polyester in which the main repeating unit of the present invention is propylene terephthalate is an aromatic dicarboxylic acid whose main component is terephthalic acid (hereinafter referred to as TPA) or an ester-forming derivative thereof, and PG is mainly used as the glycol component. It is composed of a diol or an ester-forming derivative thereof as a component.

  In addition, the polyester of the present invention includes adipic acid, isophthalic acid, sebacic acid, phthalic acid, 4,4′-diphenyldicarboxylic acid, sulfoisophthalic acid as copolymerization components within a range that does not impair the intended effect of the present invention. Alkali metal salts, dicarboxylic acids such as phosphonium salts of sulfoisophthalic acid and their ester-forming derivatives, dioxy compounds such as polyethylene glycol, diethylene glycol, ethylene glycol, hexamethylene glycol, neopentyl glycol, p- (β-oxyethoxy) Oxycarboxylic acids such as benzoic acid and ester-forming derivatives thereof may be copolymerized.

  Examples of the antimony compound in the present invention include antimony trioxide, antimony acetate, antimony pentoxide, antimony trifluoride, pyroantimonic acid, antimony oxychloride, orthoantimonic acid, metaantimonic acid, and the like. Antimony acetate is preferably used.

  The content of the antimony compound contained in the polyester composition of the present invention needs to be 0.1 to 30 ppm in terms of antimony atoms. If the amount is less than 0.1 ppm, the effect on the spinning property is insufficient, and if it exceeds 30 ppm, the antimony metal present in the polyester composition increases, so that defects in the polyester fiber tend to occur and the strength tends to decrease. . From this viewpoint, the content of the antimony compound is preferably 0.5 to 20 ppm in terms of antimony atoms, and more preferably 1.0 to 10 ppm.

  Examples of the alkali metal compound in the polyester composition of the present invention include alkali metal hydroxides and hydrates thereof, lower fatty acid carboxylates such as acetates, carbonates, propionates, butates, and hydrations thereof. Products, benzoates, 4-methylphenylcarboxylates, aromatic carboxylic salts such as naphthylcarboxylates and hydrates thereof, alkoxides such as methoxide and ethoxide, etc. Products, acetates and hydrates thereof are preferred. Here, examples of the alkali metal include lithium, sodium, and potassium. Specific examples of the alkali metal compound include potassium acetate, lithium acetate, lithium acetate dihydrate, lithium hydroxide, lithium hydroxide monohydrate, sodium acetate, and sodium acetate trihydrate. Sodium acetate and sodium acetate trihydrate are particularly preferably used.

  The content of the alkali metal compound contained in the polyester composition of the present invention needs to be 0.5 to 20 ppm in terms of alkali metal atoms. If the content is less than 0.5 ppm, the effect on the spinning property is insufficient, and if the content exceeds 20 ppm, coarse foreign matter present in the polyester composition increases, resulting in defects in the polyester fiber, and the strength tends to decrease. . From this viewpoint, the content of the alkali metal compound is preferably 1.0 to 18 ppm, more preferably 2.0 to 15 ppm in terms of alkali metal atoms.

Further, the polyester composition of the present invention is required to have Sb / M = 0.01 to 10 in terms of a molar ratio of antimony atoms to alkali metal atoms contained in 10 ⁶ g of polyester, and more preferably 0.8. It is 02-5, More preferably, it is 0.05-2.

The polyester composition of the present invention needs to contain the above-described antimony compound and an alkali metal compound. By satisfying these ranges at the same time, excellent fiber-making properties and high-strength fibers can be obtained. be able to.

  Furthermore, the intrinsic viscosity (hereinafter referred to as IV) of the polyester composition of the present invention needs to be 0.75 to 2 dl / g. If the IV is less than 0.75, the melt viscosity is low, so that the fiber forming ability becomes poor, so that the spinning property is lowered and the strength of the obtained fiber is low. On the other hand, if the IV exceeds 2, the melt viscosity is high, so that the measurement of the polymer with the gear pump is not smoothly performed, and the spinnability is lowered because the polymer cannot be extruded stably. Preferred IV is 0.80 to 1.75.

    Further, the content of dipropylene glycol (hereinafter referred to as DPG) is required to be 5.0 mol% or less. When it exceeds 5.0 mol%, the strength tends to decrease and the elastic recovery rate tends to decrease. From this viewpoint, the DPG content is preferably 4.0 mol% or less, and more preferably 2.0 mol% or less.

  In the production of the polyester composition of the present invention, a titanium compound, a germanium compound, or the like can be used as the polycondensation reaction catalyst for producing the polyester. Among them, titanium having excellent polycondensation reaction activity can be used. Compounds are preferred. As such a titanium compound, at least one organic titanium compound selected from the group consisting of titanium alkoxide, titanium acylate and titanium chelate is preferable. Specifically, tetra-n-propyl titanate, tetraisopropyl titanate, tetra- n-butyl titanate, tetra-t-butyl titanate, tetraphenyl titanate, tetracyclohexyl titanate, tetrabenzyl titanate, tetrastearoxy titanate polymer, tetra-n-propyl titanate polymer, tetraisopropyl titanate polymer, tetra-n-butyl titanate polymer, Titanium alkoxides such as tetra-t-butyl titanate polymer, or mixed titanates thereof, tri-n-butoxy titanium stearate, isopropoxy system Over preparative like titanium acylate or a mixture of these titanates, diisopropoxy titanium bis acetyl acetonate, titanium chelates such as dihydroxy bis Lac Tato titanium, or a mixture of these titanates like.

   It is preferable to add the titanium compound of this invention so that it may become 5-200 ppm in conversion of a titanium atom with respect to polyester obtained. When the addition amount is less than 5 ppm, the catalyst activity is insufficient, and as a result, only a polymer having a low molecular weight can be obtained. Moreover, when the amount exceeds 200 ppm, a side reaction tends to occur during deterioration of the polymer color tone or during the polymerization reaction, and DPG may increase. More preferably, it is 10-150 ppm, More preferably, it is 20-100 ppm.

     The polyester composition of the present invention preferably contains a specific amount of a phosphorus compound together with an antimony compound.

  The phosphorus contained in the polyester composition of the present invention is a residue of a phosphorus compound added mainly during the production process of the polyester composition. Such phosphorus compounds are not particularly limited, and examples thereof include phosphoric acid, phosphorous acid, phosphonic acid, and lower alkyl esters and phenyl esters thereof, but are not particularly limited. Specifically, for example, phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, phosphorous acid, trimethyl phosphite, methylphosphonic acid, phenylphosphonic acid, benzylphosphonic acid, methylphosphonic acid methyl ester, phenylphosphonic acid Examples include ethyl ester, benzylphosphonic acid phenyl ester, and phosphonoacetic acid ethyl ester.

  In the present invention, if the polyester composition contains 0.1 to 50 ppm in terms of phosphorus atoms, the heat resistance of the polymer is good, which is preferable. More preferably, it is 0.5-30 ppm, More preferably, it is 1.0-20 ppm.

  In addition, when the molar ratio of Sb / P = 0.01 to 10 as a phosphorus atom with respect to the antimony atom of the antimony compound, not only the heat resistance of the polyester composition tends to be improved, but also the yarn-making property is improved. Good and preferable. More preferably, Sb / P = 0.02-5, and still more preferably Sb / P = 0.05-2.

  The amount of antimony metal contained in the polyester composition of the present invention is preferably 10 ppm or less. The antimony metal is produced by reduction of the antimony compound used at the time of polyester polymerization, and such an antimony metal amount is preferable because there is no defect in the polyester fiber and the strength is improved. More preferably, it is 8 ppm or less, More preferably, it is 5 ppm or less.

  Further, in the polyester composition of the present invention, it is preferable that the number of foreign matters is small from the viewpoint of yarn-forming properties. Specifically, coarse foreign matters of 5 μm or more are 10 or less per 10 mg of polymer as an average value of 10 observation samples. Preferably there is. As a result, an increase in filtration pressure and yarn breakage at the time of yarn production, and occurrence of yarn breakage and fluff at the time of drawing are suppressed, and high productivity can be realized. The number of coarse foreign matters is preferably 5 or less, more preferably 2 or less, per 10 mg of polymer.

The polyester in the present invention is obtained by the following method.
For example, (1) dimethyl terephthalate and PG are used as raw materials, a low polymerization amount is obtained by transesterification reaction, and then produced by subsequent polycondensation reaction. (2) terephthalic acid and PG are used as raw materials and direct esterification reaction is performed. A low molecular weight PTT or an oligomer thereof can be obtained and further produced by a subsequent polycondensation reaction. Here, a titanium compound, a germanium compound or a tin compound may be used as an esterification or transesterification and / or polycondensation catalyst. After the esterification or transesterification reaction is substantially completed, the reaction is used for the reaction. For the purpose of inactivating the catalyst, a phosphorus compound may be added. Further, the polycondensation reaction may be carried out by polycondensation using the activity of the titanium compound used for esterification or transesterification as it is, or by newly adding a titanium compound or adding various catalyst compounds. .

  The production method of the present invention includes the antimony compound and the alkali metal compound of the present invention from the beginning of the series of esterification or transesterification of (1) or (2) and / or after the completion of the reaction and / or at the beginning of the polycondensation reaction. Is added, esterification or transesterification is performed, and a polycondensation reaction proceeds at a temperature of 235 to 270 ° C. under reduced pressure to obtain a PTT polymer having an intrinsic viscosity of 0.60 or more. In addition, although said reaction is implemented by forms, such as a batch type, a semibatch type, or a continuous type, the manufacturing method of this invention is applicable also to any form. Moreover, the obtained polymer can be solid-phase polymerized at a temperature of 170 to 210 ° C. under a reduced pressure of 133 Pa or less to obtain a PTT polymer having an intrinsic viscosity of 0.70 or more.

  Using the chips after solid phase polymerization thus obtained, spinning is performed by a usual melt spinning method, for example, using a die having a spinning temperature of 265 ° C. and a pore diameter of 0.3 mmφ × 24 holes at a spinning take-off speed of 500 m / min or more. To obtain an undrawn yarn. The obtained undrawn yarn is drawn using a normal hot roll drawing machine to obtain a drawn yarn of 75 dtex 24 filaments.

Hereinafter, the present invention will be described in more detail with reference to examples. In addition, each characteristic value in an Example was calculated | required with the following method.
(1) Intrinsic viscosity of polymer (hereinafter referred to as IV)
Measurement was performed at 25 ° C. using orthochlorophenol as a solvent.
(2) The metal content in the polymer was determined by atomic absorption spectrometry.
(3) DPG amount of the polymer ¹ H-NMR was measured using a UNITIANNOVA 600 model of VARIAN, and quantified from the integral ratio of the obtained signal.
(4) 40 g of antimony metal amount sample is dissolved in 500 ml of orthochlorophenol, centrifuged (12,000 rpm × 2 hr), washed and dried. The spectrum of the obtained centrifugal sedimentation particles was determined from the spectrum using an X-ray diffractometer.
(5) Number of coarse particles in polyester composition After a small amount of polymer is quantified, it is sandwiched between two cover glasses, melted at 290 ° C, pressed to a uniform film thickness, and then rapidly cooled. The sample thus obtained is observed using an optical microscope. The number of coarse particles of 5 μm or more existing in a certain area was counted, and the number of coarse particles per 10 mg of polymer was calculated from the weight of the sample and the total area after pressing. In addition, the average value of 10 observation samples was shown.
(6) Threading properties (thread breakage, fluff)
The yarn breakage in the spinning process, the yarn breakage in the drawing process, and the number of occurrences of fluff were ranked as follows, and A and B were passed.

Class A No yarn breakage during spinning, no yarn breakage during drawing, no fluff
Class B No yarn breakage during spinning, almost no yarn breakage during drawing, almost no fluff C class There is yarn breakage during spinning, there are yarn breakage during drawing, and there is fluff. Class D Many yarn breakage during spinning, yarn breakage during drawing, Fuzziness (7) Strength and elongation Values were obtained from a stress-strain curve using a Tensilon tensile tester manufactured by Toyo Baldwin Co., Ltd. under the conditions of a test length of 20 cm and a tensile speed of 10 cm / min.

Example 1
94.2 parts by weight of dimethyl terephthalate and 73.8 parts by weight of PG were charged into a reactor, 0.04 part by weight of tetrabutyl titanate was added as a transesterification reaction catalyst, and 9.6 × 10 ⁻³ parts by weight of antimony trioxide was further added. 0.0025 part by weight of potassium acetate was added, and the mixture was heated and stirred over 4 hours while stirring up to 140 to 240 ° C., thereby proceeding with the transesterification reaction. After the transesterification reaction, 1.86 × 10 ⁻³ parts by weight of phosphoric acid (5 ppm in terms of phosphorus atom) was added, and then 0.10 parts by weight of tetrabutyl titanate was added.

  Thereafter, while stirring the low polymer at 30 rpm, the reaction system was gradually heated from 240 to 260 ° C. and the pressure was reduced to 40 Pa. The time to reach the final temperature and final pressure was 60 minutes. When the predetermined torque was reached, the reaction system was purged with nitrogen, returned to normal pressure, the polycondensation reaction was stopped, discharged into cold water in a strand form, and immediately cut to obtain a polyester chip. The time from the start of decompression to the predetermined stirring torque was 3 hours and 20 minutes.

  The obtained polymer had an intrinsic viscosity of 0.85, a DPG amount of 0.73 mol%, an antimony metal amount of 0.2 ppm, and 0 foreign matter having a size of 5 μm or more. It was confirmed by atomic absorption analysis that antimony atoms were 8 ppm, potassium atoms were 10 ppm, and phosphorus atoms were 5 ppm.

  Next, the obtained polyester chip was subjected to solid phase polymerization at 200 ° C. under a reduced pressure of 133 Pa or less to obtain a chip of IV1.55 in 13.5 hours. Subsequently, using the chip after the solid phase polymerization, spinning was performed at a spinning temperature of 265 ° C., using a die having a hole diameter of 0.3 mmφ × 24 holes, and a spinning speed of 750 m / min, to obtain an undrawn yarn. The obtained undrawn yarn was drawn with a hot roll drawing machine at 1 HR 55 ° C., 2 HR 80 ° C., 3 HR 140 ° C. and a total draw ratio of 4.0 times to obtain a drawn yarn of 75 dtex 24 filaments. The strength was 5.4 cN / dtex, the elongation was 34%, and a good fiber was obtained. In addition, there was no yarn breakage or fluffing in the spinning process and the drawing process, and good spinning properties were exhibited. The results are shown in Table 1.

Examples 2-9, Comparative Examples 1-5
Polymerization was carried out in the same manner as in Example 1 except that the amount of antimony trioxide was changed as the antimony compound and the amount of potassium acetate was changed as the alkali metal compound, and spinning and stretching were performed using the chips after solid phase polymerization.

  In Examples 2 to 9 satisfying the scope of the present invention, yarn breakage and fluff were not generated in the spinning step and the drawing step, and the yarn production was good. Further, the strength of the obtained raw yarn was excellent. The results are shown in Table 1.

  On the other hand, those obtained by polymerizing an alkali metal compound alone, those polymerized without using an alkali metal compound (potassium acetate), and further using an antimony trioxide amount and an alkali metal compound (potassium acetate) amount outside the scope of the present invention. In the polymerized products, yarn breakage and fluff were generated in both the spinning process and the drawing process, and the obtained raw yarn was low in strength. The results are shown in Table 1.

実施例１０、比較例６
実施例１において得られたチップ（固有粘度０．８５）を用いて、１８０℃、１３３Ｐａ以下の減圧下にて固相重合を行い、６．５時間でＩＶ０．８９のチップを得た。このチップを用いて実施例１と同様にして紡糸・延伸した。紡糸工程および延伸工程において糸切れや毛羽の発生はなく製糸性は良好であり、得られた原糸の強度も優れていた。結果を表２に示した。

Example 10 and Comparative Example 6
Using the chip (inherent viscosity 0.85) obtained in Example 1, solid phase polymerization was performed under reduced pressure at 180 ° C. and 133 Pa or less, and a chip with IV 0.89 was obtained in 6.5 hours. Using this chip, spinning and stretching were carried out in the same manner as in Example 1. There was no yarn breakage or fluffing in the spinning process and drawing process, the spinning performance was good, and the strength of the obtained yarn was excellent. The results are shown in Table 2.

  On the other hand, in Comparative Example 6, the reaction was completed after the polycondensation reaction time of 2 hours 05 minutes from the start of decompression in Example 1, and the chip was discharged, and a chip having an intrinsic viscosity of 0.60 was obtained. Using this chip, solid phase polymerization was performed under a reduced pressure of 175 ° C. and 133 Pa or less, and a chip having an IV of 0.71 was obtained in 11 hours. Using this chip, spinning and stretching were carried out in the same manner as in Example 1. However, yarn breakage and fluff were generated in the spinning process and the stretching process, and the yarn-making property was poor. Further, the obtained raw yarn had low strength and was inferior. The results are shown in Table 2.

Examples 11 and 12 and Comparative Example 7
In Example 11 and Example 12, solid phase polymerization was performed using the chip obtained in Example 1 (intrinsic viscosity 0.85) under reduced pressure at 200 ° C. and 133 Pa or less. In Example 11, a chip having an IV of 1.01 was obtained in 10.5 hours. In Example 12, solid-state polymerization was carried out in the same manner to obtain a chip with IV 1.86 in 18.5 hours. Using this chip, spinning and stretching were carried out in the same manner as in Example 1. There was no yarn breakage or fluffing in the spinning process and drawing process, the spinning performance was good, and the strength of the obtained yarn was excellent. The results are shown in Table 2.

  On the other hand, in Comparative Example 7, using the chip obtained in Example 1 (intrinsic viscosity 0.85), solid-state polymerization was performed at 200 ° C. under reduced pressure of 133 Pa or less, and the chip of IV2.2 was obtained in 26 hours Got. Using this chip, spinning and stretching were carried out in the same manner as in Example 1. However, yarn breakage and fluff were generated in the spinning process and the stretching process, and the yarn-making property was poor. Further, the obtained raw yarn had low strength and was inferior. The results are shown in Table 2.

Example 13
Polymerization was carried out in the same manner as in Example 1 except that antimony acetate was used as the antimony compound, and spinning / stretching was performed using the chip after solid-phase polymerization.

  There was no yarn breakage or fluffing in the spinning process and drawing process, the spinning performance was good, and the strength of the obtained yarn was excellent. The results are shown in Table 2.

Example 14 and Comparative Example 8
In Example 14, polymerization was performed in the same manner as in Example 1 except that sodium acetate was used as the alkali metal compound, and spinning / stretching was performed using the chips after solid-phase polymerization. In Example 14 satisfying the scope of the present invention, yarn breakage and fluff were not generated in the spinning process and the drawing process, and the yarn production was good. Further, the strength of the obtained raw yarn was also excellent. The results are shown in Table 2.

  On the other hand, Comparative Example 8 is polymerized using magnesium acetate which is an alkaline earth metal compound instead of the alkali metal compound. In the spinning process and the drawing process, yarn breakage and fluff were generated, and the spinning performance was poor. The obtained yarn was inferior in strength. The results are shown in Table 2.

Examples 15 and 16
Polymerization was carried out in the same manner as in Example 1 except that the amount of phosphorus was changed, and spinning / stretching was performed using a chip after solid-phase polymerization. In Examples 15 and 16 satisfying the scope of the present invention, there was no yarn breakage or fluffing in the spinning process and the drawing process, and the spinning performance was good. Further, the strength of the obtained raw yarn was excellent. The results are shown in Table 2.

Examples 17 and 18, Comparative Example 9
In this example, DPG was added and polymerized in the stage before the start of polymerization in Example 1. Example 17 and Example 18 satisfying the scope of the present invention had good solid-state polymerization reactivity, and there was no yarn breakage or fluffing in the spinning process and drawing process, and the spinning performance was good. Further, the strength of the obtained raw yarn was excellent. The results are shown in Table 2.

  On the other hand, Comparative Example 9 was spun and drawn using a chip having a DPG amount of 6.5 mol%. However, yarn breakage and fluffing occurred in the spinning process and the drawing process. The strength was also inferior. The results are shown in Table 2.

Claims (5)

The main repeating unit consists of propylene terephthalate, (1) contains 0.1 to 30 ppm of antimony compound in terms of antimony atom, and (2) contains 0.5 to 20 ppm of alkali metal compound in terms of metal atom, and satisfies the following formula In which the antimony compound of (1) and the alkali metal compound of (2) are reacted at the beginning of the esterification or transesterification reaction of the polyester and / or after the polycondensation reaction. A polyester composition which is added at an initial stage and has an intrinsic viscosity of 0.75 to 2 dl / g and a dipropylene glycol content of 5.0 mol% or less.
0.01 ≦ Sb / M ≦ 10
(In the formula, Sb and M represent the number of moles of the antimony atom and the metal atom of the alkali metal compound contained in 10 ⁶ g of polyester, respectively.) The polyester composition according to claim 1, wherein the alkali metal compound is a sodium compound or a potassium compound. The phosphorus compound is contained in an amount of 0.1 to 50 ppm in terms of phosphorus atom, and the content of the antimony compound and the phosphorus compound is Sb / P = 0.01 to 10 in molar ratio. The polyester composition described. The polyester composition according to any one of claims 1 to 3, wherein the amount of antimony metal present as antimony metal is 10 ppm or less, and the number of coarse foreign matters of 5 μm or more is 10/10 mg or less. A polyester composition. A fiber obtained by melt spinning the polyester composition according to any one of claims 1 to 4.