JP2005273043A - Flame-retardant cationically dyeable polyester fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a flame-retardant cationically dyeable polyester fiber that has excellent dyeability with a cation dye and is applicable to a use requiring flame retardance and light resistance and a use requiring drawing and false twisting properties. <P>SOLUTION: The polyester fiber is formed by using a copolyester resin copolymerized so as to comprise ≥80 mol% of a repeating unit constituting a polyester, being a polyethylene terephthalate, have 0.5-5.0 mass % based on the total acid component of the polyester of a sulfonic acid base-containing acid component and 5,000-15,000 ppm calculated as a phosphorus atom content in the polyester of an organophosphorus component of a specific structure and has ≤5.0 mol% diethylene glycol content, 0.03-0.06 double refractive index ▵n, ≥1.6 cN/dtex strength, ≤150% elongation. When the fiber is drawn, the strength is preferably ≥2.6 cN/dtex and an LOI value is preferably ≥27. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flame retardant cationic dyeable polyester fiber that has excellent dyeability for cationic dyes, has flame retardancy, and has good spinnability and stretch false twistability.

  Polyester, especially polyethylene terephthalate (hereinafter abbreviated as PET), because of its excellent mechanical and chemical properties, is used for clothing and industrial fibers, as well as magnetic tape and condenser films or bottles, etc. It is widely used for moldings.

  However, polyester cannot be said to have good dyeability as a fiber for clothing, and has a defect that the dyed product has poor clarity.

  Conventionally, in order to compensate for these disadvantages, a polyester dyeable with a basic dye as described in Patent Document 1, which is obtained by copolymerizing a sulfonate group-containing component typified by 5-sodium sulfoisophthalic acid or the like (Hereinafter abbreviated as cationic dyeable polyester) is known, and fibers made of such polyester are used in the clothing field.

  However, these cationic dyeable polyester fibers have a higher melt viscosity than ordinary polyester fibers and are difficult to melt and drop during combustion. There is a problem that use is restricted.

In order to solve such a problem, Patent Document 2 proposes a multifilament using a polyester resin in which a specific phosphorus-containing dicarboxylic acid compound and a sulfonate group-containing component are copolymerized. However, when copolymerizing a sulfonate group-containing component in the polyester resin stage, the acid catalysis promotes the production of diethylene glycol during the polymerization reaction, and the diethylene glycol content in the resulting polyester tends to increase. is there. Therefore, since the phosphorus compound is copolymerized and the content of diethylene glycol is increased, there is a possibility that a problem occurs in light resistance, and the use is limited.
Japanese Patent Publication No. 34-10497 JP-A-7-109621

  The present invention solves the above problems, is flame retardant cationic dyes that are dyeable to cationic dyes, have flame retardancy and light resistance, and can be applied to applications requiring false twist processability. It is a technical subject to provide dyed polyester fibers.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors specify the sulfonate group-containing component and the content thereof, the organic phosphorus compound component and the content thereof, and the diethylene glycol content in the polyester fiber. As a result, the present inventors have found that it is dyeable with a cationic dye, has flame retardancy, and has good light resistance, and has reached the present invention.

That is, the present invention has the following configuration.
(1) 80 mol% or more of the repeating unit constituting the polyester is an ethylene terephthalate unit, and the sulfonate group-containing acid component is 0.5 to 5.0 mol% with respect to the total acid component of the polyester, and the following general formula [1] The organic phosphorus compound shown is formed using a copolymerized polyester resin copolymerized so that the phosphorus atom content in the polyester is 5000-15000 ppm, the diethylene glycol content is 5.0 mol% or less, and birefringence A flame-retardant cationic dyeable polyester fiber having a rate Δn of 0.03 to 0.06, a strength of 1.6 cN / dtex or more, and an elongation of 150% or less [hereinafter sometimes referred to as a first fiber. ].

(式中、Ｘはアルキル基の水素原子のうち2個以上がカルボキシル基で置換されたアルキル基を表す。)
（２）ポリエステルを構成する繰り返し単位の80モル％以上がエチレンテレフタレート単位であり、スルホン酸塩基含有酸成分がポリエステルの全酸成分に対して0.5〜5.0モル％と、下記一般式〔１〕で示される有機リン化合物がポリエステル中のリン原子の含有量として5000〜15000ppmとなるよう共重合された共重合ポリエステル樹脂を用いて形成され、ジエチレングリコールの含有量が5.0モル％以下であり、かつ強度が2.6cN/dtex以上であることを特徴とする難燃性カチオン可染ポリエステル繊維〔以下、第２の繊維と称することがある。〕。

(In the formula, X represents an alkyl group in which two or more of the hydrogen atoms of the alkyl group are substituted with a carboxyl group.)
(2) 80 mol% or more of the repeating unit constituting the polyester is an ethylene terephthalate unit, and the sulfonate group-containing acid component is 0.5 to 5.0 mol% with respect to the total acid component of the polyester, and the following general formula [1] The organic phosphorus compound shown is formed using a copolymerized polyester resin copolymerized so that the content of phosphorus atoms in the polyester is 5000-15000 ppm, the content of diethylene glycol is 5.0 mol% or less, and the strength is Flame retardant cationic dyeable polyester fiber [hereinafter sometimes referred to as second fiber] characterized by being 2.6 cN / dtex or more. ].

(式中、Ｘはアルキル基の水素原子のうち2個以上がカルボキシル基で置換されたアルキル基を表す。)
（３）LOI値が27以上であることを特徴とする上記（１）１又は（２）記載の難燃性カチオン可染ポリエステル繊維。

(In the formula, X represents an alkyl group in which two or more of the hydrogen atoms of the alkyl group are substituted with a carboxyl group.)
(3) The flame-retardant cationic dyeable polyester fiber according to the above (1) or (2), wherein the LOI value is 27 or more.

  The polyester fiber of the present invention is copolymerized with a sulfonate group-containing acid component, and exhibits good dyeability with respect to a cationic dye. In general, the cationic dyeable polyester fiber has a disadvantage that it is easy to burn because it has a higher melt viscosity than a normal polyester fiber, but the polyester fiber of the present invention contains a specific organophosphorus compound, Since this promotes thermal decomposition of polyester during combustion and promotes melting and dropping, the flame retardancy is excellent. In addition, the content of diethylene glycol (hereinafter abbreviated as “DEG”) is small, and the light resistance is excellent. Furthermore, the first fiber has a strong elongation and birefringence suitable for drawing false twisting, and the second fiber has a breaking elongation that can be used as it is. Yes.

  Thus, since the polyester fiber of the present invention has good dyeability with a cationic dye and is excellent in flame retardancy and light resistance, the fiber structure having such excellent performance can be used in a wide range of interior goods and the like. Applicable to usage.

  Hereinafter, the present invention will be described in detail.

  In the polyester forming the flame-retardant cationic dyeable polyester fiber of the present invention, 80 mol% or more of the repeating units are ethylene terephthalate units, and the sulfonate group-containing component is 0.5 to 5.0 mol% based on the total acid components of the polyester. And the organic phosphorus compound represented by the general formula [1] is a polyester having a phosphorus atom content in the polyester of 5000 to 15000 ppm and a DEG content of 5 mol% or less. .

  As described above, the fiber of the present invention requires that 80 mol%, preferably 90 mol% or more of the repeating units constituting the polyester be ethylene terephthalate units, and when the ethylene terephthalate units become less than 80 mol%. The good physical property peculiar to polyester falls.

  Further, it is necessary that the sulfonate group-containing acid component is copolymerized in an amount of 0.5 to 5.0 mol% with respect to the total acid component, and the copolymerization amount of the sulfonate group-containing acid component is less than 0.5 mol%, Sufficient dyeing performance cannot be obtained, and it is not dyeable to cationic dyes. If it exceeds 5 mol%, the polyester resin has a high melt viscosity, which leads to deterioration in spinning operability and yarn strength. It is not preferable.

  The sulfonate group-containing acid component is not particularly limited as long as it is a sulfonate group-containing component having a functional group that reacts with polyester. Examples thereof include 5-sodium sulfoisophthalic acid and 5-potassium sulfone. Examples include isophthalic acid, 5-lithium sulfoisophthalic acid, sodium sulfonaphthalenedicarboxylic acid, and 5-sodium sulfoterephthalic acid. Of these, 5-sodium sulfoisophthalic acid is particularly preferable because of its good color developability and spinnability with a cationic dye.

  The polyester constituting the fiber of the present invention is copolymerized so that the organophosphorus compound represented by the general formula [1] has a phosphorus atom content of 5000 to 15000 ppm, preferably 600 to 10,000 ppm. Has been. If the copolymerization amount of the organophosphorus compound is less than 5000 ppm as the phosphorus atom content, sufficient flame retardancy cannot be obtained, and if it exceeds 15000 ppm, the spinning operability is lowered or the yarn strength is insufficient, which is not preferable. .

  Specific examples of the organic phosphorus compound represented by the general formula [1] include compounds represented by the following formulas (a) to (c).

これらの中でも、有機リン化合物の安定性、繊維製造工程での有機リン化合物の揮発、飛散の少なさ、繊維物性への影響等を総合的に判断すると、式(a)で示される化合物である、9，10-ジヒドロ-9-オキサ-10-ホスファフェナントレン-10-オキシドのイタコン酸付加体 (以下、HCA-IAと略記。)が好ましい。

Among these, the overall stability of the organophosphorus compound, volatilization of the organophosphorus compound in the fiber manufacturing process, low scattering, influence on the physical properties of the fiber, and the like are the compounds represented by the formula (a). Itaconic acid adduct of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (hereinafter abbreviated as HCA-IA) is preferable.

  As a method of copolymerizing the organophosphorus compound as described in the above (a) to (c) with a polyester, a method in which the organophosphorus compound is directly added to the reaction system and reacted in the polymerization stage of the polyester is industrially preferable. The organophosphorus compound may be reacted with ethylene glycol (hereinafter abbreviated as EG), methanol or the like to form an ester and then added to the reaction system.

  The polyester fiber of the present invention is required to have a DEG content of 5.0 mol% or less. If the DEG content in the polyester fiber exceeds 5.0 mol%, the light resistance is inferior and the dyed product fades, which is not preferable.

  The DEG content tends to increase due to its acid catalysis as the copolymerization ratio of the sulfonate group-containing component increases. Further, the amount of DEG tends to increase even when the copolymerization ratio of the organophosphorus compound increases.

  This DEG content can be controlled by the addition timing of the sulfonate group-containing component and the organophosphorus compound during the polymerization of the polyester resin, and the reaction conditions after the addition. After transferring the PET oligomer to the polycondensation reaction vessel and adding EG as necessary to depolymerize, add these compounds under the temperature condition of 250 ° C or less, and then start depressurization within 15 minutes It is preferable to start the polymerization reaction.

  The polyester fiber of the present invention may contain a small amount of a copolymer component in addition to the above as long as the effects of the present invention are not impaired. Examples include aromatic dicarboxylic acid components such as isophthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, aliphatic dicarboxylic acid components such as adipic acid and sebacic acid, 1,3-propylene glycol, 1,4-cyclohexanedimethanol Glycol components such as 1,4-butanediol and polyethylene glycol, and hydroxycarboxylic acid components such as 4-hydroxybenzoic acid and ε-caprolactone.

  In addition, an antioxidant such as a hindered phenol compound, a cobalt compound, a fluorescent agent, a color improver such as a dye, a pigment such as titanium dioxide, and a cerium oxide, as long as the effect of the present invention is not impaired. Additives such as such a light resistance improving material may be included.

  In addition, the copolyester resin which forms the polyester fiber of this invention can be manufactured by the following methods, for example.

  First, a polyester oligomer (abbreviated as a PET oligomer) is synthesized by directly esterifying terephthalic acid and a diol or by transesterifying a lower alkyl ester of terephthalic acid with a diol. Next, a sulfonate group-containing component, an organophosphorus compound and the like are added to this at 250 ° C. or less, and then the polycondensation reaction is started within 15 minutes, and the internal temperature is raised to the target temperature after the reaction starts.

  The polycondensation reaction is usually extreme in the presence of a metal compound (catalyst) such as antimony, germanium, tin, titanium, zinc, aluminum, or cobalt at a temperature of 250 to 290 ° C. under a reduced pressure of about 0.12 to 12 hPa. It is preferable to carry out until the viscosity becomes 0.5 or more.

  The copolyester resin obtained as described above has good dyeability with cationic dyes, has flame retardancy and light resistance, and is excellent in false twisting and operability. It becomes the raw material of.

  The first fiber of the present invention is the above-mentioned copolymerized polyester resin as a raw material, dried by a conventional method, supplied to a normal melt spinning machine, melt-spun at a temperature 20 ° C. or higher than the melting point of the polyester, It is a fiber obtained by the POY method in which a yarn is cooled and wound as a semi-undrawn yarn by high-speed spinning of 2000 m / min or more.

  In the case of the first fiber of the present invention, it is necessary that the birefringence Δn is 0.03 to 0.06, the strength is 1.6 cN / dtex or more, and the elongation is 150% or less, and if the fiber satisfies all these physical properties. Thus, it becomes possible to carry out normal stretching false twisting with good operability. The upper limit of the strength and the lower limit of the elongation are not particularly limited, but the upper limit of the strength is about 2.3 cN / dtex in order to perform stable processing and to give practical strength to the processed yarn. The lower limit is preferably about 120% in order to perform stable processing.

  When the birefringence Δn is out of the range of 0.03 to 0.06, the strength is less than 1.6 cN / dtex, or the elongation exceeds 150%, fluff and untwisted when this fiber is drawn false twisted Is likely to occur.

  Next, the second fiber of the present invention is wound by stretching the first fiber described above, or by spinning the above resin at a high speed of 2000 m / min or higher, or by spinning at a low speed of less than 2000 m / min. It is a fiber obtained by either the two-step method of drawing and heat-treating the taken yarn or the one-step method of drawing and heat-treating in the winding process, and is a fiber having a strength of 2.6 cN / dtex or more. If the strength is 2.6 cN / dtex or more, it can be used as it is in the weaving and knitting process, and the resulting knitted or knitted fabric is unlikely to break or break. The upper limit of strength is about 5.0 cN / dtex in order to give the fiber an appropriate elongation.

  The breaking strength of this fiber is preferably 4.0 to 6.0 cN / dtex.

  The first and second fibers of the present invention preferably have an LOI value of 27 or more, and the LOI value of 27 or more can impart flame retardancy to products using these fibers. In order to set the LOI value to 27 or more, fibers may be produced using the above-described copolymer polyester resin.

  The upper limit of the LOI value is not particularly limited, but is preferably about 35 because the phosphorus atom content is restricted in order to stably spin the fiber.

  All of the polyester fibers of the present invention may be formed of the above-described copolymer polyester resin, but at least the fiber surface may be formed of the copolymer polyester resin, and the effects of the present invention are not impaired. As long as it is a composite fiber with other components. For example, the polyester fiber which has a core-sheath structure and the sheath part is formed with the said copolyester resin is contained in the polyester fiber of this invention.

  The form of the polyester fiber may be either a long fiber or a short fiber, and may be used after being subjected to post-processing such as crimping or treatment with a chemical as necessary.

  Next, the present invention will be specifically described with reference to examples.

In addition, the measurement of each characteristic value in an Example and a comparative example was performed as follows.
(A) Intrinsic viscosity ([η])
The measurement was carried out at a temperature of 20 ° C. using an equal mass mixture of phenol and tetrachloroethane as a solvent.
(B) Phosphorus atom content
Quantification was performed by a fluorescent X-ray method using a fluorescent X-ray spectrometer model 3270 manufactured by Rigaku Corporation.
(C) DEG content After polyester is hydrolyzed with alkali, the number of moles of EG and DEG is quantified by gas chromatographic method and calculated by the following formula.

DEG content = [number of moles of DEG / (number of moles of EG + number of moles of DEG)] × 100 (mol%)
(D) Elongation, strength, elongation at break Using Tensilon RTC-1210 manufactured by Orientic Corporation, a 50 cm sample was subjected to a tensile test at a speed of 50 cm / min, and the stress-strain curve was as follows. Asked.

1) Elongation is the percent elongation when the yarn is cut (%)
2) Strength is the value obtained by dividing the strength at the time of yarn cutting by the fineness (sample fineness before measurement) (cN / dtex)
3) Elongation at break is the value obtained by dividing the strength at the time of yarn cutting by the fineness (sample fineness at the time of cutting) (cN / dtex)
The sample fineness at the time of cutting is
It is calculated by (sample fineness before measurement) / (1 + elongation / 100).
(e) Fiber dyeability After the obtained filament yarn was false twisted, it was knitted into a cylinder, refined at 60 ° C for 20 minutes, then dyed at 130 ° C for 60 minutes and air-dried under the following conditions. . Next, after performing heat setting at 150 ° C for 1 minute using a small pin tenter, create a four-ply sample piece, and measure the color tone L value of the sample piece with the Minolta color difference meter CR-100 type And used as an index of dyeability. A lower L value indicates that the fiber is dyed darker, and a value of 40 or less was accepted.

Dye Astrazone Blue 0.5% omf
Leveling agent Acetic acid 0.2mL / L
Sodium acetate 0.2g / L
Bath ratio 1:50
(F) Flame retardancy
In accordance with JIS K 7201, the LOI value (limit oxygen index) was measured, and those with 27 or more were accepted.
(G) Light resistance
The light fastness to dyeing was measured according to JIS L 0841, and those of grade 4 or higher were accepted.
(Example 1)
Esterification reactor with PET oligomer is continuously supplied with a slurry with a terephthalic acid and EG mass ratio of 1: 1.6, and esterified under the conditions of a temperature of 250 ° C, a pressure of 0.1 MPa, and a residence time of 8 hours. Then, a PET oligomer having a reaction rate of 95% was continuously obtained.

After 56.8 kg of this esterified PET oligomer was transferred to a polycondensation reactor, 6.5 kg of EG was added to perform depolymerization for 40 minutes. When the temperature in the polycondensation reactor was 240 ° C, HCA- 8.5 kg of EG solution adjusted to 33% by mass of IA (corresponding to the amount that HCA-IA is 4.3 mol% with respect to the total acid component of polyester), and the concentration of titanium dioxide was adjusted to 34% by mass EG slurry 0.7 kg (corresponding to 0.4% by mass with respect to the polymer produced by titanium dioxide), 0.8 kg of EG solution with antimony trioxide concentration adjusted to 2% by mass (antimony trioxide is the total amount of polyester) acid component 1 corresponds to the amount to be 2 × 10 ^-4 mol per mol) and 5-sodium sulfoisophthalic acid ethylene glycol ester (hereinafter, SIPG abbreviated. concentration) were prepared in 35 wt% EG 4.6 kg of solution (SIPG is 1.5 mol% with respect to the total acid components of polyester) The corresponds to the amount) were added, respectively.

  Five minutes later, the pressure reduction was started, and 60 minutes later, the pressure was reduced to 1.2 hPa or less. The temperature in the reaction vessel was raised to 275 ° C. in 30 minutes after the pressure reduction started. Under these conditions, a polycondensation reaction was performed for 4 hours with stirring, and then the mixture was discharged and pelletized by a conventional method to obtain a copolyester resin.

  Next, the copolymerized polyester resin pellets were dried by a conventional method, then melt-spun at a spinning temperature of 290 ° C. using an ordinary melt spinning apparatus, and the semi-undrawn yarn was wound up at a speed of 3500 m / min. A 48f multifilament (POY) was obtained.

Next, this was drawn at a speed of 700 m / min using a normal drawing apparatus to obtain a 167 dtex / 48f multifilament yarn (FDY).
(Examples 2 to 4, Comparative Examples 1 to 4)
The same procedure as in Example 1 was conducted except that the type and copolymerization ratio of the sulfonate group-containing component and the type and copolymerization ratio of the organic phosphorus compound were variously changed as shown in Table 1.
(Comparative Example 5)
After 56.8 kg of the PET oligomer esterified as in Example 1 was transferred to the polycondensation reaction can, 6.5 kg of EG was added to perform depolymerization for 40 minutes, and the temperature in the polycondensation reaction can was 240 ° C. At this point, 8.5 kg of EG solution prepared with a concentration of HCA-IA of 33% by mass (corresponding to an amount of 4.3% by mol of HCA-IA with respect to the total acid component of the polyester), the concentration of titanium dioxide is 0.7 kg of EG slurry prepared to 34% by mass (corresponding to 0.4% by mass with respect to the polymer produced by titanium dioxide), 0.8 kg of EG solution adjusted to 2% by mass of antimony trioxide (three EG solution 4.6kg (SIPG is the total acid component of the polyester). Antimony oxide is equivalent to the amount of 2 x ^10-4 mol per mol of the total acid component of the polyester.) Corresponding to an amount of 1.5 mol%).

  Thereafter, the temperature in the reactor was raised to 275 ° C. in 30 minutes, and the pressure was gradually reduced from 20 minutes after the addition of each EG solution to 1.2 hPa or less after 60 minutes. Under these conditions, a polycondensation reaction was performed for 4 hours with stirring, and then the mixture was discharged and pelletized by a conventional method to obtain a copolyester resin.

    Next, after the copolymer polyester resin pellets were dried by a conventional method, a filament yarn (POY) of 255 dtex / 48 filament and a multifilament yarn (FDY) of 167 dtex / 48f were obtained in the same manner as in Example 1. .

  Table 1 shows the characteristic values of the copolymer polyester resin compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 5, the physical properties of the filament yarns (POY and FDY), and the evaluation results.

表1から明らかなように、実施例1〜4では、繊維化するのに適した極限粘度を有し、DEG含有量も低い共重合ポリエステル樹脂が得られ、これらを高速紡糸することにより、染色性、難燃性及び耐光性が良好であり、延伸仮撚加工性が良好な難燃性カチオン可染ポリエステル繊維（ＰＯＹ）を操業性よく得ることができた。また、これらのＰＯＹを用いた延伸糸（ＦＤＹ）は強度が2.6cN/dtex以上と、そのままで実用可能な特性を有していた。

As is apparent from Table 1, in Examples 1 to 4, a copolyester resin having an intrinsic viscosity suitable for fiberization and a low DEG content was obtained, and these were dyed by spinning at high speed. The flame retardant cationic dyeable polyester fiber (POY) having good operability, flame retardancy and light resistance and good stretch false twist processability could be obtained with good operability. In addition, these drawn yarns (FDY) using POY had a strength of 2.6 cN / dtex or more and were practical as they were.

On the other hand, in Comparative Example 1, since the copolymerization ratio of SIPG was too small, the obtained fiber was inferior in dyeability. In Comparative Example 2, since the copolymerization ratio of SIPG was too high, the melt viscosity became high, and the intrinsic viscosity of the obtained copolymerized polyester resin was not a value sufficient for fiberization, and spinning could be performed. There wasn't. In Comparative Example 3, since the copolymerization ratio of HCA-IA was too small, the phosphorus content in the copolymerized polyester resin was low, and the LOI value of the obtained fiber did not reach the target value, and satisfactory flame retardancy Was not obtained. In Comparative Example 4, since the copolymerization ratio of HCA-IA was too large, the polymerizability of the copolyester resin deteriorated, the intrinsic viscosity suitable for fiber formation was not obtained, and spinning could not be performed. In Comparative Example 5, since the time from the addition of SIPG or HCA-IA to the start of the polycondensation reaction was long and the reaction start temperature was high, the DEG content in the copolyester resin was high, and the resulting fiber The light resistance of was insufficient.

Claims (3)

More than 80 mol% of the repeating units constituting the polyester are ethylene terephthalate units, and the sulfonate group-containing acid component is 0.5 to 5.0 mol% based on the total acid component of the polyester, and an organic compound represented by the following general formula [1] The phosphorus compound is formed using a copolyester resin copolymerized so that the phosphorus atom content in the polyester is 5000 to 15000 ppm, the diethylene glycol content is 5.0 mol% or less, and the birefringence Δn is A flame-retardant cationic dyeable polyester fiber characterized by 0.03-0.06, strength of 1.6 cN / dtex or more, and elongation of 150% or less.

(In the formula, X represents an alkyl group in which two or more of the hydrogen atoms of the alkyl group are substituted with a carboxyl group.) More than 80 mol% of the repeating units constituting the polyester are ethylene terephthalate units, and the sulfonate group-containing acid component is 0.5 to 5.0 mol% based on the total acid component of the polyester, and an organic compound represented by the following general formula [1] The phosphorus compound is formed using a copolyester resin copolymerized so that the phosphorus atom content in the polyester is 5000 to 15000 ppm, the diethylene glycol content is 5.0 mol% or less, and the strength is 2.6 cN / Flame retardant cationic dyeable polyester fiber characterized by being dtex or more.

(In the formula, X represents an alkyl group in which two or more of the hydrogen atoms of the alkyl group are substituted with a carboxyl group.) The flame retardant cationic dyeable polyester fiber according to claim 1 or 2, wherein the LOI value is 27 or more.