Modified polyester composition and fibers and fiber structures thereof

Abstract

To provide a modified polyester composition, though having small fineness, capable of being colored by a cationic dye and having high strength as a fiber material, a fiber made thereof, and a fiber structure.SOLUTION: The present invention relates to a modified polyester composition, a fiber made thereof, and a fiber structure. The composition is a copolyester, in which a main repeating unit is alkylene terephthalate, and which contains isophthalic acid containing a predetermined amount of a metal sulfonate group in total dicarboxylic acid components; and includes, based on the total mass of the copolyester, a predetermined amount of an organic ionic compound expressed by the following general formula (I): RSO3X (I) (in the formula (I), R is an alkyl group of 1-30C or an aryl group of 7-40C and X is an alkali metal, etc.).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a modified polyester composition that can be dyed with cationic dyes, fibers and fiber structures made therefrom, and more particularly to a modified polyester composition that enables the production of fibers with significantly improved physical properties such as strength.

Background Art

[0002] Polyester resins represented by polyethylene terephthalate (PET) have many excellent properties and are widely used as fibers and films. However, general-purpose polyesters such as PET are generally dyed with disperse dyes, but there are problems with color development and dyeing fastness. Therefore, a method that enables dyeing with cationic dyes by copolymerizing an isophthalic acid component having a sulfonic acid metal salt such as 5-sodium sulfoisophthalic acid in the polyester main chain is known (Patent Document 1, etc.).

[0003] However, the resin obtained by this method has a significantly increased melt viscosity due to the copolymerization of the component, so when trying to adjust to the limiting viscosity common in PET fibers, the stirring load in the polycondensation process increases and the spinning operability in melt spinning deteriorates significantly, resulting in limitations in use.

[0004] In order to eliminate the drawbacks of such cationic dye-dyeable polyesters, proposals have been made regarding compositions copolymerized with an isophthalic acid component having a sulfonic acid phosphonium salt with a small intermolecular ionic bonding force (Patent Document 2, Patent Document 3). According to this method, since the thickening effect of the polymer is suppressed, the strength of the obtained fibers and the clarity when dyed with cationic dyes are improved. However, the effect of this method is limited, and when considering general use as clothing fibers, neither the strength nor the clarity can be said to be sufficient.

[0005] On the other hand, there have also been proposals for compositions containing an organic sulfonic acid metal salt that is non-reactive with the copolymerized polyester, such as an alkylbenzene sulfonic acid metal salt (Patent Document 4). It has also been shown that a high-strength cationic dyeable polyester can be obtained from such a composition. However, in the compositions obtained by this method, the color tone deteriorates as the amount of organic sulfonic acid metal salt increases, and the fibers made from these compositions have a trade-off relationship between the physical properties of the fibers, such as fiber strength, and the ability to dye deeply and vividly when dyed with cationic dyes, and it was not possible to satisfy both simultaneously. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2003-261754 [Patent Document 2] Japanese Patent Application Publication No. 1-162822 [Patent Document 3] Japanese Patent Publication No. 2006-36953 [Patent Document 4] Japanese Patent Application Publication No. 4-264126 [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of the present invention is to solve the problems of the above-mentioned prior art and to provide a modified polyester composition that is fine in diameter, can be dyed with cationic dyes, and has high strength as a fiber material, as well as fibers and fiber structures made therefrom. [Means for solving the problem]

[0008] As a result of diligent research, the inventors have solved the above problem by providing a modified polyester composition in which the main repeating unit is alkylene terephthalate and the total dicarboxylic acid component contains 1.0 to 5.0 mol% of metal sulfonate group-containing isophthalic acid, and the copolymer polyester contains 0.5 to 5.0% by mass of an organic ionic compound represented by the following general formula (I) based on the total mass of the copolymer polyester. RSO3X(I) (In formula (I) above, R represents an alkyl group having 1 to 30 carbon atoms or an aryl group having 7 to 40 carbon atoms, and X represents a cation containing one or more alkali metals, alkaline earth metals, quaternary ammonium salts, or quaternary phosphonium salts.) [Effects of the Invention]

[0009] According to the present invention, a modified polyester composition for textiles can be obtained that has high intrinsic viscosity, sufficient strength, and excellent vividness after dyeing with cationic dyes. By using the present invention, the physical properties and color tone of irregularly shaped cross-section fibers, ultrafine fibers, and false-twisted yarns, which were difficult to develop with conventional techniques due to insufficient physical properties such as strength, can be improved, and fabrics with excellent strength, vividness, and lightfastness, which are particularly required for sportswear fabrics, can be obtained. Furthermore, it can be effectively used in a wide range of fields, such as fabrics for women's innerwear, high-density woven fabrics, wiping cloths, and absorbent towels. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing an example of a false twisting apparatus for implementing the method of the present invention. [Modes for carrying out the invention]

[0011] <Copolymerized polyester> In the modified polyester composition of the present invention, the main repeating unit is alkylene terephthalate, and is preferably an alkylene terephthalate consisting of at least one of the group consisting of ethylene terephthalate, trimethylene terephthalate, and butylene terephthalate, with ethylene terephthalate being the most preferred.

[0012] As a copolymer, it is necessary that the metal sulfonate group-containing isophthalic acid component is copolymerized at a concentration of 1.0 to 5.0 mol% relative to the total dicarboxylic acid component. If the copolymerization amount is less than 1.0 mol%, the dye clarity of the fibers after cationic dye dyeing will be poor. On the other hand, if the copolymerization amount exceeds 5.0 mol%, the clarity of the cationic dye will be almost saturated, and the fibers will become more susceptible to hydrolysis, resulting in inferior physical properties such as strength. The metal component of the metal sulfonate group-containing isophthalic acid component is selected from alkali metals, with Na, K, and Li being preferred among them.

[0013] <Organoionic compounds represented by formula (I)> The key is to provide a modified polyester composition containing 0.5 to 5.0% by mass of an organic ionic compound represented by the following general formula (I), based on the total mass of the copolymerized polyester. RSO3X (I) (In formula (I) above, R represents an alkyl group having 1 to 30 carbon atoms or an aryl group having 7 to 40 carbon atoms, and X represents a cation containing one or more alkali metals, alkaline earth metals, quaternary ammonium salts, or quaternary phosphonium salts.)

[0014] In the above formula (I), when R is an alkyl group, the alkyl group may be linear or have branched side chains. In the above formula (I), X represents a cation consisting of one or more alkali metals such as Na, K, and Li, or alkaline earth metals such as Mg and Ca, or quaternary ammonium salts and quaternary phosphonium salts. Among alkali metals, Li, Na, and K are preferred. Such organic ionic compounds may be used individually or as a mixture of two or more.

[0015] Preferred specific examples include sodium stearyl sulfonate, sodium octyl sulfonate, sodium dodecyl sulfonate, a sodium alkyl sulfonate mixture with an average of 14 carbon atoms, a sodium dodecylbenzene sulfonate mixture, sodium dodecylbenzene sulfonate (hard type, soft type), lithium dodecylbenzene sulfonate (hard type, soft type), magnesium dodecylbenzene sulfonate (hard type, soft type), and the like.

[0016] In the above formula (I), it is particularly preferable that X is a quaternary phosphonium salt, particularly a quaternary phosphonium ion of sulfonic acid. It may be used alone or in combination of two or more. Preferred specific examples include tetrabutylphosphonium alkyl sulfonate with an average of 14 carbon atoms, tetraphenylphosphonium alkyl sulfonate with an average of 14 carbon atoms, butyltriphenylphosphonium alkyl sulfonate with an average of 14 carbon atoms, tetrabutylphosphonium dodecylbenzene sulfonate (hard type, soft type), tetraphenylphosphonium dodecylbenzene sulfonate (hard type, soft type), benzyltriphenylphosphonium dodecylbenzene sulfonate (hard type, soft type), and the like.

[0017] Such organic ionic compounds may be used alone or in combination of two or more. The blending amount thereof needs to be in the range of 0.5 to 5.0% by mass based on 100 parts by mass of the aromatic polyester, and more preferably 0.7 to 3.0% by mass. If the blending amount of the organic ionic compound is less than 0.5% by mass, the effect of reducing the melt viscosity is small, and if it exceeds �.0% by mass, foaming cannot be controlled in the polymerization process or the spinning process, the ruder bite-in property of the chips during melt molding decreases, and yarn breakage is likely to occur during melt spinning, resulting in unstable process conditions.

[0018] Particularly, due to the high viscosity reduction effect, in the above formula (I), using X as a quaternary phosphonium salt has a great effect. Among them, tetraalkylphosphonium ions are preferred, and tetrabutylphosphonium ions are more preferred. Further, as the organic ionic compound of the above formula (I), tetrabutylphosphonium alkylsulfonate and tetrabutylphosphonium alkylbenzenesulfonate are preferred, and among them, tetrabutylphosphonium dodecylbenzenesulfonate is even more preferred.

[0019] <Benzoic acid and / or benzoic acid derivatives> The modified polyester composition of the present invention preferably further contains benzoic acid and / or benzoic acid derivatives in an amount of 100 to 1500 ppm based on the total mass of the modified polyester composition, and particularly preferably 500 to 1000 ppm. When the content is less than 100 ppm, the thickening effect of the polymer is not sufficiently suppressed. On the other hand, when it exceeds 1000 ppm, due to the end-capping effect, the modified polyester composition cannot obtain a sufficient intrinsic viscosity, and physical properties such as strength deteriorate.

[0020] Examples of the benzoic acid derivative include p-hydroxybenzoic acid, dihydroxybenzoic acid, and hydrocarbon group-containing hydroxybenzoic acid. Specific examples of the hydrocarbon group are an alkyl group having 1 to 30 carbon atoms, an aryl group having 6 to 40 carbon atoms, or an alkylaryl group. When it is an alkyl group, it may be linear or have a branched side chain, but benzoic acid is preferred in terms of having a greater effect. The above benzoic acid and / or benzoic acid derivatives may be used alone or in combination of two or more. Particularly, when a metal ion is used for X in the above formula (I), it is effective for improving the hue.

[0021] <Intrinsic viscosity (IV)> The intrinsic viscosity (IV) of the modified polyester composition of the present invention is preferably 0.50 to 1.30 dl / g. If the intrinsic viscosity is less than 0.50 dl / g, the fiber properties such as strength will be inferior. If the intrinsic viscosity exceeds 1.30 dl / g, there are problems such as the melt viscosity becoming too high to be stirred in the polycondensation tank or discharged from the polymerization or spinning apparatus. The preferred range for the intrinsic viscosity is 0.50 to 1.10 dl / g, and the more preferred range is 0.55 to 0.90 dl / g. These also depend on the type of alkylene terephthalate, which is the main repeating unit, and the copolymerization ratio of metal sulfonate group-containing isophthalic acid.

[0022] <Method for producing modified polyester composition> The method for producing the modified polyester composition of the present invention will be described in detail. The modified polyester composition of the present invention is produced by a transesterification reaction between a dicarboxylic acid component such as terephthalic acid and an alkylene glycol component such as ethylene glycol. Of the total dicarboxylic acid component, 1.0 to 5.0 mol% is an isophthalic acid component containing a metal sulfonate group. After the transesterification reaction, the modified polyester composition can be produced by adding 0.5 to 2.5% by mass of an organic ionic compound such as tetrabutylphosphonium dodecylbenzenesulfonate ion and 100 to 1500 ppm of benzoic acid or a benzoic acid derivative, based on the total mass, and carrying out polycondensation under ultra-low pressure close to vacuum in the presence of a polycondensation catalyst. In order to form molded products such as fibers from this modified polyester composition, it is often formed into chips (pellets) using conventionally known pelletizers, but molding methods such as continuous poly-ply direct spinning, in which the molten polymer is directly connected to molding equipment such as a spinning machine, may also be used.

[0023] In the method for producing the modified polyester composition of the present invention, examples of metal sulfonate group-containing isophthalic acid components used include 5-sodium sulfisophthalic acid, dimethyl 5-sodium sulfisophthalate, diethyl 5-sodium sulfisophthalate, glycol 5-sodium sulfisophthalate, 5-lithium sulfisophthalic acid, dimethyl 5-lithium sulfisophthalate, diethyl 5-lithium sulfisophthalate, and glycol 5-lithium sulfisophthalate. Among these, 5-sodium sulfisophthalic acid and dimethyl 5-sodium sulfisophthalate are preferred.

[0024] In the method for producing the modified polyester composition of the present invention, any known transesterification catalyst can be used. For example, oxides or acetates of calcium, magnesium, manganese, and titanium are preferably used. In the case of the direct gravity method using terephthalic acid, metal sulfonate group-containing isophthalic acid, and ethylene glycol as starting materials, the catalyst may not be added.

[0025] However, when adding benzoic acid and / or benzoic acid derivatives, the timing of addition is important. Adding them before the transesterification reaction is preferable because the end-closing effect will prevent sufficient formation of bishydroxyalkyl terephthalate (BHAT) through the transesterification reaction of dicarboxylic acid and glycol. Specifically, the benzoic acid derivatives can be added and mixed before the start of the polycondensation reaction of the polyester, during the polycondensation reaction, at the end of the polycondensation reaction while the mixture is still molten, in powder form, or during the molding stage. The addition can be done in a single operation or in two or more separate additions. When adding before the end of the polycondensation reaction, the benzoic acid derivatives can also be dissolved or dispersed in a solvent such as glycol before addition.

[0026] In the method for producing the modified polyester composition of the present invention, a phosphorus compound may be added as a heat stabilizer. Examples of phosphorus compounds include orthophosphate; pentavalent phosphorus compounds such as trimethyl phosphate, triethyl phosphate, and trioctyl phosphate; phosphorous acid; and trivalent phosphorus compounds such as trimethyl phosphate and triethyl phosphate. Among these, orthophosphate, trimethyl phosphate, and triethyl phosphate are particularly preferred.

[0027] In the method for producing the modified polyester composition of the present invention, a polycondensation catalyst may be added. Examples of polycondensation catalysts include germanium compounds, antimony compounds, titanium compounds, and the like. In the method for producing the modified polyester composition of the present invention, known additives, such as antistatic agents, heat stabilizers, antioxidants, etc., can be added as long as they do not alter the essential properties of the modified polyester composition.

[0028] Furthermore, the color value of the modified polyester composition obtained in this invention is preferably transparent or white. As a method for measuring the chip color, a method is used in which the L, a, and b values ​​are calculated by using a colorimeter. The larger the L value, the better the whiteness, and the larger the b value is on the positive side, the stronger the yellowish tint. Here, the chip color is preferably L value of 40 or higher. More preferably 45 or higher, and even more preferably 50 or higher. The b value is preferably 25 or lower, even more preferably 20 or lower, and even more preferably 15 or lower.

[0029] <Fiber manufacturing method> Next, we will describe in detail the method for producing fibers using the modified polyester composition mentioned above. Stretched yarns include FOY, which is obtained in two steps: spinning unstretched yarn (UDY) and winding it, and then stretching it in a separate stretching machine; and SDY (straight-stretched yarn), which is produced in one step using a device that connects the spinning and stretching processes. However, the technical element of stretching after spinning is common to both.

[0030] First, let's outline the spinning process. To remove as much moisture as possible from the chips made of the modified polyester composition and suppress hydrolysis, the moisture content of the chips is dehumidified to 0.01% by mass or less using a chip drying device, similar to those used in the production of conventional polyester fibers. Then, the molten polymer is passed through a melt extruder such as an extruder or silver plate melter and extruded from a spinneret with a nozzle the same number as the target number of filaments. Cooling air is blown below the spinneret to cool and solidify the polymer, and it is taken up by a godted roller at a spinning speed of 100 to 5000 m / min. The yarn is then wound onto a bobbin with a winder to obtain undrawn yarn (UDY).

[0031] Furthermore, when obtaining a partially oriented yarn (POY) for the false-twisted yarn described later, the multifilament POY is obtained by high-speed spinning at a spinning speed of 1500 to 5000 m / min or more, preferably 2000 to 4000 m / min. At this time, it is necessary to adjust the birefringence (Δn) of the POY to within the range of 0.01 to 0.06. If Δn is less than 0.01, the yarn becomes brittle during the stretch false-twisting process described later, resulting in frequent yarn breakage and making the stretch false-twisting process difficult. On the other hand, if Δn exceeds 0.06, the tension becomes too high during the false-twisting process due to frequent fluffing (single-fiber breakage) and progression of crystallization, resulting in larger yarn irregularities in the false-twisted yarn and lower physical properties such as strength of the obtained false-twisted yarn, which is undesirable.

[0032] UDY is supplied to a conventionally known filament drawing machine, where it is drawn and heat-set, lubricated to improve the passability of the processed yarn, loom, and knitter, and then wound onto a paper tube using a winder to obtain a drawn yarn as FOY. In the case of SDY, the yarn is drawn to a godted roller that rotates and takes up at the spinning speed of the UDY process, and then subjected to a godted roller that rotates at an even higher speed to be drawn to a predetermined magnification. After that, it is heat-set in-line, lubricated, and wound onto a paper tube using a winder to obtain a drawn yarn as SDY.

[0033] False-twisted yarn (DTY) is obtained by feeding the aforementioned POY into a conventionally known false-twisting machine, performing false-twisting, and then winding it onto a paper tube.

[0034] Figure 1 is a simplified side view of a false twisting machine, illustrating a specific example of false twisting. In Figure 1, 1 is a package of undrawn yarn (POY) made of modified polyester composition filaments, 2 is the feed roller of the false twisting machine, 3 is the interlacing nozzle, 4 is the first delivery roller, 5 is the first heater, 6 is the cooling plate, 7 is the false twisting device, 8 is the second delivery roller, 9 is the third delivery roller, 10 is the lubrication device, and 11 is the package wound with the false twisted yarn.

[0035] In Figure 1, the undrawn yarn drawn from package 1 is subjected to a predetermined entanglement by an interlacing air injection nozzle 3 between the feed roller 2 and the first delivery roller 4. It is preferable to give the yarn 0.5 to 2% slack during the entanglement process. Subsequently, between the first delivery roller 4 and the second delivery roller 8, the yarn is stretched to a predetermined ratio while false twist is added by a false twisting device 7, and the twist is heat-set by a first heater 5 located upstream of the false twisting device 7 at a set temperature of 150 to 250°C. After that, the processed yarn, cooled by the cooling plate 6, is taken up by the second delivery roller 8, and then lubricated by an oiling device 10 via the third delivery roller 9, before being wound up as a false twist processed yarn package 11.

[0036] In this case, the peripheral speed ratio between the feed roller 2 and the first delivery roller is preferably set to 1:1 to 1:0.95 so that the above relaxation rate is achieved, and the peripheral speed ratio between the first delivery roller 4 and the second delivery roller 8 is set to a stretch ratio such that the strength and elongation of the yarn after processing is within the desired range according to the birefringence (Δn) of the POY, for example, a stretch ratio of 1.2 to 1.8 times. If necessary, a second heater may be installed between the second delivery roller 8 and the third delivery roller 9 to perform further heat setting after false twisting.

[0037] The fibers or false-twisted yarns made from the modified polyester composition thus obtained are superior to conventional polyester fibers that can be dyed with cationic dyes, possessing comparable clarity while also having high strength due to their molecular weight being as large as that of PET.

[0038] Furthermore, the drawn yarn or false-twisted yarn made from the obtained modified polyester composition can be made into any fabric, and the color of the fibers can be measured using a spectrophotometer or the like. The larger the L value, the better the whiteness, and the larger the b value, the stronger the yellowness. Here, the chip color is preferably L value of 40 or higher. More preferably 45 or higher, and even more preferably 50 or higher. The b value is preferably 10 or lower, even more preferably 7 or lower, and even more preferably 5 or lower.

[0039] Using this, it is possible to obtain textile structures such as woven or knitted fabrics that have tensile strength and tear strength comparable to PET, while also exhibiting excellent clarity, such as cationic dyed fabrics. [Examples]

[0040] The present invention will be described in more detail below with reference to the following examples. The physical properties in the examples were measured by the following method.

[0041] (1) Intrinsic viscosity of polyester (IV) The sample was dissolved in a mixed solvent of phenol:tetrachloroethane = 60:40 (mass ratio), and the intrinsic viscosity at 20°C was measured using an automatic viscometer (ALC-6C, manufactured by Sun Electronics Industry Co., Ltd.) equipped with an Ubbelohde viscosity tube.

[0042] (2) Color tone of polyester chips The samples were color-measured using a Hunter-type colorimeter manufactured by Nippon Denshoku Industries, Ltd., and the L, a, and b values ​​were calculated. A higher L value indicates better whiteness, while a larger b value indicates a stronger yellow tint.

[0043] (3) Fineness The fineness was measured according to JIS L1013:2010 8.3.1 Method A.

[0044] (4) Breaking strength, breaking elongation Breaking strength and elongation at break were measured in accordance with JIS L1013:2010 8.5.1.

[0045] (5) Crimp rate (Tc) A sample of polyester false-twist yarn was wound onto a skein frame under a tension of 0.044 cN / dtex to create a skein with a thickness of approximately 3300 dtex. Two loads, 0.00177 cN / dtex and 0.177 cN / dtex, were applied to one end of this skein, and the length S0 (cm) was measured after 1 minute. Next, with the 0.177 cN / dtex load removed from the skein, it was treated in boiling water at 100°C for 20 minutes. After the boiling water treatment, the 0.00177 cN / dtex load was removed from the skein, and it was allowed to air dry freely for 24 hours without load. Then, the loads of 0.00177 cN / dtex and 0.177 cN / dtex were applied to the skein again, and the length S1 (cm) was measured after 1 minute. Next, the load of 0.177 cN / dtex was removed from this sack, and the length S2 was measured after 1 minute. The crimping rate was calculated using the following formula, and the average of 10 measurements was calculated. Crimp rate (%)=[(S1-S2) / S0]×100

[0046] (6) Fabric color after cation dyeing Using the drawn yarn and false-twisted yarn made from the obtained modified polyester composition, single-layer circular knitted fabrics with a knitting density of 50 courses / 2.54 cm and 45 wales / 2.54 cm were prepared. After scouring and presetting by conventional methods, the fabrics were dyed at 98°C for 60 minutes in a dye bath containing 3 g / l Glauber's salt and 0.3 g / l acetic acid with ASTRAZON BLUE BG200 0.025% owf at a bath ratio of 1:400, and then soaped according to conventional methods to obtain blue fabric. Three layers of the obtained knitted fabrics were stacked, and the color was measured by measuring the reflectance of the knitted fabric samples using a Macbeth spectrophotometer (CE3100), and the L, a, and b values ​​were calculated.

[0047] [Example 1] <Manufacturing of modified polyester composition> In a reaction vessel equipped with a rectification column, 100% by mass of dimethyl terephthalate, 4.23% by mass of dimethyl 5-sodium sulfisophthalate (hereinafter abbreviated as SIP) (2.5 mol% of the dicarboxylic acid component), and 66% by mass of ethylene glycol were supplied. As a transesterification catalyst, calcium acetate hydrate was added so that the resulting polyester contained 220 ppm and 21 ppm of tetrabutoxytitanium. Subsequently, the transesterification reaction was carried out by distilling off methanol while raising the temperature of the reaction vessel from 140°C to 240°C. The esterification reaction rate at this time was 95%. Next, benzoic acid was added to the resulting polyester so that it contained 1000 ppm and 54 ppm of trimethyl phosphate, and the liquid was transferred to a polycondensation reaction vessel while filtering.

[0048] To the low polymer transferred to the polycondensation reaction vessel, tetrabutylphosphonium dodecylbenzenesulfonate (hereinafter abbreviated as DBSP), an organic ionic compound represented by formula (I), was added to the resulting polyester in an amount of 1.0% by mass relative to the total mass of the modified polyester composition. After the addition was completed, the pressure was reduced from atmospheric pressure to 0.1 kPa over 120 minutes, the temperature was raised from 240°C to 285°C, and the polycondensation reaction was carried out while maintaining a high vacuum of 0.1 kPa or less. The molten modified polyester composition was then pelletized into chips (pellet-shaped elliptical cylinders with a cross-section of elliptical major axis 3 ± 1 mm, minor axis 2 ± 1 mm, and height 3 ± 1 mm) using a pelletizer to obtain the modified polyester composition chips shown in Table 1.

[0049] <Manufacturing of drawn yarn> Modified polyester composition chips were hot-air dried according to a conventional method (160°C for 6 hours), and then supplied to a melt extruder to obtain a 290°C molten polymer. This polymer was extruded from a spinneret equipped with 36 circular discharge holes with a diameter of 0.25 mm, and drawn up at a spinning speed of 1000 m / min to obtain an undrawn yarn of 140 dtex / 36 filaments. The intrinsic viscosity of the obtained spun yarn was 0.55 dl / g. This undrawn yarn was then preheated at 80°C, heat-set at 200°C with a non-contact heater at a draw ratio of 3.50, and drawn at a winding speed of 600 m / min. The properties of the obtained drawn yarn are shown in Table 2.

[0050] <Manufacturing of false-twisted yarn> Using a modified polyester composition, after hot-air drying according to a conventional method (160°C for 6 hours), the resulting molten polymer at 290°C was supplied to a melt extruder. This molten polymer was then extruded from a spinneret equipped with 36 circular discharge holes with a diameter of 0.25 mm, and drawn up at a spinning speed of 2700 m / min to obtain POY with 90 dtex / 36 filaments. The intrinsic viscosity of the obtained spun yarn was 0.55 dl / g. The obtained POY underwent entanglement treatment and stretch false twisting in the process shown in Figure 1. In this process, the stretch ratio was 1.60, the non-contact heater temperature was 200°C, and an external friction false twisting device was used as the false twisting device, stretch false twisting was performed at 600 m / min. The properties of the obtained false twisted yarn are as shown in Table 3.

[0051] [Examples 2-5, Comparative Examples 1-6] A modified polyester composition was produced using the same process as in Example 1, except that the copolymerization amounts and addition amounts of SIP, benzoic acid, and tetrabutylphosphonium dodecylbenzenesulfonate were changed as shown in Table 1. The physical properties of the obtained modified polyester composition chips are shown in Table 1. A drawn yarn and a false-twisted yarn were also obtained using the same method as in Example 1. The physical properties of the obtained yarns are shown in Tables 2 and 3.

[0052] [Comparative Example 7] A modified polyester composition was produced using the same process as in Example 1, except that 3,5-dicarbomethoxybenzenesulfonic acid tetra-n-butylphosphonium salt (SIPP) was used instead of SIP, as shown in Table 1. The physical properties of the obtained modified polyester composition chips are shown in Table 1. A drawn yarn and a false-twisted yarn were also obtained using the same method as in Example 1. The physical properties of the obtained yarns are shown in Tables 2 and 3.

[0053] [Table 1]

[0054] [Table 2]

[0055] [Table 3] [Industrial applicability]

[0056] The modified polyester composition of the present invention exhibits unprecedented effects, such as improved vividness when dyed with cationic dyes while maintaining physical properties such as strength. Therefore, the modified polyester composition of the present invention is particularly useful when used in the form of fibers. In particular, the modified polyester composition of the present invention is especially effective when used in irregularly shaped cross-section fibers and fine fibers of 1.1 dtex or less, for which vivid cationic dyeing and physical properties such as strength have been difficult to obtain. Fibers obtained from the modified polyester composition of the present invention possess vivid color development that surpasses nylon, along with strength and softness, making them particularly useful in sportswear such as ski wear, windbreakers, or swimwear. [Explanation of Symbols]

[0057] 1 POY 2 Feed rollers 3. Interlacing air injection nozzle (interlace nozzle) 4. First Deliverola 5. First heater 6 Cooling Plate 7. False twisting device 8. Second Delivery Roller 9. Third Deliverola 10. Fueling device 11 False-twisted yarn package

Claims

1. A copolymer polyester in which the main repeating unit is alkylene terephthalate and which contains 1.0 to 2.5 mol% of metal sulfonate group-containing isophthalic acid in the total dicarboxylic acid component, and which contains 0.7 to 3.0% by mass of an organic ionic compound represented by the following general formula (I) based on the total mass of the copolymer polyester, The modified polyester composition contains 500 to 1000 ppm of benzoic acid and / or a benzoic acid derivative based on the total mass. A modified polyester composition characterized by having a chip color L value of 40 or more and a b value of 15 or less, as calculated using a colorimeter. RSO ３ X (I) (In formula (I) above, R represents an alkyl group having 1 to 30 carbon atoms or an aryl group having 7 to 40 carbon atoms, and X represents a cation containing one or more alkali metals, alkaline earth metals, quaternary ammonium salts, or quaternary phosphonium salts.)

2. The modified polyester composition according to claim 1, characterized in that it contains an organic salt compound in which X is a tetraalkylphosphonium ion in the above formula (I).

3. The modified polyester composition according to claim 1 or claim 2, wherein the intrinsic viscosity of the modified polyester composition is in the range of 0.50 to 1.30 dl / g.

4. A modified polyester composition according to any one of claims 1 to 3, characterized in that the main repeating unit is ethylene terephthalate.

5. A polyester fiber comprising the modified polyester composition according to any one of claims 1 to 4.

6. The polyester fiber according to claim 5, wherein the fineness is 1.1 dtex or less.

7. A polyester fiber structure comprising polyester fibers according to claim 5 or 6.

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