JPS6246668B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing synthetic fiber structures. More particularly, the present invention relates to a method for producing synthetic fibers made of polyester that have special micropores and exhibit improved color depth and clarity when colored. Polyester is widely used as a synthetic fiber because it has many excellent properties. However, compared to natural fibers such as wool and silk, cellulose fibers such as rayon and acetate, and acrylic fibers, polyester fibers lack the depth of color and are inferior in color development and clarity when colored. There is. Conventionally, attempts have been made to improve dyes, chemically modify polyester, etc. in an attempt to overcome this drawback, but none of them have been sufficiently effective. In addition, methods have been proposed in which a transparent thin film is formed on the surface of polyester fibers, and a method in which plasma irradiation at 80 to 500 mA·sec/cm ² is applied to the surface of the fiber to form fine irregularities on the surface of the fiber. however,
Even with these methods, the effect of improving the depth of color is insufficient, and in addition, the transparent thin film formed on the fiber surface easily falls off when washed, etc., and its durability is insufficient. In the method of applying plasma irradiation, unevenness does not occur on the surface of the fiber in the part of the fiber that will be in the shadow of the irradiated surface, so the smooth fiber surface does not appear on the surface due to the rolling of threads within the fiber structure that occurs during wear. It has the disadvantage of causing color spots. On the other hand, as a method of imparting irregularities to the surface of polyester fibers, wrinkles arranged in the fiber axis direction are produced by treating fibers made of polyoxyethylene glycol or polyester blended with polyoxyethylene glycol and a sulfonic acid compound with an alkaline aqueous solution. A method for producing hygroscopic fibers in which microscopic pores are formed on the fiber surface, or polyester fibers prepared by adding and blending fine particles of inert inorganic substances such as zinc oxide, calcium phosphate, etc. into a polyester reaction system are treated with an aqueous alkaline solution. A method for producing hygroscopic fibers has been proposed in which fine pores are formed by eluting inorganic fine particles. However, the fibers obtained by these methods do not have the effect of improving color depth, and instead show a decrease in visual density. That is, in these methods, if the treatment with the alkaline aqueous solution is not sufficient, no effect of improving the color depth is observed at all, and when the treatment with the alkaline aqueous solution is sufficient, the color depth is not improved, Perhaps due to the diffuse reflection of light by the micropores, the visual density decreases, making it look whitish even when colored in a dark color, and the strength of the resulting fibers decreases significantly.
It easily becomes fibrillated and cannot be put to practical use. In addition, fibers made of polyester containing inorganic fine particles such as silica with a particle diameter of 80 mμ or less are subjected to alkali weight loss treatment to give irregular irregularities of 0.2 to 0.7 μm on the fiber surface, and 50 to 200 microns within these irregularities.
A method has been proposed for improving the depth of color by creating microscopic irregularities of mμ. However, even with this method, the effect of improving the depth of color is insufficient, and in addition, perhaps due to the extremely complex shape of the unevenness, the unevenness is destroyed by external physical effects such as friction. There are disadvantages in that the damaged portions are significantly discolored compared to other undestructed portions, have a difference in gloss, and are easily fibrillated. The inventor of the present invention has conducted intensive studies to provide a polyester fiber that does not have the above-mentioned drawbacks and has excellent color depth and clarity by adding micropores to polyester fiber, and has found that a specific amount of 5 Without reacting a specific amount of calcium compound with a valent phosphorus compound and this pentavalent phosphorus compound in advance,
A large number of special microvoids can be formed by alkali treatment of polyester fiber obtained by melt-spinning polyester synthesized by adding it to a polyester reaction system, and after dyeing, the fiber can be further treated with a low refractive index polymer. It was discovered and proposed earlier that by coating, polyester fibers with excellent color depth and clarity, sufficiently small discoloration due to friction, and excellent fibril resistance can be obtained. However, the polyester fibers obtained in this manner can only be dyed with disperse dyes whose color vividness is not very good.
Therefore, in order to obtain even more excellent color depth and clarity, it is desirable to modify polyester fibers into a type that can be dyed with cationic dyes so that cationic dyes with excellent clarity can be used. The present inventor has developed a polyester fiber that has a large number of microvoids on the fiber surface and its vicinity, such as those obtained with the above-mentioned polyester fiber, and is dyeable with a cationic dye, and then coats it with a low refractive index polymer. In an attempt to obtain a structure with color-forming properties, various methods were investigated for adding a pentavalent phosphorus compound and a calcium compound without prior reaction during the synthesis of a polyester modified with an isophthalic acid component having an alkali metal sulfonate group. As a result, when a phosphorus compound and a calcium compound are added during the synthesis of a polyester modified with an isophthalic acid component having an alkali metal sulfonate group, it is difficult to synthesize a normal polyester that is not modified with an isophthalic acid component having an alkali metal sulfonate group. The dispersion state of the internally precipitated particles in the resulting polyester tends to be poor compared to when it is added at the same time, making it difficult to obtain a polymer with good transparency, and the resulting alkali treatment Macrovoids are formed on the surface of the polyester fiber after dyeing, and when coated with a low refractive index polymer after dyeing, it is difficult to see the effect of improving color depth and clarity, and the visual density may even decrease. I discovered that there is a problem. The inventors of the present invention have conducted extensive studies to solve this problem, and have surprisingly found that by using a lithium compound in place of a calcium compound in the above method, the internally precipitated particles can have good dispersibility. , a cationic dye-dyeable polyester with excellent transparency can be reliably obtained with good reproducibility, and by alkali treatment of polyester fibers melt-spun from this polyester, many microvoids can be formed on the fiber surface and its vicinity. When coated with a low refractive index polymer after dyeing with a cationic dye, it exhibits improved color depth and clarity, excellent color fastness, sufficiently small discoloration due to friction, and good fibril resistance. It has been found that an excellent polyester fiber structure can be obtained. The present invention was completed as a result of further studies based on this knowledge. That is, the present invention relates to the production of synthetic fibers made of polyester synthesized by the reaction of dicarboxylic acids, mainly terephthalic acid, or their ester-forming derivatives, and at least one glycol or their ester-forming derivatives. At any stage until the synthesis of the polyester is completed, (a) isophthalic acid or its ester-forming derivative having an alkali metal sulfonate group in an amount of 0.5 to 10 mol% based on the total acid component; 0.3 to 3 mol% of the following general formula [In the formula, R ¹ and R ² are a hydrogen atom or a monovalent organic group, X is a hydrogen atom, a monovalent organic group, or a metal, m
indicates 0 or 1. ] Phosphorus compound (c) represented by lithium compound without reacting (a), (b) and (c) in advance, and the total amount of equivalents of metals (b) and (c) is added in an amount of 2.0 to 3.2 times the number of moles of the phosphorus compound in (b), then the synthesis of the polyester is completed, and the resulting polyester is melt-spun, and then the phosphorus compound is added in an aqueous solution of an alkali compound. This is a polyester fiber structure characterized by dyeing polyester fibers that have eluted more than % by weight and then coating the fibers with a polymer having a lower refractive index than the fibers. The polyester in the present invention is a polyester whose main acid component is terephthalic acid, and whose main glycol component is at least one glycol, preferably at least one alkylene glycol selected from ethylene glycol, trimethylene glycol, and tetramethylene glycol. The main target is It may also be a polyester in which a part of the terephthalic acid component is replaced with another difunctional carboxylic acid component, and/or a part of the glycol component is replaced with the above glycol other than the main component or another diol component. It may also be made of polyester. Examples of difunctional carboxylic acids other than terephthalic acid used here include isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid,
Aromatic, aliphatic, and alicyclic difunctional carboxylic acids such as diphenoxyethanedicarboxylic acid, β-hydroxyethoxybenzoic acid, p-oxybenzoic acid, adipic acid, sebacic acid, and 1,4-cyclohexanedicarboxylic acid. can be given. Examples of diol compounds other than the above-mentioned glycols include aliphatic, alicyclic, and aromatic diol compounds such as cyclohexane-1,4-dimethanol, neopentyl glycol, bisphenol A, and bisphenol S, and polyoxyalkylene. Examples include glycol. Such polyesters may be synthesized by any method. For example, regarding polyethylene terephthalate, it is usually done by directly esterifying terephthalic acid and ethylene glycol, by transesterifying a lower alkyl ester of terephthalic acid such as dimethyl terephthalate with ethylene glycol, or by transesterifying terephthalic acid and ethylene glycol. The first step is to react with ethylene oxide to produce a glycol ester of terephthalic acid and/or its low polymer, and the reaction product of the first step is heated under reduced pressure to reach the desired degree of polymerization. It is produced by a second step of polycondensation reaction until the By adding and copolymerizing isophthalic acid having an alkali metal sulfonate group or an ester-forming derivative thereof to the polyester of the present invention at any stage until the synthesis is completed, alkylene is added to the main chain of the polyester. -5-Introducing alkali metal sulfoisophthalate units. Preferred specific examples of isophthalic acid having an alkali metal sulfonate group or its ester-forming derivative include sodium 3,5-di(carboxy)benzenesulfonate, lithium 3,5-di(carboxy)benzenesulfonate, and lithium 3,5-di(carboxy)benzenesulfonate. Potassium 5-di(carboxy)benzenesulfonate,
Lithium 3,5-di(carbomethoxy)benzenesulfonate, Potassium 3,5-di(carbomethoxy)benzenesulfonate, Sodium 3,5-di(β-hydroxyethoxycarbonyl)benzenesulfonate, 3,5-Di(carbomethoxy)benzenesulfonate (β-hydroxyethoxycarbonyl) lithium benzenesulfonate,
Potassium 3,5-di(β-hydroxyethoxycarbonyl)benzenesulfonate, Sodium 3,5-di(γ-hydroxypropoxycarbonyl)benzenesulfonate, Sodium 3,5-di(δ-hydroxybutoxycarbonyl)benzenesulfonate , lithium 3,5-di(δ-hydroxybutoxycarbonyl)benzenesulfonate, and the like. The amount of the isophthalic acid having an alkali metal sulfonate group or its ester-forming derivative is determined based on the total acid components constituting the polyester.
In the range 0.5-10 mol%, preferably 1-6 mol%
is within the range of The amount added is in the range of 0.5 mol%. If the amount added is less than 0.5 mol%, it will not be possible to dye the final polyester fiber with the cationic dye in sufficient concentration, and if it exceeds 10 mol%, not only will the affinity for cationic dyes be saturated, This is not preferred because the excellent physical properties unique to polyester fibers are impaired and the manufacturing cost increases significantly. The phosphorus compound used in the present invention has the following general formula: It is a phosphorus compound represented by the formula, where R ¹ and
R ² is a hydrogen atom or a monovalent organic group. This monovalent organic group is specifically an alkyl group, an aryl group, an aralkyl group, or -[(CH ₂ ) _l O] _k R ³ (however,
R ³ is preferably a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, l is an integer of 2 or more, k is an integer of 1 or more, and R ¹ and R ² may be the same or different. X is a hydrogen atom, a monovalent organic group, or a metal, and examples of the monovalent organic group include the above R ¹ and R ²
This is the same as the definition of organic group in R ¹ , R ²
The metal may be the same as or different from the metal, and particularly preferred are alkali metals and alkaline earth metals, with lithium (Li) being particularly preferred.
m is an integer of 0 or 1. Such phosphorus compounds include, for example, orthophosphoric acid,
Phosphoric acid triesters such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, phosphoric acid mono- and diesters such as methyl acid phosphate, ethyl acid phosphate, butyl acid phosphate, phosphorous acid,
Phosphite triesters such as trimethyl phosphite, triethyl phosphite, tributyl phosphite, triphenyl phosphite, phosphorous mono- and diesters such as methyl acid phosphite, ethyl acid phosphite, butyl acid phosphite, One type selected from a phosphorus compound obtained by reacting the above phosphorus compound with glycol and/or water, a phosphorus compound obtained by further reacting the above phosphorus compound with a lithium compound in an equimolar amount to the phosphorus compound, etc. The above phosphorus compounds can be used. The lithium compound to be used in combination with the above phosphorus compound is not particularly limited as long as it reacts with the above phosphorus compound to form a salt insoluble in polyester, including lithium acetate, oxalate, benzoate, phthalate. acid salts, organic carboxylates such as stearates, borates, sulfates, silicates, carbonates,
Inorganic acid salts such as bicarbonates, halides such as chlorides, chelates such as ethylenediaminetetraacetic acid complexes, hydroxides, oxides, methylates,
Alcoholates such as ethylate and glycolate,
Examples include phenolate. organic carboxylates, which are particularly soluble in ethylene glycol;
Halides, chelate compounds, and alcoholates are preferred, and organic carboxylates are particularly preferred. The above lithium compounds may be used alone or in combination of two or more. There is no need to employ any special method to melt-spun the polyester obtained in this manner to form fibers, and any ordinary melt-spinning method for polyester fibers may be employed. The fibers spun here may be solid fibers having no hollow portions or hollow fibers having hollow portions. Further, the outer shape and the shape of the hollow portion in the cross section of the fiber to be spun may be circular or irregular. Further, when spinning, a cationic dye-dyeable polyester to which the above-mentioned phosphorus compound and lithium compound are added, an unmodified polyester without the additive, and/or a cationic dye-dyeable polyester without the additive, and a phosphorus compound and a lithium compound added thereto. A core-sheath type conjugate fiber or a side-by-side type conjugate fiber with two or more layers may be used, in which the cationic dye-dyeable polyester is used as a sheath component or a layer component. To remove a part of the polyester fiber thus obtained, after subjecting it to stretching heat treatment or false twisting as necessary, or after making it into a fabric,
This can be easily carried out by treatment with an aqueous solution of an alkaline compound. Examples of the alkali compound used here include sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, sodium carbonate, potassium carbonate, and the like. Among these, sodium hydroxide and potassium hydroxide are particularly preferred. The concentration of such an aqueous solution of an alkali compound varies depending on the type of alkali compound, processing conditions, etc., but is usually preferably in the range of 0.01 to 40% by weight, particularly
A range of 0.1 to 30% by weight is preferred. The processing temperature is preferably in the range of room temperature to 100°C, and the processing time is 1 minute to 1 minute.
It is usually carried out for a period of 4 hours. Further, the amount of the alkali compound eluted and removed by treatment with the aqueous solution should be in the range of 2% by weight or more based on the weight of the fiber. By treating with an aqueous solution of an alkali compound in this manner, a large number of microvoids can be formed on the fiber surface and its vicinity. Note that the polyester fiber obtained by the method of the present invention may contain optional additives such as catalysts, color inhibitors, heat resistant agents, flame retardants, fluorescent brighteners, matting agents, colorants, etc. as necessary. May be included. Examples of polymers with a low refractive index as used in the present invention include polytetrafluoroethylene, tetrafluoroethylene-propylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, and tetrafluoroethylene-tetrafluoroethylene copolymer. Fluoropropylene copolymer, profluorovinylidene, polypentadecafluorooctyl acrylate, polyfluoroethyl acrylate, polytrifluoroisopropyl methacrylate,
Fluorine-containing polymers such as polytrifluoroethyl methacrylate, silicon-containing compounds such as polydimethylsilane, polymethylhydrodiene siloxane, and polydimethylsiloxane, ethylene-vinyl acetate copolymers, polyethyl acrylate, polyethyl methacrylate, etc. Examples include, but are not limited to, acrylic esters and polyurethane polymers. Among these polymers, one having a refractive index smaller than that of the fiber matrix constituting the fiber product may be appropriately selected and used. In this case, it is desirable to select a material that has as large a difference in refractive index as possible with the substrate fiber. The low refractive index polymer that coats the surface of porous polyester fibers is usually commercially available in the form of an organic solvent solution or an aqueous emulsion, but after dyeing,
A water-based emulsion is preferable because it involves a step of coating the surface area. The method for coating the surface of porous polyester fibers with a low refractive index polymer emulsion is preferably a paturing method, a spray method, a kiss roll method, a knife coating method, or an adsorption method in a bath for a woven or knitted fabric formed from porous polyester fibers. Any method such as the method can be used. The surface coating of the low refractive index polymer in the present invention can be applied to all types of textile products such as tow, filament, yarn woven or knitted fabric, and plain woven fabric. The reason why extremely excellent color depth and clarity can be obtained by coating the surface of a porous polyester fiber with a large number of micropores with a polymer having a lower refractive index than that of the porous polyester fiber is as follows. It is explained as follows. Except for objects that emit light by themselves, such as radiators, the color of an object is generally determined by the reflection and absorption of light, but in order to make colors appear deeper and clearer, reflect less light and absorb more light. Regarding light reflection, it is particularly necessary to reduce surface reflected light. This is because the surface-reflected light is reflected as white light, so it hardly contributes to deepening and sharpening the color of the colored body.
This surface reflected light can be broadly divided into specular reflection and diffuse reflection, but if the specular reflection component is reduced by making the surface of the fiber porous as in the present invention, the effect of deepening and sharpening the color can be achieved. It can be further increased. Furthermore, as a method for reducing the amount of surface reflected light, a technique is known both theoretically and empirically in which a material having a lower refractive index than the object constituting the substrate is applied to the surface of the object. An example of this is lens coating technology. This is a technology that reduces the amount of surface reflected light by coating the lens surface with a transparent thin film that has a lower refractive index than glass. Therefore, the synergistic effect of reducing the specular reflection component by making the surface of the fiber porous and reducing the amount of surface reflected light by coating the surface with a low refractive index polymer greatly increases the amount of absorbed light, resulting in an outstanding It is thought that a color effect can be obtained. Furthermore, in the present invention, it is of course possible to dye with disperse dyes, but it is also possible to dye with cationic dyes, which have better clarity than disperse dyes, and it is possible to obtain even more outstanding color effects. A more specific explanation will be given below with reference to Examples.
Parts and % in the examples indicate parts by weight and % by weight,
The depth of color and frictional discoloration when the resulting polyester fibers were dyed were measured by the following methods. (i) Depth of color As a measure of depth of color, bathochromicity (K/
S) was used. This value was determined by measuring the spectral reflectance (R) of the sample fabric using a Shimadzu RC-330 self-recording spectrophotometer.
−Munk). The larger this value is, the greater the deep color effect is. (Measurement wavelength 500
mμ) K/S=(1-R) ² /2R Note that K represents an absorption coefficient and S represents a scattering coefficient. (ii) Resistance to friction discoloration Using a Gakushin type flat abrasion machine for friction fastness testing, the test cloth was subjected to flat friction a specified number of times under a load of 500 g using a 100% polyethylene terephthalate dioset as the friction cloth. hand,
The degree of discoloration was determined using a gray scale for discoloration. The case where the abrasion resistance was extremely low was rated as 1st grade, and the case where it was extremely high was rated as 5th grade. For practical purposes, level 4 or above is required. Example 1 (i) Preparation of fiber substrate and dyed fabric 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol, and 0.06 part of calcium acetate monohydrate were placed in a transesterification tank and heated from 140°C to 230°C over 4 hours under nitrogen gas atmosphere. The transesterification reaction was carried out while raising the temperature to 0.degree. C. and distilling the generated methanol out of the system. Subsequently, the obtained reaction product is
Add 0.64 parts of lithium acetate anhydrous (1.88 mol % based on dimethyl terephthalate),
After 5 minutes, 0.35 parts of orthophosphoric acid (0.69 mol % based on dimethyl terephthalate) were added, and after 5 minutes, 0.04 parts of antimony trioxide were added, and the mixture was transferred to a polymerization vessel. Then, 4.8 parts of sodium 3,5-di(β-hydroxyethoxycarbonyl)benzenesulfonate (2.6 mol % based on dimethyl terephthalate) was added to the polymerization kettle. Next, the pressure was reduced from 760 mmHg to 1 mmHg over an hour, and at the same time the pressure was reduced to 1 mmHg.
The temperature was raised from 230°C to 280°C over 30 minutes.
Under reduced pressure of 1 mmHg or less, at a polymerization temperature of 280°C,
Polymerization time was 30 minutes, total 4 hours, and the intrinsic viscosity was
A polymer with a softening point of 0.512 and a softening point of 258°C was obtained. After the reaction was completed, the polymer was made into chips according to a conventional method. This chip was dried using a conventional method, and the pore size was 0.3 mm.
Melt spinning was carried out at 290° C. using a spinneret with 36 circular spinning holes, followed by drawing at a draw ratio of 3.5 times according to a conventional method to obtain a raw yarn of 75 denier/36 filaments. This yarn has S twist of 2500T/m and Z twist of 2500T/m.
The highly twisted yarn was then subjected to a steam treatment at 80° C. for 30 minutes to fix the twist. The high-twist yarn has a warp density of 47 threads/cm and a weft density of 32 threads/cm.
A pear-skinned jersey fabric was woven with two S and Z twists arranged alternately. The obtained gray fabric was relaxed with a rotary washer for 20 minutes at boiling temperature, then grained, preset using a conventional method, and then treated with a 1% aqueous sodium hydroxide solution at boiling temperature to achieve a weight loss rate of 20%. fabric was obtained.
The fabric after this alkali treatment was dyed under the following conditions and washed according to a conventional method. Disperse dye Resolin Blue FBL4% (owf) Disperse dye dyeing condition dye Disper VG 0.5g / CH ₃ COOH 0.2g / Bath ratio 1:30 Dyeing temperature: 130℃ x 60 minutes Cationic dye Aizen Cathilon Black CD-GLH8%
(owf) Aizen Cathilon Blue CD-FBLH2%
(owf) Cationic dye dyeing conditions Dye or mirabilite 2g/CH ₃ COOH 0.5g/bath ratio 1:30 Dyeing temperature: 127℃ x 60 minutes Color depth of black dyed fabric and abrasion resistance after 200 wears are shown in Table 1. The vividness of the color of the blue-dyed fabric was visually judged according to the following criteria and is shown in Table 1. ◎; Sharpness is significantly higher than the standard 〇; Sharpness is higher than the standard ST; Standard △; Sharpness is lower than the standard (ii) Production of low refractive index polymer and surface coating of polyester fibers Dimethylpolysiloxane 30 with a viscosity of 1000CS
g, tall oil fatty acid 2 containing basic oleic acid
g, 0.5 g of 28% by weight ammonia water, 0.75 g of triethanolamine, and 66.75 g of water were mixed using a homogenizer to obtain an emulsion. The dyed cloth was padded with an anionic emulsion treatment agent consisting of 5 g of polymer solids obtained under the above conditions and 300 g of water (pickup 75%), dried and then heat set at 160° C. for 1 minute. Table 1 shows the depth and sharpness of the treated fabrics obtained. Furthermore, the abrasion discoloration resistance of the black-dyed fabric after 200 abrasions was also shown. Comparative Examples 1, 2, Example 2 Example 1 except that the amounts of lithium acetate anhydride and orthophosphoric acid used in Example 1 were changed.
I did the same thing. The results were as shown in Table 1. Examples 3 to 6 The same procedure as in Example 1 was conducted except that the phosphorus compounds listed in Table 1 were added in the amounts listed in Table 1 instead of the orthophosphoric acid used in Example 1. The results were as shown in Table 1. Example 7 4 parts of sodium 3,5-di(carbomotoxy)benzenesulfonate was used instead of 4.8 parts of sodium 3,5-di(β-hydroxyethoxycarbonyl)benzenesulfonate that was added before the start of the polycondensation reaction in Example 1. was added before the start of the transesterification reaction, and 0.06 part (0.177 mol% relative to dimethyl terephthalate) of the 0.64 parts of lithium acetate anhydride added after the end of the transesterification reaction was added to the remaining 0.58 parts before the transesterification reaction. The same procedure as in Example 1 was carried out except that 50% of the transesterification reaction was added after the transesterification reaction was completed. The results were as shown in Table 1. Comparative Example 3 The lithium acetate anhydride used in Example 1 was not used, and the amount of orthophosphoric acid added after the transesterification reaction was changed to 0.04 part (0.079 mol% based on dimethyl terephthalate). The procedure was the same as in Example 1 except for this. The results were as shown in Table 1. Comparative Example 4 The same procedure as in Example 1 was conducted except that 0.85 parts of calcium acetate monohydrate (0.94 mol % based on dimethyl terephthalate) was used in place of the lithium acetate anhydride used in Example 1. The results were as shown in Table 1. 【table】

Claims (1)

[Claims] 1. A synthetic fiber made of a polyester synthesized by the reaction of a dicarboxylic acid, mainly terephthalic acid, or its ester-forming derivative, and at least one glycol or its ester-forming derivative. At any stage until the synthesis of the polyester is completed, (a) isophthalic acid or its ester-forming derivative having an alkali metal sulfonate group in an amount of 0.5 to 10 mol% based on the total acid components; 0.3 to 3 mol% of the following general formula based on the acid component [In the formula, R ¹ and R ² are a hydrogen atom or a monovalent organic group, X is a hydrogen atom, a monovalent organic group, or a metal, m
indicates 0 or 1. ] Phosphorus compound (c) represented by lithium compound without reacting (a), (b) and (c) in advance, and the total number of equivalents of metals (b) and (c) is (b) in an amount of 2.0 to 3.2 times the number of moles of the phosphorus compound, and then completes the synthesis of polyester. After melt-spinning the obtained polyester, 2 weight 1. A method for producing a polyester fiber structure, which comprises dyeing polyester fibers that have eluted % or more, and then coating the fibers with a polymer having a lower refractive index than the fibers.