Polyester resin and method for manufacturing the same

Abstract

To provide a polyester resin which is excellent in yarn quality characteristics such as thermal adhesiveness when used as a binder fiber and characteristics when used as a non-woven fabric.SOLUTION: A polyester resin is composed of a dicarboxylic acid component and a glycol component. In the total acid component, a content of an isophthalic acid is 8-30 mol%, the glycol component contains ethylene glycol, and contains diethylene glycol and triethylene glycol, and in the total glycol component, a content of the triethylene glycol is more than 0.1 mol% and 5 mol% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to polyester resin and a method for producing the same. [Background technology]

[0002] Polyester resins, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), have excellent mechanical and chemical properties and are used in a wide range of fields (for example, fibers for clothing and industrial materials, films or sheets for packaging and magnetic tapes, hollow molded bottles, casings for electrical and electronic components, and other engineering plastic molded products). Furthermore, polyester resin is used in textiles, and hot-melt binder fibers are widely used for bonding fibers that make up pillows, bedding, or nonwoven fabrics. Among polyester binder fibers, those made of copolymerized polyester resin are known. For example, Patent Document 1 describes copolymerized polyester for binder fibers with a melting point of about 130 to 200°C. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 09-12693

[0004] In recent years, there has been a demand for polyester fibers with improved yarn properties, such as heat adhesion, and properties when used in nonwoven fabrics. Furthermore, when polyester resin is chipped, drying is usually performed to suppress hydrolysis during melt spinning; however, there is a desire to shorten this drying time. [Overview of the project] [Problems that the invention aims to solve]

[0005] The objective of the present invention is to obtain a polyester resin that is even better in yarn properties such as heat adhesion and properties when used as a nonwoven fabric, has a short drying time as a raw material resin, and is suitable for binder fibers. [Means for solving the problem]

[0006] As a result of diligent research, the inventors of the present invention discovered that a fiber that solves the above problems can be obtained using a polyester resin that satisfies a specific composition, and thus arrived at the present invention.

[0007] In other words, the gist of the present invention is as follows (1)~(1 1 ) is as stated. (1) A polyester resin comprising a dicarboxylic acid component and a glycol component, wherein the isophthalic acid content in the total acid component is 8 to 30 mol%, and the glycol component includes ethylene glycol, as well as diethylene glycol and triethylene glycol, and the triethylene glycol content in the total glycol component is greater than 0.1 mol% and less than or equal to 5 mol%, The aforementioned polyester resin contains an organic sulfonic acid compound, The content of organic sulfonic acid compounds is 0.5 × 10⁻⁶ per mole of dicarboxylic acid component constituting the polyester resin. -4 ~10×10 -4 Mole It is polyester resin. (2) The polyester resin of (1), wherein the glass transition temperature is 50-65°C. (3) A polyester resin of type (1) or (2) whose melting point when fiberized is 230°C or lower. (4) Any of the polyester resins from (1) to (3) in which the tetraethylene glycol content is 2.0 mol% or less of the total glycol components. (5) Any of the polyester resins (1) to (4) having a diethylene glycol content of 2.5 mol% or more of the total glycol components. (6) A polyester resin of any of (1) to (5) in which the dicarboxylic acid component consists only of isophthalic acid and terephthalic acid. (7) Any of the polyester resins from (1) to (6) having a metal component content of 1 ppm or less. (8) A fiber made of any one of the polyester resins of (1) to (7). (9) A core-sheath composite fiber having a core-sheath composite cross-section in which the polyester resin according to any one of (1) to (7) is disposed in the sheath portion and the polyethylene terephthalate resin is disposed in the core portion. (10) A method for producing a polyester resin according to any one of (1) to (7), the method including a step of adding an organic sulfonic acid compound to a polyester raw material and performing an etherification reaction of a glycol component. 0.5 × 10⁻¹⁰ per mole of the acidic component of polyester 4 ~10×10 4 Mole The method for producing a polyester resin according to (10), including a step of adding an organic sulfonic acid compound to a polyester raw material and performing an etherification reaction of a glycol component. (11) The method for producing a polyester resin according to (10), wherein the organic sulfonic acid compound is at least one selected from 2-sulfobenzoic anhydride, o-sulfobenzoic acid, m-sulfobenzoic acid, p-sulfobenzoic acid, 5-sulfosalicylic acid, benzenesulfonic acid, o-aminobenzenesulfonic acid, m-aminobenzenesulfonic acid, p-aminobenzenesulfonic acid, p-toluenesulfonic acid, methyl p-toluenesulfonate, 5-sulfoisophthalic acid, and salts thereof.

Advantages of the Invention

[0008] According to the polyester resin of the present invention, fibers excellent in yarn quality characteristics such as thermal adhesiveness when formed into fibers and characteristics when formed into non-woven fabrics or the like can be obtained. Further, the polyester resin of the present invention has a short drying time as a raw material resin and is excellent in productivity.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the polyester resin of the present invention will be described in detail. The polyester resin of the present invention is composed of a dicarboxylic acid component and a glycol component.

[0010] <Glycol Component> The glycol component constituting the polyester resin of the present invention contains ethylene glycol, diethylene glycol, and triethylene glycol, and it is necessary that the content of triethylene glycol in the glycol component exceeds 0.1 mol% and is 5.0 mol% or less.

[0011] The polyester resin of the present invention contains ethylene glycol, diethylene glycol, and a predetermined amount of triethylene glycol in the glycol component at the same time. By setting the content of triethylene glycol within a specific range, the melting point when fiberized can be within a preferable range, and the heat adhesiveness can be improved. Therefore, fibers excellent in properties when made into non-woven fabrics or the like can be obtained. Also, the glass transition temperature can be within a preferable range.

[0012] It is necessary that the content of triethylene glycol in the glycol component of the polyester resin of the present invention exceeds 0.1 mol% and is 5.0 mol% or less. It is preferably 0.2 to 4.0 mol%, more preferably 0.3 to 3.5 mol%, and even more preferably 0.5 to 3.0 mol%. When the content of triethylene glycol in the polyester resin is 0.1 mol% or less, the melting point when fiberized cannot be within a preferable range, and the heat adhesiveness is poor, so the properties when made into non-woven fabrics or the like are inferior. On the other hand, when it exceeds 5.0 mol%, the heat resistance and yarn quality characteristics deteriorate, and the glass transition temperature goes out of the preferable range and becomes low.

[0013] The polyester resin of the present invention preferably has a glass transition temperature of 50 to 65°C, more preferably 53 to 63°C, and even more preferably 55 to 63°C. When it is less than 50°C, when drying the polyester resin, it cannot be dried at a high temperature and needs to be dried at a low temperature, so long-time drying is required. On the other hand, for a polyester resin with a glass transition temperature exceeding 65°C, since the melting point also becomes high, it becomes difficult to exhibit heat adhesiveness and may not be suitable for binder applications.

[0014] The polyester resin of the present invention exhibits excellent heat adhesion properties. As an indicator of heat adhesion, it is preferable that the melting point when fiberized is 230°C or lower. In particular, when used for binder fiber applications, it is preferable that the melting point when fiberized is 190°C or lower, and more preferably 180°C or lower. The lower limit of the melting point is preferably around 150°C. The polyester resin of the present invention has good crystallinity, a clear melting point when fiberized, and a melting point within the above range, thereby possessing heat resistance, allowing the processing temperature during heat bonding to be set at a low temperature, and improving heat adhesion properties.

[0015] In the polyester resin of the present invention, when the total amount of all glycol components is 100 mol%, ethylene glycol is 70 mol% or more of the total glycol components, and preferably 80 mol% or more. If the ethylene glycol content is less than 70 mol%, the resulting polyester resin will have inferior crystallinity and heat resistance.

[0016] The polyester resin of the present invention preferably has a diethylene glycol content of 2.5 mol% or more in the glycol component, more preferably 3.0 mol% or more, even more preferably 5 mol% or more, particularly preferably 10 mol% or more, and most preferably 14 mol% or more. When the diethylene glycol content of the polyester resin is within the above range, the melting point when it is fiberized is within a favorable range, the heat adhesion is further improved, and the properties when it is made into a nonwoven fabric or the like are superior. The upper limit of the diethylene glycol content in the glycol component is preferably 25 mol%, and more preferably 23 mol%. If the diethylene glycol content exceeds 25 mol%, the glass transition temperature may be lower.

[0017] Furthermore, in the polyester resin of the present invention, the total content of diethylene glycol and triethylene glycol in the glycol component is preferably greater than 2.6 mol% and less than or equal to 30 mol% from the viewpoint of yarn properties.

[0018] The polyester resin of the present invention preferably contains tetraethylene glycol as a glycol component, and the content of tetraethylene glycol in the glycol component is preferably 2.0 mol% or less, more preferably 0.1 to 1.5 mol%, and even more preferably 0.2 to 1.0 mol%. If the content of tetraethylene glycol in the glycol component of the polyester resin exceeds 2.0 mol%, the yarn properties may be inferior.

[0019] The polyester resin of the present invention preferably has a total content of triethylene glycol and tetraethylene glycol in the glycol component of 7.0 mol% or less, more preferably 0.2 to 7.0 mol%, even more preferably 0.3 to 6.0 mol%, and particularly preferably 0.4 to 5.5 mol%. If the total content of triethylene glycol and tetraethylene glycol in the glycol component of the polyester resin exceeds 7.0 mol%, the yarn properties may be inferior.

[0020] The polyester resin of the present invention contains ethylene glycol, and further contains diethylene glycol and triethylene glycol, preferably containing tetraethylene glycol, but may also contain other glycol components. Specific examples include 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, and 1,10-deca. Examples of aromatic glycols include aliphatic glycols such as methylene glycol and 1,12-dodecanediol, hydroquinone, 4,4'-dihydroxybisphenol, 1,4-bis(β-hydroxyethoxy)benzene, 1,4-bis(β-hydroxyethoxyphenyl)sulfone, bis(p-hydroxyphenyl) ether, bis(p-hydroxyphenyl)sulfone, bis(p-hydroxyphenyl)methane, 1,2-bis(p-hydroxyphenyl)ethane, bisphenol A, bisphenol C, 2,5-naphthalenediol, and glycols obtained by adding ethylene oxide to these glycols.

[0021] <Dicarboxylic acid component> The polyester resin of the present invention has an isophthalic acid content of 8 to 30 mol% when the total amount of all acidic components constituting the polyester is set to 100 mol%.

[0022] As described above, the polyester resin of the present invention contains ethylene glycol as a glycol component, and the content of triethylene glycol in the glycol component is within the above range. Furthermore, the content of isophthalic acid in the dicarboxylic acid component is within a specific range. This allows the melting point when fiberized to be within a desirable range, improving thermal adhesion and thus further enhancing the properties when used as a nonwoven fabric. In addition, the glass transition temperature can be set to a desirable range. The isophthalic acid content is preferably 15 to 30 mol%, more preferably 17 to 27 mol%, and even more preferably 18 to 25 mol% when used as a binder fiber. By setting the isophthalic acid content to 15 to 30 mol%, the melting point of the polyester resin when fiberized can be lowered, making it suitable for binder fiber applications.

[0023] If the isophthalic acid content is less than 8 mol%, the melting point of the polyester resin and the melting point when it is fiberized become high, making it difficult to exhibit thermal adhesion. Also, the glass transition temperature becomes higher than the desirable range. On the other hand, if the copolymerization amount of isophthalic acid exceeds 30 mol%, the resin does not undergo oriented crystallization even when spun and stretched, resulting in an amorphous material, making it difficult to impart heat resistance.

[0024] The acid component constituting the polyester resin of the present invention preferably contains terephthalic acid, from the viewpoint of resin properties and versatility. The terephthalic acid content in the acid component is preferably 65 to 92 mol%, more preferably 70 to 85 mol%, and even more preferably 70 to 80 mol%. If the proportion of terephthalic acid is less than 65 mol%, the resin may not undergo oriented crystallization even after spinning and stretching, resulting in an amorphous state, making it difficult to impart appropriate heat resistance. On the other hand, if the proportion of terephthalic acid exceeds 92 mol%, the melting point of the resin becomes high, making it difficult to exhibit thermal adhesion.

[0025] The polyester resin of the present invention may contain acid components other than terephthalic acid and isophthalic acid. Examples of such acid components include saturated aliphatic dicarboxylic acids exemplified by oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, hexadecanedicarboxylic acid, 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norbornanedicarboxylic acid, dimer acid, etc., or their ester-forming derivatives, unsaturated aliphatic dicarboxylic acids exemplified by fumaric acid, maleic acid, itaconic acid, etc. Examples include aromatic dicarboxylic acids such as rubonic acid or its ester-forming derivatives, orthophthalic acid, 5-(alkali metal) sulfoisophthalic acid, diphenic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, 4,4′-biphenylsulfondicarboxylic acid, 4,4′-biphenyletherdicarboxylic acid, 1,2-bis(phenoxy)ethane-p,p′-dicarboxylic acid, pamoic acid, anthracenedicarboxylic acid, etc., or their ester-forming derivatives, and these may be used in combination. In particular, from the viewpoint of yarn properties, the acid component constituting the polyester resin of the present invention is preferably composed solely of aromatic dicarboxylic acid components, and more preferably composed solely of terephthalic acid and isophthalic acid. When composed solely of terephthalic acid and isophthalic acid, the composition ratio (molar ratio) of terephthalic acid / isophthalic acid is preferably 92 / 8 to 70 / 30.

[0026] To adjust the respective content of diethylene glycol, triethylene glycol, and tetraethylene glycol, for example, an organic sulfonic acid compound may be used as a polymerization catalyst in the polyester resin manufacturing method described later, the amount of organic sulfonic acid compound added may be set to a preferred range, the molar ratio of glycol component (G) to acid component (A) (G / A) may be set to a preferred range, or a step for etherification reaction may be included and its temperature or time adjusted.

[0027] The polyester resin of the present invention preferably has an intrinsic viscosity of 0.45 dl / g or higher, more preferably 0.5 dl / g or higher, and even more preferably 0.6 to 0.8 dl / g. If the intrinsic viscosity is less than 0.45 dl / g, sufficient yarn properties may not be obtained when the resin is made into fibers. In this invention, the intrinsic viscosity is the value measured using an equimassive mixture of phenol and tetrachloroethane as the solvent.

[0028] The polyester resin of the present invention may contain any polymer, antistatic agent, defoaming agent, dyeability improver, dye, pigment, matting agent, fluorescent whitening agent, stabilizer, antioxidant, colorant, flame retardant, defibration enhancer, or other additives, as long as they do not impair the effects of the present invention. Examples of antioxidants include aromatic amine-based and phenol-based antioxidants. Examples of stabilizers include phosphorus-based (such as phosphoric acid or phosphate ester-based), sulfur-based, and amine-based stabilizers. Examples of defibration enhancers include titanium dioxide.

[0029] The polyester resin of the present invention may contain organic, inorganic, or organometallic toners, or fluorescent whitening agents, etc., to the extent that they do not impair the effects of the present invention. This can further suppress discoloration such as yellowing of the polyester resin. Alternatively, other resins such as polyethylene, or inorganic nucleating agents such as talc may be added to improve crystallinity.

[0030] The polyester resin of the present invention may have a cobalt compound added for purposes such as improving color tone, as long as it does not impair the effects of the present invention. The cobalt compound is not particularly limited, but examples include cobalt acetate, cobalt nitrate, cobalt chloride, cobalt acetylacetonate, cobalt naphthenate, and their hydrates. Among these, cobalt acetate tetrahydrate is particularly preferred. The amount of cobalt compound added is preferably 10 ppm or less, more preferably 5 ppm or less, and even more preferably 3 ppm or less, as cobalt atoms relative to the polyester resin.

[0031] The polyester resin of the present invention may be mixed with waste resin generated during the manufacturing process or recycled polyester resin recovered from the market (for example, PET bottles, etc.).

[0032] <Method for manufacturing polyester resin> The present invention relates to a method for producing polyester resin, which involves adding an organic sulfonic acid compound to a polyester resin raw material and then carrying out a polycondensation reaction.

[0033] Furthermore, in this invention, an etherification reaction may be carried out under specific conditions before or simultaneously with the polycondensation reaction. This makes it easier to adjust the content of diethylene glycol, triethylene glycol, and tetraethyl glycol to a specific range. As a result, a polyester resin with even better yarn properties such as heat adhesion and properties when used as a nonwoven fabric can be obtained.

[0034] Examples of raw materials for polyester resins include glycol components containing ethylene glycol as the main component, dicarboxylic acid components, and esterified products as lower-order condensates consisting of glycol components and dicarboxylic acid components.

[0035] As a method for obtaining the above esterified product, for example, when producing the esterified product using terephthalic acid as the acid component, terephthalic acid, ethylene glycol, and other copolymer components as needed are reacted directly, water is removed by distillation, and the product is esterified to obtain the esterified product as a raw material for polyester resin. Alternatively, dimethyl terephthalate, ethylene glycol, and other copolymer components as needed are reacted, methyl alcohol is removed by distillation, and the product is transesterified to obtain the esterified product.

[0036] A slurry containing preferably 1.02 to 2.5 moles, more preferably 1.03 to 1.8 moles, of ethylene glycol per mole of dicarboxylic acid or its ester derivative is prepared, and this slurry is continuously supplied to an esterification reactor to obtain an esterified product.

[0037] Esterification reactions are carried out under reflux conditions of ethylene glycol, while removing the water or alcohol produced by the reaction from the system using a rectification column. Esterification reactions can also be carried out using a multi-stage apparatus consisting of multiple esterification reactors connected in series.

[0038] The temperature of the first esterification reaction is preferably 150-270°C, and more preferably 245-265°C. The pressure is 0.2-3 kg / cm². 2 It is preferably G, and 0.5-2 kg / cm³ 2 It is more preferable that it be G.

[0039] The temperature of the final esterification reaction is preferably 150-290°C, and more preferably 255-275°C. The pressure is 0-1.5 kg / cm². 2 It is preferably G, and 0-1.3 kg / cm³ 2 It is more preferable that it be G.

[0040] When the reaction is carried out in three or more steps, the reaction conditions for the intermediate esterification reaction are preferably between those of the first and final stages. In multi-stage esterification reactions, the reaction rate is preferably increased smoothly at each stage. Ultimately, the esterification reaction rate is preferably 90% or higher, and more preferably 93% or higher. Esterified products can be obtained through these esterification reactions, and their preferred molecular weight is approximately 500 to 5000.

[0041] When terephthalic acid is used in an esterification reaction, the reaction is accelerated by the catalytic action of terephthalic acid as an acid.

[0042] To the esterified product obtained as described above, a reaction solution (esterified product) of isophthalic acid and ethylene glycol, or a dispersion of isophthalic acid and ethylene glycol, is added, and an organic sulfonic acid compound is added as a polymerization catalyst to proceed with the polycondensation reaction to obtain the polyester resin of the present invention.

[0043] (catalyst) In the present invention, by using an organic sulfonic acid compound as a polymerization catalyst, the content of diethylene glycol, triethylene glycol, and tetraethylene glycol in the resulting polyester resin can be set to a specific range. Examples of organic sulfonic acid compounds include benzenesulfonic acid, m- or p-benzenedisulfonic acid, 1,3,5-benzenetrisulfonic acid, o-, m- or p-sulfobenzoic acid, benzaldehyde-o-sulfonic acid, acetophenone-p-sulfonic acid, acetophenone-3,5-disulfonic acid, o-, m- or p-aminobenzenesulfonic acid, sulfanilic acid, 2-aminotoluene-3-sulfonic acid, phenylhydroxylamine-3-sulfonic acid, and phenylhydrazine-3-sulfonic acid. Nitrobenzene-3-sulfonic acid, 1-nitronaphthalene-3-sulfonic acid, thiophenol-4-sulfonic acid, anisole-o-sulfonic acid, 1,5-naphthalenedisulfonic acid, o-, m- or p-chlorobenzenesulfonic acid, o-, m- or p-bromobenzenesulfonic acid, o-, m- or p-nitrobenzenesulfonic acid, nitrobenzene-2,4-disulfonic acid, nitrobenzene-3,5-disulfonic acid, nitrobenzene-2,5-disulfonic acid, 2-nitrotoluene-5-sulfonic acid, 2-nitrotoluene-4 -Sulfonic acid, 2-nitrotoluene-6-sulfonic acid, 3-nitrotoluene-5-sulfonic acid, 4-nitrotoluene-2-sulfonic acid, 3-nitro-o-xylene-4-sulfonic acid, 5-nitro-o-xylene-4-sulfonic acid, 2-nitro-m-xylene-4-sulfonic acid, 5-nitro-m-xylene-4-sulfonic acid, 3-nitro-p-xylene-2-sulfonic acid, 5-nitro-p-xylene-2-sulfonic acid, 6-nitro-p-xylene-2-sulfonic acid, 2,4-dinitrobenzenesulfonic acid Fluorobenzenesulfonic acid, 3,5-dinitrobenzenesulfonic acid, o-, m- or p-fluorobenzenesulfonic acid, 4-chloro-3-methylbenzenesulfonic acid, 2-chloro-4-sulfobenzoic acid, 5-sulfosalicylic acid, 4-sulfophthalic acid, 2-sulfobenzoic anhydride, 3,4-dimethyl-2-sulfobenzoic anhydride, 4-methyl-2-sulfobenzoic anhydride, 5-methoxy-2-sulfobenzoic anhydride, 1-sulfonaphthoic acid anhydride, 8-sulfonaphthoic acid anhydride, 3,6-disulfophthalic acid anhydride, 4,Examples include 6-disulfoisophthalic anhydride, 2,5-disulfoterephthalic anhydride, methanesulfonic acid, ethanesulfonic acid, methionic acid, cyclopentanesulfonic acid, 1,1-ethanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,2-ethanedisulfonic anhydride, 3-propanedisulfonic acid, β-sulfopropionic acid, isethionic acid, nithionic acid, nithionic anhydride, 3-oxy-1-propanesulfonic acid, 2-chloroethanesulfonic acid, phenylmethanesulfonic acid, β-phenylethanesulfonic acid, α-phenylethanesulfonic acid, ammonium chlorosulfonate, methyl benzenesulfonate, ethyl p-toluenesulfonate, ethyl methanesulfonate, dimethyl 5-sulfosalicylate, trimethyl 4-sulfophthalate, and salts thereof. In particular, from the perspective of versatility, examples include 2-sulfobenzoic anhydride, o-sulfobenzoic acid, m-sulfobenzoic acid, p-sulfobenzoic acid, 5-sulfosalicylic acid, benzenesulfonic acid, o-aminobenzenesulfonic acid, m-aminobenzenesulfonic acid, p-aminobenzenesulfonic acid, p-toluenesulfonic acid, p-methyl p-toluenesulfonate, 5-sulfoizophthalic acid, and their salts.

[0044] When a metal-based catalyst is not used as the polymerization catalyst, the amount of metal components derived from the metal-based catalyst in the resulting polyester resin of the present invention can be reduced. A high content of metal components not only increases the environmental burden, but can also result in poor transparency and the generation of foreign matter during melt processing.

[0045] The content of metal components derived from the metal catalyst is preferably 1 ppm or less, more preferably 0.5 ppm or less, and even more preferably 0 ppm. Examples of metal catalysts include compounds such as antimony, germanium, tin, titanium, zinc, aluminum, iron, magnesium, potassium, calcium, sodium, manganese, nickel, and cobalt.

[0046] Organic sulfonic acid compounds can be added, for example, in solid form, slurry form, or as a solution dissolved in water, glycol, etc.

[0047] Although the addition amount of the organic sulfonic acid compound depends on its type, it is preferably 0.5×10 -4 ~10×10 -4 mol, more preferably 2.0×10 -4 ~6.0×10 -4 mol, per 1 mol of the acid component constituting the polyester resin. If the addition amount is less than the above range, it may not be possible to obtain a polyester resin with a high degree of polymerization in a short time, or it may not be possible to simultaneously contain diethylene glycol and triethylene glycol or to set the content of triethylene glycol within a specific range. On the other hand, if it exceeds the above range, it may not be possible to simultaneously contain diethylene glycol and triethylene glycol or to set the content of triethylene glycol within a specific range, or it may cause coloring of the polyester resin.

[0048] By setting the addition amount of the organic sulfonic acid compound within the above range, the sulfur component content of the obtained polyester resin can be made 5 to 500 ppm, preferably 6 to 250 ppm, more preferably 8 to 100 ppm, and even more preferably 9 to 50 ppm. If the sulfur component content is less than 5 ppm, the yarn quality characteristics may be inferior. On the other hand, if it exceeds 500 ppm, the molecular weight may not increase sufficiently, and the yarn quality characteristics may be inferior. Furthermore, hydrolysis may proceed easily, and a significant decrease in the strength of the fiber may occur, and it may not be practical in some cases.

[0049] (Polycondensation reaction) Examples of the polycondensation reaction include, for example, a melt polycondensation reaction. The polycondensation reaction may be carried out in one step or in multiple steps.

[0050] The polycondensation reaction conditions are not particularly limited, but the temperature of the first-stage polycondensation reaction is preferably 250 to 290°C, more preferably 260 to 280°C. The pressure is preferably 500 to 20 hPa, more preferably 200 to 30 hPa.

[0051] In the case of a multi-stage reaction, the temperature of the final polycondensation reaction is preferably 265 to 300°C, and more preferably 275 to 295°C. The pressure is preferably 10 to 0.1 hPa, and more preferably 5 to 0.5 hPa. When the reaction is carried out in three or more stages, the reaction conditions of the intermediate stages are preferably those between the reaction conditions of the first and final stages. It is preferable to smoothly increase the degree of polymerization in each of these stages.

[0052] (Etherification reaction) The etherification reaction may be carried out simultaneously with the esterification or polycondensation reaction. Alternatively, the etherification reaction may be carried out after the addition of an organic sulfonic acid compound. By adding an organic sulfonic acid compound as a polymerization catalyst and allowing the etherification reaction to proceed through dehydration, diethylene glycol and triethylene glycol are more readily produced.

[0053] The temperature for the etherification reaction is preferably 200°C or higher, more preferably 220-300°C, even more preferably 230-280°C, and most preferably 240-260°C. Below 200°C, the reaction does not proceed sufficiently, and the content of diethylene glycol, triethylene glycol, and tetraethylene glycol may not be within the specified range, which may result in insufficient yarn properties. Above 300°C, decomposition of the esterified product may proceed during the reaction, which may reduce the yarn properties.

[0054] By adjusting the etherification reaction time, it becomes easier to control the content of diethylene glycol, triethylene glycol, and tetraethylene glycol within a specific range. While there are no particular limitations on the etherification reaction time, it is preferably 5 to 120 minutes, and more preferably 10 to 60 minutes. If the reaction time exceeds 120 minutes, the etherification reaction may proceed too far, resulting in the content of diethylene glycol, triethylene glycol, and tetraethylene glycol not being within the specific range, or the decomposition of the esterified product may proceed during the reaction, which can lead to a decrease in yarn properties.

[0055] The etherification reaction is preferably carried out under atmospheric pressure, pressurized pressure, or reduced pressure, with the pressure being 0 to 3.0 kg / cm². 2 It is preferable that the pressure be G or 1000 to 0.1 hPa.

[0056] The amount of triethylene glycol and tetraethylene glycol produced in the polyester resin can be adjusted by adjusting the molar ratio (G / A) of the glycol component (G) to the acid component (A) in the raw materials subjected to the etherification reaction. A G / A ratio of 1.05 to 3.00 is preferred, and a ratio of 1.10 to 2.00 is more preferred. To adjust the G / A ratio, additional glycol components such as ethylene glycol may be added to the polyester raw material as needed. If the G / A ratio is less than 1.05, the amount of triethylene glycol and tetraethylene glycol produced tends to be low, while if it exceeds 3.00, the amount of triethylene glycol and tetraethylene glycol produced tends to be high.

[0057] The polyester resin of the present invention can be used to produce the fibers of the present invention. The fibers of the present invention can be manufactured by conventional melt spinning methods, such as a two-step method of spinning and drawing, or a one-step method. Furthermore, the fibers of the present invention can be crimped, heat-set, or cut to a desired length to produce staple fibers or short-cut fibers. The fibers of the present invention can also be obtained by the spunbond method.

[0058] The cross-sectional shape of the fiber is not limited to a circular shape; it may also be an irregular cross-section or a hollow cross-section, and it may be made into a dope-dyed fiber by impregnating it with a pigment. Furthermore, the fiber of the present invention may be compounded with other fibers, such as blended fibers or spun fibers, to form a yarn, or processed into a yarn using known yarn processing methods.

[0059] The fibers of the present invention may be single-phase fibers composed solely of the polyester resin of the present invention, or they may be fibers in which the polyester resin of the present invention is used in part. When used in part, they may be composite fibers combined with other resins. Examples of composite fibers combined with other resins include core-sheath composite fibers in which a resin with a higher melting point than the polyester resin of the present invention is placed in the core and the polyester resin of the present invention is placed in the sheath. When the fibers of the present invention are used as binder fibers, single-phase fibers using only the polyester resin of the present invention become fully melted binder fibers, and core-sheath composite fibers in which the polyester resin of the present invention is used only in the sheath become binder fibers in which the sheath is the binder component. Furthermore, the polyester resin of the present invention may be used in only one of the two components bonded side by side in a composite fiber. The other component in such a composite fiber may be appropriately selected according to the required fiber properties and applications. For example, a core-sheath composite fiber in which polyethylene terephthalate is placed in the core and the polyester resin of the present invention is placed in the sheath is preferred because it has excellent strength, adhesion and heat resistance. The core-to-sheath ratio (mass ratio) can be selected as appropriate, but considering the mechanical strength of the core portion that forms the skeleton without melting due to the heat bonding process, a core / sheath ratio of 4 / 6 to 8 / 2 is preferable.

[0060] The fiber form of the present invention includes long fibers (continuous fibers) and short fibers. In the case of long fibers, they may be monofilaments or multifilaments. In the case of short fibers, they may be staple fibers or short-cut fibers, and the appropriate choice can be made depending on the application.

[0061] This section describes a method for producing long fibers (continuous fibers) using the FDY method. The polyester resin of the present invention and other resins to be compounded as desired are supplied as pellets to a melt extrusion device, melted, and extruded from a spinneret. The extruded yarn bundles are cooled and solidified, and undrawn yarn is obtained by taking them up with rollers at a speed of 500 to 1500 m / min. Then, the undrawn yarn is stretched between rollers at a stretch ratio of 2 to 4 times and wound up to obtain long fibers.

[0062] Furthermore, a method for producing long fibers (continuous fibers) using the POY method will be described. In this case as well, the polyester resin of the present invention and other resins to be compounded as desired are supplied as pellets to a melt extrusion device, melted, and extruded from a spinneret. The extruded yarn bundles are cooled and solidified, and taken up by rollers at a speed of 2000 to 4000 m / min to obtain highly oriented undrawn yarn. Then, the undrawn yarn is stretched between rollers at a stretching ratio of 1.1 to 2 times and wound up to obtain the long fibers of the present invention.

[0063] Furthermore, the fibers of the present invention can also be obtained by the spunbond method. In this case as well, the polyester resin of the present invention and other resins to be compounded as desired are supplied as pellets to a melt extrusion device, melted, and extruded from a spinneret. The extruded yarn is cooled using a known cooling device, then pulled and thinned using a suction device, and deposited on a net to obtain a web. The speed of pulling and thinning (extraction speed) should be set to about 2500m to 5000m / min. The single fiber fineness of the continuous fibers produced by the spunbond method can be any fineness of about 0.5 to 15 decitex. The web formed by the spunbond method can be made into a nonwoven fabric by general nonwoven fabrication methods such as heat treatment by passing it through a hot embossing roll or entangling the fibers by needle punching. Furthermore, when heat treatment is performed by passing the material through a heat embossing roll or the like, it is preferable to arrange polyethylene terephthalate in the core and the polyester resin of the present invention in the sheath, and in the heat treatment, melt only the polyester resin in the sheath to bond the fibers together and obtain a nonwoven fabric. The resulting spunbond nonwoven fabric will have excellent heat resistance and nonwoven strength.

[0064] When the fiber form is short fiber, the staple fiber should have a fiber length of about 20 to 100 mm, and mechanical crimping should be applied using a crimper or the like, taking into consideration carding properties. Short-cut fibers are mainly used as materials for papermaking sheets, and since dispersibility in water is required, they do not have crimping due to mechanical crimping (no crimp), and the fiber length is less than about 20 mm, preferably about 2 to 15 mm.

[0065] When manufacturing short fibers, the draw ratio is not particularly limited, and either drawn or undrawn fibers may be used, and can be appropriately selected according to the application and target characteristic values. In the manufacturing of fibers, the polyester resin of the present invention can be used, and the fibers of the present invention can be obtained by appropriately selecting the spinning speed, draw ratio, and heat treatment conditions. For example, the polyester resin of the present invention is supplied as pellets to a melt extruder, melted, and extruded from a spinneret. The extruded yarn bundle is cooled and solidified, melt-spun at a take-up speed of 900 to 1200 m / min, bundled into a yarn bundle, then stretched at a stretching temperature of 40 to 80°C and a draw ratio of 2 to 5 times, and then cut to the desired length to obtain short fibers. Similarly, when obtaining composite short fibers, another resin and the polyester resin of the present invention can be supplied as pellets using a composite spinning apparatus, melted, spun, stretched, and heat-treated, and then cut to the desired length. When the short fibers of the present invention are used for dry-laid nonwoven fabrics or spun yarns, crimp can be applied after heat treatment using a stuffing box or heating gear. When used for wet-laid nonwoven fabrics, the fibers can be cut to the desired length without applying crimp.

[0066] Examples of characteristic values ​​for the fibers of the present invention include those having a single filament fineness of 0.5 to 25.0 decitex, a strength of 0.1 to 6.0 cN / decitex, and an elongation of 20 to 600%.

[0067] When the short fibers of the present invention are used as binder fibers to form a nonwoven fabric, it may be a dry-laid nonwoven fabric or a wet-laid nonwoven fabric. The basis weight of the nonwoven fabric is not particularly limited. As a method for forming a nonwoven fabric, one method is to use the polyester resin (polyester resin of the present invention) that constitutes the fibers of the present invention as a heat-bonding component, and to form a nonwoven fabric by heat bonding the fibers together. Before heat bonding, the constituent fibers may be three-dimensionally entangled by needle punching or water-flow entanglement.

[0068] The nonwoven fabric may contain fibers other than those of the present invention. Examples of other fibers include fibers made of polyester resin with a higher melting point than the polyester resin of the present invention, and polyethylene terephthalate fibers can be preferably used.

[0069] An example of a method for manufacturing nonwoven fabric is given. When mixing the short fibers of the present invention with other fibers, the other fibers are prepared and weighed in any proportion. The proportion of the fibers of the present invention when mixing can be appropriately selected according to the required characteristics of the nonwoven fabric, and is preferably about 10 to 90% by mass.

[0070] Subsequently, when manufacturing a dry nonwoven fabric, the weighed constituent fibers are fed into a carding machine and defibrated to produce a dry web. The obtained web is then passed through a heat treatment device such as a continuous heat treatment machine that applies hot air, and a heat bonding treatment is performed at a temperature at which the polyester resin of the present invention melts or softens, thereby obtaining a dry nonwoven fabric in which the constituent fibers are integrated by heat bonding.

[0071] In the production of wet-laid nonwoven fabric, the weighed raw materials are stirred and defibrated using a pulp dissociator, and then a wet web is produced using a paper machine. The obtained web is passed through a heat treatment device such as a continuous heat treatment machine that applies hot air, and a heat bonding treatment is performed at a temperature at which the polyester resin of the present invention melts or softens, thereby obtaining a wet-laid nonwoven fabric in which the constituent fibers are integrated by heat bonding. [Examples]

[0072] The present invention will be described in detail below based on examples, but the present invention is not limited thereto. Measurement and evaluation were performed by the following methods.

[0073] (1) Intrinsic viscosity The measurement was performed using an equimassive mixture of phenol and tetrachloroethane as the solvent.

[0074] (2) Composition of dicarboxylic acid component and glycol component 20 mg of the sample was dissolved in 0.6 mL of a mixed solvent of deuterated chloroform / deuterated trifluoroacetic acid = 1 1 / 1 (volume ratio), and the results were obtained using a JEOL Nuclear Magnetic Resonance Spectrometer (JNM-ECZ). 1 ¹H-NMR was measured, and the molar ratios of the dicaponic acid component, the total amount of triethylene glycol component and tetraethylene glycol component, and the other glycol components were calculated from the integrated proton peak intensities of each component in the resulting chart.

[0075] (3) Determination of triethylene glycol and tetraethylene glycol components The polyester resin was hydrolyzed in a 0.75 N potassium hydroxide / methanol solution, and then neutralized with terephthalic acid. Next, the filtrate obtained by filtration was measured by gas chromatography, and the molar ratio of triethylene glycol to tetraethylene glycol was calculated using a pre-prepared calibration curve. These molar ratios were then compared with the aforementioned method. 1 The content of triethylene glycol and tetraethylene glycol in the total glycol components was calculated from the results of 1H-NMR measurements (the molar ratio of the total amount of triethylene glycol and tetraethylene glycol to that of each other glycol component).

[0076] (4) Melting point (Tm), glass transition temperature (Tg) Measurements were taken using a PerkinElmer Diamond DSC differential scanning calorimeter in a nitrogen atmosphere, within a temperature range of 25–280°C, and at a heating rate of 20°C / min.

[0077] (5) Content of sulfur and metal components Polyester resin was melt-molded at 300°C to form a disc-shaped molded plate with a diameter of 3 cm and a thickness of 1 cm. Quantitative analysis was performed using the calibration curve method with a Rigaku ZSX Primus X-ray fluorescence analyzer.

[0078] (6) Melting point when fiberized A polyethylene terephthalate with an intrinsic viscosity of 0.70 was used as the core, and the resulting resin as the sheath. A die with 1014 holes and a hole diameter of 0.35 mm was used to perform melt spinning with a discharge rate of 566 g / min, a core-sheath mass ratio of 50 / 50, a spinning temperature of 270 °C, and a spinning speed of 1120 m / min. The resulting undrawn yarn was then gathered to form an 80 ktex tow and drawn at a drawing temperature of 60 °C and a draw ratio of 3.0. After mechanical crimping using a push-type crimper, the fibers were cut to a length of 51 mm to obtain core-sheath type composite short fibers with a fineness of 1.7 dtex. The obtained short fibers were measured using a PerkinElmer Diamond DSC differential scanning calorimeter in a nitrogen atmosphere at a temperature range of 25–280°C and a heating rate of 20°C / min.

[0079] (7) Fineness (dtex) The measurement was performed according to the method of JIS-L-1015-8-5-1-1A.

[0080] (8) Operability (adhesion) of short fiber manufacturing A "○" indicates that there was no single-fiber adhesion during the stretching process, while "×" indicates that there was no adhesion otherwise.

[0081] (9) Strong non-woven fabric The obtained nonwoven fabric was cut into 150 mm strips in the MD direction and 50 mm strips in the CD direction. The MD strength was measured using an Autograph (Shimadzu AG-50KNI) under conditions of a tensile speed of 100 mm / min and a chuck distance of 100 mm. The sample size was n=5. The tensile strength of the obtained nonwoven fabric was evaluated in the following two stages. ○: Tensile strength of 1000 cN or more ×: Tensile strength less than 1000 cN

[0082] Example 1 [Polyester resin] A slurry of terephthalic acid (TPA) and ethylene glycol (EG) (TPA / EG molar ratio = 1 / 1.6) was supplied to an esterification reactor and reacted under conditions of 250°C and 50 hPa to obtain esterified product A (number average degree of polymerization: 5) with an esterification reaction rate of 95%. In another esterification reactor, a slurry consisting of isophthalic acid (IPA) and ethylene glycol (IPA / EG molar ratio = 1 / 3.1) was charged and the esterification reaction was carried out at 200°C for 3 hours to obtain esterified product B, which is a reaction solution of isophthalic acid and ethylene glycol. 100 parts by mass of esterified compound A was charged into the polymerization reactor, followed by 30 parts by mass of esterified compound B. 2.0 × 10⁻⁶ of 5-sulfosalicylic acid dihydrate (SS) was used as the polymerization catalyst. -4 The mol / mol ratio of the acid component was added, and the etherification reaction was carried out at atmospheric pressure at 260°C for 10 minutes. Next, while maintaining the temperature at 260°C, the reactor was reduced in pressure for 60 minutes, and then a melt polycondensation reaction was carried out at a final pressure of 0.9 hPa for 3 hours to obtain a polyester resin.

[0083] Examples 2-4, 10-14, Comparative Examples 1, 2, 4, 5 A polyester resin was obtained by performing the same procedure as in Example 1, except that the amounts of esterified compounds A and B added and the etherification reaction conditions were changed as shown in Table 1.

[0084] Examples 5-9 A polyester resin was obtained by performing the same procedure as in Example 1, except that the type of organic sulfonic acid compound used as the polymerization catalyst was changed to 2-sulfobenzoic anhydride (OSB), o,m,p-aminobenzenesulfonic acid (o,m,p-ABS), and p-methyl toluenesulfonate (p-TSMe), respectively.

[0085] Examples 15 and 16 A polyester resin was obtained by performing the same procedure as in Example 1, except that a 1:1 (mass ratio) mixture of adipic acid and ethylene glycol (AD solution) was added to the raw materials in the amounts shown in Table 2.

[0086] Comparative Example 3 A polyester resin was obtained by performing the same procedure as in Example 1, except that the etherification reaction was not carried out.

[0087] Comparative Example 6 A polyester resin was obtained by performing the same procedure as in Example 1, except that antimony trioxide (Sb) was used instead of 5-sulfosalicylic acid dihydrate (SS) and the etherification reaction was not carried out.

[0088] The manufacturing conditions for the polyester resins obtained in the examples and comparative examples are shown in Tables 1-3, and their characteristic values ​​are shown in Tables 4-6.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

[0092] [Table 4]

[0093] [Table 5]

[0094] [Table 6]

[0095] As shown in Tables 4-6, the polyester resins obtained in Examples 1-16 contained diethylene glycol and triethylene glycol as glycol components, and the isophthalic acid (IPA) content and triethylene glycol content were within the ranges specified in the present invention. The glass transition temperature and melting point when fiberized were within a favorable range, resulting in excellent thermal adhesion.

[0096] On the other hand, the polyester resin obtained in Comparative Example 1 had a low isophthalic acid (IPA) content, which was outside the scope of the present invention. This polyester resin had a high melting point and glass transition temperature when it was fiberized.

[0097] The polyester resin obtained in Comparative Example 2 had an excessively high isophthalic acid (IPA) content, exceeding the scope of the present invention. This polyester resin did not undergo oriented crystallization even after spinning and stretching, remaining amorphous, and its melting point could not be measured when it was formed into fibers.

[0098] In Comparative Example 3, a polyester resin was obtained without performing an etherification reaction. This polyester resin had a triethylene glycol content that fell outside the range specified in the present invention, resulting in a higher melting point and glass transition temperature when it was fiberized.

[0099] In Comparative Example 4, a polyester resin was obtained by performing the etherification reaction at a lower temperature. This polyester resin had a triethylene glycol content that fell outside the range specified in the present invention, resulting in a higher melting point and glass transition temperature when it was fiberized.

[0100] In Comparative Example 5, a polyester resin was obtained by extending the etherification reaction time. This polyester resin had a triethylene glycol content that exceeded the scope of the present invention. The glass transition temperature was lower.

[0101] In Comparative Example 6, antimony trioxide (Sb) was used as the polymerization catalyst instead of an organic sulfonic acid compound to obtain a polyester resin. This polyester resin had a triethylene glycol content that fell outside the scope of the present invention, resulting in a higher melting point and glass transition temperature when it was fiberized.

[0102] [Manufacturing of short fibers and dry-laid nonwoven fabrics] Example 2-1 Using a die with 1014 holes and a hole diameter of 0.35 mm, melt spinning was performed with polyethylene terephthalate with an intrinsic viscosity of 0.70 as the core and the polyester resin obtained in Example 2 as the sheath, at a spinning temperature of 270°C and a spinning speed of 1120 m / min, with a discharge rate of 566 g / min, a core-sheath mass ratio of 50 / 50. Next, the obtained undrawn yarn was gathered to form a 50 ktex tow and drawn at a drawing temperature of 50°C and a drawing ratio of 3.0 times. After mechanical crimping was applied using a push-type crimper, the fibers were cut to a length of 51 mm to obtain a core-sheath type composite fiber with a fineness of 1.7 dtex. Next, polyethylene terephthalate fiber (manufactured by Unitika Corporation) <121> 1.7T51mm) is blended at a ratio of 70% by mass with the core-sheath type composite fiber obtained above as a binder fiber at a ratio of 30% by mass, and the basis weight of the nonwoven fabric after heat treatment is 50g / m². 2 To achieve this, fibers were fed into a carding machine (SC-500DI3HC, manufactured by Yamato Kiko) to create a web. Subsequently, a continuous heat treatment machine (NFD-500E2, manufactured by Tsujii Dyeing Machinery Co., Ltd.) was used to process the web at an airflow of 57 m³. 3 Dry nonwoven fabric was prepared by heat treatment under the conditions of / min at 180°C for 1 minute.

[0103] Comparative Example 3-1 In Example 2-1, a core-sheath type composite fiber was obtained and a dry nonwoven fabric was prepared in the same manner as in Example 2-1, except that the polyester resin obtained in Comparative Example 3 was used.

[0104] Comparative Examples 4-1, 5-1 In Example 2-1, core-sheath type composite fibers were obtained in the same manner as in Example 2-1, except that the polyester resin obtained in Comparative Examples 4 and 5 was used, and a dry-laid nonwoven fabric was prepared.

[0105] Comparative Example 6-1 In Example 2-1, a core-sheath composite fiber was obtained and a dry nonwoven fabric was prepared in the same manner as in Example 2-1, except that the polyester resin obtained in Comparative Example 6 was used.

[0106] [Table 7] As is clear from Table 7, in Example 2-1, the resin from Example 2 was placed in the sheath portion, and core-sheath type composite short fibers were obtained with good operability. Furthermore, the dry-laid nonwoven fabric obtained using the obtained core-sheath type composite short fibers as binder fibers had high strength. On the other hand, the heat-adhesive core-sheath composite fibers (Comparative Example 3-1, Comparative Example 4-1, Comparative Example 6-1) using the resins of Comparative Examples 3, 4, and 6 for the sheath portion did not exhibit single-fiber adhesion during stretching. However, although the polyester resins of Comparative Examples 3, 4, and 6 had a similar isophthalic acid content (approximately 20 mol%) as the polyester resin of Example 2, they had lower triethylene glycol and diethylene glycol content. As a result, their fiber melting point was approximately 30°C higher than that of the polyester resin of Example 2 (172.3°C), and they could not be heat-bonded at 180°C, resulting in dry-laid nonwoven fabrics with low strength. In the heat-adhesive core-sheath composite fiber (Comparative Example 5-1) using the resin of Comparative Example 5 in the sheath portion, the low glass transition temperature of the polyester resin of Comparative Example 5 resulted in single-fiber adhesion during stretching, leading to poor operability.

Claims

1. A polyester resin comprising a dicarboxylic acid component and a glycol component, The isophthalic acid content in the total acid components is 8 to 30 mol%, The glycol component includes ethylene glycol, as well as diethylene glycol and triethylene glycol, and the content of triethylene glycol in the total glycol component is greater than 0.1 mol% and less than or equal to 5 mol%. The aforementioned polyester resin contains an organic sulfonic acid compound, A polyester resin in which the content of organic sulfonic acid compounds is 0.5 × 10⁻⁴ to 10 × 10⁻⁴ moles per mole of the dicarboxylic acid component constituting the polyester resin.

2. The polyester resin according to claim 1, wherein the glass transition temperature is 50 to 65°C.

3. The polyester resin according to claim 1 or 2, wherein the melting point when it is fiberized is 230°C or lower.

4. A polyester resin according to any one of claims 1 to 3, wherein the tetraethylene glycol content is 2.0 mol% or less of the total glycol components.

5. The polyester resin according to any one of claims 1 to 4, wherein the diethylene glycol content is 2.5 mol% or more of the total glycol components.

6. The polyester resin according to any one of claims 1 to 5, wherein the dicarboxylic acid component consists only of isophthalic acid and terephthalic acid.

7. A polyester resin according to any one of claims 1 to 6, wherein the content of metal components is 1 ppm or less.

8. A fiber made of the polyester resin described in any one of claims 1 to 7.

9. A core-sheath composite fiber having a core-sheath type composite cross-section in which the polyester resin according to any one of claims 1 to 7 is arranged in the sheath portion and the polyethylene terephthalate resin is arranged in the core portion.

10. A method for producing a polyester resin according to any one of claims 1 to 7, comprising the step of adding an organic sulfonic acid compound to a polyester raw material in an amount of 0.5 × 10⁴ to 10 × 10⁴ moles per mole of the acid component of the polyester, and carrying out an etherification reaction of the glycol component.

11. A method for producing a polyester resin according to claim 10, wherein the organic sulfonic acid compound is one or more selected from 2-sulfobenzoic anhydride, o-sulfobenzoic acid, m-sulfobenzoic acid, p-sulfobenzoic acid, 5-sulfosalicylic acid, benzenesulfonic acid, o-aminobenzenesulfonic acid, m-aminobenzenesulfonic acid, p-aminobenzenesulfonic acid, p-toluenesulfonic acid, p-toluenesulfonate methyl, 5-sulfisophthalic acid, and salts thereof.

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