JP7729545B2 - Polyester resin and its manufacturing method - Google Patents

Description

The present invention relates to a polyester resin and a method for producing the same.

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 tape, hollow molded bottles, casings for electrical and electronic components, and other engineering plastic molded products).

Among various applications, polyester resins for fiber applications that are readily alkali-soluble are known to contain aromatic dicarboxylic acids with sulfonate groups and polyether compounds (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2008-156453

In Patent Document 1, a metal-based polycondensation catalyst is used, which causes problems such as deterioration of operability and yarn quality characteristics due to metal precipitation during polymerization, or poor color tone. Furthermore, when a metal-based polycondensation catalyst is used, heavy metals derived from the catalyst are eluted during alkali dissolution, raising concerns about environmental impacts. Therefore, polyester resins using organic catalysts are also being considered.
In recent years, there has been a demand for polyester resins with improved thread properties such as alkali solubility, strength and elongation.

The object of the present invention is to provide a polyester resin that is easily soluble in alkali, has excellent workability when made into fibers, and exhibits excellent yarn quality when made into fibers, and that can suppress the elution of heavy metals when dissolved in alkali.

As a result of extensive research to solve the above problems, the inventors discovered that polyester resins of the present invention, which contain a specified amount of polyether compound, an aromatic dicarboxylic acid having a metal sulfonate group as the dicarboxylic acid component, and a specific range of triethylene glycol content in the glycol component, have excellent alkali solubility and, when made into fibers, also have excellent yarn quality properties such as strength and elongation, leading to the present invention.

That is, the gist of the present invention is as follows (1) to ( 5 ).
(1) A polyester resin containing 0.5 to 4.3 mol % of an aromatic dicarboxylic acid having a metal sulfonate group as a dicarboxylic acid component, and 5 to 25 mass % of a polyether compound having a number average molecular weight of 500 to 15,000, wherein the glycol component of the polyester resin contains ethylene glycol as a main component and the content of triethylene glycol is 0.5 to 5.5 mol %.
(2) The polyester resin of (1), which contains diethylene glycol as a glycol component and has a diethylene glycol content of 2.5 mol % or more.
( 3 ) The polyester resin according to (1) or ( 2 ), wherein the content of sulfur components other than the aromatic dicarboxylic acid having a metal sulfonate group is 5 to 100 ppm.
( 4 ) Fibers made of any one of the polyester resins (1) to ( 3 ).
( 5 ) A method for producing the polyester resin according to any one of (1) to (3) , comprising the steps of adding an organic sulfonic acid compound to a polyester raw material, and heating the mixture at a temperature of 240°C or higher for 5 to 120 minutes under normal pressure or pressure to carry out an etherification reaction of the glycol component.

The polyester resin of the present invention allows for the production of fibers with excellent alkali solubility and excellent yarn quality characteristics such as strength and elongation, with good operational efficiency.

The polyester resin of the present invention will be described in detail below.
The polyester resin of the present invention contains an aromatic dicarboxylic acid having a metal sulfonate group as a dicarboxylic acid component. By copolymerizing the aromatic dicarboxylic acid having a metal sulfonate group, it is possible to impart alkali solubility to the polyester resin.

When the total amount of all acid components constituting the polyester is taken as 100 mol %, the content of the aromatic dicarboxylic acid having a metal sulfonate group must be 0.5 to 4.3 mol %.
If the content of the aromatic dicarboxylic acid having a metal sulfonate group is less than 0.5 mol%, sufficient alkali solubility may not be obtained when the polyester resin is used to form fibers. On the other hand, if the content exceeds 5.5 mol%, the melt viscosity of the polyester tends to be too high in the polycondensation step, making it difficult to sufficiently increase the degree of polymerization. As a result, the operability, yarn quality characteristics, and material strength (e.g., yarn strength when formed into fibers) may be reduced.
Furthermore, since the aromatic dicarboxylic acid having a metal sulfonate group acts as a catalyst in the etherification step described below, by setting the content within the above range, it becomes easier to set the contents of ethylene glycol and triethylene glycol in the glycol component within the specific range.

Examples of aromatic dicarboxylic acids having a metal sulfonate group include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 5-lithium sulfoisophthalic acid, sodium sulfonaphthalenedicarboxylic acid, sodium sulfophenyldicarboxylic acid, and 5-sodium sulfoterephthalic acid. In the present invention, 5-sodium sulfoisophthalic acid is preferred in terms of its alkali solubility, operability during melt spinning, and cost. These acids may be used as is, or ester-forming derivatives may also be used. Among these, esters with ethylene glycol are preferred in terms of operability and other factors.

The proportion of terephthalic acid in the acid component is preferably 94.5 to 99.5 mol%, and more preferably 95 to 99 mol%. If the proportion of terephthalic acid is less than 94.5 mol%, the crystallinity of the resin composition will decrease, and the melting point will be lower, which may result in reduced operability during melt spinning and drawing. On the other hand, if the proportion of terephthalic acid exceeds 99.5 mol%, the amount of aromatic dicarboxylic acid having a metal sulfonate group copolymerized will decrease, which may reduce the alkali-solubility effect.

In the polyester resin of the present invention, examples of acid components other than terephthalic acid and aromatic dicarboxylic acid having a metal sulfonate group include isophthalic acid, phthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, dodecanedioic acid, and other dimer acids, as well as trimellitic anhydride, trimellitic acid, pyromellitic acid, 1,4-cyclohexanedicarboxylic acid, sebacic acid, and dimer acids. Two or more of these may be used in combination, and ester-forming derivatives of these acids may also be used.

The polyester resin of the present invention contains triethylene glycol, and the content of triethylene glycol in the total glycol components is 0.5 to 5.5 mol %. Note that the content (mol %) of the glycol components referred to here is calculated without including the polyether compound described below.
The triethylene glycol content of the total glycol components is preferably 0.6 to 5.0 mol%, more preferably 0.7 to 4.0 mol%. If it is less than 0.5 mol%, the melting point becomes too high, resulting in poor alkali solubility and poor operability, and excellent yarn properties (strength and elongation) are not fully exhibited. On the other hand, if it exceeds 5.5 mol%, the resulting resin becomes amorphous, has a low melting point, and is poor in heat resistance, resulting in poor operability and yarn properties when made into fibers.

Of the total glycol components, the total content of triethylene glycol and tetraethylene glycol is preferably 7.0 mol% or less, more preferably 0.6 to 4 mol%, and even more preferably 0.8 to 3 mol%. If it exceeds 7.0 mol%, heat resistance may decrease, and the operability when producing fiber and the yarn quality characteristics of the fiber may be poor. On the other hand, if it is less than 0.6 mol%, the operability when producing fiber and the alkali solubility of the fiber may be poor.

Of the total glycol components, the tetraethylene glycol content is preferably 0.0 to 2.0 mol%, more preferably 0 to 1.0 mol%, and even more preferably 0.0 to 0.5 mol%. If it exceeds 2.0 mol%, heat resistance and yarn quality characteristics may deteriorate.

The polyester resin of the present invention preferably contains diethylene glycol as a glycol component. The diethylene glycol content is preferably 2.5 mol% or more of the total glycol components, more preferably 3.5 mol% or more, and even more preferably 4.5 mol% or more. By keeping the diethylene glycol content within this range, the alkali solubility of the resulting fiber can be further improved. The upper limit of the diethylene glycol content is preferably 12 mol% in terms of operability when forming the fiber and the yarn quality characteristics of the fiber.

To adjust the content of each of diethylene glycol, triethylene glycol, and tetraethylene glycol, for example, the content of aromatic dicarboxylic acid having a metal sulfonate group can be set within a preferred range, an organic sulfonic acid compound can be used as a polymerization catalyst in the polyester resin production method described below, the amount of organic sulfonic acid compound added can be set within a preferred range, the molar ratio (G/A) of glycol component (G) to acid component (A) before being subjected to the etherification reaction can be set within a preferred range, or the temperature or time of the etherification reaction can be adjusted.

The polyester resin of the present invention may contain glycol components other than those mentioned above. Specific examples include 1,2-propylene glycol, neopentyl glycol, 1,6-hexanediol, 1,4-butanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, dimer diol, an ethylene oxide adduct of bisphenol S, and an ethylene oxide adduct of bisphenol A.

The polyester resin of the present invention must contain 5 to 25% by mass of a polyether compound, preferably 6 to 20% by mass, and more preferably 7 to 15% by mass.

If the polyether compound content is less than 5% by mass, the alkali solubility of the polyester resin of the present invention will decrease. Furthermore, if the polyether compound content exceeds 25% by mass, the thermal stability of the polyester resin will be impaired, resulting in poor operability and reduced yarn quality, such as the occurrence of yarn breakage when the resulting polyester resin is made into fibers.

Examples of polyether compounds include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and copolymers of ethylene oxide and propylene oxide, with polyethylene glycol and polytetramethylene glycol being preferred.

The number-average molecular weight of the polyether compound is 500 to 15,000, preferably 1,000 to 15,000. It is more preferably 2,000 to 7,000, and even more preferably 3,000 to 6,000. If the number-average molecular weight of the polyether compound is less than 500, the alkali solubility of the polyester resin of the present invention will decrease. Furthermore, if the number-average molecular weight of the polyether compound in the polyester resin exceeds 15,000, the thermal stability of the polyester resin will be impaired, resulting in thread breakage, for example, when the resulting polyester resin is spun.

The polyester resin of the present invention preferably has an intrinsic viscosity of 0.45 dl/g or more, more preferably 0.5 dl/g or more, and even more preferably 0.6 to 0.8 dl/g. If the intrinsic viscosity is less than 0.45 dl/g, sufficient yarn quality characteristics may not be obtained when the resin is made into fibers.

In the present invention, the intrinsic viscosity is a value measured at a temperature of 20°C using an equal weight mixture of phenol and tetrachloroethane as a solvent.

The polyester resin of the present invention may contain any polymer, antistatic agent, antifoaming agent, dye, pigment, matting agent, fluorescent brightener, stabilizer, antioxidant, colorant, flame retardant, or other additives, provided the effects of the present invention are not impaired. Examples of antioxidants include aromatic amine-based and phenol-based antioxidants. Examples of stabilizers include phosphorus-based, sulfur-based, and amine-based stabilizers, such as phosphoric acid or phosphate ester-based stabilizers.

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

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 (e.g., PET bottles, etc.).

(Method for producing polyester resin)
The method for producing a polyester resin of the present invention includes a step of adding an organic sulfonic acid compound to a polyester raw material and heating the mixture at a temperature of 240°C or higher for 5 to 120 minutes under normal pressure or pressure to carry out an etherification reaction of the glycol component.

In the present invention, by including a step of performing an etherification reaction under specific conditions before the polycondensation reaction, the contents of diethylene glycol, triethylene glycol, and tetraethylene glycol can be set within specific ranges. As a result, a polyester resin can be obtained that has excellent operability when made into fibers and also has excellent alkali solubility when made into fibers.

Raw materials for polyester resins include, for example, glycol components containing ethylene glycol as the main component, dicarboxylic acid components, and esters of low-order condensates of glycol components and dicarboxylic acid components.

As a method for obtaining the above-mentioned esterified product, for example, when producing polyethylene terephthalate as a polyester resin, terephthalic acid, ethylene glycol, and, if necessary, other copolymerization components are directly reacted, water is distilled off, and the mixture is esterified to obtain the esterified product as a raw material for the polyester resin. Alternatively, dimethyl terephthalate, ethylene glycol, and, if necessary, other copolymerization components are reacted, methyl alcohol is distilled off, and the mixture is transesterified to obtain the esterified product.

The method for preparing the esterified product will be described below.
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 continuously fed to an esterification reactor to obtain an esterified product.

The esterification reaction is carried out under reflux conditions of ethylene glycol, while the water or alcohol produced by the reaction is removed from the system using a rectification column. The esterification reaction can be carried out using a multistage apparatus in which multiple esterification reactors are connected in series.

When the esterification reaction is carried out in multiple stages, the temperature of the first stage esterification reaction is preferably 240 to 270° C., more preferably 245 to 265° C. The pressure is preferably 0.2 to 3 kg/cm ² G, more preferably 0.5 to 2 kg/cm ² G.

The temperature of the final stage esterification reaction is preferably 250 to 290° C., more preferably 255 to 275° C. The pressure is preferably 0 to 1.5 kg/cm ² G, more preferably 0 to 1.3 kg/cm ² G.

When the esterification reaction is carried out in three or more stages, the reaction conditions for the intermediate stages are preferably intermediate between the reaction conditions for the first stage and the reaction conditions for the final stage.
It is preferable that the reaction rate of the multi-stage esterification reaction is increased smoothly in each stage. The final esterification reaction rate preferably reaches 90% or more, more preferably 93% or more. These esterification reactions can produce an esterified product, the molecular weight of which is preferably about 500 to 5,000.

When terephthalic acid is used in an esterification reaction, the reaction proceeds due to the catalytic action of terephthalic acid as an acid.

To the esterified product obtained as described above, a polyether compound and an aromatic dicarboxylic acid having a metal sulfonate group are added, and an organic sulfonic acid compound is added as a polymerization catalyst to carry out an etherification reaction. A polycondensation reaction is then carried out to obtain the polyester resin of the present invention. If necessary, an alkali metal compound may be added and a depolymerization reaction carried out before the etherification reaction is carried out.

The amount of aromatic dicarboxylic acid having a metal sulfonate group added relative to the esterified product is, for example, a mass ratio of (esterified product)/(aromatic dicarboxylic acid having a metal sulfonate group) = 4.0 to 70.0. This ensures that the content of aromatic dicarboxylic acid having a metal sulfonate group falls within the range of the present invention, and also makes it easier to ensure that the contents of diethylene glycol, triethylene glycol, and tetraethylene glycol in the resulting polyester resin fall within specific ranges.

The amount of polyether compound added relative to the esterified product is, for example, a mass ratio of (esterified product)/(polyether compound) = 4.0 to 60.0. This makes it easier to keep the polyether compound content within a specific range in the resulting polyester resin.

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 controlled within 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, phenylhydrazine-3-sulfonic acid, 1-nitronaphthalene-3-sulfonic acid, thiophenol-4-sulfonic acid, anisole-o-sulfonic acid, 1,5-naphthalenedisulfonic acid, and o-, m-, or p-chlorobenzene. Sulfonic acids, 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 1-p-xylene-2-sulfonic acid, 6-nitro-p-xylene-2-sulfonic acid, 2,4-dinitrobenzenesulfonic 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 anhydride, 8-sulfonaphthoic anhydride, 3,6-disulfophthalic anhydride, 4,6-disulfoisophthalic anhydride, 2,5-disulfoterephthalic anhydride Examples of the sulfonic acid include hydrates, 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, dithionic acid, dithionic 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. Among these, from the standpoint 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, methyl p-toluenesulfonate, 5-sulfoisophthalic acid, and salts thereof.

When a metal catalyst is not used as the polymerization catalyst, the content of metal components derived from the metal catalyst in the resulting polyester resin of the present invention can be reduced. If the metal component content is high, foreign matter may be generated during melt processing, or the metal components may leach out during alkaline dissolution. The metal component content 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 of antimony, germanium, tin, titanium, zinc, aluminum, iron, magnesium, manganese, nickel, cobalt, etc.

The organic sulfonic acid compound can be added, for example, in the form of a solid, a slurry, or a solution dissolved in water, glycol, etc.

The amount of organic sulfonic acid compound added varies depending on the type, but is preferably 0.5×10 ⁻⁴ to 9.0×10 ⁻⁴ mol, and more preferably 1.0 to 8.0×10 ⁻⁴ mol, per mol of the acid component constituting the polyester resin. If the amount added is too small, exceeding the above range, it may be impossible to obtain a polyester resin with a high degree of polymerization, and it may be impossible to obtain fibers with excellent strength and alkali solubility. Alternatively, the content of diethylene glycol, triethylene glycol, and tetraethylene glycol may not fall within the specified range. On the other hand, if the amount added is excessive, exceeding the above range, the content of diethylene glycol, triethylene glycol, and tetraethylene glycol may become too high, or this may cause discoloration of the polyester resin.

By adding an organic sulfonic acid compound in an amount within the above range, the content of sulfur components other than aromatic dicarboxylic acids having metal sulfonate groups (i.e., sulfur components derived from the catalyst) in the resulting polyester resin can be preferably 5 to 100 ppm, and more preferably 6 to 60 ppm. If the sulfur component content is less than 5 ppm, the resulting fiber may have poor yarn quality. On the other hand, if it exceeds 100 ppm, it may cause discoloration of the polyester.

The temperature for the etherification reaction is preferably 240°C or higher, more preferably 240 to 300°C, and even more preferably 250 to 280°C. If the temperature is below 240°C, the reaction may not proceed sufficiently, and the content of diethylene glycol, triethylene glycol, and tetraethylene glycol may not be within the specified range. If the temperature exceeds 300°C, decomposition of the esterified product may proceed during the reaction, which may result in a decrease in operability when producing fiber and in the yarn quality characteristics of the fiber.

The etherification reaction time is preferably 5 to 120 minutes, and more preferably 10 to 60 minutes. If the reaction time is less than 5 minutes, the reaction may not proceed sufficiently, and the diethylene glycol, triethylene glycol, and tetraethylene glycol contents may not fall within the specified range. If the reaction time exceeds 120 minutes, the etherification reaction may proceed too far, and the diethylene glycol, triethylene glycol, and tetraethylene glycol contents may not fall within the specified range, or decomposition of the esterified products may progress during the reaction, which may result in a decrease in operability when producing fibers and in the yarn quality characteristics of the fibers.

The etherification reaction is preferably carried out under normal pressure or under pressure, and the pressure is preferably 0 to 3.0 kg/cm ² G.

By adjusting the ratio of glycol components to acid components (G/A) in the raw materials used in the etherification reaction, the contents of diethylene glycol, triethylene glycol, and tetraethylene glycol can be adjusted to a specific range. G/A is preferably 1.05 to 3.00, and more preferably 1.10 to 2.00. To adjust G/A, additional glycol components such as ethylene glycol may be added to the polyester raw materials as needed. If the G/A ratio is less than 1.05, the amounts of diethylene glycol, triethylene glycol, and tetraethylene glycol produced tend to decrease; on the other hand, if it exceeds 3.00, the amounts of diethylene glycol, triethylene glycol, and tetraethylene glycol produced tend to increase.

After the etherification reaction, a polycondensation reaction can be carried out to obtain the polyester resin of the present invention. Examples of polycondensation reactions include melt polycondensation reactions. The polycondensation reaction may be carried out in one stage or in multiple stages.

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

In the case of a multi-stage process, the temperature of the polycondensation reaction in the final stage 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 carried out in three or more stages, the reaction conditions in the intermediate stages are preferably between those in the first stage and the final stage. It is preferable to smoothly increase the degree of polymerization in each of these stages.

Furthermore, during the polycondensation reaction, if necessary, a hindered phenol-based antioxidant and a phosphorus compound that can suppress thermal decomposition of the resin can also be added in addition to the above-mentioned polymerization catalyst.

Examples of hindered phenol antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 4,4'-butylidenebis-(3-methyl-6-t-butylphenol), tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, and 4,4'-butylidenebis-(3-methyl-6-t-butylphenol). Examples of compounds that can be used include ethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] and 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1'-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, but from the standpoint of effectiveness and cost, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane is preferred. These can be used alone or in combination of two or more.

Examples of phosphorus compounds that can be used include phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, and triphenyl phosphate. These compounds can be used alone or in combination of two or more.

(Uses of polyester resin)
The polyester resin of the present invention can be used in a variety of applications, including, for example, fibers, molded articles, and films.

The polyester resin of the present invention can be used to form the fiber of the present invention.
The fibers of the present invention can be obtained, for example, by melting and spinning a raw material containing the polyester resin of the present invention. The spinning method can be carried out under known conditions. For example, the polyester resin can be dried by a conventional method, fed to a conventional melt spinning machine, and melt-spun at a temperature at least 20°C higher than the melting point of the polyester. The resulting yarn can be wound at a speed of 1,000 to 4,000 m/min as an undrawn or semi-undrawn yarn, or the yarn can be stretched 1.5 to 3.5 times without being wound, and then heat-treated at 80 to 180°C to obtain the desired fiber.

The fibers of the present invention may be ultrafine fibers, for example, with a single filament fineness of 0.8 decitex or less (preferably 0.6 to 0.3 decitex).

The fibers of the present invention may be, for example, monofilaments, multifilaments, etc., and may be either long fibers or short fibers, etc.

The shape of the single fibers constituting the fiber of the present invention is not particularly limited, and they may have not only a round cross section but also a non-circular cross section such as a polygonal cross section.
The fibers of the present invention may be subjected to post-processing such as crimping and false twisting, if necessary.

The fibers of the present invention may be fibers in which all of the single fibers are formed from the polyester resin of the present invention, or may be composite fibers in which the polyester resin of the present invention is combined with other polyester resins (such as virgin polyester resins or polyester resins containing other copolymer components). Examples of composite fiber configurations include sheath-core, side-by-side, and islands-in-sea types.

When the fiber of the present invention is a multifilament, its properties include, for example, a single yarn fineness of 0.3 to 30 decitex, a number of single yarns of 2 to 300, a total fineness of 5 to 350, a strength of 1 to 5 cN/decitex, and an elongation of 10 to 400%.

The fibers of the present invention have excellent alkali solubility. Furthermore, they also have excellent yarn quality properties such as elongation and strength.

The present invention will be explained in detail below based on examples, but the present invention is not limited to these. Measurements and evaluations were performed using the following methods.

(1) Intrinsic viscosity [IV]
The measurement was carried out at 20°C using a solvent consisting of an equal weight mixture of phenol and tetrachloroethane.

(2) Composition of Polyester Resin 10 mg of a sample was dissolved in 1 mL of a mixed solvent of deuterated chloroform/deuterated trifluoroacetic acid = 9/1 (mass ratio), and ¹ H-NMR was measured using a JEOL LA-400 NMR. From the integrated proton peak intensity of each component in the resulting chart, the total amount of the dicarboxylic acid component, triethylene glycol component, and tetraethylene glycol component, as well as the molar ratio of each other glycol component, were calculated. Furthermore, the content (mass%) of the polyether compound in the polyester resin was calculated.

Next, the amounts of triethylene glycol and tetraethylene glycol were determined as follows.
The polyester resin was hydrolyzed in a 0.75N potassium hydroxide/methanol solution, and then neutralized by adding terephthalic acid. The filtrate obtained by filtration was then measured by gas chromatography, and the molar ratio of triethylene glycol to tetraethylene glycol was calculated using a previously prepared calibration curve. The contents of triethylene glycol and tetraethylene glycol in the total glycol components were calculated from these molar ratios and the results of the ^1H -NMR measurement (the molar ratio of the total component of triethylene glycol and tetraethylene glycol to each of the other glycol components).
The contents (mol %) of the glycol components ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol were calculated without including the polyether compound.

(4) Melting point (Tm), glass transition temperature (Tg)
The measurement was carried out using a PerkinElmer differential scanning calorimeter DSC-7 in a nitrogen stream at a temperature range of 25 to 280° C. and a temperature rise rate of 20° C./min.

(5) Sulfur Component Content of Catalyst The polyester resin was melt-molded at 300°C into a disk-shaped molded plate having a diameter of 3 cm and a thickness of 1 cm, and quantitative analysis of the sulfur component was carried out by the calibration curve method using a fluorescent X-ray analyzer ZSX Primus manufactured by Rigaku Corporation.
Next, 10 mg of the sample was dissolved in 1 mL of a mixed solvent of deuterated chloroform/deuterated trifluoroacetic acid = 9/1 (mass ratio), and ¹ H-NMR was measured using a JEOL LA-400 NMR. From the integrated proton peak intensity of each component in the obtained chart, the molar ratio of 5-Na sulfoisophthalic acid diglycol ester (SIPG) was calculated, and the sulfur content derived from SIPG was calculated therefrom.
The content of sulfur components derived from the catalyst was calculated by subtracting the content of sulfur derived from SIPG calculated by NMR from the amount of sulfur components quantitatively analyzed by a fluorescent X-ray analyzer.

The evaluation methods for fibers (operability, strength, elongation, and rate of alkali weight loss) are as follows.
(6) Operational efficiency of filament fiber production (cut yarn)
The case where the number of times of yarn breakage during 24 hours of continuous melt spinning was 3 times/(day/spindle) or less was marked as "◯", and the other cases were marked as "X".

(7) Yarn Quality Characteristics Tenacity and elongation were measured according to JIS L-1013 using an autograph DSS-500 manufactured by Shimadzu Corporation at a grip distance of 25 cm and a pulling speed of 30 cm.
In the present invention, the strength is preferably 2.0 cN/dtex or more, more preferably 3.0 cN/dtex or more, and the elongation is preferably 28% or more, more preferably 30% or more.
A yarn having both strength and elongation within the above ranges was evaluated as "Good", and a yarn having at least one of the strength and elongation not within the above ranges was evaluated as "Poor". A yarn having both strength and elongation within the above ranges is an indicator of an excellent balance of yarn quality characteristics.

(8) Alkali weight loss rate: After drying the polyester resin, a spinneret with 48 nozzles was used to spin the resin at a spinning temperature of 295°C, followed by cooling and oil application while winding up at a speed of 1,500 m/min to obtain an undrawn yarn. This was then drawn under the conditions of a draw ratio of 2.8, a roll heater temperature of 80°C, a plate heater temperature of 150°C, and a drawing speed of 600 m/min, and then wound up to obtain a drawn yarn of 75 dtex/48 filaments.
Next, this drawn yarn was made into a cylindrical knitted fabric by a conventional method, and subjected to a weight reduction treatment for 20 minutes in a 5% by mass aqueous sodium hydroxide solution with a bath ratio of 1:50 and temperature controlled at 70°C, and the weight loss was calculated using the following formula.
Weight loss rate (mass%/min) = [(AB)/A] x 100/20
Here, A indicates the mass (g) of the tubular knitted fabric before weight reduction, and B indicates the mass (g) of the tubular knitted fabric after weight reduction.
The rate of alkali weight loss of 5% by mass/min or more was marked "Good", and the rate of alkali weight loss of less than 5% by mass/min was marked "Poor".

[Preparation of esterified product]
A slurry of terephthalic acid and ethylene glycol (molar ratio 1/1.6) was continuously supplied to an esterification reactor and reacted under conditions of a temperature of 250°C and a pressure of 0.2 MPa with a residence time of 8 hours, thereby obtaining an esterified product (terephthalic acid:ethylene glycol=100:111 (molar ratio)).

Example 1
[Polyester resin]
The heat-melted esterified product, polyethylene glycol (PEG) with a number-average molecular weight of 6,000 as a polyether compound, and 5-Na sulfoisophthalic acid diglycol ester (SIPG) as an aromatic dicarboxylic acid component having a metal sulfonate group were charged in the amounts shown in Table 1 into a polycondensation reactor heated to 280°C. Next, 2.0 x ^10-4 mol/mol of acid component of 5-sulfosalicylic acid dihydrate (SS) was added as a polymerization catalyst, and an etherification reaction was carried out at 260°C for 10 minutes under atmospheric pressure. Next, while maintaining the temperature of the reactor at 280°C, the pressure of the system was gradually reduced to 0.5 hPa or less after 60 minutes. Under these conditions, the polycondensation reaction was carried out for 3 hours with stirring to obtain a polyester resin. The polyester resin contained 25 ppm of catalyst-derived sulfur components and a triethylene glycol content of 1.1 mol%.

[Production of Long Fibers]
The polyester resin thus obtained was dried and then spun at a spinning temperature of 273°C using a spinneret having 48 nozzles, followed by cooling and application of an oil, followed by winding at a speed of 1395 m/min to obtain an undrawn yarn, which was then drawn at a draw ratio of 2.5, a roll heater temperature of 80°C, a plate heater temperature of 150°C, and a drawing speed of 600 m/min, followed by winding to obtain an 84 dtex/48 filament multifilament yarn (drawn yarn).

Examples 2 to 8, Comparative Examples 1 to 9
[Polyester resin]
Polyester resins were obtained by the same procedure as in Example 1, except that the amounts of PEG, 5-Na sulfoisophthalic acid diglycol ester (SIPG), and 5-sulfosalicylic acid dihydrate (SS) added and the etherification conditions were changed as shown in Table 1.
Then, a multifilament yarn was obtained in the same manner as in Example 1.

Comparative Example 10
A polyester resin was obtained in the same manner as in Example 1, except that antimony trioxide (Sb) was used instead of 5-sulfosalicylic acid dihydrate (SS). Then, a multifilament yarn was obtained in the same manner as in Example 1.

Table 1 shows the raw material composition and production conditions of the polyester resins in the examples and comparative examples.

The property values of the polyester resins and fibers obtained in the examples and comparative examples are shown in Table 2.

As is clear from Tables 1 and 2, the polyester resins obtained in Examples 1 to 8 had a content of aromatic dicarboxylic acid having a metal sulfonate group, a content of polyether compound, and a content of triethylene glycol that were within the ranges specified in the present invention. This resulted in excellent operability when obtaining fibers, and fibers with excellent operability, yarn quality, and alkali solubility were obtained.

On the other hand, in Comparative Example 1, the triethylene glycol content in the polyester resin was higher than the range specified in the present invention. As a result, the resin was amorphous and had poor heat resistance, which resulted in poor spinning operability and inability to be drawn, and the resin was not evaluated as a fiber.

In Comparative Example 2, the triethylene glycol content in the polyester resin was low and outside the range specified in the present invention. As a result, the resin had a high melting point, and was inferior in terms of spinning operability, yarn quality characteristics when made into fiber, and alkali solubility.

In Comparative Example 3, the content of the polyether compound was low and outside the range specified in the present invention, resulting in poor alkali solubility when made into fibers.

In Comparative Example 4, the polyether compound content was higher than the range specified in the present invention, resulting in low thermal stability, poor spinning operability, and poor yarn quality when made into fiber.

In Comparative Example 5, the etherification reaction was not performed, and therefore the triethylene glycol content in the polyester resin was low and outside the range specified in the present invention. As a result, the spinning operability, the yarn quality characteristics when made into fiber, and alkali solubility were poor.

In Comparative Example 6, the etherification reaction temperature was set low, so the reaction did not proceed sufficiently, and the triethylene glycol content in the polyester resin was low and outside the range specified in the present invention. As a result, the spinning operability, the yarn quality when made into fiber, and the alkali solubility were poor.

In Comparative Example 7, the etherification reaction time was extended, resulting in a high triethylene glycol content in the polyester resin that was outside the range specified in the present invention. As a result, the resin was amorphous and had low heat resistance. Spinning operability was poor and drawing was not possible, so the fiber was not evaluated.

In Comparative Example 8, the amount of 5-sulfosalicylic acid dihydrate added as a polymerization catalyst was too high, resulting in a high triethylene glycol content in the polyester resin outside the range specified in the present invention. As a result, the resin was amorphous and had low heat resistance. Spinning operability was poor and drawing was not possible, so the fiber was not evaluated.

In Comparative Example 9, the amount of 5-sulfosalicylic acid dihydrate added as a polymerization catalyst was small, so the etherification reaction did not proceed sufficiently and the triethylene glycol content was low and outside the range specified in the present invention. As a result, spinning operability was poor, and the resulting fiber had poor yarn quality and alkali solubility.

In Comparative Example 10, the metal catalyst antimony trioxide was added as the polymerization catalyst instead of 5-sulfosalicylic acid dihydrate (SS), resulting in a lower triethylene glycol content. As a result, spinning operability was poor, and the yarn quality and alkali solubility of the resulting fiber were poor. Furthermore, in the evaluation of alkali solubility, Sb was found to be eluted during alkali dissolution.

Claims (5)

A polyester resin containing 0.5 to 4.3 mol % of an aromatic dicarboxylic acid having a metal sulfonate group as a dicarboxylic acid component, and 5 to 25 mass % of a polyether compound having a number average molecular weight of 500 to 15,000, wherein the glycol component of the polyester resin contains ethylene glycol as a main component and has a triethylene glycol content of 0.5 to 5.5 mol %. The polyester resin according to claim 1, characterized in that it contains diethylene glycol as a glycol component and the diethylene glycol content is 2.5 mol% or more. 3. The polyester resin according to claim 1 , wherein the content of sulfur components other than the aromatic dicarboxylic acid having a metal sulfonate group is 5 to 100 ppm. A fiber made of the polyester resin according to any one of claims 1 to 3 . A method for producing the polyester resin according to any one of claims 1 to 3 , comprising the steps of adding an organic sulfonic acid compound to a polyester raw material, and heating the resulting mixture at a temperature of 240°C or higher for 5 to 120 minutes under normal pressure or pressure to carry out an etherification reaction of the glycol component.