polyester fiber

Abstract

The present invention provides a polyester fiber that can be dyed under high-temperature conditions, can be used without problems for sewing clothing when used as sewing thread, has a low environmental impact when recycled, and allows clothing to be separated into its constituent parts without requiring much force. [Solution] A polyester fiber comprising a glycol component and a dicarboxylic acid component, wherein the polyester resin has a carboxyl-terminal group content of 30 to 100 equivalents / t and contains an organic sulfonic acid compound as a sulfur component at a concentration of 5 to 500 ppm, and the polyester fiber has a strength of 2.5 cN / dtex or higher.

Description

Technical Field

[0001] The present invention relates to polyester fibers made of a polyester resin having a specific composition, sewing threads made of the polyester fibers, and a method for producing the polyester fibers.

Background Art

[0002] In recent years, attempts have been made to collect and recycle used clothes from the perspective of environmental protection. Since clothes are composed of many members, in order to recycle clothes, it is first necessary to separate the recyclable parts from the clothes. For this reason, the recycling of clothes starts from separating the constituent members of clothes such as the body, sleeves, collar pieces, cuff pieces, hem pieces, buttons, and fasteners for each member, and sorting the recyclable members from the non-recyclable members. The members can be easily separated by cutting the sewing parts or extracting the sewing threads. However, usually, all of these are done by hand, and labor saving and simplification of the work have been demanded.

[0003] Therefore, in separating clothes into constituent members, it is conceivable to make the sewing threads that sew the constituent members elutable, thereby achieving labor saving and simplification of the work. For example, Patent Document 1 discloses a technique for eluting a sewing thread made of water-soluble polyvinyl alcohol fiber with hot water, and Patent Document 2 discloses a technique for eluting a sewing thread made of alkali-easily soluble polyester fiber with a strong alkali aqueous solution. By using these sewing threads, the collected clothes can be separated into constituent members for each member without taking the trouble of cutting the sewing parts or extracting the sewing threads only by immersing the clothes in hot water or a strong alkali aqueous solution.

[0004] On the other hand, since clothes are mostly dyed to cope with various color variations, the dyeing process is performed in hot water at 100°C or higher. However, in the case of the sewing thread made of water-soluble polyvinyl alcohol fiber described in Patent Document 1, the sewing thread is eluted by hot water, so dyeing of clothes using the sewing thread is substantially impossible.

[0005] Furthermore, the alkali-soluble polyester fibers described in Patent Document 2 require the use of a dissolving solution containing alkaline chemicals during elution. Additionally, metal compounds used as polymerization catalysts also elute into the dissolving solution during elution. Therefore, the treatment of the dissolving solution (waste liquid) used during clothing recycling may have adverse effects on the environment, and there was room for improvement from an environmental protection standpoint. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-81811 [Patent Document 2] Japanese Patent Application Publication No. 7-216615 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention aims to solve the above-mentioned problems by providing a polyester fiber that can be dyed under high-temperature conditions, can be used without problems for sewing clothing when used as sewing thread, has a low environmental impact when recycled, and allows clothing to be separated into its constituent parts without requiring much force. [Means for solving the problem]

[0008] The present inventors have discovered that the above problems can be solved by using fibers made from polyester resin in which the amount of carboxyl terminal groups and the content of organic sulfonic acid compounds satisfy a specific range, and have arrived at the present invention.

[0009] In other words, the present invention is summarized in the following (1) to (6). (1) A fiber made of a polyester resin containing a glycol component and a dicarboxylic acid component, The aforementioned polyester resin has a carboxyl-terminal group content of 30 to 100 equivalents / t and contains an organic sulfonic acid compound as a sulfur component at a concentration of 5 to 500 ppm. Polyester fiber with a strength of 2.5 cN / dtex or higher. (2) The polyester fiber according to (1), wherein the content of catalyst-derived metal components in the polyester resin is 1 ppm or less. (3) A polyester fiber according to either (1) or (2), wherein the strength retention rate after moist heat treatment in 130°C hot water for 1 hour is 90% or more, and the strength retention rate after moist heat treatment for 24 hours is less than 70%. (4) A spun yarn containing polyester fibers as described in any of (1) to (3). (5) Sewing thread made of polyester fibers as described in any of (1) to (3). (6) A method for producing polyester fibers according to any one of (1) to (3), comprising the following steps (a) to (d) in this order. (a) A process of polycondensing an esterified product consisting of a glycol component and a dicarboxylic acid component and an organic sulfonic acid compound at a temperature of 260 to 330°C. (b) A process to obtain a polyester resin by allowing the reactants after the polycondensation reaction to remain in a nitrogen atmosphere at a temperature of 280 to 350°C for 5 to 60 minutes. (h) A step of melt-spinning the polyester resin at a spinning temperature of 250 to 310°C to obtain spun yarn. (ii) The process of cooling and stretching the obtained spun yarn, then heat-treating it at a temperature of 100-200°C and winding it up. [Effects of the Invention]

[0010] The polyester fiber of the present invention possesses sufficient strength and can be dyed in hot water, yet it can be easily decomposed by moist heat treatment at high temperatures for a certain period of time or longer. Therefore, the polyester fiber of the present invention is suitable for use as sewing thread, and when recycling clothing after use, the garment can be easily separated into its constituent parts simply by immersing the garment, with the sewing thread attached, in hot water for a certain period of time. As a result, clothing can be recycled without using alkaline compound dissolving solutions, which have a high environmental impact, as in conventional methods, and without containing catalyst-derived metal compounds in the wastewater. [Modes for carrying out the invention]

[0011] The polyester fibers of the present invention will be described in detail below. The polyester fiber of the present invention is a fiber made of a polyester resin containing a glycol component and a dicarboxylic acid component. The glycol component and dicarboxylic acid component constituting the polyester resin will be described below.

[0012] <Glycol component> In the present invention, the glycol component constituting the polyester resin includes ethylene glycol. When the total amount of all glycol components constituting the polyester resin is 100 mol%, it is preferable that the ethylene glycol content is 20 mol% or more. It is more preferable that ethylene glycol be the main glycol component, that is, that the ethylene glycol content in the glycol component is 50 mol% or more, even more preferable that it is 70 mol% or more, and particularly preferable that it is 80 mol% or more. By having an ethylene glycol content of 20 mol% or more, polyester fibers with even greater strength can be obtained.

[0013] In the present invention, it is preferable that the glycol component contains diethylene glycol in addition to the aforementioned ethylene glycol. The content of diethylene glycol in the glycol component is preferably 2.5 to 30 mol%, more preferably 3.0 to 20 mol%, even more preferably 5 to 15 mol%, and particularly preferably 10 to 15 mol%, when the total amount of all glycol components is 100 mol%. In the present invention, if the diethylene glycol content is within the above range, the strength of the polyester fiber can be further improved.

[0014] Furthermore, in the present invention, it is preferable that the glycol component contains triethylene glycol in addition to the ethylene glycol mentioned above. The content of triethylene glycol in the glycol component is preferably 0.2 to 2.0 mol%, and more preferably 0.5 to 1.0 mol%, when the total amount of all glycol components is 100 mol%. In the present invention, the polyester resin can obtain sufficient improvement in mechanical properties by having a triethylene glycol content within the above range.

[0015] In the polyester resin of the present invention, in addition to containing ethylene glycol as a glycol component, the strength of the polyester fiber can be further improved by containing diethylene glycol and triethylene glycol in such a manner that each satisfies the above-mentioned specific range. Diethylene glycol and triethylene glycol may be contained individually, or both may be contained.

[0016] The polyester resin in the present invention preferably contains ethylene glycol and further contains diethylene glycol and triethylene glycol, but may contain glycol components other than these. Specific examples thereof include aliphatic glycols exemplified by tetraethylene glycol, 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-cyclohexanedietanol, 1,10-decamethylene glycol, 1,12-dodecanediol, etc., aromatic glycols exemplified by 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.

[0017] <Dicarboxylic acid component> As the dicarboxylic acid component constituting the polyester resin in the present invention, for example, saturated aliphatic dicarboxylic acids such as 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 ester-forming derivatives thereof, unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, etc., or ester-forming derivatives thereof, aromatic dicarboxylic acids such as orthophthalic acid, isophthalic acid, terephthalic 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'-biphenylsulfonedicarboxylic acid, 4,4'-biphenyletherdicarboxylic acid, 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid, pamoic acid, anthracenedicarboxylic acid, etc., or ester-forming derivatives thereof may be mentioned, and these may be used in combination. Among them, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid (particularly 2,6-naphthalenedicarboxylic acid) are preferable in terms of resin properties and versatility.

[0018] That is, as the polyester resin in the present invention, as the glycol component, ethylene glycol is the main component (80 mol% or more when the total glycol component is 100 mol%), and it contains both diethylene glycol and triethylene glycol, and as the dicarboxylic acid component, terephthalic acid is the main component (80 mol% or more when the total dicarboxylic acid component is 100 mol%) is preferable.

[0019] In the present invention, the amount of carboxyl terminal groups in the polyester resin is 30 to 100 equivalents / t, more preferably 40 to 90 equivalents / t, and even more preferably 45 to 80 equivalents / t. By keeping the amount of carboxyl terminal groups within the above range, the polyester fibers of the present invention made from the polyester resin will have sufficient strength and will also exhibit good decomposition properties when subjected to moist heat treatment at high temperatures for a certain period of time or longer (for example, leaving it in hot water at 130°C for 24 hours). If the amount of carboxyl terminal groups is less than 30 equivalents / t, the decomposition properties by moist heat treatment will be poor, while if the amount of carboxyl terminal groups is more than 100 equivalents / t, the strength of the multifilament will be low, making it unsuitable for sewing thread.

[0020] The polyester resin in this invention contains 5 to 500 ppm of an organic sulfonic acid compound as a sulfur component, preferably 5 to 50 ppm, from the viewpoint of the decomposability of the resulting fibers. When the content of the organic sulfonic acid compound is within the above range, the polyester fibers of this invention are less likely to decompose when subjected to moist heat treatment during dyeing, i.e., moist heat treatment at high temperatures for a short time (for example, moist heat treatment in 130°C hot water for 1 hour), and can maintain their strength. In addition, polyester fibers that decompose well when subjected to moist heat treatment at high temperatures for a certain period of time or longer (for example, treatment by leaving in 130°C hot water for 24 hours) can be obtained. If the content of the organic sulfonic acid compound is less than 5 ppm, the decomposability by moist heat treatment at high temperatures for a certain period of time or longer will be poor. On the other hand, if the content of the organic sulfonic acid compound is greater than 500 ppm, decomposition of the polyester fibers will occur due to moist heat treatment during dyeing, making it difficult to produce sewing thread with sufficient strength for practical use.

[0021] As will be described later in this invention, it is important to use an organic sulfonic acid compound as a polymerization catalyst when manufacturing polyester resin, and the organic sulfonic acid compound is contained in the polyester resin in the amount within the specific range described above as a catalyst-derived component. On the other hand, when the organic sulfonic acid compound is included as a copolymer component of the polyester resin, it is undesirable because, in an attempt to impart good decomposability by moist heat treatment to the multifilament of this invention, the amount of organic sulfonic acid compound exceeds 500 ppm, resulting in a problem of reduced strength of the multifilament itself.

[0022] 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, and thiofu. 2-nitrotoluene-5-sulfonic acid, 2-nitrotoluene-4-sulfonic acid, 2-nitrotoluene-6-sulfonic acid, 3-nitrotoluene-5-sulfonic acid, 4-nitrotoluene 1-2-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, 3,5-dinitrobenzenesulfonic acid, o-, m- or p-fluorobenzenesulfonic acid, 4-chloro-3-methylbenzenesulfonic acid, 2-chloro-4-sulfonic acid Benzoic 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-disulfisophthalic anhydride, 2,5-disulfoterephthalic anhydride, methanesulfonic acid, ethanesulfonic acid, methionic acid, cyclopentanesulfonic acid, 1,1-ethanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,Examples include 2-ethanedisulfonic acid anhydride, 3-propanedisulfonic acid, β-sulfopropionic acid, isethionic acid, nithionic acid, nithionic acid 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 viewpoint of versatility, 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-sulfoisophthalic acid, and salts thereof are preferred.

[0023] In the present invention, an organic sulfonic acid compound is used as a polymerization catalyst, and by incorporating the above-mentioned specific range amount of the organic sulfonic acid compound into the polyester resin, good degradability can be imparted to the multifilament. Furthermore, an advantage of using an organic sulfonic acid compound as a polymerization catalyst is that the amount of catalyst-derived metal components in the resulting polyester resin can be kept extremely low.

[0024] Therefore, the polyester resin in the present invention may contain metal components derived from a metal catalyst, but the 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 such as antimony, germanium, tin, titanium, zinc, aluminum, iron, magnesium, potassium, calcium, sodium, manganese, nickel, and cobalt.

[0025] The polyester fiber of the present invention has an initial strength of 2.5 cN / dtex or more before moist heat treatment, more preferably 3 cN / dtex or more, and even more preferably 3.3 cN / dtex or more. If the initial strength before moist heat treatment is less than 2.5 cN / dtex, the strength is low, which may cause practical problems when used as sewing thread.

[0026] The elongation of the polyester fiber of the present invention is preferably 5 to 100%, and more preferably 10 to 80%. If the elongation is less than 5%, it is prone to breaking when used as sewing thread, and if the elongation is greater than 100%, it may cause shrinkage or skipped stitches on the fabric when used as sewing thread.

[0027] The boiling water shrinkage rate of the polyester fibers of the present invention is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less. If the boiling water shrinkage rate is greater than 10%, the sewing thread may shrink due to heat when used as sewing thread and dyed, causing wrinkles in the sewn product.

[0028] The polyester fibers of the present invention can be dyed in hot water, meaning that they are less prone to strength reduction when subjected to short-term moist heat treatment at high temperatures. Here, the conditions for dyeing ordinary polyester fibers are known to be treatment at a temperature of 120 to 135°C for 30 to 90 minutes, and among these, treatment at a temperature of 130°C for about 60 minutes is common. Therefore, as an indicator that the present invention is less prone to strength reduction during dyeing, it is preferable that the strength retention rate after moist heat treatment in 130°C hot water for 1 hour is 90% or more, more preferably 91% or more, and even more preferably 92% or more. If the strength retention rate after moist heat treatment in 130°C hot water for 1 hour is 90% or more, the fibers will have sufficient strength even after dyeing.

[0029] As described above, the polyester fibers of the present invention are less susceptible to strength reduction when subjected to moist heat treatment at high temperatures for a short period of time, but can be easily decomposed by moist heat treatment at high temperatures for a certain period of time or longer. In the present invention, as an indicator of easy decomposition, it is preferable that the strength retention rate after moist heat treatment in 130°C hot water for 24 hours is less than 70%, more preferably less than 65%, and even more preferably less than 60%. If the strength retention rate after moist heat treatment in 130°C hot water for 24 hours is less than 70%, it is preferable because the sewing thread made of the polyester fibers of the present invention can be separated from the garment by immersing the garment in hot water for a certain period of time or longer, thereby allowing the garment to be easily separated into its constituent parts.

[0030] The polyester fibers of the present invention may have their single-fiber fineness and total fineness arbitrarily set according to the intended use, but the single-fiber fineness is preferably 1.0 to 4.0 dtex, and the total fineness is preferably 20 to 1500 dtex.

[0031] The polyester fibers of the present invention can be cut to produce short fibers, and these short fibers can be used to produce spun yarn. The amount of short polyester fibers of the present invention contained in the spun yarn is not limited, but it is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and most preferably 100% by mass, i.e., spun yarn consisting only of short polyester fibers of the present invention, is most preferable from the viewpoint of ease of recycling. In addition, the spun yarn may contain other fibers other than the short polyester fibers of the present invention. Any other fibers can be used as long fibers as long as they do not impair the effects of the present invention, but specifically, polyethylene terephthalate fibers, nylon fibers, acrylic fibers, cellulose fibers, etc. The other fibers may be in the form of long fibers or short fibers.

[0032] The thickness of the spun yarn can be set arbitrarily according to the purpose; for example, it can be between 4 and 200 counts (English cotton count).

[0033] The polyester fibers and spun yarns of the present invention are preferably used as sewing threads.

[0034] When used as sewing thread, it is preferable that the sewing thread contains 50% by mass or more of the polyester fiber or spun yarn of the present invention, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and most preferably 100% by mass, i.e., a sewing thread consisting only of the polyester fiber or spun yarn of the present invention, from the viewpoint of ease of recycling.

[0035] The polyester fibers of the present invention may be used in their raw silk state, or they may have undergone false twisting or false twisting blending. Furthermore, the form of the polyester fibers of the present invention and the spun yarn when used as sewing thread are not particularly limited, and they may be either untwisted or twisted, and may be used as a single fiber or spun yarn, or as a composite yarn made up of multiple strands. The appropriate form may be selected from the viewpoint of sewing thread strength and decomposition by moist heat treatment.

[0036] The method for producing polyester fibers according to the present invention will now be described. The method for producing polyester fibers according to the present invention preferably includes the following steps (a) to (c) in this order. (a) A process of polycondensing an esterified product consisting of a glycol component and a dicarboxylic acid component and an organic sulfonic acid compound at a temperature of 260 to 330°C. (b) A process to obtain a polyester resin by allowing the reactants after the polycondensation reaction to remain in a nitrogen atmosphere at a temperature of 280 to 350°C for 5 to 60 minutes. (h) A step of melt-spinning the polyester resin at a spinning temperature of 250 to 310°C to obtain spun yarn. (ii) The process of cooling and stretching the obtained spun yarn, then heat-treating it at a temperature of 100-200°C and winding it up.

[0037] In step (a), an esterification reaction product consisting of a glycol component and a dicarboxylic acid component and an organic sulfonic acid compound are subjected to a polycondensation reaction at a temperature of 260 to 330°C. As an esterification reaction product, for example, when producing polyethylene terephthalate as a polyester resin, terephthalic acid, ethylene glycol, and other copolymer components as needed can be reacted directly, water can be removed by distillation, and the product can be esterified to obtain an esterification reaction product that can be used as a raw material for polyester resin. Alternatively, dimethyl terephthalate, ethylene glycol, and other copolymer components as needed can be reacted, methyl alcohol can be removed by distillation, and the product can be transesterified to obtain an esterified product. The esterification reaction and transesterification reaction may be carried out in one step or in multiple steps.

[0038] In the present invention, it is preferable to use an organic sulfonic acid compound as a polymerization catalyst when carrying out the polycondensation reaction of the esterified product. By using an organic sulfonic acid compound as a polymerization catalyst, the content of the organic sulfonic acid compound in the polyester resin in the present invention can be set to a specific range, and as a result, the resulting polyester fiber can be made to have excellent decomposition properties when subjected to moist heat treatment at high temperatures for a certain period of time or longer, and the polyester fiber itself can be made to have sufficient strength. Furthermore, it is preferable to add an organic sulfonic acid compound to the esterification reaction product, then carry out an etherification reaction in advance using a known method, and then proceed with the polycondensation reaction.

[0039] The aforementioned organic sulfonic acid compounds are preferred and can be added to esterification reaction products as raw materials for polyester resins, for example, in solid form, slurry form, or as a solution dissolved in water, glycol, etc.

[0040] The amount of organic sulfonic acid compounds added varies depending on the type, but it is approximately 0.5 × 10⁻⁶ per mole of the acid component constituting the polyester resin. -4 ~40×10 -4 It is preferable to use moles, 1.0 × 10 -4 ~20.0×10 -4It is more preferable that the amount added is in moles. If the amount added is within the above range, a polyester resin suitable for producing polyester fibers with excellent decomposition properties and strength when subjected to moist heat treatment at high temperatures for a certain period of time or longer can be obtained.

[0041] The polycondensation reaction conditions are preferably at a temperature of 260 to 330°C, and more preferably at 270 to 300°C. If the polycondensation temperature is lower than 260°C, the resulting polyester resin tends to have too many carboxyl groups at the end, and the polycondensation reaction takes a long time, which may reduce productivity. On the other hand, if the temperature is higher than 330°C, thermal decomposition occurs, which also tends to result in too many carboxyl groups at the end of the resulting polyester resin, and the strength of the resulting polyester fibers may decrease, making them unsuitable for sewing thread.

[0042] In step (b), the reaction product after the polycondensation reaction between the esterification reaction product and the organic sulfonic acid compound is left to stand at a temperature of 280 to 350°C for 5 to 60 minutes under a nitrogen atmosphere to obtain a polyester resin. In the present invention, by performing step (b), the amount of carboxyl group terminals in the polyester resin can be set to the specified range, and as a result, the obtained polyester fibers can be made to have excellent decomposition properties by moist heat treatment at high temperature conditions for a certain period of time or longer.

[0043] If the temperature at which the reactants are retained under a nitrogen atmosphere is lower than 280°C, the resulting polyester resin will have fewer carboxyl-terminated groups, resulting in poor decomposition resistance to moist heat treatment at high temperatures for a certain period of time or longer. If the retention temperature is higher than 350°C, thermal decomposition occurs in the polyester resin, resulting in an excessive amount of carboxyl-terminated groups and a polyester fiber with low strength.

[0044] If the residence time is shorter than 5 minutes, the resulting polyester fibers will have fewer carboxyl-terminal groups, resulting in poor decomposition resistance to moist heat treatment at high temperatures for a certain period of time or longer. If the residence time is longer than 60 minutes, thermal decomposition occurs in the polyester resin, resulting in polyester fibers with too many carboxyl-terminal groups and low strength.

[0045] Furthermore, the resulting polyester resin can be pelletized for convenience when used in the next process of melt spinning.

[0046] In step (c), the polyester resin obtained in step (b) is melt-spun at a spinning temperature of 250 to 310°C. Before melt-spinning, drying or crystallization steps of the polyester resin may be performed as needed. If the spindle temperature during spinning is lower than 250°C, production problems such as broken yarn are likely to occur, and the strength and elongation of the resulting polyester fibers may be low. On the other hand, if the spindle temperature is higher than 310°C, thermal decomposition occurs in the polyester resin, making production problems such as broken yarn more likely, and the resulting polyester fibers will have low strength and elongation.

[0047] In process (ii), polyester fibers are obtained by cooling and stretching the spun yarn obtained by melt spinning, then heat-treating it at a temperature of 100-200°C and winding it up. If the heat treatment temperature is lower than 100°C, the resulting polyester fibers will have a high hot water shrinkage rate and will not be suitable for sewing thread. On the other hand, if the heat treatment temperature is higher than 200°C, production problems such as broken threads are more likely to occur. Heat treatment can be performed by installing a heat plate.

[0048] In the present invention, it is preferable to use a manufacturing method that includes the above steps (a) to (c) in this order, but the conditions for the melt spinning speed, drawing speed, and drawing ratio are not particularly limited. For example, when obtaining drawn yarn, one can perform melt spinning at a spinning speed of 1000 to 2000 m / min and wind up to obtain undrawn yarn, and then draw it up to about 2.0 to 4.0 times, or a spindraw method can be used in which spinning and drawing are performed continuously after melt spinning without winding up. It is also possible to obtain semi-undrawn yarn (POY), which can be obtained by melt spinning at a spinning speed of 2000 to 4000 m / min, in which case the above step (d) will not be performed.

[0049] Furthermore, as described above, the polyester fibers of the present invention can be used as raw silk or false-twisted yarn. When used as raw silk, a manufacturing method including steps (a) to (d) above in this order can be adopted. When used as false-twisted yarn, the fibers obtained after the manufacturing method of steps (a) to (c) above (undrawn yarn or semi-drawn yarn), or the fibers obtained after the manufacturing method of steps (a) to (d) above (drawn yarn) can be used as raw yarn and subjected to false-twist processing using a standard false-twisting machine.

[0050] In this invention, sewing thread can be formed using the polyester fibers obtained above. The method of forming the sewing thread is not limited to this, and the polyester fibers (multifilaments) obtained as described above can be twisted or otherwise processed as appropriate to form a sewing thread in the form of long fibers, or a sewing thread in the form of spun yarn using short fibers obtained by cutting the polyester fibers can be formed.

[0051] The polyester fibers 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, or other additives, as long as they do not impair the effects of the present invention. Examples of matting agents include inorganic oxides such as titanium dioxide, silicon dioxide, and calcium oxide. 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]

[0052] 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.

[0053] (1) Intrinsic viscosity [η] The obtained polyester resin was used as a sample, and measurements were taken at 20°C using an equimassive mixture of phenol and tetrachloroethane as the solvent. (2) Carboxylate terminal group concentration The obtained polyester multifilament was dissolved in 10 ml of benzyl alcohol, 10 ml of chloroform was added to this solution, and then the result was obtained by titration with a 1 / 10 N potassium hydroxide benzyl alcohol solution.

[0054] (3) Composition of polyester resin The obtained polyester resin was used as a sample. 10 mg of the sample was dissolved in 1 mL of a mixed solvent of deuterated chloroform / deuterated trifluoroacetic acid = 9 / 1 (mass ratio). The 1H-NMR spectrum was measured using a JEOL LA-400 NMR spectrometer, and the molar ratios of the dicarboxylic acid component, the sum of triethylene glycol and tetraethylene glycol, and the other glycol components were calculated from the integrated proton peak intensities of each component in the resulting chart. Furthermore, the polyester resin was hydrolyzed in a 0.75 N potassium hydroxide / methanol solution, and then neutralized by adding terephthalic acid. Next, the filtrate obtained by filtration was measured by gas chromatography, and quantification was performed using a pre-prepared calibration curve to calculate the molar ratio of triethylene glycol to tetraethylene glycol. From these molar ratios and the results of the 1H-NMR measurement mentioned above (the molar ratio of the total components of triethylene glycol and tetraethylene glycol to the molar ratio of each other glycol component), the molar ratio of triethylene glycol and the molar ratio of tetraethylene glycol in the total glycol components were calculated. (4) Sulfur content, metal content The obtained polyester resin was melt-molded at 300°C to obtain a disc-shaped molded plate with a diameter of 3 cm and a thickness of 1 cm. Quantitative analysis was performed using a calibration curve method with a Rigaku ZSX Primus X-ray fluorescence analyzer.

[0055] (5) Strength and elongation of polyester multifilament The strength and elongation of the obtained polyester multifilaments in their initial state before moist heat treatment were measured according to JIS L1013 8.5.1. (6) Hydrothermal contraction The resulting polyester multifilament was used to measure its thermal shrinkage rate according to JIS L1013 8.18.1.

[0056] (7) Strength retention rate after moist heat treatment A 10g portion of the obtained polyester multifilament was collected and used as a sample. The sample was sealed in a cylindrical container with a bath ratio of 1:50 between the sample and distilled water. The cylindrical container was placed in a dry oven heated to 130°C and subjected to moist heat treatment. After 1 hour or 24 hours, the sample was removed and dried at room temperature on a flat surface. The strength of the dried polyester multifilament was then measured using the method described in (5), and the strength retention rate after moist heat treatment was calculated using the following formula. Strength retention rate (%) = (Strength after moist heat treatment (cN / dtex)) / (Strength before moist heat treatment (cN / dtex)) × 100 (8) Stainability The obtained multifilaments were used to knit tubular fabric using a knitting machine (manufactured by Koike Machinery Works, 300 needles, 3.5-inch bobbin diameter). A dye solution was used with Sumikalon as the disperse dye and Disper TL as the dispersant, and the tubular fabric was dyed at 130°C for 30 minutes under conditions of 0.3% owf. Thirty dyed tubular fabrics were visually inspected to evaluate for the presence of dye streaks and uneven dyeing, and the number of good products without dye streaks or uneven dyeing was counted and evaluated as follows. ○: Number of good quality items is 27 or more. ×: The number of good quality items is 26 or less.

[0057] Example 1 A slurry of terephthalic acid and ethylene glycol (terephthalic acid:ethylene glycol = 1:1.6 (molar ratio)) was reacted at a temperature of 250°C and a pressure of 0.2 MPa, with a residence time of 8 hours, to obtain an esterified product (terephthalic acid:ethylene glycol = 100:111 (molar ratio)). The heated and melted esterified product A was added to a polycondensation reaction vessel heated to 280°C, and 2.0 × 10⁻⁶ 5-sulfosalicylic acid dihydrate (SS) was added. -4 The etherification reaction was carried out at 280°C for 10 minutes under normal pressure, with the addition of molars of the acid component.

[0058] Next, while maintaining the reaction vessel temperature at 280°C, the system pressure was gradually reduced to below 0.5 hPa after 60 minutes. Under these conditions, the polycondensation reaction was carried out with stirring. After the completion of the polycondensation reaction, the mixture was allowed to remain under a nitrogen environment at 290°C for 30 minutes, and then pelletized to obtain polyester resin. The polyester resin contained 21 ppm of sulfur. After drying the obtained polyester resin, it was fed into an extruder, extruded from a 290°C die, cooled, and then wound up. Subsequently, the obtained undrawn yarn was drawn at a temperature of 90°C, heat-treated on a 150°C heat plate, and wound up to obtain a 56dtex36fil polyester multifilament.

[0059] Example 2 A polyester multifilament was obtained in the same manner as in Example 1, except that the catalyst for the polycondensation reaction was changed to 2-sulfobenzoic anhydride (OSB).

[0060] Example 3 A polyester multifilament was obtained in the same manner as in Example 1, except that the heat treatment temperature was changed to 170°C.

[0061] Comparative Examples 1 and 2 Polyester multifilaments were obtained in the same manner as in Example 1, except that the polycondensation reaction temperature was changed to the temperature shown in Table 1. Comparative Example 3 A polyester multifilament was obtained in the same manner as in Example 1, except that the polycondensation reaction catalyst was changed to antimony trioxide.

[0062] Comparative Examples 4 and 5 Polyester multifilaments were obtained in the same manner as in Example 1, except that the residence temperature was changed to the temperature shown in Table 1. Comparative Examples 6 and 7 A polyester multifilament was obtained in the same manner as in Example 1, except that the residence time was changed to the temperature shown in Table 1.

[0063] Comparative Example 8 A polyester multifilament was obtained in the same manner as in Example 1, except that the reactant obtained after the polycondensation reaction was not allowed to remain in the environment.

[0064] Table 1 shows the results for the polyester resins and polyester fibers obtained in Examples 1-3 and Comparative Examples 1-8.

[0065] [Table 1]

[0066] The polyester multifilaments of Examples 1-3 were made of polyester resin having a specific composition, and therefore possessed sufficient strength and elongation to be practical as sewing thread. As a result, the decrease in strength was small after short-term moist heat treatment, and the decrease in strength occurred due to decomposition after prolonged moist heat treatment, making them suitable for forming sewing threads with a low environmental impact during recycling.

[0067] In Comparative Example 1, the polycondensation temperature was too low, resulting in a low molecular weight polyester resin and a high amount of carboxyl groups at the end of the structure, which led to low strength in the resulting polyester multifilament. In Comparative Example 2, the polycondensation temperature was too high, causing thermal decomposition of the polyester resin, resulting in a lower molecular weight and a higher amount of carboxyl groups at the end of the structure. Consequently, the resulting polyester multifilament had low strength.

[0068] Comparative Example 3 used antimony trioxide as a catalyst during the polycondensation reaction, and because the polyester resin did not contain sulfur components, the decomposition of the polyester multifilament by prolonged moist heat treatment was insufficient.

[0069] In Comparative Example 4, the residence temperature after the polycondensation reaction was too low, resulting in a polyester resin with a low amount of carboxyl-terminal groups. Consequently, the resulting polyester multifilament exhibited poor decomposition resistance to prolonged humid heat treatment. In Comparative Example 5, the residence temperature after the polycondensation reaction was too high, causing thermal decomposition of the polyester resin, resulting in a lower molecular weight and thus lower strength in the resulting polyester multifilament. In Comparative Example 6, the residence time after the polycondensation reaction was too short, resulting in a polyester resin with a low amount of carboxyl-terminal groups. Consequently, the resulting polyester multifilament exhibited poor decomposition resistance to prolonged humid heat treatment. In Comparative Example 7, the residence time after the polycondensation reaction was too long, causing thermal decomposition of the polyester resin, resulting in a lower molecular weight and thus lower strength in the resulting polyester multifilament. In Comparative Example 8, the reaction product obtained after the polycondensation reaction was used directly as a polyester resin without being allowed to settle, and melt spinning was performed. As a result, the polyester resin had a low amount of carboxyl-end groups, and the polyester multifilament had poor decomposition resistance to prolonged moist heat treatment.

Claims

1. A fiber made of a polyester resin containing a glycol component and a dicarboxylic acid component, The aforementioned polyester resin has a carboxyl-terminal group content of 30 to 100 equivalents / t and contains an organic sulfonic acid compound as a sulfur component at a concentration of 5 to 500 ppm. Polyester fiber with a strength of 2.5 cN / dtex or higher.

2. The polyester fiber according to claim 1, wherein the content of catalyst-derived metal components in the polyester resin is 1 ppm or less.

3. A polyester fiber according to claim 1 or 2, wherein the strength retention rate after moist heat treatment in 130°C hot water for 1 hour is 90% or more, and the strength retention rate after moist heat treatment for 24 hours is less than 70%.

4. A spun yarn containing polyester fibers as described in claim 1.

5. Sewing thread made of polyester fibers as described in claim 1.

6. A method for producing polyester fibers according to claim 1, comprising the following steps (a) to (d) in this order. (a) A process of polycondensing an esterified product consisting of a glycol component and a dicarboxylic acid component and an organic sulfonic acid compound at a temperature of 260 to 330°C. (b) A step of obtaining a polyester resin by retaining the reactants after the polycondensation reaction in a nitrogen atmosphere at a temperature of 280 to 350°C for 5 to 60 minutes. (h) A step of melt-spinning the polyester resin at a spinning temperature of 250 to 310°C to obtain a spun yarn. (ii) A process in which the obtained spun yarn is cooled and stretched, then heat-treated at a temperature of 100 to 200°C and wound up.

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