Polyester binder fiber

Abstract

To provide a polyester binder short fiber capable of favorably using as a binder fiber, exerting good adhesion effect without heightening a thermal adhesion treatment temperature, capable of improving a processing rate, and further capable of favorably using as a nonwoven fabric used for a special field such as a filter cloth and a permeable membrane for water treatment.SOLUTION: The polyester binder fiber is a binder fiber composed of a polyester resin including a dicarboxylic acid constituent, and a glycol constituent, where the glycol constituent includes ethylene glycol, and also includes diethylene glycol and triethylene glycol, the polyester resin is composed of polyester having a content of triethylene glycol in the glycol constituent of more than 0.1 mol% and 5.5 mol% or less, the fiber length is 1-30 mm, and the birefringence is lower than 0.015.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester binder fiber. [Background technology]

[0002] Conventionally, dry-laid and wet-laid nonwoven fabrics have been produced using short fibers cut to about 5 to 20 mm from fibers made of thermoplastic resins such as polyvinyl alcohol, polyamide, and polyester. In these cases, the fibers that form the main fibers are generally mixed with binder fibers having a melting point lower than that of the main fibers to produce a sheet, which is then heat-treated to melt the binder fibers and bond the main fibers together to produce a nonwoven fabric. Examples of fibers made of thermoplastic resins used as binder fibers include polyvinyl alcohol fibers, polyamide fibers, copolymer polyester fibers, etc. However, since these binder fibers are made of thermoplastic resins with low melting points, they may not have sufficient heat resistance or chemical resistance. Furthermore, in recent years, wetlaid nonwoven fabrics have also been used in specialized fields such as filter fabrics and permeation membranes for water treatment, and in such specialized fields, there is often a demand for minimal precipitation of impurities during use. Patent Document 1 discloses the use of undrawn polyester fibers as binder fibers. The polyester fibers described in Patent Document 1 have a polyetherester copolymer attached thereto to improve dispersibility in water, and when used in the above-mentioned specialized fields, impurities are likely to precipitate during use. Furthermore, since the polyester fiber of Patent Document 1 has a high birefringence, it is necessary to increase the thermal bonding temperature in the nonwoven fabric manufacturing process, and it has not been possible to increase the processing speed and improve production efficiency. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-339289 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a polyester binder staple fiber which can be suitably used as a binder fiber, which exhibits a good adhesive effect without increasing the thermal bonding temperature, which can improve the processing speed, and which can also be suitably used in nonwoven fabrics used in specialized fields such as filter cloths for water treatment and permeation membranes. [Means for solving the problem]

[0005] The present inventors have conducted extensive research to solve the above-mentioned problems and have arrived at the present invention. (1) Dicarboxylic acid component and glycol component Organic sulfonic acid compounds A binder fiber composed of a polyester resin containing The organic sulfonic acid compound is used in an amount of 0.5 × 10 per mole of the dicarboxylic acid component that constitutes the polyester resin. -4 ~40×10 -4 Molar included, A polyester in which the glycol component contains ethylene glycol, diethylene glycol, and triethylene glycol, and the content of triethylene glycol in the glycol component is more than 0.1 mol % and not more than 5.5 mol %. resin It consists of A polyester binder fiber having a fiber length of 1.0 to 30 mm and a birefringence of less than 0.015. 。 (2) The polyester binder fiber according to (1) above, wherein the glycol component contains diethylene glycol at a content of 2.5 mol % or more. (3) The polyester binder fiber according to (1) above, characterized in that the content of metal components derived from the catalyst is 1 ppm or less. (4) The polyester binder fiber according to (1) above, wherein the polyester resin is polyethylene terephthalate, the dicarboxylic acid component of which is terephthalic acid, and the glycol component of which is composed of three components: ethylene glycol, diethylene glycol, and triethylene glycol. (5) A polyester resin is obtained by a production method including a step of adding an organic sulfonic acid compound to a raw material of a polyester resin, 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, and then The method for producing polyester binder fibers according to (1) above is characterized in that the polyester resin is melt-spun, the resulting yarn is taken up at a speed of 700 to 1,500 m / min, stretched between rollers, and then cut to a length of 1 to 30 mm. (6) The method for producing polyester binder fibers according to (5) above, wherein the draw ratio between the rollers is more than 1.00 and not more than 1.10, and both the supply roller and the take-up roller are unheated rollers. [Effects of the Invention]

[0006] The polyester binder staple fiber of the present invention contains specific amounts of diethylene glycol and triethylene glycol in the polyester resin constituting the fiber, and therefore the binder fiber is easily melted, can be subjected to bonding processing by heat treatment at low temperatures, and the resulting nonwoven fabrics and the like have sufficient adhesive strength for practical use. Therefore, the processing speed in the thermal bonding treatment can be increased, and production efficiency can be improved. Furthermore, by using a sulfonic acid-based organic catalyst in the polymerization process of the polyester resin that constitutes the binder fiber, less impurities are precipitated during the use of the nonwoven fabric or paper made from the binder fiber than with fibers made using conventional metal-based catalysts, making it possible to provide high-quality synthetic fiber paper. DETAILED DESCRIPTION OF THE INVENTION

[0007] The polyester binder fiber of the present invention will be described in detail below. The present invention in The polyester resin is a mixture of a dicarboxylic acid component and a glycol component. Organic sulfonic acid compounds The polyester resin comprises: <Glycol ingredient> The glycol component constituting the polyester resin used in the polyester binder fiber of the present invention must contain ethylene glycol, as well as diethylene glycol and triethylene glycol, and the content of triethylene glycol in the glycol component must be more than 0.1 mol % and not more than 5.5 mol %.

[0008] The present inventors believe that the polyester resin constituting the binder fiber of the present invention, when its glycol component simultaneously contains ethylene glycol, diethylene glycol, and a predetermined amount of triethylene glycol, is likely to inhibit the crystalline structure of the fiber. The content of triethylene glycol in the glycol component of the polyester resin of the present invention must be greater than 0.1 mol % and less than 5.5 mol %, preferably 0.2 to 4.0 mol %. If the polyester resin contains less than 0.1 mol % triethylene glycol, the crystallinity is not easily inhibited and the resulting fiber is difficult to melt, resulting in a decrease in the adhesiveness of the resulting nonwoven fabric or paper, making it difficult to achieve the object of the present invention. On the other hand, if the content exceeds 5.5 mol %, the thermal properties and weather resistance are degraded, which is undesirable.

[0009] In the polyester resin of the present invention, an example of a method for simultaneously incorporating diethylene glycol and triethylene glycol into the glycol component and adjusting the contents thereof to fall within the above range is a method for including a step of carrying out an etherification reaction of the glycol component at a specific temperature for a specific period of time using an organic sulfonic acid compound as a polymerization catalyst in the production method for the polyester resin described below.

[0010] The polyester resin in the present invention contains ethylene glycol, diethylene glycol, and triethylene glycol, but may contain other glycol components. Specific examples thereof include 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-cyclohexanediethanol, 1 aliphatic glycols exemplified by 1,10-decamethylene glycol and 1,12-dodecanediol, and 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.

[0011] <Dicarboxylic acid component> Examples of the dicarboxylic acid component constituting the polyester resin of the present invention include 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, and dimer acids, and ester-forming derivatives thereof, and unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid. Examples of suitable aromatic dicarboxylic acids include carboxylic acids or their ester-forming derivatives, 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, and anthracenedicarboxylic acid, and their ester-forming derivatives may be used in combination. Among these, terephthalic acid and naphthalenedicarboxylic acid (especially 2,6-naphthalenedicarboxylic acid) are preferred in terms of resin properties and versatility, and terephthalic acid is more preferred.

[0012] Examples of polyesters composed of the above-mentioned components include copolymers such as polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, poly(1,4-cyclohexanedimethylene terephthalate), polyethylene naphthalate, polybutylene naphthalate, and polypropylene naphthalate. Among these, from the viewpoint of resin properties and versatility, it is preferable to use ethylene terephthalate units as the main repeating unit, and the other components mentioned above may be copolymerized. Furthermore, it is more preferable that the polyester resin in the present invention is polyethylene terephthalate in which the dicarboxylic acid component is composed of terephthalic acid and the glycol component is composed of three components: ethylene glycol, diethylene glycol, and triethylene glycol.

[0013] The polyester resin of the present invention may contain a cobalt compound for the purpose of improving color tone, etc., as long as the effects of the present invention are not impaired. The cobalt compound is not particularly limited, but specific examples include cobalt acetate, cobalt nitrate, cobalt chloride, cobalt acetylacetonate, cobalt naphthenate, and hydrates thereof. Cobalt acetate tetrahydrate is particularly preferred. The amount of the cobalt compound added is preferably 10 ppm or less, more preferably 5 ppm or less, and even more preferably 3 ppm or less, in terms of cobalt atoms, relative to the polyester resin.

[0014] <Catalyst> In the present invention, by using an organic sulfonic acid compound as a polymerization catalyst, the content of triethylene glycol and tetraethylene glycol in the obtained polyester resin can be within the range of the present invention.Examples of the organic sulfonic acid compound 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, and the like. 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-dinitrobenzene sulfonic acid 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,Examples of the sulfonyl anhydride 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, 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 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, methyl p-toluenesulfonate, 5-sulfoisophthalic acid, and salts thereof are preferred.

[0015] The organic sulfonic acid compound can be added to the polyester raw material, for example, in the form of a solid, a slurry, or a solution dissolved in water, glycol, or the like.

[0016] The amount of organic sulfonic acid compound added is , Po 0.5 × 10 for 1 mole of the acid component that constitutes the polyester resin -4 ~40×10 -4 mole and , 1.0×10 -4 ~20.0×10 -4 It is more preferable that the amount is 1 / 3 mole. If the amount added is less than the above range, a polyester resin with a high degree of polymerization cannot be obtained in a short time, and diethylene glycol and triethylene glycol cannot be simultaneously contained. Furthermore, the triethylene glycol content may become too low. On the other hand, if the amount added exceeds the above range, side reaction products may be generated or the polyester resin may become discolored.

[0017] Because an organic catalyst is used as the polymerization catalyst, the content of metal components derived from the metal catalyst in the resulting polyester resin can be reduced. If the metal component content is high, foreign matter may precipitate during the use of synthetic fiber paper obtained using binder fibers composed of this polyester resin for specific applications, resulting in defects. Because the binder fiber of the present invention also precipitates little impurities during use, synthetic fiber paper using the binder fiber of the present invention can be suitably used for filter cloths and permeation membranes for water treatment. In the binder fiber of the present invention, the content of metal components derived from the catalyst is preferably 1 ppm or less, more preferably 0.5 ppm or less, and even more preferably 0 ppm.

[0018] The binder fiber of the present invention has a birefringence of less than 0.0150, preferably 0.0100 to 0.0140. When the binder fiber of the present invention has a birefringence of less than 0.0150, the degree of molecular orientation of the polymer is insufficient, resulting in low crystallinity. Therefore, even if the thermal bonding treatment temperature is low, at least a portion of the fiber melts, and sufficient adhesive strength for bonding the constituent fibers together can be exerted.

[0019] A birefringence of less than 0.0150 can be achieved by appropriately adjusting the spinning speed during melt spinning using the polyester resin whose crystallinity is easily inhibited. Alternatively, the crystallinity can be adjusted by setting appropriate stretching conditions in the stretching step after spinning. Binder fibers with a birefringence of 0.0150 or more require high treatment temperatures during thermal bonding, which can cause deterioration of the constituent fibers (subject fibers) and hinder production efficiency.

[0020] The polyester resin constituting the binder fiber of the present invention may contain an organic, inorganic, or organometallic filler within the range that does not impair the effects of the present invention. This can suppress adhesion between fibers and improve the dispersibility of the fibers in water during the papermaking process.

[0021] The fiber length of the binder fiber of the present invention is 1 to 30 mm, preferably 3 to 20 mm, considering factors such as the dispersibility of the fibers in water during wet papermaking and the texture of the resulting synthetic fiber paper (nonwoven fabric). A fiber length of less than 1 mm not only reduces dispersibility in water, but also increases the cutting resistance during production, making the fibers stretched when cut and prone to tangling, making stable cutting difficult. The resulting fibers also tend to form clumps, significantly worsening dispersibility in water, which is undesirable. On the other hand, a fiber length exceeding 30 mm is undesirable because it deteriorates dispersibility of the fibers.

[0022] The intrinsic viscosity of the polyester resin constituting the binder fiber of the present invention is preferably 0.53 to 0.75. If the intrinsic viscosity exceeds 0.75, the nonwoven fabric or paper made from the polyester resin tends to have low tenacity. On the other hand, if the intrinsic viscosity is less than 0.53, not only will the formation of the nonwoven fabric or paper deteriorate, but the fibers will also be prone to shrinkage.

[0023] The intrinsic viscosity [η] is measured by the following method: A resin (0.2 g) is added as a sample to a solvent of an equal weight mixture of phenol and tetrachloroethane at 20°C to prepare a 0.5% solution, and the relative viscosity [ηr] is measured at 20°C according to a conventional method. The intrinsic viscosity [η] is calculated using the value obtained by the following formula.

number

[0024] Furthermore, the single fiber fineness of the binder fiber of the present invention is preferably 2.5 decitex or less, and more preferably 1.7 decitex or less. If the single fiber fineness exceeds 2.5 decitex, the increased fineness may cause the fiber to be insufficiently melted during the heat treatment step, depending on the heat treatment conditions such as the treatment speed, resulting in insufficient adhesion in the resulting nonwoven fabric or paper, and reduced strength. While there is no particular lower limit for the single fiber fineness, a value of 0.2 decitex or more is preferred for stable spinning.

[0025] The binder fiber of the present invention is suitable for use as a binder fiber in paper made by a wet papermaking process, particularly in synthetic fiber paper. Typically, when producing synthetic fiber paper, the binder fiber is fed into a papermaking machine together with polyester fiber, which is the main fiber, to produce a papermaking web, which is then subjected to a dry heat treatment to obtain the synthetic fiber paper.

[0026] The synthetic fiber paper obtained in this manner may be subjected to various processes depending on its intended use. For example, after the thermal bonding treatment, the paper may be subjected to thermocompression bonding using a calender roll to increase its density, or the paper surface may be subjected to a resin treatment to impart various functions. In such processes, a heat treatment at a temperature higher than that used in the thermal bonding treatment may be performed. However, the binder fiber of the present invention, particularly one having ethylene terephthalate as the main repeating unit, has a high polymer melting point and excellent heat resistance, and therefore does not deteriorate even when subjected to high-temperature heat treatment in these processes.

[0027] Next, an example of the method for producing the binder fiber of the present invention will be described. <Method of manufacturing polyester resin> The method for producing the polyester resin constituting the binder fiber of the present invention includes the steps of adding an organic sulfonic acid compound to a raw material for the polyester resin, 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.

[0028] In the polyester resin, by including a step of carrying out an etherification reaction under specific conditions before carrying out a polycondensation reaction, diethylene glycol and triethylene glycol are simultaneously contained, and the content of triethylene glycol can be set within the above range. Furthermore, the content of diethylene glycol and the content of triethylene glycol can be set within the preferred range.

[0029] The method for preparing the esterified product will now be described in detail. A slurry containing preferably 1.02 to 2.5 mol, more preferably 1.03 to 1.8 mol, of ethylene glycol per mol of dicarboxylic acid or its ester derivative is prepared, and this is continuously fed to an esterification reactor to obtain an esterified product. The esterification reaction is carried out using, for example, a multistage apparatus in which one to three esterification reactors are connected in series, under conditions in which ethylene glycol is refluxed, while water or alcohol produced by the reaction is removed from the system using a rectification column.

[0030] The temperature of the first stage esterification reaction is preferably 240 to 270°C, more preferably 245 to 265°C. The pressure is 0.2 to 3 kg / cm. 2 G is preferably 0.5 to 2 kg / cm 2 G is more preferred. The temperature of the final stage of the esterification reaction is preferably 250 to 290°C, more preferably 255 to 275°C. The pressure is 0 to 1.5 kg / cm. 2 G is preferably 0 to 1.3 kg / cm 2 G is more preferred.

[0031] When the esterification reaction is carried out in three or more stages, the reaction conditions for the intermediate esterification reactions are preferably between those for the first stage and the final stage. The reaction rate of the multi-stage esterification reaction is preferably 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 esterified products, the molecular weight of which is preferably about 500 to 5,000.

[0032] When terephthalic acid is used in the esterification reaction, the reaction can be carried out without a catalyst due to the catalytic action of terephthalic acid as an acid.

[0033] An organic sulfonic acid compound is added to the esterified product obtained as described above, followed by an etherification reaction, followed by a polycondensation reaction to obtain the polyester resin used in the present invention.

[0034] The amount of organic sulfonic acid compound added depends on the type, but is generally 0.5 x 10 per mole of the acid component that constitutes the polyester resin. -4 ~40×10 -4 It is preferable to use a molar ratio of 1.0 × 10 -4 ~20.0×10 -4 It is more preferable that the amount is 1 / 3 mole. If the amount added is less than the above range, a polyester resin with a high degree of polymerization cannot be obtained in a short time, and diethylene glycol and triethylene glycol cannot be simultaneously contained. Furthermore, the triethylene glycol content may become too low. On the other hand, if the amount added exceeds the above range, side reaction products may be generated or the polyester resin may become discolored.

[0035] <Etherification reaction> The temperature of 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 lower than 240°C, the reaction may not proceed sufficiently, making it impossible to simultaneously incorporate diethylene glycol and triethylene glycol into the glycol component of the polyester resin. Furthermore, the diethylene glycol content and the total triethylene glycol content may fall outside the preferred range. If the temperature of the etherification reaction exceeds 300°C, decomposition of the esterified product proceeds during the reaction, and the mechanical properties of the resulting polyester resin, such as elongation at break, may decrease when molded into a molded article.

[0036] The etherification reaction time (heating time) is preferably 5 to 120 minutes, and more preferably 10 to 60 minutes. If the reaction time is less than 5 minutes, the etherification reaction does not proceed sufficiently, and the glycol component of the polyester resin may not contain diethylene glycol and triethylene glycol simultaneously, and the triethylene glycol content may not be within a specific range. Furthermore, the diethylene glycol content, tetraethylene glycol content, and total triethylene glycol content may fall outside the preferred range. If the reaction time exceeds 120 minutes, decomposition of the esterified product proceeds during the reaction, and the mechanical properties of the resulting polyester resin may deteriorate.

[0037] The etherification reaction is preferably carried out under normal pressure or pressure, and the pressure is 0 to 3.0 kg / cm. 2 Preferably it is G.

[0038] By adjusting the molar ratio (G / A) of the glycol component (G) to the acid component (A) in the raw materials used in the etherification reaction, diethylene glycol and triethylene glycol can be simultaneously contained in the polyester resin, and the amounts of diethylene glycol and triethylene glycol produced can be adjusted. G / A is preferably 1.05 to 3.00, and more preferably 1.10 to 2.00. To adjust G / A, a glycol component such as ethylene glycol may be added to the raw materials for the polyester resin, as needed. If G / A is less than 1.05, the amount of triethylene glycol produced may be too small, while if G / A is more than 3.00, the amount of triethylene glycol produced may be too large.

[0039] <Polymerization reaction> After the etherification reaction, a polycondensation reaction is carried out to obtain the polyester resin of the present invention. Examples of the polycondensation reaction include melt polycondensation reaction. 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 in the first stage of the polycondensation reaction is preferably 250 to 290°C, more preferably 260 to 280°C. The pressure is preferably 500 to 20 Torr, more preferably 200 to 30 Torr.

[0040] <Spinning and drawing conditions> First, the polyester resin obtained by polymerization using the method described above is melt-spun using a spinning machine equipped with a screw extruder or the like, and the resulting yarn is cooled and solidified and taken up at a speed of 700 to 1,500 m / min. The resulting yarn is then collected into a yarn bundle, which is then drawn between rollers at a draw ratio equal to or less than the natural draw ratio (NDR). The draw ratio is the speed ratio between the supply roller and the take-up roller (the value obtained by dividing the speed of the take-up roller by the speed of the supply roller), and a preferred draw ratio is greater than 1.00 and equal to or less than 1.10. It is also preferable to use unheated rollers for both the supply roller and the take-up roller. The drawn yarn bundle is then coated with an oil, fed to a rotary cutter, and cut to a desired fiber length. [Example]

[0041] The present invention will be described in more detail below with reference to examples, in which various values ​​were measured as follows: (1) Composition of polyester resin 10 mg of sample was dissolved in 1 mL of a mixed solvent of deuterated chloroform / deuterated trifluoroacetic acid = 9 / 1 (mass ratio), and the sample was analyzed using a JEOL LA-400 NMR spectrometer. 1 H-NMR was measured, and the molar ratio of the dicarboxylic acid component, the total component of triethylene glycol and tetraethylene glycol, and each of the other glycol components was calculated from the integrated proton peak intensity of each component in the obtained chart. In addition, the polyester resin was hydrolyzed in a 0.75N potassium hydroxide / methanol solution, and then neutralized by adding terephthalic acid. Next, the filtrate obtained by filtration was measured by gas chromatography, and quantified using a previously prepared calibration curve to calculate the molar ratio of triethylene glycol to tetraethylene glycol. 1 The molar ratio of triethylene glycol in all glycol components was calculated from the H-NMR measurement results (the molar ratio of the total component of triethylene glycol and tetraethylene glycol to each of the other glycol components).

[0042] (2) Metallic component content The binder fibers were melted at 300°C to obtain a disk-shaped molded plate with a diameter of 3 cm and a thickness of 1 cm. Quantitative analysis was performed using a Rigaku ZSX Primus X-ray fluorescence analyzer by the calibration curve method.

[0043] (3) Single fiber fineness Measurements were performed in accordance with JIS L1015 8.5.1 Method A, except that the measurement sample was cut to a length of 20 mm, 100 fibers were taken out and the mass was measured, and the measurement was performed four times.

[0044] (4) Fiber length The measurements were carried out in accordance with JIS L1015 8.4.1 Direct Method (Method C), except that the number of measurements was set to 25.

[0045] (5) Birefringence Using a polarizing microscope with a sodium lamp as a light source, the retardation was calculated by the Berek compensator method while the binder fiber was immersed in α-bromonaphthalene. The birefringence was measured at 50 random points (n=50) along the fiber length, and the average value of these birefringences was taken as the birefringence.

[0046] (6) Dispersibility 2000cm 3 1 kg of water at 30°C was weighed into a beaker, 1.0 g of binder fiber was added, and the mixture was stirred with a DC stirrer (the stirring blade was a three-screw type with a diameter of approximately 50 mm) at a rotation speed of 3000 rpm for 1 minute. The dispersion state after 1, 5, and 10 stirrings was visually evaluated according to the following criteria. A rating of ○ to △ was considered to be acceptable. Rating Number of shives ○: 0 pieces △: 1~5 pieces ×: 6 or more

[0047] (9) Strong synthetic fiber paper A sample for strength measurement, 50 mm wide x 150 mm long, was cut from the synthetic fiber paper obtained in Example 1. The strength of each sample in the longitudinal direction was measured (n=5) in accordance with JIS L 1913 6.3.1 Tensile strength, with a gripping distance of 100 mm and a pulling speed of 100 mm / min, and the average value was taken as the strength.

[0048] Example 1 A slurry of terephthalic acid and ethylene glycol (terephthalic acid:ethylene glycol = 1:1.6 (molar ratio)) was continuously fed into 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 to obtain an esterified product A (terephthalic acid:ethylene glycol = 100:111 (molar ratio)). The heated and melted esterified product A was charged into a polycondensation reactor heated to 280°C, and 2.0 × 10 2-sulfobenzoic anhydride (OSB) was added. -4 The etherification reaction was carried out at 280°C for 10 minutes under normal pressure. Next, while maintaining the temperature of the reactor at 280°C, the pressure in the system was gradually reduced to 0.5 hPa or less after 60 minutes. Under these conditions, the polycondensation reaction was carried out with stirring for 3 hours to obtain a polyester resin. The amount of triethylene glycol was 0.8 mol%.

[0049] The polyester resin polymerized by the above method was dried at 130°C, melted at 295°C, and extruded through a spinneret (2010 spinning holes) at a throughput rate of 334 g / min. The extrusion was then taken up at a spinning speed of 1176 m / min to obtain a polyester binder continuous fiber with a single fiber fineness of 1.4 dtex. The fiber was formed into a tow of approximately 800,000 dtex, stretched at a draw ratio of 1.05 (without stretching heat treatment), oiled, squeezed to a moisture content of approximately 18% by mass, and cut to a length of 5 mm with a drum cutter to obtain a binder fiber (short cut fiber) with a single fiber fineness of 1.4 dtex.

[0050] Next, the obtained binder fiber and polyethylene terephthalate short-cut fiber (manufactured by Unitika Ltd.) with a single fiber fineness of 0.6 dtex and a length of 5 mm obtained by drawing and heat treatment were used as the main fiber. <121> 0.6T5) was used. The binder fiber / subject fiber (mass ratio) was 60 / 40 and dispersed in water, and the fiber concentration was adjusted to 0.04% by mass, and then the resultant was fed to a cylinder paper machine. After obtaining a papermaking web, the web was subjected to a dry heat treatment (2 minutes) in a Yankee dryer at 140°C to remove excess moisture from the web, and then passed through a thermal calender consisting of a pair of smooth-surfaced rolls to be subjected to thermal compression bonding (thermal bonding treatment) at a roll setting temperature of 210°C, a linear pressure of 60 kg / cm, and a processing speed of 6 m / min, resulting in a basis weight of approximately 25 g / m 2 As a result, synthetic fiber paper of

[0051] The strength of the resulting synthetic fiber paper was 112 N / 50 mm width, and the binder fibers were well melted to thermally bond the constituent fibers together, providing excellent strength.

[0052] The conditions for passing the sheet through the thermal calendaring device were a roll temperature of 200°C, a linear pressure of 60 kg / cm, and a processing speed of 5 m / min. The temperature was set low and the processing speed was increased to perform thermal compression bonding (thermal bonding treatment), resulting in a basis weight of approximately 25 g / m. 2 The synthetic fiber paper was measured for its strength, which was 110 N / 50 mm width, and was found to have excellent strength sufficient for practical use.

[0053] Furthermore, as is clear from Table 1, the binder fiber of Example 1 had physical property values ​​within the ranges specified in the present invention, and therefore had excellent dispersibility and, as described above, was a synthetic fiber paper with high adhesiveness. [Table 1]

Claims

1. A binder fiber made of a polyester resin containing a dicarboxylic acid component, a glycol component, and an organic sulfonic acid compound, the organic sulfonic acid compound is contained in an amount of 0.5×10 −4 to 40×10 −4 mol per 1 mol of the dicarboxylic acid component constituting the polyester resin, the glycol component comprises a polyester resin that contains ethylene glycol, diethylene glycol, and triethylene glycol, and the content of triethylene glycol in the glycol component is more than 0.1 mol% and not more than 5.5 mol%, A polyester binder fiber having a fiber length of 1 to 30 mm and a birefringence of less than 0.

015.

2. 2. The polyester binder fiber according to claim 1, wherein the glycol component contains diethylene glycol in an amount of 2.5 mol % or more.

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

4. 4. The polyester binder fiber according to claim 1, wherein the polyester resin is polyethylene terephthalate, the dicarboxylic acid component of which is terephthalic acid, and the glycol component of which is composed of three components: ethylene glycol, diethylene glycol, and triethylene glycol.

5. A polyester resin is obtained by a production method including a step of adding an organic sulfonic acid compound to a raw material of a polyester resin, 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 a glycol component, and then 2. The method for producing polyester binder fibers according to claim 1, wherein the polyester resin is melt-spun, the resulting yarn is taken up at a speed of 700 to 1,500 m / min, stretched between rollers, and then cut to a length of 1 to 30 mm.

6. 6. The method for producing polyester binder fibers according to claim 5, wherein the draw ratio between the rollers is more than 1.00 and not more than 1.10, and both the supply roller and the take-up roller are unheated rollers.

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