Manufacturing method of polyester fiber

Abstract

To provide a manufacturing method for obtaining a polyester fiber of thick fineness suitable for industrial material uses.SOLUTION: In a manufacturing method of a polyester fiber, when cooling a polyester fiber extruded from a spinneret and containing ethylene terephthalate as the main repeating unit, a cooling medium containing water as the main component is atomized as a mist from three or more nozzles arranged circumferencially in a cooling dome (metallic cylinder).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing polyester fibers for use in industrial materials, and to polyester fibers obtained thereby. [Background technology]

[0002] Traditionally, fibers made of polyethylene terephthalate or polyesters mainly composed of polyethylene terephthalate have been widely used not only for clothing applications but also for industrial materials applications due to their excellent mechanical properties, dimensional stability, and durability. One of the industrial material applications is industrial material nets, which come in a wide variety of forms, including safety nets that are installed to cover construction sites to absorb the impact of people falling, protective nets to prevent tools from scattering, revetment nets installed on riverbanks and coasts to protect against erosion from water flow, snow protection nets for agriculture, shading nets, and fishing nets used for various fishery applications. Common characteristics required for these nets include high strength so that they do not easily break, and fatigue resistance and weather resistance that do not easily become brittle even in outdoor environments where construction periods are long.

[0003] Furthermore, industrial material nets are prone to deterioration due to friction caused by external disturbances such as materials, animals and plants, and the fibers rubbing against each other at the knots when the net is subjected to load, so in order to prevent deterioration of the net strength, it is required that the net be made of fibers with excellent abrasion resistance.

[0004] Accordingly, there has been a demand for fibers with excellent abrasion resistance and a fineness of 50 dtex or more for use in fishing nets, ropes, etc. However, such thick fibers are usually obtained by doubling monofilaments, and in most cases, the manufacturing method involves spinning, followed by liquid cooling such as water cooling, followed by drawing, which results in a slow winding speed and high costs.

[0005] Therefore, various methods using mist, particularly water mist, to improve cooling efficiency are known.

[0006] For example, Patent Document 1 describes how, when the spun yarn is cooled and solidified and then taken up at a high speed of 6000 m / min or more, the spun yarn is cooled by spraying a liquid mist at a position 2 cm or more below the surface of the spinneret. The mist particle size is described as 0.5 μm in an example, but as a highly efficient cooling method, liquid mist with a high specific heat is used as a cooling medium to utilize the heat of vaporization, and the end point of thinning is shortened even in a high discharge region, making it possible to focus the yarn within 1 m.

[0007] In Patent Document 2, multiple spray nozzles are arranged 0.5 m to 1.5 m below a synthetic fiber discharge nozzle, and the yarn is cooled by spraying a mist of refrigerant using the spray nozzles. When the particle size of the mist is 1 / 10 to 1 / 50 of the diameter of the undrawn yarn, desirable results can be obtained, such as a good surface condition of the cooled yarn and no excess refrigerant remaining on the yarn surface.

[0008] Patent Document 3 claims that the cooling efficiency can be improved more reliably by spraying liquid mist in an oppositely charged state onto the spun yarn and by spraying liquid mist of a specific particle size.

[0009] In Patent Document 4, when synthetic fibers are melt-spun in the vertical direction, the spun yarn is passed through a cooling chamber provided below a spinneret, and a cooling medium is sprayed into the cooling chamber while sucking in internal water vapor at the bottom of the cooling chamber, thereby maintaining a constant humidity level within the cooling chamber and preventing the coolant from dripping, thereby providing a spinning cooling method and device that is safe despite being a water-cooling method, and that performs efficient cooling with a small amount of coolant.

[0010] Patent Document 5 describes a method for producing thick polyester fine yarns in which a cooling medium at 4 to 15°C is sprayed onto the yarn traveling 15 to 30 cm below a spinneret to cool it unevenly, followed by cooling with normal air, and then the yarn is passed through a heating cylinder heated to 100 to 240°C and wound up. It states that this method provides a low-cost and easy method for producing thick fine yarns in which thick parts and thin parts are randomly distributed along the fiber axis direction. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 59-66507 [Patent Document 2] Japanese Patent Application Publication No. 60-224807 [Patent Document 3] Japanese Patent Application Publication No. 58-174614 [Patent Document 4] Japanese Patent Application Publication No. 3-137209 [Patent Document 5] Japanese Patent Application Publication No. 8-209441 Summary of the Invention [Problem to be solved by the invention]

[0012] However, the technology of Patent Document 1 has a small cooling effect because the mist particle size is too small, and when the discharge rate is 100 dtex (24 g / min) or more for single fibers, cooling is insufficient and the technology is not applicable. In other words, when the single fiber is 100 dtex or more, the yarn is difficult to cool and solidify, and it melts in front of the take-up roller, making the spinnability unstable, so further cooling of the yarn is necessary. This is because the cooling time is short in high-speed spinning, and cooling is insufficient with a mist particle size of about 0.5 μm.

[0013] Although Patent Document 2 describes a method for spinning and cooling synthetic fibers, it is actually a method for spinning and cooling polypropylene fibers, and cannot be directly applied to polyester fibers, which have a higher melting point.

[0014] In Patent Document 3, the mist particle size is too small, so the cooling effect is small, and the fiber yarn fineness of the obtained fiber is small, about 10 to 40 dtex. In addition, since the mist needs to be sprayed in a reversely charged state, it is necessary to introduce equipment for charging the yarn, which leads to increased costs.

[0015] In Patent Document 4, the temperature inside the chamber is kept constant by filling the chamber with mist, but there is no description about the number of nozzles or the spraying direction during spraying, and there is a problem as to whether a sufficient cooling effect and cooling uniformity can be guaranteed for harvesting fibers with a large fineness, particularly fibers with a large fineness of 100 dtex or more.

[0016] Patent Document 5 relates to a technology for uneven cooling in order to produce thick, thin polyester yarns in which thick and thin parts are randomly distributed along the fiber axis direction, and does not provide uniform cooling properties.

[0017] The present invention was achieved as a result of extensive research into the problems that could not be solved by the above-mentioned conventional techniques. [Means for solving the problem]

[0018] The production method of the present invention for achieving the above object is a polyester fiber production method characterized in that, when cooling polyester fibers having ethylene terephthalate as a main repeating unit extruded from a spinneret, a cooling medium mainly composed of water is sprayed as a mist from three or more nozzles arranged circumferentially in a cooling cylinder (metal cylinder).

[0019] In addition, the polyester fiber obtained in the present invention preferably has a tensile strength of 5.0 cN / dtex or more and a single fiber fineness of 100 dtex or more. Effect of the Invention

[0020] According to the present invention, since the yarn can be uniformly cooled while maintaining a high cooling effect, it is possible to spin a polyester fiber having a single fiber fineness of 100 dtex or more without causing yarn breakage due to a drawing difference. In other words, by achieving both high cooling efficiency and uniform cooling, stable spinning of a large-fiber polyester fiber is possible. [Brief description of the drawings]

[0021] [Figure 1] This is a schematic diagram of an example of spraying mist onto yarn (three nozzles) seen from above. The mist sprayed from the nozzles is shown to spread out in a fan shape. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The method for producing the polyester fiber of the present invention will be described. The method for producing the polyester fiber of the present invention preferably employs melt spinning, drawing, and relaxation heat treatment of polyethylene terephthalate, which allows mass production at low cost and with little breakage of single fibers in long-term production, and will be described below using these as examples.

[0023] First, polyester chips stored in a spinning hopper under a nitrogen atmosphere are mixed with, for example, black master polyester chips, as necessary, within a range that does not impair the effects of the present invention, and then supplied to a single-shaft extruder type melt spinning device for melt spinning. The molten polymer is metered according to the final fineness of the multifilament using a gear pump, filtered through a metal nonwoven fabric filter in a spinning pack, and spun from a die with discharge holes arranged circumferentially. In addition to the single-shaft extruder, melt kneading can be performed using a twin-shaft extruder, pressure melter, etc., as long as the polyester fiber of the present invention can be obtained. When adding additives, etc., a method of directly mixing with an extruder or a method of preparing polyester chips containing additives, etc. at a high concentration in advance and mixing them before melting can be adopted. The melt spinning temperature can be appropriately changed depending on the intrinsic viscosity, the type of polymer, etc., but is preferably 270 to 330°C. When such a temperature range is satisfied, the polymer can obtain fluidity when melted, and the variation in quality can be reduced, and excessive thermal decomposition of the polymer can be suppressed, which is suitable for the polyester fiber of the present invention.

[0024] Here, as the polyester constituting the polyester fiber of the present invention, a polyester having ethylene terephthalate as the main repeating unit, in which the main acid component is terephthalic acid or its ester-forming derivative, and the main glycol component is ethylene glycol, is preferably used. Insofar as the effect of the present invention is not impaired, the polyester may contain an acid component such as isophthalic acid, adipic acid, sebacic acid, dimer acid, 2-6-naphthalenedicarboxylic acid, or 1,4-cyclohexanedicarboxylic acid, or a diol component such as butanediol, hexanediol, diethylene glycol, neopentyl glycol, or 1,4-cyclohexanediol.

[0025] Also, a polymerization aid may be contained in the polymer. For example, during the manufacturing process of the polyester fiber, polymerization aids such as magnesium acetate, calcium acetate, cobalt acetate, manganese acetate, etc. may be contained for the purpose of promoting the transesterification reaction of dimethyl terephthalate and ethylene glycol, and polymerization aids such as germanium dioxide and antimony trioxide may be contained for the purpose of promoting the polymerization reaction. Also, titanium oxide may be contained in the polymer for the purpose of matting. Furthermore, the polyester fiber for industrial material nets of the present invention may contain dyes or pigments in the raw polymer on the fiber surface, which is advantageous in terms of manufacturing costs because the dyeing process can be omitted. The colorant is not particularly limited, and inorganic colorants such as carbon black and iron oxide, and organic colorants such as cyanine, anthraquinone, azo, and perinone may be used.

[0026] In the present invention, in order to obtain excellent mechanical properties for industrial material net applications, the polyester used has a higher degree of polymerization, and the relative viscosity ηr of an 8 wt / vol% orthochlorophenol solution at 25°C is measured using an Ostwald viscometer, and the resulting intrinsic viscosity (IV) is preferably 0.8 to 1.3, and more preferably 1.0 to 1.2.

[0027] The area directly below the spinneret is surrounded by a heating cylinder and a heat insulating cylinder from the upper end of the spinneret surface, and the spun yarn is passed through the cylinder heated to a temperature of 170 to 350 ° C and then cooled. At this time, a mist made by spraying a mist of liquid is used as a cooling medium. That is, the yarn is cooled by spraying the mist on it. The mist temperature is 10 to 30 ° C, more preferably 15 to 25 ° C. The mist adheres to the yarn and removes heat when it evaporates, thereby cooling the thick fiber. The liquid of the mist is preferably a cooling medium (liquid) mainly composed of water, more preferably water. The particle size of the mist is 30 to 200 μm, preferably 50 to 150 μm. By setting the particle size within this range, it is possible to remove a sufficient amount of heat when the mist adheres to the yarn and evaporates, and it is possible to prevent yarn breakage due to uneven cooling, and it is possible to achieve both a sufficient cooling effect and uniform cooling for stable spinning of thick fibers. If the particle size is 30 μm or less, the amount of heat that the mist removes when it adheres to the yarn and vaporizes is reduced, so the cooling effect is insufficient, and the yarn melts and breaks. On the other hand, if the particle size is more than 200 μm, uneven cooling occurs between the part where the mist adheres and the part where it does not, uneven orientation occurs, and yarn breakage occurs due to stretching. The particle size of the mist refers to the average particle size measured by the method described below. The mist spray flow rate is 20 to 150 ml / min, more preferably 25 to 60 ml / min. In addition, by spraying in the cooling cylinder, a large amount of mist can adhere to the yarn, and the cooling effect can be further improved. At this time, the cooling cylinder has a diameter of 20 to 100 cm, more preferably 50 to 70 cm, and a length of 1 to 2 m, more preferably 1.2 m to 1.7 m, so that the mist can be uniformly drifted without liquefying, and uniform cooling can be achieved. In addition, the cooling cylinder is preferably made of metal, so that the cooling effect can be improved. By spraying the mist toward the yarn from the entire circumference using three or more, preferably six or more, nozzles arranged at equal intervals on the same plane, it is possible to ensure a cooling effect sufficient for harvesting thick fibers and further uniformity of cooling. The spray angle is preferably perpendicular to the yarn or directly below (in the yarn travel direction), and more preferably at an angle of about 30° from the perpendicular direction to the yarn.

[0028] The cooled yarn (undrawn yarn) is then oiled by an oiling device. Either aqueous or non-aqueous oils can be used. It is preferable to use an oil that contains a smoothing agent as the main component, a surfactant, an antistatic agent, an extreme pressure agent, etc., and excludes components that are active on polyester resin. For example, it is preferable to use a non-aqueous oil in which an alkyl ether ester as a smoothing agent component, an alkylene oxide additive of higher alcohol as a surface active agent component, and an organic phosphate salt as an extreme pressure agent component are diluted with mineral oil. The method of oiling is not limited as long as it can be applied uniformly to the fiber surface. As an example, a method of applying oil uniformly by contacting the running yarn with two oiling rolls so as to sandwich them from the left and right is preferable.

[0029] The undrawn yarn to which the oil agent has been applied is wound around a yarn feed roll (1GR) rotating at a predetermined rotation speed and taken up. The speed of the yarn feed roll (1GR) is preferably 300 to 1000 m / min or more, more preferably 500 to 800 m / min or more. In addition, since the undrawn yarn is preheated before entering the hot drawing process, the temperature of the 1GR is preferably 70 to 100°C. By satisfying such a range, the polyester fiber of the present invention can be mass-produced while obtaining good production efficiency and stable spinnability. In addition, since the cooling of the single fiber progresses sufficiently with an increase in the take-up speed, it is also suitable for suppressing deterioration in quality and grade by reducing Uster spots. The undrawn yarn taken up by the 1GR is subjected to a hot drawing treatment, but it is preferable to draw it continuously after taking up once, or without taking up once.

[0030] As an example of the drawing method, a Nelson type roll, which has two rolls as one unit like the yarn supply roll (1GR), is arranged in line with a second yarn supply roll (2GR), a first drawing roll (3GR), a heat setting roll (4GR), and a relaxation roll (5GR), and the yarn is sequentially wound around them and subjected to a drawing heat treatment.

[0031] First, between 1GR and 2GR, preliminary drawing is performed to bundle the yarn. The preliminary drawing treatment in the present invention is different from normal drawing, and is intended to improve the bundleability of the yarn and to compensate for the lack of tension due to shrinkage during heat treatment. The preliminary drawing ratio applied to the polyester fiber of the present invention is not limited as long as it does not affect the strength and elongation properties, but is preferably 1.01 to 1.10 times. The bundled yarn is subjected to one-stage drawing between 2GR and 3GR, and the temperature of 2GR is preferably 70 to 120°C, and the temperature of 3GR is preferably 100 to 140°C. By satisfying the roll temperature range, the polyester fiber can be uniformly molecular oriented while being sufficiently heated. In addition, the one-stage drawing ratio is preferably 1.0 to 6.5 times, and more preferably 3.0 to 5.0 times. By adopting such a one-stage drawing ratio, stress can be raised at a low elongation in the load-elongation curve characteristic of fibers obtained by multi-stage hot drawing, leading to high modulus and high toughness. Next, heat treatment is performed in the 4GR, but considering that the drawing tension decreases due to yarn swaying caused by fiber shrinkage, it is preferable to perform two-stage drawing between the 3GR and the 4GR, and the final drawing ratio, which is the speed ratio from the 1GR to the 4GR, is preferably 5.0 to 7.0 times. Furthermore, in the case of industrial material nets, since heat treatment is performed in the net manufacturing process, it is preferable to heat treat the yarn at a 4GR temperature of 200 to 240°C to impart thermal dimensional stability. The yarn after drawing is relaxed between the 4GR and the 5GR, and the relaxation rate when the overall draw ratio is 100% is preferably in the range of 1.0 to 8.0%. Incidentally, even within the above range, when a high draw ratio is set, the frequency of single yarn breakage tends to increase, so that appropriate conditions are selected, such as changing the melting temperature to an extent that the properties within the range specified in the present invention are obtained, and setting the heat treatment temperature on the higher side.

[0032] In order to converge the yarn and obtain a high-quality polyester fiber with less fuzzing, it is preferable to spray a high-pressure fluid onto the fiber yarn between the 2GR and the 3GR, between the 3GR and the 4GR, between the 4GR and the 5GR, and between the 5GR and the winding device, to draw the yarn while converging it, and to wind it up after imparting entanglement. The fluid pressure is preferably changed appropriately depending on the total fineness, single fiber fineness, drawing speed, etc. of the yarn, and is preferably sprayed within a range of 0.1 to 0.8 MPa.

[0033] The range of the number of entanglements is not particularly limited, but it is preferable to impart the number of entanglements as uniformly and as much as possible in the fiber longitudinal direction. By imparting entanglements, the unwinding property of the yarn from the wound product and the processability of the yarn can be improved, and the production loss rate in the advanced processing step can be reduced.

[0034] The characteristics of the polyester fiber obtained by the production method of the present invention will be described in detail below.

[0035] The tensile strength of the polyester fiber obtained by the manufacturing method of the present invention is preferably 5.0 cN / dtex or more for industrial material nets, and more preferably 5.0 cN / dtex. The upper limit is preferably 9.0 cN / dtex or less, and more preferably 8.0 cN / dtex. When the tensile strength is in the range of 5.0 cN / dtex, the fibers are not broken by applying tension during processing in the advanced processing step, and the desired net strength can be achieved.

[0036] The polyester fiber obtained by the production method preferably has an elongation of 15 to 30%, more preferably 20 to 30%. When the elongation satisfies 15 to 30%, the energy absorption performance of the net can be fully exhibited.

[0037] The total fineness of the polyester fiber obtained by the production method of the present invention is not particularly limited, but is preferably 500 to 3500 dtex, more preferably 1000 to 2000 dtex. When the total fineness satisfies 500 to 3500 dtex, uniform cooling can be obtained in the cooling step after spinning while maintaining productivity, which enables mass production with little fluff.

[0038] The single fiber fineness of the polyester fiber obtained by the production method of the present invention is preferably 50 dtex or more, more preferably 100 dtex or more. Also, it is preferably 200 dtex or less, more preferably 150 dtex or less. When the single fiber fineness satisfies the above range, the polyester fiber of the present invention can fully ensure the effect of obtaining the strength of the industrial material net.

[0039] The polyester fiber obtained by the production method of the present invention is preferably in the form of a multifilament, and the number of single fibers (number of filaments) is preferably 2 to 70, more preferably 2 to 35, and even more preferably 2 to 14. When the number of single fibers satisfies the above range, it is possible to reduce production costs and to sufficiently ensure passability through the stretching step required to develop the strength of the industrial material net.

[0040] The shape of the cross section of the single fiber of the polyester fiber obtained by the production method of the present invention is not particularly limited, but in terms of industrial material applications, a circular shape is preferable.

[0041] The polyester fibers obtained by the manufacturing method of the present invention can be applied to all types of nets, such as knotted nets such as mesh nets and frog-shaped nets, knotless nets such as Russell nets, and twisted nets, and are expected to have excellent net strength, making them suitable for industrial material nets. EXAMPLES

[0042] The present invention will now be described in detail with reference to examples. The definitions of properties and the calculation methods of various physical property values ​​used in this specification and examples are as follows.

[0043] [Mist particle size] When the mist was sprayed from the nozzle, particle size data was measured at a measurement position 300 mm away from the nozzle using a laser diffraction method, and the average particle size was taken as the particle size.

[0044] [Intrinsic viscosity] The intrinsic viscosity was measured by adding 8.0 g of sample to 100 mL of orthochlorophenol, heating and dissolving the sample at 160°C for 10 minutes, and measuring the relative viscosity ηr of the solution at 25°C using an Ostwald viscometer. The intrinsic viscosity was calculated using the following approximate formula: Intrinsic viscosity=0.0242ηr+0.2634 The calculation was made according to the following:

[0045] [Total fineness] According to JIS-L-1013 (2010) 8.3.1 Correct Fineness a) Method A, an initial load of indicated fineness x 0.045 cN / dtex was applied using a Nakayama Electric Industry Co., Ltd. measuring instrument, and the total fineness was calculated by measuring a specified yarn length of 100 m.

[0046] [Single fiber size / number of single fibers] The single fiber fineness (dtex) was calculated by dividing the total fiber fineness by the number of single fibers. The number of single fibers was calculated according to JIS L-1013 (2010) 8.4.

[0047] [Tensile strength / elongation] Tensile strength and elongation were measured in a temperature-controlled room with an air temperature of 20°C and humidity of 65% using Orientec Co., Ltd.'s "Tensilon" UCT-100 under the constant-speed elongation conditions specified in the standard test of JIS L-1013 (2010) 8.5.1. The gripping distance was 250 mm, the tensile speed was 300 mm / min, and the number of tests per level was 10. The tensile strength and elongation were measured as the stress and elongation at break.

[0048] [Spinning] The spinnability was judged as A, B, or C. The judgment criteria are as follows: A: Stable spinning of thread for one hour or more is possible. B: It is possible to harvest thread, but stable harvesting is not possible due to thread breakage. C: The thread breaks instantly when stretched, making collection impossible.

[0049] [Example 1] Manganese acetate tetrahydrate and antimony oxide were charged into an ester exchange vessel as a reaction catalyst to high-purity terephthalic acid and ethylene glycol, and the vessel was gradually heated at a temperature of 150°C to 250°C in a nitrogen atmosphere to carry out an ester exchange reaction. The polymerization reaction system was gradually depressurized over 1 hour and 30 minutes, and the temperature was raised to 280°C. The reaction was terminated when the target intrinsic viscosity of 0.7 was reached, the reaction system was returned to normal pressure with nitrogen gas, and the polyester resin composition was discharged from the bottom of the polymerization apparatus with cold water and cut to obtain a pellet-shaped polyester resin composition. The polyester resin composition was then dried and crystallized by placing it under vacuum at a temperature of 160°C for 6 hours, and then solid-phase polymerization was carried out at a temperature of 230°C and a vacuum degree of 13 Pa for 8 hours to obtain polyethylene terephthalate chips with an intrinsic viscosity of 1.30.

[0050] The polyethylene terephthalate chips obtained by the above method and having an intrinsic viscosity of 1.30 were continuously fed to an extruder-type spinning machine and melted at a temperature of 300° C. The molten polymer was passed through a piping at 290° C. and adjusted to 300 g / min by a metering pump, and then filtered through a 20 μm nonwoven filter in a spinning pack at 290° C., and then spun from a die equipped with 12 circular single holes with a hole diameter of Φ0.9 mm and a hole length of 1.2 mm arranged in a circular pattern.

[0051] The spun yarn was passed through a heating cylinder installed just below the spinneret, where the atmospheric temperature inside the cylinder was 200°C, and then cooled and solidified by spraying mist with a particle size of 100 μm, a flow rate of 40 ml / min, and a temperature of 25°C from three nozzles evenly spaced around the circumference in a metal cylinder with a diameter of 40 cm and a height of 150 cm. After cooling, a fiber oil was applied using an oiling roll, and the obtained yarn was taken up by 1GR (75°C) with a speed of 505 m / min and continuously subjected to a drawing process. The yarn that had passed through the 1GR was then drawn by continuously feeding it to the 2GR with a surface temperature of 101°C and a speed of 535 m / min, the 3GR with a speed of 110°C and a speed of 1818 m / min, the 4GR with a speed of 225°C and a speed of 2651 m / min, and the 5GR with a speed of 2700 m / min without heating, without being taken up once. The yarn bundle forming treatment was performed between 2GR-3GR, and the entanglement treatment was performed between 5GR and the winding device by spraying high-pressure air of 0.4 MPa and 0.5 MPa, respectively, and then the yarn was wound up on the winding device to produce polyethylene terephthalate fiber for industrial material nets of 1200 dtex-12f. The measurement results of the tensile strength and elongation of the polyester fiber thus obtained are shown in Table 1.

[0052] [Example 2] In Example 2, a polyester fiber of 1680 dtex-12f was obtained in the same manner as in Example 1, except that the mist particle size was 30 μm and the single fiber fineness was 140 dtex. The results are shown in Table 1.

[0053] [Example 3] In Example 3, a polyester fiber of 1680 dtex-12f was obtained in the same manner as in Example 1, except that the mist particle size was 200 μm and the single fiber fineness was 140 dtex. The results are shown in Table 1.

[0054] [Example 4] In Example 4, a polyester fiber of 600 dtex-12f was obtained in the same manner as in Example 1, except that the mist particle size was 30 μm and the single fiber fineness was 50 dtex. The results are shown in Table 1.

[0055] [Example 5] In Example 5, a polyester fiber of 600 dtex-12f was obtained in the same manner as in Example 1, except that the mist particle size was 200 μm and the single fiber fineness was 50 dtex. The results are shown in Table 1.

[0056] [Example 6] In Example 6, a polyester fiber of 1200 dtex-12f was obtained in the same manner as in Example 1, except that the number of mist nozzles was changed to 6. The results are shown in Table 1.

[0057] [Table 1]

[0058] [Comparative Example 1] In Comparative Example 1, the mist particle size was set to 300 μm and the single fiber fineness was set to 140 dtex, but the same method as in Example 1 was used, and it was not possible to obtain polyester fibers with a large fineness of 1680 dtex-12f. The results are shown in Table 2.

[0059] [Comparative Example 2] In Comparative Example 2, the mist particle size was set to 0.5 μm and the single fiber fineness was set to 140 dtex, but the same method as in Example 1 was used, and it was not possible to obtain polyester fibers with a large fineness of 1680 dtex-12f. The results are shown in Table 2.

[0060] [Comparative Example 3] In Comparative Example 3, the mist particle size was set to 300 μm and the single fiber fineness was set to 50 dtex, but the same method as in Example 1 was used, and it was not possible to obtain polyester fibers with a thick fineness of 600 dtex-12f. The results are shown in Table 2.

[0061] [Comparative Example 4] In Comparative Example 4, the same method as in Example 1 was used except that the mist particle size was 0.5 μm and the single fiber fineness was 50 dtex, but it was not possible to obtain polyester fibers with a thick fineness of 600 dtex-12f.

[0062] [Comparative Example 5] In Comparative Example 5, the same method as in Example 1 was used except that the number of mist nozzles was changed to 2, but it was not possible to obtain polyester fibers with a large fineness of 1200 dtex-12f. The results are shown in Table 2.

[0063] [Comparative Example 6] In Comparative Example 6, the same method as in Example 1 was used except that the mist was sprayed from three nozzles arranged vertically (in the direction of yarn travel) at intervals of 50 cm on one side of the yarn, but it was impossible to obtain polyester fibers with a large fineness of 1200 dtex-12f. The results are shown in Table 2.

[0064] [Comparative Example 7] In Comparative Example 7, after passing through the heating cylinder, the fibers were cooled with chimney cooling air having an air temperature of 25° C. and an air speed of 1.5 m / sec without using mist, but the same method as in Example 1 was used, and it was impossible to obtain 1200 dtex-12f polyester fibers. The results are shown in Table 2.

[0065] [Table 2] [Explanation of symbols]

[0066] 1: Mist 2: Cooling cylinder 3: Thread

Claims

1. A method for producing polyester fibers, characterized in that, when cooling polyester fibers having ethylene terephthalate as a main repeating unit extruded from a spinneret, a cooling medium mainly composed of water is sprayed as a mist from three or more nozzles arranged circumferentially inside a cooling cylinder (metal cylinder).

2. 2. A polyester fiber obtained by the method for producing a polyester fiber according to claim 1, characterized in that the polyester fiber has a tensile strength of 5.0 cN / dtex or more.

3. 3. The polyester fiber according to claim 2, wherein the single fiber fineness is 100 dtex or more.

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