Biodegradable polyester fiber and its manufacturing method

Abstract

To provide biodegradable polyester fibers being strong enough to sufficiently endure when used normally, and a manufacturing method of the biodegradable polyester fibers, the method enabling continuous and stable manufacturing, and the fibers not conglutinating with each other, having little variation in fiber diameter, and being strong enough to sufficiently endure when used normally.SOLUTION: Biodegradable polyester fibers have fineness of 200 dtex or less, strength of 1.5 cN / dtex or more, and are made from PHA. A manufacturing method comprises: a first step of melting a resin material containing PHA and discharging the resin in a fibrous state from a spinneret b; a second step of, after air-cooling fibers c made from the discharged resin material, keeping the fibers at 140°C or higher and 180°C or lower; a third step of winding up undrawn fibers obtained in the second step; a fourth step of drawing the wound-up undrawn fibers at a drawing rate of 100 m / min or more and 600 m / min or less and with a draw magnification ratio of 1.5 times or more and 3.0 times or less; and a fifth step of subjecting the drawn fibers to stress relaxation at 0.80 times or more and 0.99 times or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a biodegradable polyester fiber and a method for producing the same. [Background technology]

[0002] In recent years, concerns have arisen about the impact of microplastics on ecosystems, and biodegradable plastics have been attracting attention. Ordinary plastics are synthesized from petroleum, and there are no microorganisms in the natural environment that can decompose them. Ordinary plastics are broken down into smaller pieces by water and ultraviolet light, but they do not decompose, becoming microplastics that are difficult to recover. A particular problem with microplastics is their biodegradability in the aquatic environment, but this is only possible for a very small number of plastics.

[0003] Among plastics that are biodegradable in aqueous environments, polyhydroxyalkanoates (hereinafter sometimes referred to as PHA) are biologically derived polyester polymers, and their application to various molded products such as films and fibers is being considered. However, PHA crystallizes slowly, requiring a long time for cooling and solidification, resulting in poor productivity. In particular, when PHA is produced using the melt spinning method, cooling and solidification does not progress sufficiently before the fibers are wound, resulting in the tendency for the fibers to stick together. This makes stable, continuous production difficult. Furthermore, the resulting fibers are prone to uneven fiber diameter and low strength, which makes them difficult to process in subsequent processes and results in poor yarn quality.

[0004] Various studies have been carried out to date to address these problems with PHA-based fibers. For example, a method has been disclosed for producing PHA fibers with high tensile strength by extruding molten PHA from a spinneret in the form of fibers, passing the fibers through a liquid phase at 20 to 60°C containing a glycol-based water-soluble liquid such as polyethylene glycol, and then winding the liquid (Patent Document 1). It has also been disclosed that highly uniform PHA fibers can be produced without variation in fiber shape, fiber diameter, and tensile strength by rapidly cooling melt-extruded PHA fibers to a temperature below the glass transition temperature +10°C, maintaining the temperature at a temperature below the glass transition temperature +20°C, and stretching the fibers at room temperature while applying shear stress (Patent Document 2). In addition, polyester resin containing poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) was taken up at 1,500 m / min to 7,000 m / min, and the X-ray diffraction intensity (I β ) and X-ray diffraction intensity from α-type crystal (I α ) ratio (I β / I α ) is set to 0.02 or more, thereby improving the productivity and tensile strength of the polyester fiber (Patent Document 3). In addition, an aliphatic polyester fiber with improved productivity and increased tensile strength has been disclosed by adding a nucleating agent to a poly(3-hydroxybutyrate) resin and adjusting the spinning draft and winding speed (Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-133022 [Patent Document 2] Japanese Patent Application Publication No. 2018-159142 [Patent Document 3] International Publication No. WO2015 / 029316 [Patent Document 4] International Publication No. WO2021 / 206154 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the fiber manufacturing method described in Patent Document 1 requires passing the fiber through a liquid phase containing a glycol-based water-soluble liquid, which complicates the manufacturing process by adding a water-washing step to the fiber, and reduces productivity due to low-speed spinning, which tends to increase production costs. Furthermore, the tensile strength is insufficient and does not reach a practical level. The fiber production method described in Patent Document 2 consumes a lot of energy and requires special equipment to rapidly cool PHA, which has a glass transition temperature below room temperature, to a temperature 10°C above the glass transition temperature immediately after melt extrusion.Furthermore, there is no mention of the tensile strength of the fiber. In the fiber manufacturing method described in Patent Document 3, adhesion between fibers cannot be completely improved at a speed of less than 2000 m / min, and the tensile strength does not reach a practical level. The fiber manufacturing method described in Patent Document 4 can obtain tensile strength sufficient for practical use, but does not mention adhesion between fibers, and the obtained fibers may be difficult to unwind, making them unusable. Therefore, an object of the present invention is to provide a biodegradable polyester fiber that has sufficient strength for practical use in normal use. Another object of the present invention is to provide a method for producing biodegradable polyester fibers that allows for continuous and stable fiber production, is free from adhesion between fibers and variation in fiber diameter, and has strength sufficient for practical use. [Means for solving the problem]

[0007] The present inventors discovered conditions for suppressing adhesion between fibers even at spinning speeds of less than 2000 m / min using a simple manufacturing process when producing PHA fibers, and found that high-strength fibers can be produced stably and continuously, thereby arriving at the present invention.

[0008] That is, the gist of the present invention is, first, a biodegradable polyester fiber made of polyhydroxyalkanoate, having a fineness of 200 dtex or less, a tenacity of 1.5 cN / dtex or more, and preferably having an elongation of 100% or less, a single filament fineness of 1.5 dtex or more and 15 dtex or less, and a U% (fineness unevenness) of 3.5% or less. The second method includes a first step of melting a resin material containing polyhydroxyalkanoate and extruding it in a fibrous form from a spinneret; a second step of air-cooling the extruded resin material and then maintaining the temperature at 140°C to 180°C; a third step of winding up the undrawn fiber that has been air-cooled and maintained at a temperature; a fourth step of drawing the wound undrawn fiber at a drawing speed of 100 m / min to 600 m / min and a draw ratio of 1.5 to 3.0; and a fifth step of stress-relaxing the drawn fiber at a draw ratio of 0.80 to 0.99. The melt temperature in the first step is preferably 160°C to 180°C. The second step preferably involves placing a heat-insulating tube around the fiber. The third step preferably involves winding up the undrawn fiber at a speed of 500 m / min to less than 2000 m / min. The fourth step preferably involves relaxing the undrawn fiber at a draw ratio of 8 g or less. It is preferable to carry out a heat treatment at 80°C or higher and 110°C or lower during stress relaxation in the fifth step. [Effects of the Invention]

[0009] According to the fiber of the present invention, a biodegradable polyester fiber having sufficient strength for practical use can be provided. According to the fiber production method of the present invention, fibers can be continuously and stably produced, and the obtained fibers have little agglutination between fibers and little variation in fiber diameter, and a biodegradable polyester fiber having sufficient strength for practical use can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram illustrating a method for spinning a biodegradable polyester fiber of the present invention. [Figure 2] FIG. 1 is a schematic diagram illustrating a method for drawing the biodegradable polyester fiber of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The biodegradable polyester fiber of the present invention contains a PHA.

[0012] The PHA in the present invention is preferably selected from PHAs produced by microorganisms. PHAs produced by microorganisms are those having the structure [—CHR—CH—CO—O—: R is C n H 2n+1 where n is an integer of 1 to 15]. Specific examples of polyhydroxyalkanoic acids include 3-hydroxybutanoic acid, 3-hydroxyvaleric acid, 3-hydroxyhexanoic acid, and 4-hydroxybutanoic acid. PHA may be a homopolymer using one of these components as a repeating unit, or a copolymer containing two or more components as repeating units. Examples of copolymers include poly(3-hydroxybutanoic acid-co-3-hydroxyhexanoic acid) and poly(3-hydroxybutanoic acid-co-4-hydroxybutanoic acid). From the viewpoint of spinnability, poly(3-hydroxybutanoic acid-co-3-hydroxyhexanoic acid) is preferred. Furthermore, the biodegradable polyester fiber may contain additives such as polymers or particles other than PHA, lubricants, and antistatic agents, as long as they do not impair the properties of the biodegradable polyester fiber.

[0013] The melting point of the PHA is preferably 110°C or higher and 160°C or lower. If the melting point is lower than 110°C, practical heat resistance tends to be insufficient. It is preferably 110°C or higher, more preferably 120°C or higher. If the melting point is higher than 160°C, it is necessary to raise the temperature to a level close to the thermal decomposition temperature of the PHA when melted during melt spinning, which can result in thread breakage and fuzz generation, making it difficult to obtain the desired biodegradable polyester fiber. It is preferably 160°C or lower, more preferably 155°C or lower.

[0014] In the biodegradable polyester fiber of the present invention, the melting point of the resin refers to the value shown by the peak top of the endothermic peak when the fiber is heated to 200°C at a rate of 10°C / min in a nitrogen atmosphere using a differential scanning calorimeter (DSC).

[0015] The melt flow rate (MFR) of the PHA at 165°C and a load of 5.0 kg is preferably 1 g / 10 min or more and 30 g / 10 min or less. If the MFR is 1 g / 10 min or more, the melt temperature can be set low during melt spinning, making thermal decomposition less likely to occur. As a result, spinning stability and yarn quality are improved, and the desired biodegradable polyester fiber tends to be more easily obtained. The MFR is more preferably 2 g / 10 min or more. Even more preferably 3 g / 10 min or more. Furthermore, from the viewpoint of maintaining the strength of the biodegradable polyester fiber, the MFR is preferably 30 g / 10 min or less. More preferably, it is 25 g / 10 min or less. Even more preferably, it is 20 g / 10 min or less.

[0016] The biodegradable polyester fiber of the present invention has a strength of 1.5 cN / dtex or more. If the strength is less than 1.5 cN / dtex, yarn breakage is likely to occur in subsequent processes such as yarn processing, weaving, and knitting, which can cause problems. The strength is preferably 1.6 cN / dtex or more, and more preferably 1.7 cN / dtex or more.

[0017] The elongation of the biodegradable polyester fiber of the present invention is preferably 40% or more, and preferably 100% or less. If the elongation is less than 40%, thread breakage is likely to occur during the warping and weaving processes, resulting in poor processability. From the viewpoint of processability, the elongation is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. If the elongation exceeds 100%, dimensional stability is likely to deteriorate. From the viewpoint of dimensional stability, the elongation is preferably 100% or less, more preferably 90% or less, and even more preferably 80% or less.

[0018] The biodegradable polyester fiber of the present invention preferably has a single yarn fineness of 1.5 dtex or more and 15 dtex or less. If the single yarn fineness is less than 1.5 dtex, yarn breakage is likely to occur in subsequent processes such as yarn processing, weaving, and knitting, which can cause problems. The single yarn fineness is preferably 1.5 dtex or more, more preferably 2.0 dtex or more, and even more preferably 2.5 dtex or more. If the single yarn fineness exceeds 15 dtex, it becomes difficult to maintain uniformity in the fiber diameter, and unevenness in fineness and variation in tensile strength are likely to increase. From the viewpoint of uniformity, the single yarn fineness is preferably 15 dtex or less, more preferably 10 dtex or less, and even more preferably 8 dtex or less.

[0019] The biodegradable polyester fiber of the present invention preferably has a U% value, which is an index of fineness unevenness, of 3.5% or less. If U% exceeds 3.5%, the uniformity of the fiber deteriorates, and the tensile strength tends to vary greatly. Furthermore, fluffing and yarn breakage tend to occur in subsequent processes, resulting in poor processability. From the viewpoint of uniformity, U% is preferably 3.5% or less, more preferably 3.3% or less, and even more preferably 3.0% or less.

[0020] In the present invention, U% refers to the average deviation rate of fiber diameter. The average deviation rate is a value that represents the unevenness of fiber thickness obtained from the calculated variation in fiber diameter, which is obtained by measuring the capacitance of a biodegradable polyester fiber over 100 m using a continuous yarn unevenness tester and calculating the variation in fiber diameter from the variation in capacitance. The lower the value of this average deviation rate, the less unevenness in fineness and the more uniform the fiber.

[0021] The cross-sectional shape of the biodegradable polyester fiber of the present invention is not particularly limited, and in addition to a circular cross section, any shape such as flat, elliptical, triangular to octagonal, C-shaped, U-shaped, or W-shaped may be used.

[0022] Next, a method for producing the biodegradable polyester fiber of the present invention will be described. The biodegradable polyester fiber of the present invention can be obtained by a so-called conventional method in which an undrawn fiber is once wound up and then drawn.

[0023] The method for producing a biodegradable polyester fiber of the present invention includes at least a first step of extruding a PHA in a fibrous form, a second step of cooling the extruding PHA in a fibrous form and then heating and keeping the PHA at a constant temperature, a third step of winding up the undrawn fiber, a fourth step of drawing the wound undrawn fiber, and a fifth step of relaxing the stress on the drawn fiber. The biodegradable polyester fiber is produced by a method including these steps.

[0024] FIG. 1 shows an example of a schematic diagram of a spinning device used in melt spinning, and FIG. 2 shows an example of a schematic diagram of a device used in the drawing step. The first step is to melt the PHA and extrude it into fibers using a spinneret (b) that forms a predetermined cross-sectional shape, thereby forming a molten biodegradable polyester fiber (c). The melting temperature at which the PHA is melted is preferably 160°C or higher and 180°C or lower. Here, the melting temperature refers to the highest temperature between the extruder (a) that melts the PHA and the spinneret (b) that extrudes it into fibers. If the melting temperature is lower than 160°C, unmelted PHA may be mixed into the fibers, causing thread breakage and fuzz, and spinning stability may be reduced. Therefore, the lower limit of the melting temperature is 160°C, preferably 165°C. If the melting temperature exceeds 180°C, thermal decomposition of the PHA is likely to occur, resulting in thread breakage and fuzz, and spinning stability may be reduced. Therefore, the upper limit of the melting temperature is 180°C, preferably 175°C, and more preferably 170°C or lower.

[0025] The second step is a step in which cooling air (d) is blown onto the biodegradable polyester fiber (c) extruded in a fibrous form to gradually cool and solidify the fiber surface, and then the fiber is heated and maintained at a temperature of 140°C to 180°C. The biodegradable polyester fiber (c) extruded in a fibrous form is cooled with cooling air (d) to cool and solidify at least the fiber surface. However, since the crystallization rate of PHA is slow, it is difficult to keep the undrawn fiber ( g), when the biodegradable polyester fiber (c) is wound, adhesion occurs between the fibers, making stable continuous production difficult. Therefore, by heating and keeping the solidified biodegradable polyester fiber (c) warm, the crystallization rate can be accelerated, crystallization in the fiber can be promoted, and adhesion between the fibers can be suppressed. Furthermore, by suppressing adhesion, the occurrence of uneven fineness can also be suppressed. The method for heating the biodegradable polyester fiber is not particularly limited, but a method of heating and keeping the biodegradable polyester fiber (c) warm in a heated circular tube (e) or a method of heating and keeping the biodegradable polyester fiber (c) warm using a far-infrared heater is preferred. If the heating temperature is less than 140°C, crystallization is insufficient, and it is difficult to suppress adhesion between the fibers. Therefore, the lower limit of the heating temperature is 140°C, preferably 150°C, and more preferably 160°C. If the heating temperature exceeds 180°C, remelting occurs, making it easy for fiber breakage to occur. Therefore, the upper limit of the heating temperature is 180°C, preferably 175°C, and more preferably 170°C. The convergence point of the biodegradable polyester fiber (c) is preferably immediately before the roller (f). The closer the convergence point is to the roller (f), the longer the time the single yarns are separated from each other, making it easier to prevent adhesion between the fibers.

[0026] The third step is a step of temporarily winding up the undrawn biodegradable polyester fiber whose crystallization has been promoted. The winding speed is preferably 500 m / min or more and less than 2000 m / min. If the winding speed is less than 500 m / min, it becomes difficult to obtain a biodegradable polyester fiber having a strength of 1.5 cN / dtex or more. From the viewpoint of strength, the winding speed is preferably 500 m / min or more, more preferably 600 m / min or more, and even more preferably 700 m / min or more. If the winding speed is 2000 m / min or more, the time required to pass through the heating and warming region where crystallization is promoted becomes shorter, making it difficult for crystallization to proceed sufficiently and making the fiber more susceptible to subsequent sticking. From the viewpoint of crystallization, the winding speed is preferably less than 2000 m / min, more preferably less than 1800 m / min, even more preferably less than 1500 m / min, and particularly preferably less than 1300 m / min.

[0027] The fourth step is a step of drawing an undrawn biodegradable polyester fiber at a drawing speed of 100 m / min to 600 m / min and a draw ratio of 1.5 to 3.0. The drawing speed refers to the rotation speed of the second roller (i). A drawing speed of less than 100 m / min reduces productivity and tends to result in high-cost fibers. The drawing speed is preferably 200 m / min or more, more preferably 250 m / min or more. A drawing speed of more than 600 m / min is likely to cause fuzzing and thread breakage, making stable continuous production difficult. The drawing speed is more preferably 550 m / min or less, and even more preferably 500 m / min or less. The undrawn fiber is drawn between the first roller (h) and the second roller (i). A draw ratio of less than 1.5 makes it difficult to achieve a tenacity of 1.5 cN / dtex or more. The lower limit of the draw ratio is 1.5 times, preferably 1.6 times, more preferably 1.7 times, and even more preferably 1.8 times. If the draw ratio exceeds 3.0 times, fluffing and thread breakage are likely to occur, making stable continuous production difficult. The upper limit of the draw ratio is 3.0 times, preferably 2.7 times, more preferably 2.5 times, and even more preferably 2.3 times. The unwinding tension of the unstretched fibers is preferably 8 g or less. If the fibers are stuck together, the unwinding tension becomes high, and the unstretched fibers tend to collapse during unwinding. If the unwinding tension exceeds 8 g, the unstretched fibers tend to collapse during unwinding, making stable, continuous production difficult. The unwinding tension is preferably 8 g or less, more preferably 6 g or less, and even more preferably 5 g or less.

[0028] The fifth step is a step of stretching the stretched biodegradable polyester fiber between the second roller (i) and the third roller (j) at a draw ratio of 0.8 to 0.99, and then relaxing the stress. If the draw ratio is less than 0.8, slack occurs between the second roller (i) and the third roller (j), making it difficult to wind the stretched biodegradable polyester fiber and making stable, continuous production difficult. The draw ratio is preferably 0.85 or more, and more preferably 0.87 or more. If the draw ratio exceeds 0.99, stress relaxation is insufficient, and shrinkage stress increases during yarn processing or processing of the gray fabric, making yarn breakage more likely to occur. The draw ratio is preferably 0.97 or less, and more preferably 0.95 or less. Furthermore, when relaxing the stress, it is preferable to perform a heat treatment at 80°C to 110°C on the second roller. If the heat treatment is performed at less than 80°C, stress relaxation is insufficient, making yarn breakage more likely to occur during processing. Therefore, the lower limit of the heat treatment temperature in stress relaxation is preferably 80°C, more preferably 90°C, and even more preferably 95°C. If the heat treatment is performed at a temperature exceeding 110°C, the biodegradable polyester fiber will soften and become more susceptible to yarn breakage. Therefore, the upper limit of the heat treatment temperature in stress relaxation is preferably 110°C, more preferably 105°C, and even more preferably 100°C.

[0029] In this way, the biodegradable polyester fiber of the present invention can be produced stably and continuously, even at a low spinning speed of less than 2000 m / min, with suppressed adhesion between fibers, excellent fiber diameter uniformity, and high strength. Furthermore, since the resulting biodegradable polyester fiber has excellent strength and elongation properties, it can be used for textile structures such as woven or knitted fabrics for clothing, industrial materials, and household goods such as tea bags and draining nets. [Example]

[0030] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples described below. The methods for measuring and evaluating various physical properties are as follows.

[0031] <Fineness> According to JIS L 1013, a 100 m sample yarn length was taken using a measuring machine, and the weight was calculated from the measured weight.

[0032] <Strength, elongation> Measurements were performed using an Autograph (registered trademark) AGS-1KNG tensile tester manufactured by Shimadzu Corporation under conditions of a sample yarn length of 20 cm and a constant pulling speed of 20 cm / min in accordance with JIS L 1013. The maximum load value on the load-elongation curve was divided by the fineness to determine the strength (cN / dtex), and the elongation at that point was determined as the elongation (%).

[0033] <Fineness unevenness> A Zellweger UsterTester4 Model C was used as a continuous yarn unevenness tester, and U% was measured in normal mode while feeding the fiber at a speed of 100 m / min.

[0034] <Spinning stability> Spinning stability was evaluated based on the average number of thread breakages when 10 kg of fiber was spun. ○: The number of thread breakages is less than 1 ×: Thread breakage occurs once or more

[0035] <Inter-fiber adhesion> The undrawn fiber was unwound at 400 m / min and run through a fluff detector KH-700 manufactured by Daikosha Co., Ltd. for 10,000 m, and evaluated for the occurrence of fluff. ○: When the yarn can be unwound without any breakage or fluffing. △: Single yarn breakage and fluffing occur, but the yarn can be unwound ×: Single yarn breakage or yarn breakage occurs and the product cannot be unwound

[0036] <Unwinding tension> The yarn tension when the undrawn fiber was unwound at 400 m / min was measured twice per second for one minute, and the average value was taken as the unwinding tension.

[0037] <Extension status> ○: No single yarn breakage or fluffing ×: If there is thread breakage, single thread breakage, or fluffing

[0038] Example 1 Poly(3-hydroxybutanoic acid-co-3-hydroxyhexanoic acid) was used as the PHA and extruded from a spinneret with a circular cross section at a melt temperature of 165°C. The extruded fiber was then air-cooled and kept at 165°C in a cylindrical heat-retaining tube. The undrawn fiber was then wound at 1500 m / min. The resulting undrawn fiber was stretched at a stretching speed of 300 m / min and a stretch ratio of 1.85. Stress relaxation was then performed at a heat treatment temperature of 100°C and a stretch ratio of 0.93 to obtain a biodegradable polyester fiber of 84 dtex / 24 f. The resulting biodegradable polyester fiber had a tenacity of 1.8 cN / dtex, a U% of 2.0%, and good spinning stability. The unwinding tension of the undrawn fiber was 3.2 g, and no adhesion between fibers was observed. The results are shown in Table 1.

[0039] Example 2 The same method as in Example 1 was used to produce the biodegradable polyester fiber, except that the air-cooled fiber was kept warm in a cylindrical heat-retaining tube heated to 175°C. The resulting biodegradable polyester fiber had a strength of 1.7 cN / dtex, a U% of 2.9%, and good spinning stability. The unwinding tension of the undrawn fiber was 4.5 g, and no sticking between fibers was observed. The results are shown in Table 1.

[0040] Example 3 The biodegradable polyester fiber was produced in the same manner as in Example 1, except that the drawing speed was 400 m / min and the draw ratio was 2.1 times. The strength of the obtained biodegradable polyester fiber was 2.0 The spinning stability was also good, with a tensile strength of 1.2 cN / dtex and a U% of 2.7%. The unwinding tension of the undrawn fiber was 3.2 g, and no adhesion between fibers was observed. The results are shown in Table 1.

[0041] Example 4 The fabrication method was the same as in Example 1, except that stress relaxation was performed at a draw ratio of 0.87. The resulting biodegradable polyester fiber had a strength of 1.6 cN / dtex, a U% of 3.0%, and good spinning stability. The unwinding tension of the undrawn fiber was 3.2 g, and no sticking between fibers was observed. The results are shown in Table 1.

[0042] Example 5 The same method as in Example 1 was used to produce a biodegradable polyester fiber of 140 dtex / 24 filaments, except that the undrawn fiber was taken up at 800 m / min, drawn at a draw ratio of 2.45, and stress-relaxed at a draw ratio of 0.96 to obtain a biodegradable polyester fiber of 140 dtex / 24 filaments. The tenacity of the obtained biodegradable polyester fiber was 1.5 cN / dtex, U% was 3.4%, and the spinning stability was also good. The unwinding tension of the undrawn fiber was 5.7 g, and no sticking between fibers was observed. The results are shown in Table 1.

[0043] Example 6 The same method as in Example 1 was used to produce the fiber, except that the air-cooled fiber was kept warm in a cylindrical heat-retaining tube heated to 185°C. Frequent yarn breakage occurred during spinning. The strength of the resulting biodegradable polyester fiber was 1.7 cN / dtex. However, the U% was 4.1%, indicating poor fiber uniformity and variations in physical properties. Furthermore, the undrawn fiber exhibited adhesion between fibers, the unwinding tension was 8.4 g, and fluffing was observed during unwinding. The results are shown in Table 1.

[0044] Comparative Example 1 The same method as in Example 1 was used to produce the biodegradable polyester fiber, except that the air-cooled fiber was kept warm in a cylindrical heat-retaining tube heated to 135°C. The undrawn biodegradable polyester fiber obtained was stuck together and could not be unwound. The results are shown in Table 2.

[0045] Comparative Example 2 The fabric was produced in the same manner as in Example 1, except that the drawing speed was set to 700 m / min. Numerous fuzzing and thread breakage occurred during the drawing process, and a biodegradable polyester fiber could not be obtained. The unwinding tension of the undrawn fiber was 3.2 g, and no adhesion between fibers was observed. The results are shown in Table 2.

[0046] Comparative Example 3 The fabric was produced in the same manner as in Example 1, except that the draw ratio was set to 3.2 times. Numerous fuzzing and thread breakage occurred during the drawing process, and a biodegradable polyester fiber could not be obtained. The unwinding tension of the undrawn fiber was 3.2 g, and no adhesion between fibers was observed. The results are shown in Table 2.

[0047] Comparative Example 4 The fabrication was carried out in the same manner as in Example 1, except that stress relaxation was carried out at a draw ratio of 0.75. The drawn fiber broke during winding, and no biodegradable polyester fiber was obtained. The unwinding tension of the undrawn fiber was 3.2 g, and no adhesion between fibers was observed. The results are shown in Table 2.

[0048] Comparative Example 5 The fabrication method was the same as in Example 1, except that stress relaxation was performed at a heat treatment temperature of 110°C. The drawn fibers frequently broke during the heat treatment, and no biodegradable polyester fibers were obtained. The unwinding tension of the undrawn fibers was 3.2 g, and no adhesion between the fibers was observed. The results are shown in Table 2.

[0049] [Table 1]

[0050] [Table 2]

[0051] The biodegradable polyester fibers obtained from Examples 1 to 5 could be produced continuously and stably, were free from agglutination between fibers, had no variation in fiber diameter or physical properties, and had high strength, and Example 6 had practical strength. However, the biodegradable polyester fibers obtained from the comparative examples either could not be produced stably or suffered from at least one of the following: agglutination, variation in fiber diameter or physical properties, and low strength. [Industrial Applicability]

[0052] The biodegradable polyester fiber of the present invention can be made into various fiber structures and can be suitably used as a material for reducing the burden on the global environment because it is decomposed by microorganisms after use. [Explanation of symbols]

[0053] a. Extruder b. Spinneret c. Fiber d Cooling air e thermal tube f Roller g Unstretched fiber h First roller i Second roller j Third Roller k Stretched Fiber

Claims

1. A biodegradable polyester fiber made of polyhydroxyalkanoate having a fineness of 200 dtex or less, a strength of 1.5 cN / dtex or more, and U% (fineness unevenness) of 3.5% or less.

2. A biodegradable polyester fiber according to claim 1, having an elongation of 100% or less.

3. 3. The biodegradable polyester fiber according to claim 1 or 2, wherein the single fiber fineness is 1.5 dtex or more and 15 dtex or less.

4. A first step of melting a resin material containing polyhydroxyalkanoate and extruding it in the form of fibers from a spinneret; a second step of air-cooling the extruded fibers made of the resin material and then maintaining the temperature at 140°C or higher and 180°C or lower; a third step of winding up the undrawn fibers obtained in the second step; a fourth step of drawing the wound undrawn fiber at a drawing speed of 100 m / min or more and 600 m / min or less and a draw ratio of 1.5 times or more and 3.0 times or less; and a fifth step of stress-relaxing the drawn fiber at a ratio of 0.80 to 0.

99. A method for producing biodegradable polyester fibers.

5. 5. The method for producing biodegradable polyester fibers according to claim 4, wherein the melting temperature in the first step is 160°C or higher and 180°C or lower.

6. 6. The method for producing biodegradable polyester fibers according to claim 4 or 5, wherein in the second step, the fibers are kept warm by placing a heat-insulating tube around the fibers.

7. The method for producing a biodegradable polyester fiber according to any one of claims 4 to 6, wherein in the third step, the undrawn fiber is wound at a speed of 500 m / min or more and less than 2000 m / min.

8. The method for producing a biodegradable polyester fiber according to any one of claims 4 to 7, wherein in the fourth step, the tension when unwinding the undrawn fiber is 8 g or less.

9. The method for producing a biodegradable polyester fiber according to any one of claims 4 to 8, wherein the fifth step comprises heat treatment at a temperature of 80°C or higher and 110°C or lower.

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