EP4779068A1

EP4779068A1 - Continuous long fiber of aliphatic copolymerized polyester, and method for producing same

Info

Publication number: EP4779068A1
Application number: EP24865564.9A
Authority: EP
Inventors: Kodai HARANO; Saeko Yamaguchi; Keisuke Fujita; Yuichi Hara; Taizo Kabe; Tadahisa Iwata
Original assignee: Asahi Kasei Corp; The University of Tokyo; Asahi Chemical Industry Co Ltd
Current assignee: Asahi Kasei Corp; The University of Tokyo; Asahi Chemical Industry Co Ltd
Priority date: 2023-09-14
Filing date: 2024-09-13
Publication date: 2026-07-22
Also published as: JPWO2025058065A1; WO2025058065A1; CN121889542A; KR20260049307A

Abstract

The present invention addresses the problem of providing a continuous long fiber that comprises an aliphatic copolymerized polyester, has excellent storage stability, and can solve a problem of unwinding defects, as well as a method for producing said continuous long fiber. This continuous long fiber comprises an aliphatic copolymerized polyester, wherein the aliphatic copolymerized polyester includes 3-hydroxybutyrate as a first monomer unit and includes 4-hydroxybutyrate or 3-hydroxyvalerate as a second monomer unit, the ratio of the second monomer unit to all monomer units is 1 mol% to 9 mol% when the second monomer unit is the 4-hydroxybutyrate unit, and the ratio of the second monomer unit to all monomer units is 1 mol% to 7.6 mol% when the second monomer unit is 3-hydroxyvalerate.

Description

FIELD

The present invention relates to a continuous long fiber of an aliphatic copolymer polyester, to a multifilament yarn, to a fabric and to a method for producing the fiber.

BACKGROUND

Increasing focus has been directed in recent years toward environmental problems caused by waste plastics, leading to greater desire to shift toward a society more geared to recycling on a global scale, and this has led to increasing interest in biodegradable resins that are decomposed after use by the action of microorganisms. Aliphatic copolymer polyesters are biodegradable resins that are of interest from the viewpoint of reducing and sequestering carbon dioxide gas emissions (achieving carbon neutrality), and particularly these include polyhydroxyalkanoates (hereunder also abbreviated as "PHA") which are derived from biomaterials. Because PHAs have high biodegradability, and especially marine biodegradability (the property of decomposing in the ocean), they are being studied for their use in various molded articles such as fibers that leak out into the ocean when shed from products, and films that leak out into the ocean when dumped. Further increased demand for PHA fibers is expected in a variety of fields including clothing products such as shirts, bedding materials such as sheets, bed pads and pillowcases, medical products such as surgical suture thread, agricultural and fishery products such as bird nets, fishing lines and fishing nets, fabric products such as automobile sheets and woven fabrics, sanitary materials such as nonwoven fabrics and filters, building material products such as ropes, and packaging products for foods and the like.
Among these PHAs, it has also been attempted to use poly-3-hydroxybutyrate (hereunder abbreviated as P3HB) for molding, but it has not yet been possible to obtain a product with stable mechanical properties that more satisfactorily meet requirements for commercial products than existing resins. P3HB has a slow crystallization rate and requires a longer cooling time for solidification after hot melting during the molding process, and its productivity is therefore extremely poor. When forming fibers, for example, it is necessary to significantly lower the take-up speed during melt spinning. Moreover, because of the slower crystallization rate, practical problems have been encountered such as very poor reelability after take-up, due to aggregation between the fibers. In addition, P3HB is a resin with a slow crystallization rate but exhibiting high crystallinity and a glass transition point of below room temperature, and therefore secondary crystallization proceeds during storage, resulting in progressive deterioration with time.
PTL 1 describes a method of improving the mechanical properties of PHA by rapidly cooling it to no higher than the glass transition temperature of the polymer + 15°C immediately after it is extruded from the melt extruder, to free the filament from blocking, and then cold drawing to rapidly promote partial crystallization up to the glass transition temperature + 20°C, and further subjecting it to tensile heat treatment.
PTL 2 describes a method of following cold drawing with further stretching at above the glass transition temperature, and subsequent tensile heat treatment.
These methods improve the mechanical properties by means of modifying the production method.
Additional improvements in physical properties have also been achieved by modifying the molecular design of PHA itself. For example, PTL 3 describes fibers obtained using poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereunder, "PHBH")comprising conventional 3-hydroxybutyrate as the first component with 3-hydroxyhexanoate as a second component.
PTL 4 describes a molded article with high elasticity obtained using poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with 4-hydroxybutyrate as a second component (hereunder, "P3HB4HB").

[CITATION LIST]

[PATENT LITERATURE]

[PTL 1] Japanese Patent Publication No. 3864187
[PTL 2] Japanese Patent Publication No. 3864188
[PTL 3] Japanese Patent Publication No. 5924623
[PTL 4] International Patent Publication No. WO2020/230807

SUMMARY

[TECHNICAL PROBLEM]

The technologies described in PTLs 1 to 4 are useful for production of PHA fibers having mechanical properties that meet commercial requirements, but they do not deal with the problem of storage stability.
In light of this issue in the prior art, the problem to be solved by the invention is to provide a continuous long fiber composed of an aliphatic copolymer polyester with excellent storage stability, satisfactory reelability after take-up and stable spinnability, as well as to provide multifilament yarn made of the fiber, a fabric, and a method for producing the fiber.

[SOLUTION TO PROBLEM]

As a result of diligent experimentation with the aim of solving this problem, the present inventors have found, unexpectedly, that the problem can be solved by the following construction, and the invention has been completed upon this finding.
Specifically, the present invention provides the following.

[1] A continuous long fiber comprising an aliphatic copolymer polyester, wherein the aliphatic copolymer polyester comprises 3-hydroxybutyrate as a first monomer unit and comprises 4-hydroxybutyrate or 3-hydroxyvalerate as a second monomer unit, the percentage of the second monomer unit with respect to the total monomer units being 1 mol% to 9 mol% when the second monomer unit is a 4-hydroxybutyrate unit, and the percentage of the second monomer unit with respect to the total monomer units being 1 mol% to 7.6 mol% when the second monomer unit is 3-hydroxyvalerate.
[2] The continuous long fiber according to [1] above, wherein the second monomer unit is 4-hydroxybutyrate, and the percentage of 4-hydroxybutyrate units with respect to the total monomer units is 4 mol% to 6 mol%.
[3] The continuous long fiber according to [1] or [2] above, wherein the X-ray orientation degree of the α-structure of the aliphatic copolymer polyester is 90% or greater.
[4] The continuous long fiber according to any one of [1] to [3] above, wherein the weight-average molecular weight is 150,000 or greater and the ratio of weight-average molecular weight/number-average molecular weight is 10 or lower.
[5] The continuous long fiber according to any one of [1] to [4] above, wherein the melting point peak in DSC is 110°C to 200°C.
[6] The continuous long fiber according to any one of [1] to [5] above, wherein the proportion Iβ/Iα between β crystals and α crystals is 0 to 0.6.
[7] The continuous long fiber according to any one of [1] to [6] above, wherein the percentage of the total of the first monomer unit and second monomer unit with respect to the total monomer units is 99 mol% or greater.
[8] The continuous long fiber according to any one of [1] to [7] above, wherein the monofilament fineness is 0.1 dtex to 30 dtex.
[9] Multifilament yarn composed of the continuous long fiber according to any one of [1] to [7] above, wherein the number of filaments is 6 to 300.
[10] The multifilament yarn according to [9] above, wherein the total fineness is 1 dtex to 200 dtex.
[11] A fabric composed of the continuous long fiber or multifilament yarn according to any one of [1] to [10] above.
[12] A method for producing the continuous long fiber according to any one of [1] to [8] above, the method comprising the following steps:
- a melting step in which an aliphatic copolymer polyester is melted,
- a discharge step in which the molten aliphatic copolymer polyester is discharged from a spinneret, and
- a cold drawing step in which the discharged aliphatic copolymer polyester is simultaneously drawn while being cooled in a cooling medium, wherein
- the temperature of the cooling medium is 30°C or lower, and the draw ratio in the cold drawing step is a factor of 4 or greater.
[13] The method according to [12] above, wherein an air-gap is provided between the spinneret and the cooling medium, and the draft ratio at the air-gap section is a factor of 1.1 or greater.
[14] The method according to [13] above, wherein the time required for the aliphatic copolymer polyester discharged from the spinneret to pass through the air-gap section is 5 seconds or less.
[15] The method according to any one of [12] to [14] above, wherein the residence time of the aliphatic copolymer polyester in the melting step is 900 seconds or less.

[ADVANTAGEOUS EFFECTS OF INVENTION]

A continuous long fiber composed of an aliphatic copolymer polyester according to the invention has excellent storage stability. The continuous long fiber also has satisfactory reelability after take-up without producing aggregation of the PHA resin during spinning, while also having stable spinnability without yarn breakage, thus improving productivity.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will now be described in detail.
One embodiment of the invention is a continuous long fiber comprising an aliphatic copolymer polyester, wherein the continuous long fiber comprises 3-hydroxybutyrate as a first monomer unit and comprises 4-hydroxybutyrate or 3-hydroxyvalerate as the second monomer unit, the percentage of the second monomer unit with respect to the total monomer units being 1 mol% to 9 mol% in the case of a 4-hydroxybutyrate unit and 1 mol% to 7.6 mol% in the case of 3-hydroxyvalerate.
A continuous long fiber is a continuously spun fiber, and the fiber length may be adjusted by processing using a cutter or similar means after spinning. The fiber length is not particularly restricted but is preferably 1 cm or greater, more preferably 10 m or greater, even more preferably 100 m or greater and most preferably 1000 m or greater. A finishing agent may also be added to the fiber, such as coating of an oil after spinning.
The continuous long fiber composed of an aliphatic copolymer polyester of this embodiment must have a monomer unit of 3-hydroxybutyrate represented by [-O-CH(CH₃)-CH₂-CO-] as the first monomer unit, and must have a monomer unit of 4-hydroxybutyrate represented by [-O-CH₂-CH₂-CH₂-CO-] or 3-hydroxyvalerate represented by [-O-CH(C₂H₅)-CH₂-CO-] as the second monomer unit. By having such a second monomer unit it is possible to exhibit sufficient marine biodegradability, while also maintaining mechanical strength provided by the first monomer unit and significantly improving the molding workability, and also allowing both strength and elongation to be exhibited within desired ranges.
For a continuous long fiber comprising an aliphatic copolymer polyester according to this embodiment, the percentage of the second monomer unit with respect to the total monomer units (hereunder abbreviated as "copolymerization ratio") is 9 mol% or lower, preferably 8 mol% or lower, more preferably 7 mol% or lower and even more preferably 6 mol% or lower, when the second monomer unit is a 4-hydroxybutyrate unit. A copolymerization ratio of 9 mol% or lower will result in sufficient mechanical properties. The lower limit for the copolymerization ratio is 1 mol% or greater, preferably 3 mol% or greater and more preferably 4 mol% or greater, from the viewpoint of ensuring excellent molding workability.
When the second monomer unit is 3-hydroxyvalerate, the copolymerization ratio is 7.6 mol% or lower, preferably 7 mol% or lower and more preferably 6 mol% or lower, from the viewpoint of exhibiting satisfactory mechanical properties. The lower limit for the copolymerization ratio is 1 mol% or greater, preferably 2 mol% or greater and more preferably 3 mol% or greater, from the viewpoint of ensuring excellent molding workability.
The method of controlling the copolymerization ratio is not particularly restricted, but it may be appropriate selection of microorganisms, or adjustment of the composition conditions and culturing conditions for the fermentation starting material.
The copolymerization ratio referred to here can be measured by the following method.
The aliphatic copolymer polyester is dissolved in chloroform-d (99.8% chloroform-d by FujiFilm-Wako) to a 1.5 mass% concentration for use as a measuring sample. 1H-NMR measurement is performed using a nuclear magnetic resonance spectrometer (Bruker BioSpin AVANCE II 400), with an observation frequency of 400 MHz, 64 scans, a chemical shift reference of 7.26 ppm for chloroform (product of FujiFilm-Wako), and chloroform-d as the lock solvent.
When 4-hydroxybutyrate is present as the second monomer unit, the integral of the triplet peak observed at a chemical shift of 4.1 ppm ±0.2 is recorded as A, and the integral of the quartet peak observed at a chemical shift of 5.3 ±0.2 ppm is recorded as B. The copolymerization ratio C (mol%) is calculated by the following formula: $C = (A / 2) / (A / 2 + B) \times 100 [mol %] .$
When 3-hydroxyvalerate is present as the second monomer unit, the integral of the triplet peak observed at a chemical shift of 0.88 ±0.2 ppm is recorded as D, and the integral of the doublet peak observed at a chemical shift of 1.25 ppm ±0.2 is recorded as E. The copolymerization ratio F (mol%) is calculated by the following formula:
$F = (D / 3) / (D / 3 + E / 3) \times 100 [mol %] .$
The continuous long fiber composed of an aliphatic copolymer polyester of this embodiment preferably has a single fiber fineness of 30 dtex or lower, more preferably 20 dtex or lower and even more preferably 10 dtex or lower, from the viewpoint of obtaining a suitable feel and tactile sensation for practical use. If the monofilament fineness is 30 dtex or lower, the strength of the fiber may be insufficient or yarn breakage may occur during spinning, but this can be improved by adjusting the copolymerization ratio or the X-ray orientation degree of the α-structure. The lower limit for the single fiber fineness is preferably 0.1 dtex or greater from the viewpoint of obtaining an acceptable frequency of yarn breakage for practical use. The monofilament fineness referred to here can be measured by the following method.
The obtained continuous long fiber, as a monofilament, is humidified overnight in a loosely stretched state in an atmosphere at room temperature (23°C) and humidity of 50% RH. A 1 m portion is cut from the humidified sample and its weight is measured at 10 points, and the number-average value is multiplied by 10,000 to obtain the monofilament fineness (dtex) of the sample.
A continuous long fiber composed of an aliphatic copolymer polyester of this embodiment is preferably used in multifilament yarn. The total number of filaments is preferably 6 filaments or more and more preferably 11 filaments or more, from the viewpoint of exhibiting high mechanical properties while also having a suitable feel for practical use and a tactile sensation. The upper limit for the total number of filaments is not particularly restricted, but it is preferably no more than 300 filaments from the viewpoint of an acceptable frequency of yarn breakage for practical use.
The multifilament yarn of the embodiment preferably has a total fineness of 200 dtex or lower and more preferably 100 dtex or lower, from the viewpoint of exhibiting high mechanical properties while also having a suitable feel for practical use and a tactile sensation. The lower limit for the total fineness is preferably 1 dtex or greater from the viewpoint of an acceptable frequency of yarn breakage for practical use. The total fineness referred to here can be measured by the following method.
The obtained fiber is humidified overnight in a loosely stretched state in an atmosphere of room temperature (23°C) and humidity of 50% RH. A 1 m portion is cut out from the humidified sample and its weight is measured at 10 points, and the number-average value is multiplied by 10,000 to obtain the total fineness (dtex) of the sample.
The continuous long fiber composed of the aliphatic copolymer polyester of this embodiment has an α-structure X-ray orientation degree of preferably 90% or greater, more preferably 92% or greater and even more preferably 94% or greater. The α-structure referred to here is a lamellar crystal structure composed of folds of a helical structure, as a higher-order structure that significantly contributes to the mechanical strength of the molded article. If the X-ray orientation degree of the α-structure is 90% or greater, sufficient mechanical properties, and especially strength, will be exhibited and the storage stability will be excellent, while aggregation resulting from the amorphous structure on the surface of the molded article will also be eliminated, and reelability of the fiber will be satisfactory. The upper limit is not particularly restricted but may be 99% or lower in terms of the actual degree of orientation. In order to obtain an α-structure X-ray orientation degree of 90% or greater, it is important to produce the aliphatic copolymer polyester of this embodiment under the production conditions described below.
The X-ray orientation degree of the α-structure can be measured by the following method.
Using an X-ray structural analysis system (Rigaku, SmartLab) and a multidimensional pixel array detector (Rigaku, HiPix-3000), with Cu as the X-ray source, a collimator diameter of 0.1 mm, an X-ray wavelength of 0.1 nm, a camera length of 27 mm and an exposure time of 10 min, the test piece is set parallel to the detector and perpendicular to the X-ray beam, to obtain a 2D diffraction image. The region from diffraction angle 2θ = 15° to 18° in a WAXD image measured by wide-angle X-ray diffraction (WAXD) is isolated as the (020) plane diffraction peak, a ringshaped region including the (020) plane diffraction peak is selected, all of the diffraction intensities with the same azimuth are summed, and intensity is plotted with respect to azimuth to create a one-dimensional azimuthal profile. The full width at half maximum (FWHM: peak width at half the height of the peak) is measured for peaks at the locations of diffraction spots. Representing the average value for the full width at half maximum for each peak as H, the degree of orientation G [%] is calculated by the following formula: $G = (180 - H) / 180 \times 100 [%] .$
The continuous long fiber composed of an aliphatic copolymer polyester of this embodiment has a weight-average molecular weight of preferably 150,000 or higher, more preferably 200,000 or higher and even more preferably 250,000 or higher. If the weight-average molecular weight is 150,000 or higher, sufficient mechanical properties, and especially strength, will be exhibited. The upper limit for the weight-average molecular weight is preferably 3,000,000 or lower from the viewpoint of allowing practical and stable molding to be carried out.
The continuous long fiber composed of an aliphatic copolymer polyester of this embodiment has a ratio of weight-average molecular weight/number-average molecular weight of preferably 10 or lower, more preferably 7 or lower and even more preferably 5 or lower. If the weight-average molecular weight/number-average molecular weight ratio is 10 or lower, molding will be stable and the mechanical properties will also be stabilized. The lower limit for the weight-average molecular weight/number-average molecular weight ratio is preferably 1.1 or higher from the viewpoint of actual synthesis.
The weight-average molecular weight and number-average molecular weight referred to here can be measured by the following methods.
The aliphatic copolymer polyester is dissolved in chloroform (FujiFilm-Wako) to a 0.1 mass% concentration. A gel permeation chromatography apparatus (HLC-8320GPC by Tosoh Corp.) is used, with a guard column (TSKgel guard column SuperHZ-L by Tosoh Corp.) and an analysis column (TSKgel SuperHZM-M by Tosoh Corp.) as columns. The column temperature is 40°C, the eluent is chloroform, the flow speed is 0.35 mL/min, the injection rate is 20 µL and the detector is RI, and a polystyrene standard sample (Agilent Technologies EasiCal PS-1) is measured, drawing a calibration curve using data processing software (HLC-8320GPC Ecosec-WS by Tosoh Corp.). An aliphatic copolymer polyester compact sample is also measured in the same manner, and the weight-average molecular weight and number-average molecular weight are calculated from the calibration curve.
The melting point peak of the continuous long fiber composed of the aliphatic copolymer polyester of this embodiment is preferably 110°C or higher and more preferably 130°C or higher, from the viewpoint of ensuring practical heat resistance. The upper limit for the melting point peak is preferably 200°C or lower and more preferably 180°C or lower as the limit for obtaining a stable melt by stable practical spinning, since an excessively high melting point peak will reduce the difference with the thermal decomposition temperature and make it difficult to achieve stable melting.
The melting point peak referred to here can be measured by the following method.
The melting point peak is measured using a differential scanning calorimeter (PerkinElmer, DSC8500) equipped with an intracooler. The measuring atmosphere is nitrogen (20 ml/min), and the temperature is raised from -50°C to 200°C at 20°C/min and held for 1 minute for complete melting of the sample. It is then quenched from 200°C to -50°C at 20°C/min and held for 3 minutes, after which the temperature is again raised to 200°C at 20°C/min (this temperature increase being the second run). The melting point peak is measured using a DSC curve (thermogram) measured in the second run. As temperature increase continues, a melting peak (endothermic peak) appears in the DSC curve, and the temperature at the apex peak position is recorded as the melting point. Approximately 5 mg of sample is used, with an aluminum sample pan. Indium is used for temperature calibration.
The continuous long fiber composed of an aliphatic copolymer polyester of this embodiment has an X-ray diffraction intensity ratio Iβ/Iα (for β-structure and α-structure) of preferably 0.6 or lower, more preferably 0.3 or lower and even more preferably 0.2 or lower. The term "β-structure" here means a β-type crystal structure formed by a fully extended chain, and it has low thermodynamic stability. If the X-ray diffraction intensity ratio Iβ/Iα of the β-structure and α-structure is 0.6 or lower, the low stability β-structure will be less likely to disappear with time, resulting in superior storage stability.
The X-ray diffraction intensity ratio Iβ/Iα between the β-structure and α-structure can be measured by the following method.
Using an X-ray structural analysis system (Rigaku, SmartLab) and a multidimensional pixel array detector (Rigaku, HiPix-3000), with Cu as the X-ray source, a collimator diameter of 0.1 mm, an X-ray wavelength of 0.1 nm, a camera length of 27 mm and an exposure time of 10 min, the test piece is set parallel to the detector and perpendicular to the X-ray beam, to obtain a 2D diffraction image. When the diffraction intensity distribution in the equatorial direction of the 2D diffraction image is measured, the diffraction intensity comprises both amorphous scattering and crystal diffraction. Crystal diffraction includes diffraction due to α and β structures which produce diffraction at specific locations, with the diffraction intensity being proportional to the amount of crystals. Therefore, by taking the ratio between the diffraction intensity based on α-structure and the diffraction intensity based on β-structure, it is possible to obtain an index relating to the amount of β-structure. However, since the intensity based on amorphous scattering produces interference, it is necessary to remove the effect of intensity based on amorphous scattering in order to determine the amount of β-structure in the crystal. Since the intensity based on amorphous scattering is observed as a rise of a broader baseline than the intensity based on crystal diffraction, a line connecting angles 2θ = 15° and 21°, which are less affected by diffraction from crystals, is considered to be the intensity based on amorphous scattering, and this portion is subtracted from the diffraction intensity. In the subsequent diffraction intensity distribution, the maximum value between diffraction angles 2θ = 15° and 18° is recorded as the diffraction intensity (Iα) due α-structure, and the maximum value between diffraction angles 18° and 21° is recorded as the diffraction intensity (Iβ) due to β-structure. Their ratio Iβ/Iα is used as the β-structure/α-structure X-ray diffraction intensity ratio.
There are no particular restrictions on the method for synthesizing the aliphatic copolymer polyester, but it is preferably produced from a microorganism, with examples of microorganisms that produce aliphatic copolymer polyesters including microorganisms that can produce PHAs. Examples of P3HB-producing microorganisms include Bacillus megaterium (discovered in 1925) as well as other natural microorganisms such as Cupriavidus necator (former classification: Alcaligenes eutrophus), Ralstonia eutropha and Alcaligenes latus, which accumulate PHA in their cells.
A genetically modified microorganism having any of various PHA synthesis-related genes transferred may also be used, with optimization of the culturing conditions including substrate type.
The continuous long fiber composed of the aliphatic copolymer polyester of this embodiment may be used as a fabric obtained by secondary processing. The structure of the fabric is not particularly restricted and may be selected as appropriate for the use and purpose, such as a knitted fabric or woven fabric. The weight per unit area (basis weight) of the fabric is not particularly restricted and may be 1 to 1000 g/m², for example.
The PHA may be PHA-containing granules without purification, or it may be purified and pelletized. From the viewpoint of improving the molding workability during melt extrusion, a plasticizer, lubricant or crystal nucleating agent may be added, or another polymer may be used as a blend.
The method of melt extruding the PHA may be carried out using a common melting technique for plastic fibers, and for example, it may be carried out by heating and melting the PHA, subjecting it to a load and extruding it through an extrusion port. The extrusion method may be extrusion with a syringe or extrusion with a screw, but it is preferably extrusion with a screw to produce a continuous long fiber.
The temperature during melt extrusion will usually be at least the melting point onset peak of PHA as measured by DSC, from the viewpoint of allowing extrusion and accomplishing sufficient drawing after extrusion.
The molten PHA is extruded into a cooling medium and quenched to form a fiber. The temperature for quenching and fiber formation is preferably 30°C or lower and more preferably 20°C or lower. The lower limit is not particularly fixed but may usually be -200°C or higher from the viewpoint of economy. The quenching step converts the molten PHA into an amorphous fiber with high stretchability, and can reduce time-related deterioration during the process. The obtained fiber may be drawn and taken up into a cooling solvent.
The cooling medium is not particularly restricted, and examples include air, water (ice water), inert gases, and antifreeze solutions composed mainly of ethylene glycol or propylene glycol. The cooling method is also not particularly restricted, and for example, it may be a method of filling a bath with a cooling medium and passing through PHA, a method using a fluidized bath, a method using a cooling plate, a method using a cooling ring that allows cold air to be uniformly applied to the fiber in all directions around 360°, or a method using a blower. According to the invention, quenching can be accomplished, for example, by extruding molten PHA into a bath filled with a cooling medium at 30°C or lower, and passing it through the solvent while it is taken up with a roller in the bath.
The obtained fiber is cold drawn in the cooling step. The cold drawing may be carried out, for example, by anchoring it to a drawing machine, and it is preferably carried out with application of tensile force produced by a speed difference between two stretching rollers taking up the fiber. The draw ratio is preferably a factor of at least 4, more preferably at least 7 and even more preferably at least 10. The upper limit is not particularly restricted so long as no tearing occurs, and may be up to a factor of 50. The draw time is preferably 1 minute or less and more preferably 30 seconds or less from the viewpoint of productivity. The lower limit is not particularly fixed, but in practical terms it may be 0.001 seconds or longer.
The draw ratio referred to here can be measured by the following method.
A length of 10 cm is sampled, for both the fiber immediately before drawing and the fiber immediately after drawing. The obtained fiber is humidified overnight in a loosely stretched state in an atmosphere at room temperature (23°C) and 50% RH. The weight at 10 points of the humidified sample is measured and the number-average value is calculated. The value immediately before drawing is divided by the value immediately after drawing to obtain the draw ratio.
An air-gap is preferably provided between the cooling step and the discharge port, as an air layer for slow cooling of the extruded resin. It may be blasted or radiantly cooled through the air-gap, or the temperature may be adjusted by surrounding the air-gap with an enclosure. By providing an air-gap, the resin that has been extruded in a molten state undergoes slow cooling, thus promoting suitable crystallization on the surface while inhibiting aggregation of the fiber surface, and resulting in satisfactory reelability after the continuous long fiber has been taken up. Adjustment of crystallization and crystal growth of the fiber can also improve the mechanical properties and productivity. The air-gap temperature is not particularly restricted and may usually be in the range of 0°C to 100°C.
At the air-gap section, the appropriate drawing orientation is applied to the fiber by the difference between the discharge linear speed and the speed during take-up in the subsequent step, and this is referred to as the "draft ratio".
The draft ratio is preferably a factor of 1.1 or greater and more preferably a factor of 1.5 or greater. With a factor of 1.1 or greater, oriented crystallization will proceed by appropriate drawing, allowing the fiber surfaces to crystallize and inhibiting aggregation. In addition, yarn breakage during the subsequent cold drawing step can be suppressed and sufficient drawing treatment can be carried out, resulting in adequate mechanical strength. The upper limit for the draft ratio is not particularly fixed but may usually be a factor of 100 or lower.
The transit time of the fiber through the air-gap section is preferably 5 seconds or less, more preferably 3 seconds or less and even more preferably 1 second or less. If the transit time is 5 seconds or less, excessive crystallization of the molten resin can be inhibited and the degree of orientation of the α-structure can be effectively increased during the cold drawing step, allowing sufficient mechanical strength to be exhibited and reducing brittleness caused by excessive crystallization, thus helping to inhibit yarn breakage in the air-gap. The lower limit for the transit time of the fiber through the air-gap section is not particularly fixed, but in practice it may be 0.0001 seconds or longer.
When a PHA is heated and melted, subjected to a load and extruded from an extrusion outlet, the transit time from the PHA inlet to the extrusion outlet is referred to as the residence time in the extrusion unit. The residence time at the extrusion unit is preferably 900 seconds or less, more preferably 600 seconds or less, even more preferably 300 seconds or less and most preferably 200 seconds or less. If the residence time at the extrusion unit is 900 seconds or less it will be possible to suppress reduction in molecular weight caused by thermal decomposition of the resin, and to exhibit adequate mechanical strength. The method of extrusion is not particularly restricted, and for example, it may be extrusion with a syringe, extrusion with a single screw or extrusion with a twin screw.
The obtained fiber may also be supplied to a different step, so long as that does not affect the mechanical strength or storage stability. The other step is not particularly restricted and may be, for example, aligned winding, twilling treatment, or redrawing after completion of winding. By stabilizing the degree of crystallinity and crystal structure of the fiber by heat treatment of the fiber, it is possible to stabilize the mechanical strength and increase the storage stability. The method of heat treatment is not particularly restricted, and a warm bath, heating roller or tunnel drying furnace, for example, may be provided during the process for continuous heat treatment, or the wound fiber may be allowed to stand in a dryer or thermostatic device for heat treatment.

EXAMPLES

The present invention will now be explained in greater detail using Examples and Comparative Examples. The physical property evaluation and performance evaluation were conducted by the following methods.

(1) [Percentage of second monomer unit with respect to total monomer units (copolymerization ratio)]

The aliphatic copolymer polyester was dissolved in chloroform-d (99.8% chloroform-d by FujiFilm-Wako) to a 1.5 mass% concentration for use as a measuring sample. 1H-NMR measurement was performed using a nuclear magnetic resonance spectrometer (Bruker BioSpin AVANCE II 400), with an observation frequency of 400 MHz, 64 scans, a chemical shift reference of 7.26 ppm for chloroform, and chloroform-d as the lock solvent.
When 4-hydroxybutyrate was present as the second monomer unit, the integral of the triplet peak observed at a chemical shift near 4.1 ppm was recorded as A, the integral of the quartet peak observed at a chemical shift of 5.3 ppm was recorded as B, and the copolymerization ratio C (mol%) was calculated by the following formula: $C = (A / 2) / (A / 2 + B) [mol %] .$
When 3-hydroxyvalerate was present as the second monomer unit, the integral of the triplet peak observed at a chemical shift near 0.88 ppm was recorded as D, the integral of the doublet peak observed at a chemical shift near 1.25 ppm was recorded as E, and the copolymerization ratio F (mol%) was calculated by the following formula: $F = (D / 3) / (D / 3 + E / 3) [mol %] .$

(2) [α-structure orientation degree]

Using an X-ray structural analysis system (Rigaku, SmartLab) and a multidimensional pixel array detector (Rigaku, HiPix-3000), with Cu as the X-ray source, a collimator diameter of 0.1 mm, an X-ray wavelength of 0.1 nm, a camera length of 27 mm and an exposure time of 10 min, the test piece was set parallel to the detector and perpendicular to the X-ray beam, to obtain a 2D diffraction image. The region from diffraction angle 2θ = 15° to 18° in a WAXD image measured by wide-angle X-ray diffraction (WAXD) was isolated as the (020) plane diffraction peak, a ringshaped region including the (020) plane diffraction peak was selected, all of the diffraction intensities with the same azimuth were summed, and intensity was plotted with respect to azimuth to create a one-dimensional azimuthal profile. The full width at half maximum (FWHM: peak width at half the height of the peak) was measured for peaks at the locations of diffraction spots. Representing the average value for the full width at half maximum for each peak as H, the degree of orientation G [%] was calculated by the following formula: $G = (180 - H) / 180 \times 100 [%] .$

(3) [Weight-average molecular weight (Mw), and weight-average molecular weight (Mw)/number-average molecular weight (Mn) ratio]

The aliphatic copolymer polyester was dissolved in chloroform (FujiFilm-Wako) to a 0.1 mass% concentration. A gel permeation chromatography apparatus (HLC-8320GPC by Tosoh Corp.) was used, with a guard column (TSKgel guard column SuperHZ-L by Tosoh Corp.) and an analysis column (TSKgel SuperHZM-M by Tosoh Corp.) as columns. The column temperature was 40°C, the eluent was chloroform, the flow speed was 0.35 mL/min, the injection rate was 20 µL and the detector was RI, and a polystyrene standard sample (Agilent Technologies EasiCal PS-1) was measured, drawing a calibration curve using data processing software (HLC-8320GPC Ecosec-WS by Tosoh Corp.). An aliphatic copolymer polyester compact sample was also measured in the same manner, and the weight-average molecular weight and number-average molecular weight were calculated from the calibration curve.

(4) [Melting point peak]

This was measured using a differential scanning calorimeter (PerkinElmer, DSC8500) equipped with an intracooler. The measuring atmosphere was nitrogen (20 ml/min), and the temperature was raised from -50°C to 200°C at 20°C/min and held for 1 minute for complete melting of the sample. It was then quenched to -50°C at 200°C/min and held for 3 minutes, after which the temperature was again raised to 200°C at 20°C/min (this temperature increase being the second run). The melting point peak was measured using a DSC curve (thermogram) measured in the second run. Since a melting peak (endothermic peak) appears in the DSC curve with continued temperature increase, the temperature at the apex peak position was recorded as the melting point. Approximately 1 mg of sample was used, with an aluminum sample pan. Indium was used for temperature calibration.

(5) [X-ray diffraction intensity ratio of β-structure and α-structure (Iβ/Iα)]

Using an X-ray structural analysis system (Rigaku, SmartLab) and a multidimensional pixel array detector (Rigaku, HiPix-3000), with Cu as the X-ray source, a collimator diameter of 0.1 mm, an X-ray wavelength of 0.1 nm, a camera length of 27 mm and an exposure time of 10 min, the test piece was set parallel to the detector and perpendicular to the X-ray beam, to obtain a 2D diffraction image. A one-dimensional profile was prepared for the diffraction intensity distribution in the equatorial direction in a 2D diffraction image, a line connecting 2θ = 15° and 21° was considered to be the intensity based on amorphous scattering, and this portion was subtracted from the diffraction intensity. In the subsequent diffraction intensity distribution, the maximum value between diffraction angles 2θ = 15° and 18° is recorded as the diffraction intensity (Iα) due to α-structure, and the maximum value between diffraction angles 18° and 21° is recorded as the diffraction intensity (Iβ) due to β-structure. Their ratio Iβ/Iα was used as the β-structure/α-structure X-ray diffraction intensity ratio.

(6) [Breaking strength and breaking elongation]

Following the method of JIS L 1013, a fiber was attached to the grip section of a TENSILON universal testing machine (RTG-1250) by A&D Co., Ltd. in a loosely stretched state, a 50 N load cell was used for a tensile test at a grip spacing of 30 cm and a pull rate of 30 cm/min, the load and elongation at the time the sample cut was measured at 10 points, and the strength and ductility were calculated by the following formulas: Strength (cN/dtex) = strength at cutting or strength at maximum load (cN)/fineness of sample (dtex) Ductility (%) = elongation at cutting or elongation at maximum load (mm)/grip spacing (mm) at cutting (mm) × 100, recording the number-average values as the strength (average strength) and ductility of the sample. When the breaking strength was smaller than the strength at maximum load, the strength at maximum load and the elongation at that moment were measured.

(7) [Stable spinning time]

The time until filaments could no longer be taken up due to breakage or poor discharge at the extrusion unit was measured and recorded as the stable spinning time (min). When stable spinning could be carried out for longer than 60 minutes, the time was recorded as: >60 min.

(8) [Reelability]

The taken-up sample was manually unreeled and the condition of unreeling problems due to aggregation was assessed on the following 3-level evaluation scale.

"-": Absolutely no aggregation, absolutely no unreeling problems.
"+": Aggregation observed, some unreeling problems occurred.
"++": Considerable aggregation observed, many unreeling problems occurred.

(9) [Storage stability]

The obtained sample was stored in an atmosphere at room temperature (23°C) and 50% RH, and the breaking strength and breaking elongation of the sample were evaluated each week. The storage stability was recorded as the number of weeks of storage when the average value of the breaking strength was below 150 MPa or the average value of the breaking elongation exceeded 150%, for evaluation with N = 10. When the storage stability exceeded 48 weeks, the evaluation was: >48 weeks.

(10) [Tubular knitted fabric softness]

A fiber sample was supplied to a tubular knitting machine (NCR-ES single-loop test tubular knitting machine by Eiko Industrial Co., Ltd.), and the density was adjusted to 50 with the tubular knitting machine to produce a tubular knitted fabric. The obtained tubular knitted fabric was handled by 5 participants who subsequently answered a questionnaire regarding softness. A judgment of "excellent softness" was given when the knitted fabric had a soft feel when handled, and the evaluation assigned was "VG" for excellent softness judged by 5 persons, "G" for 4 persons, "F" for 3 persons, and "P" for 2 or fewer persons.

[Example 1]

The PHA-producing microorganism used was Cupriavidus necator H16 (ATCC17699), with appropriate adjustment of the starting materials and culturing conditions, and the PHA was used as pellets. The obtained PHA was P3HB4HB, having a copolymerization ratio of 6.0%.
The pellets were melt extruded with a melt extruder (ALM-E005-H by AIKI Riotech Corp.) heated to 170°C with a residence time of 600 seconds, and were spun using a nozzle with 12 holes and a hole diameter of 0.2 mm, applying a draft with a factor of 1.5 at the air-gap section with a 3-second transit through the air-gap section, and the mixture was cooled at 5°C in a cooling step, stretched at a draw ratio of 7 in the cooling step, and finally taken up with a winder, after which the sample was placed in a blow dryer (DKM401 by Yamato Scientific Co., Ltd.) set to 60°C, and after standing for 30 minutes, it was removed to produce a 1000 m multifilament continuous long fiber. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 2]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain P3HB4HB with a copolymerization ratio of 4.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 3]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain P3HB4HB with a copolymerization ratio of 9.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 4]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain P3HB4HB with a copolymerization ratio of 8.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 5]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain P3HB4HB with a copolymerization ratio of 7.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 6]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain P3HB4HB with a copolymerization ratio of 1.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 7]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain P3HB4HB with a copolymerization ratio of 3.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 8]

A PHA fiber was produced by the same method as Example 1, except that the cold draw ratio was 10. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 9]

A PHA fiber was produced by the same method as Example 1, except that the air-gap time was 1 second. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 10]

A PHA fiber was produced by the same method as Example 1, except that the residence time in the extrusion unit was 300 seconds. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 11]

A PHA fiber was produced by the same method as Example 1, except that the cold draw ratio was 3. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 12]

A PHA fiber was produced by the same method as Example 1, except that the draft ratio was 1.0. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 13]

A PHA fiber was produced by the same method as Example 1, except that the air-gap time was 7 seconds. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 14]

A PHA fiber was produced by the same method as Example 1, except that the residence time was 1000 seconds. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 15]

A PHA fiber was produced by the same method as Example 1, except that the composition and the culturing conditions of the fermentation starting material were changed to obtain poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (hereunder abbreviated as PHBV) with a copolymerization ratio of 6.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 16]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain PHBV with a copolymerization ratio of 7.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 17]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain PHBV with a copolymerization ratio of 7.6%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 18]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain PHBV with a copolymerization ratio of 1.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 19]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain PHBV with a copolymerization ratio of 2.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Example 20]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain PHBV with a copolymerization ratio of 3.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Comparative Example 1]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain P3HB4HB with a copolymerization ratio of 10.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Comparative Example 2]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain P3HB4HB with a copolymerization ratio of 0.6%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Comparative Example 3]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain PHBV with a copolymerization ratio of 8.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Comparative Example 4]

A PHA fiber was produced by the same method as Example 1, except that the fermentation starting material composition and the culturing conditions were changed to obtain PHBV with a copolymerization ratio of 0.6%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Comparative Example 5]

A PHA fiber was produced by the same method as Example 1, except that the composition and the culturing conditions of the fermentation starting material were changed to obtain 3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBH) with a copolymerization ratio of 6.0%. After production, the physical properties and performance were evaluated as shown in Table 1.

[Table 1]

		Production method							Physical properties					Effect
		Resin type	Copolymerization ratio	Melting temp.	Cold draw ratio	Draft ratio	Air-gap time	Residence time	α-structure orientation degree	Mol. wt. (Mw)	Mw/Mn	Melting point peak (Tm)	Iβ/Iα	Stable spinning	Poor unreeling	Breaking strength	Breaking elongation	Storage stability
			mol%	°C			sec	sec	%	×10,000		°C		min		MPa	%	week
Example	1	P3HB4HB	6.0	170	7	1.5	3	600	93	25	4.5	165	0.10	>60	-	350	85	>48
	2	P3HB4HB	4.0	175	7	1.5	3	600	93	25	7.0	170	0.15	>60	-	360	50	>48
	3	P3HB4HB	9.0	160	7	1.5	3	600	90	25	3.7	155	0.05	>60	-	250	120	>48
	4	P3HB4HB	8.0	163	7	1.5	3	600	91	25	4.1	160	0.05	>60	-	270	120	>48
	5	P3HB4HB	7.0	167	7	1.5	3	600	93	25	4.0	160	0.05	>60	-	290	90	>48
	6	P3HB4HB	1.0	180	7	1.5	3	600	93	25	8.5	175	0.20	30	-	210	20	>48
	7	P3HB4HB	3.0	175	7	1.5	3	600	93	25	7.1	170	0.20	45	-	350	35	>48
	8	P3HB4HB	6.0	170	10	1.5	3	600	95	25	4.5	165	0.15	>60	-	450	50	>48
	9	P3HB4HB	6.0	170	7	1.5	1	600	94	25	4.5	165	0.05	>60	-	380	100	>48
	10	P3HB4HB	6.0	170	7	1.5	3	300	95	35	3.1	160	0.10	>60	-	450	70	>48
	11	P3HB4HB	6.0	170	3	1.5	3	600	89	25	4.5	165	0.05	>60	+	140	85	24
	12	P3HB4HB	6.0	170	7	1.0	3	600	89	25	4.5	165	0.10	30	+	130	90	>48
	13	P3HB4HB	6.0	170	7	1.5	7	600	88	25	4.5	165	0.10	20	-	130	90	>48
	14	P3HB4HB	6.0	170	7	1.5	3	1000	88	14	10.5	170	0.10	>60	-	120	70	>48
	15	PHBV	6.0	180	7	1.5	3	600	93	30	4.4	175	0.40	>60	-	380	45	>48
	16	PHBV	7.0	180	7	1.5	3	600	92	30	4.0	175	0.30	>60	-	350	75	>48
	17	PHBV	7.6	180	7	1.5	3	600	90	30	4.3	175	0.30	>60	-	230	85	>48
	18	PHBV	1.0	180	7	1.5	3	600	94	30	6.5	175	0.60	30	-	220	20	24
	19	PHBV	2.0	180	7	1.5	3	600	93	30	6.1	175	0.60	45	-	240	25	24
	20	PHBV	3.0	180	7	1.5	3	600	93	30	4.6	175	0.50	>60	-	390	35	32
Comp. Example	1	P3HB4HB	10.0	160	7	1.5	3	600	87	25	3.7	155	0.05	>60	++	100	190	12
	2	P3HB4HB	0.6	180	7	1.5	3	600	90	25	8.8	175	0.20	5	-	140	15	12
	3	PHBV	8.0	180	7	1.5	3	600	87	30	4.8	175	0.30	5	++	140	80	12
	4	PHBV	0.6	180	7	1.5	3	600	90	30	6.9	175	0.70	5	-	130	20	12
	5	PHBH	6.0	170	7	1.5	3	600	88	30	4.1	165	0.20	10	+	120	70	12

[Example 21]

The PHA fiber produced in Example 1 was used to produce a tubular knitted fabric. The monofilament fineness was 8 dtex, the total fineness was 96 dtex, the number of filaments was 12, and the softness evaluation was "VG". The results are shown in Table 2 below.

[Example 22]

A PHA fiber was produced and a tubular knitted fabric was fabricated by the same method as Example 1, except that the spinning amount was adjusted so that the monofilament fineness was 5 dtex and the total fineness was 60 dtex. The monofilament fineness was 5 dtex, the total fineness was 60 dtex, the number of filaments was 12, and the softness evaluation was "VG". The results are shown in Table 2 below.

[Example 23]

A PHA fiber was produced and a tubular knitted fabric was fabricated by the same method as Example 1, except that a nozzle with a hole diameter of 0.2 mm and 36 holes was used, and the spinning amount was adjusted so that the monofilament fineness was 2 dtex and the total fineness was 72 dtex. The monofilament fineness was 2 dtex, the total fineness was 72 dtex, the number of filaments was 36, and the softness evaluation was "VG". The results are shown in Table 2 below.

[Example 24]

A PHA fiber was produced and a tubular knitted fabric was fabricated by the same method as Example 1, except that a nozzle with a hole diameter of 0.2 mm and 100 holes was used, and the spinning amount was adjusted so that the monofilament fineness was 0.5 dtex and the total fineness was 50 dtex. The monofilament fineness was 0.5 dtex, the total fineness was 100 dtex, the number of filaments was 100, and the softness evaluation was "VG". The results are shown in Table 2 below.

[Example 25]

A PHA fiber was produced and a tubular knitted fabric was fabricated by the same method as Example 1, except that a nozzle with a hole diameter of 0.2 mm and 6 holes was used, and the spinning amount was adjusted so that the monofilament fineness was 15 dtex and the total fineness was 90 dtex. The monofilament fineness was 15 dtex, the total fineness was 90 dtex, the number of filaments was 6, and the softness evaluation was "G". The results are shown in Table 2 below.

[Example 26]

A PHA fiber was produced and a tubular knitted fabric was fabricated by the same method as Example 1, except that the spinning amount was adjusted so that the total fineness was 192 dtex. The monofilament fineness was 16 dtex, the total fineness was 192 dtex, the number of filaments was 12, and the softness evaluation was "G". The results are shown in Table 2 below.

[Example 27]

A PHA fiber was produced and a tubular knitted fabric was fabricated by the same method as Example 1, except that the spinning amount was adjusted so that the total fineness was 252 dtex. The monofilament fineness was 21 dtex, the total fineness was 250 dtex, the number of filaments was 12, and the softness evaluation was "F" due to the large total fineness. The results are shown in Table 2 below.

[Example 28]

A PHA fiber was produced and a tubular knitted fabric was fabricated by the same method as Example 1, except that a nozzle with a hole diameter of 0.2 mm and 4 holes was used, and the spinning amount was adjusted so that the monofilament fineness was 23 dtex and the total fineness was 92 dtex. The monofilament fineness was 23 dtex, the total fineness was 92 dtex, the number of filaments was 4, and the softness evaluation was "F" due to the low number of filaments. The results are shown in Table 2 below.

[Example 29]

A PHA fiber was produced and a tubular knitted fabric was fabricated by the same method as Example 1, except that a nozzle with a hole diameter of 0.2 mm and 6 holes was used, and the spinning amount was adjusted so that the monofilament fineness was 30 dtex and the total fineness was 180 dtex. The monofilament fineness was 30 dtex, the total fineness was 180 dtex, the number of filaments was 6, and the softness evaluation was "F". The results are shown in Table 2 below.

[Example 30]

A PHA fiber was produced and a tubular knitted fabric was fabricated by the same method as Example 1, except that a nozzle with a hole diameter of 0.2 mm and 6 holes was used, and the spinning amount was adjusted so that the monofilament fineness was 35 dtex and the total fineness was 210 dtex. The monofilament fineness was 35 dtex, the total fineness was 210 dtex, the number of filaments was 6, and the softness evaluation was "P". The results are shown in Table 2 below.

[Table 2]

		Fiber			Effect
		Monofilament fineness	Total fineness	Number of filaments	Softness
		dtex	dtex	Count
	21	8	96	12	VG
	22	5	60	12	VG
	23	2	72	36	VG
	24	0.5	50	100	VG
Example	25	15	90	6	G
Example	26	16	192	12	G
	27	21	252	12	F
	28	22	92	4	F
	29	30	180	6	F
	30	35	210	6	P

[Example 31]

The fiber produced in Example 1 was peeled off using scissors in the widthwise direction of the winding tube, and a length measuring cutter (Portable Cutter PC-1Z Tokyo Ideal Co., Ltd.) was used for cutting to a width of 51 mm, to prepare staple fibers. The obtained staple fibers were used to produce spun yarn with an English cotton count of 30/1 (corresponding to a total fineness of 198 dtex) by ring spinning, to produce a tubular knitted fabric. The softness of the obtained knitted fabric was evaluated as "F".

[Example 32]

Using the same pellets as in Example 1, a cylinder-type melt extruder (IMC-19F8 by Imoto Machinery Co., Ltd.) was used to fill 5 g of pellets into a cylinder with a diameter of 6 mm, which were extruded from a 2 mm single-hole discharge die at an extrusion speed of 0.5 mm/sec. After winding up onto a roller at 23°C and allowing to stand for 30 minutes at 23°C while wound, the fiber was collected and drawn to a factor of 5 while pressing against a metal pin heated to 60°C, to produce a monofilament PHA fiber. The α-structure orientation degree was 89%, the breaking elongation was 190%, and therefore the yarn was highly elastic. Since the uniformly obtained fiber was a monofilament fiber with a fineness of greater than 200 dtex, the feel and tactile sensation were hard, and the fiber length was only about 8 m.

INDUSTRIAL APPLICABILITY

A continuous long fiber composed of an aliphatic copolymer polyester according to the invention has sufficient marine biodegradability and excellent storage stability. In addition, the method for producing a fiber according to the invention results in satisfactory reelability after wind-up as a fiber, which also exhibits stable spinnability without yarn breakage, thereby improving productivity. The continuous long fiber composed of an aliphatic copolymer polyester according to the invention therefore has excellent environmental, physical and economical properties, and can be utilized for a wide variety of purposes.

Claims

A continuous long fiber comprising an aliphatic copolymer polyester, wherein the aliphatic copolymer polyester comprises 3-hydroxybutyrate as a first monomer unit and comprises 4-hydroxybutyrate or 3-hydroxyvalerate as a second monomer unit, the percentage of the second monomer unit with respect to the total monomer units being 1 mol% to 9 mol% when the second monomer unit is a 4-hydroxybutyrate unit, and the percentage of the second monomer unit with respect to the total monomer units being 1 mol% to 7.6 mol% when the second monomer unit is 3-hydroxyvalerate.
The continuous long fiber according to claim 1, wherein the second monomer unit is 4-hydroxybutyrate, and the percentage of 4-hydroxybutyrate units with respect to the total monomer units is 4 mol% to 6 mol%.
The continuous long fiber according to claim 1 or 2, wherein the X-ray orientation degree of the α-structure of the aliphatic copolymer polyester is 90% or greater.
The continuous long fiber according to claim 1 or 2, wherein the weight-average molecular weight is 150,000 or greater and the ratio of weight-average molecular weight/number-average molecular weight is 10 or lower.
The continuous long fiber according to claim 1 or 2, wherein the melting point peak in DSC is 110°C to 200°C.
The continuous long fiber according to claim 1 or 2, wherein the proportion Iβ/Iα between β crystals and α crystals is 0 to 0.6.
The continuous long fiber according to claim 1 or 2, wherein the percentage of the total of the first monomer unit and second monomer unit with respect to the total monomer units is 99 mol% or greater.
The continuous long fiber according to claim 1 or 2, wherein the monofilament fineness is 0.1 dtex to 30 dtex.
Multifilament yarn composed of a continuous long fiber according to claim 1 or 2, wherein the number of filaments is 6 to 300.
The multifilament yarn according to claim 9, wherein the total fineness is 1 dtex to 200 dtex.
A fabric composed of a continuous long fiber according to claim 1 or a multifilament yarn according to claim 9.
A method for producing a continuous long fiber according to claim 1 or 2, the method comprising the following steps:
a melting step in which an aliphatic copolymer polyester is melted,

a discharge step in which the molten aliphatic copolymer polyester is discharged from a spinneret, and

a cold drawing step in which the discharged aliphatic copolymer polyester is simultaneously drawn while being cooled in a cooling medium, wherein

the temperature of the cooling medium is 30°C or lower, and the draw ratio in the cold drawing step is a factor of 4 or greater.
The method according to claim 12, wherein an air-gap is provided between the spinneret and the cooling medium, and the draft ratio at the air-gap section is a factor of 1.1 or greater.
The method according to claim 13, wherein the time required for the aliphatic copolymer polyester discharged from the spinneret to pass through the air-gap section is 5 seconds or less.
The method according to claim 12, wherein the residence time of the aliphatic copolymer polyester in the melting step is 900 seconds or less.