JP7705380B2 - Manufacturing method of aliphatic polyester fiber - Google Patents

Description

The present invention relates to a method for producing aliphatic polyester fibers, aliphatic polyester fibers, and multifilaments.

In recent years, plastic waste has become a major source of stress for the global environment, causing problems such as impacts on ecosystems, the generation of harmful gases during combustion, and global warming due to the large amount of heat generated by combustion. There has been active development of biodegradable plastics as a solution to this problem.

The carbon dioxide emitted when biodegradable plastics made from plant-derived raw materials are burned is the same carbon dioxide that was originally in the air, and does not increase the amount of carbon dioxide in the atmosphere. This is called carbon neutral, and is considered important under the Kyoto Protocol, which set carbon dioxide reduction targets, and active use of such plastics is desired.

Recently, from the standpoint of biodegradability and carbon neutrality, aliphatic polyester resins have been attracting attention as biodegradable plastics produced by microorganisms using plant-derived raw materials as a carbon source. In particular, polyhydroxyalkanoate (hereinafter sometimes referred to as PHA) resins, and among PHA resins, poly(3-hydroxybutyrate) homopolymer resin, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer resin, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (hereinafter sometimes referred to as P3HB3HH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer resin, and polylactic acid have been attracting attention.

However, the PHA resin has a slow crystallization rate and a glass transition temperature that is lower than room temperature (approximately 0 to 4°C), so that after heating and melting, a long cooling time is required for solidification during molding, resulting in poor productivity. In particular, when attempting to produce fibers using PHA by melt spinning, the slow solidification of the resin causes the fibers to stick to each other and to the rolls, making it difficult to produce stable fibers and resulting in low-quality fibers.

As a prior example of melt spinning technology for 3-hydroxyalkanoate polymers, Patent Document 1 describes a melt spinning method in which a polyester resin containing poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is spun at a take-up speed of 1,500 m/min to 7,000 m/min. It also describes that this method can improve spinnability and productivity, and increase tensile strength.

As another prior example, Patent Document 2 describes a melt spinning method for biodegradable aliphatic polyester fibers containing polyhydroxyalkanoate, a crystal nucleating agent, and a lubricant, in which a melt is extruded from a spinning die at a temperature of 130°C to 190°C during spinning to obtain a raw yarn, which is then drawn by a first take-up roll at a take-up speed of 300 m/min to 4,000 m/min, and then drawn by a second take-up roll at a take-up speed of 600 m/min to 7,000 m/min, thereby performing stretch spinning. It also describes that this method improves the crystallization rate of polyhydroxyalkanoate, improves suction properties, improves the spinnability and productivity of the fiber, and increases tensile strength.

In addition, as another prior example, Patent Document 3 describes how PHA is converted into fibers under specific spinning conditions, and furthermore, in the drawing process, drawing is carried out in a temperature range where no energy is wasted during production, and furthermore, excellent mechanical properties are expressed by relaxing in a heat treatment process.

International Publication No. 2015/029316 International Publication No. 2017/122679 International Publication No. 2012/133231

However, the melt spinning methods disclosed in Patent Documents 1 and 2 do not produce aliphatic polyester fibers containing poly(3-hydroxybutyrate)-based resins with sufficient tensile strength. In addition, the method disclosed in Patent Document 3 requires drawing and further heat treatment after fiberization, which requires a long time for fiber production and poor productivity.

The present invention aims to improve the productivity and increase the tensile strength of aliphatic polyester fibers containing poly(3-hydroxybutyrate) resin and a crystal nucleating agent.

The first aspect of the present disclosure relates to a method for producing an aliphatic polyester fiber containing a poly(3-hydroxybutyrate)-based resin and a crystal nucleating agent, the method comprising the steps of (i) heating a resin composition containing the poly(3-hydroxybutyrate)-based resin and the crystal nucleating agent to a temperature equal to or higher than the melting point and equal to or lower than the thermal decomposition temperature of the resin composition and discharging the resin composition from a spinning nozzle, (ii) stretching the resin composition discharged from the spinning nozzle with a stretching roll, and (iii) winding the stretched resin composition with a take-up roll, the stretching roll consisting of two or more rolls including a first roll and a second roll, a total stretch ratio of the resin composition (the take-up roll speed (m/min)/the spinning nozzle flow rate (m/min)) being 250 or more, and the take-up roll speed being 500 to 1500 m/min.

In the method for producing aliphatic polyester fibers, it is preferable that the ratio of the winding roll speed (m/min) to the first roll speed (m/min) is 1.5 or more.

In the method for producing aliphatic polyester fibers, it is preferable that the ratio of the first roll speed (m/min) to the spinning nozzle flow rate (m/min) is 55 or more.

In the method for producing the aliphatic polyester fiber, it is preferable to expose the resin composition to an air flow having a temperature equal to or higher than the glass transition temperature and equal to or lower than the crystallization temperature of the resin composition before the resin composition is discharged from the spinning nozzle and before the resin composition comes into contact with the drawing roll.

In the method for producing aliphatic polyester fibers, it is preferable that the temperature of the resin composition is set to 40 to 100°C in the (ii) stretching step.

In the method for producing aliphatic polyester fibers, it is preferable that the winding roll speed is 2 to 15% lower than the maximum roll speed of the two or more rolls that make up the drawing roll.

In the method for producing aliphatic polyester fibers, it is preferable to transport the resin composition from the spinning nozzle to the winding roll within one minute.

In the method for producing aliphatic polyester fibers, it is preferable that the spinning nozzle has 15 or more discharge holes.

In the method for producing aliphatic polyester fibers, it is preferable that the poly(3-hydroxybutyrate)-based resin contains poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and that the proportion of 3-hydroxyhexanoate among the total monomer units constituting the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is 3 to 15 mol%.

The second aspect of the present disclosure relates to an aliphatic polyester fiber containing a poly(3-hydroxybutyrate)-based resin and a crystal nucleating agent, the fiber having a single fiber fineness of 1 to 20 dtex and a single fiber tensile strength of 1.5 cN/dtex or more.

In the aliphatic polyester fiber, it is preferable that the poly(3-hydroxybutyrate)-based resin contains poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and that the proportion of 3-hydroxyhexanoate among the total monomer units constituting the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is 3 to 15 mol%.

The third aspect of the present disclosure relates to a multifilament containing 15 or more of the aliphatic polyester fibers.

According to the present invention, it is possible to improve the productivity and increase the tensile strength of aliphatic polyester fibers containing poly(3-hydroxybutyrate)-based resin and a crystal nucleating agent.

FIG. 1 is a conceptual diagram illustrating an example of a production apparatus used in a method for producing an aliphatic polyester fiber according to the present disclosure.

[Method of manufacturing aliphatic polyester fibers]
The method for producing an aliphatic polyester fiber according to the present disclosure is a method for producing an aliphatic polyester fiber containing a poly(3-hydroxybutyrate)-based resin and a crystal nucleating agent, comprising the steps of:
(i) a step of heating a resin composition containing the poly(3-hydroxybutyrate)-based resin and the crystal nucleating agent to a temperature not lower than the melting point of the resin composition and not higher than the thermal decomposition temperature of the resin composition, and discharging the resin composition from a spinning nozzle;
(ii) a step of stretching the resin composition discharged from a spinning nozzle with a stretching roll; and (iii) a step of winding up the stretched resin composition with a winding roll,
The stretching roll comprises two or more rolls including a first roll and a second roll, the total stretch ratio of the resin composition (the winding roll speed (m/min)/the spinning nozzle flow rate (m/min)) is 250 or more, and the winding roll speed is 500 to 1500 m/min.

(i) The process of heating a resin composition containing a poly(3-hydroxybutyrate)-based resin and a crystal nucleating agent to a temperature above the melting point and below the thermal decomposition temperature of the resin composition and extruding it from a spinning nozzle is described in detail below.

In this disclosure, poly(3-hydroxybutyrate)-based resin is an aliphatic polyester that contains 3-hydroxybutyrate as a monomer unit that constitutes the resin.

Poly(3-hydroxybutyrate)-based resins include resins containing poly(3-hydroxybutyrate), such as poly(3-hydroxybutyrate); and resins containing copolymer resins consisting of 3-hydroxybutyrate and other hydroxyalkanoates.

Examples of copolymer resins consisting of 3-hydroxybutyrate and other hydroxyalkanoates include P3HB3HH [poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)], PHBV [poly(3-hydroxybutyrate-co-3-hydroxyvalerate)], P3HB4HB [poly(3-hydroxybutyrate-co-4-hydroxybutyrate)], poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate, poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Of these, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred. This is because the resulting aliphatic polyester fibers are not only highly biodegradable, but also have sufficient moldability for practical use, and are excellent in tensile strength and flexibility.

In resins containing a copolymer resin consisting of 3-hydroxybutyrate and other hydroxyalkanoates, the proportion of 3-hydroxyhexanoate in the total monomer units constituting the resin is preferably 0.5 to 15 mol%, more preferably 1.5 to 15 mol%, even more preferably 3 to 15 mol%, and most preferably 3 to 8 mol%. This is because the resulting aliphatic polyester fibers have excellent tensile strength and flexibility.

The weight average molecular weight Mw of the poly(3-hydroxybutyrate) resin is preferably 50,000 to 3,000,000, more preferably 100,000 to 1,500,000, and even more preferably 200,000 to 1,000,000. If the weight average molecular weight Mw is too low, the tensile strength of the resulting aliphatic polyester fiber tends to decrease, while if the weight average molecular weight Mw is too high, processability decreases, making molding difficult.

The weight average molecular weight Mw is measured from the polystyrene equivalent molecular weight distribution using gel permeation chromatography (GPC) with chloroform eluent. As the column for the GPC, a column appropriate for measuring the molecular weight may be used.

In the present disclosure, a crystal nucleating agent is a compound that has a melting point higher than that of poly(3-hydroxybutyrate) resin and has the effect of promoting the crystallization of the resin. The compound is not particularly limited. Examples of crystal nucleating agents include inorganic substances (boron nitride, titanium oxide, talc, layered silicates, calcium carbonate, sodium chloride, metal phosphates, etc.); sugar alcohol compounds derived from natural products (pentaerythritol, erythritol, galactitol, mannitol, arabitol, etc.); polyvinyl alcohol; chitin; chitosan; polyethylene oxide; aliphatic carboxylates; aliphatic alcohols; aliphatic carboxylate esters; dicarboxylic acid derivatives (dimethyl adipate, dibutyl adipate, diisodecyl adipate, dibutyl carboxylate, diisodecyl carboxylate, dibutyl ... sebacate); cyclic compounds having C═O and a functional group selected from NH, S and O in the molecule (indigo, quinacridone, quinacridone magenta, etc.); sorbitol derivatives (bisbenzylidene sorbitol, bis(p-methylbenzylidene)sorbitol, etc.); compounds containing a nitrogen-containing heteroaromatic nucleus (pyridine ring, triazine ring, imidazole ring, etc.) (pyridine, triazine, imidazole, etc.); phosphate compounds; bisamides of higher fatty acids; metal salts of higher fatty acids; and branched polylactic acid. In addition, when the poly(3-hydroxybutyrate)-based resin is P3HB3HH, poly(3-hydroxybutyrate) having a melting point higher than that of P3HB3HH can also be used.

Among these, sugar alcohol compounds, polyvinyl alcohol, chitin, and chitosan are preferred, and pentaerythritol is more preferred, from the viewpoint of the effect of improving the crystallization rate of poly(3-hydroxybutyrate)-based resins and compatibility and affinity with poly(3-hydroxybutyrate)-based resins. These may be used alone or in combination of two or more.

In a resin composition containing a poly(3-hydroxybutyrate) resin and a nucleating agent, the content of the nucleating agent is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, and even more preferably 0.5 parts by weight or more, per 100 parts by weight of the poly(3-hydroxybutyrate) resin. The content is preferably 12 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 8 parts by weight or less, and most preferably 5 parts by weight or less. If the content of the nucleating agent is too low, the effect as a nucleating agent may be insufficient, and if the content of the nucleating agent is too high, the viscosity of the resin composition when heated may decrease.

In addition, the resin composition may contain known additives as optional components other than the poly(3-hydroxybutyrate) resin and the crystal nucleating agent, as necessary. Known additives include stabilizers such as antioxidants and ultraviolet absorbers; colorants such as dyes and pigments; plasticizers; lubricants; inorganic fillers; organic fillers; and antistatic agents. These additives may be used alone or in combination of two or more.

The plasticizer is not particularly limited, but examples thereof include adipic acid ester plasticizers, acetylated monoglyceride plasticizers, and polyglycerol fatty acid ester plasticizers. In addition, the plasticizing effect of supercritical fluids such as carbon dioxide and nitrogen can be utilized.

Lubricants include, but are not limited to, fatty acid amides such as behenamide, stearamide, erucamide, and oleamide.

When the resin composition is heated to a temperature equal to or higher than the melting point and equal to or lower than the thermal decomposition temperature of the resin composition, the heating temperature may be adjusted as appropriate depending on the type of resin composition, but is preferably equal to or higher than the melting point of the resin composition +5°C, and more preferably equal to or higher than the melting point +10°C. The heating temperature is preferably lower than the thermal decomposition temperature of the resin composition, and more preferably equal to or lower than the thermal decomposition temperature -5°C.

In this disclosure, the melting point is measured by differential scanning calorimetry (DSC). Specifically, a differential scanning calorimeter is used to measure at a heating rate of 10°C/min, and the resulting endothermic peak is taken as the melting point.

In this disclosure, the thermal decomposition temperature is the temperature at which weight loss begins as measured by thermogravimetry (TG). Specifically, a thermogravimeter is used to measure at a heating rate of 10°C/min, and the temperature at which weight loss begins is taken as the thermal decomposition temperature.

A resin composition containing a poly(3-hydroxybutyrate) resin and a crystal nucleating agent preferably has a melt flow rate (hereinafter sometimes referred to as MFR) measured at 165°C and 5 kgf of 0.1 to 100 g/10 min, more preferably 0.5 to 80 g/10 min, and even more preferably 1.0 to 60 g/10 min.

The melt flow rate was measured in accordance with JIS K7210-2:2014 at 165°C and a load of 5 kg.

The spinning nozzle is provided with an outlet hole through which the resin composition is discharged, and the shape, size, and number of the outlet holes are not particularly limited. For example, when the outlet hole is circular, the diameter Φ of the outlet hole is preferably 0.1 mm to 3.0 mm. The number of outlet holes may be, for example, 15 or more and 1,000 or less, depending on the size of the outlet hole.

The spinning nozzle flow rate, i.e., the speed at which the resin composition is extruded from the spinning nozzle, is preferably 0.05 m/min to 6.0 m/min, more preferably 0.1 m/min to 6.0 m/min, and even more preferably 0.5 m/min to 6.0 m/min.

The discharge rate from the spinning nozzle is preferably 0.10 g/min/hole or more, more preferably 0.15 g/min/hole or more. The discharge rate is preferably less than 1.0 g/min/hole, more preferably 0.90 g/min/hole or less.

It is preferable to rapidly cool the resin composition by exposing it to an air flow having a temperature between the glass transition temperature and the crystallization temperature of the resin composition before it is discharged from the spinning nozzle and contacts the stretching rolls. Such rapid cooling can promote the cooling and solidification of the resin composition, and the stretching strain imparted by the speed difference between the stretching rolls can be more effectively reflected. As a result, the tensile strength of the resulting aliphatic polyester fiber can be further increased.

In this disclosure, the glass transition temperature is measured by differential scanning calorimetry (DSC). Specifically, a differential scanning calorimeter is used to measure at a heating rate of 10°C/min, and the temperature at the inflection point of the resulting DSC curve is taken as the glass transition temperature.

The crystallization temperature is measured by differential scanning calorimetry (DSC). Specifically, a differential scanning calorimeter is used to measure at a temperature drop rate of 10°C/min, and the heat release peak of the resulting DSC curve is taken as the crystallization temperature.

The temperature of the airflow applied to the resin composition discharged from the spinning nozzle may be any temperature that is equal to or higher than the glass transition temperature and equal to or lower than the crystallization temperature of the resin composition, and may be adjusted appropriately depending on the type of the resin composition. The temperature of the airflow is preferably lower than the crystallization temperature of the resin composition, more preferably equal to or lower than the crystallization temperature -20°C, and even more preferably equal to or lower than the crystallization temperature -40°C.

The speed of the airflow is not particularly limited, but is preferably 0.1 m/s or more and 5 m/s or less, and more preferably 0.1 m/s or more and 3 m/s or less. If the speed of the airflow is less than 0.1 m/s, the cooling effect obtained will be too small, and if it exceeds 5 m/s, the resin composition discharged from the spinning nozzle will be shaken by the airflow, which may cause fusion and/or thread breakage between the discharged resin compositions, leading to a decrease in spinning stability.

The type of gas flow is not particularly limited, but air; inert gases such as nitrogen gas and argon gas, etc. are preferred.

(ii) the process of stretching the resin composition extruded from the spinning nozzle with a stretching roll, and (iii) the process of winding the stretched resin composition with a winding roll are described in detail below.

The resin composition extruded from the spinning nozzle is first taken up by a first roll and then stretched by two or more rolls including the first roll and a second roll.

The stretching rolls may include a first roll and a second roll, and the number of the stretching rolls is not particularly limited and may be appropriately selected taking into consideration the temperature control efficiency of the fiber, the stretch ratio, etc. The number of the stretching rolls may be 3 or more, 4 or more, or 5 or more. There is no particular upper limit to the number of the stretching rolls as long as it is within the scope of the object of the present invention, but from the viewpoint of not making the equipment costs and manufacturing equipment too large, it may be 10 or less.

In addition, each of the stretching rolls may be composed of a single roll, or may be composed of a set of two or more rolls with the same speed. This makes it possible to make the temperature of the fiber being stretched uniform, and to produce long fibers in a more space-saving manner.

The ratio of the first roll speed (m/min) to the spinning nozzle flow rate (m/min) (hereinafter sometimes referred to as NDR) is preferably 55 or more, more preferably 100 or more, even more preferably 150 or more, and particularly preferably 200 or more. By increasing the NDR, the alignment of the molecular chains of the resin composition can be promoted, and the diameter of the resin composition can be reduced, thereby promoting cooling and solidification. In addition, there is no upper limit to the NDR as long as fiber breakage does not occur, but it may be 1000 or less.

The ratio of the take-up roll speed (m/min) to the first roll speed (m/min) is preferably 1.5 or more, more preferably 1.7 or more, and even more preferably 1.8 or more. This is because aliphatic polyester fibers with superior tensile strength can be obtained. In addition, there is no upper limit to the ratio as long as the fiber does not break, but it may be 30 or less.

(ii) In the process of stretching the resin composition discharged from the spinning nozzle with a stretching roll, the temperature of the resin composition is preferably 40 to 100°C, and more preferably 50 to 80°C. This is because the crystallization rate of the resin composition can be increased, and the productivity and tensile strength of the aliphatic polyester fiber can be further improved. The temperature of the resin composition can be adjusted by adjusting the temperature of an object that comes into contact with the resin composition, such as a solid such as the surface of a stretching roll; a liquid such as a bathtub or droplets; or a gas such as an air current.

The stretched resin composition is wound on a winding roll, and the total stretch ratio of the resin composition is 250 or more. The total stretch ratio is preferably 270 or more, more preferably 300 or more, even more preferably 330 or more, and even more preferably 340 or more. There is no upper limit to the total stretch ratio as long as fibers of the desired fineness can be stably obtained, but it may be 2000 or less.

The total draw ratio is defined as the winding roll speed (m/min)/the spinning nozzle flow rate (m/min).

The winding roll speed is 500 to 1500 m/min, and may be adjusted appropriately within this range, taking into account the spinning nozzle flow speed and the speeds of other rolls, etc.

The winding roll speed is preferably 2 to 15% lower than the maximum roll speed of the two or more rolls constituting the stretching roll, more preferably 3 to 15% lower, and even more preferably 3 to 12% lower. This is because residual stress is less likely to remain in the resulting aliphatic polyester fiber, making it less likely that dry heat shrinkage will occur. The ratio indicated by the "%", i.e., (the maximum roll speed - the winding roll speed) / the winding roll speed x 100, can be rephrased as "relaxation rate (%)".

The time for transporting the resin composition from the spinning nozzle to the take-up roll is preferably within 1 minute, preferably within 50 seconds, more preferably within 40 seconds, and even more preferably within 30 seconds. The time may be 1 second or more. According to the manufacturing method disclosed herein, aliphatic polyester fibers having high tensile strength can be manufactured with good productivity in a short time.

[Aliphatic polyester fiber]
The aliphatic polyester fiber of the present disclosure is an aliphatic polyester fiber containing a poly(3-hydroxybutyrate)-based resin and a crystal nucleating agent, and has a single fiber fineness of 1 to 20 dtex and a single fiber tensile strength of 1.5 cN/dtex or more.

The content of the crystal nucleating agent in the aliphatic polyester fiber of the present disclosure is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, and even more preferably 0.5 parts by weight or more, relative to 100 parts by weight of the poly(3-hydroxybutyrate)-based resin. The content is preferably 12 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 8 parts by weight or less, and most preferably 5 parts by weight or less, relative to 100 parts by weight of the poly(3-hydroxybutyrate)-based resin.

In addition, it is preferable that the particle size of the crystal nucleating agent contained in the aliphatic polyester fiber is one-third or less of the minimum diagonal length of the cross section of the fiber. This is because this gives the fiber superior tensile strength.

The particle size of the nucleating agent is determined as D50 (median diameter) using laser diffraction method.

The fineness of the single fiber of the aliphatic polyester fiber of the present disclosure may be 1.5 dtex or more, or 2 dtex or more. The fineness may be 15 dtex or less, or 10 dtex or less.

The fineness of a single fiber refers to the thickness of the thread and is defined as the mass per unit length. It is expressed in units of mass (g) per 10,000 m (dtex). Specifically, it is measured by the autobibroscopic method.

The tensile strength of a single fiber of the aliphatic polyester fiber of the present disclosure is preferably 1.6 cN/dtex or more, more preferably 1.7 cN/dtex or more, even more preferably 1.8 cN/dtex or more, and most preferably 1.9 cN/dtex or more. The tensile strength is not particularly limited as long as it is within a range that does not impair the flexibility and toughness required for the application, but may be 10 cN/dtex or less. The aliphatic polyester fiber of the present disclosure has excellent tensile strength despite being thin.

The tensile strength of a single fiber is measured based on JIS L 1015:2010, chemical fiber staple test method, with an initial length of 20 mm and a speed of 20 mm/min.

[Multifilament]
The aliphatic polyester fiber of the present disclosure may constitute a multifilament. When the multifilament is constituted, the number and fineness of the aliphatic polyester fibers constituting the multifilament may be determined according to the desired characteristics, but the aliphatic polyester fibers are preferably 15 or more, more preferably 20 or more, and even more preferably 30 or more. The aliphatic polyester fibers may be 1000 or less. If the total fineness of the multifilament is the same, the more the number of fibers constituting the multifilament, the higher the flexibility and suppleness, but the more likely the durability is to decrease.

The present invention will be described in detail below with reference to examples, but the technical scope of the present invention is not limited to these examples.

Example 1
A resin composition was obtained by dry-blending 100 parts by weight of a (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (proportion of 3-hydroxyhexanoate=6 mol%, Mw=550,000, MFR(165°C, 5 kg)=3 g/10 min) as a poly(3-hydroxybutyrate)-based resin, 1 part by weight of pentaerythritol "Neuriser P" (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) as a crystal nucleating agent, and 0.5 parts by weight of erucic acid amide and 0.5 parts by weight of behenic acid amide as lubricants, and melt-kneading the mixture at 150°C using an extruder to form pellets.

The glass transition temperature of the obtained pellets (resin composition) was 2°C, the crystallization temperature was 80°C, the melting point was 142°C, and the thermal decomposition temperature was 180°C.

The process for producing aliphatic polyester fibers using the obtained pellets will be described with reference to FIG. 1. The obtained pellets are melted in a single-screw extruder (not shown) with a screw diameter of 25 mm, the flow rate is adjusted with a gear pump, and the pellets are extruded at a melt spinning temperature of 170° C. from a spinning nozzle 1 (discharge hole shape: circular) under the conditions shown in Table 1 into a first space (first quenching firm) 2 where air (quench air) at 14° C. and 1.0 m/s is blown; and into a second space (second quenching firm) where air (quench air) at 13° C. and 1.0 m/s is blown. The resin composition was then fed to a second quenching farm 3, taken up by a first roll 4 under the conditions described in Table 1, passed through a second roll 5 (896 m/min, 70° C.), a third roll 6 (1050 m/min, 70° C.), a fourth roll 7 (1050 m/min, 70° C.), and a fifth roll 8 (1010 m/min, 34° C./36° C.) in this order, and taken up by a take-up roll 9 (1000 m/min) to obtain an aliphatic polyester fiber 10. The time required for transporting the resin composition from the spinning nozzle to the take-up roll was within 30 seconds.

At this time, the first roll 4, the second roll 5, the third roll 6, and the fourth roll 7 were each configured as a pair of two rolls with the same speed and temperature. The fifth roll 8 was configured as a pair of two rolls with the same speed. In addition, NDR = first roll speed / spinning nozzle flow rate, relaxation rate (%) = (maximum roll speed - winding roll speed) / winding roll speed x 100, and total stretch ratio = winding roll speed / spinning nozzle flow rate. In this disclosure, room temperature refers to a temperature in the range of 5 to 35°C.

The monofilament size, fiber diameter, and tensile strength of the obtained aliphatic polyester fibers were measured by the following methods. The results are shown in Table 1.

(Single fiber size)
The measurement was carried out using a Search Co., Ltd. auto blower type fineness measuring instrument DENIER COMPUTER DC-11 with a sample length of 50 mm.

(Fiber diameter)
Since the shape of the discharge hole of the spinning nozzle is circular and the cross-sectional shape of the obtained fiber is also circular, the calculation was made from the cross-sectional area calculated from the previously measured monofilament size and the specific gravity of the aliphatic polyester fiber (the calculation was made assuming that the cross-sectional shape was a perfect circle).

(Tensile strength)
The tensile strength was measured under the following conditions using a tensile measuring device Autograph AG-I manufactured by Shimadzu Corporation. That is, the obtained aliphatic polyester fibers were used as samples, and the initial length of each sample was set to 20 mm, and measurements were performed at a speed of 20 mm/min using a load cell with a rated capacity of 5 N. In addition, the tensile strength per single fineness (cN/dtex) was calculated based on the single fineness measured in advance.

(Examples 2 to 9, Comparative Examples 1 to 4)
Aliphatic polyester fibers were obtained in the same manner as in Example 1, except that the conditions were changed as shown in Table 1. The time required for transporting the resin composition from the spinning nozzle to the take-up roll was within 30 seconds.

The physical properties of the obtained aliphatic polyester fiber were measured and the results are shown in Table 1.

As shown in Table 1, the aliphatic polyester fibers of Comparative Examples 1 to 4, which have a total draw ratio of less than 250 or a winding roll speed of less than 500 m/min, all have low tensile strength. In contrast, the aliphatic polyester fibers of the Examples have excellent tensile strength, even though they were produced using the same resin composition.

REFERENCE SIGNS LIST 1 Spinning nozzle 2 First quenching farm 3 Second quenching farm 4 First roll 5 Second roll 6 Third roll 7 Fourth roll 8 Fifth roll 9 Winding roll 10 Aliphatic polyester fiber

Claims (9)

A method for producing an aliphatic polyester fiber containing a poly(3-hydroxybutyrate)-based resin and a crystal nucleating agent, comprising the steps of:
(i) a step of heating a resin composition containing the poly(3-hydroxybutyrate)-based resin and the crystal nucleating agent to a temperature not lower than the melting point of the resin composition and not higher than the thermal decomposition temperature of the resin composition, and discharging the resin composition from a spinning nozzle;
(ii) a step of stretching the resin composition discharged from a spinning nozzle with a stretching roll; and (iii) a step of winding up the stretched resin composition with a winding roll,
the stretching roll includes two or more rolls including a first roll and a second roll, and a total stretch ratio of the resin composition (the winding roll speed (m/min)/the spinning nozzle flow rate (m/min)) is 250 or more,
The method for producing an aliphatic polyester fiber, wherein the winding roll speed is 500 to 1500 m/min. The method for producing aliphatic polyester fibers according to claim 1, wherein the ratio of the take-up roll speed (m/min) to the first roll speed (m/min) is 1.5 or more. The method for producing aliphatic polyester fibers according to claim 1 or 2, wherein the ratio of the first roll speed (m/min) to the spinning nozzle flow rate (m/min) is 55 or more. The method for producing aliphatic polyester fibers according to any one of claims 1 to 3, wherein the resin composition is exposed to an airflow having a temperature equal to or higher than the glass transition temperature and equal to or lower than the crystallization temperature of the resin composition before it is discharged from the spinning nozzle and before it comes into contact with the drawing roll. The method for producing aliphatic polyester fibers according to any one of claims 1 to 4, wherein the temperature of the resin composition is set to 40 to 100°C in the (ii) stretching step. The method for producing aliphatic polyester fibers according to any one of claims 1 to 5, wherein the winding roll speed is 2 to 15% lower than the maximum roll speed of the two or more rolls that make up the stretching roll. The method for producing aliphatic polyester fibers according to any one of claims 1 to 6, wherein the resin composition is transported from the spinning nozzle to the take-up roll within one minute. The method for producing aliphatic polyester fibers according to any one of claims 1 to 7, wherein the spinning nozzle has 15 or more discharge holes. the poly(3-hydroxybutyrate)-based resin comprises poly(3-hydroxybutyrate-co-3-hydroxyhexanoate);
The method for producing an aliphatic polyester fiber according to any one of claims 1 to 8, wherein a ratio of 3-hydroxyhexanoate is 3 to 15 mol% of all monomer units constituting the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

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