JP2007321294A - Sheath-core type polymer alloy fiber and hollow fiber and method for producing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheath-core type polymer alloy fiber which can stably be obtained in a state mutually dispersing nano fibers comprising a polyamide without dropping the nano fibers. <P>SOLUTION: This sea-island structure polymer alloy fiber which has a sheath-core structure and whose core component comprises at least two polymers is characterized in that the sea component contains polylactic acid as a main component; the island component contains poly(ε-caproamide) as a main component; the polymer viscosity of the island component is higher by 100 to 250 Pa s than the polymer viscosity of the sea component in the whole range of 220 to 250°C; the average fiber diameter of the island component is 50 to 300 nm; the dispersion of the fiber diameters of the island component is 10 to 30%; and the polymer melting point of the sheath component is in a range of 170 to 250°C. A method for producing the same, and a fiber having the nano fibers in a hollow fiber are also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a core-sheath polymer alloy fiber, a hollow fiber in which nanofibers are bonded to the inner wall of the hollow fiber, and a method for producing them. Since hollow fibers made of polyamide are rich in hygroscopicity, they are used as clothing fibers. Moreover, since the polyamide nanofiber fiber has a high surface area per weight, it is known that the polyamide nanofiber fiber is rich in water absorption, water retention, adhesion, and gas adsorption.

  Conventionally, a polyamide fiber has an amide group in its molecular structure, and thus is widely used as a fiber having high moisture absorption and moisture retention. Moreover, since a hollow fiber has an internal space | gap, it can contain various active ingredients inside. Moreover, since the polyamide nanofiber fiber is an ultra extra fine thread, it is richer in moisture absorption and moisture retention than the conventional polyamide fiber, and further has adhesiveness and gas adsorbability. Therefore, a fiber having a fiber diameter of a unit of 100 nm has been studied with the aim of improving characteristics such as adsorptivity and hygroscopicity in addition to the above characteristics by increasing the surface area per weight by finer fineness.

  Patent Document 1 discloses a sea-island structure fiber composed of at least two types of organic polymers having different solubility, wherein the island component is composed of a hardly soluble polymer, the sea component is composed of an easily soluble polymer, and the average diameter of the island domain is 1. Polymer alloy fibers having a diameter of ˜150 nm and 60% or more of the island domains having a diameter of 1 to 150 nm are described. In Patent Document 1, a polymer alloy fiber is used in which the melting point of the island polymer is −20 to + 20 ° C., which is the melting point of the sea polymer, and the melt viscosity of the sea polymer is 100 pa · s or less.

Patent Document 2 discloses nanofibers in hollow fibers using copolymerized polyethylene terephthalate as the core component, poly (ε-caproamide) as the island component, and poly (ε-caproamide) as the sheath component. Fibers that are microencapsulated by having are described.
JP 2004-169261 A JP 2005-023436 A

  However, nanofiber fibers having a diameter of 1 to 150 nm have a problem that after the sea polymer is dissolved, the nanofiber itself is a single fiber, and the fiber length is as short as 1 mm or less, so that it is easy to fall off. For this reason, it has been used by mixing with other fibers having a fiber diameter of μm to form a nonwoven fabric or pasting them together.

  However, dropping of nanofibers has become a problem due to the dry state and vibration of those fibers. Therefore, it is possible to suppress the dropping of the nanofibers by increasing the proportion of other fibers having a large fiber diameter, but the characteristics of the extra fine nanofiber fibers are impaired. Therefore, it is desired that nanofibers made of polyamide take advantage of their characteristics without falling off.

  The inventors of the present invention have solved the above-mentioned problems of the prior art, studied fibers that make use of the characteristics of nanofibers, and have reached the present invention.

  In addition, when copolymer polyethylene terephthalate is used as the core component of the core-sheath core component, the dissolution rate of copolymer polyethylene terephthalate in the alkaline solution is slow, so that the nanofibers obtained are immersed in an alkaline aqueous solution for a long time. There was a problem that the strength of the single body was lowered and the nanofibers were dropped from the inside of the hollow fiber depending on the vibration.

  In order to achieve the object of solving the above-described problem of dropping off nanofibers, the present invention has the following configuration.

  That is, the present invention relates to a sea-island structure fiber comprising a core-sheath structure in which the core component is composed of a polymer having at least two components, wherein the sea component is polylactic acid and the island component is poly (ε-caproamide) as main components. The island component has a polymer viscosity of 100 to 250 Pa · s higher than the polymer viscosity of the sea component in the entire range of 220 to 250 ° C., and the island component has an average fiber diameter of 50 to 300 nm, and A core-sheath polymer alloy fiber comprising a polymer alloy fiber having a fiber diameter variation of 10 to 30% and a sheath component comprising polyamide, polyester, polyolefin or copolymer thereof, and a method for producing the same.

  A more preferred embodiment is a core-sheath polymer alloy fiber in which the sheath component is made of poly (ε-caproamide), polybutylene terephthalate, polypropylene terephthalate, polypropylene, or a copolymer thereof.

Furthermore, in a preferred embodiment of the present invention, the sheath component is polyamide, polyester, polyolefin, and the inside of the fiber is dissolved in 0.01% to 5.0% alkaline aqueous solution and the sea component polylactic acid. A hollow fiber characterized in that there is a nanofiber having an average fiber diameter of (ε-caproamide) fiber of 50 to 300 nm and a variation in fiber diameter of poly (ε-caproamide) fiber of 10 to 30%. .
Further, in a preferred embodiment of the present invention, the sheath component is poly (ε-caproamide), polybutylene terephthalate, polypropylene by dissolving the polylactic acid of the sea component in 0.01 to 5.0% alkaline aqueous solution. Nanofibers are terephthalate, polypropylene, and the average fiber diameter of poly (ε-caproamide) fibers is 50 to 300 nm and the variation in fiber diameter of poly (ε-caproamide) fibers is 10 to 30%. A hollow fiber characterized in that it is a hollow fiber characterized in that the nanofiber is adhered to the inner wall of the sheath component.
Furthermore, a preferred embodiment of the present invention is a method for producing a hollow fiber, wherein the average fiber diameter A of the island component of the polymer alloy fiber and the average fiber diameter B of the nanofiber are 0.75 ≦ B / A ≦ 1. is there.

  ADVANTAGE OF THE INVENTION According to this invention, the fiber which exists in the hollow fiber of polyamide can be provided, without the nanofiber fiber which consists of polyamide dropping off.

  In the present invention, the nanofiber fibers have an average fiber diameter of 50 to 300 nm, and the fiber diameter variation of the island component is 10 to 30%.

  First, in the present invention, a core-sheath polymer alloy fiber is made of polyamide, polyester, polyolefin, or a copolymer thereof as a sheath component, and has a sea-island type polymer alloy fiber as a core component. -Caproamide) or a copolymer thereof, and the sea component is polylactic acid or a copolymer thereof.

Preferably, the sheath component has a polymer melting point of the sheath component in the range of 170 ° C to 250 ° C.
Furthermore, the island component poly (ε-caproamide) or a copolymer thereof is dispersed in the range of 220 to 250 ° C. because the island component has a polymer viscosity of 100 to 250 Pa · s higher than the sea component polymer viscosity. In the hollow fiber made of poly (ε-caproamide), polybutylene terephthalate, polypropylene terephthalate, polypropylene or a copolymer thereof, the polymer alloy fiber is obtained without reaggregation. In addition, a fiber having nanofibers made of poly (ε-caproamide) or a copolymer thereof can be obtained.

  That is, when the island component polymer viscosity is less than 100 Pa · s less than the sea component polymer viscosity in the range of 220 to 250 ° C., the island component polymer does not disperse and re-aggregates even if dispersed. To do. As a result, it is impossible to stably obtain a polymer alloy fiber having an island component average fiber diameter of 300 nm or less and an island component fiber diameter variation of 10 to 30%. Furthermore, in a state where the polymer viscosity of the island component is equal to or lower than the polymer viscosity of the sea component, the arrangement of the island component polymer and the sea component polymer is reversed. As a result, after this fiber was subjected to antkari treatment, a microporous fiber having poly (ε-caproamide) as a sheath component was obtained, and the target nanofiber could not be obtained.

  In the present invention, poly (ε-caproamide) is selected as the island component from the relationship between the melting point and viscosity of the polymer of the island component and the sea component, and polylactic acid is selected as the sea component of the core component. In the whole range, a polymer having a viscosity of poly (ε-caproamide) of 100 to 250 Pa · s higher than that of polylactic acid is preferably selected at 230 ° C. to 240 ° C. More preferably, by selecting a polymer having a high 120 to 170 Pa · s, the average fiber diameter of the island component is 50 to 300 nm, more preferably 50 to 200 nm, and the variation of the fiber diameter of the island component is 10 to 30. %, And more preferably 10-20% polymer alloy fibers can be obtained stably.

  In the present invention, the relationship between the melting point and the viscosity of the polymer of the island component and the sea component and the alkali resistance higher than that of polylactic acid is the fiber whose polymer melting point of the sheath component is in the range of 170 ° C to 250 ° C. Is preferably poly (ε-caproamide), polybutylene terephthalate, polypropylene terephthalate, polypropylene and copolymers thereof.

  In addition, the sheath component poly (ε-caproamide), polybutylene terephthalate, polypropylene terephthalate, polypropylene and copolymers thereof are not particularly specified for viscosity in the range of 220 to 250 ° C., and are melt-spun together with a core component made of polymer alloy. That's fine.

  In the polymer alloy fiber of the present invention, the wt% ratio of the polylactic acid of the sea component to the poly (ε-caproamide) of the island component in the core component is 30:70 to 70:30, preferably 40:60 to 60: 40. Outside these ranges, the polymer balance may be lost, making it difficult to obtain nanofibers. Moreover, the wt% ratio of the sheath component to the core component is 10:90 to 95: 5, and it is preferable that the nanofibers are adhered to the sheath component in the hollow fiber after sea removal.

  The polymer alloy fiber of the present invention thus obtained is preferably 0.01 to 5.0% alkali aqueous solution in 0.01 to 5.0% alkaline aqueous solution, more preferably 0.01 to 0.5% alkali. By dissolving the sea component polylactic acid in an aqueous solution, it becomes a fiber having nano-order poly (ε-caproamide) fibers of very fine fineness in polyamide, polyester, and polyolefin hollow fibers. The average fiber diameter of the poly (ε-caproamide) fiber in the nanofiber of the present invention is 50 to 300 nm, more preferably 50 to 200 nm, and the variation of the fiber diameter of the poly (ε-caproamide) fiber is 10 to 30%. More preferably, nanofibers of 10 to 20% can be stably obtained.

In the present invention, the average fiber diameter of the island component poly (ε-caproamide) of the polymer alloy fiber is A, and the average fiber diameter B of the poly (ε-caproamide) of the nanofiber after alkali treatment is 0.75 ≦ B / A ≦ 1 is preferable, and 0.9 ≦ B / A ≦ 1 is more preferable. This is because the effect of further finening the nanofibers can be obtained by alkali treatment, but if the antkari treatment is too advanced, the strength and shape maintenance of the poly (ε-caproamide) fiber itself is impaired, so the fineness after alkali treatment It prescribes.
The variation in fiber diameter is represented by the standard deviation of fiber diameter / average fiber diameter × 100.

The present invention will be specifically described below with reference to examples.
In the examples, each characteristic is measured as follows.

  Polymer viscosity: The melt viscosity of the polymer was measured by Toyo Seiki Capillograph 1B. The polymer storage time from the introduction of the polymer to the start of measurement was 10 minutes.

  Average fiber diameter: A section of a fiber cooled to −20 ° C. was cut in the fiber cross-sectional direction, and measured with a SEM apparatus (S-4000 type manufactured by Hitachi). The average fiber diameter is obtained by measuring the fiber diameter of 100 island components and calculating the average value.

  Variation in fiber diameter: A standard deviation is obtained from 100 pieces of data used for calculating the average fiber diameter. The variation in fiber diameter is indicated by the standard deviation of fiber diameter / average fiber diameter × 100.

Example 1
Poly (ε-caproamide) having a viscosity at 230 ° C. of 230 Pa · s and polylactic acid having a viscosity at 230 ° C. of 110 Pa · s are composed of 60 wt% poly (ε-caproamide) and 40 wt% polylactic acid. At a ratio of 25 mm, a biaxial vent extruder with a diameter of 25 mm, kneaded at 230 ° C. while degassing at 0.001 MPa, the extruded polymer is stretched into a wire shape, water-cooled and then cut to form a polymer alloy chip Got.

  This polymer alloy chip is melted at 250 ° C. with a general pressure melter type melting device, and is flowed to the core component side with a core-sheath die, and the sheath component has a viscosity at 230 ° C. of 230 Pa · s. (Ε-caproamide) was passed through a spinneret having a hole diameter of 0.35 mm, a discharge hole length of 0.70 mm, a die surface temperature of 235 ° C. and 300 holes, and the single-hole discharge rate of the core component was 0.6 g / min. The single-hole discharge amount of the sheath component is 0.4 g / min, the polymer temperature is spun at 230 ° C., the yarn is cooled with a cooling air of 20 ° C., and once put in the can at a take-up speed of 1200 m / min, An undrawn yarn was obtained. The obtained undrawn yarn was subjected to two-stage drawing at a draw ratio of 2.7 times using a warm bath at 80 ° C., and the obtained drawn yarn was machined at 8 to 15 pieces / 25 mm using a stuffing box. Crimping was applied, oil was applied by spraying, and the obtained tow was dried at a temperature of 100 ° C. for 10 minutes and cut to a length of 50 mm to obtain a polymer alloy short fiber 1 having a 5dTex fiber length of 50 mm ( FIG. 1). As shown in the enlarged view of FIG. 2, the obtained polymer alloy fiber 1 has a core component 2 having an average fiber diameter A of poly (ε-caproamide) island component 3 of 80 nm, and variations in the fiber diameter of island components are 24%, and the sea component 4 is made of polylactic acid. The sheath component 5 is made of poly (ε-caproamide).

  The polymer alloy short fiber obtained was immersed in a 0.5% aqueous sodium hydroxide solution for 2 hours to obtain 2.0 dtex of a poly (ε-caproamide) hollow fiber. In the hollow fiber, 6 (poly (ε-caproamide) was obtained. ) Has an average fiber diameter B of 79 nm, and a fiber diameter variation of (ε-caproamide) of 23% is obtained. The wt ratio of the poly (ε-caproamide) hollow fiber 6 and nanofiber 7 is 52:48. From the raw material (ε-caproamide), nanofibers with a nano-level fiber diameter were stably obtained with a yield of 93%. B / A was 0.99.

Example 2
In Example 1, the ratio of the core component 190 Pa · s poly (ε-caproamide) and 80 Pa · s polylactic acid polymer was changed to a ratio of 30 wt% poly (ε-caproamide) and 70 wt% polylactic acid. The sheath component uses polybutylene terephthalate having a viscosity at 230 ° C. of 240 Pa · s, the core component has a single-hole discharge rate of 0.5 g / min, and the sheath component has a single-hole discharge rate of 0.5 g / min. Except for the above, a polymer alloy short fiber having a fiber length of 5 dTex and a length of 50 mm was obtained in the same manner as in Example 1.

In the obtained polymer alloy fiber, the average fiber diameter A of the island component 3 whose core component 2 is poly (ε-caproamide) is 142 nm, the variation of the fiber diameter of the island component is 27%, and the sea component is polylactic acid. It consists of four. The sheath component 5 is made of polybutylene terephthalate.
The polymer alloy short fiber obtained was immersed in a 0.1% aqueous sodium hydroxide solution for 4 hours to obtain 2.0 dtex of a poly (ε-caproamide) hollow fiber. In the hollow fiber, 6 (poly (ε-caproamide) was obtained. ) Was obtained with a mean fiber diameter B of 140 nm and a fiber diameter variation of (ε-caproamide) of 26%. The wt ratio of the hollow fiber 6 and the nanofiber 7 of polybutylene terephthalate is 72:28. From the raw material (ε-caproamide), nanofibers with a nano-level fiber diameter were stably obtained with a yield of 93%. B / A was 0.98.

Example 3
In Example 1, the core component poly (ε-caproamide) was changed to 30 wt% and polylactic acid was changed to 70 wt%, and the sheath component was polypropylene terephthalate having a viscosity at 230 ° C. of 280 Pa · s. In the same manner as in Example 1 except that the single-hole discharge amount of the component was 0.5 g / min and the single-hole discharge amount of the sheath component was 0.5 g / min, a 5 dTex polymer alloy short fiber having a fiber length of 50 mm was used. Obtained.

In the obtained polymer alloy fiber, the average fiber diameter A of the island component whose core component 2 is poly (ε-caproamide) 3 is 75 nm, the variation of the fiber diameter of the island component is 27%, and the sea component is polylactic acid. It consists of four. The sheath component 5 is made of polypropylene terephthalate.
The polymer alloy short fiber obtained was immersed in a 0.1% aqueous sodium hydroxide solution for 4 hours to obtain 2.0 dtex of a poly (ε-caproamide) hollow fiber. In the hollow fiber, 6 (poly (ε-caproamide) was obtained. ) Average fiber diameter B was 75 nm, and the fiber diameter variation of (ε-caproamide) was 26%. The wt ratio of the hollow fiber 6 and the nanofiber 7 of polypropylene terephthalate is 76:24. From the raw material (ε-caproamide), nanofibers with a nano-level fiber diameter were stably obtained with a yield of 93%. B / A was 0.98.

Example 4
In Example 1, the core component poly (ε-caproamide) was changed to 60 wt% and polylactic acid was changed to 40 wt%, and the sheath component was polypropylene having a viscosity at 230 ° C. of 210 Pa · s. In the same manner as in Example 1, except that the single-hole discharge rate of 0.5 g / min and the single-hole discharge rate of the sheath component was 0.5 g / min, 5 dTex polymer alloy short fibers having a fiber length of 50 mm were obtained. It was.

In the obtained polymer alloy fiber, the average fiber diameter A of the island component having the core component 2 of poly (ε-caproamide) 3 is 88 nm, the variation of the fiber diameter of the island component is 30%, and the sea component is polylactic acid. It consists of four. The sheath component 6 is made of polypropylene.
The polymer alloy short fiber thus obtained was immersed in a 0.1% sodium hydroxide aqueous solution for 4 hours to obtain 2.6 dtex of poly (ε-caproamide) hollow fiber. In the hollow fiber, 6 (poly (ε-caproamide) was obtained. ) Has an average fiber diameter B of 85 nm, and a variation in the fiber diameter of (ε-caproamide) is 29%. The wt ratio of the hollow fiber 6 of polypropylene and the nanofiber 7 is 63:37. From the raw material (ε-caproamide), nanofibers having a nano-level fiber diameter were stably obtained with a yield of 95%. B / A was 0.97.

Comparative Example 1
In Example 1, a poly (hexamethylene adipamide) having a viscosity at 265 ° C. of 660 Pa · s and a polylactic acid polymer having a viscosity at 265 ° C. of 80 Pa · s were converted into poly (hexamethylene adipamide). Was obtained in the same manner as in Example 1 except that kneading was performed at 265 ° C. with a biaxial vent extruder at a ratio of 50 wt% of polylactic acid and 50 wt% of polylactic acid. This polymer alloy chip is melted at 280 ° C. as the core component, and the sheath component is used with poly (hexamethylene adipamide) having a viscosity at 265 ° C. of 660 Pa · s, and the single component discharge amount of the core component is 0.5 g. / Min, the single-hole discharge rate of the sheath component was 0.5 g / min, and spinning was performed in the same manner as in Example 1 except that spinning was performed at the die surface temperature of 275 ° C. and the polymer temperature of 270 ° C. Undrawn yarn could not be obtained.

Comparative Example 2
In Example 1, poly (ε-caproamide) having a viscosity at 230 ° C. of 110 Pa · s and polylactic acid having a viscosity at 230 ° C. of 90 Pa · s are obtained by adding 60 wt% of poly (ε-caproamide), A polymer alloy chip was obtained in the same manner as in Example 1 except that polylactic acid was adjusted to a ratio of 40 wt%.

  Under the same conditions as in Example 1, polymer alloy short fibers were obtained. In the obtained polymer alloy short fiber, the sheath component was composed of poly (ε-caproamide), poly (ε-caproamide) was the sea component, and polylactic acid was the island component.

  As a result of immersing the obtained short fiber in a 0.5% aqueous sodium hydroxide solution for 2 hours, the obtained poly (ε-caproamide) is a short fiber having a core part of 3.8 dTex and a fiber length of 50 mm. And nanofibers were not obtained.

Comparative Example 3
In Example 1, poly (ε-caproamide) having a viscosity at 230 ° C. of 480 Pa · s and polylactic acid having a viscosity at 230 ° C. of 75 Pa · s are obtained by adding 60 wt% of poly (ε-caproamide), poly A polymer alloy chip was obtained in the same manner as in Example 1 except that the ratio of lactic acid was 40 wt%.

  The polymer alloy short fiber obtained was immersed in a 0.5% aqueous sodium hydroxide solution for 2 hours to obtain 2.0 dtex of a poly (ε-caproamide) hollow fiber. In the hollow fiber, 6 (poly (ε-caproamide) was obtained. ) Has an average fiber diameter B of 1.4 μm (1400 nm), and a variation in the fiber diameter of (ε-caproamide) is 38%. Moreover, the fibers were adhered or aggregated, and nanofibers could not be produced stably. The yield from the raw material (ε-caproamide) was 82%, but nano-level fibers were not obtained. B / A was 1.00.

Comparative Example 4
In Example 1, poly (ε-caproamide) having a viscosity at 230 ° C. of 160 Pa · s and polylactic acid having a viscosity at 230 ° C. of 80 Pa · s are obtained by using 60 wt% poly (ε-caproamide), poly A polymer alloy chip was obtained in the same manner as in Example 1 except that the ratio of lactic acid was 40 wt%.

  The polymer alloy short fiber obtained was immersed in a 0.5% aqueous sodium hydroxide solution for 2 hours to obtain 2.0 dtex of a poly (ε-caproamide) hollow fiber. In the hollow fiber, 6 (poly (ε-caproamide) was obtained. ) Average fiber diameter B was 1.3 μm (1300 nm), and the variation in fiber diameter of the island component was 41%. The yield from the raw material (ε-caproamide) was 80%, but nano-level fibers were not obtained. B / A was 1.00.

Comparative Example 5
In Example 1, the ratio of 190 Pa · s poly (ε-caproamide) and 80 Pa · s polylactic acid polymer as the core components in Example 1 was 30 wt% for poly (ε-caproamide) and 70 wt% for polylactic acid. In this case, poly (hexamethylene adipamide) whose viscosity at 265 ° C. is 660 Pa · s is used as the sheath component, the single-hole discharge rate of the core component is 0.5 g / min, and the die surface temperature is 275. Spinning was carried out in the same manner as in Example 1 except that spinning was performed at a temperature of 270 ° C. and a polymer temperature of 270 ° C. However, polylactic acid was decomposed and an undrawn yarn could not be obtained.

Comparative Example 6
In Example 1, the ratio of 190 Pa · s poly (ε-caproamide) and 80 Pa · s polylactic acid polymer as the core components in Example 1 was 30 wt% for poly (ε-caproamide) and 70 wt% for polylactic acid. The copolymer component terephthalate having a viscosity of 310 Pa · s at 260 ° C. (7 mol% isophthalic acid and 4 mol% bisphenol A) was used as the sheath component. Spinning was carried out in the same manner as in Example 1 except that spinning was performed at a base surface temperature of 275 ° C. and a polymer temperature of 270 ° C. at 5 g / min, but polylactic acid was decomposed and an undrawn yarn could not be obtained.

  The nanofiber fiber of the present invention is used for clothing, automotive materials, industrial materials, agricultural materials, or medical materials. Further, it can be used for sports applications, material applications, and automobile interior materials, and examples thereof include mirror polishing of semiconductor parts and mirror polishing of hard disk storage materials. Examples of sports applications include sports equipment as a lightweight member.

The schematic perspective view which shows the one aspect | mode of the polymer alloy fiber of this invention, and its schematic longitudinal cross-sectional view Electron micrograph of a cross-sectional view of the polymer alloy fiber obtained in Example 1 of the present invention Schematic showing one embodiment of the nanofiber fiber of the present invention Schematic which shows the one aspect | mode of the fiber which has a nanofiber fiber inside the hollow fiber of this invention

Explanation of symbols

1: Polymer alloy fiber 2: Core component 3: Poly (ε-caproamide) 4: Polylactic acid 5: Sheath component 6: Hollow fiber 7: Nanofiber

Claims (7)

  A fiber having a core-sheath structure, wherein the core component is a sea-island structure fiber composed of at least two or more polymers, the sea component is polylactic acid, and the island component is poly (ε-caproamide) as a main component, The polymer viscosity of the island component is 100 to 250 Pa · s higher in the entire range of 220 to 250 ° C. than the polymer viscosity of the sea component, the average fiber diameter of the island component is 50 to 300 nm, and the fiber diameter of the island component is A core-sheath polymer alloy fiber comprising a polymer alloy fiber having a variation of 10 to 30% and having a polymer melting point of a sheath component in a range of 170 ° C to 250 ° C.   The core-sheath polymer alloy fiber according to claim 1, wherein the sheath component is selected from poly (ε-caproamide), polybutylene terephthalate, polypropylene terephthalate, polypropylene or a copolymer thereof.   A sea-island structure fiber comprising at least two or more polymer components, wherein the sea component is polylactic acid and the island component is poly (ε-caproamide) as main components, and the island component polymer is determined from the polymer viscosity of the sea component. A polymer alloy fiber having a viscosity of 100 to 250 Pa · s high in the entire range of 220 to 250 ° C., an average fiber diameter of the island component being 50 to 300 nm, and a variation in fiber diameter of the island component being 10 to 30%. A method for producing a core-sheath polymer alloy fiber, characterized in that core-sheath composite spinning is performed using a polymer having a melting point of 170 ° C. to 250 ° C. as a core component and a sheath component as a core component.   The method for producing a core-sheath polymer alloy fiber according to claim 3, wherein the sheath component is selected from poly (ε-caproamide), polybutylene terephthalate, polypropylene terephthalate, polypropylene or copolymer thereof.   A hollow fiber in which poly (ε-caproamide) nanofibers are bonded to the inner wall of the sheath component, and the sheath component is a polymer selected from poly (ε-caproamide), polybutylene terephthalate, polypropylene terephthalate, and polypropylene. A hollow fiber, wherein the poly (ε-caproamide) nanofiber has an average fiber diameter of 50 to 300 nm, and the poly (ε-caproamide) nanofiber has a fiber diameter variation of 10 to 30%. .   The core-sheath polymer alloy fiber according to claim 1 or 2 is brought into contact with 0.01 to 5.0% aqueous alkali solution to dissolve polylactic acid as a sea component, whereby poly (ε-caproamide) is formed on the inner wall of the sheath component. A nanofiber is adhered, and the sheath component is a polymer having a melting point in the range of 170 ° C to 250 ° C. The average fiber diameter of the poly (ε-caproamide) nanofiber is 50 to 300 nm, and the fiber diameter variation is 10 to 10. A method for producing a hollow fiber, which is 30%.   The method for producing a hollow fiber according to claim 6, wherein the average fiber diameter A of the island component of the polymer alloy fiber and the average fiber diameter B of the nanofiber are 0.75 ≦ B / A ≦ 1.

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