Island-sea composite fibers and porous hollow fibers

Abstract

This invention discloses a sea-island composite fiber and a porous hollow fiber, composed of sea and island components with a refractive index difference greater than 0.010. The sea-island composite fiber has more than 100 islands on the cross-section of a single fiber, and the diameter of all islands in the sea-island composite fiber is less than 2000 nm. Fabrics made from the fibers of this invention have a certain degree of shielding effect against light across the entire spectrum, and possess functions of UV protection, light penetration prevention, and heat shielding.

Description

Technical Field

[0001] This invention relates to an island-island composite fiber and a porous hollow fiber. Specifically, it relates to an island-island composite fiber that provides some shielding against light across the entire spectrum, and a porous hollow fiber formed from the island-island composite fiber after a weight reduction process. Background Technology

[0002] As people's living standards improve, the market demand for functional fibers is growing, such as functional fibers with UV protection, breathability, and heat-shielding properties.

[0003] In existing technologies, fibers can typically be endowed with UV resistance, light penetration prevention, and heat shading effects through physical or chemical methods. Among these, a relatively mature approach is to add particles with high refractive index. As the amount of high refractive index particles increases, the fiber's UV resistance, light penetration prevention, and heat shading effects improve. However, excessively high particle content can affect spinnability, increase fiber costs, and degrade the fiber's physical properties.

[0004] Chinese patent CN103069060A discloses a core-sheath composite fiber, a false-twist textured yarn formed therefrom, and its manufacturing method. By using resins with different refractive indices as the core and sheath, light is reflected at the core-sheath interface. Adding 1-3% by mass of titanium dioxide to the fiber effectively blocks solar radiant heat. However, the added functional particles, such as titanium dioxide, can cause problems in subsequent yarn-making processes, such as abrasion of the yarn guide and impact on the fiber's physical properties.

[0005] Japanese Patent JP2020165028A discloses an island-type composite fiber and porous hollow fibers formed therefrom. The island component is a sparingly soluble polymer, and the island component is a readily soluble polymer. The number of islands is 70 or more and 2000 or less, and the island diameters are uniform. The porous hollow fibers formed from this island-type composite fiber have less flattening of the hollow portion, are lightweight and have a soft hand feel, high water absorption, and few stains. However, they do not achieve functional effects such as UV protection, heat shielding, and breathability prevention.

[0006] Therefore, it is necessary to reduce the reliance on functional particles and endow fibers with UV protection, light penetration, and heat-blocking functions while maintaining the physical properties of the fibers. Summary of the Invention

[0007] The purpose of this invention is to provide a sea-island composite fiber and a porous hollow fiber that can achieve UV resistance, breathability protection and heat shading without adding inorganic particles.

[0008] The technical solution of this invention:

[0009] The island-island composite fiber has a refractive index difference between the island component and the sea component of the island-island composite fiber that is greater than 0.010; the number of islands on the cross-section of a single fiber in the island-island composite fiber is greater than 100; and the diameter of all islands in the island-island composite fiber is less than 2000 nm.

[0010] Preferably, the single fiber of the island-island composite fiber contains at least two types of islands with different diameters.

[0011] A. Diameter less than 400nm,

[0012] B. Diameter of 400–800 nm,

[0013] C. Diameter greater than 800nm.

[0014] The number of islands on the cross-section of a single fiber of the island-island composite fiber is preferably less than 10,000.

[0015] The shortest distance between the surface of the outermost island and the surface of the fiber in the island-sea composite fiber is preferably 0.10 to 2.00 μm.

[0016] The fineness of the single fiber of the island composite fiber is preferably 0.5 to 8.0 dtex.

[0017] The island component of the island-sea composite fiber is preferably an alkali-soluble polymer.

[0018] Porous hollow fiber is obtained by reducing the amount of the island composite fiber and removing the island component. The number of pores on the cross-section of a single fiber of the porous hollow fiber is more than 100. The diameter of all pores in the porous hollow fiber is less than 2000 nm.

[0019] The shortest distance between the surface of the outermost pore and the fiber surface in the porous hollow fiber is preferably 0.10 to 2.00 μm.

[0020] Preferably, the porous hollow fiber contains at least two different diameters of pores in its single fiber.

[0021] A. Diameter less than 400nm,

[0022] B. Diameter of 400–800 nm,

[0023] C. Diameter greater than 800nm.

[0024] This invention obtains island-island composite fibers with good physical properties that provide some shielding effect on light across the entire spectrum by selecting polymers with different refractive indices as the sea and island components of the composite fiber and controlling the number and size of the islands. When the island component is an alkali-soluble polymer, the porous hollow fiber obtained after weight reduction also provides some shielding effect on light across the entire spectrum because the sea component and the hollow air layer have different refractive indices. Attached Figure Description

[0025] Figure 1 This is a schematic diagram showing a single fiber cross-section of the island composite fiber as one embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of a single fiber cross-section of a porous hollow fiber as one embodiment of the present invention. Detailed Implementation

[0027] In existing technologies, adding particles with high refractive index is usually used to give fibers the functions of UV resistance, anti-permeability, and heat shielding. However, the addition of particles will not only cause problems such as filtration pressure during the spinning process, but will also deteriorate the physical properties of the fibers.

[0028] The island-island composite fiber of this invention does not have any particular limitation on the polymer types of the sea component and the island component. As long as the refractive index difference between the two is greater than 0.010, they can be the same polymer or different polymers. The polymer can be a conventional polymer used in melt spinning, specifically exemplified as follows: polyesters such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, etc.; polyolefins such as polyethylene, polypropylene, etc.; polyamides such as polyamide-4, polyamide-6, polyamide-56, polyamide-66, polyamide-510, polyamide-610, etc.; others such as polylactide (polylactic acid), polyhydroxyalkali esters, etc. In addition to the conventional polymers listed above, modified polymers or functional polymers, such as hygroscopic polymers, alkali-soluble polymers, etc., can also be used.

[0029] To achieve full-spectrum light shielding, the island-sea composite fiber described in this invention requires, in addition to satisfying the refractive index difference between the island and sea components being greater than 0.010, to have more than 100 islands on the cross-section of a single fiber, with the diameter of all islands being less than 2000 nm.

[0030] Light travels in a straight line in a homogeneous medium, but undergoes refraction, reflection, and scattering when propagating in a non-homogeneous medium. In this invention, there is a refractive index difference between the island and sea components, thus a single fiber constitutes a non-homogeneous medium. When light enters the fiber through one side of its outer surface, reflection, refraction, and scattering occur. When the number of islands in a single fiber reaches 100 or more, the non-homogeneity of the fiber is significant, and light undergoes hundreds or even thousands of reflections, refractions, and scatterings within the fiber. Therefore, very little light passes through from the opposite side of the fiber, thus enabling the fiber to achieve UV resistance, light penetration prevention, and heat shielding effects.

[0031] If the refractive index difference between the sea component and the island component is less than 0.010, the non-uniformity of the fiber as a medium decreases, reducing the reflection, refraction, and scattering of light within the fiber, thereby increasing the amount of transmitted light and failing to achieve the effect of shielding light. To improve the light shielding effect, the refractive index difference between the island component and the sea component of the island-sea composite fiber is preferably above 0.30.

[0032] If the number of islands on the cross-section of a single fiber in the island-island composite fiber is less than 100, even if the refractive index difference between the sea component and the island component reaches 0.010 or higher, the number of times light is reflected, refracted, and scattered is relatively small, and a large amount of light will still pass through the yarn, failing to achieve excellent light-blocking, heat-shielding, and UV-resistant effects. To further enhance the light-shielding effect of the fiber, the number of islands on the cross-section of a single fiber in the island-island composite fiber of this invention is preferably 278 or more.

[0033] The more islands there are, the higher the non-uniformity of the fiber as a medium, resulting in more light path paths and better light shielding. However, when the monofilament fineness is uniform, a higher number of islands leads to smaller island diameters, requiring higher precision in the spinning components, increasing costs, and potentially causing cross-sectional aberrations when the polymer passes through the spinneret. To ensure fiber cross-sectional shape retention, the number of islands on the single fiber cross-section is preferably below 10,000; to ensure the fiber's wide applicability in clothing, the number of islands on the single fiber cross-section is further preferably below 9,600.

[0034] Since the single fiber of the present invention has a large number of islands, in order to ensure the stability of the cross-sectional shape during spinning, the fineness of the single fiber is preferably above 0.5 dtex. However, if the fineness of the single fiber is too large, with a fixed island diameter and number, the volume occupied by the sea component will be too large, increasing the probability of light penetrating the fiber and weakening the light-blocking effect of the island fiber. Therefore, the fineness of the single fiber is preferably below 8.0 dtex, which ensures the excellent anti-seepage effect of the island composite fiber while meeting the size requirements of yarns for clothing textiles.

[0035] In the composite fiber of this invention, the diameter of all islands is below 2000 nm. This is because, under conventional monofilament fineness and island-island composite ratios, the larger the island diameter, the fewer the number of islands, resulting in lower internal dielectric inhomogeneity and reduced light reflection, refraction, and scattering, thus worsening the fiber's light-blocking effect. To improve the internal dielectric inhomogeneity and maximize light reflection, refraction, and scattering, the diameter of all islands in the island-island composite fiber is further preferably below 1000 nm.

[0036] Meanwhile, the wavelength of sunlight reaching the Earth's surface is generally below 2000nm. When the size of the medium through which the light passes is smaller than or equal to its wavelength, the light is diffracted and scattered at the edge of the medium, making it impossible for the light to pass directly through the material.

[0037] The sunlight includes three wavelength ranges: ultraviolet light below 400nm, visible light from 400 to 800nm, and near-infrared light from 800 to 2000nm. Ordinary lighting light mostly falls within the visible light range of 400 to 800nm. In a preferred embodiment, the single fiber of this invention contains at least two types of islands with different diameters.

[0038] A. Diameter less than 400nm,

[0039] B. Diameter of 400–800 nm,

[0040] C. Diameter greater than 800nm.

[0041] When ultraviolet light passes through an island with a diameter of less than 400 nm, the ultraviolet light is reflected, refracted, scattered, and diffracted at the island's boundary, thus achieving excellent anti-ultraviolet effect. When visible light passes through an island with a diameter of 400–800 nm, the visible light is reflected, refracted, scattered, and diffracted at the island's boundary, thus achieving excellent anti-penetration effect. When near-infrared light passes through an island with a diameter greater than 800 nm, the near-infrared light is reflected, refracted, scattered, and diffracted at the island's boundary, thus achieving excellent heat shielding effect.

[0042] It should be noted that the uniformity of the island diameters within the fiber does not preclude UV protection, light penetration prevention, and heat shading. As mentioned earlier, by reducing the homogeneity of the internal medium of the fiber, causing reflection, refraction, and scattering of light entering the fiber, better UV protection, light penetration prevention, and heat shading effects than with ordinary fibers can be achieved. It simply means that in preferred technical solutions, further controlling the presence of at least two different sizes of islands within a single fiber can further optimize the UV protection, light penetration prevention, and heat shading effects.

[0043] The shortest distance between the surface of the outermost island and the fiber surface is preferably 0.10 to 2.00 μm. If the distance is too small, the thickness of the sea component outside the island component will be too small, and the island component will be easily exposed. When the yarn is rubbed or stretched, there is a risk of the sea component breaking. If the distance is too large, light can easily pass directly through the sea component at the edge of the fiber, reducing the light-blocking effect.

[0044] To ensure the fiber's suitability for clothing applications, through the above optimization, the transmittance of the island composite fiber across the entire light spectrum is less than 50%, and the fiber exhibits excellent mechanical properties, abrasion resistance, and cross-sectional shape.

[0045] Based on the comprehensive requirements for lightweight, heat insulation, and impermeability of fibers, the island components in the island-island composite fiber of this invention can be selected from alkali-soluble polymers. The alkali-soluble polymer can be a modified polymer in which polyether and / or benzenesulfonate components have been added to a conventional polymer. By performing a weight reduction treatment using conventional methods to remove the alkali-soluble island components from the island-island composite fiber, porous hollow fibers can be obtained. This weight reduction treatment can involve first immersing the composite fiber in an alkaline solution of a certain concentration, and then heating it to above 50°C to accelerate the removal of the island components.

[0046] Of course, in addition to the above-mentioned method of obtaining porous hollow fibers by reducing the amount of island composite fibers, they can also be obtained directly by spinning through a porous hollow spinneret. This invention does not impose any particular limitation.

[0047] In the porous hollow fiber obtained by reducing the amount of the island composite fiber described in this invention, the number of pores on the cross-section of a single fiber is more than 100, and the diameter of all pores is less than 2000 nm.

[0048] Since the refractive index of air is 1.000, while the refractive index of most fiber-forming polymers is above 1.300, the interior of porous hollow fibers is also a non-uniform medium. After light shines into the fiber, it can undergo hundreds or even thousands of reflections, refractions and scatterings. The amount of light transmitted from the opposite side of the porous hollow fiber is very small, which can reduce the transmitted light and improve the fiber's impermeability.

[0049] If the number of pores on the cross-section of a single fiber in the porous hollow fiber is less than 100, the number of times light is reflected, refracted, and scattered is reduced, and a large amount of light will still pass through the yarn, failing to achieve excellent light-blocking and UV-resistant effects. To further enhance the light-blocking effect of the porous hollow fiber, the number of pores on the cross-section of a single fiber in the porous hollow fiber of the present invention is preferably 278 or more.

[0050] In the porous hollow fiber of this invention, the diameter of all pores is below 2000 nm. Under conventional monofilament fineness and hollow fiber ratio, the larger the pore diameter, the fewer the number of pores, the lower the degree of inhomogeneity of the internal medium of the fiber, the less light reflection, refraction, and scattering occur, and the worse the anti-seepage effect of the porous hollow fiber. To improve the degree of inhomogeneity of the internal medium of the porous hollow fiber and maximize the reflection, refraction, and scattering of light, the diameter of all pores in the porous hollow fiber is preferably below 1000 nm.

[0051] In a preferred embodiment, the porous hollow fiber of the present invention contains at least two types of pores with different diameters in a single fiber.

[0052] A. Diameter less than 400nm,

[0053] B. Diameter of 400–800 nm,

[0054] C. Diameter greater than 800nm.

[0055] When ultraviolet light passes through a hole with a diameter of less than 400 nm, in addition to conventional reflection, refraction, and scattering inside the porous hollow fiber, aperture diffraction also occurs, thus achieving an excellent anti-ultraviolet effect. When visible light passes through a hole with a diameter of 400–800 nm, in addition to conventional reflection, refraction, and scattering inside the porous hollow fiber, aperture diffraction also occurs, thus achieving an excellent anti-penetration effect. When near-infrared light passes through a hole with a diameter greater than 800 nm, in addition to conventional reflection, refraction, and scattering inside the porous hollow fiber, aperture diffraction also occurs, thus achieving an excellent heat shielding effect.

[0056] The shortest distance between the surface of the outermost pore and the fiber surface in the porous hollow fiber is preferably 0.10–2.00 μm. If the distance is too small, the thickness of the sea element outside the hollow pore will be too small, and there is a risk of the sea element breaking when the yarn is rubbed or stretched; if the distance is too large, light can easily pass through the sea element at the fiber edge, reducing the light blocking effect.

[0057] Through the above optimizations, the island-island composite fiber of the present invention can achieve a transmittance of less than 50% across the entire light spectrum, and the porous hollow fiber can achieve a transmittance of less than 20% across the entire light spectrum, while possessing excellent mechanical properties. It can be applied to clothing, footwear, home textiles, hygiene products, and other fields. The fabric made from the porous hollow fiber of the present invention can achieve a certain degree of light shielding across the entire light spectrum even at low basis weight, thus possessing functions of UV protection, light transmission prevention, and heat shielding.

[0058] The physical property testing method involved in this invention is as follows:

[0059] (1) Refractive index

[0060] The refractive index was measured using an Abbe refractometer of type WYA-2S. The sample was placed on the sample stage, the angle was adjusted, and the sample was visually aimed before measurement. The refractive index value was read from the LCD screen, and the average value was taken after ten tests.

[0061] (2) The diameter of the island

[0062] A fiber to be tested was taken and fixed using a perforated copper plate. The fiber was then cut with a blade to obtain the cross-section of the fiber bundle. The cross-section of the island-island composite fiber was observed and photographed using a Hitachi VHX-6000 transmission electron microscope, and the diameter of the island components was measured with a reading accuracy of 0.01 μm. The final result was the average value after 10 tests.

[0063] (3) Distance between the outer side of the island and the fiber surface

[0064] Take a fiber to be tested, cut the fiber with a blade to obtain the cross-section of the fiber bundle, attach the fiber to conductive adhesive and perform gold sputtering treatment, observe the fiber cross-section with a Hitachi TM3030plus scanning electron microscope (SEM), measure the shortest distance between the island farthest from the center on the cross-section and the fiber surface, repeat the above test process 10 times on the same fiber, and take the minimum value of the measured distance. The reading accuracy is 0.01μm.

[0065] (4) Ultraviolet transmittance

[0066] The fiber is made with a basis weight of 100±5g / m². 2 Plain weave fabric was tested for transmittance in the ultraviolet band below 400nm using a JASCO V-750 spectrophotometer. Ten locations were randomly selected on the fabric for testing, and the final transmittance was the average of the ten test results. Lower transmittance indicates better shielding of light in that wavelength band.

[0067] (5) Visible light transmittance

[0068] The fiber is made with a basis weight of 100±5g / m². 2 Plain weave fabric was tested using a JASCO V-750 spectrophotometer to measure its transmittance in the visible light band (400–800 nm). Ten locations were randomly selected on the fabric for testing, and the final transmittance was the average of the ten test results. Lower transmittance indicates better shielding of light in that wavelength band.

[0069] (6) Near-infrared transmittance

[0070] The fiber is made with a basis weight of 100±5g / m². 2Plain weave fabric was tested for transmittance in the near-infrared band (800–2000 nm) using a Hitachi U-4100 spectrophotometer. Ten locations were randomly selected on the fabric for testing, and the final transmittance was the average of the ten test results. Lower transmittance indicates better shielding of light in that wavelength band.

[0071] (7) Section forming

[0072] Take a fiber to be tested, fix the fiber with a perforated copper plate, and cut the fiber with a blade to obtain the cross-section of the fiber bundle. Observe and photograph the cross-section of the island-to-island composite fiber or porous hollow fiber using a Hitachi VHX-6000 transmission electron microscope. Cut 10 cross-sections for observation, and the final result is the average of 10 tests.

[0073] The cross-section of the island-island composite fiber is judged as excellent if the islands are independent and unadhesive to each other, and no islands are exposed on the fiber surface. It is marked with "〇". If less than 5% of the islands on the cross-section are adhered, or less than 1% of the islands on the cross-section are exposed on the fiber surface, the cross-section is judged as good. It is marked with "△". If more than 5% of the islands on the cross-section are adhered, or more than 1% of the islands on the cross-section are exposed on the fiber surface, the cross-section is judged as poor. It is marked with "×".

[0074] The cross-section of a porous hollow fiber is characterized by independent and undeformed pores with intact edges, and is rated as excellent (marked with "〇"). If less than 5% of the total number of pores on the cross-section are broken, or if less than 1% of the total number of pores on the cross-section edge are recessed, the cross-section is rated as good (marked with "△"). If more than 5% of the total number of pores on the cross-section are broken, or if more than 1% of the total number of pores on the cross-section edge are recessed, the cross-section is rated as poor (marked with "×").

[0075] The advantages of the present invention will now be described in detail through the listed embodiments and comparative examples. The present invention is not limited to the embodiments described below.

[0076] Example 1

[0077] Polyester was used as the sea component and alkali-soluble polyester as the island component, with a refractive index difference of 0.010 between the two. The sea and island components were melted and metered separately, then extruded through a specific spinning module. The sea and island components were then extruded at a specific ratio through the spinneret holes of a composite spinneret assembly with a sea-island cross-section of 278 islands. The extruded filaments were cooled, cured, oiled, bundled, and wound with rollers to obtain sea-island composite fully drawn yarn (FDY).

[0078] The obtained island-island composite long fibers all have an island diameter of 550 nm, a minimum distance of 1.00 μm between the surface of the outermost island and the fiber surface, a single fiber fineness of 3.7 dtex, and excellent fiber cross-section formation. Plain weave fabrics made from the above composite island-island fibers were tested, and the ultraviolet transmittance, visible light transmittance, and near-infrared transmittance of the fabrics were 46.1%, 35.8%, and 45.8%, respectively. The specific formulation and physical properties are shown in Table 1.

[0079] Examples 2-30

[0080] The preparation process is the same as in Example 1, and the specific formulation and properties are shown in Tables 1 to 3. The porous hollow fibers obtained in Examples 21 to 30 were obtained by removing the marine components from the island-island composite long fibers using an alkaline solution.

[0081] Comparative Example 1

[0082] The refractive index difference between the marine and island components was changed to 0.005, and the rest remained the same as in Example 1. The specific formulation and physical properties are shown in Table 4.

[0083] Because the refractive index difference between the marine and island components is too small, the reflection, refraction, and scattering of light within the fiber are reduced, resulting in a fabric with too high a transmittance of light rays, which cannot achieve the effect of shielding light.

[0084] Comparative Example 2

[0085] The total number of islands on the cross-section of the single fiber was changed to 80, while the rest remained the same as in Example 1. The specific formulation and physical properties are shown in Table 4.

[0086] Because the total number of islands is too small, the number of times light is reflected, refracted, and scattered inside the fiber is reduced, resulting in a fabric with too high transmittance of each light ray, which cannot achieve the effect of blocking light.

[0087] Comparative Example 3

[0088] The diameter and single fiber fineness of all islands in the island-sea composite fiber were changed, while the rest remained the same as in Example 4. The specific formulation and physical properties are shown in Table 4.

[0089] Because the island diameter is too large, the reflection, refraction, and scattering of light inside the fiber are reduced, resulting in a fabric with too high a light transmittance, which cannot achieve the effect of blocking light.

[0090] Comparative Example 4

[0091] The refractive index difference between the island and sea components and the total number of islands on the cross-section of the single fiber were changed, while the rest remained the same as in Comparative Example 3. The specific formulation and physical properties are shown in Table 4.

[0092] Because the refractive index difference between the sea component and the island component is too small, the island diameter is too large, and the total number of islands is insufficient, the reflection, refraction, and scattering of light inside the fiber are reduced, resulting in a fabric with too high transmittance of each light ray, which cannot achieve the effect of shielding light.

[0093] Comparative Example 5

[0094] The total number of islands, the diameter of the islands, and the number of islands of each diameter on the cross-section of the single fiber were changed, while the rest remained the same as in Comparative Example 3. The specific formulation and physical properties are shown in Table 4.

[0095] Because the island diameter of 2500nm is too large and the total number of islands is insufficient, the reflection, refraction and scattering of light inside the fiber are reduced, resulting in a fabric with too high transmittance of light rays, which cannot achieve the effect of shielding light.

[0096] Comparative Example 6

[0097] The total number of islands, the diameter of the islands, and the number of islands of each diameter on the cross-section of the single fiber were changed, while the rest remained the same as in Comparative Example 3. The specific formulation and physical properties are shown in Table 4.

[0098] Because both types of islands are too large in diameter, the island components adhere to each other on the fiber cross-section. In addition, the total number of islands is insufficient, reducing the reflection, refraction, and scattering of light within the fiber. This results in the fabric having too high a transmittance for each type of light, failing to achieve the desired light-shielding effect.

[0099] Comparative Example 7

[0100] The total number of islands on the cross-section of the single fiber was changed to 50, while the rest remained the same as in Example 1. The resulting island-island composite long fiber was then treated with an alkaline solution to remove the sea component, resulting in porous hollow fibers. The specific formulation and physical properties are shown in Table 3.

[0101] Because the total number of pores is insufficient, the reflection, refraction, and scattering of light inside the fiber are reduced, resulting in a fabric with too high a transmittance of light, which fails to achieve the effect of blocking light.

[0102] Comparative Example 8

[0103] The preparation process was the same as in Comparative Example 3. The resulting island-island composite long fibers were then treated with an alkaline solution to remove the sea components, resulting in porous hollow fibers. The specific formulation and physical properties are shown in Table 3.

[0104] Because the hollow holes are too large, the hollow holes on the fiber cross-section collapse, resulting in poor fiber cross-section formation. The fabric produced has too high a transmittance of light and cannot achieve the effect of blocking light.

[0105]

[0106]

[0107]

[0108]

Claims

1. Island-sea composite fiber, characterized in that: The refractive index difference between the island component and the sea component of the island-sea composite fiber is greater than 0.010; the number of islands on the cross-section of a single fiber in the island-sea composite fiber is greater than 100; and the diameter of all islands in the island-sea composite fiber is less than 2000 nm.

2. The island-sea composite fiber according to claim 1, characterized in that: The island-island composite fiber contains at least two islands of different diameters in its single fibers. A. Diameter less than 400nm, B. Diameter of 400–800 nm, C. Diameter greater than 800nm.

3. The island-sea composite fiber according to claim 1 or 2, characterized in that: The number of islands on the single fiber cross section is less than 10,000.

4. The island-sea composite fiber according to claim 1 or 2, characterized in that: The shortest distance between the surface of the outermost island and the fiber surface in the island-sea composite fiber is 0.10–2.00 μm.

5. The island-sea composite fiber according to claim 1 or 2, characterized in that: The fineness of the single fiber is 0.5 to 8.0 dtex.

6. The island-sea composite fiber according to claim 1 or 2, characterized in that: The island component is an alkali-soluble polymer.

7. A porous hollow fiber, obtained by reducing the island component of the island-island composite fiber as described in claim 6, characterized in that: The porous hollow fiber has more than 100 pores on its single fiber cross-section; the diameter of all pores in the porous hollow fiber is less than 2000 nm.

8. The porous hollow fiber according to claim 7, characterized in that: The shortest distance between the surface of the outermost pore and the fiber surface in the porous hollow fiber is 0.10–2.00 μm.

9. The porous hollow fiber according to claim 7, characterized in that: The porous hollow single fiber contains at least two types of pores with different diameters. A. The diameter of the pore is less than 400 nm. B. The diameter of the pore is 400–800 nm. C. The diameter of the pore is greater than 800 nm.

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