Hollow fibers

Abstract

Provided are hollow fibers that are suitable for use as clothing fibers and suppress collapse but still have hollowness. Hollow fibers according to the present invention have at least two hollows in a transverse fiber cross-section. The hollowness produced by the hollows satisfies 10<(A / B)×100<80, and the non-circularity of the hollows satisfies 1.00<r2 / r1≤2.50, the variation (CV%) in the non-circularity being equal to or less than 20.0%.

Description

Hollow fiber

[0001] This invention relates to hollow fibers. More specifically, it relates to hollow fibers that suppress hollow collapse and have a high hollow ratio.

[0002] Synthetic fibers made from thermoplastic polymers such as polyester and polyamide exhibit excellent mechanical properties and dimensional stability. Therefore, they are widely used not only in clothing but also in interiors, vehicle interiors, and industrial applications, possessing extremely high industrial value. However, with the diversification of fiber applications, the required properties have also become diverse, and often, synthetic fibers with simple, round cross-sections are insufficient. Therefore, research has been conducted to impart distinctive textures and qualities that cannot be achieved with round cross-section fibers by modifying or hollowing the fiber cross-section. While various technologies have been proposed to improve functionality through modifications to the fiber cross-section, depending on the application, hollowing the fiber cross-section has been one of the technologies that has seen active technological development.

[0003] Hollowing out the cross-section of fibers creates an air layer within the fiber, providing a soft texture while also improving functional aspects such as lightness and heat retention. Leveraging these functionalities, these fibers are used in clothing applications such as innerwear, sportswear, and winter sweaters and coats, as well as in industrial applications such as ropes and fishing nets.

[0004] In hollow fibers, a high hollow ratio is desirable because it improves functionality. However, a higher hollow ratio makes the hollow portion more susceptible to deformation when external force is applied to the fiber cross-section. Furthermore, a higher hollow ratio results in a thinner outer layer forming the hollow portion in the fiber cross-section, making it prone to fracture under external force. Therefore, there is a need for materials that maintain a high hollow ratio while preventing the hollow portion from collapsing and preserving its shape. Materials with modified fiber cross-sectional shapes have been proposed to achieve this.

[0005] Patent Document 1 proposes a monofilament for fishing line having a fiber cross-section consisting of an inner layer of hollow portions distributed equidistant from the center of the fiber cross-section, and an outer layer of hollow portions distributed equidistant from the center of the fiber cross-section, similar to the inner layer of hollow portions.

[0006] Patent Document 2 proposes a porous hollow fiber in which multiple hollow sections with 11 or more holes are arranged within the fiber's cross-section, thereby suppressing hollow collapse across the entire fiber cross-section.

[0007] Patent Document 3 proposes a technique for suppressing hollow collapse across the entire fiber cross-section by arranging multiple beam sections to separate groups of hollow sections, where multiple groups of hollow sections, each containing 10 or more holes, are arranged within the fiber cross-section.

[0008] Japanese Patent Publication No. 2008-184698, Japanese Patent Publication No. Hei 8-226009, Japanese Patent Publication No. 2020-165028

[0009] In the hollow monofilament described in Patent Document 1, the crosslinks between hollow sections in the same layer and between the inner and outer hollow sections bear stress against external forces on the fiber cross-section, potentially suppressing hollow collapse of the fiber cross-section and maintaining the hollow ratio. However, since the hollow monofilament is manufactured using a conventional hollow die, there is a problem in that the hollow section is easily compressed and collapsed due to the expansion of the polymer when the polymer is extruded from the die, making it difficult to produce fibers with a high hollow ratio.

[0010] In the porous hollow fiber described in Patent Document 2, the hollow portion is subdivided into multiple pores, so when an external force is applied to the fiber cross-section, some of the hollow portions collapse, absorbing the external force, while the remaining hollow portions do not collapse, thereby suppressing hollow collapse in the fiber cross-section and maintaining the shape of the fiber cross-section. On the other hand, in order to achieve a high hollow ratio, it is necessary to expand the diameter of the pores in the porous hollow portion, and the distance between the hollow portions becomes extremely close. Therefore, when the fiber is subjected to an external force, the cross-linking portions between close hollow portions may break, and the actual number of hollow portions decreases, which may cause most of the hollow portions to collapse.

[0011] In the porous hollow fiber described in Patent Document 3, hollow collapse is suppressed by subdividing the hollow portion into multiple pores, similar to Patent Document 2. In addition, multiple beam sections that separate the hollow sections bear stress against external forces on the fiber cross-section, thereby suppressing hollow collapse of the fiber cross-section. On the other hand, in order to achieve a high hollow ratio, it is necessary to expand the diameter of the holes in the hollow sections, which shortens the width of the beam sections between the hollow sections. Therefore, when external forces are applied to the fiber cross-section, stress concentrates at the points where the hollow sections are in contact with the shortened beam sections, and hollow collapse may occur as the beam sections collapse.

[0012] The present invention aims to solve the above-mentioned problems and provides a hollow fiber that can be suitably used as a clothing fiber while suppressing hollow collapse and maintaining the hollow ratio.

[0013] The present invention has the following configuration to solve the above problems: (1) A hollow fiber having two or more hollow sections in its cross-sectional surface and satisfying the following conditions: a) Hollow ratio (%): 10 < (A / B) × 100 < 80 where A is the total area of ​​the hollow section and B is the area of ​​the fiber cross-sectional surface b) Degree of irregularity of the hollow section: 1.00 < r ２ / r １ ≤2.50 r in the equation １ r is the radius of the inscribed circle of the hollow part. ２ c) Variation in shape: Variation in shape (degree of shape of hollow part CV%) ≤ 20.0% (2) The hollow fiber described in (1) above, wherein the variation in the distance between the centers of two adjacent hollow parts (distance between hollow parts CV%) satisfies the following condition. d) Variation in the distance between hollow parts (distance between hollow parts CV%) ≤ 20.0% (3) The hollow fiber described in (1) or (2) above, wherein the fiber cross-section satisfies the following condition. e) Thickness of the outermost layer of the fiber: 0.05 < (R - r) / R < 0.95 In the formula, r is the radius of the circle that circumscribes the outermost layer hollow part at the most points of two or more, and R is the radius of the fiber cross-section. (4) The hollow fiber described in any of (1) to (3) above, made of polyamide.

[0014] According to the present invention, even in hollow fibers with a high hollow ratio, which is difficult to achieve with conventional techniques, it is possible to suppress the collapse of the hollow portion and provide fibers that maintain a high hollow ratio. Furthermore, since a fiber with excellent lightness and heat retention properties can be obtained, it can be suitably used for clothing applications, especially as an apparel material.

[0015] This is a schematic diagram illustrating the crosslinked portion (region between adjacent hollow portions) in the hollow fiber of the present invention. In the diagram, one of the crosslinked portions is shown as an example (shaded portion). In the hollow fiber of the present invention, the r of the hollow portion １ (Inscribed circle radius) and r ２This is a schematic diagram showing the (circumscribed circle radius). In this example, the centers of circle 2 and circle 4 coincide. This diagram shows that hollow sections with a large degree of deformation are less likely to collapse. This is a schematic diagram showing the distance between hollow sections in the hollow fiber of the present invention. This is a schematic diagram showing the distance between adjacent hollow sections and the hexagon formed by the hollow sections in the hollow fiber of the present invention. This is a schematic diagram showing r (the radius of the circle that circumscribes the outermost hollow section at the most points) and R (the radius of the hollow fiber cross section) in the hollow fiber of the present invention. In this example, the centers of circle 16 and the hollow fiber cross section 17 coincide. This is a schematic diagram of an example of a composite die using a distribution plate for manufacturing the hollow fiber of the present invention. This is a cross-sectional view of a fiber of one embodiment of the hollow fiber of the present invention (Example 1, etc.). This is a cross-sectional view of a fiber of an example of a hollow fiber (Comparative Example 3). This is a cross-sectional view of a fiber of one embodiment of the hollow fiber of the present invention (Example 4). This is a cross-sectional view of a fiber of an example of a hollow fiber (Comparative Example 4). This is a cross-sectional view of a hollow fiber, an example of one (Comparative Example 5). This is a cross-sectional view of a hollow fiber, an example of one (Comparative Example 6). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 5). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 6). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 7). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 8). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 9). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 10). This is a cross-sectional view of a hollow fiber, an example of one (Comparative Example 7). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 12). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 13). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 14). This is a cross-sectional view of a hollow fiber, an embodiment of the hollow fiber of the present invention (Example 15).

[0016] The present invention relates to a hollow fiber having two or more hollow portions in its cross-section. In the hollow fiber of the present invention, the hollow portions are cavities that communicate in the direction of the fiber axis (perpendicular to the fiber cross-section) and can be observed as hollow in the fiber cross-section.

[0017] In the hollow fibers of the present invention, it is important that the hollowness ratio (%), which is expressed as the ratio of the total hollow area A in the fiber cross-section to the fiber cross-sectional area B, is greater than 10% and less than 80%.

[0018] In the hollow fibers of the present invention, by setting the hollow ratio to more than 10%, the fibers become lighter and have superior heat retention compared to solid fibers. The larger the hollow ratio, the stronger the feeling of lightness and heat retention when used in clothing. Considering the effective application of the present invention's effect, which aims to suppress hollow collapse at high hollow ratios, a hollow ratio of 20% or more is more preferable, and a hollow ratio of 30% or more is even more preferable. The hollow ratio in the present invention refers to the value measured by the method described in the Examples section.

[0019] The practical upper limit of the hollow ratio in the hollow fibers of the present invention is 80%, and by keeping the hollow ratio below 80%, sufficient distance between hollow portions in the fiber cross-section can be ensured. As a result, the merging of hollow portions and the failure of crosslinked portions during use become less likely, hollow collapse can be suppressed, and sufficient fiber strength for use as a clothing material can be guaranteed. When the hollow fibers of the present invention are used as a clothing material for sports and outdoor wear in harsh environments, or when they are used in movable parts of the elbows and knees that are subjected to repeated compressive loads, a hollow ratio of 75% or less is more preferable, and a hollow ratio of 70% or less is even more preferable. Within this range, hollow collapse of the present invention is suppressed, and quality deterioration such as discoloration and fibrillation is greatly suppressed.

[0020] In order to achieve the objective of this invention, which is to suppress hollow collapse, the number, shape, and arrangement of hollow portions in the fiber cross-section are key, and in this invention, it is important to have two or more hollow portions in the fiber cross-section. When there are two or more hollow portions, the bridging portion between the hollow portions bears the stress in response to external forces on the fiber, thereby suppressing hollow collapse in the fiber cross-section. The bridging portion referred to here is the region (1 in Figure 1) enclosed by a part of the outer circumference, such as the edge or arc, of each adjacent hollow portion and two line segments in the distance direction between the centers of the adjacent hollow portions.

[0021] The hollow fiber of the present invention preferably has three or more hollow portions. Although the larger the number of hollow portions, the better, considering that when extruded from a normal spinneret, a plurality of hollow portions may be compressed and the hollow portions may merge, or when obtaining a hollow fiber by eluting the island component from a sea-island composite fiber, uneven elution of the island component may occur, the upper limit of the number of hollow portions is preferably 500, and more preferably 100 or less.

[0022] The hollow portion of the hollow fiber of the present invention has an irregularity ratio r ２ / r １ and the irregularity ratio variation (CV%) satisfy the following conditions, which is important. Irregularity ratio of the hollow portion: 1.00 < r ２ / r １ ≤2.50 r １ : Inscribed circle radius of the hollow portion, r ２ : Circumscribed circle radius of the hollow portion Irregularity ratio variation: Variation of the irregularity ratio (hollow portion irregularity ratio CV%) ≤ 20.0% The irregularity ratio of the hollow portion and the hollow portion irregularity ratio CV% referred to here are obtained as follows. That is, the hollow fiber is embedded with an embedding agent such as an epoxy resin, and an image is taken at a magnification at which 100 or more hollow portions can be observed with a transmission electron microscope (TEM) for this cross-section. In the cross-section of one hollow fiber, if there are less than 100 hollow portions, it may be taken so that a total of 100 hollow portions can be confirmed from the cross-sections of a number of hollow fibers. The inscribed circle radius r １ and the circumscribed circle radius r ２ of 100 randomly extracted hollow portions from each image of the fiber cross-section taken are measured. The inscribed circle radius referred to here means the radius of a perfect circle inscribed in the hollow portion in the fiber cross-section, which is a cross-section perpendicular to the fiber axis from the two-dimensionally taken image. In FIG. 2, an example of an irregular hollow portion (in the case of a regular hexagon) is shown to clarify the explanation of the requirements of the present invention. The radius of the perfect circle 2 that inscribes the hollow portion 3 at two or more most points corresponds to the inscribed circle radius r １ here. The circumscribed circle radius r ２ refers to the radius of the perfect circle 4 that circumscribes the hollow portion 3 at two or more most points. From the above, based on the two-dimensional image, the inscribed circle radius and the circumscribed circle radius for 100 hollow portions are measured, and the irregularity ratio = circumscribed circle radius r ２ / Inscribed circle radius r １ From there, the average value obtained by calculating the numbers to the third decimal place was calculated. The above operation was performed for five images taken in the same manner, and the degree of deformation in this invention was obtained by rounding the simple average value from the third decimal place onwards from the evaluation results of the five images (n=5). On the other hand, the degree of deformation of the hollow part CV% in this invention was obtained by calculating the value obtained by rounding the simple numerical average value from the evaluation results of five images taken in the same manner to the second decimal place onwards from the average value and standard deviation of the degree of deformation of 100 hollow parts as follows: degree of deformation of the hollow part CV% = (standard deviation of deformation / average value of deformation) × 100 (%).

[0023] In the hollow fiber of the present invention, it is important that the degree of irregularity of the hollow portion is greater than 1.00 and 2.50 or less. If the degree of irregularity of the hollow portion is greater than 1.00, the shape of the hollow portion becomes anisotropic, either circular or polygonal. By arranging adjacent hollow portions so that their long axis directions face each other, the width of the bridging portion between the hollow portions becomes more uniform, so that the stress on the bridging portion between the hollow portions in response to an external force on the fiber cross-section becomes uniform, which is effective in suppressing hollow collapse. A more preferable degree of irregularity of the hollow portion is 1.05 or more. When the degree of irregularity of the hollow portion increases, anisotropy occurs in the second moment of area, which is a quantity that represents how difficult a certain shape is to deform. Here, a flattened quadrilateral (rectangle) with a degree of irregularity of 6.00 is shown in Figure 3. When an external force F is applied to the short side of the quadrilateral (Figure 3(a)), the second moment of area is larger and it becomes more difficult to deform compared to when an external force F is applied to the long side of the quadrilateral (Figure 3(b)). This is also true if the quadrilateral is hollow; that is, if the hollow part is a quadrilateral as shown in Figure 3, anisotropy occurs in the ease with which the hollow part collapses in response to external forces on the fiber cross-section, and the hollow part collapses easily when subjected to an external force F from the direction of the longer side where the second moment of area is small (Figure 3(b)). However, if the degree of deformation is 2.50 or less, the anisotropy of the second moment of area becomes small, making it difficult to deform even when subjected to external forces from any direction on the fiber cross-section, and thus suppressing hollow collapse. The degree of deformation of the hollow part is more preferably 2.30 or less.

[0024] In the hollow fibers of the present invention, it is important that the difference in the degree of irregularity of each hollow portion is small, that is, the degree of irregularity of the hollow portion CV% is 20.0% or less. When the degree of irregularity of the hollow portion CV% is 20.0% or less, the shape of the hollow portion within the fiber cross-section is substantially homogeneous, so that excessive differences in the second moment of area do not occur between hollow portions within the fiber cross-section. This prevents the hollow portion with a small second moment of area from collapsing in response to external forces applied to the fiber cross-section. A more preferable degree of irregularity of the hollow portion CV% is 10.0% or less.

[0025] In the hollow fiber of the present invention, the shape of the hollow portion is preferably a polygon in which all internal angles are less than 180°. When the hollow portion is a polygon, the hollow portion does not have a recess, and adjacent hollow portions can be arranged so that their sides are parallel to each other, and the width of the bridging portion between hollow portions becomes constant. As a result, when an external force is applied to the fiber, stress concentration on a part of the bridging portion can be prevented, and hollow collapse can be suppressed. Furthermore, when the hollow portion is a polygon in which all internal angles are less than 180°, it is possible to arrange the hollow portions without gaps within the fiber cross-section, compared to when the hollow portion is a circle, thus enabling a high hollow ratio of the fiber.

[0026] In the hollow fiber of the present invention, the shape of the hollow portion is preferably a regular polygon. When the shape of the hollow portion is a regular polygon, the width of the bridging portion between multiple hollow portions within the fiber cross-section becomes constant, and stress concentration at some of the bridging portions can be prevented when an external force is applied to the fiber, thereby suppressing hollow collapse. A regular polygon as used here refers to a polygon in which a figure consisting of n line segments is an n-sided polygon, and the lengths of each line segment are A1, A2, A3...An, and the average value of these line segment lengths is Lx, and the ratio of the length of each line segment to the average value Lx (A1 / Lx, A2 / Lx, A3 / Lx...An / Lx) is rounded to the third decimal place and is always between 0.93 and 1.07. Specifically, this refers to regular polygons such as equilateral triangles, regular squares, regular pentagons, regular hexagons, regular heptagons, regular octagons, regular nonagons, and regular decagons. A more preferable shape for the hollow portion is an equilateral triangle, a square, or a regular hexagon. When the shape of the hollow portion is an equilateral triangle, a square, or a regular hexagon, it is possible to fill the plane in two-dimensional space. This makes it possible to arrange the hollow portions within the fiber cross-section while maintaining a constant width between the hollow portions. This prevents stress concentration at specific points within the cross-section in response to external forces on the fiber cross-section, effectively suppressing collapse of the cross-section. Furthermore, because it is possible to fill the plane within the fiber cross-section, the hollow portions can be packed without gaps, efficiently increasing the hollowness ratio of the fiber.

[0027] A more preferable shape for the hollow section is a regular hexagon. When the hollow section is a regular hexagon, external forces from any direction can be evenly distributed to adjacent sides, resulting in excellent impact resistance. Furthermore, when multiple regular hexagonal hollow sections are arranged without gaps within the fiber cross-section, when any hollow section distributes stress, the stress propagates to adjacent hollow sections, and these hollow sections distribute stress as well. This distribution of stress across the entire group of hollow sections results in a structure with excellent impact resistance.

[0028] In the hollow fiber of the present invention, it is preferable that the variation in the distance between the centers of two adjacent hollow sections (distance between hollow sections CV%) is 20.0% or less. As shown in Figure 4(a), the distance between the centers of two hollow sections is the distance between hollow sections 5, and the center of a hollow section refers to the center of the circumscribed circle 4 of the hollow section as described above. Here, two adjacent hollow sections are, as shown in Figure 4(a), hollow sections that are adjacent on the circumference and can be considered to be arranged substantially on the same circumference with respect to the center of the fiber cross-section. Furthermore, as shown in Figure 4(b), if there is one hollow section in the inner layer of a group of hollow sections arranged on the same circumference, then in addition to adjacent hollow sections on the same circumference, the hollow section in the inner layer and the hollow section arranged in the outer layer are also two adjacent hollow sections. Furthermore, when the hollow sections are arranged concentrically as in Figure 4(c), there are two types of adjacent hollow sections: two adjacent hollow sections located on the same layer (Figure 4(c)6) and two adjacent hollow sections in the inner or outer layer (Figure 4(c)7). In other words, if we focus on hollow section 8 in a hollow fiber as shown in Figure 4(d), there are six distances between hollow sections including hollow section 8, and in a hollow fiber with hollow sections arranged in a grid as shown in Figure 4(e), there are eight distances between hollow sections including hollow section 9. These distances between hollow sections are determined by taking a two-dimensional photograph of the cross-section of the hollow fiber and measuring at 100 randomly selected locations, using the same method as for the inscribed circle radius and circumscribed circle radius of the hollow section described above. If it is not possible to evaluate more than 100 distances between hollow sections in the cross-section of a single hollow fiber, then a total of 100 distances between hollow sections can be evaluated from the cross-sections of many hollow fibers. The CV% of the distance between hollow parts is calculated from the average and standard deviation of the measured distances between hollow parts at 100 locations using the formula: CV% = (standard deviation of distance between hollow parts / average distance between hollow parts) × 100, and is calculated to two decimal places. This value was evaluated for five images taken in the same manner, and the CV% of the distance between hollow parts in this invention was obtained by rounding the simple numerical average of the results from the five images to two decimal places.

[0029] When the CV% of the hollow space distance is in the range of 20.0% or less, the distances between the hollow spaces are not excessively close or far apart, and are substantially equalized, so that the hollow spaces are regularly arranged. As a result, it becomes possible to arrange the hollow spaces regularly without gaps, and thus the hollow ratio of the fiber can be increased. Further, since the distances between the hollow spaces are substantially homogeneous, it is possible to prevent stress from concentrating on a specific crosslinked portion with respect to an external force applied to the fiber cross-section. More preferably, the CV% of the hollow space distance is 10.0% or less. Even more preferably, the CV% of the hollow space distance is 8.0% or less.

[0030] In achieving suppression of hollow collapse of the hollow fiber of the present invention, the arrangement of the hollow spaces is an important point. If the hexagon with the center-to-center distance between adjacent hollow spaces as the side and the center of the hollow space as the vertex is a regular hexagon, and all the hollow spaces in the hollow fiber are either the vertices constituting this regular hexagon or are located inside the regular hexagon formed by the hollow spaces, then the hollow spaces are arranged in a honeycomb pattern, which is preferable because the fiber cross-section has excellent crush resistance. The honeycomb arrangement means a shape filled in a plane only with regular hexagons with the regular hexagon as the constituent unit. When the hollow spaces are arranged in a honeycomb pattern, the crosslinked portions between the hollow spaces evenly bear the stress against an external force, and the stress dispersion effect is exhibited as the fiber cross-section, so that hollow collapse can be suppressed, which is preferable. Also, since planar filling is possible within the fiber cross-section, the group of hollow spaces forming a polygon is spread out without gaps, and it is possible to increase the hollow ratio of the fiber, which is preferable. Here, the regular hexagon is a hexagon in which the ratio of the length of each line segment to the average value Lx is calculated and rounded to the third decimal place, and all of An / Lx are between 0.93 and 1.07, in the same manner as the definition of the regular polygon described above. If An / Lx is between 0.95 and 1.05, the hexagon has a more regular shape, and the stress dispersion effect as a honeycomb arrangement is improved, resulting in excellent crush resistance, which is preferable. From this perspective, it is even more preferable if An / Lx is between 0.97 and 1.03.

[0031] As shown in Fig. 5(a), the arrangement of the hollow parts of the hollow fiber of the present invention may be a fiber cross-section in which the outermost hollow part forms a regular hexagon and there are hollow parts inside it. At this time, if there are hollow parts inside the regular hexagon, it is preferable because the fiber can achieve a high hollow ratio without impairing the crush resistance of the fiber cross-section due to the function of the cross-bridges between the central hollow part and each of the honeycomb-arranged hollow parts around it. Also, a honeycomb arrangement may be formed by six regular hexagons (10 to 15 in Fig. 5(b)) connecting the centers of adjacent hollow parts and a regular hexagon connecting the black dots shown in Fig. 5(b).

[0032] In achieving the suppression of hollow collapse, which is an object of the present invention, the arrangement of the hollow parts in the fiber cross-section being a honeycomb arrangement is an important point. At this time, if the shape of the hollow parts is a polygon with all interior angles less than 180°, it is preferable because the crush resistance is further improved by the synergistic effect of the shape and arrangement of the hollow parts. This is because, by arranging adjacent hollow parts so that their sides are parallel to each other, the stress unevenness at each cross-bridge when an external force is applied in the direction in which the adjacent hollow parts are compressed becomes smaller. Furthermore, when the hollow parts are regular polygons, the crush resistance due to the effect of the shape becomes larger. In particular, when the hollow parts are regular triangles, regular quadrilaterals or regular hexagons, the width of each cross-bridge becomes uniform due to the honeycomb arrangement of the hollow parts, and thus the suppression of hollow collapse due to the stress dispersion effect is further increased. From this point of view, when the hollow parts are regular hexagons, both the shape and the arrangement of the hollow parts become honeycomb-like, resulting in an ideal hollow fiber cross-section in terms of the crush resistance effect.

[0033] In the present invention, the outermost layer thickness (hereinafter referred to as sheath thickness) of the fiber cross-section is preferably greater than 0.05 and less than 0.95. As shown in Figure 6, the radius of the circle 16 that circumscribes the outermost hollow portion at two or more points is r, and the radius of the hollow fiber cross-section 17 is R, and the sheath thickness of the fiber cross-section is defined as (R - r) / R. This sheath thickness was calculated by taking two-dimensional images of the cross-section of the hollow fiber in the same manner as the inscribed circle radius and circumscribed circle radius of the hollow portion described above, measuring r and R for 100 randomly selected fibers, and calculating the average value of the sheath thickness = (R - r) / R, rounded to the third decimal place. This value was evaluated for five similarly captured images, and the sheath thickness in the present invention was evaluated by rounding the simple numerical average of the results of the five images to the third decimal place.

[0034] A sheath thickness greater than 0.05 in a hollow fiber is preferable because it indicates that there is sufficient distance between the outermost hollow portion and the outer layer of the fiber cross-section, preventing the outer layer of the fiber cross-section from being destroyed by external forces applied to the fiber cross-section and exposing the hollow portion. From this viewpoint, a sheath thickness greater than 0.10 is even more preferable. A sheath thickness less than 0.95 in a hollow fiber is preferable because the outermost hollow portion is located away from the center of the fiber cross-section, ensuring a sufficient area within a circle with radius r where the hollow portion can be placed, thus enabling a fiber with a high hollow ratio. More preferably, the sheath thickness is less than 0.90.

[0035] The polymer constituting the hollow fibers of the present invention may be any polymer used in synthetic fibers, such as polyamide and polyester, but polyamide is preferred. Polyamide is a polymer with a low modulus of elasticity, and because of its toughness due to its low modulus of elasticity, when the fiber cross-section is subjected to an external force, the outer layer of the fiber cross-section does not break and the hollow portion is not exposed, which is why it is preferred. Furthermore, when polyamide is used in the hollow fibers of the present invention, a fiber material with a soft texture can be obtained.

[0036] Preferred polyamides for the hollow fibers of the present invention include, but are not limited to, aliphatic polyamides such as nylon 6, nylon 66, nylon 12, nylon 510, nylon 610 and their copolymers, and semi-aromatic polyamides formed from aromatic diamines and dicarboxylic acids and their copolymers.

[0037] Next, the physical properties of the hollow fibers of the present invention will be described.

[0038] The fineness of the hollow fibers of the present invention is not particularly limited and can be appropriately selected according to the application and required characteristics, but 5 dtex or more and 300 dtex or less is preferred. Fineness in the present invention refers to the value measured by the method described in the Examples section. A fineness of 5 dtex or more for hollow fibers is preferred because it provides good process passability, generates less fuzz during use, and has excellent durability. It is also preferred because it ensures fiber strength suitable for use as a raw yarn for clothing. On the other hand, a fineness of 300 dtex or less for hollow fibers is preferred because it does not impair the flexibility of the fiber and fiber structure.

[0039] The strength of the hollow fibers of the present invention is preferably adjusted according to the application and required characteristics by the manufacturing method described later. Here, the strength of the present invention refers to the value measured by the method described in the Examples section. The greater the strength, the better it can withstand post-processing steps and actual use, and the less likely it is to break. On the other hand, since the hollow fibers of the present invention are made from polyamide and have a hollow portion in the fiber cross-section, there is an upper limit to the feasible strength. Considering the handling of the fiber, the strength of the fiber of the present invention is preferably 0.3 cN / dtex or more and 10.0 cN / dtex or less. Furthermore, the hollow fibers of the present invention are preferably adjusted according to the elongation required for their use, and when used in clothing applications, a strength of 0.5 cN / dtex or more and 5.0 cN / dtex or less is particularly preferred.

[0040] The elongation of the hollow fibers of the present invention is preferably adjusted according to the application and required characteristics by the manufacturing method described later. Here, the elongation of the present invention refers to the value measured by the method described in the Examples section. The higher the elongation, the less likely the fiber is to break even when subjected to rapid deformation. On the other hand, since elongation deformation during molding can sometimes make the properties of the textile product unstable, considering the handling of the fiber, it is more preferable that the elongation of the fibers of the present invention be between 30% and 60%. Furthermore, the elongation of the hollow fibers of the present invention is preferably adjusted according to the elongation required for its use. When used in clothing applications, it is particularly preferable to adjust it to between 30% and 50%, and when used in non-clothing applications, it is preferable to adjust it to between 20% and 40%.

[0041] The hollow fibers of the present invention are not particularly limited in terms of the cross-sectional shape of the fibers and can be appropriately selected according to the application and required characteristics. They may have a perfectly circular cross-section or a non-circular cross-section. However, a perfectly circular cross-section is preferable in consideration of the passability in higher processes and the avoidance of uneven application of external forces to the hollow portion of the fiber cross-section.

[0042] The hollow fibers of the present invention are not particularly limited in terms of their form and may be in any form such as monofilament, multifilament, or staple.

[0043] The hollow fibers of the present invention can be processed, such as false twisting, in the same way as ordinary fibers, and can be handled in the same way as ordinary fibers in weaving and knitting. As woven or knitted fabrics, there are no special restrictions on their form, and they may be woven fabrics, knitted fabrics, or pile fabrics according to known methods. Furthermore, the present invention may be any weave or knit structure, and plain weave, twill weave, satin weave or variations thereof, as well as warp knitting, weft knitting, circular knitting, lace knitting or variations thereof can be suitably employed. In addition, when forming a fiber structure, it may be combined with other fibers by interweaving or interknitting, or it may be a fiber structure made by blending with other fibers into a yarn.

[0044] Next, an example of a method for producing hollow fibers according to the present invention will be described in detail.

[0045] The method for producing the hollow fibers of the present invention is not particularly limited, but for example, a hollow fiber can be obtained by first producing a sea-island composite fiber, then subjecting it to advanced processing such as weaving, and finally dissolving the island portion of the sea-island composite fiber to obtain only the sea component. Here, a sea-island composite fiber is one in which two or more types of polymers form a fiber cross-section perpendicular to the fiber axis, and has a cross-sectional structure in which island components made of one polymer are scattered within sea components made of the other polymer.

[0046] Since the hollow fibers of the present invention are preferably made of polyamide, it is preferable that polyamide be selected as the sea component of the sea-island composite fiber. Even when an aqueous solvent, hot water, or alkaline aqueous solution is used to dissolve the island component, polyamide is a polymer that is poorly soluble in any of these solvents, so it is preferable that the sea component be polyamide. In addition, in order to improve the mechanical properties of the fiber, the polymer viscosity (η) Ｒ A polyamide with a larger η may also be used. Ｒ If it is 1.5 or higher, it is preferable because it can impart sufficient mechanical properties for use as a clothing fiber, and η Ｒ If the value is 5.0 or less, it is preferable because the entanglement caused by interactions between molecular chains can be easily untangled during melt spinning, and this does not affect the spinnability or physical properties of the yarn.

[0047] As island components of sea-island composite fibers, it is preferable to select from polymers that exhibit easy elution, such as polyester and its copolymers, polylactic acid, polyamide, polystyrene and its copolymers, polyethylene, and polyvinyl alcohol. Furthermore, from the viewpoint of simplifying the elution process of the island components, copolymerized polyesters, polylactic acid, and polyvinyl alcohol that exhibit easy elution to aqueous solvents or hot water are preferred as island components. In particular, polyester copolymerized with 5 mol% to 15 mol% of 5-sodium sulfoisophthalic acid and polyester copolymerized with the aforementioned 5-sodium sulfoisophthalic acid in an amount of 5% to 15% by mass of polyethylene glycol with a weight-average molecular weight of 500 to 3000 are especially preferred because they exhibit easy elution to aqueous solvents such as alkaline aqueous solutions while maintaining crystallinity.

[0048] Furthermore, the polymers used in the marine and island components may contain various additives such as inorganic substances like titanium dioxide, silica, and barium oxide, carbon black, colorants such as dyes and pigments, flame retardants, fluorescent whitening agents, antioxidants, or ultraviolet absorbers.

[0049] The manufacturing method for the aforementioned sea-island composite fibers is not particularly limited, and other methods include wet and wet-dry solution spinning, as well as melt-blown and spunbond methods suitable for obtaining sheet-like fiber structures. However, from the viewpoint of increasing productivity, melt spinning is preferred.

[0050] Furthermore, in the melt spinning method, it is possible to manufacture the polymers using a composite spinneret, as described later. The spinning temperature in this process is preferably set to a temperature at which high-melting-point and high-viscosity polymers exhibit fluidity. This fluidity temperature varies depending on the molecular weight, but it is preferable to set it between the melting point of the polymer and [melting point + 60°C] because this allows for stable production.

[0051] The hollow fibers of the present invention are manufactured by forming their characteristic fiber cross-section using a spinneret. However, from the viewpoint of ease of handling during the manufacturing process and suppressing unwanted crushing and deterioration during higher-order processing, it is preferable to manufacture them as composite fibers composed of two or more polymers and remove one component during the higher-order processing step. In this case, the fiber cross-section, which is important for achieving the present invention, may be carried out using a conventional composite spinneret. However, since it is necessary to form a complex cross-sectional shape, it is preferable to use a composite spinneret using a distribution plate described in Japanese Patent Application Publication No. 2011-208313 from the viewpoint of accuracy and stability of the cross-section.

[0052] The composite die shown in Figure 7 is assembled into a spinning pack with three main components stacked from top to bottom: a metering plate 18, a distribution plate 19, and a discharge plate 20, and is used for spinning. Incidentally, Figure 7 is an example using two types of polymers, polymer A and polymer B.

[0053] In the nozzle member illustrated in Figure 7, the metering plate 18 measures the amount of polymer per discharge hole and per distribution hole and allows it to flow in, the distribution plate 19 controls the composite cross-section and its cross-sectional shape in the cross-section of the single fiber, and the discharge plate 20 compresses the composite polymer flow formed by the distribution plate 19 and discharges it.

[0054] To avoid confusion in the explanation of the composite spinneret, although not shown in the diagram, for components stacked above the measuring plate 18, components with flow channels can be used in accordance with the spinning machine and spinning pack. By designing the measuring plate 18 to match existing flow channel components, existing spinning packs and their components can be used as is. Therefore, there is no need to exclusively use the spinning machine for this spinneret. In practice, it is also preferable to stack multiple flow channel plates between the flow channel and the measuring plate or between the measuring plate 18 and the distribution plate 19. The purpose of this is to provide flow channels that efficiently transport the polymer in the direction of the spinneret cross-section and the cross-section of the single fiber, and to introduce it into the distribution plate 19.

[0055] The discharge rate when spinning the composite fibers of the present invention can be stably discharged within a range of 0.1 g / min / hole to 20.0 g / min / hole per discharge hole. In this case, it is preferable to determine the discharge rate according to the desired fiber diameter, taking into consideration winding conditions, stretching ratio, etc.

[0056] The molten polymer flow discharged from the discharge port is cooled and solidified, then focused by the application of an oil or the like, and taken up by a roller with a specified peripheral speed. Here, this take-up speed is determined by the discharge volume and the target fiber diameter. In this invention, from the viewpoint of stably manufacturing composite fibers, the roller take-up speed is preferably set to about 500 m / min to 6000 m / min, and can be changed depending on the physical properties of the polymer and the intended use of the fibers.

[0057] From the viewpoint of improving the mechanical properties of spun composite fibers by promoting uniaxial orientation of the fibers, it is preferable to stretch them. For example, in a stretcher consisting of one or more rollers, if the fibers are made of a polymer that is generally melt-spinnable and exhibits thermoplasticity, the fibers are stretched smoothly in the axial direction and then heat-set and wound up by the peripheral speed ratio of a first roller set to a temperature above the glass transition temperature but below the melting point and a second roller set to a temperature equivalent to the crystallization temperature. In the case of polymers that do not exhibit glass transition, the dynamic viscoelasticity (tanδ) of the composite fiber is measured, and a temperature above the peak temperature on the high-temperature side of the obtained tanδ can be selected as the preheating temperature.

[0058] Furthermore, regarding the stretching process, it is possible to stretch the spun composite fibers after winding them up, or to stretch them immediately after spinning without winding them up first. However, from the perspective of enhancing the wearing comfort of the fabric by creating a complex texture and feel by changing each individual fiber into a different, uneven shape, it is more preferable to perform yarn processing that involves stretching.

[0059] In addition, it is preferable that the composite fiber in the present invention be spun as a multifilament in a melt spinning method.

[0060] While the yarn processing method is not particularly limited to known yarn processing techniques such as false twisting and uneven stretching, false twisting is preferable from the standpoint of imparting crimp to the yarn bundle and providing a fiber material with good tactile quality and texture.

[0061] The method for performing false twisting is not particularly limited to any method commonly used for polyamide, but considering productivity, it is preferable to use a friction false twisting machine that uses discs or belts.

[0062] As described above, to obtain hollow fibers from the sea-island composite fibers of the present invention, hollow fibers made of polyamide can be obtained by immersing the composite fibers in a solvent in which the easily soluble components can be dissolved and removing the easily soluble components. When the easily soluble components are copolymerized PET or polylactic acid (PLA) copolymerized with 5-sodium sulfisophthalic acid, an alkaline aqueous solution such as an aqueous sodium hydroxide solution can be used. As a method for treating the composite fibers of the present invention with an alkaline aqueous solution, for example, the composite fibers or fibrous structures made therefrom (woven fabrics, knitted fabrics, etc.) can be immersed in an alkaline aqueous solution. At this time, heating the alkaline aqueous solution to 50°C or higher is preferable because it can accelerate the progression of hydrolysis. Furthermore, if the treatment is carried out using a fluid dyeing machine or the like, a large amount can be treated at once, so productivity is good and it is preferable from an industrial standpoint. The same applies when dissolving the island components with an aqueous solvent or hot water.

[0063] The hollow fibers of the present invention will be described in detail below with reference to examples. The following evaluations were performed on the examples and comparative examples.

[0064] A. Relative viscosity of sulfuric acid (η Ｒ 0.25 g of the sample was dissolved in 100 ml of 98% by mass sulfuric acid to a concentration of 1 g / l, and the flow time (T1) at 25°C was measured using an Ostwald viscometer. Subsequently, the flow time (T2) of 98% by mass sulfuric acid alone was measured. The ratio of T1 to T2, i.e., T1 / T2, was defined as the relative viscosity of sulfuric acid.

[0065] B. Using the YC-1 electric measuring machine manufactured by Sendo Intec Co., Ltd., the weight of 100m of fiber was measured, and the value was multiplied by 100 to calculate the fineness (dtex). This measurement was repeated 10 times, and the average value was rounded to two decimal places to determine the fineness (dtex).

[0066] C. Mechanical Properties of Fibers The stress-strain curve of the fiber was measured using an Orientec Co., Ltd. Tensilon UCT-100 tensile testing machine under the conditions of a sample length of 20 cm and a tensile speed of 20 cm / min. The load at the time of fracture was read, and the fracture strength was calculated by dividing that load by the fineness. The strain at the time of fracture was read, and the value obtained by dividing it by the sample length and multiplying by 100 was calculated to determine the elongation at fracture. This operation was repeated five times for each level, and the average value of the obtained results was calculated and rounded to the second decimal place to be defined as the strength (cN / dtex) or elongation (%).

[0067] D. Hollow fibers were embedded in epoxy resin, frozen using a Reichert FC-4E cryosectioning system, and then cut with a Reichert-Nissei ultracut N (ultramicrotome) equipped with a diamond knife. The cut surface was then photographed using a Hitachi H-7100FA transmission electron microscope (TEM) at a magnification that allowed for the observation of 100 or more hollow sections. If there were not 100 or more hollow sections in the cross-section of a single composite fiber, the cross-sections of multiple hollow fibers were photographed to confirm a total of 100 hollow sections. From this image, one hollow fiber was randomly selected, and using image processing software (WINROOF), the total area of ​​the hollow portion (=A) and the cross-sectional area of ​​the fiber (=B) were measured for 100 fiber cross-sections. The hollowness ratio (%) was calculated as A / B × 100 and rounded to one decimal place, and the average of the calculated values ​​was found. The above measurements were performed for each of the five images, and the hollowness ratio was determined by rounding the average value of the five images to one decimal place.

[0068] E. Degree of deformation and variation of deformation in the hollow portion (degree of deformation of the hollow portion CV%) Using the same method as described above for the hollow ratio, the fiber cross-section of the hollow fiber is photographed, and from the image, the diameter of the circle that circumscribes the hollow portion with the most points (two or more) is determined by the radius of the circumscribed circle r. ２ Furthermore, the radius of the inscribed circle r is defined as the diameter of the circle that is inscribed at the most points (two or more points). １ As such, the degree of deformation = circumradius r ２ / Inscribed circle radius r １The degree of deformation was calculated to the third decimal place and rounded to the nearest whole number. This degree of deformation was measured for 100 randomly selected hollow sections, and the hollow section deformation CV% was calculated from the mean and standard deviation based on the following formula. If there were no more than 100 hollow sections in the cross-section of a single composite fiber, photographs were taken to confirm a total of 100 hollow sections from the cross-sections of multiple hollow fibers.

[0069] Hollow part deformation degree CV% = (Standard deviation of deformation degree / Mean value of deformation degree) × 100 This deformation degree and deformation degree variability were evaluated for five images taken in the same manner. The deformation degree was calculated by rounding the mean value of the deformation degrees of the five images to the third decimal place, and the deformation degree variability was calculated by rounding the mean value of the deformation degree variability of the five images to the second decimal place.

[0070] F. Variation in the distance between the centers of hollow sections (CV%) The distance between hollow sections is defined as the distance 5 between the centers of two adjacent hollow sections, as shown in Figure 4(a), when the center of a hollow section is defined as the center of the circumscribed circle 4 of the hollow section. This evaluation is performed in the same way as the hollow ratio described above, by taking two-dimensional photographs of the cross-section of the hollow fiber and measuring the distance between hollow sections at 100 randomly selected locations. If it is not possible to evaluate the distance between hollow sections at 100 or more locations from the cross-section of a single hollow fiber, the system is designed to evaluate the hollow section distance at a total of 100 locations from the cross-sections of multiple hollow fibers. This CV% of the distance between hollow sections is calculated from the mean and standard deviation of the 100 measured distances between hollow sections using the formula: CV% = (standard deviation of the distance between hollow sections / mean value of the distance between hollow sections) × 100, and is calculated to two decimal places. This value was evaluated for five similarly captured images, and the variation in the distance between hollow parts was defined as the simple numerical average of the results from the five images, rounded to two decimal places.

[0071] G. Outermost Layer Thickness (Sheath Thickness) Using the same method as described above for the hollowness ratio, the cross-section of the hollow fiber was photographed. From the image, the radius of the circle that circumscribes the outermost hollow portion at the most points (two or more points) was defined as r, and the radius of the hollow fiber cross-section was defined as R. For 100 randomly selected hollow fibers, r and R were measured, and the sheath thickness (R-r) / R was calculated to three decimal places. The average of the calculated values ​​was then determined. This value was evaluated for five similarly photographed images, and the sheath thickness was evaluated by rounding the simple numerical average of the results from the five images to three decimal places.

[0072] H. Hollow Structure Retention Rate (Resistance to Collapse of Hollow Fibers) Compressive force was applied to the tubular knitted material obtained after the island component elution, in accordance with JIS L1096:2020 (Compressibility and Compressive Modulus). Specifically, the tubular knitted material was cut into 15 test pieces of approximately 50 mm x 50 mm, and three samples were stacked together and compressed for 1 minute at a pressure of 19.6 kPa using a compression machine. After that, the pressure was removed and the tubular knitted material was left to stand for 1 minute, from which hollow fibers were extracted using a thread puller. For the extracted hollow fibers, the cross-section of the hollow part of the hollow fibers was photographed in the same manner as the hollow ratio described above, and 100 hollow fibers were randomly selected from the images and extracted, and the hollow ratio was calculated. The hollow ratio was measured for each of the 5 images, and the average value of the 5 images was used, rounded to the first decimal place. The process of applying pressure to the tubular knit and calculating the hollow ratio was repeated a total of five times, and the average value was taken as the hollow ratio after compression. The hollow portion retention rate was calculated based on the following formula: Hollow portion retention rate (%) = {(Hollow ratio - Hollow ratio after compression) / Hollow ratio} × 100. The resistance to crushing of the hollow fibers was judged in three stages based on the following criteria from the obtained hollow portion retention rate: S: Excellent resistance to crushing (80% ≤ hollow portion retention rate) A: Good resistance to crushing (60% ≤ hollow portion retention rate < 80%) B: Poor resistance to crushing (50% ≤ hollow portion retention rate < 60%) C: Poor resistance to crushing (Hollow portion retention rate < 50%).

[0073] I. Using a lightweight Terotec constant-pressure thickness gauge (PG-14J), the resulting tubular knitted fabric after island component elution was cut into 20 cm x 20 cm test pieces, the thickness (cm) was measured, the volume of the fabric was calculated, and the apparent density (g / cm³) of the knitted fabric was obtained by dividing the weight (g) of the knitted fabric by the obtained volume. ３The apparent density obtained was used to determine the lightness of each sample in three stages based on the following criteria: S: Excellent lightness (apparent density ≤ 0.2) A: Good lightness (0.2 < apparent density ≤ 0.5) C: Poor lightness (0.5 < apparent density).

[0074] J. Heat retention (clo value) After the tubular knitting obtained from the elution of the island components was cut into test pieces of approximately 300 mm x 300 mm, the clo value of the cushion was measured in accordance with JIS L1096:2020. The heat retention was judged in three stages based on the following criteria from the obtained clo values: S: Excellent heat retention (0.4 < clo value) A: Good heat retention (0.2 < clo value ≤ 0.4) C: Poor heat retention (clo value ≤ 0.2).

[0075] [Example 1] As a marine component, nylon 6 (polyamide, η Ｒ 2.6) and PET copolymerized with 8.0 mol% of 5-sodium sulfoisophthalic acid (copolymerized PET) as island components were melted separately at 270°C. The sea / island components were weighed to a weight ratio of 50 / 50 and poured into a spinning pack incorporating the composite die shown in Figure 7. The incoming polymer was then discharged from the discharge hole to produce a circular sea-island composite fiber as shown in Figure 8, with a hexagonal shape for the hollow sections, seven hollow sections, and equal distances between the hollow sections.

[0076] A cooling and solidification-based oil was applied to the discharged composite polymer stream, and the material was wound at a spinning speed of 1000 m / min. The resulting material was then stretched between rollers heated to 80°C and 130°C to produce 50 dtex-18 filament sea-island composite fibers.

[0077] The obtained sea-island composite fibers were knitted into tubular fibers using an Eiko Sangyo NCR-BL circular knitting machine (3.5 inches (8.9 cm) diameter, 27 gauge). These fibers were then treated in a 3% by weight sodium hydroxide aqueous solution heated to 90°C to dissolve and remove the island components, yielding hollow fibers consisting solely of sea components.

[0078] The mechanical properties of the obtained hollow fibers were 4.2 cN / dtex and elongation of 34%. When the cross-section was observed, the fiber cross-section was as shown in Figure 8, with a hollowness ratio of 50%, a hollowness degree of 1.35, a hollowness degree CV% of 1.3%, a hollowness center-to-center distance CV% of 5.1%, and a sheath thickness of 0.18.

[0079] The hollow fiber retention rate, calculated using the hollow fibers obtained by compressing and removing threads from the resulting tubular knitted material, was 90%. Furthermore, it exhibited good lightness and heat retention properties. The results are shown in Table 1.

[0080] [Examples 2 and 3, Comparative Examples 1 and 2] The methods described in Example 1 were carried out in accordance with Example 1, except that the weight ratio of sea / island was gradually changed to 70 / 30 (Example 2), 95 / 5 (Comparative Example 1), 30 / 70 (Example 3), and 10 / 90 (Comparative Example 2). The evaluation results of these hollow fibers are shown in Table 1. Examples 2 and 3, like Example 1, showed excellent uniformity in the degree of irregularity of the hollow parts and the distance between the centers of the hollow parts. In terms of fabric characteristics, the resistance to crushing of the hollow parts, lightness, and heat retention were good.

[0081] On the other hand, in Comparative Example 1, the hollow ratio was low at 4%, resulting in inferior lightness and heat retention. In Comparative Example 2, the hollow ratio was high at 88%, and the sheath thickness was 0.02, meaning the distance between the outer fiber layer and the outermost hollow layer was narrow. As a result, the hollow part ruptured, leading to inferior resistance to collapse of the hollow part, as well as inferior lightness and heat retention.

[0082] [Comparative Example 3, Example 4] The method described in Example 1 was carried out in accordance with Example 1, except that the shape of the hollow section was changed to a regular hexagon as shown in Figure 9 and the number of hollow sections was 1 (Comparative Example 3), or the shape of the hollow section was changed to a regular hexagon as shown in Figure 10 and the number of hollow sections was 2 (Example 4). The evaluation results of these hollow fibers are shown in Table 1. In Comparative Example 3, since there was only one hollow section, there was no cross-linking section formed by the arrangement of multiple hollow sections, resulting in an inability to prevent hollow section collapse. On the other hand, in Example 4, since there were two hollow sections, the resistance to hollow section collapse was good.

[0083] [Comparative Examples 4-6] The method described in Example 1 was carried out in accordance with Example 1, except that the nozzle was changed to one with a circular hollow shape and one hollow (Comparative Example 4), or one with seven hollows (Comparative Example 5), or one with 200 hollows (Comparative Example 6), as shown in Figures 11-13.

[0084] The evaluation results for these hollow fibers are shown in Table 2. In Comparative Example 4, since there was only one hollow section, there were no cross-linking sections formed by the arrangement of multiple hollow sections, resulting in an inability to prevent hollow section collapse. In Comparative Example 5, the degree of deformation of the hollow section was 1.00, and since the shape was perfectly circular, the width of the cross-linking sections between adjacent hollow sections was not uniform, resulting in poor resistance to hollow section collapse. In Comparative Example 6, although there were a large number of hollow sections (200), the degree of deformation of the hollow section was 1.00, and similar to Comparative Example 5, the width of the cross-linking sections between adjacent hollow sections was not uniform, resulting in poor resistance to hollow section collapse.

[0085]

[0086]

[0087] [Examples 5-10, Comparative Example 7] The method described in Example 1 was carried out in accordance with Example 1, except that the nozzle was changed to have the following shapes for the hollow sections: seven hexagonal (Figure 14, Example 5), seven square (Figure 15, Example 6), seven trapezoidal (square) (Figure 16, Example 7), six equilateral triangles (Figure 17, Example 8), six isosceles triangles (Figure 18, Example 9), seven star-shaped (Figure 19, Example 10), and seven flattened hexagonal (Figure 20, Comparative Example 7), as shown in Figures 14-20.

[0088] The evaluation results for these hollow fibers are shown in Table 3. In Example 5, the degree of irregularity of the hollow section was 1.48, and the width of the bridging portion between adjacent hollow sections was constant, resulting in good resistance to collapse of the hollow section. In Examples 6 to 9, the degree of irregularity of the hollow section was 1.42 (Example 6), 1.53 (Example 7), 1.98 (Example 8), and 2.40 (Example 9), respectively. Since the degree of irregularity was greater than 1.00 and within the range of 2.50 or less, the resistance to collapse of the hollow section was good, similar to Example 5. In Example 10, the degree of irregularity of the hollow section was 1.71, but the hollow section had a star shape, not a polygon with an arbitrary interior angle of less than 180°, and the width of the bridging portion between adjacent hollow sections was not constant. Therefore, although the resistance to collapse of the hollow section was not inferior, it was not good. In Comparative Example 7, the degree of deformation of the hollow portion was 3.80, and anisotropy occurred in the second moment of area of ​​the shape of the hollow portion. As a result, there was a direction in which the hollow portion was more likely to deform when subjected to an external force on the fiber cross-section, leading to a result of inferior resistance to crushing of the hollow portion.

[0089]

[0090] [Example 11, Comparative Example 8] The method described in Example 1 was followed, except that the spinning pack with the composite die shown in Figure 7 was replaced with a spinning pack that omitted the weighing plate 18 and the distribution plate 19. The evaluation results of these hollow fibers are shown in Table 4. In Example 11, although the meterability of the composite polymer decreased, the variation in the degree of deformation of the hollow portion was 18.0%. Since there was not a significant difference in the second moment of area between the hollow portions within the fiber cross-section, the resistance to crushing of the hollow portion was good. On the other hand, in Comparative Example 8, the meterability of the composite polymer decreased, the variation in the degree of deformation of the hollow portion was 25.0%, and since there was a significant difference in the second moment of area between the hollow portions within the fiber cross-section, the resistance to crushing of the hollow portion was inferior.

[0091] [Examples 12-15] The method described in Example 1 was carried out in accordance with Example 1, except that the nozzle was changed to one with 19 hollow sections, where the polygon formed by the distance between adjacent hollow sections is a regular hexagon (Figure 21, Example 12), 37 hollow sections, where the polygon formed by the distance between adjacent hollow sections is a regular hexagon (Figure 22, Example 13), and 7 hollow sections, where the polygon formed by the distance between adjacent hollow sections is a hexagon (Figures 23, 24, Examples 14, 15).

[0092] The evaluation results for these hollow fibers are shown in Table 4. In Example 12, the hollow sections were arranged in a honeycomb pattern in concentric circles, and the polygon formed by the distance between adjacent hollow sections was a regular hexagon, which allowed for stress distribution. As the width of the bridging sections between adjacent hollow sections was constant, the resistance to collapse of the hollow sections was good. In Example 13, the hollow sections were arranged in a honeycomb pattern similar to Example 12, and the resistance to collapse of the hollow sections was good. In Example 14, the polygon formed by the distance between adjacent hollow sections was a hexagon, and there was some unevenness in the width of the bridging sections between hollow sections, but the resistance to collapse of the hollow sections was not inferior. In Example 15, for the same reasons as in Example 14, the result was poor in terms of hollow collapse resistance.

[0093]

[0094] [Examples 16-19] Using the method described in Example 1, the polymer used for the marine component was η Ｒ The procedure was carried out according to Example 1, except that the high viscosity nylon 6 (Example 16), nylon 66 (Example 17), nylon 610 (Example 18), and PET (polyester) (Example 19) were changed to nylon 6 with a viscosity of 3.3.

[0095] The evaluation results for these hollow fibers are shown in Table 5. In Example 16, the strength was increased by using nylon 6 with high polymer viscosity, and it showed good mechanical properties as a clothing fiber. In Examples 17 and 18, there were no significant changes in fiber properties or fabric properties due to the change in polymer, and the lightness and heat retention were good, and the hollow collapse resistance was not inferior. In Example 19, because the elastic modulus of the PET constituting the hollow fiber was high and the toughness was poor, a part of the hollow portion deformed when the fiber cross-section was subjected to an external force, so although the hollow collapse resistance was not inferior, it was not good.

[0096]

[0097] Even with hollow fibers that have a high hollow ratio, it is possible to suppress the collapse of the hollow portion and provide fibers that maintain a high hollow ratio. Furthermore, since fibers with excellent lightness and heat retention properties can be obtained, they can be suitably used for clothing applications, especially as apparel materials.

[0098] 1: Bridged section (region between adjacent hollow sections) 2: Inscribed circle of a hollow section 3: Hollow section 4: Circumscribed circle of a hollow section 5: Distance between hollow sections (line segment connecting the centers of the hollow sections (circumscribed circles of the hollow sections)) 6, 7: Two adjacent hollow sections 8, 9: Hollow section 10-15: Regular hexagon formed by adjacent hollow sections (points in the diagram are the centers of the regular hexagons) 16: Circle circumscribed by the outermost hollow section at the most points (two or more) 17: Fiber cross-section 18: Measuring plate 19: Distribution plate 20: Discharge plate r １ : radius of the inscribed circle r ２ : Circumscribed circle radius r: Radius of the circle 16 that circumscribes the outermost hollow layer at two or more points with the maximum number of points R: Radius of the hollow fiber cross-section 17 F: External force

Claims

1. Hollow fibers having two or more hollow sections in their cross-section and satisfying the following conditions: a) Hollowness ratio (%): 10 < (A / B) × 100 < 80 where A is the total area of ​​the hollow section and B is the area of ​​the fiber cross-section b) Degree of deformation of the hollow section: 1.00 < r ２ / r １ ≤2.50 r in the equation １ r is the radius of the inscribed circle of the hollow part. ２ c) Variation in shape: Variation in the aforementioned shape (degree of shape of hollow section CV%) ≤ 20.0% 2. The hollow fiber according to claim 1, wherein the variation in the distance between the centers of two adjacent hollow portions (dimension between hollow portions CV%) satisfies the following condition: d) Variation in the distance between hollow portions (dimension between hollow portions CV%) ≤ 20.0% 3. A hollow fiber according to claim 1 or 2, satisfying the following conditions in the fiber cross-section: e) Thickness of the outermost layer of the fiber: 0.05 < (R - r) / R < 0.95, where r is the radius of the circle that circumscribes the hollow portion of the outermost layer at the most points (two or more), and R is the radius of the fiber cross-section.

4. A hollow fiber according to claim 1 or 2, made of polyamide.

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