Composite fibers, hollow fibers and textile products

Abstract

To provide a composite fiber, a hollow fiber and a multifilament suitable for obtaining a textile excellent in wearing comfort, having a moderate resilience and a soft, fluffy texture, by controlling the void structure inside the fiber and between fibers. [Solution] The present invention relates to a composite fiber in which, in the cross section of the fiber, two or more types of polymers with different dissolution rates in a solvent are layered from the fiber center toward the fiber surface, the innermost layer including the fiber center contains an easily soluble polymer, and two types of sparingly soluble polymers with different melting points are unevenly distributed in at least one layer other than the innermost layer.

Description

[Technical Field]

[0001] The present invention relates to a composite fiber, a hollow fiber, and a multifilament suitable for clothing textiles that are excellent in wearing comfort. [Background technology]

[0002] Synthetic fibers made from polyester, polyamide, etc. have excellent mechanical properties and dimensional stability, and are therefore widely used in a variety of applications, from clothing to non-clothing. However, as people's lives have become more diverse and they are seeking a better quality of life, there is a demand for fibers with more advanced textures and functions.

[0003] In particular, clothing textiles that come into contact with human skin often require excellent comfort when worn, and there is a strong demand for fibers with a texture that is directly related to comfort, such as that found in natural fibers. This is because the texture and functionality of natural fibers such as linen, wool, cotton, and silk are well-balanced, and humans find the complex appearance and feel that these fibers create attractive and luxurious.

[0004] As an example of a technology aimed at achieving the comfortable texture of natural fibers, various technologies have been proposed, such as a technology that creates a void structure that traps air within the fabric by manipulating the cross section of synthetic fibers, thereby achieving a moderate sense of resilience and a fluffy, soft texture.

[0005] Patent Document 1 proposes hollow fibers obtained using a hollow spinneret that are false-twisted to impart crimps and simultaneously deform and flatten the hollow cross section, thereby imparting a flat hollow cross section shape and twist similar to cotton.The flat hollow fibers are said to have a fluffy, resilient feel similar to cotton.

[0006] Patent Document 2 proposes a hollow fiber with a C-shaped cross section having a continuous hollow portion and openings in the fiber axis direction, which is produced by subjecting a sheath-core composite fiber having a core component made of an easily alkali-soluble polymer and a sheath component made of a poorly alkali-soluble polymer, with part of the core component exposed on the fiber surface, to false twisting and then eluting the core component by alkali treatment. When this sheath-core composite fiber is made into a woven or knitted fabric, the effect of the C-shaped hollow can impart a lightweight feel, a moderate resilience, and a soft texture.

[0007] Furthermore, Patent Document 3 proposes a bulky, lightweight multifilament having a fiber cross-section in which two or more types of polymers with different dissolution rates in a solvent are laminated in the cross-sectional direction to form an outermost layer, an intermediate layer, and an innermost layer, the polymers forming the outermost and innermost layers being easily soluble polymers, and the intermediate layer having a mixture of two or more types of single yarns with different cross-sectional shapes. In this bulky, lightweight multifilament, by configuring not only the interior of the fiber but also the surface of the fiber with an easily soluble polymer, voids can be formed inside and outside the fiber after the soluble polymer is eluted, and further, since different fiber cross-sections are mixed after elution, collapse of the voids between the fibers is suppressed, making it possible to produce a fabric that combines a lightweight feel, fluffiness, and a soft texture. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 54-151650 [Patent Document 2] Japanese Patent Publication No. 01-052839 [Patent Document 3] Japanese Patent Application Publication No. 2019-167646 Summary of the Invention [Problem to be solved by the invention]

[0009] If hollow fibers can be false-twisted to create a void structure inside and outside the fibers, as in Patent Document 1, it may be possible to reproduce to some extent the texture of cotton, a natural fiber. However, the technical idea behind Patent Document 1 is that the fibers are densely bundled by false-twisting, and the hollow portions are crushed and deformed, which can result in a lack of fullness and bouncy texture that is comfortable when worn as clothing.

[0010] Furthermore, in a method of false-twisting a core-sheath composite fiber having a core component made of an easily alkali-soluble polymer and a sheath component made of a poorly alkali-soluble polymer, the core component is eluted by alkali treatment after weaving and knitting, forming a hollow space, which prevents collapse of the hollow space during false-twisting and allows for the formation of inter-fiber voids due to a high hollow ratio and crimp morphology. However, in order to prevent uneven elution of the core component, the fiber is given a C-shaped cross section with large openings, which can cause adjacent fibers to bite into the openings, resulting in a stiff texture and in some cases a decrease in the lightness and resilience with continued use.

[0011] Furthermore, both Patent Documents 1 and 2 use a false twisting process in which the multifilament is heat-set in a twisted state and then untwisted to impart crimp. As a result, the crimp is likely to become weaker due to the heat treatment during advanced processing, and the fabric may lack the fullness required for comfortable wear. Furthermore, because the crimp of each fiber in the multifilament is uniform, the texture obtained when made into a textile is monotonous. To achieve a complex texture like that of natural fibers, advanced weaving and knitting are required, or the fabric must be blended with other materials, including natural fibers.

[0012] On the other hand, the method of utilizing interfiber voids formed by dissolving the fiber surface, as in Patent Document 3, is effective from the viewpoint of flexibility, but there is a limit to the effect of suppressing the collapse of interfiber voids obtained by mixing different fiber cross sections, and it is difficult to say that large interfiber voids large enough to cause a noticeable swelling are produced.

[0013] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional art and to provide a conjugated fiber, a hollow fiber, and a multifilament suitable for obtaining a textile having a moderate resilience and a soft, fluffy texture, and excellent wearing comfort, by controlling the void structure inside the fiber and between the fibers. [Means for solving the problem]

[0014] The object of the present invention is achieved by the following means. (1) In the cross section of the fiber, two or more types of polymers with different dissolution rates in a solvent are laminated from the center of the fiber toward the surface of the fiber, the innermost layer including the fiber core contains an easily soluble polymer; A composite fiber in which two types of hardly soluble polymers having different melting points are unevenly distributed in at least one layer other than the innermost layer. (2) The composite fiber according to (1), wherein the relationship between the inscribed circle diameter RA and the circumscribed circle diameter RB of the fiber in the cross section is 1.2≦RB / RA≦2.4. (3) A composite fiber according to (1) or (2), wherein in the fiber cross section, the readily soluble polymer is continuous from the fiber center to the fiber surface, and the width of the continuous line is 10% or less of the fiber diameter. (4) The conjugated fiber according to any one of (1) to (3), wherein in the cross section of the fiber, the outermost layer contains the easily soluble polymer. (5) A hollow fiber obtained by removing the easily soluble polymer from the conjugate fiber according to any one of (1) to (4). (6) A multifilament containing flat hollow fibers, The coefficient of variation CV of the rotation angle of the major axis of the flat hollow fibers is 15 to 50%. (7) The multifilament according to (6), wherein the flat hollow fiber has a flatness of 1.2 or more in the fiber cross section. (8) The multifilament according to (6) or (7), wherein the flat hollow fiber is composed of at least two types of polymers with different melting points in the cross section of the fiber. (9) The flat hollow fiber has openings extending from the fiber center toward the fiber surface, The multifilament according to any one of (6) to (8), wherein the width of the opening is 10% or less of the fiber diameter. (10) A textile product partially comprising the conjugated fiber according to any one of (1) to (4), the hollow fiber according to (5), or the multifilament according to any one of (6) to (9). [Effects of the Invention]

[0015] The conjugated fiber, hollow fiber, and multifilament of the present invention have the above-mentioned characteristics, and thus the void structure inside the fiber and between the fibers is precisely controlled, making it possible to obtain textiles that have an appropriate resilience and a fluffy, soft texture, and are therefore excellent in wearing comfort. [Brief explanation of the drawings]

[0016] [Figure 1] Figure 1(a), Figure 1(b), Figure 1(c), and Figure 1(d) are schematic diagrams of the cross-sectional structure of the composite fiber of the present invention. [Figure 2] 2(a), 2(b), and 2(c) are schematic diagrams of the cross-sectional structure of the composite fiber of the present invention. [Figure 3] Figures 3(a), 3(b), 3(c), and 3(d) are schematic diagrams of cross-sectional structures of the composite fibers of the present invention. [Figure 4] 4(a) and 4(b) are schematic diagrams of the cross-sectional structure of a conventional composite fiber. [Figure 5] Fig. 5 is a schematic diagram of the cross-sectional structure of the multifilament of the present invention. Fig. 5(a) is a diagram for understanding the flatness. Fig. 5(b) is a diagram for understanding the coefficient of variation CV of the rotation angle of the long axis of the fibers in the multifilament, and the dashed lines in the outer frame represent the top, bottom, left, and right sides of the photographed image. [Figure 6] 6(a), 6(b), and 6(c) are schematic diagrams of the cross-sectional structures of the fibers constituting the multifilament of the present invention. [Figure 7]7(a) is a schematic diagram of the cross-sectional structure of the fibers constituting the multifilament of Example 6. FIG. 7(b) is a schematic diagram of the cross-sectional structure of the fibers constituting the multifilament of Example 2. [Figure 8] FIG. 8 is a schematic diagram of the cross-sectional structure of the fibers constituting the multifilament of Comparative Example 3. [Figure 9] FIG. 9 is a schematic diagram of the cross-sectional structure of the fibers constituting the multifilament of the present invention. [Figure 10] FIG. 10 is a schematic diagram of the cross-sectional structure of an example of a composite fiber from which the multifilament of the present invention can be produced. [Figure 11] FIG. 11 shows an example of the crimp form of the fibers constituting the multifilament of the present invention. [Figure 12] FIG. 12 is a cross-sectional view illustrating the method for producing a composite fiber of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below together with preferred embodiments.

[0018] An analysis of the void structure of cotton, a natural material widely used for its soft, fluffy texture, reveals that in addition to the hollow spaces inside the flat fibers, there are also voids of various sizes between the fibers. This is due to the twist in each cotton fiber, and when multiple twisted fibers are bundled together to make textiles, complex voids and unevenness are formed, which is thought to create a unique feel and texture.

[0019] As a result of extensive research by the inventors to realize the formation of such complex voids that are unique to natural fibers, they discovered that by inducing a crimped morphology in fibers after advanced processing such as weaving and knitting, multiple fibers gathered within the fabric are twisted, resulting in the creation of interfiber voids of various sizes. Furthermore, by dissolving an easily soluble polymer from within the fibers to form hollow spaces within the fibers, it is possible to obtain a complex void structure that was difficult to obtain with conventional synthetic fibers or processed yarns utilizing such fibers, and this realization of a previously unseen, moderately resilient feel and a soft, fluffy texture forms the basis of the present invention.

[0020] Specifically, the requirements of the present invention are that, in the cross section of the fiber, two or more types of polymers with different dissolution rates in a solvent are layered from the fiber center toward the fiber surface, the innermost layer including the fiber center contains an easily soluble polymer, and two types of hardly soluble polymers with different melting points are unevenly distributed in at least one layer other than the innermost layer.

[0021] In the present invention, a polymer that dissolves relatively quickly in the solvent used in the dissolution treatment is referred to as an easily soluble polymer, and a polymer that dissolves slowly is referred to as a sparingly soluble polymer. Furthermore, in consideration of simplifying the dissolution treatment and shortening the time required for advanced processing, the dissolution rate ratio (easily soluble polymer / sparingly soluble polymer) is preferably 100 or more, and more preferably 1000 or more, when the sparingly soluble polymer is used as the reference. A dissolution rate ratio of 1000 or more allows the dissolution treatment to be completed in a short time, thereby increasing the process speed and preventing unnecessary degradation of the sparingly soluble polymer, thereby enabling the production of higher quality fabrics.

[0022] In the conjugated fiber of the present invention, in order to stably form a hollow portion inside the fiber regardless of the structure, such as weaving or knitting, it is necessary that two or more polymers having different dissolution rates in a solvent are layered in the fiber cross section from the fiber center toward the fiber surface, and that the innermost layer including the fiber center contains an easily soluble polymer. Furthermore, it is preferable that the innermost layer consists of an easily soluble polymer.

[0023] When made into a textile, the stable formation of hollow spaces within the fibers not only improves the fluffiness and lightness of the textile, but the presence of an air layer within the fibers also allows each fiber to flexibly deform while maintaining a moderate sense of resilience, thereby achieving the objective of the present invention of providing a soft texture with a moderate sense of resilience and fluffiness.

[0024] Furthermore, since a greater hollowness inside the fiber can provide a more pronounced sense of lightness and flexibility, the area ratio of the innermost layer including the fiber center in the conjugated fiber of the present invention is preferably 10% or more, more preferably 20% or more. While a higher area ratio of the innermost layer is preferable from the viewpoint of a lighter feel, excessive elution from the innermost layer can lead to a decrease in strength and increased likelihood of collapse of the hollow portion, which can impair the resilience, so the practical upper limit of this area ratio is 50%.

[0025] For the conjugated fiber of the present invention, it is important that the fibers develop a crimped form after undergoing advanced processing such as weaving and knitting. When the fibers in the fabric each develop crimps and twist, the crimped forms of adjacent fibers become entangled, and inter-fiber voids of various sizes can be developed, which, when made into a textile, not only develops an appropriate resilience and a soft, fluffy handle, but also provides functions such as water absorption and quick-drying properties due to the capillary phenomenon of the fine inter-fiber voids and stretchability due to the coil-like crimped form.

[0026] In order to induce a crimped form in fibers after advanced processing such as weaving and knitting, it is necessary to give the fibers a composite cross section with latent crimpability that will cause crimping upon heat treatment. By arranging polymers with different shrinkage differences in the fiber cross section so that their centers of gravity are different, the fiber will bend significantly toward the high-shrinkage polymer after heat treatment, and this will continue to form a three-dimensional spiral structure.

[0027] That is, to achieve the object of the present invention, it is important to arrange polymers with different shrinkage differences in the fiber cross section so that a sufficient distance is maintained between their centers of gravity, and in the conjugated fiber of the present invention, it is necessary for two types of hardly soluble polymers with different melting points to be unevenly distributed in at least one layer other than the innermost layer.

[0028] Here, the term "uneven distribution of hardly soluble polymers with different melting points" as used herein means that, among the lines passing through the center of the fiber and dividing the fiber cross section equally into two, there is a line (for example, line I in Figure 1(a)) such that the area ratio of the hardly soluble polymer on the high melting point side to the hardly soluble polymer on the low melting point side in the fiber cross sections on the left and right or above and below the line is 100:0 to 70:30 in one fiber cross section and 30:70 to 0:100 in the other fiber cross section.

[0029] The composite structure of the composite fiber of the present invention is not particularly limited as long as the hardly soluble polymers with different melting points are unevenly distributed. Examples of such composite structures include a side-by-side type as shown in Figure 1(a) and Figure 1(c), an islands-in-sea type as shown in Figure 1(b), an eccentric sheath-core type as shown in Figure 1(d), and a blend type. Among these, from the viewpoint of increasing the distance between the centers of gravity and increasing the crimp-producing power, it is preferable that the hardly soluble polymers with different melting points are bonded in a completely separate side-by-side type.

[0030] By joining the polymers side by side, the interface between the hardly soluble polymers with different melting points is small, which maximizes the distance between the centers of gravity of the polymers in the composite cross section, maximizing the crimping ability. In addition, the crimped form becomes a fine spiral structure, which makes it possible to impart excellent stretchability, and is preferable because it provides a fabric with moderate stretchability and stress-free wearing comfort.

[0031] In the cross section of the composite fiber of the present invention, the relationship between the inscribed circle diameter RA and the circumscribed circle diameter RB of the fiber is preferably 1.2≦RB / RA≦2.4.

[0032] Here, the inscribed circle diameter RA and the circumscribed circle diameter RB in the present invention are determined by embedding the fibers in an embedding agent such as epoxy resin, and photographing an image of the fiber cross section perpendicular to the fiber axis with a scanning electron microscope (SEM) at a magnification that allows observation of 10 or more filaments.

[0033] Fibers randomly extracted from each captured image are analyzed using image analysis software to calculate the diameter of a circle (e.g., A in (a) of Figure 2) that is inscribed with the fiber surface at at least two points (e.g., a1 and a2 in (a) of Figure 2) and exists only inside the fiber, with the largest possible diameter within the range where the circumference of the inscribed circle does not intersect with the fiber surface.This is then used to calculate a simple number average of the results for 10 filaments, and the value rounded to the nearest decimal place is used as the inscribed circle diameter RA.

[0034] In addition, the diameter of a circle (e.g., B in (a) of Figure 2) that circumscribes the fiber surface at at least two points (e.g., b1 and b2 in (a) of Figure 2), exists only outside the fiber, and has the smallest possible diameter within the range where the circumference of the circumscribed circle does not intersect with the fiber surface is calculated, and a simple number average of the results obtained by this calculation for 10 filaments is calculated, and the value rounded to the nearest decimal place is defined as the circumscribed circle diameter RB.

[0035] RB / RA is calculated by dividing the RB determined for each fiber above by RA, and then calculating the simple number average of the results for 10 filaments, rounding to two decimal places to obtain the value RB / RA.

[0036] Although the cross-sectional shape of the conjugated fiber of the present invention is not limited, it is important that after advanced processing such as weaving or knitting, the fibers each develop crimps and twist, causing the crimped forms of adjacent fibers to become entangled and creating inter-fiber voids of various sizes. From this perspective, if the fiber cross section is irregular, the inter-fiber voids created when the fibers are twisted can be made more complex and increased, so it is preferable that the ratio of the inscribed circle diameter RA to the circumscribed circle diameter RB of the fiber, RB / RA (irregularity), is 1.2 or more.

[0037] Furthermore, if RB / RA is 1.5 or more, the crimp phases between adjacent fibers will not be aligned, and inter-fiber voids can be stably formed, resulting in a fabric with a uniform appearance without streaks, etc., and this is considered a more preferable range from the viewpoint of quality control. Also, while a larger RB / RA is preferable from the viewpoint of stably forming inter-fiber voids, not only will glare occur in some cases in light reflected from the fiber surface, but a cross-sectional shape with edges may result in an unnecessarily high bending rigidity, impairing flexibility, and therefore the practical upper limit of RB / RA is 2.4.

[0038] When the cross section of the conjugated fiber of the present invention is to have a modified cross section, any modified cross section such as flat, multilobal, polygonal, gear-like, petal-like, or star-like can be used, but from the viewpoint of further enhancing a moderate resilience and flexibility, it is preferable that the fiber shape be flat as shown in Fig. 2(a) or multilobal as shown in Fig. 2(b). If the fiber has a flat shape as shown in Fig. 2(a), a high bending rigidity provides a resilience when bent along a plane perpendicular to the major axis of the flat cross section, and a low bending rigidity provides flexibility when bent along a plane perpendicular to the minor axis, thereby making it possible to obtain a feel that combines a moderate resilience and softness.

[0039] Furthermore, when the fibers are made into multifilaments, when they are twisted due to the crimped form, the inter-fiber voids due to steric hindrance increase, not only can the fibers have a more appropriate resilience and fullness, but also, since the longitudinal axis directions of the cross sections of the flat fibers are partially aligned, when the fibers are made into a textile, differences in voids and irregularities occur between the areas where the longitudinal axis directions of the cross sections of adjacent fibers are aligned and the areas where they are not, and complex voids and irregularities can be formed between the fibers. From the viewpoint of thereby being able to express the unique tactile feel that can only be achieved with natural fibers, a flat shape is also preferable.

[0040] On the other hand, a multi-lobed shape as shown in Figure 2(b) is preferable from the viewpoint that the unevenness imparted to the fiber surface reduces glare due to diffused reflection of light and improves water absorption and quick-drying properties due to the fine interfiber voids. However, if the number of uneven portions becomes too large, the spacing between the uneven portions becomes finer and the effect gradually decreases, so the practical upper limit of the number of uneven portions that the multi-lobed shape in this invention can have is 20.

[0041] Furthermore, if the fabric is flat and multi-lobed as shown in Figure 2(c), it will be possible to combine the above-mentioned features of both the flat and multi-lobed shapes. Therefore, from the viewpoint of the textile of the present invention having a moderate resilience and a soft, fluffy texture, as well as functionality such as moisture absorption and quick-drying properties, a flat and multi-lobed shape is particularly preferable.

[0042] In the cross section of the conjugate fiber of the present invention, the readily soluble polymer preferably has a continuous portion that is continuous from the center of the fiber to the surface of the fiber.

[0043] In the conjugated fiber of the present invention, it is necessary to dissolve the soluble polymer in the innermost layer in order to stably form hollow spaces inside the fiber. Since the soluble polymer is dissolved and removed by a solvent starting from the fiber surface, if a continuous section can be formed from the fiber surface to the innermost layer, not only can the time required for dissolving the soluble polymer be significantly shortened, but also water absorption and water retention can be imparted by capillary action at the openings formed after the soluble polymer is dissolved. From this perspective, it is preferable that the soluble polymer be continuous from the fiber center to the fiber surface.

[0044] The interconnected width of the easily soluble polymer is preferably 10% or less of the fiber diameter. The fiber diameter in the present invention is determined by embedding a composite fiber in an embedding agent such as epoxy resin and photographing the fiber cross section perpendicular to the fiber axis with a scanning electron microscope (SEM) at a magnification that allows observation of 10 or more filaments. The diameter of a fiber randomly selected within each photographed image is measured in μm units to the first decimal place. This measurement is then carried out for 10 filaments to determine a simple number average, which is then rounded to the nearest whole number to determine the fiber diameter (μm). If the fiber cross section perpendicular to the fiber axis is not a perfect circle, its area is measured, and the diameter calculated as a perfect circle is used.

[0045] To determine the interconnection width of the present invention, first, the composite fiber of the present invention is embedded in an embedding agent such as epoxy resin, and an image of the fiber cross section perpendicular to the fiber axis is taken with a transmission electron microscope (TEM) at a magnification that allows observation of 10 or more fibers. If the readily soluble polymer in the composite fiber in the image obtained is interconnected from the fiber center to the fiber surface, the image is analyzed using image analysis software to calculate the shortest width W (e.g., W in Figure 3(c)) of the interconnection portion perpendicular to a line S (e.g., S in Figure 3(c)) that passes through the fiber center G and is parallel to the interconnection portion, in μm units. This is performed for 10 filaments, and a simple number average is calculated. The value is rounded to one decimal place to determine the interconnection width.

[0046] In addition, the severing width determined for each filament is divided by the fiber diameter and multiplied by 100 to calculate the value. This is then carried out for 10 filaments, and the simple number average of the results is calculated. The value is rounded to the nearest whole number, and this value is used as the ratio (%) of the interconnected width to the fiber diameter.

[0047] By setting the interconnection width of the soluble polymer to 10% or less of the fiber diameter, it is possible to prevent the openings formed after removing the soluble polymer from being too wide, which would result in the fibers getting caught in each other or the hollow portions being crushed due to misalignment of the openings, thereby preventing the loss of an appropriate sense of resilience and a soft, fluffy texture.

[0048] Furthermore, if the interconnection width is 5% or less of the fiber diameter, not only can fibrillation due to fiber abrasion caused by the openings formed after the elution of the readily soluble polymer be suppressed, but also, when post-processing such as applying a functional agent is performed, the functional agent that has entered the hollow portions can be prevented from falling off by washing, etc., thereby significantly improving the performance durability of the functional agent, and therefore this range is cited as a more preferable range. However, if the interconnection width is too narrow, it becomes difficult to dissolve the readily soluble polymer, so the practical lower limit of the interconnection width is 1% of the fiber diameter.

[0049] In the cross section of the conjugated fiber of the present invention, the outermost layer preferably contains an easily soluble polymer, and more preferably consists of an easily soluble polymer, although the outermost layer in the present invention refers to a layer that covers 80% or more of the fiber surface.

[0050] If the outermost layer is made of an easily soluble polymer, the inter-fiber voids will naturally expand when the easily soluble polymer is removed, allowing the fibers fixed at the binding points of the woven or knitted fabric to move, resulting in improved flexibility and a lighter feel due to a reduced apparent density at high void ratios.

[0051] From this viewpoint, it is preferable that the area ratio of the outermost layer in the cross section of the composite fiber is high, and an area ratio of 10% or more is considered to be within the preferred range because it is possible to obtain sufficient effects of improving flexibility and lightness regardless of the fabric weave. However, if the area ratio is too high, it may also cause a decrease in resilience due to a decrease in bending rigidity, so the practical upper limit is 30%.

[0052] The composite fiber of the present invention can be subjected to advanced processing such as weaving and knitting, followed by heat treatment to develop a crimped form, and then the easily soluble polymer in the innermost layer can be removed to obtain a hollow fiber consisting only of the poorly soluble polymer, and a multifilament consisting of the hollow fiber. From the multifilament, it is possible to obtain a textile that has an appropriate resilience and a fluffy, soft texture due to its unique fiber cross-sectional shape and inter-fiber voids, and that further has functions such as moisture absorption, quick drying, and stretchability, and is therefore highly comfortable to wear.

[0053] Furthermore, in order to maximize the unique feel and texture of the multifilament due to the complex voids and unevenness that are unique to natural fibers, the inventors conducted extensive research and discovered that by controlling the twist of the flat fibers and appropriately aligning the long axis direction of the cross section, it is possible to form complex voids and unevenness that were difficult to obtain with conventional synthetic fibers or processed yarns utilizing these fibers.

[0054] That is, in a multifilament made of flat fibers that do not have a twist, the longitudinal axes of the cross sections of the fibers are all aligned, resulting in small voids and flat irregularities. On the other hand, in a multifilament made of flat fibers that have been twisted by false twisting, the twist in each fiber is uniform and the longitudinal axes of the cross sections are oriented in different directions during untwisting, so although voids and irregularities are obtained, they may be monotonous.

[0055] In contrast, if the twist is controlled so that the long axis directions of the cross sections of the flat fibers in the multifilament are partially aligned, differences in the voids and unevenness will occur between the areas where the long axis directions of the cross sections of adjacent fibers are aligned and the areas where they are not, when the fabric is made into a textile, and complex voids and unevenness can be formed between the fibers. This not only makes it possible to achieve the unique tactile feel that is unique to natural materials, but also creates hollow spaces inside the fibers, which, combined with the complex voids and unevenness between the fibers, can create a moderate sense of resilience and a soft, fluffy texture.

[0056] The present invention is constituted by a fiber design based on this idea, and specifically, the multifilament of the present invention contains flat hollow fibers. The multifilament of the present invention is preferably made of flat hollow fibers, and a requirement of the present invention is that the coefficient of variation CV of the rotation angle of the major axis of the flat hollow fibers in the multifilament is 15 to 50%.

[0057] In the present invention, it is important that the fibers constituting the textile are flat hollow fibers.

[0058] If the fiber cross section is made flat as shown in Figure 5(a), when it is bent along a plane perpendicular to the long axis of the flat cross section, a resilient feel due to high bending rigidity is obtained, and when it is bent along a plane perpendicular to the short axis, flexibility due to low bending rigidity is obtained, resulting in a texture that combines a moderate resilience and softness.

[0059] To achieve the above-mentioned effect, the flatness is preferably 1.2 or more, and more preferably 1.5 or more. By setting the flatness within this range, voids are formed between the fibers due to steric hindrance when the flat hollow fibers are twisted, and the resulting textile has a bulging texture.

[0060] Furthermore, while a higher degree of flatness is preferable from the viewpoint of stably forming inter-fiber voids, the light reflected from the fiber surface may not only produce an uneven appearance (glare) in some cases, but also the cross-sectional shape with edges may make the bending rigidity higher than necessary, thereby impairing flexibility, and therefore the upper limit of the degree of flatness in the present invention is 2.4.

[0061] The flatness in this invention is determined by embedding a multifilament in an embedding medium such as epoxy resin and photographing the fiber cross section perpendicular to the fiber axis with a scanning electron microscope (SEM) at a magnification large enough to observe 10 or more fibers. Randomly selected fibers within each image are analyzed using image analysis software. As shown in Figure 5(a), the major axis is defined as the line (c1-c2) connecting the two most distant arbitrary points (c1, c2) on the fiber periphery, and the minor axis is defined as the line (d1-d2) passing through the midpoint of the major axis and perpendicular to the major axis. The flatness is calculated by dividing the length of the major axis by the length of the minor axis. This calculation is performed on 10 fibers, and the simple average is calculated. The result is rounded to two decimal places.

[0062] Furthermore, having a hollow space inside the fiber not only improves the fluffiness and lightness of the textile, but also allows each fiber to flexibly deform while still having a moderate sense of resilience, further highlighting the effects of the flat cross section described above.

[0063] Furthermore, since a larger hollow ratio inside the fiber results in a more pronounced sense of volume and lightness, the area ratio of the hollow portion, including the fiber center, in the flat hollow fiber of the multifilament of the present invention is preferably 10% or more. Furthermore, in order to improve the void ratio in the fiber bundle, enhance the lightness, and also enhance the flexibility when made into a fabric, a more preferable range for the area ratio of the hollow portion is 20% or more. In this range, in the case of the flat cross section described above, directionality is created in the deformation of the single fibers, and the fiber bundle exhibits a twisted form, which is a characteristic of the present invention, resulting in complex deformation and a very pleasant feel that cannot be achieved with conventional yarn processing.

[0064] A higher area ratio of the hollow portions is preferable in terms of significantly enhancing the lightweight feel of the fiber bundle or textile, but as the thickness of the polymer constituting the fiber becomes thinner, the strength decreases and the hollow portions are more likely to be crushed, which may result in some portions not being able to properly achieve the comfortable rebound feel that is the objective of the present invention, so the practical upper limit of the area ratio of the hollow portions in the present invention is 50%.

[0065] The hollowness ratio in this invention is determined by embedding a multifilament in an embedding agent such as epoxy resin and photographing a cross section of the fiber perpendicular to the fiber axis with a scanning electron microscope (SEM) at a magnification that allows observation of 10 or more fibers. When a fiber randomly selected from each of the photographed images has a hollow portion, such as H in Figure 5(a), the area of ​​the fiber, including the hollow portion, and the area of ​​the hollow portion are calculated by analyzing the fiber using image analysis software. The area of ​​the hollow portion is then divided by the area of ​​the fiber including the hollow portion and multiplied by 100. This process is repeated for 10 fibers, and the simple average is calculated. The result is rounded to one decimal place to obtain the hollowness ratio (%).

[0066] Furthermore, it is preferable that the cross-sectional shape of the fiber be a flat shape as shown in Figure 5(a), as well as a cross-sectional shape with convex portions on the fiber surface (such as multi-leaf, polygonal, gear-like, petal-like, or star-like). This is because it is possible to suppress uneven appearance (glare) caused by diffuse reflection of light and to increase water absorption due to the fine interfiber voids. However, as the number of convex portions becomes too large, the effect gradually decreases, so the practical upper limit for the number of convex portions is 20.

[0067] In the present invention, if the twist is controlled so that the longitudinal axes of the cross sections of the flat fibers in the multifilament are partially aligned, differences in voids and irregularities will occur between the areas where the longitudinal axes of the cross sections of adjacent fibers are aligned and the areas where they are not aligned when the fabric is made into a textile. In order to enable the formation of complex voids between fibers and irregularities on the textile surface, which are the characteristics of the present invention, it is important that the coefficient of variation CV of the rotation angle of the longitudinal axes of the flat hollow fibers in the multifilament is 15 to 50%.

[0068] The coefficient of variation of the rotation angle of the long axis referred to in the present invention is determined by photographing a cross section of a multifilament fabric perpendicular to the longitudinal direction of the fabric and perpendicular to the fiber axis direction of the multifilament with a scanning electron microscope (SEM) at a magnification that allows observation of 20 or more fibers. When the fibers in the obtained image have a flat cross section, the image is analyzed using image analysis software. As shown in Figure 5(b), the line (c1-c2) connecting the two most distant points (c1, c2) on the outer periphery of the fiber is taken as the long axis. A line passing through the midpoint of the long axis of the flat hollow fiber and parallel to the bottom edge of the photographed image is rotated counterclockwise around the midpoint of the long axis, and the rotation angle (θ) is evaluated when the inclination of the line coincides with the long axis.

[0069] This evaluation was performed on 20 fibers ((1) to (20) in Figure 5(b)) randomly selected from the multifilament in the same image, and the standard deviation and average value of the results were calculated. The standard deviation was divided by the average value and multiplied by 100 to calculate the coefficient of variation CV (%) of the rotation angle of the major axis.

[0070] In the present invention, the coefficient of variation CV of the rotation angle of the major axis of the flat hollow fibers in the multifilament must be 15% or more. By setting this range, the major axis directions of the cross sections become non-uniform, resulting in unevenness on the textile surface, which causes large friction fluctuations when the fabric surface is touched, resulting in a smooth feel. Furthermore, complex voids are created between the fibers, which, combined with the hollow spaces inside the fibers, also result in a moderate sense of resilience and a soft, fluffy texture.

[0071] In the present invention, the coefficient of variation CV of the rotation angle of the major axis is more preferably 25 to 40%, and within this range, the pitch of the irregularities becomes finer, not only resulting in a more pronounced smooth feel, but also increasing the interfiber voids, which reduces the apparent density when made into a fabric and improves fluffiness. On the other hand, if the coefficient of variation CV becomes too large, the irregularities become too fine, reducing the frictional fluctuation and resulting in a monotonous feel, so the coefficient of variation CV has a substantial upper limit of 50%.

[0072] One possible method for controlling the coefficient of variation of the rotation angle of the major axis of flat hollow fibers in a multifilament is to separately prepare flat hollow fibers with different twists by false twisting or the like, and then mix and bundle the fibers by entanglement or the like. Alternatively, if flat hollow fibers with latent crimpability that can be developed by heat treatment can be used and a crimp morphology can be developed in the flat hollow fibers after advanced processing such as weaving or knitting, a crimp phase difference between the fibers will be locally generated during the development of crimp, and the coefficient of variation CV of the rotation angle of the major axis of flat hollow fibers in a multifilament can easily be set within the desired range.

[0073] From this viewpoint, in order to obtain a fiber with latent crimpability that develops crimp upon heat treatment, it is preferable that the cross section of the flat hollow fiber in the multifilament of the present invention is composed of at least two polymers with different melting points. If the fiber is composed of polymers with different melting points, the difference in shrinkage resulting from the difference in melting points causes the fiber to bend significantly toward the high-shrinkage polymer after heat treatment, and this bending continues to form a three-dimensional spiral structure.

[0074] To increase this crimp-developing ability, it is preferable to have a composite cross section in which polymers with different melting points maintain a sufficient distance between their centers of gravity, and from this perspective, it is more preferable to join polymers with different melting points in a side-by-side configuration as shown in (a) of Figure 6. In other words, by making the interface between the polymers with different melting points small, it is possible to maximize the distance between the centers of gravity between the polymers in the composite cross section, thereby maximizing the crimp-developing ability.

[0075] Furthermore, the fine spiral structure of the crimped form makes it possible to impart excellent stretchability, resulting in a fabric with moderate elasticity that provides stress-free comfort when worn.

[0076] Furthermore, it is particularly preferable to give the flat hollow fibers in the multifilament a cross-sectional shape in which the orientation (angle) of the joining planes of the polymers with different melting points is random for each single fiber (the four types in Figure 9 are examples of such cross-sectional shapes), and the crimp morphology that appears upon heat treatment differs for each single fiber due to differences in the distance between the centers of gravity, thereby increasing the crimp phase difference between fibers. This effect allows the coefficient of variation (CV) of the rotation angle of the major axis of the flat hollow fibers in the multifilament to approach an optimal range.

[0077] In the multifilament of the present invention, in order to stably form hollow portions in the flat hollow fibers without being influenced by the weave or knitting structure while keeping the coefficient of variation of the rotation angle of the major axes of the flat hollow fibers in the multifilament within a target range, it is preferable to use the following conjugated fiber: That is, it is preferable to use a conjugated fiber in which, in the cross section of the fiber, two or more types of polymers having different dissolution rates in a solvent are layered from the fiber center toward the fiber surface, the innermost layer including the fiber center being made of an easily soluble polymer, and at least one layer other than the innermost layer being made of two types of hardly soluble polymers having different melting points.

[0078] After subjecting the composite fiber to advanced processing such as weaving or knitting, a crimped form is developed by heat treatment, and then the easily soluble polymer in the innermost layer is removed. This results in a multifilament consisting of flat hollow fibers that are stably formed without the hollow portions being crushed during advanced processing, and the development of crimp allows the coefficient of variation of the rotation angle of the major axes of the flat hollow fibers in the multifilament to fall within the desired range.

[0079] When the flat hollow fibers in the multifilament of the present invention are subjected to a crimping process by heat treatment, the crimping process preferably has a crimping peak count of 5 peaks / cm or more.

[0080] The number of crimps referred to in the present invention can be determined by the following method. Specifically, a multifilament is pulled out of a fabric made of multifilaments without plastic deformation, and one end of the multifilament is fixed. A load of 1 mg / dtex is applied to the other end for 30 seconds or more, and then a marking is made at any point 1 cm apart in the fiber axis direction of the multifilament.

[0081] The fibers are then separated from the multifilament without causing plastic deformation, and the space between the pre-applied markings is adjusted to the original 1 cm, and the sample is fixed on a glass slide. An image of this sample is taken with a digital microscope at a magnification that allows the 1 cm markings to be observed. If the image shows that the multifilament has a twisted crimped form as shown in Figure 11, the number of crimp peaks present between the markings is determined. This procedure is performed on 10 fibers made of the same polymer, and the simple number average is calculated, rounded to one decimal place, to obtain the number of crimp peaks (peaks / cm).

[0082] If the crimp morphology has a crimp peak count of 5 peaks / cm or more, a crimp phase difference between fibers occurs locally when the crimp occurs, and the coefficient of variation CV of the rotation angle of the major axis of the flat hollow fibers in the multifilament can be set within the desired range.

[0083] Furthermore, if the number of crimped peaks is 10 peaks / cm or more, not only can the excluded volume effect between fibers increase the interfiber voids, thereby improving the fluffiness, but the crimped form becomes a fine spiral structure, which can also impart stretchability, making this a more preferable range.

[0084] From the viewpoint of imparting stretchability, it is preferable to increase the number of crimp peaks, but if the number of crimp peaks is excessive, the coefficient of variation CV of the rotation angle of the major axis of the flat hollow fibers in the multifilament also increases, which may result in a monotonous feel depending on the structure of the woven or knitted fabric, etc. Therefore, the practical upper limit of the number of crimp peaks in the present invention, which aims to impart a favorable feel, is 50 peaks / cm.

[0085] The flat hollow fibers in the multifilament of the present invention preferably have openings extending from the fiber center toward the fiber surface. If the openings communicate with the hollow portions, not only will water absorption be achieved by capillary action at the openings, but the increased fiber surface area will also increase the effective area of ​​the functional agent when post-processing such as coating with the functional agent is performed, thereby improving the performance of the functional agent.

[0086] The width of the opening is preferably 10% or less of the fiber diameter. The fiber diameter in the present invention is determined by embedding a multifilament in an embedding agent such as epoxy resin and photographing the fiber cross section perpendicular to the fiber axis with a scanning electron microscope (SEM) at a magnification that allows observation of 10 or more filaments. The area of ​​randomly sampled fibers within each photographed image is measured, and the diameter calculated as a perfect circle is measured in μm units to the first decimal place. This measurement is performed for 10 filaments, and the simple number average is calculated. The value is rounded to the nearest decimal place to determine the fiber diameter (μm). If a hollow portion is present in the fiber cross section perpendicular to the fiber axis, the area of ​​the hollow portion is added to the area of ​​the fiber.

[0087] The opening width in the present invention can be determined by the following method. Specifically, a multifilament is embedded in an embedding agent such as epoxy resin, and an image of the fiber cross section perpendicular to the fiber axis is taken with a transmission electron microscope (TEM) at a magnification that allows observation of 10 or more fibers. If the fibers in the obtained image have openings extending from the fiber center to the fiber surface, the image is analyzed using image analysis software to calculate the shortest opening width W' (e.g., W' in FIG. 6(b)) in μm units, perpendicular to a line S' (e.g., S' in FIG. 6(b)) that passes through the fiber center G and is parallel to the opening. This is performed for 10 filaments, and the simple number average is calculated, rounded to one decimal place, to determine the opening width. The opening width calculated for each filament is divided by the fiber diameter and multiplied by 100 to calculate the simple number average of the results for 10 filaments, and the simple number average is rounded to the nearest whole number to determine the ratio (%) of the opening width to the fiber diameter referred to in the present invention.

[0088] In the present invention, it is preferable that the width of the openings is 10% or less of the fiber diameter. In other words, within this range, it is possible to prevent the fibers from getting caught in each other due to excessively wide openings, or to prevent the hollow space from collapsing due to misalignment of the openings, and to prevent loss of texture such as a lightweight feel and a moderate resilience.

[0089] Furthermore, it is more preferable to set the width of the openings to 5% or less of the fiber diameter, which not only suppresses fibrillation due to fiber abrasion caused by the openings but also prevents the functional agent that has entered the hollow parts from falling off during washing or other post-processing such as applying a functional agent, thereby significantly improving the performance durability of the functional agent. However, if the width of the openings is too narrow, the water absorption due to capillary action at the openings may be weakened or the functional agent may not sufficiently penetrate into the hollow parts when applied, so the substantial lower limit of the width of the openings in the present invention is 1% of the fiber diameter.

[0090] The polymer constituting the composite fiber, hollow fiber, and flat hollow fiber in the multifilament of the present invention is preferably a thermoplastic polymer because of its excellent processability. Preferred polymers constituting the fibers include, for example, polyester-based, polyethylene-based, polypropylene-based, polystyrene-based, polyamide-based, polycarbonate-based, polymethyl methacrylate-based, polyphenylene sulfide-based polymers, and copolymers thereof.

[0091] In particular, from the viewpoint of being able to impart high interfacial affinity and obtaining fibers without abnormalities in the composite cross section, it is preferable that the thermoplastic polymers used for the composite fiber, hollow fiber, and flat hollow fiber in the multifilament of the present invention are all from the same polymer group or copolymers thereof.

[0092] The polymer may also contain various additives, such as inorganic substances such as titanium oxide, silica, and barium oxide; colorants such as carbon black, dyes, and pigments; flame retardants; fluorescent brighteners; antioxidants; and UV absorbers. It is particularly preferable for the poorly soluble polymer to contain 1.0% by mass or more of titanium oxide. This allows the titanium oxide precipitated on the surface of the poorly soluble polymer to fall off when the readily soluble polymer is dissolved, creating surface irregularities that diffuse light and suppress glare, thereby improving the appearance. Furthermore, the titanium oxide present inside the fiber also provides functionality such as preventing transparency and blocking UV rays.

[0093] The easily soluble polymer is preferably selected from polymers that are melt-moldable and exhibit greater solubility than other components, such as polyesters and copolymers thereof, polylactic acid, polyamides, polystyrene and copolymers thereof, polyethylene, and polyvinyl alcohol.

[0094] Furthermore, from the viewpoint of simplifying the elution process of the easily soluble polymer, the easily soluble polymer is preferably a copolymerized polyester, polylactic acid, polyvinyl alcohol, etc., which is easily soluble in aqueous solvents or hot water, etc. In particular, since it is easily soluble in aqueous solvents such as alkaline aqueous solutions while maintaining crystallinity, polyesters copolymerized with 5 mol % to 15 mol % of 5-sodium sulfoisophthalic acid and polyesters copolymerized with the above-mentioned 5-sodium sulfoisophthalic acid and 5 % by mass to 15 % by mass of polyethylene glycol having a weight average molecular weight of 500 to 3,000 are preferred from the viewpoint of passability through advanced processing, in that fusion between composite fibers does not occur even in false twist processing, etc., in which rubbing is imparted under heat.

[0095] In the present invention, the hardly soluble polymers having different melting points refer to a combination of polymers having melting points that differ by 10°C or more, selected from a group of melt-moldable thermoplastic polymers such as polyesters, polyethylenes, polypropylenes, polystyrenes, polyamides, polycarbonates, polymethyl methacrylates, and polyphenylene sulfide, and copolymers thereof.

[0096] In the composite fiber, hollow fiber, and flat hollow fiber in the multifilament of the present invention, the objective is to express the crimp morphology by the difference in shrinkage between hardly soluble polymers with different melting points. Therefore, when combining hardly soluble polymers with different melting points, it is preferable to use one type of low-melting polymer with high shrinkage and the other type of high-melting polymer with low shrinkage. In particular, from the perspective of suppressing peeling and imparting stability to advanced processing and durability to the fabric, it is more preferable to select the polymer combination from the same group of polymers with the same bonds in the main chain, such as polyesters with ester bonds and polyamides with amide bonds.

[0097] Examples of such combinations of low-melting point polymers and high-melting point polymers within the same polymer group include various combinations such as copolymerized polyethylene terephthalate / polyethylene terephthalate, polybutylene terephthalate / polyethylene terephthalate, polytrimethylene terephthalate / polyethylene terephthalate, thermoplastic polyurethane / polyethylene terephthalate, polyester elastomer / polyethylene terephthalate, polyester elastomer / polybutylene terephthalate as polyesters; nylon 66 / nylon 610, nylon 6-nylon 66 copolymer / nylon 6 or 610, PEG copolymerized nylon 6 / nylon 6 or 610, thermoplastic polyurethane / nylon 6 or 610 as polyamides; and ethylene-propylene rubber finely dispersed polypropylene / polypropylene and propylene-α-olefin copolymer / polypropylene as polyolefins.

[0098] Among these, it is preferable to use a polyester-based combination of hardly soluble polymers with different melting points, from the viewpoint that the high bending rigidity prevents the hollow portion inside the fiber from collapsing and that good color development can be obtained when dyed.

[0099] Furthermore, examples of copolymerization components in copolymerized polyethylene terephthalate include succinic acid, adipic acid, azelaic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, maleic acid, phthalic acid, isophthalic acid, and 5-sodium sulfoisophthalic acid. From the viewpoint of maximizing the difference in shrinkage from polyethylene terephthalate, it is preferable to use polyethylene terephthalate in which 5 to 15 mol % of isophthalic acid is copolymerized.

[0100] Furthermore, with environmental issues receiving increasing attention, the use of plant-derived biopolymers and recycled polymers in the present invention is also preferable from the viewpoint of reducing the environmental load, and the polymers used in the present invention described above can be recycled polymers that have been recycled by any of chemical recycling, material recycling, and thermal recycling methods.

[0101] Even when biopolymers or recycled polymers are used, polyester resins can accentuate the features of the present invention as a polymer characteristic, and as described above, their high bending rigidity prevents the hollow space inside the fiber from collapsing, and good color development can be achieved when dyed. From these viewpoints, recycled polyesters can be suitably used in the present invention.

[0102] The area ratio of the low-melting-point hardly soluble polymer to the high-melting-point polymer in the composite fiber, hollow fiber, and flat hollow fiber in the multifilament of the present invention is preferably in the range of 70 / 30 to 30 / 70 (low melting point / high melting point).Within this range, the low-melting-point polymer is not affected by hardening of the texture due to clogging caused by high shrinkage during heat treatment, and the crimp morphology due to the shrinkage difference can be fully expressed, resulting in larger inter-fiber voids.

[0103] From the viewpoint of achieving a softer feel, the fiber diameter of the composite fiber, hollow fiber, and flat hollow fiber in the multifilament of the present invention is preferably 20 μm or less. This range ensures sufficient resilience in addition to flexibility, making it suitable for clothing applications such as pants and shirts that require a firm and resilient feel.

[0104] Furthermore, it is more preferable that the fiber diameter be 15 μm or less, which increases the flexibility of the fiber bundles and fabrics made from the fiber bundles, making them suitable for use in clothing applications such as innerwear and blouses that come into contact with the skin. However, if the fiber diameter is less than 8 μm, the fiber diameter may be too thin, resulting in portions with reduced bending recovery and reduced color development. Therefore, it is preferable that the fiber diameter of the fibers in the present invention be 8 μm or more.

[0105] Furthermore, in the textile products of the present invention, which contain at least a portion of the conjugated fiber, hollow fiber, or multifilament of the present invention, when the textile products are made, differences in voids and unevenness occur between adjacent fibers at locations where the longitudinal axes of the cross sections are aligned and locations where they are not, and complex voids and unevenness can be formed between the fibers, resulting in a unique, smooth feel. Furthermore, the provision of hollow spaces within the fibers, combined with the complex voids and unevenness between the fibers, allows for the production of textiles with excellent wearability, which also achieve a moderate sense of resilience and a soft, fluffy texture.

[0106] Therefore, the conjugated fiber, hollow fiber, and multifilament of the present invention can be suitably used in a wide range of textile products, from general clothing such as jackets, skirts, pants, and underwear to sports clothing and clothing materials, and, taking advantage of their comfort, in interior products such as carpets and sofas, vehicle interior products such as car seats, cosmetics, cosmetic masks, and health products for daily use.

[0107] An example of a method for producing the composite fiber, hollow fiber, and multifilament of the present invention will be described in detail below.

[0108] Methods for spinning the conjugated fiber, hollow fiber, and multifilament of the present invention include melt spinning, which is intended to produce continuous fibers, wet and dry-wet solution spinning, and melt-blowing and spunbonding, which are suitable for obtaining sheet-like fiber structures. From the viewpoint of increasing productivity, however, melt spinning is preferred.

[0109] In the melt spinning method, production is possible by using a composite spinneret, which will be described later, and the spinning temperature is preferably set to a temperature at which the polymers used, mainly high-melting-point or high-viscosity polymers, exhibit fluidity. The temperature at which fluidity is exhibited varies depending on the molecular weight, but stable production is possible when it is set between the melting point of the polymer and melting point + 60°C.

[0110] The spinning speed is preferably about 500 to 6000 m / min, and can be changed depending on the physical properties of the polymer and the intended use of the fiber. From the perspective of achieving high orientation and improving mechanical properties, a spinning speed of 500 to 4000 m / min followed by drawing is particularly preferable, as this promotes uniaxial orientation of the fiber. During drawing, it is preferable to appropriately set the preheating temperature based on the softening temperature, such as the glass transition temperature of the polymer. The upper limit of the preheating temperature is preferably set to a temperature at which spontaneous elongation of the fiber does not cause yarn path disturbance during the preheating process. For example, in the case of PET (polyethylene terephthalate), which has a glass transition temperature of around 70°C, the preheating temperature is usually set to about 80 to 95°C.

[0111] Furthermore, the composite fibers, hollow fibers, and multifilaments of the present invention can be produced stably when the discharge rate per hole in the spinneret is about 0.1 to 10 g / min / hole. The discharged polymer flow is cooled and solidified, then an oil is added, and the polymer is taken up by rollers set to a specified peripheral speed. The polymer is then stretched by heated rollers to produce the desired composite fibers, hollow fibers, and multifilaments.

[0112] Furthermore, in the composite fiber of the present invention, which is made up of two or more types of polymers, it is preferable to set the melt viscosity ratio of the polymers used to less than 5.0 and the difference in solubility parameter values ​​to less than 2.0, since this allows a stable formation of a composite polymer flow and enables the production of a fiber with a good composite cross section.

[0113] As a composite spinneret used when producing the composite fiber of the present invention made of two or more types of polymers, for example, the composite spinneret described in JP-A-2011-208313 is suitably used.

[0114] The composite spinneret of the present invention shown in Fig. 12 is assembled into a spin pack and used for spinning, with three main components stacked from top to bottom: a metering plate 1, a distributor plate 2, and a discharge plate 3. Incidentally, Fig. 12 shows an example in which three types of polymers, i.e., polymer A, polymer B, and polymer C, are used. With conventional composite spinnerets, it is difficult to composite three or more types of polymers, so it is preferable to use a composite spinneret that utilizes fine flow channels as shown in Fig. 12.

[0115] In the spinneret member shown in Fig. 12, the amount of polymer per each discharge hole and the amount of polymer per each distribution hole are metered by the metering plate 1. The metered polymer streams are arranged by the distribution plate 2 to form a composite cross section of a single fiber, and the composite polymer streams formed by the distribution plate 2 are compressed and discharged by the discharge plate 3.

[0116] Although not shown in the figure to avoid complicating the explanation of the composite spinneret, the components stacked above the metering plate 1 can be components with flow paths formed to match the spinning machine and spin pack. By designing the metering plate 1 to match existing flow path components, the existing spin pack and its components can be used as they are.

[0117] Therefore, there is no need to dedicate a spinning machine specifically to the spinneret. Furthermore, in practice, it is advisable to stack multiple flow path plates between the flow path and the metering plate or between the metering plate 1 and the distributor plate 2. This is intended to provide a flow path that efficiently transports the polymer in the cross-sectional direction of the spinneret and the cross-sectional direction of the single fiber, and to configure the structure so that the polymer is introduced into the distributor plate 2. The composite polymer stream discharged from the discharge plate 3 is cooled and solidified according to the above-mentioned production method, and then an oil is added, and the composite polymer stream is taken up by rollers set to a specified peripheral speed. It is then stretched by a heated roller to produce the desired composite fiber.

[0118] To obtain a hollow fiber consisting only of a slightly soluble polymer by dissolving the easily soluble polymer in the innermost layer from the composite fiber of the present invention, the easily soluble polymer can be removed by immersing the composite fiber in a solvent that dissolves the easily soluble polymer. When the easily soluble polymer is a copolymerized polyethylene terephthalate copolymerized with 5-sodium sulfoisophthalic acid or polyethylene glycol, or polylactic acid, an alkaline aqueous solution such as an aqueous sodium hydroxide solution can be used.

[0119] The method for treating the composite fiber of the present invention with an alkaline aqueous solution can be, for example, to form a fiber structure from the composite fiber and then immerse it in an alkaline aqueous solution. In this case, it is preferable to heat the alkaline aqueous solution to 50°C or higher, as this can accelerate the progress of hydrolysis. Furthermore, using a fluid dyeing machine or the like is preferable from an industrial point of view, as it allows for large-scale treatment at one time. [Example]

[0120] The conjugate fiber and hollow fiber of the present invention will be specifically described below with reference to examples.

[0121] The following evaluations were carried out for the Examples and Comparative Examples. A. Melt viscosity of polymer The polymer chips were dried in a vacuum dryer to a moisture content of 200 ppm or less, and the melt viscosity was measured by a Toyo Seiki Capillograph at a strain rate of 1216 s. The measurement temperature was the same as the spinning temperature, and the time from the time the sample was placed in the heating furnace under a nitrogen atmosphere to the start of the measurement was 5 minutes. -1 The value was evaluated as the melt viscosity of the polymer.

[0122] B. Melting point of the polymer The polymer chips were dried in a vacuum dryer to a moisture content of 200 ppm or less, and approximately 5 mg was weighed out. A TA Instruments Q2000 differential scanning calorimeter (DSC) was used to measure the temperature from 0°C to 300°C at a rate of 16°C / min, followed by a 5-minute hold at 300°C. The melting point was calculated from the melting peak observed during the temperature rise. Each sample was measured three times, and the average value was used as the melting point. When multiple melting peaks were observed, the melting point was determined to be the top of the highest melting peak.

[0123] C. Fineness The weight of 100 m of fiber was measured and the weight was multiplied by 100. This operation was repeated 10 times, and the average value was rounded to one decimal place to obtain the fineness (dtex).

[0124] D. Cross-sectional parameters of composite fibers (RB / RA) The composite fibers were embedded in an embedding medium such as epoxy resin, and the fiber cross-sections perpendicular to the fiber axis were photographed using a Hitachi scanning electron microscope (SEM) at a magnification that allowed observation of 10 or more filaments. Randomly selected fibers within each image were analyzed using the Mitani Corporation WinROOF computer software to calculate the diameter of the largest possible circle (e.g., A in Figure 2(a)) that inscribed the fiber surface at at least two points (e.g., a1 and a2 in Figure 2(a)) and existed only within the fiber, without intersecting the fiber surface. The simple number average of the results for 10 filaments was calculated, and the value rounded to the nearest whole number was used as the inscribed circle diameter RA.

[0125] In addition, the diameter of a circle (e.g., B in (a) of Figure 2) that circumscribes the fiber surface at at least two points (e.g., b1 and b2 in (a) of Figure 2) and exists only outside the fiber, and has the smallest possible diameter within the range where the circumference of the circumscribed circle does not intersect with the fiber surface, was calculated. This was performed on 10 filaments, and the simple number average was calculated, rounded to the nearest whole number, to obtain the circumscribed circle diameter RB. The RB calculated for each fiber was divided by RA, and the simple number average was calculated, rounded to the nearest whole number, to obtain the RB / RA.

[0126] E. Fiber diameter Composite fibers and multifilaments were embedded in an embedding medium such as epoxy resin, and images of the fiber cross section perpendicular to the fiber axis were taken with a scanning electron microscope (SEM) at a magnification that allowed observation of 10 or more filaments. The area of ​​a randomly selected fiber within each image was measured, and the diameter calculated as a perfect circle was measured in μm units to one decimal place. This was repeated for 10 filaments, and the simple number average was calculated, rounded to one decimal place, to determine the fiber diameter (μm). If a hollow portion was present in the fiber cross section perpendicular to the fiber axis, the area of ​​the hollow portion was added to the area of ​​the fiber.

[0127] F. Communication width The composite fibers were embedded in an embedding medium such as epoxy resin, and images of the fiber cross sections perpendicular to the fiber axis were taken using a transmission electron microscope (TEM) at a magnification sufficient to observe at least 10 fibers. In the composite fiber images obtained, if the readily soluble polymer was interconnected from the fiber center to the fiber surface, the image was analyzed using computer software WinROOF (Mitani Corporation). The shortest width W (e.g., W in Figure 3(c)) of the interconnected portion perpendicular to a line S (e.g., S in Figure 3(c)) passing through the fiber center G and parallel to the interconnected portion was calculated in μm units. This was performed on 10 filaments, and the simple number average was calculated. The value was rounded to the nearest tenth to obtain the interconnected width. The severing width calculated for each filament was then divided by the fiber diameter and multiplied by 100 to obtain the simple number average of the results for 10 filaments. This value was rounded to the nearest tenth to obtain the ratio (%) of the interconnected width to the fiber diameter.

[0128] G. Flatness Multifilaments were embedded in an embedding medium such as epoxy resin, and cross-sections of the fibers perpendicular to the fiber axis were captured using a Hitachi scanning electron microscope (SEM) at a magnification large enough to observe at least 10 fibers. Randomly selected fibers within each image were analyzed using image analysis software. As shown in Figure 5(a), the line connecting the two most distant points (c1, c2) on the fiber periphery (c1-c2) was defined as the long axis, and the line passing through the midpoint of the long axis and perpendicular to it (d1-d2) was defined as the short axis. The flatness was calculated by dividing the length of the long axis by the length of the short axis. This was performed on 10 fibers, and the simple average was calculated. The value was rounded to two decimal places.

[0129] H. Hollowness ratio The multifilament was embedded in an embedding agent such as epoxy resin, and the cross section of the fiber perpendicular to the fiber axis was photographed using a Hitachi scanning electron microscope (SEM) at a magnification that allowed for observation of 10 or more fibers. When a fiber randomly selected from each photographed image contained a hollow portion, the area calculated from the outer shape of the fiber, including the hollow portion, and the area of ​​the hollow portion were calculated by analyzing the fiber using image analysis software. The area of ​​the hollow portion was then divided by the area calculated from the outer shape of the fiber, including the hollow portion, and multiplied by 100 to calculate the hollow ratio (%). This was performed on 10 fibers, and the simple average was calculated, rounded to one decimal place.

[0130] I. Opening width Multifilaments were embedded in an embedding medium such as epoxy resin, and images of the fiber cross sections perpendicular to the fiber axis were taken using a transmission electron microscope (TEM) at a magnification sufficient to observe 10 or more fibers. If the fibers in the resulting images had openings extending from the fiber center to the fiber surface, the image analysis software was used to calculate the shortest opening width W' (e.g., W' in Figure 6(b)) perpendicular to a line S' (e.g., S' in Figure 6(b)) passing through the fiber center G and parallel to the opening. The simple number average of the results for 10 filaments was calculated and rounded to two decimal places to obtain the opening width. The opening width calculated for each filament was also divided by the fiber diameter and multiplied by 100 to obtain the simple number average of the results for 10 filaments. The ratio of the opening width to the fiber diameter (opening ratio) (%) was calculated and rounded to the nearest whole number.

[0131] J. Number of crimped mountains (mountains / cm) A multifilament fabric was extracted from the fabric without plastic deformation, one end of the multifilament was fixed, and a load of 1 mg / dtex was applied to the other end for at least 30 seconds. After this, markings were made at random locations 1 cm apart along the fiber axis of the multifilament. The fibers were then separated from the multifilament without plastic deformation, and the sample was fixed on a glass slide, adjusting the spacing between the pre-marked marks to the original 1 cm. Images of this sample were taken with a digital microscope at a magnification that allowed the 1 cm markings to be observed. If the multifilament had a twisted crimp morphology, as shown in Figure 11, the number of crimp peaks between the markings was counted. This procedure was performed on 10 fibers composed of the same polymer. The simple average of the results was calculated and rounded to one decimal place to determine the number of crimp peaks (peaks / cm).

[0132] K. Coefficient of variation of the rotation angle of the major axis, CV For multifilament fabrics, cross-sections of the fabric perpendicular to the length of the fabric and perpendicular to the fiber axis of the multifilament were photographed using a Hitachi scanning electron microscope (SEM) at a magnification sufficient to observe 20 or more fibers. When the fibers in the photographs had flat cross-sections, the image was analyzed using image analysis software. As shown in Figure 5(b), the line (c1-c2) connecting the two most distant points (c1, c2) on the periphery of the fiber was defined as the long axis. A line passing through the midpoint of the long axis of the flat hollow fiber and parallel to the bottom edge of the photographed image was rotated counterclockwise around the midpoint of the long axis, and the angle of rotation (θ) at which the inclination of the line coincided with the long axis was evaluated. This evaluation was performed on 20 fibers randomly selected from the multifilament fabric, and the standard deviation and average of the results were calculated. The standard deviation was divided by the average value and multiplied by 100 to calculate the coefficient of variation CV (%) of the rotation angle of the major axis. The value was rounded to the nearest whole number.

[0133] L. Texture evaluation (lightness, flexibility, resilience, smoothness, roughness) A 3 / 1 twill fabric was produced by adjusting the number of fibers so that the warp cover factor (CFA) was 800 and the weft cover factor (CFB) was 1200. Here, CFA and CFB refer to the warp density and weft density of the fabric measured in a 2.54 cm section according to JIS-L-1096:2010 8.6.1, where CFA = warp density × (warp fineness). 1 / 2 , CFB = weft density × (weft fineness) 1 / 2 The obtained fabric was subjected to scouring, wet heat treatment, alkali treatment and heat setting, and then evaluated for five textures, namely lightness, flexibility, resilience, smoothness and roughness, using the following methods.

[0134] The lightness was evaluated by the following method: the thickness (cm) of a 20 cm x 20 cm woven fabric was measured under a constant pressure (0.7 kPa) using a Terotec constant pressure thickness measuring instrument (PG-14J), the volume of the woven fabric was calculated, and the weight (g) of the woven fabric was divided by the obtained volume to obtain the apparent density (g / cm) of the woven fabric. 3 From the apparent density obtained, the lightness was judged into three levels based on the following criteria.

[0135] ◎: Excellent lightness (apparent density ≦ 0.34) ○: Good lightness (0.34<apparent density≦0.44) ×: Poor lightness (0.44<apparent density)

[0136] The flexibility was evaluated using a pure bending tester (KES-FB2) manufactured by Kato Tech Co., Ltd., as follows: A 20 cm × 20 cm woven fabric was held with an effective sample length of 20 cm × 1 cm, and the maximum curvature in the weft direction was ±2.5 cm. -1 The curvature was 0.5cm. -1 and 1.5cm -1 The difference in bending moment per unit width (gf cm / cm) is calculated by dividing the curvature difference by 1 cm. ―1 Divided by the value and curvature -0.5cm -1 and -1.5cm -1 The difference in bending moment per unit width (gf cm / cm) is calculated by dividing the curvature difference by 1 cm. ―1This operation was performed three times at each location, and the simple number average of the results was calculated for a total of 10 locations. The value was rounded to the fourth decimal place and then divided by 100 to obtain the bending hardness B x 10 -2 (gf·cm 2 / cm). The obtained bending hardness B × 10 -2 The flexibility was assessed on a three-point scale based on the following criteria.

[0137] ◎: Excellent flexibility (bending hardness B x 10 -2 ≦1.0) ○: Good flexibility (1.0 < bending hardness B × 10 -2 ≦2.0) ×: Poor flexibility (2.0<Bending hardness B×10 -2 )

[0138] The resilience was evaluated by the following method: A 20 cm x 20 cm woven fabric was held with an effective sample length of 20 cm x 1 cm and bent in the weft direction using a pure bending tester (KES-FB2) manufactured by Kato Tech. The curvature was ±1.0 cm. -1 This operation was performed three times at each location, and the hysteresis width (gf cm / cm) was calculated. The simple number average of the results was calculated for a total of 10 locations, rounded to the fourth decimal place, and then divided by 100 to obtain the bending recovery 2HB x 10 -2 (gf cm / cm). The bending recovery obtained was 2HB × 10 -2 The repulsive feeling was judged on a three-point scale based on the following criteria.

[0139] ◎: Excellent resilience (bending recovery 2HB x 10 -2 ≦1.0) ○: Good resilience (1.0 < bending recovery 2HB × 10 -2 ≦2.0) ×: Poor resilience (2.0<bending recovery 2HB×10 -2 )

[0140] Smoothness and roughness were evaluated using the following method. Using a Kato Tech automated surface tester (KES-FB4), a 10 cm x 10 cm area of ​​a 20 cm x 20 cm piece of fabric was slid over a 1 cm x 1 cm terminal wrapped with piano wire at a speed of 1.0 mm / sec, with a 50 g load applied. The average coefficient of friction (MIU) and the variation in the average coefficient of friction (MMD) were then calculated. This procedure was repeated three times per location, for a total of 10 locations. The average coefficient of friction (MIU) was calculated by simply averaging the results, and the value was rounded to one decimal place to obtain the coefficient of friction. From the obtained coefficient of friction, smoothness was evaluated on a three-point scale based on the following criteria.

[0141] ◎: Excellent smoothness (friction coefficient <0.5) ○: Good smoothness (0.5≦friction coefficient<1.0) ×: Poor smoothness (1.0 or less coefficient of friction)

[0142] In addition, the variation in the mean coefficient of friction (MMD) was calculated as a simple number average, and the value was rounded to three decimal places to determine the friction variation. From the obtained friction variation, the roughness was evaluated on a three-point scale based on the following criteria.

[0143] ◎: Excellent roughness (0.9≦friction fluctuation) ○: Good roughness (0.5≦friction coefficient<0.9) ×: Poor roughness (friction coefficient <0.5)

[0144] M. Functionality evaluation (moisture absorption, quick drying, stretchability) A 3 / 1 twill fabric was produced by adjusting the number of fibers so that the warp cover factor (CFA) was 800 and the weft cover factor (CFB) was 1200. Here, CFA and CFB refer to the warp density and weft density of the fabric measured in a 2.54 cm section according to JIS-L-1096:2010 8.6.1, where CFA = warp density × (warp fineness). 1 / 2 , CFB = weft density × (weft fineness) 1 / 2The obtained fabric was subjected to scouring, wet heat treatment, alkali treatment and heat setting, and then evaluated for its two functions of moisture absorption, quick drying and stretchability using the following methods.

[0145] The moisture absorption and quick-drying properties were evaluated using the following method. Specifically, 0.1 cc of water was dropped onto a 10 cm x 10 cm piece of fabric, and the fabric was weighed every 5 minutes in an environment with a temperature of 20°C and a relative humidity of 65% RH. The time (minutes) until the residual moisture content reached 1.0% or less was determined. This procedure was performed at a total of three locations, and the simple average of the results was calculated. The value was rounded off to the nearest whole number to determine the moisture diffusion time (minutes). The moisture absorption and quick-drying properties were evaluated based on the obtained moisture diffusion time, and each was ranked into one of three levels according to the following criteria.

[0146] ◎: Excellent moisture absorption and quick drying (moisture diffusion time ≦ 20) ○: Good moisture absorption and quick drying (20<moisture diffusion time≦40) ×: Poor moisture absorption and quick drying (40<moisture diffusion time)

[0147] Stretchability was evaluated using the following method. Specifically, it was performed in accordance with the elongation A method (constant rate elongation method) described in Section 8.16.1 of JIS L1096:2010. The strip method was used with a load of 17.6 N (1.8 kg), and the test conditions were a sample width of 5 cm, length of 20 cm, clamp spacing of 10 cm, and a pulling speed of 20 cm / min. The initial load was a weight equivalent to a sample width of 1 m, in accordance with the method of JIS L1096:2010. The test was performed three times in the weft direction of the fabric, and the simple average of the results was calculated. The value was rounded to the nearest whole number to obtain the fabric elongation (%). From the obtained fabric elongation, stretchability was evaluated on a three-level scale based on the following criteria.

[0148] ◎: Excellent stretchability (elongation rate 15 or less) ○: Good stretchability (5≦elongation rate<15) ×: Poor stretchability (elongation rate <5)

[0149] N. Abrasion resistance A plain weave fabric was produced by adjusting the number of fibers so that the warp cover factor (CFA) was 1100 and the weft cover factor (CFB) was 1100. The resulting fabric was dyed black using the disperse dye Sumikaron Black S-3B (10% owf). After dyeing, the fabric was cut into a 10 cm diameter circle, moistened with distilled water, and attached to a disk. Further, a 30 cm square piece of fabric was cut and fixed onto a horizontal board while still dry.

[0150] A disk with a fabric moistened with distilled water attached was placed horizontally against a fabric fixed on a horizontal plate, and the disk was moved circularly for 10 minutes at a load of 420 g and a speed of 50 rpm so that the center of the disk drew a circle with a diameter of 10 cm, causing friction between the two fabrics. After the friction was completed and the fabric was left for 4 hours, the degree of discoloration of the fabric attached to the disk was assessed using a discoloration gray scale, rated from 1 to 5 in 0.5-grade increments. From the results of the rating, abrasion resistance was rated on a three-level scale based on the following criteria.

[0151] ◎: Excellent abrasion resistance (grade: grade 4 or higher) ○: Good abrasion resistance (grade: grade 3 or 3.5) ×: Poor abrasion resistance (Grade: Less than Grade 3)

[0152] [Example 1] As polymer 1, polyethylene terephthalate copolymerized with 8 mol% of 5-sodium sulfoisophthalic acid and 9 mass% of polyethylene glycol (SSIA-PEG copolymerized PET, melt viscosity: 100 Pa·s, melting point: 233°C) was prepared. As polymer 2, polyethylene terephthalate copolymerized with 7 mol% isophthalic acid (IPA copolymerized PET, melt viscosity: 140 Pa·s, melting point: 232°C) was prepared. As polymer 3, polyethylene terephthalate (PET, melt viscosity: 130 Pa·s, melting point: 254°C) was prepared.

[0153] These polymers were melted separately at 290°C, and then weighed out to a weight ratio of polymer 1 / polymer 2 / polymer 3 of 20 / 40 / 40, and poured into a spinning pack equipped with a composite spinneret as shown in Figure 5. The polymers were discharged from the nozzle to form a flat composite fiber as shown in Figure 3(a), with polymer 1 located in the innermost layer and in the continuous regions extending from the fiber center to the fiber surface, and polymer 2 and polymer 3 bonded side-by-side in the outermost layer.

[0154] After cooling and solidifying the extruded composite polymer stream, an oil agent was added, the stream was wound up at a spinning speed of 1500 m / min, and stretched between rollers heated to 90°C and 130°C to produce a composite fiber of 56 dtex-36 filaments (fiber diameter 12 μm).

[0155] The ratio RB / RA of the inscribed circle diameter RA to the circumscribed circle diameter RB of the obtained composite fiber was 1.8. The interconnected width was 0.5 μm, which was 4% of the fiber diameter of 12 μm, confirming that the composite fiber was the present invention.

[0156] The obtained composite fiber was woven, and subjected to a scouring treatment at 80°C and a wet heat treatment at 130°C, followed by treatment in a 1% by mass aqueous solution of sodium hydroxide heated to 90°C (bath ratio 1:50), thereby removing 99% or more of the easily soluble polymer, Polymer 1. During this treatment, due to the presence of interconnected portions extending from the fiber center to the fiber surface, Polymer 1 in the innermost layer was rapidly eluted within 10 minutes of starting the elution treatment.

[0157] The fabric was then heat-set at 180°C to obtain a multifilament woven fabric consisting of flat hollow fibers with a flatness of 1.8, a hollow ratio of 18%, and a crimped peak count of 17 peaks / cm, as shown in Figure 2(b). The flat hollow fibers had openings with a width of 0.5 µm, which was 4% of the fiber diameter.

[0158] The woven fabric made of this multifilament had a coefficient of variation (CV) of 27% for the rotation angle of the long axis of the flat hollow fibers in the multifilament. Therefore, the long axis direction of the cross section became irregular, resulting in the appearance of unevenness on the textile surface. As a result, when the fabric surface was touched, it felt smooth (friction coefficient: 0.3) but also rough (friction variation: 0.9 x 10 -2 Furthermore, the fabric has complex voids between the fibers, which, combined with the hollow spaces inside the fibers, gives it a moderate resilience (bending recovery 2HB: 0.9 x 10 -2 gf·cm / cm) and swelling (apparent density: 0.33g / cm 3 ) with a soft texture (bending hardness B: 0.9 x 10 -2 gf·cm 2 / cm). The fabric also had excellent stretchability (fabric elongation: 16%) and quick-drying properties due to the presence of openings (moisture diffusion time: 25 minutes), making it a fabric with excellent wearability that combined texture and functionality, which are directly related to human comfort.

[0159] Furthermore, because the openings in the fabric are narrow, the voids within the fibers remain intact even after processing. Furthermore, when a functional agent is applied, it enters the hollow spaces and is not removed by washing, etc., significantly improving the durability of the functional agent. Furthermore, the fabric exhibits good abrasion resistance (frosting: grade 4), with no discoloration due to fibrillation caused by the openings. The results are shown in the table below.

[0160] [Examples 2 and 3] The same procedures as in Example 1 were carried out except that the cross-sectional shape was changed to a multi-lobe shape as shown in FIG. 3(b) (Example 2) or a flat multi-lobe shape as shown in FIG. 3(c) (Example 3).

[0161] In Example 2, unevenness was formed on the fiber surface, which reduced uneven gloss (glare) on the fabric due to diffused reflection of light, and the fine inter-fiber voids improved water absorption and quick-drying properties.

[0162] In Example 3, the flat and multi-lobed fibers had complex inter-fiber voids caused by twisting of the flat fibers, and the fine inter-fiber voids due to the multi-lobed fiber surface irregularities, which combined to further improve the texture, such as a lightweight feel and a resilient feel, as well as the functionality, such as moisture absorption and quick-drying properties. The results are shown in the table below.

[0163] [Example 4] The same procedures as in Example 1 were carried out except that the composite structure was changed to a structure in which the readily soluble polymer was present in the outermost layer as shown in FIG. 3(d).

[0164] In Example 4, the interfiber voids created when the easily soluble polymer in the outermost layer was removed allowed the fibers fixed at the binding points of the woven or knitted fabric to move, improving flexibility, and the apparent density reduced at high void ratio, improving the lightweight feel. The results are shown in the table below.

[0165] [Examples 5 and 6] The same procedures as in Example 1 were repeated except that the ratio of the inscribed circle diameter RA to the circumscribed circle diameter RB of the fiber, RB / RA (irregularity), was changed to RB / RA = 1.3 (Example 5) and RB / RA = 1.0 (Example 6) as shown in Figure 1(c).

[0166] In Examples 5 and 6, as the degree of deformation decreased, the effect of steric hindrance during twisting decreased, reducing the roughness, while the crimp morphology developed during heat treatment became finer and closer to a coil shape, increasing not only stretchability but also fine interfiber voids and improving flexibility. The results are shown in the table below.

[0167] [Example 7] The same procedures as in Example 1 were carried out except that the cross-sectional shape of the composite fiber was changed so that the joining surface of the polymers with different melting points and the communicating portion were on a straight line, and the direction (angle) of the straight line was random (the four types in Figure 10 are examples of such cross-sectional shapes).

[0168] In Example 7, the crimp morphology developed by heat treatment differed for each single fiber due to the difference in the distance between the centers of gravity, and this increased the coefficient of variation (CV) of the rotation angle of the major axis, resulting in an increased roughness, which not only made the fabric feel smoother to the touch, but also improved the lightweight feel due to the increased inter-fiber voids. The results are shown in the table below.

[0169] [Comparative Example 1] The same procedure as in Example 1 was repeated except that polymer 2 was changed to the same PET as polymer 3.

[0170] In Comparative Example 1, although a certain degree of lightweight feel was achieved due to the hollow spaces inside the fibers, the lack of crimping resulted in a lack of unevenness on the textile surface and a lack of roughness. Furthermore, the lack of interfiber voids meant that the textile lacked flexibility and resilience. Furthermore, the textile lacked the properties of quick-drying and stretchability. The results are shown in the table below.

[0171] Comparative Example 2 After stretching, the yarn was subjected to false twist processing using a friction disc at a rotation speed of 3000 T / m between rollers at a processing speed of 250 m / min and a stretch ratio of 1.05, while being heated with a heater set to 180°C.

[0172] In Comparative Example 2, although a crimped form was obtained by false twisting, the unevenness of the textile surface was monotonous and lacked a rough feel. The results are shown in the table below.

[0173] Comparative Example 3 The same procedure as in Example 1 was repeated except that the composite structure was changed to a structure in which round, hardly soluble polymers with different melting points were laminated in the direction from the center of the fiber toward the surface of the fiber, as shown in FIG. 4(b).

[0174] In Comparative Example 2, the removal of the easily soluble polymer from the innermost layer resulted in the formation of voids within the fibers, resulting in a certain degree of lightweight feel, but the sparingly soluble polymer with a different melting point was not distributed evenly, and the crimped form due to heat treatment was hardly expressed, resulting in a lack of flexibility, resilience, and roughness, as well as a lack of functions such as quick-drying and stretchability. The results are shown in the table below.

[0175] Comparative Example 4 Polymer 2 was polyethylene terephthalate copolymerized with 7 mol% isophthalic acid (IPA copolymerized PET, melt viscosity: 140 Pa·s, melting point: 232°C), and polymer 3 was polyethylene terephthalate (PET, melt viscosity: 130 Pa·s, melting point: 254°C).

[0176] These polymers were melted separately at 290°C, and then weighed to give a weight ratio of 50 / 50 polymer 2 / polymer 3. The inflow polymers were discharged from the discharge hole to form a hollow composite fiber as shown in Figure 4(a), with a hollow ratio of 20% and a composite structure in which polymer 2 and polymer 3 were bonded side-by-side.

[0177] After cooling and solidifying the extruded composite polymer stream, an oil agent was added, the stream was wound up at a spinning speed of 1500 m / min, and stretched between rollers heated to 90°C and 130°C to produce a composite fiber of 56 dtex-36 filaments (fiber diameter 13 μm).

[0178] The obtained composite fiber was woven, and subjected to a scouring treatment at 80°C and a wet heat treatment at 130°C, followed by heat setting at 180°C to obtain a woven fabric composed of the above composite fiber.

[0179] In Comparative Example 4, the hollow cores were already present inside the fibers during fiber production, but they were crushed by the onset of crimp during the weaving process and heat treatment, resulting in a woven fabric that not only lost its light weight but also lacked flexibility and resilience. The results are shown in the table below.

[0180] [Examples 8 and 9] The same procedures as in Example 1 were carried out except that the interconnection width due to the easily soluble polymer was changed to 8% (Example 8) and 16% (Example 9) of the fiber diameter.

[0181] In Examples 8 and 9, the larger the openings formed after removing the readily soluble polymer, the more likely the openings were to catch on the fingers when touched with a hand, increasing the coefficient of friction. Furthermore, the surface area of ​​the fiber that comes into contact with water droplets when dropped on it also increases, improving the moisture absorption and quick-drying properties. The results are shown in the table below.

[0182] [Examples 10 and 11] The same procedures as in Example 1 were repeated except that the weight ratio of polymer 2 / polymer 3 was changed to 60 / 20 (Example 10) and 20 / 60 (Example 11).

[0183] In Examples 10 and 11, the higher the proportion of polymer 2, which is the high shrinkage component, the stronger the crimp morphology, resulting in a lighter fabric. Furthermore, the higher the proportion of polymer 3, the low shrinkage component, the more effectively the fabric was prevented from clogging due to the high shrinkage rate of the high shrinkage component during heat setting, resulting in superior flexibility. The results are shown in the table below.

[0184] [Examples 12 and 13] The same procedures as in Example 1 were repeated except that the weight ratio of polymer 1 / polymer 2 / polymer 3 was changed to 10 / 45 / 45 (Example 12) and 30 / 35 / 35 (Example 13).

[0185] In Examples 12 and 13, decreasing the weight ratio of polymer 3 and decreasing the hollow ratio increased the bending stiffness, resulting in a characteristically bouncy feel. Furthermore, increasing the weight ratio of polymer 3 and increasing the hollow ratio increased the amount of air trapped inside the fibers, resulting in a lighter feel and superior flexibility and resilience. The results are shown in the table below.

[0186] [Examples 14 and 15] The same procedures as in Example 1 were carried out except that the discharge rate was changed so that the fiber diameter was 17 μm (Example 14) or 24 μm (Example 15).

[0187] In Examples 14 and 15, the increased fiber diameter resulted in larger loops in the crimped form that appeared upon heat treatment, improving the roughness and lightness of the fabric. In addition, the increased bending stiffness resulted in a characteristically elastic feel. The results are shown in the table below.

[0188] [Example 16] The same procedures as in Example 1 were repeated except that polymer 3 was changed to polyethylene terephthalate containing 5.0 mass % of titanium oxide (TiO2-containing PET).

[0189] In Example 16, when the readily soluble polymer was removed, the titanium oxide that had precipitated on the surface of Polymer 3 also fell off, creating surface irregularities that diffused light, suppressing glare due to the angle of incidence of light. Not only did this change the appearance of the fabric, but the titanium oxide inside the fiber also provided functionality such as preventing transparency and blocking UV rays. The results are shown in the table below.

[0190] [Example 17] The same procedures as in Example 1 were repeated except that polymer 2 was changed to polypropylene terephthalate (PPT).

[0191] In Example 17, the rubber elasticity of PPT was combined to produce a lighter, more flexible feel and significantly improved stretchability. Furthermore, because PPT has a lower refractive index than PET, the resulting woven fabric also had excellent color development. The results are shown in the table below.

[0192] [Example 18] Polymer 1 was polyethylene terephthalate copolymerized with 8 mol% 5-sodium sulfoisophthalic acid and 9 mass% polyethylene glycol (SSIA-PEG copolymerized PET, melt viscosity: 100 Pa·s, melting point: 233°C), polymer 2 was nylon 6-nylon 66 copolymer (N6-66 copolymer, melt viscosity: 240 Pa·s, melting point: 195°C), and polymer 3 was nylon 6 (N6, melt viscosity: 190 Pa·s, melting point: 223°C).

[0193] These polymers were melted separately at 280°C, and then weighed out to a weight ratio of polymer 1 / polymer 2 / polymer 3 of 20 / 40 / 40, and poured into a spinning pack equipped with a composite spinneret as shown in Figure 5. The polymers were extruded from the nozzle to form a flat composite fiber as shown in Figure 2(a), with polymer 1 in the innermost layer and polymer 2 and polymer 3 bonded side-by-side in the outermost layer.

[0194] After cooling and solidifying the extruded composite polymer stream, an oil agent was added, the stream was wound up at a spinning speed of 1500 m / min, and stretched between rollers heated to 90°C and 130°C to produce a composite fiber of 56 dtex-36 filaments (fiber diameter 12 μm).

[0195] The obtained composite fiber was woven, and subjected to a scouring treatment at 80°C and a wet heat treatment at 130°C, followed by treatment in a 1% by mass aqueous solution of sodium hydroxide heated to 90°C (bath ratio 1:50) to remove over 99% of the easily soluble polymer, Polymer 1. Then, heat setting was performed at 180°C to obtain a woven fabric composed of multifilaments of flat hollow fibers with a flatness of 1.8, a hollowness of 20%, and a crimp peak count of 12 peaks / cm, as shown in Figure 6(a).

[0196] In Example 18, the properties of nylon, which has lower density and elasticity than polyester, combined to provide not only an excellent lightweight feel but also a softer texture. The results are shown in the table below.

[0197]

Table 1

[0198]

Table 2

[0199]

Table 3

[0200]

Table 4

[0201]

Table 5

[0202]

Table 6

[0203]

Table 7

[0204]

Table 8

[0205]

Table 9

[0206]

Table 10

[0207]

Table 11

[0208] [Table 12]

[0209] The meanings of the abbreviations in the table are as follows: PET: Polyethylene terephthalate PEG: polyethylene glycol SSIA: 5-Sodium sulfoisophthalate IPA: Isophthalic acid PPT: Polypropylene terephthalate N6: Nylon 6 N6-66 copolymer: nylon 6-nylon 66 copolymer TiO2: Titanium oxide

[0210] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese patent applications filed on August 18, 2020 (Patent Application No. 2020-137899) and November 24, 2020 (Patent Application No. 2020-194085), the contents of which are incorporated herein by reference. [Industrial Applicability]

[0211] The conjugated fiber, hollow fiber, and multifilament of the present invention have a precisely controlled void structure within the fiber and between the fibers, thereby enabling the production of textiles with a moderate resilience and a fluffy, soft texture, which are excellent in wearing comfort. Therefore, the conjugated fiber, hollow fiber, and multifilament of the present invention can be suitably used in a wide range of textile products, from general clothing such as jackets, skirts, pants, and underwear to sportswear and clothing materials, and, taking advantage of their comfort, in interior products such as carpets and sofas, vehicle interior parts such as car seats, and daily uses such as cosmetics, cosmetic masks, and health products. [Explanation of symbols]

[0212] x: Easily soluble polymer y: Low-melting point, poorly soluble polymer z: Low-solubility polymer with high melting point a1, a2: Intersection of the fiber surface and the inscribed circle b1, b2: Intersection of the fiber surface and the circumscribed circle c1, c2: The two most distant points on the fiber periphery d1, d2: Intersection of the fiber surface and a straight line passing through the midpoint of the line connecting the two most distant points on the fiber periphery A: A circle that is inscribed in the fiber surface at at least two points, exists only inside the fiber, and has the largest possible diameter within the range where the circumference of the inscribed circle does not intersect with the fiber surface. B: A circle that circumscribes the fiber surface at at least two points, exists only inside the fiber, and has the smallest possible diameter within the range where the circumference of the circumscribed circle does not intersect with the fiber surface. G: Fiber center H: Hollow part I: A line that passes through the center of the fiber and divides the fiber cross section equally into two, and on the left and right or top and bottom of the line, the area ratio of the hardly soluble polymer on the high melting point side to the hardly soluble polymer on the low melting point side is 100:0 to 70:30 on one side of the fiber cross section, and is in the range of 30:70 to 0:100 on the other side of the fiber cross section. S: A straight line that passes through the fiber center G and is parallel to the connecting part W: Width of the connecting part in the direction perpendicular to the line S S': A straight line passing through the fiber center G and parallel to the opening W': Width of the opening perpendicular to the line S' 1: Weighing plate 2: Distribution plate 3: Discharge plate

Claims

1. In the cross section of the fiber, two or more types of polymers having different dissolution rates in a solvent are laminated from the center of the fiber toward the surface of the fiber, the innermost layer including the fiber core contains an easily soluble polymer; A composite fiber in which two types of hardly soluble polymers having different melting points are unevenly distributed in at least one layer other than the innermost layer.

2. 2. The composite fiber according to claim 1, wherein the relationship between the inscribed circle diameter RA and the circumscribed circle diameter RB of the fiber in the cross section satisfies 1.2≦RB / RA≦2.

4.

3. 3. The composite fiber according to claim 1, wherein the readily soluble polymer is continuous from the center of the fiber to the surface of the fiber in the cross section of the fiber, and the width of the continuous line is 10% or less of the fiber diameter.

4. The conjugated fiber according to any one of claims 1 to 3, wherein in the cross section of the fiber, the outermost layer contains the easily soluble polymer.

5. A hollow fiber obtained by removing the easily soluble polymer from the composite fiber according to any one of claims 1 to 4.

6. A textile product comprising, as a part thereof, the conjugated fiber according to any one of claims 1 to 4 or the hollow fiber according to claim 5.

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