Fiber bundle made of flat ultrafine fibers

Abstract

To provide a flat ultrafine fiber that efficiently contains a functional substance and yields a functional material having excellent durability.SOLUTION: There is provided a fiber having a flattened fiber cross section. A degree of flatness thereof, which is a value obtained by dividing a length of a major axis of the cross section by a length of a minor axis, is 15 or more. An average length of the minor axis is 1000 nm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention is a flat ultrafine fiber A fiber bundle consisting of It is related to. [Background technology]

[0002] Fibers made from thermoplastic polymers such as polyester and polyamide have excellent mechanical properties and dimensional stability, and are therefore widely used not only for clothing but also for interior decoration, vehicle interiors, industrial applications, etc. However, as people's lives become more affluent, they are seeking greater comfort, and as applications and lifestyles become more diverse, the functionality required of textile products is also becoming more diverse, leading to a trend toward ever higher functionality.

[0003] In functional textile products, the basic principle is to make the most of the characteristics of the fiber itself, but there are also textile materials that utilize functional substances in order to further enhance functionality or to give the textile materials functions that are not inherent in the fiber itself.

[0004] As a method for imparting functionality, there is a method of imparting functional substances to fiber materials such as woven or knitted fabrics and nonwoven fabrics by post-processing.

[0005] In the so-called functional processing, which is the post-processing of this functional material, (1) A method in which functional substances are mixed with a binder, and then the binder is impregnated into the fiber material and fixed. (2) A method of adsorbing functional substances onto fiber materials will be carried out.

[0006] Patent Documents 1 and 2 propose a method in which an aqueous dispersion containing functional fine particles and a hydrophilic binder resin or a hydrophobic binder resin is prepared, and the hydrophilic binder resin containing the functional fine particles is attached in the form of a coating to the single fibers that constitute the fiber structure under specific conditions.

[0007] The methods described in Patent Documents 1 and 2 utilize the thin and long morphological characteristics of fibers, and utilize the surface area per unit weight, which is a feature of fiber materials, to attach large amounts of functional substances to the fiber materials.In order to further improve functionality, there are also attempts to increase the efficiency of attachment of functional substances by giving single fibers irregular cross-sections or making them extremely thin.

[0008] In Patent Document 3, the specific surface area of ​​a fiber material is increased by using modified cross-section fibers, with the aim of increasing the amount of functional substance attached and improving durability in practical use. Also, Patent Document 4 proposes a fiber structure including slit fibers having radial slits in the cross section of a single fiber, and impregnating the slits with a functional substance, in order to increase the attachment rate of the functional substance and further improve durability.

[0009] Patent Document 5 proposes a nanofiber fiber structure with a small fiber diameter variation of 10 to 200 nm on average, with the aim of reducing the fiber diameter of the single fiber and increasing the specific surface area of ​​the fiber material, and discloses a functional fiber structure in which this nanofiber contains a functional substance. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent Document 1: JP 2005-273068 A Claims [Patent Document 2] Patent Publication No. 2006-200082 Claims [Patent Document 3] JP 5-239709 A Scope of Claims [Patent Document 4] Patent Publication No. 2008-106400 Solution and Claims [Patent Document 5] Patent Document 1: JP 2005-036376 A Claims Summary of the Invention [Problem to be solved by the invention]

[0011] Patent Documents 1 and 2 disclose a method of attaching functional particles to a fiber structure via a binder resin, taking advantage of the fact that the binder resin is more easily attached to the fiber by treating the binder resin in saturated steam before heating and drying it.

[0012] The aim is to achieve a durable functional fiber structure by improving the efficiency of binder resin adhesion through a special treatment, thereby preventing the functional substance from falling off. However, post-processing using a binder results in the functional substance being fixed to the surface layer of the fabric, which is not a problem for short-term use, but there have been cases where there have been issues with the functional substance being more likely to fall off in areas that are subject to physical contact, such as long-term use or repeated abrasion.

[0013] Furthermore, in methods that utilize binder resins, such as those described in Patent Documents 1 and 2, or that premix the resin and coat the fibers, the functional substance is imparted with functionality by being fixed to the fiber surface, and the amount of functional substance that can be attached to the fiber material is limited due to the limitations on the specific surface area of ​​the base fiber.

[0014] There have also been proposals to increase the specific surface area of ​​fibers by forming them into irregular cross sections, as in Patent Documents 3 and 4, and to utilize the binder effect of the unevenness of the fiber surface to prevent functional substances from falling off and ensure durability.

[0015] However, when fibers are given a modified cross section, it is certainly possible to attach a large amount of functional substances due to an increase in the specific surface area of ​​the fiber material, etc., but when the unevenness of the fiber surface layer is used as exemplified in Patent Document 4, it is difficult to say that the uneven parts have excellent durability against external loads such as repeated rubbing, and pilling and the like may occur, making it difficult to maintain quality over long periods of use and causing the functional substances to fall off, so durability over long periods of use may also be an issue in this case.

[0016] Patent Document 5 utilizes extremely thin fibers with a single fiber diameter of 10 to 200 nm, and in addition to increasing the specific surface area, achieves a fiber structure that is efficiently impregnated with functional substances through the special fiber bundle structure that results.

[0017] Patent Document 5 utilizes extremely thin fibers, i.e., nanofibers, and by increasing the specific surface area of ​​the fiber material, it is possible to increase the adsorption and inclusion of functional substances, thereby potentially increasing the adhesion efficiency of the functional substances.

[0018] However, in materials utilizing ultrafine fibers such as those disclosed in Patent Document 5, the fiber diameter of the single fiber is extremely small, resulting in low single fiber strength and poor durability against repeated abrasion, etc., and the material is sometimes subjected to surface treatments such as calendaring before use. In particular, Patent Document 5 is produced by blending two types of polymers, forming them into fibers, and eluting one component. The ultrafine fibers have a finite length of approximately several μm, and the fiber bundle contains many fiber ends, making it difficult to say that the fiber material has excellent properties in terms of durability. This is not limited to Patent Document 5; similar technical issues exist in other cases of ultrafine fibers obtained by blending two types of polymers and eluting one component, which can sometimes pose challenges in terms of fiber material design.

[0019] As described above, although there are technical disclosures aimed at high-performance fiber materials that increase the specific surface area of ​​the base fiber material in order to impart functional substances, there are no technical disclosures that are suitable for ensuring long-term durability from the perspective of functionality and fiber material quality. In response to recent demands, there has been a demand for fiber materials that are easy to mold, can be deployed in a variety of application fields, efficiently contain functional substances, and are suitable for functional materials with excellent durability. [Means for solving the problem]

[0020] The above object can be achieved by the following means: (1) The fiber has a flat cross section, and the flatness, which is the value obtained by dividing the length of the major axis of the cross section by the length of the minor axis, is 15 or more, and the average length of the minor axis is 1000 nm or less. The variation in the length of the minor axis of the cross section (CV value) is 20% or more, and the fiber has a continuous form in the fiber axis direction. A fiber bundle made of flat ultrafine fibers, characterized in that (2) In fibers with a flat cross section, The cross-sectional irregularity is 20% or more A fiber bundle made of the flat ultrafine fibers according to (1). (3) A fiber bundle made of flat ultrafine fibers according to (1) or (2), characterized in that the polymer constituting the flat ultrafine fibers is at least one polymer selected from the group consisting of polyester, polyamide, and polyolefin. (4) A fiber bundle made of flat ultrafine fibers according to any one of (1) to (3), characterized in that a functional substance is encapsulated within the fiber bundle. (5) A textile product at least partly comprising fiber bundles made of the flat ultrafine fibers according to any one of (1) to (4). [Effects of the Invention]

[0021] The present invention is based on a unique fiber bundle structure, which significantly increases the number of fibers arranged per unit volume, making it possible to adsorb large amounts of functional substances, and as these are encapsulated in the fiber bundles, it is suitable for use as a functional material with excellent durability. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram of an example of the cross-sectional structure of a flat ultrafine fiber of the present invention. [Figure 2] 1 is a schematic diagram of an example of the cross-sectional structure of a fiber bundle made of flat ultrafine fibers of the present invention. [Figure 3] FIG. 1 is a schematic diagram showing an example of the cross-sectional structure of a fiber bundle when a functional substance is added to the flat ultrafine fibers of the present invention. [Figure 4] 1 is a schematic diagram of an example of the cross-sectional structure of a multi-layer laminated fiber used as a raw material for the flat ultrafine fiber of the present invention. [Figure 5] FIG. 2 is a cross-sectional view illustrating an example of a method for producing a multilayer laminated fiber. [Figure 6]FIG. 1 is a schematic diagram of an example of a cross-sectional structure of a conventional flat fiber. [Figure 7] FIG. 1 is a schematic diagram of an example of a cross-sectional structure of a fiber bundle made of conventional flat fibers. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described in detail below together with preferred embodiments.

[0024] The flat ultrafine fibers of the present invention (FIG. 1) are characterized in that the cross section of the fiber is flat, the degree of flatness is extremely high, and the length of the minor axis is short.

[0025] The flat shape referred to here refers to a shape such as a rectangle or ellipse in which the length of the major axis and the length of the minor axis are different, and the degree of flatness of this shape is defined as the flatness, which is the value obtained by dividing the length of the major axis by the length of the minor axis. In the flat ultrafine fibers of the present invention, the flatness in the fiber cross section must be 15 or more.

[0026] The flatness referred to in the present invention is determined as follows (see also FIG. 1).

[0027] The flat ultrafine fibers of the present invention are embedded in an embedding agent such as epoxy resin, and the fiber cross section is cut using a microtome equipped with a diamond knife. This cross section is then photographed using a scanning electron microscope (SEM) or the like at a magnification that allows the cross section to be identified. For the cross section of a single fiber present in the photographed image, the maximum length of the cross section is measured using image analysis software, and this value is expressed as the length of the long axis of the single fiber, as an integer in nm, rounded to the nearest integer. Next, the length at the midpoint of the maximum length where a line segment perpendicular to the line segment of the maximum length intersects with the fiber cross section is measured, and this value is expressed as the length of the short axis of the single fiber, as an integer in nm, rounded to the nearest integer. The long axis length and short axis length are used to calculate the flatness of the single fiber using the following formula: Flatness = length in the major axis direction (nm) / length in the minor axis direction (nm) The above measurement is carried out for 100 fibers to calculate the flatness of each fiber, and the arithmetic average of these is defined as the flatness in the present invention.

[0028] The first requirement of the flat ultrafine fibers of the present invention is that they have a high degree of flatness in the fiber cross section, and as an index of the cross-sectional shape, the degree of flatness must be at least 15. If the degree of flatness is within this range, the specific surface area of ​​the fibers is increased by at least two times compared to that of a fiber with a round cross section of the same fineness, and the adsorption efficiency of the functional substance targeted by the present invention can be increased.

[0029] Furthermore, if the flatness is 15 or more, a unique fiber bundle structure (Figure 2) results from the shape. In other words, the high shape anisotropy places restrictions on the fiber arrangement direction, and each flat fiber overlaps with the same direction. This fiber bundle structure results in a significant increase in the number of fibers arranged per unit volume, which, combined with the effect of increasing the specific surface area of ​​each fiber mentioned above, achieves better adsorption efficiency.

[0030] The fiber bundle referred to here is not limited to any particular form of assembly, as long as it is an assembly of a plurality of flat ultrafine fibers, and includes bundles in which the individual fibers are clearly separated and bundles of individual fibers that appear to be a single coarse fiber.

[0031] Based on the above-mentioned technical concept, the higher the flatness, the greater the specific surface area of ​​the fiber, and the closer the fiber orientation becomes, resulting in a more closely packed arrangement that is advantageous for generating a larger fiber area. In other words, if the flatness is 30 or more, not only does the specific surface area of ​​the fiber increase by more than three times compared to round cross-section fibers of the same fineness, but the denser arrangement also results, resulting in a more pronounced increase in surface area. In such cases, the adsorption efficiency of functional substances is further improved, allowing their functions to be more effectively expressed, so a flatness of 30 or more is preferred.

[0032] Furthermore, if the flatness is 40 or more, the pronounced shape anisotropy prevents the fibers from overlapping due to the disordered fiber direction in some parts of the fiber bundle, resulting in a dense arrangement in which the fibers are uniformly oriented overall. Such an arrangement allows for uniform functionality without unevenness throughout the entire fiber bundle, so a flatness of 40 or more is more preferable.

[0033] Furthermore, if the flatness is 50 or more, even when fiber bundles made of flat ultrafine fibers are twisted into yarn, the fibers are arranged radially without disorder from the center of the fiber bundle, and the arrangement direction can be changed as desired while maintaining a uniform fiber orientation. This characteristic is highly effective in controlling the strength of the function derived from the functional substance, and when it is desired to change the fiber orientation direction, a flatness of 50 or more is particularly preferable.

[0034] Furthermore, as the flatness of the cross section increases, bending or cracking tends to occur more easily in the longitudinal direction of the cross section when an external force is applied during the processing step. However, if the flatness is less than 500, there is no problem in practical use, and the object of the present invention can be achieved.

[0035] As described above, the flat ultrafine fibers of the present invention have a very high degree of flatness, which increases the specific surface area (surface area per weight) compared to ordinary fibers, and furthermore, the fibers are densely arranged, which results in an extremely large fiber surface when made into a fiber assembly.

[0036] The specific surface area of ​​a single fiber is greatly affected not only by the flatness of the cross section but also by the fiber diameter, and the fiber diameter is also an important factor in order to fully utilize the surface area-increasing effect resulting from the cross-sectional shape. As an index of fiber diameter, the second factor for the flat ultrafine fibers of the present invention is that the length of the minor axis of the cross section is short, and the average length of the minor axis must be 1,000 nm or less.

[0037] The average minor axis length referred to here is the arithmetic mean of the minor axis lengths of 100 fibers measured above, rounded off to the nearest integer in nm.

[0038] In the flat ultrafine fibers of the present invention, if the average length of the minor axis thereof is 1000 nm or less, a specific surface area equal to or greater than that of ordinary ultrafine fibers can be obtained, and high adsorption efficiency can be achieved. For this reason, the average length of the minor axis of the cross section of the flat ultrafine fibers of the present invention must be 1000 nm or less.

[0039] As described above, the shorter the length of the minor axis of the cross section, the more effectively the specific surface area of ​​the single fiber is increased. Furthermore, since the length of the minor axis also affects the bending rigidity of the fiber, it also has an excellent effect on densifying the fiber bundle. In other words, the bending rigidity in the minor axis direction decreases in proportion to the cube of the length of the minor axis. As the length of the minor axis decreases, the fibers can flexibly deform to conform to irregularities and other conditions, making the fiber bundle structure more likely to be densified. If the average length of the minor axis is 800 nm or less, not only is the effect of increasing the specific surface area even greater, but the fibers can also deform to conform to the shape, effectively preventing the formation of large voids between the fibers, making it easier to form a dense structure. For these reasons, it is preferable that the average length of the minor axis is 800 nm or less.

[0040] Furthermore, if the average minor axis length is 500 nm or less, the flexibility of the fiber becomes extremely low, and the action of intermolecular forces such as van der Waals forces results in a fiber bundle in which the individual fibers are bonded together. In such cases, the gaps between the fibers become extremely small, ranging from several to several hundred nanometers, which is an excellent effect in terms of the expression of the high durability function described below, and therefore it is more preferable that the average minor axis length is 500 nm or less.

[0041] Furthermore, if the average length of the minor axis is 300 nm or less, the above-mentioned structure of aggregated single fibers will be uniform throughout the fiber bundle, and when functional processing is performed, uniform functionality will be exhibited throughout. For these reasons, it is particularly preferable that the average length of the minor axis is 300 nm or less.

[0042] In the flat ultrafine fibers of the present invention, as the length of the minor axis of the cross section becomes shorter, the fibers tend to be more likely to break when an external force is applied during the processing step. However, as long as the average length of the minor axis is 50 nm or more, the fibers can be used practically without any problems, and the object of the present invention can be achieved.

[0043] As described above, the flat ultrafine fibers of the present invention have a cross-sectional shape with a high degree of flatness, which significantly increases the specific surface area of ​​the fibers. Furthermore, the fibers are arranged in a dense, uniformly oriented bundle, resulting in a very large fiber surface per unit volume. Utilizing this large fiber surface not only dramatically increases the adsorption efficiency of functional substances, but also dramatically improves durability due to the unique fiber bundle structure. That is, when the flat ultrafine fibers of the present invention are functionally processed, not only is a large amount of the functional substance adsorbed onto the fiber surface, but it also penetrates between the flat ultrafine fibers that are aligned and overlapped, as shown in Figure 3. Therefore, while a large amount of the functional substance is encapsulated inside the fiber bundle, it is distributed in a way that it is hardly exposed on the surface of the fiber bundle. This makes it difficult for the functional substance to fall off due to abrasion, etc., and improves durability in terms of functionality.

[0044] From the viewpoint of utilizing the characteristics of the flat ultrafine fibers of the present invention to effectively exhibit their functions through functional processing, the ease with which functional substances can be impregnated is also important, and the variation in the length of the minor axis is a noteworthy indicator.

[0045] The variation in minor axis length referred to here is determined by calculating the arithmetic mean and standard deviation using the minor axis lengths of the 100 fibers measured above, and then dividing the standard deviation by the arithmetic mean to obtain a coefficient of variation, which is then rounded off to the nearest integer in percentage.

[0046] As described above, the bending rigidity of a fiber varies greatly depending on the length of the minor axis of the cross section, and therefore, if there is a moderate variation in the length of the minor axis, the behavior of each single fiber will be non-uniform, and for example, each single fiber will behave differently in a liquid containing a functional substance, resulting in good dispersion. In such a case, the fiber surface will be exposed to the liquid without being obstructed by other fibers, and the functional substance will be able to be efficiently adsorbed.

[0047] If the variation in the length of the minor axis is 10% or more, the single fibers tend to disperse well in a liquid, etc., and are easily impregnated with a functional substance, so it is preferable that the variation in the length of the minor axis is 10% or more.

[0048] Taking this idea further, the greater the variation in the minor axis length, the more non-uniform the behavior of each single fiber becomes and the more likely the single fibers are to be dispersed. If you want to effectively expose the surface of the single fiber and complete functional processing in a short time, it is more preferable that the variation in the minor axis length be 20% or more.

[0049] Furthermore, if the variation in the length of the minor axis is 40% or more, even in the case of a high-density woven or knitted fabric in which the yarn is tightly constrained, the liquid will be able to easily penetrate between the individual fibers, and if efficient functional processing is desired for a high-density woven or knitted fabric, a variation in the length of the minor axis of 40% or more is particularly preferable.

[0050] Furthermore, as the variation in the length of the minor axis increases, fibers with short minor axes are more likely to break when external forces are applied during the processing step. However, if the variation in the length of the minor axis is less than 70%, there is no problem in practical use, and the object of the present invention can be achieved.

[0051] Furthermore, the degree of unevenness on the fiber surface can sometimes improve the dispersion of single fibers during functional processing, and the degree of unevenness on the cross section is also a notable indicator. In other words, the presence of appropriate unevenness on the fiber surface creates tiny voids of several to several hundred nanometers between the fibers, and these tiny voids serve as starting points for the effective dispersion of single fibers in liquids containing functional substances.

[0052] The irregularity referred to here is determined by measuring the length of each line segment perpendicular to the maximum length line segment at each of the ten equal points on the image of the fiber cross section, calculating the arithmetic mean and standard deviation of these 10 lengths, and then dividing the standard deviation by the average value and rounding off to the nearest decimal place to obtain the irregularity of a single fiber. Similar measurements are performed on the cross sections of 10 fibers, and the arithmetic mean of the irregularities of the 10 fibers is the irregularity referred to here.

[0053] If the unevenness is 20% or more, the individual fibers are easily dispersed from the minute gaps between the fibers, and functional processing can be completed in a short time, so the unevenness is preferably 20% or more.

[0054] On the other hand, as the degree of unevenness increases, the load tends to concentrate on one part of the cross section, making it more likely to crack. However, if the degree of unevenness is less than 60%, there is no problem in practical use, and the object of the present invention can be achieved.

[0055] The flat ultrafine fibers of the present invention have a unique cross-sectional shape that allows the specific surface area to be significantly increased while maintaining the cross-sectional area of ​​the fiber. Therefore, the strength of the single fiber is equivalent to that of ordinary fibers, and there is no problem of unnecessary deterioration in the quality of textile products, resulting in excellent handleability. Furthermore, the flat ultrafine fibers of the present invention have a continuous form in the fiber axis direction, and since there are fewer fiber ends in the fiber bundle, the quality of textile products is less likely to be impaired and the handleability is excellent. The polymer constituting the flat ultrafine fibers is preferably a crystalline polymer in consideration of passability in ordinary advanced processing steps and practical use, and the polymer constituting the flat ultrafine fibers is preferably at least one polymer selected from the group consisting of polyesters, polyamides, and polyolefins. In addition to the above advantages, these polymers are thermoplastic, which allows the flat ultrafine fibers of the present invention to be produced by a highly productive melt spinning method and is also suitable from the viewpoint of adjusting mechanical properties, such as by highly oriented crystallization in the drawing step.

[0056] In the flat ultrafine fibers of the present invention, in consideration of practical use, the fiber strength is preferably 1 cN / dtex or more, and when used as fabrics or sheets to be used in relatively harsh environments, the fiber strength is preferably 2 cN / dtex or more, which is a more preferred range.

[0057] By utilizing the characteristics of the flat ultrafine fibers of the present invention, not only can a large amount of functional substance be adsorbed by functional processing to effectively exhibit its function, but also, by encapsulating the functional substance in the fiber bundles due to the unique fiber bundle structure, the functional substance is less likely to fall off, thereby exhibiting excellent durability. Furthermore, by utilizing this, a sustained release effect can be obtained in which the functional substance is gradually released by diffusing within the fiber bundles or by the fiber bundles being deformed by an external force. Therefore, when the flat ultrafine fibers of the present invention are used as a functional material in combination with a functional substance, it is preferable to process them into a state in which the functional substance is encapsulated in the flat ultrafine fiber bundles.

[0058] The term "functional substance" as used herein refers to a substance that actively imparts functionality to fibers, and is not particularly limited as long as it is a compound having a function. Furthermore, the functional substance may be an organic compound or an inorganic compound. Examples of the functionality include UV protection, fragrance, deodorization, antibacterial, insect repellent, moisture absorption, antistatic, flame retardant, stain resistance, beauty and health care, etc., but are not limited to these functions.

[0059] Furthermore, functional substances may exist in fibers in various forms, including chemical bonding, exhaustion, and physical adsorption. To dramatically improve functionality and improve durability and texture, it is preferable to process functional substances by making good use of the properties of the flat ultrafine fibers of the present invention. For example, by incorporating a specific functional substance into a fiber bundle through functional processing in a general solution, and then forming a film of another functional substance on the surface of the fiber bundle using a pad-drying method or the like, it is possible to combine two or more functions or to maximize the functionality achieved by the mutual effects of different functional substances.

[0060] As described above, by utilizing the characteristics of the flat ultrafine fibers of the present invention, a functional material having excellent durability and efficiently containing functional substances can be obtained. Therefore, the flat ultrafine fibers of the present invention can be used in a wide range of applications, from general clothing applications such as innerwear and outerwear to interior applications such as curtains and cloths, vehicle interior applications such as car seats, daily life applications such as wiping cloths and health products, applications for removing harmful substances such as filters, and industrial material applications such as battery separators.

[0061] An example of the method for producing the flat ultrafine fibers of the present invention will be described in detail below.

[0062] The method for producing the flat ultrafine fibers of the present invention is not particularly limited, but they can be obtained, for example, by removing the easily soluble polymer from a multi-layer laminated fiber (Figure 4) made of a hardly soluble polymer and an easily soluble polymer.

[0063] The term "multilayer laminated fiber" as used herein refers to a fiber having a laminated structure in which two or more types of polymers are laminated alternately or in random order in the cross section. The laminated structure may be one in which the lamination direction is the same in the fiber cross section, or one in which the lamination direction is radial, concentric, or irregularly changing, or a combination of these.

[0064] The method for producing the above-mentioned multilayer laminated fiber is not particularly limited, but it can be produced by a spinning process using a composite spinneret as described below, and from the viewpoint of high productivity, it is preferable to adopt melt spinning.

[0065] As the composite spinneret, for example, a composite spinneret shown in Figure 5 is preferably used, which is composed of three laminated components: a metering plate E, a composite plate F, and a discharge plate G. Incidentally, Figure 5 shows an example in which two types of polymers, i.e., component A and component B, are used; however, three or more types of polymers may be used for spinning if necessary. In this composite spinneret, the metering plate E measures the amount of polymer per hole in the composite plate F, the composite plate G combines the metered streams of different types of polymers to form a composite stream, which is then split and recombined to double the number of layers constituting the composite stream, and the discharge plate G compresses the composite stream formed in the composite plate F and discharges it. The composite stream referred to here means a fluid whose cross section perpendicular to the flow direction is composed of two or more types of polymers.

[0066] The composite plate F has microchannels H with confluences and branching sections, the number of which is greater than or equal to the number of discharge holes in the discharge plate G. The arrangement of the confluences and branching sections can be adjusted as needed to form a desired cross section. Note that the confluence section here refers to a section where two or more streams converge, and the branching section refers to a section where a stream splits into two or more. With this configuration, when different types of polymers pass through the composite plate F, the polymers flowing from each channel hole merge at the confluence section to form a composite stream, which then splits at the branching section. By repeating this process, the number of layers constituting the composite stream doubles, resulting in a multilayered structure. Note that the confluence and splitting mentioned here do not need to be repeated; the streams may merge and then recombine, or split and then split again. Furthermore, the fluid supplied to the microchannels of the composite plate F may be a pre-blended mixture of two polymers, or a composite stream formed by other methods may be used.

[0067] Furthermore, the microchannels of the composite plate F are configured to minimize turbulence in the flow channels, making it possible to produce multilayer laminated fibers. Incidentally, the above-mentioned microchannels can be said to have the same characteristics as conventional static mixers in that they merge or split fluids within the channels, but general static mixers have channels designed for mixing two types of polymers, which causes turbulence in the flow, making it difficult even for those skilled in the art to produce the above-mentioned multilayer laminated fibers.

[0068] Although not shown in the figure to avoid confusing the explanation of the composite spinneret, the components stacked above the metering plate E may be components that form flow paths in accordance with the spinning machine and spin pack. By designing the metering plate E to match existing flow path components, the existing spin pack and its components can be utilized as is. Therefore, there is no need to dedicate a spinning machine specifically to this spinneret. In practice, it is also advisable to stack multiple flow path plates between the flow path and the metering plate F or between the metering plate E and the composite plate F. 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 introduce the polymer into the composite plate F. The composite stream discharged from the discharge plate G is cooled and solidified, then coated with an oil and taken up by rollers at a specified peripheral speed to form a multilayer laminated fiber.

[0069] The composite spinneret described above can be used to produce multi-layer laminated fibers. It goes without saying that the use of the composite spinneret also makes it possible to produce multi-layer laminated fibers using a spinning method that uses a solvent, such as solution spinning.

[0070] When melt spinning is selected, the polymer constituting the multilayer laminate fiber can be, for example, a melt-moldable polymer such as polyethylene terephthalate or its copolymer, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, polyamide, polylactic acid, or thermoplastic polyurethane. Polycondensation polymers, such as polyester and polyamide, are particularly preferred because of their high melting points. These polymers may also contain various additives, such as inorganic substances such as titanium oxide, silica, or barium oxide; colorants such as carbon black, dyes, or pigments; flame retardants; fluorescent brighteners; antioxidants; or ultraviolet absorbers. When a polymer containing these additives is selected, unevenness will be generated in each layer of the multilayer laminate fiber depending on the particle size of the additive microparticles, and this can be used to impart any desired unevenness to the resulting flat ultrafine fibers.

[0071] A multi-layer laminated fiber is constructed by combining two or more of these polymers, and the combination of polymers is also important from the viewpoint of improving the laminated structure.

[0072] In other words, the smaller the difference in solubility parameters (SP values) between the combined polymers, the better the laminate structure formed without interlayer merging, and it is preferable to select polymers so that the difference in solubility parameters between the two polymers forming the interface is 3.0 or less. The solubility parameter (SP value) referred to here means a parameter that reflects the cohesive strength of a substance, defined as (evaporation energy / molar volume)1 / 2, and can be calculated, for example, from the values ​​listed on page 189 of "Plastics Data Book," co-edited by Asahi Kasei Amidas Co., Ltd. and the Plastics Editorial Department. The absolute value of the difference in solubility parameters referred to in the present invention is the difference in solubility parameters between one component and the other.

[0073] Furthermore, by using polymers with different solubilities, the easily soluble polymer in the multilayer laminated fiber can be removed, and flat ultrafine fibers made of the hardly soluble polymer can be efficiently produced. For example, if the polymers constituting the multilayer laminated fiber are an alkali-soluble polyester and an alkali-difficult-to-solve polyester, or an alkali-soluble polyester and a polyamide (which is hardly soluble in alkali), the alkali reduction treatment will effectively produce flat ultrafine fibers made of the hardly soluble polymer. In particular, it is preferable to use a polyester copolymerized with polyethylene glycol and sodium sulfoisophthalate, either alone or in combination, as the easily soluble polyester, from the viewpoints of spinnability and ease of solubility in low-concentration aqueous solvents. Examples of suitable polymer combinations for generating flat ultrafine fibers from multilayer laminated fibers include polyethylene terephthalate copolymerized with 5 mol % to 15 mol % of 5-sodium sulfoisophthalic acid as the readily soluble component, and polyethylene terephthalate copolymerized with the aforementioned 5-sodium sulfoisophthalic acid and 5 wt % to 15 wt % of polyethylene glycol having a weight average molecular weight of 500 to 3000 as the poorly soluble component, in terms of melting point, and polyethylene terephthalate or polyamide-6 as the poorly soluble component.

[0074] The spinning temperature for spinning multi-layer laminated fibers is set to the temperature at which the two or more polymers, primarily the high-melting-point or high-viscosity polymer, exhibit fluidity. The temperature at which fluidity is exhibited varies depending on the molecular weight, but it is preferably set between the melting point of the polymer and melting point + 60°C. A temperature below this level is preferable because it prevents thermal decomposition of the polymer in the spinning head or spin pack, thereby suppressing molecular weight reduction. Stable production of multi-layer laminated fibers can be achieved by setting the output rate for spinning to 0.1 g / min·hole to 20.0 g / min·hole. Furthermore, the ratio of component A to component B can be selected from a range of 5 / 95 to 95 / 5 in terms of the weight ratio of component A / component B based on the output rate. When flat ultrafine fibers are produced from multilayer laminated fibers using a hardly soluble polymer as component A and a readily soluble polymer as component B, a higher ratio of hardly soluble polymer is preferable from the viewpoint of productivity of flat ultrafine fibers, and when the ratio of component A / component B is 50 / 50 to 90 / 10, multilayer laminated fibers can be stably produced without any breaks in the laminated structure, and flat ultrafine fibers can be produced with high production efficiency.

[0075] The polymer stream thus discharged is cooled and solidified, and then applied with an oil and taken up by rollers with a specified peripheral speed to form a composite fiber. The take-up speed can be determined based on the discharge rate and the desired fiber diameter, but is preferably in the range of 100 to 7000 m / min to ensure stable production of the composite fiber used in the present invention. Drawing of the multilayer laminated fiber is recommended in order to achieve high orientation and improve its mechanical properties. This drawing can be performed after the fiber has been temporarily wound up in the spinning process, or it can be performed immediately without winding. For example, in a drawing machine consisting of one or more pairs of rollers, a fiber made of a polymer exhibiting thermoplasticity that can generally be melt-spun can be comfortably drawn in the fiber axis direction, heat-set, and then taken up, using a peripheral speed ratio between a first roller set at a temperature above the glass transition temperature and below the melting point and a second roller set at the crystallization temperature, to obtain a composite fiber having a composite cross section as shown in FIG. 1. The upper limit of the temperature of the first roller is preferably set to a temperature at which the fiber path is not disturbed during the preheating process. For example, in the case of polyethylene terephthalate, which has a glass transition temperature of around 70°C, the preheating temperature is usually set to around 80 to 95°C.

[0076] To obtain the flat ultrafine fibers of the present invention from the multilayer laminated fibers obtained as described above, the multilayer laminated fibers are immersed in a solvent capable of dissolving the easily soluble polymer to remove the easily soluble polymer, thereby obtaining flat ultrafine fibers made of a sparingly soluble polymer, and then fiber bundles thereof. When the easily soluble polymer is copolymerized polyethylene terephthalate copolymerized with 5-sodium sulfoisophthalic acid or the like, an alkaline aqueous solution such as a sodium hydroxide aqueous solution can be used. For example, the multilayer laminated fibers or a textile made thereof may be immersed in the alkaline aqueous solution. Heating the alkaline aqueous solution to 50°C or higher is preferred because it accelerates the progress of hydrolysis. While the method for generating flat ultrafine fibers from multilayer laminated fibers is not limited to the dissolution treatment described above, dissolving and removing the easily soluble polymer ensures separation into single flat ultrafine fibers made of a sparingly soluble polymer while minimizing fiber damage, thereby successfully producing the flat ultrafine fibers of the present invention. [Example]

[0077] The conjugate fiber of the present invention will be specifically described below with reference to examples. The examples and comparative examples were evaluated as follows.

[0078] A. Melt viscosity of polymer The measurement temperature was the same as the spinning temperature, and the melt viscosity of 1216 s-1 is recorded in the examples and comparative examples. The measurement was carried out in a nitrogen atmosphere, with a time interval of 5 minutes from when the sample was placed in the heating furnace to when the measurement started.

[0079] 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 differential scanning calorimeter (DSC) Model Q2000 manufactured by TA Instruments was used to measure the temperature from 0°C to 300°C at a heating 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 heating process. 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.

[0080] C. Solubility parameter difference The solubility parameter (SP value) is a parameter that reflects the cohesive strength of a substance, defined as the square root of (evaporation energy / molar volume). It can be determined by immersing a polymer in various solvents and using the (evaporation energy / molar volume) value of the solvent at which the swelling pressure is maximized as the (evaporation energy / molar volume) of the polymer. SP values ​​determined in this manner are listed, for example, on page 189 of "Plastics Data Book," co-edited by Asahi Kasei Amidas Corporation and the Plastics Editorial Department, and these values ​​can be used. The difference in solubility parameters between combined polymers is calculated as the absolute value of (SP value of component A minus SP value of component B).

[0081] D. Fineness The weight of 100 m of the composite fiber was measured and multiplied by 100. This measurement was repeated 10 times, and the average value was taken as the fineness (dtex). The value obtained by dividing the fineness by the number of filaments was taken as the single yarn fineness (dtex).

[0082] E. Worcester U% Using a Zellweger UT-4 fineness unevenness measuring device, the Worcester U% (H) of the composite fiber was measured under the conditions of a yarn supply speed of 100 m / min, a twister rotation speed of 6000 rpm, and a measurement length of 100 m.

[0083] F. Flatness The flattened ultrafine fibers were embedded in an embedding medium such as epoxy resin, frozen using a Reichert FC-4E cryosectioning system, and sectioned using a Reichert-Nissei Ultracut N (ultramicrotome) equipped with a diamond knife. Images of the sectioned surfaces were then taken using a Hitachi H-7100FA transmission electron microscope (TEM) at a magnification sufficient to visualize the cross section. Using image analysis software (WINROOF), the maximum length of the cross section of the single fiber was measured. This value was used as the long axis length of the single fiber, rounded to the nearest integer in nm. Next, the length of the line segment perpendicular to the longest line at the midpoint of the maximum length intersecting the fiber cross section was measured. This value was used as the short axis length of the single fiber, rounded to the nearest integer in nm. The flatness of the single fiber was calculated using the following formula: Flatness = length in the major axis direction (nm) / length in the minor axis direction (nm) The above measurement was carried out for 100 fibers to calculate the flatness of each fiber, and the arithmetic mean of these values ​​was rounded off to the nearest whole number to calculate the flatness.

[0084] G. Mean length of minor axis The arithmetic mean of the lengths of the minor axes of the 100 fibers measured above was rounded off to the nearest integer in nm to calculate the average length of the minor axis.

[0085] H. Variation in minor axis length (CV value) The arithmetic mean and standard deviation were calculated using the short axis lengths of the 100 fibers measured above, and the coefficient of variation obtained by dividing the standard deviation by the arithmetic mean was calculated by rounding off the decimal point to an integer in percentage units to calculate the variation in the short axis lengths.

[0086] I. Irregularity Using the image of the fiber cross section taken above, the maximum length of the cross section was divided into 10 equal parts, and the lengths at which line segments perpendicular to the maximum length intersected the fiber cross section were measured. The arithmetic mean and standard deviation of these 10 lengths were calculated, and the standard deviation was divided by the mean value and rounded to the nearest percent to calculate the irregularity of the single fiber. Similar measurements were made on the cross sections of 10 fiber pieces, and the arithmetic mean of the irregularities of the 10 single fibers was calculated as the irregularity.

[0087] J. Distribution of Functional Substances To model the distribution of functional substances when treated on fiber bundles, fabrics were treated with a dye solution containing Dystar's acid dye Telon Black LD02, which is non-dyeable to polyester, adjusted to 10% owf at a liquor ratio of 1:50, at a treatment temperature of 30°C, and for 30 minutes. The surface and cross section of the fabric were then observed with a Keyence VHX-6000 digital microscope. The distribution was evaluated based on the following criteria: Within the fiber bundle: Dye (coloring matter) is present between the fibers in the cross section of the fiber bundle. None: There is no dye (coloring matter) between the fibers in the cross section of the fiber bundle.

[0088] K. Functional processing (deodorizing processing) The fabric was treated with a 10% aqueous solution of dodecanedioic acid dihydrazide, which has the ability to adsorb acetaldehyde, at a solid content of 20% owf, a bath ratio of 1:20, a treatment temperature of 130°C, and a treatment time of 1 hour.

[0089] L. Deodorizing properties (acetaldehyde concentration) In a humidity-controlled environment of 20°C and 65%RH, 1 g of fabric was placed in a 5 L tetra bag, and 3 L of acetaldehyde with a concentration of 30 ppm was poured into the tetra bag. The gas concentration (ppm) inside the tetra bag after 10 minutes was measured using a gas detector tube (manufactured by Gastec Corporation).

[0090] M. Functional substance content The fabric before processing was dried at 110°C for 2 hours and its weight was measured (W1). The fabric after functional processing was dried at 110°C for 2 hours and its weight was measured (W2). From the weights before and after processing, the following formula was used: Functional substance content = (W2-W1) / W1 x 100 (%) The content of the functional substance was calculated by the above formula.

[0091] N. Functional substance content after washing The processed fabric was washed for 15 minutes, then dehydrated for 1 minute, rinsed for 6 minutes, then dehydrated for 1 minute, and dried for 50 cycles. The washing conditions were a water temperature of 40°C, a bath ratio of 1:30, and 0.5 g / L of "Top" (Lion Corporation) detergent. The rinsing conditions were a water temperature of 20°C, and an overflow bath ratio.

[0092] After washing, the fabric was dried at 110°C for 2 hours and weighed (W3). Functional substance content after washing = (W3-W1) / W1 x 100 (%) The content of the functional substance was calculated by the above formula.

[0093] [Example 1] The components A and B were polyethylene terephthalate (PET, melt viscosity: 120 Pa s, melting point: 254°C, SP value: 21.4 MPa), and polyethylene terephthalate copolymerized with 8.0 mol% 5-sodium sulfoisophthalic acid and 9 wt% polyethylene glycol (SSIA-PEG copolymerized PET, melt viscosity: 95 Pa s, melting point: 233°C, SP value: 22.9 MPa), respectively. The difference in solubility parameters between these polymers was 1.5 MPa.

[0094] After melting components A and B separately at 290°C, the resulting mixture was fed into a spinning pack equipped with a composite spinneret (see Figure 5) with a composite ratio of 80 / 20. A composite polymer stream was extruded from the extrusion holes. The composite plate had a microchannel F capable of laminating the two components alternately in 128 layers. The composite stream was extruded to form a composite structure with alternating multilayer laminations of the two polymers in one direction, as shown in Figure 4. The extruded composite polymer stream was cooled and solidified, then coated with an oil and wound at a spinning speed of 1000 m / min to obtain an undrawn fiber with a diameter of 300 dtex and 24 filaments (total throughput of 30 g / min). The wound undrawn fiber was drawn 3.6 times between rollers heated to 90°C and 130°C, yielding a drawn fiber with a diameter of 84 dtex and 24 filaments. The fineness uniformity index (U%(H)) was 0.6%, demonstrating excellent thickness uniformity along the fiber axis. When the cross-sectional shape of the obtained multi-layer laminated fiber was observed, it was found to have a plate-like laminated structure with the lamination direction aligned as shown in FIG.

[0095] This multi-layer laminated fiber was immersed in a 1% sodium hydroxide aqueous solution (bath ratio 1:50) heated to 90°C for 30 minutes, removing over 99% of the SSIA-PEG copolymerized PET (component B), yielding flat ultrafine fibers. A fabric woven from the multi-layer laminated fiber was also treated in the same way, yielding a fabric composed of flat ultrafine fibers.

[0096] Observation of the cross section of the obtained flat ultrafine fibers revealed a ribbon-like cross section with significantly different lengths of the major and minor axes, a flatness of 80, and an average minor axis length of 225 nm. The variation in the length of the minor axis of the cross section was 36%, and the irregularity was 30%, indicating a moderate variation in the length of the minor axis and moderate irregularities on the surface. Observation of the cross section of the obtained woven flat ultrafine fibers revealed that numerous flat ultrafine fibers were overlapping with their minor axes aligned, forming a dense fiber bundle structure. Furthermore, the individual flat ultrafine fibers were aggregated as if they were bonded together, and extremely fine gaps of several to several hundred nanometers were present between the fibers.

[0097] A fabric made of flat ultrafine fibers was immersed in a dye solution containing a dye-resistant dye (acid black dye) adjusted to 10% owf, with a bath ratio of 1:50, a processing temperature of 30°C, and a processing time of 30 minutes.In the cross section, the spaces between the flat ultrafine fibers were colored black, the dye was contained within the fiber bundles, and the surface of the fabric was also colored black.

[0098] A fabric composed of flat ultrafine fibers was treated with a 10% aqueous solution of dodecanedioic acid dihydrazide at 20% owf solids, a bath ratio of 1:20, a treatment temperature of 130°C, and a treatment time of 1 hour to achieve a deodorizing finish. When the acetaldehyde removal ability was evaluated, the initial concentration of 30 ppm was reduced to 2 ppm in 10 minutes, demonstrating high deodorizing properties. Furthermore, the functional substance content was 5.0%, and the content after washing did not decrease significantly, at 4.2%, demonstrating that a large amount of the functional substance was adsorbed, yet was highly durable and resistant to shedding. The results are shown in Table 1.

[0099] [Examples 2 and 3] The same procedure as in Example 1 was repeated, except that the composite plate used had microchannels in which both components were stacked in 64 layers (Example 2) and 32 layers (Example 3). These multilayer laminated fibers were subjected to the same dissolution treatment as described above to produce flat ultrafine fibers. The evaluation results of these flat ultrafine fibers are shown in Table 1. Examples 2 and 3 had extremely thin cross-sectional shapes with high flatness, although to different degrees, and moderate minor axis length variation and irregularity. Similar to Example 1, the flat ultrafine fibers had a dense fiber bundle structure in which the directions of the flat ultrafine fibers were aligned and stacked. However, compared to Example 1, the flatness decreased and the average minor axis length increased, resulting in coarse interfiber spaces in the fiber bundles and fewer aggregated individual fibers. When immersed in a dye-resistant dye, the dye was distributed as if encapsulated within the fiber bundles. Compared to Example 1, the specific surface area decreased, resulting in a slight decrease in the content of the functional substance, but a high content remained, demonstrating sufficient deodorizing properties. Furthermore, even after washing, the content of the functional substance was maintained at a high level, and the functional substance was less likely to come off.

[0100] [Examples 4 and 5] The same procedure as in Example 1 was repeated, except that the composite plate used was changed to one with microchannels, in which both components were stacked in 256 layers (Example 4) and 512 layers (Example 5). These multilayer laminated fibers were subjected to the same dissolution treatment as described above to produce flat ultrafine fibers. The evaluation results of these flat ultrafine fibers are shown in Table 1. In Examples 4 and 5, the flat ultrafine fibers had an extremely thin, ribbon-like cross section with extremely high flatness, moderate minor axis length variation, and unevenness. Similar to Example 1, the flat ultrafine fibers had a dense fiber bundle structure in which the flat ultrafine fibers were aligned and stacked. However, compared to Example 1, the flatness increased and the average minor axis length decreased, resulting in extremely small interfiber voids of several to several tens of nanometers. The individual fibers were aggregated throughout the fiber bundle, as if they were bonded together. When immersed in a dye-resistant dye, the dye was distributed as if it were encapsulated in the fiber bundle. During functional processing, the average length of the minor axis was extremely short, so the fabric was excessively soft and had poor handleability. Compared to Example 1, the specific surface area increased, so the content of the functional substance increased, resulting in excellent deodorizing properties. Furthermore, because the fiber bundles had a strong agglomerated structure that encapsulated the functional substance, the content of the functional substance was less likely to decrease even after washing, and the functional substance was able to be retained with high durability.

[0101] [Comparative Example 1] The same procedures as in Example 1 were carried out using polyethylene terephthalate (PET, melt viscosity: 120 Pa s, melting point: 254°C, SP value: 21.4 MPa) melted at 290°C, then introduced into a single spinning pack and extruded from the nozzle. The evaluation results of this single fiber are shown in Table 1. It was a round cross-section fiber with a typical fiber diameter, a small specific surface area, and a sparse structure with large distances between individual fibers even in a fiber bundle. Even when immersed in a dye-resistant dye, no dye adhesion was observed. Furthermore, due to the small specific surface area, the content of the functional substance was low, resulting in poor deodorizing properties. Furthermore, the content of the functional substance decreased to nearly zero upon washing, and the functional substance attached to the fiber surface was easily removed.

[0102] Comparative Example 2 The same procedures as in Example 1 were carried out, except that a spinning pack incorporating a 64-island-sea composite spinneret in which component A was an island component and component B was a sea component was used. The sea-island composite fibers were subjected to the same dissolution treatment as described above to produce ultrafine fibers. The evaluation results of the ultrafine fibers are shown in Table 1. The ultrafine fibers had a significantly reduced fiber diameter and a large specific surface area. Furthermore, the distance between the individual fibers in the fiber bundle was short. When immersed in a dye-resistant dye, the fabric was not colored, and no dye adhesion was observed between the fibers. When functional processing was performed, the increase in specific surface area due to the ultrafine fiber size resulted in moderate adhesion of the functional substance, but did not result in high deodorizing properties, and the amount of functional substance adsorbed was significantly reduced by washing.

[0103] Comparative Example 3 The same procedure as in Example 1 was repeated, except that a composite plate with microchannels was used to stack both components in eight layers. The multilayer laminated fiber was subjected to the same dissolution treatment as described above to produce flat fibers. The evaluation results of the flat fibers are shown in Table 1. They had a cross-sectional shape with low flatness, as shown in Figure 6. Furthermore, due to the low flatness, the flat fibers were not aligned in the same direction, resulting in a fiber bundle structure with large distances between individual fibers, as shown in Figure 7. Even when immersed in a dye-resistant dye, no dye adhesion was observed. Furthermore, due to the small specific surface area, the content of the functional substance was low, resulting in poor deodorizing properties. Furthermore, the content of the functional substance decreased to nearly zero upon washing, and the functional substance attached to the fiber surface was easily removed.

[0104] [ reference Example 6] The method described in Example 1 was carried out in the same manner as in Example 1, except that a composite plate with a different flow path diameter from the micro flow path F having a junction and a branching portion was used. The multilayer laminated fiber was subjected to the same dissolution treatment as above to generate flat ultrafine fibers. The evaluation results of these flat ultrafine fibers are shown in Table 2, and they had an extremely thin cross-sectional shape with a high degree of flatness similar to that of Example 1. However, due to changes in the flow path design of the composite plate, the minor axis length variation and unevenness were small and uniform. Furthermore, similar to Example 1, the fiber bundle structure was dense, with the flat ultrafine fibers aligned and stacked, but due to the small unevenness, there was a higher proportion of fine voids of several to several hundred nanometers between the fibers of the fiber bundles compared to Example 1. When immersed in a dye-resistant dye, the dye was encapsulated in the fiber bundles but was not uniformly distributed throughout, and some areas were observed where the dye was not encapsulated. Furthermore, compared to Example 1, the dispersibility of the single fibers was low, so the functional substance content was somewhat lower, but the functional substance was less likely to come off during washing.

[0105] [Example 7] The same procedure as in Example 1 was repeated, except that the component A was polyamide-6 (N6, melt viscosity: 100 Pa s, melting point: 225°C, SP value: 23.7 MPa) and the component B was polyethylene terephthalate copolymerized with 8.0 mol% 5-sodium sulfoisophthalic acid and 9 wt% polyethylene glycol (SSIA-PEG copolymerized PET, melt viscosity: 95 Pa s, melting point: 233°C, SP value: 22.9 MPa), and the fibers were spun at 280°C. The difference in solubility parameters between the combined polymers was 0.8 MP. This multilayer laminated fiber was subjected to the same dissolution treatment as above to produce flat ultrafine fibers. The evaluation results of this flat ultrafine fiber are shown in Table 2. It had a highly flat and ultrathin cross-sectional shape similar to that of Example 1, but due to the hydrogen bonding between the fibers, the fiber bundle had a more densely aggregated structure than that of Example 1. When functionally processed, the fabric showed the same content of functional substances as in Example 1. However, because the fibers were connected by hydrogen bonds, they swelled during washing and were easily redispersed into individual fibers, and the functional substances were more likely to fall off during washing than in Example 1.

[0106] [Example 8] The same procedure as in Example 1 was repeated, except that component A was polypropylene (PP, melt viscosity: 70 Pa·s, melting point: 165°C, SP value: 16.8 MPa) and component B was polyethylene terephthalate copolymerized with 8.0 mol% 5-sodium sulfoisophthalic acid and 9 wt% polyethylene glycol (SSIA-PEG copolymerized PET, melt viscosity: 95 Pa·s, melting point: 233°C, SP value: 22.9 MPa), and the fibers were spun at 280°C. The difference in solubility parameters between the combined polymers was 6.1 MPa. Observation of the cross-sectional morphology of this multilayer laminated fiber revealed that the large difference in solubility parameters resulted in unstable cross-sectional formability and, unlike Example 1, an irregular laminated structure in which the lamination direction changed locally on the cross section was observed. This multilayer laminated fiber was subjected to the same dissolution treatment as described above to produce flat ultrafine fibers. The evaluation results of this flat ultrafine fiber are shown in Table 2. Compared to Example 1, the flatness was lower and the specific surface area was reduced, so the content of the functional substance was reduced, but the content was high and the functional substance was less likely to fall off when washed.

[0107] [Table 1]

[0108] [Table 2] [Explanation of symbols]

[0109] A: Flat ultrafine fiber B: Functional substance C:A component D:B component E: Weighing plate F: Composite plate G: Discharge plate H: Fine channel I: Flat fiber

Claims

1. A fiber bundle made of flat ultrafine fibers, characterized in that the fibers have a flat cross section, the degree of flatness, which is the value obtained by dividing the length of the major axis of the cross section by the length of the minor axis, is 15 or more, the average length of the minor axis is 1000 nm or less, the variation in the length of the minor axis of the cross section (CV value) is 20% or more, and the fiber bundle has a continuous form in the fiber axis direction.

2. 2. The fiber bundle of claim 1, wherein the flat ultrafine fibers have a cross-sectional irregularity of 20% or more in the fibers having a flat cross section.

3. 3. The fiber bundle made of flat ultrafine fibers according to claim 1 or 2, wherein the polymer constituting the flat ultrafine fibers is at least one polymer selected from the group consisting of polyester, polyamide, and polyolefin.

4. A fiber bundle made of flat ultrafine fibers according to any one of claims 1 to 3, characterized in that a functional substance is encapsulated within the fiber bundle.

5. A textile product at least partly comprising fiber bundles made of the flat ultrafine fibers according to any one of claims 1 to 4.

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