composite fiber

Abstract

The present invention provides a composite fiber wherein the sum of the lengths of interfaces that are formed by two or more kinds of polymers that constitute a fiber cross-section is extremely large. A composite fiber according to the present invention has a fiber cross-section which is composed of two or more kinds of polymers that form a plurality of interfaces; the value obtained by dividing the sum of the interface lengths between two kinds of polymers by the area of the fiber cross-section is 0.0010 nm-1 or more; and the interfaces are continuous in the fiber axis direction.

Description

[Technical Field]

[0001] The present invention relates to bicomponent fibers and multifilaments composed of two or more components. [Background technology]

[0002] Synthetic fibers made from polyester, polyamide, and other materials have excellent mechanical properties and dimensional stability, making them suitable for a wide range of applications, from clothing to industrial use. In recent years, the diversification of applications has progressed, and the required properties have become more sophisticated and multifunctional, which may not be possible with fibers made from existing polymers. While it is possible to achieve the required properties by designing a new polymer, the composite spinning method of combining existing polymers is often chosen to reduce the development costs and time required.

[0003] In fibers produced by the conjugate spinning method, so-called conjugated fibers, the main polymer is coated with another polymer in the fiber cross section (cross section in the axial direction of the fiber), and this allows for the impartation of aesthetic effects such as appearance and texture that cannot be achieved with fibers made of a single polymer. Furthermore, even if a functional polymer has problems with chemical resistance, heat resistance, etc. and is therefore not suitable for practical use when used alone, conjugated fibers can be used with dramatically improved chemical resistance, heat resistance, etc. by coating it with another polymer.

[0004] There are a wide variety of composite fibers with different composite forms and intended effects, but a common problem is that if the polymers being combined have poor compatibility, the interface where the two polymers come into contact will peel when the fiber is subjected to an external force such as an impact. This interfacial peeling not only impairs the intended effect, but also causes cracks to propagate to the fiber surface, leading to frequent yarn breakage during spinning and advanced processing, making stable production itself difficult.

[0005] These problems may be solved by devising a composite form of the composite fiber. For example, Patent Documents 1, 2 and 3 propose composite fiber forms.

[0006] Patent Document 1 proposes a fiber with a composite cross section in which a series of laminated structures in which two types of polymers are alternately laminated are joined in a direction perpendicular to the lamination direction. This technology aims to improve processability by forming a large number of film-like elements that make up the fiber cross section, increasing the interface area of ​​each film-like element, and by having a backbone-like skeleton that connects the laminated structures act as a core to support each film-like element, thereby suppressing interfacial delamination.

[0007] Patent Document 2 proposes a composite fiber in which the outer periphery of a laminated structure in which two types of polymers are alternately laminated is covered with a protective layer. Like Patent Document 1, this is a technology aimed at suppressing interfacial delamination of the laminated structure, and aims to improve abrasion resistance by covering the outer periphery of the laminated structure with a high-strength polymer of a specific thickness.

[0008] Patent Document 3 also proposes a composite fiber in which the entire periphery of a laminated structure in which two types of polymers are alternately laminated is coated. The provision of a coating on the outermost periphery of the laminated structure aims to reduce peeling and splitting during processing and improve processability, which is a technical idea similar to that of Patent Document 2. However, this technology aims to produce ultrafine fibers by deteriorating the outermost periphery coating through treatment under specific conditions, thereby promoting peeling and splitting. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP-A-1-132812 (pages 1-2) [Patent Document 2] JP 11-181630 A (Claims) [Patent Document 3] JP 2000-282333 A (pages 1-3) Summary of the Invention [Problem to be solved by the invention]

[0010] Although Patent Document 1 describes that the fiber cross section is composed of many film-like elements, the examples actually produced consist of two structures, each of which is made up of at most 50 to 65 layers, joined side by side, and there is a limit to the interfacial length, which is sometimes insufficient to prevent peeling of each film-like element. Furthermore, even if an attempt was made to increase the number of layers by devising a manufacturing method, it was impossible to stably increase the number of layers due to the principles of the manufacturing method.

[0011] In Patent Documents 2 and 3, the presence of a protective layer that provides abrasion resistance may be effective in suppressing interfacial delamination against weak friction acting on the fiber surface. However, the laminated structure inside the fiber only has the same number of layers as in Patent Document 1, and interfacial delamination may occur when a large external force is applied or when repeatedly rubbed. Furthermore, when interfacial delamination occurs, cracks caused by the delamination may propagate to the protective layer on the fiber surface, making the structure relatively weak, particularly against repeated rubs. When the multilayer laminated structure is exposed to the surface, exposure to chemicals or heat may significantly impair the fiber's properties and significantly reduce its quality.

[0012] As described above, it has been difficult to prevent interfacial peeling inside the fibers obtained by conventional conjugate spinning methods. Moreover, even if apparent fiber splitting or the like can be prevented by covering the outer periphery of the laminate structure, there is a high possibility that interfacial peeling will occur in the internal laminate structure, and there have been cases where the use of such a method has been limited from the viewpoint of durability.

[0013] For this reason, there has been a strong demand for composite fibers with improved durability, such as abrasion resistance, chemical resistance, and heat resistance. [Means for solving the problem]

[0014] The above object can be achieved by the following means. (1) A composite fiber made of two or more polymers, having a fiber cross section in which multiple interfaces are formed, and the sum of the lengths of the interfaces of the two polymers divided by the area of ​​the fiber cross section is 0.0010 nm -1 The composite fiber is as described above, and the interface is continuous in the fiber axial direction. (2) The sum of the interfacial lengths of the two polymers divided by the cross-sectional area of ​​the fiber is 0.0050 nm -1 The conjugated fiber according to (1) above. (3) The composite fiber according to (1) or (2), wherein the cross section of the fiber has a multilayer structure in which two types of polymers are alternately laminated. (4) The conjugated fiber according to any one of (1) to (3) above, wherein the layer thickness variation (CV value) of at least one type of polymer is 10% or more. (5) The composite fiber according to any one of (1) to (4) above, wherein the average layer thickness of at least one of the polymers is 1000 nm or less. (6) A multifilament consisting of flat ultrafine fibers composed of one type of polymer obtained by removing one type of polymer from the two types of polymers constituting the multilayer laminate structure from the composite fiber described in (3) above. (7) The flat ultrafine fibers have a flat cross section, a 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 of the cross section, of 15 or more, and an average thickness of the flat ultrafine fibers is 1000 nm or less. (8) The multifilament according to (6) or (7), wherein the thickness variation (CV value) of the flat ultrafine fibers is 10% or more. (9) The multifilament according to any one of (6) to (8), wherein the polymer constituting the flat ultrafine fibers includes at least one polymer selected from the group consisting of polyester, polyamide, and polyolefin. (10) The multifilament according to any one of (6) to (9) above, wherein a functional substance is encapsulated within the fiber bundle made of the flat ultrafine fibers. (11) A textile product at least partly comprising the conjugated fiber according to any one of (1) to (5) above or the multifilament according to any one of (6) to (10) above. [Effects of the Invention]

[0015] In the conjugated fiber of the present invention, even when an external force is applied to the fiber, the increased interfacial length between the polymers distributes the force evenly among the multiple interfacial surfaces present in the fiber cross section, preventing the load from concentrating on one part of the fiber cross section, and therefore, even in a fiber formed by conjugating two or more types of polymers, peeling between the components is significantly prevented. Thus, conjugated fibers and multifilaments having excellent durability, such as abrasion resistance, chemical resistance, and heat resistance, can be provided. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of a cross section of a unidirectional laminated fiber according to one embodiment of the present invention. [Figure 2] FIG. 2 is a partially enlarged view of FIG. [Figure 3] FIG. 3 is a schematic diagram of a cross section of a radially laminated fiber according to another embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram of a cross section of a concentric circular laminate fiber according to another embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram of a cross section of a flat ultrafine fiber constituting the multifilament of the present invention. [Figure 6] FIG. 6 is a schematic diagram of a cross section of a multifilament of the present invention. [Figure 7] FIG. 7 is a schematic diagram of a cross section of a multifilament of the present invention to which a functional substance has been applied. [Figure 8] FIG. 8 is a cross-sectional view of a composite spinneret for illustrating an example of the method for producing a composite fiber of the present invention. [Figure 9] FIG. 9 is a schematic diagram of a cross section of a conventional coated unidirectional laminated fiber. [Figure 10] FIG. 10 is a schematic diagram of a cross section of a conventional flat fiber. [Figure 11] FIG. 11 is a schematic diagram of a cross section of a fiber bundle made of conventional flat fibers. DETAILED DESCRIPTION OF THE INVENTION

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

[0018] The composite fiber referred to in the present invention is a fiber composed of two or more polymers. The composite fiber of the present invention is characterized by having a composite morphology in which the total length of the interfaces (interface lengths) formed by the two polymers is much longer than that of conventional composite fibers in a cross section (fiber cross section) taken along the axial direction of the fiber. The composite morphology in which the sum of the interfacial lengths formed by the two types of polymers is extremely large is defined by the sum of the interfacial lengths and the area of ​​the fiber cross section (hereinafter also referred to as the fiber cross section area). The interfacial length is the length of the interface between the two types of polymers that is continuous in the fiber axis direction in the fiber cross section, and the value obtained by dividing the sum of the interfacial lengths by the fiber cross section area is 0.0010 nm. -1 It refers to a complex form that is the above.

[0019] The value obtained by dividing the sum of the interfacial lengths by the cross-sectional area of ​​the fiber in the present invention is determined as follows. That is, a multifilament made of the composite fiber is embedded in an embedding agent such as epoxy resin, and an image of the cross section is taken with a transmission electron microscope (TEM) at a magnification that allows the interfaces of each polymer to be identified. If an entire interface cannot fit within a single image, the position where the first image was taken is set as the starting position, and a series of images can be taken by tracing the same interface within the fiber cross section until it returns to the starting position. Note that if the interface extends to the outer periphery of the fiber cross section, a series of images can be taken by tracing the outer periphery until it returns to the starting position. In this case, it is preferable to apply electronic staining to only a specific polymer, as this will clarify the contrast of the interface and allow the measurements described below to be carried out efficiently.

[0020] Using image analysis software, the measurement start point is arbitrarily determined for one interface in the image from the start position of the shooting, and the same interface is traced from the measurement start point through a series of cross-sectional images, measuring the length until it returns to the measurement start point. In this case, if the measurement reaches the outer periphery of the fiber cross section before returning to the measurement start point, the length of the part passing through the outer periphery is not included in the measurement. This value is the interface length of one interface, and is expressed as an integer in nm (rounded to the nearest integer). Similar measurements are performed on all interfaces in the fiber cross section, and the sum of the interface lengths is added up and divided by the fiber cross-sectional area to calculate the value in nm. -1 The fiber cross-sectional area is calculated by taking a two-dimensional image of a single fiber cross-section using a stereo microscope at a magnification that allows the entire cross-section to be observed, extracting the cross-section using image analysis software and binarizing it, and calculating the area in nm 2 It is determined by rounding off to the nearest integer. When the cross section of the conjugated fiber of the present invention is composed of three or more types of polymers, it is the sum of the interfacial lengths of the interfaces of all combinations of polymers, not just the interfaces of two specific types of polymers.

[0021] The composite fiber of the present invention is characterized by having a composite morphology in which the sum of the lengths (interface lengths) of the interfaces formed by two adjacent polymers in the cross section of the fiber is extremely large, and an index of the composite morphology is a value obtained by dividing the sum of the interface lengths by the cross-sectional area of ​​the fiber of 0.0010 nm. -1 or more, and the interface must be continuous in the fiber axial direction. This range means that the interfacial length per unit area of ​​the fiber cross section is extremely large, and that the two or more polymers forming the composite cross section are finely divided into many elements. The term "elements" used here refers to polymers that are separated by being surrounded by different types of polymers in the fiber cross section.

[0022] As described above, the composite fiber of the present invention is characterized in that, in the cross section of the fiber, different types of polymers are finely divided into an extremely large number of elements, and the composite morphology has an extremely large total interfacial length formed by the two types of polymers compared to conventional fibers. This composite morphology can provide a variety of excellent effects, such as those described below.

[0023] That is, since the sum of the interfacial lengths of the composite fiber of the present invention is extremely large, even when an external force is applied to the fiber, the force is distributed to the multiple interfaces present in the cross section of the fiber, and the load is prevented from concentrating on one part of the fiber cross section. Therefore, even in a fiber composed of two or more types of polymers combined together, peeling between the components can be significantly prevented.

[0024] The sum of the interface lengths of the composite fiber of the present invention divided by the cross-sectional area of ​​the fiber is 0.0010 nm -1 If the above conditions are met, even when a composite fiber is made from two types of polymers with poor affinity, interfacial peeling between the components is unlikely to occur, and yarn breakage is unlikely to occur during spinning or advanced processing. Not only does this ensure good operability, but it also allows the fiber to be processed into a high-quality textile.

[0025] The larger the value obtained by dividing the sum of the interfacial lengths by the cross-sectional area of ​​the fiber, the more suitable it is in terms of evenly distributing the force to the multiple interfaces present in the cross-sectional area of ​​the fiber. -1 If the above condition is met, even if a composite fiber is made of two types of polymers with poor affinity and is used in applications such as ordinary clothing where it is subjected to relatively weak abrasion, the effect of suppressing peeling between the components can be obtained, and this can be cited as a preferred embodiment. -1If the value is more than this, even when the composite fiber composed of two types of polymers with poor affinity is used in applications where it is subjected to moderate abrasion, such as outdoor products, peeling between the components can be effectively suppressed, and this can be cited as a more preferable embodiment. -1 If the above conditions are met, peeling between components is suppressed even when the film is used in applications where it is repeatedly subjected to strong abrasion, such as workwear, and this can be cited as a particularly preferred embodiment.

[0026] In addition, in the composite fiber of the present invention, the value obtained by dividing the sum of the interface lengths by the cross-sectional area is 0.0050 nm -1 As a result, in addition to the improved mechanical properties described above, even if one of the components constituting the composite fiber is a polymer with poor chemical resistance or heat resistance, excellent chemical resistance or heat resistance can be imparted by using a polymer with excellent chemical resistance or heat resistance as the other component. The improved chemical and thermal properties are achieved by a layer formed near the interface, which combines the properties of two polymers, becoming apparent due to a dramatic increase in the interface length. That is, in layers formed near the interface of different polymers, molecular chains of the different polymers may interpenetrate, forming an interface layer combining the properties of the two polymers. When the interface length in the fiber cross section is dramatically increased, as in the composite fiber of the present invention, the interface layer accounts for a large proportion, and the properties of the interface layer become apparent, thereby demonstrating an excellent effect in terms of combining the polymer properties.

[0027] In the composite fiber of the present invention, the value obtained by dividing the sum of the interface lengths by the cross-sectional area of ​​the fiber is 0.0050 nm -1If the value is greater than or equal to this, the ratio of the interface layer in the fiber cross section is high, and even when a composite fiber composed of an easily soluble polymer and a sparingly soluble polymer is subjected to a dissolution treatment, the weight loss of the fiber after the treatment is slight, and excellent chemical resistance is obtained, so this can be cited as a preferred embodiment. The larger the value obtained by dividing the sum of the interface lengths by the cross-sectional area of ​​the fiber, the more preferable it is from the viewpoint of increasing the ratio of the interface layer in the fiber cross section, and the value obtained by dividing the sum of the interface lengths by the cross-sectional area is 0.0200 nm or less. -1 If the fiber has a thickness of 0.050 nm or more, even if the fiber is subjected to a chemical treatment for a long time, the loss in fiber weight can be kept extremely small, and this can be cited as a more preferable embodiment. -1 If the above conditions are met, deterioration of fiber properties such as mechanical properties is significantly suppressed even after long-term chemical treatment, and therefore this can be cited as a particularly preferred embodiment.

[0028] In this way, in the composite fiber of the present invention, the larger the value obtained by dividing the sum of the interfacial lengths by the cross-sectional area of ​​the fiber, the more remarkable the effect of the characteristic cross-sectional shape becomes. A preferable upper limit of this value is 1.000 nm. -1 In general, the interface where different types of polymers come into contact is prone to hydrodynamic instability, and when the interface length is extremely long as in the present invention, it may be difficult to stably form a continuous interface. The value obtained by dividing the sum of the interface lengths by the cross-sectional area of ​​the fiber is 1.000 nm. -1 If the upper limit is less than this, even when polymers with different rheological properties are composited, a continuous interface in the fiber axial direction can be formed relatively easily, making it possible to apply a variety of polymer combinations to the composite fiber of the present invention, and this can be considered as a preferred upper limit.

[0029] As described above, the conjugated fiber of the present invention is characterized by having a conjugated morphology in which the interfacial length formed by the two types of polymers is extremely large, and this conjugated morphology not only brings about excellent effects in terms of mechanical properties, but also makes it possible to achieve excellent effects in terms of chemical properties and thermal properties due to the further increase in the interfacial length. Although there are a wide variety of conjugated morphologies in which the interfacial length is extremely large, from the viewpoint of enhancing the effects achieved by the conjugated fiber of the present invention, it is preferable that the cross section of the conjugated fiber of the present invention has a multilayer laminate structure in which two types of polymers are alternately laminated.

[0030] With the composite fiber of the present invention, different types of polymers are finely divided into an extremely large number of film-like elements (layers) in the cross section of the fiber, and even if a crack occurs due to interfacial delamination in one of the many layers constituting the cross section, the fine structure of the layers can prevent the crack from propagating. This prevents the fracture from progressing in the radial direction of the fiber cross section, and effectively prevents fibrillation and fiber splitting even when the fiber is subjected to repeated abrasion.

[0031] From the perspective of preventing crack propagation, the greater the number of layers in the multilayer laminate structure of the fiber cross section, the more precisely the cracks can be contained within a smaller area. For applications such as industrial products that are subject to repeated strong abrasion, a number of layers of two polymers of 250 or more can effectively suppress fibrillation of the fiber surface, and this is considered a preferred range. Furthermore, for applications where cracks are particularly likely to occur, such as repeated bending, a number of layers of 500 or more can effectively prevent crack propagation within an extremely small area of ​​the fiber cross section, and this is considered a more preferred range. The number of layers here refers to the total number of film-like elements of the two polymers present in the fiber cross section.

[0032] The multilayer laminate structure can be formed in a variety of different configurations, including two types of polymers alternately laminated in one direction (unidirectional laminate: unidirectional laminate fiber 1 shown in Figures 1 and 2), radially laminated (radially laminated: radially laminated fiber 2 shown in Figure 3), and concentrically laminated (concentrically laminated: concentrically laminated fiber 3 shown in Figure 4). From the perspective of minimizing crack propagation, the multilayer laminate structure is preferably unidirectional or concentrically laminated. Unidirectional or concentrically laminated multilayer structures prevent the film-like elements (layers) from becoming coarse at the periphery of the fiber cross section, and can limit crack propagation to a small area even in the periphery, which is prone to large loads due to bending deformation. These structures can be considered preferable.

[0033] As described above, the composite fiber of the present invention can enhance the effect of improving mechanical properties by having a multilayer laminate structure in its cross section, and moreover, by making the layer thickness variation (CV value) of at least one type of polymer constituting the multilayer laminate structure relatively large, at 10% or more, interfacial peeling between components can be more effectively suppressed.

[0034] The layer thickness variation referred to here is calculated by measuring the thickness of the layers present on the line perpendicularly bisecting the long side of each layer for 100 layers of one type of polymer that make up the fiber cross section, in integers in nm, and dividing the standard deviation by the arithmetic mean to obtain a coefficient of variation, rounded to the nearest integer in percentage. In the case of radial lamination or concentric lamination, for which the layer thickness cannot be measured using the above method, the thickest and thinnest points of each layer can be visually selected, and the average value can be taken as the layer thickness. The layer thickness variation can then be calculated from the arithmetic mean and standard deviation for the 100 layers. If the number of layers in the cross section of a single composite fiber is less than 100, the cross sections of multiple composite fibers should be used to obtain a total of 100 layers.

[0035] Relatively large variations in the layer thickness of one polymer constituting the multilayer laminate structure result in thin and thick layer regions within the fiber cross section. The interfacial layer has a relatively strong effect in the thin layer regions, reducing stress concentration, while thick layer regions experience deformation near the interface, dispersing stress. These synergistic effects result in complex changes in stress generation within the cross section, alleviating stress throughout the fiber and effectively suppressing interfacial delamination between components. A layer thickness variation of 10% or more for at least one polymer constituting the multilayer laminate structure results in complex stress distribution within the cross section, reducing fuzzing of the composite fiber even when subjected to compressive deformation during twisting or other processes. A layer thickness variation of 30% or more for at least one polymer constituting the multilayer laminate structure reduces fuzzing due to interfacial delamination even when subjected to strong compressive deformation under heat during false twisting or other processes, allowing for high-quality processing into textiles. This range is even more preferable.

[0036] Furthermore, from the viewpoint of further enhancing the effect of improving the mechanical properties of the composite fiber of the present invention, it is preferable that the average layer thickness of at least one type of polymer constituting the multilayer laminate structure is 1000 nm or less. The average layer thickness of the polymer is more preferably 300 nm or less, even more preferably 100 nm or less, particularly preferably 50 nm or less, and most preferably 30 nm or less. The average layer thickness here is calculated by rounding off the arithmetic mean of the layer thicknesses of 100 layers of one type of polymer constituting the fiber cross section calculated above to an integer in nm. If the number of layers in the cross section of a single composite fiber is less than 100, the cross sections of multiple composite fibers are used to make up a total of 100 layers.

[0037] By making the layer thickness relatively thin, the proportion of the interface layer per layer increases relatively, making it easier for stress to be transmitted between adjacent interface layers.Even if the fiber undergoes deformation such as bending deformation that causes stress to be concentrated locally on the cross section, the stress is distributed throughout the cross section, making it less likely for the interface to peel off.

[0038] Furthermore, by making the average layer thickness of at least one of the polymers constituting the multilayer laminate structure 50 nm or less, the effects in terms of chemical properties and thermal properties can be made more pronounced.

[0039] As mentioned above, in layers near interfaces formed by different types of polymers, molecular chains of the different polymers may interpenetrate, forming an interface layer that combines the properties of both polymers. The typical thickness of such an interface layer is said to be several nanometers to several tens of nanometers. That is, when the layer thicknesses of the polymers constituting the multilayer laminate structure approach the thickness of the interface layer, the majority of a layer is constituted by the interface layer, and the effect of the interface layer in each layer becomes extremely significant, resulting in a significant effect of combining the polymer properties. In the cross section of the composite fiber of the present invention, if the average layer thickness of at least one type of polymer constituting the multilayer laminate structure is 50 nm or less, the majority of the polymer layer will be occupied by the interface layer. As a result, even if a readily soluble polymer is used as the polymer, if a sparingly soluble polymer is selected as the other polymer, the readily soluble polymer will be hardly dissolved even when subjected to a dissolution treatment, demonstrating excellent chemical resistance, which can be considered a preferred range. Furthermore, when a low-melting-point polymer and a high-melting-point polymer are selected and alternately laminated to form a multilayer structure such that the average layer thickness of the low-melting-point polymer is 50 nm or less, the effect of suppressing interfiber fusion is achieved even when exposed to high temperatures equal to or higher than the melting point of the low-melting-point polymer. A smaller average layer thickness is preferable because it allows the interfacial layer to become more apparent in each layer constituting the fiber cross section. An average layer thickness of 30 nm or less for one type of polymer is the most preferred range because it suppresses fiber weight loss and interfiber fusion even when a composite fiber made of the above-mentioned combination of polymers is subjected to long-term dissolution treatment or heat treatment.

[0040] Furthermore, by having the average layer thickness of at least one type of polymer constituting the multilayer laminate structure be 50 nm or less, the mechanical properties of the composite fiber of the present invention may be further improved from the viewpoint of improving the dispersibility of additives. Specifically, the polymers constituting the composite fiber generally contain additives such as titanium oxide, but these additives exist in an aggregated state, and peeling is likely to occur at the interface between the coarse aggregates and the polymer. By confining the additives contained in the polymer within the thin film of the multilayer laminate structure below the aggregate size, shear force breaks down the aggregated state, improving dispersibility and suppressing the occurrence of cracks even when repeatedly rubbed. When the average layer thickness of at least one type of polymer is 50 nm or less, the additives are confined in a layer significantly thinner than the aggregate diameter of typical additives, improving the dispersibility of the additives and providing excellent effects in terms of abrasion resistance, and this can be considered a preferred range.

[0041] Furthermore, the composite fiber of the present invention is suitable because the difference in solubility parameters (SP values) between the two polymers to be composited in the cross section of the fiber is 3.0 or less, which stabilizes thinning just below the spinneret and results in excellent thickness uniformity in the fiber axis direction. Note that the solubility parameter difference referred to here is defined as (evaporation energy / molar volume) 1 / 2 It can be calculated from the values ​​described on page 189 of "Plastics Data Book," co-edited by Asahi Kasei Amidas Corporation and the Plastics Editorial Department, for example, and the absolute value obtained by subtracting the solubility parameter of one component from the solubility parameter of the other component means the solubility parameter difference referred to in the present invention.

[0042] Generally, in composite fibers composed of two or more polymers, the elongation deformation behavior of each polymer differs, making the elongation deformation unstable during the spinning and drawing processes. In particular, when the difference in solubility parameters between the two polymers constituting the composite fiber is large, this instability is exacerbated, and thickness unevenness in the fiber axis direction tends to increase. By setting the difference in solubility parameters between the two polymers constituting the composite fiber to 3.0 or less, elongation deformation during the spinning and drawing processes is stabilized, and excessive thickness unevenness in the fiber axis direction is suppressed. As a result, even when an external force such as tension is applied, stress can be borne evenly in the fiber axis direction, and load concentration in a portion in the fiber axis direction is suppressed, thereby more effectively suppressing the occurrence of cracks at the interface between the components. Based on the above, to further enhance the effect of improving the mechanical properties of the composite fiber of the present invention, it is preferable that the difference in solubility parameters between the two polymers constituting the composite fiber be 3.0 or less.

[0043] The thickness unevenness in the fiber axis direction referred to here can be expressed as the Worcester (fineness unevenness) U% value, which is an index of fineness unevenness, and U% is preferably 1.5% or less. If U% is 1.5% or less, even when external forces such as repeated tension are applied, load concentration in a part in the fiber axis direction can be suppressed, thereby suppressing peeling between components constituting the fiber cross section and the occurrence of cracks. Furthermore, from the viewpoint of chemical and thermal properties, when fineness unevenness is small, chemical resistance and heat resistance in the fiber axis direction become uniform and defects caused by extremely thick and thin portions are reduced, so it is preferable to control U% to 1.5% or less.

[0044] The conjugated fiber of the present invention not only exhibits excellent effects in improving mechanical properties due to the formation of a conjugated form with an extremely large interfacial length, which has not been seen in conventional fibers, but also exhibits excellent effects in chemical properties and thermal properties by appropriately selecting the polymers to be combined. For this reason, the conjugated fiber 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.

[0045] Furthermore, in the conjugate fiber of the present invention, by removing one of the two types of polymers constituting the multilayer laminate cross section, a multifilament composed of flat ultrafine fibers composed of the other type of polymer can be obtained. That is, when one type of polymer is removed from a conjugate fiber having a multilayer laminate cross section in which two types of polymers are alternately connected as film-like elements (layers), many layers composed of the other type of polymer are separated. Each of these layers forms a flat ultrafine fiber, and a multifilament 5 composed of flat ultrafine fibers 4 having a cross section shaped like a thin layer, as shown in Figures 5 and 6, can be obtained.

[0046] In the case of the multifilament, the generation of fuzz and the like is low due to the characteristic of the conjugated fiber that interfacial peeling is unlikely to occur, and therefore it can be processed into high-quality textile products. In addition, the characteristic of the conjugated fiber that the interfacial length is extremely long results in the generation of an extremely large specific surface area. Due to the effect of this specific surface area, when the multifilament is subjected to functional processing, it can adsorb a large amount of a functional substance and exhibit excellent functionality.

[0047] In terms of ensuring long-term durability in terms of the functionality and fiber material quality described above, the cross-sectional shape of the flat ultrafine fibers constituting the multifilament of the present invention is important, and it is important that the fiber cross section has a flat shape, the degree of flatness is extremely high, and the thickness is thin.

[0048] The flat shape referred to here means 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 value obtained by dividing the length of the major axis by the length of the minor axis. In the multifilament of the present invention, the flatness in the fiber cross section must be 15 or more.

[0049] The flatness referred to in the present invention is determined as follows (see also FIG. 5). The multifilament of the present invention is 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. The maximum length of the cross section of the single fiber (flat ultrafine fiber) present in the photographed image is measured using image analysis software, and this value is expressed as the length of the major axis of the single fiber, as an integer in nm, rounded to the nearest integer. Next, the length of the line segment perpendicular to the line segment of the maximum length at the midpoint of the maximum length intersects with the fiber cross section, and this value is expressed as the length of the minor axis of the single fiber, as an integer in nm, rounded to the nearest integer. The length of the major axis and the length of the minor axis 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.

[0050] The first requirement of the multifilament of the present invention is that the flat ultrafine fibers constituting the multifilament have a high degree of flatness in the fiber cross section, and as an index of the cross-sectional shape, the degree of flatness needs to be 15 or more. If the degree is within this range, the specific surface area of ​​the fiber will be increased by more than twice 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.

[0051] Furthermore, if the flatness of the flat ultrafine fibers is 15 or more, the multifilaments 5 have a unique fiber bundle structure derived from the shape of the flat ultrafine fibers 4, as shown in Figure 6. That is, the high shape anisotropy of the flat ultrafine fibers creates restrictions on the fiber arrangement direction, and the individual flat ultrafine fibers overlap 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 described above, allows for the achievement of better adsorption efficiency.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Furthermore, if the flatness is 50 or more, even when fiber bundles 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.

[0056] 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.

[0057] As described above, the multifilament of the present invention has a large specific surface area (surface area per weight) compared to ordinary fibers due to the extremely high flatness of the fiber cross-sections of the flat ultrafine fibers that make up the multifilament, and furthermore, the fibers are densely arranged, resulting in an extremely large fiber surface when made into a fiber assembly.

[0058] 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 effect of increasing the surface area resulting from the cross-sectional shape. As an index of the fiber diameter, the second factor for the multifilament of the present invention is the thickness of the flat ultrafine fibers, i.e., the length of the minor axis of the fiber cross section, and the average thickness must be 1,000 nm or less. The average thickness referred to here is the arithmetic mean of the lengths of the minor axes of 100 fibers measured above, rounded off to the nearest integer in nm.

[0059] If the average thickness of the flat ultrafine fibers 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 these reasons, the average thickness of the flat ultrafine fibers in the multifilament of the present invention must be 1000 nm or less.

[0060] As described above, the thinner the average thickness of the flat ultrafine fibers, the more effectively they increase the specific surface area of ​​the single fibers. Furthermore, since the thickness also affects the bending rigidity of the fibers, this also has an excellent effect on densifying the fiber bundle. That is, the bending rigidity in the minor axis direction decreases in proportion to the cube of the fiber thickness. As the thickness 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 thickness is 800 nm or less, not only is the effect of increasing the specific surface area even stronger, 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, the average thickness is preferably 800 nm or less.

[0061] Furthermore, if the average thickness 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 nanometers to several hundred nanometers, which is an excellent effect in terms of the expression of the high durability function described below, and therefore an average thickness of 500 nm or less is more preferable.

[0062] Furthermore, if the average thickness 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.

[0063] In the multifilament of the present invention, as the average thickness of the fiber cross section decreases, the multifilament tends to be more susceptible to breakage when an external force is applied during the processing step. However, if the average thickness is 50 nm or more, there is no problem in practical use, and the object of the present invention can be achieved.

[0064] As described above, the multifilament of the present invention has a significantly increased specific surface area due to the extremely flat cross-sectional shape of the flat ultrafine fibers constituting the multifilament. Furthermore, the uniformly oriented dense fiber bundles produce a very large fiber surface per unit volume. By utilizing this large fiber surface, not only can the adsorption efficiency of functional substances be dramatically increased, but the unique fiber bundle structure can also dramatically improve durability. That is, when the multifilament of the present invention is functionally processed, not only is a large amount of the functional substance adsorbed onto the fiber surface, but the functional substance D also penetrates between the aligned, overlapping flat ultrafine fibers 4, as shown in FIG. 7 . As a result, while a large amount of the functional substance is encapsulated within the fiber bundle, it is distributed in a way that it is barely exposed on the fiber bundle surface. This makes the functional substance less likely to fall off due to abrasion or the like, improving durability in terms of functionality.

[0065] From the viewpoint of utilizing the characteristics of the multifilament of the present invention to effectively express its functions through functional processing, the ease of impregnation with functional substances is also important, and the variation in the thickness of the flat ultrafine fibers is an index to note.

[0066] The thickness variation referred to here is determined by calculating the arithmetic mean and standard deviation using the short axis lengths of the 100 fibers measured above, dividing the standard deviation by the arithmetic mean to obtain a coefficient of variation, and rounding off any decimal point to an integer in percentage units.

[0067] As described above, since the bending stiffness of a fiber varies greatly depending on the thickness, if there is a moderate variation in thickness, 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 is exposed to the liquid without being obstructed by other fibers, and the functional substance can be efficiently adsorbed.

[0068] If the thickness variation is 10% or more, the single fibers tend to disperse well in a liquid or the like and are easily impregnated with a functional substance, so it is preferable that the thickness variation is 10% or more.

[0069] Taking this idea further, the greater the variation in fiber thickness, 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 period of time, it is more preferable that the thickness variation be 20% or more.

[0070] Furthermore, if the thickness variation is 40% or more, even in the case of a high-density woven or knitted fabric in which the yarns are tightly constrained, the liquid will be more likely to penetrate between the individual fibers, and if efficient functional processing is desired for a high-density woven or knitted fabric, a thickness variation of 40% or more is particularly preferable.

[0071] Furthermore, as the thickness variation increases, thinner fibers are more likely to break when external forces are applied during the processing step. However, if the thickness variation is less than 70%, there is no problem in practical use, and the object of the present invention can be achieved.

[0072] 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.

[0073] 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 the decimal point to the nearest whole number 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.

[0074] If the unevenness is 20% or more, the single 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.

[0075] 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.

[0076] The multifilament of the present invention has 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 are no problems such as 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 preferably contains 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 multifilament 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.

[0077] In the multifilament of the present invention, in consideration of practical use, the fiber strength is preferably 1 cN / dtex or more, and when used as a woven fabric or sheet material to be used in a relatively severe environment, the strength is preferably 2 cN / dtex or more, which can be mentioned as a more preferable range.

[0078] By utilizing the characteristics of the multifilament 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 within the fiber bundles due to the unique fiber bundle structure, the functional substance is less likely to fall off, resulting in excellent durability. Furthermore, by utilizing this, a sustained release effect can be achieved in which the functional substance is gradually released by diffusing within the fiber bundle or by the fiber bundle being deformed by an external force. Therefore, when the multifilament of the present invention is used as a functional material in combination with a functional substance, it is preferable to process it into a state in which the functional substance is encapsulated within the fiber bundles made of flat ultrafine fibers.

[0079] 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.

[0080] 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.

[0081] As described above, by utilizing the characteristics of the multifilament of the present invention, a functional material with excellent durability that efficiently contains functional substances can be obtained. Therefore, the multifilament 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.

[0082] An example of a method for producing the composite fiber and multifilament of the present invention will be described in detail below. The composite fiber and multifilament of the present invention 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 employ melt spinning.

[0083] The composite spinneret used in the present invention is preferably a composite spinneret 10 shown in FIG. 8, which is formed by stacking three types of members: a metering plate E, a composite plate F, and a discharge plate G. Incidentally, FIG. 8 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 the composite spinneret 10, the metering plate E measures the amount of polymer per hole in the composite plate F, the composite plate F merges the metered streams of different types of polymers to form a composite stream having an interface, which is then split and recombined to increase the interface in the cross section of the composite stream, and the discharge plate G compresses the composite stream formed by 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.

[0084] The composite plate F has microchannels H with confluences and branching sections, the number of which is equal to or greater than the number of discharge holes in the discharge plate G. The confluences and branching sections can be appropriately positioned to form a desired cross section. 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 join at the confluence section to form a composite stream, which is then split at the branching section. Repeating this process forms a composite cross section, characterized by the sum of the interfacial lengths of the two types of polymers required for the composite fiber of the present invention being extremely large relative to the cross-sectional area of ​​the fiber. The confluence and splitting process referred to here does not need to be repeated; the streams may merge and then merge again, or split and then split again. 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.

[0085] The microchannels used in the production of the present invention have a channel configuration that minimizes flow turbulence within the channel, making it possible to produce the composite fiber of the present invention. Incidentally, the above-mentioned microchannels can be said to have similar characteristics to conventional static mixers in that they merge or split fluids within the channel. However, typical static mixers have a channel design intended for mixing two types of polymers, which causes turbulence in the inserted polymer flow, making it difficult even for those skilled in the art to produce the composite fiber of the present invention. Incidentally, by carefully designing the channel configuration of the microchannel of the present invention, it is possible to control the thickness and other morphologies of the layers that make up the laminated composite flow formed within the channel, making it possible to form a fiber cross-section with any composite shape.

[0086] 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 E 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 polymer stream discharged from the discharge plate G is cooled and solidified, then given an oil agent and taken up by a roller at a specified peripheral speed to form a composite fiber.

[0087] The composite spinneret described above can be used to produce the composite fiber of the present invention. It goes without saying that the use of the composite spinneret also makes it possible to produce the composite fiber of the present invention using a spinning method that uses a solvent, such as solution spinning.

[0088] When melt spinning is selected, the polymers constituting the composite fiber of the present invention are as described above. Examples include melt-moldable polymers such as polyethylene terephthalate or its copolymers, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, polyamide, polylactic acid, and thermoplastic polyurethane. Polycondensation polymers, such as polyester and polyamide, have high melting points and are particularly preferred. 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 ultraviolet absorbers. When a polymer containing such 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.

[0089] Two or more of these polymers are combined to form a multi-layer laminated fiber, and the combination of polymers is also important from the viewpoint of improving the laminated structure. In other words, the smaller the difference in solubility parameters (SP values) of the polymers to be combined, the better the laminate structure formed without interlayer merging, and it is preferable to select polymers so that the difference in solubility parameters of the two polymers forming the interface is 3.0 or less. The solubility parameter referred to here is as described above.

[0090] Furthermore, from the viewpoint of realizing the interfacial layer formed near the interface and combining the properties of two types of polymers, which is a feature of the conjugated fiber of the present invention, if the polymers are polyesters, the interfacial layer is formed more extensively at one interface, which is preferable. In particular, when a readily soluble polyester copolymerized with a metal sulfonate salt group is used as one polymer, it is preferable to use a sparingly soluble polyester as the other polymer, since this can impart excellent chemical resistance even to fibers containing a readily soluble polyester. In particular, when a polyester copolymerized with a metal sulfonate salt group is used, a polyester copolymerized with sodium sulfoisophthalic acid and polyethylene glycol, either alone or in combination, is used as the polyester copolymerized with a metal sulfonate salt group, since this provides excellent chemical resistance and also good color development after dyeing, which is preferable. An example of this polymer combination is one in which, in view of the relationship of melting points, polyethylene terephthalate copolymerized with 5 mol% to 15 mol% of 5-sodium sulfoisophthalic acid is used as one polymer, and polyethylene terephthalate copolymerized with the above-mentioned 5-sodium sulfoisophthalic acid and 5 wt% to 15 wt% of polyethylene glycol having a weight average molecular weight of 500 to 3000 is used as the other polymer, with polyethylene terephthalate being used as the other polymer.

[0091] The spinning temperature when spinning the conjugated fiber of the present invention is set to a temperature at which the two or more polymers, primarily the high-melting-point or high-viscosity polymer, exhibits fluidity. The temperature at which this fluidity is exhibited varies depending on the molecular weight, but is preferably set between the melting point of the polymer and melting point + 60°C. A temperature below this range is preferred because the polymer does not thermally decompose in the spinning head or spin pack, thereby suppressing a decrease in molecular weight. The conjugated fiber of the present invention can be spun at a throughput of 0.1 g / min·hole to 20.0 g / min·hole to ensure stable production. In particular, a single-hole throughput rate that results in a single fiber fineness of less than 4 dtex after drawing is preferred because the fineness of the fiber results in a soft texture when woven.

[0092] The ratio of component A to component B when spinning the composite fiber of the present invention can be selected from a component A / component B ratio range of 5 / 95 to 95 / 5 based on the throughput rate. Even when a polymer with poor chemical resistance or heat resistance is used, if it is desired to impart excellent chemical resistance or heat resistance by increasing the interface between the components, it is preferable to composite one polymer with excellent chemical resistance or heat resistance as the other and increase the ratio between them. For example, when component A is a highly chemical-resistant polymer and component B is a low chemical-resistant polymer, an A / component B ratio of 99 / 1 to 70 / 30 is preferred because the weight loss of the fiber is slight even when subjected to a long-term dissolution treatment.

[0093] The polymer stream thus discharged is cooled and solidified, and is then applied with an oil and taken up by rollers with a specified peripheral speed to form composite fibers. 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 stably produce the composite fibers used in the present invention. The composite fibers may be drawn to achieve high orientation and improve their mechanical properties. Drawing may be performed after the fibers have been wound up in the spinning process, or may be performed immediately without winding.

[0094] As for the drawing conditions, for example, in a drawing machine consisting of one or more pairs of rollers, fibers made of a polymer exhibiting thermoplasticity that can generally be melt-spun can be stretched reasonably in the fiber axis direction by 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 a temperature equivalent to the crystallization temperature, and the fibers are then heat-set and wound up to obtain a composite fiber having a composite cross section as shown in Figure 1. The upper limit of the temperature of the first roller is preferably set to a temperature at which fiber path disturbance does not occur during the preheating process; for example, in the case of polyethylene terephthalate, whose glass transition temperature is around 70°C, the preheating temperature is usually set to about 80 to 95°C.

[0095] As described above, the method for producing the conjugated fiber of the present invention has been explained based on the general melt spinning method. However, it goes without saying that the conjugated fiber can also be produced by the melt blowing method and the spunbonding method, and further, it can also be produced by solution spinning methods such as wet and dry-wet methods.

[0096] To obtain the multifilament of the present invention from the composite fiber having a multilayer laminate structure obtained as described above, the multilayer laminate fiber is 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 poorly soluble polymer, and then a fiber bundle 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 laminate fiber 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 the multifilament from the multilayer laminate fiber 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 poorly soluble polymer while minimizing fiber damage, thereby successfully generating the multifilament of the present invention. [Example]

[0097] The conjugate fiber of the present invention will be specifically described below with reference to examples.

[0098] The examples and comparative examples were evaluated as follows.

[0099] A. Melt viscosity 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 changing the strain rate stepwise using a Capillograph manufactured by Toyo Seiki Seisakusho Co., Ltd. The measurement temperature was the same as the spinning temperature, and in the examples and comparative examples, a shear rate of 1216 s -1 The melt viscosity is shown in Table 1. The measurement was carried out in a nitrogen atmosphere, with 5 minutes elapsed between the time the sample was placed in the heating furnace and the start of the measurement.

[0100] B. Melting point Approximately 5 mg of polymer chips were weighed and dried in a vacuum dryer to a moisture content of 200 ppm or less. Using a TA Instruments Japan Corporation, differential scanning calorimeter (DSC) Model Q2000, the sample was heated from 25°C to 300°C at a rate of 16°C / min, and then held at 300°C for 5 minutes. 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.

[0101] C. Solubility parameter difference The solubility parameter (SP value) is a parameter that reflects the cohesive strength of a substance and is defined as the square root of (evaporation energy / molar volume). It was 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 was calculated as the absolute value of (SP value of component A minus SP value of component B).

[0102] D. Fineness The weight of 100 m of the composite fiber was measured, and the weight was 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 above fineness by the number of filaments was taken as the single fiber fineness (dtex).

[0103] E. Worcester U% Using a fineness unevenness measuring device (UT-4) manufactured by Zellweger, 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.

[0104] F. Sum of interfacial lengths / fiber cross-sectional area (nm -1 ) The composite 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 identify the interface formed between the two polymers. Using image analysis software (WINROOF), the length of each interface was measured from an arbitrarily determined measurement start point to the return point. The length of each interface (interface length) was calculated in nm units, rounded to the nearest integer. If the fiber cross-section extended beyond the periphery before returning to the measurement start point, the length from the measurement start point to the interface and periphery was measured, excluding the portion that passed through the periphery. Similar measurements were performed for all interfaces present in the fiber cross-section, and the total interfacial length was calculated by adding all interfacial lengths. The sum of the interfacial lengths obtained was divided by the cross-sectional area of ​​the fiber, and the value of the sum of the interfacial lengths / cross-sectional area of ​​the fiber was calculated in nm. -1 The fiber cross-sectional area was calculated by cutting the composite fiber perpendicular to the fiber axis at an arbitrary position in the fiber axis direction, photographing the cut surface two-dimensionally using an OLYMPUS optical microscope at a magnification that allowed the entire cross section of one single yarn to be observed, extracting the cross section of one single yarn using image analysis software (WINROOF), and then calculating the fiber cross section from the cross-sectional parameters obtained through binarization processing to an integer in nm by rounding off the decimal point.

[0105] G. Layer Thickness Variation (Composite Fiber) The layer thickness was defined as the length of the layer present on the line perpendicularly bisecting the long side of one layer (film-like element) constituting the fiber cross section. From the cross-sectional image of the composite fiber taken in the same manner as measuring the sum of the interfacial lengths described above, 100 elements of component B were randomly extracted, and their layer thicknesses were measured by rounding off the decimal point to an integer in nm. If the number of layers in the cross section of one composite fiber was less than 100, the total number of layers was measured from the cross sections of multiple composite fibers to make it 100. The arithmetic mean and standard deviation of the obtained values ​​were calculated, and the coefficient of variation obtained by dividing the standard deviation by the arithmetic mean was obtained, and the coefficient was rounded off to an integer in % to calculate the variation in layer thickness. In the case of radial or concentric laminations, for which the layer thickness cannot be measured using the above method, the thickest and thinnest points of each layer were visually selected, and the average value was taken as the thickness of each layer. As described above, the standard deviation was divided by the arithmetic mean to obtain the coefficient of variation, which was then used to calculate the variation in layer thickness.

[0106] H. Average layer thickness (composite fiber) The layer thickness was defined as the length of a layer present on a line perpendicularly bisecting the long side of one layer constituting the fiber cross section. From a cross-sectional image of the composite fiber taken in the same manner as measuring the sum of the interfacial lengths described above, 100 elements of component B were randomly selected, and their layer thicknesses were measured by rounding off the decimal point to an integer in nm. If the number of layers in the cross section of a single composite fiber was less than 100, the cross sections of multiple composite fibers were used to measure the total to 100 layers. The average layer thickness was calculated by rounding off the decimal point to an integer in nm. In the case of radial or concentric lamination, where the layer thickness cannot be measured by the above method, the thickest and thinnest points of each layer were visually selected, and the average was taken as the thickness of each layer. This arithmetic mean was calculated as the average layer thickness in the same manner as above.

[0107] I. Abrasion resistance A plain weave fabric was prepared by adjusting the number of fibers to a weave density of 180 fibers per 2.54 cm. Plain weave fabric was cut to a diameter of 10 cm and placed in the sample holder of a Daiei Scientific Instruments Co., Ltd. appearance and retention tester (ART type testing machine). A pressure load of 3.9 N was applied to the fabric, and the fabric was rubbed with a silicon carbide friction plate (3K). The friction plate was stopped after each rotation, and the number of rubs required to confirm the formation of fibrils on the fiber surface was counted and calculated as the average of five measurements. The number of rubs was rounded to the nearest whole number, and the abrasion resistance of the fabric was evaluated using the following four-point scale. [Evaluation criteria] A (Excellent): 100 or more friction cycles B (Good): 50 to less than 100 friction cycles C (Acceptable): Number of frictions: 20 or more but less than 50 D (Not acceptable): Less than 20 frictions

[0108] J. Chemical resistance A cylindrical knitted fabric was prepared from the composite fiber and treated with a 1% aqueous solution of sodium hydroxide at 90°C for 30 minutes, then rinsed with water and thoroughly dried at 60°C. The weight loss rate was calculated from the weight before and after treatment. The weight loss rate here is rounded to one decimal place, and chemical resistance was evaluated using the following four-point scale. [Evaluation criteria] A (Excellent): Weight loss rate is 0.0% or more and less than 2.0% B (Good): Weight loss rate is 2.0% or more and less than 5.0% C (Acceptable): Weight loss rate is 5.0% or more and less than 10.0% D (unacceptable): Weight loss rate is 10.0% or more

[0109] K. Heat resistance Using a measuring machine with a 1.0 m circumference, a skein of composite fiber wound 10 times was taken and measured for pre-treatment skein length under a load of 0.0294 cN / dtex. The skein was placed in a hot air dryer at 160°C without load and treated for 15 minutes. The skein was then removed and measured for post-treatment skein length under a load of 0.0294 cN / dtex. The dry heat shrinkage was calculated from the pre-treatment and post-treatment skein lengths using the formula: [Dry heat shrinkage (%) = (pre-treatment skein length - post-treatment skein length) / pre-treatment skein length × 100]. The dry heat shrinkage was calculated from five measurements, and the arithmetic mean was calculated by rounding to the nearest tenth. The fiber surface of the post-treatment skein was also observed using an Olympus optical microscope to confirm the presence of inter-fiber fusion. Heat resistance was evaluated using the following three-point scale: [Evaluation criteria] A (Good): Dry heat shrinkage is less than 15.0% and there is no inter-fiber fusion. B (Acceptable): Dry heat shrinkage rate is 15.0% or more and there is no inter-fiber fusion C (unacceptable): Interfiber fusion

[0110] L. Flatness Multifilaments composed of 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 large enough to visualize the cross section. Using image analysis software (WINROOF), the maximum length of the cross section of a single fiber was measured. This value was used as the long axis length of the single fiber, rounded to the nearest integer in nanometers. 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 nanometers. 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 average of these was rounded off to the nearest whole number to calculate the flatness of the flat ultrafine fibers.

[0111] M. Average fiber thickness (flat ultrafine fiber) The arithmetic average of the lengths of the short axes of the 100 fibers measured above was rounded off to the nearest integer in nm to calculate the average thickness of the flat ultrafine fibers.

[0112] N. Variation in fiber thickness (flat ultrafine fibers) The arithmetic mean and standard deviation were calculated using the short axis lengths of the 100 fibers measured above, and the standard deviation was divided by the arithmetic mean to obtain a coefficient of variation, which was then rounded off to the nearest integer in percentage to calculate the variation in thickness of the flat ultrafine fibers.

[0113] O.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 whole number to calculate the unevenness of the single fiber. Similar measurements were made for 10 fiber cross sections, and the arithmetic mean of the unevenness of the 10 single fibers was calculated as the unevenness of the flat ultrafine fibers.

[0114] P. Distribution of functional substances To model the distribution of functional substances when treated on fiber bundles, fabrics were treated with a dye solution containing 10% owf of Dystar's acid dye Telon Black LD02, which is non-dyeable to polyester, at a liquor ratio of 1:50, a treatment temperature of 30°C, and a treatment time of 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: [Evaluation 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.

[0115] Q. 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.

[0116] R. Deodorizing properties (acetaldehyde concentration) In a humidity-controlled environment at a temperature of 20°C and a humidity of 65% RH, 1 g of the functionally processed fabric treated in Q above 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, and the gas concentration (ppm) inside the tetra bag after 10 minutes was measured using a gas detector tube (manufactured by Gastec Corporation).

[0117] S. Functional substance content The unprocessed fabric was dried at 110°C for 2 hours and weighed (W1). The functionally processed fabric treated in Q above was dried at 110°C for 2 hours and weighed (W2). The content (%) of the functional substance was calculated from the weight before and after processing using the following formula: Functional substance content (%) = (W2-W1) / W1 x 100

[0118] T. Functional substance content after washing The functionally treated fabrics treated with Q above were subjected to 50 cycles of washing (15 minutes), spin-drying (1 minute), rinsing (6 minutes), spin-drying (1 minute), and drying. The washing conditions were a water temperature of 40°C, a bath ratio of 1:30, and 0.5g / L of "Top" (manufactured by Lion Corporation). The rinsing conditions were a water temperature of 20°C, and an overflow bath ratio. After washing, the fabric was dried at 110°C for 2 hours and weighed (W3). The content (%) of the functional substance was calculated from the weight before and after washing using the following formula: Functional substance content after washing (%) = (W3-W1) / W1 x 100

[0119] [Example 1] Component A: polyethylene terephthalate (PET, melt viscosity: 120 Pa·s, melting point: 254°C, SP value: 21.4 MPa) 1 / 2 ) and, as component B, polyethylene terephthalate copolymerized with 8.0 mol% of 5-sodium sulfoisophthalic acid and 9 wt% of polyethylene glycol (SSIA-PEG copolymer PET, melt viscosity: 95 Pa·s, melting point: 233°C, SP value: 22.9 MPa). 1 / 2 ) was prepared.

[0120] After melting components A and B separately at 290°C, the resulting mixture was introduced into a spinning pack equipped with a composite spinneret 10 (see Figure 8) with a 90 / 10 A / B ratio. A composite polymer stream was extruded from the extrusion holes. The composite plate F was equipped with microchannels H, which allowed for 1024 alternating layers of the two components. The composite polymer stream was extruded to form a composite structure with alternating multilayer laminations of the two polymers in one direction, as shown in Figure 1. 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 yarn with a diameter of 200 dtex and 24 filaments (total throughput of 20 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 56 dtex and 24 filaments. The fineness uniformity index (U%(H)) was 0.6%, demonstrating excellent thickness uniformity along the fiber axis.

[0121] When the cross section of the obtained composite fiber was observed, the sum of the interfacial lengths / cross-sectional area of ​​the fiber was 0.0557 nm -1 The sum of the lengths of the interfaces relative to the cross-sectional area of ​​the fiber was extremely large, and the same interfaces were continuous in the fiber axis direction. The average layer thickness of component B was 4 nm, and the layer thickness variation was relatively large at 32%, indicating that the component B was divided into extremely thin film-like elements.

[0122] The resulting composite fiber was woven into a fabric, and the fabric was evaluated for peel resistance. No fibril formation was observed even after rubbing over 100 times. Incidentally, when the cross section of the composite fiber after the abrasion resistance evaluation was observed with a scanning electron microscope (SEM) manufactured by Hitachi, Ltd., no peeling between the components was observed.

[0123] The resulting cylindrical knitted fabric of the composite fiber was immersed for 30 minutes in a 1% sodium hydroxide aqueous solution (bath ratio 1:50) heated to 90°C, and the weight loss was 0.6%.

[0124] The results are shown in Table 1.

[0125] [Examples 2, 3, 4, 5, and 6] The same procedures as in Example 1 were carried out, except that the composite plates were changed to have a microchannel structure in which the total number of layers of components A and B was stacked to 512 (Example 2), 256 (Example 3), 128 (Example 4), 64 (Example 5), and 32 (Example 6). The evaluation results of these composite fibers are shown in Table 1.

[0126] The composite fibers of Examples 2 to 6 had a composite structure as shown in Figure 1, in which two types of polymers were alternately laminated in multiple layers in one direction, and the same interfaces were continuous in the fiber axis direction. In Example 2, no fibrillation was observed even when the number of friction cycles was 100 or more. However, in Examples 3 to 6, as compared with Example 2, the number of layers of the two types of polymers in the fiber cross section decreased, and the value of the sum of the interface lengths / fiber cross-sectional area decreased. Therefore, fibrils were observed in several single fibers when the number of friction cycles was 50 or more. When the cross section of the fibrillated composite fiber was observed using the same method as described above, it was found that the fiber was split in the direction in which the two types of polymers were bonded together, which was presumed to be due to peeling between the components. Furthermore, in Examples 2 and 3, as the value of the sum of the interface lengths / fiber cross-sectional area decreased, the weight loss rate slightly increased, but was less than 2.0%, demonstrating excellent chemical resistance. On the other hand, in Examples 5 and 6, in which the value of the sum of interface lengths / fiber cross-sectional area was further reduced, the weight loss rate increased to 5.0% or more, resulting in a decrease in chemical resistance compared to Examples 1 to 3.

[0127] [Comparative Example 1] The same procedure as in Example 1 was carried out, except that the composite plate was changed to one with microchannels in which the total number of layers of component A and component B was stacked to 8 (Comparative Example 1). The evaluation results of these composite fibers are shown in Table 1.

[0128] The composite fiber of Comparative Example 1 had a composite structure in which two types of polymers were alternately laminated in one direction in multiple layers, as shown in Figure 1. However, the number of divisions (number of layers) was significantly smaller than that of the composite fiber of the present invention, resulting in a smaller value for the sum of interface lengths / fiber cross-sectional area. Therefore, when the number of friction cycles was increased to 20 or more, fibrils were observed in many single fibers, and the abrasion resistance was poor. Furthermore, when the chemical resistance of a tubular knitted fabric made from the resulting composite fiber was evaluated, the weight loss rate was 10.0% or more, indicating poor chemical resistance. Incidentally, when the tubular knitted fabric after the chemical resistance evaluation was dyed under the same conditions as above, the tubular knitted fabric was not dyed, suggesting that almost all of the easily soluble SSIA-PEG copolymerized PET constituting the composite fiber had dissolved during the chemical resistance evaluation.

[0129] [Example 7] In the method described in Example 1, component B was polyethylene terephthalate copolymerized with 21 mol% of spiroglycol and 29 mol% of cyclohexanedicarboxylic acid (SPG-CHDC copolymer PET, melt viscosity 75 Pa·s, melting point: none [glass transition temperature: 76°C], SP value: 23.0 MPa). 1 / 2 ) and melted at 285°C to make the A / B component ratio 50 / 50, all the same procedures as in Example 1 were carried out. The evaluation results of this composite fiber are shown in Table 2.

[0130] The composite fiber of Example 7 had a composite structure as shown in Figure 1, in which two types of polymers were alternately laminated in one direction, with the same interface continuing in the fiber axis direction. When the peel resistance of a fabric woven from the resulting composite fiber was evaluated, no fibril formation was observed even after 100 or more rubs. Furthermore, when a skein of the resulting composite fiber was treated in a hot air dryer at 160°C for 15 minutes, the dry heat shrinkage was less than 15.0%, demonstrating excellent thermal dimensional stability. Despite the use of amorphous SPG-CHDC copolymerized PET, whose glass transition temperature was below the treatment temperature of the hot air dryer, no fusion between fibers was observed.

[0131] [Examples 8 and 9] The same procedure as in Example 7 was carried out, except that the composite plate was changed to one equipped with microchannels in which the total number of layers of component A and component B was stacked to 512 layers (Example 8) and 256 layers (Example 9). The evaluation results of these composite fibers are shown in Table 2.

[0132] In Example 8, no fibril formation was observed even when the number of friction cycles was 100 or more. However, in Example 9, as the number of layers of the two polymers in the fiber cross section decreased compared to Example 8, the value of the sum of the interface lengths / fiber cross-sectional area decreased, and fibrils were observed in several single fibers when the number of friction cycles was 50 or more. Furthermore, as the composite ratio of SPG-CHDC copolymerized PET, which has poor heat resistance, increased, the dry heat shrinkage rate increased, resulting in a decrease in heat resistance in Example 9, although it was not a problem. Furthermore, in Example 9, two polymers with different properties were alternately layered at a layer thickness that caused thin-film interference of visible light, and the resulting composite fiber exhibited a blue structural color.

[0133] Comparative Example 2 The same procedures as in Example 7 were carried out except that a composite plate equipped with microchannels in which the total number of layers of components A and B was stacked to 8 was used. The evaluation results of these composite fibers are shown in Table 2.

[0134] Although the composite fiber of Comparative Example 2 had a composite structure in which two types of polymers were alternately laminated in one direction in multiple layers as shown in Figure 1, the number of divisions (number of layers) was significantly smaller than that of the composite fiber of the present invention, and the value of the sum of interface lengths / fiber cross-sectional area was small, so when the number of friction cycles was increased to 20 or more, fibrils were observed in many single fibers, and the abrasion resistance was poor. Furthermore, when the heat resistance of a tubular knitted fabric of the obtained composite fiber was evaluated, the dry heat shrinkage was 20.0% or more, there was significant fusion between fibers, and the hand of the hank was very hard.

[0135] [Examples 10, 11, and 12] In the method described in Example 7, component B was replaced with polyamide-6 (N6, melt viscosity 100 Pa·s, melting point: 225°C), SP value: 23.7 MPa 1 / 2 ) and melted at 280°C, and the two components were laminated in 1024 layers (Example 10), 512 layers (Example 11), or 256 layers (Example 12) using composite plates equipped with microchannels. The evaluation results of these composite fibers are shown in Table 3.

[0136] In Examples 10 to 12, the composite fibers were constructed by combining polymers with large differences in solubility parameters, so fibrils were observed in several single fibers when the number of friction cycles was increased to 50 or more, but the abrasion resistance was generally good.

[0137] [Examples 13 and 14] In the method described in Example 10, the composite plate was changed to one equipped with fine flow channels in which the total number of layers of components A and B was stacked to 256, and the flow channel arrangement was changed to a concentric stacked structure (Example 13) or a radial stacked structure (Example 14), except that the method was the same as in Example 10. The evaluation results of these composite fibers are shown in Table 3.

[0138] In Example 13, two types of polymers were alternately laminated in a concentric pattern to form a composite structure as shown in Figure 4, while in Example 14, two types of polymers were alternately laminated in a radial pattern to form a composite structure as shown in Figure 3, with the same interface continuing in the fiber axial direction. Because the composite fiber was made by combining polymers with large differences in solubility parameters, fibrils were observed in several single fibers after 50 or more friction cycles, but the abrasion resistance was generally good.

[0139] Comparative Example 3 The same procedure as in Example 10 was carried out, except that a composite plate equipped with microchannels in which a total of eight layers of components A and B were laminated was used. The evaluation results of this composite fiber are shown in Table 3.

[0140] The composite fiber of Comparative Example 3 had a composite structure in which two types of polymers were alternately laminated in one direction in multiple layers as shown in Figure 1, but the number of divisions (number of layers) was significantly smaller than that of the composite fiber of the present invention, and the value of the sum of the interface lengths / fiber cross-sectional area was small, so that even when the number of friction cycles was 20 or less, fibrillation occurred in many single fibers, resulting in poor abrasion resistance. Furthermore, fibrillation occurred in the weaving process, causing frequent yarn breakage and problems with passability through advanced processing.

[0141] Comparative Example 4 The method described in Comparative Example 3 was carried out in the same manner as in Comparative Example 3, except that a composite plate was used in which a flow path for discharging only component A was provided around a fine flow path for laminating both components in eight layers. The evaluation results of this composite fiber are shown in Table 3, and although it was a composite structure in which the multilayer laminate structure shown in Figure 9 was coated with component A (coated unidirectional laminate fiber 6), the number of layers was significantly less than that of the composite fiber of the present invention, and the value of the sum of the interface lengths / fiber cross-sectional area was smaller. Therefore, even when a coating was provided on the fiber surface, many single fibers fibrillated after 20 or fewer friction cycles, and the abrasion resistance was poor.

[0142] [Example 15] Component A: polyethylene terephthalate (PET, melt viscosity: 120 Pa·s, melting point: 254°C, SP value: 21.4 MPa) 1 / 2 ) and, as component B, polyethylene terephthalate copolymerized with 8.0 mol% of 5-sodium sulfoisophthalic acid and 9 wt% of polyethylene glycol (SSIA-PEG copolymer PET, melt viscosity: 95 Pa·s, melting point: 233°C, SP value: 22.9 MPa). 1 / 2 The difference in solubility parameters between these polymers was 1.5 MPa. 1 / 2 This becomes:

[0143] After melting components A and B separately at 290°C, the resulting mixture was fed into a spinning pack equipped with a composite spinneret 10 (see Figure 8) with a composite ratio of 80 / 20. A composite polymer stream was extruded from the extrusion holes. The composite plate F was equipped with microchannels H 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 1. 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 yarn 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.

[0144] When the cross-sectional morphology of the obtained composite fiber was observed, it was confirmed that it had a plate-like laminated structure with the lamination direction aligned as shown in Figure 1, and was a multi-layer laminated fiber.

[0145] The resulting composite fiber was woven into a fabric, and the fabric was evaluated for peel resistance. No fibril formation was observed even after 50 or more rubs. Incidentally, when the cross section of the composite fiber after the abrasion resistance evaluation was observed with a scanning electron microscope (SEM) manufactured by Hitachi, Ltd., no peeling between the components was observed, demonstrating excellent abrasion resistance.

[0146] This composite fiber was immersed in a 1% sodium hydroxide aqueous solution (bath ratio 1:50) heated to 90°C for more than 30 minutes, removing more than 99% of the SSIA-PEG copolymerized PET (component B), to obtain a multifilament composed of flat ultrafine fibers. A fabric woven from the composite fiber was also treated in the same way, to obtain a fabric composed of flat ultrafine fibers.

[0147] Observation of the cross section of the obtained flat ultrafine fibers revealed that they had a ribbon-like cross section with significantly different major and minor axis lengths, a flatness of 80, and an average thickness of 225 nm. The variation in cross-sectional thickness was 36%, and the irregularity was 30%, indicating that there was a moderate variation in thickness and that the surface had a moderate irregularity.

[0148] When the cross section of the obtained flat ultrafine fiber woven fabric was also observed, it was found that many flat ultrafine fibers were overlapping with their short axes aligned, forming a dense fiber bundle structure. Furthermore, the flat ultrafine fibers were aggregated as if they were glued together, and extremely fine gaps ranging from several nanometers to several hundred nanometers existed between the fibers.

[0149] 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.

[0150] 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%. A large amount of the functional substance was adsorbed, and the fabric was highly durable and resistant to shedding.

[0151] The results are shown in Table 4.

[0152] [Examples 16 and 17] The same procedure as in Example 15 was carried out, except that the composite plate was changed to one equipped with microchannels in which the total number of layers of component A and component B was stacked to 64 layers (Example 16) and 32 layers (Example 17). These composite fibers were subjected to the same dissolution treatment as above to produce flat ultrafine fibers. The evaluation results of these composite fibers and flat ultrafine fibers are shown in Table 4.

[0153] Examples 16 and 17 had extremely thin cross-sectional shapes with high flatness, although the degree of variation varied, and had moderate minor axis length variation and unevenness. Similar to Example 15, they had a dense fiber bundle structure in which the flat ultrafine fibers were aligned and stacked. However, compared to Example 15, the flatness decreased and the average layer thickness increased, resulting in coarse interfiber spaces in the fiber bundles and fewer aggregates of single fibers. When immersed in a dye-resistant dye, the dye was distributed as if encapsulated within the fiber bundles. Compared to Example 15, the specific surface area decreased, resulting in a slight decrease in the content of the functional substance, but the content remained high, demonstrating sufficient deodorizing properties. Even after washing, the content of the functional substance remained high, and the functional substance was less likely to come off.

[0154] [Examples 18 and 19] The same procedure as in Example 15 was carried out, except that the composite plate was changed to one equipped with microchannels in which the total number of layers of component A and component B was stacked to 256 layers (Example 18) and 512 layers (Example 19). These composite fibers were subjected to the same dissolution treatment as above to produce flat ultrafine fibers. The evaluation results of these composite fibers and flat ultrafine fibers are shown in Table 4.

[0155] In Examples 18 and 19, the cross sections were extremely thin and ribbon-like, with extremely high flatness and moderate minor axis length variation and irregularity. Similar to Example 15, the flat ultrafine fibers had a dense fiber bundle structure in which they were stacked in the same direction. However, compared to Example 15, the flatness increased and the average minor axis length decreased, resulting in extremely small interfiber voids of several to several tens of nanometers. The fibers aggregated throughout the fiber bundle as if they were glued 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 minor axis length was extremely short, resulting in excessive flexibility and poor handling. Compared to Example 15, the specific surface area increased, resulting in an increased content of the functional substance, resulting in excellent deodorizing properties. Furthermore, because the fiber bundles had a strong aggregate structure encapsulating 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.

[0156] Comparative Example 5 The procedure was the same as in Example 15, except that polyethylene terephthalate (PET, melt viscosity: 120 Pa s, melting point: 254°C, SP value: 21.4 MPa) was used, melted at 290°C, and then introduced into a single spinning pack and extruded from the nozzle. The evaluation results of this single fiber are shown in Table 4.

[0157] Comparative Example 5 was a fiber with a round cross section and a typical fiber diameter, had a small specific surface area, and had a sparse structure with large distances between individual fibers even in the 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, upon washing, the content of the functional substance decreased to nearly zero, and the functional substance attached to the fiber surface easily fell off.

[0158] Comparative Example 6 The same operations as in Example 15 were carried out, except that a spin pack incorporating an 8-island-sea composite spinneret in which component A was used as island components and component B was used as the sea component was used. The sea-island composite fibers were subjected to the same dissolution treatment as above to produce ultrafine fibers. The evaluation results of the ultrafine fibers are shown in Table 4.

[0159] In Comparative Example 6, the fiber diameter was significantly reduced to ultrafine fibers, resulting in a large specific surface area. Furthermore, the distance between 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 functionally processed, the increased specific surface area due to ultrafine fiber size resulted in moderate adhesion of the functional substance, but did not result in high deodorizing properties, and washing significantly reduced the amount of functional substance adsorbed.

[0160] Comparative Example 7 The same procedure as in Example 15 was repeated, except that the composite plate was changed to one with microchannels, in which a total of eight layers of components A and B were laminated. The composite fiber was subjected to the same dissolution treatment as above to produce flat fibers. The evaluation results of the composite fiber and flat fibers are shown in Table 4.

[0161] As shown in Figure 10, the flat fiber 7 of Comparative Example 7 had a cross-sectional shape with low flatness. Furthermore, due to the low flatness, the flat fibers 7 in the multifilament were not aligned in the same direction, resulting in a fiber bundle structure with large distances between the individual fibers, as shown in Figure 11. 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 easily fell off.

[0162] [Example 20] The same procedure as in Example 15 was carried out, except that a composite plate with microchannels having a junction and a branch, each having a different channel diameter, was used. The composite fiber was subjected to the same dissolution treatment as above to produce flat ultrafine fibers. The evaluation results of the composite fiber and the flat ultrafine fibers are shown in Table 5.

[0163] Example 20 had a highly flat, ultrathin cross-sectional shape similar to Example 15. However, due to changes in the flow path design of the composite plate, the minor axis length variation and unevenness were small and uniform. It also had a dense fiber bundle structure in which the flat ultrafine fibers were aligned and stacked, similar to Example 15. However, 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 15. 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 15, the dispersibility of the single fibers was low, resulting in a slightly lower content of the functional substance, but the functional substance was less likely to come off during washing.

[0164] [Example 21] In the method described in Example 15, component A was replaced with polyamide-6 (N6, melt viscosity: 100 Pa·s, melting point: 225°C, SP value: 23.7 MPa). 1 / 2 ), component B is polyethylene terephthalate copolymerized with 8.0 mol% of 5-sodium sulfoisophthalic acid and 9 wt% of polyethylene glycol (SSIA-PEG copolymer PET, melt viscosity: 95 Pa·s, melting point: 233°C, SP value: 22.9 MPa 1 / 2 The same procedure as in Example 1 was carried out except that the spinning temperature was 280°C. The difference in solubility parameters of the combined polymers was 0.8MP. 1 / 2 The composite fiber was subjected to the same dissolution treatment as above to generate flat ultrafine fibers. The evaluation results of the composite fiber and the flat ultrafine fibers are shown in Table 5.

[0165] Example 21 had a highly flat, extremely thin cross-sectional shape similar to Example 15, but due to the hydrogen bonding between the fibers, the fiber bundle had a more densely aggregated structure than Example 15. When functionally processed, it showed the same content of functional substance as Example 15. Because the fibers were connected by hydrogen bonds, it swelled during washing and was more likely to be redispersed into single fibers, and the functional substance was more likely to fall off during washing than Example 15.

[0166] [Example 22] In the method described in Example 15, component A was replaced with polypropylene (PP, melt viscosity: 70 Pa·s, melting point: 165°C, SP value: 16.8 MPa 1 / 2 ), component B is polyethylene terephthalate copolymerized with 8.0 mol% of 5-sodium sulfoisophthalic acid and 9 wt% of polyethylene glycol (SSIA-PEG copolymer PET, melt viscosity: 95 Pa·s, melting point: 233°C, SP value: 22.9 MPa 1 / 2 The same procedure as in Example 15 was carried out except that the spinning temperature was 280°C. The difference in solubility parameters of the combined polymers was 6.1 MPa. 1 / 2 When the cross-sectional form of this composite fiber was observed, it was found that the large difference in solubility parameters resulted in unstable cross-section formability, and that the composite fiber had an irregular layer structure in which the layering direction changed locally on the cross section, different from that of Example 15. This composite fiber was subjected to the same dissolution treatment as above to produce flat ultrafine fibers. The evaluation results of this composite fiber and the flat ultrafine fibers are shown in Table 5.

[0167] Although Example 22 had a lower flatness and a smaller specific surface area than Example 15, resulting in a lower content of functional substance, it still had a high content and the functional substance was less likely to fall off when washed.

[0168] [Table 1]

[0169] [Table 2]

[0170] [Table 3]

[0171] [Table 4]

[0172] [Table 5]

[0173] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2020-210112) filed on December 18, 2020, the entire contents of which are incorporated by reference. [Explanation of symbols]

[0174] 1: Unidirectional laminated fiber 2: Radial laminated fiber 3: Concentric laminated fiber 4: Flat ultrafine fiber 5: Multifilament 6: Coated unidirectional laminated fiber 7: Flat fiber 10: Composite nozzle A: Component A B:B component D: Functional substance E: Weighing plate F: Composite plate G: Discharge plate H: Fine channel

Claims

1. A composite fiber made of two or more polymers, having a fiber cross section in which a plurality of interfaces are formed, and the value obtained by dividing the sum of the lengths of the interfaces of the two polymers by the area of ​​the fiber cross section is 0.0010 nm －１ The above-mentioned interface is continuous in the fiber axial direction, the fiber cross section has a multilayer laminate structure in which two types of polymers are alternately laminated, and the variation in layer thickness (CV value) of at least one type of polymer is 30% or more.

2. The sum of the interfacial lengths of the two polymers divided by the cross-sectional area of ​​the fiber is 0.0050 nm －１ The composite fiber according to claim 1 .

3. 3. The composite fiber according to claim 1 or claim 2, wherein the average layer thickness of at least one polymer is 1000 nm or less.

4. A textile product at least partly comprising the conjugated fiber according to any one of claims 1 to 3.

Images