Core-sheath composite fibers and nonwoven fabrics formed therefrom

Abstract

The present invention aims to provide core-sheath composite fibers and the like that can form nonwoven fabrics with good texture and excellent wet-back resistance. [Solution] The present invention relates to a core-sheath composite fiber comprising a core containing a first component thermoplastic resin and a sheath containing a second component thermoplastic resin having a melting point at least 40°C lower than the melting point of the resin, wherein both the core and the entire cross-section have a Y-shape in the fiber cross-section, the core content is 45% by mass or more and 80% by mass or less of the total fiber, and in the fiber cross-section, when the diameter of the inscribed circle of the core is DI1, the diameter of the circumscribed circle of the core is DO1, the diameter of the inscribed circle of the entire cross-section is DI2, and the diameter of the circumscribed circle of the entire cross-section is DO2, the sheath thickness ratio expressed as (DO2-DO1) / (DI2-DI1) is greater than 2.5 and 7.0 or less, the core deformation degree expressed as DO1 / DI1 is 3.2 or more and 5.0 or less, the tip of the core protrusion is contained within a triangle formed by connecting the tip of the sheath protrusion and two adjacent sheath recesses, and the core protrusion has a shape in which the width dimension decreases from the base to the tip.

Description

Technical Field

[0001] The present invention relates to core-sheath composite fibers and non-woven fabrics formed therefrom, which are used in applications such as sanitary materials for sanitary napkins, diapers, etc., medical and health materials, life-related materials, general medical materials, bedding materials, nursing care products, and pet products.

Background Art

[0002] There is a demand for further enhanced functionality in non-woven fabrics used in sanitary napkins, diapers, etc. For example, in terms of the tactile sensation where the top sheet feels crisp when worn, and in the case of sanitary napkins, it is desired to transfer the absorbed menstrual blood from the top sheet to the lower layer promptly, thereby maintaining the crisp tactile sensation. Thus, in non-woven fabrics, it is desired to have a good texture, but it is also desired to have a performance with a small amount of reverse flow of the absorbed liquid (hereinafter referred to as wet-back resistance).

[0003] As a conventional technology related to non-woven fabrics, Patent Document 1 is known. In Patent Document 1, in order to obtain a non-woven fabric having excellent flexibility and thermal bonding properties, bicomponent trilobal-shaped staple fibers or short-cut fibers composed of a core and a sheath are described. Further, Patent Document 2 describes profiled cross-section composite fibers having 3 or more and 16 or less convex portions as heat-bonding composite fibers for separator materials.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, for example, Patent Document 1 does not describe a suitable cross-sectional shape for exhibiting performance resulting from a Y-shaped cross-section as a deformed cross-section of the fiber. While it states that the sheath preferably has a constant thickness, in the case of such fibers, there is a concern that the degree of fiber deformation will decrease significantly after heat treatment due to surface tension, as the sheath resin tends to gather in the center due to surface tension during the formation of the nonwoven fabric. Furthermore, since the sheath thickness is constant around the entire circumference of the fiber cross-section, the degree of deformation of the fiber as a whole is small, and it is thought that the desired tactile feel cannot be obtained from a nonwoven fabric formed from such fibers. In addition, Patent Document 1 does not describe any wet-back resistance or means for controlling it.

[0006] Patent Document 2 proposes a fiber cross-sectional shape that is easily flattened in order to firmly bond fibers together in order to improve the density and mechanical properties of separator materials. However, Patent Document 2 does not describe a means to produce a desired tactile feel or to control wet-back resistance using Y-shaped core-sheath composite fibers.

[0007] On the other hand, the inventors found that the cooling conditions during spinning are problematic in the production of Y-shaped core-sheath composite fibers, leading to a decrease in texture and wet-back resistance. They proceeded with the development of core-sheath composite fibers that can solve these problems. In other words, the present invention aims to provide a core-sheath composite fiber capable of forming a nonwoven fabric with good texture and excellent wet-back resistance, and a nonwoven fabric formed therefrom. [Means for solving the problem]

[0008] The core-sheath composite fiber of the present invention, which has achieved the above objective, has the following characteristics. The core-sheath composite fiber of the present invention is a core-sheath composite fiber comprising a core containing a first component thermoplastic resin and a sheath containing a second component thermoplastic resin having a melting point 40°C or more lower than the melting point of the resin, In the fiber cross-section, both the core and the entire cross-section have a Y-shape. The core content is 45% by mass or more and 80% by mass or less of the total fiber. In a fiber cross-section, if the diameter of the inscribed circle of the core is DI1, the diameter of the circumscribed circle of the core is DO1, the diameter of the inscribed circle of the entire cross-section is DI2, and the diameter of the circumscribed circle of the entire cross-section is DO2, The sheath thickness ratio expressed as (DO2-DO1) / (DI2-DI1) is greater than 2.5 and 7.0 or less. The core deformation degree, expressed as DO1 / DI1, is 3.2 or higher and 5.0 or lower. The tip of the core protrusion is located within the triangle formed by the tip of the sheath protrusion and the two adjacent recesses of the sheath. The core protrusion is characterized by having a shape in which the width dimension decreases from the base to the tip.

[0009] In the present invention, it is preferable that the sheath thickness ratio, expressed as (DO2-DO1) / (DI2-DI1), is 3.45 or higher, and the single filament fineness is preferably 1.2 dtex or higher and 10.0 dtex or lower. It is also a desirable requirement that the cross-sectional shape of the fiber after being treated with 130°C hot air at a wind speed of 0.55 m / s for 10 seconds be Y-shaped. Another aspect of the present invention includes a nonwoven fabric formed from the core-sheath composite fibers. In the nonwoven fabric of the present invention, it is preferable that the amount of wet back measured under the following conditions is 6.4 g or less. [An absorbent material was placed beneath a 30gsm nonwoven fabric, and 50ml of artificial urine was injected three times from the nonwoven fabric side. After letting it stand for one hour, a filter paper was placed in the center of the injection site, and a 5.0kg weight was placed on top of the filter paper. Then, after 5 minutes, the weight was removed, and the mass of the filter paper was measured. The change in mass (mass of filter paper after weight removal - mass of filter paper before weight placement) was defined as the wet bag volume.] [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a core-sheath composite fiber capable of forming a nonwoven fabric with a good texture and excellent wet-back resistance, and a nonwoven fabric formed therefrom. [Brief explanation of the drawing]

[0011] [Figure 1]Figure 1 shows a cross-section of a core-sheath composite fiber according to one embodiment of the present invention, including the circumscribed and inscribed circles of the core, the circumscribed and inscribed circles of the entire cross-section, and their diameters. [Figure 2] Figure 2 shows the relationship between the convex and concave portions of the entire cross-section and the convex portion of the core in a cross-section of a core-sheath composite fiber according to one embodiment of the present invention. [Figure 3] Figure 3 shows the relationship between the convex and concave portions of the core in a cross-section of a core-sheath composite fiber according to one embodiment of the present invention. [Modes for carrying out the invention]

[0012] The present invention will be described in more detail below based on the embodiments described below. However, the present invention is not limited by the embodiments described below, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention. In addition, hatching and component reference numerals may be omitted in the drawings for convenience, in which case please refer to the specification or other drawings. Furthermore, the dimensions of various components in the drawings may differ from the actual dimensions, as priority has been given to helping to understand the features of the present invention.

[0013] The core-sheath composite fiber of the present invention is a core-sheath composite fiber comprising a core containing a first component thermoplastic resin and a sheath containing a second component thermoplastic resin having a melting point 40°C or more lower than the melting point of the resin, In the fiber cross-section, both the core and the entire cross-section have a Y-shape. The core content is 45% by mass or more and 80% by mass or less of the total fiber. In a fiber cross-section, if the diameter of the inscribed circle of the core is DI1, the diameter of the circumscribed circle of the core is DO1, the diameter of the inscribed circle of the entire cross-section is DI2, and the diameter of the circumscribed circle of the entire cross-section is DO2, The sheath thickness ratio expressed as (DO2-DO1) / (DI2-DI1) is greater than 2.5 and 7.0 or less. The core deformation degree, expressed as DO1 / DI1, is 3.2 or higher and 5.0 or lower. The tip of the core convex portion enters into the triangle connecting two of the most concave portions of the sheath adjacent to the tip of the sheath convex portion. The core convex portion is characterized in that the dimension in the width direction decreases from the root to the tip. Since the core-sheath composite fiber of the present invention has the above structure in the fiber cross section and has the above physical properties, it is possible to form a non-woven fabric with good texture and excellent wet-back resistance.

[0014] <Structure of core-sheath composite fiber> The structure of the core-sheath composite fiber of the present invention will be described with reference to FIG. 1. FIG. 1 shows a cross section of a core-sheath composite fiber 10 composed of a core 1 and a sheath 2 covering the core 1 (hereinafter, the sheath 2 may sometimes be referred to as the entire cross section).

[0015] In the fiber cross section, both the core 1 and the sheath 2 have a Y-shaped configuration. That is, the core 1 and the sheath 2 (the entire cross section) have three convex portions. It is preferable that the core 1 and the sheath 2 have the same center of gravity (center).

[0016] The convex portions of the core 1 and the entire cross section forming the Y-shaped configuration are preferably evenly arranged when viewed from the center of the core 1, and the angles formed by the straight lines connecting the center and the tips of the respective convex portions are more preferably 120° each. It is preferable that the angles formed by the straight lines connecting the center and the tips of the respective convex portions are the same, but they may be different. When the angles formed by the straight lines connecting the center and the tips of the respective convex portions are different, the angles may preferably be different in the range of 120° ± 10°, more preferably in the range of 120° ± 5°.

[0017] From the viewpoint of obtaining the circumscribed circle of the core 1, it is preferable that the heights of the three convex portions of the core 1 are the same, but the heights of two of the convex portions of the core 1 may be the same and the height of the remaining one convex portion may be different. From the viewpoint of obtaining the circumscribed circle of the core 1 or the entire cross section, it is preferable that the heights of the three convex portions of the sheath 2 or the entire cross section are the same, but the heights of two of the convex portions of the sheath 2 or the entire cross section may be the same and the height of the remaining one convex portion may be different.

[0018] Preferably, the tip (most convex part) of the convex part of core 1 coincides with the circumscribed circle of core 1, and preferably, the tip (most convex part) of the convex part of sheath 2 (entire cross-section) coincides with the circumscribed circle of sheath 2 (entire cross-section). Preferably, the peripheral portion including the tip (most convex part) of the convex part of core 1 and the peripheral portion including the tip (most convex part) of the convex part of sheath 2 (entire cross-section) have a curved surface shape with the tip as the apex and both sides of the tip curved, having a predetermined radius of curvature.

[0019] The width of the protrusions of the core 1 and sheath 2 (overall cross-section) is preferably largest at the base and smallest at the tip, as described later, and preferably gradually decreases from the base to the tip. It is preferable that the protrusions of the core 1 and sheath 2 (overall cross-section) do not have recesses from the base to the tip. If recesses exist from the base to the tip, stress may be applied to the recesses during manufacturing or heat fusion, potentially causing the protrusions to break.

[0020] It is preferable that the core 1 and sheath 2 (overall cross-section) have recesses between the convex portions. In other words, it is preferable that the core 1 and sheath 2 (the entire cross-section) have three protrusions and three recesses. It is preferable that both the peripheral portion of the core 1, including the deepest recess, and the peripheral portion of the sheath 2 (entire cross-section), including the deepest recess, form a gently curved surface. Preferably, the deepest recess of the core 1 coincides with the inscribed circle of the core 1, and preferably, the deepest recess of the sheath 2 (entire cross-section) coincides with the inscribed circle of the sheath 2 (entire cross-section).

[0021] The core 1 is preferably a solid structure, but may also be a hollow structure, and there may be two or more hollow structures in the core.

[0022] The cross-sectional structure of a core-sheath composite fiber is represented based on the circumscribed and inscribed circles of the core 1, as well as the circumscribed and inscribed circles of the entire cross-section formed by the sheath 2 covering the core 1, and their diameters.

[0023] Specifically, in Figure 1, the diameter of the circumscribed circle of core 1 is shown as DO1, the diameter of the inscribed circle of core 1 is shown as DI1, the diameter of the circumscribed circle of the entire cross-section is shown as DO2, and the diameter of the inscribed circle of the entire cross-section is shown as DI2. The cross-sectional structure of the core-sheath composite fiber is represented in more detail based on the sheath thickness ratio ((DO2-DO1) / (DI2-DI1)), core deformation (DO1 / DI1), overall cross-sectional deformation (DO2 / DI2), and overall cross-sectional deformation after heat treatment (DO2 / DI2). Furthermore, the relationship between diameter size and size is DO2 > DO1 > DI2 > DI1. Furthermore, it is preferable that the relationship (DO2-DO1)>(DI2-DI1) is satisfied, the thickness of the protrusion of the sheath is preferably (DI2-DI1) or greater and (DO2-DO1) or less, and the thickness of the tip of the protrusion of the sheath is preferably (DO2-DO1). The thickness of the recess in the sheath is preferably greater than 0 and less than or equal to (DI2-DI1), and the thickness of the deepest recess in the sheath is preferably (DI2-DI1).

[0024] <Sheath Thickness Ratio> (DO2-DO1) / (DI2-DI1) The sheath thickness ratio may also be expressed as the ratio of the sheath thickness at the tip of the convex portion of the entire cross-section to the sheath thickness of the concave portion of the entire cross-section, and can be considered an indicator of the degree of deformation of the sheath thickness at the tip of the convex portion of the entire cross-section relative to the sheath thickness of the concave portion of the entire cross-section.

[0025] The sheath thickness ratio expressed as (DO2-DO1) / (DI2-DI1) is greater than 2.5 and 7.0 or less, preferably 3.45 or more and 6.9 or less, more preferably 3.5 or more and 6.8 or less, even more preferably 3.55 or more and 6.7 or less, even more preferably 3.6 or more and 6.6 or less, particularly preferably 3.65 or more and 6.5 or less, and most preferably 3.7 or more and 6.4 or less.

[0026] If the sheath thickness ratio is 2.5 or less, or less than 3.45, the amount of thermoplastic resin, the second component, remaining at the tip of the protrusions during melting will be small. This may reduce the overall degree of deformation of the fiber, making it difficult to obtain the Y-shape effect, and potentially increasing the amount of wet back in the nonwoven fabric. Furthermore, the sheath thickness at the tip of the protrusions will be thin, which may lead to sheath peeling, or in severe cases, the core may be exposed, potentially degrading the performance of the nonwoven fabric. If the sheath thickness ratio exceeds 7.0, the tip of the convex part of the entire cross-section becomes too sharp, resulting in a high degree of deformation, and there is a risk of the sheath breaking or peeling off during manufacturing (for example, during the crimping process).

[0027] <Core shape variation> (DO1 / DI1) Core deformation can be considered an indicator of the height of the core protrusion. The core deformation degree represented by DO1 / DI1 is 3.2 or higher and 5.0 or lower, preferably 3.3 or higher and 4.9 or lower, more preferably 3.4 or higher and 4.8 or lower, even more preferably 3.5 or higher and 4.7 or lower, even more preferably 3.6 or higher and 4.6 or lower, particularly preferably 3.7 or higher and 4.5 or lower, and most preferably 3.8 or higher and 4.4 or lower.

[0028] If the core deformation degree is less than 3.2, it is not possible to increase the overall deformation degree of the fibers, and there is a risk that the deformation degree will further decrease after heat treatment, resulting in a large amount of wet back in the nonwoven fabric formed from Y-shaped sheath composite fibers. If the core deformation degree exceeds 5.0, the tip of the core protrusion will become pointed, which may prevent the sheath ratio of the fiber protrusion tip from being increased. Furthermore, when nonwoven fabrics are manufactured using the air-through method, there is a risk that the core may become exposed, potentially degrading the nonwoven fabric's properties. In addition, during the crimping process using a crimper, sheath peeling may occur, convex parts may break, or the entire cross-section may become flattened, making it difficult to obtain the desired Y-shape effect.

[0029] <Overall Cross-Sectional Deformity> (DO2 / DI2) The overall degree of irregularity in the cross-section can be considered an indicator of the height of the protrusions in the fibers. The overall cross-sectional deformation, represented by DO2 / DI2, is preferably 2.0 or more and 4.5 or less, more preferably 2.1 or more and 4.2 or less, even more preferably 2.2 or more and 3.9 or less, and even more preferably 2.3 or more and 3.6 or less.

[0030] If the overall degree of deformation in the cross-section is less than 2.0, the degree of deformation of the core-sheath composite fiber as a whole is low, and there is a risk that the degree of deformation will decrease even further after heat treatment, resulting in a large amount of wet back in the nonwoven fabric formed from the core-sheath composite fiber. On the other hand, if the overall degree of deformation in the cross-section exceeds 4.5, the degree of deformation of the core-sheath composite fiber as a whole increases, but there is a risk of the sheath peeling off or breaking.

[0031] <Overall cross-sectional deformation after heat treatment> (DO2 / DI2) Since the core-sheath composite fiber of the present invention is heat-treated during the formation of the nonwoven fabric, it is preferable that the entire cross-section has a predetermined degree of deformation after heat treatment, from the viewpoint of providing a good tactile feel for the nonwoven fabric. Although the thermoplastic resin, the second component constituting the sheath, tends to round due to surface tension caused by the thermal history, reducing the overall degree of deformation in the cross-section, it is sufficient if it maintains a relatively good degree of deformation.

[0032] The degree of irregularity of the entire cross-section may be evaluated by the fiber cross-sectional shape, and the fiber cross-sectional shape after heat treatment based on the following conditions is preferably Y-shaped. One heat treatment condition involves applying hot air at 130°C at a wind speed of 0.55 m / s for 10 seconds.

[0033] If the fiber cross-sectional shape after heat treatment is not Y-shaped, the overall degree of deformation of the core-sheath composite fiber will decrease, making it difficult to obtain capillary action due to increased surface area. This may lead to an increase in the amount of wet back of the nonwoven fabric formed from the core-sheath composite fiber, or the overall degree of deformation of the core-sheath composite fiber may become too high, potentially causing the sheath to peel off or break.

[0034] Next, referring to Figure 2, the relationship between the convex and concave parts and the core convex part of the sheath (the entire cross-section) will be explained. In Figure 2, the tip 3 of the sheath projection coincides with the circumscribed circle of the entire cross-section, the deepest recess 4 of the sheath coincides with the inscribed circle of the entire cross-section, and the tip 5 of the core projection coincides with the circumscribed circle of the core. As shown in Figure 2, the tip of the core protrusion 5 is located within a triangle formed by the tip of the sheath protrusion 3 and the two adjacent recesses 4 of the sheath. It is preferable that the tip of the core protrusion 5 and the tip of the sheath protrusion 3 lie on a straight line connecting the center of the circumscribed circle and the inscribed circle of the tip 5 and the tip 3. By keeping the distance between the tip of the core protrusion 5 and the tip of the sheath protrusion 3 as close as possible in this way, it is possible to suppress sheath peeling during manufacturing or post-processing. If the tip 5 of the core protrusion does not fit within the triangle, the degree of core deformation will not increase, and the degree of fiber deformation will not increase, which may lead to a decrease in the properties of the nonwoven fabric.

[0035] Furthermore, the relationship between the core protrusion and core recess will be explained with reference to Figure 3. The tip 5 of the core's convex portion coincides with the circumscribed circle of the core, and the innermost recess 6 of the core coincides with the inscribed circle of the core. The core protrusion has a shape in which the width dimension decreases from the base to the tip. If the width dimension is partially reduced from the base of the core to the tip, there is a risk that the sheath may break or peel off due to external force during manufacturing or post-processing, with the smaller portion acting as the starting point. Furthermore, there is a risk that the amount of wet back in the nonwoven fabric formed from the core-sheath composite fiber will increase.

[0036] <Composition of core-sheath composite fibers> The core-sheath composite fiber of the present invention contains a first component thermoplastic resin in the core and a second component thermoplastic resin in the sheath, wherein the first component thermoplastic resin has a melting point at least 40°C higher than that of the second component thermoplastic resin.

[0037] <core> The melting point of the first component thermoplastic resin constituting the core is preferably 50°C or more higher than the melting point of the second component thermoplastic resin, and more preferably 60°C or more higher. If the melting point of the first component thermoplastic resin is less than the melting point of the second component thermoplastic resin + 40°C, the fibers may soften during air passage, and the nonwoven fabric may be formed with a narrowed inter-fiber distance due to the surface tension of the sheath, which may result in the nonwoven fabric not having sufficient properties. Furthermore, by employing specific cooling conditions during spinning, the yarn cools more quickly, allowing it to solidify before its shape relaxes. This increases the degree of core deformation and reduces the amount of wet back.

[0038] The first component, a thermoplastic resin, can be any resin that exhibits strength and low shrinkage as a core component. Examples include polyester resins such as polyethylene terephthalate (melting point 255°C), polybutylene terephthalate (melting point 230°C), polytrimethylene terephthalate (melting point 230°C), polyethylene naphthalate (melting point 265°C), and polybutylene naphthalate (melting point 243°C); and polyamide resins such as nylon 6 (melting point 220°C), nylon 66 (melting point 265°C), and nylon 56 (melting point 255°C).

[0039] In particular, the thermoplastic resin of the first component preferably contains a polyester resin having a melting point of 210°C or higher (preferably 220°C or higher, more preferably 230°C or higher and 280°C or lower), from the viewpoint of strength and low shrinkage, and from the viewpoint of using a resin whose melting point is 40°C or higher than that of the thermoplastic resin of the second component used as a sheath component. It is more preferably that it contains polyethylene terephthalate (melting point 255°C), polybutylene terephthalate (melting point 230°C), polytrimethylene terephthalate (melting point 230°C), polyethylene naphthalate (melting point 265°C), and polybutylene naphthalate (melting point 243°C), and is especially preferably that it contains polyethylene terephthalate. The thermoplastic resin of the first component may be one type or two or more types.

[0040] The first component thermoplastic resin may have a predetermined intrinsic viscosity, and the intrinsic viscosity (IV) of the first component thermoplastic resin is preferably 0.3 to 2.0 dl / g, more preferably 0.5 to 1.5 dl / g, and even more preferably 0.55 to 0.80 dl / g. The intrinsic viscosity (IV) of the first component thermoplastic resin can be determined by pulverizing and drying the sample, dissolving it in a 6 / 4 (mass ratio) mixed solvent of phenol / 1,1,2,2-tetrachloroethane, centrifuging the solution to remove inorganic particles, and then measuring the viscosity at 30°C using an Ubbelohde viscometer.

[0041] The content of the first component thermoplastic resin having a melting point of 210°C or higher is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 97% by mass or more, particularly preferably 99% by mass or more, and most preferably 100% by mass, out of 100% by mass of the first component thermoplastic resin. When the content of the first component thermoplastic resin having a melting point of 200°C or higher is within the above range, the core strength can be improved.

[0042] The content of the first component thermoplastic resin is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, preferably 100% by mass or less, more preferably 98% by mass or less, even more preferably 97% by mass or less, and even more preferably 96% by mass or less, based on 100% by mass of the core. If the content of the first component, thermoplastic resin, is less than 80% by mass, there is a risk that the strength of the core will decrease and the adhesion between the core and the sheath will decrease.

[0043] From the viewpoint of core strength, the content of the first component thermoplastic resin is 45% by mass or more and 80% by mass or less relative to the total fiber, preferably 50% by mass or more and 75% by mass or less, and more preferably 55% by mass or more and 70% by mass or less. If the content of the first component thermoplastic resin is lower than 45% by mass, the second component thermoplastic resin will tend to curl due to surface tension when melted during the air-through heat bonding process in nonwoven fabric processing. This reduces the overall degree of irregularity of the fibers, and there is a risk that the resulting nonwoven fabric will not achieve the enhanced capillary action expected from a Y-shaped cross-section or the dry touch feeling due to reduced contact area with the skin. If the content of the first component thermoplastic resin is higher than 80% by mass, there is a risk that the second component thermoplastic resin, which forms the sheath, will peel off from the first component thermoplastic resin, which forms the core, during the spinning process. Furthermore, if the core, which is made of the thermoplastic resin of the first component, is exposed, the oil applied to the surface of the sheath may adhere to the core, potentially reducing the hydrophilicity of the fibers and thus degrading the properties of the nonwoven fabric.

[0044] The core may contain inorganic particles that modify the properties of the first component thermoplastic resin. Examples of inorganic particles include titanium dioxide, calcium carbonate, talc, silica, and aluminum oxide.

[0045] The inorganic particle content is preferably 0 to 15% by mass, more preferably 1 to 15% by mass, even more preferably 2 to 13% by mass, and even more preferably 3 to 11% by mass, based on 100% by mass of the core.

[0046] The core may contain components other than those mentioned above, as long as it achieves the effects of the present invention. Additives such as antioxidants, antistatic agents, antiblocking agents, pigments, heat stabilizers, ultraviolet absorbers, and lubricants may be added to the extent that they do not interfere with the effects of the present invention.

[0047] <Sheath> The thermoplastic resin of the second component constituting the sheath is not particularly limited as long as its melting point is 40°C or more lower than that of the thermoplastic resin of the first component. Examples include polyethylene such as low-density polyethylene (melting point 100-115°C), medium-density polyethylene (melting point 115-125°C), high-density polyethylene (melting point 125°C-137°C), and ultra-high molecular weight polyethylene (melting point 135-140°C), and polyolefin resins such as polypropylene (melting point 165°C); and polyester resins such as polylactic acid (melting point 170-175°C), polybutylene succinate (melting point 115°C), polycaprolactone (melting point 55-60°C), polyhydroxyalkanoate (melting point ~180°C), and polybutylene adipate terephthalate (melting point 225-228°C).

[0048] In particular, the second component thermoplastic resin preferably has a melting point of 170°C or lower (preferably 160°C or lower and 70°C or higher), more preferably contains polyethylene or polypropylene, and even more preferably contains polyethylene. The second component thermoplastic resin may be one type or two or more types.

[0049] The second component thermoplastic resin may have a predetermined melt flow rate (MFR) as measured according to JIS K 6922-2, and the melt flow rate (MFR) of the second component thermoplastic resin is preferably 8 to 25 g / 10 min, more preferably 9 to 21 g / 10 min, under conditions of a load of 2.16 kg and a temperature of 190 °C.

[0050] The content of the second component thermoplastic resin having a melting point of 170°C or lower is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass, based on 100% by mass of the second component thermoplastic resin. When the content of the second component thermoplastic resin is within the above range, a nonwoven fabric with high adhesion between fibers can be produced by heat fusion.

[0051] The content of the second component, thermoplastic resin, is preferably 85% by mass or more, more preferably 87% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, preferably 100% by mass or less, more preferably 98% by mass or less, even more preferably 97% by mass or less, and even more preferably 96% by mass or less, based on 100% by mass of the sheath.

[0052] The content of the second component, thermoplastic resin, is preferably 20% to 55% by mass, more preferably 25% to 50% by mass, even more preferably 30% to 45% by mass, and even more preferably 35% to 45% by mass, relative to the total fiber.

[0053] The sheath may contain inorganic particles that modify the properties of the second component, the thermoplastic resin. Examples of inorganic particles include titanium dioxide, calcium carbonate, talc, silica, and aluminum oxide.

[0054] The inorganic particle content is preferably 0 to 15% by mass, more preferably 1 to 15% by mass, even more preferably 2 to 13% by mass, and even more preferably 3 to 11% by mass, based on 100% by mass of the sheath.

[0055] The sheath may contain components other than those mentioned above, as long as it achieves the effects of the present invention. Additives such as antioxidants, antistatic agents, antiblocking agents, pigments, heat stabilizers, ultraviolet absorbers, and lubricants may be added to the extent that they do not interfere with the effects of the present invention.

[0056] In the core-sheath composite fiber of the present invention, the mass ratio of the core component to the sheath component is preferably less than 7.0, more preferably 5.0 or less, even more preferably 4.0 or less, even more preferably 3.0 or less, particularly preferably 2.0 or less, and preferably 0.2 or more or 0.3 or more. By setting the mass ratio of core component to sheath component within the above range, the appropriate fiber strength and elongation for the nonwoven fabric can be achieved.

[0057] <Physical properties of core-sheath composite fibers> The core-sheath composite fiber of the present invention preferably has a predetermined maximum point elongation, maximum point stress, and fineness as physical properties. The maximum point elongation of the core-sheath composite fiber is preferably 21% or more, more preferably 30% or more, even more preferably 40% or more, even more preferably 50% or more, and preferably 150% or less or 120% or less. If the maximum elongation is lower than 21%, there is a risk of yarn breakage during spinning, which may result in a deterioration of the texture. Furthermore, yarn breakage may occur during post-processing, and fly may form during carding, potentially contaminating the equipment.

[0058] The maximum point stress of the core-sheath composite fiber is preferably 1.0 cN / dtex or more, more preferably 1.2 cN / dtex to 15 cN / dtex, even more preferably 1.4 cN / dtex to 12 cN / dtex, and even more preferably 1.6 cN / dtex to 10 cN / dtex. If the maximum point stress is less than 1.0 cN / dtex, thread breakage may occur during post-processing, and a phenomenon called "flying" may occur during carding, potentially contaminating the equipment. The maximum point elongation and maximum point stress can be measured, for example, according to JIS L1015 8.7.1.

[0059] The single filament fineness of the core-sheath composite fiber is preferably 1.2 dtex or more and 10 dtex or less, more preferably 1.4 dtex or more and 8 dtex or less, even more preferably 1.6 dtex or more and 6 dtex or less, and even more preferably 1.8 dtex or more and 5 dtex or less. If the single yarn fineness is less than 1.2 dtex, the fibers may be too soft, and the bulkiness of the nonwoven fabric may not be sufficient. Conversely, if the single yarn fineness is greater than 10 dtex, the nonwoven fabric may feel too stiff. The fineness of a single filament of a core-sheath composite fiber can be measured, for example, by the Denicon method.

[0060] <Method for preparing core-sheath composite fibers> The core-sheath composite fiber of the present invention preferably uses a first thermoplastic resin as the core component and a second thermoplastic resin as the sheath component, and preferably includes at least the steps of preparing an undrawn yarn under cooling conditions after melt spinning in a core-sheath shape, and drawing the undrawn yarn under heating conditions.

[0061] For example, it is preferable to obtain undrawn yarn using a nozzle with a different cross-section by a known melt spinning method, using polyethylene terephthalate as the first thermoplastic resin and polyethylene as the second thermoplastic resin. The spinning temperature is preferably 10°C or more higher than the melting point of the first thermoplastic resin, and more preferably 20°C or more higher than the melting point of the first thermoplastic resin.

[0062] The single-hole discharge rate of the nozzle can be appropriately adjusted according to the melting point and content of the first component thermoplastic resin and the second component thermoplastic resin, for example, 0.4 to 1.0 g / min·H, preferably 0.45 to 0.9 g / min·H, and more preferably 0.50 to 0.8 g / min·H.

[0063] In the method for producing core-sheath composite fibers of the present invention, the melt-spun yarn is wound up at a predetermined speed after exiting the nozzle to become an undrawn yarn. It is preferable that the melt-spun yarn be cooled after it is extruded from the nozzle and before it is wound up. Cooling means include air cooling (e.g., gaseous refrigerant), liquid cooling (e.g., liquid refrigerant, preferably water), and solid cooling (e.g., cooling rolls). Among these, air cooling is preferred, and cooling air is more preferred.

[0064] When employing a cooling method, it is preferable to adjust the temperature, speed or rotational speed of the cooling method, the distance from the nozzle or spinning rod, etc. The temperature of the cooling means (preferably cooling air) is preferably 10-30°C, more preferably 15-30°C, even more preferably 20-30°C, and particularly preferably 23-27°C. The speed of the cooling means (preferably cooling air) is, for example, greater than 0.8 m / s, preferably 0.85 m / s or more and less than 1.4 m / s, more preferably 0.9 m / s or more and 1.35 m / s or less, even more preferably 0.95 m / s or more and 1.3 m / s or less, and even more preferably 1.0 m / s or more and 1.25 m / s or less. If the speed is too high, the texture may deteriorate. The distance (LNz-QCH) between the cooling means (preferably cooling air) and the nozzle is preferably 10 mm to 80 mm, more preferably 15 mm to 70 mm, even more preferably 20 mm to 60 mm, and even more preferably 25 mm to 50 mm. If this range is exceeded, it may not be possible to obtain core-sheath composite fibers with an appropriate structure, and the cross-sectional shape of the fibers after hot air treatment may not be Y-shaped.

[0065] The obtained undrawn yarn may be drawn as needed. The drawing method is not particularly limited, but may consist of one or more stages of drawing. For example, the first stage of drawing may be performed at the glass transition temperature of the first component thermoplastic resin, and the second stage of drawing may be performed at a temperature above the glass transition temperature. The method of heating the fibers during drawing is not particularly limited, but examples include heating the fibers in hot water or with a heated roll.

[0066] In the case of single-stage stretching, stretching is preferably carried out at a temperature of 60 to 90°C (preferably 60 to 80°C) and a stretching ratio of 1.1 to 3.0 times (preferably 1.2 times to 2.9 times, more preferably 1.3 times to 2.85 times, and even more preferably 1.4 times to 2.80 times).

[0067] In the case of two-stage stretching, the first stage of stretching is preferably carried out at a temperature of 60 to 90°C (preferably 60 to 80°C) and a stretching ratio of 2.0 to 4.0 times (preferably 3.6 times or less, more preferably 3.2 times or less). The second stage of stretching is preferably carried out at a temperature of 90 to 130°C (preferably 100 to 120°C) and a stretching ratio of 0.8 to 1.2 times (preferably 0.9 to 1.1 times).

[0068] The method for producing core-sheath composite fibers of the present invention may include, in addition to the above steps, a crimping step, a post-heat treatment step, and a cutting step. The crimping process can be carried out using a crimping machine such as a Stafferbox type crimping machine. The post-heat treatment step may, for example, involve treating the resulting fibers at a temperature of 90-140°C (preferably 100-130°C) without applying tension to them.

[0069] When core-sheath composite fibers are cut to form short fibers, the average length of the short fibers is preferably 30 to 80 mm, more preferably 31 to 70 mm, and even more preferably 32 to 60 mm.

[0070] The resulting drawn yarn may be treated with surfactants or other substances as needed to enable it to exhibit its properties later. For example, if polyethylene is used as the second component thermoplastic resin, the fiber surface can be made hydrophilic by applying a surfactant to the surface.

[0071] The core-sheath composite fiber of the present invention may be a long fiber (filament), a short fiber (staple), or a combination thereof.

[0072] This invention encompasses nonwoven fabrics formed from core-sheath composite fibers. The nonwoven fabric is preferably formed by conventionally known fleece formation or fleece bonding. Fleece formation can be carried out using dry methods, wet methods, spunbond methods, melt flow methods, etc., and fleece bonding can be carried out using thermal bonding methods, chemical bonding methods, needle punching methods, spunlace methods, stitch bonding methods, steam jet methods, etc. Fleece formation and fleece bonding can be selected from the above options depending on the desired nonwoven fabric.

[0073] The nonwoven fabric of the present invention has the desired wet-back resistance, that is, the ability to reduce the amount of absorbed liquid that flows back. The amount of wet bag measured under the following conditions is preferably 6.4 g or less, more preferably 6.3 g or less, even more preferably 6.2 g or less, even more preferably 6.1 g or less, particularly preferably 6.0 g or less, and most preferably 5.5 g or less. Measurement conditions: An absorbent material was placed under a 30gsm nonwoven fabric, and 50 ml of artificial urine was injected three times from the nonwoven fabric side. After the three injections, it was left for one hour, then filter paper was placed in the center of the injection site, and a 5.0 kg weight was placed on the filter paper. After 5 minutes, the weight was removed, and the mass of the filter paper was measured. The change in mass (mass of filter paper after weight removal - mass of filter paper before weight placement) was defined as the wet bag volume. [Examples]

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention. In the following, unless otherwise specified, "parts" means "parts by mass" and "%" means "percent mass".

[0075] (1) Fineness, single yarn fineness Measurements were taken using the DENICON method with a "DENICON DC-21" manufactured by SEARCH CO.LTD.

[0076] (2) Maximum stress, maximum elongation Using "TENSILON / UTM-2-20" manufactured by TOYO BALDWIN CO.,LTD, the initial sample length was set to 20 mm in accordance with JIS L1015 8.7.1, the stress at the maximum load was defined as the stress at the maximum point, and the elongation rate at the maximum load was defined as the elongation at the maximum point.

[0077] (3) Core deformation degree and sheath thickness ratio Magnified cross-sectional images of core-sheath composite fibers were taken with a NIKON ECLIPSE CI-L microscope (400x magnification), and the degree of core deformation and sheath thickness ratio were measured using the following method.

[0078] <Core deformation degree> The core deformation degree was calculated by dividing DO1 by DI1, where DI1 is the diameter of the inscribed circle of the core and DO1 is the diameter of the circumscribed circle of the core.

[0079] <Sheath thickness ratio> The sheath thickness ratio was calculated by dividing (DO2-DO1) by (DI2-DI1), where DI2 is the diameter of the inscribed circle of the entire cross-section and DO2 is the diameter of the circumscribed circle of the entire cross-section.

[0080] (4) Fiber cross-sectional shape after heat treatment The fabricated fibers were treated with 130°C hot air at a wind speed of 0.55 m / s for 10 seconds. Magnified images of the fiber surface were then taken using a JCM-6000Plus desktop scanning electron microscope (200-500x magnification), and the fiber cross-sectional shape was evaluated.

[0081] (5) Evaluation of texture A sensory evaluation of nonwoven fabrics (smooth texture) was conducted by multiple individuals using a 5-point scale (1 to 5 points). Products with an average sensory evaluation score of less than 3 points were marked with an "X," and those with an average score of 3 points or higher were marked with an "O."

[0082] (6) Evaluation of wet bag (WB) volume An absorbent material was placed beneath a 30gsm nonwoven fabric, and 50 ml of artificial urine was injected three times from the nonwoven fabric side. After the three injections, it was left for one hour, then filter paper was placed in the center of the injection site, and a 5.0 kg weight was placed on top of the filter paper. After 5 minutes, the weight was removed, and the mass of the filter paper was measured. The change in mass (mass of filter paper after weight removal - mass of filter paper before weight placement) was defined as the wet bag volume.

[0083] [Examples 1-2, Comparative Examples 1-5] A Y-shaped core-sheath composite fiber was prepared using polyethylene terephthalate with an intrinsic viscosity IV of 0.63 dl / g as the first component and high-density polyethylene (Nipolon Hard®, manufactured by Tosoh Corporation) with an MFR of 20 g / 10 min (load 2.16 kg, temperature 190 °C) as the second component, according to a predetermined method. The spinning speed was 1200 m / min, and Examples 1-2 and Comparative Examples 1-5 were all spun using the single-hole discharge volume, core-sheath content, spinning temperature, distance from nozzle surface to cooling air, and cooling air velocity shown in Table 1. The obtained undrawn yarns were drawn at 70 °C at each draw ratio and heat-treated at 105 °C to obtain drawn yarns. The single-fiber fineness, maximum point stress, maximum point elongation, fiber cross-sectional shape after heat treatment, texture, and wet-back amount of the obtained drawn yarns are shown in Table 1.

[0084] The core-sheath composite fiber of Example 1 had good core deformation and sheath thickness ratio, the fiber cross-sectional shape after heat treatment was Y-shaped, the texture evaluation was ○, and the wet back amount was 4.59 g.

[0085] The core-sheath composite fiber of Example 2 was obtained by adjusting the spinning and drawing conditions of Example 1 to increase the single-fiber fineness. The core-sheath composite fiber of Example 2 had good core deformation and sheath thickness ratio, the fiber cross-sectional shape after heat treatment was Y-shaped, the texture evaluation was ○, and the wet back amount was 2.56 g.

[0086] The core-sheath composite fiber of Comparative Example 1 was obtained by increasing the distance from the nozzle surface to the cooling air and increasing the quench air volume compared to Example 1, and the fiber had the same fineness as in Example 1. The core-sheath composite fiber of Comparative Example 1 had low core deformation and sheath thickness ratio, and the fiber cross-sectional shape after heat treatment was elliptical. Although the texture evaluation was good, the wet back amount was high at 11.14 g.

[0087] The core-sheath composite fiber of Comparative Example 2 was obtained by increasing the distance from the nozzle surface to the cooling air and increasing the quench air volume, resulting in a fiber of the same fineness as that of Example 2. The core-sheath composite fiber of Comparative Example 2 had a low degree of core deformation and a low ratio of sheath thickness, and the cross-sectional shape of the fiber after heat treatment was elliptical. Although the texture evaluation was good, the wet back amount was high at 6.46 g.

[0088] The core-sheath composite fiber in Comparative Example 3 is a single-fiber fiber with a round shape and a fineness of 2.2T. Although the core-sheath composite fiber of Comparative Example 3 received a good texture evaluation, the wet-back amount was high at 10.36g.

[0089] Comparative Example 4's core-sheath composite fiber is a single-fiber fiber with a round shape and a fineness of 3.4T. Although Comparative Example 4's core-sheath composite fiber received a good texture evaluation, its wet-back amount was high at 14.86g.

[0090] The core-sheath composite fiber in Comparative Example 5 is a single-fiber fiber with a round shape and a fineness of 5.2T. The core-sheath composite fiber in Comparative Example 5 received a "×" in the texture evaluation, and the wet-back amount was high at 10.95g.

[0091] [Table 1] [Explanation of Symbols]

[0092] DI1 Diameter of the inscribed circle of the core DO1 Diameter of the circumscribed circle of the core DI2 Diameter of the inscribed circle of the entire cross-section Diameter of the circumscribed circle of the entire DO2 cross-section 1 core (1st component) 2 Sheath (second component) 3. Tip of the sheath projection 4. The deepest part of the sheath recess. 5. Tip of the protruding part 6. The deepest recess of the core recess. 10 Core-sheath composite fibers

Claims

1. A core-sheath composite fiber comprising a core containing a first component thermoplastic resin and a sheath containing a second component thermoplastic resin having a melting point at least 40°C lower than the melting point of the aforementioned resin, In the fiber cross-section, both the core and the entire cross-section have a Y-shape. The core content is 45% by mass or more and 80% by mass or less relative to the total fiber weight. In a fiber cross-section, if the diameter of the inscribed circle of the core is DI1, the diameter of the circumscribed circle of the core is DO1, the diameter of the inscribed circle of the entire cross-section is DI2, and the diameter of the circumscribed circle of the entire cross-section is DO2, The sheath thickness ratio expressed as (DO2 - DO1) / (DI2 - DI1) is greater than 2.5 and 7.0 or less. The core deformation degree expressed as DO1 / DI1 is 3.2 or higher and 5.0 or lower. The tip of the core protrusion is located within the triangle formed by the tip of the sheath protrusion and the two adjacent recesses of the sheath. A core-sheath composite fiber characterized by a core protrusion having a shape in which the width dimension decreases from the base to the tip.

2. The core-sheath composite fiber according to claim 1, wherein the sheath thickness ratio expressed as (DO2-DO1) / (DI2-DI1) is 3.45 or more.

3. The core-sheath composite fiber according to claim 1 or 2, wherein the single filament fineness is 1.2 dtex or more and 10.0 dtex or less.

4. The core-sheath composite fiber according to claim 1 or 2, wherein the cross-sectional shape of the fiber after being treated with 130°C hot air at a wind speed of 0.55 m / s for 10 seconds is Y-shaped.

5. A nonwoven fabric formed from core-sheath composite fibers according to claim 1 or 2.

6. The nonwoven fabric according to claim 5, wherein the amount of wet bag measured under the following conditions is 6.4 g or less. [An absorbent material was placed beneath a 30 gsm nonwoven fabric, and 50 ml of artificial urine was injected three times from the nonwoven fabric side. After letting it stand for one hour, a filter paper was placed in the center of the injection site, and a 5.0 kg weight was placed on the filter paper. Then, after 5 minutes, the weight was removed, and the mass of the filter paper was measured. The change in mass (mass of filter paper after weight removal - mass of filter paper before weight placement) was defined as the wet bag volume.]

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