Composite fibers, heat-bondable nonwoven fabrics containing the same, and methods for manufacturing the same.

Abstract

The present invention provides a composite fiber that can produce a heat-bondable nonwoven fabric with high strength and good flexibility, a heat-bondable nonwoven fabric containing the same, and a method for producing the same. [Solution] The material comprises a core component and a sheath component arranged substantially concentrically, the core component containing 60% by mass or more of polyester resin, and the sheath component containing 60% by mass or more of polyethylene, the dry heat dimensional change rate at 140°C being 3.5% to 8.0%, and the polyethylene having a density of 0.93 g / cm³ 3 The present invention relates to a composite fiber wherein at least one of the following satisfies a specific range: the apparent Young's modulus of the composite fiber, the degree of crystallinity of the [010] plane of the polyester resin contained in the core component, and the ratio of the degree of crystallinity of the [200] plane to the degree of crystallinity of the [110] plane of the polyethylene contained in the sheath component. The composite fiber can be produced by high-temperature spinning of the core component and the sheath component, lowering the temperature of the stretched yarn in a tensioned state from after stretching until before heat treatment, and then performing low-temperature heat treatment on the stretched yarn in a relaxed state.

Description

[Technical Field]

[0001] The present invention relates to a composite fiber using polyester resin as a core component and polyethylene as a sheath component, a heat-bondable nonwoven fabric containing the same, and a method for producing the same. [Background technology]

[0002] One type of composite fiber using two thermoplastic resins with different melting points is the core-sheath type, in which the thermoplastic resin with the lower melting point is placed on the outside of the fiber (this resin component is called the sheath component), and the other thermoplastic resin with the higher melting point is placed on the inside of the fiber (this resin component is called the core component). For example, Patent Documents 1 to 4 describe a composite fiber using polyester resin as the core component and polyethylene as the sheath component. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-246246 [Patent Document 2] Japanese Patent Application Publication No. 9-49122 [Patent Document 3] Patent No. 6228699 [Patent Document 4] Japanese Patent Publication No. 2017-214662 [Overview of the project] [Problems that the invention aims to solve]

[0004] Heat-bonded nonwoven fabrics, obtained by using core-sheath type composite fibers with polyester resin as the core component and polyethylene as the sheath component, as described in Patent Documents 1 to 4, and by melting the sheath component to bond the fibers together, generally tend to have excellent bulkiness and flexibility. On the other hand, when polyester resin is used as the core component, the bulkiness reduces the nonwoven fabric density, resulting in a problem of inferior strength. Furthermore, Patent Document 1 states that the apparent Young's modulus of the composite fiber is 210 kg / mm². 2 (=2058N / mm 2 The following was the case, which resulted in poor card acceptance. Furthermore, in Patent Document 2, it was necessary to use a specific polyethylene as a sheath component in order to obtain a nonwoven fabric that was both strong and flexible in texture. Furthermore, while Patent Document 3 achieves both processability to nonwoven fabric and the physical properties of nonwoven fabric by setting the ratio of the breaking strength to the elongation at break of the composite fiber within a predetermined range, there was a risk of inferior strength. Furthermore, in Patent Document 4, the degree of orientation and crystallinity of the polyester resin core component, as well as the elongation of the composite fibers, are adjusted to give the nonwoven fabric flexibility and bulkiness, but there was a problem with inferior strength.

[0005] To solve the above-mentioned problems, the present invention provides a composite fiber that can produce a heat-bondable nonwoven fabric with high strength and good flexibility, a heat-bondable nonwoven fabric containing the same, and a method for producing the same. [Means for solving the problem]

[0006] The present invention relates to a composite fiber comprising a core component and a sheath component, wherein the core component and the sheath component are substantially concentrically arranged, the core component contains 60% by mass or more of polyester resin, and the sheath component contains 60% by mass or more of polyethylene, the polyethylene having a density of 0.93 g / cm³ 3 The present invention relates to a composite fiber that is ultra-high quality, has a dry heat dimensional change rate of 3.5% or more and 8.0% or less at 140°C, and satisfies at least one of the following requirements (1) to (3). (1) The apparent Young's modulus of the composite fiber is 2100 N / mm². 2 More than 3150N / mm 2 The following is (2) The degree of crystallinity of the

[0010] plane of the polyester resin contained in the core component is 10.0% or more and 23.0% or less. (3) The ratio of the crystallinity of the

[0200] plane to the crystallinity of the

[0110] plane of the polyethylene contained in the sheath component (

[0200] plane crystallinity /

[0110] plane crystallinity) is 0.38 or more and 0.60 or less

[0007] The present invention also relates to a composite fiber containing a core component and a sheath component, wherein the core component and the sheath component are arranged substantially concentrically, the core component contains 60% by mass or more of a polyester resin, the sheath component contains 60% by mass or more of polyethylene, and the polyethylene has a density of 0.93 g / cm 3 or more, and the composite fiber satisfies the following requirements (I) and (II) when heat-treated under the following conditions. (Heat treatment conditions) Using 100% by mass of the composite fiber, a fiber web is produced by a roller carding machine, and the obtained fiber web is heat-treated for 9.1 seconds by blowing hot air from directly above at a wind speed of 0.97 m / s using a hot air blowing device set at 135°C. The basis weight is 17 ± 3 g / m 2 of the heat-bonded nonwoven fabric <~ (I) The ratio of the stress at 10% elongation in the longitudinal direction to the longitudinal and transverse tensile strength per unit basis weight calculated by the following formula 1 of the heat-bonded nonwoven fabric obtained by heat treatment is 0.10 [(N / 50 mm) / (g / m 2 )] or more [Formula 1] Ratio of stress at 10% elongation in the longitudinal direction to longitudinal and transverse tensile strength per unit basis weight [(N / 50 mm) / (g / m 2 )] = [Stress at 10% elongation in the longitudinal direction (N / 50 mm) / Basis weight (g / m 2 )] / {[Longitudinal tensile strength (N / 50 mm) / Basis weight (g / m 2 )] / [Transverse (N / 50 mm) / Basis weight (g / m 2 )]} (II) The stiffness per unit basis weight calculated by the following formula 2 of the heat-bonded nonwoven fabric obtained by heat treatment is 2.05 [cN / (g / m 2 )] or less [Formula 2] [[ID=...]] Stiffness per unit basis weight [cN / (g / m [[ID=3...]] 2 )] = Stiffness (cN) / Stiffness basis weight (g / m 2 )

[0008] The present invention also relates to a heat-bondable nonwoven fabric containing 10% by mass or more of the composite fibers, wherein at least some of the composite fibers are bonded together by a sheath component.

[0009] The present invention also relates to a method for producing a composite fiber comprising a core component and a sheath component, wherein the core component, comprising 60% by mass or more of polyester resin, is extruded at an extrusion temperature of [Tm1 + 55°C] or higher and [Tm1 + 125°C] or lower, with the melting point of the polyester resin contained in the core component being Tm1, and the density being 0.93 g / cm³. 3 The present invention relates to a method for manufacturing composite fibers, comprising the steps of: supplying a sheath component containing 60% by mass or more of polyethylene, to a concentric core-sheath composite nozzle configured such that the sheath component covers the surface of the composite fiber in the fiber cross-section and the core component and sheath component are substantially concentrically arranged, at an extrusion temperature of [Tm2 + 100°C] or more and [Tm2 + 200°C] or less, where Tm2 is the melting point of the polyethylene contained in the sheath component, and extruding it to obtain an undrawn fiber tow consisting of the core component and the sheath component; drawing the undrawn fiber tow to obtain a drawn fiber tow; and heat-treating the drawn fiber tow in a relaxed state at a temperature of 50°C or more and 90°C or less, wherein the surface temperature of the drawn fiber tow in a tensioned state from after the step of obtaining the drawn fiber tow to before the heat-treating step is less than 60°C. [Effects of the Invention]

[0010] According to the composite fiber of the present invention, a heat-bondable nonwoven fabric with high strength and excellent flexibility can be obtained. Furthermore, the present invention can provide a heat-bondable nonwoven fabric that has high strength and excellent flexibility. Furthermore, by using the composite fibers obtained by the composite fiber manufacturing method of the present invention, a heat-bonded nonwoven fabric with high strength and excellent flexibility can be obtained. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional diagram showing the fiber cross-section of one example of a composite fiber. [Figure 2] This is a schematic cross-sectional diagram showing the fiber cross-section of another example of composite fiber. [Modes for carrying out the invention]

[0012] The inventors of this invention conducted diligent research to solve the above problems and found that a core component containing 60% by mass or more of polyester resin and a density of 0.93 g / cm³ is desirable. 3 In a composite fiber in which sheath components containing 60% by mass or more of ultrapolyethylene are arranged substantially concentrically, the dry heat dimensional change rate at 140°C is 3.5% to 8.0%, and requirement (1): apparent Young's modulus is 2100 N / mm 2 More than 3150N / mm 2 It has been found that by satisfying at least one of the following requirements, the composite fiber exhibits excellent processability into a heat-bonded nonwoven fabric, and the resulting heat-bonded nonwoven fabric has high strength (particularly in terms of initial elongation stress) and good flexibility. Specifically, the processability into a heat-bonded nonwoven fabric refers to web-forming properties (e.g., card passability), processability during heat treatment (e.g., dimensional stability), and nonwoven fabric formation properties (e.g., fabric texture).

[0013] In this invention, the core component contains 60% by mass or more of polyester resin, and the density is 0.93 g / cm³. 3 When manufacturing a composite fiber in which sheath components containing 60% or more by mass of ultrapolyethylene are arranged substantially concentrically, an undrawn fiber tow is produced by high-temperature spinning, the drawn fiber tow is subjected to low-temperature heat treatment in a relaxed state, and the surface temperature of the drawn fiber tow in a tensile state is lowered from after drawing until before heat treatment, thereby obtaining a composite fiber that satisfies the above-mentioned physical properties. High-temperature spinning, specifically, extruding a core component containing 60% by mass or more of polyester resin at an extrusion temperature of [Tm1+55°C] to [Tm1+125°C], where Tm1 is the melting point of the polyester resin contained in the core component (if multiple polyester resins are contained in the core component, the melting point of the polyester resin with the highest melting point, and so on), results in a density of 0.93 g / cm³. 3 By supplying a sheath component containing 60% or more by mass of ultrapolyethylene to a concentric core-sheath composite nozzle, where the sheath component covers the surface of the composite fiber in the fiber cross-section and the core component and sheath component are substantially arranged concentrically, at an extrusion temperature of [Tm2 + 100°C] or more and [Tm2 + 200°C] or less, with Tm2 being the melting point of the polyethylene contained in the sheath component (if multiple polyethylenes are contained in the sheath component, the melting point of the polyethylene with the highest melting point, the same applies hereinafter), and extruding it to produce an undrawn fiber tow, it is estimated that the dry heat dimensional change rate is reduced, the apparent Young's modulus of the composite fiber and / or the degree of crystallinity of the

[0010] plane of the polyester resin in the core component is reduced, the processability of the composite fiber into a heat-bondable nonwoven fabric is improved, and the heat-bondable nonwoven fabric using the composite fiber is likely to be flexible. Furthermore, by lowering the surface temperature of the stretched fiber tow in a tensioned state from after stretching until before heat treatment, and by heat-treating the stretched fiber tow at a low temperature in a relaxed state, the dry heat dimensional change rate is higher compared to when the stretched fiber tow is treated at a high temperature, the apparent Young's modulus of the composite fiber is higher, the degree of crystallinity of the

[0010] plane of the polyester resin in the core component is lower, and / or the PE

[0200] / PE

[0110] is higher, which improves the processability of the composite fiber into a heat-bondable nonwoven fabric, specifically the carding properties, and it is presumed that the heat-bondable nonwoven fabric using the composite fiber will have improved strength while maintaining flexibility. However, this presumption does not limit the present invention.

[0014] In this invention, the core component also contains 60% by mass or more of polyester resin and has a density of 0.93 g / cm³. 3In manufacturing a composite fiber in which a sheath component containing 60% or more by mass of polyethylene is arranged substantially concentrically, an undrawn fiber tow is produced by high-temperature spinning, the drawn fiber tow is subjected to low-temperature heat treatment in a relaxed state, and the surface temperature of the drawn fiber tow in a tensioned state is lowered from after drawing until before heat treatment, thereby producing a composite fiber containing a core component and a sheath component, wherein the core component and the sheath component are arranged substantially concentrically, the core component contains 60% or more by mass of polyester resin, and the sheath component has a density of 0.93 g / cm³. 3 The composite fiber contains 60% by mass or more of ultra-high-grade polyethylene, and when the composite fiber is heat-treated under the conditions described above, a composite fiber that satisfies the requirements of (I) and (II) above can be obtained.

[0015] <Composite Fibers> The composite fiber of the present invention is a core-sheath type composite fiber having a concentric structure in which a core component and a sheath component are substantially arranged concentrically. The composite fiber does not have to have a hollow portion continuous in the direction of the fiber axis in the center of the fiber cross-section, and may be a hollow composite fiber having a hollow portion. In the following description of the composite fiber, unless otherwise specified, the description applies to both composite fibers without a hollow portion and hollow composite fibers.

[0016] (core component) The core component of the composite fiber of the present invention contains 60% by mass or more of polyester resin. Preferably, the core component contains 75% by mass or more of polyester resin, more preferably 85% by mass or more, and particularly preferably 90% by mass or more. There is no particular upper limit to the polyester resin content in the core component, and the core component may be composed entirely of polyester resin. The polyester resin contained in the core component may be one type or two or more types.

[0017] While the polyester resin is not particularly limited, it is preferable that it has a melting point 50°C or more higher than the melting point of the polyethylene contained in the sheath component, as described later. A melting point of 50°C or more higher than the melting point of the polyethylene contained in the sheath component not only improves spinnability during melt spinning, but also results in appropriate tensile strength for the resulting composite fibers and the heat-bonded nonwoven fabric containing the composite fibers. It is more preferable that the polyester resin has a melting point 80°C or more higher than the melting point of the polyethylene contained in the sheath component, and even more preferable that it has a melting point 100°C or more higher. In this specification, the melting point of the resin refers to the melting peak temperature measured according to JIS K 7121:1987, and is the melting point of the resin before it is fiberized.

[0018] As the polyester resin, for example, aliphatic polyester resins, aromatic polyester resins, copolymers thereof, and copolymers with other components can all be used. More specifically, examples of polyester resins include polylactic acid (PLA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), and polyethylene naphthalate (PEN). The polyester resin has a density of 0.93 g / cm³ in its sheath component. 3 Since the polyester resin has a melting point that is preferably 50°C or higher, more preferably 80°C or higher, than that of ultra-high polyethylene, and especially high-density polyethylene, it is preferably an aromatic polyester resin, and more preferably at least one polyester resin selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate. It is particularly preferable that the core component contains 60% by mass or more of polyethylene terephthalate as the polyester resin. Compared to polytrimethylene terephthalate and polybutylene terephthalate, polyethylene terephthalate is inexpensive, and the resin itself has high rigidity, which gives stiffness to the fibers, so the carding properties of the composite fibers tend to be good.

[0019] When the core component contains 60% by mass or more of polyethylene terephthalate, the intrinsic viscosity of the polyethylene terephthalate is preferably greater than 0.55 dL / g and less than or equal to 0.75 dL / g. Intrinsic viscosity, also called intrinsic viscosity, depends on the molecular weight of polyethylene terephthalate. If the intrinsic viscosity of polyethylene terephthalate is greater than 0.55 dL / g, the strength and rigidity of the core component will be good, and the tensile strength of the resulting composite fiber will tend to be high. Also, if the intrinsic viscosity is 0.75 dL / g or less, the viscosity when the polyethylene terephthalate is melted will not be too high, and the spinnability during melt spinning will tend to be improved. The intrinsic viscosity of polyethylene terephthalate is preferably 0.58 dL / g or more and less than or equal to 0.70 dL / g, and more preferably 0.60 dL / g or more and less than or equal to 0.68 dL / g.

[0020] When the core component contains 60% by mass or more of polyethylene terephthalate, the melting point of polyethylene terephthalate is not particularly limited, but is preferably, for example, 230°C to 280°C. When the melting point of polyethylene terephthalate is within the above range, when the core component is extruded at a temperature of [Tm1 + 55°C] to [Tm1 + 125°C] and the sheath component is extruded at a temperature of [Tm2 + 100°C] to [Tm2 + 200°C], microcrystals of polyester resin are likely to form, and the resulting nonwoven fabric containing composite fibers tends to be flexible. The melting point of polyethylene terephthalate is more preferably 240°C to 270°C, and even more preferably 250°C to 260°C.

[0021] The core component described above may include thermoplastic resins other than the polyester resin described above, as long as it does not impair the function of the present invention. Examples of thermoplastic resins other than the polyester resin include polyolefins, polyamides, polycarbonates, and polystyrene.

[0022] (sheath component) In the composite fiber of the present invention, the sheath component has a density of 0.93 g / cm³. 3It contains 60% by mass or more of ultra-high density polyethylene (hereinafter simply referred to as polyethylene). Examples of polyethylene include linear polyethylene, medium-density polyethylene, and high-density polyethylene. In particular, it contains polyethylene with a density of 0.94 g / cm³. 3 Preferably, the polyethylene content is 60% by mass or more, and particularly preferably, high-density polyethylene is included at a concentration of 60% by mass or more. This tends to result in composite fibers with high rigidity and good card passage properties. In this invention, high-density polyethylene (also referred to as PE-HD or HDPE) refers to a density of 0.940 g / cm³ as measured in accordance with JIS K 7112:1999. 3 This refers to the polyethylene described above. The density of the polyethylene described above is 0.945 g / cm³. 3 More than 0.965g / cm 3 Preferably, it is 0.950 g / cm³. 3 More than 0.960g / cm 3 The following is preferable: The polyethylene content in the sheath component is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably the sheath component is composed entirely of polyethylene resin.

[0023] In the sheath component of the composite fiber described above, the melting point of polyethylene is not particularly limited, but is preferably 105°C to 140°C, more preferably 125°C to 140°C, and even more preferably 128°C to 138°C. When the melting point of polyethylene is within the above range, the carding properties of the composite fiber, as well as the productivity, strength, and heat resistance of the heat-bonded nonwoven fabric tend to be good. The melting point of polyethylene described above refers to the melting point of the polymer and is different from the melting point after fiberization.

[0024] In the composite fiber of the present invention, the sheath component may contain resins other than polyethylene, as long as it does not impair the effects of the present invention. The resins other than polyethylene are not particularly limited, but examples include polyolefins other than polyethylene, polyester resins, polyamides, polycarbonates, and polystyrene. The polyolefin resins other than polyethylene are not particularly limited, but examples include polypropylene, polymethylpentene, polybutene-1, copolymers or graft polymers of these with at least one selected from the group consisting of unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and maleic acid, esters of unsaturated carboxylic acids such as acrylic acid esters, methacrylic acid esters, and maleic acid esters, and anhydrides of unsaturated carboxylic acids such as acrylic acid anhydride, methacrylic acid anhydride, and maleic acid anhydride, as well as elastomers thereof. The polyester resins mentioned above are not particularly limited, but include, for example, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, copolymers thereof with acid components such as isophthalic acid, succinic acid, and adipic acid, glycol components such as 1,4-butanediol and 1,6-hexanediol, polytetramethylene glycol, polyoxymethylene glycol, etc., and elastomers thereof. The polyamides mentioned above are not particularly limited, but include, for example, nylon 6, nylon 66, nylon 11, and nylon 12.

[0025] In the composite fiber of the present invention, the cross-sectional structure is a concentric structure in which the center of gravity of the core component substantially coincides with the center of gravity of the composite fiber. That is, in the fiber cross-section, the center of gravity of the core component does not substantially deviate from the center of gravity of the composite fiber. Figure 1 is a schematic diagram of the fiber cross-section (transverse plane) of one example of a concentric composite fiber. A sheath component 11 is arranged around the core component 12, and the sheath component 11 surrounds the core component 12, so that in the composite fiber 10, the fiber surface other than the cut surface is covered by the sheath component 11. Both the composite fiber 10 and the core component 12 have a circular cross-sectional shape. As a result, when a fiber web composed of composite fibers is heat-bonded, the surface of the sheath component 11 melts, and the fibers are heat-bonded to each other. In the composite fiber 10, since the core component 12 is not eccentric, i.e., has a concentric structure, the thickness of the sheath component 11 in the fiber cross-section is substantially constant at all points in the fiber cross-section. As a result, when a fiber web composed of composite fibers is heat-treated, the sheath component on the fiber surface of the composite fiber softens and melts, and regardless of which part other fibers come into contact with, a heat-bonding point of uniform strength is formed. Therefore, the heat-bonded nonwoven fabric using the above composite fibers has high adhesive strength, is resistant to friction, and is less prone to fraying. The center of gravity position 13 of the core component 12 is not substantially deviated from the center of gravity position 14 of the composite fiber 10. The statement that the center of gravity position of the core component is not substantially deviated from the center of gravity position of the composite fiber means that the deviation rate (hereinafter also referred to as the eccentricity rate) determined by the following method is 10% or less, preferably 7% or less, particularly preferably 5% or less, and most preferably 3% or less.

[0026] <Eccentricity> The fiber cross-section of the composite fiber 10 was magnified and photographed using a scanning electron microscope, and the centroid position 13 of the core component 12 was defined as C1, and the centroid position 14 of the composite fiber 10 was defined as C f Let the radius 15 of the composite fiber 10 be r f In that case, the calculation is performed using formula 3 below.

[0027]

number

[0028] Figure 2 is a schematic diagram of a fiber cross-section (transverse plane) of another example of a concentric composite fiber. The composite fiber 20 of this embodiment has a sheath component 11 and a core component 12 that are concentric in nature, with the center of gravity of the core component substantially coinciding with the center of gravity of the composite fiber, except that it has a hollow portion 16 that is continuous in the fiber axis direction in the center of the fiber. The center of gravity (center position) 17 of the hollow portion is also substantially not deviated from the center of gravity 13 of the core component 11 and the center of gravity 14 of the composite fiber 20 (sheath component 12).

[0029] In hollow-core-sheath composite fibers, the hollowness ratio is not particularly limited, but from the viewpoint of bulkiness and heat retention, it is preferably 6% to 28%, more preferably 7% to 25%, and even more preferably 8% to 22%. In this specification, the hollowness ratio is defined as the area St (μm²) of the region surrounded by the outer circumference of the fiber cross-section. 2 ) and the area Sh (μm²) of the region enclosed by the outer periphery of the hollow part. 2 Based on this, it can be calculated using the following formula I, and specifically, it can be measured and calculated as described in the examples. [Formula I] Hollow rate (%)=100×[Sh / St]

[0030] In the above-mentioned composite fiber, the composite ratio of core component to sheath component is not particularly limited, as long as the sheath component can cover the fiber surface in the fiber cross-section. However, for example, it is preferable that the composite ratio of core component to sheath component is 30 / 70 or more and 70 / 30 or less by mass ratio. When the mass ratio of core component to sheath component in the above-mentioned composite fiber is 30 / 70 or more and 70 / 30 or less, the carding properties of the composite fiber and the adhesive strength and tactile feel of the heat-bonded nonwoven fabric containing the composite fiber tend to improve. Because the sheath component and the mass ratio of the sheath component are within the above-mentioned range, the proportion of the sheath component covering the fiber surface, i.e., polyethylene with a lower melting point, in the composite fiber does not become too large. Therefore, during melt spinning, the resin extruded from the nozzle can be sufficiently cooled before being withdrawn, and the occurrence of fused fibers and thread breakage is suppressed. Furthermore, the proportion of sheath components that contribute to the thermal bonding between constituent fibers is within an appropriate range, and the sheath components exist as a layer that moderately covers the circumferential surface of the composite fiber. As a result, heat treatment makes it easier for thermal bonding points between constituent fibers to be within an appropriate range, and the strength of the nonwoven fabric is easily improved. In the above composite fiber, the composite ratio of core component to sheath component is more preferably 35 / 65 or more and 65 / 35 or less by mass ratio, and even more preferably 40 / 60 or more and 60 / 40 or less.

[0031] In the above-mentioned composite fiber, the shape of the fiber cross-section may be circular or irregular (non-circular). The irregular shape is not particularly limited and examples include elliptical, Y-shaped, X-shaped, grid-shaped, polygonal, and star-shaped. Furthermore, the shape of the fiber cross-section of the core component may be circular or irregular, such as elliptical, Y-shaped, X-shaped, grid-shaped, polygonal, and star-shaped. Furthermore, the shape of the fiber cross-section of the hollow portion may be circular or irregular, such as elliptical, Y-shaped, X-shaped, grid-shaped, polygonal, and star-shaped.

[0032] The above-mentioned composite fibers have a dry heat dimensional change rate of 3.5% to 8.0% at 140°C. When the dry heat dimensional change rate of the composite fibers at 140°C is 3.5% or higher, the strength of the heat-bonded nonwoven fabric containing the composite fibers, particularly the initial elongation stress, specifically the 10% elongation stress, tends to be higher, resulting in good practical strength. Furthermore, when the dry heat dimensional change rate of the composite fibers at 140°C is 8.0% or lower, the processability of the composite fibers into a heat-bonded nonwoven fabric, specifically in terms of dimensional change and texture when made into a nonwoven fabric, is improved. In addition, the heat generated during processing into a nonwoven fabric causes the fibers to shrink moderately, reducing crimp. This results in a denser nonwoven fabric with an increased number of adhesive intersections, which tends to improve the 10% elongation stress in the longitudinal direction (also called the machine direction or MD). The dry heat dimensional change rate of the above composite fiber at 140°C is preferably 3.8% to 7.5%, more preferably 4.0% to 7.0%, and even more preferably 4.5% to 6.8%. The dry heat dimensional change rate of the above composite fiber at 140°C can be measured in accordance with JIS L 1015:2010.

[0033] The above composite fiber has an apparent Young's modulus of 2100 N / mm². 2 More than 3150N / mm 2 Preferably, the apparent Young's modulus of the composite fiber is 2100 N / mm². 2 As a result, the processability of the composite fiber into a heat-bonded nonwoven fabric, specifically its carding properties, tend to be good. Furthermore, the high initial rigidity of the fiber suppresses excessive bulk reduction when it is made into a nonwoven fabric, improving the initial elongation stress of the nonwoven fabric, specifically the MD10% elongation stress. The apparent Young's modulus of the composite fiber is 3150 N / mm². 2 The flexibility of the heat-bonded nonwoven fabric containing the composite fiber tends to be good if the following conditions are met: The apparent Young's modulus of the composite fiber is 2350 N / mm². 2 More than 3050N / mm 2 The following is more preferable: 2550 N / mm 2 More than 3100N / mm 2The following is even more preferable. In this specification, the apparent Young's modulus of the composite fiber can be calculated using the following formula 4, based on the initial tensile resistance measured and calculated in accordance with the method for measuring initial tensile resistance in JIS L 1015:2010 8.11, and specifically, it can be measured and calculated as described in the examples.

[0034]

number

[0035] In the above-mentioned composite fiber, it is preferable that the crystallinity of the

[0010] plane of the polyester resin contained in the core component is 10.0% or more and 23.0% or less. When the crystallinity of the

[0010] plane of the polyester resin contained in the core component is 10.0% or more, the processability of the composite fiber into a heat-bondable nonwoven fabric, specifically the carding passability, tends to be good. When the crystallinity of the

[0010] plane of the polyester resin contained in the core component is 23.0% or less, the strength of the heat-bondable nonwoven fabric containing the composite fiber, particularly the MD10% elongation stress, tends to be good. When the crystallinity of the

[0010] plane of the polyester resin contained in the core component is within the above range, the fibers have appropriate rigidity, resulting in good carding passability, and when made into a nonwoven fabric, it becomes denser, increasing the number of fiber bonding intersections, which tends to improve the initial elongation stress, specifically the MD10% elongation stress. The degree of crystallinity of the

[0010] plane of the polyester resin contained in the core component is more preferably 11.0% to 22.0%, even more preferably 12.0% to 21.0%, and even more preferably 13.0% to 20.0%. In this specification, the degree of crystallinity of the

[0010] plane of the polyester resin contained in the core component of the composite fiber can be measured by X-ray diffraction (XRD), and specifically can be measured as described in the examples.

[0036] In the above-mentioned composite fiber, the ratio of the diffraction peak intensity of the

[0110] plane of polyethylene (hereinafter also simply referred to as "PE") contained in the sheath component to the diffraction peak intensity of the

[0200] plane of polyethylene (PE

[0200] / PE

[0110] ) is preferably 0.38 or more and 0.60 or less, and more preferably 0.40 or more and 0.55 or less. This results in good strength and flexibility of the heat-bonded nonwoven fabric using the composite fiber, and also tends to improve the dimensional stability and texture of the nonwoven fabric. It is estimated that a larger ratio of PE

[0200] / PE

[0110] , that is, a higher proportion of PE

[0200] oriented along the easily meltable a-axis, improves the dimensional change rate at 140°C dry heat. When the ratio of PE

[0200] / PE

[0110] is 0.38 or higher, the dimensional change rate at 140°C dry heat increases, and the crimping weakens. As a result, the nonwoven fabric becomes denser, increasing the number of fiber bonding intersections, which improves the initial elongation stress of the nonwoven fabric, specifically the MD10% elongation stress. When the ratio of PE

[0200] / PE

[0110] is 0.60 or lower, the proportion of PE

[0200] does not become too high, the dimensional change rate at 140°C dry heat becomes moderate, moderate crimping can be maintained, the nonwoven fabric becomes denser, improving the number of fiber bonding intersections, and the entanglement of fibers in the nonwoven fabric is maintained, making it easier to improve the initial elongation stress, specifically the MD10% elongation stress. In this specification, PE

[0200] / PE

[0110] can be measured by X-ray diffraction (XRD), specifically as described in the examples.

[0037] The composite fibers of the present invention are not particularly limited, but for example, it is preferable that the single fiber fineness is 0.60 dtex or more and 100 dtex or less, more preferably 0.80 dtex or more and 80 dtex or less, even more preferably 1.0 dtex or more and 70 dtex or less, even more preferably 1.5 dtex or more and 5.0 dtex or less, and most preferably 2.0 dtex or more and 4.0 dtex or less. For example, for sanitary material applications, it is preferable that the fineness is 0.80 dtex or more and 15 dtex or less, more preferably 0.90 dtex or more and 10 dtex or less, and from the viewpoint of making the heat-bonded nonwoven fabric easier to touch, it is even more preferably 1.0 dtex or more and 8.0 dtex or less, even more preferably 1.5 dtex or more and 5.0 dtex or less, and most preferably 2.0 dtex or more and 4.0 dtex or less. For example, for filter applications, the fineness is preferably 1.5 dtex or more and 100 dtex or less, more preferably 2.0 dtex or more and 80 dtex or less, and even more preferably 2.2 dtex or more and 70 dtex or less. When manufacturing a card web, it is preferably 0.60 dtex or more and 80 dtex or less, and if it is within this range, the card passability is good. In this specification, the single fiber fineness of the composite fiber can be measured according to JIS L 1015:2010.

[0038] The tensile strength of the composite fiber is not particularly limited, but is preferably 1.80 cN / dtex or more and 3.00 cN / dtex or less, more preferably 1.90 cN / dtex or more and 2.90 cN / dtex or less, and even more preferably 2.00 cN / dtex or more and 2.80 cN / dtex or less. When the single fiber strength of the composite fiber satisfies the above range, the composite fiber will have appropriate strength and appropriate rigidity, and the carding properties of the composite fiber and the handling properties of the fiber web during nonwoven fabric production will be improved.

[0039] The elongation of the composite fiber described above is not particularly limited, but is preferably 30.0% to 200.0%, more preferably 30.0% to 150.0%, even more preferably 30.0% to 120.0%, even more preferably 30.0% to 100.0%, even more preferably 30.0% to 90.0%, even more preferably 30.0% to 80.0%, and most preferably 30.0% to 70.0%. When the elongation at break of the composite fiber satisfies the above range, the composite fiber will have appropriate strength and appropriate rigidity, and the carding properties of the composite fiber and the handling properties of the fiber web during nonwoven fabric production will be improved. In this specification, the tensile strength and elongation of the composite fiber can be measured in accordance with JIS L 1015:2010.

[0040] In the above-mentioned composite fiber, it is preferable that the ratio of tensile strength to elongation (tensile strength [cN / dtex] / elongation [%]) is greater than 0.040 and 0.060 or less. The ratio of tensile strength to elongation increases as the composite fiber has high strength and low elongation, and decreases as the composite fiber has low strength and high elongation. When the ratio of tensile strength to elongation of the composite fiber satisfies the above range, the composite fiber tends to become a fiber with a good balance of tensile strength and elongation, possessing appropriate elasticity and rigidity, and improving card passage. It is more preferable that the tensile strength and elongation (tensile strength [cN / dtex] / elongation [%]) of the composite fiber be between 0.041 and 0.055, and even more preferable that be between 0.041 and 0.050.

[0041] The fiber length of the composite fiber described above is not particularly limited, but when used in heat-bonded nonwoven fabrics, it is preferably, for example, 3 mm to 105 mm. When the composite fiber is made into a heat-bonded nonwoven fabric using the carding method, the fiber length of the composite fiber is preferably 25 mm to 105 mm, and more preferably 25 mm to 75 mm. When the fiber length is within this range, carding passability is easily improved, and it is easier to obtain a fiber web (card web) with good form. When the composite fiber is made into a heat-bonded nonwoven fabric using the wet papermaking method or the airlaid method, the fiber length of the composite fiber is preferably 3 mm to 15 mm, and more preferably 3 mm to 12 mm.

[0042] When the above composite fibers are heat-treated under the following conditions to form a nonwoven fabric, the ratio of MD 10% elongation stress / lengthwise and transverse tensile strength per unit basis weight, calculated using the following formula 1 for the nonwoven fabric, is 0.10 [(N / 50mm) / (g / m 2 It is preferable that the value is 0.11[(N / 50mm) / (g / m 2 It is more preferable that the result be greater than or equal to ).

[0043] Heat treatment conditions: Using 100% by mass of composite fibers, a fiber web was prepared using a roller carding machine. The resulting fiber web was then subjected to a heat treatment using a hot air blowing device set to 135°C, with hot air blown directly from above at a wind speed of 0.97 m / s for 9.1 seconds, resulting in a basis weight of 17.0 ± 3.0 g / m². 2 Heat-bonded nonwoven fabric

[0044] [Formula 1] Stress / tensile strength ratio at MD10% elongation per unit basis weight [(N / 50mm) / (g / m)] 2 )]=[MD 10% Elongation Stress (N / 50mm) / MD Basis Weight (g / m 2 )] / {[MD Tensile Strength (N / 50mm) / MD Basis Weight (g / m 2 )] / [Horizontal direction (N / 50mm) / Horizontal weight (g / m 2 )]}

[0045] In this specification, the MD and transverse (also referred to as CD) tensile strengths of nonwoven fabrics, and the stress at 10% MD elongation, can be measured in accordance with JIS L 1913:2010. Furthermore, in this specification, MD basis weight refers to the basis weight measured using a sample used for the MD tensile test, and CD basis weight refers to the basis weight measured using a sample used for the CD tensile test.

[0046] When the above composite fibers are heat-treated under the following conditions to form a nonwoven fabric, the stiffness per unit basis weight [cN / (g / m²)] is calculated using the following formula (2) for the nonwoven fabric, from the viewpoint of excellent flexibility. 2 It is preferable that the ratio is 2.05 or less. In this specification, stiffness can be measured in accordance with JIS L 1913:2010. In Formula 2 below, stiffness basis refers to the basis of the sample used for stiffness measurement.

[0047] Heat treatment conditions: Using 100% composite fibers, a fiber web was prepared using a roller carding machine. The resulting fiber web was then subjected to a heat treatment using a hot air blowing device set to 135°C, with hot air blown directly from above at a wind speed of 0.97 m / s for 9.1 seconds. The resulting material weight was 17.0 ± 3.0 g / m². 2 Heat-bonded nonwoven fabric

[0048] [Formula 2] Stiffness per unit basis weight [cN / (g / m 2 )] = rigidity (cN) / rigidity basis weight (g / m 2 )

[0049] The composite fibers of the present invention can be modified by adding various known additives to the core component and / or sheath component, provided that the effects of the present invention are not hindered and the fiber productivity, nonwoven fabric productivity, heat adhesion, and tactile properties are not affected. Examples of such additives include nucleating agents, antistatic agents, pigments, matting agents, heat stabilizers, light stabilizers, anti-fusing agents, flame retardants, antibacterial agents, lubricants, plasticizers, softeners, antioxidants, and ultraviolet absorbers. Among these, when obtaining a nonwoven fabric for absorbent articles using the composite fibers of the present invention, it is preferable that the composite fibers contain an inorganic filler. This is because nonwoven fabrics for absorbent articles require not only a white appearance but also opacity to conceal the color of absorbed menstrual blood, urine, or loose stools. The amount of inorganic filler contained in the composite fibers is not particularly limited, but it is preferable that the inorganic filler be contained in an amount of 0.1% to 10% by mass per 100% by mass of the composite fibers. Including an inorganic filler within the above range results in superior whiteness of the heat-adhesive nonwoven fabric containing the composite fibers. The above-mentioned composite fiber preferably contains 0.2% to 8.0% by mass of inorganic filler per 100% by mass of composite fiber, more preferably 0.3% to 6.0% by mass, and particularly preferably 0.4% to 5.0% by mass.

[0050] The inorganic filler described above is preferably an inorganic powder with high whiteness, as it is related to making the composite fiber appear white and improving the opacity when the heat-bonded nonwoven fabric containing this composite fiber is used as a surface sheet for an absorbent article. Specifically, white inorganic powders such as titanium dioxide, zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, silica (silicon dioxide), mica, zeolite, and talc can be incorporated into the composite fiber as an inorganic filler. The inorganic filler preferably contains at least one selected from the group consisting of titanium dioxide, zinc oxide, calcium carbonate, barium sulfate, silica, and talc, more preferably contains at least titanium dioxide, and is particularly preferably contains substantially only titanium dioxide as the inorganic filler.

[0051] The inorganic filler described above may be contained in either the sheath component or the core component that constitutes the composite fiber, or in both. From the viewpoint of the productivity of the composite fiber and the properties of the composite fiber and the nonwoven fabric manufactured using the composite fiber, it is preferable to contain the inorganic filler in at least the core component, and more preferable to contain the inorganic filler only in the core component. It is presumed that by containing the inorganic filler in at least the core component, the composite fiber and the nonwoven fabric containing the composite fiber tend to appear whiter, improving opacity, and also suppressing the excessive hardening of the core component containing a highly rigid polyester resin. The amount of inorganic filler contained in the core component is preferably 0.1% by mass or more and 10.0% by mass or less, more preferably 0.2% by mass or more and 8.0% by mass or less, even more preferably 0.3% by mass or more and 6.0% by mass or less, and particularly preferably 0.4% by mass or more and 4.0% by mass or less, when the core component is considered as 100% by mass.

[0052] <Method for manufacturing composite fibers> The present invention's method for producing composite fibers will be described below. The method for producing composite fibers of the present invention includes the steps of: supplying a core component containing 60% by mass or more of polyester resin at an extrusion temperature of [Tm1 + 55°C] to [Tm1 + 125°C] and a sheath component containing 60% by mass or more of polyethylene at an extrusion temperature of [Tm2 + 100°C] to [Tm2 + 200°C] to a concentric core-sheath composite nozzle configured such that the sheath component covers the surface of the composite fiber in the fiber cross-section and the core component and sheath component are arranged substantially concentrically, and extruding to obtain an undrawn fiber tow consisting of the core component and the sheath component; stretching the undrawn fiber tow to obtain a drawn fiber tow; and heat-treating the drawn fiber tow in a relaxed state at a temperature of 50°C to 90°C, wherein the surface temperature of the stretched fiber tow in a tensioned state from after the step of obtaining the drawn fiber tow to before the heat-treating step is preferably less than 60°C. In this specification, "relaxed state" refers to a state in which the magnification applied to the stretched fiber toe is less than 1, meaning a tensionless state in which no tension is applied to the stretched fiber toe. On the other hand, "tensioned state" refers to a state in which the magnification applied to the stretched fiber toe is 1 or more, meaning a state in which tension is applied to the stretched fiber toe.

[0053] First, in the melt spinning process, a core component containing 60% by mass or more of polyester resin and a sheath component containing 60% by mass or more of polyethylene are supplied to a concentric core-sheath type composite nozzle configured such that the sheath component covers the surface of the composite fiber in the fiber cross-section and the core component and sheath component are arranged substantially concentrically, and extruded to obtain an undrawn fiber tow consisting of the core component and sheath component. The composite ratio of the core component and sheath component is not particularly limited, as long as the sheath component can cover the surface of the fiber in the fiber cross-section of the composite fiber. For example, the mass ratio of the core component to the sheath component is preferably 30 / 70 or more and 70 / 30 or less, more preferably 35 / 65 or more and 65 / 35 or less, and even more preferably 40 / 60 or more and 60 / 40 or less. This improves spinnability and makes it easier to improve the cardability of the obtained composite fiber, as well as the strength and feel of the heat-bonded nonwoven fabric containing the composite fiber.

[0054] In the spinning process described above, the extrusion temperature of the core component is between [Tm1 + 55°C] and [Tm1 + 125°C], and the extrusion temperature of the sheath component is between [Tm2 + 100°C] and [Tm2 + 200°C]. This makes it possible to obtain a composite fiber in which the dry heat dimensional change rate, apparent Young's modulus, crystallinity of the

[0010] plane of the polyester resin such as PET in the core component, and / or PE

[0200] / PE

[0110] satisfy the ranges described in the section on composite fibers. Specifically, the core component is extruded under high-temperature conditions of [Tm1 + 55°C] or higher, i.e., a high difference from the melting point of the polyester resin, and the sheath component is extruded under high-temperature conditions of [Tm2 + 100°C] or higher, i.e., a high difference from the melting point of polyethylene. In other words, by spinning the core component and sheath component at high temperatures, the dry heat dimensional change rate, apparent Young's modulus, and / or the degree of crystallinity of the

[0010] plane of the polyester resin such as PET in the core component are reduced. For example, the dry heat dimensional change rate is 8.0% or less, and the apparent Young's modulus is 3150 N / mm². 2 The following composite fibers can be obtained in which the crystallinity of the

[0010] plane of the polyester resin in the core component is 23.0% or less, and / or the PE

[0200] / PE

[0110] ratio is reduced. Furthermore, by extruding (melt spinning) the core component at [Tm1 + 125°C] or less and the sheath component at [Tm2 + 200°C] or less, spinnability is improved. The core component and sheath component are as described in the section on composite fibers, and are therefore omitted from this explanation.

[0055] From the viewpoint of easily adjusting the dry heat dimensional change rate of the composite fiber, the apparent Young's modulus and / or the degree of crystallinity of the

[0010] plane of the polyester resin in the core component and / or PE

[0200] / PE

[0110] to a preferred range, the extrusion temperature of the core component is more preferably [Tm1+65℃] or higher and [Tm1+115℃] or lower, and even more preferably [Tm1+70℃] or higher and [Tm1+105℃] or lower. The extrusion temperature of the sheath component is more preferably [Tm2+110℃] or higher and [Tm2+190℃] or lower, and even more preferably [Tm2+120℃] or higher and [Tm2+180℃] or lower. Furthermore, the nozzle temperature is preferably between [Tm2 + 100°C] and [Tm2 + 200°C], more preferably between [Tm2 + 110°C] and [Tm2 + 190°C], and even more preferably between [Tm2 + 120°C] and [Tm2 + 180°C]. For example, when the polyester resin is polyethylene terephthalate, the extrusion temperature of the core component is preferably 310°C or higher, more preferably 320°C or higher, and even more preferably 330°C or higher. For example, when the polyethylene resin is high-density polyethylene, the extrusion temperature of the core component is preferably 240°C or higher, more preferably 250°C or higher, even more preferably 260°C or higher, and particularly preferably 270°C or higher.

[0056] In the above-described concentric core-sheath type composite nozzle (hereinafter simply referred to as the nozzle), the number of holes (hereinafter referred to as the number of holes) provided in the nozzle for extruding (melt spinning) the molten core component and sheath component is not particularly limited, but is preferably 300 to 5000, and more preferably 450 to 3500. The stability of melt spinning is improved when the number of holes satisfies the above range.

[0057] In the above-described nozzle, the diameter of the holes (hereinafter referred to as the hole diameter) provided in the nozzle for melt-spinning the molten core component and sheath component is not particularly limited, but is preferably 0.2 mm or more and 1.0 mm or less, and more preferably 0.25 mm or more and 0.75 mm or less. The stability of melt spinning is improved when the hole diameter is within the above range.

[0058] In the spinning process described above, the nozzle temperature (spinning temperature) of the concentric core-sheath type composite nozzle is preferably 270°C or higher. More preferably 280°C or higher, and even more preferably 290°C or higher. When the nozzle temperature (spinning temperature) is within the above range, a composite fiber can be obtained in which the dry heat dimensional change rate, apparent Young's modulus, crystallinity of the

[0010] plane of the polyester resin such as PET in the core component, and / or PE

[0200] / PE

[0110] satisfy the range described in the section on composite fibers.

[0059] Furthermore, when manufacturing hollow composite fibers, an undrawn fiber tow can be obtained in the same manner as described above, except that a concentric spinning nozzle for hollow core-sheath composite fibers is used as the nozzle.

[0060] The single fiber fineness of the above-mentioned undrawn fiber tow (a bundle of undrawn composite fibers consisting of a core component and a sheath component) is not particularly limited, but is preferably 2.50 dtex or more and 200.00 dtex or less, more preferably 3.00 dtex or more and 8.00 dtex or less, and preferably 4.00 dtex or more and 6.00 dtex or less. In this specification, the single fiber fineness of the undrawn fiber tow can be measured in accordance with JIS L 1013:2010.

[0061] Next, in the stretching process, the unstretched fiber tow is stretched to obtain stretched fiber tow (also called stretched yarn). In the stretching process, the stretching temperature and stretching ratio are not particularly limited and can be appropriately set according to the single fiber fineness of the unstretched fiber tow and the single fiber fineness of the target composite fiber. For example, the stretching temperature is preferably 70°C to 90°C, and more preferably 75°C to 85°C. When the stretching temperature is within the above range, it is easy to obtain a composite fiber with good carding properties and suppressed fusion between fibers. The stretching ratio is preferably greater than 1.0 and 4.0 and more preferably greater than 1.0 and 3.0 and even more preferably greater than 1.2 and 2.8 and most preferably greater than 1.5 and 2.5. When the stretching ratio is within the above range, it is easy to obtain a fiber with good carding properties, and fiber breakage during stretching is also less likely to occur.

[0062] The stretching method is not particularly limited, and known stretching processes such as wet stretching, in which the unstretched fiber tow is stretched while being heated using a high-temperature liquid such as hot water as a medium, and dry stretching, in which the fiber is stretched while being heated in a high-temperature gas or with a high-temperature metal roll, can be used. Among these, wet stretching using hot water or dry stretching using a high-temperature gas or a high-temperature metal roll is preferred, and wet stretching is more preferred because the tension and heat during stretching can be easily and evenly applied to the single fibers constituting the unstretched fiber tow. The stretching process may be a so-called one-stage stretch, where the stretching process is only one stage, a two-stage stretch, or a multi-stage stretch with more than two stages.

[0063] Next, in the crimping step, crimping may be applied to the stretched fiber tow using a known crimping machine such as a stuffing box type crimper. In the crimping step, the surface temperature of the stretched fiber tow in a tensioned state is less than 60°C. By applying crimping, composite fibers with good carding properties can be obtained. Furthermore, when applying crimping, if the surface temperature of the stretched fiber tow in a tensioned state immediately before the crimping step, specifically immediately before entering a crimping machine such as a stuffing box type crimper, is less than 60°C, the apparent Young's modulus of the composite fiber can be reduced while applying crimping, thereby improving the flexibility and increasing the strength of the heat-bonded nonwoven fabric containing the composite fiber. In the crimping step, the surface temperature of the stretched fiber tow in a tensioned state immediately before the crimping step, specifically immediately before entering a crimping machine such as a stuffing box type crimper, is preferably 55°C or lower, and more preferably 50°C or lower. In the crimping process, the lower limit of the surface temperature of the stretched fiber tow in a tensioned state immediately before the crimping process, specifically just before it enters a crimping machine such as a stuffing box type crimper, is not particularly limited as long as it can impart crimp, but is preferably 40°C or higher. In this specification, the surface temperature of the stretched fiber tow immediately before crimping is the average of the temperatures measured five times using a non-contact thermometer on the surface of the stretched fiber tow just before it enters the crimping machine.

[0064] In the crimping process, the number of crimps imparted to the drawn fiber tow is not particularly limited, but from viewpoints such as card passability and apparent Young's modulus, it is preferable that it be 5.0 crimps / 25mm or more and 28.0 crimps / 25mm or less, more preferably 8.0 crimps / 25mm or more and 25.0 crimps / 25mm or less, and particularly preferably 10.0 crimps / 25mm or more and 20.0 crimps / 25mm or less.

[0065] In the method for producing composite fibers of the present invention, the drawn fiber tow may be treated with a fiber treatment agent before or after crimping, if necessary. By treating with a fiber treatment agent, the composite fibers can be given antistatic properties that make them less prone to generating static electricity. As a result, the resulting composite fibers will have superior cardability. Furthermore, by selecting an appropriate fiber treatment agent, it is possible to impart water affinity, i.e., hydrophilicity, or water repellency to the nonwoven fabric produced using the resulting composite fibers.

[0066] The above-mentioned fiber treatment agents are appropriately selected depending on the application of the composite fiber. For example, if the composite fiber of the present invention is to be used as a surface sheet for an absorbent article, a fiber treatment agent containing a hydrophilic component can be selected as the fiber treatment agent. If it is to be used as a nonwoven fabric constituting the gathered portion or back sheet (also called the back sheet) of an absorbent article, a water-repellent fiber treatment agent that does not mix with water can be selected. The method of applying a solution (treatment liquid) containing the fiber treatment agent to the fiber surface is not particularly limited and includes known methods such as spraying, impregnation, and roll-touching. Specifically, a stretched fiber tow may be impregnated in a treatment tank filled with an aqueous solution of the fiber treatment agent, and excess aqueous solution of the fiber treatment agent may be squeezed off with a nip roll or the like.

[0067] Next, the crimped stretched fiber tow (or the stretched fiber tow that has been crimped and then treated with a fiber treatment agent) is heat-treated (also called low-temperature heat treatment) in a relaxed state at a temperature of 50°C to 90°C. The heat treatment temperature is preferably 60°C to 90°C, and more preferably 70°C to 90°C. By ensuring that the surface temperature of the stretched fiber tow in a tensioned state is below 60°C between the time of stretching and before heat treatment, and by heat-treating the stretched fiber tow in a relaxed state at a temperature of 90°C or lower, the apparent Young's modulus and dry heat dimensional change rate of the composite fiber can be increased, and / or the degree of crystallinity of the polyester resin core component can be decreased. This allows for the acquisition of a composite fiber in which the dry heat dimensional change rate, apparent Young's modulus, degree of crystallinity of the

[0010] plane of the polyester resin in the core component, and PE

[0200] / PE

[0110] satisfy the ranges described in the section on composite fiber description, resulting in good flexibility and strength of the heat-bonded nonwoven fabric containing the composite fiber. Specifically, by ensuring that the degree of crystallinity of the

[0010] plane of the polyester resin contained in the core component is within a predetermined range, the dry heat dimensional change rate of the composite fiber becomes appropriate. As a result, while maintaining a moderate crimp, the fibers shrink due to the heat generated during processing into a nonwoven fabric, reducing the crimp. This makes the nonwoven fabric denser, improving the initial elongation stress of the nonwoven fabric, specifically the MD10% elongation stress. Furthermore, by heat-treating the relaxed stretched fiber tow at a temperature of 50°C or higher, the stretched fiber tow is dried, and the crimped shape is maintained to some extent, resulting in good carding properties. In addition, dry heat shrinkage is not excessive, and a composite fiber can be obtained in which the dry heat dimensional change rate satisfies the above-mentioned range, resulting in good flexibility of the heat-bonded nonwoven fabric containing the composite fiber. Preferably, the surface temperature of the stretched fiber tow in a tensioned state from after stretching to before heat treatment is 55°C or lower, and more preferably 50°C or lower.

[0068] The drawn fiber tow obtained above may be used as is as a composite fiber (filament), or it may be cut as needed to be used as a composite fiber (short fiber, staple) of a predetermined length. For example, the composite fiber can be used as a staple in a heat-bonded nonwoven fabric.

[0069] (thermal adhesive nonwoven fabric) As an example of a nonwoven fabric containing the composite fibers of the present invention, a heat-bonded nonwoven fabric will be described along with its manufacturing method. The heat-bonded nonwoven fabric contains 10% by mass or more of the composite fibers, and at least some of the composite fibers are bonded together by a sheath component. The heat-bonded nonwoven fabric can also be obtained by preparing a fiber web containing 25% by mass or more of the composite fibers, heat-bonding the obtained fiber web, and integrating the fibers together. Other fibers that can be used include, for example, natural fibers, regenerated fibers, refined cellulose fibers, semi-synthetic fibers, and synthetic fibers. Examples of natural fibers include cotton, silk, wool, hemp, and pulp. Examples of regenerated fibers include rayon and cupro. Examples of refined cellulose fibers include Tencel and lyocell. Examples of semi-synthetic fibers include acetate and triacetate. Examples of synthetic fibers include acrylic fibers, polyester fibers, polyamide fibers, polyolefin fibers, and polyurethane fibers. Other fibers can be selected from the above-mentioned fibers, one or more of them as appropriate depending on the application. The other fibers may be used in combination with the composite fibers of the present invention, or a fiber web made of the composite fibers of the present invention may be used by laminating a fiber web made of the other fibers.

[0070] Examples of fiber webs used in manufacturing the above-mentioned heat-bonded nonwoven fabric include parallel webs, semi-random webs, random webs, cross webs, crisscross webs, and other card webs, as well as airlaid webs. When the heat-bonded nonwoven fabric is used in absorbent articles, especially when used as a surface sheet for absorbent articles, bulkiness, flexibility, and the presence of some voids between the fibers are required, so the fiber web is preferably a card web. The above-mentioned heat-bonded nonwoven fabric may be made by laminating two or more different types of fiber webs from the above-mentioned fiber webs.

[0071] It is preferable to obtain a nonwoven fabric in the form of a heat-bonded nonwoven fabric by heat-treating the above fiber web to heat-bond the fibers together with sheath components. This is because the heat-bonded nonwoven fabric exhibits the effects brought about by the composite fibers of the present invention, such as the smooth texture of the nonwoven fabric surface, in a remarkable manner. In order to entangle the fibers, the fiber web may be subjected to entanglement treatments such as needle punching or water jet entanglement treatment before and / or after heat treatment, as necessary.

[0072] To obtain a heat-bondable nonwoven fabric, the fiber web is subjected to heat treatment by known heat treatment methods. Preferably, heat treatment machines that do not apply excessive pressure, such as air pressure, to the fiber web are used, such as hot air penetration heat treatment machines, hot air blowing heat treatment machines, and infrared heat treatment machines. In other words, the heat treatment is preferably performed by an air-through method, and the heat-bondable nonwoven fabric is preferably an air-through nonwoven fabric. The heat treatment conditions, such as the heat treatment temperature, are selected and implemented under conditions that, for example, the sheath component is sufficiently melted and / or softened, allowing the fibers to bond at contact points or intersections without crushing the crimp. For example, the heat treatment temperature is preferably in the range of Tm2 or higher and (Tm2 + 40°C) or lower, where Tm2 is the melting point of the polyethylene contained in the sheath component (or, if multiple polyethylenes are contained in the sheath component, the melting point of the polyethylene with the highest melting point).

[0073] The basis weight of the heat-bondable nonwoven fabric of the present invention is not particularly limited, but is 10 g / m². 2 More than 80g / m 2 Preferably, it is 15 g / m 2 More than 60g / m 2 More preferably, the following is true: 15 g / m 2 More than 30g / m 2The following is most preferable. However, the basis weight of the heat-bonded nonwoven fabric of the present invention may be outside these ranges depending on the application of the heat-bonded nonwoven fabric. Furthermore, when the above heat-bonded nonwoven fabric is used for various applications, such as the surface sheet of various disposable diapers and sanitary napkins, the back sheet of various disposable diapers, or the second sheet placed directly beneath the surface sheet of absorbent articles, the basis weight is appropriately selected according to the application. For example, 10 g / m² is suitable for sanitary material applications. 2 More than 60g / m 2 Preferably, it is 15 g / m 2 More than 40g / m 2 More preferably, the following is true: 15 g / m 2 More than 30g / m 2 The following is most preferable:

[0074] The specific volume of the above heat-bonded nonwoven fabric is not particularly limited, but 30 cm³ 3 / g or more 100cm 3 Preferably less than / g, 40cm 3 / g or more 90cm 3 It is more preferable that it be less than / g, 45cm 3 / g or more 85cm 3 It is even more preferable that the value be less than or equal to / g. This can improve flexibility and initial tensile stress, specifically the MD10% tensile stress.

[0075] The above-mentioned heat-bonded nonwoven fabric has good flexibility and excellent strength. Such heat-bonded nonwoven fabric can be used for various sheets that make up absorbent articles, such as surface sheets, second sheets (also called liquid diffusion sheets), core wrap sheets that enclose the absorbent material, and back sheets that form the outer surface of infant diapers and adult diapers. [Examples]

[0076] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0077] The measurement and evaluation methods used in this embodiment are as follows.

[0078] (Melting point) The melting peak temperature, measured according to JIS K 7121:1987, was defined as the melting point of the resin.

[0079] (Single fiber fineness of undrawn fiber tow) The single fiber fineness of undrawn fiber tow was measured according to JIS L 1013:2010.

[0080] (X-ray diffraction method) The composite fibers were cut into 2.5 cm lengths. 12.5 mg of the cut sample was weighed, and the ends were tied together with enameled wire to form the sample. The fiber bundle, which was the sample, was fixed in a holder perpendicular to the direction of X-ray incidence, and wide-angle X-ray diffraction was performed. The measurement conditions were as follows: X-ray diffractometer: Rigaku Corporation's "MiniFlex(registered trademark) II for polymers" X-ray source: CuKα rays (using a Ni filter) Output: 30kV 15mA Slit system: DS:1.25°SS:1.25°mm RS:0.3mm Measurement direction: Fiber radial scanning Scanning method: Continuous scan Measurement range: 2θ = 2~45° Step: 0.02° Scan speed: 2° / min

[0081] (Degree of crystallinity of the

[0010] surface of polyester resin) The X-ray diffraction pattern of the core component (polyester resin) obtained by XRD analysis was used to measure the area of ​​the function approximated by the least squares method and the total area (2θ range: 10~30°), and the degree of crystallinity of the

[0010] plane of the polyester resin was calculated using the following formula. The degree of crystallinity (%) of the

[0010] plane of polyester resin = Area of ​​the function approximated by the least squares method / Total area (2θ range: 10~30°) × 100

[0082] (Diffraction peak intensity ratio of polyethylene) In the X-ray diffraction pattern of the sheath component (polyethylene) obtained by XRD analysis, the diffraction peak intensities of the polyethylene

[0110] plane and the polyethylene

[0200] plane were measured, and PE

[0200] / PE

[0110] was calculated using the following formula. PE

[0200] / PE

[0110] = Diffraction peak intensity of the

[0200] plane of polyethylene / Diffraction peak intensity of the

[0110] plane of polyethylene

[0083] (Number of contractions) Measurements were taken in accordance with JIS L 1015:2010.

[0084] (Single fiber fineness and fiber length of composite fibers) The single fiber fineness of the composite fiber (staple) was measured according to JIS L 1015:2010 8.5 (vibration method). The fiber length of the composite fiber (staple) was also measured according to JIS L 1015:2010 8.4.

[0085] (Tensile strength and elongation of composite fibers) Measurements were taken according to JIS L 1015:2010 8.7 Tensile strength and elongation.

[0086] (Dry heat dimensional change rate of composite fibers) Measurements were taken in accordance with JIS L 1015:2010 8.15 b). The heat treatment temperature was 140°C and the heat treatment time was 30 minutes. The initial load was Tex × 5.88 mN, and the gripping distance was 20 mm.

[0087] (Apparent Young's modulus of composite fibers) The initial tensile resistance (N / tex) was measured and calculated in accordance with JIS L 1015:2010 8.11. The average value of 30 measurements was used. Next, the apparent Young's modulus was calculated based on the initial tensile resistance using the following formula 4.

number

[0088] (Hollow rate) After filling a 1 mm diameter hole with composite fibers (drawn fiber tow), a photograph (range: 300 μm × 560 μm) was taken at 200x magnification using an optical microscope (Nikon, "ECLIPSE LV100ND"). Fifty fiber cross-sections were arbitrarily selected (approximately half of the observation range), and the area St (μm²) of the region enclosed by the outer circumference of each fiber cross-section was measured. 2 ) and the area Sh (μm²) of the region enclosed by the outer periphery of the hollow part. 2 The hollowness of the fiber was measured, and the hollowness ratio was calculated using the following formula 3. The average value of the hollowness ratios of 50 fiber cross-sections was taken as the hollowness ratio of the composite fiber. [Formula 3] Hollow rate (%)=100×[Sh / St]

[0089] (Balance weight of nonwoven fabric) The nonwoven fabric was cut to A4 size (210 mm x 297 mm), and the mass (g) of the cut nonwoven fabric was measured and calculated using the following formula. Weight (g / m 2 ) = Mass of nonwoven fabric (g) / (0.210m × 0.297m)

[0090] (Thickness of nonwoven fabric) The thickness of the nonwoven fabric was measured using a thickness measuring instrument (product name: THICKNESS GAUGE, model: CR-60A, manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.) on a 1 cm sample. 2 Measurements were taken with a load of 2.94 cN applied per unit area. The average thickness of 10 nonwoven fabric samples cut to A4 size was evaluated using a N=3 scale.

[0091] (Specific volume of nonwoven fabric) The specific volume of the nonwoven fabric was calculated using the following formula. Specific volume of nonwoven fabric (cm³) 3 / g) = Thickness (mm) × 1000 / Basis weight of nonwoven fabric (g / m 2 )

[0092] (Tensile strength and stress at 10% elongation of nonwoven fabric) In accordance with JIS L 1096:2010 8.14.1 Method A (strip method), tensile tests were conducted using a constant-speed tension tensile testing machine under the conditions of a sample width of 5 cm, grip spacing of 10 cm, and tensile speed of 30 ± 2 cm / min. The load value at break (tensile strength) and the stress at 10% elongation were measured. The tensile tests were performed with the MD and CD nonwoven fabrics as the tensile direction. The evaluation results are shown as the average of the values ​​measured for three samples.

[0093] (Rigidity of nonwoven fabric) The stiffness and flexibility of the nonwoven fabric were measured according to the handle ometer method, as specified in JIS L 1913:2010 6.7.5. Specifically, the measurement was performed using the following procedure. A sample piece measuring 20 cm in length and 20 cm in width was placed on the sample stage so that the measurement direction of the sample piece was perpendicular to the slot (gap width 10 mm). Next, the penetrator blade, adjusted to be 8 mm below the surface of the sample stage, was lowered, and the sample piece was pressed in. The resistance to the pressure was read at a position 6.7 cm (1 / 3 of the width of the sample piece) from either side, at different locations on the front and back of both the MD and CD. The maximum value (cN) indicated by the microammeter was read as the resistance value. The sum of the maximum values ​​from all four sides was calculated, and the average of three readings was determined to be the dry stiffness (cN) of the sample.

[0094] <Examples 1-12, Comparative Examples 1-9> (Fabrication of composite fibers) High-density polyethylene (melting point 133°C, manufactured by Nippon Polyethylene Co., Ltd., product name "HE481") was used as the sheath component, and polyethylene terephthalate (melting point: 255°C, manufactured by INDORAMA, TEXTILE GRADE (SEMIDULL)) was used as the core component. The prepared sheath and core components were melt-spun using a concentric core-sheath composite nozzle, adjusting the discharge rate of each component so that the composite ratio of core and sheath components, i.e., the mass ratio of core component / sheath component, was the value shown in Tables 1 to 3. The extrusion temperatures of the sheath and core components were set to the temperatures shown in Table 1 below, and the nozzle temperature (spinning temperature) was set to 290°C. The extruded molten core and sheath components formed filaments were taken up to obtain undrawn fiber tow (undrawn yarn) with the single fiber fineness shown in Tables 1 to 3 below. The obtained undrawn fiber tow was wet-drawn in 80°C hot water at the drawing ratios shown in Table 1 below to obtain drawn fiber tow (drawn yarn). Next, the drawn fiber tow was impregnated in a treatment tank filled with an aqueous solution of a fiber treatment agent that imparts hydrophilicity, and then the excess aqueous solution of the fiber treatment agent was squeezed off with a resin roll (nip roll) to adjust the moisture content so that the component of the fiber treatment agent was 0.40 ± 0.05 mass% when the mass of the composite fiber (drawn yarn) was 100 mass%. Mechanical crimping was applied to the drawn fiber tow treated with the fiber treatment agent using a stuffing box type crimper without tow heat treatment. The surface temperature of the tensioned drawn fiber tow immediately before crimping is shown in Tables 1 to 3 below. Note that the surface temperature of the tensioned drawn yarn from after drawing until before heat treatment is the same as the surface temperature of the tensioned drawn fiber tow immediately before crimping. Then, the relaxed fibers were heat-treated for 15 minutes at the temperatures shown in Tables 1-3 using a hot air blowing device. After that, the stretched fiber tow was cut to 51 mm to obtain composite fibers. (Preparation of heat-bonded nonwoven fabric) Using the composite fibers obtained above, a fiber web was prepared using a roller-type carding machine. The obtained fiber web was subjected to a heat treatment for 9.1 seconds by blowing hot air from directly above at a wind speed of 0.97 m / s using a hot air blowing device set to the temperatures shown in Tables 1 to 3, melting the sheath component to obtain a heat-bonded nonwoven fabric having the basis weight shown in Tables 1 to 3 below.

[0095] <Example 13, Comparative Example 10> (Fabrication of composite fibers) Hollow composite fibers were obtained in the same manner as in Example 4, except that a concentric spinning nozzle for hollow core-sheath composite fibers was used as the nozzle. The hollowness ratio of the hollow composite fibers obtained in Example 13 was 13.8%, and the hollowness ratio of the hollow composite fibers obtained in Comparative Example 10 was 12.0%. (Preparation of heat-bonded nonwoven fabric) Using the composite fibers obtained above, a fiber web was prepared using a roller-type carding machine. The obtained fiber web was subjected to a heat treatment for 9.1 seconds by blowing hot air from directly above at a wind speed of 0.97 m / s using a hot air blowing device set to the temperatures shown in Tables 2 and 3, melting the sheath component to obtain a heat-bonded nonwoven fabric having the basis weight shown in Tables 2 and 3 below.

[0096] The performance of the composite fibers and nonwoven fabrics obtained in each example and comparative example was measured as described above, and the results are shown in Tables 1 to 3 below.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Table 3]

[0100] In Examples 1-13, spinning at high temperature and lowering the surface temperature of the tensioned drawn yarn before crimping (the surface temperature of the tensioned drawn fiber tow from after drawing until before heat treatment), and then heat-treating the drawn yarn at a low temperature in a relaxed state, resulted in a dry heat dimensional change rate of 3.5% to 8.0% at 140°C and an apparent Young's modulus of 2100 N / mm². 2 More than 3150N / mm 2As described below, we were able to obtain composite fibers in which the crystallinity of the

[0010] plane of the polyester resin contained in the core component was 10.0% to 23.0%, and / or PE

[0200] / PE

[0110] was 0.38 to 0.60. Furthermore, the composite fibers obtained in Examples 1 to 13 had good processability for heat-bonded nonwoven fabrics, and when the hot air treatment temperature was 132°C or higher, the resulting heat-bonded nonwoven fabric had high strength and good flexibility. Specifically, the MD 10% elongation stress / longitudinal and transverse tensile strength ratio per unit basis weight was 0.10 [(N / 50mm) / (g / m 2 )] or greater, and the stiffness per unit basis weight is 2.05 [cN / (g / m 2 )] was below.

[0101] On the other hand, the composite fiber of Comparative Example 1, which was spun at a low temperature, showed a dry heat dimensional change rate of over 8.0% at 140°C, and an apparent Young's modulus of 3150 N / mm². 2 Furthermore, the crystallinity of the

[0010] plane of the polyester resin contained in the core component exceeds 23.0%, and the heat-bonded nonwoven fabric using this composite fiber has poor flexibility, specifically, the stiffness per unit basis weight is 2.05 [cN / (g / m²). 2 It was beyond [a certain point] and very hard. The composite fiber of Comparative Example 2, in which a relaxed drawn yarn was heat-treated at a high temperature, had a dry heat dimensional change rate of less than 3.5% at 140°C, and the crystallinity of the

[0010] plane of the polyester resin contained in the core component exceeded 23.0%. As a result, the heat-bonded nonwoven fabric using this composite fiber had inferior strength. Specifically, the MD10% elongation stress / longitudinal and transverse tensile strength ratio per unit basis weight was 0.10 [(N / 50mm) / (g / m 2 It was less than ). In Comparative Example 3, the surface temperature of the stretched fiber tow in a tensioned state from the step of obtaining the stretched fiber tow to the step of heat treatment exceeded 60°C. The composite fiber had a dry heat dimensional change rate of less than 3.5% at 140°C, and a PE

[0200] / PE

[0110] ratio of less than 0.38. The heat-bonded nonwoven fabric using this composite fiber had inferior strength. Specifically, the MD 10% elongation stress / longitudinal and transverse tensile strength ratio per unit basis weight was 0.10 [(N / 50mm) / (g / m 2 It was less than ). The composite fibers of Comparative Examples 4, 6 to 10 obtained by heat-treating the relaxed drawn yarn at a high temperature had a dry heat dimensional change rate at 140°C of less than 3.5%, a PE

[0200] / PE

[0110] of less than 0.38, and the heat-bonded nonwoven fabric using the composite fiber had inferior strength. Specifically, the MD 10% elongation stress / ratio of longitudinal and transverse tensile strengths per unit basis weight was less than 0.10 [(N / 50 mm) / (g / m 2 )]. The surface temperature of the tensioned drawn fiber tow from after the step of obtaining the drawn fiber tow to before the step of heat-treating exceeds 60°C. The composite fiber of Comparative Example 5 obtained by heat-treating the relaxed drawn yarn at a high temperature had a dry heat dimensional change rate at 140°C of less than 3.5%, the crystallinity of the

[0010] plane of the polyester resin contained in the core component also exceeded 23.0%, a PE

[0200] / PE

[0110] of less than 0.38, and the heat-bonded nonwoven fabric using the composite fiber had inferior strength. Specifically, the MD 10% elongation stress / ratio of longitudinal and transverse tensile strengths per unit basis weight was less than 0.10 [(N / 50 mm) / (g / m 2 )].

[0102] The present invention includes, for example, one or more of the following embodiments. [1] A composite fiber including a core component and a sheath component, wherein the core component and the sheath component are arranged substantially concentrically, the core component contains 60% by mass or more of a polyester resin, the sheath component contains 60% by mass or more of polyethylene, the polyethylene has a density exceeding 0.93 g / cm 3 , the dry heat dimensional change rate of the composite fiber at 140°C is 3.5% or more and 8.0% or less, a composite fiber satisfying at least one of the following requirements (1) to (3). (1) The apparent Young's modulus of the composite fiber is 2100 N / mm 2 or more and 3150 N / mm 2 or less (2) The crystallinity of the

[0010] plane of the polyester resin contained in the core component is 10.0% or more and 23.0% or less (3) The ratio of the crystallinity of the

[0200] plane to the crystallinity of the

[0110] plane of the polyethylene contained in the sheath component (

[0200] plane crystallinity /

[0110] plane crystallinity) is 0.38 or more and 0.60 or less. [2] The composite fiber according to [1], wherein the ratio of the tensile strength to the elongation ratio of the composite fiber ((tensile strength [cN / dtex]) / elongation ratio [%]) is greater than 0.040 and 0.060 or less. [3] The composite fiber according to [1] or [2], wherein the tensile strength of the composite fiber is 1.80 cN / dtex or more and 3.00 cN / dtex or less. [4] A composite fiber containing a core component and a sheath component, wherein the core component and the sheath component are arranged substantially concentrically, the core component contains 60% by mass or more of a polyester resin, the sheath component contains 60% by mass or more of polyethylene, the polyethylene has a density of 0.93 g / cm 3 or more, the composite fiber satisfies the following requirements (I) and (II) when heat-treated under the following conditions. (Heat treatment conditions) Using 100% of the composite fiber, a fiber web was produced with a roller carding machine, and the obtained fiber web was subjected to hot air blowing from directly above at a wind speed of 0.97 m / s using a hot air blowing device set at 135°C, and heat-treated for 9.1 seconds. The basis weight was 17.0 ± 3.0 g / m 2 of the thermally bonded nonwoven fabric (I) The ratio of the longitudinal 10% elongation stress per unit basis weight to the longitudinal and transverse tensile strength ratio calculated by the following formula 1 for the thermally bonded nonwoven fabric obtained by heat treatment is 0.10 [(N / 50 mm) / (g / m 2 )] or more [Formula ①] Ratio of longitudinal 10% elongation stress per unit basis weight to longitudinal and transverse tensile strength [(N / 50 mm) / (g / m 2 )]=[Longitudinal 10% elongation stress (N / 50 mm) / Longitudinal basis weight (g / m 2 )] / {[Longitudinal tensile strength (N / 50 mm) / Longitudinal basis weight (g / m 2 )] / [Transverse tensile strength (N / 50 mm) / Transverse basis weight (g / m2 )]} (II) The stiffness per unit basis weight of the heat-bonded nonwoven fabric obtained by heat treatment is 2.05 [cN / (g / m²) 2 )] is below [Formula 2] Stiffness per unit basis weight [cN / (g / m 2 )] = rigidity (cN) / rigidity basis weight (g / m 2 ) [5] The composite fiber according to any one of [1] to [4], wherein the composite ratio of the core component to the sheath component (mass ratio of core component to sheath component) in the composite fiber is 30 / 70 to 70 / 30. [6] The composite fiber according to any one of [1] to [5], wherein the composite fiber has a hollow portion in the center of the fiber in the fiber cross-section that is continuous in the direction of the fiber axis. [7] A heat-bondable nonwoven fabric containing 10% by mass or more of the composite fibers described in any of [1] to [6], wherein at least some of the composite fibers are bonded together by a sheath component. [8] A method for producing a composite fiber comprising a core component and a sheath component, A core component containing 60% by mass or more of polyester resin, with the melting point of the polyester resin in the core component being Tm1, is extruded at an extrusion temperature of [Tm1 + 55°C] to [Tm1 + 125°C], with a density of 0.93 g / cm³. 3 A process to obtain an undrawn fiber tow consisting of the core component and the sheath component, by supplying a sheath component containing 60% by mass or more of polyethylene, to a concentric core-sheath type composite nozzle configured such that, when the melting point of the polyethylene contained in the sheath component is Tm2, ​​the sheath component covers the surface of the composite fiber in the fiber cross-section and the core component and the sheath component are arranged substantially concentrically, at an extrusion temperature of [Tm2 + 100°C] or more and [Tm2 + 200°C] or less, and extruding it to obtain an undrawn fiber tow consisting of the core component and the sheath component. A step of stretching the aforementioned unstretched fiber tow to obtain stretched fiber tow, The process includes heat treatment of the stretched fiber tow in a relaxed state at a temperature of 50°C to 90°C. A method for producing composite fibers, wherein the surface temperature of the stretched fiber tow in a tensioned state from the step of obtaining the stretched fiber tow to the step of heat treatment is less than 60°C. [9] The method for producing a composite fiber according to [8], wherein the stretching ratio in the step of obtaining the stretched fiber tow is greater than 1.0 and less than or equal to 4.0.

[10] A method for producing a composite fiber according to [8] or [9], comprising the step of imparting crimp to the stretched fiber tow before the heat treatment step.

[11] A method for producing a composite fiber according to any one of [8] to

[10] , comprising the step of applying a fiber treatment agent to the stretched fiber tow before the step of imparting crimp. [Industrial applicability]

[0103] The composite fibers of the present invention can be incorporated into a heat-bonded nonwoven fabric, which can be preferably used as a surface sheet for various absorbent articles such as sanitary napkins, infant diapers, adult diapers, animal diapers including mammals, panty liners, and incontinence liners. It can also be preferably used as a back sheet for infant diapers and adult diapers, and as a second sheet located on the absorbent side of the surface sheet in absorbent articles, for example, directly below the surface sheet. Furthermore, the composite fibers of the present invention can be used in drip sheets that quickly absorb excess moisture and oil from food, as well as in sanitary masks, industrial air filters, battery separators, and automotive interior substrates. [Explanation of Symbols]

[0104] 10, 20 Composite Fibers 11 Sheath component 12 core components 13. Centricular position of the fiber cross-section of the core component 14. Centricular position in the fiber cross-section of composite fibers 15 Radius in the fiber cross-section of composite fibers 16 Hollow part 17. Centricular position in the fiber cross-section of the hollow section

Claims

1. It is a composite fiber containing a core component and a sheath component. The core component and the sheath component are arranged substantially concentrically. The core component contains 60% by mass or more of polyester resin. The aforementioned sheath component contains 60% by mass or more of polyethylene. The polyethylene has a density of 0.93 g / cm³. 3 It is super, The dry heat dimensional change rate of the composite fiber at 140°C is 3.5% or more and 8.0% or less. A composite fiber that satisfies at least one of the following requirements (1) to (3). (1) The apparent Young's modulus of the composite fiber is 2100 N / mm². 2 More than 3150N / mm 2 The following is (2) The degree of crystallinity of the [010] plane of the polyester resin contained in the core component is 10.0% or more and 23.0% or less. (3) The ratio of the crystallinity of the [200] plane to the crystallinity of the [110] plane of polyethylene contained in the sheath component (crystallinity of the [200] plane / crystallinity of the [110] plane) is 0.38 or more and 0.60 or less.

2. The composite fiber according to claim 1, wherein the ratio of the tensile strength to the elongation (tensile strength [cN / dtex] / elongation [%]) of the composite fiber is greater than 0.040 and less than or equal to 0.

060.

3. The composite fiber according to claim 1, wherein the tensile strength of the composite fiber is 1.80 cN / dtex or more and 3.00 cN / dtex or less.

4. The composite fiber according to claim 1, wherein the composite ratio of the core component to the sheath component (mass ratio of core component to sheath component) in the composite fiber is 30 / 70 to 70 / 30.

5. The composite fiber according to claim 1, wherein the composite fiber has a hollow portion in the center of the fiber cross-section that is continuous in the direction of the fiber axis.

6. It is a composite fiber containing a core component and a sheath component. The core component and the sheath component are arranged substantially concentrically. The core component contains 60% by mass or more of polyester resin. The aforementioned sheath component contains 60% by mass or more of polyethylene. The polyethylene has a density of 0.93 g / cm³. 3 It is super, The composite fiber is a composite fiber that satisfies the requirements of (I) and (II) below when heat-treated under the following conditions. (Heat treatment conditions) Using 100% by mass of the composite fiber, a fiber web was prepared using a roller carding machine. The obtained fiber web was then subjected to heat treatment for 9.1 seconds by blowing hot air from directly above at a wind speed of 0.97 m / s using a hot air blowing device set to 135°C, resulting in a basis weight of 17 ± 3 g / m². 2 Heat-bonded nonwoven fabric (I) The stress / tensile strength ratio per unit basis weight at 10% longitudinal elongation, calculated using the following formula 1 for the heat-bonded nonwoven fabric obtained by heat treatment, is 0.10 [(N / 50mm) / (g / m 2 ) That's all. [Formula 1] Tensile stress at 10% elongation in the longitudinal direction per unit areal density / ratio of longitudinal to transverse tensile strength [(N / 50 mm) / (g / m 2 )] = [Tensile stress at 10% elongation in the longitudinal direction (N / 50 mm) / Areal density in the longitudinal direction (g / m 2 )] / {[Tensile strength in the longitudinal direction (N / 50 mm) / Areal density in the longitudinal direction (g / m 2 )] / [Tensile strength in the transverse direction (N / 50 mm) / Areal density in the transverse direction (g / m 2 )]} (II) The stiffness per unit basis weight of the heat-bonded nonwoven fabric obtained by heat treatment is 2.05 [cN / (g / m²)], calculated by the following formula 2. 2 ) ] Below [Formula 2] Stiffness per unit basis weight [cN / (g / m)] 2 )] = rigidity (cN) / rigidity basis weight (g / m 2 )

7. A heat-bondable nonwoven fabric containing 10% by mass or more of the composite fibers described in any one of claims 1 to 6, wherein at least some of the composite fibers are bonded together by a sheath component.

8. A method for producing a composite fiber containing a core component and a sheath component, A core component containing 60% by mass or more of polyester resin, with the melting point of the polyester resin in the core component being Tm1, is extruded at an extrusion temperature of [Tm1 + 55°C] to [Tm1 + 125°C] with a density of 0.93 g / cm³. 3 A process to obtain an undrawn fiber tow consisting of the core component and the sheath component, by supplying a sheath component containing 60% by mass or more of polyethylene, to a concentric core-sheath type composite nozzle configured such that, when the melting point of the polyethylene contained in the sheath component is Tm2, ​​the sheath component covers the surface of the composite fiber in the fiber cross-section and the core component and the sheath component are arranged substantially concentrically, at an extrusion temperature of [Tm2 + 100°C] or more and [Tm2 + 200°C] or less, and extruding it to obtain an undrawn fiber tow consisting of the core component and the sheath component. A step of stretching the aforementioned unstretched fiber tow to obtain stretched fiber tow, and The process includes heat treatment of the stretched fiber tow in a relaxed state at a temperature of 50°C to 90°C. A method for producing composite fibers, wherein the surface temperature of the stretched fiber tow in a tensioned state from the step of obtaining the stretched fiber tow to the step of heat treatment is less than 60°C.

9. The method for producing a composite fiber according to claim 8, wherein the stretching ratio in the step of obtaining the stretched fiber tow is greater than 1.0 times and less than or equal to 4.0 times.

10. A method for producing a composite fiber according to claim 8, comprising the step of imparting crimp to the stretched fiber tow before the heat treatment step.

11. A method for producing a composite fiber according to claim 10, comprising the step of applying a fiber treatment agent to the stretched fiber tow before the step of imparting crimp.

Images