Spun-bonded nonwoven fabric, method for producing same, and sanitary material

Abstract

In order to provide a spun-bonded nonwoven fabric which has excellent cushioning properties, a spun-bonded nonwoven fabric according to the present invention is configured from composite fibers that are composed of a polypropylene resin and a polyethylene resin. The composite fibers are side-by-side type composite fibers or eccentric core-sheath type composite fibers, the composite fibers are crimped fibers, and the composite fibers satisfy formula 1 and formula 2.　Formula (1): 1.1 ≤ f1PP / fPE ≤ 10.0, Formula (2): 0.0 ≤ fPE ≤ 2.0 In the formulae, fPP is the molecular orientation degree (no unit) of the polypropylene resin in the composite fibers, and fPE is the molecular orientation degree (no unit) of the polyethylene resin in the composite fibers.

Description

Spunbond nonwoven fabric, method for manufacturing the same, and sanitary materials

[0001] This invention relates to spunbond nonwoven fabrics, methods for producing the same, and sanitary materials.

[0002] With the global proliferation of sanitary materials such as disposable diapers, sanitary napkins, and masks, the demands on the performance and quality of the materials used have increased in recent years. In particular, materials that come into direct contact with the user's skin, such as the top sheet of a diaper, require appropriate cushioning (a characteristic where the material has bulkiness while providing a pleasant rebound when pressed with fingers or the palm of the hand) to improve comfort during wear.

[0003] Conventionally, so-called air-through nonwoven fabrics, which are made by forming short fibers into a sheet using a carding method and then self-fusing them by hot air treatment, have been suitably used in such areas. These air-through nonwoven fabrics are widely used because they have excellent cushioning properties. However, because the structure is simply formed by heat bonding short fibers at their intersections, the mechanical properties of the nonwoven fabric are relatively low, making it difficult to produce them at lower basis weights or at high speeds.

[0004] Therefore, so-called spunbond nonwoven fabrics, which are generally stronger and relatively easy to produce at high speed, have been attracting attention in recent years.

[0005] For example, Patent Document 1 contains thermoplastic polymer fibers, and the thickness, compression work, and pressure are 0.5 gf / cm². ２ Thickness and pressure at 50 gf / cm² ２ A spunbond nonwoven fabric has been proposed in which the thickness, basis weight, and rigidity in the longitudinal (MD) and transverse (CD) directions are within a specific range. It is stated that this spunbond nonwoven fabric provides a spunbond nonwoven fabric that is bulky, highly flexible, and has low bending rigidity.

[0006] Furthermore, Patent Document 2 proposes a composite long-fiber nonwoven fabric comprising a polypropylene resin as a first component and a polyethylene resin as a second component, characterized in that the number of fiber contact points, the distance between fiber contacts in the thickness direction, and the compression work of the nonwoven fabric are within a specific range. It is stated that this composite long-fiber nonwoven fabric has the ability to achieve both bulkiness with cushioning softness and high strength, and is suitable for use as a top sheet and back sheet for sanitary materials.

[0007] International Publication No. 2020 / 152890, Japanese Patent Publication No. 2019-85661

[0008] However, spunbond nonwoven fabrics generally have insufficient bulkiness, which results in inadequate cushioning.

[0009] In spunbond nonwoven fabrics, such as those proposed in Patent Document 1, the manufacturing process attempts to ensure bulkiness by adjusting the Rockwell hardness and embossing aspect ratio of the embossing roll when the nonwoven fiber web is heat-pressed with the embossing roll. However, in the method specifically disclosed in Patent Document 1, as with general spunbond nonwoven fabrics, there are many areas where the nonwoven web is strongly pressed by the embossing roll, resulting in the nonwoven fabric becoming thinner than necessary. As a result, there are limitations to the bulkiness and cushioning properties of the resulting spunbond nonwoven fabric.

[0010] On the other hand, the technology described in Patent Document 2 attempts to obtain a bulky long-fiber nonwoven fabric by bonding fibers together in a nonwoven web composed of composite long fibers containing polypropylene resin and polyethylene resin through a two-stage temporary bonding process. However, the method specifically disclosed in Patent Document 2 tends to result in a low proportion of fibers oriented in the thickness direction, making the nonwoven fabric weak against compression in the thickness direction and easily crushed, thus presenting challenges in terms of cushioning properties.

[0011] Therefore, in view of the above circumstances, the object of the present invention is to provide a spunbond nonwoven fabric with excellent cushioning properties.

[0012] In order to achieve the above objectives, the inventors conducted extensive research and found that by using a composite fiber composed of a polypropylene resin and a polyethylene resin, which is either a side-by-side type composite fiber or an eccentric core-sheath type composite fiber, and furthermore, by using a crimped composite fiber, a spunbond nonwoven fabric with a certain degree of cushioning could be produced. However, the effect was still not sufficient. Therefore, after further research, they found that by setting the ratio of the molecular orientation degrees of the polypropylene resin and polyethylene resin constituting the composite fiber, and the molecular orientation degree of the polyethylene resin, within a specific range, it is possible to achieve unprecedented and excellent cushioning properties. Furthermore, it was found that because the adhesion between the fibers constituting this spunbond nonwoven fabric is good, it exhibits sufficient durability against friction.

[0013] This invention was completed based on these findings, and according to this invention, the following inventions are provided.

[0014] [1] A spunbond nonwoven fabric composed of composite fibers made of a polypropylene resin and a polyethylene resin, wherein the composite fibers are side-by-side type composite fibers or eccentric core-sheath type composite fibers, the composite fibers are crimped fibers, and furthermore, the composite fibers satisfy the following formulas 1 and 2.

[0015] 1.1 ≤ f ＰＰ / f ＰＥ ≦10.0 ... (Formula 1) 0.0≦f ＰＥ ≤ 2.0 ... (Equation 2) where f ＰＰ f is the degree of molecular orientation (unitless) of the polypropylene resin in the composite fiber, ＰＥ This represents the degree of molecular orientation (unitless) of the polyethylene resin in the composite fiber.

[0016] [2] The spunbond nonwoven fabric according to [1], wherein the coil width of the composite fiber is 400 μm or more and 1200 μm or less.

[0017] [3] The bulk density of the spunbond nonwoven fabric is 0.010 g / cm³ ３ 0.050g / cm or more３ The spunbond nonwoven fabric according to the above [1] or [2].

[0018] [4] The basis weight of the spunbond nonwoven fabric is 10 g / m ２ or more and 50 g / m ２ The spunbond nonwoven fabric according to any one of the above [1] to [3].

[0019] [5] The average single fiber diameter of the composite fiber is 7.5 μm or more and 30.0 μm or less, and the spunbond nonwoven fabric according to any one of the above [1] to [4].

[0020] [6] A sanitary material, at least a part of which is composed of the spunbond nonwoven fabric according to any one of the above [1] to [5].

[0021] [7] A sanitary material, wherein the spunbond nonwoven fabric according to any one of the above [1] to [5] is disposed at a portion that contacts the skin surface of the wearer.

[0022] [8] A sanitary material, wherein the spunbond nonwoven fabric according to any one of the above [1] to [5] is included in the topsheet.

[0023] [9] A method for producing a spunbond nonwoven fabric, comprising the steps of: melting a polypropylene-based resin and a polyethylene-based resin respectively and supplying them to a composite spinning die, discharging a composite polymer stream from a discharge hole of the composite spinning die, and then spraying air onto the composite polymer stream to form composite fibers that are crimped fibers; depositing the composite fibers on a belt to form a fiber web composed of the composite fibers; and thermally bonding the fiber web with heated air. In the step of forming the composite fibers, the composite fibers are side-by-side type composite fibers or eccentric core-sheath type composite fibers, and the melt viscosity η ＰＰ (Pa·s) of the polypropylene-based resin and the melt viscosity η ＰＥA method for producing a spunbond nonwoven fabric, wherein (Pa·s) satisfies the following formula 3, the temperature of the air is 10°C or more and 30°C or less, the air velocity is 1.0 m / s or more and 5.0 m / s or less, the spinning speed in the composite fiber formation step is 1000 m / min or more and 3000 m / min or less, and in the heat bonding step, the temperature of the heated air is 100°C or more and 160°C or less, the air velocity of the heated air is 0.5 m / s or more and 10.0 m / s or less, and the following formulas 1 and 2 are satisfied.

[0024] 1.1 ≤ f ＰＰ / f ＰＥ ≦10.0 ... (Formula 1) 0.0≦f ＰＥ ≦2.0 ... (Formula 2) 2.0≦η ＰＰ / η ＰＥ ≤ 20.0 ... (Equation 3) where f ＰＰ f is the degree of molecular orientation (unitless) of the polypropylene resin in the composite fiber, ＰＥ This represents the degree of molecular orientation (unitless) of the polyethylene resin in the composite fiber.

[0025] According to the present invention, a spunbond nonwoven fabric with excellent cushioning properties can be obtained. Furthermore, since this spunbond nonwoven fabric also has excellent durability against friction, it is suitable for use in sanitary materials such as diapers.

[0026] Figure 1 is a cross-sectional conceptual diagram illustrating and explaining one embodiment of a side-by-side type composite fiber among the composite fibers according to the present invention. Figure 2 is a cross-sectional conceptual diagram illustrating and explaining one embodiment of an eccentric core-sheath type composite fiber among the composite fibers according to the present invention. Figure 3 is a scanning electron microscope image illustrating and explaining one embodiment of a crimped fiber among the composite fibers according to the present invention. Figure 4 is a diagram illustrating a method for measuring the coil width of the composite fiber according to the present invention.

[0027] The spunbond nonwoven fabric of the present invention is a spunbond nonwoven fabric composed of composite fibers made of a polypropylene resin and a polyethylene resin, wherein the composite fibers are side-by-side type composite fibers or eccentric core-sheath type composite fibers, the composite fibers are crimped fibers, and furthermore, the following formulas 1 and 2 are satisfied: 1.1 ≤ f ＰＰ / f ＰＥ ≦10.0 ... (Formula 1) 0.0≦f ＰＥ ≤ 2.0 ... (Equation 2) where f ＰＰ f is the degree of molecular orientation (unitless) of the polypropylene resin in the composite fiber, ＰＥ This is the degree of molecular orientation (unitless) of the polyethylene resin in the composite fiber. The components will be described in detail below, but the present invention is not limited to the scope described below, as long as it does not exceed the gist of the invention, and various modifications are possible without departing from the gist of the invention.

[0028] [Composite Fibers] The spunbond nonwoven fabric of one embodiment of the present invention (hereinafter also referred to as "this embodiment") is first composed of composite fibers made of a polypropylene resin and a polyethylene resin. Here, in the present invention, a polypropylene resin means a resin in which the mole fraction of polypropylene units in the repeating unit is 80 mol% or more and 100 mol% or less, and a polyethylene resin means a resin in which the mole fraction of polyethylene units in the repeating unit is 80 mol% or more and 100 mol% or less. Hereafter, thermoplastic resins referred to as "...-type resins" shall have the same meaning. By having one thermoplastic resin of the composite fiber be a polypropylene resin, a spunbond nonwoven fabric with a smooth feel and suitable for use as a sanitary material is obtained. Furthermore, by having the other thermoplastic resin be a polyethylene resin, the adhesion between fibers is improved, resulting in a spunbond nonwoven fabric with excellent durability against friction.

[0029] Examples of polypropylene-based resins include polypropylene homopolymers, copolymers of polypropylene and other α-olefins (copolymerized polypropylene), and mixed resins (blended resins) of these.

[0030] Among these, polypropylene (a homopolymer of propylene) is preferred, as polypropylene provides high dimensional stability and results in a spunbond nonwoven fabric with a soft texture.

[0031] Furthermore, this polypropylene resin may contain inorganic particles such as titanium dioxide particles, lubricants, pigments, heat stabilizers, ultraviolet absorbers, conductive agents, heat storage agents, antibacterial agents, etc., to the extent that they do not hinder the objectives of the present invention, depending on the purpose.

[0032] Furthermore, examples of polyethylene-based resins include polyethylene homopolymers, copolymers of polyethylene and α-olefins (copolymerized polyethylene), and mixed resins (blended resins) thereof. In addition, either high-density polyethylene (HDPE) or low-density polyethylene (LDPE) can be suitably used as the type of polyethylene-based resin.

[0033] Among these, polyethylene (a homopolymer of ethylene) is preferred, as polyethylene provides good adhesion between fibers, resulting in a spunbond nonwoven fabric with excellent mechanical properties.

[0034] Naturally, this polyethylene resin can contain inorganic particles such as titanium dioxide particles, lubricants, pigments, heat stabilizers, ultraviolet absorbers, conductive agents, heat storage agents, antibacterial agents, etc., to the extent that they do not hinder the objectives of the present invention, depending on the purpose.

[0035] Next, the composite fiber according to this embodiment is either a side-by-side composite fiber or an eccentric core-sheath composite fiber. Here, in this embodiment, a side-by-side composite fiber is a composite fiber (side-by-side composite fiber (1)) in which, when its cross-section is observed, a plurality of resin parts (11, 12) as illustrated in Figure 1 can be observed, and these resin parts (11, 12) are arranged in parallel. An eccentric core-sheath composite fiber is a composite fiber (eccentric core-sheath composite fiber (2)) in which, when its cross-section is observed, a plurality of resin parts (21, 22) as illustrated in Figure 2 can be observed, one resin part (21) completely covers the other resin part (22), and in the cross-section, the center of gravity of the completely covered resin part and the center of gravity of the composite fiber are different.

[0036] Because the center of gravity of the resin portion differs in the cross-section of these composite fibers, when released from tension during the spinning process, the composite fibers bend according to the difference in the amount of elastic recovery between the resins. This curvature continues in the axial direction of the composite fiber, resulting in crimp and becoming the crimped fiber described later.

[0037] In particular, in the spunbond nonwoven fabric of this embodiment, the distance between the center of gravity positions of the resin portion in the cross-section of the composite fiber can be increased, and furthermore, the crimping shape can be precisely controlled, resulting in a spunbond nonwoven fabric that provides an appropriate resilience when compressed. Therefore, a side-by-side type composite fiber is preferable.

[0038] On the other hand, it is also preferable that the composite fiber be of the eccentric core-sheath type. In this case, since the polyethylene resin is the sheath component, the composite fiber has good adhesion, which is preferable because it results in a spunbond nonwoven fabric with excellent tensile strength.

[0039] Here, the composite fiber according to this embodiment is not limited to the case where the composite fiber is an eccentric core-sheath type composite fiber, but also when it is a side-by-side type composite fiber. In this case, the crimping shape of the composite fiber can be controlled by the difference in the centroid position in the cross-section of the fiber, so the centroid position, i.e., the cross-sectional shape, can be controlled to obtain the desired physical properties. In particular, when the distance between the centroid positions is increased, it is preferable for the composite fiber to be a side-by-side type composite fiber as described above, but it is also preferable for the composite fiber to be an eccentric core-sheath type composite fiber having a thin skin portion, as disclosed in International Publication No. 2020 / 095861.

[0040] The cross-sectional shape of the composite fiber according to the present invention is not particularly limited as long as it does not impair the effects of the present invention. It may be a round cross-section, or an elliptical cross-section, a triangular cross-section, a quadrilateral cross-section, a hexagonal cross-section, or other polygonal cross-sections (including those with rounded corners, rectangles, etc., that have differences in aspect ratio), and the cross-section of a single fiber may have a hollow portion or the like.

[0041] Furthermore, the composite fiber according to this embodiment is a crimped fiber. Here, in this embodiment, a crimped fiber is a crimped fiber (31) that has at least a portion that is substantially coil-shaped (spiral-shaped, or helical spring-shaped) and forms one or more coil crimps, as illustrated in Figure 3 (hereinafter sometimes referred to as the coil portion). As a result of being such a crimped fiber, the composite fibers repel each other, resulting in a spunbond nonwoven fabric with excellent bulkiness.

[0042] Furthermore, the composite fiber according to this embodiment satisfies the following equations 1 and 2: 1. 1 ≤ f ＰＰ / f ＰＥ ≦10.0 ... (Formula 1) 0.0≦f ＰＥ ≤ 2.0 ... (Equation 2) where f ＰＰ f is the degree of molecular orientation (unitless) of the polypropylene resin in the composite fiber, ＰＥ is the degree of molecular orientation (unitless) of the polyethylene resin in the composite fiber. If the composite fiber according to this embodiment satisfies the above formulas 1 and 2, it becomes a spunbond nonwoven fabric having appropriate cushioning properties and good durability against friction.

[0043] In formula 1, the degree of molecular orientation f of the polypropylene resin in the composite fiber ＰＰ The ratio (f) of the molecular orientation of the polyethylene resin in the composite fiber to the degree of molecular orientation of the polyethylene resin in the composite fiber (unitless). ＰＰ / f ＰＥ hereafter, this may be simply abbreviated as "molecular orientation ratio.") When the lower limit of the molecular orientation ratio is 1.1 or higher, preferably 2.0 or higher, and more preferably 3.0 or higher, the crimp of the fibers is moderately loosened, resulting in a spunbond nonwoven fabric that feels soft to the touch when pressed. On the other hand, when the upper limit of the molecular orientation ratio is 10.0 or lower, preferably 7.5 or lower, and more preferably 5.0 or lower, the crimp of the fibers becomes moderately fine, providing resilience when pressed, and the fibers become more intertwined, resulting in a spunbond nonwoven fabric that is less prone to fuzzing when subjected to friction.

[0044] Next, in formula 2, the degree of molecular orientation f of the polyethylene resin in the composite fiber ＰＥ With respect to (unitless), if its lower limit is 0.0 or higher, preferably 0.5 or higher, and more preferably 1.0 or higher, the crimp of the fibers is moderately loosened, resulting in a spunbond nonwoven fabric that has a soft feel when pressed. On the other hand, the degree of molecular orientation f of the polyethylene resin in the composite fiber ＰＥ Regarding the range, if the upper limit is 2.0 or less, preferably 1.8 or less, and more preferably 1.5 or less, the crimp of the fibers becomes appropriately fine, providing resilience when pressed, and the fibers intertwine more closely together, resulting in a spunbond nonwoven fabric that is less prone to fuzzing when subjected to friction.

[0045] In addition, it is preferable that the composite fiber according to this embodiment satisfies not only the following formulas 1 and 2, but also the following formula 8: 3.0 ≤ f ＰＰ ≤ 10.0 ... (Equation 8) In Equation 8, the degree of molecular orientation f of the polypropylene resin in the composite fiber ＰＰRegarding (unitless), the lower limit is preferably 3.0 or higher, and preferably 4.0 or higher, which results in a spunbond nonwoven fabric that is moderately dense in its crimp, provides resilience when pressed, and further entangles the fibers more tightly, making it less prone to fuzzing when subjected to friction. On the other hand, the molecular orientation f of the polypropylene resin in the composite fiber ＰＰ Regarding the range, the upper limit is preferably 10.0 or less, and preferably 8.0 or less, which moderately loosens the crimp of the fibers, resulting in a spunbond nonwoven fabric that has a soft feel when pressed.

[0046] Furthermore, the degree of molecular orientation f of the polypropylene resin in the composite fiber. ＰＰ (Unitless), degree of molecular orientation f of the polyethylene resin ＰＥ (Unitless), molecular orientation ratio f ＰＰ / f ＰＥ (Unitless) refers to a value measured or calculated by the following method.

[0047] <Degree of molecular orientation f of polypropylene resin> ＰＰ (Unitless) > (i) Five 1 cm square test pieces are randomly cut from the spunbond nonwoven fabric. (ii) Using polarized Raman spectroscopy, the Raman spectrum of the test pieces is measured at the location where the single fibers constituting the test piece are oriented longitudinally. For this measurement, a polarized Raman spectrometer such as the "LabRAM HR Evolution (HR-MT / ORS-Type III)" manufactured by Horiba, Ltd. can be used. In this case, the beam spot depth of the measurement light is preferably sufficiently large relative to the thin-sheath portion when the composite fiber is a thin-sheath eccentric core-sheath fiber, for example, 4 μm to 6 μm is preferred. (iii) The type of resin is determined by comparing the Raman spectrum obtained in this way with the Raman spectrum of known polypropylene. (iv) If the resin determined in (iii) is polypropylene, the wavenumber in the above Raman spectrum is 820 cm⁻¹. －１ Raman intensity (unitless) at wavenumber 840 cm －１Calculate the intensity ratio to the Raman intensity (unitless) at time. (v) Measure at five locations for each test specimen, and round the arithmetic mean (unitless) of the intensity ratios obtained in (iv) to two decimal places.

[0048] <Degree of molecular orientation f of polyethylene resin> ＰＥ (Unitless) > (i) and (ii) are < Molecular orientation f of polypropylene resin ＰＰ (Unitless) > The measurement and calculation method is the same. (iii) The type of resin is determined by comparing the Raman spectrum obtained in this way with the Raman spectrum of known polyethylene. (iv) If the resin determined in (iii) is polyethylene, the wavenumber in the above Raman spectrum is 1130 cm⁻¹. －１ The Raman intensity (unitless) at time is 1065 cm². －１ Calculate the intensity ratio to the Raman intensity (unitless) at time. (v) Measure at five locations for each test specimen, and round the arithmetic mean (unitless) of the intensity ratios obtained in (iv) to two decimal places.

[0049] <Molecular orientation ratio f ＰＰ / f ＰＥ (Unitless) > f obtained by the measurement and calculation method described above ＰＰ (Unitless) is the value obtained by the measurement and calculation method described above for f ＰＥ Divide by (unitless) and round to two decimal places.

[0050] Furthermore, the degree of molecular orientation f of polypropylene resin in composite fibers ＰＰ This can be adjusted by the melt viscosity of the polypropylene resin and the cooling rate during spinning, and the molecular orientation f of the polyethylene resin in the composite fiber. ＰＥ This can be adjusted by the melt viscosity of the polyethylene resin and the cooling rate during spinning, and therefore the molecular orientation ratio f ＰＰ / f ＰＥ This can be adjusted by controlling the melt viscosity of these polyethylene-based and polypropylene-based resins and the cooling rate during spinning.

[0051] In this embodiment, the composite fiber is more preferably 400 μm or more and 1200 μm or less in coil width. When the coil width of the composite fiber is preferably 400 μm or more, more preferably 500 μm or more, and even more preferably 600 μm or more, the fibers have sufficiently large diameter crimp, and the proportion of fibers in the spunbond nonwoven fabric that are oriented in the thickness direction with a certain length or more is high, resulting in a spunbond nonwoven fabric with a soft feel. On the other hand, when the coil width of the composite fiber is preferably 1200 μm or less, more preferably 1100 μm or less, and even more preferably 1000 μm or less, the fibers have fine crimp, and when the nonwoven fabric is compressed, it generates an appropriate resilience, resulting in a spunbond nonwoven fabric with excellent cushioning properties.

[0052] Here, the coil width (μm) of the composite fiber is a value measured and calculated by the following method: (i) Five 5 cm square test pieces are randomly cut from the spunbond nonwoven fabric. (ii) The surface of the cut spunbond nonwoven fabric is observed with a scanning electron microscope (SEM, for example, "VHX-6000" manufactured by Keyence Corporation), and fibers exhibiting crimp as illustrated in Figure 4 are searched for while no load is applied to the fibers, and an image is taken at a magnification that allows three or more fibers to be observed. (iii) In the crimped fiber (31) as illustrated in Figure 4, two adjacent peaks are selected, and a straight line L is drawn passing through their respective vertices (41A, 41B). The distance d (μm) between the straight line L and the vertex (41C) of the valley between the vertices of the two adjacent peaks is determined. (iv) Measure five fibers exhibiting crimp for each test specimen, and round the arithmetic mean (μm) of the distance d (μm) obtained in (iii) to the first decimal place.

[0053] Furthermore, the coil width of the composite fiber can be adjusted by factors such as the melt viscosity of the polyethylene-based resin and polypropylene-based resin, and the cooling rate during spinning.

[0054] In this embodiment, the composite fibers preferably have an average single fiber diameter of 7.5 μm or more and 30.0 μm or more. When the average single fiber diameter of the composite fibers is preferably 7.5 μm or more, more preferably 10.0 μm or more, and even more preferably 12.5 μm or more, the fibers become less likely to bend even when a load is applied, resulting in a spunbond nonwoven fabric with excellent cushioning properties. On the other hand, when the average single fiber diameter of the composite fibers is preferably 30.0 μm or less, more preferably 25.0 μm or less, and even more preferably 20.0 μm or less, the fibers can deform appropriately when subjected to force, resulting in a spunbond nonwoven fabric with a soft feel.

[0055] Here, the average single fiber diameter in the composite fiber is a value measured and calculated by the following method: (i) Randomly cut out 20 1 cm square test pieces from the spunbond nonwoven fabric. (ii) Cool one of the test pieces to -30°C and embed it in ice, then prepare a section using a microtome (e.g., "AUTOCUT R" manufactured by Leica Microsystems Inc.) and place it on a glass slide. (iii) Using a microscope (e.g., "VHX-X1" manufactured by Keyence Corporation), photograph the section at a magnification that allows observation of 10 or more single fiber cross-sections. (iv) Using image analysis software (e.g., "WinROOF2015" manufactured by Mitani Corporation) on the captured image, determine the area A formed by the cross-sectional contours of three single fibers present in the image. ｆ (μm ２ ) Measure this area A. ｆ The diameter D (μm) of a perfect circle with the same area is calculated for each. (vi) The same measurement is performed on the remaining 19 test pieces, and the arithmetic mean (μm) of the diameters D (μm) of all fibers is rounded to the second decimal place.

[0056] Furthermore, it is preferable that the composite fibers in this embodiment have micro-fused portions at least a portion of the contact points between the composite fibers. The micro-fused portions referred to here are portions that are fused with adjacent composite fibers in portions other than the macro-fused portions (non-macro-fused portions) described later, and the contact points between composite fibers include not only these micro-fused portions but also portions where the composite fibers are entangled with each other and portions where the composite fibers are simply in contact without fusing. The presence of micro-fused portions in the composite fibers of the spunbond nonwoven fabric of this embodiment results in a spunbond nonwoven fabric with excellent cushioning properties and sufficient strength.

[0057] If the composite fibers have the above-mentioned micro-fused portions, these can be confirmed by observing the composite fibers from a cross-section of the spunbond nonwoven fabric using a microscope (for example, Keyence Corporation's "VW-9000") or a scanning electron microscope (SEM, for example, Keyence Corporation's "VHX-6000"). In this case, if the spunbond nonwoven fabric has macro-fused portions as described later, the micro-fused portions should be confirmed in the non-macro-fused portions.

[0058] [Spunbond Nonwoven Fabric] The spunbond nonwoven fabric of the present invention is composed of the composite fibers described above. These composite fibers are long fibers, and by being composed of these composite fibers, sufficient mechanical properties can be obtained even with a low basis weight. Furthermore, by being composed of long fibers of the composite fibers, a spunbond nonwoven fabric with higher cushioning properties is obtained. This is because when the spunbond nonwoven fabric is compressed, the load is propagated in the direction of its surface, making it difficult for compressive stress to be unevenly distributed.

[0059] Furthermore, the spunbond nonwoven fabric of the present invention has a basis weight of 10 g / m². ２ 50g / m or more ２ The following is preferable: The basis weight is preferably 10 g / m². ２ Above a comfortable 20 g / m² ２ As a result of the above, a spunbond nonwoven fabric with mechanical strength suitable for practical use is obtained. On the other hand, the basis weight is preferably 50 g / m². ２ More preferably, 40 g / m ２The following conditions result in a spunbond nonwoven fabric with appropriate flexibility suitable for use as a nonwoven fabric for sanitary materials.

[0060] The basis weight referred to here is a value measured and calculated based on "6.2 Mass per unit area" of JIS L1913:2010 "General Test Methods for Nonwoven Fabrics".

[0061] Furthermore, the spunbond nonwoven fabric of the present invention has a bulk density of 0.010 g / cm³. ３ 0.050g / cm or more ３ The following is preferable. By controlling the bulk density within this range, sufficient bulkiness can be felt when touching the spunbond nonwoven fabric. On the other hand, the bulk density is preferably 0.030 g / cm³. ３ More preferably, 0.025 g / cm³ ３ The following conditions result in a spunbond nonwoven fabric with excellent bulkiness.

[0062] The bulk density referred to here is the value obtained by dividing the basis weight (W) of the spunbond nonwoven fabric by its thickness (H), and is measured by the following procedure. (i) Measure the thickness (H) of the spunbond nonwoven fabric using the following procedure (i-1) to (i-5). (i-1) Take five 25 mm x 40 mm test pieces from the spunbond nonwoven fabric from areas without wrinkles or folds. (i-2) Place the test pieces on the measuring stand of a 3D microscope (for example, Keyence Corporation's "VR-3050"). (i-3) Place a plastic plate measuring 80 mm x 80 mm and 1 mm thick with a 20 mm x 20 mm hole in the center on top of the test pieces, so that one half of the hole (10 mm x 20 mm) is occupied by the test piece, and fix the test piece so that it is horizontal to the measuring stand. (i-4) The thickness of the test piece inside the hole in the plastic plate is measured randomly at eight points in μm. (i-5) The remaining four test pieces are measured in the same manner, and the arithmetic mean of the measured values ​​is rounded to the first decimal place in μm, and this value is taken as the thickness (H) of the spunbond nonwoven fabric. (ii) The basis weight W (g / m²) of the spunbond nonwoven fabric measured by the above method is determined. ２The value obtained by dividing ) by the thickness H (μm) of the spunbond nonwoven fabric is rounded to the fourth decimal place.

[0063] The spunbond nonwoven fabric of the present invention may have macro-fused portions for the purpose of adjusting bulkiness, provided that the effects of the present invention are not impaired.

[0064] In this context, a macro-fused area refers to a region in a spunbond nonwoven fabric where the fiber cross-sectional shape is deformed to a degree that differs from the shape of other parts due to pressure applied in the cross-sectional direction, and where the fibers melt and fuse together to the point where the area becomes a lump or film. Specifically, this includes areas that have been heat-pressed by a heat embossing roll or areas that have been heat-fused by ultrasonic vibration.

[0065] When heat is applied to a portion of a material during heat bonding or heat fusion, if sufficient heat is applied to that portion and the entire composite fiber in that portion is fused together, the shape and area of ​​the bonding portion of the heat embossing roll used can be considered identical to the shape and area of ​​the macro-fused portion. For example, in the case of heat bonding using a heat embossing roll, when heat bonding is performed using a pair of rolls with protrusions and indentations, as described later, the shape and area of ​​the macro-fused portion can be considered identical to the shape and area of ​​the portion where the protrusions of the upper roll and the lower roll overlap and contact the nonwoven fiber web. Furthermore, when heat bonding is performed using a roll with protrusions and an unfolded roll and a flat roll, as described later, the shape and area of ​​the macro-fused portion can be considered identical to the shape and area of ​​the portion where the protrusions of the roll with protrusions contact the nonwoven fiber web.

[0066] In the spunbond nonwoven fabric of the present invention, it is preferable to set the area ratio of the macro-fused portion to 1% or more and 30% or less, as this allows for good bulkiness.

[0067] The spunbond nonwoven fabric of the present invention has a compression work capacity of 5.0 mN·cm / cm ２ The above is 20.0 mN·cm / cm ２ The following is preferable: The compression work is preferably 5.0 mN·cm / cm ２ More preferably, 10.0 mN·cm / cm ２ More preferably 12.0 mN·cm / cm ２By being as described above, the resistance when crushed becomes large, and it becomes a spunbond nonwoven fabric having a cushioning property with appropriate resilience. On the other hand, the compression work amount is preferably 20.0 mN·cm / cm ２ or less, more preferably 19.0 mN·cm / cm ２ or less. By being as described below, it becomes a spunbond nonwoven fabric with a soft touch.

[0068] The compression work amount referred to here is measured and calculated by the following procedure. (i) Randomly obtain 10 test pieces of 5 cm × 5 cm from the spunbond nonwoven fabric. (ii) Place the test piece on the metal sample table of a compression testing machine device (for example, "KES-G5" manufactured by Kato Tech Co., Ltd.). (iii) Between steel plates having a circular plane with a pressurized area of 2 cm ２ , while compressing the test piece at a compression speed of 0.020 mm / s until the compression load reaches 500 mN / cm ２ , measure the compression stress (mN / cm ２ ). (iv) Draw a graph (compression characteristic curve) with the x-axis being the thickness (mm) of the test piece and the y-axis being the compression stress (mN / cm ２ ). (v) Calculate the thickness (T ２ ) when the compression load is 5.00 mN / cm and the thickness (T ０ ) when the compression load is 500 mN / cm ２ in units of mm. (vi) Calculate the area S (mN·mm / cm Ｍ ) of the region surrounded by the compression characteristic curve, the x-axis (y = 0), x = T ０ , x = T Ｍ described in (iv) to (v) by the above compression testing machine device, divide this by 10, and set the unit to mN·cm / cm ２ . (vii) Repeat the procedures of (ii) to (vi) for the remaining 9 test pieces, take the arithmetic mean value (mN·cm / cm ２ ) of the area S, and round it to the second decimal place. ２

[0069] Furthermore, the amount of compression work varies depending on the fiber morphology and the rigidity of the fibers themselves in the spunbond nonwoven fabric, and can be controlled, for example, by the coil width. Therefore, it is advisable to adjust the coil width according to the desired amount of compression work.

[0070] The spunbond nonwoven fabric of the present invention preferably has a fluff grade of 3.0 or higher, as measured by the following procedure. More preferably, it has a fluff grade of 3.5 or higher. A fluff grade within this range indicates that the spunbond nonwoven fabric has sufficient durability against friction when used in sanitary materials.

[0071] The fluffiness grade of the spunbond nonwoven fabric of the present invention is a value measured and calculated by the following method: (i) Five 25 mm x 300 mm test pieces are randomly taken from the spunbond nonwoven fabric. (ii) Place a test piece in a Japan Society for the Promotion of Science type fastness tester (for example, the "RT-200" dye fastness tester manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.), set the friction load to 200g, and attach a cloth adhesive tape with a dynamic friction coefficient of 0.055 to 0.060 (for example, "Linley Cloth - Heavy Packaging No. 317" manufactured by Linley Tape Co., Ltd.) to the friction side, and run it 50 times. Here, the dynamic friction coefficient of the cloth adhesive tape is measured and calculated by the procedure shown in (ii-1) to (ii-5) below. (ii-1) Cut the cloth adhesive tape to a width of 3 cm and a length of 27 cm, and attach it to the measuring stand of a friction tester (for example, "KES-SE" manufactured by Kato Tech Co., Ltd.). (ii-2) Place a friction element measuring 1 cm x 1 cm with 1 mm piano wire wrapped around it on the cloth adhesive tape, and apply a load so that the total weight including the friction element is 50 g. (ii-3) Move the friction element at a speed of 1.0 mm / sec and a stroke length of 20 mm, measure the friction coefficient in dimensionless units, and plot the graph with the horizontal axis representing the stroke length and the vertical axis representing the friction coefficient. (ii-4) Take the average value of the friction coefficient between 5.0 mm and 15.0 mm from the graph plotted in (ii-3). (ii-5) Measure the friction coefficient at three different locations on the cloth adhesive tape using the procedure in (ii-1) to (ii-4), and round the average value to the fourth decimal place. (iii) Visually inspect the sample after measurement and grade the fluffiness according to the following criteria: ・Grade 1.0: The fibers are stripped off to the point that the test piece is damaged.・Grade 2.0: The fibers are severely stripped away, to the point where the test piece becomes thin. ・Grade 2.5: Large, clearly visible pilling is observed, and fibers are beginning to lift in multiple places. ・Grade 3.0: Clear pilling is beginning to form, or multiple small pills are visible. ・Grade 3.5: The material is slightly fuzzy, with small pilling beginning to form in one place. ・Grade 4.0: No fuzzyness. (iv) Turn the test piece over and grade the fuzzyness of the reverse side following the procedure in (ii) to (iii).(v) The grades for the front and back sides of the remaining four test pieces are determined using the same procedure as in (ii) to (iv). The average value of the 10 grade data points for both sides of each sample is calculated and rounded to two decimal places.

[0072] Furthermore, the fluffiness grade of spunbond nonwoven fabric can be increased to 3.0 or higher by adjusting the coil width of the crimped composite fibers and strengthening the adhesion between the fibers.

[0073] Furthermore, the spunbond nonwoven fabric of the present invention may be used in lamination with other sheet members. In this case, it is preferable that at least the surface layer be the spunbond nonwoven fabric, as this provides a good tactile feel and cushioning due to its bulkiness.

[0074] Other sheet materials include nonwoven fabric materials such as spunbond nonwoven fabrics and meltblown nonwoven fabrics, and film materials such as microporous films and stretchable films.

[0075] [Hygienic Material] Since the hygienic material of the present invention has the above-mentioned properties, it is preferable that at least a portion of it is composed of the spunbond nonwoven fabric. In particular, it is preferable that the spunbond nonwoven fabric is arranged in the part that comes into contact with the wearer's skin, and that the spunbond nonwoven fabric is included in the top sheet. By doing so, excellent cushioning can be felt, and the wearing comfort is excellent.

[0076] Specifically, the sanitary materials of the present invention are mainly disposable items used for health-related purposes such as medical care and nursing, and include disposable diapers, sanitary napkins, gauze, bandages, masks, gloves, adhesive bandages, etc., as well as their constituent components, such as the top sheet, back sheet, and side gathers of disposable diapers.

[0077] [Method for manufacturing spunbond nonwoven fabric] Next, a preferred embodiment of the method for manufacturing the spunbond nonwoven fabric according to the present invention will be specifically described. The method for manufacturing the spunbond nonwoven fabric according to the present invention is preferably as follows. That is, a polypropylene-based resin and a polyethylene-based resin are each melted and supplied to a composite spinning die, and after discharging a composite polymer stream from the discharge holes of the composite spinning die, air is blown onto the composite polymer stream to form composite fibers that are crimped fibers, a step of depositing the composite fibers on a belt to form a fiber web composed of the composite fibers, and a step of thermally bonding the fiber web with heated air. A method for manufacturing a spunbond nonwoven fabric having, in the step of forming the composite fibers, the composite fibers being side-by-side type composite fibers or eccentric core-sheath type composite fibers, the melt viscosity η ＰＰ (Pa·s) of the polypropylene-based resin and the melt viscosity η ＰＥ (Pa·s) of the polyethylene-based resin satisfy the following formula 3, the temperature of the air is 10°C or higher and 30°C or lower, the wind speed of the air is 1.0 m / s or higher and 5.0 m / s or lower, the spinning speed in the step of forming the composite fibers is 1000 m / min or higher and 3000 m / min or lower, in the step of thermally bonding, the temperature of the heated air is 100°C or higher and 160°C or lower, the wind speed of the heated air is 0.5 m / s or higher and 10.0 m / s or lower, and a method for manufacturing a spunbond nonwoven fabric that satisfies the following formulas 1 and 2.

[0078] 1.1 ≤ f ＰＰ / f ＰＥ ≤ 10.0... (Formula 1) 0.0 ≤ f ＰＥ ≤ 2.0... (Formula 2) 2.0 ≤ η ＰＰ / η ＰＥ ≤ 20.0... (Formula 3) Here, f ＰＰ is the molecular orientation degree (unitless) of the polypropylene-based resin in the composite fiber, and f ＰＥ is the molecular orientation degree (unitless) of the polyethylene-based resin in the composite fiber. Details thereof will be described below.

[0079] (a) Process for forming composite fibers In this process, a polypropylene resin and a polyethylene resin are melted and supplied to a composite spinneret, and after the composite polymer flow is discharged from the discharge hole of the composite spinneret, air is blown into the composite polymer flow to form a crimped composite fiber. In this process, (a-1) the composite fiber is a side-by-side type composite fiber or an eccentric core-sheath type composite fiber, and (a-2) the melt viscosity η of the polypropylene resin ＰＰ (Pa·s) and the melt viscosity η of the polyethylene resin ＰＥ (Pa·s) satisfies equation 3 below, and 2.0 ≤ η ＰＰ / η ＰＥ ≤20.0 ... (Equation 3) (a-3) The temperature of the air is set to 10°C or more and 30°C or less, and the wind speed of the air is set to 1.0 m / s or more and 5.0 m / s or less, (a-4) The spinning speed in this process is set to 1000 m / min or more and 3000 m / min or less. These will be explained in more detail below.

[0080] First, regarding (a-1), it is as explained above in the section on [composite fibers].

[0081] To form these composite fibers, the spinneret used in this process is preferably equipped with a mechanism capable of forming side-by-side composite fibers or eccentric core-sheath composite fibers. Here, the spinneret equipped with a mechanism capable of forming eccentric core-sheath composite fibers is preferably a spinneret capable of spinning eccentric core-sheath composite fibers having a thin sheath portion, as shown in International Publication No. 2020 / 095861. Furthermore, the shape of the discharge hole of the spinneret can be freely selected from circular holes, elliptical holes, rectangular holes, etc., as long as the effects of the present invention are not impaired. However, from the viewpoint of spinning stability, a circular hole is preferred, and a perfectly circular circular hole is more preferred.

[0082] Next, with respect to (a-2), in this process, the melt viscosity η of the polypropylene resin ＰＰ The melt viscosity η of the polyethylene resin (Pa·s) ＰＥ Ratio η to (Pa·s) ＰＰ / η ＰＥThe melt viscosity ratio (unitless; hereafter sometimes simply referred to as the melt viscosity ratio) is set to be between 2.0 and 20.0. By setting the lower limit of the melt viscosity ratio range to 2.0 or higher, preferably 2.5 or higher, and more preferably 3.0 or higher, the degree of molecular orientation of the polypropylene resin and polyethylene resin and the coil width of the composite fibers can be easily controlled. This makes it possible to make the fiber web less susceptible to compression in the process of heat-bonding the fiber web with heated air, as described later, and as a result, a spunbond nonwoven fabric with excellent cushioning properties can be easily obtained. On the other hand, by setting the upper limit of the melt viscosity ratio range to 20.00 or lower, preferably 10.00 or lower, and more preferably 6.00 or lower, the difference in flow velocity between the two thermoplastic resins in the spinneret can be kept within a certain range, and the phenomenon of the polymer flow bending sharply after extrusion is less likely to occur. As a result, the spunbond nonwoven fabric of the present invention can be stably obtained without yarn breakage.

[0083] The melt viscosity ratio referred to here is measured and calculated as follows: (i) Take 10 g each of the polypropylene resin and polyethylene resin, and heat them to the spinning temperature using a rheometer (for example, "Rheosol-G3000" manufactured by UBM Co., Ltd.) at a shear rate of 0.3 s. －１ The viscosity (Pa·s) when shear is applied is measured, and this is used to determine the melt viscosity η of the polypropylene resin. ＰＰ (Pa·s) and the melt viscosity η of polyethylene resins ＰＥ (Pa・s). (ii) η ＰＰ (Pa・s) to η ＰＥ Divide by (Pa·s) and round to two decimal places.

[0084] Furthermore, with respect to (a-3), in this process, the air temperature is set to 10°C or more and 30°C or less, and the wind speed is set to 1.0 m / s or more and 5.0 m / s or less. By keeping within this range, a spunbond nonwoven fabric can be obtained in which the fibers have a moderately fine crimp, resulting in a soft feel and cushioning properties.

[0085] First, the temperature of the air is set to 10°C or higher and 30°C or lower. By setting the air temperature to 10°C or higher, preferably 15°C or higher, or by setting the air temperature to 30°C or lower, preferably 25°C or lower, more preferably 20°C or lower, the cooling rate of the polypropylene resin or polyethylene resin can be appropriately controlled, and the degree of molecular orientation of the resin and the coil width of the composite fibers can be easily controlled. As a result, a spunbond nonwoven fabric can be obtained in which the fibers have a moderately fine crimp, a soft feel, and cushioning properties.

[0086] Furthermore, the wind speed is set to 1.0 m / s or more and 5.0 m / s or less. By setting the air wind speed to 1.0 m / s or more, preferably 2.0 m / s or more, or to 5.0 m / s or less, preferably 4.0 m / s or less, the cooling rate of the polypropylene resin or polyethylene resin can be appropriately controlled, and the degree of molecular orientation of the resin and the coil width of the composite fibers can be controlled. As a result, a spunbond nonwoven fabric can be obtained in which the fibers have a moderately fine crimp, a soft feel, and cushioning properties.

[0087] Furthermore, with respect to (a-4), in this process, the spinning speed in this process is set to 1,000 m / min or more and 3,000 m / min or less. By setting this spinning speed to 1,000 m / min or more, preferably 1,500 m / min or more, or to 3,000 m / min or less, preferably 2,500 m / min or less, the difference in molecular orientation and elastic recovery of the resin can be appropriately controlled, and the coil width of the composite fiber can be precisely controlled. As a result, a spunbond nonwoven fabric can be obtained in which the fibers have a moderately fine crimp, a soft feel, and cushioning properties.

[0088] In this process, it is preferable to use an air traction unit. An air traction unit, in this context, is a device that flows compressed air in at least one direction, accelerating and tractioning the polymer flow with that airflow. By using this air traction unit, the molecules constituting the resin can be oriented in a specific direction, thereby increasing the tensile strength of the fibers. As a result, a spunbond nonwoven fabric with high tensile and tear strength values, which is less prone to tearing during use, can be obtained.

[0089] Furthermore, in this process, the melt viscosity of the polyethylene resin is preferably 20 Pa·s or more and 700 Pa·s or less. By setting the melt viscosity to preferably 20 Pa·s or more, and more preferably 50 Pa·s or more, the degree of molecular orientation of the polyethylene resin in the composite fibers can be kept low, the amount of elastic recovery can be made more pronounced, and the coil width of the composite fibers can be precisely controlled, so that the fibers have a moderately dense crimp, and a spunbond nonwoven fabric with a soft feel and cushioning properties can be obtained. On the other hand, by setting the melt viscosity to preferably 700 Pa·s or less, and more preferably 600 Pa·s or less, the tension during the composite fiber formation process can be kept moderate, and the yarnability can be improved, so that a spunbond nonwoven fabric without defects and with a smooth feel can be obtained.

[0090] Furthermore, in this process, it is preferable that the discharge ratio of the polyethylene resin when the composite polymer flow is discharged from the discharge hole of the composite spinneret be 10% by mass or more and 90% by mass or less. More preferably, it is 40% by mass or more and 90% by mass or less. Since the polyethylene resin melts and adheres in the step of blowing heated air described later, sufficient adhesive strength can be obtained, and the rigidity of the fibers can be maintained when melted in the bonding step. As a result, a spunbond nonwoven fabric that is less likely to tear and less likely to fray can be obtained when used.

[0091] Furthermore, in the method for producing spunbond nonwoven fabric according to the present invention, the discharge amount per discharge hole of the die (single-hole discharge amount) is preferably changed arbitrarily according to the desired average single fiber diameter, taking into consideration the spinning speed.

[0092] (b) Step of forming a fiber web: In this step, the fibers are deposited on a belt to form a fiber web composed of the composite fibers.

[0093] In this process, the bulk density of the fiber web manufactured as described above is set to 0.010 g / cm³. ３ 0.050g / cm or more ３The following is preferable: By setting the bulk density of the fiber web within this range, the permeability of the heated air in the heat bonding process described later can be improved, and heat bonding can be applied uniformly in the thickness direction. As a result, both bulkiness and cushioning can be achieved, and the touch when the surface is run over by hand can also be improved. Specifically, the bulk density of this fiber web is preferably 0.010 g / cm³. ３ The above is more than 0.012 g / cm³. ３ By doing so, a spunbond nonwoven fabric with appropriate cushioning properties is obtained. On the other hand, the bulk density of the aforementioned fiber web is 0.050 g / cm³. ３ More preferably, 0.035 g / cm³ ３ By doing the following, a spunbond nonwoven fabric with a soft texture can be obtained.

[0094] In this invention, the bulk density of the fiber web is the value obtained by taking a sample of the fiber web collected on the belt before heat bonding, as described later, and measuring it using the same method as the measurement and calculation method for the bulk density of the spunbond nonwoven fabric described above.

[0095] Furthermore, although the fibers constituting the fiber web obtained in the previous step have a certain degree of crimp, in this step, after forming the fiber web, a crimping and densification process may be applied to the fiber web. The crimping and densification process referred to here is a process in which the fiber web collected on the belt is heated or stretched to change the shape of the fibers constituting the fiber web, and is a separate process from the heated air blowing process described later. Among these, it is preferable to apply a heat treatment that can uniformly change the fibers within the fiber web.

[0096] (c) Heat bonding process: In this process, the fiber web obtained in the previous process is heat-bonded with heated air. More specifically, the fiber web obtained in the previous process is heat-bonded by blowing heated air from above the fiber web toward the belt side.

[0097] In this process, the temperature of the heated air is set to be between 100°C and 160°C, and the wind speed is set to be between 0.5 m / s and 10.0 m / s. By satisfying these two conditions, a spunbond nonwoven fabric with excellent cushioning and strength can be easily obtained. Note that the air in this process includes water vapor. Furthermore, "wind speed" in this process refers to the speed of the wind moving vertically downward along the belt at a point 0.50 cm above the top surface of the fiber web on the belt.

[0098] First, it is preferable to set the temperature of the heated air to between 100°C and 160°C. By setting the temperature of the heated air to preferably 100°C or higher, and more preferably 110°C or higher, the polyethylene resin is appropriately melted, and a spunbond nonwoven fabric with excellent strength can be obtained. On the other hand, by setting the temperature of the heated air to preferably 160°C or lower, and more preferably 150°C or lower, the rigidity of the polypropylene resin is maintained, and a spunbond nonwoven fabric with excellent cushioning properties can be obtained.

[0099] Next, it is preferable to set the wind speed of the heated air to 0.5 m / s or more and 10.0 m / s or less. By setting the wind speed of the heated air to preferably 0.5 m / s or more, heat can be transferred to the entire fiber web, and the polyethylene resin can be appropriately melted, thereby obtaining a spunbond nonwoven fabric with excellent strength. On the other hand, by setting the wind speed of the heated air to preferably 10.0 m / s or less, more preferably 5.0 m / s or less, and even more preferably 2.0 m / s or less, heat bonding can be performed without excessively compressing the fiber web in the thickness direction, thereby obtaining a spunbond nonwoven fabric with excellent cushioning properties.

[0100] Furthermore, in this process, it is preferable to heat-bond the fiber web with heated air as described above, while simultaneously drawing this heated air downwards from the belt. By doing so, the heated air diffuses into the fiber web without crushing it, enabling uniform bonding in the thickness direction. As a result, a more uniform spunbond nonwoven fabric with superior cushioning properties can be obtained.

[0101] In this suction process, it is preferable that the wind velocity Va (m / sec) of the heated air and the wind velocity Vb (m / sec) of the suctioned air satisfy the following equation 4: 0.5 ≤ Vb ≤ Va ... (Equation 4) In this invention, the suctioned wind velocity refers to the velocity directed vertically downward along the belt, directly above the belt, and is the value measured at a position 0.50 cm above the top surface of the belt without blowing air from above the belt. By satisfying the above equation 4, heat is transferred to the entire fiber web, and the polyethylene resin is appropriately melted, thereby obtaining a spunbond nonwoven fabric with excellent strength.

[0102] Furthermore, as long as equation 4 is satisfied, the wind speed Va (m / sec) of the heated air and the wind speed Vb (m / sec) of the aspirated air preferably satisfy the following equation 5, more preferably the following equation 6, and even more preferably the following equation 7. 0.0 ≤ Va - Vb ≤ 3.0 ... (Equation 5) 0.0 ≤ Va - Vb ≤ 2.0 ... (Equation 6) 0.0 ≤ Va - Vb ≤ 1.0 ... (Equation 7) By having the above relationship between Va (m / sec) and Vb (m / sec), the difference between the wind speed of the heated gas and the aspirated air is controlled to the relevant range, thereby preventing excessive compression of the web and allowing the heated gas to be uniformly heat-treated without stagnation within the web, thus obtaining a spunbond nonwoven fabric with excellent cushioning and strength. Regarding equations 5 to 7, "as long as equation 4 is satisfied" means, for example, if Va is 2.0 m / s, then according to equation 4, Vb must be between 0.5 m / s and 2.0 m / s, and the difference between Va and Vb should be at most 1.5 m / s. Therefore, equation 5 inevitably becomes equation 5' below: 0.0 ≤ Va - Vb ≤ 1.5 ... (equation 5').

[0103] Furthermore, before or after this process, nip processing may be performed between a pair of opposing rolls to control the bulk density. The rolls used here may be flat rolls or rolls with an uneven surface, or a combination of these may be used. In particular, it is preferable to use one roll with an uneven surface (embossed roll) and the other roll as a flat roll. With such a configuration, the polyethylene resin can be appropriately melted and the composite fibers can be bonded together appropriately, resulting in a spunbond nonwoven fabric with excellent strength.

[0104] Furthermore, the pair of rolls may be heated. In this case, the nip between the rolls becomes the macro-fused portion mentioned above. When one roll is a roll with irregularities and the other is a flat roll, it is preferable that the area ratio of the protrusions on the roll with irregularities be between 1% and 30%. By making the area ratio of the protrusions on the roll 1% or more, the polyethylene resin is appropriately melted, and a spunbond nonwoven fabric with excellent strength can be obtained. On the other hand, by making the area ratio of the protrusions on the roll 30% or less, the rigidity of the polypropylene resin is maintained, and a spunbond nonwoven fabric with excellent cushioning can be obtained.

[0105] (d) Other finishing processes In the method for producing the spunbond nonwoven fabric of the present invention, it is also preferable to perform various finishing processes, similar to those for general spunbond nonwoven fabrics. Of course, in the present invention, the spunbond nonwoven fabric obtained by performing these finishing processes is also considered to be the spunbond nonwoven fabric of the present invention.

[0106] For example, when using the spunbond nonwoven fabric of the present invention as a top sheet for diapers, a hydrophilization treatment may be performed by applying a chemical such as "HydroThru PS-887" manufactured by Sanyo Chemical Industries, Ltd. This hydrophilization treatment can be appropriately selected from known methods such as the spray method, nip-dip method, or kiss-roll method.

[0107] In addition, the finishing process may include processes such as forming protrusions, printing patterns, cutting to create notches, and joining to connect with other components.

[0108] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples. In the case of spunbond nonwoven fabric, the machine direction in manufacturing is defined as the MD direction, and the direction perpendicular to the MD direction is defined as the CD direction.

[0109] [Measurement Method] Each characteristic value in the examples was determined by the following method. Unless otherwise specified, measurements were performed based on the method described above.

[0110] (1) Melt viscosity η of polypropylene resin ＰＰ (Pa·s), melt viscosity of polyethylene resin η ＰＥ (Pa·s), the ratio of these η ＰＰ / η ＰＥ (Unitless): The Rheosol-G3000, manufactured by UBM Co., Ltd., was used as the rheometer, and the measurements and calculations were performed according to the method described above.

[0111] (2) Bulk density of the fiber web (g / cm³) ３ ), bulk density of spunbond nonwoven fabric (g / cm³) ３ ): As a 3D microscope, for example, the "VR-3050" manufactured by Keyence Corporation was used to measure and calculate according to the method described above. The bulkiness of the spunbond nonwoven fabric was evaluated based on the measurement results as follows, from A (excellent bulkiness) to C (poor bulkiness). A: Bulk density is 0.010 g / cm³ ３ 0.030g / cm or more ３ Below, B: Bulk density is 0.030 g / cm³ ３ Larger, 0.050 g / cm ３ Below, C: Bulk density is 0.010 g / cm³. ３ Less than or equal to 0.050 g / cm³ ３ Larger.

[0112] (3) Degree of molecular orientation f of polypropylene resin ＰＰ (Unitless), degree of molecular orientation f of polyethylene resin ＰＥ (Unitless), their ratio f ＰＰ / f ＰＥ (Unitless): As a polarized Raman spectrometer, for example, the "LabRAM HR Evolution (HR-MT / ORS-Type III)" manufactured by Horiba, Ltd. was used for measurement and calculation according to the method described above.

[0113] (4) Presence or absence of crimping of composite fibers, coil width (μm): A scanning electron microscope, "VHX-6000" manufactured by Keyence Corporation, was used to determine, measure, or calculate these according to the method described above.

[0114] (5) Average single fiber diameter (μm): This was measured and calculated according to the method described above, using a Leica Microsystems "AUTOCUT R" as the microtome, a Keyence "VHX-X1" as the microscope, and WinROOF2015 from Mitani Corporation as the image analysis software.

[0115] (6) Basis weight of spunbond nonwoven fabric (g / m²) ２ ): Measured and calculated according to the method described above.

[0116] (7) Work done by compression (mN·cm / cm ２ ): A KES-G5 compression test machine manufactured by Kato Tech Co., Ltd. was used as the compression test device, and measurements and calculations were performed according to the method described above.

[0117] (8) Cushioning (grade): The cushioning was measured and calculated according to the following method. (i) 10 cm x 10 cm test pieces were randomly taken from the spunbond nonwoven fabric. (ii) Ten healthy adults pressed the test pieces with their fingers to compress them in the thickness direction and evaluated each spunbond nonwoven fabric according to the following criteria. The average score of the evaluation results for each nonwoven fabric was taken as the cushioning of that nonwoven fabric. 5: Easily crushed with fingers, and a slight rebound force is felt when pressed. 3: Easily crushed with fingers, and little rebound force is felt when pressed. 1: When crushed with fingers, it does not rebound at all and retains its crushed shape, or it is so hard that it cannot be crushed with fingers at all.

[0118] (9) Pile grade: The RT-200 dye friction fastness tester manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd. was used as the Japan Society for the Promotion of Science type fastness tester, Rinrei Tape Co., Ltd.'s Rinrei Cloth - Heavy Packaging No. 317 was used as the cloth adhesive tape, and Kato Tech Co., Ltd.'s KES-SE was used as the friction tester, and the grade was measured and calculated according to the method described above.

[0119] (10) Area ratio of macro-fused areas (%): The area ratio of macro-fused areas was measured and calculated according to the following method: (i) Five samples (100 × 100 mm) were randomly taken from the spunbond nonwoven fabric. (ii) Using a scanning electron microscope (VHX-6000) manufactured by Keyence Corporation, the area of ​​the repeating unit of the arrangement of macro-fused areas (S １ ) and the area of ​​the macro-fusion part included in the repeating unit (S ２ ) was measured at five locations, S ２ to S １ The average of the area ratios (%) obtained by dividing by was calculated. (iii) The same measurements and calculations were performed for the remaining four samples, and the average of the area ratios (%) for all 25 locations was obtained and rounded to the first decimal place.

[0120] [Resins Used] The resins used in the examples and comparative examples are as follows: ・iPP1: Isotactic polypropylene with a melting point of 160°C and a melt viscosity of 360 Pa·s at 230°C. ・iPP2: Isotactic polypropylene with a melting point of 160°C and a melt viscosity of 240 Pa·s at 230°C. ・iPP3: Isotactic polypropylene with a melting point of 160°C and a melt viscosity of 720 Pa·s at 230°C. ・Copolymerized PP1: Copolymerized polypropylene with a melting point of 145°C and a melt viscosity of 290 Pa·s at 230°C, copolymerized with 3% by mass of ethylene. ・PE1: Melting point of 127°C, solid density of 0.955 g / cm³. ３ Polyethylene with a melt viscosity of 80 Pa·s at 280°C. PE2: Melting point 127°C, solid density 0.955 g / cm³. ３ Polyethylene with a melt viscosity of 120 Pa·s at 280°C. PE3: Melting point 127°C, solid density 0.955 g / cm³. ３ Polyethylene with a melt viscosity of 360 Pa·s at 280°C. PE4: Melting point 127°C, solid density 0.955 g / cm³. ３ Polyethylene with a melt viscosity of 30 Pa·s at 280°C.

[0121] [Example 1] (a) Process for forming composite fibers iPP1 was used as the polypropylene resin and PE1 as the polyethylene resin. These were melted in separate extruders, and a rectangular spinning die that yields a side-by-side type composite cross section was used as the composite spinning die. The spinning temperature was set to 280°C, and a composite polymer flow was extruded from the composite spinning die with an extrusion rate of 0.65 g / min per hole and an extrusion mass ratio of thermoplastic resin A: thermoplastic resin B = 50:50.

[0122] Subsequently, while blowing 15°C air at a wind speed of 2.5 m / s onto the composite polymer flow, a rectangular ejector was used as an air traction unit to traction the composite polymer flow, thereby forming crimped composite fibers. At this time, the spinning speed was set to 2310 m / min.

[0123] (b) Forming a fiber web: Subsequently, the resulting composite fibers are deposited onto a moving collection belt, with a bulk density of 0.015 g / cm³. ３ It formed a fiber web.

[0124] (c) Heat bonding process The fiber web obtained in this way is heat-bonded by blowing air heated to 140°C at a wind speed of 1.5 m / s from above the fiber web toward the vertically downward side of the belt, while simultaneously drawing air toward the vertically downward side of the collection belt at a wind speed of 0.5 m / s, thereby achieving a basis weight of 30.0 g / m ２ A spunbond nonwoven fabric was obtained. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 1.

[0125] [Example 2] (a) In the process of forming composite fibers, the composite spinneret was changed to a rectangular spinneret that yields an eccentric core-sheath type composite cross section, polypropylene resin (iPP1) was used as the core component and polyethylene resin (PE1) as the sheath component, and the spinning speed was set to 2383 m / min. (b) In the process of forming the fiber web, the bulk density was 0.020 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 1.

[0126] [Example 3] (a) In the process of forming composite fibers, the polyethylene resin was changed to PE2 and the spinning speed was set to 2334 m / min, and (b) In the process of forming the fiber web, the bulk density was 0.025 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 1.

[0127] [Example 4] (a) In the process of forming composite fibers, the polypropylene resin was changed to iPP2 and the spinning speed was set to 2358 m / min, and (b) In the process of forming the fiber web, the bulk density was 0.021 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 1.

[0128] [Example 5] (a) In the process of forming composite fibers, the temperature of the air blown into the composite polymer stream was set to 25°C and the spinning speed to 2287 m / min. Furthermore, (b) In the process of forming the fiber web, the bulk density was set to 0.020 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 1.

[0129] [Example 6] (a) In the process of forming composite fibers, the temperature of the air blown into the composite polymer stream was set to 10°C and the spinning speed to 2334 m / min. Furthermore, (b) In the process of forming the fiber web, the bulk density was set to 0.019 / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 1.

[0130] [Example 7] (a) In the process of forming composite fibers, the air velocity blown into the composite polymer stream was set to 4.0 m / sec and the spinning speed to 2358 m / min. Furthermore, (b) In the process of forming the fiber web, the bulk density was set to 0.027 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 2.

[0131] [Example 8] (a) In the process of forming composite fibers, the wind speed of the air blown into the composite polymer stream was set to 1.5 m / sec and the spinning speed to 2334 m / min. Furthermore, (b) In the process of forming the fiber web, the bulk density was set to 0.029 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 2.

[0132] [Example 9] (b) In the process of forming a fiber web, the bulk density is 0.015 g / cm³. ３ After obtaining the fiber web, the obtained fiber web is further passed between a flat roll and an embossed roll (pattern specification: diamond pattern, compression area ratio 11%) with the roll surface temperature set to 80°C, and the fiber web is partially compressed with a linear pressure of 50 N / cm, resulting in a bulk density of 0.050 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had both micro-fused and macro-fused regions. The results are shown in Table 2.

[0133] [Example 10] (a) In the process of forming composite fibers, the polyethylene resin was changed to PE4, and (b) In the process of forming a fiber web, the bulk density was 0.031 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 1.

[0134]

[0135]

[0136] [Comparative Example 1] (a) In the process of forming composite fibers, the polyethylene resin was changed to copolymerized PP1, and the spinning speed was set to 2442 m / min. Furthermore, (b) In the process of forming the fiber web, the bulk density was 0.033 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 3.

[0137] [Comparative Example 2] (a) In the process of forming composite fibers, the composite spinneret was changed to a rectangular spinneret that yields concentric core-sheath type composite fibers, and the spinning speed was set to 2334 m / min. Furthermore, (b) In the process of forming the fiber web, the bulk density was 0.056 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 2, except that a fiber web was formed. In this case, the fibers in the fiber web did not have crimp. The obtained spunbond nonwoven fabric had micro-fused areas but no macro-fused areas. The results are shown in Table 3.

[0138] [Comparative Example 3] (a) In the process of forming composite fibers, the polyethylene resin was changed to PE3 and the spinning speed was set to 2287 m / min, and (b) in the process of forming the fiber web, the bulk density was set to 0.045 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 3.

[0139] [Comparative Example 4] (a) In the process of forming composite fibers, the wind speed of the air blown into the composite polymer stream was set to 6.0 m / sec and the spinning speed to 2358 m / min, and (b) in the process of forming the fiber web, the bulk density was set to 0.033 g / cm³. ３A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 3.

[0140] [Comparative Example 5] (a) In the process of forming composite fibers, the polypropylene resin was changed to iPP3 and the polyethylene resin to PE4, and the spinning speed was set to 2287 m / min. Furthermore, (b) In the process of forming the fiber web, the bulk density was set to 0.040 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 3.

[0141] [Comparative Example 6] (a) In the process of forming composite fibers, the temperature of the air blown into the composite polymer stream was set to 40°C, and (b) In the process of forming the fiber web, the bulk density was set to 0.040 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 1.

[0142] [Comparative Example 7] (a) In the process of forming composite fibers, the temperature of the air blown into the composite polymer stream was set to 5°C, and (b) In the process of forming the fiber web, the bulk density was set to 0.040 g / cm³. ３ A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a fiber web was formed. The obtained spunbond nonwoven fabric had micro-fused regions but no macro-fused regions. The results are shown in Table 1.

[0143]

[0144] As shown in Tables 1 and 2, the spunbond nonwoven fabrics of Examples 1 to 10 exhibited excellent cushioning and fluff resistance. In particular, Examples 1 and 2 achieved a high level of both cushioning and fluff resistance. In Examples 3 to 8 and 10, changes in the melt viscosity of the polypropylene resin and polyethylene resin, as well as changes in the temperature and wind speed of the air blown into the composite polymer stream during the fiber-obtaining process, altered the molecular orientation of the polypropylene resin and polyethylene resin, resulting in changes in bulk density and compression work. However, they still achieved a good balance of cushioning and fluff resistance. In Example 9, changes in bulkiness and compression work were observed due to the presence of macro-fused areas, but it still achieved a good balance of cushioning and fluff resistance.

[0145] On the other hand, as shown in Table 3, the spunbond nonwoven fabrics of Comparative Examples 1 to 7 were insufficient in at least one of the following: cushioning properties or fluffiness grade. In Comparative Example 1, the use of copolymerized PP1 as a substitute for polyethylene resin prevented the molecular orientation ratio of the composite fibers from being controlled within an appropriate range, resulting in a larger coil width and a higher bulk density of the resulting fiber web, which in turn resulted in poor cushioning properties. Furthermore, copolymerized PP1 was difficult to melt with heated air, resulting in poor adhesion and significantly inferior fluffiness grade. In Comparative Example 2, the composite fibers lacked crimp, resulting in insufficient cushioning properties. In Comparative Examples 3 to 4 and Comparative Examples 6 to 7, the inability to control the molecular orientation ratio of the composite fibers and the molecular orientation of the polyethylene resin within an appropriate range resulted in a larger coil width and a higher bulk density of the resulting web, which in turn resulted in poor cushioning properties. In Comparative Example 5, the melt viscosity ratio of the polypropylene resin and the polyethylene resin could not be controlled within an appropriate range, which resulted in an inability to control the molecular orientation ratio of the composite fibers within an appropriate range. This led to a smaller coil width and a lower proportion of fibers oriented in the thickness direction with a certain length or longer, resulting in inferior softness.

[0146] 1: Side-by-side composite fiber 11, 12: Resin part 2: Eccentric core sheath composite fiber 21, 22: Resin part 31: Crimped fiber 41A, 41B: Vertex 41C: Vertex of valley L: Straight line d: Distance

Claims

1. A spunbond nonwoven fabric composed of composite fibers made of a polypropylene resin and a polyethylene resin, wherein the composite fibers are side-by-side type composite fibers or eccentric core-sheath type composite fibers, the composite fibers are crimped fibers, and furthermore, the composite fibers satisfy the following formulas 1 and 2.

1. 1 ≤ f ＰＰ / f ＰＥ ≦10.0 ... (Formula 1) 0.0≦f ＰＥ ≤ 2.0 ... (Equation 2) where f ＰＰ f is the degree of molecular orientation (unitless) of the polypropylene resin in the composite fiber, ＰＥ This represents the degree of molecular orientation (unitless) of the polyethylene resin in the composite fiber.

2. The spunbond nonwoven fabric according to claim 1, wherein the coil width of the composite fiber is 400 μm or more and 1200 μm or less.

3. The bulk density of the spunbond nonwoven fabric is 0.010 g / cm³. ３ 0.050g / cm or more ３ The spunbond nonwoven fabric according to claim 1 or 2, which is as follows:

4. The basis weight of the spunbond nonwoven fabric is 10 g / m ２ or more and 50 g / m ２ or less. The spunbond nonwoven fabric according to claim 1 or 2.

5. The spunbond nonwoven fabric according to claim 1 or 2, wherein the average single fiber diameter of the composite fibers is 7.5 μm or more and 30.0 μm or less.

6. A sanitary material comprising at least a portion of the spunbond nonwoven fabric described in claim 1 or 2.

7. A sanitary material comprising a spunbond nonwoven fabric according to claim 1 or 2, provided in a portion that comes into contact with the wearer's skin.

8. A sanitary material comprising a top sheet containing the spunbond nonwoven fabric described in claim 1 or 2.

9. A method for producing a spunbond nonwoven fabric, comprising the steps of: melting a polypropylene resin and a polyethylene resin separately and supplying them to a composite spinneret, discharging a composite polymer flow from the discharge port of the composite spinneret, and then blowing air onto the composite polymer flow to form crimped composite fibers; depositing the composite fibers on a belt to form a fiber web composed of the composite fibers; and heat-bonding the fiber web with heated air, wherein in the step of forming the composite fibers, the composite fibers are side-by-side type composite fibers or eccentric core-sheath type composite fibers, and the melt viscosity of the polypropylene resin is η ＰＰ (Pa·s) and the melt viscosity η of the polyethylene resin ＰＥ A method for producing a spunbond nonwoven fabric, wherein (Pa·s) satisfies the following formula 3, the temperature of the air is 10°C or more and 30°C or less, the air velocity is 1.0 m / s or more and 5.0 m / s or less, the spinning speed in the composite fiber formation step is 1000 m / min or more and 3000 m / min or less, and in the heat bonding step, the temperature of the heated air is 100°C or more and 160°C or less, the air velocity of the heated air is 0.5 m / s or more and 10.0 m / s or less, and the following formulas 1 and 2 are satisfied. ＰＰ / f ＰＥ ≦10.0 ... (Formula 1) 0.0≦f ＰＥ ≦2.0 ... (Formula 2) 2.0≦η ＰＰ / η ＰＥ ≤ 20.0 ... (Equation 3) where f ＰＰ f is the degree of molecular orientation (unitless) of the polypropylene resin in the composite fiber, ＰＥ This represents the degree of molecular orientation (unitless) of the polyethylene resin in the composite fiber.

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