TWI888701B - Spunbond nonwoven fabrics and composite fibers - Google Patents

Abstract

The subject of the present invention is to provide a spunbond nonwoven fabric which has excellent softness and skin touch, uniform texture, sufficient strength to withstand practical use, and excellent productivity. The present invention is a spunbond nonwoven fabric, which is a spunbond nonwoven fabric composed of composite fibers with polyethylene resin as the main component, the spunbond nonwoven fabric having a welded portion and a non-welded portion, and the softening temperature Tss (℃) of the surface layer of the composite fibers in the non-welded portion and the softening temperature Tsc (℃) of the inner layer of the composite fibers in the non-welded portion satisfy the following formula (a). (Tss+5)≦Tsc≦(Tss+30)　　・・・(a)

Description

Spunbond nonwoven fabrics and composite fibers

The present invention relates to polyethylene spunbond nonwoven fabric and composite fiber.

Generally speaking, nonwoven fabrics used in sanitary materials such as diapers and sanitary napkins require skin-friendly feel, softness, and high productivity. In particular, the top sheet of diapers is one of the applications that has such high requirements because it is a material that directly contacts the skin.

As a means of improving skin touch and softness, the use of polyethylene having a lower elastic modulus and friction coefficient than polypropylene has been considered in the past. For example, there is a proposal for a polyethylene spunbond nonwoven fabric composed of a resin composition mixed with linear low-density polyethylene of different densities (see patent document 1).

In addition, there is also a proposal for a polyethylene spunbond nonwoven fabric, which is composed of polyethylene fibers having a density of 0.930 to 0.965 g/cm ³ and an average single fiber diameter of 8.0 to 16.5 μm, and has a complex viscosity of 90 Pa‧sec or less at a temperature of 230°C and 6.23 rad/sec (see Patent Document 2).

Indeed, these non-woven fabrics have high softness due to the properties of polyethylene resin.

[Prior Art Literature] [Patent Literature]

Patent document 1: Japanese Patent Publication No. 2008-274445

Patent document 2: Japanese Patent Publication No. 2019-26954

However, it has been a major issue in the past to give sufficient strength to spunbond nonwoven fabrics made of polyethylene resins. Even with the methods disclosed in Patent Document 1 or Patent Document 2, it is difficult to achieve strength that is practical.

Therefore, the object of the present invention is to provide a spunbond nonwoven fabric which has excellent softness and skin touch, uniform texture, sufficient strength to withstand practical use, and excellent productivity.

Furthermore, another object of the present invention is to provide a composite fiber that has excellent softness and skin touch, and has excellent spinning stability and thermal adhesion.

The spunbonded nonwoven fabric of the present invention is a spunbonded nonwoven fabric composed of composite fibers with polyethylene resin as the main component. The spunbonded nonwoven fabric has a welded portion and a non-welded portion. The softening temperature Tss (℃) of the surface layer of the composite fibers in the non-welded portion and the softening temperature Tsc (℃) of the inner layer of the composite fibers in the non-welded portion satisfy the following formula (a); (Tss+5)≦Tsc≦(Tss+30)‧‧‧(a).

According to a preferred embodiment of the spunbond nonwoven fabric of the present invention, the solid density of the polyethylene resin is greater than or equal to 0.935 g/cm ³ and less than or equal to 0.970 g/cm ³ .

According to the preferred embodiment of the spunbond nonwoven fabric of the present invention, the aforementioned spunbond nonwoven fabric has a single melting peak temperature Tm (℃) in the differential scanning calorimetry method, and Tm (℃) and Tss (℃) satisfy the following formulas (b) and (c); 100≦Tm≦150‧‧‧(b)

(Tm-40)≦Tss≦(Tm-10)‧‧‧(c).

According to the preferred embodiment of the spunbond nonwoven fabric of the present invention, the aforementioned composite fiber is a core-sheath type composite fiber.

According to a preferred embodiment of the spunbonded nonwoven fabric of the present invention, the tensile strength in the transverse direction per unit area weight of the spunbonded nonwoven fabric is greater than 0.20 (N/25mm)/(g/m ² ).

According to a preferred embodiment of the spunbonded nonwoven fabric of the present invention, the stress at 5% elongation in the longitudinal direction per unit area weight of the spunbonded nonwoven fabric is greater than 0.20 (N/25mm)/(g/m ² ).

Furthermore, the composite fiber of the present invention is a composite fiber with polyethylene resin as the main component, and the softening temperature Tss (℃) of the surface layer of the composite fiber and the softening temperature Tsc (℃) of the inner layer of the composite fiber satisfy the following formula (a); (Tss+5)≦Tsc≦(Tss+30)‧‧‧(a).

According to a preferred embodiment of the composite fiber of the present invention, the solid density of the polyethylene resin is not less than 0.935 g/cm ³ and not more than 0.970 g/cm ³ .

According to the preferred embodiment of the composite fiber of the present invention, the composite fiber has a single melting peak temperature Tm (℃) in differential scanning calorimetry, and Tm (℃) and Tss (℃) satisfy the following formulas (b) and (c); 100≦Tm≦150‧‧‧(b)

(Tm-40)≦Tss≦(Tm-10)‧‧‧(c).

According to a preferred embodiment of the composite fiber of the present invention, the composite fiber is a core-sheath type composite fiber.

According to the present invention, a polyethylene spunbond nonwoven fabric can be obtained, which has excellent softness and skin touch, uniform texture, sufficient strength to withstand practical use, and excellent productivity. Based on these characteristics, the spunbond nonwoven fabric of the present invention is particularly suitable for use as a sanitary material.

Furthermore, according to the present invention, a composite fiber can be obtained, which has excellent softness and skin touch, and has excellent yarn stability and thermal adhesion. The spunbonded nonwoven fabric made of the composite fiber of the present invention has the above-mentioned excellent characteristics.

[Form used to implement the invention]

The spunbonded nonwoven fabric of the present invention is a spunbonded nonwoven fabric composed of composite fibers with polyethylene resin as the main component. The spunbonded nonwoven fabric has a welded portion and a non-welded portion. The softening temperature Tss (℃) of the surface layer of the composite fibers in the non-welded portion and the softening temperature Tsc (℃) of the inner layer of the composite fibers in the non-welded portion satisfy the following formula (a); (Tss+5)≦Tsc≦(Tss+30)‧‧‧(a).

By doing so, a polyethylene spunbond nonwoven fabric can be formed which has excellent softness and skin touch, uniform texture, sufficient strength to withstand practical use, and excellent productivity.

Furthermore, the composite fiber of the present invention is a composite fiber with polyethylene resin as the main component, and the softening temperature Tss (℃) of the surface layer of the composite fiber and the softening temperature Tsc (℃) of the inner layer of the composite fiber satisfy the following formula (a); (Tss+5)≦Tsc≦(Tss+30)‧‧‧(a).

By doing so, a composite fiber can be obtained, which has excellent softness and skin touch, and has excellent yarn stability and thermal adhesion. The spunbond nonwoven fabric made of the composite fiber of the present invention can be a polyethylene spunbond nonwoven fabric that has excellent softness and skin touch, uniform texture, sufficient strength to withstand practical use, and excellent productivity.

The constituent elements of the present invention are described in detail below. However, the present invention is not limited to the scope of the following description as long as it does not exceed its gist.

[Polyethylene resin]

The composite fiber of the present invention and the composite fiber constituting the spunbonded nonwoven fabric of the present invention (hereinafter, these may be collectively referred to as "the composite fiber of the present invention") are made of polyethylene resin as the main component. By using polyethylene resin as the main component, a composite fiber having both excellent yarn stability and thermal adhesion can be obtained. In addition, a spunbonded nonwoven fabric having excellent softness and skin touch can be obtained.

The so-called polyethylene resin refers to a resin having ethylene units as repeating units, and examples thereof include ethylene homopolymers or copolymers of ethylene and various α-olefins. Among them, in order to prevent the reduction of the stability and strength of the spinning, ethylene homopolymers are preferred.

When using copolymers of ethylene and various α-olefins, heptene or octene is preferred as the copolymer component, and octene is more preferred in terms of excellent spinning stability. In addition, in order to prevent the reduction of spinning stability and strength, the copolymerization ratio is preferably less than 5 mol%, more preferably less than 3 mol%, and particularly preferably less than 1 mol%.

Regarding the polyethylene resin used in the present invention, the proportion of ethylene homopolymer is preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. By doing so, good spinnability can be maintained and strength can be improved.

As the polyethylene resin used in the present invention, medium-density polyethylene, high-density polyethylene (hereinafter sometimes referred to as HDPE) or linear low-density polyethylene (hereinafter sometimes referred to as LLDPE) can be cited. From the perspective of excellent spinnability, LLDPE is preferably used.

Furthermore, the polyethylene resin used in the present invention may be a mixture of two or more kinds, and resin compositions containing other polyolefin resins such as polypropylene, poly-4-methyl-1-pentene, thermoplastic elastomers, low-melting polyesters, and low-melting polyamides may also be used. However, in order to fully demonstrate the characteristics of polyethylene, the ratio of other thermoplastic resins mixed is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

In the polyethylene resin used in the present invention, in order to improve the skin touch and softness, it is preferred to contain a fatty acid amide compound with a carbon number of 23 or more and 50 or less.

By setting the carbon number of the aforementioned fatty acid amide compound preferably to 23 or more, more preferably to 30 or more, the fatty acid amide compound can be prevented from being excessively exposed on the fiber surface, and the spinning property and processing stability are excellent, and high productivity is maintained. On the other hand, by setting the carbon number of the aforementioned fatty acid amide compound preferably to 50 or less, more preferably to 42 or less, the fatty acid amide compound becomes easy to move to the fiber surface, and the slipperiness and softness can be imparted to the spunbond nonwoven fabric.

As the fatty acid amide compound with a carbon number of 23 or more and 50 or less used in the present invention, there can be cited saturated fatty acid monoamide compounds, saturated fatty acid diamide compounds, unsaturated fatty acid monoamide compounds and unsaturated fatty acid diamide compounds, etc.

More specifically, the following can be cited: tetracosylamide, hexacosylamide, octacosylamide, tetracosenoylamide, tetracospentaenoylamide, tetracosahexenoylamide, ethyldilaurate, methylenedilaurate, ethyldistearamide, ethyldihydroxystearate, ethyldi Behenic acid amide, hexamethylenebisstearamide, hexamethylenebisbehenic acid amide, hexamethylenehydroxystearic acid amide, distearyl adipamide, distearyl sebacic acid amide, ethyl dioleic acid amide, ethyl dierucic acid amide and hexamethylene dioleic acid amide, etc. These can also be used in combination of multiple types.

In the present invention, among the fatty acid amide compounds, ethyl distearate amide, which is a saturated fatty acid diamide compound, is particularly preferred because it can impart high slip and softness, and has excellent spinnability.

In the present invention, for the aforementioned polyethylene resin, the addition amount of the aforementioned fatty acid amide compound is preferably 0.01 mass%~5 mass%. By setting the addition amount of the fatty acid amide compound preferably to 0.01 mass%~5 mass%, more preferably to 0.1 mass%~3 mass%, and most preferably to 0.1 mass%~1 mass%, it is possible to impart appropriate slip and softness while maintaining spinnability.

The amount of addition mentioned here refers to the mass fraction of the fatty acid amide compound in the entire polyethylene resin constituting the spunbonded nonwoven fabric of the present invention. For example, even when the fatty acid amide compound is added only to the sheath component constituting the core-sheath type composite fiber, the addition ratio relative to the total amount of the core-sheath component is calculated.

As a method for determining the amount of fatty acid amide compound added to fibers made of polyethylene resin, for example, there can be cited a method of extracting the additive from the aforementioned fibers with a solvent and performing quantitative analysis using liquid chromatography mass spectrometry (LC/MS). At this time, the extraction solvent is appropriately selected according to the type of fatty acid amide compound. For example, in the case of ethylenediamine, a method using a chloroform-methanol mixed solution can be cited as an example.

In the polyethylene resin used in the present invention, within the scope that does not damage the effect of the present invention, commonly used antioxidants, weathering stabilizers, light-resistant stabilizers, heat-resistant stabilizers, antistatic agents, charging aids, antifogging agents, anti-adhesion agents, lubricants including polyethylene wax, crystallization nucleating agents and pigments, etc., or other polymers can be added as needed.

The melting point Tmr of the polyethylene resin used in the present invention is preferably 100°C to 150°C. By setting the melting point Tmr preferably to 100°C or more, more preferably to 110°C or more, and particularly preferably to 120°C or more, it is easy to obtain heat resistance that can withstand practical use. In addition, by setting Tmr preferably to 150°C or less, more preferably to 140°C or less, and particularly preferably to 135°C or less, it becomes easy to cool the yarn spit out from the nozzle, suppress the fusion of the fibers, and even a thin fiber diameter can be spun stably. The melting point Tmr here refers to the maximum melting peak temperature obtained by measuring the resin by differential scanning calorimetry (DSC).

The melt flow rate (hereinafter sometimes referred to as MFR) of the polyethylene resin used in the present invention is preferably 1 g/10 minutes to 300 g/10 minutes. By setting the MFR of the polyethylene resin preferably to 1 g/10 minutes or more, more preferably to 10 g/10 minutes or more, and particularly preferably to 30 g/10 minutes or more, even fine fibers can be spun stably, and a spunbond nonwoven fabric having excellent skin touch, uniform texture, and sufficient strength to withstand practical use can be obtained. On the other hand, by setting the MFR of the polyethylene resin preferably below 300g/10min, the decrease in the strength of the single yarn can be suppressed, and at the same time, excessive softening during heat bonding can be prevented, which can cause operational problems such as adhesion to the heat roller, etc.

When the composite fiber of the present invention is a core-sheath composite fiber, the MFR of the polyethylene resin of the core component is preferably 1 g/10 minutes to 100 g/10 minutes. Since the MFR of the polyethylene resin of the core component is preferably 1 g/10 minutes or more, more preferably 10 g/10 minutes or more, and particularly preferably 30 g/10 minutes or more, even a thin fiber diameter can be stably spun, and a spunbond nonwoven fabric with excellent skin touch, uniform texture, and sufficient strength to withstand practical use can be obtained. On the other hand, by making the MFR of the polyethylene resin preferably 100 g/10 min or less, more preferably 80 g/10 min or less, and even more preferably 60 g/10 min or less, the decrease in the single yarn strength of the composite fiber can be suppressed, and a spunbond nonwoven fabric having sufficient strength to withstand practical use can be obtained.

When the composite fiber of the present invention is a core-sheath composite fiber, the MFR of the polyethylene resin of the sheath component is preferably 5 g/10 minutes to 200 g/10 minutes greater than the MFR of the polyethylene resin of the core component. By making the MFR of the polyethylene resin of the sheath component preferably 5 g/10 minutes greater than the MFR of the polyethylene resin of the core component, more preferably 10 g/10 minutes greater, and even more preferably 20 g/10 minutes greater, the spinning stress can be concentrated on the core component during spinning, thereby promoting the molecular orientation of the core component and inhibiting the molecular orientation of the sheath component. On the other hand, if the MFR of the polyethylene resin of the sheath component is greater than the MFR of the polyethylene resin of the core component by more than 200g/10min, the single yarn strength of the core-sheath type composite fiber will decrease, and it will be easily over-softened during heat bonding, causing problems in operation such as attachment to hot rollers, which is not suitable.

The MFR of polyethylene resin is the value measured by ASTM D1238 (Method A). According to this specification, polyethylene is measured at a load of 2.16 kg and a temperature of 190°C. The polyethylene resin of the present invention is also measured at the same load and temperature.

Of course, the MFR of the polyethylene resin used in the present invention can be adjusted by blending two or more resins with different MFRs in an arbitrary ratio. In this case, the MFR of the resin blended with the polyethylene resin that accounts for the largest mass fraction of the main polyethylene resin, i.e., the polyethylene resin, is preferably 10 to 1000 g/10 minutes, more preferably 20 to 800 g/10 minutes, and particularly preferably 30 to 600 g/10 minutes. By doing so, it is possible to prevent the viscosity from being partially uneven in the blended polyethylene resin, make the single fiber diameter and single fiber density uniform, or even fine fibers can be stably spun.

Furthermore, in the polyethylene resin used in the present invention, it is preferred not to add any agent that decomposes the polyethylene resin and reduces the MFR, such as peroxides, especially free radicals such as dialkyl peroxides. By doing so, it is possible to prevent the occurrence of partial viscosity unevenness caused by uneven decomposition or gelation, making the single fiber uniform, or even fine fibers can be spun stably. In addition, it is possible to prevent the deterioration of spinnability due to bubbles generated by decomposed gas.

The solid density of the polyethylene resin used in the present invention is preferably 0.935 g/cm ³ to 0.970 g/cm ^3. By setting the solid density of the polyethylene resin preferably to 0.935 g/cm ³ or more, more preferably to 0.940 g/cm ³ or more, and particularly preferably to 0.945 g/cm ³ or more, it is possible to prevent the problem of excessive softening during heat bonding and adhesion to the heat roller. In addition, by setting the solid density of the polyethylene resin preferably to 0.970 g/cm ³ or less, more preferably to 0.965 g/cm ³ or less, and particularly preferably to 0.960 g/cm ³ or less, the spinnability can be improved, and even thin fibers can be spun stably.

[Compound fiber]

As the composite form of the composite fiber of the present invention, for example, a concentric core-sheath type, an eccentric core-sheath type, and an island type composite form can be used. Among them, from the perspective of excellent spinnability and the ability to evenly connect the fibers to each other by heat welding, a core-sheath type composite form is preferred, and a concentric core-sheath type composite form is more preferred.

When the composite fiber of the present invention is a sea-island type composite fiber, when measuring and explaining the characteristic values, the "sheath component" is renamed as "sea component" and the "core component" is renamed as "island component" before performing the measurement, etc.

The mass ratio of the sheath component of the composite fiber of the present invention is preferably 20 mass% to 80 mass%. By making the mass ratio of the sheath component preferably 20 mass% or more, more preferably 30 mass% or more, and particularly preferably 40 mass% or more, the sheath components can be firmly fused to each other during heat bonding, and a spunbonded nonwoven fabric with sufficient strength to withstand practical use can be obtained. On the other hand, by making the mass ratio of the sheath component preferably 80 mass% or less, more preferably 70 mass% or less, and particularly preferably 60 mass% or less, the proportion of the core component with high orientation can be increased, so that the single yarn strength of the composite fiber is improved, and a spunbonded nonwoven fabric with sufficient strength to withstand practical use can be obtained.

In the composite fiber of the present invention and the composite fiber of the non-welded portion of the spunbonded nonwoven fabric of the present invention, the softening temperature Tss (℃) of the surface layer and the softening temperature Tsc (℃) of the inner layer satisfy the following formula (a).

(Tss+5)≦Tsc≦(Tss+30)‧‧‧(a).

By setting Tsc(℃) to (Tss+5)℃ or more, preferably (Tss+7)℃ or more, and more preferably (Tss+10)℃ or more, only the components forming the fiber surface layer can be softened during heat bonding. In addition, by doing so, the fibers can be firmly heat-bonded to each other while the molecular orientation of the fiber inner layer remains, thereby achieving a spunbond nonwoven fabric with strength that can withstand practical use. On the other hand, by setting the softening temperature Tsc (℃) of the inner layer of the composite fiber to below (Tss+30)℃, preferably below (Tss+25)℃, and more preferably below (Tss+20)℃, it is possible to prevent the fiber surface from being excessively softened during heat bonding, thereby preventing problems in operation such as adhesion to a heat roller, etc.

Tsc (℃) is calculated by the following procedure based on nanoscale-Thermomechanical Analysis (nano-TMA). The nano-TMA is a device that can perform thermal analysis in the sub-micrometer range and uses a temperature sensor with a heater installed on the probe (cantilever) of an atomic force microscope (AFM).

In the spunbonded nonwoven fabric of the present invention, the Tss (℃) and Tsc (℃) of the non-welded portion are measured and calculated according to the following procedure after collecting 20 composite fibers from the non-welded portion of the spunbonded nonwoven fabric.

(1) Fix the composite fiber on the sample table and fix the AFM probe with a heater and temperature sensor near the center of the fiber diameter.

(2) Raise the temperature of the probe from 25°C to 150°C at a rate of 10°C/s, and measure the change in probe height (a.u.).

(3) The temperature (softening temperature (°C)) at which the probe is inserted into the sample is measured from the change in the probe height, and the order of observations from the lowest temperature is set as Ts1, Ts2, Ts3...

(4) Perform the same measurement on 20 fibers, round off the average value of Ts1 to the second decimal place and use it as Tss (℃). Also, round off the average value of Ts2 to the second decimal place and use it as Tsc (℃). In addition, sometimes Ts2 is not observed in a part of the composite fiber due to the contact position of the AFM probe. In this case, only the observed Ts2 is averaged to obtain the softening temperature Tsc (℃) of the inner layer.

Tss and Tsc can be controlled by the MFR, melting point, additives, mass ratio of components constituting the composite fiber (for core-sheath composite fibers, the mass ratio of the sheath component) of the aforementioned polyethylene resin and/or the spinning temperature and spinning speed described later.

As the cross-sectional shape of the composite fiber of the present invention, a circular cross-section, a flat cross-section, and an irregular cross-section such as a Y-shaped or C-shaped cross-section can be used. Among them, a circular cross-section is a better state because it does not have the bending difficulty caused by the flat cross-section or the irregular cross-section structure, and can become a spunbond nonwoven fabric that utilizes the softness of polyethylene resin. In addition, although a hollow cross-section can also be applied as a cross-sectional shape, a solid cross-section is a better state because it has excellent spinnability and can be spun stably even with a thin fiber diameter.

The composite fiber of the present invention preferably has an average single fiber fineness of 0.5 dtex to 3.0 dtex. By setting the average single fiber fineness preferably to 0.5 dtex or more, more preferably to 0.6 dtex or more, and particularly preferably to 0.7 dtex or more, it is possible to prevent the reduction of spinnability and produce a spunbond nonwoven fabric with excellent production stability. On the other hand, by setting the average single fiber fineness preferably to 3.0 dtex or less, more preferably to 2.4 dtex or less, and particularly preferably to 2.0 dtex or less, it is possible to produce a spunbond nonwoven fabric with excellent skin touch, uniform texture, and sufficient strength to withstand practical use.

The average single fiber fineness can be controlled by the spinning temperature, single hole discharge amount, spinning speed, etc. described below.

The composite fiber of the present invention preferably has an average single fiber diameter of 8 to 20 μm. By setting the average single fiber diameter preferably to 8 μm or more, more preferably to 9 μm or more, and particularly preferably to 10 μm or more, the reduction of spinnability can be prevented, and a spunbond nonwoven fabric with excellent production stability can be obtained. On the other hand, by setting the average single fiber diameter preferably to 20 μm or less, more preferably to 18 μm or less, and particularly preferably to 16 μm or less, a spunbond nonwoven fabric with excellent skin touch, uniform texture, and sufficient strength to withstand practical use can be obtained.

Furthermore, in the present invention, the average single fiber diameter (μm) of the composite fiber is a value calculated by the following procedure.

(1) For composite fibers, take surface photos at 500-2000 times magnification using a microscope or scanning electron microscope, and measure the width (diameter) of 100 different composite fibers in total. When the cross-section of the composite fiber is irregular, measure the cross-sectional area and find the diameter of a perfect circle with the same cross-sectional area.

(2) The average of the 100 measured diameters is rounded off to the second decimal place and is taken as the average single fiber diameter (μm).

In addition, the average single fiber diameter (μm) of the composite fiber constituting the aforementioned spunbonded nonwoven fabric is the value calculated by the following procedure.

(1) Randomly collect 10 small samples (100×100 mm) from spunbond nonwoven fabric.

(2) Take surface photos at 500-2000 times magnification using a microscope or scanning electron microscope, and measure the width (diameter) of 10 non-welded composite fibers from each sample and a total of 100 fibers. When the cross-section of the composite fiber is irregular, measure the cross-sectional area and find the diameter of a perfect circle with the same cross-sectional area.

(3) The average value of the 100 measured diameters is rounded off to the second decimal place and regarded as the average single fiber diameter (μm).

The average single fiber diameter can be controlled by the spinning temperature, single hole discharge, spinning speed, etc. described below.

The composite fiber and the spunbond nonwoven fabric of the present invention preferably have a single melting peak temperature Tm in differential scanning calorimetry (DSC). In the present invention, the phrase "the composite fiber has a single melting peak temperature Tm in differential scanning calorimetry" and "the spunbond nonwoven fabric has a single melting peak temperature Tm in differential scanning calorimetry" means that only one peak of the melting endothermic peak described in (3) of the following measurement method is substantially observed. By doing so, when the composite fiber of the present invention is used as a fiber constituting a spunbonded nonwoven fabric, for example, there will be no operational problems such as low-melting-point components melting and adhering to a heat roller during heat bonding in the spunbonded nonwoven fabric of the present invention, and the fibers can be firmly heat-bonded to each other at a sufficient temperature, so that a spunbonded nonwoven fabric having a strength that can withstand practical use can be easily obtained.

The melting peak temperature Tm of the composite fiber or spunbond nonwoven fabric obtained by differential scanning calorimetry (DSC) is the value calculated by the following procedure.

(1) Take a sample of 0.5~5mg of composite fiber or spunbond nonwoven fiber sheet.

(2) Using differential scanning calorimetry (DSC), the temperature was raised from room temperature to 200°C at a heating rate of 20°C/min to obtain the DSC curve.

(3) Read the peak temperature of the melting endothermic peak from the DSC curve and take it as the melting peak temperature Tm (℃).

Furthermore, when the composite fiber of the present invention is used as the fiber constituting the spunbonded nonwoven fabric of the present invention, the Tm of the composite fiber and the Tm of the spunbonded nonwoven fabric are considered to show the same value.

Furthermore, the composite fiber and the spunbonded nonwoven fabric of the present invention preferably satisfy the following formulas (b) and (c).

100≦Tm≦150‧‧‧(b)

(Tm-40)≦Tss≦(Tm-10)‧‧‧(c)

By doing so, composite fibers and spunbond nonwoven fabrics can be obtained that have heat resistance and strength sufficient for practical use, and excellent spinning stability and handling stability.

First, regarding formula (b), the melting peak temperature Tm (℃) of the composite fiber measured by differential scanning calorimetry (DSC) is preferably 100℃ or more and 150℃ or less. By making the melting peak temperature Tm (℃) preferably 100℃ or more, more preferably 110℃ or more, and particularly preferably 120℃ or more, heat resistance that can withstand practical use can be imparted. Furthermore, by making the melting peak temperature Tm (℃) preferably 150℃ or less, more preferably 140℃ or less, and particularly preferably 135℃ or less, it becomes easy to cool the yarn spitted out from the nozzle, suppressing the fusion of the fibers, and making it easy to spin even a thin fiber diameter stably.

Secondly, regarding formula (c), the softening temperature Tss (℃) of the surface layer of the composite fiber is preferably (Tm-40)℃ or higher and (Tm-10)℃ or lower. By making Tss (℃) preferably (Tm-40)℃ or higher, more preferably (Tm-35)℃ or higher, and particularly preferably (Tm-30)℃ or higher, it is possible to prevent the fiber surface layer from being excessively softened during heat bonding, thereby preventing problems in operation such as adhesion to a heat roller, etc. On the other hand, by making Tss (℃) preferably (Tm-10)℃ or lower, more preferably (Tm-15)℃ or lower, and particularly preferably (Tm-20)℃ or lower, the fibers can be firmly heat-bonded to each other during heat bonding, and a spunbonded nonwoven fabric having strength that can withstand practical use can be obtained.

Furthermore, the composite fiber of the present invention melts after the composite fiber is softened, so the softening temperature Tsc (°C) of the inner layer is less than the melting peak temperature Tm (°C) measured by differential scanning calorimetry (DSC). Moreover, the softening temperature Tsc (°C) of the inner layer of the composite fiber is preferably above (Tm-20)°C and below (Tm-1)°C. By making the softening temperature Tsc (°C) of the inner layer preferably above (Tm-20)°C, more preferably above (Tm-15)°C, and particularly preferably above (Tm-10)°C, the strength of the inner layer of the fiber can be improved, and a spunbond nonwoven fabric having a strength that can withstand practical use after heat bonding can be obtained. On the other hand, by setting Tsc (℃) preferably below (Tm-1)℃, more preferably below (Tm-3)℃, and even more preferably below (Tm-5)℃, the fibers can be firmly bonded to each other during thermal bonding, and a spunbond nonwoven fabric with strength that can withstand practical use can be obtained.

The composite fiber of the present invention and the composite fiber of the non-welded part of the spunbonded nonwoven fabric of the present invention have an orientation parameter Ofs of the sheath component, and Ofs is preferably smaller than the orientation parameter Ofc of the core component. By doing so, the molecular orientation of the inner layer of the fiber can be left during heat bonding, while only the surface layer of the fiber is softened so that the fibers can be firmly heat-bonded to each other, thereby achieving a spunbonded nonwoven fabric with strength that can withstand practical use.

Here, the so-called alignment parameter in the present invention is the following index (without unit): the larger the value, the more the molecular chain is aligned in a specific direction, and the smaller the value, the more randomly the molecular chain is aligned. Moreover, the alignment parameter becomes 1.2 when the alignment is completely random.

Moreover, in the present invention, the so-called "having an orientation parameter" means that the orientation parameter measured by the following method is greater than 1.2.

(1) Use bisphenol-based epoxy resin to embed the composite fiber or spunbond nonwoven fabric sample.

(2) After the resin hardens, slices are cut with a microtome, and the slice thickness is set to 2μm. At this time, the slice is cut obliquely from the fiber axis in such a way that the cut surface becomes an ellipse. Afterwards, the thickness of the short axis of the ellipse is selected to represent a certain thickness and measured. Moreover, since the cutting angle is set within 4°, it can be regarded as parallel to the fiber axis within the film thickness of 2μm.

When the sample is spunbond nonwoven fabric,

(2) After the resin has hardened, slices are cut using a microtome so that the center of the non-welded portion of the spunbond nonwoven fabric (the portion approximately equidistant from the surrounding welded portions) becomes the cross section. The slice thickness is set to 2μm. Select the composite fibers of the non-welded portion and the portion where the cutting angle is within 4° from the fiber axis for subsequent measurements.

(3) In a composite fiber slice, from the fiber surface to the center, polarized light parallel to the fiber axis is incident, and Raman spectrum line measurement is performed.

(4) Calculate the Raman band intensities _I1130 and _I1060 at the positions of the core component and the sheath component respectively, near 1130 cm ^-1 and 1060 cm ^-1 , and calculate the alignment parameter from the intensity ratio according to the following formula (d). When the core component is divided into multiple independent regions, measure the alignment parameter in all regions and adopt the highest value.

Orientation parameter = I ₁₁₃₀ /I ₁₀₆₀ ‧‧‧(d).

(5) In the axial direction of the composite fiber, change the position and perform the same measurement at 3 locations, calculate the average value of the orientation parameter, and round off the second decimal place.

When the sample is spunbond nonwoven fabric,

(5) For different non-welded parts of the spunbond nonwoven fabric, perform the same measurement at 3 locations, calculate the average value of the orientation parameter, and round off the second decimal place.

The composite fiber of the present invention and the composite fiber of the non-welded part of the spunbonded nonwoven fabric of the present invention preferably have an orientation parameter Ofs of the sheath component of 2 to 8. By preferably having Ofs of 2.0 or more, more preferably having Ofs of 2.5 or more, and particularly preferably having Ofs of 3.0 or more, it is possible to prevent the fiber surface from being excessively softened during heat bonding, thereby preventing problems in operation such as adhesion to a heat roller. On the other hand, by preferably having Ofs of 8.0 or less, more preferably having Ofs of 7.0 or less, and particularly preferably having Ofs of 6.0 or less, the fiber surface becomes easily softened during heat bonding, and the fibers can be firmly heat bonded to each other, thereby providing a spunbonded nonwoven fabric having strength that can withstand practical use.

Ofs can be controlled by the MFR, melting point, additives of the aforementioned polyethylene resin, the mass ratio of the sheath component of the composite fiber and/or the spinning temperature and spinning speed described later.

The composite fiber of the present invention and the composite fiber of the non-welded part of the spunbonded nonwoven fabric of the present invention preferably have an orientation parameter Ofc of the core component of 6 to 18. By having Ofc preferably being 6.0 or more, more preferably being 7.0 or more, and particularly preferably being 8.0 or more, the strength of the inner layer of the fiber can be improved, and a spunbonded nonwoven fabric with strength that can withstand practical use after thermal bonding can be obtained. In addition, the problem of excessive softening of the fiber surface during thermal bonding and the occurrence of operational problems such as adhesion to a heat roller can be prevented. On the other hand, by having Ofc preferably being 18.0 or less, more preferably being 16.0 or less, and particularly preferably being 14.0 or less, excessive extension stress concentration on the inner layer of the fiber during spinning can be suppressed, and spinning stability can be improved.

Ofc can be controlled by the MFR, melting point, additives of the aforementioned polyethylene resin, the mass ratio of the core component of the composite fiber and/or the spinning temperature and spinning speed described later.

The composite fiber of the present invention and the composite fiber of the non-welded portion of the spunbonded nonwoven fabric of the present invention preferably has a ratio of the orientation parameter Ofs of the sheath component to the orientation parameter Ofc of the core component, Ofs/Ofc, of 0.10 to 0.90. By having Ofs/Ofc preferably being 0.10 or more, more preferably 0.15 or more, and particularly preferably 0.20 or more, it is possible to prevent the tensile stress from being excessively concentrated on the inner layer of the fiber where the core component exists during spinning, thereby reducing the spinning stability. On the other hand, by having Ofs/Ofc preferably being 0.90 or less, more preferably 0.70 or less, and particularly preferably 0.50 or less, it is possible to soften only the surface layer of the fiber during heat bonding. By doing so, the molecular orientation of the inner layer of the fiber can be retained while the fibers can be firmly thermally bonded to each other. Moreover, as the spunbonded nonwoven fabric of the present invention, it can be a polyethylene spunbonded nonwoven fabric that is soft and has excellent skin touch, uniform texture, sufficient strength to withstand practical use, and excellent productivity.

The composite fiber of the present invention preferably has a solid density of 0.935 g/cm ³ to 0.970 g/cm ^3. By setting the solid density of the polyethylene resin preferably to 0.935 g/cm ³ or more, more preferably to 0.940 g/cm ³ or more, and particularly preferably to 0.945 g/cm ³ or more, it is possible to prevent the fiber from being overly softened during heat bonding and causing problems in operation such as adhesion to a heat roller. Furthermore, by setting the solid density of the polyethylene resin preferably to 0.970 g/cm ³ or less, more preferably to 0.965 g/cm ³ or less, and particularly preferably to 0.960 g/cm ³ or less, the spinnability can be improved, and even thin fibers can be spun stably.

Furthermore, in the present invention, the solid density (g/cm ³ ) of the composite fiber is a value calculated by the following procedure.

(1) Wash the composite fiber test piece in ethanol and dry it in the air.

(2) For the composite fiber test piece, the density was determined by the floating-sinking method using a water-ethanol mixed liquid system.

(3) Perform the same measurement five times using different test pieces, average the measured density values (g/cm ³ ), and round off the fourth decimal place to be the solid density (g/cm ³ ) of the composite fiber.

The solid density (g/cm ³ ) of the composite fiber constituting the spunbonded nonwoven fabric is a value calculated by the following procedure.

(1) Randomly collect 5 small pieces from the spunbond nonwoven fabric.

(2) Wash the small piece in ethanol and dry it in the air.

(3) For small pieces of spunbond nonwoven fabric, use a water-ethanol mixed liquid system to calculate the density by the floating-sinking method.

(4) Perform the same measurement on 5 small pieces, average the measured density values (g/cm ³ ), and round off the fourth decimal place to obtain the solid density (g/cm ³ ) of the composite fiber.

[Spunbond nonwoven fabric]

The spunbond nonwoven fabric of the present invention is composed of composite fibers with polyethylene resin as the main component.

The spunbonded nonwoven fabric of the present invention has a welded portion and a non-welded portion. By forming this shape, the spunbonded nonwoven fabric can maintain the softness and skin touch derived from the polyethylene resin while having sufficient strength to withstand practical use. The so-called welded portion refers to the portion where the composite fibers are welded to each other, and the so-called non-welded portion refers to the portion where the composite fibers are not welded to each other and maintain the cross-sectional shape.

The spunbonded nonwoven fabric of the present invention is a composite fiber in the aforementioned welded portion, and the orientation parameter Obs of the sheath component is preferably 1.2~3.0. When Obs is 1.2, the molecular chain is in a completely random orientation state, and it does not become a value smaller than it. On the other hand, by making the orientation parameter Obs of the sheath component preferably less than 3.0, more preferably less than 2.5, and particularly preferably less than 2.0, the sheath components forming the fiber surface are firmly heat-bonded to each other, and a spunbonded nonwoven fabric with strength that can withstand practical use can be obtained.

The orientation parameter Obs of the sheath component in the composite fiber of the welded portion can be controlled by appropriately adjusting the orientation parameter Ofs of the sheath component of the composite fiber and/or the conditions of the thermal bonding described later (temperature, line pressure, etc.).

The spunbonded nonwoven fabric of the present invention is a composite fiber in the aforementioned welded portion, and the orientation parameter Obc of the core component is preferably 2 to 10. By having Obc preferably be 2.0 or more, more preferably be 2.5 or more, and particularly preferably be 3.0 or more, the strength of the core component can be improved, and a spunbonded nonwoven fabric with strength that can withstand practical use can be obtained. In addition, it can prevent the fiber surface from being excessively softened during heat bonding, thereby preventing problems in operations such as attachment to a heat roller. On the other hand, by having Obc preferably be 10.0 or less, more preferably be 9.0 or less, and particularly preferably be 8.0 or less, it can suppress excessive extension stress concentration on the core component during spinning, and improve spinning stability.

The orientation parameter Obc of the core component in the composite fiber of the welded portion can be controlled by appropriately adjusting the orientation parameter Ofc of the core component of the composite fiber and/or the conditions of the thermal bonding described later (temperature, line pressure, etc.).

Obs and Obc are measured by the following procedure.

(1) The spunbond nonwoven fabric sample was embedded in a bisphenol epoxy resin.

(2) After the resin is cured, slices are cut using a microtome so that the center of the welded part of the spunbond nonwoven fabric becomes the cross-section. The slice thickness is set to 2μm. Select a location with a cutting angle within 4° from the fiber axis for subsequent measurements. In addition, when the direction of the fiber axis is difficult to distinguish, the polarization direction is rotated every 15 degrees at the same point, and the polarized Raman spectrum is obtained in each direction. The direction showing the maximum orientation parameter is regarded as the fiber axis direction.

(3) Polarized light parallel to the fiber axis is incident on the center of the composite fiber slice at the welded portion, and Raman spectrum line measurement is performed.

(4) Calculate the Raman band intensities _I1130 and _I1060 at the positions of the sheath component and the core component of the composite fiber at the welded portion, respectively, near 1130 cm ^-1 and 1060 cm ^-1 , and calculate the orientation parameter from the intensity ratio according to the following formula (d). When the core component is divided into multiple independent regions, measure the orientation parameter in all regions and adopt the highest value.

Orientation parameter = I ₁₁₃₀ /I ₁₀₆₀ ‧‧‧(d).

(5) For different welded parts of the spunbond nonwoven fabric, perform the same measurement at 3 locations, calculate the average value of the orientation parameter, and round off the second decimal place.

The surface roughness SMD of at least one side of the spunbond nonwoven fabric of the present invention measured by the KES method is preferably 1.0~3.0μm. Since the surface roughness SMD measured by the KES method is preferably 1.0μm or more, more preferably 1.3μm or more, and particularly preferably 1.6μm or more, the spunbond nonwoven fabric can be prevented from being overly dense and having a poor hand feel or loss of softness. On the other hand, since the surface roughness SMD measured by the KES method is preferably 3.0μm or less, more preferably 2.8μm or less, and particularly preferably 2.5μm or less, the surface can be smooth, the roughness is small, and the skin touch is excellent.

The surface roughness SMD measured by the KES method can be controlled by appropriately adjusting the average single fiber diameter of the composite fiber, the texture of the spunbonded nonwoven fabric, and/or the conditions of the thermal bonding described later (shape of the bonding part, compression ratio, temperature, linear pressure, etc.).

Furthermore, the surface roughness SMD measured by the KES method in the present invention is measured as follows.

(1) Collect three test pieces with a width of 200 mm × 200 mm at equal intervals in the width direction of the spunbond nonwoven fabric.

(2) Place the test piece on the test bench.

(3) Use a contact head for surface roughness measurement (material: Φ0.5mm piano wire, contact length: 5mm) with a load of 10gf to scan the surface of the test piece and measure the average deviation of the surface concave and convex shape.

(4) Carry out the above measurements in the longitudinal direction (length direction of the nonwoven fabric) and transverse direction (width direction of the nonwoven fabric) of all test pieces, average the average deviation of the total 6 points, round off the second decimal place, and use it as the surface roughness SMD (μm).

The friction coefficient MIU of the spunbonded nonwoven fabric of the present invention measured by the KES method is preferably 0.01 to 0.30. By making the friction coefficient MIU preferably below 0.30, more preferably below 0.20, and particularly preferably below 0.15, the slipperiness of the nonwoven surface can be improved, and a spunbonded nonwoven fabric with excellent skin touch can be obtained. On the other hand, by making the friction coefficient MIU preferably above 0.01, more preferably above 0.03, and particularly preferably above 0.05, it is possible to prevent the yarns from sliding against each other and deteriorating the texture uniformity when the spun yarns are captured on the capturing conveyor belt.

The friction coefficient MIU measured by the KES method can be controlled by appropriately adjusting the additives of the aforementioned polyethylene resin, the average single fiber diameter of the composite fiber, the texture of the spunbond nonwoven fabric, and/or the conditions of the thermal bonding described later (shape of the bonding part, compression rate, temperature, linear pressure, etc.).

Furthermore, the friction coefficient MIU measured by the KES method in the present invention is measured as follows.

(1) Collect three test pieces with a width of 200mm×200mm at equal intervals in the width direction of the spunbond nonwoven fabric.

(2) Place the test piece on the test bench.

(3) Scan the surface of the test piece with a contact friction head (material: Φ0.5 mm piano wire (20 parallel lines), contact area: 1 cm ² ) with a load of 50 gf to measure the friction coefficient.

(4) Carry out the above measurements in the longitudinal direction (length direction of the nonwoven fabric) and transverse direction (width direction of the nonwoven fabric) of all test pieces, average the average deviation of the total of 6 points, round off the fourth decimal place, and use it as the friction coefficient MIU.

The MFR of the spunbond nonwoven fabric of the present invention is preferably 1g/10min~300g/10min. Since the MFR of the spunbond nonwoven fabric is preferably 1g/10min or more, more preferably 10g/10min or more, and particularly preferably 30g/10min or more, even fine fiber diameters can be spun stably, and a spunbond nonwoven fabric with excellent skin touch, uniform texture, and sufficient strength to withstand practical use can be obtained. On the other hand, since the MFR of the polyethylene resin is preferably 300g/10min or less, the strength reduction can be suppressed, and at the same time, the problem of excessive softening during heat bonding, which causes adhesion to the heat roller, can be prevented.

The MFR of the spunbonded nonwoven fabric of the present invention is the value measured by ASTM D1238 (Method A). According to this specification, polyethylene is measured at a load of 2.16 kg and a temperature of 190°C.

The unit area weight of the spunbond nonwoven fabric of the present invention is preferably 10 g/m ² to 100 g/m ² . By preferably having a unit area weight of 10 g/m ² or more, more preferably 13 g/m ² or more, and particularly preferably 15 g/m ² or more, a spunbond nonwoven fabric having sufficient strength to withstand practical use can be obtained. On the other hand, by preferably having a unit area weight of 100 g/m ² or less, more preferably 50 g/m ² or less, and particularly preferably 30 g/m ² or less, a spunbond nonwoven fabric having softness suitable for use as a nonwoven fabric for sanitary materials can be obtained.

Furthermore, in the present invention, the unit area weight of the spunbond nonwoven fabric is based on "6.2 Mass per unit area" of JIS L1913:2010 "General nonwoven fabric test methods", and is measured using the following procedure.

(1) Collect 3 test pieces of 20cm×25cm for every 1m of the sample width.

(2) Weigh the respective masses (g) under standard conditions.

(3) The average value is expressed as mass per 1m ² (g/m ² ).

The thickness of the spunbond nonwoven fabric of the present invention is preferably 0.05mm~1.5mm. With a thickness of preferably 0.05~1.5mm, more preferably 0.08~1.0mm, and particularly preferably 0.10~0.8mm, the spunbond nonwoven fabric has softness and moderate cushioning properties, and can be used as a sanitary material, especially a spunbond nonwoven fabric suitable for use in diapers.

Furthermore, in the present invention, the thickness (mm) of the spunbond nonwoven fabric is based on "5.1" of JIS L1906:2000 "General long-fiber nonwoven fabric test method", and is measured by the following procedure.

(1) Using a 10mm diameter pressure head, measure the thickness of ten points per 1m at equal intervals in the width direction of the nonwoven fabric at a load of 10kPa in units of 0.01mm.

(2) Round off the third decimal place of the average of the above ten points.

In addition, the apparent density of the spunbonded nonwoven fabric of the present invention is preferably 0.05 g/cm ³ to 0.30 g/cm ^3. By making the apparent density preferably 0.30 g/cm ³ or less, more preferably 0.25 g/cm ³ or less, and particularly preferably 0.20 g/cm ³ or less, it is possible to prevent the fibers from being densely packed and damaging the softness of the spunbonded nonwoven fabric. On the other hand, by making the apparent density preferably 0.05 g/cm ³ or more, more preferably 0.08 g/cm ³ or more, and particularly preferably 0.10 g/cm ³ or more, it is possible to suppress the occurrence of fuzzing or interlayer delamination, and to obtain a spunbonded nonwoven fabric having strength or operability to withstand practical use.

The apparent density can be controlled by appropriately adjusting the average single fiber diameter of the composite fiber and/or the conditions of the thermal bonding described later (shape of the bonding part, compression ratio, temperature and linear pressure, etc.).

Furthermore, in the present invention, the apparent density (g/cm ³ ) is calculated from the unit area weight and thickness before rounding according to the following formula, with the third decimal place rounded off.

Apparent density (g/cm ³ ) = [unit area weight (g/m ² )] / [thickness (mm)] × 10 ^-3 ... (formula).

The stiffness of the spunbonded nonwoven fabric of the present invention is preferably below 60 mm. By making the stiffness preferably below 60 mm, more preferably below 50 mm, and particularly preferably below 40 mm, the spunbonded nonwoven fabric used as a sanitary material can obtain excellent softness that is particularly suitable for use in paper diapers. In addition, since the operability is poor when the stiffness is extremely low, the stiffness is preferably above 10 mm.

The stiffness can be controlled by appropriately adjusting the MFR of the aforementioned polyethylene resin, additives, average single fiber diameter of the composite fiber, unit area weight of the spunbonded nonwoven fabric, softening temperature Tss (℃) of the surface layer of the composite fiber in the non-welded part of the spunbonded nonwoven fabric, softening temperature Tsc (℃) of the inner layer of the composite fiber in the non-welded part of the spunbonded nonwoven fabric, and/or the conditions of the heat bonding described later (shape of the bonding part, compression rate, temperature and linear pressure, etc.).

The tensile strength per unit area weight of the spunbonded nonwoven fabric of the present invention in the transverse direction is preferably 0.20 (N/25mm)/(g/m ² ) or more, more preferably 0.20 (N/25mm)/(g/m ² ) to 2.00 (N/25mm)/(g/m ² ). By making the tensile strength per unit area weight preferably 0.20 (N/25mm)/(g/m ² ) or more, more preferably 0.25 (N/25mm)/(g/m ² ) or more, and particularly preferably 0.30 (N/25mm)/(g/m ² ) or more, the spunbonded nonwoven fabric can have a strength that can withstand practical use. On the other hand, by setting the tensile strength in the transverse direction per unit area weight to be preferably 2.00 (N/25mm)/(g/m ² ) or less, the softness of the spunbond nonwoven fabric can be prevented from being reduced or the hand feel being damaged. Moreover, the tensile strength of the spunbond nonwoven fabric is in the longitudinal direction and the transverse direction, but generally speaking, the tensile strength in the transverse direction is smaller than that in the longitudinal direction. Therefore, by setting the tensile strength in the transverse direction per unit area weight to be 0.2~2.00 (N/25mm)/(g/m ² ), the spunbond nonwoven fabric can be made to have a practical strength in the longitudinal direction.

The transverse tensile strength per unit area weight can be controlled by appropriately adjusting the MFR of the aforementioned polyethylene resin, additives, average single fiber diameter of the composite fiber, softening temperature Tss (℃) of the surface layer of the composite fiber in the non-welded part of the spunbonded nonwoven fabric, softening temperature Tsc (℃) of the inner layer of the composite fiber in the non-welded part of the spunbonded nonwoven fabric, and/or the spinning speed and heat-bonding conditions (shape of the bonded part, compression ratio, temperature and linear pressure, etc.) described later.

Furthermore, in the present invention, the transverse tensile strength per unit area weight of the spunbonded nonwoven fabric is based on "6.3 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "General nonwoven fabric test methods", and adopts the value measured by the following procedure.

(1) With the long side of the nonwoven fabric in the transverse direction (the width direction of the nonwoven fabric), collect three test pieces of 25mm×200mm for every 1m of the nonwoven fabric width.

(2) Place the test piece in the tensile testing machine with a clamp spacing of 100 mm.

(3) Carry out a tensile test at a tensile speed of 100 mm/min and measure the maximum strength.

(4) Obtain the average value of the maximum strength measured on each test piece and calculate the tensile strength per unit area weight according to the following formula, rounding off the third decimal place.

Transverse tensile strength per unit area weight ((N/25mm)/(g/m ² )) = [average value of maximum strength (N/25mm)]/unit area weight (g/m ² )... (formula).

The spunbonded nonwoven fabric of the present invention preferably has a longitudinal stress at 5% elongation per unit area weight of 0.20 (N/25mm)/(g/m ² ) or more, more preferably 0.20 (N/25mm)/(g/m ² ) to 2.00 (N/25mm)/(g/m ² ). By setting the stress per unit area weight at 5% elongation in the longitudinal direction preferably to 0.20 (N/25mm)/(g/m ² ) or more, more preferably to 0.25 (N/25mm)/(g/m ² ) or more, and particularly preferably to 0.30 (N/25mm)/(g/m ² ) or more, the elongation caused by tension during the production of the spunbond nonwoven fabric or during processing as a sanitary material can be suppressed, and the fabric can be produced stably with a high yield. In addition, by setting the stress per unit area weight at 5% elongation in the longitudinal direction preferably to 2.00 (N/25mm)/(g/m ² ) or less, the softness of the spunbond nonwoven fabric can be prevented from being reduced or the hand feel can be prevented from being damaged.

The stress at 5% elongation in the longitudinal direction per unit area weight can be controlled by appropriately adjusting the MFR of the aforementioned polyethylene resin, additives, average single fiber diameter of the composite fiber, softening temperature Tss (℃) of the surface layer of the composite fiber in the non-welded part of the spunbonded nonwoven fabric, softening temperature Tsc (℃) of the inner layer of the composite fiber in the non-welded part of the spunbonded nonwoven fabric, and/or the spinning speed and heat-bonding conditions (shape of the bonded part, compression ratio, temperature and linear pressure, etc.) described later.

Furthermore, in the present invention, the stress at 5% elongation in the longitudinal direction of the spunbonded nonwoven fabric per unit area weight is based on "6.3 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "General nonwoven fabric test methods", and adopts the value measured by the following procedure.

(1) With the long side of the nonwoven fabric in the longitudinal direction (length direction of the nonwoven fabric), collect three test pieces of 25mm×200mm for every 1m of the nonwoven fabric width.

(2) Place the test piece in the tensile testing machine with a clamp spacing of 100 mm.

(3) Carry out a tensile test at a tensile speed of 100 mm/min and measure the stress at 5% elongation (stress at 5% elongation).

(4) Obtain the average value of the stress at 5% elongation measured on each test piece, and calculate the stress at 5% elongation in the longitudinal direction per unit area weight according to the following formula, rounding off the third decimal place.

The stress at 5% elongation in the longitudinal direction per unit area weight ((N/25mm)/(g/m ² )) = [average stress at 5% elongation (N/25mm)]/unit area weight (g/m ² )...(formula).

[Manufacturing method of spunbond nonwoven fabric]

Next, the preferred method for manufacturing the spunbonded nonwoven fabric of the present invention is specifically described.

The spunbonded nonwoven fabric of the present invention is a long-fiber nonwoven fabric manufactured by the spunbonding method. In addition to excellent productivity and mechanical strength, the spunbonding method can also suppress the fuzzing and fiber shedding that are easy to occur in short-fiber nonwoven fabrics. In addition, laminating the captured spunbonded nonwoven fiber net or the heat-pressed spunbonded nonwoven fabric in multiple layers is also a better embodiment because of the improved productivity and texture uniformity.

In the spunbond method, the molten thermoplastic resin is first spun out as long fibers from a spinning nozzle, and then the fibers are drawn out by compressed air through an ejector, and then captured on a moving net to obtain a nonwoven fiber web. The obtained nonwoven fiber web is further subjected to a heat-bonding treatment to obtain a spunbond nonwoven fabric.

There is no particular restriction on the shape of the spinning nozzle or the ejector. For example, various shapes such as round or rectangular can be used. Among them, the combination of a rectangular nozzle and a rectangular ejector is more suitable because the use of compressed air is relatively small and the energy cost is excellent, the yarns are not easily welded or rubbed, and the yarns are easy to open.

In the present invention, the polyethylene resin is melted and measured in an extruder, and supplied to a spinning nozzle to be spun out as a long fiber. The spinning temperature when the polyethylene resin is melt-spinned is preferably 180°C to 250°C, more preferably 190°C to 240°C, and particularly preferably 200°C to 230°C. By setting the spinning temperature within the above range, a stable molten state can be achieved, and excellent spinning stability can be obtained.

The spun filament yarn is then cooled. As a method for cooling the spun yarn, for example, there can be cited: a method of forcibly blowing cold air to the yarn, a method of naturally cooling the yarn with the ambient temperature around the yarn, and a method of adjusting the distance between the spinning nozzle and the injector, or a method combining these methods. In addition, the cooling conditions can be appropriately adjusted and adopted in consideration of the discharge amount per single hole of the spinning nozzle, the spinning temperature, and the ambient temperature.

The cooled and solidified yarn is then pulled and stretched by compressed air ejected from the ejector.

The spinning speed is preferably 3000m/min to 6000m/min, more preferably 3500m/min to 5500m/min, and particularly preferably 4000m/min to 5000m/min. By setting the spinning speed to 3000m/min to 6000m/min, high productivity is achieved, and the fiber orientation crystallization is carried out, so that high-strength long fibers can be obtained. As mentioned above, the composite fiber with polyethylene resin as the main component of the present invention has excellent spinning stability and can be stably produced even at a fast spinning speed.

Then, the obtained long fibers are captured on a moving mesh to obtain a nonwoven fiber web.

In the present invention, for the aforementioned nonwoven fiber net, it is also preferable to abut the hot flat roller from one side of the net so that it is temporarily connected. By doing so, it is possible to prevent the surface layer of the nonwoven fiber net from rolling up or floating during transportation on the net and deteriorating the quality, or improve the transportation performance from collecting the yarn to hot pressing.

Next, by fusing the obtained nonwoven fiber web to form a fusion bonded portion, the desired spunbonded nonwoven fabric can be obtained.

There is no particular limitation on the method of welding the nonwoven web. For example, there can be cited: a method of heat welding by various rollers, wherein the aforementioned various rollers are heat embossing rollers with engravings (concave and convex parts) applied on the upper and lower roller surfaces, respectively; a heat embossing roller composed of a roller with a flat (smooth) surface and another roller with engravings (concave and convex parts) applied on the roller surface; and a heat embossing roller composed of a combination of an upper and lower pair of flat (smooth) rollers; a method of heat welding by ultrasonic vibration of a welding head (horn); and a method of allowing hot air to penetrate the nonwoven web to soften or melt the surface of the composite fiber and heat weld the intersections of the fibers to each other.

Among them, it is preferable to use a hot stamping roller with engravings (convex and concave parts) on the upper and lower roller surfaces, or a hot stamping roller composed of a roller with a flat (smooth) surface and another roller with engravings (convex and concave parts) on the roller surface. By doing so, productivity is good, and a welded part that improves the strength of the spunbond nonwoven fabric and a non-welded part that improves the hand feel and skin touch can be provided.

As the surface material of the hot embossing roller, in order to obtain a sufficient hot pressing effect and prevent the engraving (convex and concave parts) of one embossing roller from being transferred to the surface of the other roller, the best way is to pair metal rollers.

The embossing bonding area ratio by such a hot embossing roller is preferably 5-30%. By setting the bonding area ratio preferably to 5% or more, more preferably to 8% or more, and particularly preferably to 10% or more, a strength that can withstand practical use can be obtained as a spunbond nonwoven fabric. On the other hand, by setting the bonding area ratio preferably to 30% or less, more preferably to 25% or less, and particularly preferably to 20% or less, a spunbond nonwoven fabric used as a sanitary material can be obtained with a degree of softness that is particularly suitable for use in disposable diapers. When using ultrasonic bonding, the bonding area ratio is also preferably in the same range.

The bonding area ratio mentioned here refers to the ratio of the bonding part to the whole spunbond nonwoven fabric. Specifically, when heat bonding is performed by a pair of rollers with concave and convex surfaces, it refers to the ratio of the part where the convex part of the upper roller overlaps with the convex part of the lower roller and abuts against the nonwoven web (bonding part) to the whole spunbond nonwoven fabric. Also, when heat bonding is performed by a roller with concave and convex surfaces and a flat roller, it refers to the ratio of the part where the convex part of the roller abuts against the nonwoven web (bonding part) to the whole spunbond nonwoven fabric. In addition, when ultrasonic bonding is performed, it refers to the ratio of the part (bonding part) thermally welded by ultrasonic processing to the whole spunbond nonwoven fabric. When sufficient heat is applied to the joining portion during heat welding and the composite fibers in the joining portion are completely fused, the areas of the joining portion and the fused portion can be considered equal.

The shape of the joining part formed by the hot embossing roller or ultrasonic bonding is not particularly limited, and for example, a circle, an ellipse, a square, a rectangle, a parallelogram, a rhombus, a regular hexagon, and a regular octagon can be used. In addition, the joining part is preferably evenly present at a certain interval in the length direction (conveying direction) and the width direction of the spunbond nonwoven fabric. By doing so, the strength deviation of the spunbond nonwoven fabric can be reduced.

The surface temperature of the heat embossing roller during heat bonding is preferably set to a temperature 30°C lower than the melting point Tm (°C) of the thermoplastic resin used and 10°C higher, that is, set to be above Tm-30°C and below Tm+10°C. By setting the surface temperature of the heat roller to be above Tm-30°C, more preferably above Tm-20°C, and even more preferably above Tm-10°C, it is possible to achieve a strong heat bonding and obtain a spunbond nonwoven fabric with a strength that can withstand practical use. Furthermore, by setting the surface temperature of the heat embossing roller preferably below Tm+10°C, more preferably below Tm+5°C, and most preferably below Tm+0°C, excessive heat bonding can be suppressed, and the spunbond nonwoven fabric used as a sanitary material can obtain a moderate softness that is particularly suitable for use in diapers.

The linear pressure of the heat embossing roller during heat bonding is preferably set to 50N/cm~500N/cm. By setting the linear pressure of the roller preferably to 50N/cm or more, more preferably to 100N/cm or more, and particularly preferably to 150N/cm or more, a spunbond nonwoven fabric with strength that can withstand practical use can be obtained by firmly heat bonding. On the other hand, by setting the linear pressure of the heat embossing roller preferably to 500N/cm or less, more preferably to 400N/cm or less, and particularly preferably to 300N/cm or less, a spunbond nonwoven fabric used as a sanitary material can be obtained with a moderate softness that is particularly suitable for use in disposable diapers.

Furthermore, in the present invention, in order to adjust the thickness of the spunbond nonwoven fabric, before and/or after the heat bonding using the above-mentioned heat embossing roller, heat embossing can be performed using a heat embossing roller formed by a pair of upper and lower flat rollers. The so-called upper and lower pair of flat rollers are metal rollers or elastic rollers with no unevenness on the surface of the rollers, and metal rollers can be used in pairs, or metal rollers can be used in pairs with elastic rollers.

In addition, the elastic roller referred to here is a roller made of a material that is more elastic than a metal roller. Examples of the elastic roller include paper rollers such as paper, cotton, and aromatic polyamide paper, and resin rollers made of urethane resins, epoxy resins, silicone resins, polyester resins, hard rubber, and mixtures thereof.

The spunbonded nonwoven fabric of the present invention is soft, has excellent skin touch, has uniform texture, has sufficient strength to withstand practical use, and has excellent productivity, so it can be widely used in sanitary materials, medical materials, daily materials, and industrial materials. In particular, in sanitary materials, it can be used as the base fabric of disposable diapers, sanitary products, and wet cloth materials, and in medical materials, it can be used as protective clothing or surgical gowns, etc.

[Implementation example]

Next, the spunbonded nonwoven fabric of the present invention is specifically described based on the embodiments. However, the present invention is not limited to these embodiments. Furthermore, in the measurement of various physical properties, those without special records are measured according to the above-mentioned methods.

[Measurement method]

(1) Resin melt flow rate (MFR) (g/10 minutes)

The MFR of the resin is measured under the conditions of a load of 2.16kg and a temperature of 190°C.

(2) Average single fiber diameter of composite fibers constituting spunbond nonwoven fabric (μm)

The average single fiber diameter of the composite fiber was measured using the electron microscope "VHX-D500" manufactured by KEYENCE Co., Ltd. using the above method.

(3) Solid density of composite fibers constituting spunbond nonwoven fabric (g/cm ³ )

The solid density of the composite fiber is measured by the above method.

(4) Spinning speed (m/min)

From the above average single fiber diameter and the solid density of the resin used, the mass per 10,000 m of length is taken as the average single fiber fineness (dtex), and the second decimal place is rounded off and calculated. From the average single fiber fineness and the amount of resin discharged from a single hole of the spinning nozzle set under various conditions (hereinafter referred to as single hole discharge amount) (g/minute), the spinning speed is calculated according to the following formula.

Spinning speed (m/min) = (10000×[single hole output (g/min)])/[average single fiber fineness (dtex)]...(formula).

(5) Softening temperature of composite fiber (℃) and non-welded part of spunbond nonwoven fabric Softening temperature of composite fiber (℃)

The measurement was performed using the Nano-TA device "Nano-TA2" manufactured by Analysis Instruments, the AFM device "Nano-R" manufactured by PACIFIC NANOTECHNOLOGY, and the probe "PNI-AN2-300" manufactured by Analysis Instruments. The measurement was performed using the above method. The measurement conditions were implemented as follows.

‧Measurement method: nano-TMA (nano-thermal mechanical analysis)

‧Measurement temperature: 25~150℃

‧Heating rate: 10℃/second (600℃/minute)

‧Measurement environment: in the atmosphere.

(6) Orientation parameters of composite fibers, orientation parameters of composite fibers in the non-welded portion of spunbonded nonwoven fabrics, and orientation parameters of composite fibers in the welded portion of spunbonded nonwoven fabrics

In the measurement device, a triple Raman spectrometer "T-64000" manufactured by Atago Bussan Co., Ltd. was used to perform the measurement using the above method. The measurement conditions were implemented as follows.

‧Measurement mode: Micro Raman (polarization measurement)

‧Objective lens: ×100

‧Beam diameter: 1μm

‧Light source: Ar ⁺ laser/514.5nm

‧Laser power: 100mW

‧Diffraction grating: Single 1800gr/mm

‧Cross stitch: 100μm

‧Detector: CCD/Jobin Yvon 1024×256.

(7) Melting peak temperature Tm (℃) of spunbond nonwoven fabric

The measurement was performed using the DSC8500 manufactured by Perkin-Elmer as the measuring device. The measurement conditions were as follows.

‧Environment inside the device: Nitrogen (20mL/min)

‧Temperature‧Heat correction: High purity indium (Tm=156.61℃, △Hm=28.70J/g)

‧Temperature range: 20℃~200℃

‧Heating rate: 20℃/min

‧Amount of sample: about 0.5~4mg

‧Sample container: standard aluminum container.

(8) Longitudinal stiffness of spunbond nonwoven fabric (mm)

The stiffness of spunbond nonwoven fabrics is measured in the longitudinal direction (length direction) of the nonwoven fabric according to the method described in "6.7 Stiffness (JIS method and ISO method)" and "6.7.4 Gray method" of JIS L1913:2010 "General nonwoven fabric test methods". In addition, the stiffness of any spunbond nonwoven fabric in the longitudinal direction (length direction) is greater than the stiffness in the transverse direction (width direction). The stiffness in the longitudinal direction is considered acceptable if it is less than 50mm.

(9) Tensile strength per unit area weight and stress at 5% elongation per unit area weight of spunbond nonwoven fabric (N/25mm/(g/ ^m2 ))

The measurement was performed using the RTG-1250 manufactured by A and D (A&D) Co., Ltd. The tensile strength in the transverse direction per unit area weight was 0.2 (N/25mm)/(g/m ² ) or more, and the stress at 5% elongation in the transverse direction per unit area weight was 0.2 (N/25mm)/(g/m ² ) or more.

[Implementation Example 1]

A polyethylene resin composed of a homopolymer of linear low-density polyethylene (LLDPE) having a melt flow rate (MFR) of 30 g/10 min, a melting point of 128°C, and a solid density of 0.955 g/ ^cm3 was used as a core component, and a polyethylene resin composed of a homopolymer of LLDPE having an MFR of 60 g/10 min, a melting point of 127°C, and a solid density of 0.940 g/ ^cm3 was used as a sheath component. Each of them was melted in an extruder, and a concentric core-sheath type composite fiber having a sheath component ratio of 40 mass% was spun from a spinning nozzle having a hole diameter of 0.40 mm and a hole depth of 8 mm at a spinning temperature of 220°C and a single hole discharge of 0.50 g/min.

After the spun yarn is cooled and solidified, it is pulled and stretched by compressed air in the ejector, and captured on the moving mesh to form a spunbond nonwoven fiber net made of polyethylene long fibers. The properties of the composite fiber constituting the formed nonwoven fiber net are that the average single fiber diameter is 11.6μm and the solid density is 0.949g/ ^cm3 , and the spinning speed converted from this is 5000m/min. Regarding the spinnability, no yarn breakage was observed during the 1-hour spinning, which is good.

Next, the formed nonwoven web was heat-bonded using a pair of upper and lower heat-embossing rolls consisting of an upper roll and a lower roll at a linear pressure of 300 N/cm and a heat-bonding temperature of 120°C to obtain a spunbond nonwoven fabric with a unit area weight of 20 g/ ^m2 .

Upper roller: Metal embossing roller with a water drop pattern engraved on it and a bonding area ratio of 16%

Lower roller: metal flat roller

The obtained spunbond nonwoven fabric has uniform texture and excellent skin feel. The evaluation results are shown in Table 1.

[Example 2]

A spunbond nonwoven fabric was obtained by the same method as in Example 1, except that the ratio of the sheath component was set to 50% by mass and the flow rate of the compressed air of the ejector was reduced. The properties of the fibers constituting the formed spunbond nonwoven fiber web were an average single fiber diameter of 13.7 μm and a solid density of 0.948 g/cm ³ , and the spinning speed converted therefrom was 3600 m/min. Regarding the spinnability, no yarn breakage was observed during the 1-hour spinning, which was good. The obtained spunbond nonwoven fabric had a uniform texture and excellent skin touch. The evaluation results are shown in Table 1.

[Implementation Example 3]

A spunbond nonwoven fabric was obtained by the same method as in Example 1, except that the sheath component ratio was set to 30% by mass and the flow rate of the compressed air of the ejector was reduced. The properties of the fibers constituting the formed spunbond nonwoven fiber web were an average single fiber diameter of 15.5 μm and a solid density of 0.951 g/cm ³ , and the spinning speed converted therefrom was 2800 m/min. Regarding the spinnability, no yarn breakage was observed during the 1-hour spinning, which was good. The obtained spunbond nonwoven fabric had a uniform texture and excellent skin touch. The evaluation results are shown in Table 1.

[Implementation Example 4]

A spunbond nonwoven fabric was obtained by the same method as in Example ² except that a polyethylene resin composed of a homopolymer of LLDPE having an MFR of 30 g/10 min, a melting point of 128°C, and a solid density of 0.955 g/cm ^{3 was used as the core component, and a polyethylene resin composed of a homopolymer of LLDPE having an MFR of 50 g/10 min, a melting point of 128°C, and a solid density of 0.950 g/cm 3} was used as the sheath component. The properties of the fibers constituting the formed spunbond nonwoven fiber web were an average single fiber diameter of 13.7 μm and a solid density of 0.953 g/cm ³ , and the spinning speed converted therefrom was 3600 m/min. Regarding the spinnability, yarn breakage occurred several times during the spinning for 1 hour. The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

[Implementation Example 5]

A spunbond nonwoven fabric was obtained by the same method as in Example ² except that a polyethylene resin composed of a homopolymer of high-density polyethylene (HDPE) having an MFR of 30 g/10 min, a melting point of 130°C, and a solid density of 0.960 g/cm ³ was used as the core component, and a polyethylene resin composed of a homopolymer of high-density polyethylene (HDPE) having an MFR of 100 g/10 min, a melting point of 130°C, and a solid density of 0.950 g/cm 3 was used as the sheath component. The properties of the fibers constituting the formed spunbond nonwoven fiber web were an average single fiber diameter of 13.7 μm and a solid density of 0.955 g/cm ³ , and the spinning speed converted therefrom was 3600 m/min. Regarding the spinnability, no yarn breakage was observed during the 1-hour spinning, which was considered good. The obtained spunbond nonwoven fabric had a uniform texture and excellent skin feel. Table 1 shows the evaluation results.

[Comparative example 1]

A spunbond nonwoven fabric was obtained by the same method as in Example 2 except that a polyethylene resin composed of a homopolymer of LLDPE having an MFR of 30 g/10 min, a melting point of 128°C, and a solid density of 0.955 ^g /cm 3 was used for single-component spinning. The properties of the fibers constituting the formed spunbond nonwoven fiber web were an average single fiber diameter of 13.9 μm and a solid density of 0.955 g/cm ³ , and the spinning speed converted therefrom was 3500 m/min. Regarding the spinnability, yarn breakage occurred frequently during the spinning for 1 hour, resulting in a defect. The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

[Comparative example 2]

A spunbond nonwoven fabric was obtained by the same method as in ^{Example 2} except that a polyethylene resin composed of a homopolymer of LLDPE having an MFR of 60 g/10 min, a melting point of 127°C, and a solid density of 0.940 g/cm ^{3 was used for single-component spinning and the heat-bonding temperature was set to 115°C. The properties of the fibers constituting the formed spunbond nonwoven fiber web were an average single fiber diameter of 13.7 μm and a solid density of 0.940 g/cm 3} , and the spinning speed converted therefrom was 3600 m/min. The spinnability was good, with no yarn breakage observed during the spinning for 1 hour. Furthermore, when the heat bonding temperature was set to 120°C, the sheet broke when attached to the heat embossing roll, and production could not be carried out. Table 1 shows the evaluation results of the obtained spunbond nonwoven fabric.

[Comparative example 3]

A spunbond nonwoven fabric was obtained by the same method as in Example 2, except that the polyethylene resin composed of a homopolymer of LLDPE having an MFR of 100 g/10 min, a melting point of 115°C, and a solid density of 0.933 g/cm ³ was used as a single component for spinning according to the method disclosed in Reference Patent Document 2 (Japanese Patent Laid-Open No. 2019-26954). The properties of the fibers constituting the formed spunbond nonwoven fiber web were an average single fiber diameter of 15.2 μm and a solid density of 0.933 g/cm ³ , and the spinning speed converted therefrom was 3500 m/min, which was equivalent to Example 1 of Patent Document 2. The spinnability was good because no yarn breakage was observed during the spinning for 1 hour. The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

[Comparative example 4]

A spunbond nonwoven fabric was obtained by the same method as in Example ² except that a polyethylene resin composed of a homopolymer of LLDPE having an MFR of 30 g/10 min, a melting point of 128°C, and a solid density of 0.955 g/cm ^{3 was used as the core component, and a polyethylene resin composed of a homopolymer of LLDPE having an MFR of 40 g/10 min, a melting point of 128°C, and a solid density of 0.950 g/cm 3} was used as the sheath component. The properties of the fibers constituting the formed spunbond nonwoven fiber web were an average single fiber diameter of 13.7 μm and a solid density of 0.953 g/cm ³ , and the spinning speed converted therefrom was 3600 m/min. Regarding the spinnability, yarn breakage occurred frequently during the spinning for 1 hour, which was considered defective. The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

The spunbond nonwoven fabrics of Examples 1 to 5 are composed of composite fibers with polyethylene resin as the main component, and the softening temperature Tss (℃) of the surface layer of the composite fibers in the non-welded part and the softening temperature Tsc (℃) of the inner layer of the composite fibers in the non-welded part satisfy (Tss+5)≦Tsc≦(Tss+30). They are soft and have excellent skin touch, uniform texture, sufficient strength to withstand practical use, and excellent productivity.

On the other hand, the spunbond nonwoven fabrics shown in Comparative Examples 1 to 4 have low transverse tensile strength per unit area weight or 5% longitudinal elongation stress per unit area weight, and are poor in strength.

without.

Claims (8)

A spunbond nonwoven fabric is a spunbond nonwoven fabric composed of a composite fiber with a polyethylene resin as a main component. The spunbond nonwoven fabric has a fused portion and a non-fused portion. The softening temperature Tss (°C) of the surface layer of the composite fiber in the non-fused portion and the softening temperature Tsc (°C) of the inner layer of the composite fiber in the non-fused portion satisfy the following formula (a). The spunbond nonwoven fabric is a spunbond nonwoven fabric in a differential scanning type In the calorimetry, it has a single melting peak temperature Tm (℃), and the Tm (℃) and the Tss (℃) satisfy the following formulas (b) and (c); (Tss+5)≦Tsc≦(Tss+30)　　・・・(a)100≦Tm≦150　　　　　　・・・(b)(Tm-40)≦Tss≦(Tm-10)　　・・・(c). The spunbond nonwoven fabric of claim 1, wherein the solid density of the composite fiber is greater than or equal to 0.935 g/cm ³ and less than or equal to 0.970 g/cm ³ . The spunbonded nonwoven fabric of claim 1 or 2, wherein the composite fiber is a core-sheath composite fiber. The spunbond nonwoven fabric of claim 1 or 2, wherein the tensile strength per unit area weight of the spunbond nonwoven fabric in the transverse direction is greater than 0.20 (N/25 mm)/(g/m ² ). The spunbonded nonwoven fabric of claim 1 or 2, wherein the stress per unit area weight of the spunbonded nonwoven fabric at 5% elongation in the longitudinal direction is 0.20 (N/25 mm)/(g/m ² ) or more. A composite fiber having a polyethylene resin as a main component, wherein the softening temperature Tss (°C) of the surface layer of the composite fiber and the softening temperature Tsc (°C) of the inner layer of the composite fiber satisfy the following formula (a), and the composite fiber has a single melting peak temperature Tm (°C) in differential scanning calorimetry, and the Tm (°C) and the Tss (°C) satisfy the following formulas (b) and (c); (Tss+5)≦Tsc≦(Tss+30)　　…(a)100≦Tm≦150　　　　　　…(b)(Tm-40)≦Tss≦(Tm-10)　　…(c). The composite fiber of claim 6, wherein the solid density of the composite fiber is greater than or equal to 0.935 g/cm ³ and less than or equal to 0.970 g/cm ³ . The composite fiber of claim 6 or 7, wherein the composite fiber is a core-sheath type composite fiber.