spunbond nonwoven fabric

Abstract

To provide a high-strength spun-bonded nonwoven fabric practically usable even with a reduced basis weight.SOLUTION: A spun-bonded nonwoven fabric composed of fiber of polypropylene-based resin having a branching index g of 0.950 or more and 0.990 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a spunbond nonwoven fabric that can be suitably used for hygiene materials such as disposable diapers and sanitary napkins, masks, etc. [Background technology]

[0002] Spunbond nonwoven fabrics are often used for hygiene materials such as disposable diapers and sanitary napkins, as well as for masks, etc., because they are inexpensive and have the flexibility and physical properties required for practical use. As these products are often disposed of after a single use and then incinerated or landfilled, there is a need to reduce the amount of plastic used from an environmental perspective.

[0003] Reducing the amount of plastic in spunbond nonwovens specifically means reducing the amount of plastic in 1m 2 The mass of nonwoven fabric per unit area (g / m 2 However, the lower the basis weight, the lower the tensile strength, which is a physical property of nonwoven fabrics, generally becomes, and problems such as tearing during actual use become apparent. Therefore, various methods for improving the strength of spunbond nonwoven fabrics have been studied.

[0004] Generally, there are two methods for improving the strength of spunbonded nonwoven fabrics: improving the strength of the yarn and improving the thermal adhesiveness. As an example of the former, Patent Document 1 describes adding 0.1 to 1 part by weight of a high-melt-strength polypropylene to a polypropylene resin with a molecular weight distribution of less than 3, thereby achieving both high tenacity and good extensibility of the yarn. As an example of the latter, Patent Document 2 describes controlling the melt mass-flow rate and spinning conditions of the polypropylene resin to reduce the crystallite size, thereby setting the melting point and heat of fusion within specific ranges, thereby improving the thermal adhesiveness in the manufacturing process of the spunbonded nonwoven fabric. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2008-523231 [Patent Document 2] Japanese Patent Application Publication No. 2019-196576 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method disclosed in Patent Document 1 can improve the strength of the yarn to some extent, but the amount of high melt strength polypropylene added is small, so the thermal adhesiveness is not affected, and it is difficult to significantly improve the strength of the spunbonded nonwoven fabric.On the other hand, the method disclosed in Patent Document 2 can improve the thermal adhesiveness to some extent, but the yarn strength is low due to the small crystallite size, so it is difficult to significantly improve the strength of the spunbonded nonwoven fabric.

[0007] In view of the above problems, an object of the present invention is to provide a high-strength spunbond nonwoven fabric that can withstand practical use even when the fabric has a low basis weight. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that by adjusting the branching index g of the polypropylene resin fibers constituting the spunbonded nonwoven fabric to fall within a specific range, it is possible to improve both the strength and thermal adhesion of the fibers constituting the spunbonded nonwoven fabric, and to obtain a spunbonded nonwoven fabric with higher strength than ever before.

[0009] The present invention has been completed based on these findings, and provides the following inventions.

[0010] The spunbond nonwoven fabric of the present invention is a spunbond nonwoven fabric composed of fibers made of a polypropylene-based resin, and the branching index g of the polypropylene-based resin constituting the fibers is 0.950 or more and 0.990 or less.

[0011] According to a preferred embodiment of the spunbonded nonwoven fabric of the present invention, the average single fiber diameter of the fibers constituting the spunbonded nonwoven fabric is 6.5 μm or more and 14.5 μm or less.

[0012] According to a preferred embodiment of the spunbond nonwoven fabric of the present invention, the polypropylene resin constituting the fibers has a melt flow rate of 155 g / 10 min or more and 850 g / 10 min or less.

[0013] According to a preferred embodiment of the spunbond nonwoven fabric of the present invention, the mesopentad fraction (mmmm) of the polypropylene resin constituting the fibers is 0.950 or more and 0.995 or less.

[0014] According to a preferred embodiment of the spunbonded nonwoven fabric of the present invention, the basis weight of the spunbonded nonwoven fabric is 5 g / m 2 More than 100g / m 2 The following is the result. [Effects of the Invention]

[0015] According to the present invention, a spunbond nonwoven fabric having higher strength than conventional spunbond nonwoven fabrics can be obtained. Therefore, even if the spunbond nonwoven fabric has a relatively low basis weight, it has physical properties that can withstand practical use, and is suitable for use as an environmentally friendly nonwoven fabric that reduces the amount of plastic raw material used, for hygiene materials such as disposable diapers and sanitary napkins, masks, etc. DETAILED DESCRIPTION OF THE INVENTION

[0016] The spunbond nonwoven fabric of the present invention is a spunbond nonwoven fabric made of fibers made of a polypropylene resin, and the branching index g of the polypropylene resin making up the fibers is 0.950 or more and 0.990 or less.

[0017] These components of the present invention will be described in detail below, but the present invention is not limited to the scope of the following description as long as it does not deviate from the gist of the invention.

[0018] [Polypropylene resin] The spunbond nonwoven fabric of the present invention is composed of fibers whose main component is polypropylene-based resin. Polypropylene-based resins are preferred because they have superior spinnability and strength properties compared to other polyolefin-based resins such as polyethylene-based resins. Examples of polypropylene-based resins used in the present invention include propylene homopolymers and copolymers of propylene and various α-olefins.

[0019] In the polypropylene-based resin constituting the fiber according to the present invention, the proportion of propylene homopolymer is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, which can maintain good spinnability and improve strength.

[0020] The polypropylene resin may be a mixture of two or more kinds, or a resin composition containing other olefin resins such as polyethylene and poly-4-methyl-1-pentene, or a thermoplastic elastomer, etc. may also be used.

[0021] The melting point of this polypropylene resin is preferably 80° C. or higher and 200° C. or lower. By setting the melting point to preferably 80° C. or higher, more preferably 100° C. or higher, and even more preferably 120° C. or higher, heat resistance sufficient for practical use is more likely to be obtained. By setting the melting point to preferably 200° C. or lower, more preferably 180° C. or lower, it becomes easier to cool the yarn discharged from the spinneret, suppressing fusion between the fibers and facilitating stable spinning.

[0022] Furthermore, this polypropylene-based resin may contain a fatty acid amide compound having 23 to 50 carbon atoms to improve slipperiness and flexibility. By making the carbon number of the fatty acid amide compound mixed with the polypropylene-based resin preferably 23 or more, more preferably 30 or more, excessive exposure of the fatty acid amide compound on the fiber surface is suppressed, resulting in excellent spinnability and processing stability and maintaining high productivity. On the other hand, by making the carbon number of the fatty acid amide compound preferably 50 or less, more preferably 42 or less, the fatty acid amide compound is more likely to migrate to the fiber surface, imparting slipperiness and flexibility to the spunbonded nonwoven fabric.

[0023] Examples of the fatty acid amide compound having 23 to 50 carbon atoms used in the present invention include saturated fatty acid monoamide compounds, saturated fatty acid diamide compounds, unsaturated fatty acid monoamide compounds, and unsaturated fatty acid diamide compounds.

[0024] Specific examples of fatty acid amide compounds having 23 to 50 carbon atoms include tetradocosanoic acid amide, hexadocosanoic acid amide, octadocosanoic acid amide, nervonic acid amide, tetracosapentaenoic acid amide, nisinic acid amide, ethylene bislauric acid amide, methylene bislauric acid amide, ethylene bisstearic acid amide, ethylene bishydroxystearic acid amide, ethylene bisbehenic acid amide, hexamethylene bisstearic acid amide, hexamethylene bisbehenic acid amide, hexamethylene hydroxystearic acid amide, distearyl adipic acid amide, distearyl sebacic acid amide, ethylene bisoleic acid amide, ethylene biserucic acid amide, and hexamethylene bisoleic acid amide. Among these, ethylene bisstearic acid amide is preferred because it has excellent thermal stability, allowing it to be melt-spun, and can produce spunbond nonwoven fabrics with excellent lubricity and softness while maintaining high spinning stability.

[0025] In the present invention, the amount of fatty acid amide compound contained in the polypropylene-based resin constituting the fiber (hereinafter, sometimes simply referred to as the fatty acid amide compound content) is preferably 0.01% by mass to 5% by mass. By setting the fatty acid amide compound content to 0.01% by mass or more, more preferably 0.1% by mass or more, it is possible to impart appropriate slip properties and flexibility. On the other hand, by setting the fatty acid amide compound content to 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, it is possible to suppress a decrease in spinnability.

[0026] The content of the fatty acid amide compound here refers to the ratio (%) of the mass of the fatty acid amide compound to the mass of the entire fiber made of polypropylene resin. That is, for example, if the fiber is a sheath-core composite fiber and the fatty acid amide compound is contained only in the sheath component of this sheath-core composite fiber, the ratio of the mass of the fatty acid amide compound to the entire mass of the sheath-core composite fiber is calculated.

[0027] The content of the fatty acid amide compound can be measured, for example, by extracting the additive from the fiber with a solvent and quantitatively analyzing it using liquid chromatography mass spectrometry (LS / MS) etc. The extraction solvent is selected appropriately depending on the type of fatty acid amide compound, and in the case of ethylene bisstearic acid amide, for example, a method using a chloroform-methanol mixture can be mentioned.

[0028] To the polypropylene-based resin constituting the fiber according to the present invention, additives such as commonly used antioxidants, weathering stabilizers, light stabilizers, heat stabilizers, antistatic agents, antistatic aids, spinning agents, antiblocking agents, crystal nucleating agents, and pigments, or other polymers may be added as needed to impart other properties to the extent that the effects of the present invention are not impaired.

[0029] The polypropylene-based resin constituting the fiber according to the present invention is a polypropylene-based resin having long-chain branches in its main chain. A polypropylene-based resin having long-chain branches in its main chain is a polypropylene having polypropylene chains branched from the polypropylene main chain. By using a polypropylene having long-chain branches in its main chain, the long-chain branches act as tie molecules that pseudo-crosslink between microcrystals from the melt extrusion stage, and fine crystals are preferentially formed, particularly on the fiber surface, during the subsequent spinning process. The fine crystal size and pseudo-crosslinking between microcrystals make it difficult for crystal orientation to proceed, lowering the softening temperature of the fiber surface. Therefore, the fibers are strongly fused together during the spunbonding thermal bonding process, improving the strength of the spunbonded nonwoven fabric.

[0030] In the present invention, the branching index g of the polypropylene resin constituting the fiber is 0.950 or more and 0.990 or less. The branching index g of the polypropylene resin is an index indicating the degree of branching of the long chains of the polypropylene resin, and is described, for example, in "Developments in Polymer Characterization-4" (J.V. Dawkins, Applied Science Publishers, 1983). A branching index g of 0.950 or more, preferably 0.965 or more, and more preferably 0.980 or more, prevents excessively high melt tension and ensures stable spinning without insufficient stretchability during melt spinning and drawing. This is presumably because the inclusion of polypropylene with long-chain branches in the main chain promotes entanglement of tie molecules in the amorphous phase that penetrate the crystallites in the system during cooling and solidification (a pseudo-crosslinking effect between crystallites). During the subsequent drawing process, the drawing stress is uniformly transmitted throughout the system (leading to uniform drawing), thereby reducing voids within the fiber and suppressing yarn breakage. Furthermore, when the branching index g is 0.990 or less, the softening temperature is lowered due to the effect of forming microcrystals and the effect of inhibiting crystal orientation, and the fibers are strongly fused together in the thermal bonding step of spunbonding, thereby improving the strength of the spunbonded nonwoven fabric.

[0031] In the present invention, the branching index g of the polypropylene resin is measured by the following method. (1) Take three 10 mg samples from the spunbond nonwoven fabric. (2) Dissolve the above sample in 1,2,4-trichlorobenzene to a concentration of 1 mg / mL. (3) A gel permeation chromatography (GPC) device (e.g., Alliance GPC / V2000 manufactured by Waters) equipped with a differential refractometer (RI) and a viscometer, and GPCV analysis software compatible with the device (e.g., Millennium 32 ", etc.) and measure the intrinsic viscosity of the sample under the following measurement conditions. The arithmetic mean value of the intrinsic viscosity thus obtained is rounded to the fourth decimal place to obtain [η] br Let's say. Mobile phase solvent: 1,2,4-trichlorobenzene ·Flow rate: 1mL / min Column: Two connected "GMHHR-H(S)HT" columns manufactured by Tosoh Corporation Column temperature, sample injection temperature, and detector temperatures: 140°C Sample injection volume (sample loop volume): 0.2175 mL for the Waters Alliance GPC / V2000 mentioned above (4) The weight average molecular weight of the sample is measured by low angle laser light scattering photometry. (5) Under the same conditions as in (3), measure the intrinsic viscosity of a linear polypropylene resin having a weight-average molecular weight equivalent to that obtained in (4). Alternatively, if it is not possible to measure the intrinsic viscosity of a linear polypropylene resin having a weight-average molecular weight equivalent to that obtained in (4), the logarithm of the intrinsic viscosity of a linear polypropylene resin is linearly related to the logarithm of the molecular weight, as is known from the Mark-Houwink-Sakurada equation. Therefore, measure the intrinsic viscosity of a commercially available linear polypropylene resin (e.g., "Novatec PP (registered trademark) FY6" manufactured by Japan Polypropylene Corporation) and extrapolate the intrinsic viscosity to the low or high molecular weight side as appropriate to obtain a numerical value. The arithmetic mean value of the intrinsic viscosity thus obtained is rounded to four decimal places to obtain [η]. lin Let's say. (6) Calculate the branching index g using the following formula (1), and round off the obtained value to the fourth decimal place.

[0032] g=[η] br / [η] lin ···(1) Generally, when a long chain branch structure is introduced into a polymer molecule, the radius of gyration becomes smaller compared to a linear polymer molecule of the same molecular weight. As the radius of gyration becomes smaller, the intrinsic viscosity also becomes smaller. Therefore, as the long chain branch structure is introduced, the intrinsic viscosity ([η]) of a linear polypropylene of the same molecular weight becomes smaller. lin ) versus the intrinsic viscosity of branched polymers ([η] br ) ratio ([η] br / [η] lin ) tends to be smaller.

[0033] The weight average molecular weight (Mw) of the polypropylene resin constituting the fiber according to the present invention is 1.0 × 10 5 The weight average molecular weight (Mw) of this polypropylene resin is preferably 1.0×10 or more. 5 or more, preferably 1.5 x 10 5 More preferably, 2.0 × 10 5By setting the weight average molecular weight (Mw) of the polypropylene resin to 5.0×10 or more, the pseudo-crosslinking effect between the microcrystals can be sufficiently obtained. 6 The weight average molecular weight (Mw) of polypropylene can be measured, for example, by the method disclosed in M.L. McConnell, "POLYMER MOLECULAR WEIGHTS AND MOLECULAR WEIGHT DISTRIBUTIONS BY LOW-ANGLE LASER LIGHT SCATTERING," American Laboratory, May 1978, Vol. 10, pp. 63-75, i.e., by low-angle laser light scattering photometry.

[0034] The melt flow rate (hereinafter sometimes referred to as MFR) of the polypropylene-based resin constituting the fibers in the present invention is preferably 155 g / 10 min or more and 850 g / 10 min or less. By setting the MFR to 155 g / 10 min or more, more preferably 170 g / 10 min or more, and even more preferably 190 g / min or more, a spunbond nonwoven fabric with excellent texture, flexibility, and spinnability during production, and with a uniform texture, can be obtained. On the other hand, by setting the MFR to 850 g / 10 min or less, more preferably 600 g / 10 min or less, and even more preferably 400 g / 10 min or less, a decrease in the strength of the spunbond nonwoven fabric can be suppressed.

[0035] The MFR of polypropylene resins is measured according to ASTM D1238 (Method A), which specifies that polypropylene should be measured under a load of 2.16 kg and at a temperature of 230°C.

[0036] The MFR of the polypropylene resin can also be adjusted by blending two or more polypropylene resins with different MFRs in any ratio. In this case, the MFR of the resin blended with the main polypropylene resin is preferably 10 g / 10 min or more, more preferably 20 g / 10 min or more, and even more preferably 30 g / 10 min or more. It is also preferably 1000 g / 10 min or less, more preferably 800 g / 10 min or less, and even more preferably 600 g / 10 min or less. By adjusting the MFR to the above range, partial viscosity unevenness in the blended polypropylene resin can be suppressed, and non-uniformity in fineness and deterioration of spinnability can be prevented.

[0037] The MFR can be controlled by the weight-average molecular weight of the polypropylene resin. The higher the weight-average molecular weight of the polypropylene resin, the smaller the MFR. Alternatively, the MFR may be adjusted by adding at least one radical generator selected from the group consisting of organic peroxides, azo compounds, and nitroxides to the polypropylene resin to decompose the polypropylene resin.

[0038] The mesopentad fraction (mmmm) of the polypropylene resin constituting the fiber in the present invention is preferably 0.950 or more and 0.995 or less, more preferably 0.965 or more, and particularly preferably 0.980 or more.

[0039] The mesopentad fraction (mmmm) is an index of the stereoregularity of the crystalline phase of polypropylene measured by nuclear magnetic resonance (NMR). A higher value indicates higher stereoregularity, and therefore higher crystallinity and melting point. When the mesopentad fraction of a polypropylene resin is 0.950 or higher, the high crystallinity improves the strength of the spunbond yarn, resulting in a spunbond nonwoven fabric with sufficient mechanical strength for practical use. A mesopentad fraction of 0.995 or lower maintains spinnability during melt spinning, enabling stable spunbond nonwoven fabrics. This is because the preferential formation and growth of microcrystalline nuclei prevents yarn sway during fineness reduction and prevents yarns from fusing together even when they come into contact with each other, thereby preventing yarn breakage due to the entanglement of surrounding yarns.

[0040] The mesopentad fraction (mmmm) is 13 C nuclear magnetic resonance ( 13 The isotactic fraction is the pentad unit in the polypropylene molecular chain measured using C-NMR, and is measured by a well-known method (for example, the method described in A. Zambelli, "Macromolecules", 1973, Vol. 6, p. 625, or the same, "Macromolecules", 1975, Vol. 8, p. 687). 13 It is measured by the intensity fraction of the [mmmm] peak among all absorption peaks in the methyl carbon region of the C-NMR spectrum.

[0041] [Fibers that make up spunbond nonwoven fabric] The fibers constituting the spunbonded nonwoven fabric of the present invention preferably have an average single fiber diameter of 6.5 μm or more and 14.5 μm or less. By having an average single fiber diameter of preferably 6.5 μm or more, more preferably 7.5 μm or more, and even more preferably 8.4 μm or more, a spunbonded nonwoven fabric with a smooth surface feel suitable for sanitary materials, masks, etc. can be obtained. During production, a decrease in spinnability can be prevented, enabling the stable production of high-quality spunbonded nonwoven fabrics. On the other hand, by having an average single fiber diameter of preferably 14.5 μm or less, more preferably 11.7 μm or less, and even more preferably 11.2 μm or less, single fibers are more likely to fuse together, increasing the number of fused fiber sites per unit area, and therefore a spunbonded nonwoven fabric with high strength can be obtained.

[0042] The average single fiber diameter (μm) of the fibers constituting the spunbonded nonwoven fabric of the present invention is calculated by the following procedure. (1) Ten small samples of spunbond nonwoven fabric are randomly taken. (2) Surface photographs are taken at a magnification of 500 to 1000 times using a scanning electron microscope (SEM, for example, Keyence Corporation's "VHX-D500"), and the widths of 10 fibers from each surface photograph are measured, for a total of 100 fibers. (3) The average single fiber diameter (μm) was calculated by taking the arithmetic mean value (μm) of the measured values ​​of 100 fibers to the first decimal place.

[0043] The coefficient of variation of the single fiber diameter of the fibers constituting the spunbonded nonwoven fabric (hereinafter sometimes simply referred to as the CV value of the single fiber diameter) is preferably 7% or less. By setting the CV value of the single fiber diameter to preferably 7% or less, more preferably 6% or less, and even more preferably 5% or less, it is possible to prevent the surface from feeling rough and to obtain a highly uniform spunbonded nonwoven fabric. The CV value of the single fiber diameter is largely determined by the uniformity of the spinneret back pressure, yarn cooling conditions, and drawing conditions, and can be controlled by appropriately adjusting these.

[0044] [Spunbond nonwoven fabric] The basis weight of the spunbond nonwoven fabric of the present invention is 5 g / m 2 More than 100g / m 2 The basis weight is preferably 5 g / m or less. 2 More preferably, 10 g / m 2 More preferably, it should be 15 g / m or more. 2 By adjusting the weight to the above, a spunbond nonwoven fabric having a mechanical strength sufficient for practical use can be obtained. On the other hand, the weight per unit area is preferably 100 g / m 2 Less than 50 g / m 2 or less, more preferably 30 g / m 2 By making the following, it is possible to obtain a spunbond nonwoven fabric having appropriate flexibility suitable for practical use of the nonwoven fabric.

[0045] In the present invention, the basis weight of the spunbond nonwoven fabric is determined in accordance with "6.2 Mass per unit area" of JIS L1913:2010 "Testing methods for general nonwoven fabrics" and is measured by the following procedure. (1) Take three 20cm x 25cm test pieces per meter of sample width. (2) Weigh the mass (g) of each at standard conditions. (3) The arithmetic mean value is 1 m 2 Mass per unit (g / m 2 ) and round off to the first decimal place.

[0046] The thickness of the spunbond nonwoven fabric of the present invention is preferably 0.05 mm or more and 1.5 mm or less. By having a thickness of preferably 0.05 mm or more, more preferably 0.08 mm or more, and even more preferably 0.1 mm or more, or by having a thickness of preferably 1.5 mm or less, more preferably 1 mm or less, and even more preferably 0.8 mm or less, the spunbond nonwoven fabric can be provided with flexibility and appropriate cushioning properties, making it suitable for practical use.

[0047] In the present invention, the thickness (mm) of the spunbond nonwoven fabric is the value measured in accordance with "5.1 Thickness" of JIS L1906:2000 "Testing methods for general long-fiber nonwoven fabrics."

[0048] The apparent density of the spunbond nonwoven fabric of the present invention is 0.05 g / cm 3 More than 0.30g / cm 3 The apparent density of the spunbond nonwoven fabric is preferably 0.30 g / cm or less. 3 or less, more preferably 0.25 g / cm 3 or less, more preferably 0.20 g / cm 3 By satisfying the above condition, it is possible to achieve a soft texture without impairing the strength of the spunbonded nonwoven fabric.

[0049] On the other hand, the apparent density of the spunbond nonwoven fabric is preferably 0.05 g / cm 3 More preferably, 0.08 g / cm 3 More preferably, it is 0.10 g / cm 3 By doing so, it is possible to suppress the occurrence of fluffing and delamination and to obtain a spunbond nonwoven fabric having sufficient strength for practical use.

[0050] In the present invention, the apparent density (g / cm 3 ) is calculated from the basis weight and thickness above before rounding using the following formula, and is rounded to the third decimal place. Apparent density (g / cm 3 ) = [weight (g / m 2 )] / [Thickness (mm)]×10 -3 .

[0051] In the present invention, the tensile strength per unit area of ​​a spunbond nonwoven fabric is determined in accordance with "6.3 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "Testing methods for general nonwoven fabrics" and is measured by the following procedure. (1) Take three 50mm x 300mm test pieces per meter of nonwoven fabric width, with the long side facing the longitudinal direction (lengthwise direction of the nonwoven fabric) and the transverse direction (widthwise direction of the nonwoven fabric). (2) Set the test piece in the tensile testing machine with a gripping distance of 200 mm. (3) A tensile test is carried out at a tensile speed of 100 mm / min, and the maximum strength is measured. (4) Obtain the average value of the maximum strength measured for each test piece, calculate the tensile strength per unit area based on the following formula, and round off to the first decimal place. Tensile strength per unit area ((N / 25mm) / (g / m 2 )) = [Average maximum strength (N / 25mm)] / Weight (g / m 2 ).

[0052] The spunbond nonwoven fabric of the present invention has a longitudinal tensile strength per unit area of ​​1.4 (N / 25 mm) / (g / m 2 ) or more 3.0(N / 25mm) / (g / m 2 ) or less. The tensile strength per unit area is preferably 1.4 (N / 25 mm) / (g / m 2 ) or more, more preferably 1.5 (N / 25mm) / (g / m 2 ) or more, more preferably 1.6 (N / 25mm) / (g / m 2 ) or more, a spunbond nonwoven fabric having a strength sufficient for practical use can be obtained. On the other hand, the tensile strength in the transverse direction per basis weight is preferably 3.0 (N / 25 mm) / (g / m 2 ) or less, it is possible to prevent the flexibility of the spunbonded nonwoven fabric from decreasing and the texture from being impaired. The tensile strength in the machine direction per unit weight can be controlled by appropriately adjusting the MFR of the polypropylene resin, additives, average single fiber diameter, and / or the spinning speed and thermal bonding conditions (shape of the bonded part, compression ratio, temperature, linear pressure, etc.) described below.

[0053] The tensile strength in the cross direction per unit area of ​​the spunbond nonwoven fabric of the present invention is 0.4 (N / 25 mm) / (g / m 2) or more 2.0(N / 25mm) / (g / m 2 The tensile strength per unit area is preferably 0.4 (N / 25 mm) / (g / m 2 ) or more, more preferably 0.6 (N / 25mm) / (g / m 2 ) or more, more preferably 0.8 (N / 25mm) / (g / m 2 ) or more, a spunbond nonwoven fabric having a strength sufficient for practical use can be obtained. On the other hand, the tensile strength in the transverse direction per basis weight is preferably 2.0 (N / 25 mm) / (g / m 2 ) or less, it is possible to prevent the flexibility of the spunbond nonwoven fabric from decreasing and the texture from being damaged. Spunbond nonwoven fabrics have tensile strength in both the longitudinal and transverse directions, but the transverse tensile strength is generally smaller than the longitudinal tensile strength. Therefore, it is necessary to set the transverse tensile strength per basis weight to 0.4 (N / 25mm) / (g / m 2 ) or more 2.0(N / 25mm) / (g / m 2 ) or less, a spunbonded nonwoven fabric having sufficient strength for practical use in the machine direction can be obtained. The tensile strength in the machine direction per unit area can be controlled by appropriately adjusting the MFR of the polypropylene resin, additives, average single fiber diameter, and / or the spinning speed and thermal bonding conditions (shape of the bonded portion, compression ratio, temperature, linear pressure, etc.) described below.

[0054] The spunbond nonwoven fabric of the present invention has physical properties that allow it to withstand practical use even when made with a low basis weight, and as an environmentally friendly nonwoven fabric that can reduce the amount of plastic raw materials, it can be widely used in hygiene materials, medical materials, daily living materials, industrial materials, etc. In particular, it can be suitably used in hygiene materials such as disposable diapers, sanitary products, and base fabrics for compresses, and in medical materials such as protective clothing and surgical gowns.

[0055] [Manufacturing method of spunbond nonwoven fabric] Next, a preferred embodiment of the method for producing the spunbonded nonwoven fabric of the present invention will be specifically described.

[0056] The spunbond nonwoven fabric of the present invention is a long-fiber nonwoven fabric produced by the spunbonding method. The spunbonding method is excellent in productivity and mechanical strength, and also suppresses the fuzzing and fiber shedding that are common in short-fiber nonwoven fabrics. Furthermore, laminating multiple layers of collected spunbond nonwoven fiber webs or thermocompression-bonded spunbond nonwoven fabrics (both denoted as S) in SS, SSS, and SSSS configurations is a preferred embodiment, as it improves productivity and uniformity of fabrication.

[0057] The raw material resin used in the method for producing the spunbonded nonwoven fabric of the present invention is a propylene-based resin in which the main repeating unit is propylene. Here, "main repeating unit" means that the repeating unit accounts for 90 mol% or more of the entire resin. Therefore, specific examples of the raw material resin include a propylene homopolymer or a copolymer of propylene and various α-olefins. When a copolymer of propylene and various α-olefins is used as the raw material resin, the copolymerization ratio of the various α-olefins is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 3 mol% or less, from the viewpoint of increasing strength.

[0058] The raw material resin used in the present invention may be blended with other component resins as long as the effects of the present invention are not impaired. Examples of other component resins include polyolefin resins such as polyethylene and poly-4-methyl-1-pentene, which have melting points close to those of polypropylene, as well as low-melting-point polyester resins and low-melting-point polyamide resins. Low-crystalline olefin resins are preferred for imparting flexibility. For example, ethylene-propylene copolymers are suitable as low-crystalline olefin resins. The mass ratio of the other component resin is preferably 20% by mass or less, more preferably 10% by mass or less, in order to fully exhibit the properties of the polypropylene resin.

[0059] The raw resin may also be a so-called recycled resin, which is a material recycled resin. The resin raw material to be recycled must have a melt flow rate that allows it to be melt-spun by the spunbonding method. Therefore, recycled raw materials with the desired melt flow rate may be remelted and used. If the raw resin does not have the desired melt flow rate, at least one radical generator selected from the group consisting of organic peroxides, azo compounds, and nitroxides may be added to the raw resin to reduce the molecular weight of the raw resin and adjust the melt flow rate. The use of recycled resins is desirable because it reduces the amount of virgin petrochemical raw materials used and reduces the environmental impact during the production of spunbonded nonwoven fabrics.

[0060] Examples of the organic peroxides include ketone peroxides such as methyl ethyl ketone peroxide and methyl isobutyl ketone peroxide, diacyl peroxides such as dibenzoyl peroxide, di-(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, didecanoyl peroxide and di-(2,4-dichlorobenzoyl) peroxide, hydroperoxides such as t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide and 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3, α,α'-bis(t-butylperoxide), and α,α'-bis(t-butylperoxide). peroxyketals such as 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane and 2,2-bis(t-butylperoxy)butane; alkyl peresters such as t-butyl peroxyoctoate, t-butyl peroxypivalate, t-butyl peroxyneodecanoate and t-butyl peroxybenzoate; and peroxycarbonates such as di-(2-ethylhexyl)peroxydicarbonate, diisopropyl peroxydicarbonate, bis(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butyl peroxydicarbonate and t-butylperoxyisopropyl carbonate. Among these, dialkyl peroxides are preferred because of their easy control of MFR.

[0061] Examples of the azo compounds include azobisisobutyronitrile and azobisisovaleronitrile.

[0062] The nitroxide may be a sterically hindered hydroxylamine ester.

[0063] When the raw material resin is directly melt-spun, a method using an extruder such as a single-screw or twin-screw extruder can be applied. The radical generator may be kneaded and pelletized in an extruder before being subjected to spinning to form a polypropylene-based resin, or a method may be employed in which the raw material resin and the radical generator are kneaded during spinning using the extruder of a spinning machine to obtain the polypropylene-based resin simultaneously with melt spinning.

[0064] In the present invention, in order to set the branching index g within the above range, in addition to the method of using a polypropylene resin having a branching index g corresponding to the above range, a method of blending a branched polypropylene resin having a branched structure with a linear polypropylene resin, a method of introducing a long-chain branched structure into polypropylene molecules as described in JP-A-62-121704, or a method as described in Japanese Patent No. 2869606 are preferably used. Among these, the method of blending a branched polypropylene resin with a linear polypropylene resin is preferred because it allows for easy adjustment of the branching index g.

[0065] The amount of branched polypropylene resin blended with the linear polypropylene resin is preferably 1% by mass or more and 20% by mass or less. By adding an amount of preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, crystal growth in the fibers is inhibited, resulting in finer crystals. This inhibits crystal orientation, lowering the softening temperature of the fiber surface, allowing the fibers to fuse firmly together during the spunbonding thermal bonding process, resulting in a high-strength spunbond nonwoven fabric. By adding an amount of preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, yarn strength can be increased while maintaining the thermal adhesiveness of the spunbonding process, without excessively inhibiting crystal growth in the fibers.

[0066] Specific examples of the branched chain polypropylene resin include polypropylene manufactured by Basell (for example, type names: "PF-814," "PF-633," "PF-611," "SD-632," etc.), polypropylene manufactured by Borealis (for example, type name: "WB130HMS"), and polypropylene manufactured by Dow (for example, type names: "D114," "D201," "D206," etc.).

[0067] The term "branched polypropylene" as used herein refers to polypropylene having five or less internal tri-substituted olefins per 10,000 carbon atoms. The presence of these internal tri-substituted olefins is 1 This can be confirmed by the proton ratio in the H-NMR spectrum.

[0068] The spinning temperature when melting and spinning the polypropylene-based resin is preferably 200° C. or higher and 270° C. or lower, more preferably 210° C. or higher, even more preferably 220° C. or higher, and more preferably 260° C. or lower, even more preferably 250° C. or lower. By setting the spinning temperature within the above range, a stable molten state can be achieved, and excellent spinning stability can be obtained.

[0069] The back pressure of the spinneret is preferably 0.1 MPa or more and 6.0 MPa or less. By setting the back pressure to preferably 0.1 MPa or more, more preferably 0.3 MPa or more, and even more preferably 0.5 MPa or more, it is possible to suppress deterioration of discharge uniformity and the occurrence of fiber diameter variations. On the other hand, by setting the back pressure to 6.0 MPa or less, it is possible to prevent the spinneret from being enlarged in order to increase pressure resistance. The back pressure of the spinneret can be adjusted by the nozzle hole diameter, nozzle hole depth, spinning temperature, etc. of the spinneret, and among these, the nozzle hole diameter has a large contribution.

[0070] Subsequently, the spun continuous fiber yarn is cooled. Examples of methods for cooling the spun yarn include forcibly blowing cold air onto the yarn, naturally cooling at the ambient temperature around the yarn, and adjusting the distance between the spinneret and the ejector. Alternatively, a combination of these methods can be used. The cooling conditions can be appropriately adjusted taking into account the output per hole of the spinneret, the spinning temperature, the ambient temperature, and the like.

[0071] The cooled and solidified filaments are drawn by compressed air injected from an ejector. The spinning speed is preferably 3500 m / min to 6500 m / min, more preferably 4000 m / min to 6500 m / min, and even more preferably 4500 m / min to 6500 m / min. Setting the spinning speed to 3500 m / min to 6500 m / min results in high productivity, promotes fiber orientation and crystallization, and enables the production of high-strength long fibers. Normally, increasing the spinning speed deteriorates spinnability and makes it difficult to stably produce filaments. However, by using a polypropylene-based resin having an MFR within a specific range, the intended polypropylene fiber can be spun stably.

[0072] The resulting long fibers are then collected on a moving net or the like to obtain a nonwoven fiber web. When the fibers are drawn at a high spinning speed, the fibers coming out of the ejector are collected on the net under controlled conditions by a high-speed airflow, making it easier to obtain a nonwoven fabric with minimal fiber entanglement and high uniformity.

[0073] In this case, it is a preferred embodiment that the ratio of spinning speed to line speed is at least 18. By setting the ratio of spinning speed to line speed to preferably at least 18, more preferably at least 20, the fibers can be collected on the moving net in a state where they are oriented in the machine direction, and a nonwoven fabric with high strength in the machine direction can be obtained.

[0074] Methods for uniformly aligning the fiber orientation of the yarn ejected from the ejector include a method of guiding the yarn by placing an angled flat plate between the ejector and the net, a method of providing the above-mentioned flat plate with multiple grooves at different angles to separate the yarn into yarns that fall along the flat plate and yarns that fall along the grooves, and dispersing and spreading them in the flow direction of the nonwoven fiber web, and a method of arranging multiple flat plates with different angles in a comb-like pattern at the ejector outlet and causing the yarns to fall along each plate, thereby further dispersing and spreading them in the flow direction of the nonwoven fiber web.

[0075] Among these, a method in which a plurality of flat plates with different angles are arranged in a comb-like pattern at the outlet of an ejector and the yarns are dropped along each of the flat plates to spread them is a preferred embodiment for aligning the orientation direction of the fibers, since this method efficiently disperses the fine fiber diameter yarns in the flow direction of the nonwoven fiber web and allows for spreading in a controlled manner without slowing down the web as much as possible.

[0076] In another preferred embodiment, a nonwoven fiber web obtained by collecting fibers on a net is temporarily bonded by contacting one side of the web with a hot flat roll on the net. This prevents the surface layer of the nonwoven fiber web from turning over or being blown away while being transported on the net, thereby improving transportability from collecting the yarns to thermal bonding.

[0077] The nonwoven fiber web thus obtained can then be thermally bonded to obtain the intended spunbond nonwoven fabric. The method for thermally bonding the nonwoven fiber web is not particularly limited, and examples include methods using various rolls, such as a thermal embossing roll, each of which has an engraved (uneven) surface on the surface of a pair of upper and lower rolls, a thermal embossing roll consisting of a combination of one roll with a flat (smooth) surface and the other with an engraved (uneven) surface, and a thermal calender roll consisting of a combination of a pair of upper and lower flat (smooth) rolls, as well as a method using ultrasonic vibrations from a horn (ultrasonic bonding).

[0078] Among these, a preferred embodiment is to use a heat embossing roll in which a pair of upper and lower rolls each have an engraved (uneven) surface, or a heat embossing roll consisting of a combination of a roll with one flat (smooth) surface and a roll with an engraved (uneven) surface, because these rolls are highly productive, provide strength in the partially bonded areas, and retain the texture and feel unique to nonwoven fabrics in the non-bonded areas.

[0079] As for the surface material of the hot embossing roll, a pair of metal rolls is preferred in order to obtain a sufficient thermocompression effect and to prevent the engraving (concave and convex portions) of one embossing roll from being transferred to the surface of the other roll.

[0080] The embossed adhesive area ratio using a hot embossing roll is preferably 5% or more and 30% or less. By setting the adhesive area to preferably 5% or more, more preferably 8% or more, and even more preferably 10% or more, it is possible to obtain a strength sufficient for practical use as a spunbond nonwoven fabric. On the other hand, by setting the adhesive area to preferably 30% or less, more preferably 25% or less, and even more preferably 20% or less, it is possible to obtain appropriate flexibility suitable for practical use. Even when ultrasonic bonding is used, it is preferable that the adhesive area ratio be in a similar range.

[0081] The bonded area ratio here refers to the proportion of the bonded area to the entire spunbonded nonwoven fabric. Specifically, when thermal bonding is performed using a pair of uneven rolls, it refers to the proportion of the area (bonded area) where the convex areas of the upper roll and the convex areas of the lower roll overlap and contact the nonwoven fiber web to the entire spunbonded nonwoven fabric. When thermal bonding is performed using an uneven roll and a flat roll, it refers to the proportion of the area (bonded area) where the convex areas of the uneven roll contact the nonwoven fiber web to the entire spunbonded nonwoven fabric. When ultrasonic bonding is performed, it refers to the proportion of the area (bonded area) that is thermally welded by ultrasonic processing to the entire spunbonded nonwoven fabric.

[0082] The shape of the bonded areas formed by hot embossing or ultrasonic bonding is not particularly limited, but may be, for example, a circle, ellipse, square, rectangle, parallelogram, rhombus, regular hexagon, or regular octagon. Furthermore, it is preferable that the bonded areas are uniformly spaced at regular intervals in both the longitudinal direction (machine direction) and the width direction of the spunbonded nonwoven fabric. This reduces the variation in strength of the spunbonded nonwoven fabric.

[0083] In a preferred embodiment, the surface temperature of the hot embossing roll during thermal bonding is at least -50°C and at most -10°C lower than the melting point of the polypropylene resin used (hereinafter sometimes referred to as Tm (°C)) (i.e., (Tm - 50°C) to (Tm - 10°C)). By setting the surface temperature of the hot roll to at least -50°C (i.e., Tm - 50°C, hereinafter the same) lower than the melting point of the polypropylene resin, and more preferably at least -45°C (Tm - 45°C), a spunbond nonwoven fabric with adequate thermal bonding strength can be obtained. Furthermore, by setting the surface temperature of the hot embossing roll to at most -10°C (Tm - 10°C) lower than the melting point of the polypropylene resin, and more preferably at most -15°C (Tm - 15°C), excessive thermal bonding can be suppressed, and appropriate flexibility for practical use can be obtained.

[0084] The linear pressure of the hot embossing roll during thermal bonding is preferably 50 N / cm or more and 500 N / cm or less. By setting the roll linear pressure to preferably 50 N / cm or more, more preferably 100 N / cm or more, and even more preferably 150 N / cm or more, it is possible to obtain a spunbond nonwoven fabric with adequate thermal bonding strength for practical use. On the other hand, by setting the linear pressure of the hot embossing roll to preferably 500 N / cm or less, more preferably 400 N / cm or less, and even more preferably 300 N / cm or less, it is possible to obtain adequate flexibility for practical use.

[0085] Furthermore, in order to adjust the thickness of the spunbonded nonwoven fabric, it is possible to apply thermocompression bonding using a thermal calendar roll consisting of a pair of upper and lower flat rolls before and / or after thermal bonding using the above-mentioned thermal embossing roll. The pair of upper and lower flat rolls refers to metal rolls or elastic rolls with smooth surfaces, and a pair of metal rolls or a pair of metal rolls and elastic rolls can be used.

[0086] The term "elastic roll" used herein refers to a roll made of a material that has greater elasticity than a metal roll, and examples of the elastic roll include so-called paper rolls made of paper, cotton, aramid paper, etc., and resin rolls made of urethane resin, epoxy resin, silicon resin, polyester resin, hard rubber, and mixtures of these.

[0087] In the method for producing a spunbonded nonwoven fabric of the present invention, a functional agent may be added to the obtained spunbonded nonwoven fabric. Examples of the functional agent include, but are not limited to, a hydrophilic agent, a water repellent agent, an oil repellent agent, an antistatic agent, an antibacterial agent, an antiviral agent, a deodorizer, an aromatic agent, and a cooling agent.

[0088] The method for applying the functional agent is not particularly limited, and impregnation, spraying, kiss roll, etc. can be used. [Example]

[0089] Next, the spunbond nonwoven fabric of the present invention will be described in detail based on examples. However, the present invention is not limited to these examples. In addition, the physical properties were measured according to the above-mentioned methods unless otherwise specified.

[0090] [Measurement method] (1) Melt flow rate (MFR) of polypropylene resin (g / 10 min): Measurements were taken at 230°C and 2.16 kg in accordance with JIS K7210-1 (2014). (2) Branching index g(-) of polypropylene resin: The branching index g of polypropylene resins was measured using a gel permeation chromatography (GPC) device equipped with a differential refractometer (RI) and a viscometer, "Alliance GPC / V2000" manufactured by Waters, and GPCV analysis software, "Millennium" manufactured by Waters. 32 " was used as the mobile phase solvent, 1,2,4-trichlorobenzene to which the antioxidant "Irganox 1076" manufactured by BASF Japan Ltd. was added at a concentration of 0.5 mg / mL, and "Novatec PP (registered trademark) FY6" manufactured by Japan Polypropylene Corporation was used as the linear polypropylene resin. The sample injection volume (sample loop volume) was set to 0.2175 mL, and measurements were carried out according to the above-mentioned method.

[0091] (3) Mesopentad fraction of polypropylene resin (mmmm) (-) A polypropylene resin sample is dissolved in a solvent. 13 The mesopentad fraction (mmmm) was determined using C-NMR under the following conditions. In addition to the above-mentioned literature, the measurement was performed with reference to "New Edition Polymer Analysis Handbook" edited by the Japan Society for Analytical Chemistry and the Polymer Analysis Research Forum, Kinokuniya Shoten, January 1995, pp. 609-611. A. Measurement conditions Equipment: Bruker "DRX-500" Measurement nuclei: 13 C nucleus (resonance frequency: 125.8MHz) ·Measurement concentration: 10% by mass Solvent: Benzene / d-o-dichlorobenzene = 1:3 mass ratio mixed solution ·Measurement temperature: 130℃ Spin speed: 12Hz NMR sample tube: 5mm tube Pulse width: 45° (4.5μs) Pulse repetition time: 10 seconds Data points: 64K Conversion count: 10,000 Measurement mode: complete decoupling B.Analysis conditions Fourier transformation was performed with a line broadening factor (LB) of 1.0, and the mmmm peak was determined to be 21.86 ppm. Peak splitting was performed using WINFIT software (Bruker). Peak splitting was performed as follows, starting from the peak on the high magnetic field side, and automatic peak fitting was performed using the accompanying software. After optimizing the peak splitting, the sum of the mmmm peak fractions was calculated. The above measurement was performed five times, and the average value was used as the mesopentad fraction (mmmm) of this sample. ·peak (a)mrrm (b)mrrr (c)rrrr (d)rmrm (e)rmrr (f)mmrm (g)mmrr (h)rmmr (i) mmmr (j)mmmm.

[0092] (4) Average single fiber diameter (μm): The scanning electron microscope (SEM) used was a VHX-D500 manufactured by Keyence Corporation, and measurements were carried out according to the above-mentioned method.

[0093] (5) Weight (g / m 2 ): Based on JIS L1913:2010 "General nonwoven fabric test method" 6.2 "Mass per unit area", 20cm x 25cm test pieces are taken, three pieces per 1m width of the sample, and the mass (g) of each piece is measured under standard conditions, and the average value is calculated for 1m. 2 Mass per unit (g / m 2 ) is expressed as

[0094] (6) Tensile strength per unit area of ​​spunbond nonwoven fabric ((N / 25mm) / (g / m 2 )): The measurement was performed using the RTG-1250 manufactured by A&D Co., Ltd. using the method described above.

[0095] [Example 1] (Polypropylene resin) The linear polypropylene resin used was a polypropylene with an MFR of 200 g / 10 min, a branching index g of 1.000, and a mesopentad fraction (mmmm) of 0.990. The branched polypropylene resin used was a polypropylene with an MFR of 2.7 g / 10 min, a branching index g of 0.600, and a mesopentad fraction (mmmm) of 0.940 (Basell's "Profax PF-814"). These resins were mixed so that the linear polypropylene resin was 97% by mass and the branched polypropylene resin was 3% by mass, resulting in a polypropylene resin with an MFR of 197 g / 10 min, a branching index g of 0.988, a mesopentad fraction of 0.989, and a melting point of 160°C.

[0096] (spunbond nonwoven fabric) The polypropylene resin was fed into a single-screw extruder, melted at a spinning temperature of 240°C, and spun from a rectangular die with a hole diameter of 0.40 mm at a single-hole throughput rate of 0.40 g / min. The resulting filaments were cooled and solidified, and then pulled and stretched in a rectangular ejector using compressed air at a pressure of 0.45 MPa. The spinning speed was 4019 m / min. The filaments were then collected on a moving net to obtain a nonwoven fiber web. The resulting nonwoven fiber web was then thermally bonded under conditions of a linear pressure of 500 N / cm and a thermal bonding temperature of 140°C, resulting in an average single fiber diameter of 11.8 μm and a basis weight of 30 g / m. 2 A spunbond nonwoven fabric of the above formula was obtained. The heat embossing rolls used were a pair of upper and lower heat embossing rolls, with the upper roll being a metal embossing roll engraved with a polka dot pattern and having an adhesive area ratio of 11%, and the lower roll being a metal flat roll. The tensile strength per unit area in the machine direction and cross direction of the obtained spunbond nonwoven fabric was evaluated. The results are shown in Table 1.

[0097] [Example 2] In Example 1 (polypropylene resin), the linear polypropylene resin was mixed in an amount of 96 mass% and the branched polypropylene resin in an amount of 4 mass%, resulting in a polypropylene resin having an MFR of 193 g / 10 min, a branching index g of 0.984, a mesopentad fraction of 0.988, and a melting point of 160°C. In Example 1 (spunbond nonwoven fabric), the single-hole output rate was changed to 0.50 g / min and the spinning speed to 4858 m / min, but the same procedures were followed as in Example 1, resulting in a fiber having an average single fiber diameter of 12.0 μm and a basis weight of 30 g / m. 2 The spunbonded nonwoven fabric was thus obtained. The tensile strength per unit area in the machine direction and the cross direction of the obtained spunbonded nonwoven fabric was evaluated. The results are shown in Table 1.

[0098] [Example 3] In Example 1 (polypropylene resin), the linear polypropylene resin was mixed in an amount of 92 mass% and the branched polypropylene resin in an amount of 8 mass%, resulting in a polypropylene resin having an MFR of 184 g / 10 min, a branching index g of 0.968, a mesopentad fraction of 0.986, and a melting point of 160°C. In Example 1 (spunbond nonwoven fabric), the single-hole output rate was changed to 0.50 g / min, and the spinning speed was changed to 5024 m / min. The same procedures as in Example 1 were repeated except that the average single fiber diameter of the constituent fibers was 11.8 μm and the basis weight was 30 g / m. 2 The spunbonded nonwoven fabric was thus obtained. The tensile strength per unit area in the machine direction and the cross direction of the obtained spunbonded nonwoven fabric was evaluated. The results are shown in Table 1.

[0099] [Example 4] In Example 1 (polypropylene resin), the linear polypropylene resin was mixed in an amount of 89 mass% and the branched polypropylene resin in an amount of 11 mass%, resulting in a polypropylene resin having an MFR of 173 g / 10 min, a branching index g of 0.956, a mesopentad fraction of 0.985, and a melting point of 160°C. In Example 1 (spunbond nonwoven fabric), the single-hole output rate was changed to 0.60 g / min, and the spinning speed was changed to 3586 m / min. The same procedures as in Example 1 were repeated except that the average single fiber diameter of the constituent fibers was 15.3 μm and the basis weight was 30 g / m.2 The spunbonded nonwoven fabric was evaluated for tensile strength per unit area in the machine direction and cross direction. The results are shown in Table 1.

[0100] [Example 5] In Example 1 (polypropylene resin), the linear polypropylene resin was mixed in an amount of 90 mass% and the branched polypropylene resin in an amount of 10 mass%, resulting in a polypropylene resin having an MFR of 176 g / 10 min, a branching index g of 0.960, a mesopentad fraction of 0.958, and a melting point of 160°C. In Example 1 (spunbond nonwoven fabric), the single-hole output rate was changed to 0.60 g / min, and the spinning speed was changed to 3586 m / min. The same procedures as in Example 1 were repeated except that the average single fiber diameter of the constituent fibers was 15.3 μm and the basis weight was 30 g / m. 2 The spunbonded nonwoven fabric was evaluated for tensile strength per unit area in the machine direction and cross direction. The results are shown in Table 1.

[0101] [Table 1]

[0102] [Comparative Example 1] In Example 1 (polypropylene resin), only polypropylene having an MFR of 200 g / 10 min, a branching index g of 1.000, and a mesopentad fraction (mmmm) of 0.940 was used as the linear polypropylene resin, and no branched polypropylene resin was used. The same procedure as in Example 1 was repeated except that the average single fiber diameter of the constituent fibers was 11.8 μm and the basis weight was 30 g / m. 2 The spunbonded nonwoven fabric was thus obtained. The tensile strength per unit area in the machine direction and the cross direction of the obtained spunbonded nonwoven fabric was evaluated. The results are shown in Table 2.

[0103] Comparative Example 2 In Example 1 (polypropylene resin), polypropylene having an MFR of 200 g / 10 min, a branching index g of 1.000, and a mesopentad fraction (mmmm) of 0.940 was used as the linear polypropylene resin, and the linear polypropylene resin and the branched polypropylene resin were mixed in amounts of 85 mass% and 15 mass% to obtain a polypropylene resin having an MFR of 166 g / 10 min, a branching index g of 0.940, a mesopentad fraction of 0.940, and a melting point of 160°C. In Example 1 (spunbond nonwoven fabric), the spinning speed was changed to 3823 m / min, but the same procedures were followed as in Example 1, with the exception that the average single fiber diameter of the constituent fibers was 12.1 μm and the basis weight was 30 g / m. 2 The spunbonded nonwoven fabric was thus obtained. The tensile strength per unit area in the machine direction and the cross direction of the obtained spunbonded nonwoven fabric was evaluated. The results are shown in Table 2.

[0104] [Table 2]

[0105] In the spunbond nonwoven fabrics of Examples 1 to 5, the branching index g of the polypropylene resin is 0.950 or more and 0.990 or less, and the tensile strength per basis weight is 1.4 ((N / 25 mm) / (g / m 2 )) or more, width is 0.4 ((N / 25mm) / (g / m 2 )) As a result, a high-strength spunbond nonwoven fabric was obtained.

[0106] On the other hand, the spunbonded nonwoven fabric of Comparative Example 1 had a branching index g of the polypropylene resin greater than 0.995, which resulted in strong adhesion in the thermal bonding process and a weak tensile strength per unit area weight.The spunbonded nonwoven fabric of Comparative Example 2 had a branching index g of the polypropylene resin less than 0.950, which resulted in weak yarn strength and a weak tensile strength per unit area weight.

[0107] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

Claims

1. A spunbond nonwoven fabric made of fibers made of a polypropylene-based resin, wherein the branching index g of the polypropylene-based resin constituting the fibers is 0.950 or more and 0.990 or less.

2. 2. The spunbonded nonwoven fabric according to claim 1, wherein the average single fiber diameter of the fibers constituting the spunbonded nonwoven fabric is 6.5 μm or more and 14.5 μm or less.

3. 3. The spunbond nonwoven fabric according to claim 1, wherein the polypropylene resin constituting the fibers has a melt flow rate of 155 g / 10 min or more and 850 g / 10 min or less.

4. The spunbond nonwoven fabric according to any one of claims 1 to 3, wherein the mesopentad fraction (mmmm) of the polypropylene-based resin constituting the fibers is 0.950 or more and 0.995 or less.

5. The basis weight of the spunbond nonwoven fabric is 5 g / m ２ More than 100g / m ２ The spunbond nonwoven fabric according to any one of claims 1 to 4, wherein:

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