WO2024070467A1

WO2024070467A1 - Spunbond nonwoven fabric and production method therefor, laminated nonwoven fabric, and hygenic material and clothing using spunbond nonwoven fabric and laminated nonwoven fabric

Info

Publication number: WO2024070467A1
Application number: PCT/JP2023/031734
Authority: WO
Inventors: 昇平原; 匠平土屋; 大士勝田; 健太郎梶原; 茂俊前川
Original assignee: 東レ株式会社
Priority date: 2022-09-27
Filing date: 2023-08-31
Publication date: 2024-04-04

Abstract

In order to provide a spunbond nonwoven fabric that has flexibility and excellent mechanical properties and that allows easy high-level processing such as pleating and bonding with other members, this spunbond nonwoven fabric is formed from fibers constituted of a polypropylene resin and satisfies conditions (1) to (3) below, the average single fiber diameter being 5.0 μm to 20.0 μm. Conditions: (1) the amount of organic peroxide is 100 ppm to 1000 pm; (2) the melt flow rate is 20 g/10 min to 400 g/10 min; and (3) the branching degree λ per one molecule of the polypropylene resin is 1.0×10^-7 to 1.0×10^-3.

Description

Spunbond nonwoven fabric, its manufacturing method, laminated nonwoven fabric, and sanitary materials and clothing made using the same

The present invention relates to a spunbond nonwoven fabric that has excellent mechanical properties and high-level processability in addition to flexibility, a method for producing the same, and hygiene materials and clothing made using the same.

Spunbond nonwoven fabrics made from polyolefins, especially polypropylene spunbond nonwoven fabrics, are low cost and easy to process, so they are widely used, primarily for sanitary material applications.

In recent years, there has been a demand for further improvement in the flexibility of polypropylene spunbond nonwoven fabrics used in sanitary material applications. Several proposals have been made to achieve this.

For example, Patent Document 1 proposes a microfiber nonwoven web formed from reactant particles of a treated polymer, the polymer having a specific molecular weight distribution and a melt flow rate equal to or higher than a certain level.

Patent Document 2 also proposes a method for producing a nonwoven fabric, in which a propylene-based polymer and an organic peroxide are fed into an extruder equipped with a screw equipped with a cross saw and a unimelt, the propylene-based polymer resin composition containing the propylene-based polymer and the organic peroxide in the extruder is melt-kneaded, and the melt-kneaded propylene-based polymer resin composition is spun into fibers to produce a nonwoven fabric. It is described that this method for producing a nonwoven fabric suppresses thread breakage and produces a nonwoven fabric with excellent spinnability.

Patent Document 3 proposes an organic peroxide-containing polypropylene resin composition, which is a resin composition in which a certain amount of organic peroxide is blended with a propylene-α-olefin random copolymer polymerized with a metallocene catalyst and having certain characteristics, and is characterized in that the ratio of the melt flow rate of the resin composition to the melt flow rate after the resin composition has been subjected to a vacuum constant temperature drying process is equal to or less than a certain value. It also describes that such a resin composition can be used as a useful resin composition that can adjust the melt viscosity during molding processing, either alone or in combination with other polypropylene resins as a master batch.

Japanese Patent Application Laid-Open No. 7-119014 Patent No. 6599078 JP 2003-138075 A

Patent Document 1 describes that according to the technology, the polymer is treated to narrow the molecular weight distribution and also to reduce the molecular weight of the polymer, i.e., to increase the melt flow rate, and as a result, the nonwoven web according to the present invention can be produced with high efficiency by the melt blowing method. However, when an attempt is made to obtain a spunbonded nonwoven fabric by adjusting the melt flow rate to a low value, the fiber strength decreases, and the mechanical properties of the nonwoven fabric decrease significantly, making advanced processing such as pleating and bonding to other members difficult, and there are problems with the mechanical properties of the final product itself being deteriorated.

In addition, in the techniques proposed in Patent Documents 2 and 3, while it is possible to improve spinnability to some extent by increasing the melt flow rate of the resin, the strength of the fibers that make up the nonwoven fabric decreases. This results in a significant decrease in the mechanical properties of the nonwoven fabric, making it difficult to carry out advanced processing such as pleating or joining with other components, and there are problems with the mechanical properties of the final product itself being deteriorated.

The object of the present invention is to provide a spunbond nonwoven fabric that, in addition to flexibility, has excellent mechanical properties and is easy to process in advanced ways, such as pleating and bonding to other components.

As a result of further investigations, the inventors have found that in order to make a spunbond nonwoven fabric more flexible, the fiber diameter must be made finer, and excellent mechanical properties can be achieved by increasing the strength of the fibers themselves.

Incidentally, to make the fiber diameter thinner, it is effective to use a raw material with a high melt flow rate and increase the spinning speed (pulling speed). However, as mentioned above, when a raw material with a high melt flow rate is used, the strength of the resulting fiber decreases, so the two tend to be contradictory.

As a result of further investigations, the inventors came up with the idea of using a certain amount of peroxide, which is used as a radical generator to increase the melt flow rate of the raw material, as a crystal nucleating agent by leaving it in the spunbond nonwoven fabric, and further, of setting the branching degree λ within a specific range.

The inventors conducted extensive research based on this knowledge to achieve the above object, and discovered that by setting the amount of organic peroxide and the degree of branching λ of the polypropylene resin in the fibers constituting the spunbond nonwoven fabric within a specific range, and further setting the melt flow rate of the spunbond nonwoven fabric within a specific range, the fiber diameter can be made finer, thereby improving flexibility, and defects that occur in the nonwoven fabric due to fiber breakage can be suppressed, resulting in a high-quality spunbond nonwoven fabric; and by suppressing the orientation relaxation of the resulting fibers and increasing the molecular orientation (Δn), which in turn increases the strength of the fibers, resulting in a spunbond nonwoven fabric with excellent mechanical properties and that is easy to process in advanced ways, such as pleating and bonding to other members, thereby completing the present invention.

The present invention aims to solve the above problems, and provides the following inventions:

[1] A spunbond nonwoven fabric composed of fibers made of a polypropylene-based resin, the spunbond nonwoven fabric satisfying the following conditions (1) to (3), and the average single fiber diameter of the fibers is 5.0 μm or more and 20.0 μm or less.
(1) The amount of organic peroxide extracted by ultrasonic treatment of the spunbonded nonwoven fabric immersed in a chloroform/methanol solvent in a volume ratio of 1:1 for 15 minutes at 45 kHz and a solution temperature of 30° C. is 100 ppm or more and 1000 ppm or less. (2) The melt flow rate of the polypropylene-based resin is 20 g/10 min or more and 400 g/10 min or less. (3) The branching degree λ per molecule of the polypropylene-based resin is 1.0 x 10 ^-7 or more and 1.0 x 10 ^-3 or less, calculated from the molecular weight and radius of gyration determined by gel permeation chromatography/multi-angle light scattering measurement device using trifunctional random branching theory. [2] The spunbonded nonwoven fabric according to the above item [1], wherein the polypropylene-based resin further satisfies the following conditions (4) and (5):
(4) 2.50≦Mw/Mn≦3.20
(5) 1.82≦Mz/Mw≦2.20
Here, Mw, Mn, and Mz are the weight average molecular weight, number average molecular weight, and z-average molecular weight, respectively, determined by gel permeation chromatography.

[3] A step of adding an organic peroxide to a raw material resin and decomposing the raw material resin to obtain a polypropylene-based resin prepared so as to satisfy the following conditions (1) to (3);
a step of spinning the polypropylene-based resin to obtain fibers having an average single fiber diameter of 5.0 μm or more and 20.0 μm or less;
and collecting the fibers.
(1) The amount of residual organic peroxide extracted by ultrasonic treatment of the spunbonded nonwoven fabric immersed in a chloroform/methanol solvent in a volume ratio of 1:1 for 15 minutes at 45 kHz and a solution temperature of 30° C. is 100 ppm or more and 1000 ppm or less. (2) The melt flow rate of the polypropylene-based resin is 20 g/10 min or more and 400 g/10 min or less. (3) The branching degree λ per molecule of the polypropylene-based resin is 1.0 x 10 ^-7 or more and 1.0 x 10 ^-3 or less, calculated using trifunctional random branching theory from the molecular weight and radius of gyration determined by gel permeation chromatography/multi-angle light scattering measurement device. [4] The method for producing a spunbonded nonwoven fabric according to the above item [3], wherein the raw material resin is a recycled resin.

[5] A laminated nonwoven fabric comprising the spunbond nonwoven fabric described in [1] or [2] above.

[6] A sanitary material comprising the spunbond nonwoven fabric described in [1] or [2] above, or the laminated nonwoven fabric described in [5] above.

[7] Clothing made using the spunbond nonwoven fabric described in [1] or [2] above, or the laminated nonwoven fabric described in [5] above.

The spunbond nonwoven fabric of the present invention has high quality and flexibility, and because a certain amount of organic peroxide remains in the nonwoven fabric, it acts as a crystal nucleating agent to promote oriented crystallization. Furthermore, by setting the branching degree λ per molecule within a specific range, it is possible to suppress relaxation of the fiber orientation after pulling in the spunbonding process, and it exhibits excellent mechanical properties. It also exhibits excellent properties in terms of ease of advanced processing such as pleating and joining with other components.

The spunbond nonwoven fabric of the present invention is a spunbond nonwoven fabric composed of fibers made of a polypropylene-based resin, and the spunbond nonwoven fabric satisfies the following conditions (1) to (3), and the average single fiber diameter of the fibers is 5.0 μm or more and 20.0 μm or less.
(1) The amount of organic peroxide extracted by ultrasonic treatment of the spunbonded nonwoven fabric immersed in a chloroform/methanol solvent having a volume ratio of 1:1 for 15 minutes at 45 kHz and a solution temperature of 30° C. is 100 ppm or more and 1000 ppm or less. (2) The melt flow rate is 20 g/10 min or more and 400 g/10 min or less. (3) The branching degree λ per molecule of the polypropylene resin is 1.0×10 ⁻⁷ or more and 1.0×10 ⁻³ or less, calculated using the trifunctional random branching theory from the molecular weight and radius of gyration determined by gel permeation chromatography/multi-angle light scattering measurement device. The spunbonded nonwoven fabric of the present invention will be described in detail below, but the present invention is not limited to the scope described below as long as it does not deviate from the gist of the invention, and various modifications are possible without departing from the gist of the invention.

[Polypropylene resin]
The spunbonded nonwoven fabric of the present invention is composed of fibers (polypropylene fibers) composed of a polypropylene-based resin. In the present invention, the polypropylene-based resin means a resin in which the molar fraction of propylene units in the repeating units is 80 mol % to 100 mol %. By using the polypropylene-based resin, a spunbonded nonwoven fabric that is low cost and has excellent flexibility can be obtained.

The polypropylene-based resin used in the present invention may be a homopolymer of propylene or a copolymer of propylene and various α-olefins. When a copolymer of propylene and various α-olefins is used as the polypropylene-based 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, in order to give the fibers higher tensile strength.

The polypropylene resin used in the present invention can be blended with other component resins to the extent that 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 polyester resins and low-melting polyamide resins. From the viewpoint of imparting flexibility, low-crystalline olefin resins are preferably used. As low-crystalline olefin resins, for example, ethylene-propylene copolymers are preferably used. In this case, the mass ratio of the other component resin is preferably 20% by mass or less, and more preferably 10% by mass or less, when the total mass ratio of the polypropylene resin and the other component resins is 100% by mass, in order to fully express the properties of the polypropylene resin.

The polypropylene resin used in the present invention can contain additives such as pigments for coloring, antioxidants, lubricants such as polyethylene wax and fatty acid amide compounds, and heat stabilizers, as long as the effects of the present invention are not impaired.

Furthermore, according to a preferred embodiment of the spunbonded nonwoven fabric of the present invention, the polypropylene resin further satisfies the following conditions (4) and (5).
(4) 2.50≦Mw/Mn≦3.20
(5) 1.82≦Mz/Mw≦2.20
The present inventors have found that the smaller the Mw/Mn and Mz/Mw, the higher the molecular orientation (Δn) of the fibers obtained even at the same spinning speed, and the higher the fiber strength. From this viewpoint, Mw/Mn≦2.95 and Mz/Mw≦1.98 are more preferable. On the other hand, by making 2.50≦Mw/Mn and 1.82≦Mz/Mw, the molecular orientation of the fibers is made appropriate, and yarn breakage is suppressed, resulting in a high-quality spunbonded nonwoven fabric with few sheet defects.

The Mw of the polypropylene resin used in the present invention, as determined by gel permeation chromatography (hereinafter, GPC), is preferably 120,000 or more and 350,000 or less. Mw is correlated with MFR, and an Mw of 350,000 or less increases the fluidity of the polypropylene resin, improving spinnability and reducing thread breakage defects. From this perspective, the smaller the Mw, the more preferable it is, with 250,000 or less being more preferable, 210,000 or less being even more preferable, and 180,000 or less being particularly preferable. On the other hand, by setting the Mw to preferably 120,000 or more, more preferably 130,000 or more, even more preferably 150,000 or more, and particularly preferably 200,000 or more, fiber strength can be improved and sheet defects due to thread breakage can be suppressed.

In the present invention, Mw, Mn, and Mz refer to values measured and calculated by the following methods.
(1) Five test pieces each weighing 5 mg are randomly taken from the area of the spunbond nonwoven fabric excluding the ends. The ends of the spunbond nonwoven fabric refer to an area of 10% of both ends of the spunbond nonwoven fabric in the width direction.
(2) 5 mL of 1,2,4-trichlorobenzene (e.g., Fujifilm Wako Pure Chemical Industries, Ltd.) is added to the test piece obtained in (1). Depending on the nature of the sample, the solution may be heated at 165°C for 20 minutes to facilitate dissolution. The solution is then filtered using a PTFE filter (pore size: 0.45 μm) to prepare a sample solution. Here, the PTFE filter may be, for example, "T010A" manufactured by Advantec Toyo Co., Ltd.
(3) The sample solution obtained in (2) is measured using GPC under the following conditions. For example, Mw, Mn, and Mz can be obtained by analyzing the emission curve in GPC using "Empower" manufactured by Wyatt Technology.
Apparatus: For example, "PL-220" manufactured by Polymer Laboratories, etc. Detector: Differential refractive index detector RI
Column: Shodex HT-G (guard column) + Shodex HT-806M x 2 (8.0 mm x 30 cm, for example, manufactured by Showa Denko K.K.)
Solvent: 1,2,4-trichlorobenzene (with 0.1% BHT)
Flow rate: 1.0 mL/min Column temperature: 145° C.
Injection volume: 0.20 mL
Standard samples: monodisperse polystyrene (for example, manufactured by Tosoh Corporation), dibenzyl (for example, manufactured by Tokyo Chemical Industry Co., Ltd.).

[fiber]
The spunbonded nonwoven fabric of the present invention is composed of fibers made of the polypropylene-based resin. The average single fiber diameter of the fibers is 5.0 μm or more and 20.0 μm or less. The upper limit of the range of the average single fiber diameter is 20.0 μm or less, preferably 16.0 μm or less, so that the surface of the spunbonded nonwoven fabric feels smooth to the touch. In addition, the small fiber diameter leads to a decrease in the moment of inertia of area, resulting in a spunbonded nonwoven fabric with excellent flexibility. On the other hand, the lower limit of the range of the average single fiber diameter is 5.0 μm or more, preferably 8.0 μm or more, so that the spunbonded nonwoven fabric has high tensile strength and few defects.

In this invention, the average single fiber diameter (μm) of the fibers refers to the value obtained by taking 10 5 mm x 5 mm test pieces at random from the area excluding the ends of the spunbond nonwoven fabric, observing the side of the fibers constituting the spunbond nonwoven fabric in the area other than the embossed bonded area of each test piece using a digital microscope (such as "VHX-2000" manufactured by Keyence Corporation), determining the fiber diameter, and rounding off the arithmetic mean value (μm) of the fiber diameter measured for each test piece to one decimal place. Note that the ends of the spunbond nonwoven fabric refer to an area that is 10% of both ends of the width of the spunbond nonwoven fabric.

The Δn, which is an index of the molecular orientation of the fibers that make up the spunbond nonwoven fabric of the present invention, is preferably 0.020 or more. With a Δn of 0.020 or more, the orientation of the fibers is improved, and the fiber strength and sheet strength are increased. In addition, heat resistance is also increased, allowing thermal bonding such as embossing to be carried out at high temperatures, making it easier to thermally bond the fibers, resulting in a spunbond nonwoven fabric with good mechanical properties and easy advanced processing such as pleating and bonding to other members.

The Δn of the fibers constituting the spunbond nonwoven fabric of the present invention refers to the value obtained by taking ten test pieces at random using the same method as the above-mentioned method for measuring the average single fiber diameter, extracting ten single yarns from the parts of the test pieces other than the embossed bonded parts, and using a polarizing microscope (such as "BH2" manufactured by Olympus Corporation) to determine the retardation using the compensator method while the sample is immersed in liquid paraffin. The arithmetic mean value (without units) of the calculated value is rounded off to the fourth decimal place.

The tensile strength of the fibers constituting the spunbond nonwoven fabric of the present invention is preferably 2.0 cN/dtex or more. With a fiber tensile strength of 2.0 cN/dtex or more, the strength of the sheet is high, resulting in a spunbond nonwoven fabric with good mechanical properties and easy advanced processing such as pleating and bonding to other members.

The tensile strength of the fibers constituting the spunbonded nonwoven fabric of the present invention refers to a value measured and calculated by the following method.
(1) Using the same method as in the measurement of the average single fiber diameter described above, ten test pieces are randomly taken from locations, and ten single yarns are extracted from the portions of the test pieces other than the embossed bonded portions.
(2) In accordance with "8.7 Tensile strength and elongation" of JIS L1015:2010 "Test methods for synthetic fiber staples", a single yarn is set in a tensile testing machine (e.g., "UTM-III-100" manufactured by Orientec Co., Ltd.) with a gripping distance of 20 mm, and a tensile test is performed at a pulling speed of 20 mm/min to measure the maximum load (cN).
(3) Next, the arithmetic mean value (cN/dtex) obtained by dividing the maximum point load by the single yarn fineness (dtex) calculated using the following formula is rounded off to one decimal place.

Single fiber fineness (dtex)=π×(average single fiber diameter of fiber (μm)/2) ² ×0.91 (g/cm ³ )×100,000 (cm).

The cross-sectional shape of the fibers constituting the spunbonded nonwoven fabric of the present invention is not particularly limited as long as it does not impair the effects of the present invention, and may be a round cross-section or an irregular cross-section such as a triangle, ellipse, hexagon, or hollow, but a round cross-section is preferred because it is highly productive and has excellent flexibility. That is, when the cross-sectional shape of the polypropylene fibers constituting the spunbonded nonwoven fabric of the present invention is an irregular cross-section, there is a bending direction in which the second moment of area for the same cross-sectional area is larger than that of a circular cross-section, and therefore the spunbonded nonwoven fabric may have high rigidity, but with a circular cross-section, there is no such bending direction, and the flexibility is particularly excellent.

The fibers constituting the spunbond nonwoven fabric of the present invention are preferably composite fibers made by combining two or more types of resin. Composite fibers can be appropriately selected from sheath-core, sea-island, side-by-side, eccentric sheath-core, etc., but among them, the composite form of sheath-core, especially concentric sheath-core, is preferred because of its excellent spinnability and the ability to uniformly bond the fibers together by thermal bonding.

[Spunbond nonwoven fabric]
The spunbond nonwoven fabric of the present invention is a spunbond nonwoven fabric composed of the fibers made of the polypropylene-based resin described above. By doing so, as described above, a spunbond nonwoven fabric is obtained that has excellent mechanical properties in addition to flexibility and is easy to process in advanced steps such as pleating and bonding to other members.

The spunbond nonwoven fabric of the present invention satisfies the following conditions (1) to (3).
(1) The amount of organic peroxide extracted by ultrasonically treating the spunbonded nonwoven fabric immersed in a chloroform/methanol solvent with a volume ratio of 1:1 for 15 minutes at 45 kHz and a solution temperature of 30° C. is 100 ppm or more and 1000 ppm or less. (2) The melt flow rate is 20 g/10 min or more and 400 g/10 min or less. (3) The branching degree λ per molecule of the polypropylene resin is 1.0×10 ⁻⁷ or more and 1.0×10 ⁻³ or less, calculated using the trifunctional random branching theory from the molecular weight and radius of gyration determined by gel permeation chromatography/multi-angle light scattering measurement device. By satisfying all of these conditions (1) to (3), a spunbonded nonwoven fabric is obtained that has excellent mechanical properties in addition to flexibility and is easy to process in higher levels, such as pleating and bonding to other members. These will be described in more detail.

First, the polypropylene resin constituting the spunbond nonwoven fabric of the present invention has an organic peroxide content of 100 ppm or more and 1000 ppm or less, which is extracted by ultrasonically treating the spunbond nonwoven fabric immersed in a chloroform/methanol solvent with a volume ratio of 1:1 for 15 minutes at 45 kHz. By setting the lower limit of the range of the organic peroxide content to 100 ppm or more, preferably 200 ppm or more, more preferably 300 ppm or more, the organic peroxide acts as a crystal nucleating agent during the cooling and solidifying process during spinning, promoting molecular orientation and crystallization. This makes it possible to increase the molecular orientation (Δn) and fiber strength of the fibers constituting the spunbond nonwoven fabric, and to obtain a spunbond nonwoven fabric with excellent mechanical properties. On the other hand, by setting the upper limit of the organic peroxide content to 1000 ppm or less, preferably 800 ppm or less, the risk of skin troubles such as rashes caused by organic peroxides can be minimized when the fabric is used for applications in which the fabric comes into direct contact with the human body, such as sanitary materials and protective clothing.

In the present invention, the amount of organic peroxide refers to a value measured and calculated by the following method.
(1) Five test pieces each weighing 25 mg are randomly taken from the area of the spunbond nonwoven fabric excluding the ends. The ends of the nonwoven fabric refer to an area of 10% of both ends of the nonwoven fabric in the width direction.
(2) The test piece obtained in (1) is immersed in a chloroform/methanol solvent with a volume ratio of 1:1, and ultrasonically treated for 15 minutes at 45 kHz and a solution temperature of 30° C. For this ultrasonic treatment, for example, an ultrasonic cleaner "VS-100III" manufactured by AS ONE Corporation can be used. The amount of the solvent relative to the mass of the test piece is 0.8 mL of solvent per 1 mg of the test piece, and extraction is performed while cooling with a cooling agent or the like so that the solution temperature is maintained at 30° C.
(3) The ultrasonically treated solution obtained in (2) is filtered through a polytetrafluoroethylene (PTFE) filter (hereinafter, simply referred to as a "PTFE filter"; pore size: 0.45 μm) to obtain a sample solution. The PTFE filter may be, for example, "T010A" manufactured by Advantec Toyo Co., Ltd.
(4) 0.1 g of organic peroxide is dissolved in 10 mL of a chloroform/methanol solution with a volume ratio of 1:1 to prepare a standard stock solution (10 μg/mL). Then, this standard stock solution is diluted with the chloroform/methanol solution to prepare standard solutions of each concentration (0.1 μg/mL, 0.2 μg/mL, 0.5 μg/mL, 1.0 μg/mL). At this time, the above organic peroxides include the following, and standard solutions of each concentration are prepared for each of them. In addition, when it is clear that an organic peroxide other than the following organic peroxides is contained by other methods (e.g., iodometric titration method, polarographic method, etc.), or when it is at least suspected that it is contained, a standard solution of the organic peroxide is also prepared.
・Methyl ethyl ketone peroxide・Methyl isobutyl ketone peroxide・Dibenzoyl peroxide・Di-(3,5,5-trimethylhexanoyl) peroxide・Dilauroyl peroxide・Didecanoyl peroxide・Di-(2,4-dichlorobenzoyl) peroxide・t-butyl hydroperoxide・Cumene hydroperoxide・Diisopropylbenzene hydroperoxide・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)hexane syn-3,α,α'-bis(t-butylperoxy)diisopropylbenzene, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,2-bis(t-butylperoxy)butane, t-butylperoxyoctoate, t-butylperoxypivalate, t-butylperoxyneodecanoate, t-butylperoxybenzoate, di-(2-ethylhexyl)peroxydicarbonate, diisopropylperoxydicarbonate, bis(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyisopropylcarbonate (5) The above sample solution is subjected to liquid chromatography mass spectrometry (LC/MS/MS) under the following conditions.
High performance liquid chromatography (HPLC): For example, Shimadzu Corporation's "LC-20A" Mass spectrometer (MS): For example, Sciex's "API4000" Column: ODS column (for example, Sumika Chemical Analysis Center's "SUMIPAX ODS A series" etc.)
Mobile phase: 0.1% formic acid aqueous solution + methanol (gradient extraction conditions)
Injection volume: 5 μL
Ionization: Electrospray ionization (ESI)
(6) The organic peroxides are identified from the mass spectrum (MS) of each sample solution, and the amount of organic peroxide (ppm) is quantified from the peak area using a calibration curve obtained from the standard solution of the organic peroxide.
(7) The arithmetic mean value (ppm) measured for each test piece is rounded off to one decimal place to determine the amount of organic peroxide (ppm).

In addition, the amount of organic peroxide in the polypropylene resin that constitutes the spunbond nonwoven fabric of the present invention can be controlled by the form and temperature at which the organic peroxide is added to the raw resin.

The organic peroxides used in the present invention include ketone peroxides such as "methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide", diacyl peroxides such as "dibenzoyl peroxide, di-(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, didecanoyl peroxide, di-(2,4-dichlorobenzoyl) peroxide", hydroperoxides such as "t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 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-butylperoxy)diisopropyl Examples of peroxycarbonates include dialkyl peroxides such as "1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,2-bis(t-butylperoxy)butane", peroxyketals such as "t-butylperoxyoctoate, t-butylperoxypivalate, t-butylperoxyneodecanoate, t-butylperoxybenzoate", and peroxycarbonates such as "di-(2-ethylhexyl)peroxydicarbonate, diisopropylperoxydicarbonate, bis(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyisopropylcarbonate". Among these, dialkyl peroxides are preferred because they allow easy control of the melt flow rate, Mw/Mn, and Mz/Mw with a small amount of addition.

Next, the melt flow rate (hereinafter sometimes simply referred to as MFR) of the spunbond nonwoven fabric of the present invention is 20 g/10 min or more and 400 g/10 min or less. With respect to the above-mentioned MFR range, if the lower limit is 20 g/10 min or more, preferably 60 g/10 min or more, more preferably 100 g/10 min or more, the spunbond nonwoven fabric will have excellent flexibility. On the other hand, with respect to the above-mentioned MFR range, if the upper limit is 400 g/10 min or less, preferably 300 g/10 min or less, the mechanical strength of the embossed portion of the spunbond nonwoven fabric will be increased, resulting in a spunbond nonwoven fabric with high tensile strength.

The MFR of the spunbond nonwoven fabric in the present invention is determined in accordance with "Chapter 8, Method A: Mass measurement" of JIS K7210-1:2014 "Plastics - Determination of melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastic plastics - Part 1: Standard test method", by randomly taking 5 test pieces of 20 g each from the area of the spunbond nonwoven fabric excluding the ends, and rounding off the first decimal place of the arithmetic mean value (g/10 min) measured under conditions of a load of 2160 g and a temperature of 230°C for each test piece. The ends of the nonwoven fabric refer to the area of 10% of both ends of the nonwoven fabric in the width direction. For the measurement, for example, a melt indexer "F-F01" manufactured by Toyo Seiki Seisakusho Co., Ltd. can be used.

The MFR of spunbond nonwoven fabric 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 melt flow rate. The weight average molecular weight can be controlled by the weight average molecular weight of the raw resin and the amount of organic peroxide added.

The spunbonded nonwoven fabric of the present invention has a branching degree λ per molecule of the polypropylene resin (hereinafter, sometimes simply abbreviated as "branching degree λ per molecule") of 1.0×10-7 or more and 1.0× ^10-3 or less, calculated from the molecular weight and radius of gyration determined by gel permeation chromatography/multi-angle light scattering measurement (hereinafter, sometimes simply abbreviated as "GPC-MALS") using trifunctional random branching theory. With regard to the range of the branching degree λ per molecule, if the lower limit is ^1.0 × ^10-7 or more, preferably 1.0× ^10-6 or more, more preferably 5.0× ^10-6 or more, the molecules of the polypropylene resin will have a more branched structure, resulting in a spunbonded nonwoven fabric with higher fiber strength and excellent mechanical properties. On the other hand, by setting the upper limit of the above range to 1.0 × ^10-3 or less, preferably 1.0 × ^10-4 or less, and more preferably 5.0 × ^10-5 or less, yarn breakage during spinning due to an excessively branched structure can be suppressed, resulting in a high-quality spunbonded nonwoven fabric with few defects.

In the present invention, the degree of branching λ per molecule refers to a value measured and calculated by the following method.
(1) Five test pieces each weighing 5 mg are randomly taken from the area of the spunbond nonwoven fabric excluding the ends. The ends of the nonwoven fabric refer to an area of 10% of both ends of the nonwoven fabric in the width direction.
(2) 5 mL of 1,2,4-trichlorobenzene (e.g., Fujifilm Wako Pure Chemical Industries, Ltd.) is added to the test piece obtained in (1). If the sample is difficult to dissolve, the solution may be heated at 165°C for 20 minutes to dissolve it. Next, the solution is filtered using a PTFE filter (pore size: 0.45 μm, e.g., Advantec Toyo Co., Ltd.'s "T010A") to prepare a sample solution.
(3) The sample solution obtained in (2) is subjected to measurement using GPC-MALS under the following conditions:
Gel permeation chromatograph (GPC): For example, "HLC-8321GPC/HT" manufactured by Tosoh Corporation. Differential refractive index detector: For example, "HL-8321GPC/HT" manufactured by Tosoh Corporation. Multi-angle light scattering detector (MALS): For example, "DAWNNEON" manufactured by Wyatt Technology. Column: For example, "Shodex HT-806M" manufactured by Showa Denko K.K. Solvent: 1,2,4-trichlorobenzene (0.1% BHT added, for example, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
Column temperature/detector temperature: 145° C./145° C.
Sample solution injection volume: 0.300 mL
Data processing unit: GPC: for example, "Empower" manufactured by Wyatt Technology, MALS: for example, "ASTRA 8.0.1.21" manufactured by Wyatt Technology, etc. (4) For each sample solution, the molecular weight and radius of gyration at each elution time are calculated from the obtained GPC-MALS curve using the above-mentioned data processing software. Here, regarding the relationship between molecular weight and radius of gyration, it is known that a polypropylene resin having a branched structure has a smaller radius of gyration at the same molecular weight than a linear polypropylene resin having no branched structure (for example, "Novatec" (registered trademark) PP FY6 manufactured by Japan Polypropylene Corporation). In the trifunctional random branching theory, the following formula is established between the radius of gyration S and the number of branch points λ ^M at each molecular weight.

(Here, g = (radius of gyration of sample S) ² / (radius of gyration of linear polypropylene S) ^2. )
(5) Using the above formula, the number of branching points λ ^M of each sample is calculated. Next, the number of branching points λ ^M is divided by the corresponding absolute molecular weight (unitless), and the value is rounded off to one decimal place to calculate the number of branching points per molecule (unitless).
(6) Among the number of branching points per molecule calculated in (5), the maximum value in the region of absolute molecular weight of 100,000 or more is defined as the branching degree per molecule λ. Note that when the branching degree per molecule λ is 1.0×10 ⁻⁸ or less, it is below the lower limit of detection and is therefore regarded as 0.

The branching degree λ per molecule can be controlled by the branching degree λ per molecule of the raw material resin used. For example, the greater the branching degree λ per molecule of the raw material resin, the greater the branching degree λ of the polypropylene resin.

The basis weight of the spunbonded nonwoven fabric of the present invention is preferably 3 g/ ^m2 or more and 50 g/ ^m2 or less. The lower limit of the above basis weight range is preferably 3 g/ ^m2 or more, more preferably 5 g/ ^m2 or more, so that the spunbonded nonwoven fabric has sufficient strength, is less likely to break in a later process, and has excellent processability. The upper limit of the above basis weight range is preferably 50 g/ ^m2 or less, or 30 g/ ^m2 or less, so that the flexibility of the spunbonded nonwoven fabric can be suitably expressed.

The basis weight of the spunbond nonwoven fabric in the present invention is determined in accordance with "6.2 Mass per unit area (ISO method)" of JIS L1913:2010 "Testing methods for general nonwoven fabrics" by randomly taking three 20 cm x 25 cm test pieces per 1 m width from the portion of the spunbond nonwoven fabric excluding the ends, measuring the mass (g) of each piece under standard conditions, calculating the arithmetic mean value (g), converting it to mass per ^m2 (g/ ^m2 ), and rounding off to the nearest whole number. The ends of the nonwoven fabric refer to an area that is 10% of both ends of the nonwoven fabric in the width direction.

The spunbond nonwoven fabric of the present invention preferably has a tensile strength per unit area weight of 0.30 (N/25 mm)/(g/ ^m2 ) or more and 5.00 (N/25 mm)/(g/ ^m2 ) or less. The lower limit of the range of the tensile strength per unit area weight is preferably 0.3 (N/25 mm)/(g/ ^m2 ) or more, more preferably 0.50 (N/25 mm)/(g/ ^m2 ) or more, and even more preferably 0.70 (N/25 mm)/(g/ ^m2 ) or more, so that the fabric can withstand the process of manufacturing paper diapers and the like and can withstand use as a product, and the upper limit of the range is preferably 5.00 (N/25 mm)/(g/ ^m2 ) or less, so that the fabric is flexible.

In the present invention, the tensile strength per unit area weight of the spunbond nonwoven fabric refers to a value measured by the following procedure in accordance with "6.3 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "General nonwoven fabric testing methods."
(1) Three test pieces of 25 mm x 30 mm are randomly taken from the area of the spunbond nonwoven fabric excluding the ends in the length direction and width direction of the nonwoven fabric. The ends of the nonwoven fabric refer to 10% of the area on both ends of the nonwoven fabric in the width direction.
(2) Place the test piece in the tensile testing machine with a gripping distance of 20 mm.
(3) A tensile test is carried out at a tensile speed of 20 mm/min, the maximum point load (N/25 mm) is measured, and the arithmetic average value (N/25 mm) of all maximum point loads measured in the length direction and width direction for each test piece is calculated.
(4) From the basis weight (g/ ^m2 ) and the arithmetic mean value of the maximum point load (N/25 mm) measured by the method described above, calculate the tensile strength per basis weight according to the formula below and round off to two decimal places.

Tensile strength per unit area (N/25 mm)/(g/m ² )=arithmetic mean value of maximum point load (N/25 mm)/unit area (g/m ² ).

The bending resistance of the spunbond nonwoven fabric of the present invention is preferably 0.5 mN·cm or more and 3.0 mN·cm or less. The bending resistance is an index of flexibility, and a bending resistance of 3.0 mN·cm or less provides high flexibility. The lower the bending resistance, the better the flexibility, so a bending resistance of 2.0 mN·cm or less is more preferable. On the other hand, if the bending resistance is too low, the fabric is easily taken up by the roll, making advanced processing such as pleating and joining to other components difficult, so a bending resistance of 0.5 mN·cm or more is preferable, and 1.0 mN·cm or more is more preferable.

The bending resistance of the spunbond nonwoven fabric of the present invention refers to a value measured by the following procedure in accordance with "6.7.3 41.5° cantilever method" of JIS L1913:2010 "General nonwoven fabric testing method."
(1) Three test pieces of 25 mm x 250 mm are randomly taken from the area of the spunbond nonwoven fabric excluding the ends in the length direction and width direction of the nonwoven fabric. The ends of the nonwoven fabric refer to 10% of the area on both ends of the nonwoven fabric in the width direction.
(2) Place the test piece on a 41.5° cantilever-type testing machine, and push the steel ruler and the test piece together slowly toward the inclined surface at a constant speed.
(3) Move the steel ruler until the test piece comes into contact with the inclined surface, and read the protruding length of the test piece to the nearest 1 mm from the steel ruler. For each test piece, measure the front, back, and both ends four times, and take half of the arithmetic mean value as the bending length (cm).
(4) Further, the arithmetic mean value (cm) of the bending length of all the test pieces in each of the length direction and width direction is calculated, and rounded off to one decimal place to obtain the overall average bending length (cm).
(5) From the basis weight (g/m ² ) and the total average bending length (cm) measured by the above-mentioned method, calculate the bending resistance (mN·cm) according to the following formula and round off to one decimal place.
Bending resistance (mN·cm)=weight per unit area (g/m ² )×[total average bending length (cm)] ³ ×10 ⁻³ .

[Method of manufacturing spunbond nonwoven fabric]
The method for producing a spunbonded nonwoven fabric of the present invention includes the steps of: adding an organic peroxide to a raw material resin and decomposing the raw material resin to obtain a polypropylene-based resin prepared so as to satisfy the following conditions (1) to (3); spinning the polypropylene-based resin to obtain fibers having an average single fiber diameter of 5.0 μm or more and 20.0 μm or less; and collecting the fibers.
(1) The amount of residual organic peroxide extracted by soaking the spunbond nonwoven fabric in a chloroform/methanol solvent in a 1:1 volume ratio and subjecting it to ultrasonic treatment at 45 kHz for 15 minutes is 100 ppm or more and 1000 ppm or less. (2) The melt flow rate of the polypropylene-based resin is 20 g/10 min or more and 400 g/10 min or less. (3) The branching degree λ per molecule of the polypropylene-based resin is 1.0 x 10 ^-7 or more and 1.0 x 10 ^-3 or less, calculated using trifunctional random branching theory from the molecular weight and radius of gyration determined by gel permeation chromatography/multi-angle light scattering measurement device. Specific examples of this will be described.

(a) Step of Obtaining Polypropylene Resin In the method for producing the spunbonded nonwoven fabric of the present invention, first, an organic peroxide is added to the raw resin to decompose the raw resin. The raw resin used at this time means a resin in which the molar fraction of propylene units in the repeating units is 80 mol% to 100 mol%. Therefore, specific examples of the raw resin include a homopolymer of propylene, or a copolymer of propylene and various α-olefins. When a copolymer of propylene and various α-olefins is used as the raw 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 in order to increase the tensile strength of the spunbonded nonwoven fabric.

Alternatively, it is also a preferred embodiment that the raw resin is a recycled resin. In the present invention, recycled resin refers to resin in which 10% by mass or more of the resin is made up of process waste generated during product manufacturing or used products. Examples of process waste generated during product manufacturing include film scraps, textiles, and scraps of nonwoven fabric. This technology decomposes raw resin to meet specific conditions, and raw resins with a wide range of MFR can be used, making it suitable for using recycled resin. In this way, the amount of virgin petrochemical raw materials used can be reduced, and the environmental impact during the production of spunbond nonwoven fabric can be reduced.

The raw resin used in the present invention may contain additives such as pigments for coloring, antioxidants, lubricants such as polyethylene wax and fatty acid amide compounds, and heat stabilizers, as long as the additives do not impair the effects of the present invention.

The organic peroxides used in the manufacturing method of the spunbond nonwoven fabric of the present invention include the organic peroxides described in [Spunbond nonwoven fabric].

As described above, the polypropylene-based resin prepared by adding the organic peroxide to the raw resin and decomposing the raw resin so as to satisfy the above conditions (1) to (3) can be directly subjected to the spinning described below without drying or the like. The organic peroxide may be kneaded in an extruder and pelletized to form a polypropylene-based resin before being subjected to the spinning described below, but a method may also be adopted in which the organic peroxide and polypropylene-based resin are kneaded during spinning using the extruder used during spinning, and the polypropylene-based resin is obtained at the same time as melt spinning.

Here, regarding the method of adjusting the MFR of polypropylene-based resin, the MFR of the resulting polypropylene-based resin can be increased by increasing the amount of organic peroxide added. Also, if the amount added is constant, the higher the MFR of the raw material resin, the higher the MFR of the resulting polypropylene-based resin. Also, the MFR of the raw material resin is measured in the same manner as the method of measuring the MFR of the spunbond nonwoven fabric described above, in accordance with "Chapter 8, Method A: Mass measurement method" of JIS K7210-1:2014 "Plastics - Determination of melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics - Part 1: Standard test methods", by preparing five samples of 20 g each of raw material resin, and rounding off the first decimal place of the arithmetic mean value of the values (g/10 min) measured for each sample under conditions of a load of 2160 g and a temperature of 230°C. For the measurement, for example, a melt indexer "F-F01" manufactured by Toyo Seiki Seisakusho Co., Ltd. can be used.

From the viewpoint of obtaining a spunbonded nonwoven fabric having high tensile strength, the branching degree λ per molecule of the raw resin, calculated using the trifunctional random branching theory from the molecular weight and radius of gyration determined by gel permeation chromatography/multi-angle light scattering measurement device, is preferably as large as possible, and is preferably 1.0×10 ⁻⁷ or more. On the other hand, by setting the branching degree λ per molecule of the raw resin to preferably 1.0×10 ⁻³ or less, thread breakage during spinning due to an increase in the elongational viscosity of the resulting polypropylene-based resin can be suppressed.

The branching degree λ per molecule of the raw material resin can be measured and calculated in the same manner as the branching degree λ per molecule of the polypropylene resin described above.

Furthermore, the raw resin used in the present invention can be blended with other component resins to the extent that the effect of the present invention is 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. From the viewpoint of imparting flexibility, low-crystalline olefin resins are preferably used. As low-crystalline olefin resins, for example, ethylene-propylene copolymers are preferably used. In this case, the mass ratio of the other component resin is preferably 20 mass% or less, more preferably 10 mass% or less, so as not to impair the properties of the polypropylene resin, particularly the heat resistance of the spunbond nonwoven fabric.

The amount of organic peroxide remaining in the polypropylene resin can be controlled by the temperature and form of the peroxide when the organic peroxide is added to the raw resin.

First, when an organic peroxide is added to the raw resin in an extruder, increasing the extrusion temperature reduces the amount of remaining organic peroxide. On the other hand, decreasing the extrusion temperature increases the amount of remaining organic peroxide. In consideration of the melting point of the polypropylene resin, which is the raw resin, the extrusion temperature is preferably 180°C or higher, and more preferably 200°C or higher. On the other hand, in order to prevent the risk of yellowing or fire due to oxidative decomposition of the polypropylene resin, the extrusion temperature is preferably 280°C or lower, and more preferably 260°C or lower.

As for the form of the organic peroxide, by adding the organic peroxide in the form of a masterbatch of polypropylene resin, self-decomposition in the extruder is suppressed under conditions of constant addition amount and extrusion temperature, so that a large amount of the organic peroxide can remain in the polypropylene resin.

(b) Step of Obtaining Fibers In this step, the polypropylene-based resin is spun to obtain fibers having an average single fiber diameter of 5.0 μm or more and 20.0 μm or less.

In this spinning, a melt spinning technique using an extruder such as a single-screw or twin-screw extruder can be applied. The polypropylene resin extruded from the extruder passes through piping, is metered by a metering device such as a gear pump, passes through a filter to remove foreign matter, and is then guided to the spinneret. At this time, the temperature from the resin piping to the spinneret (spinning temperature) is preferably set to 180°C or higher and 280°C or lower to increase fluidity.

The spinneret used for extrusion preferably has a nozzle hole diameter D of 0.1 mm or more and 1.0 mm or less, and L/D, defined as the quotient of the land length L of the nozzle hole (the length of the straight tube section that is the same as the nozzle hole diameter) divided by the hole diameter D, is preferably 1 or more and 10 or less.

The yarn discharged from the nozzle holes may be cooled and solidified by blowing air onto it. In this case, the temperature of the cooling air can be determined in consideration of the cooling efficiency and the cooling air speed, but it is preferable that the temperature be between 0°C and 20°C from the viewpoint of uniformity of fineness. By setting the temperature of the cooling air to 0°C or higher, and more preferably 2°C or higher, it is possible to prevent condensation and freezing in the air piping and cooling air discharge section, and it is possible to supply a stable cooling air. Furthermore, by setting the temperature of the cooling air to 20°C or lower, more preferably 16°C or lower, and even more preferably 12°C or lower, the cooling effect of the fibers is improved, uniformity is increased, and a spunbond nonwoven fabric with fewer yarn breakage defects is obtained.

The cooling gas is blown almost perpendicularly to the yarn (when the fibers are running up and down, this means a direction parallel to the ground) to cool the yarn. In this case, the speed of the cooling air is preferably 10 m/min to 100 m/min. By making the cooling air speed preferably 10 m/min or more, the cooling effect is enhanced, the uniformity is increased, and a spunbond nonwoven fabric with fewer thread breakage defects is obtained. In addition, by making the cooling air speed preferably 100 m/min or less, thread shaking caused by the cooling air can be suppressed, thereby reducing thread breakage during spinning.

The distance from the nozzle hole of the spinneret to the position where cooling begins is preferably 20 mm or more and 800 mm or less. By setting the lower limit of the above distance range to preferably 20 mm or more, the nozzle surface temperature does not drop excessively and discharge is stabilized, reducing thread breakage during spinning. Furthermore, by setting the upper limit of the above distance range to preferably 800 mm or less, the cooling effect is enhanced, uniformity is increased, and a spunbond nonwoven fabric with fewer thread breakage defects is obtained.

The yarn discharged from the nozzle hole is air-pulled (pulled by accelerated air flow) preferably at a position between 400 mm and 7000 mm from the spinneret, regardless of whether cooling air is blown. The accelerated air flow can be achieved by sealing the area where the cooling air is blown and gradually reducing the cross-sectional area of the sealed area as it moves downstream of the spinning line, thereby accelerating the air flow rate, but in order to obtain a higher air flow rate, it is preferable to use an ejector. The yarn is accelerated by this air flow rate, and the spinning speed, which is the running speed of the fiber, reaches a speed close to the air flow rate. In the present invention, the gas used for air-pulling is not limited to ordinary air, but may be nitrogen or water vapor as long as the humidity is 100% RH or less.

In order to reduce the average single fiber diameter, it is preferable for the spinning speed to be 3 km/min or more, and more preferably 4 km/min. Similarly, it is preferable for the air flow rate to be 3 km/min or more. The upper limit of the spinning speed is about 12 km/min.

The spinning speed is calculated by the following formula: Spinning speed (km/min) = Q·1000/((W/2) ² ×π×ρ)
(In the formula, Q represents the single-hole output rate (g/min), W represents the average single fiber diameter (μm), and ρ represents the density (g/cm ³ ). For the polypropylene-based resin used in the present invention, a density value of 0.91 is used. The average single fiber diameter value is the value measured and calculated by the method described above in [Fibers].)

In this way, fibers are formed with an average single fiber diameter of 5.0 μm or more and 20.0 μm or less.

(c) Step of Collecting Fibers The air-drawn yarn (fibers) is opened by passing through a fiber-opening section that reduces the surrounding air flow speed, and then the yarns land on a net conveyer that sucks air from the back side and is collected as a fiber web.

(d) Post-processing step The collected fiber web may be directly used as a spunbonded nonwoven fabric, but more preferably, the fiber web is conveyed at a speed of 10 m/min to 1000 m/min and subjected to a thermal bonding process or the like to obtain a spunbonded nonwoven fabric. Methods for integrating the fibers constituting the fiber web by thermal bonding include methods of thermal bonding using various rolls, such as a thermal embossing roll having engraved (uneven) portions on the surfaces of a pair of upper and lower rolls, a thermal embossing roll consisting of a combination of a roll with one flat (smooth) surface and a roll with engraved (uneven) portions on the surface of the other roll, and a thermal calendar roll consisting of a combination of a pair of upper and lower flat (smooth) rolls.

The embossed adhesive area ratio during thermal bonding is preferably 5% or more and 30% or less. By setting the adhesive area to 5% or more, the nonwoven fabric has a high tensile strength that can be practically used as a spunbond nonwoven fabric, and it is easy to perform advanced processing such as pleating and bonding with other members. On the other hand, by setting the adhesive area to 30% or less, sufficient flexibility can be obtained, especially when used as a spunbond nonwoven fabric for sanitary materials.

In the present invention, the adhesive area refers to the proportion of the entire nonwoven fabric where the convex parts of the upper roll and the convex parts of the lower roll overlap and come into contact with the fiber web, when thermal bonding is performed using a pair of uneven rolls. Also, when thermal bonding is performed using an uneven roll and a flat roll, the adhesive area refers to the proportion of the entire nonwoven fabric where the convex parts of the uneven roll come into contact with the fiber web.

The shapes of the engravings applied to the hot embossing roll can be circles, ellipses, squares, rectangles, parallelograms, diamonds, regular hexagons, and regular octagons.

The key point in the process of manufacturing the spunbonded nonwoven fabric of the present invention is that high-speed spinning allows for the thinning of the average single fiber diameter and stable production. Although the mechanism behind this is unclear, the spunbonded nonwoven fabric of the present invention uses a polypropylene resin with a high MFR as a raw material, which improves the deformation followability of the polypropylene resin in the thinning behavior during the spinning process, significantly reducing thread breakage defects.

On the other hand, if only the above points are considered, the resulting spunbond nonwoven fabric will have problems such as low tensile strength and difficulty in advanced processing such as pleating and bonding to other components due to its high MFR. Therefore, another important point in the process of manufacturing the spunbond nonwoven fabric of the present invention is that the crystal nucleating effect of the organic peroxide and the effect of suppressing orientation relaxation due to the branched structure can increase Δn, which is an index of the molecular orientation of the fibers, and increase the strength of the fibers.

The spunbond nonwoven fabric obtained in this way has excellent flexibility and sufficient tensile strength for use in spunbond nonwoven fabrics, making it easy to perform advanced processing such as pleating and bonding to other components.

[Laminated nonwoven fabric]
The laminated nonwoven fabric of the present invention includes the spunbonded nonwoven fabric. The spunbonded nonwoven fabric of the present invention has excellent tensile strength even when used alone, but when laminated with a heat-fusible nonwoven fabric, it exhibits even more excellent mechanical properties. Examples of the heat-fusible nonwoven fabric include a melt-blown nonwoven fabric having a low softening temperature and excellent heat fusion, and a spunbonded nonwoven fabric made of a low-melting polypropylene resin polymerized with a metallocene catalyst. The laminated nonwoven fabric may have a lamination structure of S/M, S/S, S/M/M, M/S/M, S/S/M, S/M/M/S, S/M/M/M/S, or S/M/M/M/S, with the spunbonded nonwoven fabric being S and the melt-blown nonwoven fabric being M. A preferred method for producing the laminated nonwoven fabric includes a method in which each nonwoven fabric layer discharged from a plurality of spinnerets is laminated on a conveyor, and the resulting laminated web is partially bonded using an embossing roll or the like.

[Hygiene materials, clothing]
The sanitary materials and clothing of the present invention are at least partially comprised of a spunbonded nonwoven fabric or the laminated nonwoven fabric described above. The spunbonded nonwoven fabric and the laminated nonwoven fabric have excellent flexibility and feel, uniform texture, and sufficient tensile strength for practical use, so that the sanitary materials and clothing obtained are comfortable to wear.

The sanitary materials and clothing referred to here are primarily disposable items used for health-related purposes, such as medical care and nursing care.

The sanitary material of the present invention includes disposable diapers, sanitary napkins, gauze, bandages, masks, gloves, bandages, etc., and also includes the components thereof, such as the top sheet, back sheet, and side gathers in the case of disposable diapers. In particular, it is suitable for use in the back sheet of disposable diapers, which requires high tensile strength and flexibility.

Clothing according to the present invention includes protective clothing, examination gowns, and surgical outerwear used in medical settings, as well as work clothes and dust-proof clothing used in clean rooms, and the components thereof, such as the inner layer of protective clothing that comes into direct contact with bare skin, and the intermediate and outer layer members that require a barrier function, are also included. In particular, the present invention is suitable for use in the inner layer of protective clothing that requires high tensile strength and flexibility.

Next, the spunbond nonwoven fabric of the present invention will be explained in more detail using examples.

[Measurement and evaluation method]
The respective property values in the examples were determined by the following methods. In addition, unless otherwise specified, the measurement method was measured by the above-mentioned method.

A. MFR of raw material resin and spunbond nonwoven fabric:
The MFR of the spunbond nonwoven fabric was measured using a melt indexer "F-F01" manufactured by Toyo Seiki Seisakusho Co., Ltd. according to the above-mentioned method.

B. Quantitative determination of organic peroxides in raw resin and spunbond nonwoven fabric:
The amount of organic peroxide in the spunbond nonwoven fabric was measured and calculated using a high performance liquid chromatograph (HPLC) "LC-20A" manufactured by Shimadzu Corporation, a mass spectrometer (MS) "API4000" manufactured by Sciex, and a column "SUMIPAX ODS A Series" manufactured by Sumika Chemical Analysis Service Co., Ltd.

The detection limit in the above measurement is 5 ppm, so if no organic peroxides were detected, this is indicated as < 5 ppm in the table.

C. Branching degree λ of raw material resin and spunbond nonwoven fabric:
The branching degree λ of the spunbond nonwoven fabric was measured using a gel permeation chromatograph (GPC) manufactured by Tosoh Corporation's "HLC-8321GPC/HT," a differential refractive index detector manufactured by Tosoh Corporation's "HL-8321GPC/HT," a multi-angle light scattering detector (MALS) manufactured by Wyatt Technology's "DAWNNEON," and a column manufactured by Showa Denko K.K.'s "Shodex HT-806M." Data analysis of the discharge curve was performed using Wyatt Technology's "Empower" and Wyatt Technology's "ASTRA 8.0.1.21," and Japan Polypropylene Corporation's "Novatec" (registered trademark) PP FY6 was used as a linear polypropylene resin having no branched structure, and the measurements and calculations were performed using the above-mentioned methods.

D. Mn, Mw, and Mz of raw material resin and spunbond nonwoven fabric:
The Mn, Mw, and Mz of the polypropylene resin were measured by the above-mentioned method using a PTFE filter "T010A" manufactured by Advantec Toyo Co., Ltd., an apparatus "PL-220" manufactured by Polymer Laboratories, a column Shodex HT-G (guard column) + Shodex HT-806M x 2 (8.0 mm x 30 cm, manufactured by Showa Denko K.K.), and standard samples monodisperse polystyrene manufactured by Tosoh Corporation and dibenzyl manufactured by Tokyo Chemical Industry Co., Ltd., and the data analysis of the discharge curve was performed using "Empower" manufactured by Wyatt Technology.

E. Average Single Fiber Diameter and Spinning Speed:
The average single fiber diameter of the fibers was measured using a "VHX-2000" manufactured by Keyence Corp. The spinning speed (km/min) was calculated from the obtained average single fiber diameter using the above formula.

F. Molecular orientation of fiber Δn:
The molecular orientation Δn of the fibers was measured by the above-mentioned method using a polarizing microscope "BH2" manufactured by Olympus Corporation.

G. Tensile Strength of Fiber:
The tensile strength (cN/dtex) of the fiber was measured by the above-mentioned method using a tensile tester "UTM-III-100" manufactured by Orientec Co., Ltd.

H. Basis weight of spunbond nonwoven fabric:
The basis weight of the spunbond nonwoven fabric was measured and calculated by the method described above.

I. Tensile strength per unit area of spunbond nonwoven fabric:
The tensile strength per unit area weight of the spunbonded nonwoven fabric was measured using a tensile tester "UTM-III-100" manufactured by Orientec Co., Ltd., and was measured and calculated according to the above-mentioned method.

J. Bending resistance of spunbond nonwoven fabric:
The bending resistance of the spunbonded nonwoven fabric was measured by the method described above.

K. Number of defects in spunbond nonwoven fabric:
A 10 cm square area of the spunbonded nonwoven fabric other than the end was visually observed with a magnifying glass, and defects were counted for those in which the fiber diameter was twice or more larger than the average fiber diameter due to thread breakage, and those in which the fiber ends were rounded and looked twice or more larger than the average fiber diameter. This observation was repeated five times in the longitudinal (MD) direction of the nonwoven fabric, and the total number was taken as the number of defects (pieces) of the spunbonded nonwoven fabric. The end of the nonwoven fabric refers to an area of 10% of both ends of the nonwoven fabric in the width direction.

L. Advanced processability of spunbond nonwoven fabric:
In order to grasp the ease of advanced processing such as pleating and joining with other members, a sheet-like test piece (width: 100 mm, length: 300 m) was prepared without the ends of the spunbonded nonwoven fabric, and the test piece was run between a pair of silicone rubber (hardness: 12°) rollers (rubber part outer diameter: 15 cm, surface roughness Ra: 6.3 μm) at a linear pressure of 300 N/cm for 10 minutes at 20 m/min. The presence or absence of adhesion of fibers to the rolls and the state of the spunbonded nonwoven fabric were observed at this time, and the processability (points) was determined by scoring according to the following criteria. A spunbonded nonwoven fabric with a score of 4 or more was judged to be excellent in processability. The ends of the nonwoven fabric refer to the areas of both ends that are 10% of the length of the nonwoven fabric in the width direction.
5 points: No fibers attached to the roll, and no fuzz or tears in the nonwoven fabric.
4 points: There is fiber adhesion to the roll, but no fuzz or tears in the nonwoven fabric are observed.
3 points: There is fiber adhesion to the roll and some fuzz in the nonwoven fabric, but no tears are observed.
2 points: There is fiber adhesion to the roll, the nonwoven fabric is frayed, and there are tears.
1 point: The sheet breaks and the nonwoven fabric wraps around the roll.

M. Effects of spunbond nonwoven fabrics on the skin:
A 10 cm square test piece taken from an area excluding the end of the spunbond nonwoven fabric was cultured in a medium together with "LabCyte EPI-MODEL 24well 6-day culture product" (human epidermis model for assumed sensitive skin) manufactured by Japan Tissue Engineering Co., Ltd. for 24 hours at 37°C. After the culture, 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay was added to perform dye detection based on ISO 10993-5:2009 "Biological evaluation of medical devices" Annex C, and the cell viability (%) was calculated by measuring the absorbance at OD570 and evaluated according to the following criteria (◯, △, ×).
- ◯: Cell viability is 99% or more - △: Cell viability is 95% or more but less than 99% - ×: Cell viability is less than 95% Note that the ends of the nonwoven fabric refer to 10% of the area on both ends of the width direction of the nonwoven fabric.

[Raw resin, polypropylene masterbatch, organic peroxide]
The raw material resins, polypropylene master batches, and organic peroxides used in the examples and comparative examples are as follows.

(Raw material resin A)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 6 g/10 min, an Mw of 458,000, an Mw/Mn of 5.31, an Mz/Mw of 2.79, and a branching degree λ of 1.0×10 ⁻⁶ .

(Raw material resin B)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 0.3 g/10 min, an Mw of 1,319,362, an Mw/Mn of 6.31, an Mz/Mw of 3.06, and a branching degree λ of 1.0×10 ⁻⁶ .

(Raw material resin C)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 0.05 g/10 min, Mw of 2,483,427, Mw/Mn of 7.55, Mz/Mw of 4.79, and a branching degree λ of 1.0×10 ⁻⁶ .

(Raw material resin D)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 10 g/10 min, Mw of 382638, Mw/Mn of 4.90, Mz/Mw of 2.54, and a branching degree λ of 1.0×10 ⁻⁶ .

(Raw material resin E)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 15 g/10 min, an Mw of 331610, an Mw/Mn of 4.55, an Mz/Mw of 2.45, and a branching degree λ of 1.0×10 ⁻⁶ .

(Raw material resin F)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 0.01 g/10 min, Mw of 4,383,165, Mw/Mn of 7.98, Mz/Mw of 5.11, and a branching degree λ of 1.0×10 ⁻⁶ .

(Raw material resin G)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 0.3 g/10 min, an Mw of 1,319,362, an Mw/Mn of 6.31, an Mz/Mw of 3.06, and a branching degree λ of 1.0×10 ⁻⁵ .

(Raw material resin H)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 0.3 g/10 min, an Mw of 1,319,362, an Mw/Mn of 6.31, an Mz/Mw of 3.06, and a branching degree λ of 1.0×10 ⁻⁷ .

(Raw Material Resin I)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 60 g/10 min, an Mw of 204987, an Mw/Mn of 7.98, an Mz/Mw of 5.11, a melting point of 160° C., and a branching degree λ of 1.0×10 ⁻⁶ .

(Raw material resin J)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 230 g/10 min, an Mw of 151,000, an Mw/Mn of 5.31, an Mz/Mw of 2.70, and a branching degree λ of 0.

(Raw material resin K)
A propylene homopolymer obtained using a Ziegler-Natta catalyst, having an MFR of 3.3 g/10 min, an Mw of 575,000, an Mw/Mn of 6.69, an Mz/Mw of 3.20, and a branching degree λ of 0.

(Polypropylene masterbatch α)
Polytechs'"VMPP10X" (polypropylene masterbatch: containing 10% by mass of 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane).

(Organic peroxide β)
"Perhexa 25B" manufactured by NOF Corporation (organic peroxide: 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane).

[Example 1]
(a) Step of obtaining polypropylene-based resin 2.5 parts by mass of polypropylene master batch α was chip-blended with 100 parts by mass of raw material resin A. The chips blended in the above were melt-extruded at 230°C by a single-screw extruder, and the molten resin was supplied to a spinneret while being metered by a gear pump. The MFR of the obtained polypropylene-based resin was 200g/10min, Mw was 132899, Mw/Mn was 2.95, Mz/Mw was 1.85, and the branching degree λ was 1.0× ^10-6 .

(b) Step of Obtaining Fibers Subsequently, the polypropylene-based resin was extruded at a single-hole extrusion rate of 0.4 g/min from a nozzle hole having a hole diameter D of 0.30 mm and a land length L of 0.75 mm at a spinning temperature (spinneret temperature) of 230° C. A spinneret was used in which the introduction hole located directly above the nozzle hole was a straight hole, and the connection portion between the introduction hole and the nozzle hole was tapered.

Then, the extruded fibrous resin was cooled and solidified by applying cooling air at a temperature of 12°C and a speed of 30 m/min from the outside, and then the fiber was obtained by pulling the resin with the air flow at a spinning speed of 4.0 km/min using a rectangular ejector. At this time, the distance from the nozzle hole of the spinneret to the ejector inlet, where the above cooling begins, was set to 550 mm.

(c) Step of collecting fibers Next, the fibers obtained above were opened by passing through a fiber opening section where the surrounding air flow speed was reduced, and then the fibers were collected by landing on a net conveyer where air was sucked from the back side, to obtain a fiber web. Thereafter, the fiber web was transported at a speed of 11 m/min.

(d) Post-processing step Subsequently, the fiber web obtained as described above was thermally bonded at a temperature of 130°C using a pair of upper and lower thermal embossing rolls consisting of an upper roll made of a metal and engraved with a polka dot pattern and having a bonding area ratio of 16%, and a lower roll made of a metal flat roll, to obtain a spunbonded nonwoven fabric having a basis weight of 30 g/ ^m2 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 1. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 12.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.89 (N/25 mm)/(g/m ² ), a bending resistance of 1.6 mN·cm, and two defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with high-order processability.

[Example 2]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin B, and in step (b), the spinning speed was changed from 4.0 km/min to 3.5 km/min. The polypropylene resin obtained in step (a) had an MFR of 55 g/10 min, an Mw of 209623, an Mw/Mn of 2.97, an Mz/Mw of 1.91, and a branching degree λ of 1.0× ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 1. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 13.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.91 (N/25 mm)/(g/m ² ), a bending resistance of 1.8 mN·cm, and three defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with high-order processability.

[Example 3]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin C, and in step (b), the spinning speed was changed from 4.0 km/min to 2.5 km/min. The polypropylene resin obtained in step (a) had an MFR of 20 g/10 min, an Mw of 299587, an Mw/Mn of 2.98, an Mz/Mw of 1.93, and a branching degree λ of 1.0× ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 1. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 15.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.89 (N/25 mm)/(g/m ² ), a bending resistance of 2.0 mN·cm, and five defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with high-order processability.

[Example 4]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin D, and in step (b), the spinning speed was changed from 4.0 km/min to 4.5 km/min. The polypropylene resin obtained in step (a) had an MFR of 380 g/10 min, an Mw of 105955, an Mw/Mn of 2.92, an Mz/Mw of 1.83, and a branching degree λ of 1.0× ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 1. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 11.2 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.79 (N/25 mm)/(g/m ² ), a bending resistance of 1.2 mN·cm, and one defect. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with high-order processability.

[Comparative Example 1]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin E, and in step (b), the spinning speed was changed from 4.0 km/min to 4.5 km/min. The polypropylene resin obtained in step (a) had an MFR of 500 g/10 min, an Mw of 96,173, an Mw/Mn of 2.90, an Mz/Mw of 1.81, and a branching degree λ of 1.0× ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 2. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 11.4 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.45 (N/25 mm)/(g/m ² ), a bending resistance of 0.9 mN·cm, and one defect. The obtained nonwoven fabric had excellent flexibility and few defects, but was inferior in mechanical properties compared to Example 1 and had problems with high-order processability.

[Comparative Example 2]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin F, and in step (b), the spinning speed was changed from 4.0 km/min to 2.0 km/min. The polypropylene resin obtained in step (a) had an MFR of 10 g/10 min, an Mw of 382637, an Mw/Mn of 3.00, an Mz/Mw of 1.95, and a branching degree λ of 1.0× ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 2. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 16.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.70 (N/25 mm)/(g/m ² ), a bending resistance of 3.5 mN·cm, and more than 20 defects, and the obtained nonwoven fabric had excellent mechanical properties and no problems with advanced processability, but was poor in flexibility and had many defects.

[Example 5]
In step (a), 2.5 parts by mass of polypropylene masterbatch α was chip-blended with 100 parts by mass of raw material resin A, whereas 0.25 parts by mass of organic peroxide β was chip-blended with 100 parts by mass of raw material resin B, and in step (b), the spinning speed was changed from 4.0 km/min to 3.5 km/min. Except for this, a spunbonded nonwoven fabric was obtained in the same manner as in Example 1. The polypropylene resin obtained in step (a) had an MFR of 55 g/10 min, an Mw of 209623, an Mw/Mn of 2.97, an Mz/Mw of 1.91, and a branching degree λ of 1.0 × ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 2. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 13.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.87 (N/25 mm)/(g/m ² ), a bending resistance of 1.8 mN·cm, and three defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with advanced processability.

[Example 6]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 2, except that in step (a), the temperature during melt extrusion was changed from 230° C. to 200° C. The polypropylene resin obtained in step (a) had an MFR of 55 g/10 min, an Mw of 209623, an Mw/Mn of 2.97, an Mz/Mw of 1.96, and a branching degree λ of 1.0× ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 2. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 13.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.93 (N/25 mm)/(g/m ² ), a bending resistance of 1.8 mN·cm, and two defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with advanced processability.

[Example 7]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin G, and in step (b), the spinning speed was changed from 4.0 km/min to 1.5 km/min. The polypropylene resin obtained in step (a) had an MFR of 55 g/10 min, an Mw of 209623, an Mw/Mn of 2.97, an Mz/Mw of 1.91, and a branching degree λ of 1.0× ^10-5 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 3. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 16.4 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.71 (N/25 mm)/(g/m ² ), a bending resistance of 1.8 mN·cm, and eight defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with advanced processability.

[Example 8]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin H, and in step (b), the spinning speed was changed from 4.0 km/min to 3.5 km/min. The polypropylene resin obtained in step (a) had an MFR of 55 g/10 min, an Mw of 209623, an Mw/Mn of 2.96, an Mz/Mw of 1.91, and a branching degree λ of 1.0× ^10-7 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 3. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 13.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.85 (N/25 mm)/(g/m ² ), a bending resistance of 3.0 mN·cm, and three defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with advanced processability.

[Comparative Example 3]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin I, polypropylene masterbatch α was not used (organic peroxide was not added), and in step (b), the spinning speed was changed from 4.0 km/min to 3.5 km/min. The polypropylene resin obtained in step (a) had an MFR of 55 g/10 min, an Mw of 209623, an Mw/Mn of 3.22, an Mz/Mw of 2.36, and a branching degree λ of 1.0× ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 3. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 13.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.52 (N/25 mm)/(g/m ² ), a bending resistance of 1.8 mN·cm, and three defects. The obtained nonwoven fabric had excellent flexibility and few defects, but was inferior in mechanical properties compared to Example 2 and had problems with high-order processability.

[Comparative Example 4]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 2, except that in step (a), the temperature during melt extrusion was changed from 230° C. to 180° C. The polypropylene resin obtained in step (a) had an MFR of 55 g/10 min, an Mw of 209623, an Mw/Mn of 2.97, an Mz/Mw of 1.96, and a branching degree λ of 1.0× ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 3. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 13.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.89 (N/25 mm)/(g/m ² ), a bending resistance of 1.6 mN·cm, and three defects, and the obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with advanced processability. However, in terms of the effects on the skin, in an evaluation using a human epidermis model assuming sensitive skin, the cell survival rate after culture was less than 95%.

[Comparative Example 5]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin J, polypropylene masterbatch α was not used (organic peroxide was not added), and in step (b), the spinning speed was changed from 4.0 km/min to 4.2 km/min. The polypropylene resin obtained in step (a) had an MFR of 230 g/10 min, an Mw of 151,000, an Mw/Mn of 5.31, an Mz/Mw of 2.70, and a branching degree λ of 0.

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 4. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 11.7 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.90 (N/25 mm)/(g/m ² ), a bending resistance of 0.8 mN·cm, and one defect. The obtained nonwoven fabric had excellent mechanical properties and few defects, but had problems with high-order processability.

[Example 9]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), 2.5 parts by mass of polypropylene masterbatch α was chip-blended per 100 parts by mass of raw material resin A, but 1.1 parts by mass of polypropylene masterbatch α was chip-blended, and in step (b), the spinning speed was changed from 4.0 km/min to 3.5 km/min. The polypropylene resin obtained in step (a) had an MFR of 55 g/10 min, an Mw of 209,000, an Mw/Mn of 3.71, an Mz/Mw of 2.26, and a branching degree λ of 5.0 × ^10-7 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 4. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 12.8 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.90 (N/25 mm)/(g/m ² ), a bending resistance of 2.0 mN·cm, and three defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with advanced processability.

[Example 10]
In step (a), 2.5 parts by mass of polypropylene masterbatch α was chip-blended with respect to 100 parts by mass of raw material resin A, but other than this, 3.5 parts by mass of polypropylene masterbatch α was chip-blended with respect to 100 parts by mass of raw material resin A. A spunbonded nonwoven fabric was obtained in the same manner as in Example 1. The polypropylene resin obtained in step (a) had an MFR of 380 g/10 min, an Mw of 105,000, an Mw/Mn of 2.80, an Mz/Mw of 1.80, and a branching degree λ of 5.0 × ^10-5 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 4. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 12.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.85 (N/25 mm)/(g/m ² ), a bending resistance of 1.5 mN·cm, and two defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with advanced processability.

[Comparative Example 6]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (a), raw material resin A was changed to raw material resin K, and in step (b), the spinning speed was changed from 4.0 km/min to 3.6 km/min. The polypropylene resin obtained in step (a) had an MFR of 220 g/10 min, an Mw of 147,000, an Mw/Mn of 2.96, an Mz/Mw of 1.91, and a branching degree λ of 0.

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 4. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 12.5 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 0.90 (N/25 mm)/(g/m ² ), a bending resistance of 0.7 mN·cm, and one defect. The obtained nonwoven fabric had excellent mechanical properties and few defects, but had problems with high-order processability.

[Example 11]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in step (c), the adhesion temperature in the hot embossing roll was changed from 130° C. to 135° C. The polypropylene resin obtained in step (a) had an MFR of 200 g/10 min, an Mw of 132,899, an Mw/Mn of 2.95, an Mz/Mw of 1.85, and a branching degree λ of 1.0× ^10-6 .

The evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 5. The obtained spunbonded nonwoven fabric had an average single fiber diameter of 12.0 μm, a tensile strength per unit area of the spunbonded nonwoven fabric of 1.09 (N/25 mm)/(g/m ² ), a bending resistance of 1.9 mN·cm, and two defects. The obtained nonwoven fabric had excellent mechanical properties in addition to flexibility, few defects, and no problems with advanced processability.

Claims

A spunbond nonwoven fabric composed of fibers made of a polypropylene-based resin, the spunbond nonwoven fabric satisfying the following conditions (1) to (3), and the average single fiber diameter of the fibers is 5.0 μm or more and 20.0 μm or less.
(1) The amount of organic peroxide extracted by ultrasonically treating the spunbond nonwoven fabric immersed in a chloroform/methanol solvent with a volume ratio of 1:1 for 15 minutes at 45 kHz and a solution temperature of 30° C. is 100 ppm or more and 1000 ppm or less. (2) The melt flow rate is 20 g/10 min or more and 400 g/10 min or less. (3) The branching degree λ per molecule of the polypropylene resin is calculated using the trifunctional random branching theory from the molecular weight and radius of gyration determined by gel permeation chromatography/multi-angle light scattering measurement device and is 1.0 × 10 -7 or more and 1.0 × 10 -3 or less.
The spunbond nonwoven fabric according to claim 1, wherein the polypropylene-based resin further satisfies the following conditions (4) and (5).
(4) 2.50≦Mw/Mn≦3.20
(5) 1.82≦Mz/Mw≦2.20
Here, Mw, Mn, and Mz are the weight average molecular weight, number average molecular weight, and z-average molecular weight, respectively, determined by gel permeation chromatography.
a step of adding an organic peroxide to a raw material resin and decomposing the raw material resin to obtain a polypropylene-based resin prepared so as to satisfy the following conditions (1) to (3);
a step of spinning the polypropylene-based resin to obtain fibers having an average single fiber diameter of 5.0 μm or more and 20.0 μm or less;
The method for producing a spunbonded nonwoven fabric according to claim 1 or 2, further comprising the step of collecting the fibers.
(1) The amount of organic peroxide extracted by ultrasonically treating the spunbond nonwoven fabric immersed in a chloroform/methanol solvent with a volume ratio of 1:1 for 15 minutes at 45 kHz and a solution temperature of 30° C. is 100 ppm or more and 1000 ppm or less. (2) The melt flow rate is 20 g/10 min or more and 400 g/10 min or less. (3) The branching degree λ per molecule of the polypropylene resin is calculated using the trifunctional random branching theory from the molecular weight and radius of gyration determined by gel permeation chromatography/multi-angle light scattering measurement device and is 1.0 × 10 -7 or more and 1.0 × 10 -3 or less.
The method for producing a spunbond nonwoven fabric according to claim 3, wherein the raw resin is a recycled resin.
A laminated nonwoven fabric comprising the spunbond nonwoven fabric according to claim 1.
A sanitary material comprising the spunbond nonwoven fabric according to claim 1 or the laminated nonwoven fabric according to claim 5.
A garment comprising the spunbonded nonwoven fabric according to claim 1 or the laminated nonwoven fabric according to claim 5.