Spun-bonded nonwoven fabric, laminated nonwoven fabric, pleated body, dust-collecting filter, and dust-collecting device

Abstract

The present invention addresses the problem of providing a spun-bonded nonwoven fabric which, in addition to having a high collection performance (low pressure-loss and high collection-efficiency) and high air permeability, exhibits high pleat processability. The spun-bonded nonwoven fabric is composed of a composite fiber. The composite fiber includes a polypropylene-based resin P1 and a polypropylene-based resin P2 having a melting point Tm2 (°C) which is lower than the melting point Tm1 (°C) of the polypropylene-based resin P1 by 20°C or more and 60°C or less. The apparent density of the spun-bonded nonwoven fabric is 0.10 g / cm3 or more and 0.20 g / cm3 or less, and the bending resistance per unit basis weight in the vertical direction of the spun-bonded nonwoven fabric is 1.5 mg / (g / m2) or more and 10.0 mg / (g / m2) or less.

Description

Spunbond nonwoven fabrics, laminated nonwoven fabrics, pleated bodies, dust collection filters, and dust collection devices

[0001] The present invention relates to a spunbond nonwoven fabric.

[0002] In recent years, filters for air purifiers used in automobiles and homes have become increasingly sophisticated, and there has been much research into filter media that combine high dust removal performance with high breathability (low pressure loss).

[0003] Furthermore, with the adoption of the Sustainable Development Goals (SDGs) at the United Nations Summit, efforts to create a sustainable society are accelerating worldwide. In this context, there is a growing need for environmentally friendly products, including the filters for the air purifiers mentioned above.

[0004] These filters are commonly made of pleated nonwoven fabrics made of short or long fibers, which greatly increases the filtering area and facilitates increased dust removal performance and breathability.

[0005] Various proposals have been made for nonwoven fabrics for forming such pleated bodies, and for example, Patent Document 1 proposes a spunbond nonwoven fabric for filters made of conjugated polyester fibers in which a low-melting-point polyester is disposed around a high-melting-point polyester, and the single fiber fineness of the conjugated polyester fiber, the basis weight of the spunbond nonwoven fabric, apparent density, air permeability per basis weight, and bending resistance per basis weight are all within specific ranges.It is described that this results in a spunbond nonwoven fabric for filters that has high rigidity and breathability while also having excellent dust removal properties.

[0006] Patent Document 2 proposes a laminated electret nonwoven fabric formed by laminating a spunbond nonwoven fabric layer made of fibers formed from a polyolefin resin and a meltblown nonwoven fabric layer made of fibers formed from a polyolefin resin, in which the content, basis weight, and content of a hindered amine compound in the meltblown nonwoven fabric layer are within specific ranges. It describes that this laminated electret nonwoven fabric exhibits high filtering performance with low pressure loss, and further that this laminated electret nonwoven fabric can be made to have excellent processability and moldability into a filter shape, resulting in an air filter unit and air purifier with excellent filtering performance.

[0007] Furthermore, Patent Document 3 proposes a nonwoven fabric made of core-sheath composite fibers in which the core component is made of polyester resin and the sheath component is made of polyolefin resin, and the nonwoven fabric is subjected to electret processing. It is described that this nonwoven fabric has excellent dust collection performance, and further has excellent mechanical properties and dimensional stability.

[0008] International Publication No. 2017 / 110365 International Publication No. 2021 / 153296 Japanese Patent Application Laid-Open No. 2008-150753

[0009] The spunbond nonwoven fabric for filters disclosed in Patent Document 1 has high rigidity and excellent dust-removing properties, but there is still room for improvement in terms of breathability.

[0010] The laminated electret nonwoven fabric disclosed in Patent Document 2 exhibits high collection performance with low pressure loss, but in order to make it into a filter medium with sufficient strength, it is necessary to bond it to a reinforcing material when making it into a pleated body, and as a result, there is still room for improvement in the breathability of the filter medium when made into a filter medium.

[0011] The nonwoven fabric disclosed in Patent Document 3 has a certain level of collection performance, but because it is produced at a high spinning temperature, the sheath component tends to melt excessively, making it difficult to produce a bulky nonwoven fabric, and the breathability is insufficient.

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a spunbond nonwoven fabric that not only has high collection performance (low pressure loss, high collection efficiency) and high breathability, but also exhibits high pleating processability.

[0013] As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that a spunbond nonwoven fabric composed of composite fibers containing a specific polypropylene resin, having an apparent density and bending resistance within specific ranges, can achieve significantly improved collection performance (low pressure loss, high collection efficiency) and breathability, and further exhibit excellent pleating properties and shape retention.

[0014] Furthermore, when used as a dust collection filter, this spunbond nonwoven fabric not only makes it possible to reduce the basis weight compared to conventional methods, but because it is a mono-material, it is easy to recycle and opens the way for reuse, thereby contributing to reducing the environmental burden.

[0015] The present invention has been completed based on these findings, and provides the following inventions.

[0016] [1] A spunbond nonwoven fabric made of composite fibers, wherein the composite fibers are made of a polypropylene-based resin P1 and a polypropylene-based resin P2 having a melting point T ｍ２ (°C) is the melting point T ｍ１ and a polypropylene-based resin P2 having a temperature 20°C or more and 60°C or less lower than (°C), and the apparent density of the spunbond nonwoven fabric is 0.10 g / cm 3 0.20g / cm or more 3 The bending resistance per unit area weight in the warp direction of the spunbond nonwoven fabric is 1.5 mg / (g / m ２ ) or more 10.0mg / (g / m ２ ) or less, spunbond nonwoven fabric.

[0017] [2] The spunbond nonwoven fabric according to [1], wherein at least some of the contact points between the composite fibers have micro-fused portions having a length of 5 μm or more and 100 μm or less in the fiber axis direction.

[0018] [3] The spunbond nonwoven fabric according to [1] or [2], wherein the conjugated fiber contains a hindered amine compound.

[0019] [4] The spunbond nonwoven fabric according to any one of [1] to [3], wherein the average single fiber diameter of the conjugated fibers is 10 μm or more and 40 μm or less.

[0020] [5] The spunbond nonwoven fabric according to any one of [1] to [4] above, which has been subjected to electret processing.

[0021] [6] Polypropylene resin P1 and a melting point T ｍ２ (°C) is the melting point T ｍ１ and a polypropylene-based resin P2 having a temperature 20°C or more and 60°C or less lower than (°C) from a conjugate spinning nozzle, and the spun-out polypropylene-based resin P1 and the polypropylene-based resin P2 are pulled and stretched to form conjugate fibers; a step of depositing the conjugate fibers to form a fiber web composed of the conjugate fibers; and a step of thermally bonding the fiber web, wherein the thermal bonding is performed by passing a gas that satisfies the following formula 1 through the fiber web. ｍ２ -20≦T Ｗ ≦T ｍ２ +20 ... (Equation 1) where, T Ｗ is the temperature of the gas (°C).

[0022] [7] A laminated nonwoven fabric obtained by laminating the spunbonded nonwoven fabric according to any one of [1] to [5] above and a meltblown nonwoven fabric.

[0023] [8] A pleated body comprising the spunbonded nonwoven fabric according to any one of [1] to [5] above or the laminated nonwoven fabric according to [7] above.

[0024] [9] A dust-collecting filter using the pleated body according to [8].

[0025]

[10] A dust collecting device using the dust collecting filter according to [9] above.

[0026] The present invention provides a spunbond nonwoven fabric that not only exhibits high collection performance (low pressure loss, high collection efficiency), significantly improved breathability, and excellent pleating processability and shape retention, but also contributes to reducing environmental impact. Due to these properties, the spunbond nonwoven fabric of the present invention is particularly suitable for use as a dust collection filter or dust collection device.

[0027] FIG. 1 is a conceptual diagram of a collection efficiency measuring device for measuring the air permeability of the spunbond nonwoven fabric of the present invention.

[0028] The spunbonded nonwoven fabric of the present invention is a spunbonded nonwoven fabric composed of composite fibers, and the composite fibers are made of a polypropylene-based resin P1 and a cellulose ester having a melting point T ｍ２ (°C) is the melting point T ｍ１ and a polypropylene-based resin P2 whose apparent density is 0.10 g / cm 3 0.20g / cm or more 3 The bending resistance per unit area weight in the warp direction of the spunbond nonwoven fabric is 1.5 mg / (g / m ２ ) or more 10.0mg / (g / m ２ ) below.

[0029] In the present invention, the longitudinal direction refers to the sheet conveyance direction during the production of the spunbond nonwoven fabric, i.e., the winding direction of the nonwoven fabric roll, and the transverse direction refers to the direction perpendicular to the sheet conveyance direction, i.e., the winding direction of the nonwoven fabric roll. When the spunbond nonwoven fabric is not in a rolled state, for example, because it is cut, the longitudinal and transverse directions are determined according to the procedures (i-1) to (i-4) below. (i-1) A single direction is arbitrarily determined within the plane of the spunbond nonwoven fabric, and a test piece measuring 38.1 mm in length (effective sample length L = 25.4 mm) and 25.4 mm in width is taken along that direction. (i-2) Similarly, test pieces measuring 38.1 mm in length (effective sample length L = 25.4 mm) and 25.4 mm in width are taken in directions rotated 30°, 60°, and 90° from the direction in which the test piece was taken. (i-3) For the test pieces in each direction, the bending resistance of those test pieces is measured in accordance with the method described in "6.7.4 Gurley method" of "6.7 Bending resistance (JIS method and ISO method)" of JIS L1913:2010 "Testing methods for general nonwoven fabrics." (i-4) The direction in which the bending resistance value obtained by measurement is the highest is taken as the warp direction of the spunbond nonwoven fabric, and the direction perpendicular to this is taken as the weft direction. However, if there are two or more directions with the highest bending resistance, the following shall apply. The direction in which the bending resistance in the direction perpendicular to the "highest direction" is lower is taken as the warp direction of the spunbond nonwoven fabric. For example, when the bending resistance of the test piece at 0 degrees and 30 degrees is the highest, the bending resistance in the perpendicular direction, i.e., 90 degrees and 120 degrees, is compared, and if the bending resistance of the 90 degree test piece is low, 0 degrees is taken as the longitudinal direction, and if the bending resistance of the 120 degree test piece is low, 30 degrees is taken as the longitudinal direction. When the bending resistance in the direction perpendicular to the "highest direction" is also equal, for example, when the bending resistance in all six directions is equal, any of the six directions is taken as the longitudinal direction, and the direction perpendicular to this is taken as the transverse direction.

[0030] The components will be described in detail below, but the present invention is not limited to the scope described below as long as it does not go beyond the gist of the present invention, and various modifications are possible within the scope of the present invention.

[0031] [Polypropylene Resin P1] The conjugate fiber constituting the spunbonded nonwoven fabric of the present invention contains polypropylene resin P1. The polypropylene resin refers to a resin having propylene units as repeating units, and examples thereof include propylene homopolymers and copolymers of propylene with ethylene or various α-olefins. Among these, propylene homopolymers are preferred in order to prevent a decrease in spinning stability and strength.

[0032] When a copolymer of propylene and various α-olefins is used, ethylene or butene is preferred as the copolymerization component, as they have excellent spinning stability, and ethylene is more preferred. In addition, the copolymerization ratio is preferably 15 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less, in order to prevent a decrease in spinning stability and strength.

[0033] The α-olefin species and α-olefin content in the polymerization components of the polypropylene resin can be calculated, for example, from the peak positions and peak area ratios detected by a nuclear magnetic resonance spectrometer (NMR, for example, "ECZ-600R" manufactured by JEOL RESONANCE).

[0034] The polypropylene resin P1 used in the present invention preferably contains propylene homopolymers in an amount of 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, which can maintain good spinnability and improve strength.

[0035] Here, the melting point (T ｍ１ ) is preferably 120°C or higher and 200°C or lower. ｍ１) is preferably 120°C or higher, more preferably 130°C or higher, and even more preferably 140°C or higher, resulting in a spunbond nonwoven fabric with even better heat resistance. Furthermore, by having a melting point of preferably 200°C or lower, more preferably 180°C or lower, and even more preferably 170°C or lower, the thermoplastic resin P2, which has a lower melting point than the polyester-based resin P1 described below, is less susceptible to thermal degradation during the production of the spunbond nonwoven fabric, resulting in a spunbond nonwoven fabric with excellent strength and rigidity. In addition, during the production process, the yarns discharged from the spinneret can be easily cooled, suppressing excessive fusion between the fibers, resulting in a spunbond nonwoven fabric with excellent uniformity of texture.

[0036] In addition, the melting point of the polypropylene-based resin P1 refers to the maximum melting peak temperature obtained by measuring the polypropylene-based resin P1 by differential scanning calorimetry (DSC) when the melting point of the polypropylene-based resin P1 can be measured and calculated using only the polypropylene-based resin P1. On the other hand, when measuring the melting point of the polypropylene-based resin P1 from a spunbond nonwoven fabric or the conjugated fibers constituting the spunbond nonwoven fabric, a value calculated by the following procedure is used. (1) A conjugated fiber piece of approximately 2 mg is collected from the spunbond nonwoven fabric. When measuring from the conjugated fibers, the conjugated fibers are cut into conjugated fiber pieces of approximately 2 mg. (2) The conjugated fiber piece of (1) is heated from room temperature to 200°C at a heating rate of 20°C / min using a differential scanning calorimeter (DSC, for example, a Perkin-Elmer "DSC 8500") to obtain a DSC curve. (3) The peak top temperature (melting peak temperature) of the melting endothermic peak is read from the DSC curve, and the highest melting peak temperature (°C) is rounded to one decimal place to obtain the melting point T of the polypropylene resin P1. ｍ１ (℃).

[0037] The melt flow rate (hereinafter sometimes abbreviated as MFR) of the polypropylene-based resin P1 is preferably 10 g / 10 min or more and 100 g / 10 min or less. By setting the lower limit of the MFR of the polypropylene-based resin to preferably 10 g / 10 min or more, more preferably 20 g / 10 min or more, and even more preferably 30 g / 10 min or more, the spinnability during the production process is excellent, resulting in a spunbond nonwoven fabric with few defects. On the other hand, by setting the upper limit of the MFR of the polypropylene-based resin P1 to preferably 100 g / 10 min or less, more preferably 80 g / 10 min or less, and even more preferably 60 g / 10 min or less, the single yarn strength of the composite fiber is increased, resulting in a spunbond nonwoven fabric with excellent strength.

[0038] The MFR of the polypropylene resin P1 according to the present invention and the polypropylene resin P2 described below are both values ​​measured by ASTM D1238 (Method A). This standard stipulates that the MFR of polypropylene resins be measured under a load of 2.16 kg and at a temperature of 230°C.

[0039] The MFRs of the polypropylene resin P1 used in the present invention and the polypropylene resin P2 described below can also be adjusted by blending two or more resins having different MFRs in any desired ratio. In this case, the MFR of the resin blended with the main polypropylene resin (referring to the polypropylene resin that accounts for the largest mass % of the polypropylene resins) is preferably 10 g / 10 min or more and 1,000 g / 10 min or less, more preferably 20 g / 10 min or more and 800 g / 10 min or less, and even more preferably 30 g / 10 min or more and 600 g / 10 min or less. Using such a blend of resins prevents the blended polypropylene resin from causing local viscosity unevenness, makes it possible to uniformize the single fiber diameter and single fiber fineness of the composite fiber, and also enables stable spinning, resulting in a spunbond nonwoven fabric with few defects.

[0040] To the polypropylene resin P1 used in the present invention, additives such as commonly used antioxidants, weathering stabilizers, light resistance stabilizers, heat resistance stabilizers, antistatic agents, antistatic aids, spinning agents, antiblocking agents, matting agents, antifungal agents, antibacterial agents, antiviral agents, flame retardants, metal oxides, hydrophilic agents, crystal nucleating agents, pigments, lubricants including polyethylene wax, aliphatic bisamides and / or aliphatic monoamides, or other polymers may be added as needed, provided that the effects of the present invention are not impaired.

[0041] [Polypropylene-based resin P2] The conjugate fiber according to the present invention has a melting point T ｍ２ (°C) is the melting point T ｍ１ (°C), the polypropylene-based resin P2 has a melting point T ｍ２ (°C) is (T ｍ１ -60)℃ or more (T ｍ１ -20) °C or lower.

[0042] The melting point T of this polypropylene resin P2 ｍ２ (°C), the lower limit of which is (T ｍ１ -60) ° C or higher, preferably (T ｍ１ -50) ° C or higher, more preferably (T ｍ１ By setting the melting point T to -40°C or higher, the thermal adhesiveness is improved during heat fusion, and a spunbond nonwoven fabric having excellent strength and rigidity is obtained. ｍ２ (°C), the upper limit of which is (T ｍ１ -20) ° C or less, preferably (T ｍ１ -25) ° C. or less, more preferably (T ｍ１ By keeping the temperature at or below -30°C, the spunbond nonwoven fabric has heat resistance sufficient for practical use.

[0043] In addition, when the melting point of the polypropylene-based resin P2 can be measured and calculated using only the polypropylene-based resin P2, it refers to the maximum melting peak temperature obtained by measuring the polypropylene-based resin P2 by differential scanning calorimetry (DSC). On the other hand, when measuring the melting point of the polypropylene-based resin P2 from a spunbond nonwoven fabric or the conjugated fibers constituting the spunbond nonwoven fabric, a value calculated by the following procedure is used. (1) A conjugated fiber piece of approximately 2 mg is collected from the spunbond nonwoven fabric. When measuring from the conjugated fiber, the conjugated fiber is cut into a conjugated fiber piece of approximately 2 mg. (2) The conjugated fiber piece of (1) is heated from room temperature to 250°C at a heating rate of 20°C / min using a differential scanning calorimeter (DSC, for example, a Perkin-Elmer "DSC 8500") to obtain a DSC curve. (3) The peak top temperature (melting peak temperature) of the melting endothermic peak is read from the DSC curve, and the lowest melting peak temperature (°C) is rounded to one decimal place to obtain the melting point T of the polypropylene resin P2. ｍ２ (℃).

[0044] The polypropylene resin P2 is preferably the same resin as the polypropylene resin P1 in terms of resin type. That is, a propylene homopolymer or a copolymer of propylene with ethylene or various α-olefins is preferred. Among these, a propylene homopolymer is particularly preferred because it improves spinning stability during the production process, resulting in a spunbond nonwoven fabric with higher strength. When a copolymer of propylene with various α-olefins is used, ethylene is preferred as the copolymerization component because of its excellent spinning stability. In this case, the copolymerization ratio is preferably 15 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less, in order to prevent a decrease in spinning stability and strength. The α-olefin species and α-olefin content in the polymerization components of the polypropylene resin can be measured and calculated using the same method as for the polypropylene resin P1 described above.

[0045] The MFR of the polypropylene-based resin P2 is preferably 10 g / 10 min or more and 100 g / 10 min or less. By setting the lower limit of the MFR of the polypropylene-based resin to preferably 10 g / 10 min or more, more preferably 20 g / 10 min or more, and even more preferably 30 g / 10 min or more, the spinnability during the production process is excellent, resulting in a spunbond nonwoven fabric with few defects. On the other hand, by setting the upper limit of the MFR of the polypropylene-based resin P1 to preferably 100 g / 10 min or less, more preferably 80 g / 10 min or less, and even more preferably 60 g / 10 min or less, the single yarn strength of the composite fiber is increased, resulting in a spunbond nonwoven fabric with excellent strength.

[0046] Furthermore, to the polypropylene-based resin P2, additives such as commonly used antioxidants, weathering stabilizers, light resistance stabilizers, heat resistance stabilizers, antistatic agents, antistatic aids, spinning agents, antiblocking agents, matting agents, antifungal agents, antibacterial agents, antiviral agents, flame retardants, metal oxides, hydrophilic agents, crystal nucleating agents, pigments, lubricants including polyethylene wax, aliphatic bisamides and / or aliphatic monoamides, or other polymers may be added as needed, provided that the effects of the present invention are not impaired.

[0047] [Hindered amine compound] The conjugated fiber constituting the spunbonded nonwoven fabric of the present invention preferably further contains a hindered amine compound, and more preferably contains a hindered amine compound represented by the following general formula (1):

[0048]

[0049] (where R １ ~R ３ is hydrogen or an alkyl group having 1 to 2 carbon atoms, R ４ (wherein R is hydrogen or an alkyl group having 1 to 6 carbon atoms.) This results in a spunbond nonwoven fabric that has high chargeability and charge retention after electret processing, as described below. Since such a spunbond nonwoven fabric has excellent dust removal performance as a filter, the spunbond nonwoven fabric of the present invention can be used alone as a coarse dust filter.

[0050] Examples of the hindered amine compound include poly[(6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidyl)imino)hexamethylene((2,2,6,6-tetramethyl-4-piperidyl)imino)] (manufactured by BASF Japan Ltd., "Chimassorb" (registered trademark) 944LD), and polycondensation product of dimethyl succinate-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine (manufactured by BASF Japan Ltd., "Tinuvin" (registered trademark) 6 22LD), bis(1,2,2,6,6-pentamethyl-4-piperidyl) 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butylmalonate (manufactured by BASF Japan Ltd., "Tinuvin" (registered trademark) 144), and polycondensate of dibutylamine / 1,3,5-triazine / N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine / N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine (manufactured by BASF Japan Ltd., "Chimassorb" (registered trademark) 2020FDL).

[0051] Examples of the hindered amine compound represented by the general formula (1) include poly[(6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidyl)imino)hexamethylene((2,2,6,6-tetramethyl-4-piperidyl)imino)] (manufactured by BASF Japan Ltd., "Chimassorb" (registered trademark) 944LD), di and a polycondensate of butylamine, 1,3,5-triazine, N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine, N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine (manufactured by BASF Japan Ltd., "Chimassorb" (registered trademark) 2020FDL). Needless to say, a combination of multiple types of hindered amine compounds may also be used.

[0052] The presence of a hindered amine compound in a composite fiber is determined as follows: (1) Five small sample pieces are taken from the spunbond nonwoven fabric of the present invention in the transverse direction of the nonwoven fabric. (2) The small sample pieces are subjected to Soxhlet extraction with a methanol / chloroform mixed solution, and the extract is repeatedly subjected to HPLC fractionation. (3) Each fraction is subjected to IR measurement, GC measurement, GC / MS measurement, MALDI-MS measurement, １ H-NMR measurement, and １３ The structure is identified using instrumental analysis such as C-NMR measurement.

[0053] With regard to the hindered amine compound, the content of the hindered amine compound in the composite fiber is preferably 0.1% by mass or more and 5.0% by mass or less. With regard to the range of the content, the lower limit is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.5% by mass or more, thereby resulting in a spunbond nonwoven fabric with high chargeability and charge retention after electret processing. On the other hand, with regard to the range of the content, the upper limit is preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably 3.0% by mass or less, thereby resulting in excellent spinnability in the production process and therefore a spunbond nonwoven fabric with few defects.

[0054] The content (mass%) of hindered amine compounds in the composite fiber is a value measured and calculated as follows: (1) Randomly collect small samples of 5 g or more from the spunbond nonwoven fabric and measure the mass (g). (2) The small samples are subjected to Soxhlet extraction with a methanol / chloroform mixed solution, and only the extract is further separated and subjected to high performance liquid chromatography (HPLC). This HPLC separation is performed under the following conditions: Column: organic silica hybrid (particle diameter 1 μm to 5 μm) Mobile phase: aqueous ammonia solution, ammonia methanol solution, and mixtures thereof (3) Each separated sample is subjected to IR measurement, GC measurement, GC / MS measurement, MALDI-MS measurement, 1H-NMR measurement, and １３The structure is identified using instrumental analysis such as C-NMR measurement. (4) The total mass (mg) of the fractions containing the hindered amine compound obtained from the small sample pieces is divided by the total mass (g) of the small sample pieces, and the resulting value is expressed as a percentage and rounded to one decimal place to determine the content of the hindered amine compound.

[0055] [Conjugated Fibers Comprising Polypropylene Resin as a Main Component] The spunbonded nonwoven fabric of the present invention is composed of conjugated fibers containing the polypropylene resin P1 and the polypropylene resin P2.

[0056] The composite form of the composite fiber may be, for example, a concentric sheath-core type, an eccentric sheath-core type, an islands-in-the-sea type, a side-by-side type, etc. Among these, the concentric sheath-core type and the eccentric sheath-core type are more preferred because they have excellent spinnability, can uniformly bond fibers together by thermal bonding, and can improve dust removal performance, and the concentric sheath-core type is a particularly preferred embodiment from the viewpoints of thermal bonding properties and dust removal performance.

[0057] The cross-sectional shape of the conjugated fiber may be a round cross-section, a flat cross-section, or a modified cross-section such as a Y-shape or a C-shape. Of these, a round cross-section is a more preferred embodiment because it has excellent spinnability and can be spun at a high spinning speed to produce a conjugated fiber with excellent single yarn strength. Although a hollow cross-section can also be used as the cross-sectional shape, a solid cross-section is a preferred embodiment because it suppresses yarn breakage during spinning in the production process described below and results in a spunbonded nonwoven fabric with few surface defects.

[0058] In the composite fiber according to the present invention, at least some of the contact points between the composite fibers preferably have micro-fused portions having a length of 5 μm to 100 μm in the fiber axial direction. Here, the "micro-fused portions" refer to portions other than the macro-fused portions (non-macro-fused portions) described below, where adjacent fibers are fused to each other. The "contact points between fibers" also include, in addition to the micro-fused portions, portions where fibers are entangled with each other and portions where fibers are simply in contact with each other without being fused to each other.

[0059] The micro-fused portions preferably have a length of 5 μm to 100 μm in the fiber axis direction. The presence of such micro-fused portions results in a spunbond nonwoven fabric that is excellent in strength and stiffness and also highly breathable.

[0060] When the composite fiber has the above-mentioned micro-fused portions, this can be confirmed by observing the composite fiber from the cross section of the spunbonded nonwoven fabric using a microscope (for example, "VW-9000" manufactured by Keyence Corporation) or a scanning electron microscope (for example, "VHX-D500" manufactured by Keyence Corporation). In this case, when the spunbonded nonwoven fabric has macro-fused portions described below, the micro-fused portions are confirmed in the non-macro-fused portions.

[0061] The ratio of the number of contact points having micro-fused portions to the total number of contact points between fibers is preferably 20% to 100%, more preferably 50% to 100%, and even more preferably 80% to 100%. In this way, a spunbond nonwoven fabric with even greater strength and rigidity can be obtained by increasing the ratio of micro-fused portions to the total number of contact points between fibers.

[0062] The ratio of the number of contacts having micro-fused portions is calculated by the following procedure. (1) Five small sample pieces (100 mm x 100 mm) are randomly taken from the spunbond nonwoven fabric, and a cross-sectional sample in the transverse direction is cut out from each small sample piece. If the spunbond nonwoven fabric has macro-fused portions (described below), the cross-sectional sample is cut out so as to pass through the center of the non-macro-fused portion (non-macro-fused portion). (2) A cross-sectional photograph of each small sample piece is taken at 100 to 500 magnification using a microscope (e.g., Keyence Corporation's "VW-9000") or a scanning electron microscope (e.g., Keyence Corporation's "VHX-D500"), with the entire thickness of the spunbond nonwoven fabric included in the photograph. If the spunbond nonwoven fabric has macro-fused portions (described below), the photograph is taken at the center between the macro-fused portions. (3) For all fiber cross sections in the cross-sectional photograph, count the number of fiber contacts and the number of contacts with micro-fused portions. (4) Divide the total number of fiber contacts with micro-fused portions in all cross-sectional photographs by the total number of fiber contacts in all cross-sectional photographs, express the result as a percentage, and round off to one decimal place to obtain the ratio of the number of contacts with micro-fused portions.

[0063] The presence of the micro-fused portions can be achieved by appropriately adjusting the composite form of the composite fiber, the volume ratio of the polypropylene-based resin P1 to the polypropylene-based resin P2 in the composite fiber, and / or the spinning temperature, the output rate per single hole of the spinneret, the spinning cooling conditions (such as the temperature and volume of the cooling air), and the conditions for thermally fusing the fiber contacts by passing hot air through them (such as the temperature and time for passing the hot air). The number ratio (%) of the contacts having the micro-fused portions can be controlled by appropriately adjusting the composite form of the composite fiber, the volume ratio of the polypropylene-based resin P1 to the polypropylene-based resin P2 in the composite fiber, the apparent density of the spunbonded nonwoven fabric (described below), the average center-to-center distance of the nearest neighbor fibers, and / or the spinning temperature, the output rate per single hole of the spinneret, the spinning cooling conditions (such as the temperature and volume of the cooling air), and the conditions for thermally fusing the fiber contacts by passing hot air through them (such as the temperature and time for passing the hot air).

[0064] The conjugated fiber according to the present invention preferably has an average single fiber diameter of 10 μm or more and 40 μm or less. With regard to this range of average single fiber diameter, if the lower limit is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and particularly preferably 25 μm or more, a spunbonded nonwoven fabric with excellent breathability will be obtained. On the other hand, with regard to the above range, if the upper limit is preferably 40 μm or less, more preferably 35 μm or less, even more preferably 32 μm or less, and particularly preferably 30 μm or less, a spunbonded nonwoven fabric with excellent dust removal performance and excellent strength and rigidity will be obtained due to an increase in micro-fused portions.

[0065] The average single fiber diameter (μm) of the composite fibers constituting the spunbonded nonwoven fabric is calculated using the following procedure: (1) Ten small samples (100 mm x 100 mm) are randomly collected from the spunbonded nonwoven fabric. (2) Surface photographs are taken at 300x to 1000x magnification using a microscope (e.g., Keyence Corporation's "VW-9000") or a scanning electron microscope (e.g., Keyence Corporation's "VHX-D500"), and the widths (diameters) of five composite fibers from each sample (50 total) are measured for the non-fused portions of the composite fibers. If the composite fiber has an irregular cross-section, the cross-sectional area is measured, and the diameter of a perfect circle with the same cross-sectional area is determined. The non-fused portion is the portion where the fibers are not fused or deformed. (3) The 50 measured diameter values ​​are averaged, and the average is rounded to one decimal place.

[0066] This average single fiber diameter can be controlled by appropriately adjusting the volume ratio of the polypropylene-based resin P1 to the polypropylene-based resin P2 in the composite fiber, and / or the spinning temperature, the output per single hole in the spinneret, the spinning speed, etc., which will be described later.

[0067] In the conjugated fiber according to the present invention, the volume ratio of the polypropylene-based resin P1 is preferably 50% by volume or more and 90% by volume or less. By setting the volume ratio of the polypropylene-based resin P1 to preferably 50% by volume or more, more preferably 60% by volume or more, and even more preferably 70% by volume or more, the strength of the single yarn is improved, resulting in a spunbonded nonwoven fabric having sufficient strength for practical use. On the other hand, by setting the volume ratio of the polypropylene-based resin P1 to preferably 90% by volume or less, more preferably 80% by volume or less, and even more preferably 70% by volume or less, the polypropylene-based resins P2 are firmly fused together during thermal bonding, resulting in a spunbonded nonwoven fabric having excellent strength and rigidity.

[0068] [Spunbonded nonwoven fabric] The spunbonded nonwoven fabric of the present invention is composed of the conjugated fiber. The spunbonded nonwoven fabric has an apparent density of 0.10 g / cm ３ 0.20g / cm or more ３The lower limit of the apparent density range of the spunbond nonwoven fabric is preferably 0.10 g / cm or less. ３ More preferably, 0.13 g / cm ３ More preferably, 0.15 g / cm ３ By satisfying the above conditions, the number of contact points where micro-fused portions are formed between the composite fibers increases, resulting in a spunbond nonwoven fabric having sufficient strength and rigidity for practical use. ３ or less, more preferably 0.19 g / cm ３ More preferably, 0.18 g / cm or less ３ The spunbond nonwoven fabric has excellent breathability when:

[0069] In the present invention, the apparent density (g / cm ３ ) is the basis weight (g / m) before rounding, measured by the method described below. ２ ) and thickness (mm) according to the following formula, and rounded to two decimal places. Apparent density (g / cm ３ ) = {[Basis weight (g / m ２ ) ] / [thickness (mm)] × 10 －３ ···(formula).

[0070] In addition, the spunbond nonwoven fabric of the present invention has a bending resistance per unit area weight in the warp direction of 1.5 mg / (g / m ２ ) or more 10.0mg / (g / m ２ ) or less. Here, the range of the bending resistance per unit basis weight in the warp direction of the spunbond nonwoven fabric is expressed in SI units as 15 μN / (g / m ２ ) or more 98μN / (g / m ２ ) as follows.

[0071] The lower limit of the bending resistance in the longitudinal direction of the spunbond nonwoven fabric is preferably 1.5 mg / (g / m ２ ) or more (in SI units, 15 μN / (g / m ２ ) or more, and the same applies below.), and more preferably 2.0 mg / (g / m ２ ) or more (20μN / (g / m ２) or more), and more preferably 2.5 mg / (g / m ２ ) or more (25μN / (g / m ２ ) or more), the spunbond nonwoven fabric has excellent pleatability and rigidity. ２ ) or less (98μN / (g / m ２ ) or less), more preferably 9.0 mg / (g / m ２ ) or less (88μN / (g / m ２ ) or less), and more preferably 8.0 mg / (g / m ２ ) or less (78μN / (g / m ２ ) below), it is possible to prevent quality defects such as creases from occurring during sheet conveyance or roll winding in the manufacturing process, resulting in a spunbond nonwoven fabric with few defects such as creases or wrinkles.

[0072] In the present invention, the bending resistance per unit area weight in the longitudinal direction (mg / (g / m ２ )) is a value measured and calculated by the following method in accordance with "6.7 Bending resistance (JIS method and ISO method)" of "6.7.4 Gurley method (JIS method)" in JIS L1913:2010 "General nonwoven fabric testing methods." (i) Five test pieces each having a length of 38.1 mm in the warp direction (effective sample length L = 25.4 mm) and a length of d = 25.4 mm in the weft direction are taken from a spunbond nonwoven fabric in the width direction. (ii) Attach each of the collected test pieces to a chuck and fix the chuck by aligning it with the 1 1 / 2" (1.5 inches = 38.1 mm) scale on the movable arm A. In this case, 1 / 2" (0.5 inches = 12.7 mm) of the sample length is 1 / 4" (0.25 inches = 6.35 mm) on the chuck, and 1 / 4" (0.25 inches = 6.35 mm) is applied to the tip of the pendulum at the free end of the sample, so the effective sample length L for measurement is the test piece length minus 1 / 2" (0.5 inches = 12.7 mm). (iii) Next, attach appropriate weights W from the fulcrum of pendulum B to the lower weight attachment holes a, b, and c (mm). ａ , W ｂ , W ｃ(g) is attached to the movable arm A, and the movable arm A is rotated at a constant speed, and the scale RG (mgf) is read when the test piece separates from the pendulum B. The scale is read to one decimal place. The weight attached to the weight attachment hole can be selected as appropriate, but it is preferable to set it so that the scale RG is 4 to 6. (iv) Measurements are carried out 5 times on each of the front and back sides of five points on the test piece, for a total of 50 times. (v) The bending resistance value (Br (mg)) is calculated from the obtained scale RG value using the following formula.

[0073]

[0074] (vi) The bending resistance value (Br (mg)) is converted into the basis weight (g / m) before rounding, which is measured by the method described below. ２ (vii) Further, the mg / (g / m ２ The bending resistance (Brx) of the spunbond nonwoven fabric in the warp direction, expressed in units of μN / (g / m), is expressed in SI units (μN / (g / m)). ２ When describing a value (referred to as Bry) indicated in units of Bry (μN / (g / m), convert the unit using the following conversion formula and round off the obtained value to the nearest whole number: Bry (μN / (g / m) ２ ))=Brx(mg / (g / m ２ ))×9.807...(Formula).

[0075] The bending resistance per unit area weight in the warp direction of the spunbonded nonwoven fabric can be controlled by appropriately adjusting the volume ratio of the polypropylene-based resin P1 to the polypropylene-based resin P2 of the composite fiber, the average single fiber diameter, the thickness, the apparent density, and / or the spinning speed and thermal bonding conditions (heat roll compression rate, temperature, linear pressure, hot air temperature, time for passing the hot air, etc.) described below.

[0076] The spunbond nonwoven fabric of the present invention has a basis weight of 40 g / m ２ 150g / m or more ２It is preferable that the weight per unit area of ​​the spunbonded nonwoven fabric is 40 g / m or less. Even in this range, the spunbonded nonwoven fabric of the present invention has excellent strength and rigidity, and is therefore sufficiently durable when used as a filter. In addition, the amount of plastic used in the filter can be reduced, which in turn reduces the environmental load. The lower limit of the weight per unit area of ​​the spunbonded nonwoven fabric is preferably 40 g / m or less. ２ More preferably, 50 g / m ２ More preferably, 60 g / m ２ By setting the density to 150 g / m or more, a spunbond nonwoven fabric having excellent strength and rigidity can be obtained. On the other hand, the upper limit of the above range is preferably 150 g / m ２ or less, more preferably 120 g / m ２ More preferably, 100 g / m or less ２ By satisfying the following conditions, a spunbond nonwoven fabric having excellent breathability and pleatability can be obtained.

[0077] In the present invention, the basis weight of a spunbond nonwoven fabric is determined in accordance with "6.2 Mass per unit area" of JIS L1913:2010 "Testing methods for general nonwoven fabrics," and is measured by the following procedure. (1) Three test pieces measuring 20 cm x 25 cm are taken per meter of sample width. (2) The mass (g) of each piece is measured under standard conditions. (3) The arithmetic mean value is calculated as the mass per meter. ２ Mass per unit (g / m ２ ) and round the value to the nearest tenth.

[0078] The weight per unit area can be controlled by appropriately adjusting the discharge rate per hole of the spinneret, the speed of the net conveyor that collects the yarn, and the like.

[0079] The spunbond nonwoven fabric of the present invention preferably has a thickness of 0.20 mm or more and 1.0 mm or less. By setting the lower limit of the thickness range of the spunbond nonwoven fabric to preferably 0.20 mm or more, more preferably 0.25 mm or more, and even more preferably 0.30 mm or more, the spunbond nonwoven fabric has excellent rigidity and a sufficient dust retention capacity as a filter aggregate. By setting the upper limit of the thickness range to preferably 1.0 mm or less, more preferably 0.90 mm or less, and even more preferably 0.80 mm or less, the number of pleats can be increased during pleating of the filter, thereby increasing the filtration area, resulting in a spunbond nonwoven fabric that is easy to use as a filter with excellent dust removal performance and breathability.

[0080] In the present invention, the thickness (mm) of a spunbond nonwoven fabric is determined in accordance with "5.1" of JIS L1906:2000 "Testing Methods for General Long-Fiber Nonwoven Fabrics" and is measured by the following procedure: (1) Using a pressure probe with a diameter of 10 mm and a load of 10 kPa, the thickness is measured at 10 points per meter of the nonwoven fabric at equal intervals in the width direction to the nearest 0.01 mm. (2) The average value of the 10 points is rounded to two decimal places.

[0081] The thickness of the spunbonded nonwoven fabric can be controlled by appropriately adjusting the volume ratio of the polypropylene-based resin P1 to the polypropylene-based resin P2 in the composite fibers, the average single fiber diameter, and / or the thermal bonding conditions (shape of the macro-fused portions, shortest distance between adjacent macro-fused portions, compression rate, temperature, linear pressure, hot air temperature, and time for passing the hot air, etc.) described below.

[0082] The air permeability of the spunbond nonwoven fabric of the present invention is 100 cm ３ / (cm ２ ・Seconds) or more 700cm ３ / (cm ２ Within this range, when used as a filter, power consumption during operation can be kept low, and the environmental load can be reduced. The lower limit of the range of the air permeability of the spunbond nonwoven fabric is preferably 100 cm ３ / (cm ２seconds) or more, more preferably 150 cm ３ / (cm ２ sec) or more, more preferably 200 cm ３ / (cm ２ By setting the upper limit of the above range to 700 cm or more, the spunbond nonwoven fabric has excellent breathability when used as a filter. ３ / (cm ２ seconds) or less, more preferably 600 cm ３ / (cm ２ seconds) more preferably 500 cm ３ / (cm ２ ・seconds), the resulting spunbond nonwoven fabric has strength and rigidity.

[0083] In the present invention, the air permeability of a spunbond nonwoven fabric is a value (cm ) measured using an air permeability tester (for example, "FX3300-IV" manufactured by TEXTEST Co., Ltd.) in accordance with "6.8.1 Frazier method" in "6.8 Air Permeability (JIS method)" of JIS L1913:2010 "Testing methods for general nonwoven fabrics." ３ / (cm ２ The value obtained by rounding off the time (seconds) to the first decimal place shall be used.

[0084] The air permeability of the spunbonded nonwoven fabric can be controlled by appropriately adjusting the average single fiber diameter, thickness, apparent density, and / or the thermal bonding conditions (shape of the macrofused portions, shortest distance between adjacent macrofused portions, compression rate, temperature, linear pressure, hot air temperature, time for passing hot air, etc.) described below.

[0085] The spunbonded nonwoven fabric of the present invention preferably has regularly arranged macro-fused portions. Here, the term "macro-fused portion" refers to a location where the fibers are fused together after being compressed in the thickness direction of the spunbonded nonwoven fabric, for example, to such an extent that the cross-sectional shape of the fibers is deformed to a degree different from the shape of the remaining portions, and furthermore, the fibers melt to the point of forming a mass or film at that location. Specifically, this refers to a portion that is thermocompression-bonded by a pair of thermal embossing rolls, at least one of which has an engraved surface, or a portion that is thermally fused by ultrasonic vibration. When sufficient heat is applied to a portion during thermocompression or thermal fusion bonding to fuse the entire composite fiber in that portion, the shape and area of ​​the compressed portion of the thermal embossing roll or the like used can be considered to be identical to the shape and area of ​​the macro-fused portion. For example, in the case of thermocompression bonding using a hot embossing roll, when thermal bonding is performed using a pair of rolls having projections and recesses as described below, the shape and area of ​​the macro-fused portion are considered to be the same as the shape and area of ​​the portion where the projections of the upper roll and the projections of the lower roll overlap and contact the nonwoven fiber web. Furthermore, when thermal bonding is performed using a roll having projections and recesses and a flat roll as described below, the shape and area of ​​the macro-fused portion are considered to be the same as the shape and area of ​​the portion where the projections of the roll having projections and recesses contact the nonwoven fiber web. The presence of the macro-fused portions described above results in a spunbond nonwoven fabric with excellent strength.

[0086] In the present invention, "regularly arranged" refers to a structure in which the centers of the macro-fused portions are regularly arranged at regular intervals in both the longitudinal and transverse directions of the spunbonded nonwoven fabric. This reduces the variation in strength of the spunbonded nonwoven fabric. Specific arrangements include those in which the centers of the macro-fused portions are arranged in a polygonal lattice pattern, such as a triangular lattice, a quadrangular lattice, a hexagonal lattice, or other lattice formed from shapes such as a triangular lattice, a rectangular lattice, a trapezoid, a parallelogram, or a rhombic lattice. Naturally, lattices in which each side has the same length, such as a square lattice, an equilateral triangular lattice, or a regular hexagonal lattice, are also included. A staggered arrangement is also included in the above-mentioned polygonal lattice arrangement.

[0087] In the spunbonded nonwoven fabric of the present invention, the shape of the macro fused portions can be selected depending on the application for which the spunbonded nonwoven fabric is to be used, and examples thereof include circles, ellipses, squares, rectangles, parallelograms, rhombuses, regular hexagons, and regular octagons.

[0088] When the spunbonded nonwoven fabric of the present invention has regularly arranged macro-fused portions, the shortest distance between adjacent macro-fused portions is preferably 0.5 mm or more and 2.0 mm or less. By setting the lower limit of the range of the shortest distance between adjacent macro-fused portions to preferably 0.5 mm or more, more preferably 0.7 mm or more, and even more preferably 0.9 mm or more, voids within the spunbonded nonwoven fabric are secured, resulting in a spunbonded nonwoven fabric with excellent breathability. On the other hand, by setting the upper limit of the range to preferably 2.0 mm or less, more preferably 1.8 mm or less, and even more preferably 1.6 mm or less, the composite fibers are efficiently gripped by the macro-fused portions, resulting in a spunbonded nonwoven fabric with excellent strength.

[0089] The shortest distance between adjacent macrofused portions is measured and calculated using the following procedure: (1) Five small sample pieces (100 mm x 100 mm) are randomly collected from the spunbond nonwoven fabric. (2) For each small sample piece, a surface photograph is taken at 20x to 300x magnification using a microscope (e.g., Keyence Corporation's "VW-9000") or a scanning electron microscope (e.g., Keyence Corporation's "VHX-D500") so that at least one regularly arranged repeating unit of the macrofused portions is included. (3) Three macrofused portions are randomly selected from each photograph, and the shortest distance between adjacent macrofused portions is measured. The boundary between the macrofused portion and the non-macrofused portion is used as the start and end points of the distance. If multiple fused portions exist around one macrofused portion, the distance to the nearest macrofused portion is measured. (4) The shortest distance values ​​measured at 15 points are averaged and rounded off to one decimal place to obtain the shortest distance (mm) between adjacent macro-fused portions.

[0090] When regularly arranged macro-fused portions are formed in the spunbonded nonwoven fabric of the present invention, the area of ​​each of the macro-fused portions is 0.10 mm ２ Over 1.00 mm ２ The lower limit of the area range of each macro-fused portion is preferably 0.10 mm or less. ２ More preferably, 0.15 mm ２ More preferably, 0.20 mm or more ２ By setting the thickness to 1.00 mm or more, the composite fibers are firmly fused together by the macro-fused portions, resulting in a spunbonded nonwoven fabric with excellent strength. ２ Less than or equal to 0.70 mm, more preferably ２ Less than 0.40 mm, more preferably ２ By satisfying the above condition, voids are secured within the spunbonded nonwoven fabric, resulting in a spunbonded nonwoven fabric with excellent breathability.

[0091] In the present invention, the area of ​​each of the macro-fused portions is a value measured and calculated by the following procedure. (1) Five small sample pieces (100 mm x 100 mm) are randomly taken from the spunbond nonwoven fabric. (2) For each small sample piece, a surface photograph is taken at 20 to 300 magnifications using a microscope (for example, Keyence Corporation's "VW-9000") or a scanning electron microscope (for example, Keyence Corporation's "VHX-D500") so that at least one regularly arranged repeating unit of the macro-fused portions is included. (3) Three macro-fused portions are randomly selected from each photograph, and their areas are measured. A total of 15 areas (mm ２ ) was calculated and rounded to two decimal places to obtain the individual areas (mm ２ )

[0092] When the spunbond nonwoven fabric of the present invention has regularly arranged macrofused portions, the ratio of the total area of ​​the macrofused portions to the surface of the spunbond nonwoven fabric (hereinafter sometimes simply referred to as the macrofused portion area ratio) is preferably 5% or more and 30% or less. When the lower limit of the macrofused portion area ratio range is 5% or more, more preferably 8% or more, and even more preferably 10% or more, the spunbond nonwoven fabric has excellent strength. On the other hand, when the upper limit of the range is preferably 30% or less, more preferably 20% or less, and even more preferably 15% or less, the spunbond nonwoven fabric has sufficient breathability for practical use as a filter aggregate.

[0093] The adjacent macro-fused portion area ratio is a value measured and calculated by the following procedure: (1) Five small sample pieces (100 mm x 100 mm) are randomly taken from the spunbond nonwoven fabric. (2) For each small sample piece, the area (S1) of the repeating unit of the macro-fused portion arrangement and the area (S2) of the macro-fused portion contained in the repeating unit are measured at five locations using a microscope (e.g., Keyence Corporation's "VW-9000") or a scanning electron microscope (e.g., Keyence Corporation's "VHX-D500"), and S2 is divided by S1 to calculate the area ratio (%). (3) The area ratios (%) of the 25 total locations are averaged and rounded to the nearest whole number to obtain the macro-fused portion area ratio (%).

[0094] In one preferred embodiment, the spunbond nonwoven fabric of the present invention contains a functional agent. Specific examples include those in which a thin film of the functional agent is attached to the fiber surface (i.e., the fiber surface is coated with the functional agent), those in which particles of the functional agent are attached to the fiber surface, and those in which the functional agent added to the fiber is exposed on the fiber surface.

[0095] Examples of functional agents include antistatic agents, antibacterial agents, antifungal agents, antiallergen agents, antiviral agents, vitamins, flame retardants, hydrophilic agents, water repellents, and oil repellents.

[0096] The spunbonded nonwoven fabric of the present invention is preferably electret-processed by the method described below. By using such a spunbonded nonwoven fabric, dust removal performance can be improved by utilizing electrostatic action in addition to physical action.

[0097] Whether or not the spunbond nonwoven fabric of the present invention has been subjected to electret processing can be confirmed, for example, by a method of evaluation using a spectrophotometer with a red positively charged toner and a blue negatively charged toner, as described in International Publication No. 2017 / 110299.

[0098] [Method for producing spunbonded nonwoven fabric] Next, a method for producing the spunbonded nonwoven fabric of the present invention will be described. The method for producing the spunbonded nonwoven fabric of the present invention comprises mixing a polypropylene-based resin P1 and a polypropylene-based resin P2 having a melting point T ｍ２ (°C) is the melting point T ｍ１ (°C), and a polypropylene-based resin P2 having a temperature that is 20°C or more and 60°C or less than (°C), the polypropylene-based resin P1 and the polypropylene-based resin P2 being melt-extruded from a conjugate spinneret, and the spun polypropylene-based resin P1 and the polypropylene-based resin P2 are pulled and stretched to form conjugate fibers; a step of depositing the conjugate fibers to form a fiber web composed of the conjugate fibers; and a step of thermally bonding the fiber web, wherein the thermal bonding is performed by passing a gas that satisfies the following formula 1 through the fiber web: T ｍ２ -20≦T Ｗ ≦T ｍ２ +20 ... (Equation 1) where, T Ｗ is the temperature (°C) of the gas. By using this production method, a spunbonded nonwoven fabric having excellent breathability and rigidity can be stably obtained. Each step of the above embodiment will be described in further detail below.

[0099] (A) Step of forming composite fiber In this step, polypropylene-based resin P1 and a polymer having a melting point T ｍ２ (°C) is the melting point T ｍ１(°C), and a polypropylene-based resin P2 having a temperature 20°C or more and 60°C or less lower than that of the polypropylene-based resin P1 are melt-extruded from a conjugate spinneret, and the spun polypropylene-based resin P1 and the polypropylene-based resin P2 are pulled and stretched to form a conjugate fiber.

[0100] First, polypropylene-based resin P1 and polypropylene-based resin P2 are melt-extruded through a composite spinneret. The polypropylene-based resin P1 and polypropylene-based resin P2 are the same as those described above. Then, for example, polypropylene-based resin P1 and polypropylene-based resin P2 are melted in separate extruders, metered, and fed to the composite spinneret.

[0101] In this case, by setting the temperature of the composite spinneret, i.e., the spinning temperature when spinning the composite fiber, to preferably 180°C or higher and 260°C or lower, more preferably 200°C or higher and 250°C or lower, and even more preferably 220°C or higher and 240°C or lower, it is possible to suppress thermal degradation of the polypropylene-based resin P1 and the polypropylene-based resin P2 while maintaining a stable molten state and obtaining excellent spinnability.

[0102] The composite spinneret may be of various shapes such as round or rectangular, but a rectangular spinneret is preferred because it is less likely for the yarns to melt or rub against each other.

[0103] The polypropylene resin P1 and the polypropylene resin spun out by melt extrusion are preferably then cooled. Examples of methods for cooling the spun yarn include forcibly blowing cold air onto the yarn, naturally cooling at the ambient temperature around the yarn, and adjusting the distance between the spinneret and the ejector. Alternatively, a combination of these methods can be used. The cooling conditions can be appropriately adjusted in consideration of the output per hole of the spinneret, the spinning temperature, the ambient temperature, and the like.

[0104] Subsequently, the polypropylene resin P1 and the polypropylene resin P2 that have been melt-extruded and spun are pulled and stretched.

[0105] During this pulling and drawing, it is preferable to suction and draw the yarn with compressed air using an ejector (air sucker). Various shapes of ejector, such as round or rectangular, can be used, but a rectangular ejector is preferred because it uses a relatively small amount of compressed air, is excellent in energy cost, and facilitates yarn spreading. In particular, by using a rectangular conjugate spinneret in combination with a rectangular ejector, it is possible to use a relatively small amount of compressed air, is excellent in energy cost, is less likely to cause fusion or abrasion between the yarns, and facilitates yarn spreading.

[0106] The spinning speed is preferably 3,000 m / min or more and 6,000 m / min or less, more preferably 3,500 m / min or more and 5,500 m / min or less, and even more preferably 4,000 m / min or more and 5,000 m / min or less, which not only ensures high productivity but also promotes the orientation and crystallization of the fibers, thereby enabling the production of high-strength long fibers.

[0107] In the present invention, the spinning speed refers to a value measured and calculated by the following method. Specifically, the average single fiber fineness (dtex) is calculated by rounding off to one decimal place from the mass per 10,000 m of length based on the average single fiber diameter and the solid density of the resin used. The spinning speed is then calculated to two significant digits based on the average single fiber fineness and the total throughput (g / min) of polypropylene resins P1 and P2 discharged from one outlet hole of the composite spinneret set under each condition (hereinafter abbreviated as single-hole throughput) according to the following formula: Spinning speed (m / min) = (10,000 × [single-hole throughput (g / min)]) / [average single fiber fineness (dtex)] (formula).

[0108] The spinning speed can be controlled by appropriately adjusting the spinning temperature, the discharge rate per single hole of the spinneret, the distance between the spinneret and the ejector, the conditions for cooling the spun yarn (temperature, volume, etc. of the cold air), etc.

[0109] (B) Step of forming a fiber web In this step, the composite fibers are deposited to form a fiber web made of the composite fibers.

[0110] In the present invention, it is also a preferred embodiment to temporarily bond the fiber web by contacting one side of the fiber web with a hot flat roll on a net, which prevents the surface layer of the fiber web from turning over or being blown away while being transported on the net, thereby improving transportability from collecting the yarns to thermal bonding.

[0111] Furthermore, the collected fiber web or the temporarily bonded spunbond nonwoven fabric (both of which are denoted as S) can be laminated in multiple layers, such as SS, SSS, and SSSS, which is a preferred embodiment because it improves productivity and uniformity of the fabrication.

[0112] (C) Step of thermally bonding the fiber web In this step, the fiber web is thermally bonded. This thermal bonding is performed by passing a gas that satisfies the following formula 1 through the fiber web: T ｍ２ -20≦T Ｗ ≦T ｍ２ +20 ... (Equation 1) Note that T Ｗ , T ｍ２ is as described above.

[0113] The temperature T of the gas passing through the fiber web Ｗ is the melting point T of the polypropylene resin P2 used. ｍ２ At least 20°C lower than T ｍ２ The temperature is 20°C higher than the temperature of the temperature range of formula 1, that is, the temperature range of formula 1. ｍ２ 20°C lower than that (i.e., T ｍ２ -20 (°C), the same applies below) or higher, preferably T ｍ２ -10 (°C) or higher, more preferably T ｍ２ (°C) or more, the contact points between the composite fibers can be firmly heat-fused to obtain a spunbonded nonwoven fabric having excellent strength and rigidity. ｍ２ In contrast to T ｍ２ +20 (°C) or less, preferably T ｍ２ +15 (°C) or less, more preferably T ｍ２By setting the temperature at +10°C or less, it is possible to prevent the spunbond nonwoven fabric from being partially melted or broken due to excessive heat being applied.

[0114] The time for passing the gas through the fiber web is preferably 1 second or more and 20 seconds or less. By passing the gas for preferably 1 second or more, more preferably 3 seconds or more, and even more preferably 5 seconds or more, the contact points between the composite fibers can be firmly heat-fused even in areas where the basis weight is partially high and hot air is difficult to penetrate, thereby producing a spunbonded nonwoven fabric with excellent strength and rigidity. On the other hand, by passing the gas for preferably 20 seconds or less, more preferably 15 seconds or less, and even more preferably 10 seconds or less, the spunbonded nonwoven fabric can be prevented from being partially melted or broken due to excessive heat.

[0115] Furthermore, the gas velocity when passing the gas through the fiber web is preferably 0.5 m / s or more and 30 m / s or less. By setting the gas velocity to be preferably 0.5 m / s or more, more preferably 3.0 m / s or more, and even more preferably 5.0 m / s or more, the gas can be passed through to the interior of the fiber web, and the contact points between the fibers can be firmly heat-fused to form a spunbonded nonwoven fabric with excellent strength and rigidity. On the other hand, by setting the gas velocity to be preferably 30 m / s or less, more preferably 25 m / s or less, and even more preferably 20 m / s or less, the fiber web can be prevented from folding or wrinkling.

[0116] Here, the gas may be air, water vapor, nitrogen, an inert gas (argon, etc.), etc., with air being more preferred from the viewpoints of worker safety and cost.

[0117] Furthermore, before or after the step of passing a gas through the fiber web, the fiber web may be heat-sealed with a heated roll to form regularly arranged macro-fused portions.

[0118] The method of heat fusing using a heated roll is not particularly limited, and examples thereof include a method of heat fusing using various rolls such as a heat embossing roll in which each of a pair of upper and lower rolls has an engraving (uneven portion) on its surface, a heat embossing roll consisting of a combination of a roll with one flat (smooth) surface and a roll with an engraving (uneven portion) on its surface, and a heat calender roll consisting of a combination of a pair of upper and lower flat (smooth) rolls, and a method of heat fusing using ultrasonic vibration of a horn.

[0119] Among these, it is preferable to use a pair of heat embossing rolls, each of which has an engraved (uneven) surface, or a heat embossing roll consisting of a combination of a roll with one flat (smooth) surface and a roll with an engraved (uneven) surface, which improves productivity and also makes it possible to provide regularly arranged macro-fused portions that improve the strength of the spunbonded nonwoven fabric.

[0120] As for the surface material of the hot embossing roll, a pair of metal rolls is preferred in order to obtain a sufficient thermocompression effect and to prevent the engraving (concave and convex portions) of one embossing roll from being transferred to the surface of the other roll.

[0121] The shape of the pressing part of the heat embossing roll or the like can be selected depending on the application for which the spunbond nonwoven fabric is to be used, and examples thereof include a circle, an oval, a square, a rectangle, a parallelogram, a rhombus, a regular hexagon, and a regular octagon.

[0122] In order to ensure that the centers of the compressed portions are regularly spaced at regular intervals in both the warp and weft directions of the spunbonded nonwoven fabric, it is preferable that the centers of the compressed portions are regularly arranged in the form exemplified above, thereby reducing the variation and anisotropy of the strength of the spunbonded nonwoven fabric.

[0123] As described above, when forming regularly arranged macro-fused portions, the surface temperature of the hot embossing roll is set to a temperature equal to or higher than the melting point T of the polyolefin resin P2 used. ｍ２ 30℃ lower than Tｍ２ 10°C higher than the temperature, i.e., (T ｍ２ -30℃) or more (T ｍ２ It is preferable that the surface temperature of the hot embossing roll is in the range of T ｍ２ 30°C lower than that (i.e., T ｍ２ -30 (°C), the same applies below) or higher, and preferably T ｍ２ -20 (°C) or higher, more preferably T ｍ２ By setting the temperature at -10°C or higher, it is possible to obtain a spunbonded nonwoven fabric having a strength sufficient for practical use by achieving strong thermal bonding. ｍ２ In contrast to T ｍ２ +10 (°C) or less, preferably T ｍ２ +5 (°C) or less, more preferably T ｍ２ By setting the temperature at or below (°C), it is possible to suppress a decrease in tear strength due to excessive heat bonding, and to prevent the spunbond nonwoven fabric from sticking to the heat roll during heat bonding.

[0124] The linear pressure of the hot embossing roll during thermal bonding is preferably 50 N / cm or more and 500 N / cm or less. By setting the linear pressure of the roll to preferably 50 N / cm or more, more preferably 100 N / cm or more, and even more preferably 150 N / cm or more, strong thermal bonding can be achieved, resulting in a spunbond nonwoven fabric with practical strength. On the other hand, by setting the linear pressure of the hot embossing roll to preferably 500 N / cm or less, more preferably 400 N / cm or less, and even more preferably 300 N / cm or less, it is possible to prevent a decrease in tear strength due to excessive thermal bonding.

[0125] However, although heat fusion using a heat roll can form macro-fused portions and improve tensile strength, the macro-fused portions can have poor breathability and the reduced thickness can result in insufficient rigidity and poor pleating processability. Therefore, the step of heat fusion using a heat roll can be omitted depending on the application and the target performance.

[0126] (D) Other post-processing steps In the method for producing the spunbond nonwoven fabric of the present invention, it is preferable to further carry out various post-processing steps, as in the case of general spunbond nonwoven fabrics. Of course, in the present invention, the spunbond nonwoven fabric obtained by carrying out these post-processing steps is also considered to be the spunbond nonwoven fabric of the present invention.

[0127] For example, functional agents such as the above-mentioned antibacterial agents, antifungal agents, antiallergen agents, antiviral agents, vitamin supplements, flame retardants, etc. may be attached to the fiber surface by post-processing. In particular, when the spunbond nonwoven fabric of the present invention is used as a filter, the effect of imparting these functions can be significantly improved compared to conventional filters.

[0128] Preferred methods for attaching a functional agent to a fiber surface include a coating method using a gravure roll or a kiss roll, an impregnation method, a spray method, etc. In addition, the solvent used to dilute the functional agent is preferably aqueous, as it is safe and has a low environmental impact. Here, aqueous solvents include water alone, or aqueous solutions containing water-soluble organic solvents such as lower alcohols such as methanol and ethanol, lower ketones such as acetone and methyl ethyl ketone, lower carboxylic acids such as acetic acid, and glycols such as ethylene glycol, propylene glycol, and diethylene glycol, and can be selected depending on the purpose.

[0129] Furthermore, by subjecting the spunbond nonwoven fabric of the present invention to electret processing, the dust removal performance is improved by utilizing electrostatic action in addition to physical action, and the fabric can be used alone as a coarse dust filter.

[0130] The electret processing method is not particularly limited, but suitable methods include corona charging, charging a nonwoven fabric sheet by adding water and then drying it (e.g., methods described in JP-A-9-501604 and JP-A-2002-249978), and thermal electret processing. In the case of corona charging, the electric field strength is preferably 15 kV / cm or more, and more preferably 20 kV / cm. This strengthens the charge and improves the electrostatic collection performance. The charging process may be carried out continuously during the production of the nonwoven fabric, or the nonwoven fabric may be wound up once produced and processed in a separate process.

[0131] [Laminated nonwoven fabric] The spunbonded nonwoven fabric of the present invention can be laminated with another filter layer in order to further improve dust removal performance.As the method for obtaining such filter filter material, the filter layer of dust removal performance further improves and the spunbonded nonwoven fabric of the present invention can be sprayed with thermoplastic resin, heat-melting fiber, and the method of bonding through heat path, or the method of spraying with moisture-curing urethane resin etc. by spraying method and bonding.

[0132] In addition, as the filter layer that further improves the dust removal performance, the melt-blown nonwoven fabric obtained by the melt-blown method, the nanofiber nonwoven fabric obtained by the electrospinning method (electrospinning method), the dry nonwoven fabric obtained by forming short fibers into a web by the carding method or the air-laid method, the wet nonwoven fabric obtained by dispersing short fibers in water and combing them onto a net, etc. can be mentioned.Among them, because they have excellent dust removal performance, melt-blown nonwoven fabric and nanofiber nonwoven fabric are preferably used.In addition, this filter layer can also be electret melt-blown nonwoven fabric or nanofiber nonwoven fabric that is subjected to electret processing.By doing this, dust removal performance can be further improved.

[0133] [Pleated body, dust collection filter, dust collection device] The spunbond nonwoven fabric of the present invention can be used as a filter medium in the form of a sheet by incorporating it into a frame material to form a filter unit.

[0134] A pleated article containing the spunbonded nonwoven fabric or the laminated nonwoven fabric is also a preferred embodiment. This pleated article can be obtained by pleating the spunbonded nonwoven fabric or the laminated nonwoven fabric by repeatedly folding the fabric in mountain and valley directions.

[0135] The dust collecting filter according to the present invention is preferably made using this pleated body. This dust collecting filter can be obtained by setting the pleated body in a frame, and such a dust collecting filter has a large filtration area and is excellent in dust removal performance and pressure loss. Specific examples of this dust collecting filter, from the viewpoint of fine dust collection efficiency, include filters for air conditioners, filters for air purifiers, and automobile cabin filters.

[0136] Furthermore, a dust collecting device according to the present invention includes this dust collecting filter. Specific examples of this dust collecting device include home air conditioners, building air conditioners, air purifiers, and vehicle air conditioners.

[0137] The spunbond nonwoven fabric of the present invention can be suitably used not only for the above-mentioned dust collection filter applications but also for other filter applications used in vehicle materials, daily necessities, industrial materials, etc.

[0138] Next, the spunbond nonwoven fabric of the present invention will be described in detail based on examples, although the present invention is not limited to these examples.

[0139] [Measurement Methods] The evaluation methods and measurement conditions used in the examples are explained below. Unless otherwise specified, the measurements of each physical property were carried out according to the above-mentioned methods.

[0140] (1) Spinning speed (m / min): The spinning speed was measured and calculated by the method described above.

[0141] (2) Average single fiber diameter (μm) of composite fiber, presence or absence of micro-fused portions, and number ratio (%) of contact points having micro-fused portions: These were measured and calculated using an electron microscope “VHX-D500” manufactured by Keyence Corporation according to the above-mentioned method.

[0142] (3) Thickness (mm) and basis weight (g / m ２ ), apparent density (g / cm 3 The thickness, basis weight and apparent density of the spunbond nonwoven fabric were measured and calculated by the above-mentioned methods. The thickness was measured using a Teclock SM-123 device.

[0143] (4) Bending resistance (mg) per unit area weight in the warp direction of spunbond nonwoven fabric: Measurement was performed using a "No. 311 Gurley type softness tester" manufactured by Yasuda Seiki Seisakusho Co., Ltd., according to the method described above.

[0144] (5) Airflow (cm ３ / (cm ２ (Seconds)) The measurement was carried out using a TEXTEST "FX3300-IV" measuring device according to the method described above.

[0145] (6) Pleating Processability: 400 pleats were continuously pleated using a reciprocating pleating machine under the following conditions: pleat height: 25 mm, pleating speed: 40 pleats / min, and back pressure: 0.1 MPa. The pleating processability of the spunbonded nonwoven fabric was evaluated by observing the pleat shape and pitch of the pleats when released after pleating. The evaluation was rated according to the following three levels, with "A" being acceptable. A: The peak shape and pitch spacing were stable. B: Disorders were observed in the peak shape and pitch spacing. C: A pleat shape could not be formed.

[0146] (7) Shape retention: A spunbond nonwoven fabric pleated by the above method was fixed to a frame so that the pleat pitch was 4 mm, and left for 24 hours with a load of 5 kPa applied from one side. The shape of the pleats was then observed to evaluate the shape retention of the spunbond nonwoven fabric. The evaluation was rated on the following three levels, with "A" being acceptable. A: No deformation of the pleats was observed. B: Partial collapse or deformation of the pleats was observed. C: Overall collapse or deformation of the pleats was observed.

[0147] (8) Dust Removal Performance Evaluation [Collection Efficiency (%), Pressure Loss (Pa)]: Three measurement samples measuring 15 cm x 15 cm were taken from the spunbond nonwoven fabric in the width direction, and the collection efficiency of each measurement sample was measured using the collection efficiency measurement device shown in Figure 1. The collection efficiency measurement device shown in Figure 1 has a dust storage box 2 connected upstream of a sample holder 1 in which the measurement sample M is set, and a flow meter 3, a flow control valve 4, and a blower 5 connected downstream. A particle counter 6 is attached to the sample holder 1, and the number of dust particles on the upstream and downstream sides of the measurement sample M can be measured via a selector cock 7. The sample holder 1 is also equipped with a pressure gauge 8, which allows the static pressure difference between the upstream and downstream sides of the measurement sample M to be read.

[0148] To measure the collection efficiency, a 10% solution of polystyrene 0.309U (manufacturer: Nacalai Tesque, Inc.) was diluted 200 times with distilled water and filled into the dust collection box 2. Next, the measurement sample M was set in the sample holder 1, and the air flow rate was adjusted with the flow control valve 4 so that the filter passing speed was 3.2 m / min, and the dust concentration was adjusted to 10,000 to 40,000 particles / 2.83 × 10 －４ m ３ (0.01 ft ３ ) and stabilized within the range, the number of dust particles D upstream and the number of dust particles d downstream of the measurement sample M were measured three times per measurement sample using a particle counter 6 ("KC-01D" manufactured by Rion Co., Ltd.), and the collection efficiency (%) for particles of 0.3 μm to 0.5 μm was calculated using the following formula based on JIS K0901:1991 "Test methods for shape, dimensions and performance of filter media for collecting dust samples in gas." The average value of the five measurement samples was calculated and rounded to one decimal place to obtain the final collection efficiency (%): Collection efficiency (%) = [1 - (d / D)] x 100 (formula) (where d represents the total number of downstream dust particles measured three times, and D represents the total number of upstream dust particles measured three times). The more excellent the dust removal efficiency of a nonwoven fabric, the lower the number of downstream dust particles and therefore the higher the collection efficiency value.

[0149] The pressure loss was determined by reading the static pressure difference between the upstream and downstream of the measurement sample M during the measurement of the collection efficiency using a pressure gauge 8. The average value of the five measurement samples was calculated, and the value was rounded to one decimal place to obtain the final pressure loss (Pa).

[0150] [Polypropylene Resins and Hindered Amine Compounds Used] Next, the resins used in the Examples and Comparative Examples are described in detail. Polypropylene Resin P1: Melt flow rate (MFR) of 34 g / 10 min, melting point of 160°C, solid density of 0.91 g / cm ３ Polypropylene resin consisting of a homopolymer of the above. Polypropylene resin P2: Melt flow rate (MFR) 25 g / 10 min, melting point 125 ° C, solid density 0.91 g / cm ３ Polypropylene resin consisting of a homopolymer of the above Hindered amine compound: hindered amine compound "Chimasorb" (registered trademark) 944 (manufactured by BASF Japan Ltd., represented as "HA-D" in Tables 1 to 3).

[0151] [Heat Rolls Used During Heat Fusion Bonding] Furthermore, the details of the heat rolls used during heat fusion bonding in the Examples and Comparative Examples are described below. Metallic embossing roll: An embossing roll made of an engraved metal roll (referred to as "M-EMB" in Tables 1 to 3) Metallic flat roll: A metallic flat roll (referred to as "M-FLT" in Tables 1 to 3).

[0152] (Example 1) (Step of forming composite fiber) The polypropylene-based resin P1 and the polypropylene-based resin P2 containing the hindered amine-based compound in an amount of 1.0% by mass relative to the mass of the composite fiber were each melted at a temperature of 220° C. Thereafter, the polypropylene-based resin P1 as the core component and the polypropylene-based resin P2 as the sheath component were spun from the outlet holes of a composite spinneret capable of forming concentric sheath-core composite fibers at a spinneret temperature (corresponding to the spinning temperature) of 240° C., a mass ratio of core component:sheath component = 60:40, and a throughput per single hole (single-hole throughput rate) of 2.0 g / min, and then pulled and drawn by an ejector at a spinning speed of 3,300 m / min to form concentric sheath-core composite fibers having a circular cross-sectional shape.

[0153] (Step of forming a fiber web) The obtained composite fibers were deposited on a net conveyor while controlling the fiber arrangement with a fiber spreading plate, to form a fiber web composed of composite fibers having an average single fiber diameter of 29.1 μm.

[0154] (Step of thermally bonding fiber web) Subsequently, the obtained fiber web was thermally fused using a thermal embossing roll consisting of a metal embossing roll engraved with staggered circular protrusions and a metal flat roll, under conditions where the surface temperatures of both the upper and lower rolls were 100°C and the linear pressure applied to the fiber web was 300 N / cm, so that the area ratio of macrofused portions was 11% and the shortest distance between macrofused portions was 1.1 mm, thereby imparting regularly arranged macrofused portions.

[0155] Thereafter, air at a temperature of 130°C and a wind speed of 15 m / sec was passed through the fiber web having the macro-fused portions for 10 seconds to form micro-fused portions at the contact points between the composite fibers, resulting in a fiber web with a basis weight of 80 g / m. ２ A spunbond nonwoven fabric of 100g was obtained.

[0156] (Other post-processing steps) Furthermore, the obtained spunbond nonwoven fabric was made to travel along the water surface of a water tank to which pure water was supplied, and a slit-shaped suction nozzle was brought into contact with the surface to suck the water, thereby permeating the entire surface of the spunbond nonwoven fabric, and after draining the water, the spunbond nonwoven fabric was allowed to dry naturally, thereby obtaining an electret-processed spunbond nonwoven fabric. The evaluation results are shown in Table 1.

[0157] (Example 2) An electret-processed spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that in the (step of forming the composite fiber), the single-hole output rate was changed to 1.5 g / min and the spinning speed was changed to 4500 m / min to form composite fibers with an average single fiber diameter of 21.6 μm. The evaluation results are shown in Table 1.

[0158] (Example 3) An electret-processed spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that in the (step of forming the composite fiber), the polypropylene-based resin P2 did not contain the hindered amine-based compound and the spinning temperature was 220° C. The evaluation results are shown in Table 1.

[0159] (Example 4) In the (step of forming a fiber web), the speed of the net conveyor was adjusted to make the basis weight 100 g / m ２ Except for this, an electret-processed spunbond nonwoven fabric was obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0160]

[0161] (Example 5) In the (step of forming a fiber web), the speed of the net conveyor was adjusted to make the basis weight 60 g / m ２ Except for this, an electret-processed spunbond nonwoven fabric was obtained in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0162] Example 6: An electret-processed spunbonded nonwoven fabric was obtained by the same method as in Example 1, except that in the (step of thermally bonding the fibrous web), the step of heat-sealing the collected fibrous web using a hot embossing roll was omitted, and heated air was passed directly through the fibrous web obtained in the (step of forming the fibrous web) to form micro-fused portions at the contact points between the composite fibers. The evaluation results are shown in Table 2. Example 7: An electret-processed spunbonded nonwoven fabric was obtained by the same method as in Example 1, except that in the (step of forming the composite fiber), the core component:sheath component mass ratio was changed to 70:30, and in the (step of thermally bonding the fibrous web), the step of heat-sealing the collected fibrous web using a hot embossing roll was omitted, and heated air was passed directly through the fibrous web obtained in the (step of forming the fibrous web) to form micro-fused portions at the contact points between the composite fibers. The evaluation results are shown in Table 2.

[0163] Example 8 A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that (other post-processing steps) were not performed. The evaluation results are shown in Table 2.

[0164]

[0165] (Comparative Example 1) (Step of forming composite fiber) The polypropylene resin P1 and the polypropylene resin P1 containing the hindered amine compound in an amount of 1.0 mass % relative to the mass of the composite fiber were each melted at a temperature of 220° C. Thereafter, the polypropylene resin P1 as the core component and the polypropylene resin P1 containing the hindered amine compound as the sheath component were spun through the holes of a composite spinneret capable of forming concentric sheath-core composite fibers at a spinneret temperature (corresponding to the spinning temperature) of 240° C., a mass ratio of core component:sheath component = 60:40, and a throughput per hole (single-hole throughput) of 2.0 g / min, and then pulled and drawn by an ejector at a spinning speed of 3,400 m / min to form a concentric sheath-core composite fiber having a circular cross section.

[0166] (Step of forming a fiber web) The obtained composite fibers were deposited on a net conveyor while controlling the fiber arrangement with a fiber spreading plate, to form a fiber web composed of composite fibers having an average single fiber diameter of 28.5 μm.

[0167] (Step of thermally bonding fiber web) Subsequently, the obtained fiber web was thermally fused using a thermal embossing roll consisting of a metal embossing roll engraved with staggered circular protrusions and a metal flat roll, under conditions where the surface temperatures of both the upper and lower rolls were 150°C and the linear pressure applied to the fiber web was 300 N / cm, so that the area ratio of macrofused portions was 11% and the shortest distance between macrofused portions was 1.1 mm, thereby imparting regularly arranged macrofused portions.

[0168] Thereafter, air at a temperature of 160°C and a wind speed of 15 m / sec was passed through the fiber web having the macro-fused portions for 10 seconds to form micro-fused portions at the contact points between the composite fibers, resulting in a fiber web with a basis weight of 80 g / m. ２ A spunbond nonwoven fabric of 100g was obtained.

[0169] (Other post-processing steps) Furthermore, the obtained spunbonded nonwoven fabric was made to travel along the water surface of a water tank to which pure water was supplied, and a slit-shaped suction nozzle was brought into contact with the surface to suck the water, thereby allowing the water to penetrate the entire surface of the spunbonded nonwoven fabric, and after draining the water, the spunbonded nonwoven fabric was allowed to dry naturally, thereby obtaining an electret-processed spunbonded nonwoven fabric. The evaluation results are shown in Table 3.

[0170] (Comparative Example 2) In the (step of forming composite fibers), the polypropylene-based resin P1 and the polypropylene-based resin P1 containing the hindered amine-based compound in an amount of 1.0 mass % relative to the mass of the composite fiber were each melted at a temperature of 220° C. Thereafter, the polypropylene-based resin P1 as the core component and the polypropylene-based resin P1 containing the hindered amine-based compound as the sheath component were spun from the holes of a composite spinneret capable of forming concentric sheath-core composite fibers at a spinneret temperature (corresponding to the spinning temperature) of 240° C., a mass ratio of core component to sheath component of 60:40, and a throughput per single hole (single hole throughput) of 2.0 g / min. The resulting mixture was then pulled and drawn by an ejector at a spinning speed of 3,400 m / min to form concentric sheath-core composite fibers having a circular cross section. In the (step of forming a fiber web), the speed of the net conveyor was adjusted to a basis weight of 140 g / m. ２ An electret-processed spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that in the step of thermally bonding the fiber web, the collected fiber web was thermally fused using a heat embossing roll consisting of a combination of a metal embossing roll and a metal flat roll, under conditions where the surface temperatures of both the upper and lower rolls were 150°C and the linear pressure applied to the fiber web was 700 N / cm, thereby imparting regularly arranged macro-fused portions. The evaluation results are shown in Table 3.

[0171] (Comparative Example 3) In the (step of thermally bonding the fiber web), instead of using the above-mentioned hot embossing roll for the collected fiber web, a hot calendar roll consisting of a pair of upper and lower metal flat rolls was used to heat-bond the fiber web under conditions where the surface temperatures of both the upper and lower rolls were 120°C and the linear pressure applied to the fiber web was 700 N / cm. An electret-processed spunbond nonwoven fabric was obtained in the same manner as in Example 1. The evaluation results are shown in Table 3.

[0172] Comparative Example 4 In the (composite fiber forming step), the mass ratio of core component to sheath component was changed to 70:30, and the collected fiber web was heat-fused using a heat embossing roll consisting of a combination of a metal embossing roll and a metal flat roll, under conditions where the surface temperature of both the upper and lower rolls was 100°C and the linear pressure applied to the fiber web was 300 N / cm, thereby imparting regularly arranged macro-fused portions, but the spunbonded nonwoven fabric was obtained without subsequently passing heated air through the fiber web by the same method as in Example 1. The evaluation results are shown in Table 3.

[0173] (Comparative Example 5) In the (step of thermally bonding the fiber web), the collected fiber web was heat-fused using a heat embossing roll consisting of a combination of a metal embossing roll and a metal flat roll, under conditions where the surface temperature of both the upper and lower rolls was 120°C and the linear pressure applied to the fiber web was 700 N / cm, thereby imparting regularly arranged macro-fused portions, but after that, heated air was not passed through the fiber web to obtain a spunbonded nonwoven fabric. An electret-processed spunbonded nonwoven fabric was obtained in the same manner as in Example 1. The evaluation results are shown in Table 3.

[0174]

[0175] The spunbond nonwoven fabrics of Examples 1 to 8 had sufficient rigidity for practical use, and exhibited excellent pleating processability and shape retention, as well as excellent breathability. In particular, the spunbond nonwoven fabrics of Examples 1, 2, and 4 to 7 exhibited high collection performance and were therefore suitable for use in filters.

[0176] On the other hand, since the spunbonded nonwoven fabric of Comparative Example 1 was composed only of polypropylene-based resin P1, the entire fiber softened during thermal bonding, resulting in low bending resistance per unit weight in the warp direction and poor pleatability and shape retention. Furthermore, Comparative Examples 2 and 3 had high apparent density and poor breathability and pressure loss. Comparative Examples 4 and 5 did not have a heated gas passage process, resulting in low bending resistance per unit weight in the warp direction and poor pleatability and shape retention.

[0177] 1: Sample holder 2: Dust storage box 3: Flow meter 4: Flow rate adjustment valve 5: Blower 6: Particle counter 7: Switch cock 8: Pressure gauge M: Measurement sample

Claims

1. A spunbond nonwoven fabric made of composite fibers, the composite fibers comprising: a polypropylene-based resin P1 and a polymer having a melting point T ｍ２ (°C) is the melting point T ｍ１ and a polypropylene-based resin P2 having a temperature 20°C or more and 60°C or less lower than (°C), and the apparent density of the spunbond nonwoven fabric is 0.10 g / cm 3 0.20g / cm or more 3 The bending resistance per unit area weight in the warp direction of the spunbond nonwoven fabric is 1.5 mg / (g / m ２ ) or more 10.0mg / (g / m ２ ) or less, spunbond nonwoven fabric.

2. The spunbond nonwoven fabric according to claim 1, wherein at least some of the contact points between the composite fibers have micro-fused portions having a length of 5 μm or more and 100 μm or less in the fiber axial direction.

3. The spunbond nonwoven fabric according to claim 1 or 2, wherein the composite fiber contains a hindered amine compound.

4. The spunbond nonwoven fabric according to claim 1 or 2, wherein the average single fiber diameter of the composite fibers is 10 μm or more and 40 μm or less.

5. The spunbond nonwoven fabric according to claim 1 or 2, which has been subjected to electret processing.

6. Polypropylene resin P1 and melting point T ｍ２ (°C) is the melting point T ｍ１ (°C), and a polypropylene-based resin P2 having a temperature that is 20°C or more and 60°C or less lower than (°C), the method comprising the steps of: melt-extruding the polypropylene-based resin P1 and the polypropylene-based resin P2 from a conjugate spinneret, and pulling and stretching the spun-out polypropylene-based resin P1 and the polypropylene-based resin P2 to form conjugate fibers; depositing the conjugate fibers to form a fiber web composed of the conjugate fibers; and thermally bonding the fiber web, wherein the thermal bonding is performed by passing a gas that satisfies the following formula 1 through the fiber web. ｍ２ -20≦T Ｗ ≦T ｍ２ +20 ... (Equation 1) where, T Ｗ is the temperature of the gas (°C).

7. A laminated nonwoven fabric comprising the spunbonded nonwoven fabric according to claim 1 and a meltblown nonwoven fabric.

8. A pleated article comprising the spunbond nonwoven fabric of claim 1 or the laminated nonwoven fabric of claim 7.

9. A dust-collecting filter made using the pleated molded article according to claim 8.

10. A dust collecting device using the dust collecting filter according to claim 9.

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