Nonwoven fabric and method for producing same, and laminated nonwoven fabric

Abstract

The present invention addresses the problem of providing nonwoven fabric that has both excellent strength and rigidity.　This nonwoven fabric is composed of hollow fibers containing a propylene-based resin as a main component, wherein: the ratio (Mz / Mw) between the Z average molecular weight Mz and the weight average molecular weight Mw of the propylene-based resin is 2.0-6.0; the hollow fibers have an average single fiber diameter of 5.0-50.0 μm and an average hollow ratio of 31.0%-60.0%; and the nonwoven fabric has a melt mass flow rate of 16-55 g per 10 minutes.

Description

Nonwoven fabric, its manufacturing method, and laminated nonwoven fabric

[0001] The present invention relates to nonwoven fabrics.

[0002] Nonwoven fabrics made of polyolefin resins, particularly nonwoven fabrics made of propylene resins, are inexpensive and have excellent processability and flexibility, and are therefore widely used primarily as sanitary materials.

[0003] In recent years, in order to reduce the amount of polymers derived from petrochemical raw materials used in response to environmental considerations, there has been a demand for a reduction in the basis weight of nonwoven fabrics made from propylene-based resins used in sanitary and industrial material applications. Furthermore, even with a reduced basis weight, there is a demand for these nonwoven fabrics to exhibit strength equivalent to that of current products and to have excellent rigidity to improve handleability.

[0004] In response to such demands, various methods have been proposed for improving the strength of nonwoven fabrics, such as using hollow fibers as the fibers forming the nonwoven fabrics.

[0005] For example, Patent Document 1 proposes a long-fiber nonwoven fabric made of hollow fibers of a propylene polymer having a ratio (Mz / Mw) of Z-average molecular weight Mz to weight-average molecular weight Mw within a specific range. It is described that this invention provides a nonwoven fabric having higher fiber strength, particularly single-fiber strength, than conventional hollow-fiber nonwoven fabrics, and a high hollow ratio even when the fiber diameter of the propylene polymer fibers forming the nonwoven fabric is reduced.

[0006] Patent Document 2 proposes a spunbond nonwoven fabric made of hollow fibers of a propylene polymer having a degree of C-axis orientation, an average fiber diameter, and an average hollowness within specific ranges. It also describes that this invention provides a nonwoven fabric with high uniformity, strength, and flexibility even at a low basis weight, and that it is possible to ensure sufficient strength even at a basis weight lower than conventional fabrics, thereby enabling weight reduction.

[0007] International Publication No. WO 2010 / 024268 International Publication No. WO 2012 / 111723

[0008] The technique proposed in Patent Document 1 makes it possible to obtain a nonwoven fabric having a relatively high hollow ratio and a certain strength by controlling the molecular weight, but there is still a problem with the rigidity of the nonwoven fabric.

[0009] The technology proposed in Patent Document 2 produces a nonwoven fabric that is relatively strong and flexible by using hollow fibers with a high molecular orientation, but the rigidity is still insufficient and there are issues with handling.

[0010] As described above, nonwoven fabrics using hollow fibers made of propylene-based resins tend to have high strength depending on the manufacturing conditions, but tend to be soft and have low rigidity. Therefore, the nonwoven fabrics are difficult to handle and are unsuitable for applications requiring high rigidity, such as industrial materials. Therefore, an object of the present invention is to provide a nonwoven fabric that combines excellent strength and rigidity.

[0011] As a result of extensive research, the present inventors have found that in a nonwoven fabric containing hollow fibers of a propylene-based resin having an average single fiber diameter and an average hollowness within specific ranges, a nonwoven fabric having excellent strength and rigidity can be obtained only by adjusting the melt mass-flow rate and the ratio of the Z-average molecular weight Mz to the weight-average molecular weight Mw (Mz / Mw) within specific ranges, and have thus completed the present invention.

[0012] The present invention aims to solve the above problems, and provides the following inventions.

[0013] [1] A nonwoven fabric composed of hollow fibers whose main component is a propylene-based resin, wherein the propylene-based resin has a ratio (Mz / Mw) of Z-average molecular weight Mz to weight-average molecular weight Mw of 2.0 or more and 6.0 or less, the hollow fibers have an average single fiber diameter of 5.0 μm or more and 50.0 μm or less and an average hollow ratio of 31.0% or more and 60.0% or less, and the nonwoven fabric has a melt mass flow rate of 16 g / 10 min or more and 55 g / 10 min or less.

[0014] [2] The nonwoven fabric according to [1], wherein the propylene-based resin further has a ratio of weight-average molecular weight Mw to number-average molecular weight Mn (Mw / Mn) of 3.0 or more and 10.0 or less.

[0015] [3] The nonwoven fabric according to [1] or [2], wherein the heat of crystalline fusion of the nonwoven fabric is 80 J / g or more and 120 J / g or less.

[0016] [4] The nonwoven fabric according to any one of [1] to [3], wherein the nonwoven fabric is a spunbonded nonwoven fabric.

[0017] [5] A method for producing a nonwoven fabric having a melt mass flow rate of 16 g / 10 min or more and 55 g / 10 min or less, comprising the steps of: melting a propylene-based resin having a ratio (Mz / Mw) of Z-average molecular weight Mz to weight-average molecular weight Mw of 2.0 or more and 6.0 or less; and extruding the propylene-based resin from hollow spinneret holes having a minimum circumscribed circle diameter of 1.2 mm or more and 5.0 mm or less to form hollow fibers having an average single fiber diameter of 5.0 μm or more and 50.0 μm or less and an average hollow ratio of 31.0% or more and 60.0% or less; depositing the hollow fibers to form a fiber web composed of the hollow fibers; and thermally bonding the fiber web.

[0018] [6] The method for producing a nonwoven fabric according to [5], wherein the number of slits in the hollow die hole is 5 or more and 12 or less.

[0019] [7] A laminated nonwoven fabric comprising a layer of the nonwoven fabric according to any one of [1] to [4] above, and a fiber layer different from the nonwoven fabric layer and / or a film layer.

[0020] According to the present invention, a nonwoven fabric having both excellent strength and rigidity can be obtained.

[0021] FIG. 1 is a conceptual diagram showing an example of a hollow die hole in the method for producing a nonwoven fabric of the present invention.

[0022] The nonwoven fabric of the present invention is a nonwoven fabric composed of hollow fibers whose main component is a propylene-based resin, wherein the propylene-based resin has a ratio of Z-average molecular weight Mz to weight-average molecular weight Mw (Mz / Mw) of 2.0 to 6.0, the hollow fibers have an average single fiber diameter of 5.0 μm to 50.0 μm and an average hollow ratio of 31.0% to 60.0%, and the nonwoven fabric has a melt mass-flow rate of 16 g / 10 min to 55 g / 10 min. In the present invention, "hollow fibers whose main component is a propylene-based resin" refers to hollow fibers in which the propylene-based resin, described below, accounts for more than 50 mass% of the components constituting the hollow fibers.

[0023] The nonwoven fabric of the present invention will be described in detail below, but the present invention is not limited to the scope described below as long as it does not deviate from the gist of the present invention, and various modifications are possible within the scope of the present invention.

[0024] [Propylene-based resin] The nonwoven fabric of the present invention is composed of hollow fibers whose main component is a propylene-based resin. By using a propylene-based resin, a low-cost nonwoven fabric with excellent strength can be obtained.

[0025] The propylene-based resin refers to a resin with a propylene fraction of 50% or more, as described below. Specific examples include not only propylene homopolymers, but also copolymers of propylene and ethylene, and copolymers of propylene and various α-olefins. Here, α-olefin refers to a hydrocarbon in which the double bond is at the α-position, such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadecene, and 4-methyl-1-pentene.

[0026] The propylene-based resin used in the present invention preferably has a propylene fraction of 94% or more and 100% or less. When the propylene fraction of the propylene-based resin is preferably 94% or more, more preferably 96% or more, and even more preferably 98% or more, the tensile strength of the fiber is increased, resulting in a nonwoven fabric with excellent strength. Furthermore, the upper limit of the propylene fraction of the propylene-based resin that can be achieved in the present invention is 100%.

[0027] The propylene fraction (%) of the propylene-based resin referred to here is a value measured and calculated by the following procedure: (1) Propylene-based resin, which is the raw material for the fiber, is weighed and dissolved in orthodichlorobenzene-d ４ (orthodichlorobenzene in which hydrogen has been replaced with deuterium) and heated to 135°C to dissolve. (2) The resulting solution is used as a sample and analyzed using a nuclear magnetic resonance apparatus (for example, JEOL RESONANCE's "ECZ-600"). １３ C-NMR measurement is performed, and the peak area due to propylene units and the peak areas due to ethylene units and α-olefin units are obtained as integral values ​​of the NMR spectrum. (3) The sum A of the peak areas corresponding to propylene units, ethylene units, and α-olefin units ＡＰ Peak area A corresponding to propylene units ＰＰ The ratio (A ＰＰ / A ＡＰ (4) For each level, carry out the above steps (1) to (3) three times, and calculate the three (A ＰＰ / A ＡＰ ) and rounding to one decimal place to obtain an arithmetic average, which is the propylene fraction (%) of the propylene-based resin.

[0028] The propylene fraction of the propylene-based resin used in the present invention can be controlled, for example, by the composition of the raw material monomers. Specifically, the propylene fraction of the propylene-based resin can be increased by increasing the propylene ratio of the raw material monomers used in polymerization of the propylene-based resin.

[0029] The propylene-based resin according to the present invention has a ratio (Mz / Mw) of Z-average molecular weight Mz to weight-average molecular weight Mw of 2.0 or more and 6.0 or less. When the propylene-based resin has an Mz / Mw of 2.0 or more, preferably 2.2 or more, and more preferably 2.3 or more, the molecular orientation is not excessively high, improving adhesiveness, resulting in a nonwoven fabric with excellent strength. When the propylene-based resin has an Mz / Mw of 6.0 or less, preferably 5.0 or less, and more preferably 4.0 or less, yarn breakage during spinning can be suppressed, resulting in a nonwoven fabric with fewer defects caused by the inclusion of extremely thick fibers or polymer clumps.

[0030] In the nonwoven fabric of the present invention, the propylene-based resin preferably has a ratio of weight-average molecular weight Mw to number-average molecular weight Mn (Mw / Mn) of 3.0 or more and 10.0 or less. By setting the Mw / Mn of the propylene-based resin to preferably 3.0 or more, more preferably 4.0 or more, and even more preferably 4.5 or more, the molecular orientation is prevented from becoming excessively high, improving adhesiveness, resulting in a nonwoven fabric with excellent strength. Furthermore, by setting the Mw / Mn of the propylene-based resin to preferably 10.0 or less, more preferably 9.0 or less, and even more preferably 8.0 or less, yarn breakage during spinning can be suppressed, resulting in a nonwoven fabric with fewer defects caused by the inclusion of extremely thick fibers or polymer clumps.

[0031] The Mz / Mw and Mw / Mn of the propylene-based resin are values ​​measured and calculated by the following procedure: (1) 5 mg of the propylene-based resin used as the raw material for the fiber is collected. When measuring from a nonwoven fabric, 5 mg of a test piece is collected. (2) 5 mL of 1,2,4-trichlorobenzene is added to the collected propylene-based resin or 5 mg of the test piece, and the mixture is heated at 165°C for 20 minutes to dissolve the propylene-based resin, thereby obtaining a propylene-based resin solution. (3) The obtained propylene-based resin solution is filtered using a PTFE filter (for example, "T010A (pore size: 0.45 μm)" manufactured by Advantec Toyo Co., Ltd.) to prepare a sample solution. (4) The prepared sample solution is loaded into a high-temperature GPC apparatus (for example, "PL-220" manufactured by Polymer Laboratories, etc.), and measurement is carried out at a column temperature of 145°C. The GPC discharge curve is analyzed to determine the Z-average molecular weight Mz, weight-average molecular weight Mw, and number-average molecular weight Mn, and Mz / Mn and Mw / Mn are calculated. (5) For each level, steps (1) to (4) are carried out three times, and the obtained Mz / Mn and Mw / Mn values ​​are arithmetically averaged. The values ​​obtained by rounding to one decimal place are used as the Mz / Mw (unitless) and Mw / Mn (unitless) of the propylene-based resin.

[0032] The Mz / Mw and Mw / Mn of the propylene-based resin can be controlled by, for example, a polymerization catalyst. Specifically, the use of a Ziegler-Natta catalyst can increase the Mz / Mw and Mw / Mn of the propylene-based resin compared to the use of a metallocene catalyst.

[0033] The hollow fiber containing a propylene-based resin as a main component according to the present invention may contain, as necessary, additives commonly used in the art, such as antioxidants, weathering stabilizers, light stabilizers, heat stabilizers, antistatic agents, antistatic aids, spinning agents, antiblocking agents, lubricants including polyethylene wax, crystal nucleating agents, and pigments, or other polymers, within the range that does not impair the effects of the present invention, in order to further enhance the effects of the present invention or to impart other properties to the fiber.

[0034] The propylene-based resin used in the present invention preferably has a melt mass flow rate of 16 g / 10 min or more and 55 g / 10 min or less. The melt mass flow rate of the propylene-based resin is preferably 16 g / 10 min or more, more preferably 20 g / 10 min or more, even more preferably 25 g / 10 min or more, and most preferably 30 g / 10 min or more, which improves stability during spinning and results in a nonwoven fabric with excellent quality. Furthermore, the melt mass flow rate of the propylene-based resin is preferably 55 g / 10 min or less, more preferably 50 g / 10 min or less, and even more preferably 45 g / 10 min or less, which increases the tensile strength of the fiber and makes the bonded joints less susceptible to fracture, resulting in a nonwoven fabric with excellent strength.

[0035] The melt mass flow rate (g / 10 min) of a propylene-based resin referred to here is a value measured and calculated in accordance with ASTM D1238 (Method A) by the following procedure. This standard stipulates that propylene-based resins be measured under a load of 2.16 kg and at a temperature of 230°C. (1) 20 g of the propylene-based resin that will be used as the raw material for the fiber is sampled. (2) The sampled propylene-based resin is placed in a melt mass flow rate measuring device (such as the "MELT INDEXER F-F01" manufactured by Toyo Seiki Seisaku-sho, Ltd.) heated to 230°C, and measurement is performed under conditions of a load of 2.16 kg and a temperature of 230°C. (3) For each level, the above steps (1) and (2) are carried out five times, and the five measured values ​​obtained are arithmetically averaged. The value (g / 10 min) obtained by rounding off to one decimal place is used as the melt mass flow rate (g / 10 min) of the propylene-based resin.

[0036] The melt mass flow rate of the propylene-based resin used in the present invention can be controlled, for example, by the molecular weight of the propylene-based resin or the ratio of the Z-average molecular weight Mz to the weight-average molecular weight Mw (Mz / Mw). Specifically, the melt mass flow rate of the propylene-based resin can be reduced by increasing the molecular weight of the propylene-based resin and decreasing Mz / Mw.

[0037] The propylene-based resin according to the present invention preferably contains 0.01% by mass or more and 5.0% by mass or less of a fatty acid amide compound in order to improve the slipperiness of the nonwoven fabric. By making the content of the fatty acid amide compound preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, the fatty acid amide compound acts as a lubricant on the fiber surface, resulting in a nonwoven fabric with excellent tactile feel. Furthermore, by making the content of the fatty acid amide compound preferably 5.0% by mass or less, more preferably 4.0% by mass or less, and even more preferably 3.5% by mass or less, the crystallinity of the fiber can be increased, resulting in a nonwoven fabric with excellent strength and rigidity.

[0038] [Hollow Fibers] The nonwoven fabric of the present invention is composed of hollow fibers containing the propylene-based resin as the main component. By using hollow fibers, the nonwoven fabric has excellent strength.

[0039] The hollow fiber according to the present invention may be a composite fiber in which two or more types of resins are composited. When the hollow fiber is a composite fiber, the composite form is not particularly limited as long as it does not impair the effects of the present invention, and can be appropriately selected from a core-sheath type, an island-in-sea type, a side-by-side type, a blend type, etc.

[0040] The hollow fibers used in the nonwoven fabric of the present invention have an average single fiber diameter of 5.0 μm or more and 50.0 μm or less. An average single fiber diameter of 5.0 μm or more, preferably 8.0 μm or more, and more preferably 10.0 μm or more increases the bending moment of the fibers, resulting in a nonwoven fabric with excellent rigidity. Furthermore, an average single fiber diameter of 50.0 μm or less, preferably 40.0 μm or less, and more preferably 35.0 μm or less increases the number of fibers when compared at the same basis weight, resulting in a nonwoven fabric with excellent uniformity of texture.

[0041] The average single fiber diameter (μm) of hollow fibers is a value measured and calculated by the following procedure: (1) A 5 mm × 5 mm test piece is taken from a nonwoven fabric. (2) An image of the non-bonded portion of the nonwoven fabric surface where fibers are not bonded to each other is taken with a scanning electron microscope (e.g., "SU1510" manufactured by Hitachi High-Technologies Corporation) at a magnification that allows the side surfaces of 10 or more fibers to be observed. (3) From the image, 10 fibers constituting the nonwoven fabric are randomly selected, and their fiber diameters (μm) are measured. (4) For each level, steps (1) to (3) are performed 10 times, using different test piece collection locations, and the arithmetic mean of the resulting 100 fiber diameters is calculated. This value is rounded to one decimal place and used as the average single fiber diameter (μm).

[0042] In the above-mentioned step (2), and the steps (2) for determining the average hollow ratio of hollow fibers and (2) for determining the ratio of the number of hollow fibers, which will be described later, the "surface of the nonwoven fabric" refers to the surface facing the observation direction when observed from the thickness direction of the nonwoven fabric, and when the nonwoven fabric can be observed from both sides, it refers to the surfaces facing both observation directions.

[0043] The average single fiber diameter of the hollow fiber according to the present invention can be controlled by, for example, the melt mass flow rate of the propylene-based resin, the average hollow ratio of the hollow fiber, the spinning temperature in the production process, the single-hole throughput, the spinning speed, etc. Specifically, the average single fiber diameter of the hollow fiber can be reduced by decreasing the melt mass flow rate of the propylene-based resin, decreasing the average hollow ratio, increasing the spinning temperature, decreasing the single-hole throughput, or increasing the spinning speed.

[0044] The hollow fibers according to the present invention have an average hollow ratio of 31.0% or more and 60.0% or less. An average hollow ratio of 31.0% or more, preferably 33.0% or more, more preferably 35.0% or more, and even more preferably 37.0% or more makes bonded joints less susceptible to fracture and increases the bending moment of the fibers in non-bonded joints, resulting in a nonwoven fabric with excellent strength and rigidity. An average hollow ratio of 60.0% or less, preferably 55.0% or less, and more preferably 50.0% or less suppresses a decrease in bending moment due to cross-sectional shape deformation (from substantially circular to substantially elliptical) that occurs when the fibers are bent, resulting in a nonwoven fabric with excellent rigidity.

[0045] The average hollowness (%) of hollow fibers is a value measured and calculated by the following procedure: (1) A 5 mm x 5 mm test piece is taken from a nonwoven fabric. (2) On the surface of the nonwoven fabric, fibers in non-bonded portions that are at least 10% away from bonded portions relative to the distance between adjacent bonded portions are embedded in an embedding agent such as epoxy resin, and the fibers are cut with a razor in a direction perpendicular to the fiber axis to expose the fiber cross-sections. Images are then taken with a scanning electron microscope (e.g., "SU1510" manufactured by Hitachi High-Technologies Corporation) at a magnification that allows observation of 10 or more fiber cross-sections. (3) From the taken images, the perimeter L of the approximately circular portion formed by the hollow portion of the hollow fiber is calculated using image analysis software (e.g., "WinROOF2015" manufactured by Mitani Shoji Co., Ltd.). ｉｎ (μm), and the outer circumferential length L of the approximately circular portion formed on the outside of the resin portion ｏｕｔ (μm) was measured, and the outer periphery was calculated by the following formula. ｉｎ and L ｏｕｔ The area of ​​the perfect circle A is the same as ｉｎ (μm ２ ) and A ｏｕｔ (μm ２ ), and calculate the hollow ratio H (%). ｉｎ (μm ２ ) = L ｉｎ ２ ÷4π A ｏｕｔ (μm ２ ) = L ｏｕｔ ２ ÷4π H (%) = A ｉｎ / Aｏｕｔ × 100 (where π represents the ratio of the circumference of a circle to its circumference). (4) For each level, the above steps (1) to (3) are carried out 10 times, with the test specimens being taken from different locations, and the hollow ratios H (%) of a total of 100 specimens obtained are arithmetically averaged, and the value obtained by rounding off to one decimal place is used as the average hollow ratio (%).

[0046] The average hollow ratio of the hollow fiber according to the present invention can be controlled by, for example, the melt mass flow rate of the propylene-based resin, the shape of the hollow spinneret holes in the production process, the spinning temperature, the throughput rate per hole, the cooling conditions, etc. Specifically, the average hollow ratio of the hollow fiber can be increased by decreasing the melt mass flow rate of the propylene-based resin, increasing the minimum circumscribed circle diameter of the hollow spinneret holes, increasing the number of slits in the hollow spinneret holes, lowering the spinning temperature, lowering the throughput rate per hole, or lowering the temperature of the cooling air.

[0047] The hollow fibers according to the present invention preferably have a fiber length of 30 mm or more. A fiber length of 30 mm or more, more preferably 40 mm or more, and even more preferably 45 mm or more increases the number of entanglement points per fiber, resulting in a nonwoven fabric with excellent strength. There is no particular upper limit to the fiber length, and for example, long fibers with almost no fiber ends can also be used.

[0048] [Nonwoven Fabric] The nonwoven fabric of the present invention is made of the hollow fibers. Here, the term "nonwoven fabric made of hollow fibers" does not only refer to nonwoven fabrics made only of hollow fibers, but also includes nonwoven fabrics made of hollow fibers and other fibers, in which the proportion of hollow fibers by number is 60% or more.

[0049] The percentage of hollow fibers (%) is measured and calculated using the following procedure: (1) A 5 mm x 5 mm test piece is taken from a nonwoven fabric. (2) Fibers in non-bonded areas on the surface of the nonwoven fabric, which are at least 10% away from bonded areas relative to the distance between adjacent bonded areas, are embedded in an embedding agent such as epoxy resin, and the nonwoven fabric is cut with a razor to expose the fiber cross-sections. Images are then taken with a scanning electron microscope (e.g., the "SU1510" manufactured by Hitachi High-Technologies Corporation) at a magnification that allows observation of 10 to 50 fiber cross-sections. (3) For each level, steps (1) and (2) are repeated while changing the location of the test piece to be taken until a total of 200 fiber cross-sections have been photographed, and the number of fibers with hollows therein is counted from the photographed images. (4) The number of hollow fibers is divided by the number of observed fibers (200), and the quotient is expressed as a percentage. The value obtained by rounding off to one decimal place is the percentage of the number of hollow fibers (%).

[0050] The nonwoven fabric of the present invention may be a long-fiber nonwoven fabric such as a spunbonded nonwoven fabric or a meltblown nonwoven fabric, or a short-fiber nonwoven fabric such as a needle-punched nonwoven fabric or a paper-made nonwoven fabric. Among these, a long-fiber nonwoven fabric is preferred from the viewpoint of excellent productivity and strength, and a spunbonded nonwoven fabric is more preferred because it is easy to reduce the basis weight and easily achieve both excellent strength and rigidity.

[0051] The nonwoven fabric of the present invention may be a single-layer nonwoven fabric consisting of only a layer of nonwoven fabric described below, i.e., a nonwoven fabric consisting of multiple layers of the same type of nonwoven fabric. The term "same type of nonwoven fabric" as used herein refers to nonwoven fabrics each consisting of fibers whose main component is a propylene-based resin. However, if the nonwoven fabric of the present invention has a fiber layer of a different type from the layer of the nonwoven fabric of the present invention, for example, if the nonwoven fabric of the present invention is a spunbond nonwoven fabric, a layer of meltblown nonwoven fabric, a layer of papermaking nonwoven fabric, or a layer of woven fabric or knitted fabric, it is considered to be a laminated nonwoven fabric described below.

[0052] The nonwoven fabric of the present invention has a melt mass flow rate of 16 g / 10 min or more and 55 g / 10 min or less. A melt mass flow rate of 16 g / 10 min or more, preferably 20 g / 10 min or more, more preferably 25 g / 10 min or more, and even more preferably 30 g / 10 min or more improves stability during spinning, resulting in a nonwoven fabric with excellent quality and adhesiveness, and therefore excellent strength. Furthermore, a melt mass flow rate of 55 g / 10 min or less, preferably 50 g / 10 min or less, and more preferably 45 g / 10 min or less improves the tensile strength of the fibers and makes the adhesive joints less susceptible to fracture, resulting in a nonwoven fabric with excellent strength.

[0053] The melt mass flow rate (g / 10 min) of a nonwoven fabric is a value measured and calculated in accordance with ASTM D1238 (Method A) by the following procedure: (1) A 20 g test piece is collected from the nonwoven fabric. (2) The collected test piece is placed in a melt mass flow rate measuring device (e.g., the "MELT INDEXER F-F01" manufactured by Toyo Seiki Seisaku-sho, Ltd.) heated to 230°C, and measurement is performed under conditions of a load of 2.16 kg and a temperature of 230°C. (3) Steps (1) and (2) above are performed five times for each level, and the five measured values ​​obtained are arithmetically averaged. The value (g / 10 min) obtained by rounding to one decimal place is defined as the melt mass flow rate (g / 10 min) of the nonwoven fabric.

[0054] The melt mass flow rate of the nonwoven fabric of the present invention can be controlled by, for example, selecting the melt mass flow rate of the propylene-based resin used as the raw material. Specifically, the melt mass flow rate of the nonwoven fabric can be reduced by selecting a propylene-based resin with a low melt mass flow rate.

[0055] The nonwoven fabric of the present invention preferably has a heat of crystalline fusion of 80 J / g or more and 120 J / g or less. By making the heat of crystalline fusion of the nonwoven fabric 80 J / g or more, preferably 85 J / g or more, and more preferably 88 J / g or more, the degree of crystallization of the nonwoven fabric can be appropriately increased, resulting in a nonwoven fabric with excellent strength and rigidity. Furthermore, the upper limit of the heat of crystalline fusion of the nonwoven fabric achievable in the present invention is about 120 J / g.

[0056] The heat of crystalline fusion (J / g) of a nonwoven fabric is a value measured and calculated by the following procedure. (1) A 2.0 mg test piece is taken from the nonwoven fabric and placed in a differential scanning calorimeter (e.g., a "Q2000" manufactured by TA Instruments). (2) Differential scanning calorimetry (1st DSC) is performed under nitrogen at a heating rate of 16°C / min and a measurement temperature range of 50°C to 230°C, followed by rapid cooling at a heating rate of 100°C / min, followed by differential scanning calorimetry (2nd DSC) again under nitrogen at a heating rate of 16°C / min and a measurement temperature range of 50°C to 230°C. (3) The endothermic heat (J / g) of the largest endothermic peak in the DSC curve of the 2nd DSC is calculated. (4) For each level, the above steps (1) to (3) are carried out three times by changing the location of the specimen, and the three endothermic values ​​obtained are arithmetically averaged. The value (J / g) obtained by rounding off to the nearest tenth place is regarded as the heat of crystalline fusion (J / g).

[0057] The heat of crystalline fusion of the nonwoven fabric of the present invention can be controlled, for example, by the propylene fraction of the propylene-based resin. Specifically, the heat of crystalline fusion of the nonwoven fabric can be increased by increasing the propylene fraction of the propylene-based resin.

[0058] The nonwoven fabric of the present invention has a basis weight of 5 g / m ２ More than 300g / m ２ The basis weight is preferably 5 g / m or less. ２ More preferably, 10 g / m ２ More preferably, 12 g / m ２ By satisfying the above conditions, the nonwoven fabric has a uniform texture and excellent strength. ２ or less, more preferably 250 g / m ２ More preferably 200 g / m or less ２ By ensuring that the thickness is equal to or less than 100 μm, fluffing due to insufficient adhesion is suppressed, resulting in a nonwoven fabric of excellent quality.

[0059] The basis weight of the nonwoven fabric (g / m ２) is a value measured and calculated by the following procedure in accordance with "6.2 Mass per unit area (ISO method)" of JIS L1913:2010 "General nonwoven fabric testing methods." (1) A 20 cm x 25 cm test piece is taken from the nonwoven fabric. However, if a 20 cm x 25 cm test piece cannot be taken, a test piece with a total area of ​​500 cm is taken. ２ (2) For the test pieces taken, measure the mass (g) under standard conditions and calculate the area of ​​1 m ２ Mass per unit (g / m ２ (3) For each level, the above steps (1) and (2) are carried out three times by changing the location of the specimen, and the three masses obtained are calculated as an arithmetic average. The value is rounded off to the nearest tenth to obtain the unit of the digit (g / m ２ ) is the basis weight (g / m ２ )

[0060] The basis weight of the nonwoven fabric of the present invention can be controlled, for example, by the single-hole discharge rate, the number of spinneret holes, the conveying speed of the fiber web, etc. Specifically, the basis weight of the nonwoven fabric can be increased by increasing the single-hole discharge rate, increasing the number of spinneret holes, or decreasing the conveying speed.

[0061] The nonwoven fabric of the present invention has a tensile strength per unit area of ​​1.40 (N / 25 mm) / (g / m ２ ) or more 3.00 (N / 25mm) / (g / m ２ The tensile strength per unit area is preferably 1.40 (N / 25 mm) / (g / m ２ ) or more, more preferably 1.50 (N / 25mm) / (g / m ２ ) or more, the nonwoven fabric has excellent strength. In addition, the upper limit of the tensile strength per unit area of ​​the nonwoven fabric that can be achieved by the present invention is 3.00 (N / 25 mm) / (g / m ２ ) is about the same.

[0062] The tensile strength per unit area of ​​the nonwoven fabric ((N / 25 mm) / (g / m ２)) is a value measured and calculated by the following procedure in accordance with "6.3 Tensile Strength and Elongation (ISO Method)" of JIS L1913:2010 "General Nonwoven Fabric Testing Methods." (1) 25 mm x 40 mm test pieces are taken from the nonwoven fabric in both the machine direction (longitudinal direction) and the transverse direction (width direction) of the nonwoven fabric. (2) The long side direction (40 mm) of the taken test piece is set as the tensile direction, and the test piece is set in a tensile tester (such as the "RTC-1210A" manufactured by A&D Co., Ltd.) with a grip spacing of 20 mm. (3) A tensile test is carried out at a pulling speed of 20 mm / min, and the maximum point load (N / 25 mm) is measured. (4) For each level, the test specimens were taken from different locations and the above (1) to (3) were carried out five times in both the longitudinal and transverse directions. The arithmetic mean of the ten maximum point load measurements was calculated, and the value obtained by rounding off to two decimal places was taken as the average maximum point load (N / 25mm). The tensile strength per unit area ((N / 25mm) / (g / m)) was calculated using the following formula. ２ )) to calculate the tensile strength per unit area ((N / 25mm) / (g / m ２ )) = Maximum point load (N / 25mm) / basis weight (g / m ２ )...(formula).

[0063] The tensile strength per unit area of ​​the nonwoven fabric of the present invention can be controlled by, for example, the propylene fraction of the propylene-based resin, the average hollowness of the hollow fibers, the melt mass-flow rate, Mz / Mw, Mw / Mn, heat of crystalline fusion of the nonwoven fabric, and the bonding conditions in the manufacturing process (bonding rate, temperature, linear pressure, etc.). Specifically, the tensile strength per unit area of ​​the nonwoven fabric can be increased by increasing the propylene fraction of the propylene-based resin, increasing the average hollowness of the hollow fibers, decreasing the melt mass-flow rate of the nonwoven fabric, increasing Mz / Mw, increasing Mw / Mn, increasing the heat of crystalline fusion, or adjusting the bonding rate, temperature, and pressure during bonding in the manufacturing process.

[0064] The nonwoven fabric of the present invention preferably has a bending resistance of 35 mm or more and 300 mm or less. A bending resistance of preferably 35 mm or more, more preferably 40 mm or more, results in excellent rigidity and therefore excellent handleability. Furthermore, a bending resistance of preferably 300 mm or less, more preferably 250 mm or less, results in excellent processability.

[0065] The bending resistance (mm) of a nonwoven fabric is a value (mm) obtained by measuring three times each in the machine direction (longitudinal direction of the nonwoven fabric) and the cross direction (width direction of the nonwoven fabric) of the nonwoven fabric in accordance with "6.7 Bending resistance (JIS method and ISO method)" "6.7.3 41.5° cantilever method" of JIS L1913:2010 "Testing methods for general nonwoven fabrics," and then calculating the arithmetic average of all six measured values ​​in the machine direction and the cross direction, rounding the result to one decimal place.

[0066] The bending resistance of the nonwoven fabric of the present invention can be controlled by, for example, the propylene fraction of the propylene-based resin, the average single fiber diameter of the hollow fibers, the average hollowness, the melt mass-flow rate, heat of crystalline fusion, and basis weight of the nonwoven fabric, and the bonding conditions in the manufacturing process (bonding ratio, temperature, linear pressure, etc.). Specifically, the bending resistance of the nonwoven fabric can be increased by increasing the propylene fraction of the propylene-based resin, increasing the average single fiber diameter of the hollow fibers, setting the average hollowness within a specific range, decreasing the melt mass-flow rate of the nonwoven fabric, increasing the heat of crystalline fusion, increasing the basis weight, or adjusting the bonding ratio, temperature, and pressure during bonding in the manufacturing process.

[0067] The nonwoven fabric of the present invention can be widely used for medical and sanitary materials, daily necessities, industrial materials, etc., but because of its excellent strength and rigidity, it is particularly suitable for use as an industrial material. The industrial material referred to here means a part of industrial equipment or a material used in the civil engineering or agricultural fields, and examples thereof include filters, transpiration materials, embankment reinforcement materials, bank protection sheets, drainage materials, weed control sheets, agricultural mulch, cheesecloth, etc., and also includes components thereof.

[0068] [Method for Producing Nonwoven Fabric] Next, the method for producing a nonwoven fabric of the present invention will be described. The method for producing a nonwoven fabric of the present invention has a melt mass flow rate of 16 g / 10 min to 55 g / 10 min, and includes the steps of melting a propylene-based resin having a ratio (Mz / Mw) of Z-average molecular weight Mz to weight-average molecular weight Mw of 2.0 to 6.0 and extruding the propylene-based resin through a hollow spinneret hole having a minimum circumscribed circle diameter of 1.2 mm to 5.0 mm to form hollow fibers having an average single fiber diameter of 5.0 μm to 50.0 μm and an average hollow ratio of 31.0% to 60.0%; depositing the hollow fibers to form a fiber web composed of the hollow fibers; and thermally bonding the fiber web. This production method allows for the consistent production of a nonwoven fabric that exhibits both excellent strength and rigidity. Each step will be described in more detail below.

[0069] (a) Step of Forming Hollow Fibers In this step, a propylene-based resin having a ratio (Mz / Mw) of Z-average molecular weight Mz to weight-average molecular weight Mw of 2.0 or more and 6.0 or less is melted and extruded from a hollow spinneret hole having a minimum circumscribed circle diameter of 1.2 mm or more and 5.0 mm or less. This produces a nonwoven fabric having both excellent strength and rigidity.

[0070] In the method for producing a nonwoven fabric of the present invention, the propylene-based resin basically refers to the above-mentioned propylene-based resin, and preferably has the properties described in [Propylene-based resin], such as the propylene fraction, the ratio of weight-average molecular weight Mw to number-average molecular weight Mn (Mw / Mn), and the melt mass-flow rate.

[0071] However, in the nonwoven fabric manufacturing method of the present invention, the propylene-based resin has a ratio of Z-average molecular weight Mz to weight-average molecular weight Mw (Mz / Mw) of 2.0 or more and 6.0 or less, as described above. By ensuring that the Mz / Mw of the propylene-based resin is 2.0 or more, preferably 2.2 or more, and more preferably 2.3 or more, the molecular orientation is not excessively high, facilitating bonding and improving adhesion, resulting in a nonwoven fabric with excellent strength. Furthermore, by ensuring that the Mz / Mw of the propylene-based resin is 6.0 or less, preferably 5.0 or less, and more preferably 4.0 or less, yarn breakage during spinning can be suppressed, resulting in a nonwoven fabric with fewer defects caused by the inclusion of extremely thick fibers or polymer clumps.

[0072] In the method for producing a nonwoven fabric of the present invention, the propylene-based resin is preferably a propylene-based resin produced using a Ziegler-Natta catalyst as a polymerization catalyst. When the propylene-based resin is a propylene-based resin produced using a Ziegler-Natta catalyst, the propylene-based resin tends to have larger Mz / Mw and Mw / Mn than propylene-based resins produced using a metallocene catalyst, and therefore the adhesiveness is improved, resulting in a nonwoven fabric with excellent strength.

[0073] Next, as a method for obtaining hollow fibers, a melt spinning method using an extruder such as a pressure melter type, a single-screw extruder, or a twin-screw extruder type can be applied. The molten and extruded propylene-based resin passes through a pipe, is metered by a metering device such as a gear pump, passes through a filter to remove foreign matter, and is then introduced into a spinneret.

[0074] At this time, the temperature from the resin pipe to the spinneret (spinning temperature) is preferably 180° C. or higher and 280° C. or lower. By setting the spinning temperature within the above range, a stable molten state is achieved, and thread breakage during spinning can be suppressed, resulting in a nonwoven fabric with fewer defects caused by the inclusion of extremely thick fibers or polymer lumps.

[0075] The discharge holes of the spinneret used for discharge are hollow nozzle holes having a minimum circumscribed circle diameter of 1.2 mm to 5.0 mm. When the minimum circumscribed circle diameter of the hollow nozzle holes is preferably 1.2 mm or more, more preferably 1.5 mm or more, hollow fibers with a high hollowness can be obtained. Furthermore, when the minimum circumscribed circle diameter of the hollow nozzle holes is preferably 5.0 mm or less, more preferably 4.5 mm or less, yarn breakage during spinning can be suppressed, and a nonwoven fabric with fewer defects caused by the inclusion of extremely thick fibers or polymer lumps can be obtained.

[0076] The minimum circumscribing circle diameter (mm) of the hollow nozzle hole referred to here means the diameter (4) of the smallest circle (1) that can encompass all the discharge holes (2) necessary to form single fibers when viewed from the discharge surface of the nozzle in the spinneret, as exemplified in Figure 1.

[0077] The hollow spinneret hole preferably has a number of slits of 5 to 12. By having the number of slits in the hollow spinneret hole preferably 5 or more, more preferably 6 or more, and even more preferably 7 or more, air can be easily incorporated into the fiber, resulting in a hollow fiber with a high hollowness. Furthermore, by having the number of slits in the hollow spinneret hole preferably 12 or less, more preferably 11 or less, and even more preferably 10 or less, yarn breakage during spinning can be suppressed, resulting in a nonwoven fabric with fewer defects caused by the inclusion of extremely thick fibers or polymer lumps.

[0078] The number of slits in the hollow spinneret holes refers to the number of discharge holes (2) required to form a single fiber in the spinneret when viewed from the discharge surface of the spinneret, as exemplified in Figure 1. In the example of Figure 1, the number of slits in the hollow spinneret holes is 8.

[0079] Furthermore, the slit width of the hollow nozzle hole is preferably 0.02 mm or more and 0.40 mm or less. By making the slit width of the hollow nozzle hole preferably 0.02 mm or more, more preferably 0.04 mm or more, and even more preferably 0.05 mm or more, discharge defects due to clogging of the nozzle hole by foreign matter can be suppressed, improving stability during spinning and resulting in a nonwoven fabric with fewer defects caused by the inclusion of extremely thick fibers or polymer lumps. Furthermore, by making the slit width of the hollow nozzle hole preferably 0.40 mm or less, more preferably 0.30 mm or less, and even more preferably 0.25 mm or less, metering at the spinneret hole can be improved, resulting in a nonwoven fabric with excellent uniformity.

[0080] The slit width (mm) of the hollow nozzle hole refers to the width (3) of the nozzle hole required to form a single fiber when viewed from the nozzle outlet face of the spinneret, as exemplified in Figure 1. When the slit width differs for each nozzle hole (2), it is preferable that the arithmetic mean value thereof is within the above range.

[0081] Here, the land length of the hollow nozzle hole is preferably 0.1 mm or more and 5.0 mm or less. By making the land length of the hollow nozzle hole preferably 0.1 mm or more, more preferably 0.2 mm or more, and even more preferably 0.3 mm or more, the metering ability at the hollow nozzle hole can be improved, resulting in a nonwoven fabric with excellent uniformity. Furthermore, by making the land length of the hollow nozzle hole preferably 5.0 mm or less, more preferably 4.0 mm or less, and even more preferably 3.5 mm or less, excessive pressure increase can be suppressed, thereby enabling stable spinning over a long period of time.

[0082] The land length (mm) of the hollow nozzle hole refers to the length of the straight tube portion in the spinneret that has the same cross section as the hole shape of the nozzle hole when viewed from the nozzle discharge surface.

[0083] The propylene-based resin spun out from the spinneret is then preferably cooled. Examples of methods for cooling the propylene-based resin discharged from the spinneret include a method of forcibly blowing cold air onto the propylene-based resin, a method of allowing the propylene-based resin to cool naturally at the ambient temperature around the propylene-based resin discharged from the spinneret, and the like, or a combination of these methods can be used.

[0084] The temperature of the cooling air can be determined in consideration of the balance with the cooling air speed from the viewpoint of cooling efficiency, but is preferably 30° C. or less. By setting the upper limit of the cooling air temperature to preferably 30° C. or less, more preferably 20° C. or less, and even more preferably 15° C. or less, the cooling efficiency of the propylene-based resin discharged from the spinneret is increased, and spinnability can be improved. In addition, the lower limit of the cooling air temperature is preferably 0° C. or more from the viewpoint of the cost of cooling the air and from the viewpoint of preventing moisture from adhering to the fibers due to cooling.

[0085] The cooling air is preferably blown in a direction substantially perpendicular to the propylene-based resin discharged from the spinneret (when fibers are running vertically, this refers to a direction parallel to the ground). In this case, the speed of the cooling air is preferably 10 m / min or more from the viewpoint of cooling efficiency and uniformity of fineness, and is preferably 100 m / min or less from the viewpoint of spinning stability.

[0086] It is also preferable to start cooling at a distance of 0 mm or more and 300 mm or less downstream from the hollow nozzle hole of the spinneret. By setting the lower limit of the distance from the spinneret to the start of cooling to preferably 0 mm or more, more preferably 5 mm, it is possible to stabilize discharge without causing a decrease in the nozzle surface temperature. By setting the upper limit of the distance from the spinneret to preferably 300 mm or less, more preferably 100 mm or less, it is possible to stabilize the thinning behavior of the hollow fiber and improve spinnability.

[0087] Next, the cooled and solidified filaments are preferably drawn. When a spunbonding method is employed, the filaments obtained by cooling and solidifying the propylene-based resin discharged from the spinneret are drawn and drawn by compressed air injected from an ejector disposed below the spinneret without being wound up.

[0088] In the spunbonding method, various shapes of spinneret and ejector can be used, such as round and rectangular shapes. Among them, it is preferable to use a combination of a rectangular spinneret and a rectangular ejector, from the viewpoints that the amount of compressed air used is relatively small and fusion and abrasion between the yarns are unlikely to occur.

[0089] In this case, the distance from the spinneret to the ejector inlet is preferably 400 mm or more and 3000 mm or less. By making the distance from the spinneret to the ejector inlet preferably 400 mm or more, the hollow fibers enter the ejector after being cooled and solidified, thereby obtaining excellent spinning stability. Furthermore, by making the distance from the spinneret to the ejector inlet preferably 3000 mm or less, the spinning stress does not become excessively high, thereby suppressing thread breakage and obtaining a nonwoven fabric with fewer defects caused by the inclusion of extremely thick fibers or polymer lumps.

[0090] The yarn entering the ejector is accelerated by the accelerating air flow, and the running speed of the yarn, that is, the spinning speed, reaches a speed close to the air flow speed.

[0091] The spinning speed is preferably 1.5 km / min or more and 6.0 km / min or less. By setting the spinning speed to preferably 1.5 km / min or more, more preferably 1.8 km / min or more, and even more preferably 2.0 km / min or more, the average single fiber diameter becomes small, making it possible to obtain a nonwoven fabric with excellent uniformity of texture. Furthermore, by setting the spinning speed to preferably 6.0 km / min or less, it is possible to suppress yarn breakage during spinning and improve spinning stability.

[0092] The spinning speed referred to here is a value measured and calculated by the following procedure: (1) The outer circumferential length L of the approximately circular portion formed by the hollow portion of the yarn is measured in the same manner as in the "Method for measuring and calculating the average hollow ratio of hollow fibers" above. ｉｎ (μm) and the outer circumferential length L of the approximately circular portion formed by the outer side of the resin portion ｏｕｔ (μm) The area A of a perfect circle that is the same ｉｎ (μm ２ ) and A ｏｕｔ (μm ２ ) is calculated. (2) The propylene-based resin discharged from the spinneret is collected for 1 minute and weighed, and the value obtained is the discharge rate (g / min). This operation is carried out three times, and the arithmetic mean value is divided by the number of spinneret holes to obtain the single-hole discharge rate Q (g / min). (3) The value obtained by rounding off to one decimal place using the following formula is used as the spinning speed: Spinning speed (km / min) = Q × 1000 / ((A ｏｕｔ -A ｉｎ )×0.91) ... (Formula).

[0093] In this manner, hollow fibers having an average single fiber diameter of 5.0 μm or more and 50.0 μm or less and an average hollow ratio of 31.0% or more and 60.0% or less can be formed.

[0094] (b) Step of forming a fiber web In this step, the hollow fibers obtained in the previous step are deposited to form a fiber web composed of the hollow fibers. Specifically, for example, the hollow fibers are spread by passing through a spreading section where the surrounding air flow speed is reduced, and then the fibers are landed on a net conveyer that sucks air from the back side, and collected as a fiber web.

[0095] The collected fiber web is preferably transported at a transport speed of 5 m / min or more and 1200 m / min or less.

[0096] The material of the net used for collection is not particularly limited, and examples include metal nets such as stainless steel, iron, and nickel, as well as resin nets made of polyester or fluororesin, rubber nets, etc. Among these, it is preferable to use a resin net from the viewpoint of collection properties and releasability from the conveyor.

[0097] In another preferred embodiment, the collected fiber web is temporarily bonded by contacting one side of the 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 the transportability from collection of the yarns to thermal bonding.

[0098] In the nonwoven fabric manufacturing method of the present invention, the method for forming the fiber web can be selected from known manufacturing methods such as the meltblowing method and the staple fiber carding method in addition to the spunbonding method described above. However, the spunbonding method is preferred due to its superior productivity. The spunbonding method not only has excellent productivity and mechanical strength, but also suppresses the fuzzing and fiber shedding that often occur in staple fiber nonwoven fabrics. Furthermore, by laminating multiple layers of collected spunbonded nonwoven fiber webs or thermally bonded spunbonded nonwoven fabrics (both denoted as S) in the form of SS, SSS, and SSSS, productivity and uniformity of texture are improved. Note that even when multiple layers of spunbonded nonwoven fabrics are laminated, if all of the layers are made of the same resin, they are treated as a single-layer nonwoven fabric in the present invention, as described above.

[0099] (c) Step of thermally bonding the fiber web In this step, the fiber web obtained in the previous step is thermally bonded. The thermal bonding method is not particularly limited, and examples include a method of thermally fusing the fiber web using various rolls, such as a heat embossing roll, each of which has an engraved (concave or convex) surface on a pair of upper and lower rolls; a heat embossing roll consisting of a combination of one roll with a flat (smooth) surface and the other with an engraved (concave or convex) surface; and a heat calender roll consisting of a combination of upper and lower flat (smooth) rolls; a method of thermally fusing the fiber web using ultrasonic vibrations from a horn; and a method of passing hot air through the nonwoven fiber web to soften or melt the surfaces of the islands-in-sea composite fibers and thermally fusing the fiber intersections. Among these, it is preferable to use a heat embossing roll, each of which has an engraved (concave or convex) surface on a pair of upper and lower rolls; or a heat embossing roll consisting of a combination of one roll with a flat (smooth) surface and the other with an engraved (concave or convex) surface. This not only increases productivity but also provides bonded portions that improve the strength of the nonwoven fabric and non-bonded portions that improve the texture and breathability of the fabric.

[0100] The adhesion rate during thermal bonding is preferably 5% or more and 30% or less. By setting the adhesion rate to preferably 5% or more, more preferably 10% or more, a nonwoven fabric with excellent strength and rigidity can be obtained. Furthermore, by setting the adhesion rate to preferably 30% or less, more preferably 20% or less, a nonwoven fabric with excellent breathability and processability can be obtained.

[0101] Here, the term "bonding rate" refers to the area ratio of the bonded portion to the entire nonwoven fabric. Specifically, when thermal bonding is performed using a pair of uneven rolls, the term refers to the area ratio of the portion of the nonwoven fabric where the convex portions of the upper roll and the convex portions of the lower roll overlap and contact the nonwoven fiber web (bonded portion). When thermal bonding is performed using an uneven roll and a flat roll, the term refers to the area ratio of the portion of the uneven roll where the convex portions of the uneven roll contact the nonwoven fiber web (bonded portion) to the entire nonwoven fabric. When ultrasonic bonding is performed, the term refers to the area ratio of the portion of the nonwoven fabric that is thermally bonded by ultrasonic processing (bonded portion).

[0102] The shape of the bonded portions formed by the hot embossing roll or ultrasonic bonding is not particularly limited, but for example, a circle, ellipse, square, rectangle, parallelogram, rhombus, regular hexagon, or regular octagon can be used. Furthermore, it is preferable that the bonded portions are uniformly spaced at regular intervals in both the longitudinal direction (machine direction) and the width direction of the nonwoven fabric. This reduces the variation in strength of the nonwoven fabric.

[0103] The surface temperature of the hot embossing roll during thermal bonding is preferably 100° C. or higher and 150° C. or lower. By setting the surface temperature of the hot embossing roll to preferably 100° C. or higher, more preferably 110° C. or higher, moderate thermal bonding can be achieved, resulting in a nonwoven fabric with excellent strength and rigidity. Furthermore, by setting the surface temperature of the hot embossing roll to preferably 150° C. or lower, more preferably 145° C. or lower, strength reduction due to excessive thermal bonding can be suppressed, resulting in a nonwoven fabric with excellent strength.

[0104] The linear pressure of the hot embossing roll during thermal bonding is preferably 10 N / mm or more and 200 N / mm or less. By setting the linear pressure of the hot embossing roll to preferably 10 N / mm or more, more preferably 20 N / mm or more, and even more preferably 30 N / mm or more, sufficient thermal bonding can be achieved, resulting in a nonwoven fabric with excellent strength and rigidity. Furthermore, by setting the linear pressure of the hot embossing roll to preferably 200 N / mm or less, more preferably 150 N / mm or less, and even more preferably 100 N / mm or less, a decrease in strength due to excessive thermal bonding can be suppressed, resulting in a nonwoven fabric with excellent strength.

[0105] Furthermore, in order to adjust the thickness of the nonwoven fabric, after the thermal bonding by the above-mentioned thermal embossing roll, thermocompression bonding can be further performed by a thermal calender roll consisting of a pair of upper and lower flat rolls. The pair of upper and lower flat rolls refers to metal rolls or elastic rolls with smooth surfaces, and a pair of metal rolls or a pair of metal rolls and elastic rolls can be used.

[0106] Here, the elastic roll refers to a roll made of a material that has greater elasticity than a metal roll. Examples of elastic rolls include so-called paper rolls made of paper, cotton, aramid paper, etc., and resin rolls made of urethane resin, epoxy resin, silicone resin, polyester resin, hard rubber, and mixtures of these.

[0107] (d) Other post-processing steps The spunbond nonwoven fabric of the present invention can be post-processed to the extent that the effects of the present invention are not impaired. Examples of post-processing include physical processing such as drilling and rubbing, and chemical processing such as hydrophilization and charging.

[0108] [Laminated Nonwoven Fabric] The nonwoven fabric of the present invention can be used as it is, but it is also preferable to form a laminated nonwoven fabric having a layer of the nonwoven fabric and a fiber layer of a type different from that of the nonwoven fabric layer and / or a film layer.

[0109] Here, the term "a fiber layer of a type different from that of the nonwoven fabric" as used herein refers to a fiber layer whose main component is a material other than a propylene-based resin or a fiber layer manufactured by a different method. For example, when the nonwoven fabric is a spunbond nonwoven fabric, a fiber layer manufactured by a different method refers to a melt-blown nonwoven fabric layer formed by a melt-blowing method, a staple fiber nonwoven fabric layer formed by a papermaking method, or a woven or knitted layer made of long fibers or spun yarns.

[0110] The laminated nonwoven fabric according to the present invention has a lamination structure in which at least one layer of the nonwoven fabric of the present invention is laminated. By laminating at least one layer of the nonwoven fabric, the nonwoven fabric acts as a reinforcing material, resulting in a laminated nonwoven fabric with excellent strength.

[0111] Furthermore, the method for producing the laminated nonwoven fabric according to the present invention is not particularly limited, but examples include a method in which the nonwoven fabric of the present invention is overlaid on a fiber layer or film layer of a type different from that of the nonwoven fabric layer without bonding, or a method in which part or all of the layers are integrated using an adhesive or thermal bonding processing.

[0112] The resin constituting the structure other than the nonwoven fabric of the present invention is not particularly limited, but is preferably a propylene-based resin because it is easy to bond.

[0113] The laminated nonwoven fabric of the present invention can be used for medical and hygienic materials, daily necessities, industrial materials, etc. depending on the types of layers to be laminated, but because it has excellent strength and rigidity, it is particularly suitable for use in industrial materials. For example, laminating a meltblown layer can improve collection performance, making it suitable for use in various filters.

[0114] Next, the nonwoven fabric of the present invention will be described in more detail based on examples, although the present invention is not limited to these examples.

[0115] [Measurement and Evaluation Methods] The property values ​​in the examples were determined by the following methods. Unless otherwise specified, measurements were carried out according to the methods described above.

[0116] A. Propylene Fraction of Propylene-Based Resin and Nonwoven Fabric Measurements were carried out as described above using a nuclear magnetic resonance apparatus "ECZ-600" manufactured by JEOL RESONANCE under the following conditions. Measurement method: Single １３ C pulse with inverse gated １ H decoupling Observation kernel: １３ C Observation frequency: 150.9 MHz Chemical shift reference: orthodichlorobenzene-d ４ (133.0ppm) - Measurement temperature: 135°C.

[0117] B. Mz / Mw and Mw / Mn of Propylene-Based Resins Measurements were carried out as described above using a "PL-220" manufactured by Polymer Laboratories as a high-temperature GPC apparatus under the following conditions: Standard sample: monodisperse polystyrene manufactured by Tosoh Corporation, dibenzyl manufactured by Tokyo Chemical Industry Co., Ltd. Injection volume: 0.200 mL Flow rate: 1.0 mL / min Guard column: Shodex HT-G manufactured by Showa Denko K.K. Column: Shodex HT-806M (2 columns) manufactured by Showa Denko K.K. Detector: differential refractive index detector RI.

[0118] C. Melt Mass Flow Rate (MFR) of Propylene-Based Resin and Nonwoven Fabric Measurements were carried out as described above in accordance with ASTM D1238 (Method A) using a "MELT INDEXER F-F01" manufactured by Toyo Seiki Seisaku-sho, Ltd. as a melt mass flow rate measuring device.

[0119] D. Average Single Fiber Diameter and Average Hollow Ratio Measurements were carried out as described above using a scanning electron microscope "SU1510" manufactured by Hitachi High-Technologies Corporation as the scanning electron microscope and "WinROOF2015" manufactured by Mitani Shoji Co., Ltd. as the image analysis software.

[0120] E. Melting Point and Heat of Crystalline Fusion Measurements were carried out as described above using a differential scanning calorimeter "DSC Q2000" manufactured by TA Instruments.

[0121] F. Basis Weight Measurement was carried out as described above in accordance with "6.2 Mass per unit area" of JIS L1913:2010 "Test methods for general nonwoven fabrics."

[0122] G. Tensile strength per unit area A tensile tester "RTC-1210A" manufactured by A&D Co., Ltd. was used, and measurements were carried out as described above in accordance with "6.3 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "General nonwoven fabric testing methods."

[0123] H. Bending Resistance Measurement was carried out as described above in accordance with "6.7.3 41.5° Cantilever Method" in "6.7 Bending Resistance (JIS Method and ISO Method)" of JIS L1913:2010 "Testing Methods for General Nonwoven Fabrics."

[0124] I. Number of Defects In the nonwoven fabrics having a width obtained in the Examples, the number of defects due to thread breakage was measured over a length of 1000 m or more, and the number of defects due to thread breakage per 1000 m was calculated. A defect with 3 defects / 1000 m or less was evaluated as A, a defect with more than 3 defects / 1000 m but 8 defects / 1000 m or less was evaluated as B, and a defect with more than 8 defects / 1000 m was evaluated as C.

[0125] [Propylene-based resin] The propylene-based resins used in the examples of the present invention are as follows.

[0126] [Propylene-based Resin A] This is a propylene homopolymer obtained using a Ziegler-Natta catalyst (denoted as "ZN" in Table 1). This propylene-based resin A has a propylene fraction of 100.0%, an MFR of 35 g / 10 min, an Mz / Mw of 2.5, and an Mw / Mn of 6.3.

[0127] [Propylene-based Resin B] This is a propylene homopolymer obtained using a Ziegler-Natta catalyst. The propylene fraction of this propylene-based resin B is 100.0%, the MFR is 45 g / 10 min, the Mz / Mw is 2.4, and the Mw / Mn is 5.6.

[0128] [Propylene-based Resin C] This is a propylene homopolymer obtained using a Ziegler-Natta catalyst. The propylene fraction of this Propylene-based Resin C is 100.0%, the MFR is 60 g / 10 min, the Mz / Mw is 2.3, and the Mw / Mn is 3.8.

[0129] [Propylene-based Resin D] This is a propylene homopolymer obtained using a Ziegler-Natta catalyst. Propylene-based Resin D has a propylene fraction of 100.0%, an MFR of 25 g / 10 min, an Mz / Mw ratio of 2.7, and an Mw / Mn ratio of 6.9.

[0130] [Propylene-based Resin E] This is a propylene homopolymer obtained using a Ziegler-Natta catalyst. The propylene fraction of this Propylene-based Resin E is 100.0%, MFR is 9 g / 10 min, Mz / Mw is 3.4, and Mw / Mn is 8.7.

[0131] [Propylene-based Resin F] This is a propylene homopolymer obtained using a metallocene catalyst (denoted as "M" in Table 1). The propylene fraction of this Propylene-based Resin F is 100.0%, the MFR is 35 g / 10 min, the Mz / Mw is 2.0, and the Mw / Mn is 3.2.

[0132] [Propylene-based Resin G] This is a propylene homopolymer obtained using a metallocene catalyst. The propylene fraction of this Propylene-based Resin G is 100.0%, MFR is 35 g / 10 min, Mz / Mw is 1.8, and Mw / Mn is 2.3.

[0133] [Propylene-based Resin H] This is an ethylene-propylene copolymer obtained using a Ziegler-Natta catalyst. The propylene fraction of this Propylene-based Resin H is 97.0%, the MFR is 30 g / 10 min, the Mz / Mw is 3.2, and the Mw / Mn is 4.9.

[0134] [Propylene-based Resin I] This is a propylene homopolymer obtained using a Ziegler-Natta catalyst. The propylene fraction of this Propylene-based Resin I is 100.0%, the MFR is 35 g / 10 min, the Mz / Mw is 4.8, and the Mw / Mn is 9.8.

[0135]

[0136] [Example 1] (a) Step of forming hollow fibers Propylene-based resin A was melt-extruded using a single-screw extruder and supplied to a rectangular spinneret while being metered using a gear pump. At this time, the melt extrusion temperature was set to 230°C, and the propylene-based resin A was extruded through the hollow spinneret holes, which had a minimum circumscribed circle diameter of 2.0 mm, 8 slits, a slit width of 0.08 mm, and a land length of 0.3 mm, at a single-hole throughput rate of 0.60 g / min.

[0137] The extruded fibrous resin was cooled and solidified by blowing cooling air at a temperature of 10°C and a speed of 18 m / min from the outside, and then pulled by an air flow using a rectangular ejector to obtain fibers. At this time, the distance from the spinneret to the ejector inlet was 550 mm.

[0138] (b) Step of forming a fiber web Subsequently, the fibers obtained above were spread by passing through a spreading section where the surrounding air flow velocity was reduced, and then the fibers were landed on a net conveyer where air was sucked from the back side, to obtain a fiber web made of composite fibers. Thereafter, the collected fiber web was transported at a speed of 10 m / min.

[0139] (c) Step of bonding the obtained fiber web Subsequently, the fiber web made of the composite fiber obtained as described above was thermally bonded using a pair of upper and lower thermal embossing rolls consisting of an upper roll made of metal and engraved with a polka dot pattern and having a bonding area ratio of 11%, and a lower roll made of metal and flat, at a surface temperature of 135°C and a linear pressure of 50 N / mm to obtain a nonwoven fabric with a width of 20 cm. The evaluation results of the obtained nonwoven fabric are shown in Table 2.

[0140] [Examples 2 to 5, Comparative Examples 1 to 3, Example 10] Nonwoven fabrics were obtained in the same manner as in Example 1, except that in the (a) fiber-forming step, the propylene-based resin was changed from propylene-based resin A to propylene-based resin B in Example 2, propylene-based resin C in Comparative Example 1, propylene-based resin D in Example 3, propylene-based resin E in Comparative Example 2, propylene-based resin F in Example 4, propylene-based resin G in Comparative Example 3, propylene-based resin H in Example 5, and propylene-based resin I in Example 10. The evaluation results of the obtained nonwoven fabrics are shown in Table 2.

[0141]

[0142] [Examples 6 and 7, Comparative Examples 4 and 5] (a) In the step of forming the fiber, the minimum circumscribed circle diameter of the hollow spinneret hole was changed from 2.0 mm to 1.0 mm in Comparative Example 4, 1.5 mm in Example 6, 3.0 mm in Example 7, and 4.8 mm in Comparative Example 5, except that nonwoven fabrics were obtained in the same manner as in Example 1. The evaluation results of the obtained nonwoven fabrics are shown in Table 3.

[0143] [Comparative Example 6] (a) In the step of forming fibers, the spinneret holes were changed from hollow holes to round holes with a spinneret hole diameter of 0.3 mm and a land length of 0.3 mm, and a nonwoven fabric was obtained in the same manner as in Example 1. The evaluation results of the obtained nonwoven fabric are shown in Table 3.

[0144] [Examples 8 and 9] (a) In the step of forming fibers, nonwoven fabrics were obtained in the same manner as in Example 1, except that the number of slits in the hollow spinneret holes was changed from 8 to 6 in Example 8 and 10 in Example 9. The evaluation results of the obtained nonwoven fabrics are shown in Table 3.

[0145]

[0146] The nonwoven fabrics of Examples 1 to 10 were nonwoven fabrics constituted by hollow fibers containing a propylene-based resin as a main component, and the hollow fibers had an average single fiber diameter of 5.0 μm or more and 50.0 μm or less and an average hollow ratio of 31.0% or more and 60.0% or less. The nonwoven fabrics had a melt mass flow rate of 16 g / 10 min or more and 55 g / 10 min or less and an Mz / Mw of 2.0 or more and 6.0 or less, and therefore were nonwoven fabrics excellent in strength and rigidity.

[0147] On the other hand, the nonwoven fabric of Comparative Example 1 had a low hollow ratio and a high melt mass-flow rate, while the nonwoven fabrics of Comparative Examples 4 and 6 had low hollow ratios, so all of them were poor in tensile strength and bending resistance per unit area weight. Furthermore, the nonwoven fabric of Comparative Example 2 had a low melt mass-flow rate, so in addition to having low tensile strength per unit area weight, it also had many defects. Furthermore, the nonwoven fabric of Comparative Example 3 had a small Mz / Mw, and the nonwoven fabric of Comparative Example 5 had a high hollow ratio, so it was poor in bending resistance.

[0148] 1: Minimum circumscribing circle 2: Slit (discharge hole) 3: Slit width 4: Diameter of minimum circumscribing circle

Claims

1. A nonwoven fabric composed of hollow fibers whose main component is a propylene-based resin, wherein the propylene-based resin has a ratio (Mz / Mw) of Z-average molecular weight Mz to weight-average molecular weight Mw of 2.0 or more and 6.0 or less, the hollow fibers have an average single fiber diameter of 5.0 μm or more and 50.0 μm or less and an average hollow ratio of 31.0% or more and 60.0% or less, and the nonwoven fabric has a melt mass flow rate of 16 g / 10 min or more and 55 g / 10 min or less.

2. The nonwoven fabric according to claim 1, wherein the propylene-based resin further has a ratio of weight average molecular weight Mw to number average molecular weight Mn (Mw / Mn) of 3.0 or more and 10.0 or less.

3. The nonwoven fabric according to claim 1 or 2, wherein the heat of crystalline fusion of the nonwoven fabric is 80 J / g or more and 120 J / g or less.

4. The nonwoven fabric according to claim 1 or 2, wherein the nonwoven fabric is a spunbond nonwoven fabric.

5. A method for producing a nonwoven fabric having a melt mass flow rate of 16 g / 10 min or more and 55 g / 10 min or less, comprising the steps of: melting a propylene-based resin having a ratio (Mz / Mw) of Z-average molecular weight Mz to weight-average molecular weight Mw of 2.0 or more and 6.0 or less, and extruding the propylene-based resin from a hollow nozzle hole of a spinneret having a minimum circumscribed circle diameter of 1.2 mm or more and 5.0 mm or less to form hollow fibers having an average single fiber diameter of 5.0 μm or more and 50.0 μm or less and an average hollow ratio of 31.0% or more and 60.0% or less; stacking the hollow fibers to form a fiber web composed of the hollow fibers; and thermally bonding the fiber web.

6. The method for producing a nonwoven fabric according to claim 5, wherein the number of slits in the hollow die hole is 5 or more and 12 or less.

7. A laminated nonwoven fabric comprising a layer of the nonwoven fabric according to claim 1 or 2, and a fiber layer and / or a film layer different from the nonwoven fabric layer.