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

Abstract

To provide a nonwoven fabric which is bulky while having excellent strength, and on the other hand, from which a hot-melt material does not ooze out when formed into a laminated nonwoven fabric.SOLUTION: A nonwoven fabric comprising fibers containing a propylene-based resin as a main component, wherein the nonwoven fabric has fused portions and non-fused portions, a flatness of the fibers in the fused portions is 5.8 or more and 10.0 or less, and a ratio Mz / Mw of a Z average molecular weight Mz to a weight average molecular weight Mw of the nonwoven fabric is 2.0 or more and 6.0 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to nonwoven fabrics. [Background technology]

[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 petroleum-derived polymers used in response to environmental considerations, there has been a demand to reduce the mass per unit area (basis weight) of nonwoven fabrics made from propylene-based resins used in sanitary and industrial materials. Furthermore, even with a lower basis weight, there is a demand for the fabric to exhibit high mechanical strength while remaining the same thickness as current products, and for the hot melt material to not bleed when laminated.

[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-based polymer in which the ratio Mz / Mw of the Z-average molecular weight Mz to the weight-average molecular weight Mw is within a specific range. This invention describes that a nonwoven fabric can be obtained that has higher fiber strength, particularly single-fiber strength, than conventional hollow-fiber nonwoven fabrics, and that maintains a high hollow ratio even when the fiber diameter of the propylene-based 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. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2010 / 024268 [Patent Document 2] International Publication No. 2012 / 111723 Summary of the Invention [Problem to be solved by the invention]

[0008] The technology proposed in Patent Document 1 allows for the production of nonwoven fabrics with a relatively high hollow ratio and a certain strength by controlling the molecular weight distribution. However, when the basis weight is low, the number of fibers decreases, and the thickness of the nonwoven fabric tends to be small, which still poses a problem in that the nonwoven fabric feels like thin paper when in use.

[0009] The technology proposed in Patent Document 2 uses hollow fibers with a high molecular orientation, which allows for the production of a nonwoven fabric that is relatively strong and flexible. However, if the basis weight is low, the nonwoven fabric becomes thin, which causes the hot melt material to seep out.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a nonwoven fabric that has excellent strength and bulk, and that does not allow hot melt material to seep out when used to form a laminated nonwoven fabric. [Means for solving the problem]

[0011] As described above, nonwoven fabrics using hollow fibers made of propylene-based resins can have high strength depending on the manufacturing conditions, but because the thickness of the nonwoven fabric is insufficient, the nonwoven fabric tends to have a paper-like feel as the basis weight decreases. Therefore, the present inventors have conducted extensive research and found that, in a nonwoven fabric containing propylene-based resin fibers in which the flatness of the fibers in the fused portions is set within a specific range, only by setting the ratio of the Z-average molecular weight Mz to the weight-average molecular weight Mw (Mz / Mw) within a specific range can a nonwoven fabric be obtained that has excellent strength and bulk, yet does not exude the hot melt material in the laminated nonwoven fabric, 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 made of fibers whose main component is propylene-based resin, the nonwoven fabric has a fused portion and a non-fused portion, the flatness of the fibers in the fused portion is 5.8 or more and 10.0 or less, The ratio Mz / Mw of the Z-average molecular weight Mz to the weight-average molecular weight Mw of the nonwoven fabric is 2.0 or more and 6.0 or less. Nonwoven fabric.

[0014] [2] The nonwoven fabric according to [1], wherein the average single fiber diameter of the fibers in the non-fused portions is 10.0 μm or more and 50.0 μm or less.

[0015] [3] The nonwoven fabric according to [1] or [2], wherein the melt mass flow rate of the nonwoven fabric is 16 g / 10 min or more and 55 g / 10 min or less.

[0016] [4] The nonwoven fabric according to any one of [1] to [3], wherein the melting temperature of the nonwoven fabric is 150°C or higher and 170°C or lower.

[0017] [5] The nonwoven fabric according to any one of [1] to [4], wherein the cross-sectional shape of the fibers in the non-fused portions is hollow.

[0018] [6] The nonwoven fabric according to any one of [1] to [5] above, wherein the nonwoven fabric is a spunbonded nonwoven fabric.

[0019] [7] A step 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 die hole to form a fiber having an average single fiber diameter of 10.0 μm or more and 50.0 μm or less; depositing the fibers to form a fiber web composed of the fibers; and a step of thermally bonding the fiber web to form fused portions and non-fused portions in the fiber web, and adjusting the flatness of the fibers in the fused portions to 5.8 or more and 10.0 or less.

[0020] [8] A laminated nonwoven fabric comprising the nonwoven fabric according to any one of [1] to [6].

[0021] [9] The laminated nonwoven fabric according to [8], further comprising a hot melt material.

[0022]

[10] A sanitary material comprising the nonwoven fabric according to any one of [1] to [6] above. [Effects of the Invention]

[0023] According to the present invention, a nonwoven fabric can be obtained which has excellent strength and bulkiness, but which does not exude hot melt material when made into a laminated nonwoven fabric. [Brief explanation of the drawings]

[0024] [Figure 1] 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. DETAILED DESCRIPTION OF THE INVENTION

[0025] The nonwoven fabric of the present invention is a nonwoven fabric composed of fibers containing a propylene-based resin as a main component, the nonwoven fabric having fused portions and non-fused portions, the flatness of the fibers in the fused portions being 5.8 to 10.0, and the ratio Mz / Mw of the Z-average molecular weight Mz to the weight-average molecular weight Mw of the nonwoven fabric being 2.0 to 6.0. In the present invention, "fibers containing a propylene-based resin as a main component" refers to fibers in which the mass proportion of the propylene-based resin described below among the components constituting the fiber exceeds 50 mass%.

[0026] 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.

[0027] [Propylene-based resin] The nonwoven fabric of the present invention is made of fibers whose main component is a propylene-based resin. By using a propylene-based resin, the nonwoven fabric can be produced at low cost and with excellent strength.

[0028] The propylene-based resin refers to a resin with a propylene fraction of 50% or more, as described below. Specific examples include propylene homopolymers, as well as copolymers of propylene and ethylene, and copolymers of propylene and various α-olefins. Here, α-olefin refers to a hydrocarbon with a double bond 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.

[0029] 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%.

[0030] The propylene fraction (%) of the propylene-based resin referred to here is a value measured and calculated by the following procedure. (1) Weigh out the propylene resin that will be used as the raw material for the fiber, add orthodichlorobenzene-d4 (orthodichlorobenzene in which the hydrogen has been replaced with deuterium) to a sample concentration of 8 mass / v%, and heat to 135°C. (2) The obtained solution is analyzed using a nuclear magnetic resonance apparatus (e.g., JEOL RESONANCE "ECZ-600"). 13 C-NMR measurement is carried out, and the peak area due to propylene units and the peak areas due to ethylene units and α-olefin units are calculated from the NMR spectrum. (3) Sum of peak areas due to propylene units, ethylene units, and α-olefin units, A AP Peak area A due to propylene units PP The ratio (A PP / A AP ) as a percentage. (4) Take three measurements for each level and round off the arithmetic mean value to the nearest tenth.

[0031] 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.

[0032] To the propylene-based resin according to 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, lubricants including polyethylene wax, crystal nucleating agents, and pigments, or other polymers may be added as needed, in order to further enhance the effects of the present invention or to impart other properties, within the range that does not impair the effects of the present invention.

[0033] In particular, the propylene-based resin according to the present invention preferably contains 0.01% by mass or more and 5.00% by mass or less of a fatty acid amide compound to improve the slipperiness of the nonwoven fabric. When the content of the fatty acid amide compound is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% 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, when the content of the fatty acid amide compound is preferably 5.00% by mass or less, more preferably 4.00% by mass or less, and even more preferably 3.50% by mass or less, the degree of crystallinity of the fiber can be increased, resulting in a nonwoven fabric with excellent strength.

[0034] Examples of the fatty acid amide compound include saturated fatty acid monoamide compounds such as tetracosanoic acid amide, saturated fatty acid diamide compounds such as ethylene bisstearic acid amide, unsaturated fatty acid monoamide compounds such as oleic acid amide, and unsaturated fatty acid diamide compounds such as ethylene bisoleic acid amide.

[0035] The amount of fatty acid amide compound added to a nonwoven fabric made of a propylene-based resin can be measured, for example, by extracting the additive from the nonwoven fabric with a solvent and quantitatively analyzing it using liquid chromatography mass spectrometry (LS / MS) etc. The extraction solvent used here is appropriately selected depending on the type of fatty acid amide compound, and in the case of ethylene bisstearic acid amide, for example, a method using a chloroform-methanol mixture can be mentioned.

[0036] 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. A propylene-based resin having a melt mass flow rate of 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 particularly preferably 30 g / 10 min or more improves spinning stability during the production process, resulting in a nonwoven fabric of higher quality. Furthermore, a propylene-based resin having a melt mass flow rate of 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 increases the tensile strength of the fibers and makes bonded joints less susceptible to fracture, resulting in a nonwoven fabric of superior strength.

[0037] The melt mass flow rate (g / 10 min) of a propylene-based resin referred to here is a value measured and calculated by the following procedure in accordance with ASTM D1238 (Method A). This standard specifies that the melt mass flow rate of a propylene-based resin should be measured under a load of 2.16 kg and at a temperature of 230°C. (1) Collect 20 g of propylene resin, which is the raw material for the fiber. (2) The sampled propylene-based resin is placed in a melt mass flow rate measuring device (for example, "MELT INDEXER F-F01" manufactured by Toyo Seiki Seisakusho Co., 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) Five measurements are taken for each level, and the arithmetic mean value (g / 10 min) is rounded to the nearest whole number to calculate the melt mass flow rate (g / 10 min) of the propylene-based resin.

[0038] 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 Z-average molecular weight Mz to 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.

[0039] [fiber] The nonwoven fabric of the present invention is made of fibers containing the propylene-based resin as a main component.

[0040] The cross-sectional shape of the fibers according to the present invention is not particularly limited as long as it does not impair the effects of the present invention, but it is preferable that the cross-sectional shape of the fibers in the non-fused portions described below be hollow. The hollow cross-section relatively increases the bonding area between the fibers in the resulting nonwoven fabric compared with fibers of the same fineness, resulting in a nonwoven fabric with greater strength.

[0041] The fiber according to the present invention may be a composite fiber in which two or more types of resins are combined. When the 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.

[0042] Regarding the fibers according to the present invention, the average single fiber diameter of the fibers in the non-fused portions described below is preferably 10.0 μm or more and 50.0 μm or less. By setting the average single fiber diameter to preferably 10.0 μm or more, more preferably 12.0 μm or more, and even more preferably 15.0 μm or more, a bulkier nonwoven fabric is obtained. Furthermore, by setting the average single fiber diameter to preferably 50.0 μm or less, more preferably 40.0 μm or less, and even more preferably 35.0 μm or less, the number of fibers increases when compared at the same basis weight, resulting in a nonwoven fabric with excellent uniformity of texture and reduced exudation of the hot melt material.

[0043] The average single fiber diameter (μm) of the fibers is a value measured and calculated by the following procedure. (1) Randomly sample 5 mm x 5 mm test pieces from the nonwoven fabric so as to include as many unfused portions as possible, as described below. (2) For the unfused portion of the test piece, an image is taken using a scanning electron microscope (for example, "SU1510" manufactured by Hitachi High-Technologies Corporation) at a magnification that allows observation of the sides of 10 or more fibers. (3) From the captured image, 10 fibers that make up the nonwoven fabric are randomly selected and their fiber diameters (μm) are measured. (4) For each level, measure 10 times by changing the location of the test specimen, and round off the arithmetic mean value of 100 specimens to the nearest tenth.

[0044] The average single fiber diameter of the 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 spinneret in the production process, the spinning temperature, the single-hole output rate, the spinning speed, etc. Specifically, the average single fiber diameter of the fiber can be reduced by reducing the melt mass flow rate, using a hollow cross section with a small hollow ratio, increasing the spinning temperature, decreasing the single-hole output rate, or increasing the spinning speed.

[0045] When the fibers according to the present invention have a hollow cross section, the average hollow ratio of the non-fused portions of the fibers is preferably 31.0% or more and 60.0% or less. An average hollow ratio of preferably 31.0% or more, more preferably 35.0% or more, even more preferably 38.0% or more, and most preferably 40.0% or more makes the fused portions less susceptible to breakage and increases the fiber diameter relative to the fiber fineness, resulting in a nonwoven fabric with excellent strength and thickness. Furthermore, an average hollow ratio of preferably 60.0% or less, more preferably 55.0% or less, and even more preferably 50.0% or less suppresses deformation of the fiber cross-sectional shape (from substantially circular to substantially elliptical) and crushing of the fibers that occur when the nonwoven fabric is compressed, resulting in a bulkier nonwoven fabric.

[0046] The average hollow ratio (%) of the non-fused portion of the fiber (hollow fiber) is a value measured and calculated by the following procedure. (1) Take a 5mm x 5mm test piece from the nonwoven fabric. (2) On the surface of the test piece, non-fused fibers located at a distance of 10% or more from the fused portion relative to the distance between adjacent fused portions are embedded in an embedding agent such as epoxy resin, and the fibers are cut perpendicular to the fiber axis using a razor to expose the fiber cross-sections. Images are then taken using a scanning electron microscope (e.g., Hitachi High-Technologies Corporation's "SU1510") at a magnification that allows observation of 10 or more fiber cross-sections. (3) From the photographed image, the perimeter length Lin (μm) of the approximately circular part formed by the hollow part of the hollow fiber and the perimeter length L of the approximately circular part formed by the outer side of the resin part are calculated using image analysis software (for example, "WinROOF2015" manufactured by Mitani Corporation). out (μm) and calculate the outer circumference as L in and L out The area of ​​the perfect circle A is the same as in (μm 2 ) and A out (μm 2 ), calculate the hollow ratio H (%) A in (μm 2 )=L in 2 ÷4π A out (μm 2 )=L out 2 ÷4π H(%)=A in / A out ×100 (In the formula, π represents the constant of the circumference of a circle.) (4) For each level, measurements are taken 10 times by changing the location of the test specimen, and the arithmetic mean value (%) of the 100 specimens in total is rounded to the second decimal place to calculate the average hollowness (%).

[0047] The average hollow ratio in the non-fused portions of the 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 per hole, the cooling conditions, etc. Specifically, the average hollow ratio in the non-fused portions of the fiber can be increased by decreasing the melt mass flow rate, 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 per hole, or lowering the temperature of the cooling air.

[0048] The 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 that have substantially no fiber ends can also be used.

[0049] [Nonwoven fabric] The nonwoven fabric of the present invention is made of the above-mentioned fibers. Here, 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 papermaking 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 achieve excellent strength.

[0050] 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.

[0051] The nonwoven fabric of the present invention has fused portions and non-fused portions. In the present invention, the term "fused portions" refers to portions where the fibers are fused together by being compressed in the cross-sectional direction of the nonwoven fabric, or the like, causing the cross-sectional shape of the fibers to deform to an extent that it differs from the shape of the remaining portions, and furthermore, the fibers melt to the point that the portion becomes a lump or film-like shape, and the non-fused portions refer to portions other than the fused portions.

[0052] In the nonwoven fabric of the present invention, the flatness of the fibers in the fused portions is 5.8 to 10.0. A fiber flatness of 5.8 or more, preferably 6.0 or more, and more preferably 6.5 or more increases the bonding area between the fibers, resulting in a nonwoven fabric with excellent strength. Furthermore, a fiber flatness of 10.0 or less, preferably 8.9 or less, and more preferably 8.0 or less makes the fibers in the non-fused portions less likely to be crushed, resulting in a bulkier nonwoven fabric.

[0053] The flatness (unitless) of the fibers in the fused portion of the nonwoven fabric is a value measured and calculated by the following procedure. (1) Take a 5mm x 5mm test piece from the nonwoven fabric. (2) On the surface of the test piece, among the fibers in the fused portion, those in the fused portion where the shape of each fiber can be visually identified are embedded in an embedding agent such as epoxy resin, and the fibers are cut perpendicular to the fiber axis using a razor to expose the fiber cross section. An image is then taken at a magnification that allows observation of the fiber cross section using a scanning electron microscope (for example, the "SU1510" manufactured by Hitachi High-Technologies Corporation). (3) From the captured image, the length of the long axis of the fiber in the test piece, L, is determined using image analysis software (for example, "WinROOF2015" manufactured by Mitani Shoji Co., Ltd.). L (μm) and the length of the minor axis of the fiber L S (μm) and measure the major axis length of the fiber L L is the length of the minor axis of the fiber L S Calculate the value divided by . (4) For each level, measurements are taken 10 times by changing the location of the test piece, and the arithmetic mean value (no unit) of the 10 pieces is rounded to the second decimal place to calculate the flatness (no unit) of the fibers in the fused section.

[0054] The flatness of the fibers in the fused portions of the nonwoven fabric according to the present invention can be controlled, for example, by the cross-sectional shape of the fibers, the pressure applied during fusion, etc. Specifically, the flatness of the fibers in the fused portions can be increased by using fibers with a high hollow ratio in the hollow cross section or by increasing the pressure applied during fusion.

[0055] The nonwoven fabric 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. By setting this Mz / Mw to preferably 2.0 or more, more preferably 2.2 or more, and even more preferably 2.3 or more, molecular orientation is not excessively high, resulting in a nonwoven fabric with excellent bulk and thickness. Furthermore, by setting the Mz / Mw to preferably 6.0 or less, more preferably 5.0 or less, and even more preferably 4.0 or less, molecular orientation is high and the fiber strength is high, resulting in a nonwoven fabric with excellent strength.

[0056] The Mz / Mw of the nonwoven fabric is a value measured and calculated by the following procedure. The Mz / Mw of the propylene-based resin can also be measured and calculated in the same manner. In this case, in the following procedure (1), 5 mg of the propylene-based resin from which the test piece is made is randomly sampled. Procedures (2) and thereafter are carried out in the same manner. (1) Take 5 mg of propylene resin, which is the raw material for the fiber. If measuring randomly from nonwoven fabric, take 5 mg of test pieces. (2) 5 mL of 1,2,4-trichlorobenzene is added to 5 mg of the collected propylene-based resin or test piece, and this is heated at 165°C for 20 minutes to dissolve the propylene-based resin, thereby obtaining a propylene-based resin solution. (3) The resulting 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 placed in a high-temperature GPC apparatus (e.g., "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 and the weight-average molecular weight Mw, and Mz / Mn is calculated. (5) Measurements are taken three times for each level, and the arithmetic mean value (no unit) is rounded to one decimal place to calculate the Mz / Mw (no unit) of the propylene-based resin.

[0057] The Mz / Mw of the propylene-based resin can be controlled by, for example, a polymerization catalyst for the propylene-based resin. Specifically, the use of a Ziegler-Natta catalyst can increase the Mz / Mw of the propylene-based resin compared to the use of a metallocene catalyst, thereby increasing the Mz / Mw of the nonwoven fabric.

[0058] The nonwoven fabric of the present invention preferably 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 the nonwoven fabric of 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 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 the nonwoven fabric of 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 increases the tensile strength of the fibers and makes the fused joints less susceptible to fracture, resulting in a nonwoven fabric with excellent strength.

[0059] The melt mass flow rate (g / 10 min) of the nonwoven fabric is a value measured and calculated according to the following procedure in accordance with ASTM D1238 (Method A). (1) Take a 20g test piece from the nonwoven fabric. (2) The collected test piece 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) Five measurements are taken for each level, and the arithmetic mean value (g / 10 min) is rounded to the nearest whole number to calculate the melt mass flow rate (g / 10 min) of the nonwoven fabric.

[0060] The melt mass flow rate of the nonwoven fabric of the present invention can be controlled by, for example, the melt mass flow rate of the propylene-based resin. Specifically, the melt mass flow rate of the nonwoven fabric can be reduced by reducing the melt mass flow rate of the propylene-based resin.

[0061] The nonwoven fabric of the present invention preferably has a melting temperature of 150°C or higher and 170°C or lower. By having a melting temperature of preferably 150°C or higher, more preferably 155°C or higher, and even more preferably 160°C or higher, the temperature range for thermal bonding of the fibers is wide, which suppresses thermal shrinkage of the nonwoven fabric and results in a nonwoven fabric of excellent quality. Furthermore, the upper limit of the melting temperature of the nonwoven fabric achievable in the present invention is about 170°C because the main component is a propylene-based resin.

[0062] The melting temperature (°C) of the nonwoven fabric is a value measured and calculated according to the following procedure. (1) A 2.0 mg test piece is taken from the nonwoven fabric and set in a differential scanning calorimeter (for example, "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 temperature drop rate of 100°C / min, and then differential scanning calorimetry (2nd DSC) is performed again under nitrogen at a heating rate of 16°C / min and a measurement temperature range of 50°C to 230°C. (3) Calculate the temperature (°C) of the largest endothermic peak in the DSC curve of the second DSC. (4) For each level, measurements are taken three times by changing the location of the test piece, and the arithmetic mean value (°C) is rounded to the first decimal place to calculate the melting temperature (°C).

[0063] The melting temperature of the nonwoven fabric of the present invention can be controlled by, for example, the propylene fraction of the propylene-based resin or the mesopentad fraction of the propylene-based resin. Specifically, the melting temperature of the nonwoven fabric can be increased by increasing the propylene fraction of the propylene-based resin or the mesopentad fraction of the propylene-based resin.

[0064] 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.

[0065] The basis weight of the nonwoven fabric (g / m 2 ) is a value measured and calculated using 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 20cm x 25cm test piece is taken from the nonwoven fabric. However, if a 20cm x 25cm test piece cannot be taken, the total area of ​​the test pieces shall be 500cm. 2 A plurality of test pieces are taken from the nonwoven fabric so that the (2) Measure the mass (g) of the collected test piece under standard conditions and measure the area of ​​1 m 2 Mass per unit (g / m 2 ) (3) For each level, measurements were taken three times by changing the location of the test piece, and the arithmetic mean value (g / m 2 ) is rounded to the nearest tenth and is calculated as the basis weight (g / m 2 ) is calculated as

[0066] 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.

[0067] The nonwoven fabric of the present invention has a specific volume of 10.0 cm 3 / g or more 15.0cm 3 / g or less. The specific volume of the nonwoven fabric is preferably 10.0 cm 3 / g or more, more preferably 10.5 cm 3 / g or more, the nonwoven fabric has an excellent feel. 3 / g or less, more preferably 13.0 cm 3 / g or less, the fibers are sufficiently entangled with each other, resulting in a nonwoven fabric with excellent strength.

[0068] The specific volume of the nonwoven fabric (cm 3 / g) is a value measured and calculated by the following procedure. (1) Impregnate the nonwoven fabric with PVA or epoxy resin and dry it for at least 3 hours, taking care not to expose the PVA or epoxy resin on the surface of the nonwoven fabric. (2) From the nonwoven fabric that has been subjected to the above treatment, test pieces measuring 125 mm in the MD or CD direction and 1 mm in the direction perpendicular to the MD or CD direction are cut out. (3) The test piece is placed on the observation stage so that the cross section of the nonwoven fabric on the longitudinal side can be observed. (4) Take an image using a scanning electron microscope (for example, Hitachi High-Technologies Corporation's "SU1510") at a magnification that fits the entire thickness of the nonwoven fabric within the field of view. (5) The operation of (4) is photographed along the entire length of the test piece. (6) All the images taken in (5) are linked together, and the thickness (μm) of the unfused portion is measured every 5 mm from the edge of the sample, and the arithmetic average value is calculated. (7) For each level, the steps (1) to (6) are carried out 10 times, and the arithmetic mean value is rounded to two decimal places to determine the average thickness T (μm) of the nonwoven fabric. The specific volume (cm) is calculated using the following formula: 3 / g) Specific volume (cm 3 / g) = average thickness T (μm) / basis weight (g / m 2 )...(expression) The basis weight referred to here is the basis weight of the nonwoven fabric measured and calculated by the above-mentioned method.

[0069] The thickness per unit area of ​​the nonwoven fabric of the present invention can be controlled by, for example, the average single fiber diameter, the average hollowness in the non-fused portions of the fibers, and the bonding conditions in the manufacturing process (bonding rate, temperature, linear pressure, etc.). Specifically, the thickness per unit area can be increased by increasing the average single fiber diameter, increasing the average hollowness in the non-fused portions of the fibers, or adjusting the bonding rate, temperature, and pressure during bonding in the manufacturing process.

[0070] 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 ) degree.

[0071] The tensile strength per unit area of ​​nonwoven fabric ((N / 25mm) / (g / m 2)) is a value measured and calculated using the following procedure in accordance with "6.3 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "General nonwoven fabric testing methods." (1) Take test pieces of 25 mm x 40 mm from the nonwoven fabric in both the longitudinal direction (lengthwise direction) and the transverse direction (widthwise direction) of the nonwoven fabric. (2) The long side direction (40 mm) of the collected test piece is set as the tensile direction, and the test piece is set in a tensile testing machine (for example, the RTC-1210A manufactured by A&D Co., Ltd.) with a gripping distance of 20 mm. (3) A tensile test is carried out at a tensile speed of 20 mm / min, and the maximum point load (N / 25 mm) is measured. (4) For each level, measure five times in both the longitudinal and transverse directions by changing the sampling location of the test piece. The arithmetic mean value (N / 25mm) of the ten measurements, rounded to three decimal places, is taken as the average maximum point load (N / 25mm). The tensile strength per unit area ((N / 25mm) / (g / m 2 Calculate Tensile strength per unit area ((N / 25mm) / (g / m 2 )) = Maximum point load (N / 25mm) / Weight (g / m 2 )...(expression).

[0072] 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 in the non-fused portions of the fibers, the melt mass-flow rate (Mz / Mw) 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 in the non-fused portions of the fibers, decreasing the melt mass-flow rate of the nonwoven fabric, or adjusting the bonding rate, temperature, and pressure during bonding in the manufacturing process.

[0073] The nonwoven fabric of the present invention is * It is preferable that the value is 60.0 or more. *When the value is preferably 60.0 or more, more preferably 63.0 or more, and even more preferably 65.0 or more, less light passes through the nonwoven fabric, resulting in a nonwoven fabric with less exudation of the hot melt material.

[0074] In addition, the nonwoven fabric L * The values ​​are measured and calculated by the following procedure. (1) Take a 50mm x 50mm test piece from the nonwoven fabric. (2) Using a spectrophotometer (for example, Minolta's spectrophotometer "CM-3700d"), measure the L under the conditions of D65 light source, a viewing angle of 10°, and SCE (specular reflection excluded) optical conditions. * Measure the value. (3) (1) and (2) are performed three times for each level, and the arithmetic mean is calculated as L * value.

[0075] In addition, the L of the nonwoven fabric of the present invention * The L value can be controlled by, for example, the average single fiber diameter, the average hollow ratio in the non-fused portions of the fibers, and the basis weight of the nonwoven fabric. Specifically, the L value of the nonwoven fabric can be controlled by reducing the average single fiber diameter, increasing the average hollow ratio in the non-fused portions of the fibers, and increasing the basis weight. * The value can be increased.

[0076] [Nonwoven fabric manufacturing method] Next, a method for producing the nonwoven fabric of the present invention will be described. a step 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 die hole to form a fiber having an average single fiber diameter of 10.0 μm or more and 50.0 μm or less; depositing the fibers to form a fiber web composed of the fibers; and a step of thermally bonding the fiber web to form fused and unfused portions in the fiber web, with the flatness of the fibers in the fused portions being 5.8 to 10.0. By using this manufacturing method, a nonwoven fabric having excellent strength and thickness and free from exudation of the hot melt material can be reliably obtained. Each step will be described in more detail below.

[0077] (a) Fiber formation process First, 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 die hole, thereby producing a nonwoven fabric with excellent strength.

[0078] 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 and melt mass flow rate.

[0079] In the method for producing a nonwoven fabric 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, similar to the nonwoven fabric 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, 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 clumps.

[0080] In the method for producing a nonwoven fabric of the present invention, the propylene-based resin is preferably a propylene-based resin polymerized using a Ziegler-Natta catalyst as a polymerization catalyst. When the propylene-based resin is a propylene-based resin polymerized using a Ziegler-Natta catalyst, the propylene-based resin tends to have a larger Mz / Mw ratio than a propylene-based resin produced using a metallocene catalyst, and this improves adhesiveness, resulting in a nonwoven fabric with excellent strength.

[0081] Next, as a method for obtaining fibers, a melt spinning method using an extruder such as a pressure melter type, single-screw or 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.

[0082] In this case, 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.

[0083] Here, the land length of the spinneret hole is preferably 0.1 mm or more and 5.0 mm or less. By making the land length of the spinneret 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 spinneret hole can be improved, resulting in a nonwoven fabric with excellent uniformity. Furthermore, by making the land length of the spinneret 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 increases can be suppressed, enabling stable spinning over long periods of time.

[0084] The land length (mm) of the 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.

[0085] 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.

[0086] The temperature of the cooling air can be determined in consideration of the cooling efficiency and the cooling air speed, 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 extruded from the spinneret is increased, thereby improving spinnability. 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 preventing moisture from adhering to the fibers due to cooling. The cooling air temperature referred to here is the temperature at a position 80 mm away from the spun propylene-based resin.

[0087] 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.

[0088] Furthermore, it is preferable to start cooling at a distance of 0 mm or more and 300 mm or less downstream from the 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 drop in the nozzle surface temperature. Furthermore, by setting the upper limit of the distance from the spinneret to the start of cooling to preferably 300 mm or less, more preferably 100 mm or less, it is possible to stabilize the fiber thinning behavior and improve spinnability.

[0089] 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.

[0090] 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.

[0091] 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 fibers enter the ejector after being cooled and solidified, thereby achieving 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 enabling the production of a nonwoven fabric with fewer defects caused by the inclusion of extremely thick fibers or polymer lumps.

[0092] 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.

[0093] 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 thinner, 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.

[0094] The spinning speed referred to here is a value measured and calculated by the following procedure. (1) Take a 5mm x 5mm test piece from the nonwoven fabric. (2) For the non-bonded areas on the surface of the nonwoven fabric where the fibers are not bonded to each other, images are taken using a scanning electron microscope (e.g., Hitachi High-Technologies Corporation's "SU1510") at a magnification that allows the sides of 10 or more fibers to be observed. (3) From the captured image, 10 fibers were randomly selected from the fibers that make up the nonwoven fabric, and the cross-sectional area (μm 2 ) is measured. (4) For each level, measurements were taken 10 times by changing the location of the test piece, and the arithmetic mean value of 100 pieces was rounded to the second decimal place to obtain the average fiber cross-sectional area A (μm 2 ) is calculated as (5) The propylene-based resin extruded from the spinneret is collected for 1 minute and weighed, and the resulting value is the extrusion 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 extrusion rate Q (g / min) per hole. (6) Using the following formula, calculate the spinning speed by rounding to two decimal places. Spinning speed (km / min) = Q × 1000 / (A × 0.91) (equation).

[0095] In this way, fibers having an average single fiber diameter of 10.0 μm or more and 50.0 μm or less can be formed.

[0096] (b) forming a fibrous web In this step, the fibers obtained in the previous step are deposited to form a fiber web. Specifically, for example, the fibers are spread by passing through a spreading part where the surrounding air flow speed is reduced, and then the fibers are landed on a net conveyor that sucks air from the back side and collected as a fiber web.

[0097] The collected fiber web is preferably transported at a transport speed of 5 m / min or more and 1200 m / min or less.

[0098] 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.

[0099] 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.

[0100] 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 occurs with 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) with SS, SSS, and SSSS, productivity and uniformity of texture are improved.

[0101] (c) A step of thermally bonding the fiber web In this step, the fiber web obtained in the previous step is thermally bonded to give the fiber web fused portions and non-fused portions, and the flatness of the fibers in the fused portions is set to 5.8 to 10.0. The thermal bonding method is not particularly limited, but examples include a method of thermally fusing the fibers using various rolls, such as a heat embossing roll, a heat embossing roll consisting of a pair of upper and lower rolls, each with an engraving (concave and recessed portions), a heat embossing roll consisting of a combination of one roll with a flat (smooth) surface and the other with an engraving (concave and recessed portions), and a heat calender roll consisting of a pair of upper and lower flat (smooth) rolls; a method of thermally fusing the fibers 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, a pair of upper and lower rolls, each with an engraving (concave and recessed portions), or a heat embossing roll consisting of a combination of one roll with a flat (smooth) surface and the other with an engraving (concave and recessed portions). 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.

[0102] 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 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.

[0103] Here, the bond 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 bond rate refers to the area ratio of the portion (bonded portion) where the convex portions of the upper roll and the convex portions of the lower roll overlap and contact the nonwoven fiber web to the entire nonwoven fabric. When thermal bonding is performed using an uneven roll and a flat roll, the bond rate refers to the area ratio of the portion (bonded portion) where the convex portions of the uneven roll contact the nonwoven fiber web to the entire nonwoven fabric. When ultrasonic bonding is performed, the bond rate refers to the area ratio of the portion (bonded portion) thermally bonded by ultrasonic processing to the entire nonwoven fabric.

[0104] 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.

[0105] 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. Furthermore, by setting the surface temperature of the hot embossing roll to preferably 150°C or lower, more preferably 145°C or lower, reduction in strength due to excessive thermal bonding can be suppressed, resulting in a nonwoven fabric with excellent strength.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] (d) Other post-processing steps The product that has undergone the above steps may be used as a nonwoven fabric as is, but it is also preferable to subject it to various post-processing steps, as in the general nonwoven fabric manufacturing method, to produce a nonwoven fabric. Of course, it goes without saying that a nonwoven fabric that has undergone post-processing is also considered a nonwoven fabric in the present invention.

[0110] Examples of post-processing that can be carried out on the nonwoven fabric of the present invention include physical processing such as perforation and rubbing, and chemical processing such as hydrophilization and charging.

[0111] [Laminated nonwoven fabric] The nonwoven fabric of the present invention can be used as is, but it is also preferable to form a laminated nonwoven fabric containing a layer of the nonwoven fabric. For example, it is preferable to further contain a hot melt material in addition to the nonwoven fabric. It is also preferable to form a laminated nonwoven fabric having a fiber layer of a different type from the nonwoven fabric layer and / or a film layer. 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.

[0112] Here, the term "a fiber layer of a type different from the layer of the nonwoven fabric" as used herein refers to a fiber layer whose main component is a resin other than a propylene-based resin, or a fiber layer produced by a different method, such as, when the nonwoven fabric is a spunbond nonwoven fabric, a meltblown nonwoven fabric layer formed by a meltblowing 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.

[0113] 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.

[0114] 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.

[0115] [Hygiene materials] The nonwoven fabric of the present invention has excellent strength and bulkiness, and yet when made into a laminated nonwoven fabric, the hot melt material does not bleed out. Therefore, the nonwoven fabric of the present invention is suitable for use in a variety of applications, including medical materials, sanitary materials, daily necessities, and industrial materials.

[0116] Among these, sanitary materials containing the nonwoven fabric are preferred because they can make the most of the characteristics of excellent strength and thickness even at low basis weights.

[0117] The same is true for the laminated nonwoven fabric according to the present invention, and in particular, by having a melt-blown nonwoven fabric layer in the laminated nonwoven fabric, the fabric has excellent collection performance and is therefore suitable for use in various filters. [Example]

[0118] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0119] [Measurement method] Unless otherwise specified, the measurement and calculation methods for each physical property were carried out according to the methods described above.

[0120] A. Propylene fraction of propylene resin The nuclear magnetic resonance apparatus used was a JEOL RESONANCE "ECZ-600," and measurements and calculations were carried out as described above under the following conditions. Measurement method: single 13 C pulse with inverse gated 1 H decoupling Observation core: 13 C Observation frequency: 150.9MHz Chemical shift reference: orthodichlorobenzene-d4 (133.0 ppm) ·Measurement temperature: 135℃.

[0121] B. Mz / Mw of propylene resin and nonwoven fabric The high-temperature GPC apparatus used was a Polymer Laboratories PL-220, and measurements and calculations were carried out as described above under the following conditions. Standard samples: Monodisperse polystyrene manufactured by Tosoh Corporation, dibenzyl manufactured by Tokyo Chemical Industry Co., Ltd. ·Injection volume: 0.200mL ·Flow rate: 1.0mL / min Guard column: Shodex HT-G manufactured by Showa Denko K.K. Column: Showa Denko Shodex HT-806M (2 columns) · Detector: Differential refractive index detector RI.

[0122] C. Melt mass flow rate (MFR) of propylene resin and nonwoven fabric The melt mass flow rate was measured and calculated as described above using a "MELT INDEXER F-F01" manufactured by Toyo Seiki Seisaku-sho, Ltd. as a melt mass flow rate measuring device.

[0123] D. Average single fiber diameter of fibers, average hollowness of fibers in non-fused portions, and flatness of fibers in fused portions The scanning electron microscope used was the "SU1510" scanning electron microscope manufactured by Hitachi High-Technologies Corporation, and the image analysis software was "WinROOF2015" manufactured by Mitani Shoji Co., Ltd., and measurements and calculations were carried out as described above.

[0124] E. Melting temperature of nonwoven fabric The differential scanning calorimeter used was a "DSC Q2000" manufactured by TA Instruments, and measurements and calculations were carried out as described above.

[0125] F. Nonwoven fabric basis weight Measurements and calculations were carried out as described above.

[0126] G. Tensile strength per unit area of ​​nonwoven fabric The tensile testing machine used was the RTC-1210A manufactured by A&D Co., Ltd., and measurements and calculations were carried out as described above.

[0127] H. Specific volume of nonwoven fabric The scanning electron microscope used was a scanning electron microscope "SU1510" manufactured by Hitachi High-Technologies Corporation, and measurements and calculations were carried out as described above.

[0128] I. Nonwoven fabric L * value The spectrophotometer used was a Minolta spectrophotometer "CM-3700d" and measurements and calculations were carried out as described above.

[0129] [Propylene-based resin] The propylene-based resins used in the examples and comparative examples of the present invention are as shown in Table 1. Here, propylene-based resins A to D and F are propylene homopolymers obtained using a Ziegler-Natta catalyst (denoted as "ZN" in Table 1), and propylene-based resin E is a propylene homopolymer obtained using a metallocene catalyst (denoted as "M" in Table 1).

[0130] [Table 1]

[0131] [Example 1] (a) Fiber formation process Propylene-based resin A was melt-extruded using a single-screw extruder and metered with a gear pump while being fed to a rectangular spinneret. At this time, the melt extrusion temperature was set to 230°C, and propylene-based resin A was extruded from the hollow nozzle holes having a minimum circumscribed circle diameter of 2.0 mm, six slits (the shape of which is exemplified in Figure 1), a slit width of 0.08 mm, and a land length of 0.3 mm, at a single-hole extrusion rate of 0.60 g / min.

[0132] 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 the air flow using a rectangular ejector to obtain fibers. The distance from the spinneret to the ejector inlet was 550 mm, and the spinning speed was as shown in Table 2.

[0133] (b) forming a fibrous web The fibers thus obtained were then spread by passing through a spreading section where the surrounding air flow velocity was reduced, and then landed on a net conveyer where air was sucked from the backside to obtain a fiber web made of composite fibers. The collected fiber web was then transported at a speed of 10 m / min.

[0134] (c) A step of adhesively processing the obtained fiber web The fiber web made of the composite fiber obtained as described above was then thermally bonded using a pair of upper and lower thermal embossing rolls consisting of an upper metal embossing roll engraved with a polka dot pattern and having an adhesion area ratio of 11% and a lower metal flat roll 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.

[0135] [Examples 2 to 4, Comparative Examples 1 and 2] (a) In the step of forming fibers, 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, and propylene-based resin F in Example 4, and the spinning speed was changed from 2.2 km / min to the speeds shown in Table 2, 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 2.

[0136] [Table 2]

[0137] [Examples 5 to 7] (a) In the step of forming fibers, the single-hole output rate was changed from 0.60 g / min to 0.40 g / min in Example 5, 0.80 g / min in Example 6, and 0.15 g / min in Example 7, and the spinning speed was changed from 2.2 km / min to the rates shown in Table 3, 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.

[0138] [Comparative Examples 3 to 5] (a) In the step of forming fibers, nonwoven fabrics were obtained in the same manner as in Example 1, except that the minimum circumscribed circle diameter of the hollow spinneret hole was changed from 2.0 mm to 4.8 mm in Comparative Example 3 and from 1.0 mm in Comparative Examples 4 and 5, the single-hole output rate was changed from 0.60 g / min to 0.40 g / min in Comparative Example 4, and the spinning speed was changed from 2.2 km / min to the values ​​shown in Table 3. The evaluation results of the obtained nonwoven fabrics are shown in Table 3.

[0139] [Comparative Examples 6 and 7] (a) In the step of forming fibers, nonwoven fabrics were obtained in the same manner as in Example 1, except that the spinneret holes, which were hollow, were changed to round-hole spinnerets with a spinneret hole diameter of 0.3 mm and a land length of 0.3 mm, the single-hole output rate, which was 0.60 g / min, was changed to 0.80 g / min in Comparative Example 6 and 0.40 g / min in Comparative Example 7, and the spinning speed, which was 2.2 km / min, was changed to the rates shown in Table 3. The evaluation results of the obtained nonwoven fabrics are shown in Table 3.

[0140] [Table 3]

[0141] [Examples 8 to 10] (a) In the step of forming fibers, nonwoven fabrics were obtained in the same manner as in Example 1, except that the extrusion temperature was changed from 230°C to 200°C in Example 8, 210°C in Example 9, and 250°C in Example 10, the single-hole output rate was changed from 0.60 g / min to 0.40 g / min in Example 10, and the spinning speed was changed from 2.2 km / min to the rates shown in Table 4. The evaluation results of the obtained nonwoven fabrics are shown in Table 4.

[0142] [Examples 11 to 14] (a) In the step of forming fibers, nonwoven fabrics were obtained in the same manner as in Example 1, except that the propylene-based resin in Example 13 was propylene-based resin B instead of propylene-based resin A, the number of slits in the hollow spinneret holes was 4 instead of 6 in Example 11, 8 in Examples 12 and 13, and 10 in Example 14, the output rate per hole was 0.60 g / min instead of 0.40 g / min in Example 13, and the spinning speed was 2.2 km / min instead of being changed as shown in Table 4. The evaluation results of the obtained nonwoven fabrics are shown in Table 4.

[0143] [Table 4]

[0144] The nonwoven fabrics of Examples 1 to 14 were nonwoven fabrics composed of hollow fibers whose main component was a propylene-based resin, and the flatness of the fibers in the fused portions of the nonwoven fabrics was 5.8 or more and 10.0 or less, and the Mz / Mw of the nonwoven fabrics was 2.0 or more and 6.0 or less, indicating that the nonwoven fabrics were excellent in strength, thickness, and anti-transparency.

[0145] On the other hand, the nonwoven fabrics of Comparative Examples 1 and 4 to 7 had low flatness of the fibers in the fused portions, and therefore all had poor tensile strength per unit area. The nonwoven fabric of Comparative Example 2 had low Mz / Mw, and therefore had poor thickness per unit area. The nonwoven fabric of Comparative Example 3 had high flatness of the fibers in the fused portions, and therefore had poor L * It was inferior in value. [Explanation of symbols]

[0146] 1: Minimum circumscribed circle 2: Slit (discharge hole) 3: Slit width 4: Diameter of the smallest circumscribed circle

Claims

1. A nonwoven fabric made of fibers whose main component is a propylene-based resin, the nonwoven fabric has a fused portion and a non-fused portion, the flatness of the fibers in the fused portion is 5.8 or more and 10.0 or less, The ratio Mz / Mw of the Z-average molecular weight Mz to the weight-average molecular weight Mw of the nonwoven fabric is 2.0 or more and 6.0 or less. Nonwoven fabric.

2. 2. The nonwoven fabric according to claim 1, wherein the average single fiber diameter of the fibers in the non-fused portions is 10.0 μm or more and 50.0 μm or less.

3. 3. The nonwoven fabric according to claim 1, wherein the melt mass flow rate of the nonwoven fabric is 16 g / 10 min or more and 55 g / 10 min or less.

4. The nonwoven fabric according to claim 1 or 2, wherein the melting temperature of the nonwoven fabric is 150°C or higher and 170°C or lower.

5. The nonwoven fabric according to claim 1 or 2, wherein the cross-sectional shape of the fibers in the non-fused portions is hollow.

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

7. a step 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 die hole to form a fiber having an average single fiber diameter of 10.0 μm or more and 50.0 μm or less; depositing the fibers to form a fiber web composed of the fibers; and a step of thermally bonding the fiber web to form fused portions and non-fused portions in the fiber web, and adjusting the flatness of the fibers in the fused portions to 5.8 or more and 10.0 or less.

8. A laminated nonwoven fabric comprising the nonwoven fabric according to claim 1 or 2.

9. The laminated nonwoven fabric of claim 8 , further comprising a hot melt material.

10. A sanitary material comprising the nonwoven fabric according to claim 1 or 2.

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