Layered nonwoven fabric and sanitary material

Abstract

The present invention is a layered nonwoven fabric in which at least one each of a nonwoven fabric layer (A) composed of a first thermoplastic resin fiber and a nonwoven fabric layer (B) composed of a second thermoplastic resin fiber are layered, wherein: the cross-section of the first thermoplastic resin fiber has a plurality of lobes, and is a modified cross-section with a lobularity of 5% or more; the ratio (Db / Da) of the average single-fiber diameter Db of the second thermoplastic resin fiber to the average single-fiber diameter Da of the first thermoplastic resin fiber is 1.0 or more; and the nonwoven fabric layer (B) is layered on at least one of the outermost layers. This layered nonwoven fabric has water-absorption speed and water-absorbing / quick-drying properties sufficient to enable the fabric to be utilized as a sanitary nonwoven fabric. By employing this layered nonwoven fabric as at least a portion of a sanitary material, a sanitary material having excellent water absorbability and excellent quick-drying properties can be obtained.

Description

TECHNICAL FIELD

[0001] The present invention relates to a layered nonwoven fabric having a different cross-section, which is excellent in water-absorbing and quick-drying property and particularly suitable for sanitary material applications, and a sanitary material using the same.BACKGROUND ART

[0002] In general, sanitary materials such as disposable diapers, sanitary napkins, and masks quickly remove moisture such as urine and sweat, and keep a member surface dry, thereby becoming a sanitary material comfortable for a human body.

[0003] For this reason, a surface member directly in contact with the skin needs to have both "water absorbability" for quickly absorbing moisture and "quick-drying property" for transferring the absorbed moisture from the outermost surface layer to make the surface dry.

[0004] In the related art, various nonwoven fabrics subjected to a hydrophilization treatment have been widely used for the surface member. These materials can induce moisture from the outermost surface layer to the nonwoven fabric or an absorber as an inner layer, but moisture tends to remain in the outermost surface layer, and the materials are poor in "quick-drying property".

[0005] In order to obtain a surface member in which moisture hardly remains in the outermost surface layer and which is excellent in "quick-drying property", Patent Document 1 proposes a nonwoven fabric in which a web layer (skin surface side) formed of fine fineness fibers having a round cross-section and a web layer formed of thick fineness fibers having a modified cross-section are layered. Patent Document 2 proposes a sheet in which sheets having different fiber densities are layered, and a sheet having a low fiber density is used as a surface layer that comes into contact with the skin.PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent Laid-openPublication No. 5-31137Patent Document 2: Japanese Patent Laid-open Publication No. 1-20844SUMMARY OF THE INVENTIONPROBLEMS TO BE SOLVED BY THE INVENTION

[0007] However, in the technique disclosed in Patent Document 1, since the web layer formed of fine fineness fibers on the skin surface side has a dense structure, liquid permeability is reduced, moisture cannot be quickly absorbed, and it is difficult to obtain "water absorbability". Furthermore, moisture tends to remain in dense inter-fiber gaps on the fine fineness side, and it is difficult to obtain "quick-drying property".

[0008] On the other hand, in the technique disclosed in Patent Document 2, due to the difference in capillary effect different for each fiber density, it is possible to guide a certain amount of moisture absorbed in the outermost surface layer to a second layer (layer opposite to the skin surface) . However, in the second layer, since the liquid diffusion performance in the sheet surface direction is poor, the transfer of moisture to the second layer has a limited effect, and the "quick-drying property" is insufficient.

[0009] Therefore, an object of the present invention is to provide a layered nonwoven fabric having a water absorption rate sufficient for maintaining comfort in a member using a nonwoven fabric for a sanitary material and having quick drying property.SOLUTIONS TO THE PROBLEMS

[0010] As a result of intensive studies to achieve the above object, the present inventors have obtained a finding that, in a layered nonwoven fabric, a nonwoven fabric layer made of specific modified cross-sectional fibers and a nonwoven fabric layer made of fibers of a specific size are layered in a specific configuration, thereby obtaining a layered nonwoven fabric having sufficient water-absorbing and quick-drying property to be used as a nonwoven fabric for a sanitary material.

[0011] A layered nonwoven fabric of the present invention is a layered nonwoven fabric in which at least one nonwoven fabric layer (A) formed of a first thermoplastic resin fiber and at least one nonwoven fabric layer (B) formed of a second thermoplastic resin fiber are layered, wherein a cross-section of the first thermoplastic resin fiber has a plurality of convex parts, and has a modified cross-section in which a lobularity of the cross-section is 5.0% or more, a ratio (Db / Da) of an average single-fiber diameter Db of the second thermoplastic resin fiber to an average singlefiber diameter Da of the first thermoplastic resin fiber is 1.0 or more, and the nonwoven fabric layer (B) is layered to be at least one outermost layer.

[0012] In addition, at least a part of a sanitary material of the present invention is formed of the layered nonwoven fabric.

[0013] Furthermore, a diaper of the present invention includes a top sheet formed of the layered nonwoven fabric.

[0014] In addition, a mask of the present invention includes an inner surface layer formed of the layered nonwoven fabric.EFFECTS OF THE INVENTION

[0015] The layered nonwoven fabric of the present invention has a water absorption rate sufficient for use as a nonwoven fabric for a sanitary material and a water- absorbing and quick-drying property. By using the layered nonwoven fabric of the present invention as at least a part of a sanitary material, a sanitary material having excellent water absorbability and excellent quick-drying property can be obtained.

[0016] The layered nonwoven fabric of the present invention can be used as a part of a sanitary material such as a disposable diaper, a sanitary napkin, gauze, a bandage, a mask, a glove, or an adhesive plaster.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Fig. 1 is an example of a cross-section of a first thermoplastic resin fiber constituting a nonwoven fabric layer (A) of a layered nonwoven fabric of the present invention, and is a view for illustrating a fiber cross-section having a plurality of convex parts.Fig. 2 is an example of a cross-section of a first thermoplastic resin fiber constituting a nonwoven fabric layer (A) of the layered nonwoven fabric of the present invention, and is a view for explaining a lobularity in the fiber cross-section.EMBODIMENTS OF THE INVENTION

[0018] A layered nonwoven fabric of the present invention is a layered nonwoven fabric in which at least one nonwoven fabric layer (A) formed of a first thermoplastic resin fiber and at least one nonwoven fabric layer (B) formed of a second thermoplastic resin fiber are layered, wherein a cross-section of the first thermoplastic resin fiber has a plurality of convex parts, and has a modified cross-section in which a lobularity of the cross-section is 5.0% or more, a ratio (Db / Da) of an average single-fiber diameter Db of the second thermoplastic resin fiber to an average single fiber diameter Da of the first thermoplastic resin fiber is 1.0 or more, and the nonwoven fabric layer (B) is layered to be at least one outermost layer. Hereinafter, the components will be described in detail.

[0019] [Thermoplastic resin fiber]The layered nonwoven fabric of the present invention includes a nonwoven fabric layer (A) made of a first thermoplastic resin fiber and a nonwoven fabric layer (B) made of a second thermoplastic resin fiber.

[0020] In the first thermoplastic resin fiber and the second thermoplastic resin fiber, the term "thermoplastic resin fiber" refers to a fiber made of a thermoplastic resin.Such a thermoplastic resin may be one kind or may be made of a plurality of thermoplastic resins.

[0021] Examples of the thermoplastic resin to be used in the thermoplastic resin fiber according to the present invention include aromatic polyester-based polymers such as "polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyhexamethylene terephthalate" and copolymers thereof, aliphatic polyester-based polymers such as ''polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, a lyhydroxybutyrate-polyhydroxyvalerate copolymer, polycaprolactone" and copolymers thereof, aliphatic polyamide-based polymers such as 'Polyamide 6, Polyamide 66, Polyamide 610, Polyamide 10, Polyamide 12, Polyamide 6-12" and copolymers thereof, polyolefin-based polymers such as 'Polypropylene, polyethylene, polybutene, polymethylpentene" and copolymers thereof, water-insoluble ethylene-vinyl alcohol copolymer-based polymers containing 25 mol% to 70 mol% of ethylene units, polystyrene-based, polydiene-based, chlorine-based, polyolefin-based, polyester-based, polyurethane-based, polyamide-based, and fluorine-based elastomer-based polymers. The thermoplastic resin can be selected from these resins and used. In addition, in the polymer may contain various additives such as inorganic substances including titanium oxide, silica and barium oxide, coloring agents such as carbon black, dyes and pigments, flame retardants, fluorescent whitening agents, antioxidants, and ultraviolet absorbers.

[0022] In the thermoplastic resin to be used for the thermoplastic resin fiber according to the present invention, it is preferable that at least a part of the thermoplastic resin contains a fatty acid amide compound. When the content of the fatty acid amide compound is preferably 0.5 mass% or more, more preferably 0.7 mass% or more, and still more preferably 1.0 mass% or more, the fatty acid amide compound acts as a lubricant on the fiber surface, so that a layered nonwoven fabric excellent in touch feeling can be obtained. The upper limit of the content of the fatty acid amide compound in the present invention is not particularly limited, and preferably 5.0 mass% or less from the viewpoint of cost and productivity.

[0023] In the present invention, the content of the fatty acid amide compound contained in the thermoplastic resin is preferably 0.5 to 5.0 mass%, more preferably 0.7 mass% to 5.0 mass%, and still more preferably 1.0 mass% to 5.0 mass%.

[0024] When the thermoplastic resin to be used for the thermoplastic resin fiber according to the present invention contains the fatty acid amide compound, the carbon number of the fatty acid amide compound is preferably 15 or more and 50 or less. Examples of the fatty acid amide compound having 15 or more and 50 or less carbon atoms include saturated fatty acid monoamide compounds, saturated fatty acid diamide compounds, unsaturated fatty acid monoamide compounds, and unsaturated fatty acid diamide compounds. The number of carbon atoms in the present invention means the number of carbon atoms contained in a molecule. Specific examples of the fatty acid amide compound include palmitic acid amide, palmitoleic acid amide, stearic acid amide, oleic acid amide, elaidic acid amide, bacenoic acid amide, linoleic acid amide, linolenic acid amide, pinolenic acid amide, eleostearic acid amide, stearidonic acid amide, boseopentaenoic acid amide, arachidinic acid amide, gadoleic acid amide, eicosenoic acid amide, eicosadienoic acid amide, mead acid amide, eicosatrienoic acid amide, arachidonic acid amide, eicosatetraenoic acid amide, eicosapentaenoic acid amide, henicosylic acid amide, behenic acid amide, erucic acid amide, docosadienoic acid amide, adrenic acid amide, osbondic acid amide, sardine acid amide, docosahexaenoic acid amide, lignoceric acid amide, nervonic acid amide, tetracosapentaenoic acid amide, herring acid amide, cerotic acid amide, montanic acid amide, melicic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide, methylene bislauric acid amide, ethylene bisstearic acid amide, ethylene bisoleic acid amide, ethylene bishydroxystearic acid amide, ethylene bisbechenic acid amide, ethylene bis-erucic acid amide, hexamethylene bisstearic acid amide, hexamethylene bisbechenic acid amide, hexamethylene hydroxystearic acid amide, distearyl adipic acid amide, disstearyl sebacic acid amide, and hexamethylenebisoleic acid amide, and combinations thereof can be used. By setting the carbon number of the fatty acid amide compound to preferably 15 or more, more preferably 23 or more, and still more preferably 30 or more, excessive precipitation of the fatty acid amide compound on the fiber surface can be suppressed, the spinnability and processing stability are excellent, and high productivity can be maintained. When the carbon number of the fatty acid amide compound is set to preferably 50 or less, more preferably 45 or less, and still more preferably 42 or less, the fatty acid amide compound is moderately precipitated on the fiber surface, so that a layered nonwoven fabric excellent in touch feeling is obtained. The carbon number of the fatty acid amide compound is preferably 15 to 50, more preferably 23 to 45, and still more preferably 30 to 42.

[0025] The first thermoplastic resin fiber and the second thermoplastic resin fiber may have the same or different thermoplastic resins.

[0026] [Nonwoven fabric layer (A) made of first thermoplastic resin fiber]The nonwoven fabric layer (A) according to the layered stretchable nonwoven fabric of the present invention is made of the first thermoplastic resin fiber, and the cross-section of the first thermoplastic resin fiber has a plurality of convex parts.

[0027] Here, the fact that the cross-section of the fiber has a plurality of convex parts refers to a cross-sectional shape described below, and will be described with reference to Fig. 1.

[0028] Fig. 1 illustrates an example of a fiber crosssection having a plurality of convex parts. In this fiber cross-section, it means a cross-sectional shape capable of drawing at least two lines (for example, L11) that are straight lines passing through two points (S11, S12) on a contour (C1) of the cross-section and in which a line segment between two points of S11 and S12 does not pass through the contour (C1).

[0029] The cross-sectional shape as described above is a fiber cross-section having a plurality of convex parts.With such a fiber cross-section, a groove continuous in the fiber axis direction is formed on the fiber side surface.A fiber cross-section having a plurality of convex parts is one of important elements for exerting the effect of the present invention. That is, when such fibers are formed into a nonwoven fabric, the groove portion on the fiber side surface serves as a liquid passage path, so that moisture in the nonwoven fabric surface direction, which has been difficult so far, can be diffused. Therefore, in the layered nonwoven fabric of the present invention, the water absorption rate and the liquid transfer from the surface layer can be remarkably improved by including the nonwoven fabric layer (A) capable of diffusing moisture in the surface direction.

[0030] In order to make the moisture diffusion effect in the plane direction remarkable, the form of the convex part of the fiber cross-section is important, and it is also important that the fiber cross-section is a modified cross- section having a lobularity of 5.0% or more.

[0031] The lobularity of the fiber cross-section is measured by a method described below, and will be described in detail with reference to Fig. 2.

[0032] Fig. 2 illustrates an example of a cross-section of fibers constituting the nonwoven fabric layer (A) according to the layered nonwoven fabric of the present invention.

[0033] First, an image is captured at a magnification at which one single fiber can be observed with a scanning electron microscope (SEM) in the cross-section of the fiber constituting the nonwoven fabric layer (A). Using the captured fiber cross-sectional image, a straight line passing through two points (S21, S22 in Fig. 2) on the contour (C2 in Fig. 2) of the cross-section in the same cross-section, a line (for example, L21 in Fig. 2) in which a line segment between two points of S21 and S22 does not pass through the contour (C2) is drawn, and a distance a (unit: μm) between the points S21 and S22 is measured.Next, a line (for example, L22) that is parallel to the straight line (L21) and has only one intersection (V21) between the points S21 and 22 in the contour (C2) is drawn. Then, a distance b (unit: μm) between the straight line(L21) and the straight line (L22) is measured.Furthermore, the percentage of the ratio of b to a (b / a x 100, unit: %) was determined. A simple number average of results of performing the same operation on 20 different fibers is obtained, and the value obtained by rounding off the simple number average to the second decimal place is the lobularity referred to in the present invention.

[0034] The higher the value of the lobularity, the deeper the grooves are on the fiber side surface. The higher the lobularity, the higher the moisture diffusion effect in the surface direction when the nonwoven fabric is formed, and thus the lobularity is more preferably 10.0% or more. In order to obtain the layered nonwoven fabric of the present invention with high quality by suppressing peeling of the convex parts due to friction during production, the lobularity is more preferably 60% or less. Even more preferably, the lobularity is 10% to 60%.

[0035] The first thermoplastic resin fiber constituting the nonwoven fabric layer (A) of the present invention has a plurality of convex parts in a cross-section, and the cross-section has the lobularity of 5.0% or more. In the fiber made of the first thermoplastic resin constituting the nonwoven fabric layer (A) of the present invention, the shape of the convex part and the number of convex parts per fiber are not limited.

[0036] The average single-fiber diameter of the first thermoplastic resin fibers constituting the nonwoven fabric layer (A) is preferably 1.0 to 25.0 μm from the viewpoint of sufficiently acting the moisture diffusion effect in the nonwoven fabric surface direction by the grooves in the fiber side surface. Furthermore, from the viewpoint that water absorption performance due to a capillary effect can be improved by densifying the nonwoven fabric layer, the average single-fiber diameter of the first thermoplastic resin fiber is more preferably 20.0 μm or less. The average single-fiber diameter of the first thermoplastic resin fibers constituting the nonwoven fabric layer (A) is still more preferably 1.0 to 20.0 μm.

[0037] The average single-fiber diameter is determined as follows.

[0038] Using the image taken to measure the lobularity of the fiber cross-section described above, the area Af formed by the cross-sectional contour of the single fiber is measured using image analysis software ("WinROOF 2015" manufactured by MITANI CORPORATION), and a diameter of a perfect circle having the same area as the area Af is calculated. The obtained diameter is measured for 20 single fibers optionally extracted from the same nonwoven fabric layer, a simple number average is obtained, the unit is μm, and the value obtained by rounding off the simple number average to the second decimal place is the average single-fiber diameter referred to in the present invention.

[0039] [Nonwoven fabric layer (B) made of second thermoplastic resin fiber]The nonwoven fabric layer (B) according to the layered stretchable nonwoven fabric of the present invention is formed of the thermoplastic resin fibers. The thermoplastic resin fiber constituting the nonwoven fabric layer (B) of the present invention may be either a single component fiber or a composite fiber.

[0040] The shape of the fiber cross-section can be freely selected as long as the effect of the present invention is not impaired. A preferable fiber cross-sectional shape is a round cross-section. When the fiber cross-section is a round cross-section, inter-fiber gaps of the nonwoven fabric layer (B) can be expanded, and liquid permeability is improved.

[0041] From the viewpoint of the liquid permeability, the average single-fiber diameter of the second thermoplastic resin fibers constituting the nonwoven fabric layer (B) is preferably 3.0 to 30.0 μm. Furthermore, when used as a sanitary material, the average single-fiber diameter of the second thermoplastic resin fiber is more preferably 25.0 μm or less, and is still more preferably 3.0 to 25.0 μm.

[0042] [Average single-fiber diameter of nonwoven fabric layer (A) and nonwoven fabric layer (B)]In the layered nonwoven fabric of the present invention, a ratio (Db / Da, hereinafter, may be simply abbreviated as average single-fiber diameter ratio) of an average single-fiber diameter Db of the second thermoplastic resin fibers constituting the nonwoven fabric layer (B) to an average single-fiber diameter Da of the first thermoplastic resin fibers constituting the nonwoven fabric layer (A) is 1.0 or more.

[0043] Images of the transverse cross-sections of the fibers constituting the nonwoven fabric layer (A) and the nonwoven fabric layer (B) were captured at a magnification at which one single fiber can be observed with a scanning electron microscope (SEM), and the average single-fiber diameter Da of the first thermoplastic resin fibers constituting the nonwoven fabric layer (A) and the average single-fiber diameter Db of the second thermoplastic resin fibers constituting the nonwoven fabric layer (B) were measured. The average single-fiber diameter ratio is a ratio (Db / Da) between the average single-fiber diameter Da of the first thermoplastic resin fibers constituting the nonwoven fabric layer (A) and the average single-fiber diameter Db of the second thermoplastic resin fibers constituting the nonwoven fabric layer (B), and is a value obtained by rounding off the ratio to the second decimal place.

[0044] In general, in a nonwoven fabric, the size of gaps formed by fibers varies depending on the average single fiber diameter of the fibers constituting the nonwoven fabric. Therefore, when nonwoven fabric layers having different average single-fiber diameters are stacked, nonwoven fabric layers having different inter-fiber gap sizes are stacked, and when moisture adheres, the moisture absorbed by the nonwoven fabric layer made of thick fibers can be quickly transferred to the nonwoven fabric layer made of thin fibers due to a difference in capillary effect.

[0045] In order that this capillary effect acts and good water absorption performance is obtained, the ratio (Db / Da) of the average single-fiber diameters is 1.0 or more, preferably 1.2 or more.

[0046] [Layered nonwoven fabric]The layered nonwoven fabric of the present invention is a layered nonwoven fabric in which at least one nonwoven fabric layer (A) and at least one nonwoven fabric layer (B) are layered, and the nonwoven fabric layer (B) is layered to be at least one outermost layer.

[0047] By layering the nonwoven fabric layer (B) having a large average single-fiber diameter and a large inter-fiber gap in the nonwoven fabric layer to be the outermost layer, when moisture adheres to the nonwoven fabric layer (B) side, the moisture is promptly transferred to the nonwoven fabric layer (A) , so that quick-drying property can be obtained on the outermost surface on the nonwoven fabric layer (B) side.

[0048] The layered nonwoven fabric of the present invention preferably has a water absorption rate measured from at least one surface of 20 seconds or less.

[0049] The water absorption rate is measured in accordance with "7.1.1 Dropwise addition method" of JIS L 1907: 2010"water absorbability test method for textile products".A water drop is dropped onto the layered nonwoven fabric, and the time from absorption to disappearance of specular reflection of the surface is measured. A simple average of the values measured at 10 different points is calculated, the unit is seconds, and the value obtained by rounding off the simple average to the first decimal place is defined as the water absorption rate.

[0050] A water absorption rate of 20 seconds or less indicates that the performance of removing moisture adhering to the surface is good. The water absorption rate is more preferably 10 seconds or less.

[0051] The basis weight of the layered nonwoven fabric of the present invention is preferably 10 to 100 g / m2.

[0052] By setting the basis weight to preferably 10 g / m2 or more, more preferably 13 g / m2 or more, and still more preferably 15 g / m2 or more, a layered nonwoven fabric having mechanical strength that can be put to practical use can be obtained. On the other hand, by setting the basis weight to preferably 100 g / m2 or less, more preferably 50 g / m2 or less, a layered nonwoven fabric having appropriate flexibility suitable for use as a nonwoven fabric for sanitary materials can be obtained. The basis weight of the layered nonwoven fabric of the present invention is preferably 13 to 50 g / m2.

[0053] The basis weight (g / m2) of the layered nonwoven fabric refers to a mass (g) per 1 m2 (g / m2) calculated from an average value of mass obtained by taking three sample pieces each having a size of 20 cm × 25 cm per 1 m of width of the sample, and the mass (g) of each of the sample pieces under a normal state based on "6.2 mass per unit area" in "General test methods for nonwovens" specified in JIS L 1913 (2010) .

[0054] In the layered nonwoven fabric of the present invention, the nonwoven fabric layer (A) and the nonwoven fabric layer (B) are preferably integrated. The term "integration" as used herein means that these layers are joined by interlacement of fibers, fixation by components such as an adhesive, and fusion of thermoplastic resins constituting the respective layers.

[0055] The layered nonwoven fabric of the present invention may be provided with a hydrophilic agent for the purpose of further improving water absorbability.

[0056] [Sanitary Material]In addition, at least a part of the sanitary material of the present invention is formed of the layered nonwoven fabric. The sanitary material of the present invention has excellent water absorbability and excellent quick-drying property. The sanitary material of the present invention is mainly a disposable article used for health purposes such as medical care and nursing care. Examples of the sanitary material of the present invention include a disposable diaper, a sanitary napkin, gauze, a bandage, a mask, a glove, an adhesive plaster, and the like, and also include constituent members thereof, for example, a top sheet, a back sheet, a side gather, and the like of the disposable diaper. Among them, the following aspects are preferable.

[0057] A first preferred embodiment of the sanitary material of the present invention is a diaper in which a top sheet is formed of the layered nonwoven fabric. In particular, when the layered nonwoven fabric is used such that the nonwoven fabric layer (B) is placed on the skin surface side of the top sheet of the diaper, excreted urine is quickly absorbed, and the liquid is quickly transferred to the nonwoven fabric layer (A), so that the surface of the layered nonwoven fabric can be kept dry.

[0058] A second preferred embodiment of the sanitary material of the present invention is a mask in which the inner surface layer is formed of the layered nonwoven fabric. The inner surface layer referred to in the present invention refers to a layer placed closest to the mouth side among the surfaces covering the mouth. When the layered nonwoven fabric is used such that the nonwoven fabric layer (B) is placed on the skin surface side, even if sweat or exhalation condenses and moisture adheres to the skin surface side, the moisture is immediately absorbed inside the layered nonwoven fabric and the skin surface can be kept dry, so that there is no discomfort when worn, and the layered nonwoven fabric is preferably used.

[0059] [Method for producing layered nonwoven fabric]Next, a preferred embodiment for producing the layered nonwoven fabric of the present invention will be specifically described.

[0060] The method for producing the nonwoven fabric layer (A) and the nonwoven fabric layer (B) constituting the layered nonwoven fabric of the present invention can be selected from known production methods such as a spunbonding method, a melt blow method, and a short fiber card method.

[0061] Among them, the spunbonding method is a preferable method because it is excellent in productivity.

[0062] Hereinafter, a preferred aspect of producing the layered nonwoven fabric of the present invention based on the spunbonding method will be described, but the present invention is not limited thereto.

[0063] The spunbonding method is a method for producing a nonwoven fabric that requires the steps of melting a thermoplastic resin as a raw material, spinning the resin from a spinneret, towing and extending the yarn obtained by cooling and solidifying the thermoplastic resin with an ejector, collecting the fiber group on a moving net to form a nonwoven fiber web, and thermally bonding the web.

[0064] In the spunbonding method, various shapes such as a round shape and a rectangular shape can be employed as the spinneret and the ejector to be used. In particular, a combination of a rectangular spinneret and a rectangular ejector is preferably used, from the viewpoint that such combination relatively reduces the amount of use of compressed air and hardly causes fusion and abrasion between yarns.

[0065] Furthermore, since the shape of the fiber cross-section can be controlled by changing the shape of the polymer discharge provided in the spinneret, it is preferable for the production of the nonwoven fabric layer (A) in the layered nonwoven fabric of the present invention.

[0066] When the layered nonwoven fabric of the present invention is produced, the spinning temperature is preferably (the melting temperature of the thermoplastic resin as a raw material + 10°C) or higher and (the melting temperature of the thermoplastic resin as a raw material + 100°C) or lower. The spinning temperature is set within the aforementioned ranges, and thus, a stable melt state can be obtained. Accordingly, excellent spinning stability can be obtained.

[0067] The spun yarns are then cooled. As the method for cooling the spun yarns, a method in which cold air is forcibly blown to the yarns, a method in which the yarns are naturally cooled at the ambient temperature around the yarns, and a method in which the distance between the spinneret and the ejector is adjusted, or a method in which these methods are combined can be employed. A cooling condition can be appropriately adjusted in consideration of a discharge amount per single hole of the spinneret, a spinning temperature, and an ambient temperature.

[0068] Next, the cooled and solidified yarns are towed and extended by the compressed air injected from the ejector.

[0069] In the layered nonwoven fabric of the present invention, it is important to control the average single fiber diameter of the fibers constituting the nonwoven fabric layer (A) and the nonwoven fabric layer (B).

[0070] The average single-fiber diameter of the fibers is determined by the discharge amount per discharge hole of the spinneret and the towing speed, that is, the spinning speed. Therefore, it is preferable to determine the discharge amount and the spinning speed according to the desired average single-fiber diameter.

[0071] The spinning speed is preferably 2,000 m / min or more, and more preferably 3,000 m / min or more. The spinning speed is set to 2,000 m / min or more, and thus, high manufacturability can be obtained. As a result, the oriented crystallization of the fibers can be promoted, and thus, it is possible to obtain filaments having high strength.

[0072] The filament yarn stretched by towing in this manner is collected on a moving net to be formed into a sheet, and then subjected to a step of thermal bonding.

[0073] The layered nonwoven fabric of the present invention is a layered nonwoven fabric obtained by layering at least one nonwoven fabric layer (A) and at least one nonwoven fabric layer (B). As a method for layering the two nonwoven fabric layers, for example, a method in which the nonwoven fabric layer obtained by collecting the second thermoplastic resin fibers by the spunbonding method is continuously collected in-line on a nonwoven fabric layer obtained by collecting the first thermoplastic resin fibers by the spunbonding method on the collection net as described above, and layered and integrated, a method in which the nonwoven fabric layer (A) and the nonwoven fabric layer (B) obtained separately are overlapped off-line, and layered and integrated by thermocompression bonding or the like can be employed. Among them, a method in which the nonwoven fabric layer obtained by collecting the second thermoplastic resin fibers by a spunbonding method is continuously collected in-line and layered and integrated by thermal bonding on the nonwoven fabric layer obtained by collecting the first thermoplastic resin fibers by a spunbonding method on a collection net is preferable because it is excellent in productivity.

[0074] Examples of the method for layering and integrating the layered nonwoven fabric of the present invention by thermal bonding include a method in which heat bonding is performed using various rolls such as heat embossing rolls with engraving (irregularity portion) on each of the surfaces of a pair of upper and lower rolls, a heat embossing roll composed of a combination of a roll with a flat (smooth) surface on one roll and a roll with engraving (irregularity portion) on the surface of the other roll, and a heat calender roll composed of a combination of a pair of upper and lower flat (smooth) rolls, and a thermocompression bonding method such as ultrasonic bonding that heat-welds by ultrasonic vibration of the horn.

[0075] When the layered nonwoven fabric of the present invention is produced by thermocompression bonding, the plurality of nonwoven fabric layers are sufficiently bonded to increase the mechanical strength of the layered nonwoven fabric, which is preferable.

[0076] On the other hand, as a method for layering and integrating the layered nonwoven fabric of the present invention by thermal bonding, a so-called air-through method, which is a method of blowing hot air, can also be mentioned.

[0077] When the layered nonwoven fabric of the present invention is produced by this air-through method, it is preferable because it is bulky and excellent in texture.

[0078] In the layered nonwoven fabric of the present invention, it is sufficient that the nonwoven fabric layer (B) is layered on at least one surface layer, and the number and combination of the layers can adopt any configuration depending on the purpose.EXAMPLES

[0079] Next, the present invention will be described in detail, based on Examples. However, the present invention is not limited only to these Examples. Unless otherwise described, physical properties are measured based on the above methods.

[0080] (1) Lobularity of fiber cross-sectionSingle fiber samples were randomly collected from a nonwoven fiber web collected on a net, and the crosssection of the fiber was captured with a scanning electron microscope (SEM) "S-5500" manufactured by Hitachi High-Technologies Corporation at a magnification at which one fiber can be observed.

[0081] (2) Ratio (Db / Da) of average single-fiber diameter Db of second thermoplastic resin fibers to average single-fiber diameter Da of first thermoplastic resin fibers"WinROOF2015" manufactured by MITANI CORPORATION was used as image analysis software.

[0082] (3) Water absorption rateThe water absorption rate was measured in accordance with "7.1.1 Dropwise addition method" of JIS L 1907: 2010 "water absorbability test method for textile products". A water drop was dropped onto the layered nonwoven fabric, and the time from absorption to disappearance of specular reflection of the surface was measured. A simple average of the values measured at 10 different points was calculated, the unit was seconds, and the value was obtained by rounding off the simple average to the first decimal place.

[0083] (4) Water-absorbing and quick-drying propertyIn the layered nonwoven fabric, one drop of a water droplet was dropped on the surface of the nonwoven fabric layer (B), and dry feeling of the surface after a lapse of 1 minute was touched by a healthy general adult (15 men and 15 women, 30 persons in total) by hand and evaluated according to the following 3 grades. The average score of the evaluation results was calculated for each nonwoven fabric, and used as the texture of the layered nonwoven fabric.5: Surface is dry and does not feel moisture 3: There is no moisture on the surface, but the surface is moist.1: There is moisture on the surface and the surface is moist.

[0084] [Example 1](Nonwoven Fabric Layer (A))Polypropylene (PP) was melted with an extruder, and spun as six-leaf cross-section fibers from a rectangular spinneret at a single hole discharge rate of 0.56 g / min.The spun yarn was cooled and solidified, then towed and extended by compressed air in a rectangular ejector under a pressure of 0.08 MPa in the ejector, and collected on a moving net to obtain a nonwoven fiber web. The characteristics of the fibers constituting the obtained spunbonded nonwoven fabric layer (A) were as follows: the average single-fiber diameter was 15.5 μm, and the lobularity was 8.8.

[0085] (Nonwoven fabric layer (B) )Polypropylene (PP) was melted with an extruder, and spun as round cross-sectional fibers from a rectangular spinneret having a hole diameter of 0.4 mm at a single hole discharge rate of 0.90 g / min. The spun yarn was cooled and solidified, then towed and extended by compressed air in a rectangular ejector under a pressure of 0.10 MPa in the ejector, and collected on a moving net to obtain a nonwoven fiber web. The characteristics of the fibers constituting the obtained spunbonded nonwoven fabric layer (B) were as follows: the average single-fiber diameter was 20.4 μm.

[0086] (Layered nonwoven fabric)The nonwoven fabric layer (B) was directly collected on the nonwoven fabric layer (A) obtained above (in Table 1, the layering method was described as "in-line") to obtain a layered fiber web having a two-layer structure of a spunbonded nonwoven fabric layer-spunbonded nonwoven fabric layer (in Table 1, a layer configuration was described as "A / B").

[0087] The layered fiber web thus obtained was thermally bonded at a linear pressure of 300 N / cm and a thermal bonding temperature of 125°C using a metal embossing roll in which regular circular convex parts were arranged in a staggered manner at the same pitch in both MD and CD on an upper roll and an embossing roll having a pair of upper and lower heating mechanisms constituted by metal flat rolls on a lower roll to obtain a layered nonwoven fabric having a basis weight of 40 g / m2.

[0088] The obtained layered nonwoven fabric was subjected to hydrophilic processing, and then the average single-fiber diameter ratio, the water absorption rate, and the waterabsorbing and quick-drying property were evaluated. The results are shown in Table 1.

[0089] [Example 2]A layered nonwoven fabric was obtained in the same manner as in Example 1 except that the fiber cross-section of the nonwoven fabric layer A was changed to a three-leaf cross-section. The evaluation results of the obtained layered nonwoven fabric are shown in Table 1.

[0090] [Example 3]A layered nonwoven fabric was obtained in the same manner as in Example 1 except that the single hole discharge rate was 0.65 g / min in the production method of the nonwoven fabric layer B. The evaluation results of the obtained layered nonwoven fabric are shown in Table 1.

[0091] [Example 4]Fibers of the nonwoven fabric layer (A) were collected on a conveyor in the same manner as in Example 1, and thermally bonded in the same manner as in Example 1 to obtain a nonwoven fabric layer (A) . Similarly for the nonwoven fabric layer (B), fibers of the nonwoven fabric layer (B) were collected on a conveyor in the same manner as in Example 1, and thermally bonded in the same manner as in Example 1 to obtain a nonwoven fabric layer (B). The nonwoven fabric layer (A) and the nonwoven fabric layer (B) thus obtained were layered (in Table 1, the layering method was described as "off-line"), and thermally bonded in the same manner as in Example 1 to obtain a layered nonwoven fabric. The evaluation results of the obtained layered nonwoven fabric are shown in Table 1.

[0092] [Example 5]A polymer used for the nonwoven fabric layer (A) and the nonwoven fabric layer (B) was polyethylene terephthalate copolymerized with polyethylene glycol (the copolymerization ratio of copolymerized PET and polyethylene glycol is 8 mass% of the polymer).

[0093] (Nonwoven Fabric Layer (A))A nonwoven fiber web was obtained in the same manner as in Example 1 except that copolymerized PET was used as the polymer. The characteristics of the fibers constituting the obtained spunbonded nonwoven fabric layer(A) were as follows: the average single-fiber diameter was 12.5 μm, and the lobularity was 22.2.

[0094] (Nonwoven fabric layer (B) )A nonwoven fiber web was obtained in the same manner as in Example 1 except that copolymerized PET was used as the polymer. The characteristics of the fibers constituting the obtained spunbonded nonwoven fabric layer(B) were as follows: the average single-fiber diameter was 16.9 μm.

[0095] (Layered nonwoven fabric)A layered nonwoven fabric was obtained in the same manner as in Example 1 except that the thermal bonding temperature was set to 200°C. The evaluation results of the obtained layered nonwoven fabric are shown in Table 2.

[0096] [Example 6]The nonwoven fabric layer (A) was collected on the nonwoven fabric layer (C) described below in the same manner as in Example 1, the nonwoven fabric layer (B) was further collected thereon, and thermal bonding was performed in the same manner as in Example 1 to obtain a layered nonwoven fabric (in Table 2, the layer configuration was denoted as "C / A / B"). The evaluation results of the obtained layered nonwoven fabric are shown in Table 2.

[0097] (Nonwoven fabric layer (C))Polypropylene (PP) was melted with an extruder, and spun as round cross-sectional fibers from a rectangular spinneret having a hole diameter of 0.4 mm at a single hole discharge rate of 0.65 g / min. The spun yarn was cooled and solidified, then towed and extended by compressed air in a rectangular ejector under a pressure of 0.10 MPa in the ejector, and collected on a moving net to obtain a nonwoven fiber web. The characteristics of the fibers constituting the obtained spunbonded nonwoven fabric layer (C) were as follows: the average single-fiber diameter was 16.0 μm.

[0098] [Comparative Example 1]A layered nonwoven fabric was obtained in the same manner as in Example 1 except that the discharge hole shape of the spinneret used in the nonwoven fabric layer (A) was a round shape. All the fibers of the nonwoven fabric layer (A) had a round cross-section, and the lobularity was not able to be measured. The evaluation results of the obtained layered nonwoven fabric are shown in Table 2.

[0099] [Comparative Example 2]A layered nonwoven fabric was obtained in the same manner as in Example 1 except that in the production method of the nonwoven fabric layer (B), the single hole discharge rate was 0.55 g / min, and the pressure in the ejector was 0.08 MPa. The fibers of the nonwoven fabric layer (B) had an average single-fiber diameter of 15.0 μm. The evaluation results of the obtained layered nonwoven fabric are shown in Table 2.

[0100] [Comparative Example 3]The nonwoven fabric layer (A) was collected on the nonwoven fabric layer (C) described below in the same manner as in Example 1, and the nonwoven fiber web obtained by collecting the nonwoven fabric layer (B) thereon was thermally bonded in the same manner as in Example 1 to obtain a layered nonwoven fabric (in Table 2, the layer configuration was denoted as "A / B / C"). The evaluation results of the obtained layered nonwoven fabric are shown in Table 2.

[0101] (Nonwoven fabric layer (C) )Polypropylene (PP) was melted with an extruder, and spun as round cross-sectional fibers from a rectangular spinneret having a hole diameter of 0.4 mm at a single hole discharge rate of 0.55 g / min. The spun yarn was cooled and solidified, then towed and extended by compressed air in a rectangular ejector under a pressure of 0.08 MPa in the ejector, and collected on a moving net to obtain a nonwoven fiber web. The characteristics of the fibers constituting the obtained spunbonded nonwoven fabric layer (C) were as follows: the average single-fiber diameter was 15.0 μm.

[0102] [Table 1]PP: Polypropylene (MFR: 200 g / 10 min)Copolymerized PET: Polyethylene glycol copolymerized polyethylene terephthalate (8 mass%)

[0103] [Table 2]PP: Polypropylene (MFR: 200 g / 10 min)Copolymerized PET: Polyethylene glycol copolymerized polyethylene terephthalate (8 mass%)

[0104] As shown in Tables 1 and 2, it can be seen that the water-absorbing and quick-drying property is excellent in Examples 1 to 6. In particular, in Example 1, Example 5, and Example 6, both the water absorption rate and the water-absorbing and quick-drying property were achieved at a high level. On the other hand, in Comparative Examples 1 to 3, the water-absorbing and quick-drying property was low.INDUSTRIAL APPLICABILITY

[0105] The layered nonwoven fabric of the present invention has a water absorption rate sufficient for use as a nonwoven fabric for a sanitary material, and a water absorbing and quick-drying property. By using the layered nonwoven fabric of the present invention as at least a part of a sanitary material, a sanitary material having excellent water absorbability and excellent quick-drying property can be obtained.

[0106] The layered nonwoven fabric of the present invention can be used as a part of a sanitary material such as a disposable diaper, a sanitary napkin, gauze, a bandage, a mask, a glove, or an adhesive plaster.DESCRIPTION OF REFERENCE SIGNS

[0107] C1: Cross-sectional contourL11: Straight line passing through two points (S11, S12) on contour (C1) of cross-section in fiber cross-sectionS11, S12: Point on contour (C1) of cross-section in fiber cross-sectionC2: Cross-sectional contourL21: Straight line passing through two points (S21, S22) on contour (C2) of cross-section in fiber cross-sectionL22: Line that is parallel to straight line (L21) and has only one intersection (V21) between points S21 and 22 in contour (C2)S21, S22, V21: Point on contour (C2) of cross-section in fiber cross-sectiona: Distance between points S21 and S22 b: Distance between straight line (L21) and straight line (L22)

Claims

1. A layered nonwoven fabric in which at least one nonwoven fabric layer (A) formed of a first thermoplastic resin fiber and at least one nonwoven fabric layer (B) formed of a second thermoplastic resin fiber are layered, wherein a cross-section of the first thermoplastic resin fiber has a plurality of convex parts, and has a modified cross-section in which a lobularity of the cross-section is 5% or more, a ratio (Db / Da) of an average single-fiber diameter Db of the second thermoplastic resin fiber to an average single-fiber diameter Da of the first thermoplastic resin fiber is 1.0 or more, and the nonwoven fabric layer (B) is layered to be at least one outermost layer.

2. The layered nonwoven fabric according to claim 1, wherein a water absorption rate measured from at least one surface of the layered nonwoven fabric is 20 seconds or less.

3. A sanitary material comprising the layered nonwoven fabric according to claim 1 or 2 as at least a part of the sanitary material.

4. A diaper comprising a top sheet formed of the layered nonwoven fabric according to claim 1 or 2.

5. A mask comprising an inner surface layer formed of the layered nonwoven fabric according to claim 1 or 2.