Nonwoven fabric for absorbent articles and its manufacturing method, top sheet for absorbent articles and absorbent articles including the same

Abstract

To provide a nonwoven fabric for absorbent articles suited for use as a top-sheet or the like, which nonwoven fabric has a smoother feel, is less prone to fluffing, and has superior liquid absorbency.CONSTITUTION: The nonwoven fabric for absorbent articles includes a first fibrous layer and a second fibrous layer, wherein one surface of the first fibrous layer forms a surface of the nonwoven fabric, the other surface is in contact with the second fibrous layer, the fiber layer includes an adhesive fiber and a first hydrophilic fiber, the second fiber layer includes a second hydrophilic fibers, the adhesive fibers in the first fiber layer allow the fibers to adhere to each other, the first fiber layer and the second fiber layer are integrated by entangling the fibers, the radius of curvature (φ1) of the fiber on the surface of the first fiber layer is 30 μm or more, the radius of curvature (φ2) of the fibers on the surface of the second fiber layer is 40 μm or less, φ1>φ2 is satisfied, and the first fiber layer is arranged closer to the user's skin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a nonwoven fabric for absorbent articles and a method for producing the same, as well as a top sheet for absorbent articles and an absorbent article including the same. [Background technology]

[0002] One application of nonwoven fabrics is as a component of absorbent articles such as panty liners, sanitary napkins, disposable diapers for babies, and disposable diapers for nursing care, for example, a top sheet (also called a surface sheet or surface material).To date, various nonwoven fabrics have been proposed for use as top sheets for absorbent articles, from the viewpoints of feel on the skin, comfort when using the absorbent article, ability to absorb body fluids when released, and ability to prevent return of fluid.

[0003] For example, Patent Document 1 discloses a nonwoven fabric that includes a cellulose fiber and an adhesive fiber, includes bonded points between the adhesive fiber and the cellulose fiber and / or the adhesive fiber, includes entangled points between the cellulose fiber and the cellulose fiber and / or the adhesive fiber, and has an index of bonded intersections of 1 to 60 / mm 2 The paper proposes that nonwoven fabrics with a thickness reduction rate of 30 to 45% be used in absorbent articles and other applications that come into direct contact with human skin.

[0004] Patent Document 2 proposes a fiber sheet containing cotton fibers and two or more different synthetic fibers, in which the two or more synthetic fibers form a nonwoven fabric, the cotton fibers penetrate into and are entangled with the fiber network of the nonwoven fabric, and a cotton fiber layer is formed on one side of the nonwoven fabric in a state where it is partially embedded in the nonwoven fabric, and the fiber sheet contains a specific combination of two or more synthetic fibers. Patent Document 2 proposes incorporating this fiber sheet into an absorbent article so that the cotton fiber layer faces the user's body. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 151527 Brochure [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-324038 Summary of the Invention [Problem to be solved by the invention]

[0006] Because the top sheet of an absorbent article comes into direct contact with the user's skin, its feel is important, as is its ability to quickly absorb blood, excrement, and the like and transfer them to the absorbent body (liquid absorption). Furthermore, because absorbent articles are used in delicate areas, the components that make them up are naturally manufactured with hygiene in mind, and there is also a tendency for them to be desired to give a clean and hygienic impression in appearance. For example, in the case of a top sheet, if the fuzz of the fibers is noticeable upon opening or during use, it can give the user the impression of unhygienic conditions and cause them to hesitate to use it. Furthermore, if the fuzzed fibers fall off and stick to the user's body or clothing, the user's discomfort will be further increased.

[0007] The present disclosure provides a nonwoven fabric for absorbent articles that has a smoother feel, is less likely to produce fluff, and exhibits good liquid absorbency, making it suitable for use as a top sheet or the like. [Means for solving the problem]

[0008] The present disclosure provides: A nonwoven fabric for absorbent articles comprising a first fiber layer and a second fiber layer, one surface of the first fiber layer forms a surface of the nonwoven fabric, and the other surface is in contact with the second fiber layer; the first fibrous layer includes adhesive fibers and first hydrophilic fibers; the first fiber layer contains the adhesive fiber in an amount of 40% by mass or more and 75% by mass or less and the first hydrophilic fiber in an amount of 25% by mass or more and 60% by mass or less, based on the total mass of the first fiber layer; the second fibrous layer includes second hydrophilic fibers; the second fiber layer contains the second hydrophilic fibers in an amount of 70% by mass or more and 100% by mass or less based on the total mass of the second fiber layer; In the first fiber layer, the fibers are bonded to each other by the adhesive fibers, the first fiber layer and the second fiber layer are integrated by entanglement of the fibers, the radius of curvature (φ1) of the fibers on the surface of the first fiber layer is 30 μm or more, the radius of curvature (φ2) of the fibers on the surface of the second fiber layer is 40 μm or less, and φ1>φ2 is satisfied; The first fiber layer is positioned closer to the user's skin. A nonwoven fabric for absorbent articles is provided. [Effects of the Invention]

[0009] The nonwoven fabric for absorbent articles according to the present disclosure comprises a first fiber layer containing hydrophilic fibers and adhesive fibers, and a second fiber layer having a hydrophilic fiber ratio equal to or greater than a predetermined value, wherein the hydrophilic fibers and adhesive fibers are bonded in the first fiber layer, and the fibers are entangled to different degrees in each fiber layer. With this configuration, in the nonwoven fabric for absorbent articles according to the present disclosure, the surface of the first fiber layer closest to the user's skin provides a smooth feel, and the second fiber layer serves to draw in bodily fluids. Furthermore, since both the first fiber layer and the second fiber layer contain hydrophilic fibers and are entangled with each other, the generation of fluff is further suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an electron microscope photograph showing the surface of the second fiber layer side of the nonwoven fabric produced in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Background to the present embodiment) Patent Document 1 proposes a technology for producing a nonwoven fabric by forming a web using a carding machine using cellulosic fibers and adhesive fibers, then performing a bonding treatment and a hydroentanglement treatment to achieve a soft texture and reduced fuzz. The same document also describes a nonwoven fabric produced by laminating webs containing two types of fibers at different blend ratios and performing a bonding treatment and a hydroentanglement treatment. However, the nonwoven fabric described in Patent Document 1 still has room for improvement in terms of fuzz reduction and liquid absorbency.

[0012] As a result of extensive research, the inventors have found that in nonwoven fabrics using hydrophilic fibers, particularly cellulosic fibers, it is more effective to entangle the fibers more firmly than to fix the fibers together by thermal bonding or the like in order to suppress fuzz. To achieve stronger entanglement, for example, it is necessary to increase the water pressure during the hydroentanglement treatment and / or increase the number of times the water jets are sprayed onto the web. However, increasing the degree of entanglement of the fibers makes the streaky irregularities formed on the surface of the nonwoven fabric due to the water jets more pronounced, which reduces the smoothness of the surface of the nonwoven fabric. Furthermore, when hydrophilic fibers are used, the greater the degree of entanglement of the fibers, the more likely the softness of the entire nonwoven fabric is to be impaired, and the smaller or fewer voids between the fibers tend to reduce the liquid absorbency.

[0013] Patent Document 2 proposes a configuration combining a nonwoven fabric made of thermal adhesive fibers with a cotton fiber layer, with the assumption that the cotton fiber layer side will contact the user's skin. Therefore, when the nonwoven fabric described in this document is used as a top sheet of an absorbent article, the user's body fluids first come into contact with the cotton fiber layer and then move toward the absorbent core. Because cotton fibers have high water absorption and liquid retention properties, the nonwoven fabric described in this document tends to retain liquid in the cotton fiber layer, resulting in significant liquid return. Excessive liquid return can leave the skin wet during use, which can cause discomfort to the user. Furthermore, when the cotton fiber layer retains body fluids (especially blood), the color of the body fluids is likely to appear on the surface of the nonwoven fabric, which can cause discomfort to the user during use or when disposing of the nonwoven fabric after use.

[0014] In view of these problems, the inventors have investigated a laminated nonwoven fabric structure in which each fiber layer contains a predetermined proportion of hydrophilic fibers, thereby suppressing fuzzing due to entanglement of the hydrophilic fibers and forming a hydrophilic gradient in the thickness direction, thereby improving liquid absorbency. Furthermore, the fiber layer on the side that contacts the user's skin contains adhesive fibers, which allow the fibers in this fiber layer to be bonded to one another to some extent, and the degree of entanglement in the fiber layer on the skin side is less than that of the fiber layer on the opposite side. As a result, the nonwoven fabric for absorbent articles of this embodiment (hereinafter simply referred to as "nonwoven fabric") achieves a smooth feel, improved liquid absorbency, and reduced fuzzing. This structure can be achieved by subjecting the fiber layer on the skin side, which contains hydrophilic fibers and adhesive fibers, to an adhesive treatment, and then laminating it with a fiber layer containing a higher proportion of hydrophilic fibers, followed by entanglement and integration using a predetermined method. The nonwoven fabric of this embodiment will be described below.

[0015] (First embodiment) The nonwoven fabric of this embodiment is a nonwoven fabric for absorbent articles comprising a first fiber layer and a second fiber layer, one surface of the first fiber layer forms a surface of the nonwoven fabric, and the other surface is in contact with the second fiber layer; the first fibrous layer includes adhesive fibers and first hydrophilic fibers; the first fiber layer contains the adhesive fiber in an amount of 40% by mass or more and 75% by mass or less and the first hydrophilic fiber in an amount of 25% by mass or more and 60% by mass or less, based on the total mass of the first fiber layer; the second fibrous layer includes second hydrophilic fibers; the second fiber layer contains the second hydrophilic fibers in an amount of 70% by mass or more and 100% by mass or less based on the total mass of the second fiber layer; In the first fiber layer, the fibers are bonded to each other by the adhesive fibers, the first fiber layer and the second fiber layer are integrated by entanglement of the fibers, the radius of curvature (φ1) of the fibers on the surface of the first fiber layer is 30 μm or more, the radius of curvature (φ2) of the fibers on the surface of the second fiber layer is 40 μm or less, and φ1>φ2 is satisfied; The first fiber layer is positioned closer to the user's skin. A nonwoven fabric for absorbent articles. In the following, the fibers constituting the nonwoven fabric of this embodiment will first be described.

[0016] (adhesive fiber) The term "adhesive fiber" refers to a fiber that exhibits adhesiveness through a bonding process (e.g., thermal bonding process, electron beam irradiation, ultrasonic welding (ultrasonic welder), etc.) and can bond fibers together to form bonded areas, and is not particularly limited as long as the nonwoven fabric intended by the present disclosure can be obtained.

[0017] The adhesive fibers include, for example, synthetic fibers made of thermoplastic resin. Thermoplastic resins are not particularly limited and include, for example, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, polybutylene succinate, and copolymers thereof; polyolefin resins such as polypropylene, polyethylene (including high-density polyethylene, low-density polyethylene, and linear low-density polyethylene), polybutene-1, propylene copolymers primarily composed of propylene (including propylene-ethylene copolymers and propylene-butene-1-ethylene copolymers), ethylene-acrylic acid copolymers, and ethylene-vinyl acetate copolymers; polyamide resins such as nylon 6, nylon 12, and nylon 66; acrylic resins; engineering plastics such as polycarbonate, polyacetal, polystyrene, and cyclic polyolefins, as well as elastomers thereof. Synthetic fibers may be produced using one or more thermoplastic resins selected from these.

[0018] The synthetic fiber may be a single fiber made of one or more thermoplastic resins selected from the above, or a conjugated fiber made of two or more components (also referred to as "sections"). In the conjugated fiber, each component may be made of a single thermoplastic resin, or a mixture of two or more thermoplastic resins. The conjugated fiber may be, for example, a sheath-core conjugated fiber, an islands-in-sea conjugated fiber, or a side-by-side conjugated fiber. The sheath-core conjugated fiber may be an eccentric sheath-core conjugated fiber in which the center of the core component and the center of the sheath component do not coincide in the fiber cross section, or a concentric sheath-core conjugated fiber in which the center of the core component and the center of the sheath component coincide in the fiber cross section. In this embodiment, a concentric sheath-core conjugated fiber may be used to make the nonwoven fabric smoother to the touch. The concentric sheath-core conjugated fiber can make the nonwoven fabric denser. The conjugated fiber may also be a splittable conjugated fiber.

[0019] Whether single fiber or composite fiber, synthetic fibers may have a circular cross section or a modified cross section (non-circular cross section). In the case of sheath-core composite fibers and islands-in-sea composite fibers, the core component and / or island component may have a modified cross section in the fiber cross section. When the synthetic fiber has a non-circular cross section, the cross section may be elliptical, polygonal, star-shaped, or a shape in which multiple projections are joined at their bases (for example, cloverleaf shape). In this embodiment, two or more synthetic fibers may be used in combination as the synthetic fibers.

[0020] When the synthetic fiber is a composite fiber, two or more components may be arranged so that the thermoplastic resin with a lower melting point forms part of the fiber surface. The thermoplastic resin with a low melting point (low-melting component) melts or softens when heat is applied during the process of producing a nonwoven fabric, becoming an adhesive component. The low-melting component contributes to the adhesion of fibers to each other or to other components, and can form adhesive sites. When the synthetic fiber is a composite fiber, the low-melting point component may be exposed over, for example, 40% or more of the circumferential length of the fiber in the cross section, particularly 50% or more, more particularly 60% or more, and even more particularly 80% or more. Alternatively, the low-melting point component may be exposed over the entire circumferential length of the fiber.

[0021] When the synthetic fiber is a core-sheath type composite fiber, the core-to-sheath composite ratio (volume ratio, core / sheath) may be, for example, 80 / 20 to 20 / 80, and particularly 60 / 40 to 40 / 60. When the core / sheath composite ratio is within this range, the fibers are bonded appropriately. Furthermore, when a nonwoven fabric is produced by performing an entanglement step after the bonding step, excessive peeling at the bonded portions during the entanglement step does not occur. Furthermore, when the core / sheath composite ratio is within this range, the core component easily maintains the fiber shape, and the strength of the nonwoven fabric can be favorably achieved.

[0022] The adhesive component of the adhesive fiber (or the low-melting component in the case of bicomponent fibers) may be a copolymer of an olefin and an unsaturated carboxylic acid or its derivative. Such a copolymer exhibits good adhesion to cellulosic fibers, an example of hydrophilic fibers. Examples of unsaturated carboxylic acids include maleic acid, acrylic acid, methacrylic acid, fumaric acid, and itaconic acid. Examples of derivatives include anhydrides of unsaturated carboxylic acids, methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate, and dimethylaminoethyl methacrylate, as well as similar acrylic acid esters, glycidyl acrylate, glycidyl methacrylate, butenecarboxylic acid esters, allyl glycidyl ether, 3,4-epoxybutene, 5,6-epoxy-1-hexene, and vinylcyclohexene monoxide. An ethylene-acrylic acid copolymer in which the olefin is ethylene and the unsaturated carboxylic acid or its derivative is acrylic acid or its derivative is particularly preferred.

[0023] Combinations of thermoplastic resins that make up the composite fiber include, for example, combinations of polyolefin resins and polyester resins (polyolefin resin / polyester resin), such as polyethylene / polyethylene terephthalate, polypropylene / polyethylene terephthalate, and propylene copolymer / polyethylene terephthalate, as well as combinations of two types of polyolefin resins, such as polyethylene / polypropylene, propylene copolymer / polypropylene, and ethylene-acrylic acid copolymer / polypropylene, and combinations of two types of polyester resins with different melting points.

[0024] When the synthetic fiber is a sheath-core composite fiber in which a thermoplastic resin with a lower melting point constitutes the sheath portion, examples of core / sheath combinations include polyethylene terephthalate / polyethylene, polyethylene terephthalate / polypropylene, polyethylene terephthalate / propylene copolymer, polytrimethylene terephthalate / polyethylene, polybutylene terephthalate / polyethylene, polyethylene terephthalate / copolymer polyester (e.g., polyethylene terephthalate copolymerized with isophthalic acid), polypropylene / ethylene-acrylic acid copolymer, and polylactic acid / polybutylene succinate. These combinations can also be applied to composite fibers other than sheath-core composite fibers. Sheath-core composite fibers in which the sheath is polyethylene (e.g., high-density polyethylene, low-density polyethylene, or linear low-density polyethylene) or a copolymer polyester have the property that, when heat-treated at a temperature above the melting point of the thermoplastic resin constituting the sheath, the sheath melts or softens, bonding the fibers together and forming bonded areas.

[0025] The thermoplastic resins exemplified as constituent components of the single fiber or composite fiber may contain other components as long as they contain 50% by mass or more of the specifically specified thermoplastic resin. For example, in the combination of polyethylene / polyethylene terephthalate, the "polyethylene" may contain other thermoplastic resins and additives, etc., as long as it contains 50% by mass or more of polyethylene. This also applies to the examples below.

[0026] When the adhesive fibers are synthetic fibers, the surfaces of the fibers may be coated with a hydrophilic fiber treatment agent. When the nonwoven fabric of this embodiment is produced by a method including an entanglement treatment using a high-pressure fluid flow (particularly a water flow), the surfaces of the hydrophobic synthetic fibers are made hydrophilic, which promotes entanglement of the fibers and makes it easier to obtain a nonwoven fabric that is advantageous in terms of touch and / or mechanical properties.

[0027] The hydrophilic fiber treatment agent to be applied to the adhesive fiber is not particularly limited, and any known agent in the technical field of synthetic fibers or a similar agent may be used. Examples of hydrophilic fiber treatment agents include fiber treatment agents containing various surfactants. Examples of surfactants that can be used include anionic, cationic, zwitterionic, and nonionic surfactants.

[0028] Examples of anionic surfactants include alkyl phosphate sodium salt, alkyl ether phosphate sodium salt, dialkyl phosphate sodium salt, dialkyl sulfosuccinate sodium salt, alkyl benzene sulfonate sodium salt, alkyl sulfonate sodium salt, and alkyl sulfate sodium salt. In the anionic surfactants, it is preferable that all alkyls have 6 to 22 carbon atoms. In addition, in these anionic surfactants, other alkali metal salts such as potassium salts or alkaline earth metal salts (e.g., magnesium salts) can be used instead of sodium salts.

[0029] Examples of cationic surfactants include alkyl (or alkenyl) trimethyl ammonium halides, dialkyl (or alkenyl) dimethyl ammonium halides, and alkyl (or alkenyl) pyridinium halides. The cationic surfactants preferably have an alkyl or alkenyl group having 6 to 18 carbon atoms. Examples of halogens in the halide compounds include chlorine and bromine.

[0030] Examples of the amphoteric surfactant include betaine-type amphoteric surfactants such as alkyldimethylbetaine, amino acid-type amphoteric surfactants, and aminosulfonic acid-type amphoteric surfactants. Examples of nonionic surfactants include polyhydric alcohol fatty acid esters such as glycerin fatty acid esters, polyglycerin fatty acid esters, and sorbitan fatty acid esters; alkylene oxide adducts of the above polyhydric alcohol fatty acid esters, such as polyoxyalkylene-modified silicones; and amino-modified silicones.

[0031] The hydrophilic fiber treatment agent applied to the adhesive fiber may be a primary hydrophilic fiber treatment agent. Here, a primary hydrophilic fiber treatment agent refers to a treatment agent that imparts to the fiber the property of significantly reducing its hydrophilicity once it comes into contact with water. Adhesive fibers coated with a primary hydrophilic fiber treatment agent retain the inherent hydrophobicity of synthetic fibers after hydroentanglement treatment, thereby promoting entanglement during production while utilizing the properties of hydrophobic fibers (dry feel, reduced ability to retain excessive liquid) when used in nonwoven fabrics, as described below.

[0032] The primary hydrophilic fiber treatment agent may be, for example, one that, when applied to the surface of a synthetic adhesive fiber, causes the initial settling velocity of the fiber to be less than 60 seconds, particularly 30 seconds or less, and causes the settling velocity of the fiber after rubbing and washing in 40°C warm water for 2 minutes (settlement velocity after washing) to be 60 seconds or more, particularly 90 seconds or more. The initial settling velocity corresponds to the settling velocity of the fiber when not exposed to liquid, and is the settling velocity measured immediately after fiber production or before hydroentanglement treatment. Such a primary hydrophilic fiber treatment agent is, for example, an alkyl phosphate salt having 8 to 12 carbon atoms.

[0033] The amount of the hydrophilic fiber treatment agent applied may be 0.1% by mass to 2.0% by mass, particularly 0.15% by mass to 1.0% by mass, and more particularly 0.2% by mass to 0.6% by mass, when the fiber mass (the mass of the fiber excluding the fiber treatment agent) is taken as 100% by mass.

[0034] Two or more adhesive fibers may be included. In this case, the melting points of the adhesive components of these fibers may be different from each other. For example, when two types of adhesive fibers are included, the difference in melting points of the adhesive components of these fibers may be 10°C or more and 40°C or less, particularly 15°C or more and 30°C or less.

[0035] The fineness of the adhesive fibers is not particularly limited, but in this embodiment, adhesive fibers with a relatively small fineness (but which do not produce ultrafine fibers) are preferably used so that the first fiber layer containing the adhesive fibers has a smoother feel. Specifically, the fineness of the adhesive fibers may be 0.3 dtex to 2.5 dtex, particularly 0.5 dtex to 2.0 dtex, and more particularly 0.6 dtex to 1.5 dtex. When the fineness of the adhesive fibers is within the above range, the resulting nonwoven fabric has a smooth feel.

[0036] The fiber diameter of the adhesive fiber may be, for example, 6 μm to 19 μm, particularly 8 μm to 17 μm, and more particularly 10 μm to 15 μm. When the fiber diameter of the adhesive fiber is within the above range, the nonwoven fabric tends to have a smooth feel.

[0037] The fiber length of the adhesive fiber may be, for example, 25 mm to 100 mm, particularly 28 mm to 70 mm, and more particularly 30 mm to 60 mm. When the fiber length of the adhesive fiber is within the above range, the degree of entanglement of the fibers tends to be favorable. In particular, when a nonwoven fabric is produced by the method described below, the fiber length within the above range makes it easier to control the degree of entanglement of the fibers in the first fiber layer and the second fiber layer.

[0038] (hydrophilic fiber) The nonwoven fabric of this embodiment contains hydrophilic fibers in both the first fiber layer and the second fiber layer. In this specification, the hydrophilic fibers contained in the first fiber layer are referred to as "first hydrophilic fibers" and the hydrophilic fibers contained in the second fiber layer are referred to as "second hydrophilic fibers." However, these names are used to identify the fiber layers in which they are contained, and both are hydrophilic fibers. Therefore, in the following description, matters common to the first and second hydrophilic fibers will be described as matters related to "hydrophilic fibers."

[0039] Hydrophilic fibers include, for example, cellulosic fibers, protein-based fibers, and synthetic fibers having hydrophilic properties. In this embodiment, cellulosic fibers are preferably used as the hydrophilic fibers because they are easy to maintain their hydrophilic properties. The hydrophilic fibers in this embodiment do not exhibit adhesive properties under conditions under which adhesive fibers exhibit adhesive properties.

[0040] "Cellulosic fibers" are also called cellulose fibers and generally refer to fibers made from cellulose. Cellulosic fibers include, for example: (1) Natural fibers derived from plants such as cotton, flax, flax, ramie, jute, banana, bamboo, kenaf, shell ginger, hemp, and kapok; (2) solvent-spun cellulose fibers such as viscose-derived rayon and polynosic, cupra-derived cuprammonium-derived, and solvent-spun Tencel® and Lyocell®, as well as other regenerated fibers; (3) cellulose fibers obtained by melt spinning; and (4) Semi-synthetic fibers such as acetate fibers The type of cellulosic fiber is not particularly limited.

[0041] Protein-based fibers include natural fibers such as silk and wool. Examples of hydrophilic synthetic fibers include synthetic fibers made of hydrophilic thermoplastic resins, synthetic fibers made by kneading a hydrophilizing agent into hydrophobic thermoplastic resins, synthetic fibers made by applying a hydrophilic fiber treatment agent to hydrophobic synthetic fibers, and synthetic fibers made by applying a hydrophilizing treatment (corona discharge treatment, sulfonation treatment, graft polymerization treatment, etc.) to hydrophobic synthetic fibers. Examples of thermoplastic resins that make up synthetic fibers are as described above in relation to adhesive fibers. Since many of the thermoplastic resins listed above are hydrophobic, when using these, they need to be hydrophilized by kneading a hydrophilizing agent into them or applying a hydrophilic fiber treatment agent, etc.

[0042] Examples of hydrophilic fiber treatment agents include fiber treatment agents containing surfactants. Examples of surfactants that can be used include anionic, cationic, zwitterionic, and nonionic surfactants. Examples of surfactants are as described in relation to adhesive fibers. The content of the hydrophilic fiber treatment agent may be 0.1% by mass or more and 2.0% by mass or less, when the fiber mass (mass of fibers excluding the fiber treatment agent) is taken as 100% by mass. The content of the hydrophilic fiber treatment agent may particularly be 0.15% by mass or more and 1.0% by mass or less, more particularly 0.2% by mass or more and 0.6% by mass or less.

[0043] Hydrophilic fibers obtained by coating synthetic fibers with a hydrophilic fiber treatment agent on their surfaces are hydrophobic, and have a sedimentation rate of, for example, 60 seconds or more when measured using the method described below without the hydrophilic fiber treatment agent. Furthermore, in synthetic fibers coated with a hydrophilic treatment agent, the hydrophobic thermoplastic resin is exposed at the fiber end surfaces, making them less susceptible to liquid (especially water) absorption and less likely to swell upon liquid absorption. Cellulosic fibers, on the other hand, are hydrophilic throughout and tend to swell upon absorbing liquid, resulting in a decrease in fiber rigidity. Therefore, compared to cellulosic fibers, synthetic fibers coated with a hydrophilic fiber treatment agent are less susceptible to entanglement between fibers due to high-pressure liquid flow (especially high-pressure water flow), and tend to produce bulkier nonwoven fabrics.

[0044] The hydrophilic fiber treatment agent applied to the hydrophilic fibers may be a durable, durable hydrophilic fiber treatment agent. The durable hydrophilic fiber treatment agent has the property of remaining on the fiber surface and maintaining the hydrophilicity of the fibers even after entanglement treatment with a high-pressure fluid stream (particularly a water stream) when the nonwoven fabric of this embodiment is produced by the production method described below. Specifically, the durable hydrophilic fiber treatment agent is one that causes the initial settling velocity of the fibers to be 60 seconds or less and the settling velocity after washing, which is performed three times with 40°C warm water for 2 minutes, to be 60 seconds or less. The settling velocity after washing may be lower than the initial settling velocity as long as it is 60 seconds or less. For example, the durable hydrophilic fiber treatment agent may cause the initial settling velocity of the fibers to be 30 seconds or less, particularly 20 seconds or less, more particularly 15 seconds or less, and the settling velocity after washing with 40°C warm water to be 40 seconds or less, particularly 30 seconds or less, more particularly 20 seconds or less. Such a durable hydrophilic fiber treatment agent is, for example, an ethylene glycol-based fiber treatment agent.

[0045] The fineness of the hydrophilic fibers is not particularly limited, but in this embodiment, hydrophilic fibers with a relatively small fineness are preferably used. Specifically, the fineness may be 0.3 dtex to 2.8 dtex, more preferably 0.5 dtex to 2.3 dtex, particularly 0.6 dtex to 1.7 dtex, and more particularly 0.7 dtex to 1.5 dtex. By using hydrophilic fibers with a relatively small fineness as the first hydrophilic fibers, the surface that contacts the skin (the surface of the first fiber layer) can be made smoother and denser. Furthermore, by using hydrophilic fibers with a relatively small fineness as the second hydrophilic fibers, the impact on the tactile feel of the fibers exposed to the first fiber layer can be reduced. Furthermore, hydrophilic fibers with a small fineness are more firmly entangled when entangled by the method described below. Therefore, when these fibers are used as the first hydrophilic fibers and / or the second hydrophilic fibers, the resulting nonwoven fabric is less likely to generate fluff and to lose less fluff.

[0046] The fiber diameter of the hydrophilic fibers may be, for example, 4 μm to 15 μm, particularly 5 μm to 12 μm, and more particularly 6 μm to 10 μm. By using hydrophilic fibers having a fiber diameter within the above range as the first hydrophilic fibers, the surface that comes into contact with the skin (the surface of the first fiber layer) can be made smoother and denser. Furthermore, by using the second hydrophilic fibers having a fiber diameter within the above range, the impact on the tactile feel of the fibers exposed to the first fiber layer can be minimized. Furthermore, hydrophilic fibers having a fiber diameter within the above range are more firmly entangled when entangled using the method described below. Therefore, when these fibers are used as the first and / or second hydrophilic fibers, the resulting nonwoven fabric is less likely to produce fluff and less likely to lose fluff. Here, when the cross section of the hydrophilic fiber is non-circular, the fiber diameter is defined as the average value of the length of the major axis of the fiber cross section and the longest length across two points on the fiber cross section that are perpendicular to the major axis.

[0047] The fiber length of the hydrophilic fibers may be, for example, 25 to 100 mm, particularly 28 to 70 mm, and more particularly 30 to 60 mm. When the fiber length of the hydrophilic fibers is within the above range, the entanglement of the fibers tends to be favorable when a nonwoven fabric is produced by the method described below (especially a method in which the entanglement treatment includes a hydroentanglement treatment). Furthermore, by setting the fiber length of the first hydrophilic fibers and / or the second hydrophilic fibers within the above range, it becomes easier to control the degree of entanglement of the fibers in the first fiber layer and the second fiber layer.

[0048] The cross section of the hydrophilic fiber (transverse cross section, or cross section perpendicular to the length direction of the fiber) may be circular or noncircular. Examples of noncircular shapes include oval, Y-shaped, X-shaped, square, multi-lobed, polygonal, star-shaped, and chrysanthemum-shaped. When the cross section of the fiber is circular, the adhesion area with the adhesive fiber is relatively small, so the texture of the nonwoven fabric can be softer than when fibers with a noncircular shape are used. When the cross section of the fiber is noncircular, the adhesion area with the adhesive fiber is relatively large, so the strength of the nonwoven fabric can be increased.

[0049] As an example of a hydrophilic fiber, a cellulosic fiber may be used, such as a chemical fiber, such as a regenerated fiber or a semi-synthetic fiber. The variation in fineness and / or fiber diameter, as well as fiber length, of chemical fibers is smaller than that of natural fibers, making it easier to adjust the degree of entanglement of the nonwoven fabric. Furthermore, regenerated fibers, such as rayon and solvent-spun cellulose fibers, have a good balance of softness and strength when wet, making it easier to achieve the softness and strength suitable for the texture of a nonwoven fabric. Furthermore, solvent-spun cellulose fibers are preferred because they have relatively high single fiber strength, which results in better strength of the nonwoven fabric. Rayon, while having lower single fiber strength than solvent-spun cellulose fibers, is preferred because it results in a softer nonwoven fabric and a high degree of entanglement.

[0050] The hydrophilic fibers can be used alone or in combination. For example, the first hydrophilic fiber can be one or more types of cellulosic fiber, or one type of cellulosic fiber and one type of hydrophilic synthetic fiber. The same applies to the second hydrophilic fiber. Furthermore, the first hydrophilic fiber and the second hydrophilic fiber can be different or the same.

[0051] The degree of hydrophilicity of a hydrophilic fiber can be evaluated using, for example, values ​​such as the sedimentation velocity of the fiber. The settling velocity (or settling time (seconds)) of the hydrophilic fibers used in this embodiment may be, for example, less than 60 seconds, particularly 50 seconds or less, more particularly 40 seconds or less, even more particularly 30 seconds or less, and even more particularly 20 seconds or less. The smaller the settling velocity (or settling time) of the hydrophilic fibers, the higher the entanglement of the hydrophilic fibers tends to be.

[0052] The settling velocity of the fibers can be measured by the following method. 17 g of fiber is collected to measure the sedimentation rate. The collected fiber is opened (using a parallel carding machine) to form a carded web. 5 g of the carded web is weighed and packed into a cage (cylindrical, 5 cm diameter, 8 cm height, 3 g mass) made of copper wire (0.55 mm diameter). Next, prepare a thermostatic water bath, fill it with tap water, and adjust the water temperature to 25°C while stirring. Once the water temperature reaches 25°C, stop stirring the thermostatic water bath and begin measuring the sedimentation rate. Gently drop the basket filled with fibers using the procedure above from a position 1 cm above the water surface, and start the stopwatch as soon as the basket hits the water surface. The fibers gradually absorb water, and stop the stopwatch as soon as the 8 cm high basket completely sinks below the water surface. The sedimentation rate is the time from when the basket hits the water surface to when it sinks below the water surface, and the average of the two measurements is taken as the sedimentation rate of that fiber.

[0053] Note that natural fibers such as cotton and wool have the property of repelling water that comes into contact with the fiber surface due to oils attached to the fiber surface and the structure of the fiber surface, which may cause deterioration in the texture when the fibers are integrated by hydroentanglement treatment as described below. Therefore, when natural fibers are used as hydrophilic fibers in this embodiment, oils may be removed and the fiber surface may be modified.

[0054] When the hydrophilic fibers are regenerated cellulose fibers or synthetic fibers coated with a hydrophilic fiber treatment agent, they may contain additives typically found in these fibers. One such additive is titanium oxide, which imparts opacity to the fibers. Nonwoven fabrics with a first fiber layer containing regenerated cellulose fibers with a higher titanium oxide content tend to exhibit smaller MMDs (especially in the CD direction) compared to those using regenerated cellulose fibers with a lower titanium oxide content. This is presumably because titanium oxide changes the mechanical properties of the fibers, affecting their entanglement. More specifically, regenerated cellulose fibers with a higher titanium oxide content are presumably more rigid and less susceptible to entanglement by high-pressure fluid flow (especially water flow). As a result, the unevenness caused by nozzle streaks (also known as nozzle streaks) formed on the surface of the nonwoven fabric during submerged spraying is reduced, improving the surface smoothness of the nonwoven fabric.

[0055] (other fibers) The nonwoven fabric of this embodiment may contain fibers other than hydrophilic fibers and adhesive fibers (hereinafter referred to as "other fibers"). The other fibers contained in the first fiber layer are, for example, synthetic fibers that are neither adhesive fibers nor hydrophilic fibers (for example, hydrophobic synthetic fibers that do not melt or soften when the adhesive component of the adhesive fiber is melted and do not exhibit adhesiveness), and are not particularly limited. The other fibers contained in the second fiber layer include adhesive fibers in addition to the above-mentioned fibers that are not hydrophilic fibers and synthetic fibers that are not adhesive fibers.

[0056] The other fibers may be contained in a proportion of 30% by mass or less, particularly 25% by mass or less, and more particularly 20% by mass or less, when the total amount of fibers constituting each fiber layer is 100% by mass.

[0057] (Nonwoven fabric composition) The nonwoven fabric of this embodiment includes a first fiber layer and a second fiber layer, the first fiber layer forming one surface of the nonwoven fabric and the second fiber layer being disposed in contact with the first fiber layer. The first fiber layer contains 40% to 75% by mass of adhesive fibers and 25% to 60% by mass of first hydrophilic fibers, based on the total mass of the first fiber layer. The second fiber layer contains 70% to 100% by mass of second hydrophilic fibers, based on the total mass of the second fiber layer.

[0058] The surface of the nonwoven fabric formed by the first fiber layer is located on the side of the user's skin when the nonwoven fabric is incorporated into an absorbent article, and particularly comes into contact with the skin. Therefore, in this embodiment, the first fiber layer contains adhesive fibers to impart a smooth feel. Because the adhesive fibers are synthetic fibers as described above, even when the fibers are entangled and integrated by the action of a high-pressure fluid (particularly a high-pressure water stream) as described below, entanglement is relatively difficult to progress, reducing unevenness caused by the injection marks of the high-pressure fluid and making the surface of the nonwoven fabric smoother. Therefore, it is preferable that the surface of the nonwoven fabric formed by the first fiber layer be a flat surface without any raised or depressed portions.

[0059] In this embodiment, the first fiber layer contains first hydrophilic fibers. This, together with the second fiber layer containing second hydrophilic fibers, allows the hydrophilic fibers to be more firmly entangled between the first and second fiber layers, thereby suppressing fluffing and shedding on the surface of the first fiber layer. Here, "fluffing" refers to the state in which single fibers stand up on the surface of the nonwoven fabric, and "shedding" refers to the shedding of such single fibers.

[0060] Furthermore, in this embodiment, since the second fiber layer is located adjacent to the first fiber layer, it is believed that entanglement of the hydrophilic fibers in both fiber layers is facilitated, and a gradient in the proportion of hydrophilic fibers is likely to occur from the first fiber layer to the second fiber layer, forming a kind of "hydrophilic gradient," which is believed to improve liquid absorbency and suppress return of liquid.

[0061] The proportion of adhesive fibers in the first fiber layer may be 40% by mass or more and 75% by mass or less, particularly 45% by mass or more and 70% by mass or less, more particularly 50% by mass or more and 65% by mass or less, and even more particularly 55% by mass or more and 65% by mass or less. If the proportion of adhesive fibers is too low, it becomes difficult to make the surface of the first fiber layer smooth, and the amount of liquid return tends to be large. If the proportion of adhesive fibers is too high, the liquid absorbency decreases, and fluffing and shedding are more likely to occur.

[0062] The proportion of the first hydrophilic fiber in the first fiber layer may be 25% by mass or more and 60% by mass or less, particularly 30% by mass or more and 55% by mass or less, more particularly 35% by mass or more and 50% by mass or less, and even more particularly 35% by mass or more and 45% by mass or less. If the proportion of the first hydrophilic fiber is too small, the first fiber layer and the second fiber layer are insufficiently entangled, which tends to cause fluffing and shedding, and also reduces liquid absorbency. If the proportion of the first hydrophilic fiber is too high, the surface smoothness of the first fiber layer decreases and the amount of liquid return tends to increase. In particular, when the first hydrophilic fiber is a cellulosic fiber, the fiber itself has a greater liquid-retaining property than synthetic fibers, and therefore, if the proportion of the first hydrophilic fiber is too high, the amount of liquid return tends to increase.

[0063] The proportion of the second hydrophilic fibers in the second fiber layer may be 70% by mass or more and 100% by mass or less, particularly 80% by mass or more and 100% by mass or less, and more particularly 90% by mass or more and 100% by mass or less, or the second fiber layer may be composed only of the second hydrophilic fibers.

[0064] The second fiber layer contacts the first fiber layer and serves to rapidly transfer body fluid that reaches the first fiber layer to the absorbent while diffusing the fluid two-dimensionally in the surface direction to some extent. Therefore, if the proportion of the second hydrophilic fibers in the second fiber layer is too small, body fluid may not be transferred smoothly, and the absorption rate may decrease. Furthermore, the second hydrophilic fibers are entangled with the first hydrophilic fibers in the first fiber layer, and serve to fix the fibers (especially the first hydrophilic fibers) in the first fiber layer. Therefore, if the proportion of the second hydrophilic fibers is too small, pilling and shedding are likely to occur.

[0065] The proportion of the second hydrophilic fibers in the second fiber layer may be greater than the proportion of the first hydrophilic fibers in the first fiber layer. This configuration makes it easier to form a gradient in the proportion of hydrophilic fibers in the thickness direction of the nonwoven fabric (a gradient that increases from the first fiber layer to the second fiber layer), which tends to further improve the liquid absorbency of the nonwoven fabric.

[0066] In the nonwoven fabric of this embodiment, the first fiber layer contains adhesive fibers and first hydrophilic fibers in the above-mentioned ratio, so that hydrophobic fibers and hydrophilic fibers are present on the surface of the nonwoven fabric, allowing the properties of the fibers with different affinities for water to be exhibited in a balanced manner. As described above, the adhesive fibers are synthetic fibers that tend to be inherently hydrophobic. When hydrophobic fibers that are difficult to absorb liquids are included in the nonwoven fabric for absorbent articles, the nonwoven fabric feels dry to the touch and prevents the fibers that make up the nonwoven fabric from retaining too much liquid, thereby reducing the amount of liquid return. Meanwhile, in absorbent articles, where it is desirable to quickly absorb liquid excreted from the human body, etc., hydrophilic fibers serve to quickly attract liquid and transfer it to the absorbent body. Therefore, the nonwoven fabric of this embodiment can be provided as a nonwoven fabric with a good balance between feel and liquid absorption due to the hydrophobic and hydrophilic fibers present in the first fiber layer, and together with setting φ1 and φ2 to a predetermined range, as described below, it exhibits properties suitable for use in absorbent articles.

[0067] In the nonwoven fabric of this embodiment, the fibers are bonded together by the adhesive fibers contained in the first fiber layer, and the fibers constituting the first and second fiber layers are entangled, thereby integrating the fibers. When the nonwoven fabric is manufactured by the method described below, only the fibers contained in the first fiber layer may be bonded together by the adhesive fibers, in which case the fibers in the second fiber layer are not bonded together. With this configuration, bonding points are present only in the first fiber layer, and the overall feel of the nonwoven fabric can be made soft. Furthermore, when the nonwoven fabric is manufactured by the method described below, entangling the fibers constituting the first and second fiber layers while bonding points are present only in the first fiber layer can improve the entanglement of the fibers between the layers.

[0068] Alternatively, in the nonwoven fabric of this embodiment, the fibers may also be bonded to each other in the second fiber layer. The bonding between the fibers in the second fiber layer may be due to adhesive fibers in the first fiber layer that have migrated to the second fiber layer by the entanglement treatment, or may be due to adhesive fibers contained in the second fiber layer. The bonding in the second fiber layer is achieved by performing an entanglement treatment and then an adhesive treatment in the manufacturing method described below. When the fibers are bonded to each other in the second fiber layer, the strength of the nonwoven fabric is increased, which is advantageous in terms of the handleability of the nonwoven fabric. However, such nonwoven fabrics tend to be stiff to the touch.

[0069] At the locations where the fibers are bonded to each other, the adhesive component of the adhesive fiber melts or softens and then solidifies again to form the bonded portion. The fibers may be entangled by, for example, a hydroentanglement treatment, as described below.

[0070] In the nonwoven fabric of this embodiment, the degree of entanglement in the first fiber layer is smaller than that in the second fiber layer, thereby ensuring the smoothness of the surface of the first fiber layer. In this embodiment, the radius of curvature of the fibers contained in each fiber layer after fiber entanglement is used as an index representing the degree of entanglement. Fibers contained in fiber layers other than the entangled fiber layer may enter each fiber layer after fiber entanglement and appear on the surface of the fiber layer. However, the radius of curvature including fibers from the other fiber layers is measured to evaluate the degree of entanglement in each fiber layer. Therefore, in this embodiment, the radius of curvature of the fibers (which may be any of the first hydrophilic fibers, second hydrophilic fibers, adhesive fibers, and other fibers) on the surface of both the first fiber layer and the second fiber layer is used to evaluate the degree of entanglement of each fiber layer.

[0071] The radius of curvature of the fibers at the surface of each fiber layer is measured as follows. The surface of the fiber layer to be measured was observed using a scanning electron microscope (SEM, accelerating voltage: 10.0 kV, magnification: 100x). In the SEM image, where the fiber curved semicircularly in a direction approximately parallel to the image plane, a circle was drawn along the semicircle, and the radius of the drawn circle was taken as the radius of curvature of the fiber. The radius of curvature was calculated using the image analysis software "Micro Measure" (Scalar Corporation). For each SEM image, 10 values ​​were extracted from the measured radii of curvature, from the smallest to the tenth smallest.

[0072] This measurement and extraction was performed on five different SEM images, and the average value of a total of 50 values ​​was calculated and used as the radius of curvature of the fiber on the surface of the fiber layer. If the number of measurable radius of curvatures on one SEM image is less than 10, all values ​​of the radius of curvature obtained from that image are extracted, and the average value is calculated by adding the values ​​of the radius of curvature measured and extracted using other SEM images to the number of SEM images and measuring and extracting the values ​​so that the total number is 50 or more.

[0073] In the SEM image, whether or not the fiber was curved in a semicircular shape in a direction approximately parallel to the image plane was confirmed by visually observing the SEM image and by observing the circle drawn in the curved part when calculating the radius of curvature using the image analysis software. Specifically, if the circle drawn by the image analysis software was clearly smaller than the others (with a radius of curvature of less than 5 μm), it was determined that the fiber was curved in a direction perpendicular to the image plane and was excluded from the measurement target, while only those curved in a direction approximately parallel to the image plane were measured.

[0074] When measuring the radius of curvature, 10 loops with small radii of curvature are selected from the SEM image because such loops result from more advanced entanglement of fibers in the region shown in the image and provide a good indication of the degree of entanglement in that region. In nonwoven fabrics, even entangled fibers may appear substantially straight in the SEM image, depending on their location. Therefore, a large radius of curvature does not necessarily accurately indicate the degree of entanglement of the fibers. On the other hand, the above method measures loops resulting from entanglement. The inventors have confirmed that if the radii of curvature of these loops are small, other loops also tend to be small, and that these radii of curvature determine, to some extent, the overall degree of entanglement. Therefore, the degree of entanglement of fibers can be more accurately evaluated from 10 loops with small radii of curvature.

[0075] The smaller the radius of curvature of the fibers measured by the above method, the more pronounced the curvature of the fibers, including the hydrophilic fibers, due to entanglement, and the more advanced the entanglement of the fibers in the fiber layer. In this embodiment, it is preferable that the radius of curvature (φ1) of the fibers on the surface of the first fiber layer is 30 μm or more, and the radius of curvature (φ2) of the fibers on the surface of the second fiber layer is 40 μm or less, and that φ1 > φ2 is satisfied. In such a nonwoven fabric, the degree of entanglement of the fibers in the first fiber layer is smaller than that in the second fiber layer, which results in a smooth surface feel of the first fiber layer. If φ1 is too small, excessive entanglement may result in uneven entanglement or fibers with a high degree of curvature may be exposed on the surface, resulting in a decrease in surface smoothness.

[0076] In contrast, since φ2 is 40 μm or less and φ1>φ2, the degree of entanglement of the fibers in the second fiber layer is greater than that in the first fiber layer, and some of the fibers in the first fiber layer are fixed by being tightly entangled in the second fiber layer, effectively suppressing fuzzing on the surface of the first fiber layer.

[0077] Furthermore, by reducing φ2 to a certain extent, entanglement between the fibers of the first fiber layer and the fibers of the second fiber layer, particularly between the first hydrophilic fibers of the first fiber layer and the second hydrophilic fibers of the second fiber layer, progresses at the interface between the fiber layers, improving the "communication" (or unity) of the fibers (particularly the hydrophilic fibers) between the two fiber layers. As a result, a kind of gradient is formed in which the proportion of hydrophilic fibers gradually increases from the first fiber layer to the second fiber layer. Such a gradient acts as a hydrophilic gradient, and when bodily fluids such as excrement or menstrual blood come into contact with the surface of the first fiber layer, the bodily fluids are quickly drawn into the second fiber layer, thereby increasing the liquid absorption rate. If φ2 is too large, entanglement between the first fiber layer and the second fiber layer is insufficient, which tends to cause fluffing and shedding, and also reduces the liquid absorption rate.

[0078] A nonwoven fabric in which φ1 and φ2 are within the above ranges and φ1 > φ2 is satisfied also means that a relatively large number of fibers with a relatively large radius of curvature are present on the surface of the first fiber layer. In this embodiment, the first fiber layer contains hydrophilic fibers and adhesive fibers. When subjected to entanglement treatment (particularly hydroentanglement) under the same conditions, the adhesive fibers tend to exhibit a larger radius of curvature than the hydrophilic fibers, and therefore the proportion of adhesive fibers occupying the surface of the nonwoven fabric is likely to be high. Therefore, when the first fiber layer side of the nonwoven fabric of this embodiment is used as the skin-contacting surface, the nonwoven fabric can exhibit a smaller amount of liquid return by having φ1 and φ2 satisfy the specified conditions. Adhesive fibers, which are typically synthetic fibers and have hydrophobic properties, do not easily retain liquid, so once the liquid has passed through the first fiber layer and transferred to the absorbent, the fibers themselves can release less liquid even when pressure is applied.

[0079] The predetermined ranges of φ1 and φ2 can be easily achieved by making the fineness or fiber diameter of the adhesive fibers, first hydrophilic fibers, and second hydrophilic fibers constituting the first and second fiber layers relatively small. Specific finenesses and fiber diameters are as described above and will not be described here.

[0080] Alternatively, the specified ranges of φ1 and φ2 may be obtained by changing the pressure and / or frequency of the high-pressure fluid flow (particularly high-pressure water flow) when producing the nonwoven fabric of this embodiment using the method described below. For example, if the first fiber layer contains a relatively large proportion of hydrophilic fibers, the hydrophilic fibers may become entangled and occupy a large portion of the fiber layer, resulting in a decrease in the radius of curvature and making it impossible to obtain a φ1 within the specified range. In this case, increasing the pressure of the high-pressure fluid stream sprayed onto the side of the fiber web that will become the first fiber layer and / or increasing the number of sprays will cause the first hydrophilic fibers to move toward the second fiber layer, exposing more of the adhesive fibers to the surface. As a result, φ1 measured by the above method will increase, making it possible to obtain a φ1 within the specified range.

[0081] When φ1 is 135 μm or less, the degree of entanglement is good, fluffing and shedding are less likely to occur, and the distance between the first fiber layer and the second fiber layer and the absorbent body is shortened, which tends to increase the liquid absorption rate. φ1 may particularly be 100 μm or less, more particularly 65 μm or less. When φ2 is 5 μm or more, excessive entanglement does not proceed, and the nonwoven fabric can be prevented from becoming too hard. φ2 may particularly be 8 μm or more, more particularly 10 μm or more.

[0082] When the nonwoven fabric of this embodiment is formed using fibers with a small fineness, the fibers become more entangled, resulting in a higher fiber density, a smoother surface, and a smoother feel. On the other hand, as the fiber density at the surface of the nonwoven fabric increases, the interfiber voids decrease, resulting in fewer areas to temporarily "retain" body fluids released onto the surface of the nonwoven fabric, resulting in a decrease in absorbency. However, in the nonwoven fabric of this embodiment, the hydrophilic fibers are tightly entangled between the two fiber layers, improving the integrity of the hydrophilic fibers at the interface between the layers and forming a gradient of hydrophilic fibers. These configurations compensate for the decrease in absorbency that occurs as a trade-off between improved smoothness, allowing the nonwoven fabric of this embodiment to exhibit good absorbency.

[0083] In this embodiment, the basis weight of the first fiber layer is, for example, 10 g / m 2 More than 40g / m 2 or less, in particular 12 g / m 2 More than 35g / m 2 Below, more particularly 15 g / m 2 More than 25g / m 2 The first fiber layer is the surface closest to the user's skin and is primarily responsible for providing a smooth feel and preventing liquid return. In addition, the first fiber layer, together with the second fiber layer, forms a gradient in the ratio of hydrophilic fibers in the thickness direction of the nonwoven fabric, thereby improving liquid absorbency.

[0084] Therefore, if the basis weight of the first fiber layer is too small, the thickness of the first fiber layer will be small, and the highly curved loops of the second hydrophilic fibers contained in the second fiber layer will be more likely to appear on the surface of the first fiber layer, which may impair smoothness. Furthermore, the reduced amount of adhesive fiber may result in a greater amount of liquid return. If the basis weight of the first fiber layer is too large, the hydrophilic fibers between the first and second fiber layers will be insufficiently entangled, which may result in fuzzing and shedding. Furthermore, insufficient fiber entanglement between the fiber layers may reduce the "connection" (or unity) of the hydrophilic fibers between the fiber layers, making it difficult to form a hydrophilic fiber gradient, which may result in reduced liquid absorbency.

[0085] The basis weight of the second fiber layer is, for example, 10 g / m 2 More than 40g / m 2 or less, in particular 15 g / m 2 More than 37g / m 2 Below, more particularly 25 g / m 2 More than 35g / m 2 The second fiber layer has a high mixing ratio of second hydrophilic fibers, which are well entangled with the hydrophilic fibers contained in the first fiber layer, and serves to more firmly fix the fibers constituting the first fiber layer. The second fiber layer also serves to increase the liquid absorbency of the nonwoven fabric.

[0086] Therefore, if the basis weight of the second fiber layer is too small, the fibers in the first fiber layer will be weakly fixed, which may lead to fuzzing and shedding. Also, if the basis weight of the second fiber layer is too small, the liquid absorbency may decrease. If the basis weight of the second fiber layer is too large, the basis weight of the first fiber layer will be correspondingly small, which may cause the above-mentioned problems. Alternatively, if the basis weight of the second fiber layer is too large, the basis weight of the entire nonwoven fabric may become too large, making it unsuitable for use in absorbent articles. Alternatively, the fibers may be insufficiently entangled, making it difficult to form a hydrophilic fiber gradient, which may result in reduced liquid absorbency.

[0087] The ratio of the basis weight of the first fiber layer to the basis weight of the second fiber layer may be, for example, 2:8 (1st:2nd) to 8:2, particularly 3:7 to 7:3, and more particularly 4:6 to 6:4.

[0088] The basis weight of the entire nonwoven fabric is appropriately selected depending on the type of absorbent article, the location where the nonwoven fabric is placed in the absorbent article, etc. The basis weight of the entire nonwoven fabric is, for example, 20 g / m 2 More than 80g / m 2 Below, especially 30g / m 2 More than 70g / m 2 Below 40 g / m 2 More than 60g / m 2 For example, when the nonwoven fabric is used as a top sheet of a sanitary napkin or a panty liner, the basis weight may be 30 g / m 2 More than 70g / m 2 Below, especially 40g / m 2 More than 60g / m 2 It may be the following:

[0089] The nonwoven fabric of this embodiment may have a thickness (measured under a load of 294 Pa) of 0.20 mm or more and 1.50 mm or less, particularly 0.30 mm or more and 1.25 mm or less, and more particularly 0.40 mm or more and 1.00 mm or less. When the nonwoven fabric has a thickness in the above range, the nonwoven fabric tends to have a smoother feel.

[0090] The nonwoven fabric of this embodiment has a density of, for example, 0.020 g / cm 3 More than 0.150g / cm 3 It may have a fiber density of 0.030 g / cm 3 More than 0.140g / cm 3 It may have a fiber density of 0.040 g / cm or less, more particularly 0.040 g / cm 3 More than 0.130g / cm 3 The fiber density of the entire nonwoven fabric can be determined from the basis weight and thickness (thickness measured by applying a load of 294 Pa). When the nonwoven fabric has a density in the above range, the nonwoven fabric tends to exhibit a shorter liquid absorption time (i.e., a higher liquid absorption rate) and also tends to provide a smoother feel to the touch.

[0091] The fiber density of the nonwoven fabric tends to be lower, for example, 0.065 g / cm, when either or both of the first and second hydrophilic fibers are synthetic fibers containing a hydrophilic fiber treatment agent. 3 Nonwoven fabrics with such fiber densities tend to be bulky and soft to the touch.

[0092] The tensile strength in the MD (longitudinal or machine direction) of the nonwoven fabric of this embodiment may be, for example, 20.0 N / 5 cm or more and 200.0 N / 5 cm or less, particularly 30.0 N / 5 cm or more and 190.0 N / 5 cm or less, and more particularly 40.0 N / 5 cm or more and 180.0 N / 5 cm or less. The tensile strength in the CD (cross direction) of the nonwoven fabric of this embodiment may be, for example, 2.5 N / 5 cm or more and 50.0 N / 5 cm or less, particularly 5.0 N / 5 cm or more and 40.0 N / 5 cm or less, and more particularly 7.5 N / 5 cm or more and 35.0 N / 5 cm or less. When the tensile strength of the nonwoven fabric is within the above-mentioned range, the shape stability of the nonwoven fabric tends to be further improved.

[0093] The nonwoven fabric of this embodiment may have an MD elongation of, for example, 10% to 100%, particularly 20% to 60%, and an CD elongation of, for example, 40% to 200%, particularly 75% to 120%. When the elongation of the nonwoven fabric is within the above range, the flexibility of the nonwoven fabric tends to be further improved.

[0094] The nonwoven fabric of this embodiment may have a stress at 10% elongation in the MD of, for example, 16.5 N / 5 cm to 50.0 N / 5 cm, particularly 17.0 N / 5 cm to 40.0 N / 5 cm, and more particularly 17.5 N / 5 cm to 30.0 N / 5 cm. The nonwoven fabric of this embodiment may have a stress at 10% elongation in the CD of, for example, 0.1 N / 5 cm to 10.0 N / 5 cm, particularly 0.2 N / 5 cm to 7.5 N / 5 cm, and more particularly 0.3 N / 5 cm to 5.0 N / 5 cm. The nonwoven fabric of this embodiment has hydrophilic fibers entangled relatively firmly between the first and second fiber layers, so that the stress at 10% elongation in the MD is likely to be particularly high. When the stress at 10% elongation in the MD and CD directions is within the above range, the handleability of the nonwoven fabric is improved, which can have a more favorable effect on the processability when assembling an absorbent article and the operability when a user handles the absorbent article.

[0095] In the nonwoven fabric of this embodiment, when either or both of the first and second hydrophilic fibers are synthetic fibers containing a hydrophilic fiber treatment agent, the stress at 10% elongation in the MD direction of the nonwoven fabric may be, for example, 2.0 N / 5 cm to 40.0 N / 5 cm, particularly 2.5 N / 5 cm to 35.0 N / 5 cm, and more particularly 3.0 N / 5 cm to 30.0 N / 5 cm. Furthermore, the stress at 10% elongation in the CD direction of the nonwoven fabric of this embodiment may be, for example, 0.1 N / 5 cm to 10.0 N / 5 cm, particularly 0.2 N / 5 cm to 7.5 N / 5 cm, and more particularly 0.3 N / 5 cm to 5.0 N / 5 cm. When the stress at 10% elongation in the MD and CD directions is within the above ranges, the nonwoven fabric using synthetic fibers containing a hydrophilic fiber treatment agent tends to be bulkier and more flexible.

[0096] The nonwoven fabric of this embodiment is provided as one in which fluffing and shedding are suppressed as described above. Specifically, the nonwoven fabric of this embodiment can be provided as one in which the amount of fluff shedding measured on the surface of the first fiber layer by the following method is, for example, 3.0 mg or less, particularly 2.0 mg or less, and more particularly 1.0 mg or less. If the amount of fluff shedding exceeds 3.0 mg, when used in an absorbent article, fluff may adhere to the user's skin or clothing during use, or the surface fluffing may be noticeable, making the nonwoven fabric unsuitable for use in absorbent articles. Furthermore, the lower the amount of fluff shedding, the more firmly the fibers in the first fiber layer are entangled, resulting in a smoother surface. The amount of fluff shedding can be used to determine the entanglement state of the fibers in the first fiber layer.

[0097] (Method for measuring the amount of fluff shedding) a) A disk (70 mm diameter, 350 g) covered with urethane foam (manufactured by Inoac Corporation, trade name Malt Filter MF-30, ester-based polyurethane, cell count 30, average cell diameter 410 μm, mean coefficient of friction (MIU) 0.69, mean coefficient of friction variation (MMD) 0.043, thickness 5 mm) is attached to a rotating shaft so that the rotating shaft is positioned 20 mm away from the center of the disk. b) The same urethane foam as above is laid on the table, and the nonwoven fabric is fixed on the table so that the first fiber layer of the nonwoven fabric is the exposed surface. c) Place the disk on the nonwoven fabric, with the only load applied to the nonwoven fabric being the disk's own weight. d) Rotate the rotating shaft and rotate the disk over the nonwoven fabric. 10 sets of rotations are performed, each set consisting of two rotations clockwise and two rotations counterclockwise. The rotation speed is approximately 3 seconds per rotation. e) After three sets of rotation, collect the fibers that have fallen off the nonwoven fabric and adhered to the surface of the urethane foam covering the disk. f) The above steps a) to e) are carried out for n=3 pieces of nonwoven fabric. The mass of the fallen fibers is measured for each of the three pieces of nonwoven fabric, and the average value is taken as the amount of fallen fluff (mg). Instead of the urethane foam, the amount of shedding may be measured using another urethane foam, as long as the number of cells, average cell diameter, MIU, MMD, and thickness are different by ±25%. If the amount of shedding measured using such another urethane foam is within the above range, the measured amount of shedding is considered to be measured using the specific urethane foam.

[0098] The nonwoven fabric of this embodiment may exhibit an absorption time of, for example, 35 seconds or less, particularly 33 seconds or less, and more particularly 30 seconds or less, when measured for a sanitary napkin using the method described in the Examples. The lower limit of the absorption time may be, for example, 5 seconds. The shorter the absorption time, the less discomfort the user feels when liquid (e.g., vaginal discharge, menstrual blood) is discharged.

[0099] When the amount of wetback of the nonwoven fabric of this embodiment is measured using a sanitary napkin as described in the Examples, it may be, for example, 0.35 g or less, particularly 0.33 g or less, and more particularly 0.30 g or less. The lower limit of the amount of wetback may be, for example, 0 g. The smaller the amount of wetback, the less wet the user feels during use.

[0100] The nonwoven fabric of this embodiment may exhibit an MMD in the MD direction of 0.0010 to 0.0090, particularly 0.0020 to 0.0080, and more particularly 0.0030 to 0.0070, when the mean coefficient of friction variation (MMD) of the surface of the first fiber layer is measured as described in the Examples. The nonwoven fabric of this embodiment may also exhibit an MMD in the CD direction of the surface of the first fiber layer of 0.0010 to 0.0120, particularly 0.0020 to 0.0110, and more particularly 0.0030 to 0.0100. The nonwoven fabric of this embodiment may also exhibit an average value of the MMD in the MD direction and the MMD in the CD direction of the surface of the first fiber layer of 0.0030 to 0.0110, particularly 0.0040 to 0.0100, and more particularly 0.0050 to 0.0090. If the MMD value is within the above range, a smoother feel is likely to be obtained.

[0101] In the nonwoven fabric of this embodiment, when either or both of the first and second hydrophilic fibers are synthetic fibers containing a hydrophilic fiber treatment agent, the average coefficient of friction (MIU) of the surface of the first fiber layer, as described in the Examples, may be measured in the MD direction and may be 0.170 to 0.300, particularly 0.175 to 0.295, and more particularly 0.180 to 0.290. Furthermore, in the nonwoven fabric of this embodiment, when either or both of the first and second hydrophilic fibers are synthetic fibers containing a hydrophilic fiber treatment agent, the MIU of the surface of the first fiber layer in the CD direction may be 0.180 to 0.300, particularly 0.185 to 0.295, and more particularly 0.190 to 0.290. As mentioned above, synthetic fibers containing hydrophilic fiber treatment agents are less likely to become entangled by liquid flow (especially water flow) than cellulosic fibers, and because the fibers have a high degree of freedom in nonwoven fabrics, they are more likely to deform when force is applied, which tends to result in a higher MIU than nonwoven fabrics made with cellulosic fibers.

[0102] (Application) The nonwoven fabric described as the first embodiment is for absorbent articles, and is therefore suitable for use as a component of absorbent articles such as disposable diapers, sanitary napkins, incontinence pads, and panty liners. The nonwoven fabric of this embodiment is particularly suitable for use as a component that comes into direct contact with human skin, and can be used, for example, as a top sheet for absorbent articles. The nonwoven fabric of this embodiment may also be provided in a state where it is incorporated into an absorbent article as, for example, a top sheet.

[0103] The second fiber layer of the nonwoven fabric of this embodiment can function as a diffusion sheet. A diffusion sheet is located between the top sheet and absorbent body in an absorbent article, and serves to diffuse bodily fluid from the top sheet and transfer it to the absorbent body. The second fiber layer constituting the nonwoven fabric of this embodiment is located on the side farthest from the user's skin (i.e., the side closer to the absorbent body) and contains a higher proportion of hydrophilic fibers. Therefore, when this layer draws in bodily fluid and transfers it to the absorbent body, the bodily fluid is easily diffused in the surface direction of the second fiber layer. Therefore, if the nonwoven fabric of this embodiment is used as a top sheet, there may be no need to provide a diffusion sheet, and the number of components in the absorbent article can be reduced.

[0104] (Second embodiment) Next, a method for producing the nonwoven fabric of the first embodiment will be described as a second embodiment. The manufacturing method of this embodiment is as follows: A method for manufacturing a nonwoven fabric for absorbent articles, the nonwoven fabric comprising a first fiber layer and a second fiber layer, the first fiber layer forming one surface of the nonwoven fabric, the second fiber layer being in contact with the other surface of the nonwoven fabric, and the first fiber layer being positioned closer to the skin of a user, comprising: a step of preparing a first fiber web containing adhesive fibers in an amount of 40% by mass or more and 75% by mass or less and first hydrophilic fibers in an amount of 25% by mass or more and 60% by mass or less, based on the total mass of the first fiber web; preparing a second fiber web containing second hydrophilic fibers in an amount of 70% by mass or more and 100% by mass or less, based on the total mass of the second fiber web; a bonding step of bonding the fibers of the first fiber web together with the adhesive fibers; a lamination step of laminating the first fiber web and the second fiber web after the bonding step to obtain a laminated fiber web; an entanglement step of entangling the fibers of the first fiber web and the second fiber web of the laminated fiber web to integrate them together, the entanglement step includes a hydroentanglement treatment in which a water stream is sprayed on the side of the second fiber web to entangle the fibers, and then a water stream is sprayed on the side of the first fiber web to entangle the fibers, and in the hydroentanglement treatment, a total energy E1 of the water stream sprayed on the side of the first fiber web is higher than a total energy E2 of the water stream sprayed on the side of the second fiber web, and a value of the ratio of E1 to E2 (E1 / E2) is 2.5 or more and 12.0 or less, In this method for producing a nonwoven fabric for absorbent articles, the first fiber web becomes the first fiber layer, and the second fiber web becomes the second fiber layer.

[0105] Both the first and second fiber webs may be produced by known methods. The first and second fiber webs may be in any form, such as a parallel web, a cross web, a carded web (e.g., a semi-random web, or a random web), an air-laid web, or a wet-laid web. When the first fiber web is a parallel web, the surface of the nonwoven fabric tends to be smoother. When the second fiber web is a parallel web, the fibers are oriented in one direction, making them more likely to be entangled with the constituent fibers of the first fiber layer. Therefore, when the basis weight of the second fiber web is small, making the second fiber web a parallel web tends to promote integration of the first and second fiber webs. The form of the second fiber web may be the same as or different from the form of the first fiber web. When the forms are the same, the fibers of each web are similarly oriented, making it easier for the layers to be entangled.

[0106] In the manufacturing method of this embodiment, the first fiber web is subjected to a bonding step, in which the fibers of the first fiber web are bonded together by the adhesive fibers. The bonding treatment may be, for example, a heat treatment (thermal bonding treatment). According to the heat treatment, the component with the lowest melting point (thermal bonding component) among the resin components constituting the adhesive fibers melts or softens by heat during the heat treatment, thereby bonding the fibers constituting the fiber web together. The heat treatment may be, for example, a hot air processing treatment in which hot air is blown, a heat roll processing (e.g., a hot embossing roll processing), or a heat treatment using infrared rays. The hot air processing treatment is preferred because it tends to improve the texture of the nonwoven fabric. The hot air processing treatment may be carried out using a device that blows hot air at a predetermined temperature onto the fiber web, such as a hot air penetration type heat treatment machine or a hot air blowing type heat treatment machine.

[0107] When the bonding treatment is a hot air processing treatment, the hot air may be blown multiple times. When the hot air is blown multiple times, it is preferable that the temperature of the hot air blown the second time is higher than the temperature of the hot air blown the first time.

[0108] When the bonding treatment is a hot air processing treatment, the hot air speed may be, for example, 0.1 m / min to 3.0 m / min, particularly 0.2 m / min to 2.5 m / min, more particularly 0.3 m / min to 2.0 m / min. If the hot air speed is too low, the fibers may not be bonded well to each other throughout the fiber web, whereas if it is too high, unbonded fibers may be blown away by the hot air, making it difficult to obtain a uniform texture and reducing the smoothness of the nonwoven fabric.

[0109] The heat treatment temperature may be the temperature at which the component (thermal adhesive component) with the lowest melting point among the resin components constituting the adhesive fiber softens or melts, for example, a temperature equal to or higher than the melting point of that component. For example, if the component with the lowest melting point among the resin components constituting the adhesive fiber is high-density polyethylene, hot air at a temperature of 130°C or higher and 150°C or lower may be blown when hot air processing is performed. For example, if the component with the lowest melting point among the resin components constituting the adhesive fiber is ethylene-acrylic acid copolymer, hot air at a temperature of 90°C or higher and 140°C or lower may be blown, particularly hot air at a temperature of 95°C or higher and 130°C or lower, and more particularly hot air at a temperature of 100°C or higher and 120°C or lower may be blown when hot air processing is performed. Furthermore, taking into consideration the texture of the resulting nonwoven fabric, the heat treatment temperature is preferably at least 0°C and not more than 5°C higher than the melting point or softening point of the thermal adhesive component, more preferably at least 1°C and not more than 4°C higher, and even more preferably at least 2°C and not more than 3°C higher.

[0110] The bonding treatment may be by irradiation with an electron beam or the like, or ultrasonic welding. These bonding treatments also allow the resin component constituting the adhesive fiber to bond the fibers together.

[0111] In the manufacturing method of this embodiment, a lamination step is performed in which a first fiber web that has been bonded in the bonding step is laminated with a separately prepared second fiber web to obtain a laminated fiber web. The first fiber web that has been bonded has a certain degree of integrity due to the fibers being bonded to each other, and can therefore be called a thermally bonded nonwoven fabric.

[0112] The manufacturing method according to an embodiment of the present invention may include a cooling step after the bonding step and before the entangling step. That is, a cooling step for cooling the first fiber web and / or the laminated fiber web may be performed after the bonding step and before the laminating step, and / or after the first fiber web and the second fiber web are laminated and before the entangling step. Examples of cooling methods include air cooling and water cooling. If the first fiber web is not sufficiently cooled after the bonding step, the adhesive component of the adhesive fiber may be in a softened state. If the laminated fiber web is subjected to the entangling step in this state, the bonded portions may be prone to peeling, and the nonwoven fabric may be prone to fuzzing.

[0113] In this embodiment, after the bonding step, the first fiber web is subjected to the entanglement step together with the second fiber web without being wound onto a roll. This facilitates entanglement of the fibers. This is because, while the bulk of the first fiber web tends to decrease once it is wound onto a roll after the bonding step, the greater the bulk of the first fiber web, the more easily voids are formed between the fibers for entanglement with the second fiber web, and the more easily entanglement progresses.

[0114] The entanglement process is, for example, a needle punch process or a high-pressure fluid flow (particularly a water flow) entanglement process. In a high-pressure fluid flow process, the high-pressure fluid is, for example, a high-pressure gas such as compressed air or a high-pressure liquid such as high-pressure water. In the production of nonwoven fabrics, a water flow entanglement process using high-pressure water as the high-pressure fluid is often used, and in this embodiment, the water flow entanglement process is preferably used from the viewpoints of ease of implementation and ease of entanglement of hydrophilic fibers. Below, an entanglement process using high-pressure water (hereinafter simply referred to as "water flow") as the high-pressure fluid will be described.

[0115] The hydroentanglement treatment is carried out, for example, by spraying a water stream at a pressure of 1 MPa to 15 MPa from a nozzle having orifices with a hole diameter of 0.05 mm to 0.5 mm, spaced at intervals of 0.3 mm to 1.5 mm. The water pressure is preferably 1 MPa to 10 MPa, more preferably 1 MPa to 7 MPa, and particularly preferably 1 MPa to 6 MPa.

[0116] In this embodiment, the hydroentanglement treatment may be performed by spraying water onto the surfaces of the second and first fiber webs of the laminated fiber webs (i.e., both surfaces of the laminated fiber webs). In this case, the water pressure of the water jet sprayed onto the surface of the first fiber web may be higher than the water pressure of the water jet sprayed onto the surface of the second fiber web. Furthermore, it is preferable to spray the water jet onto the first fiber web more frequently than onto the second fiber web. This hydroentanglement treatment makes it easier to obtain a nonwoven fabric in which the first and second fiber layers have φ1 and φ2 within the above-mentioned predetermined ranges, respectively, and the relationship φ1 > φ2 is satisfied.

[0117] Since both the first and second fiber webs contain hydrophilic fibers that are easily entangled when sprayed with water, in this embodiment, the degree of entanglement of the hydrophilic fibers is controlled to obtain a desired nonwoven fabric. Specifically, the degree of entanglement is controlled by controlling the water pressure and the number of sprays so that the action of the water flow on the second fiber web is smaller than the action of the water flow on the first fiber web, i.e., by reducing the water flow energy input to the second fiber web.

[0118] Because the second fiber web contains a higher proportion of hydrophilic fibers, excessive water flow on the fiber web can cause excessive entanglement of the fibers. As a result, loops of the second hydrophilic fibers with a small radius of curvature can appear on the surface of the first fiber layer, resulting in a poor tactile feel. Therefore, in this embodiment, the water flow is increased on the first fiber web, which contains adhesive fibers and is therefore less susceptible to entanglement by water flow overall. This allows the hydrophilic fibers in the two fiber webs to be sufficiently entangled while preventing excessive entanglement.

[0119] In this embodiment, the water pressure of the water stream sprayed onto the second fiber web may be, for example, 1 MPa to 10 MPa, in particular, 1 MPa to 8 MPa. The number of times the water stream is sprayed onto the second fiber web may be, for example, 1 to 3 times. The water pressure of the water stream sprayed onto the first fiber web may be, for example, 1 MPa to 15 MPa, in particular, 1 MPa to 10 MPa. The number of times the water stream is sprayed onto the first fiber web may be, for example, 2 to 4 times.

[0120] The difference in water pressure between the second fibrous web and the first fibrous web may be, for example, 1 MPa to 10 MPa, particularly 1 MPa to 8 MPa. The number of times the water is sprayed onto the first fibrous web may be, for example, 1 to 4 times more, particularly 1 to 3 times more, than that onto the second fibrous web.

[0121] The hydroentanglement treatment may be carried out by first spraying a water stream a predetermined number of times onto the second fiber web side, and then spraying a water stream a predetermined number of times onto the first fiber web side. This order allows the second hydrophilic fibers in the second fiber web to form a base for entanglement, and even if a water stream with higher water pressure is sprayed from the first fiber web side, scattering of fibers due to the water stream is reduced, thereby preventing the nonwoven fabric from becoming unevenly densified.

[0122] The hydroentanglement treatment may be carried out by placing the fiber web on a support and spraying a water stream onto the support. If the surface of the nonwoven fabric is flat and has no irregularities, the support should have an open area of ​​0.2 mm 2 It is preferable to use a support that does not have openings exceeding 100 mesh and that does not have projections or patterns formed thereon. For example, it is preferable to use a plain woven support having a mesh size of 80 mesh or more and 100 mesh or less.

[0123] The energy (E) applied to the fiber web by the jetted water stream can be calculated using the following formula: When jetting multiple times under different conditions, such as the number of nozzle orifices and water pressure, the total energy E1 and E2 should be calculated for each jet and the sum of these should be used as E1 and E2.

[0124] E=W×N×T / (M / 1000×U×60) / 1000 E: Energy applied per 1 kg of fiber web per 1 m width per hour (kWh / kg / m) W: Power (W) of the fluid (water in this embodiment) per nozzle orifice N: Number of orifices per 1m width in the nozzle T: Number of injections M: Basis weight of the target for hydroentanglement treatment (g / m 2 ) U: Conveying speed (m / min)

[0125] W in the above formula (the power of the fluid per nozzle orifice) can be calculated using the following formula. W=P1×(F / 100)×0.163 W: Power of the fluid per nozzle orifice (W) P1: Water pressure (kgf / cm 2 ) F: Flow rate of water discharged from one orifice of the nozzle (cm 3 / min)

[0126] In the above formula, F (the flow rate of water discharged from one orifice of the nozzle) is calculated by the following formula. F=S×V F: Flow rate of water discharged from one orifice of the nozzle (cm 3 / min) S: Area of ​​fluid discharged from one orifice of the nozzle (mm 2 ) V: Flow velocity of the fluid discharged from the nozzle (m / min)

[0127] V in the above formula (flow velocity of the fluid discharged from the nozzle) can be calculated by the following formula. V = (20 × g × (P1 - P2) / ρ) 1 / 2 ×60 V: Flow velocity of the fluid discharged from the nozzle (m / min) g:Gravity acceleration, 9.8m / s 2 P1: Water pressure (kgf / cm 2 ) P2: Atmospheric pressure (kgf / cm 2 ) ρ: Fluid density (g / cm 3 ) Details of the method for determining E etc. are described in Japanese Patent No. 4893256.

[0128] The ratio of E1 to E2 (E1 / E2) may be 2.7 or more and 11.0 or less, and particularly 3.0 or more and 10.0 or less.

[0129] E1 is preferably 0.03 kWh / kg / m or more and 3.50 kWh / kg / m or less, and more preferably 0.05 kWh / kg / m or more and 3.30 kWh / kg / m or less. When E1 is within the above range, φ1 is promoted to be larger and φ2 is promoted to be smaller, the first hydrophilic fibers in the first fiber layer are promoted to be more migrated toward the second fiber layer, and fluffing and shedding are further reduced. In addition, a hydrophilic gradient is formed in which the proportion of hydrophilic fibers gradually increases from the first fiber layer to the second fiber layer, and the amount of liquid return can be reduced. E2 is preferably 0.01 kWh / kg / m or more and 0.50 kWh / kg / m or less, and more preferably 0.03 kWh / kg / m or more and 0.40 kWh / kg / m or less. When E2 is within the above range, the first fiber layer and the second fiber layer can be firmly entangled without impairing the texture of the nonwoven fabric.

[0130] When hydroentangling is performed in the entangling step, a drying step may be performed after the entangling step. The drying step can be performed, for example, by a hot air processing step in which hot air is blown. The temperature of the drying step may be lower than the softening or melting temperature of the adhesive component (thermal adhesive component) of the adhesive fiber contained in the first fiber web. The temperature of the drying step may be, for example, 10°C or more lower than the melting point or softening point of the thermal adhesive component, particularly 15°C or more lower, and more particularly 20°C or less lower. By not softening or melting the adhesive fiber after the entangling step, a nonwoven fabric in which the fibers in the second fiber layer are not bonded to each other can be obtained. To obtain such a nonwoven fabric, it is preferable to perform not only the drying step but also processing steps (e.g., dyeing) of the laminated fiber web or nonwoven fabric performed after the entangling step at a temperature lower than the softening or melting temperature of the adhesive component of the adhesive fiber contained in the first fiber web.

[0131] If the second fibrous web contains adhesive fibers, the fibers may be bonded to each other using the adhesive fibers of the second fibrous web (hereinafter referred to as "second adhesive fibers" to distinguish them from the adhesive fibers contained in the first fibrous web) after the entangling step (post-entangling bonding step). In particular, it is preferable to set the melting point of the second adhesive fibers lower than the melting point of the adhesive component of the adhesive fibers contained in the first fibrous web (hereinafter referred to as "first adhesive fibers" to distinguish them from the second adhesive fibers), and to melt the adhesive component of the second adhesive fibers at a temperature lower than the melting temperature of the adhesive component of the first adhesive fibers to bond the fibers to each other. This suppresses re-melting or softening and solidification of the first adhesive fibers, preventing the nonwoven fabric from becoming hard.

[0132] In a manufacturing method that involves hydroentanglement, the adhesive fibers may be synthetic fibers coated with the primary hydrophilic fiber treatment. Such adhesive fibers exhibit hydrophilicity during hydroentanglement, promoting entanglement of the fibers. After hydroentanglement, the fiber treatment is removed, resulting in a hydrophobic nonwoven fabric that exhibits the advantages of hydrophobic fibers in terms of touch, wet-back, and the like, as described above. Furthermore, in a manufacturing method that involves hydroentanglement, if the first and second hydrophilic fibers are synthetic fibers treated with a hydrophilic fiber treatment, it is preferable to use a durable hydrophilic fiber treatment agent so that the hydrophilicity, as measured by the sedimentation rate, does not decrease after hydroentanglement. This is because synthetic fibers coated with a hydrophilic fiber treatment exhibit hydrophobicity and are unable to function as hydrophilic fibers if the hydrophilic fiber treatment agent is removed. [Example]

[0133] The nonwoven fabric and the method for producing the same according to the present disclosure will be described below with reference to examples. The fibers used to produce the nonwoven fabrics of the Examples and Comparative Examples are shown below. <Adhesive fiber 1> A concentric core-sheath composite fiber (NBF(H) (product name) manufactured by Daiwabo Co., Ltd.) with a core of polypropylene (melting point: approximately 160°C) and a sheath of high-density polyethylene (melting point: approximately 133°C), a core-sheath ratio (volume ratio of core component to sheath component) of 50 / 50, and the core and sheath components arranged concentrically, with a fineness of 1.0 dtex (fiber diameter 11.8 μm) and a fiber length of 38 mm.

[0134] <Adhesive fiber 2> A concentric core-sheath composite fiber with a core of polypropylene (melting point: approximately 160°C) and a sheath of high-density polyethylene (melting point: approximately 133°C), a core-sheath ratio (volume ratio of core component to sheath component) of 50 / 50, in which the core component and sheath component are concentrically arranged, a fineness of 1.0 dtex (fiber diameter 11.8 μm), and a fiber length of 38 mm, and an alkyl phosphate-based primary hydrophilic fiber treatment agent is applied to the fiber surface at a rate of 0.30 mass%.

[0135] <Adhesive fiber 3> A concentric core-sheath composite fiber with a core of polypropylene (melting point: approximately 160°C) and a sheath of high-density polyethylene (melting point: approximately 133°C), a core-sheath ratio (volume ratio of core component / sheath component) of 50 / 50, in which the core component and sheath component are concentrically arranged, a fineness of 2.2 dtex (fiber diameter 17.5 μm), and a fiber length of 51 mm, and an alkyl phosphate-based primary hydrophilic fiber treatment agent is applied to the fiber surface at a rate of 0.30 mass%.

[0136] <Hydrophilic fiber A> Viscose rayon fiber (BH (trade name) manufactured by Daiwabo Rayon Co., Ltd.) with a fineness of 0.9 dtex (fiber diameter 8.2 μm), a fiber length of 38 mm, a chrysanthemum-shaped fiber cross section, and a sedimentation rate of 14 seconds <Hydrophilic fiber B> Viscose rayon fiber (BH (trade name) manufactured by Daiwabo Rayon Co., Ltd.) with a fineness of 0.6 dtex (fiber diameter 7.1 μm), a fiber length of 32 mm, a chrysanthemum-shaped cross section, and a sedimentation velocity of 9.1 seconds

[0137] <Hydrophilic fiber C> Semi-dull viscose rayon fiber (CD (product name) manufactured by Daiwabo Rayon Co., Ltd.) with a fineness of 1.1 dtex (fiber diameter 9.7 μm), a fiber length of 38 mm, a chrysanthemum-shaped fiber cross section, and a sedimentation velocity of 7.7 seconds <Hydrophilic fiber D> Semi-dull viscose rayon fiber (CD (trade name) manufactured by Daiwabo Rayon Co., Ltd.) with a fineness of 1.4 dtex (fiber diameter 11.4 μm), a fiber length of 44 mm, a chrysanthemum-shaped fiber cross section, and a sedimentation velocity of 5.9 seconds

[0138] <Hydrophilic Fiber E> Viscose rayon fiber (manufactured by Daiwabo Rayon Co., Ltd.) with a fineness of 1.4 dtex (fiber diameter 11.4 μm), a fiber length of 44 mm, a chrysanthemum-shaped fiber cross section, a higher titanium oxide content than hydrophilic fiber D, and a sedimentation rate of 5.9 seconds. <Hydrophilic fiber F> Semi-dull viscose rayon fiber (CD (product name) manufactured by Daiwabo Rayon Co., Ltd.) with a fineness of 3.3 dtex (fiber diameter 15.4 μm), a fiber length of 51 mm, a chrysanthemum-shaped fiber cross section, and a sedimentation velocity of 4.8 seconds

[0139] <Hydrophilic Fiber G> Average fineness 2.5 dtex (average fiber diameter 13.0 μ m), an average fiber length of 30 mm, and a sedimentation velocity of 8.1 seconds (Marusan Sangyo Co., Ltd., MSD (product name)) <Hydrophilic Fiber I> Durably hydrophilic polyethylene terephthalate fiber (manufactured by Toray Industries, Inc.) with a fineness of 1.6 dtex (fiber diameter 12 μm), fiber length of 51 mm, and a sedimentation velocity of 2.4 seconds, with a hydrophilic fiber treatment applied to the fiber surface.

[0140] The initial settling velocity and the settling velocity after washing for adhesive fibers 2 and 3 and hydrophilic fiber I are shown in Table 1. The settling velocity after washing is the settling velocity measured after the fibers were washed three times with warm water at 40°C for 2 minutes each.

[0141] [Table 1]

[0142] From Table 1, it was confirmed that the hydrophilic fiber treatment agents applied to adhesive fibers 2 and 3 were primary hydrophilic, and that the hydrophilic fiber treatment agent applied to hydrophilic fiber I was durable.

[0143] <Production of Nonwoven Fabric of Example 1> 60% by mass of adhesive fiber and 40% by mass of hydrophilic fiber A as the first hydrophilic fiber were mixed, and the mixture was carded using a parallel carding machine to a target density of about 20 g / m 2 A first fibrous web was prepared. This first fiber web was heated at 135°C for approximately 5 seconds using a hot air penetration type heat treatment machine, and the fibers were thermally bonded (bonded) to each other by the sheath component of the adhesive fiber to obtain a thermally bonded nonwoven fabric that would become the first fiber layer.

[0144] Using hydrophilic fiber A as the second hydrophilic fiber, a parallel carding machine was used to obtain a target weight of approximately 30 g / m 2 A second fibrous web was produced by laminating the obtained second fibrous web on the surface side (air surface side) of the first fibrous layer that had been exposed to hot air to obtain a laminated fibrous web.

[0145] The above-described laminated fiber web was placed on a plain weave net with a warp diameter of 0.132 mm, a weft diameter of 0.132 mm, and a mesh count of 90. While the laminated fiber web was traveling at a speed of 4 m / min, a water stream at a water pressure of 3.5 MPa was sprayed once onto the surface of the laminated fiber web facing the second fiber web using a water supplier. The nozzle of the water supplier had orifices with a hole diameter of 0.12 mm spaced 0.6 mm apart. The distance between the surface of the laminated fiber web and the orifices was 15 mm. Subsequently, a water stream at a water pressure of 5.0 MPa was sprayed twice onto the surface of the laminated fiber web facing the first fiber layer using the same water supplier. The total energy E1 of the water stream sprayed onto the first fiber web side was 1.55 kWh / kg / m, and the total energy E2 of the water stream sprayed onto the second fiber web side was 0.45 kWh / kg / m, resulting in a ratio of E1 to E2 (E1 / E2) of 3.4.

[0146] The layered fiber web after the hydroentanglement treatment was subjected to a drying treatment at 80°C using a hot air penetration type heat treatment machine, thereby obtaining a nonwoven fabric with a two-layer layered structure of Example 1, in which the first fiber web became the first fiber layer and the second fiber web became the second fiber layer.

[0147] <Production of Nonwoven Fabric of Example 2> A nonwoven fabric of Example 2 was obtained in the same manner as in Example 1, except that the fiber blend ratio of the first fiber web was 50% by mass of adhesive fiber and 50% by mass of hydrophilic fiber A.

[0148] <Production of nonwoven fabric of Example 3> A nonwoven fabric of Example 3 was obtained in the same manner as in Example 1, except that the fiber blend ratio of the first fiber web was 70 mass % adhesive fiber and 30 mass % hydrophilic fiber A.

[0149] <Production of nonwoven fabrics of Examples 4 to 8 and 10 to 14> Nonwoven fabrics of Examples 4 to 8 and 10 to 16 were obtained in the same manner as in Example 1, except that the types and blend ratios of fibers used in the first fiber web and the types of fibers used in the second fiber web were as shown in Tables 4 to 6.

[0150] <Production of nonwoven fabric of Example 9> The types and blend ratios of fibers used in the first fiber web and the types of fibers used in the second fiber web were as shown in Tables 4 to 6, and the procedure was the same as in Example 1, except that a water stream with a water pressure of 5.0 MPa was sprayed four times onto the first fiber web side. In producing this nonwoven fabric, the total energy E1 of the water stream sprayed onto the first fiber web side was 3.10 kWh / kg / m, the total energy E2 of the water stream sprayed onto the second fiber web side was 0.45 kWh / kg / m, and the ratio of E1 to E2 (E1 / E2) was 6.9.

[0151] <Production of Nonwoven Fabric of Comparative Example 1> A nonwoven fabric of Comparative Example 1 was obtained in the same manner as in Example 1, except that the hydroentanglement treatment was carried out by spraying a water stream at a water pressure of 5.0 MPa twice onto the surface of the laminated fiber web facing the second fiber web, and then spraying a water stream at a water pressure of 3.5 MPa once onto the surface of the laminated fiber web facing the first fiber web. E1 was 0.45 kWh / kg / m, E2 was 1.55 kWh / kg / m, and the ratio of E1 to E2 (E1 / E2) was 0.3.

[0152] <Production of Nonwoven Fabric of Comparative Example 2> A nonwoven fabric of Comparative Example 2 was obtained in the same manner as in Example 1, except that the hydroentanglement treatment was performed by spraying a water stream at a water pressure of 2.0 MPa once onto the surface of the laminated fiber web facing the second fiber web, and then spraying a water stream at a water pressure of 3.0 MPa once onto the surface of the laminated fiber web facing the first fiber web. E1 was 0.36 kWh / kg / m, E2 was 0.19 kWh / kg / m, and the ratio of E1 to E2 (E1 / E2) was 1.9.

[0153] <Production of Nonwoven Fabric of Comparative Example 3> A nonwoven fabric of Comparative Example 3 was obtained in the same manner as in Example 1, except that the fiber blend ratio of the first fiber web was 80 mass % adhesive fiber and 20 mass % hydrophilic fiber A.

[0154] <Production of Nonwoven Fabric of Comparative Example 4> 60% by mass of adhesive fiber and 40% by mass of hydrophilic fiber A as the first hydrophilic fiber were mixed, and the mixture was carded using a parallel carding machine to a target density of about 20 g / m 2 A first fiber web that would become the first fiber layer was prepared in this manner. Using hydrophilic fiber A as the second hydrophilic fiber, a parallel carding machine was used to obtain a target weight of approximately 30 g / m 2 A second fibrous web was prepared by laminating the obtained second fibrous web on the first fibrous web to obtain a laminated fibrous web.

[0155] The above-described laminated fiber web was placed on a plain weave net with a warp diameter of 0.132 mm, a weft diameter of 0.132 mm, and a mesh count of 90. While the laminated fiber web was traveling at a speed of 4 m / min, a water stream at a water pressure of 3.5 MPa was sprayed once onto the surface of the laminated fiber web facing the second fiber web using a water supplier. The nozzle of the water supplier had orifices with a hole diameter of 0.12 mm spaced 0.6 mm apart. The distance between the surface of the laminated fiber web and the orifices was 15 mm. Then, a water stream at a water pressure of 5.0 MPa was sprayed twice onto the surface of the laminated fiber web facing the first fiber web using the same water supplier. E1 was 1.55 kWh / kg / m, E2 was 0.45 kWh / kg / m, and the ratio of E1 to E2 (E1 / E2) was 3.4.

[0156] The layered fiber web after the hydroentanglement treatment was heated at 135°C for approximately 5 seconds using a hot air penetration type heat treatment machine, and dried. At the same time, the fibers were thermally bonded (adhesive treatment) to each other using the sheath component of the adhesive fiber, thereby obtaining a nonwoven fabric with a two-layer laminate structure of Comparative Example 4.

[0157] <Production of Nonwoven Fabric of Comparative Example 5> 24% by mass of adhesive fiber and 76% by mass of hydrophilic fiber A were mixed and carded using a parallel carding machine to a target weight of approximately 50 g / m.2 A fiber web was prepared. This fiber web was heated at 135°C for about 5 seconds using a hot air penetration type heat treatment machine, and the fibers were thermally bonded (bonded) by the sheath component of the adhesive fiber to obtain a thermally bonded nonwoven fabric.

[0158] The thermally bonded nonwoven fabric described above was placed on a plain weave net with a warp diameter of 0.132 mm, a weft diameter of 0.132 mm, and a mesh count of 90. While the thermally bonded nonwoven fabric was advanced at a speed of 4 m / min, a water stream at a pressure of 3.5 MPa was sprayed once onto the surface of the thermally bonded nonwoven fabric that had been exposed to the hot air (the air side) using a water supplier. The nozzle of the water supplier had orifices with a hole diameter of 0.12 mm spaced 0.6 mm apart. The distance between the surface of the thermally bonded nonwoven fabric and the orifices was 15 mm. Subsequently, a water stream at a pressure of 5.0 MPa was sprayed twice onto the surface opposite the water stream using the same water supplier. The total energy E' of the water stream sprayed onto the air side was 0.45 kWh / kg / m, and the total energy E" of the water stream sprayed onto the side opposite the air side was 1.55 kWh / kg / m. The hydroentangled thermally bonded nonwoven fabric was then dried at 80° C. using a hot air penetration type heat treatment machine to obtain a single-layer nonwoven fabric of Comparative Example 5.

[0159] <Production of Nonwoven Fabric of Comparative Example 6> A nonwoven fabric of Comparative Example 6 was obtained in the same manner as in Comparative Example 5, except that the fiber content of the fiber web was 60 mass % adhesive fiber and 40 mass % hydrophilic fiber A.

[0160] <Production of Nonwoven Fabrics of Comparative Examples 7 and 8> The nonwoven fabrics of Comparative Examples 7 and 8 were obtained in the same manner as in Example 1, except that the type and blend ratio of fibers used in the first fiber web and the type of fibers used in the second fiber web were as shown in Table 6.

[0161] The nonwoven fabrics obtained in each of the Examples and Comparative Examples were evaluated as follows. The evaluation results are shown in Tables 2 to 6.

[0162] <Thickness and density of nonwoven fabric> The thickness of the nonwoven fabric was measured using a thickness gauge (THICKNESS GAUGE Model CR-60A (trade name) manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.) while a load of 294 Pa or 1.96 kPa was applied to the nonwoven fabric. The density of the nonwoven fabric was calculated based on the basis weight of the nonwoven fabric and the thickness of the nonwoven fabric measured by applying a load of 294 Pa.

[0163] <Strength and elongation> The strength and elongation were measured in accordance with JIS L 1913:2010 6.3. Using a constant-speed tension tensile tester, the tensile test was conducted under the conditions of a sample piece (nonwoven fabric) width of 5 cm, a grip spacing of 10 cm, and a tensile speed of 30±2 cm / min. The load value at break (tensile strength), elongation, and stress at 10% elongation were measured. The tensile test was conducted in the machine direction (MD) and cross direction (CD) of the nonwoven fabric as the tensile direction. The evaluation results were all expressed as the average of the values ​​measured for three samples.

[0164] <Smoothness (KES)> To evaluate smoothness, the mean coefficient of friction (MMD) was measured using a friction tester (KES-SE, Kato Tech Co., Ltd.). 5 cm × 10 cm nonwoven fabric specimens were prepared. Two specimens were prepared, one with the long side in the MD direction and the other with the long side in the CD direction. A piano wire sensor (Kato Tech Co., Ltd.) was used as the contact terminal of the measuring instrument. The specimen was fixed to the measurement table, and a contact terminal (25 g) was moved unidirectionally at a speed of 1.0 mm / sec over a distance of 30 mm on the surface of the first fiber layer of the specimen (the surface where the water jet was last sprayed in the case of a single-layer structure). The MMD was evaluated between points 5 mm and 25 mm from the starting point of the movement. Three measurements were performed on specimens with the long side in the MD direction, and three measurements on specimens with the long side in the CD direction. The average of the three measurements was used as the MMD in each direction. Furthermore, the average of the six measurements was calculated.

[0165] <Shedding> The shedding was evaluated by measuring the amount (mg) of fibers that fell off from the nonwoven fabric by the following method. a) A disk (70 mm diameter, 350 g) covered with urethane foam (manufactured by Inoac Corporation, trade name Malt Filter MF-30, ester-based polyurethane, cell count 30, average cell diameter 410 μm, mean coefficient of friction (MIU) 0.69, mean coefficient of friction variation (MMD) 0.043, thickness 5 mm) is attached to a rotating shaft so that the rotating shaft is positioned 20 mm away from the center of the disk. b) Place the same urethane foam as above on the table, and then fix the nonwoven fabric on top of it so that the first fiber layer of the nonwoven fabric is the exposed surface. For single-layer nonwoven fabrics, the surface that was last sprayed with water is the exposed surface. c) Place the disk on the nonwoven fabric, with the only load applied to the nonwoven fabric being the disk's own weight. d) Rotate the rotating shaft and rotate the disk over the nonwoven fabric. 10 sets of rotations are performed, each set consisting of two rotations clockwise and two rotations counterclockwise. The rotation speed is approximately 3 seconds per rotation. e) After three sets of rotation, collect the fibers that have fallen off the nonwoven fabric and adhered to the surface of the urethane foam covering the disk. f) The above steps a) to e) are carried out for n=3 pieces of nonwoven fabric. The mass of the fallen fibers is measured for each of the three pieces of nonwoven fabric, and the average value is taken as the amount of fallen fluff (mg). For nonwoven fabrics with a shedding amount of 3.0 mg or less, it can be said that shedding is effectively prevented.

[0166] <Absorbency (absorption time and amount of liquid returning)> When a nonwoven fabric was used as a top sheet of a sanitary napkin, the liquid absorption performance of the nonwoven fabric was evaluated. (1) The top sheet of a commercially available sanitary napkin (manufactured by Kao Corporation, product name "Lorrie Shiawase Suhada") was peeled off to expose the absorbent core, and a sample of the nonwoven fabric to be evaluated, cut to 220 mm x 80 mm (longitudinal x transverse), was placed on top of the absorbent core. The nonwoven fabric was positioned so that the first fiber layer was the exposed surface. For single-layer nonwoven fabrics, the surface onto which the water jet was last sprayed was the exposed surface.

[0167] A plate with an injection tube (a two-stage cylindrical plate with a height of 75 mm, an upper inner diameter of 25 mm, and a lower inner diameter of 10 mm) was placed on the first fiber layer, and 5 cc of artificial menstrual blood (viscosity 8 mPa s, temperature 37°C) was injected into the injection tube of the plate with the injection tube. The time (in seconds) required for the liquid to disappear from the surface of the nonwoven fabric (liquid absorption time) was measured. The artificial menstrual blood had a composition of 12.61 mass% glycerin, 84.88 mass% distilled water, 0.45 mass% CMC (sodium carboxymethylcellulose), 0.97 mass% NaCl (sodium chloride), 1.04 mass% Na2CO3 (sodium carbonate), and 0.06 mass% red powder.

[0168] (2) To measure the liquid absorption time, 10 minutes after the artificial menstrual blood was poured, 10 sheets of filter paper (manufactured by Toyo Roshi Kaisha, Ltd., trade name ADVANTEC (registered trademark) No. 2, 10 cm × 10 cm) were placed on the nonwoven fabric, and a weight with a mass of 1 kg (shape: square, 10 cm × 10 cm) was placed on the filter paper. 20 seconds after the weight was placed, the filter paper was removed, and the mass of the filter paper that had absorbed the artificial menstrual blood was measured. The mass of the filter paper before being placed on the nonwoven fabric was subtracted from this to calculate the amount of liquid return (g). Five samples of the nonwoven fabric to be evaluated were prepared, and the average values ​​of the liquid absorption time and the amount of liquid rewetted measured for each of the five samples were taken as the liquid absorption time and the amount of liquid rewetted of the nonwoven fabric. If the absorption time measured by the above method is 35 seconds or less, the nonwoven fabric can be said to have a good absorption rate, and if the amount of liquid wetting back is 0.35 g or less, the nonwoven fabric can be said to have good resistance to wetting back.

[0169] <Fiber curvature radius> The surface of the nonwoven fabric (fiber layer) to be measured was observed using a scanning electron microscope (SEM, accelerating voltage: 10.0 kV, magnification: 100x). In the SEM image, where the fiber curved semicircularly in a direction approximately parallel to the image plane, a circle was drawn along the semicircle, and the radius of the drawn circle was taken as the radius of curvature of the fiber. The radius of curvature was calculated using image analysis software "Micro Measure" (Scalar Corporation). For each SEM image, 10 values ​​were extracted from the measured radii of curvature, from the smallest to the tenth smallest.

[0170] This measurement and extraction was performed on five different SEM images, and the average value of a total of 50 values ​​was calculated and used as the radius of curvature of the fibers on the surface of the nonwoven fabric. If the number of measurable radius of curvatures on one SEM image is less than 10, all values ​​of the radius of curvature obtained from that image are extracted, and the average value is calculated by adding the values ​​of the radius of curvature measured and extracted using other SEM images to the number of SEM images and measuring and extracting the values ​​so that the total number is 50 or more.

[0171] Figure 1 shows an electron microscope photograph (SEM image) (magnification: 100) of the surface of the second fiber layer side of the nonwoven fabric produced in Example 1. For ease of understanding, in Figure 1, the circle drawn when measuring φ1 is shown by a white dashed line.

[0172] In Tables 2 to 6, for the single-layer nonwoven fabric, the radius of curvature measured on the surface onto which the water jet was last sprayed is φ1, and the radius of curvature measured on the opposite surface is φ2.

[0173] [Table 2]

[0174] [Table 3]

[0175] [Table 4]

[0176] [Table 5]

[0177] [Table 6]

[0178] As shown in Table 2, all of Examples 1 to 3 satisfied the conditions of φ1≧30 μm, φ2≦40 μm, and φ1>φ2, and exhibited a small CD MMD and a smooth feel. Furthermore, these Examples exhibited a relatively short absorption time (i.e., a high absorption rate) and a relatively small amount of liquid return, demonstrating good absorbency. In Examples 1 to 3, the fiber blend ratio of the first fiber layer was varied. No significant differences were observed in smoothness among these Examples. The amount of fluff shedding tended to increase as the proportion of adhesive fiber increased, indicating that the entanglement of hydrophilic fibers in the first and second fiber layers contributed to suppressing fluff shedding. The absorption time tended to increase as the proportion of adhesive fiber increased (i.e., as the proportion of hydrophilic fiber decreased).

[0179] In Comparative Example 1, the hydroentanglement treatment was carried out by spraying a water stream with higher water pressure twice on the second fiber layer side and a water stream with lower water pressure once on the first fiber layer side to entangle the fibers. In the nonwoven fabric of Comparative Example 1, φ1 was less than 30 μm. This is presumably because the hydrophilic fibers were more entangled due to the application of greater water jet energy to the second fiber layer, which contains a larger amount of hydrophilic fibers. As a result, the unevenness caused by the water jetting became more pronounced, and the MMD in the CD direction became larger.

[0180] The liquid absorption time of Comparative Example 1 was longer than that of Example 1. This is presumably because the hydrophilic fibers were more entangled, which increased the fiber density and reduced the interfiber voids that temporarily store liquid.

[0181] Furthermore, Comparative Example 1 showed a greater amount of fluff shedding compared to Example 1, which was different only in the hydroentanglement treatment conditions. This is presumably because in Comparative Example 1, entanglement of the fibers was more advanced, so that more of the hydrophilic fibers in the second fiber layer were exposed to the surface of the first fiber layer, resulting in more fibers being present on the surface of the first fiber layer and, therefore, more fibers shedding as fluff.

[0182] In Comparative Example 2, the water pressure during the hydroentanglement treatment was set lower than that used in the production of Example 1, and the number of jets was reduced to entangle the fibers. In the nonwoven fabric of Comparative Example 2, φ2 exceeded 40 μm, and φ1 was also relatively large. This means that the degree of entanglement of fibers during the hydroentanglement treatment was smaller than that of the Examples. Therefore, the amount of fluff shedding was large in Comparative Example 2. Furthermore, the liquid absorption time of Comparative Example 1 was longer than that of either Example. This is presumably because the degree of entanglement of the hydrophilic fibers between the first and second fiber layers was small, resulting in insufficient "communication" between the hydrophilic fibers of the two fiber layers, making it difficult for liquid to be drawn from the first fiber layer to the second fiber layer.

[0183] Comparative Example 3 is an example in which the proportion of adhesive fibers in the first fiber layer was the highest. This nonwoven fabric had a first fiber layer that was comparable in smoothness to the Examples, but the liquid absorption time of Comparative Example 3 was longer than that of any of the Examples. This is thought to be because the hydrophilic fibers in the first fiber layer presumably play a role in transferring liquid to the second fiber layer, and the proportion of hydrophilic fibers in the first fiber layer was low. Furthermore, Comparative Example 3 was thicker than the Examples, and the longer distance from the nonwoven fabric surface to the absorbent core presumably made it more difficult for liquid to be absorbed, which also affected the liquid absorption time.

[0184] Comparative Example 4 was produced by carrying out the entanglement step first and then the bonding step. In this comparative example, φ1 was less than 30 μm, and the degree of entanglement in the first fiber layer was greater than that in the examples. This is presumably because the laminated fiber web was subjected to the hydroentanglement treatment in a state in which the fibers in the first fiber layer were not bonded to each other, resulting in more advanced entanglement of the fibers. Comparative Example 4 showed the largest MMD in the CD direction among all the examples and comparative examples. This is presumably due to the more pronounced irregularities caused by the water jet spray.

[0185] Both Comparative Examples 5 and 6 have a single layer structure, with Comparative Example 5 containing more hydrophilic fibers and Comparative Example 6 containing more adhesive fibers. In Comparative Example 5, both φ1 and φ2 were small. This is thought to be due to the high proportion of hydrophilic fibers and the high degree of entanglement between the fibers. Therefore, no fluffing occurred. On the other hand, the amount of liquid return was relatively large. This is thought to be because the viscose rayon fiber used as the hydrophilic fiber in this example and the comparative example is itself absorbent and retains a certain amount of liquid when absorbing liquid, which is released when pressure is applied, which is one of the causes of liquid return. However, the high proportion of hydrophilic fibers also increases the total amount of liquid released.

[0186] In Comparative Example 6, the adhesive fibers were contained throughout the single layer, and the proportion of hydrophilic fibers was low, which is thought to have made it difficult for the fibers to be entangled by the hydroentanglement treatment. This resulted in a large φ2. Furthermore, the hydrophilic fibers were uniformly distributed throughout the layer, making it difficult to form a gradient in the proportion of hydrophilic fibers, resulting in a long absorption time.

[0187] Examples 4 to 7 and Comparative Example 8 differed from Example 1 in the fiber diameter of the hydrophilic fibers used, and Example 8 differed in the fiber diameters of the hydrophilic fibers and adhesive fibers from Example 1. Comparative Example 8 had a larger fiber diameter for the hydrophilic fibers, which increased their rigidity, making them less likely to bend during the hydroentanglement treatment, and had larger φ1 and φ2.

[0188] These examples show that the larger the fiber diameter of the hydrophilic fiber, the larger the average value (AVE) of the MD and CD MMDs. This is thought to be because the larger the fiber diameter, the fewer fibers make up a fiber layer with the same basis weight, resulting in a decrease in surface density. However, for the nonwoven fabric of Example 4, the AVE of MMD was actually larger. This is thought to be due to the small fiber diameter, which caused neps to form due to entanglement of fibers.

[0189] Furthermore, the larger the diameter of the hydrophilic fibers, the smaller the amount of liquid wetting. This is thought to be because the number of constituent hydrophilic fibers decreases, which reduces the amount of liquid they can hold. On the other hand, the larger the diameter of the hydrophilic fibers, the shorter the liquid absorption time. This is thought to be because the smaller number of fibers increases the voids between the fibers. Example 8, which had a large adhesive fiber fineness, showed a relatively large amount of fluff shedding. This is thought to be because the number of adhesive fibers constituting the fiber layer decreased as the adhesive fiber fineness increased, resulting in a corresponding decrease in the number of adhesive points.

[0190] In Comparative Example 7, the proportion of hydrophilic fibers in the first fiber layer was higher than in Example 1, and φ1 was less than 30 μm. This is thought to be because the hydrophilic fibers, which are prone to entanglement by water flow, had a relatively large "bent" due to entanglement and the hydrophilic fibers occupied a large portion of the fiber surface. Furthermore, Comparative Example 7 showed a relatively large amount of liquid return. This is thought to be because a large amount of hydrophilic fibers, which easily retain liquid, was present on the fiber surface.

[0191] In Example 9, the first fiber layer contained hydrophilic fibers in the same proportion as in Comparative Example 7, but the number of times the water jet was sprayed onto the first fiber layer was increased. In Example 9, φ1 was 30 μm or more, and the amount of liquid return was small. This is thought to be because the application of a large amount of water jet energy to the first fiber layer caused the hydrophilic fibers to move toward the inside of the nonwoven fabric, exposing adhesive fibers with a relatively large radius of curvature to the surface of the nonwoven fabric.

[0192] In Example 10, the hydrophilic fibers contained a larger amount of titanium oxide, and the MMD in all directions was smaller, especially in the CD direction, compared with Example 7. This is thought to be because the increased titanium oxide content slightly increased the rigidity of the hydrophilic fibers, slightly reducing entanglement, and therefore making it less likely for unevenness to occur due to the water jet spray.

[0193] Example 11 used cotton as the hydrophilic fiber, and its MMD was higher than that of Example 1, but its liquid absorption rate was lower than that of Example 1. This is thought to be because the cross section of cotton fibers is more irregular and has irregularities than that of rayon, and these irregularities form a relatively large number of interfiber voids.

[0194] Example 1 2 is The nonwoven fabrics used in Examples 1 and 2 were made using polyethylene terephthalate fibers ("hydrophilic synthetic fibers") coated with a hydrophilic fiber treatment agent in both the first and second fiber layers, and Examples 15 and 16 were made using hydrophilic synthetic fibers in one of the fiber layers. Example 12 had a low fiber density and was bulkier than Example 1. Example 12 also tended to exhibit a higher AVE of MMD than Example 1, and also tended to exhibit a higher MIU than other examples using cellulosic fibers as the first and second hydrophilic fibers. This is thought to be because hydrophilic synthetic fibers have a higher rigidity than rayon and are less likely to entangle with each other than rayon, resulting in a greater degree of freedom for the fibers in the nonwoven fabric.

[0195] On the other hand, although Examples 13 and 14 had lower fiber densities than Example 1, the AVE of MMD was lower than Example 12. This is thought to be because the inclusion of rayon, which is prone to entanglement due to water flow, in one of the fiber layers achieved a balance of entanglement between the rayon and the hydrophilic synthetic fiber.

[0196] (Aspect 1) A nonwoven fabric for absorbent articles comprising a first fiber layer and a second fiber layer, one surface of the first fiber layer forms a surface of the nonwoven fabric, and the other surface is in contact with the second fiber layer; the first fibrous layer includes adhesive fibers and first hydrophilic fibers; the first fiber layer contains the adhesive fiber in an amount of 40% by mass or more and 75% by mass or less and the first hydrophilic fiber in an amount of 25% by mass or more and 60% by mass or less, based on the total mass of the first fiber layer; the second fibrous layer includes second hydrophilic fibers; the second fiber layer contains the second hydrophilic fibers in an amount of 70% by mass or more and 100% by mass or less based on the total mass of the second fiber layer; In the first fiber layer, the fibers are bonded to each other by the adhesive fibers, the first fiber layer and the second fiber layer are integrated by entanglement of the fibers, the radius of curvature (φ1) of the fibers on the surface of the first fiber layer is 30 μm or more, the radius of curvature (φ2) of the fibers on the surface of the second fiber layer is 40 μm or less, and φ1>φ2 is satisfied; The first fiber layer is positioned closer to the user's skin. Nonwoven fabric for absorbent articles. (Aspect 2) The nonwoven fabric for absorbent articles of aspect 1, wherein the fiber diameter of the first hydrophilic fibers is 4 μm or more and 15 μm or less, the fiber diameter of the second hydrophilic fibers is 4 μm or more and 15 μm or less, and the fiber diameter of the adhesive fibers is 6 μm or more and 19 μm or less. (Aspect 3) 3. The nonwoven fabric for absorbent articles according to aspect 1 or 2, wherein the fibers in the second fiber layer are not bonded to each other. (Aspect 4) A nonwoven fabric for absorbent articles comprising a first fiber layer and a second fiber layer, one surface of the first fiber layer forms a surface of the nonwoven fabric, and the other surface is in contact with the second fiber layer; the first fibrous layer includes adhesive fibers and first hydrophilic fibers; the first fiber layer contains the adhesive fiber in an amount of 40% by mass or more and 75% by mass or less and the first hydrophilic fiber in an amount of 25% by mass or more and 60% by mass or less, based on the total mass of the first fiber layer; the second fibrous layer includes second hydrophilic fibers; the second fiber layer contains the second hydrophilic fibers in an amount of 70% by mass or more and 100% by mass or less based on the total mass of the second fiber layer; In the first fiber layer, the fibers are bonded to each other by the adhesive fibers, the first fiber layer and the second fiber layer are integrated by entanglement of the fibers, the fiber diameter of the first hydrophilic fibers is 4 μm or more and 15 μm or less, the fiber diameter of the second hydrophilic fibers is 4 μm or more and 15 μm or less, and the fiber diameter of the adhesive fibers is 6 μm or more and 19 μm or less; The amount of fluff shedding of the first fiber layer, measured according to the following method, is 3.0 mg or less. Nonwoven fabric for absorbent articles. (Method for measuring the amount of fluff shedding) a) A disk (70 mm diameter, 350 g) covered with urethane foam (5 mm thick) is attached to the rotating shaft so that the rotating shaft is 20 mm off-center from the center of the disk. b) The same urethane foam as above is laid on the table, and the nonwoven fabric is fixed on the table so that the first fiber layer of the nonwoven fabric is the exposed surface. c) Place the disk on the nonwoven fabric, with the only load applied to the nonwoven fabric being the disk's own weight. d) Rotate the rotating shaft and rotate the disk over the nonwoven fabric. 10 sets of rotations are performed, each set consisting of two rotations clockwise and two rotations counterclockwise. The rotation speed is approximately 3 seconds per rotation. e) After three sets of rotation, collect the fibers that have fallen off the nonwoven fabric and adhered to the surface of the urethane foam covering the disk. f) The above steps a) to e) are carried out for n=3 pieces of nonwoven fabric. The mass of the fallen fibers is measured for each of the three pieces of nonwoven fabric, and the average value is taken as the amount of fallen fluff (mg). (Aspect 5) The fibers in the second fiber layer are not bonded to each other, 5. The nonwoven fabric for absorbent articles according to any one of Aspects 1 to 4, wherein the stress at 10% elongation in the MD direction is 16.5 N / 5cm or more and 50.0 N / 5cm or less. Nonwoven fabric for absorbent articles. (Aspect 6) The nonwoven fabric for absorbent articles of any one of aspects 1 to 5, wherein the first fiber layer contains 55% by mass or more and 75% by mass or less of the adhesive fiber and 25% by mass or more and 45% by mass or less of the first hydrophilic fiber, based on the total mass of the first fiber layer. (Aspect 7) The first fiber layer has a basis weight of 10 g / m 2 More than 40g / m 2 the second fiber layer has a basis weight of 10 g / m or less 2 More than 40g / m 2 A nonwoven fabric for absorbent articles according to any one of Aspects 1 to 6, which is as follows: (Aspect 8) A nonwoven fabric for absorbent articles according to any one of Aspects 1 to 7, wherein the adhesive fibers are concentric core-sheath type composite fibers. (Aspect 9) A nonwoven fabric for absorbent articles according to any one of Aspects 1 to 8, wherein either or both of the first hydrophilic fibers and the second hydrophilic fibers are cellulosic fibers. (Aspect 10) Aspect 10. The nonwoven fabric for absorbent articles according to aspect 9, wherein the cellulosic fibers are regenerated fibers. (Aspect 11) 11. The nonwoven fabric for absorbent articles according to any one of aspects 1 to 10, wherein at least one of the first hydrophilic fibers and the second hydrophilic fibers is a synthetic fiber coated with a hydrophilic fiber treatment agent. (Aspect 12) Density is 0.065g / cm 3 is less than When the mean coefficient of friction variation (MMD) of the surface of the first fiber layer is measured, the average value of the MMD in the machine direction and the MMD in the cross direction is 0.0100 or less. A nonwoven fabric for absorbent articles according to embodiment 11. (Aspect 13) A top sheet for absorbent articles comprising the nonwoven fabric for absorbent articles according to any one of aspects 1 to 12, wherein the first fibrous layer is disposed closer to the skin of a user. (Aspect 14) 14. An absorbent article comprising the topsheet of embodiment 13, wherein the first fibrous layer is positioned closer to the skin of a user. (Aspect 15) A method for manufacturing a nonwoven fabric for absorbent articles, the nonwoven fabric comprising a first fiber layer and a second fiber layer, the first fiber layer forming one surface of the nonwoven fabric, the second fiber layer being in contact with the other surface of the nonwoven fabric, and the first fiber layer being positioned closer to the skin of a user, comprising: a step of preparing a first fiber web containing adhesive fibers in an amount of 40% by mass or more and 75% by mass or less and first hydrophilic fibers in an amount of 25% by mass or more and 60% by mass or less, based on the total mass of the first fiber web; preparing a second fiber web containing second hydrophilic fibers in an amount of 70% by mass or more and 100% by mass or less, based on the total mass of the second fiber web; a bonding step of bonding the fibers of the first fiber web together with the adhesive fibers; a lamination step of laminating the first fiber web and the second fiber web after the bonding step to obtain a laminated fiber web; an entanglement step of entangling the fibers of the first fiber web and the second fiber web of the laminated fiber web to integrate them together, the entanglement step includes a hydroentanglement treatment in which a water stream is sprayed on the side of the second fiber web to entangle the fibers, and then a water stream is sprayed on the side of the first fiber web to entangle the fibers, and in the hydroentanglement treatment, a total energy E1 of the water stream sprayed on the side of the first fiber web is higher than a total energy E2 of the water stream sprayed on the side of the second fiber web, and a value of the ratio of E1 to E2 (E1 / E2) is 2.5 or more and 12.0 or less, A method for manufacturing a nonwoven fabric for absorbent articles, wherein the first fiber web becomes the first fiber layer and the second fiber web becomes the second fiber layer. (Aspect 16) A method for producing a nonwoven fabric for absorbent articles according to aspect 15, wherein the adhesive fibers are synthetic fibers having a surface coated with a hydrophilic fiber treatment agent, and have an initial settling rate of less than 60 seconds, and a post-wash settling rate of 60 seconds or more after three 2-minute rubbing washes in 40°C warm water. (Aspect 17) 17. The method for producing a nonwoven fabric for absorbent articles according to aspect 15 or 16, wherein either or both of the first hydrophilic fibers and the second hydrophilic fibers are cellulosic fibers. (Aspect 18) 18. The method for producing a nonwoven fabric for absorbent articles according to any one of aspects 15 to 17, wherein either or both of the first hydrophilic fibers and the second hydrophilic fibers are synthetic fibers having a hydrophilic fiber treatment agent applied to the fiber surface. (Aspect 19) A method for producing a nonwoven fabric for absorbent articles according to aspect 18, wherein the synthetic fibers having a surface coated with a hydrophilic fiber treatment agent have an initial settling rate of less than 60 seconds, and a post-wash settling rate of less than 60 seconds after three 2-minute rubbing washes in 40°C warm water. [Industrial Applicability]

[0197] The nonwoven fabric for absorbent articles of this embodiment has a smooth feel and excellent liquid absorbency, and can therefore be used to form top sheets for disposable diapers, panty liners, sanitary napkins, and the like.

Claims

1. A nonwoven fabric for absorbent articles comprising a first fiber layer and a second fiber layer, one surface of the first fiber layer forms a surface of the nonwoven fabric, and the other surface is in contact with the second fiber layer; the first fibrous layer includes adhesive fibers and first hydrophilic fibers; the first fiber layer contains the adhesive fiber in an amount of 40% by mass or more and 75% by mass or less and the first hydrophilic fiber in an amount of 25% by mass or more and 60% by mass or less, based on the total mass of the first fiber layer; the second fibrous layer includes second hydrophilic fibers; the second fiber layer contains the second hydrophilic fibers in an amount of 70% by mass or more and 100% by mass or less based on the total mass of the second fiber layer; In the first fiber layer, the fibers are bonded to each other by the adhesive fibers, the first fiber layer and the second fiber layer are integrated by entanglement of the fibers, the radius of curvature (φ1) of the fibers on the surface of the first fiber layer is 30 μm or more, the radius of curvature (φ2) of the fibers on the surface of the second fiber layer is 40 μm or less, and φ1>φ2 is satisfied; The first fibrous layer is positioned closer to the user's skin. Nonwoven fabric for absorbent articles.

2. 2. The nonwoven fabric for absorbent articles according to claim 1, wherein the fiber diameter of the first hydrophilic fibers is 4 μm or more and 15 μm or less, the fiber diameter of the second hydrophilic fibers is 4 μm or more and 15 μm or less, and the fiber diameter of the adhesive fibers is 6 μm or more and 19 μm or less.

3. The nonwoven fabric for absorbent articles according to claim 1 or 2, wherein the fibers in the second fiber layer are not bonded to each other.

4. A nonwoven fabric for absorbent articles comprising a first fiber layer and a second fiber layer, one surface of the first fiber layer forms a surface of the nonwoven fabric, and the other surface is in contact with the second fiber layer; the first fibrous layer includes adhesive fibers and first hydrophilic fibers; the first fiber layer contains the adhesive fiber in an amount of 40% by mass or more and 75% by mass or less and the first hydrophilic fiber in an amount of 25% by mass or more and 60% by mass or less, based on the total mass of the first fiber layer; the second fibrous layer includes second hydrophilic fibers; the second fiber layer contains the second hydrophilic fibers in an amount of 70% by mass or more and 100% by mass or less based on the total mass of the second fiber layer; In the first fiber layer, the fibers are bonded to each other by the adhesive fibers, the first fiber layer and the second fiber layer are integrated by entanglement of the fibers, the fiber diameter of the first hydrophilic fibers is 4 μm or more and 15 μm or less, the fiber diameter of the second hydrophilic fibers is 4 μm or more and 15 μm or less, and the fiber diameter of the adhesive fibers is 6 μm or more and 19 μm or less; the amount of fluff shedding of the first fiber layer is 3.0 mg or less, and the amount of liquid return is less than 0.33 g, as measured by the following method: Nonwoven fabric for absorbent articles. (Method for measuring the amount of fluff shedding) a) A disk (70 mm diameter, 350 g) covered with urethane foam (5 mm thick) is attached to a rotating shaft so that the rotating shaft is positioned 20 mm off the center of the disk. b) The same urethane foam as above is laid on the table, and the nonwoven fabric is fixed on the table so that the first fiber layer of the nonwoven fabric is the exposed surface. c) The disk is placed on the nonwoven fabric, with the only load applied to the nonwoven fabric being the disk's own weight. d) Rotate the rotating shaft to rotate the disk over the nonwoven fabric. The rotation is performed 10 times, with one set consisting of two clockwise rotations and two counterclockwise rotations. The rotation speed is approximately 3 seconds per rotation. e) After three sets of rotation, collect the fibers that have fallen off the nonwoven fabric and adhered to the surface of the urethane foam covering the disk. f) Repeat steps a) to e) above for n=3 pieces of nonwoven fabric. Measure the mass of the fallen fibers for each of the three pieces of nonwoven fabric, and take the average value as the amount of fallen fuzz (mg).

5. The fibers in the second fiber layer are not bonded to each other, The nonwoven fabric for absorbent articles according to any one of claims 1 to 4, wherein the stress at 10% elongation in the MD direction is 16.5 N / 5 cm or more and 50.0 N / 5 cm or less. Nonwoven fabric for absorbent articles.

6. The nonwoven fabric for absorbent articles according to any one of claims 1 to 5, wherein the first fiber layer contains 55% by mass or more and 75% by mass or less of the adhesive fiber and 25% by mass or more and 45% by mass or less of the first hydrophilic fiber, based on the total mass of the first fiber layer.

7. The first fiber layer has a basis weight of 10 g / m 2 More than 40g / m 2 the weight of the second fiber layer is 10 g / m or less 2 More than 40g / m 2 The nonwoven fabric for absorbent articles according to any one of claims 1 to 6, wherein:

8. The nonwoven fabric for absorbent articles according to any one of claims 1 to 7, wherein the adhesive fiber is a concentric core-sheath type composite fiber.

9. 9. The nonwoven fabric for absorbent articles according to claim 1, wherein either or both of the first hydrophilic fibers and the second hydrophilic fibers are cellulosic fibers.

10. The nonwoven fabric for absorbent articles according to claim 9 , wherein the cellulosic fibers are regenerated fibers.

11. The nonwoven fabric for absorbent articles according to any one of claims 1 to 10, wherein at least one of the first hydrophilic fibers and the second hydrophilic fibers is a synthetic fiber coated with a hydrophilic fiber treatment agent.

12. Density is 0.065 g / cm ３ is less than When the mean coefficient of friction variation (MMD) of the surface of the first fiber layer is measured, the average value of the MMD in the machine direction and the MMD in the cross direction is 0.0100 or less. The nonwoven fabric for absorbent articles according to claim 11.

13. A top sheet for absorbent articles, comprising the nonwoven fabric for absorbent articles according to any one of claims 1 to 12, wherein the first fibrous layer is positioned closer to the skin of a user.

14. 14. An absorbent article comprising the topsheet of claim 13, wherein the first fibrous layer is positioned closer to the user's skin.

15. A method for manufacturing a nonwoven fabric for absorbent articles, comprising the first fiber layer according to any one of claims 1 to 12 and a second fiber layer, a step of preparing a first fiber web containing adhesive fibers in an amount of 40% by mass or more and 75% by mass or less and first hydrophilic fibers in an amount of 25% by mass or more and 60% by mass or less, based on the total mass of the first fiber web; preparing a second fiber web containing second hydrophilic fibers in an amount of 70% by mass or more and 100% by mass or less based on the total mass of the second fiber web; a bonding step of bonding the fibers of the first fiber web together with the adhesive fibers; a lamination step of laminating the first fiber web and the second fiber web after the bonding step to obtain a laminated fiber web; an entanglement step of entangling fibers of the first fiber web and the second fiber web of the laminated fiber web to integrate them together, the entanglement step includes a hydroentanglement treatment in which a water stream is sprayed onto the second fiber web side to entangle the fibers, and then a water stream is sprayed onto the first fiber web side to entangle the fibers, and in the hydroentanglement treatment, a total energy E1 of the water stream sprayed onto the first fiber web side is higher than a total energy E2 of the water stream sprayed onto the second fiber web side, and a ratio of E1 to E2 (E1 / E2) is 2.5 or more and 12.0 or less; E1 is 0.03 kWh / kg / m or more and 3.50 kWh / kg / m or less, and E2 is 0.01 kWh / kg / m or more and 0.50 kWh / kg / m or less, The method for manufacturing a nonwoven fabric for an absorbent article, wherein the first fiber web becomes the first fiber layer and the second fiber web becomes the second fiber layer.

16. 16. The method for producing a nonwoven fabric for absorbent articles according to claim 15, wherein the adhesive fibers are synthetic fibers having a hydrophilic fiber treatment agent applied to the fiber surface, and have an initial settling velocity of less than 60 seconds, and a settling velocity after washing in 40°C warm water for 2 minutes three times is 60 seconds or more.

17. The method for producing a nonwoven fabric for absorbent articles according to claim 15 or 16, wherein either or both of the first hydrophilic fibers and the second hydrophilic fibers are cellulosic fibers.

18. The method for producing a nonwoven fabric for absorbent articles according to any one of claims 15 to 17, wherein either one or both of the first hydrophilic fibers and the second hydrophilic fibers are synthetic fibers having a hydrophilic fiber treatment agent applied to the fiber surface.

19. 19. The method for producing a nonwoven fabric for absorbent articles according to claim 18, wherein the synthetic fibers having a surface coated with a hydrophilic fiber treatment agent have an initial settling rate of less than 60 seconds, and a post-washing settling rate of less than 60 seconds after three 2-minute rubbing washes in 40°C warm water.

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