Nonwoven fabrics for absorbent articles, top sheets for absorbent articles, and absorbent articles containing the same

Abstract

To provide a nonwoven fabric that is improved in terms of at least one selected from texture, wet back amount, liquid absorbing speed, diffusion length, repetition durability (for wet back amount, liquid absorbing speed, and diffusion length), preservability, and the like.SOLUTION: Provided is a nonwoven fabric having a structure comprising at least two layers that are a first fiber layer and a second fiber layer, wherein: each of the first fiber layer and the second fiber layer has a specific fineness; the fiber diameter of the first fiber layer is larger than the fiber diameter of the second fiber layer; each of the first fiber layer and the second fiber layer has such a hydrophilicity that allows the level thereof to be kept even after contact with water; and both the first fiber layer and the second fiber layer have the same hydrophilicity.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a nonwoven fabric, a sheet for absorbent articles, and an absorbent article containing the same. More specifically, it relates to a nonwoven fabric used in an absorbent article, a top sheet for an absorbent article containing the same, and an absorbent article containing the same. [Background technology]

[0002] Nonwoven fabrics with a two-layer structure have been proposed as top sheets for absorbent articles such as disposable diapers, sanitary napkins, incontinence pads, and panty liners. For example, Patent Document 1 describes a two-layer nonwoven fabric having a first fiber layer that comes into contact with the user's skin and a second fiber layer adjacent thereto, wherein the fibers of the first fiber layer have a specific smaller fiber diameter (11-18 μm), and the fibers of the second fiber layer have a specific larger fiber diameter (19-31 μm), and the basis weight of both the first and second fiber layers is a specific value (7-30 g / m²). 2 We propose an absorbent top sheet made of a nonwoven fabric that has the following characteristics. Patent Document 1 states that because the nonwoven fabric has these characteristics, the texture of the top sheet can be improved and the amount of wet back can be reduced.

[0003] Furthermore, Patent Document 1 states that it is preferable for both the first fiber layer and the second fiber layer to be hydrophilic, and for the fibers of the first fiber layer to be hydrophilic in such a way that their degree of hydrophilicity decreases more easily upon contact with water compared to the fibers of the second fiber layer, because this can further reduce the amount of wet back.

[0004] Furthermore, Patent Document 2 proposes a surface sheet for an absorbent article, which is made of a laminated nonwoven fabric having an upper layer placed on the skin side and a lower layer placed on the absorbent side, characterized in that before liquid permeation, the hydrophilicity of the lower layer is higher than or nearly equal to that of the upper layer, and after liquid permeation, a hydrophilic oil agent is selected for use in the upper layer whose water resistance is clearly higher than that of the hydrophilic oil agent used in the lower layer, thereby resulting in the hydrophilicity of the upper layer being clearly higher than that of the lower layer. Patent Document 2 states that, according to the surface sheet for the absorbent article, liquid permeability is maintained in a stable state when the absorbent article is in use, and surface flow of liquids such as urine and menstrual blood and wet bags can be prevented for a long time during use. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2004-166832 [Patent Document 2] Japanese Patent Publication No. 2005-324010 [Overview of the project] [Problems that the invention aims to solve]

[0006] In addition to texture and wet bag capacity, absorbent materials require improvements in properties such as absorption rate, diffusion length, repeated durability (of wet bag capacity, absorption rate, and diffusion length), shelf life, and cost. Furthermore, since diapers and similar items are not changed immediately after becoming wet, the ability to withstand repeated excretion (i.e., repeated durability) is extremely important. Patent Document 1 describes the hydrophilization of a two-layer nonwoven fabric, and states that it is preferable for the fibers of the first fiber layer to easily decrease in hydrophilicity when in contact with water. However, Patent Document 1 does not specifically describe the degree of hydrophilicity and its water resistance in its examples, nor does it show any properties other than texture and wet-back amount.

[0007] Furthermore, the nonwoven fabric and surface sheet described in Patent Documents 1 and 2 are characterized in that the strength of hydrophilicity to liquids (degree of hydrophilization) and the ability to maintain hydrophilicity even when in contact with liquids, or in other words, the durability to hydrophilic liquids, differ between the upper and lower fiber layers: the fiber layer that is positioned on the skin side and forms the surface that comes into contact with the wearer's skin during use (generally also called the skin-contact surface), and the fiber layer that forms the surface opposite the skin-contact surface and does not come into contact with the wearer's skin during use, and forms the surface facing the absorbent.

[0008] To obtain such nonwoven fabrics and surface sheets, a hydrophilizing agent (also called a fiber treatment agent) is applied to the surface of the synthetic fibers constituting these fiber layers, taking into consideration their affinity for liquids (e.g., hydrophilicity) and durability when in contact with liquids (resistance to shedding from the fibers even when in contact with liquids), before manufacturing the nonwoven fabric.

[0009] However, when manufacturing a two-layer nonwoven fabric, the fabric is manufactured, stored, and shipped in a rolled state, during which fibers with different properties are stored in close contact with each other. If the rolled state persists for a long period, and the storage environment is hot and humid, the hydrophilic agents used in the treatment agents may migrate between the fiber layers that come into contact with each other. This could prevent the absorbent material from performing as designed. [Means for solving the problem]

[0010] To our surprise, the present inventors have found that a nonwoven fabric having at least two layers, a first fiber layer and a second fiber layer, wherein both the first and second fiber layers each have a specific fineness, the fiber diameter of the first fiber layer is smaller than the fiber diameter of the second fiber layer, both the first and second fiber layers maintain a high degree of hydrophilicity even when in contact with water, and both the first and second fiber layers are substantially the same in terms of hydrophilicity, thereby improving at least one of the following: texture, wet back amount, liquid absorption time, diffusion length, repeated durability (of wet back amount, liquid absorption time, and diffusion length), and storability. More preferably, they have found that at least one of the repeated durability (of wet back amount, liquid absorption time, and diffusion length) is improved, leading to the completion of the present invention.

[0011] In other words, in one aspect of the present invention, A nonwoven fabric having a first fiber layer and a second fiber layer adjacent to the first fiber layer, The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex. The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex. The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer. Both the fibers forming the first fiber layer and the fibers forming the second fiber layer have been treated to maintain a high degree of hydrophilicity (degree of hydrophilization) even when the fibers come into contact with water (i.e., the degree of hydrophilization of the fibers has water resistance), and their hydrophilicity (degree of hydrophilicity and water resistance) is substantially the same. The present invention provides a nonwoven fabric for absorbent articles, wherein the nonwoven fabric is arranged so that the first fiber layer faces human skin.

[0012] The affinity between a nonwoven fabric surface and water can be expressed by the magnitude of the contact angle formed between the fiber surface constituting the nonwoven fabric and the water droplet. In other words, a small contact angle indicates high affinity (hydrophilicity) between the nonwoven fabric and the liquid, while a large contact angle indicates low affinity (hydrophilicity). Furthermore, the durability of the nonwoven fabric against hydrophilic liquids can be expressed by the change in the contact angle before and after the liquid has permeated through it.

[0013] Therefore, in another aspect, the present invention is a nonwoven fabric having a first fiber layer and a second fiber layer adjacent to the first fiber layer, where the fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex, the fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex, the fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer, the contact angle (A1) of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer before contact with water and the contact angle (A2) of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer before contact with water satisfy the following (I), (I): A1 ≤ 80°, A2 ≤ 80°, |A1 - A2| < 12 the contact angle (B1) of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer after contact with water and the contact angle (B2) of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer after contact with water satisfy the following (II), (II): -5 ≤ (B1 - A1) < 40°, -5 ≤ (B2 - A2) < 40°[[ID=...]] [[ID=...]] The nonwoven fabric for absorbent articles is arranged such that the first fiber layer faces the human skin. is provided.

Advantages of the Invention

[0014] Since the present invention has the above-described characteristics, at least one selected from the texture, wet-back amount, liquid absorption time, diffusion length, repeated durability (of the wet-back amount, liquid absorption time, and diffusion length), storage stability, etc. is improved. More preferably, at least one selected from the repeated durability of the wet-back amount, liquid absorption time, and diffusion length is improved.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 schematically shows the contact angle formed by a water droplet and a fiber (surface). [Figure 2]Figure 2 schematically shows a stainless steel plate used to attach water droplets to a nonwoven fabric sample in order to measure the contact angle after water permeation. [Modes for carrying out the invention]

[0016] This invention provides a nonwoven fabric for absorbent articles. Absorbent articles generally include a liquid-retaining absorbent, a liquid-impermeable backsheet, and a liquid-permeable topsheet, with the backsheet positioned between the absorbent and the topsheet. In the embodiment of the present invention, the nonwoven fabric for absorbent articles is positioned as the topsheet that comes into contact with the wearer's skin. The backsheet and absorbent can be those commonly used in absorbent articles. For example, a thermoplastic resin film with or without moisture permeability can be used as the backsheet. For example, as the absorbent, an absorbent can be used which is made by wrapping or sandwiching pulp fibers, superabsorbent polymer particles, or a mixture thereof in paper such as tissue paper.

[0017] Nonwoven fabrics for absorbent articles according to embodiments of the present invention are A nonwoven fabric having at least two layers, each having a first fiber layer and a second fiber layer adjacent to the first fiber layer. The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex. The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex. The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer. The fibers forming the first fiber layer and the fibers forming the second fiber layer both possess hydrophilicity such that their degree of hydrophilicity is maintained even when they come into contact with water, and their hydrophilicity is the same. The nonwoven fabric is positioned so that the first fiber layer faces the human skin, that is, so that it faces outward from the absorbent article.

[0018] The nonwoven fabric for absorbent articles according to the above embodiment of the present invention can also be described as follows by using the contact angle between the fiber surface and water, to express the strength of hydrophilicity, which is the ease with which the surface of the fibers constituting the nonwoven fabric is attracted to liquids containing water, and the property that hydrophilicity does not decrease easily even when in contact with such liquids.

[0019] Nonwoven fabrics for absorbent articles according to embodiments of the present invention are A nonwoven fabric having a first fiber layer and a second fiber layer adjacent to the first fiber layer, The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex. The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex. The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer. The contact angle of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer before contact with water (A1), and the contact angle of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer before contact with water (A2) satisfy the following (I): (I):A1≦80°, A2≦80°, |A1-A2|<12 The contact angle of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer after contact with water (B1) and the contact angle of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer after contact with water (B2) satisfy the following (II): (II):-5≦(B1-A1)<40°, -5≦(B2-A2)<40° The nonwoven fabric is arranged so that the first fiber layer faces human skin.

[0020] The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex, preferably 1.5 to 2.6 dtex, and more preferably 1.7 to 2.3 dtex. The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex, preferably 2.0 to 5.0 dtex, and more preferably 2.6 to 4.0 dtex. Furthermore, the fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer. Therefore, in the present invention, thinner fibers are used in the first fiber layer that faces human skin, and thicker fibers than those in the first fiber layer are used in the second fiber layer that faces the absorbent. The fibers of the first fiber layer that come into contact with human skin have a specific fineness that is finer than the fibers of the second fiber layer, which is preferable as it improves texture and feel.

[0021] In addition, it is preferable that all fibers forming the first fiber layer and the second fiber layer have a fiber fineness within the aforementioned range, but fibers outside the aforementioned range may be included as long as they do not impair the desired effects of the present invention. The fiber diameter of the fibers forming the first fiber layer is preferably 10 to 20 μm, more preferably 12 to 19 μm, and even more preferably 14 to 18 μm. The fiber diameter of the fibers forming the second fiber layer is preferably 13 to 28 μm, more preferably 15 to 26 μm, even more preferably 17 to 24 μm, and even more preferably 17 to 21 μm.

[0022] The fibers (raw materials or materials) of the first fiber layer are not particularly limited as long as the nonwoven fabric for which the present invention is intended can be obtained. The fibers of the first fiber layer may include, for example, the following: natural fibers such as cotton, silk, and wool; regenerated fibers such as viscose rayon, cupro, and solvent-spun cellulose fibers (e.g., Lentinguliocell® and Tencel®); and synthetic fibers such as polyolefin fibers, polyester fibers, polyamide fibers, (poly)acrylic fibers made of acrylonitrile, polycarbonate fibers, polyacetal fibers, polystyrene fibers, and cyclic polyolefin fibers. The fibers in the first fiber layer can be made of a single type of resin, or of composite material made of two or more types of resin (for example, concentric or eccentric core-sheath composite fibers, sea-island composite fibers, or side-by-side composite fibers). Furthermore, if natural fibers are included, their fineness or fiber diameter can be calculated in accordance with the method specified in JIS L 1019 7.4.1 Micronear.

[0023] As the fibers of the first fiber layer, synthetic fibers are preferred, and polyester fibers, polyolefin fibers, and combinations thereof are more preferred. The fibers of the first fiber layer may include synthetic fibers, regenerated fibers, and / or natural fibers, as long as the nonwoven fabric for which the present invention is intended is obtained. The fibers of the first fiber layer may include, for example, polyester fibers such as polyethylene terephthalate; and polyolefin fibers such as polyethylene (high-density polyethylene, low-density polyethylene, linear low-density polyethylene), polypropylene, ethylene-propylene copolymer, ethylene-butene-1-propylene ternary copolymer; and fibers combining these.

[0024] High-density polyethylene is even more preferable because it allows for easy crimping. In the present invention, a fiber treatment agent may be used to impart hydrophilicity to the fibers, as will be described later. When crimping can be easily imparted to the fibers, the need for the fiber treatment agent to contain additional components, for example, to impart water repellency, may be reduced, and unwanted effects on liquid absorption properties can be suppressed. These fibers can be used individually or in combination.

[0025] When combining two types of fibers, the form of the combination is not particularly limited as long as the desired nonwoven fabric can be obtained, such as simply mixing the fibers together, or using concentric or eccentric core-sheath type composite fibers. Concentric or eccentric core-sheath type composite fibers are preferred, and concentric core-sheath type composite fibers are more preferred because they allow for a thinner first fiber layer. A thinner nonwoven fabric reduces the distance to the absorbent, resulting in better liquid mobility and potentially improved absorption time and wet-back volume. Therefore, a thinner first fiber layer is preferable. A concentric or eccentric core-sheath type composite fiber composed of a polyester resin and a polyolefin resin is even more preferable. In particular, a core-sheath type composite fiber in which the core component is a polyester resin and the sheath component is a polyolefin resin is preferred.

[0026] The fibers of the first fiber layer preferably contain 50% by mass or more of concentric core-sheath type composite fibers, more preferably 70% by mass or more, and it is particularly preferable that all the fibers forming the first fiber layer are concentric core-sheath type composite fibers. When the fibers of the first fiber layer contain 50% by mass or more of concentric core-sheath type composite fibers, the increase in the thickness of the nonwoven fabric can be further suppressed. The fibers of the first fiber layer may contain additives such as titanium dioxide to improve texture and feel. It is preferable that such additives are present in an amount of 0.1 to 10% by mass, and more preferably 1 to 5% by mass, based on 100% by mass of the entire fiber including the additives. Furthermore, if the fibers of the first fiber layer are core-sheath type composite fibers, it is preferable that the additives are present in a larger proportion of the core component, or even more preferably only in the core component. If the additives are present in the sheath component, they may damage manufacturing equipment for nonwoven fabrics, etc.

[0027] In the case of core-sheath type composite fibers, the composite ratio of core component to sheath component is preferably 80:20 to 40:60 by mass ratio, more preferably 70:30 to 50:50, and even more preferably 65:35 to 55:45. When the composite ratio is within this range, it is particularly preferable when the core component is more abundant in the composite ratio (by mass ratio), as this can reduce unevenness in the basis weight and texture of the nonwoven fabric.

[0028] The fibers (raw materials or materials) of the second fiber layer are not particularly limited as long as the nonwoven fabric for which the present invention is intended can be obtained. The fibers of the second fiber layer may include, for example, the following: natural fibers such as cotton, silk, and wool; regenerated fibers such as viscose rayon, cupro, and solvent-spun cellulose fibers (e.g., lentinglyocell® and Tencel®); and synthetic fibers such as polyolefin fibers, polyester fibers, polyamide fibers, (poly)acrylic fibers made of acrylonitrile, polycarbonate fibers, polyacetal fibers, polystyrene fibers, and cyclic polyolefin fibers. The fibers in the second fiber layer can be made not only from a single type of resin, but also from composite fibers made from two or more types of resin (for example, concentric or eccentric core-sheath composite fibers, sea-island composite fibers, or side-by-side composite fibers). Furthermore, if natural fibers are included, their fineness or fiber diameter can be calculated in accordance with the method specified in JIS L 1019 7.4.1 Micronear.

[0029] As the fibers of the second fiber layer, synthetic fibers are preferred, and polyester fibers, polyolefin fibers, and combinations thereof are more preferred. The fibers of the second fiber layer may include synthetic fibers, regenerated fibers, and / or natural fibers, as long as the nonwoven fabric for which the present invention is intended is obtained. The fibers of the second fiber layer may include, for example, polyester fibers such as polyethylene terephthalate; and polyolefin fibers such as polyethylene (high-density polyethylene, low-density polyethylene, linear low-density polyethylene), polypropylene, ethylene-propylene copolymer, ethylene-butene-1-propylene ternary copolymer; and fibers combining these.

[0030] High-density polyethylene is even more preferable because it allows for easy crimping. In the present invention, a fiber treatment agent may be used to impart hydrophilicity to the fibers, as will be described later. When crimping can be easily imparted to the fibers, the need for the fiber treatment agent to contain additional components, for example, to impart water repellency, may be reduced, and unwanted effects on liquid absorption properties can be suppressed. These fibers can be used individually or in combination.

[0031] When combining two types of fibers, the form of the combination is not particularly limited as long as the desired nonwoven fabric can be obtained, such as simply mixing the fibers together, or using concentric or eccentric core-sheath type composite fibers. Concentric or eccentric core-sheath type composite fibers are preferred, and concentric core-sheath type composite fibers are more preferred because they allow for a thinner second fiber layer. A thinner nonwoven fabric reduces the distance to the absorbent, resulting in better liquid mobility and potentially improved absorption time and wet-back volume. Therefore, a thinner second fiber layer is preferable. A concentric or eccentric core-sheath type composite fiber composed of a polyester resin and a polyolefin resin is even more preferable. In particular, a core-sheath type composite fiber in which the core component is a polyester resin and the sheath component is a polyolefin resin is preferred.

[0032] The fibers of the second fiber layer preferably contain 50% by mass or more of concentric core-sheath type composite fibers, more preferably 70% by mass or more, and it is particularly preferable that all fibers forming the second fiber layer are concentric core-sheath type composite fibers. When the fibers of the second fiber layer contain 50% by mass or more of concentric core-sheath type composite fibers, the increase in the thickness of the nonwoven fabric can be further suppressed. The fibers of the second fiber layer may contain additives such as titanium dioxide to improve the texture and feel. Such additives are preferably present in an amount of 0.1 to 10% by mass, and more preferably 1 to 5% by mass, based on 100% by mass of the entire fiber of the second fiber layer including the additives. Furthermore, when the fibers of the second fiber layer are core-sheath type composite fibers, it is preferable that the additive is present in a larger amount in the core component, and more preferably in only the core component. If the additive is present in the sheath component, it may damage the manufacturing equipment for nonwoven fabrics, etc.

[0033] In the case of core-sheath type composite fibers, the composite ratio of core component to sheath component is preferably 80:20 to 40:60 by mass ratio, more preferably 70:30 to 50:50, and even more preferably 65:35 to 55:45. When the composite ratio is within this range, it is particularly preferable when the core component is more abundant in the composite ratio (by mass ratio), as this can reduce unevenness in the basis weight and texture of the nonwoven fabric.

[0034] Furthermore, the overall weight of the nonwoven fabric is 10-80 g / m². 2 Preferably, it is 15-50 g / m². 2 And more preferably 17-40 g / m² 2 That is the case. For disposable diapers, the basis weight of the entire non-woven fabric is preferably as low as possible in terms of cost, and in that case, the basis weight is preferably 10 to 50 g / m 2 and more preferably 15 to 40 g / m 2 is even more preferred.

[0035] Also, the thickness of the non-woven fabric is preferably 0.2 to 3.0 mm, more preferably 0.3 to 1.5 mm, and even more preferably 0.35 to 0.8 mm. For disposable diapers, the thickness of the non-woven fabric is preferably as low as possible in terms of cost, and in that case, the thickness is preferably 0.2 to 1.0 mm, and more preferably 0.3 to 0.8 mm.

[0036] The basis weight of the first fiber layer is preferably 3 to 40 g / m 2 and more preferably 5 to 15 g / m 2 is even more preferred. The basis weight of the second fiber layer is preferably 3 to 40 g / m 2 and more preferably 8 to 20 g / m 2 is even more preferred.

[0037] The ratio of the basis weight of the second fiber layer to the basis weight of the first fiber layer (basis weight of the second fiber layer / basis weight of the first fiber layer) is preferably 0.8 to 3.0, more preferably 1.0 to 2.0, and even more preferably 1.3 to 1.7. In particular, when the basis weight of the first fiber layer with a smaller fiber diameter is smaller than the basis weight of the second fiber layer, that is, when the ratio of the basis weight of the second fiber layer to the basis weight of the first fiber layer (basis weight of the second fiber layer / basis weight of the first fiber layer) is greater than 1, it is more preferred because better liquid absorption characteristics can be obtained while having a texture and touch.

[0038] The fibers forming the first fiber layer and the fibers forming the second fiber layer are both given hydrophilicity such that the degree of hydrophilicity (degree of hydrophilization) is maintained even when in contact with water (that is, the fibers have hydrophilicity with water resistance). "Hydrophilicity that maintains a high degree of hydrophilicity even when in contact with water" is preferably defined as a water resistance index of 15 or less, more preferably 14 or less, and particularly preferably 10 or less, obtained by the water resistance index measurement method described below. The smaller the water resistance index, the higher the water resistance of the hydrophilicity is considered to be. When the water resistance index is 15 or less, the repeated liquid absorption properties (durability of liquid absorption properties), especially the repeated wet-back properties (durability of wet-back properties), are better and more preferable.

[0039] Furthermore, "hydrophilicity that maintains a high degree of hydrophilicity even when in contact with water" may be expressed by the ratio of the "first absorption time (seconds)" to the "third absorption time (seconds)" (third absorption time (seconds) / first absorption time (seconds)), obtained by the same method as for calculating the water resistance index. The value of such a ratio is preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. When the value of such a ratio is 30 or less, the repeated absorption characteristics (durability of absorption characteristics), and especially the repeated wet-back characteristics (durability of wet-back), become better and are more preferable.

[0040] The hydrophilic water resistance (water resistance index) of the fiber treatment agent is evaluated as follows. (1) A concentric core-sheath composite fiber (fineness: 2.0 dtex, fiber length: 45 mm) (for example, NBF® product code (SH) manufactured by Daiwabo Polytech Co., Ltd.) with polyethylene terephthalate as the core and high-density polyethylene as the sheath, and a composite ratio (core / sheath, mass ratio) of 60 / 40, was treated with 0.40% by mass of a fiber treatment agent. A nonwoven fabric sample (basis weight: 20.0 g / m²) was then processed using the parallel carding method and the air-through method (heating temperature: 135°C, processing time: 10 seconds, air velocity: 1.0 m / s). 2 We manufactured and prepared a product with the following dimensions: 10.0cm (height) x 10.0cm (width), and a thickness of 1.2mm. The following items were also prepared. Plate with injection tube (using the Strike-through plate described in NWSP 070.3.R0 (15) of EDANA Nonwovens Standard Procedures - Edition 2015) 0.90% physiological saline (colored with blue dye) Filter paper (product name: Lister Paper (Grade 989, 10cm x 10cm) manufactured by MEZGER inc.)

[0041] (2) The liquid absorption time of the nonwoven fabric sample was measured by the following method. (i) Three sheets of filter paper were stacked, and a nonwoven fabric sample was stacked on top of that. A plate with an injection tube was placed on top of that. (ii) 5.0 ml of physiological saline solution warmed to approximately 37°C was injected through the tube. The time from injection until the physiological saline solution was no longer visible on the surface of the nonwoven fabric (when the physiological saline solution could no longer be detected as a liquid) was measured and defined as the absorption time. (iii) After standing for 30 seconds after absorption, the above (ii) was repeated and measurements were taken twice. A total of three absorption times were measured. (iv) The water resistance index was calculated using the following formula. Formula: Water resistance index = 3rd absorption time (seconds) - 1st absorption time (seconds)

[0042] The degree of hydrophilicity exhibited by the fibers of the first fiber layer and the fibers of the second fiber layer when wet is not particularly limited as long as an absorbent nonwoven fabric for absorbent articles, which is the target of the present invention, can be obtained. The degree of hydrophilicity when wet is evaluated by the run-off evaluation method described below, and the sum of the 2nd to 5th run-offs is preferably 9.0 to 30, more preferably 9.5 to 20, and particularly preferably 10.0 to 15. When the sum of the 2nd to 5th run-off values ​​is between 9.0 and 30, the repeated liquid absorption characteristics, especially the repeated wet-back characteristics, are better and more preferable.

[0043] Furthermore, the "degree of hydrophilicity" may be expressed by the value obtained by the following formula (runoff index) for the runoff values ​​of the 1st to 5th runoffs, which are obtained by the same method as calculating the sum of the 2nd to 5th runoffs.

number

[0044] The degree of hydrophilicity of the fiber treatment agent was evaluated by measuring the run-off distance as described below. A concentric core-sheath composite fiber (fineness: 2.0 dtex, fiber length: 45 mm) (for example, NBF® product code (SH) manufactured by Daiwabo Polytech Co., Ltd.) with polyethylene terephthalate as the core and high-density polyethylene as the sheath, and a composite ratio (core / sheath, mass ratio) of 60 / 40, was treated with 0.40% by mass of a fiber treatment agent. A nonwoven fabric sample (basis weight: 20.0 g / m²) was then processed using the parallel carding method and the air-through method (heating temperature: 135°C, processing time: 10 seconds, air velocity: 1.0 m / s). 2 We manufactured and prepared a product with the following dimensions: 18.0 cm (height) x 7.0 cm (width), and a thickness of 0.70 mm.

[0045] A triangular prism with a base shaped like an isosceles right triangle was laid on its side to prepare a support base with an inclined surface at a 45-degree angle to the horizontal plane. Two sheets of filter paper (MEZGER inc. product name Lister Paper (Grade 989, 27.5cm x 14cm)) were placed on top of each other on the inclined surface, and a nonwoven fabric sample was placed on top and secured.

[0046] 0.90% physiological saline (colored with blue dye) was dripped from a microtube pump or burette at a rate of 1.0 g / 30 sec over 30 seconds, 1 cm below the top edge of the nonwoven fabric, until the total amount dripped was 1.0 g. The position of the tip of the saline droplet was measured when all of the saline was absorbed by the nonwoven fabric and the saline droplet disappeared from the surface of the nonwoven fabric. The distance between this position and the position where the saline was dropped onto the nonwoven fabric surface, i.e., the longest distance the saline droplet traveled across the nonwoven fabric surface, was determined.

[0047] For the second run-off measurement, the same nonwoven fabric sample used in the first run-off measurement was used. 30 seconds after the end of the first run-off measurement, saline solution was dropped at the same location as in the first run-off measurement, and the distance the saline solution flowed across the nonwoven fabric surface was determined. For the third and subsequent run-off measurements, the same process was repeated using the previous nonwoven fabric sample.

[0048] Furthermore, the fibers forming the second fiber layer are given substantially the same hydrophilicity as the fibers forming the first fiber layer. Because the fibers of the first and second fiber layers have such hydrophilicity, the repeated liquid absorption characteristics, more specifically, at least one of the repeated durability selected from wet-back amount, liquid absorption time, and diffusion length, can be further improved. Furthermore, it is preferable that the fibers forming the first fiber layer and the fibers forming the second fiber layer are given substantially the same hydrophilicity, so that the hydrophilicity of the first fiber layer and the second fiber layer do not mix and the liquid absorption characteristics do not change.

[0049] In an absorbent nonwoven fabric according to an embodiment of the present invention, the degree of hydrophilicity of the first fiber layer and the second fiber layer (degree of hydrophilization or strength of hydrophilicity), and the hydrophilic water resistance (water resistance index, or the durability of the hydrophilicity of each fiber layer when it comes into contact with water) exhibited by the fiber treatment agent applied to the surface of the fibers constituting each fiber layer can be expressed using the angle (contact angle) between the fiber surface and the surface of a water droplet placed thereon. The contact angle is measured by the method described later.

[0050] That is, the nonwoven fabric for absorbent articles according to the embodiment of the present invention is The contact angle of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer before contact with water (A1), and the contact angle of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer before contact with water (A2) satisfy the following (I): (I):A1≦80°, A2≦80°, |A1-A2|<12 The contact angle of the deionized water with respect to the surface of the fibers forming the first fiber layer after contact with water (B1), and the contact angle of the deionized water with respect to the surface of the fibers forming the second fiber layer after contact with water (B2), satisfy the following condition (II). (II):-5≦(B1-A1)<40°, -5≦(B2-A2)<40°

[0051] In the nonwoven fabric for absorbent articles according to an embodiment of the present invention, the contact angle (A1) of ion-exchanged water with the surface of the fibers forming the first fiber layer and the contact angle (A2) of ion-exchanged water with the surface of the fibers forming the second fiber layer will be described. A1 and A2 refer to the angle formed between the surface of a tiny droplet of ion-exchanged water (approximately 20°C) that adheres to the surface of the fiber when ion-exchanged water is sprayed onto the surface of the fiber forming each fiber layer, and the surface of the fiber. A1 and A2 indicate the degree of hydrophilicity on the surface of the fiber layer before receiving liquids discharged from the wearer of the absorbent article (including humans and mammals), such as urine or menstrual blood, in the nonwoven fabric for absorbent articles according to the embodiment of the present invention.

[0052] In the nonwoven fabric for absorbent articles according to the embodiment of the present invention, both A1 and A2 are 80° or less (A1 ≤ 80°, A2 ≤ 80°). Since both A1 and A2 have a temperature of 80° or less, the hydrophilicity of both the first fiber layer and the second fiber layer is sufficiently high. When urine, menstrual blood, loose stool, etc. are discharged and come into contact with the nonwoven fabric, the moisture contained in these liquids and discharges easily blends with the fibers, and the nonwoven fabric can easily absorb these liquids and moisture instantly. Both A1 and A2 are preferably 20° to 80°, more preferably 30° to 75°, particularly preferably 35° to 75°, and most preferably 40° to 70°.

[0053] In the embodiment of the present invention, the nonwoven fabric for absorbent articles has the same degree of hydrophilicity (degree of hydrophilization) between the first fiber layer and the second fiber layer. Therefore, in the nonwoven fabric for absorbent articles according to the embodiment of the present invention, the absolute value of the difference between A1 and A2 is less than 12 (|A1-A2|<12). Since the absolute value of the difference between A1 and A2 is less than 12, the nonwoven fabric for absorbent articles in the embodiment of the present invention has a similar degree of hydrophilicity between the first fiber layer before contact with water and the second fiber layer before contact with water. In other words, for example, the hydrophilicity of the fiber treatment agent used to treat the fibers constituting the first fiber layer is about the same as the hydrophilicity of the fiber treatment agent used to treat the fibers constituting the second fiber layer. Since the absolute difference between A1 and A2 is less than 12, the degree of hydrophilicity of the first fiber layer and the degree of hydrophilicity of the second fiber layer are about the same, and their affinity for urine and menstrual blood is about the same. It is unlikely that one layer will be extremely hydrophilic compared to the other, making it difficult for it to retain liquids such as urine and menstrual blood. The absolute value of the difference between A1 and A2 is preferably 10 or less, more preferably 8 or less, and particularly preferably 6 or less.

[0054] Next, the contact angle (B1) of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer after contact with water (after liquid permeation) and the contact angle (B2) of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer after contact with water will be described for the nonwoven fabric for absorbent articles according to the embodiment of the present invention. B1 and B2 refer to the angle formed between the surface of a microscopic droplet and the surface of a fiber after passing 0.04 ml of deionized water at approximately 20°C through a nonwoven fabric, allowing the fabric to air dry, and then spraying deionized water at approximately 20°C onto the surface of the nonwoven fabric where the water passed through. B1 and B2 are not particularly limited as long as an absorbent nonwoven fabric for absorbent articles according to the embodiment of the present invention can be obtained, but it is preferable that they be less than 90°. When B1 and B2 are less than 90°, the hydrophilicity of the first and second fiber layers is maintained to some extent, allowing for sufficient absorption even when urine or menstrual blood is repeatedly discharged. B1 and B2 are more preferably 30° to 85°, particularly preferably 40° to 80°, and most preferably 45° to 80°.

[0055] The absolute value of the difference between B1 and B2 is not particularly limited as long as an absorbent nonwoven fabric for articles of the present invention can be obtained, but it is preferably less than 14. If the absolute value of the difference between B1 and B2 is less than 14, it means that the hydrophilicity of the surface of the fibers forming the first and second fiber layers remains about the same even after contact with water (after liquid permeation). In other words, the hydrophilicity (degree of hydrophilization) of the first and second fiber layers is about the same, and the affinity for urine and menstrual blood remains about the same even after these liquids have passed through. This makes it unlikely that one layer will be extremely hydrophilic compared to the other, making it easier to retain liquids such as urine and menstrual blood. The absolute value of the difference between B1 and B2 is more preferably 12 or less, particularly preferably 10 or less, and most preferably 8 or less.

[0056] In the nonwoven fabric for absorbent articles according to the embodiment of the present invention, the following relationship exists between the contact angles before contact with water (A1, A2) and the contact angles after contact with water (B1 and B2). -5≦(B1-A1)<40°, -5≦(B2-A2)<40° Since B1-A1 and B2-A2 are within the aforementioned range, the durability of the hydrophilicity of the fiber surface forming the first and second fiber layers, that is, the durability of the fiber treatment agent applied to the fiber surface against water (for example, liquids such as urine and menstrual blood, or moisture contained in loose stools), is appropriate, and it can be a fiber treatment agent that dissolves gradually and little by little in water. While fiber layers treated with such fiber treatment agents maintain a degree of hydrophilicity that allows them to absorb and pass water multiple times, the degree of hydrophilicity gradually decreases. As a result, each fiber layer becomes less able to retain water, and it is thought that the amount of liquid return (so-called wet back) from the liquid remaining in the fiber layer to the nonwoven fabric surface can be reduced.

[0057] If B1-A1 and B2-A2 are less than -5°, the amount of liquid return may increase because the fiber layer becomes too hydrophilic after contact with water, and the change in hydrophilicity is large. When B1-A1 and B2-A2 are 40° or higher, that is, when the degree of hydrophilicity decreases significantly upon contact with water, this fiber layer is not only prone to a decrease in hydrophilicity upon contact with water, but also exhibits a low degree of hydrophilicity after contact with water. Because such a fiber layer has low water resistance in terms of hydrophilicity, its degree of hydrophilicity decreases significantly upon contact with water, making it difficult to absorb and pass water (e.g., urine or menstrual blood) multiple times, and thus making water leakage (e.g., urine or menstrual blood) more likely to occur. B1-A1 and B2-A2 are preferably -3° to 35°, more preferably 0° to 30°, particularly preferably 3° to 25°, and most preferably 5° to 20°.

[0058] In the nonwoven fabric for absorbent articles according to the embodiment of the present invention, it is preferable that the change in contact angle in the first fiber layer before and after contact with water (B1-A1) and the change in contact angle in the second fiber layer before and after contact with water (B2-A2) are of similar magnitude. In other words, it is preferable that the absolute value of the difference between B1-A1 and B2-A2, (B1-A1)-(B2-A2), (|(B1-A1)-(B2-A2)|) is 18 or less. Since the change in the contact angle of the first fiber layer and the change in the contact angle of the second fiber layer before and after contact with water are of similar magnitude, the hydrophilic durability of the first fiber layer and the hydrophilic water resistance of the second fiber layer (i.e., the durability of the fiber treatment agent attached to the surface of the fibers forming the first fiber layer against liquid and the durability of the fiber treatment agent attached to the fibers forming the second fiber layer against water) are of similar strength, and the degree of hydrophilization due to the fiber treatment agent may decrease to a similar extent upon contact with water. Since neither the first fiber layer nor the second fiber layer exhibits extremely high or extremely low hydrophilicity (affinity for liquid) after contact with water, the amount of liquid return is likely to decrease further. It is more preferable that the absolute value of the difference between B1-A1 and B2-A2 ((B1-A1)-(B2-A2)) is 15 or less, particularly preferable that it is 12 or less, and most preferable that it is 10 or less.

[0059] [Contact angle measurement before liquid permeation] The water contact angle between the fiber surface forming the first fiber layer and the water contact angle between the fiber surface forming the second fiber layer is determined by spraying deionized water onto the surface of each fiber layer and measuring the angle between the fiber surface forming each fiber layer and the surface of the water droplet. The contact angle between water and the fiber surface can be measured using the following method. The measuring unit, which has a zoom lens (manufactured by Keyence Corporation, model number: VH-Z100R) attached to a Keyence VHX-1000 microscope, is fixed in a horizontal position. A nonwoven fabric containing fibers to be measured for contact angle is cut to a size of 50 mm x 10 mm in length (MD direction) x width (CD direction) to prepare a measurement sample. With the measurement surface of the measurement sample facing upwards, the measurement sample is placed on the test stand with the CD direction of the nonwoven fabric perpendicular to the lens surface of the zoom lens (i.e., the observation direction is parallel to the CD direction), and both ends are secured with tape. The observation direction (the direction in which the object is viewed through the zoom lens) is not particularly limited, as long as it is selected so that the fibers extend in a direction perpendicular to the observation direction. Depending on the type of nonwoven fabric, the observation direction may be a direction that forms an angle, for example, 45° with the CD direction of the nonwoven fabric.

[0060] Next, using a spray bottle designed to produce a fine, consistent mist, droplets of deionized water (at approximately 20°C) are sprayed onto the sample for measurement. Within 5 seconds of spraying, the droplets on the fiber surface are observed using a zoom lens at 50 to 1000x magnification, depending on the fiber diameter, and images are captured. The spraying and image capture process is repeated to obtain 20 images in which the droplets are clearly visible. From these images, select those in which the fiber is horizontal. This is because the contact angle changes when the fiber is tilted. If the number of selected images is 10 or more, the contact angle is determined using these images. If the number of images in which the fiber is horizontal is less than 10, another 20 images are obtained, and the process of selecting images in which the fiber is horizontal is repeated until the total number of images in which the fiber is horizontal is 10 or more.

[0061] As shown in Figure 1, the contact angle was defined as the angle between the tangent line drawn to the water droplet at the point where the air-contacting surface of the water droplet touches the fiber. The contact angle was measured using image analysis software (for example, the 2D image analysis software "MicroMeasure" available from Scala Corporation) or a protractor. The contact angle was measured for each selected image, and the average value (arithmetic mean) was calculated to determine the contact angle of the fiber being measured. The contact angle may also be measured by removing the constituent fibers from the measurement surface and spraying water droplets onto them, rather than using a nonwoven fabric.

[0062] When measuring the contact angle, please pay attention to the following points. (1) Measure the contact angle of a water droplet resting on a fiber. Do not measure the contact angle of water droplets that have hung down to the bottom of the fiber or water droplets that span two or more fibers. (2) If the fibers have fine crimping, such as a spiral, measure in an area with little crimping, or stretch the fibers to eliminate the crimping. (3) The contact angle measurement result is obtained by selecting 10 or more images in which the fiber is horizontal, changing the measurement location or measurement sample as described above, and averaging the measured values. If the degree of hydrophilicity of the fiber is high, water droplets may move on the fiber when measuring the contact angle (i.e., the shape of the water droplets may change). In that case, the "contact angle" is determined taking into account the circumstances of that movement. If the water droplet moves in less than 40% of the total number of measurements (total number of measurement points where the water droplet was photographed, total number of cases where the water droplet moved and cases where it did not move during photography) before the number of contact angle measurement points reaches 20, select 10 or more images where the fiber is horizontal and average the measured values ​​to determine the contact angle. If the water droplet moves in more than 40% of the total number of measurements before the number of contact angle measurement points reaches 20, the contact angle will be considered to be 20° or less.

[0063] [Measurement of contact angle after liquid permeation] Except for preparing the nonwoven fabric sample for contact angle measurement as described below, the measurement is performed in the same manner as the method for measuring the contact angle before liquid permeation described above.

[0064] [Preparation of nonwoven fabric samples] Prepare a measurement sample by cutting the nonwoven fabric to dimensions of 22 cm in the vertical direction and 5 cm in the horizontal direction. Next, prepare a stainless steel plate with 15 mm diameter holes spaced at equal intervals (20 mm between the centers of the holes), as shown in Figure 2. Mark four locations within the holes on the plate with an oil-based marker. Place the plate on the measurement surface of the measurement sample. With the stainless steel plate still on the measurement sample, drop 0.04 ml of deionized water, adjusted to approximately 20°C, onto the measurement surface of the measurement sample located at the center of the holes in the stainless steel plate using a Pasteur pipette or burette. After dropping the deionized water, allow the measurement sample to absorb the deionized water. After the dropped water droplets disappear from the surface of the measurement sample, dry the measurement sample in an atmosphere of 20-50°C. Alternatively, when dropping water droplets onto the measurement sample and allowing them to absorb, the remaining water droplets can be aspirated to force the moisture into the lower layer (second fiber layer, if any).

[0065] The dried sample is cut along a straight line passing through points 1 and 2 in the holes of the stainless steel plate shown in Figure 2. Deionized water at approximately 20°C is sprayed onto the cut surface of the sample corresponding to the points where the deionized water was dropped, using the aforementioned spray bottle, to allow the water droplets to adhere to the fibers of the sample. The following method, similar to the method used to measure the contact angle before liquid permeation, involves observing water droplets on the fibers of the sample to measure the contact angle after water permeation.

[0066] It is preferable that both the first fiber layer and the second fiber layer have their fibers treated with the same fiber treatment agent to impart substantially the same degree of hydrophilicity. It is preferable that the fiber treatment agent can maintain a similar degree of high hydrophilicity when wet, even when in contact with water, and has a similar degree of hydrophilic water resistance.

[0067] Examples of such fiber treatment agents include substances that do not easily detach from the fiber surface even when in contact with water, such as polyglycerin fatty acid esters, polyether-polyester block copolymers, polyether-modified silicones, and fatty acid esters of ethylene oxide-added polyhydric alcohols. For example, by applying such a fiber treatment agent to the surface of the fiber, substantially the same degree of hydrophilicity can be imparted to the first fiber layer and the second fiber layer, and furthermore, the degree of hydrophilicity can be substantially maintained, that is, the hydrophilicity is substantially water-resistant. The fiber treatment using the fiber treatment agent may be performed either before or after the fiber forms a fiber layer.

[0068] It is preferable that the fibers of the first fiber layer and the fibers of the second fiber layer have the above-mentioned fiber treatment agent attached to them in an amount of 0.1 to 1.5% by mass, more preferably 0.2 to 1.0% by mass, and even more preferably 0.25 to 0.8% by mass, based on 100% by mass of the entire fiber including the fiber treatment agent. It is preferable that a predetermined amount of the fiber treatment agent is attached to the fibers because it improves the desired liquid absorption characteristics, especially the wet-back characteristics.

[0069] The first and second fiber layers used in this invention can be manufactured using various fiber web manufacturing methods. The manufacturing method is not particularly limited as long as it can produce the nonwoven fabric for absorbent articles that is the target of this invention. Examples of such manufacturing methods include carding methods for parallel webs, cross webs, crisscross webs, semi-random webs, and random webs, as well as air-lay methods.

[0070] The nonwoven fabric for absorbent articles according to the present invention can be manufactured by overlapping and integrating a first fiber web and a second fiber web. The manufacturing method is not particularly limited as long as the nonwoven fabric for absorbent articles that is the target of the present invention can be obtained. Examples of such manufacturing methods include the air-through method (hot air penetration heat treatment method), the hot air blowing heat treatment method, the heat roll method, the infrared heat treatment method, the needle punch method, and the like. The fibers of the first fiber layer and the fibers of the second fiber layer of the integrated nonwoven fabric may be bonded together. The nonwoven fabric for absorbent articles according to the embodiment of the present invention may, if necessary, further have additional layers that nonwoven fabrics typically have.

[0071] The nonwoven fabric for absorbent articles according to the embodiment of the present invention may be subjected to additional processing such as embossing as necessary, and may have such additional forms and shapes.

[0072] In the embodiment of the present invention, the nonwoven fabric for absorbent articles preferably has a strength of 3.5 N / 5 cm or more at 10% elongation in the MD direction (machine direction), more preferably 6.0 N / 5 cm or more, even more preferably 8.5 N / 5 cm or more, and even more preferably 10.0 N / 5 cm or more. Furthermore, the strength at 20% elongation in the MD direction preferably has 8.0 N / 5 cm or more, more preferably 10.0 N / 5 cm or more, even more preferably 13.0 N / 5 cm or more, even more preferably 15.0 N / 5 cm or more, and particularly preferably 18.0 N / 5 cm or more. Having the strength at low elongation within this range provides good dimensional stability of the nonwoven fabric, suppresses width inclusion of the nonwoven fabric when processed into absorbent articles, and improves the processability of the nonwoven fabric. Furthermore, from the viewpoint of the tactile feel of the nonwoven fabric, such as its drape, it is preferable that the strength at 10% elongation in the MD direction be 30.0 N / 5cm or less, preferably 25.0 N / 5cm or less, and even more preferably 20.0 N / 5cm or less. The above strength is measured in accordance with JIS L 1096 6.12.1 Method A (strip method).

[0073] The nonwoven fabric for absorbent articles according to the embodiment of the present invention can be used in various absorbent articles such as disposable diapers, sanitary napkins, incontinence pads, and panty liners. Furthermore, the present invention can provide various absorbent articles, including nonwoven fabrics for such absorbent articles. [Examples]

[0074] The present invention will be described below using examples and comparative examples, but these examples are for illustrative purposes only and do not limit the present invention in any way.

[0075] The fibers used to produce the nonwoven fabrics in the examples and comparative examples are listed below. Fiber 1: A concentric core-sheath composite fiber with a polyethylene terephthalate core and a high-density polyethylene sheath, a composite ratio (core / sheath, mass ratio) of 60 / 40, a fineness of 2.0 dtex (fiber diameter 15 μm), and a fiber length of 45 mm (manufactured by Daiwabo Polytech Co., Ltd., product name NBF (registered trademark), product number (SH)) Fiber 2: A concentric core-sheath composite fiber with polyethylene terephthalate as the core and high-density polyethylene as the sheath, with a composite ratio (core / sheath, mass ratio) of 60 / 40, a fineness of 3.3 dtex (fiber diameter 19 μm), and a fiber length of 51 mm (product name NBF (registered trademark), product number (SH) manufactured by Daiwabo Polytech Co., Ltd.). Fiber 3: A concentric core-sheath composite fiber with polyethylene terephthalate as the core and high-density polyethylene as the sheath, with a composite ratio (core / sheath, mass ratio) of 60 / 40, a fineness of 4.4 dtex (fiber diameter 22 μm), and a fiber length of 51 mm (product name NBF (registered trademark), product number (SH) manufactured by Daiwabo Polytech Co., Ltd.).

[0076] The fiber treatment agents (hydrophilizing agents) used to produce the nonwoven fabrics in the examples and comparative examples are shown below. The hydrophilicity and durability of the fiber treatment agents were evaluated as follows. The fiber treatment agent was applied at approximately 0.40% by mass, with the total mass of the fiber including the fiber treatment agent being 100%. Fiber treatment agent A: Contains C12 alkyl phosphate potassium salt, is water-resistant, and is a water-resistant hydrophilic fiber treatment agent. Fiber treatment agent B: Contains C12 alkyl phosphate potassium salt and has higher water resistance than fiber treatment agent A; a water-resistant hydrophilic fiber treatment agent. A water-resistant, hydrophilic fiber treatment agent containing fiber treatment agent C: C12 alkyl phosphate potassium salt, which has higher hydrophilicity than fiber treatment agent B. A hydrophilic fiber treatment agent containing C12 alkyl phosphate potassium salt, which does not have water resistance.

[0077] [High hydrophilicity of the fiber treatment agent when wet (sum of values ​​after 2-5 run-off cycles)] The level of hydrophilicity of fiber treatment agents A to D when wet was determined by the sum of the values ​​obtained from 2 to 5 run-off tests, as described below. A smaller value for each run-off test indicates higher hydrophilicity, and a smaller change in the value even with an increasing number of run-off tests indicates higher water resistance. As a result, a smaller sum of the values ​​from 2 to 5 run-off tests suggests higher hydrophilicity when wet.

[0078] A concentric core-sheath composite fiber (fineness: 2.0 dtex, fiber length: 45 mm) (manufactured by Daiwabo Polytech Co., Ltd., NBF®, product number (SH)) with polyethylene terephthalate as the core and high-density polyethylene as the sheath, and a composite ratio (core / sheath, mass ratio) of 60 / 40, was treated with 0.40% by mass of a fiber treatment agent. A nonwoven fabric sample (basis weight: 20.0 g / m²) was then processed using the parallel carding method and the air-through method (heating temperature: 135°C, processing time: 10 seconds, air velocity: 1.0 m / s). 2 We manufactured and prepared a product with the following dimensions: 18.0 cm (height) x 7.0 cm (width), and a thickness of 0.70 mm.

[0079] A triangular prism with a base shaped like an isosceles right triangle was laid on its side to prepare a support base with an inclined surface at a 45-degree angle to the horizontal plane. Two sheets of filter paper (MEZGER inc. product name Lister Paper (Grade 989, 27.5cm x 14cm)) were placed on top of each other on the inclined surface, and a nonwoven fabric sample was placed on top and secured.

[0080] 0.90% physiological saline (colored with blue dye) was dripped from a microtube pump or burette at a rate of 1.0 g / 30 sec over 30 seconds, 1 cm below the top edge of the nonwoven fabric, until the total amount dripped was 1.0 g. The position of the tip of the saline droplet was measured when all of the saline was absorbed by the nonwoven fabric and the saline droplet disappeared from the surface of the nonwoven fabric. The distance between this position and the position where the saline was dropped onto the nonwoven fabric surface, i.e., the longest distance the saline droplet traveled across the nonwoven fabric surface, was determined.

[0081] For the second run-off measurement, the same nonwoven fabric sample used in the first run-off measurement was used. 30 seconds after the end of the first run-off measurement, saline solution was dropped at the same location as in the first run-off measurement, and the distance the saline solution flowed across the nonwoven fabric surface was determined. For the third and subsequent run-off measurements, the same process was repeated using the previous nonwoven fabric sample. The results are shown in Table 1. It is thought that the hydrophilicity of the fibers increases in the order of fiber treatment agents D, A, B, and C when wet.

[0082] [Table 1]

[0083] Furthermore, when we calculated the runoff indicator mentioned above, the results were as follows. Fiber treatment agent A: 19.5 Fiber treatment agent B: 14.9 Fiber treatment agent C: 13.6 Fiber treatment agent D: 61.4

[0084] [Water resistance of hydrophilic fiber treatment agents (water resistance index)] The water resistance index of fiber treatment agents A to D was evaluated using the following method. (1) A concentric core-sheath composite fiber (fineness: 2.0 dtex, fiber length: 45 mm) (manufactured by Daiwabo Polytech Co., Ltd., NBF®, product number (SH)) with polyethylene terephthalate as the core and high-density polyethylene as the sheath, and a composite ratio (core / sheath, mass ratio) of 60 / 40, was treated with 0.40% by mass of a fiber treatment agent. A nonwoven fabric sample (basis weight: 20.0 g / m²) was then processed using the parallel carding method and the air-through method (heating temperature: 135°C, processing time: 10 seconds, air velocity: 1.0 m / s). 2 We manufactured and prepared a product with the following dimensions: 10.0cm (height) x 10.0cm (width), and a thickness of 1.2mm. The following items were also prepared. Plate with injection tube (using the Strike-through plate described in NWSP 070.3.R0 (15) of EDANA Nonwovens Standard Procedures - Edition 2015) 0.90% physiological saline (colored with blue dye) Filter paper (product name: Lister Paper (Grade 989, 10cm x 10cm) manufactured by MEZGER inc.)

[0085] (2) Method The absorption time was measured using the following method. (i) Three sheets of filter paper were stacked, and a nonwoven fabric sample was stacked on top of that. A plate with an injection tube was placed on top of that. (ii) 5.0 ml of physiological saline solution warmed to approximately 37°C was injected through the tube. The time from injection until the physiological saline solution was no longer visible on the surface of the nonwoven fabric (when the physiological saline solution could no longer be detected as a liquid) was measured and defined as the absorption time. (iii) After standing for 30 seconds after absorption, the above (ii) was repeated and measurements were taken twice. A total of three absorption times were measured. (iv) The water resistance index was calculated using the following formula. Formula: Water resistance index = 3rd absorption time (seconds) - 1st absorption time (seconds)

[0086] The water resistance index values ​​for fiber treatment agents A to D are as follows. Fiber treatment agent A: 6.2 Fiber treatment agent B: 1.0 Fiber treatment agent C: 1.0 Fiber treatment agent D: 49.0 The lower the water resistance index, the higher the water resistance is considered to be. It is believed that the water resistance increases in the order of fiber treatment agents D, A, B, and C (however, B and C are almost the same).

[0087] Furthermore, based on the absorption time used to calculate the above water resistance index, the ratio of the third absorption time (seconds) to the first absorption time (seconds) for fiber treatment agents A to D (third absorption time (seconds) / first absorption time (seconds)) was as follows. A smaller value for this ratio indicates higher water resistance. Fiber treatment agent A: 8.0 Fiber treatment agent B: 2.3 Fiber treatment agent C: 2.0 Fiber treatment agent D: 50.5

[0088] [Thickness of nonwoven fabric] The thickness of the nonwoven fabric was measured using a thickness measuring instrument (product name THICKNESS GAUGE model CR-60A, manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.) with a load of 300 Pa applied to the nonwoven fabric.

[0089] [Measurement of contact angle before and after liquid passage] The contact angles of the nonwoven fabric before and after liquid permeation were measured using the method described above. The measurement results are shown in Table 4.

[0090] [Example 1] Using fiber 1 treated with 0.40% by mass of fiber treatment agent A, a first fiber web, which would become the first fiber layer, was manufactured using a parallel carding machine. The basis weight of the first fiber web was approximately 8 g / m². 2 That was the case. Using fiber 2 treated with 0.4% by mass of fiber treatment agent A, a second fiber web, which would become the second fiber layer, was manufactured using a parallel carding machine. The basis weight of the second fiber web was approximately 12 g / m². 2 That was the case. The first fiber web and the second fiber web were overlapped and heat-treated at 135°C using a hot air penetration heat treatment machine to integrate them and obtain the nonwoven fabric of Example 1. The basis weight of the nonwoven fabric of Example 1 was 18.2 g / m². 2 The thickness was 1.32 mm.

[0091] [Examples 2-4] and [Comparative Examples 4-5] For Examples 2-4 and Comparative Examples 4-5, the nonwoven fabrics for Examples 2-4 and Comparative Examples 4-5 were obtained using the fibers and fiber treatment agents described in Tables 2-3, and the same method as the method for producing the nonwoven fabric in Example 1 described above.

[0092] [Comparative Examples 1-3 and 6] For Comparative Examples 1-3 and 6, the nonwoven fabrics of Comparative Examples 1-3 and 6 were obtained using the same method as the method for producing the nonwoven fabric of Example 1 described above, except that a second fiber web was not produced and laminated using the fibers and fiber treatment agents described in Table 3.

[0093] The nonwoven fabrics obtained in this manner were used to produce absorbent articles for evaluation, and their absorbency was assessed. [Manufacturing of absorbent articles] An absorbent article with a three-layer structure of top sheet / second sheet / absorbent core was removed from a commercially available diaper (product name GOO.N®, manufactured by Daio Paper Corporation). The top sheet was peeled off and removed from the absorbent article, and the nonwoven fabrics from the above-described examples and comparative examples were laminated in its place to obtain an absorbent article for evaluation. During lamination, the first fiber layer was positioned to face outwards. The liquid absorbency (wet back, liquid absorption time, and diffusion length) of the nonwoven fabrics from the examples and comparative examples was evaluated using this absorbent article for evaluation.

[0094] [Wetback] The wet bags of the nonwoven fabrics in the examples and comparative examples were evaluated by the following method. (1) The following items were prepared to measure the amount of wet bag. Absorbent articles for evaluation of the above-described examples and comparative examples Plate with injection tube (inner diameter of the tube bottom: 2.5 cm) 0.90% physiological saline (colored with blue dye) Filter paper (ADVANTEC® No.2, manufactured by Toyo Filter Paper Co., Ltd.) 10cm x 10cm Weight (5kg) 10cm x 10cm

[0095] (2) Method The amount of wet back was measured according to the following procedure. (i) The absorbent material for evaluation was placed with the nonwoven fabric (42 cm long x 21 cm wide) facing upwards, and the plate with the injection tube was placed on top of it. (ii) 50 ml of physiological saline solution warmed to approximately 37°C was poured into the tube. The tube was left to stand until the physiological saline solution was no longer visible on the surface of the nonwoven fabric (physiological saline solution could no longer be detected as a liquid). (iii) Remove the plate with the injection chamber and let it stand for 10 minutes. (iv) Thirty sheets of filter paper, whose mass had been measured beforehand, were placed on a nonwoven fabric, and a 5 kg weight was placed on top of them for 20 seconds. After that, the mass of the filter paper was measured. The difference between the mass of the filter paper before it was placed on the nonwoven fabric and the mass of the filter paper after it was placed on the nonwoven fabric and the weight was placed on top of it corresponds to the amount of wet back. (vi) Returning to (i) above, (i) to (iv) were repeated three times to perform the measurement. A total of four wet back tests were performed.

[0096] Three samples were prepared for each sample (nonwoven fabric). The average of the wet back volume measured for each of the three samples was defined as the wet back volume of that sample. The results are shown in Tables 2 and 3. A lower wet back value is preferable because less moisture seeping from the nonwoven fabric means less stuffiness on the skin.

[0097] [Absorption time] During the measurement of the wet bag described above, the time from the injection of saline solution until the saline solution was no longer visible on the nonwoven fabric surface (i.e., the saline solution could no longer be detected as a liquid) was measured and defined as the absorption time. The results are shown in Tables 2 and 3. Since faster absorption results in less moisture on the skin, a smaller absorption time (in seconds) is preferable.

[0098] [Diffusion length] During the measurement of the wet bag described above, the length of the absorbent material in the vertical direction that absorbed the saline solution was measured 5 minutes after the injection of saline solution, and this was defined as the diffusion length. The results are shown in Tables 2 and 3. A larger diffusion length (cm) is preferable, as it is considered that the entire absorbent material can be effectively utilized.

[0099] [Table 2]

[0100] [Table 3]

[0101] [Table 4]

[0102] Examples 1 and 4 are compared with Comparative Examples 1 and 3, respectively. It can be seen that laminating a single layer improves the repeated durability in terms of the amount of wet back, i.e., the 3rd or 4th wet back. Example 3 is compared with Comparative Example 2. It can be seen that laminating the single layer significantly improves the repeated durability in terms of the 2nd to 4th liquid absorption times. Examples 1, 3, and 4, and Comparative Examples 1 to 3, used fiber treatment agents A to C. Fiber treatment agents A to C all possess high hydrophilicity and high water resistance. It was found that using these fiber treatment agents in the examples improved repeated durability by laminating the single layer.

[0103] Examples 1, 3-4 were compared with Comparative Example 4. In Examples 1, 3-4, fiber treatment agents A-C, which have high hydrophilicity and high water resistance, were used for both the first and second fiber layers, while in Comparative Example 4, fiber treatment agent D, which has high hydrophilicity but low water resistance, was used for both the first and second fiber layers. It was found that using a fiber treatment agent with high hydrophilicity and high water resistance improved the repeated durability in terms of the amount of wet back and the repeated durability in terms of the liquid absorption time, i.e., the wet back amount, for the third and fourth wet back tests.

[0104] For the sake of comparison, Comparative Example 4 is compared with Comparative Example 6. In both cases, fiber treatment agent D, which has high hydrophilicity but low water resistance, is used. When using fiber treatment agent D, if a single layer is laminated, the absorption time for the 3rd to 4th time is not significantly different, but the amount of wet back for the 3rd to 4th time actually worsens. Therefore, it can be understood that when creating a laminated structure, it is important to use a fiber treatment agent that has both high hydrophilicity and high water resistance.

[0105] Examples 1, 3-4 were compared with Comparative Example 5. Both the first and second fiber layers were treated with fiber treatment agents A-C, which possess high hydrophilicity and high water resistance. In Examples 1, 3-4, the same fiber treatment agent was used for the first and second fiber layers. However, in Comparative Example 5, different fiber treatment agents were used for the first and second fiber layers. In this case, no significant differences were observed regarding wet back and liquid absorption rate.

[0106] However, using different fiber treatment agents for the first and second fiber layers is more complicated and costly compared to using the same fiber treatment agent. Furthermore, if the nonwoven fabric is rolled up and stored for a long period, especially in high-temperature environments, the two fiber treatment agents may mix, preventing the fabric from performing as intended. In such cases, the benefit of using different fiber treatment agents to create different hydrophilicity levels may be effectively eliminated.

[0107] We compare Example 1 and Example 4. It can be seen that using fiber treatment agent A (Example 1), which has a high hydrophilicity and not excessively high water resistance, improves the wet-back process after the third or fourth repetition compared to using fiber treatment agent C (Example 4).

[0108] Furthermore, the contact angle measurement results are substantially the same as those obtained using run-off. [Industrial applicability]

[0109] The present invention provides nonwoven fabrics, sheets for absorbent articles, and absorbent articles containing the same. These are preferably improved in at least one of the following: texture, wet back volume, liquid absorption time, diffusion length, repeated durability (of wet back volume, liquid absorption time, and diffusion length), cost, and shelf life.

Claims

1. A method for manufacturing a nonwoven fabric for absorbent articles having a first fiber layer and a second fiber layer adjacent to the first fiber layer, A process for producing a first fiber web containing 50% by mass or more of concentric core sheath type composite fibers, which will form the first fiber layer, by the carding method. A process for manufacturing a second fiber web containing 70% or more by mass of concentric core sheath type composite fibers, which will become the second fiber layer, by the carding method. A process of overlapping the first fiber web and the second fiber web, and integrating the overlapped first fiber web and the second fiber web by an air-through method. Includes, The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex. The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex. The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer. The fibers forming the first fiber layer and the fibers forming the second fiber layer both possess hydrophilicity such that their degree of hydrophilicity is maintained even when they come into contact with water, and their hydrophilicity is the same. The contact angle of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer before contact with water (A1), and the contact angle of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer before contact with water (A2) satisfy the following (I): (I): A1≦80°, A2≦80°, |A1-A2|<12 The contact angle of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer after contact with water (B1) and the contact angle of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer after contact with water (B2) satisfy the following (II): (II): -5≦(B1-A1)<40°, -5≦(B2-A2)<40° A method for manufacturing a nonwoven fabric for absorbent articles, wherein the nonwoven fabric is arranged so that the first fiber layer faces human skin.

2. A method for manufacturing a nonwoven fabric for absorbent articles having a first fiber layer and a second fiber layer adjacent to the first fiber layer, A process for producing a first fiber web containing 50% by mass or more of concentric core sheath type composite fibers, which will form the first fiber layer, by the carding method. A process for manufacturing a second fiber web containing 70% or more by mass of concentric core sheath type composite fibers, which will become the second fiber layer, by the carding method. A process of overlapping the first fiber web and the second fiber web, and integrating the overlapped first fiber web and the second fiber web by an air-through method. Includes, The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex. The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex. The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer. The fibers forming the first fiber layer and the fibers forming the second fiber layer both possess hydrophilicity such that their degree of hydrophilicity is maintained even when they come into contact with water, and their hydrophilicity is the same. For the first fiber web, which forms the first fiber layer, and the second fiber web, which forms the second fiber layer, the water resistance index, determined from the liquid absorption time measured by the following method, is 15 or less. A method for manufacturing a nonwoven fabric for absorbent articles, wherein the nonwoven fabric is arranged so that the first fiber layer faces human skin. Liquid absorption time and water resistance index Using the fibers constituting the first fiber web, which will form the first fiber layer, and the fibers constituting the second fiber web, which will form the second fiber layer, nonwoven fabric samples (basis weight: 20.0 g / m², dimensions: 10.0 cm x 10.0 cm, thickness: 1.2 mm) are manufactured and prepared using the parallel card method and the air-through method (heating temperature: 135°C, processing time: 10 seconds, air velocity: 1.0 m / s). Please also prepare the following items. Plate with injection tube (Strike-through plate as described in NWSP 070.3.R0 (15) of EDANA Nonwovens Standard Procedures - Edition 2015) 0.90% physiological saline (colored with blue dye) Filter paper (product name Lister Paper (Grade 989, 10cm x 10cm) manufactured by MEZGER inc.) The liquid absorption time of each nonwoven fabric sample is measured using the following method. (i) Stack three sheets of filter paper, then stack a nonwoven fabric sample on top. Place the plate with the injection tube on top of that. (ii) Inject 5.0 ml of physiological saline solution warmed to 37°C through the tube. Measure the time from injection until the physiological saline solution is no longer visible on the surface of the nonwoven fabric (when the physiological saline solution can no longer be detected as a liquid), and define this as the absorption time. (iii) After standing for 30 seconds after absorption, repeat (ii) above and take measurements twice. Measure the absorption time a total of three times. (iv) The water resistance index shall be calculated using the following formula. Water resistance index = Time to absorb liquid during the third absorption (seconds) - Time to absorb liquid during the first absorption (seconds)

3. A method for manufacturing a nonwoven fabric for absorbent articles having a first fiber layer and a second fiber layer adjacent to the first fiber layer, A process for producing a first fiber web containing 50% by mass or more of concentric core sheath type composite fibers, which will form the first fiber layer, by the carding method. A process for manufacturing a second fiber web containing 70% or more by mass of concentric core sheath type composite fibers, which will become the second fiber layer, by the carding method. A process of overlapping the first fiber web and the second fiber web, and integrating the overlapped first fiber web and the second fiber web by an air-through method. Includes, The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex. The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex. The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer. The fibers forming the first fiber layer and the fibers forming the second fiber layer both possess hydrophilicity such that their degree of hydrophilicity is maintained even when they come into contact with water, and their hydrophilicity is the same. For the first fiber web which forms the first fiber layer and the second fiber web which forms the second fiber layer, the ratio of the third absorption time (seconds) to the first absorption time (seconds) (third absorption time (seconds) / first absorption time (seconds)) measured by the method described below is 30 or less. A method for manufacturing a nonwoven fabric for absorbent articles, wherein the nonwoven fabric is arranged so that the first fiber layer faces human skin. Liquid absorption time Using the fibers constituting the first fiber web, which will form the first fiber layer, and the fibers constituting the second fiber web, which will form the second fiber layer, nonwoven fabric samples (basis weight: 20.0 g / m², dimensions: 10.0 cm x 10.0 cm, thickness: 1.2 mm) are manufactured and prepared using the parallel card method and the air-through method (heating temperature: 135°C, processing time: 10 seconds, air velocity: 1.0 m / s). Please also prepare the following items. Plate with injection tube (Strike-through plate as described in NWSP 070.3.R0 (15) of EDANA Nonwovens Standard Procedures - Edition 2015) 0.90% physiological saline (colored with blue dye) Filter paper (product name Lister Paper (Grade 989, 10cm x 10cm) manufactured by MEZGER inc.) The liquid absorption time of each nonwoven fabric sample is measured using the following method. (i) Stack three sheets of filter paper, then stack a nonwoven fabric sample on top. Place the plate with the injection tube on top of that. (ii) Inject 5.0 ml of physiological saline solution warmed to 37°C through the tube. Measure the time from injection until the physiological saline solution is no longer visible on the surface of the nonwoven fabric (when the physiological saline solution can no longer be detected as a liquid), and define this as the absorption time. (iii) After standing for 30 seconds after absorption, repeat (ii) above and take measurements twice. Measure the absorption time a total of three times.

4. A method for manufacturing a nonwoven fabric for absorbent articles having a first fiber layer and a second fiber layer adjacent to the first fiber layer, A process for producing a first fiber web containing 50% by mass or more of concentric core sheath type composite fibers, which will form the first fiber layer, by the carding method. A process for manufacturing a second fiber web containing 70% or more by mass of concentric core sheath type composite fibers, which will become the second fiber layer, by the carding method. A process of overlapping the first fiber web and the second fiber web, and integrating the overlapped first fiber web and the second fiber web by an air-through method. Includes, The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex. The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex. The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer. The fibers forming the first fiber layer and the fibers forming the second fiber layer both possess hydrophilicity such that their degree of hydrophilicity is maintained even when they come into contact with water, and their hydrophilicity is the same. For the first fiber web, which forms the first fiber layer, and the second fiber web, which forms the second fiber layer, the run-off index measured by the following method is between 13.7 and 55. A method for manufacturing a nonwoven fabric for absorbent articles, wherein the nonwoven fabric is arranged so that the first fiber layer faces human skin. Runoff indicator Using the fibers constituting the first fiber web, which will form the first fiber layer, and the fibers constituting the second fiber web, which will form the second fiber layer, nonwoven fabric samples (basis weight: 20.0 g / m², dimensions: 10.0 cm x 10.0 cm, thickness: 1.2 mm) are manufactured and prepared using the parallel card method and the air-through method (heating temperature: 135°C, processing time: 10 seconds, air velocity: 1.0 m / s). A triangular prism with a base shaped like an isosceles right triangle is laid on its side to create a support base with an inclined surface at a 45-degree angle to the horizontal plane. Two sheets of filter paper (product name Lister Paper (Grade 989, 27.5 cm x 14 cm) manufactured by MEZGER inc.) are placed on top of each other, and a nonwoven fabric sample is placed on top of them and secured. 0.90% physiological saline (colored with blue dye) is dripped from a microtube pump or burette at a rate of 1.0 g / 30 sec over 30 seconds, 1 cm below the top edge of the nonwoven fabric, until the total amount dripped is 1.0 g. The position of the tip of the saline droplet is measured when all of the saline is absorbed by the nonwoven fabric and the saline droplet disappears from the surface of the nonwoven fabric. The distance between this position and the position where the saline was dropped onto the nonwoven fabric surface, i.e., the longest distance the saline droplet traveled across the nonwoven fabric surface, is determined. For the second run-off measurement, use the same nonwoven fabric sample as in the first run-off measurement. 30 seconds after the end of the first run-off measurement, drop saline solution onto the same spot where it was dropped in the first run-off measurement, and measure the distance the saline solution traveled across the nonwoven fabric surface. For the third and subsequent run-off measurements, use the same nonwoven fabric sample as before and repeat the measurement process. Runoff measurements are taken five times, and the runoff index is calculated from the runoff values ​​of the first to fifth measurements using the following formula.

5. A method for producing a nonwoven fabric for absorbent articles according to any one of claims 1 to 4, wherein the fibers forming the first fiber layer and the fibers forming the second fiber layer are fibers that have been treated to make them hydrophilic such that the degree of their hydrophilicity and water resistance are substantially the same.

6. Both the fibers forming the first fiber layer and the fibers forming the second fiber layer are subjected to hydrophilic treatment by applying a hydrophilic fiber treatment agent as part of the hydrophilic treatment. The method for producing a nonwoven fabric for absorbent articles according to claim 5, wherein the hydrophilic fiber treatment agent contains a C12 alkyl phosphate potassium salt as a hydrophilizing agent.

7. A method for producing a nonwoven fabric for absorbent articles according to claim 4, wherein the sum of run-offs 2 to 5, which is the degree of hydrophilicity of the hydrophilizing agent attached to the fibers forming the first fiber layer and the fibers forming the second fiber layer, is 8.8 to 30.

8. A method for producing a nonwoven fabric for absorbent articles according to any one of claims 1 to 7, wherein the fibers forming the first fiber layer and the fibers forming the second fiber layer are treated with the same fiber treatment agent.

9. A method for producing a nonwoven fabric for absorbent articles according to any one of claims 1 to 8, wherein the fibers forming the first fiber layer include concentric core-sheath composite fibers in which the core component is polyester and the sheath component is high-density polyethylene.

10. A method for producing a nonwoven fabric for absorbent articles according to any one of claims 1 to 9, wherein the ratio of the basis weight of the second fiber layer to the basis weight of the first fiber layer (basis weight of the second fiber layer / basis weight of the first fiber layer) is 0.8 to 3.

0.

11. A method for producing a nonwoven fabric for absorbent articles according to claim 1, wherein the absolute value of the difference between B1-A1 and B2-A2, i.e., (B1-A1)-(B2-A2), in the contact angles before contact with water (A1, A2) and after contact with water (B1, B2), satisfies the following (III). (III):|(B1-A1)-(B2-A2)|≦18

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