Nonwoven fabric for absorbent article

Abstract

To provide a nonwoven fabric for absorbent article, which contains cellulose fibers and suppresses liquid return during use.SOLUTION: A nonwoven fabric for absorbent article contains 90 mass% or more of cellulose fibers and is formed by entangling fibers with each other. The nonwoven fabric for absorbent article has a first surface and a second surface positioned on the opposite side thereto. The first surface has protrusions and bottoms. The bottom has a plurality of apertures. Ratio B2 / B1 representing a ratio of basis weight B2 of the protrusion to basis weight B1 of a portion excluding the apertures on the bottom is 2 or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a nonwoven fabric for absorbent articles. [Background technology]

[0002] Conventionally, nonwoven fabrics made of resins such as polyethylene, polypropylene, polyester, and polyamide have been used for absorbent articles. However, nonwoven fabrics made of these resins have the disadvantages of being poorly biodegradable and placing a high burden on the environment. In recent years, therefore, nonwoven fabrics containing cellulose fibers, which have higher biodegradability, have been proposed.

[0003] Patent Document 1 describes a topsheet for use in absorbent articles, comprising a first layer made of a spunlace nonwoven fabric containing at least 15% by weight of natural fibers, and a second layer joined to the first layer. The first layer includes a plurality of protrusions and a plurality of holes, the plurality of holes being located between the protrusions. The first layer also at least partially penetrates the second layer of the topsheet at the holes. The topsheet of Patent Document 1 having such structural characteristics is described as having excellent structural strength and mechanical strength.

[0004] Patent Document 2 describes a nonwoven fabric for absorbent articles that contains more than 90% by mass of cellulosic fibers and has entangled fibers. The nonwoven fabric has a plurality of first entangled parts spaced apart from each other and a plurality of second entangled parts spaced apart from each other, and each of the first entangled parts has a regular pattern formed of a plurality of areas of high fiber density and a plurality of areas of low fiber density. It is described that a sheet for absorbent articles containing the nonwoven fabric described in Patent Document 2 has little fuzz and is excellent in design. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2020-536707 [Patent Document 2] International Publication No. 2019 / 004369 Summary of the Invention [Problem to be solved by the invention]

[0006] Since cellulose fibers do not have sufficient water retention, nonwoven fabrics for absorbent articles containing cellulose fibers have room for improvement in terms of liquid return during use. This can also lead to sticky discomfort and skin rashes, and there is room for improvement in this respect as well. However, the nonwoven fabrics for absorbent articles described in Patent Documents 1 and 2 have not fully addressed this issue, and therefore do not adequately suppress liquid return. Therefore, an object of the present invention is to provide a nonwoven fabric for absorbent articles which contains cellulose fibers and is suppressed from causing liquid return during use. [Means for solving the problem]

[0007] The present invention relates to a nonwoven fabric for absorbent articles, which contains 90% by mass or more of cellulose fibers and in which the fibers are entangled with each other, The nonwoven fabric for absorbent articles has a first surface and a second surface located on the opposite side. In one embodiment of the nonwoven fabric for absorbent articles of the present invention, the first surface preferably has a protrusion and a bottom. In one embodiment of the nonwoven fabric for absorbent articles of the present invention, the bottom portion preferably has a plurality of openings. In one embodiment of the nonwoven fabric for absorbent articles of the present invention, it is preferable that the ratio B2 / B1 of the basis weight B2 of the protrusions to the basis weight B1 of the portions other than the apertures in the bottom is 2 or more. Other features, advantages and embodiments of the present invention are described below. Effect of the Invention

[0008] According to the present invention, there is provided a nonwoven fabric for absorbent articles which is suppressed from causing liquid return during use. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic perspective view of a first surface side of one embodiment of a nonwoven fabric for absorbent articles of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view that diagrammatically shows a cross section taken along line AA in FIG. 1 (a cross section along the machine direction MD and thickness direction). [Diagram 3] FIG. 3 is a schematic cross-sectional view of the protrusion shown in FIG. [Figure 4] FIG. 4 is a schematic diagram of a main part (a hydroentangling device) of a suitable embodiment of the manufacturing device for the nonwoven fabric for absorbent articles of the present invention. [Diagram 5] FIG. 5 is a schematic perspective view of the concave-convex surface (surface on which the web is placed) of the concave-convex support body shown in FIG. [Figure 6] Figure 6(a) is a schematic plan view of the uneven surface (the surface on which the web is placed) of the uneven support shown in Figure 5, Figure 6(b) is a cross-sectional view showing a schematic cross-section along line BB (cross-section along the machine direction MD and thickness direction) of Figure 6(a), and Figure 6(c) is a cross-sectional view showing a schematic cross-section along line CC (cross-section along the vertical direction CD and thickness direction) of Figure 6(a). [Figure 7] 7(a) to 7(c) are schematic views showing one embodiment of a water jetting step using the device shown in FIG. 4, and are cross-sectional views along the machine direction and thickness direction of the concave-convex support body. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described below based on preferred embodiments with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings are basically schematic, and the ratio of each dimension may differ from the actual one.

[0011] First, the nonwoven fabric for absorbent articles of the present invention (hereinafter, "nonwoven fabric for absorbent articles" may also be simply referred to as "nonwoven fabric") will be described. Figures 1 to 3 show a nonwoven fabric 1, which is one embodiment of the nonwoven fabric. The nonwoven fabric 1 contains cellulose fibers and is formed by intertwining the fibers. The nonwoven fabric 1 has a first surface 1a and a second surface 1b located on the opposite side. The first surface 1a has a protrusion 2 and a bottom 6. More specifically, on the first surface 1a, a recess 3 exists between adjacent protrusions 2, 2. The recess 3 is a space defined by a plurality of protrusions 2 and a fiber layer connecting the plurality of protrusions 2, and the fiber layer forms a bottom 6 of the recess 3 (hereinafter, the "bottom of the recess" may also be simply referred to as the "bottom").

[0012] It is preferable that the angle 42 formed by the protrusions 2 and the bottom 6 is 60° to 120° in a cross-sectional view taken along the thickness direction of the nonwoven fabric 1 as shown in FIG. Angle 42 is the angle between tangent 40 to bottom 6 and tangent 41 to protrusion 2. Tangent 40 extends along bottom 6 on first surface 1a of nonwoven fabric 1 and is perpendicular to the thickness direction of nonwoven fabric 1 (the vertical direction in FIG. 3). There may be multiple tangents 41 depending on the cross-sectional shape of protrusion 2, and in that case, point of contact 43 with protrusion 2 is regarded as the point farthest from the center of protrusion 2 in plan view. The contact point 43 is located at the boundary between the protrusion 2 and the bottom 6. In other words, with an imaginary straight line passing through the contact point 43 and extending in the thickness direction of the nonwoven fabric 1 as the boundary, one side is the protrusion 2 and the other side (the side where the protrusion 2 is not formed) is the bottom 6.

[0013] The first surface 1a is an uneven surface having an uneven shape formed by protrusions 2 and recesses 3. On the other hand, the second surface 1b is substantially flat. The term "substantially flat" as used herein includes a flat surface without any irregularities and a surface having minute irregularities that are clearly smaller than those of the first surface 1a. In the latter case, minute depressions (not shown) may be present on the surface of the protrusion 2 on the second surface 1b side. The minute depressions typically do not have a constant depression depth, but have a maximum depth at the center of the protrusion 2 in a plan view, and have a relatively gentle arc-shaped contour line with the maximum depth as its bottom. Due to the presence of the convex portions 2 in the nonwoven fabric 1, when the nonwoven fabric 1 is used with the first surface 1a facing the skin of the user, the contact area between the nonwoven fabric 1 and the skin of the user is reduced, thereby preventing liquid from returning.

[0014] The protrusions 2 are preferably filled with fibers and have a solid structure. The solid structure of the protrusions 2 can improve the cushioning properties of the nonwoven fabric 1 having the protrusions 2. In addition, the protrusions 2 are less likely to be crushed even when the nonwoven fabric 1 is subjected to pressure due to contact with the skin of the user, etc., so that the return of liquid in the nonwoven fabric 1 can be further suppressed.

[0015] The nonwoven fabric 1 has a plurality of openings 4 penetrating the nonwoven fabric 1 in the thickness direction. The openings 4 are areas where the constituent fibers of the nonwoven fabric 1 are not present, and are formed in the bottoms 6 of the recesses 3. Unlike the fine holes formed between the fibers, the openings 4 are holes formed by processing, and have an open area much larger than the fine holes formed between the fibers. In the nonwoven fabric 1, as shown in FIG. 1, on the first surface 1a, the protrusions 2 and the openings 4 are alternately arranged in a direction X and also alternately arranged in a direction Y perpendicular to the direction X. The open pores 4 have the effect of improving the liquid permeability of the nonwoven fabric 1 .

[0016] Direction X corresponds to the machine direction (MD) during production of nonwoven fabric 1, i.e., the running direction of nonwoven fabric 1 or its raw material or intermediate product (e.g., a web), and direction Y corresponds to the vertical direction (CD; cross machine direction) perpendicular to MD.

[0017] The opening area of ​​the openings 4 on the first surface 1a side (the protruding surface side of the convex portion) is not particularly limited, but from the viewpoint of the balance between the effects that can be achieved by the openings 4 (the effect of improving air permeability and liquid permeability, etc.) and ensuring sufficient strength for practical use, it is preferably 1 mm 2 More than 2mm, preferably 2 More than 5mm, preferably 2 Less than 4mm, more preferably 2 Less than 3 mm, more preferably 2 From the same viewpoint, the area ratio of the total area of ​​the open holes in the nonwoven fabric of the present invention is preferably 15% or more, more preferably 30% or more, and preferably 50% or less, more preferably 40% or less. That is, the area ratio of the total area of ​​the open holes in the nonwoven fabric of the present invention is preferably 15% or more and 50% or less. The "area ratio of the total area of ​​the openings" is the ratio of the total area of ​​the openings 4 to the area of ​​the first surface 1a. The open area of ​​the openings 4 and the area ratio of the total area of ​​the openings are measured by the following method.

[0018] <Method for measuring the open area of ​​the openings in a nonwoven fabric> Using a microscope VHX6000 (product name, manufactured by Keyence Corporation), the nonwoven fabric is placed on the base of the microscope with the first surface 1a of the nonwoven fabric facing up. Next, the magnification is increased to 50 times to focus on the nonwoven fabric, and the open area of ​​the opening 4 is measured using a built-in function according to the following procedure. (1) Method for determining the opening 4 The edge of the aperture 4 is determined by the automatic area measurement function of the microscope. The threshold value is set to 0, and the bright (white) parts are extracted, and the boundary between the parts that are not extracted and the parts that are extracted is taken as the edge of the aperture 4. By measuring the area of ​​the bright (white) parts, the aperture area (mm 2 ) is calculated.

[0019] <Method of measuring the total area of ​​the openings 4 relative to the area of ​​the first surface 1a (area ratio of the total area of ​​the openings)> Using a high-precision shape measurement system KS-1100 (product name, manufactured by Keyence Corporation), a laser beam is irradiated to measure the surface shape (the height and depth of the thickness that rises and falls along the surface direction of the measurement surface) of the second surface 1b of the nonwoven fabric in a no-load state (natural state without load), and an image is captured. At this time, the measurement is performed by scanning a 1 cm x 1 cm measurement range at a moving speed of 10 cm / sec over the entire measurement surface of the 5 x 5 cm measurement sample (measurement pitch: vertical 20 μm, horizontal 20 μm). The image captured above is analyzed using a shape analysis application called KS-Analyzer (product name, manufactured by Keyence Corporation). Specifically, a portion that is thinner than the thickness of the nonwoven fabric (minimum measurable scale: 0.01 μm) is extracted and binarized to obtain a surface image of that portion. The surface image of the thin portion is captured and processed using image processing software NewQube (Ver. 4.22, product name, manufactured by Nexus Co., Ltd.), and its area is measured. This area is the total area of ​​the openings 4 (hereinafter also referred to as the "total opening area"). The "area ratio of the total area of ​​the openings" is calculated by dividing the measured total area of ​​the openings by the area of ​​the second surface 1b of the measurement sample (measurement points: 251,001 points (=501 x 501)). In addition, since the area of ​​the first surface 1a and the area of ​​the second surface 1b of the measurement sample can be regarded as being the same, the "area ratio of the total area of ​​the openings" can also be regarded as being the same on the first surface 1a side and the second surface 1b side.

[0020] The three-dimensional shape of the nonwoven fabric of the present invention is formed by spraying a water flow onto a web (a fiber aggregate with no inter-fiber bonding) which is a precursor of the nonwoven fabric, and rearranging and reentangling the constituent fibers of the web, in a water flow spraying step in a suitable manufacturing method of the nonwoven fabric of the present invention described later. The three-dimensional shape includes the convex portions 2, the bottom portions 6, and the openings 4. The minute depressions which may be present on the second surface 1b of the nonwoven fabric 1 are also included in the three-dimensional shape. For example, in the water flow spraying step in a suitable manufacturing method of the nonwoven fabric 1 in the illustrated form, water is sprayed from the first surface 20a side of the uneven support 20 toward the second surface 20b side (from the second surface 1b side of the web placed on the uneven support 20 toward the first surface 1a side), and typically, the fibers in the web at the sites where the bottom portions 6 and the openings 4 are to be formed are moved by the water flow to the sites where the convex portions 2 are to be formed, and as a result, the bottom portions 6 or the openings 4 are formed at the origin of the fibers, and the convex portions 2 are formed at the destination of the fibers. The projections 2, bottoms 6 and openings 4 formed by such rearrangement and reentanglement of the fibers can each maintain their own shape.

[0021] In nonwoven fabric 1, the basis weight of the constituent fibers is non-uniform, with the basis weight being relatively large at protrusions 2 and relatively small at bottom 6. The basis weight at openings 4 provided at bottom 6 is zero. Note that nonwoven fabric 1 is typically composed only of fibers, and in that case, the "basis weight of the nonwoven fabric" is the same as the "basis weight of the constituent fibers of the nonwoven fabric." In addition, in this specification, the "basis weight of bottom 6" means the "basis weight of the portions of bottom 6 other than openings 4."

[0022] The basis weight of the nonwoven fabric 1 is not particularly limited, but from the viewpoint of the balance of various properties such as appearance, strength, cushioning properties, and portability in the form of a product such as an absorbent article, it is preferably 15 g / m 2 More preferably, 25 g / m 2 More than 100 g / m 2 Less than 80 g / m 2 The following is the result. The basis weight B2 of the protrusion 2 is larger than the basis weight B1 of the bottom 6, and is preferably 40 g / m 2 More preferably, 50 g / m2 More preferably, 55 g / m 2 More than 70 g / m 2 Less than 65g / m 2 The following is the result. The basis weight B1 of the bottom portion 6 is preferably 5 g / m2, assuming that it is smaller than the basis weight of the protrusions 2. 2 More preferably, 7 g / m 2 More preferably, 9 g / m 2 More than 20 g / m 2 Less than 14g / m 2 The following is the result. The ratio B2 / B1 of the basis weight B2 of the protrusions to the basis weight B1 of the bottom is 2 or more. Furthermore, B2 / B1 is preferably 3 or more, more preferably 3.5 or more, even more preferably 4 or more, even more preferably 4.5 or more, and even more preferably 4.6 or more. Furthermore, B2 / B1 is preferably 10 or less, more preferably 7 or less, and even more preferably 5 or less. By making B2 / B1 2 or more, it is possible to suppress the collapse of the nonwoven fabric due to pressure, and also to shorten the absorption time and improve the liquid return performance. Furthermore, it is possible to impart a cushioning feel to the nonwoven fabric 1. Furthermore, by making B2 / B1 10 or less, the softness of the protrusions 2 can be ensured, and in addition to suppressing any discomfort felt when worn, a good appearance can be maintained. The basis weight of parts of the nonwoven fabric such as the protrusions 2 and the bottoms 6 is measured by the following method.

[0023] <Method for measuring the basis weight of some nonwoven fabrics> A measurement sample is obtained by cutting out an area of ​​5 cm square in plan view from the nonwoven fabric to be measured (e.g., nonwoven fabric 1). If the area cannot be secured due to the small area of ​​the nonwoven fabric to be measured, an area as large as possible is cut out and used as the measurement sample. A measurement target portion is cut out from the measurement sample, and the mass of the measurement target portion is measured in grams using an electronic balance, and the measured value is divided by the area of ​​the measurement target portion to calculate the basis weight of the measurement target portion. The above operation is performed three times, and the average value of the three measured values ​​(basis weight of the measurement target portion) is used as the basis weight of the measurement target portion. The measurement of the basis weight of the projections 2 and the bottom 6 of the nonwoven fabric 1 will be described as an example. First, a measurement sample of 5 cm square cut out from the nonwoven fabric 1 is cut into the projections 2 and the bottom 6 using a cutting tool such as scissors. The boundaries between the projections 2 and the bottom 6 are defined as described above. Next, the total mass of the cut projections 2 and the total mass of the bottom 6 are measured using an electronic balance. Separately, the "sum of the area of ​​all projections present on the measurement surface of the measurement sample" (hereinafter also referred to as "total projection area") and the "sum of the area of ​​all bottoms present on the measurement surface of the measurement sample" (hereinafter also referred to as "total bottom area") are measured separately by the <Method for measuring the area of ​​projections and bottoms of a nonwoven fabric> described below. Then, the basis weight of the projections 2 is calculated by dividing the total mass of the projections 2 by the total projection area. The basis weight of the bottom 6 is also calculated by dividing the total mass of the bottom 6 by the total bottom area.

[0024] <Method for measuring the total area of ​​protrusions and bottoms of nonwoven fabric> This measurement method is carried out in accordance with the following steps (1) to (7). (1) A measurement sample is prepared by cutting out an area of ​​5 cm square in plan view from the nonwoven fabric to be measured (e.g., nonwoven fabric 1). If the area cannot be secured due to the small area of ​​the nonwoven fabric to be measured, an area as large as possible is cut out and used as the measurement sample. The area of ​​this measurement sample should be the same as the area of ​​the measurement sample used in the above <Method for measuring the basis weight of a portion of a nonwoven fabric>. (2) Place the measurement sample with the uneven surface, which is the measurement surface, facing up. For example, if the measurement sample is cut out from the nonwoven fabric 1, the first surface 1a is the measurement surface, so place the measurement sample with the first surface 1a facing upward. (3) Using a high-precision shape measurement system KS-1100 (product name, manufactured by Keyence Corporation), a laser beam is irradiated onto the measurement surface of the measurement sample to measure the surface shape (the height and depth of the thickness that rises and falls along the surface direction of the measurement surface) in a no-load state (natural state without load), and an image is captured. At this time, the measurement is performed by scanning a 1 cm x 1 cm measurement range at a moving speed of 10 cm / sec over the entire measurement surface of the 5 x 5 cm measurement sample (measurement pitch: vertical 20 μm, horizontal 20 μm). (4) A transparent acrylic plate with a mass of 170 g is placed on the measurement surface of the measurement sample, and a weight with a mass of 600 g is placed on the acrylic plate to apply a pressure of 3 kPa. In this state, the surface shape of the measurement surface is measured and an image is captured in the same manner as in (3) above. The plate used is large enough to cover the entire measurement surface of the measurement sample. (5) The images captured in (3) and (4) above are analyzed using a shape analysis application called KS-Analyzer (product name, manufactured by Keyence Corporation). Specifically, the area where the thickness changes from the no-load state to the application of a pressure of 3 kPa (minimum measurable scale: 0.01 μm) is extracted and binarized to obtain a surface image of that area. (6) The surface images of the "parts with changed thickness" obtained in (5) above are imported and processed using image processing software NewQube (Ver. 4.22, product name, manufactured by Nexus Co., Ltd.), and their areas are measured. The parts with changed thickness can be regarded as convex parts (convex parts 2 in the case of nonwoven fabric 1) on the measurement surface of the measurement sample. Therefore, the sum of the areas measured for the parts corresponds to the total convex part area. (7) Calculate the total bottom area of ​​the measurement sample using the following formula. In the formula, "area of ​​nonwoven fabric" is the area in a plan view of the uneven surface of the measurement sample (first surface 1a if the measurement sample is nonwoven fabric 1) or the opposite surface (second surface 1b if the measurement sample is nonwoven fabric 1). The total area of ​​open holes can be measured by the method described in <Method of measuring the total area of ​​open holes 4 relative to the area of ​​first surface 1a (area ratio of the total area of ​​open holes)> above. Total area of ​​bottom = area of ​​nonwoven fabric - total area of ​​convex parts - total area of ​​openings

[0025] The contact area ratio of the protrusions in the nonwoven fabric 1 is preferably 20% or more and 50% or less. The "contact area ratio of the protrusions" is determined by placing a flat plate covering the entire first surface 1a on the first surface 1a at a pressure of 12 g / cm 2 This is the ratio of the contact area between the flat plate and the protrusions 2 to the area of ​​the first surface 1a when a load of 100 g is applied. By setting the contact area ratio of the protrusions within the above range, when a worn article or the like including the nonwoven fabric of the present invention is worn, the contact area between the wearer's skin and the nonwoven fabric can be appropriately controlled, and liquid return can be suppressed while ensuring a sufficient liquid absorption rate of the nonwoven fabric. This makes it difficult for liquid to remain on the wearer's skin. The contact area ratio of the protrusions is more preferably 25% or more, even more preferably 30% or more, and even more preferably 50% or less, even more preferably 40% or less. The contact area ratio of the protrusions is measured by the following method.

[0026] <Method for measuring the contact area ratio of convex parts> This measurement method is carried out in accordance with the following steps (1) to (5). (1) A measurement sample is prepared by cutting out an area of ​​5 cm square in plan view from the nonwoven fabric to be measured (e.g., nonwoven fabric 1). If the area of ​​the nonwoven fabric to be measured is too small, etc., the measurement sample is prepared by cutting out an area of ​​as large an area as possible. (2) Place the measurement sample with its measurement surface facing up. For example, if the measurement sample is cut out from the nonwoven fabric 1, the first surface 1a (uneven surface) is the measurement surface, so place the measurement sample with the first surface 1a facing upward. (3) A transparent acrylic plate with a mass of 300 g is placed on the measurement surface of the measurement sample, and the measurement is performed at a density of 12 g / cm 2 A load of 10 ... (4) The image captured in (3) above is analyzed using a shape analysis application KS-Analyzer (product name, manufactured by Keyence Corporation). 2 The contact area with the acrylic plate (minimum measurable scale: 0.01 μm) with the load applied is extracted and binarized to obtain a surface image of that area. (5) The surface image obtained in (4) above is imported and processed using image processing software NewQube (Ver. 4.22, product name, manufactured by Nexus Co., Ltd.), and their areas are measured. The area is regarded as the contact area of ​​the protrusions, and this is divided by the area of ​​the measurement sample to calculate the contact area ratio of the protrusions.

[0027] The area ratio of the bottom portion in the nonwoven fabric 1 is preferably 10% or more and 50% or less. The "area ratio of the bottom portion" is the ratio of the area of ​​the bottom portion 6 present on the first surface 1a to the area of ​​the first surface 1a. By setting the area ratio of the bottom portion within the above range, the appearance of the nonwoven fabric can be maintained and the strength required of the nonwoven fabric can be ensured. The area ratio of the bottom portion is more preferably 10% or more, even more preferably 15% or more, and more preferably 50% or less, even more preferably 40% or less.

[0028] The apparent thickness AT of the nonwoven fabric 1 (see FIG. 2) is not particularly limited, but is preferably 0.4 mm or more, more preferably 0.8 mm or more, and preferably 3.0 mm or less, more preferably 2.5 mm or less, from the viewpoint of the balance of various properties such as appearance, strength, cushioning, and portability in the form of a product such as an absorbent article. The apparent thickness AT of the nonwoven fabric 1 refers to the length along the thickness direction between the top of the protrusion 2 and the second surface 20b as shown in FIG. 2, and when the nonwoven fabric 1 has a fiber-free portion such as a hollow portion, it may include the thickness of the fiber-free portion. The apparent thickness of the nonwoven fabric is measured by the following method.

[0029] <Method for measuring the apparent thickness of nonwoven fabric> A measurement sample is prepared by cutting out an area of ​​5 cm square in plan view from the nonwoven fabric to be measured (e.g., nonwoven fabric 1). If the area cannot be secured due to the small area of ​​the nonwoven fabric to be measured, an area of ​​as large an area as possible is cut out and used as the measurement sample. With a load of 0.5 Pa applied to the measurement sample, the thickness of the measurement sample is measured using a laser thickness meter (e.g., Omron Corporation's "ZSLD-80"). The above operation is carried out three times, and the average of the three measured values ​​obtained is used as the apparent thickness of the nonwoven fabric.

[0030] In the illustrated embodiment, each of the plurality of protrusions 2 is dome-shaped and has a circular shape in a plan view of the first surface 1a. In the present invention, the shape of the protrusions 2 is not particularly limited, and any shape may be selected. In addition, the shapes of the plurality of protrusions 2 may be different from each other. In the illustrated embodiment, each of the multiple openings 4 has an elliptical shape that is long in one direction (direction X) in a plan view. In the present invention, the shape of the openings 4 is not particularly limited, and any shape may be selected. Furthermore, the multiple openings 4 may have different shapes. Furthermore, although the nonwoven fabric 1 in the illustrated form has a single layer structure, the nonwoven fabric of the present invention may have a laminated structure in which two or more fiber layers are laminated in the thickness direction.

[0031] The nonwoven fabric of the present invention contains cellulose fibers. As the cellulose fibers, any fiber that can be used for this type of cloth product can be used without any particular limitation. Examples of the cellulose fibers include natural cellulose fibers such as cotton fibers harvested from cotton plants, regenerated cellulose fibers such as rayon, cupra, lyocell, and tencel, and pulp. Among the above cellulose fibers, cotton fibers, rayon, lyocell, and tencel are preferred, and cotton fibers are more preferred from the viewpoint of improving liquid absorption. The nonwoven fabric of the present invention may contain two or more types of cellulose fibers.

[0032] In the nonwoven fabric of the present invention, the content of cellulose fibers is 90% by mass or more based on the total mass of the nonwoven fabric. This more reliably achieves the effects (improved quality, reduced environmental impact, etc.) of using cellulose fibers as the constituent fibers of the nonwoven fabric. The content of cellulose fibers in the nonwoven fabric of the present invention is more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may be 100% by mass, i.e., the entire nonwoven fabric is cellulose fibers.

[0033] The nonwoven fabric of the present invention may contain fibers other than cellulose fibers. In this case, the distribution form of the other fibers in the nonwoven fabric is not particularly limited, and for example, the other fibers may be uniformly distributed throughout the nonwoven fabric together with the cellulose fibers, or may be unevenly distributed. A specific example of the latter is a nonwoven fabric having a first layer mainly composed of cellulose fibers and a second layer containing other fibers (for example, thermoplastic fibers), and both layers are laminated in the thickness direction.

[0034] An example of the other fibers is a thermoplastic fiber mainly made of a thermoplastic resin. By incorporating thermoplastic fibers into a nonwoven fabric, it is expected that the strength of the fabric can be improved. Examples of thermoplastic resins include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate; polyamides such as nylon 6 and nylon 66; polyacrylic acid, polymethacrylic acid alkyl esters, polyvinyl chloride, and polyvinylidene chloride. The thermoplastic fiber may be a single fiber made of one type of thermoplastic resin or a blend polymer made by mixing two or more types of thermoplastic resins, or may be a composite fiber. A composite fiber is typically obtained by combining two or more types of thermoplastic resins with different components using a spinneret and spinning them simultaneously, and each of the multiple components has a structure that is continuous in the length direction of the fiber and is mutually bonded within the single fiber. The form of the composite fiber includes a core-sheath type, a side-by-side type, and the like, and is not particularly limited. In order to obtain the effect of the thermoplastic fibers without reducing the effect of the cellulose fibers, the content of the thermoplastic fibers in the nonwoven fabric of the present invention is preferably 15 mass% or more, more preferably 20 mass% or more, and preferably 75 mass% or less, more preferably 50 mass% or less, and even more preferably 35 mass% or less, relative to the total mass of the nonwoven fabric.

[0035] The nonwoven fabric of the present invention may be a spunlace nonwoven fabric, a needle-punched nonwoven fabric, etc. Among these, from the viewpoint of the strength and good appearance of the nonwoven fabric, the nonwoven fabric of the present invention is preferably a spunlace nonwoven fabric.

[0036] The nonwoven fabric of the present invention typically has water absorption, breathability, and liquid permeability, and is therefore suitable for applications requiring such properties. An example of the application of the nonwoven fabric of the present invention is an absorbent article, which is a type of wearable article and has the function of absorbing and retaining body fluids such as urine and sweat. Specific examples of absorbent articles include disposable diapers, sanitary napkins, panty liners, and incontinence pads. When the nonwoven fabric of the present invention is used in a wearable article, it is preferable to make the uneven surface having intermittent convexities, that is, the first surface 1a in the case of the nonwoven fabric 1 described above, the skin-facing surface facing the skin of the wearer of the wearable article, since this makes the most of the pleasant feel of the uneven surface.

[0037] Next, a preferred method and apparatus for producing the nonwoven fabric of the present invention will be described. Figure 4 shows a main part (hydroentanglement device 12) of a production apparatus 10, which is one embodiment of a preferred production apparatus for the nonwoven fabric of the present invention. In the method for producing the nonwoven fabric using the production apparatus 10, the nonwoven fabric 1 described above is produced.

[0038] The manufacturing apparatus 10 includes a hydroentanglement device 12. The hydroentanglement device 12 is an apparatus for manufacturing a nonwoven fabric 1 by subjecting a web 11 containing cellulose fibers to a hydroentanglement treatment, and includes a conveying mechanism 13 for conveying the web 11, a concave-convex support 20 on which the web 11 is placed while being conveyed by the conveying mechanism 13, and a water flow nozzle 17 for spraying a water flow onto the web 11 placed on the concave-convex support 20.

[0039] The conveying mechanism 13 includes a plurality of rolls 14 supported rotatably around a rotation axis, an endless conveyor belt 15 that is stretched across the plurality of rolls 14 and rotates in the direction of arrow R passing under a water flow nozzle 17, and a suction means 16 installed in the orbit of the conveyor belt 15. The conveyor belt 15 has a configuration that allows the water sprayed from the water flow nozzle 17 to pass through it, and may be, for example, a plain woven mesh support made of a wire material made of metal or synthetic resin, a porous support such as a punching plate, etc. The suction means 16 is disposed opposite the water flow nozzle 17 across the conveyor belt 15, and is configured to be able to suck in the water sprayed from the water flow nozzle 17 and permeating the conveyor belt 15.

[0040] The water flow nozzles 17 are disposed on the surface (lower surface) of the water flow spraying device 18 disposed above the transport mechanism 13 facing the conveyor belt 15. On the surface of the water flow spraying device 18 facing the conveyor belt 15, a plurality of water flow nozzles 17 are intermittently disposed over the entire length of the CD of the web 11 being transported below the facing surface to form a nozzle row extending in the CD, and a plurality of such nozzle rows are intermittently disposed in the MD. The nozzle rows are preferably disposed intermittently in 2 to 5 rows, more preferably 2 to 4 rows, in the MD. This group of water flow nozzles 17 makes it possible to spray the water flow 30 over the entire CD of the web 11 being transported in the MD by the transport mechanism 13.

[0041] The components of the hydroentanglement device 12, such as the transport mechanism 13 and the water jet device 18, other than the uneven support 20, may be configured in the same manner as those of the conventional hydroentanglement devices.

[0042] The concave-convex support body 20, which is one of the main characteristic parts of the manufacturing apparatus 10, will be described below. As shown in Figures 5 and 6, the uneven support 20 has a first surface 20a which is an uneven surface on which a plurality of protrusions 22 are formed, and a second surface 20b located on the opposite side. When the hydroentanglement treatment of the web 11 is performed by the hydroentanglement device 12, the web 11 is placed directly on the first surface 20a. In the illustrated embodiment, no protrusions are formed on the second surface 20b of the concave-convex support body 20, and the areas of the second surface 20b other than the through-holes 23 are flat. In the illustrated embodiment, the uneven support 20 is fixed to the conveyor belt 15 of the transport mechanism 13 via the second surface 20b, and rotates together with the conveyor belt 15 in the direction of arrow R. The method for fixing the uneven support 20 to the conveyor belt 15 is not particularly limited, provided that it does not impede the hydroentanglement treatment of the web 11, and examples of the method include a method using a fixing tool such as a bolt, an adhesive, or other known fixing means.

[0043] The uneven support body 20 forms a first surface 20a, which is an uneven surface, on which the web 11 of the uneven support body 20 is placed, and has a base plate 21 which forms the main body of the uneven support body 20, a plurality of protrusions 22 arranged on a surface of the base plate 21 which corresponds to the first surface 20a, and a plurality of through holes 23 which penetrate the base plate 21 in the thickness direction.

[0044] In the illustrated embodiment, the concave-convex support 20 is an integrally molded product made of a predetermined material, and the base plate 21 and the projections 22 are made of a common material and are inseparably integrated. In the illustrated embodiment, the base plate 21 is not formed by weaving wires, such as a wire mesh, but is a plate-like object made of a predetermined material. Note that in the present invention, a base plate formed by weaving wires may also be used as the base plate 21. The material of the uneven support 20 (base plate 21, protrusions 22) is not particularly limited, provided that it can be used in the hydroentanglement treatment of a web, and examples thereof include metal and plastic.

[0045] The protrusions 22 and through-holes 23 are scattered on the first surface 20a of the uneven support 20, i.e., the uneven surface on which the web 11 is placed during hydroentanglement treatment. "Scattered" here means that the protrusions 22 and through-holes 23 are each present scattered on the first surface 20a. For example, the protrusions 22 and / or through-holes 23 may be present only in a part of the first surface 20a, such as the central part or peripheral part, but from the viewpoint of improving the cushioning properties of the obtained uneven nonwoven fabric 1, it is preferable that the protrusions 22 and / or through-holes 23 are present scattered over the entire area of ​​the first surface 20a.

[0046] The protrusions 22 and through holes 23 scattered on the first surface 20a of the concave-convex support 20 may be arranged regularly or randomly. Here, "arranged regularly" refers to the protrusions 22 and through holes 23 being arranged according to a certain rule, while "arranged randomly" refers to an arrangement in which no such rule can be found. In the illustrated embodiment, the protrusions 22 and the through holes 23 are regularly arranged. Specifically, as shown in Figs. 5 and 6, the protrusions 22 and the through holes 23 are arranged in a staggered manner. Taking the protrusions 22 as an example, the "staggered arrangement" refers to an arrangement in which a plurality of rows of the protrusions 22 arranged at equal intervals in one direction (MD or CD) are arranged in a plurality of rows in a direction perpendicular to the one direction (CD or MD), and the protrusions 22 are shifted from each other between two adjacent rows in the direction perpendicular to the one direction. The same applies to the staggered arrangement of the through holes 23. Since the protrusions 22 and the through holes 23 are arranged in a staggered manner, the protrusions 22 and the through holes 23 are alternately arranged on the first surface 20a in both the MD and CD that are perpendicular to each other, and the protrusions 22 are arranged at equal intervals at four locations around one through hole 23. In the illustrated embodiment, the through hole 23 is located in the center between the protrusions 22, 22 adjacent to each other in both the MD and CD.

[0047] The protrusions 22 promote the formation of the openings 4 or the bottoms 6 of the recesses 3 during the hydroentanglement treatment of the web 11. Typically, when a water flow is sprayed onto the portions of the web 11 overlapping with the protrusions 22 during the hydroentanglement treatment, the fibers move from the portions to the surrounding areas, and as a result, the portions (the source of the fiber movement) become the openings 4 in the nonwoven fabric 1 where no fibers are present, or the bottoms 6 of the recesses 3 having a smaller basis weight than before the hydroentanglement treatment. The shape of the protrusions 22 is not particularly limited, and any shape may be selected, provided that the function of the protrusions 22 can be fully exerted. The shapes of the multiple protrusions 22 may be different from one another.

[0048] In the illustrated embodiment, each of the multiple protrusions 22 has an elongated shape in the MD in a plan view as shown in Fig. 6(a), and has a pair of first surfaces 22A, 22A facing each other in the CD, and a second surface 22B connecting to the periphery of both surfaces 22A, 22A. Each surface 22A, 22B of the protrusion 22 may be a flat surface or a curved surface. In the illustrated embodiment, the first surface 22A is a flat surface, and the second surface 22B is a curved surface, and the second surface 22B has a convex arc shape toward the outside of the MD in a plan view as shown in Fig. 6(a). In addition, in the illustrated form, each of the multiple protrusions 22 has a tapered shape in which the width (length of MD) gradually decreases as it moves away from the base plate 21 when viewed in a cross-sectional view along the MD and thickness direction of the uneven support body 20 (height direction of the protrusions 22) as shown in Figure 6 (b), and the tip of the protrusion 22 is not sharp but has a rounded arc shape.

[0049] The through holes 23 are sites where the protrusions 2 are formed during the hydroentanglement treatment of the web 11. The shape of the through holes 23 is not particularly limited, and any shape may be selected, provided that the function of the through holes 23 can be fully exerted. In the illustrated embodiment, each of the multiple through holes 23 has a circular shape in a plan view as shown in Fig. 6(a), but instead of this, the multiple through holes 23 may have, for example, an elliptical shape, a triangular shape, or a rectangular shape. Furthermore, the multiple through holes 23 may have different shapes.

[0050] The opening area of ​​the through hole 23 on the first surface 20a (concave-convex surface) is preferably 2 mm 2 More than 3mm, preferably 3mm 2 More than 8mm, preferably 2 Less than 7mm, preferably 2 As described above, the through holes 23 are the sites where the protrusions 2 of the nonwoven fabric 1 are formed during the hydroentanglement treatment of the web 11, and if the open area of ​​the through holes 23 on the uneven surface side (the side on which the web 11 is placed) is too small, it becomes difficult to form the protrusions 2, which may reduce the water retention of the nonwoven fabric 1. Furthermore, if the open area of ​​the through holes 23 on the uneven surface side is too large, there is a risk that the formation of the nonwoven fabric and the appearance of the nonwoven fabric may be deteriorated.

[0051] The thickness T of the base plate 21 (see Figs. 5, 6(b) and 6(c)) is preferably 2.5 mm or more, more preferably 3 mm or more. If the thickness T of the base plate 21 is too small, the depth of the through-holes 23 will be relatively shallow, and the protruding height of the convex portions 2 (the height difference between the convex portions 2 on the first surface 1a and the bottoms of the concave portions 3) will be insufficient, and the apparent thickness AT of the nonwoven fabric 1 (see Fig. 2) will be insufficient, which may result in the nonwoven fabric 1 lacking in three-dimensionality. There is no particular upper limit to the thickness T, but from the viewpoint of convex portion formation and the appearance of the nonwoven fabric, it is preferably 5 mm or less, more preferably 4 mm or less. When the thickness T of the base plate 21 is not uniform, it is preferable that the minimum value of the thickness T is within the above-mentioned specific range.

[0052] It is preferable that the opening area of ​​the through hole 23 is set within the above-mentioned specific range not only on the first surface 20a (concave-convex surface) side but also on the second surface 20b side located on the opposite side. In the illustrated embodiment, such a preferable embodiment is adopted. That is, in the concave-convex support body 20 shown in Figures 5 and 6, the opening area of ​​the through hole 23 is constant over the entire length in the depth direction of the through hole 23 (thickness direction of the base plate 21), and the opening area of ​​the through hole 23 is the same on the first surface 20a side and the second surface 20b side.

[0053] The ratio (H / T) of the height H of the protrusions 22 to the thickness T of the base plate 21 (see Figs. 6(b) and (c)) is preferably 0.5 or more, more preferably 0.7 or more, and preferably 1.5 or less, more preferably 1.3 or less. When H / T is within the above-mentioned specific range, the uneven structure of the obtained nonwoven fabric becomes more pronounced and liquid return becomes less likely to occur.

[0054] From the viewpoint of reliably producing the nonwoven fabric of the present invention, represented by nonwoven fabric 1, the ratio (T / Lmax) of the thickness T of base plate 21 to the maximum diameter length Lmax of through hole 23 (see Figure 6) is preferably 0.5 or more, more preferably 1 or more, and preferably 3 or less, more preferably 2 or less.

[0055] In this specification, the "diameter length of a through hole" refers to the length of a virtual line drawn in a plan view of the through hole from one end to the other end of the through hole through the center of the through hole. If there are multiple virtual lines, the length of the one with the longest length in the extension direction is the "maximum diameter length Lmax," and the length of the one with the shortest length in the extension direction is the "minimum diameter length Lmin." The diameter of the through hole may vary depending on the measurement site. For example, the through hole 23 in the illustrated form has a cylindrical overall shape, a circular shape in a plan view, and a constant shape and size throughout the entire length of the through hole 23 in the depth direction (thickness direction of the base plate 21), so the through hole 23 has only one diameter, which is the diameter of the circle, and both the maximum diameter Lmax and the minimum diameter Lmin are equal to the diameter.

[0056] From the viewpoint of reliably producing the nonwoven fabric of the present invention, it is preferable to set the dimensions of each part of the uneven support 20 as follows. The height H of the projections 22 (see FIGS. 6(b) and (c)) is preferably 1.5 mm or more, more preferably 2 mm or more, and preferably 7 mm or less, more preferably 5 mm or less. The length L1 in the MD of the projection 22 (see FIGS. 6(a) and (b)) is preferably 1 mm or more, more preferably 2 mm or more, and preferably 10 mm or less, more preferably 3.5 mm or less. The length L2 (see Figs. 6(a) and (c)) of the projection 22 in the CD direction is preferably 0.5 mm or more, more preferably 1 mm or more, and is preferably 4 mm or less, more preferably 2 mm or less.

[0057] The maximum diameter length Lmax (see FIG. 6) of the through hole 23 is preferably 1 mm or more, more preferably 2 mm or more, and is preferably 10 mm or less, more preferably 4 mm or less. The minimum diameter Lmin of the through hole 23 is preferably 1.5 mm or more, more preferably 2 mm or more, and preferably 3.5 mm or less, more preferably 3 mm or less. It is preferable that the preferred ranges of the maximum diameter length Lmax and the minimum diameter length Lmin are filled at least at the opening end of the through hole 23 on the first surface 20a (uneven surface) side, and it is more preferable that they are filled over the entire area of ​​the through hole 23, as in the cylindrical through hole 23 shown in the figure.

[0058] The pitch 22P1 in the MD of the protrusions 22 (see FIGS. 6(a) and 6(b)) is preferably 4 mm or more, more preferably 5 mm or more, and preferably 14 mm or less, more preferably 8 mm or less. The "pitch 22P1" refers to the length along the MD between the centers of the MD of two adjacent protrusions 22, 22 in the MD. The pitch 22P2 (see FIGS. 6(a) and 6(c)) of the protrusions 22 in the CD is preferably 2 mm or more, more preferably 3 mm or more, and preferably 12 mm or less, more preferably 7 mm or less. The "pitch 22P2" refers to the length along the CD between the centers of the CDs of two adjacent protrusions 22, 22 in the CD. The pitch 23P1 in the MD of the through holes 23 (see FIGS. 6(a) and 6(b)) is preferably 4 mm or more, more preferably 6 mm or more, and preferably 14 mm or less, more preferably 7 mm or less. The "pitch 23P1" refers to the length along the MD between the centers of the MD of two adjacent through holes 23, 23 in the MD. The pitch 23P2 (see FIGS. 6(a) and 6(c)) of the through holes 23 in the CD is preferably 1 mm or more, more preferably 3 mm or more, and preferably 10 mm or less, more preferably 7 mm or less. The "pitch 23P2" refers to the length along the CD between the centers of each of two adjacent through holes 23, 23 in the CD.

[0059] The open area ratio of the through holes 23 in the uneven support 20, i.e., "the ratio of the total open area of ​​all the through holes 23 arranged on the surface corresponding to the first surface 20a of the uneven support 20 in the base plate 21 to the total area of ​​the surface corresponding to the first surface 20a of the uneven support 20," is not particularly limited, but from the viewpoint of reliably producing the nonwoven fabric of the present invention and ensuring the strength of the base plate 21, it is preferably 20% or more, more preferably 25% or more, and preferably 50% or less, more preferably 40% or less.

[0060] The manufacturing apparatus 10 may include a web forming apparatus (not shown) in addition to the hydroentanglement apparatus 12. The web forming apparatus forms the web 11 to be subjected to hydroentanglement treatment in the hydroentanglement apparatus 12, and is disposed upstream of the hydroentanglement apparatus 12 in the MD. As the web forming apparatus, any apparatus that produces a web using a known web forming method such as a dry method or a wet method can be used without any particular limitation. The web forming apparatus typically includes a carding machine, and forms a web by a carding method, which is a type of dry method. In the present invention, the web may have a single layer structure, or may have a laminated structure in which two or more layers are laminated.

[0061] In the present invention, the term "web" refers to a fiber assembly in which the fibers are not substantially bonded to each other, i.e., the fibers are not bonded to each other. Specifically, the term "web" refers to a fiber assembly formed by a known web forming method such as a dry method, and which has not been subjected to a treatment by a known interfiber bonding method such as a hydroentanglement method, a thermal bond method, a chemical bond method, or a needle punch method.

[0062] In a preferred method for producing the nonwoven fabric of the present invention, the web is subjected to a water jetting step to subject the web to hydroentanglement, thereby entangling the constituent fibers of the web and substantially bonding them together. When the web is composed mainly of cellulose fibers such as cotton fibers as its constituent fibers (specifically, for example, when the mass ratio of cellulose fibers to the total mass of the constituent fibers of the web is preferably 50 mass% or more, more preferably 75 mass% or more), typically, as in the first manufacturing method described below, the web is subjected to the hydroentanglement treatment and then dried as necessary, whereby the web becomes a nonwoven fabric in which the constituent fibers are substantially bonded to each other. In addition, when the web contains thermoplastic fibers in addition to cellulose fibers as constituent fibers, it is preferable to further subject the web to a heat treatment after the hydroentanglement treatment, as in the second manufacturing method described below. The heat treatment is a treatment in which the web is heated at a temperature equal to or higher than the melting point of the thermoplastic fibers contained in the web, whereby the thermoplastic fibers are fused together and substantially bonded. Therefore, in a web that has been subjected to both the hydroentanglement treatment and the heat treatment, the cellulose fibers are substantially bonded together by entanglement, the thermoplastic fibers are substantially bonded together by fusion, and further, the cellulose fibers and the thermoplastic fibers can be bonded together by fusion.

[0063] The manufacturing apparatus 10 may be provided with a drying device (not shown) for removing moisture from the nonwoven fabric manufactured by the hydroentanglement device 12. The drying device is basically intended to remove moisture from the fiber aggregate (drying treatment), but may also be used to melt and fuse the thermoplastic fibers contained in the web (heat treatment). In a preferred manufacturing method for the nonwoven fabric of the present invention, the drying device may be used to simultaneously dry and heat the fiber aggregate. The drying device is disposed downstream of the hydroentanglement device 12 in the MD. As the drying device, any device that can be used for drying the hydroentangled nonwoven fabric in the manufacturing apparatus for spunlace nonwoven fabric can be used without any particular restrictions. Specific examples of the drying treatment applied to the nonwoven fabric by the drying device include blowing hot air, blowing dry gas, heating with a heater, irradiation with infrared rays, contact with a heating roll, and suction of moisture using a suction roll or the like.

[0064] Next, a preferred method for producing the nonwoven fabric of the present invention will be described by taking as an example a method for producing the nonwoven fabric 1 using the above-mentioned production apparatus 10. A suitable method for producing the nonwoven fabric of the present invention includes at least a water jetting step, in which, as shown in Fig. 4, a web 11 containing cellulose fibers is placed on the first surface 20a (concave-convex surface) of a concave-convex support 20, and water jets 30 are sprayed onto the web 11 from a water jet nozzle 17 to entangle the fibers contained in the web 11 and form convex portions 2 (see Figs. 1, 7, etc.) in the web 11.

[0065] Since the nonwoven fabric 1 which is the object of manufacture has the openings 4, in the water jetting step, the water jets 30 are jetted onto the portions of the web 11 which correspond to the projections 22 to form the openings 4.

[0066] The water jetting step is shown in Fig. 7. Fig. 7(a) shows the state in which the web 11 is placed on the first surface 20a of the uneven support 20, immediately before the hydroentanglement treatment is performed. The web 11 before the hydroentanglement treatment is substantially flat, without any unevenness. From the state shown in Fig. 7(a), with the rotation of the conveyor belt 15 fixed to the uneven support 20 via the second surface 20b, the web 11 and the uneven support 20 are transported together to the MD, and when they reach directly below the water jetting device 18, as shown in Fig. 7(b), a water jet 30 jetted from the water jet nozzle 17 equipped to the water jetting device 18 is sprayed onto the web 11. As described above, the water jet 30 is sprayed uniformly over the entire CD area of ​​the web 11, and is sprayed approximately perpendicularly to the web 11. In the portion of the web 11 where the water jet 30 is sprayed, the constituent fibers of the portion are entangled, and the portion is pressed toward the uneven support 20, and is deformed to fit the first surface 20a (uneven surface). At this time, the constituent fibers of the web 11 at the sites corresponding to the protrusions 22 are separated by the water streams 30 sprayed from above and the protrusions 22 supporting the sites from below, and are penetrated by the protrusions 22, ultimately forming openings 4 (sites with zero fiber basis weight) as shown in FIG. 7(c). The fibers separated from the sites corresponding to the protrusions 22 in the web 11 in this way are moved into the through holes 23 by the water flowing from the protrusions 22 toward the through holes 23 on the first surface 20a of the uneven support 20. During the hydroentanglement treatment, the open end of the through holes 23 on the second surface 20b side (the open end opposite the inflow side of the water and fibers) is blocked by the conveyor belt 15 at least to an extent that the fibers are difficult to flow out, so that the fibers that have moved from the surrounding area are accumulated inside the through holes 23, and ultimately, the protrusions 2 are formed as shown in FIG. 7(c). Furthermore, the areas of the first surface 20a of the uneven support 20 other than the protrusions 22 and the through-holes 23 are flat and free of unevenness, and the areas of the web 11 corresponding to these flat areas are pressed toward the flat areas by the water flow 30, ultimately becoming the bottoms 6 of the recesses 3 as shown in Figure 7(c). In this manner, the hydroentanglement treatment forms the protrusions 2, the bottoms of the recesses 3, and the openings 4 in the web 11, and the constituent fibers of the web 11 are entangled with each other, turning the web 11 into the nonwoven fabric 1. In addition, when web 11 contains cellulose fibers such as cotton fibers and thermoplastic fibers, it is preferable to subject web 11 to a heating step after hydroentanglement treatment of web 11, as in the second manufacturing method described below, and to perform a heat treatment in which web 11 is heated at a temperature equal to or higher than the melting point of the thermoplastic fibers contained in web 11, whereby the thermoplastic fibers are substantially bonded to each other by fusion, and web 11 becomes nonwoven fabric 1.

[0067] In particular, as shown in FIG. 6(a) and the like, the concave-convex support 20 has a plurality of (four) protrusions 22 arranged on the first surface 20a so as to surround one through hole 23 at the center, and thus water sprayed onto the first surface 20a during the hydroentanglement treatment tends to converge from the plurality of protrusions 22 toward the one through hole 23. Therefore, the fibers of the web 11 that have moved with the water from the surrounding plurality of protrusions 22 tend to accumulate in the through hole 23, and thus the protrusions 2 tend to be formed. In addition, when the fibers move from the plurality of places around the through hole 23 and accumulate in the through hole 23 in this way to form the protrusions 2, the micro recesses tend to be formed on the side opposite to the top of the protrusions 2. The micro recesses are expected to have the effect of increasing the cushioning and water retention of the nonwoven fabric 1 together with the protrusions 2.

[0068] In the water jetting step, the MD conveying speed of the web 11 and the water pressure of the water jet sprayed from the water jet nozzle 17 are not particularly limited, but from the viewpoint of reliably producing the nonwoven fabric of the present invention, it is preferable to set them as follows. The MD transport speed of the web 11 is preferably 1 m / min or more, more preferably 3 m / min or more, and preferably 120 m / min or less, more preferably 100 m / min or less. The water pressure of the water jetted from the water jet nozzle 17 is preferably 0.1 MPa or more, more preferably 0.3 MPa or more, and is preferably 10 MPa or less, more preferably 8 MPa or less. The nozzle hole diameter of the water flow nozzle 17 is preferably 0.03 mm or more, more preferably 0.05 mm or more, even more preferably 0.08 mm or more, and preferably 0.50 mm or less, more preferably 0.30 mm or less, even more preferably 0.20 mm or less. When multiple water flow nozzles 17 are intermittently arranged over the entire length of the CD, the nozzle hole pitch of the water flow nozzles 17 is preferably 0.1 mm or more, more preferably 0.3 mm or more, even more preferably 0.5 mm or more, and preferably 3.0 mm or less, more preferably 2.0 mm or less, even more preferably 1.0 mm or less.

[0069] As in the water flow jetting device 18 shown in FIG. 4, when a nozzle row consisting of a water flow nozzle or a plurality of water flow nozzles intermittently arranged in the CD is intermittently arranged in the MD, the water pressure of the water flow jetted from the water flow nozzle located on the upstream side of the MD may be made different from that of the water flow nozzle located on the downstream side. Specifically, for example, the water pressure of the water flow jetted from the water flow nozzle may be gradually increased from the upstream side to the downstream side of the MD. Similarly, the nozzle hole diameter of the water flow nozzle located on the upstream side of the MD may be made different from that of the water flow nozzle located on the downstream side. Specifically, for example, the nozzle hole diameter may be gradually increased from the upstream side to the downstream side of the MD. Furthermore, when a nozzle row consisting of a plurality of water flow nozzles intermittently arranged in the CD is intermittently arranged in the MD, the nozzle hole pitch of the nozzle row located on the upstream side of the MD may be made different from that of the nozzle row located on the downstream side. Specifically, for example, the nozzle hole pitch may be gradually decreased from the upstream side to the downstream side of the MD. This can improve the texture of the nonwoven fabric.

[0070] After the water jet spraying step, a drying step may be carried out as necessary to remove moisture from the nonwoven fabric 1 obtained in the water jet spraying step. That is, a suitable method for producing the nonwoven fabric of the present invention may include the drying step after the water jet spraying step. The drying step can be carried out in a conventional manner using the drying device.

[0071] Suitable methods for producing the nonwoven fabric of the present invention include an embodiment in which the drying step is carried out as necessary after the water jetting step (hereinafter also referred to as the "first production method"), and an embodiment in which the drying step is carried out as necessary after the water jetting step, and a heating step is further included in which the web is heat-treated (hereinafter also referred to as the "second production method"). The first production method is as described above. The second production method is the same as the first production method, except that it includes a heating step. Typically, the first production method is applied when the nonwoven fabric to be produced contains only cellulose fibers such as cotton fibers as constituent fibers, and the second production method is applied when the nonwoven fabric to be produced contains cellulose fibers and thermoplastic fibers as constituent fibers. The web used in the first production method contains only cellulose fibers, and the web used in the second production method contains cellulose fibers and thermoplastic fibers.

[0072] The second manufacturing method will be described below. In addition to the water jetting step, the second manufacturing method further includes a heating step of heating the web that has been subjected to the water jetting step at a temperature equal to or higher than the melting point of the thermoplastic fibers contained in the web. By subjecting a web containing cellulose fibers and thermoplastic fibers to the water jetting step, the cellulose fibers are substantially bonded to each other by entanglement, and by subjecting the web to the heating step, the thermoplastic fibers are substantially bonded to each other by fusion to form a nonwoven fabric. In the heating step, not only the thermoplastic fibers but also the thermoplastic fibers and the cellulose fibers can be bonded to each other by fusion. According to the second manufacturing method, the bonding strength of the web is improved, the handleability of the web in the manufacturing process is improved, and the strength of the finally obtained nonwoven fabric can be improved. When two or more types of thermoplastic fibers with different melting points are used, it is preferable to heat the web in the heating step at a temperature equal to or higher than the highest melting point. When the second manufacturing method is carried out using the above-mentioned manufacturing apparatus 10, a heating device for carrying out the heating step is disposed downstream in the MD from the hydroentanglement device 12. Specific examples of the heat treatment performed on the web by the heating device include blowing hot air, heating with a heater, contact with a heating roll, and irradiation with infrared rays.

[0073] In the second production method, the thermoplastic fiber content in the web may be adjusted to be the same as the thermoplastic fiber content in the nonwoven fabric which is the intended product, as described above. The distribution form of the thermoplastic fibers in the web is not particularly limited, and may be, for example, uniformly distributed throughout the web together with the cellulose fibers, or may be unevenly distributed. A specific example of the latter is a form in which the web has a first layer mainly composed of cellulose fibers and a second layer containing thermoplastic fibers, and both layers are laminated in the thickness direction.

[0074] While the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above-described embodiments and can be modified as appropriate without departing from the spirit of the present invention. EXAMPLES

[0075] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to such examples.

[0076] [Examples 1 to 7, Comparative Examples 1 to 3] A nonwoven fabric was produced by the first production method. Specifically, a nonwoven fabric was produced by subjecting a web to hydroentanglement treatment using an apparatus having a similar basic configuration to the production apparatus (hydroentanglement apparatus) shown in FIG. 4. Only cotton fibers, a type of cellulose fiber, were used as the raw fiber of the web, and a single-layered web was formed by a carding method in the usual manner. The hydroentanglement treatment was carried out by spraying water onto the web in a state in which the web was placed on one side (concave-convex side) of a concave-convex support. In the hydroentanglement treatment, a nozzle row consisting of a plurality of water nozzles intermittently arranged in the CD and three rows intermittently arranged in the MD was used as the water jetting apparatus, and the hydroentanglement treatment was carried out by introducing the web into the water jetting apparatus twice. Regarding the above-mentioned water flow nozzles, if the water flow nozzle in the nozzle row located at the most upstream of the MD was designated as water flow nozzle A, and the nozzles were designated as water flow nozzle B and water flow nozzle C toward the downstream side of the MD, the water pressure of water flow nozzle A was 1 MPa, the water pressure of water flow nozzle B was 3 MPa, and the water pressure of water flow nozzle C was 4 MPa. The web transport speed was 5 m / min. The water flow nozzles A and B had a nozzle hole diameter of 0.10 mm and a nozzle hole pitch of 1.0 mm, and the water flow nozzle C had a nozzle hole diameter of 0.12 mm and a nozzle hole pitch of 0.6 mm. In Examples 1 to 7, the support used was the corrugated support 20 shown in Figs. 6 and 7. As described above, the corrugated support 20 has the protrusions 22 and the through holes 23. On the other hand, in Comparative Example 1, a support was used that did not have the protrusions 22 and the through holes 23. In Comparative Example 2, a support was used that had the protrusions 22 but did not have the through holes 23. In Comparative Example 3, a support was used that had the through holes 23 but did not have the protrusions 22. Details of the supports used in each of the Examples and Comparative Examples are shown in Table 1 below.

[0077] The nonwoven fabrics of each of the examples and comparative examples obtained were subjected to measurements of basis weight, apparent thickness, etc. The measurement items and the measurement results are shown in Table 1 below. The measurement method for each measurement item has already been explained, so the explanation will be omitted here. In Table 1, "area ratio of the total area of ​​the convex portions" represents the ratio of the total area of ​​the convex portions on the uneven surface of the nonwoven fabric (the surface corresponding to the first surface 1a of the nonwoven fabric 1) to the area of ​​the uneven surface. The area ratio of the total area of ​​the convex portions was calculated by dividing the total area of ​​the convex portions measured according to the method described in <Method for measuring the total area of ​​the convex portions and bottom portions of the nonwoven fabric> above, by the area of ​​the measurement sample used to measure the total area of ​​the convex portions.

[0078] <Evaluation of liquid return amount> The nonwoven fabrics of the examples and comparative examples were arranged so that the uneven surface (the surface corresponding to the first surface 1a of the nonwoven fabric 1) faced the skin of the user to produce an absorbent article (sanitary napkin). The size of the nonwoven fabric was 8 cm x 7 cm. The configuration of the absorbent article other than the nonwoven fabric was the same as that of a sanitary napkin manufactured by Kao Corporation (Laurier (registered trademark) F Happy Skin Soft Type 22.5 cm, manufactured in 2018). The sanitary napkin was placed on a flat table with the uneven surface of the nonwoven fabric facing upward. An acrylic liquid injection plate with a cylinder of 10 mm diameter and 50 mm height integrally molded thereon was placed on the nonwoven fabric with the liquid injection hole positioned at the center of the nonwoven fabric. In this state, 6 g of artificial blood was injected into the cylinder at once. One minute after the injection, the liquid injection plate was removed and the sanitary napkin was left to stand for 2 minutes. Then, a pre-weighed tissue paper (whose mass is W1) was placed on the area of ​​the nonwoven fabric where the artificial blood was injected and on the area adjacent thereto. Then, a pressure of 2.5 gf / cm was applied on the tissue paper. 2 A weight was placed on the tissue so that a load of 1000 g was applied, and the tissue was left to stand for 5 seconds. The load was then removed, and the mass W2 of the tissue was measured. The amount of liquid return was calculated by subtracting mass W1 from mass W2. The smaller the value of the amount of liquid return, the less likely the absorbed liquid was to return to the first surface side of the nonwoven fabric. The results are shown in Table 1. The simulated blood used in the above measurements was horse defibrinated blood manufactured by Japan Bio Test Laboratory Co., Ltd. When horse defibrinated blood is left to stand, the high viscosity parts (red blood cells, etc.) settle, while the low viscosity parts (plasma) remain as the supernatant. In this measurement, the mixing ratio of these parts was adjusted so that the viscosity of the simulated blood was 8.0 cP at 25°C. The viscosity of the simulated blood was measured using a TVB10 viscometer manufactured by Toki Sangyo Co., Ltd. The measurement condition was 30 rpm.

[0079] [Table 1]

[0080] The nonwoven fabrics of Examples 1 to 7 all had multiple protrusions, bottoms, and openings, and the ratio of the basis weight of the protrusions to the bottoms, B2 / B1, was 2 or more. On the other hand, the nonwoven fabrics of Comparative Examples 1 to 3 did not have at least one of the protrusions and the openings. As shown in Table 1, it can be seen that the nonwoven fabrics of Examples 1 to 7 are superior to the nonwoven fabrics of Comparative Examples 1 to 3 in that they had a smaller amount of liquid return. [Explanation of symbols]

[0081] 1. Nonwoven fabric 1a 1st side of nonwoven fabric 1b Second side of nonwoven fabric 2 Convex 4 Opening part 6 Bottom of the recess

Claims

1. A nonwoven fabric for absorbent articles containing 90% by mass or more of cellulose fibers, the fibers being entangled with each other, The nonwoven fabric for absorbent articles has a first surface and a second surface located opposite the first surface, the first surface has a protrusion and a bottom; the bottom has a plurality of apertures; A nonwoven fabric for absorbent articles, wherein the ratio B2 / B1 of the basis weight B2 of the convex portions to the basis weight B1 of the portions other than the perforations in the bottom portion is 2 or more.

2. the contact area ratio of the protrusions is 20% or more and 50% or less, The contact area ratio of the protrusions is 12 g / cm when a flat plate covering the entire first surface is placed on the first surface. ２ 2. The nonwoven fabric for absorbent articles according to claim 1, wherein the ratio of the contact area between the flat plate and the protrusions to the area of ​​the first surface when a load of 100 kJ / cm is applied.

3. the area ratio of the total area of ​​the openings is 15% or more and 50% or less, The nonwoven fabric for absorbent articles according to claim 1 or 2, wherein the area ratio of the total area of ​​the open holes is the ratio of the total area of ​​the open holes to the area of ​​the first surface.

4. The nonwoven fabric for absorbent articles according to claim 1 or 2, wherein the nonwoven fabric for absorbent articles is a spunlace nonwoven fabric.

Images