Spun lace nonwoven fabric for absorbent article and manufacturing method thereof

Abstract

To provide a spun lace nonwoven fabric for absorbent articles having cushioning property.SOLUTION: A spun lace nonwoven fabric for absorbent articles 1 of the invention has a first surface 1a and a second surface 1b positioned on the opposite side thereof. A plurality of protrusions 2 are intermittently disposed at least on the first surface 1a. A concavity 3 is disposed between the protrusions 2, 2 adjacent to each other. Fiber orientation degree of the protrusion 2 of the nonwoven fabric 1 is 50% or more and 60% or less. A plurality of apertures 4 penetrating the nonwoven fabric 1 in a thickness direction may be formed on a bottom of the concavity 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a spunlace nonwoven fabric suitable as a constituent member of an absorbent article. [Background technology]

[0002] Spunlace nonwoven fabrics are produced by a process in which a water flow is sprayed onto a web, which is a fiber assembly, to entangle the fibers contained in the web. Spunlace nonwoven fabrics are superior in flexibility, texture, etc. compared to other nonwoven fabrics, and taking advantage of these characteristics, they are used as components of absorbent articles such as disposable diapers and sanitary napkins (for example, Patent Document 1).

[0003] Patent Document 2 describes a spunlace nonwoven fabric that is suitable as a wiping cloth because it has good surface irregularity retention, and is mainly made of cotton fibers and has many convex portions and concave portions connecting the convex portions, with each convex portion having an area of ​​0.5 to 6 mm. 2 The spunlace nonwoven fabric described in Patent Document 2 is produced by a process in which a web is placed on a perforated support made of a coarse woven fabric having an opening size of 6 to 10 mesh, and a water stream is sprayed onto the web to move the constituent fibers of the web to the open holes of the perforated support, thereby entangling the constituent fibers with each other.

[0004] Patent Document 3 describes a manufacturing apparatus for a spunlace nonwoven fabric having an opening, which includes a conveyor belt for transporting a web and a support placed on the conveyor belt, and is configured to spray a water flow onto the web while transporting the web with the conveyor belt in a state where the web is placed on the support. The support described in Patent Document 3 has a plurality of pyramid-shaped protrusions arranged on the web placement surface, and a plurality of holes arranged around the protrusions and penetrating the support in the thickness direction. As shown in FIG. 1 of Patent Document 3, the spunlace nonwoven fabric manufactured by the apparatus described in Patent Document 3 has relatively large openings at positions corresponding to the protrusions of the support during manufacturing, and is substantially flat with little unevenness overall, and is difficult to call an uneven nonwoven fabric. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2020-536707 [Patent Document 2] JP 2003-183968 A [Patent Document 3] Special Publication No. 8-502100 Summary of the Invention [Problem to be solved by the invention]

[0006] Although spunlace nonwoven fabrics are excellent in flexibility, texture, etc., many of them are relatively thin due to the process of spraying a high-pressure water flow onto the web, and there is room for improvement in terms of cushioning. Spunlace nonwoven fabrics for absorbent articles are required to have excellent cushioning properties.

[0007] An object of the present invention is to provide a spunlace nonwoven fabric for absorbent articles having excellent cushioning properties. [Means for solving the problem]

[0008] The present invention is a spunlace nonwoven fabric for absorbent articles having a first surface and a second surface located opposite the first surface, with a plurality of convex portions intermittently arranged on at least the first surface and with concave portions arranged between adjacent convex portions. In one embodiment of the spunlace nonwoven fabric for absorbent articles of the present invention, the degree of fiber orientation of the protrusions, measured by the following method, is preferably 50% or more and 60% or less.

[0009] The present invention also relates to a method for producing the spunlace nonwoven fabric for absorbent articles of the present invention, which includes a water jet spraying step of spraying a water jet onto a web placed on an uneven surface of a uneven support having an uneven surface on which a plurality of protrusions are formed, thereby entangling the fibers contained in the web and forming the protrusions on the web. In one embodiment of the manufacturing method of the spunlace nonwoven fabric for absorbent articles of the present invention, the uneven support has a base plate that forms the surface of the uneven support on which the web is placed, a plurality of protrusions arranged on a surface of the base plate corresponding to the uneven surface, and a plurality of through holes that penetrate the base plate in the thickness direction, and it is preferable that the protrusions and the through holes are scattered on the uneven surface. In one embodiment of the method for producing a spunlace nonwoven fabric for absorbent articles of the present invention, the opening area of ​​the through-holes on the uneven surface side is 3.5 mm 2 More than 20mm 2 It is preferable that: In one embodiment of the method for producing a spunlace nonwoven fabric for absorbent articles of the present invention, the base plate preferably has a thickness of 2.5 mm or more. Other features, advantages and embodiments of the present invention are described below. Effect of the Invention

[0010] According to the present invention, a spunlace nonwoven fabric for absorbent articles having excellent cushioning properties can be obtained. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic perspective view of a first surface side of a spunlace 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 an explanatory diagram of a method for measuring the degree of fiber orientation according to the present invention, and is a schematic plan view of an image of a nonwoven fabric observed with an electron microscope. [Figure 4]FIG. 4 is a schematic diagram of a main part (a hydroentangling device) of one embodiment of an apparatus that can be used to carry out the method of producing a spunlace 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

[0012] 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.

[0013] 1 and 2 show a nonwoven fabric 1, which is one embodiment of the spunlace nonwoven fabric for absorbent articles of the present invention (hereinafter, also simply referred to as "nonwoven fabric"). The nonwoven fabric 1 has a first surface 1a and a second surface 1b located on the opposite side thereof, with a plurality of protruding portions 2 intermittently arranged on at least the first surface 1a, and recessed portions 3 existing between adjacent protruding portions 2, 2. The recessed portions 3 are spaces defined by the plurality of protruding portions 2 and a fiber layer (low basis weight portion 6 described below) connecting the plurality of protruding portions 2, and the fiber layer forms the bottom of the recessed portions 3.

[0014] 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 surface, a minute recess (not shown) may be present on the opposite side of the protrusions 2 at a portion of the second surface 1b that overlaps with the protrusions 2 in a plan view (the position of the low basis weight portion 6 described later). The minute recess typically does not have a constant recess depth, but has a maximum depth at a portion that overlaps with the top of the protrusions 2 in a plan view, and the recess depth gradually decreases from the portion having the maximum depth toward the opening edge of the minute recess.

[0015] The inside of the protrusion 2 is filled with fibers and has a solid structure. The protrusion 2 is dome-shaped and has a circular shape when viewed from the first surface 1a. In the present invention, the shape of the protrusion 2 is not particularly limited and any shape may be selected. In addition, the shapes of the multiple protrusions 2 may differ from one another.

[0016] The nonwoven fabric 1 is characterized in that the degree of fiber orientation of the protrusions 2 is 50% or more and 60% or less, as measured by the following method. The degree of fiber orientation indicates the degree of variation in the arrangement (extension) direction of the fibers in two mutually perpendicular directions (MD and CD) in a plan view of the nonwoven fabric 1, and is "the ratio of the number of fibers extending in the direction in which the number of fibers is relatively greater out of the total number of fibers arranged in one of the two directions and the other."

[0017] <Method for measuring fiber orientation> Using an electron microscope, the nonwoven fabric of the measurement sample is observed in a planar state from one side, and an observation image of the measurement target portion is obtained. When the measurement sample is the nonwoven fabric of the present invention, taking the nonwoven fabric 1 as an example, the measurement target portion is the convex portion 2 of the first surface 1a, so an observation image of the convex portion 2 from the first surface 1a side is obtained. A square consisting of two first reference lines parallel to each other and two second reference lines perpendicular to the two first reference lines is added to the obtained observation image. The extension direction of the first reference lines is aligned with the machine direction (MD) during the manufacture of the nonwoven fabric of the measurement sample, and the extension direction of the second reference lines is aligned with the vertical direction (CD) perpendicular to the machine direction. The length of each of the four reference lines is 0.5 mm. For each of the four reference lines, the number of fibers passing through the reference line (hereinafter also referred to as the "number of passing fibers") is counted, and the sum of the numbers of passing fibers for the two first reference lines is the "first fiber number," and the sum of the numbers of passing fibers for the two second reference lines is the "second fiber number." Of the two fiber numbers, the one with the larger number is designated A and the one with the smaller number is designated B, and the degree of fiber orientation is calculated by the following formula. Fiber orientation degree (%) = [A / (A+B)] x 100 For the same measurement sample, the observation images are obtained at three locations, the fiber orientation degree is calculated based on each of the observation images, and the average value of the calculated fiber orientation degrees is taken as the fiber orientation degree of the measurement target portion of the measurement sample (convex portion 2 of nonwoven fabric 1).

[0018] 3 shows a schematic diagram of an observation image 50, which is an example of an observation image of a nonwoven fabric obtained by an electron microscope in the above-mentioned <Method for Measuring Fiber Orientation Degree>. In the observation image 50, a plurality of fibers Fb are present, and each fiber Fb extends in various directions including MD and CD. In addition, in the observation image 50, two first reference lines 51 that are parallel to each other and extend in MD and two second reference lines 52 that are parallel to each other and extend in CD are drawn, and these four reference lines 51, 52 form a square with a side length of 0.5 mm. The "black circles" drawn on each of the reference lines 51, 52 indicate intersections 53 between the reference lines and the fibers Fb. The first fiber number is the total number of intersections 53 that overlap with each of the two first reference lines 51, 51, and the second fiber number is the total number of intersections 53 that overlap with each of the two second reference lines 52, 52. Both fiber numbers are total numbers. For example, when one fiber Fb passes through one reference line (the first reference line 51 or the second reference line 52) twice, the number of passes of the one fiber Fb "2" is counted as the number of passes of the one reference line "2". In addition, when one fiber Fb passes through multiple reference lines (the first reference line 51 and / or the second reference line 52), the number of passes of the one fiber Fb at each reference line is counted as the number of passes of the one reference line. Moreover, when the fiber Fb passes through an intersection point (a corner of the square) between the first reference line 51 and the second reference line 52, the fiber Fb is not counted as the number of passing fibers.

[0019] As used herein, "MD" refers to the machine direction in which a nonwoven fabric is manufactured, i.e., the direction in which the nonwoven fabric or its raw materials or intermediate products (e.g., webs) run.

[0020] When the number of fibers aligned in the MD and the number of fibers aligned in the CD in the protrusions 2 are equal, the fiber orientation degree of the protrusions 2 is 50%. When the fibers are aligned in only one of the MD and the CD in the protrusions 2, the fiber orientation degree of the protrusions 2 is 100%. In other words, the closer the fiber orientation degree value is to 50%, the smaller the difference between the number of fibers aligned (extending) in the MD and the number of fibers aligned (extending) in the CD in the protrusions 2, and the less bias in the fiber orientation. The nonwoven fabric 1 has excellent cushioning properties because the degree of fiber orientation in the protrusions 2 is 50% or more and 60% or less, and there is relatively little bias in the fiber orientation in the protrusions 2. This is presumably because there are relatively many contact points between fibers in the protrusions 2, and the protrusions 2 themselves have excellent cushioning properties. This is demonstrated by the examples described later. The degree of fiber orientation of the protrusions 2 is preferably 50% or more, more preferably 53% or more, and is preferably 60% or less, more preferably 58% or less.

[0021] The degree of fiber orientation of the protrusions 2 of the nonwoven fabric 1 can be set to the specific range by appropriately adjusting the conditions of the hydroentanglement treatment carried out in the manufacturing process of the nonwoven fabric 1. That is, the nonwoven fabric of the present invention, represented by the nonwoven fabric 1, is produced by subjecting a web (a fiber assembly with no inter-fiber bonding) that is a precursor of the nonwoven fabric to a hydroentanglement treatment in which a water stream is sprayed onto the web, and rearranging and reentangling the constituent fibers of the web. By appropriately adjusting the conditions of the hydroentanglement treatment, specifically, for example, the water pressure of the water stream, the shape of the support that supports the web from the side opposite to the side where the water stream is sprayed during the hydroentanglement treatment, and the like, it is possible to set the degree of fiber orientation of the protrusions 2 of the finally obtained nonwoven fabric 1 to the specific range. The web to be subjected to the hydroentanglement treatment is typically formed by a conventionally known carding method, and the degree of fiber orientation of the web formed by the carding method, as measured by the above method, is usually 61 to 80%. The method for producing the nonwoven fabric of the present invention described below makes it possible to efficiently produce the nonwoven fabric 1 using a web formed by a carding method due to the characteristic structure of the support.

[0022] The measurement sample for the <Method of Measuring the Fiber Orientation Degree> is prepared by the following procedure. First, a nonwoven fabric 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, etc., a nonwoven fabric sample is prepared by cutting out an area of ​​as large an area as possible. Next, a backing is fixed to each side of the nonwoven fabric sample (for example, the first side 1a and the second side 1b if the sample is cut out from nonwoven fabric 1) using an adhesive, thereby obtaining a measurement sample having a structure in which a backing is adhesively fixed to both sides of the nonwoven fabric sample.

[0023] In addition, when the nonwoven fabric to be measured is bonded to other members by an adhesive in an article consisting of multiple members such as an absorbent article, it is preferable to reduce the adhesive strength of the adhesive part before removing the nonwoven fabric. Examples of the method for reducing the adhesive strength include a method of removing the adhesive using an organic solvent and a method of spraying the adhesive part with a cold spray. This method can be appropriately applied to all measurements in this specification.

[0024] In the above <Method for Measuring the Degree of Fiber Orientation>, the electron microscope used to obtain the observation image may be, for example, a scanning electron microscope. A specific example of the scanning electron microscope is a product name "JCM-5100" manufactured by JEOL Ltd. An example of a method for observing a nonwoven fabric using an electron microscope is a method in which the nonwoven fabric 1 is observed in plan view from the first surface 1a at a magnification of 100 times. Regarding the <method for measuring the degree of fiber orientation>, the method for measuring the degree of fiber orientation described in JP 2019-44321 A can be appropriately applied.

[0025] In the illustrated embodiment, a plurality of openings 4 penetrating the nonwoven fabric 1 in the thickness direction are formed at the bottom of the recess 3. The openings 4 are areas where there are no constituent fibers of the nonwoven fabric 1. The openings 4 are different from so-called interfiber voids which are naturally formed between constituent fibers of a fiber aggregate such as a nonwoven fabric and have a minute pore size, but are holes which are intentionally formed by processing such as hydroentanglement, and have an opening area far larger than the interfiber voids. 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 can be selected. In addition, the multiple openings 4 may have different shapes.

[0026] 1, on the first surface 1a of the nonwoven fabric 1, 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 direction X coincides with the MD of the nonwoven fabric 1, and the direction Y coincides with the CD.

[0027] The three-dimensional shape of the nonwoven fabric 1 is formed by subjecting the web to a hydroentanglement treatment. The three-dimensional shape is configured to include at least the bottoms of the protrusions 2 and the recesses 3, and further includes the apertures 4 in the illustrated embodiment. The micro-depressions that 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 hydroentanglement treatment in the manufacturing method of the nonwoven fabric 1 in the illustrated embodiment, typically, the fibers in the bottoms of the recesses 3 and the portions of the apertures 4 to be formed in the web are moved by the water flow to the portions of the protrusions 2 to be formed, and as a result, the bottoms of the recesses 3 or the apertures 4 are formed at the origin of the fibers, and the protrusions 2 are formed at the destination of the fibers. In the water jetting step, for example, with the web 11 placed on the first surface 20a, which is the uneven surface of the uneven support 20 shown in Fig. 5, a water jet is sprayed from the first surface 20a toward the second surface 20b of the uneven support 20, that is, from the surface side corresponding to the second surface 1b of the web 11 placed on the uneven support 20 toward the surface side corresponding to the first surface 1a, thereby rearranging and reentangling the constituent fibers of the web 11 (see Fig. 7). The convex portions 2, the bottoms of the concave portions 3, and the openings 4 formed by such rearrangement and reentanglement of the fibers can each maintain their shape by themselves.

[0028] Nonwoven fabric 1 has non-uniform fiber basis weights, with high basis weight sections 5 having a relatively large basis weight and low basis weight sections 6 having a relatively small basis weight. In the illustrated embodiment, nonwoven fabric 1 further has open sections 4 having a basis weight of zero. Protrusions 2 are the portions of high basis weight sections 5 that exist on first surface 1a of nonwoven fabric 1 (portions that protrude from the surface of first surface 1a), and the bottoms of recesses 3 are made of low basis weight sections 6. Nonwoven fabric 1 is typically composed only of fibers, in which case "basis weight of nonwoven fabric" is the same as "basis weight of constituent fibers of nonwoven fabric".

[0029] The ratio of the total opening area of ​​the openings 4 on the first surface 1a side (the side where the convex portion is located) to the area of ​​the first surface 1a (hereinafter also referred to as the "opening area ratio"), i.e., "the ratio of the total opening area on the first surface 1a side of all openings 4 formed on the first surface 1a when the area of ​​the first surface 1a of the nonwoven fabric 1 is taken as 100" is preferably 20% or more, more preferably 25% or more, and preferably 50% or less, more preferably 48% or less. As described above, the protrusions 2 (high basis weight parts 5) can be formed by including fibers that have migrated from the regions of the web where the openings 4 are to be formed during the hydroentanglement treatment of the web, which is the precursor of the nonwoven fabric 1, and a large opening area ratio indicates that the constituent fibers of the nonwoven fabric 1 are distributed to the protrusions 2 to a large extent. The presence of a relatively large amount of fibers in the protrusions 2 is beneficial for improving the cushioning properties of the nonwoven fabric 1. Therefore, from the viewpoint of improving the cushioning properties of the nonwoven fabric 1, the larger the opening area ratio, the better. On the other hand, if the opening area ratio is too large, there is a concern that the strength of the nonwoven fabric 1 may decrease. The preferred range of the opening area ratio has been set from this viewpoint.

[0030] The area of ​​the openings 4 on the first surface 1a side is not particularly limited, but from the same viewpoint as the preferred range of the opening area ratio described above, it is preferably 1 mm 2 More than 2mm, preferably 2 More than 2.3mm 2 More than 5mm, preferably 2 Less than 4mm, more preferably 2 Below, further 3mm 2 When the open area of ​​each hole 4 is within the above-mentioned preferred range, it is possible to impart sufficient strength for practical use to the nonwoven fabric 1 and further improve the cushioning properties of the nonwoven fabric 1. The open area of ​​the hole 4 is measured by the following method.

[0031] <Method for measuring the open area of ​​the openings in a nonwoven fabric> A microscope is used to observe one side of the nonwoven fabric to be measured (e.g., nonwoven fabric 1), and the open area of ​​the openings is measured based on the observed image. An example of a microscope suitable for this measurement is the "VHX6000" manufactured by Keyence Corporation. For example, when measuring the opening area on the first surface 1a side of the opening 4 of the nonwoven fabric 1 using the VHX6000, the nonwoven fabric 1 is placed on the base of the VHX6000 with its first surface 1a side facing up, the observation magnification of the VHX6000 is set to 50 times and the nonwoven fabric 1 is focused on, and the opening 4 is identified and its opening area is measured using the built-in function of the VHX6000. Specifically, the edge of the opening 4 is first determined using the automatic area measurement function built into the VHX6000. In this determination process, the threshold value is set to 0, and the part of the nonwoven fabric 1 with high brightness (white part) is extracted, and the boundary between the extracted part (white part) and the part not extracted is determined to be the edge of the opening 4. The area (unit: mm 2 ) is measured, and the measured value is regarded as the open area of ​​the opening 4.

[0032] The ratio of the basis weight P of the portion overlapping with the protrusions 2 in a planar view (i.e., the high basis weight portion 5) to the basis weight Q of the portion overlapping with the non-formed portion of the openings 4 at the bottom of the recesses 3 in a planar view (i.e., the low basis weight portion 6), expressed as basis weight P / basis weight Q, is preferably 2.8 or more, more preferably 3 or more, even more preferably 3.3 or more, and preferably 5 or less, more preferably 4.5 or less. When the ratio is within the preferred range, the fibers are appropriately unevenly distributed in the protrusions 2, and the nonwoven fabric 1 can have an even better balance between cushioning properties and strength.

[0033] The basis weight of each portion of the nonwoven fabric 1 is not particularly limited, but from the standpoint of improving cushioning properties, ensuring sufficient strength for practical use, etc., it is preferable to set it as follows. The basis weight P of the high basis weight portion 5 is preferably 30 g / m 2 or more, provided that the basis weight P is greater than the basis weight Q of the low basis weight portion 6. 2 More preferably, 50 g / m 2 More than 110 g / m 2 Less than 90g / m 2 The following is the result. The basis weight Q of the low basis weight portion 6 is preferably 10 g / m 2 on the assumption that it is smaller than the basis weight P of the high basis weight portion 5. 2 More preferably, 15 g / m 2More than 40 g / m 2 Less than or equal to 35 g / m 2 The following is the result. The basis weight of parts of the nonwoven fabric, such as the high basis weight part 5 and the low basis weight part 6, is measured by the following method.

[0034] <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 of ​​as large an area 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 carried out 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 weights of the high basis weight portion 5 and the low basis weight portion 6 of the nonwoven fabric 1 will be described as an example. First, a measurement sample of 5 cm square cut from the nonwoven fabric 1 is cut into the high basis weight portion 5 (portion including the convex portion 2) and the low basis weight portion 6 (portion including the bottom of the concave portion 3) using a cutting tool such as scissors. At this time, the boundary between the high basis weight portion 5 and the low basis weight portion 6 is cut with the cutting tool, and the boundary is the starting point 2S (see FIG. 2) of the rise of the convex portion 2 of the high basis weight portion 5 from the concave portion 3. Next, the total mass of the cut high basis weight portion 5 and the cut low basis weight portion 6 is measured using an electronic balance. Separately, the "total area of ​​high basis weight portions 5 (protrusions 2)" ("total protrusion area" described below) and the "total area of ​​low basis weight portions 6 (parts that overlap in plan view with non-formed portions of apertures 4 at the bottoms of recesses 3)" ("total bottom area" described below) are measured using the <Method for measuring the total area of ​​protrusions and bottoms of nonwoven fabric> described below. The total mass of the high basis weight portions 5 is then divided by their total area (total protrusion area) to calculate the basis weight P of the high basis weight portions 5. The total mass of the low basis weight portions 6 is then divided by their total area (total bottom area) to calculate the basis weight Q of the low basis weight portions 6.

[0035] <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 (8). (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) The measurement sample is placed with its uneven surface facing up (the uneven surface is the measurement surface). For example, if the measurement sample is cut out from the nonwoven fabric 1, the nonwoven fabric 1 is placed so that the first surface 1a, which is the uneven surface, faces upward. (3) Using a high-precision shape measurement system KS-1100 (product name, manufactured by Keyence Corporation) for the uneven surface of the measurement sample, 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 measurement surface in a no-load state (natural state without load) and an image is captured. 2 (Measurement pitch: 20 μm vertically, 20 μm horizontally), and the movement speed is 10 cm / sec. (4) A transparent acrylic plate with a mass of 300 g is placed on the uneven surface of the measurement sample, and the plate is heated to 12 g / cm 2 In the state where the pressure is applied, the surface shape of the uneven surface is measured and an image is taken in by the same method as in (3) above. The flat plate used is of a size capable of covering the entire uneven 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 image of the "part where the thickness has changed" obtained in (5) above is imported and processed using image processing software NewQube (Ver. 4.22, product name, manufactured by Nexus Co., Ltd.), and its area is measured. The part where the thickness has changed is the convex part of the uneven surface of the measurement sample (in the case of nonwoven fabric 1, convex part 2 (high basis weight part 5)), and the area measured for that part corresponds to the "sum of the areas of all convex parts present on the uneven surface of the measurement sample" (hereinafter also referred to as the "total convex part area"). (7) The surface opposite to the uneven surface of the measurement sample is used as the measurement surface, and the area of ​​the openings of the measurement sample is measured. For example, if the measurement sample is cut out from nonwoven fabric 1, nonwoven fabric 1 is placed so that second surface 1b faces upward, and the total opening area of ​​all openings 4 present on second surface 1b is measured on the second surface 1b side in accordance with the above <Method of measuring the opening area of ​​openings in nonwoven fabric>. This measurement value corresponds to the "sum of the area of ​​all openings present on the surface opposite to the uneven surface of the measurement sample" (hereinafter also referred to as the "total opening area"). (8) The area of ​​the bottoms of the recesses of the measurement sample (hereinafter also referred to as "total bottom area") is calculated 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). Total bottom area = area of ​​nonwoven fabric - total area of ​​protrusions - total area of ​​openings

[0036] The basis weight of the nonwoven fabric 1 is preferably 15 g / m from the viewpoint of the balance of various properties such as appearance, strength, and cushioning. 2 More preferably, 25 g / m 2 More than 100 g / m 2 Less than 80 g / m 2 The following is the result.

[0037] The apparent thickness AT of the nonwoven fabric 1 (see FIG. 2) is not particularly limited, but is preferably 0.5 mm or more, more preferably 1 mm or more, and preferably 10 mm or less, more preferably 5 mm or less, 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. 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.

[0038] <Method for measuring the apparent thickness of nonwoven fabric> 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 of ​​as large an area as possible is cut out and used as the measurement sample. With a load of 0.05 kPa applied to the measurement sample, the thickness of the measurement sample is measured using a laser thickness meter (e.g., "LK-080" manufactured by Keyence Corporation). 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.

[0039] 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. As the constituent fibers of the nonwoven fabric of the present invention, those conventionally used as constituent fibers of spunlace nonwoven fabrics for absorbent articles can be used without any particular limitation. A typical constituent fiber of the nonwoven fabric is a thermoplastic fiber.

[0040] The nonwoven fabric of the present invention preferably contains cellulose fibers. When the nonwoven fabric contains cellulose fibers, it is expected that the quality of the nonwoven fabric, such as the feel of use, can be improved, the burden on the environment can be reduced, and the product image can be improved by using natural fibers instead of synthetic fibers such as thermoplastic fibers. Due to the poor thermoplasticity of cellulose fibers, conventional nonwoven fabrics using cellulose fibers have been poor in three-dimensional appearance and cushioning properties, as compared with nonwoven fabrics using thermoplastic fibers, because it is difficult to form three-dimensional shapes such as unevenness and open holes in the nonwoven fabric. However, the nonwoven fabric of the present invention is unlikely to suffer from the disadvantages attributable to the use of cellulose fibers, because the degree of fiber orientation of the convex portions is set within the above-mentioned specific range, and it is possible to fully utilize the advantages of using cellulose fibers.

[0041] The cellulose fibers usable for the nonwoven fabric of the present invention can be any fibers usable for this type of fabric product without any particular limitations. 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 these 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.

[0042] In the nonwoven fabric of the present invention, the content of cellulose fibers is not particularly limited, but from the viewpoint of more reliably achieving the functional effects of containing cellulose fibers (improved quality, reduced environmental impact, etc.), the content is preferably 10 mass% or more, more preferably 30 mass% or more, even more preferably 50 mass% or more, even more preferably 70 mass% or more, and even more preferably 90 mass% or more, relative to the total mass of the nonwoven fabric, and may even be 100 mass%, i.e., the entire nonwoven fabric is cellulose fibers.

[0043] The nonwoven fabric of the present invention may contain cellulose fibers and other 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.

[0044] 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 in 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.

[0045] When the nonwoven fabric of the present invention contains cellulose fibers and thermoplastic fibers, the content of the thermoplastic fibers is, from the viewpoint of obtaining the effect of the thermoplastic fibers without reducing the effect of the cellulose fibers, 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.

[0046] 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 an 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 1 is used for a wearable article, it is preferable that the first surface 1a, which is an uneven surface on which the convex portions 2 are intermittently arranged, is the skin-facing surface that faces the skin of the wearer of the wearable article, since this makes the most of the pleasant feel of the uneven surface.

[0047] Next, the method 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 an apparatus that can be used to carry out the production method 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The protrusions 22 promote the formation of the openings 4 or the bottoms of the recesses 3 during the hydroentanglement treatment of the web 11. Typically, when a water flow is sprayed onto the portion of the web 11 overlapping with the protrusions 22 during the hydroentanglement treatment, the fibers move from that portion to the surrounding area, and as a result, that portion (the source of the fiber movement) becomes the openings 4 in the nonwoven fabric 1 where no fibers are present, or the bottoms 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.

[0058] 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 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.

[0059] 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.

[0060] The uneven support 20 is characterized in that the opening area of ​​the through hole 23 and the thickness of the base plate 21 are each set within a specific range. 2 More than 20mm 2 and the thickness T of the base plate 21 (see FIGS. 5, 6(b) and 6(c)) is 2.5 mm or more. As described above, the through holes 23 are the sites where the convex portions 2 of the nonwoven fabric 1 are formed during the hydroentanglement treatment of the web 11. The open area of ​​the through holes 23 on the convex-concave surface side (the surface side on which the web 11 is placed) is 3.5 mm 2 If the opening area of ​​the through-holes 23 on the uneven surface side is less than 20 mm2, it may be difficult to form the protrusions 2, and the nonwoven fabric 1 may have a poor three-dimensional appearance. 2 If it exceeds this value, the amount of fiber required to form one protrusion 2 increases, and the produced nonwoven fabric may lack a three-dimensional appearance. If the thickness T of the base plate 21 is less than 2.5 mm, 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, which in turn will result in an insufficient apparent thickness AT (see FIG. 2) of the nonwoven fabric 1, which may result in the nonwoven fabric 1 lacking in three-dimensionality. In addition, it may be difficult to set the fiber orientation degree of the convex portions 2 within the specific range. 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 specific range. The opening area of ​​the through hole 23 on the first surface 20a (concave-convex surface) is preferably 3.5 mm 2 More than 4.7mm, preferably 4.7mm 2 More than 20mm, preferably 2 Less than 10mm, more preferably 2 The following is the result. The thickness T of the base plate 21 is preferably 2.5 mm or more, and more preferably 3 mm or more. There is no particular upper limit to the thickness T, but from the viewpoint of forming a uniform concave-convex shape, it is preferably less than 5 mm, and more preferably 4 mm or less.

[0061] 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.

[0062] In order to ensure the effects of the present invention, it is preferable to set the dimensions of each part of the concave-convex support body 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] The area ratio of the through holes 23 in the uneven support 20, i.e., "the ratio of the total opening 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 being taken as 100" is not particularly limited, but from the viewpoint of ensuring the effects 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.

[0067] 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.

[0068] In the present invention, the term "web" refers to a fiber assembly in which the fibers are not substantially bonded to each other and the degree of freedom of fiber movement is ensured, in other words, the integrity of the sheet is not ensured and 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 not 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.

[0069] In the method for producing a nonwoven fabric of the present invention, the web is subjected to a water jetting step to perform hydroentanglement treatment, 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.

[0070] The manufacturing apparatus 10 may include a drying device (not shown) that removes moisture from the web that has been hydroentangled 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 (heating treatment). In the method for manufacturing a nonwoven fabric with unevenness 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 to dry a web that has been hydroentangled in a spunlace nonwoven fabric manufacturing apparatus can be used without any particular restrictions. Specific examples of the drying treatment 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.

[0071] The method for manufacturing the nonwoven fabric 1 using the manufacturing apparatus 10 includes at least a water jetting step. In the water jetting step, as shown in Fig. 4, a water jet 30 is sprayed onto the web 11 from a water jet nozzle 17 while the web 11 is placed on the first surface 20a (concave-convex surface) of the concave-convex support 20, thereby entangling the fibers contained in the web 11 and forming convex portions 2 (see Fig. 1, etc.) in the web 11. As described above, the web 11 preferably contains cellulose fibers. 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.

[0072] 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 the 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 opening ends of the through holes 23 on the second surface 20b side (the opening ends opposite the inflow side of the water and fibers) are 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 (high basis weight parts 5) 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 areas without any 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 of the recesses 3 (low basis weight areas 6) as shown in Fig. 7(c). In this way, 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, turning the web 11 into a nonwoven fabric 1 (first manufacturing method). 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. The nonwoven fabric 1 produced in this manner has a fiber orientation degree of 50% or more and 60% or less in the protrusions 2 as described above, and since there is relatively little deviation in the fiber orientation in the protrusions 2, the nonwoven fabric 1 has excellent cushioning properties.

[0073] In particular, as shown in FIG. 6(a) and the like, the concave-convex support 20 in the illustrated embodiment has a plurality of (four) protrusions 22 arranged on the first surface 20a so as to surround one through hole 23 whose open area is within the specific range. Therefore, water sprayed onto the first surface 20a during the hydroentanglement treatment is likely 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 are likely to accumulate in the through hole 23, and thus the convex portion 2 (high basis weight portion 5) is likely to be formed, and further, the fiber orientation degree of the convex portion 2 is likely to be 50% or more and 60% or less. In addition, when the convex portion 2 is formed by fibers moving from a plurality of places around the through hole 23 and accumulating in the through hole 23 in this way, the micro recessed portion is likely to be formed on the opposite side to the top of the convex portion 2. The micro recessed portion is expected to have the effect of increasing the cushioning property of the nonwoven fabric 1 together with the convex portion 2.

[0074] In the water flow spraying process, the water pressure of the water flow sprayed from the water flow nozzle 17 is not particularly limited, but from the viewpoint of more reliably achieving the effects of the present invention, it is preferably 0.1 MPa or more, more preferably 0.3 MPa or more, and 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.

[0075] 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. In the water jetting process, the MD conveying speed of the web 11 is not particularly limited, but from the viewpoint of more reliably achieving the effects of the present invention, it 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.

[0076] 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, the method for producing a 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.

[0077] The method for producing a nonwoven fabric of the present invention includes 1) 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 2) an embodiment in which the drying step is carried out as necessary after the water jetting step, and further includes a heating step of heat-treating the web (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.

[0078] 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.

[0079] 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.

[0080] 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. Although the nonwoven fabric 1 of the above embodiment has openings 4, the nonwoven fabric of the present invention does not have to have openings. When a nonwoven fabric having no openings is produced by the above-mentioned production method of the present invention, the water pressure of the water stream sprayed onto the web and the shape of the protrusions of the uneven support may be appropriately adjusted in the water stream spraying step of the production method. EXAMPLES

[0081] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to such examples.

[0082] [Examples 1 to 4, 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. Cotton fibers, which are 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 (the corrugated mounting surface) of a corrugated 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 a water jetting apparatus, and the hydroentanglement treatment was carried out by introducing the web into the water jetting apparatus twice. The conditions for the hydroentanglement treatment and the details of the corrugated support are shown in Table 1 below. In Table 1 below, the water flow nozzles in the nozzle row arranged at the most upstream of the MD are designated as water flow nozzle A, followed by water flow nozzle B and water flow nozzle C toward the downstream side of the MD. Note that water flow nozzles A and B have a nozzle hole diameter of 0.1 mm and a nozzle hole pitch of 1.0 mm, and water flow nozzle C has a nozzle hole diameter of 0.12 mm and a nozzle hole pitch of 0.6 mm.

[0083] The nonwoven fabrics produced in the Examples and Comparative Examples were evaluated for unevenness and cushioning properties by the following methods. The results are shown in Table 1 below.

[0084] <Method of evaluating unevenness> The nonwoven fabrics to be evaluated were visually observed and rated according to the following evaluation criteria. The evaluation was carried out by 10 trained panelists. In the following evaluation criteria, "A" is a better evaluation than "C". (Evaluation criteria for uneven shape) A: The bumps and grooves are clearly visible. B: Slight irregularities are visible. C: Does not appear uneven.

[0085] <How to evaluate cushioning> Compression work (hereinafter, also referred to as "WC") is used as an index of the cushioning properties of the nonwoven fabric to be evaluated. The higher the WC value, the higher the cushioning properties of the fabric to be evaluated. It is generally known that WC can be expressed as a measurement value using the KES (Kawabata Evaluation System) manufactured by Kato Tech Co., Ltd. (Reference: Standardization and Analysis of Texture Evaluation (2nd Edition), author Kawabata Toshio, published July 10, 1980). Specifically, the WC of the nonwoven fabric to be evaluated is measured using the compression tester KES-G5 manufactured by Kato Tech Co., Ltd. The WC measurement procedure is as follows. First, a measurement sample is prepared by cutting out an area of ​​5 cm square in a plan view from the nonwoven fabric to be evaluated. If the area cannot be secured due to the small area of ​​the nonwoven fabric to be evaluated, an area as large as possible is cut out as the measurement sample. The measurement sample is attached to the test table of the compression test device. Next, the measurement sample is placed on a 2 cm 2 The specimen is compressed between steel plates with circular flat surfaces. The compression speed is 0.2cm / sec, and the maximum compression load is 2450mN / cm. 2 , SENS is 10, and DEF is 20. WC is expressed by the following formula (1) and its unit is "gf cm / cm 2 In the following formula (1), T m is 2450mN / cm 2 (4.9kPa) Load Thickness, T O is 4.902mN / cm 2 (49 Pa). In the following formula (1), Pa represents the measured load (mN / cm 2 ) is shown.

[0086]

number

[0087] [Table 1]

[0088] As shown in Table 1, the nonwoven fabrics of the examples had a fiber orientation degree of 50% or more and 60% or less in the convex portions, and therefore had a better uneven shape, a larger compression work load, and better cushioning properties than the nonwoven fabrics of the comparative examples which did not satisfy this requirement. [Explanation of symbols]

[0089] 1 Spunlace nonwoven fabric for absorbent articles 1a 1st side of nonwoven fabric 1b Second side of nonwoven fabric 2 Convex 3. Recess 11. Web 20 Concave and convex support 20a: First surface (concave-convex surface) of the uneven support 21 Base plate 22 protrusions 23 Through hole

Claims

1. A spunlace nonwoven fabric for absorbent articles, a first surface and a second surface located opposite the first surface, a plurality of convex portions intermittently arranged on at least the first surface, and concave portions present between adjacent convex portions; A spunlace nonwoven fabric for absorbent articles, wherein the degree of fiber orientation of the convex portions is 50% or more and 60% or less, as measured by the following method. <Method for measuring the degree of fiber orientation> Using an electron microscope, the nonwoven fabric, which is a measurement sample, is observed in a planar view from the first surface, and an observation image of the convex portion, which is the measurement target site, is obtained. A square consisting of two first reference lines parallel to each other and two second reference lines perpendicular to the two first reference lines is added to the obtained observation image. The extension direction of the first reference lines is aligned with the machine direction during manufacture of the nonwoven fabric of the measurement sample, and the extension direction of the second reference lines is aligned with a vertical direction perpendicular to the machine direction. The length of each of the four reference lines is 0.5 mm. For each of the four reference lines, the number of fibers passing through that reference line is counted, and the sum of the numbers for the two first reference lines is defined as the "first fiber number," and the sum of the numbers for the two second reference lines is defined as the "second fiber number." Of the two fiber counts, the one with the larger number is defined as A and the one with the smaller number is defined as B, and the fiber orientation degree is calculated using the following formula: Fiber orientation degree (%) = [A / (A + B)] × 100 For the same measurement sample, the observation images are obtained at three locations, the fiber orientation degree is calculated based on each of the observation images, and the average value of the calculated fiber orientation degrees is taken as the fiber orientation degree of the measurement target portion of the measurement sample.

2. A plurality of openings penetrating the nonwoven fabric in a thickness direction are formed at the bottom of the recess, The spunlace nonwoven fabric for absorbent articles according to claim 1, wherein the ratio of the total open area of ​​the openings on the first surface side to the area of ​​the first surface is 20% or more and 50% or less.

3. The opening area of ​​the opening portion on the first surface side is 1 mm ２ More than 5mm ２ The spunlace nonwoven fabric for absorbent articles according to claim 2, which is as follows:

4. 4. The spunlace nonwoven fabric for absorbent articles according to claim 2 or 3, wherein the ratio of the basis weight of the portion overlapping with the convex portion in a planar view to the basis weight of the portion overlapping with the non-forming portion of the hole portion at the bottom of the concave portion in a planar view, as the former / latter, is 3 or more and 5 or less.

5. The spunlace nonwoven fabric for absorbent articles according to claim 1 or 2, which contains cellulose fibers.

6. A method for producing a spunlace nonwoven fabric for absorbent articles, comprising: a water jetting step of jetting a water jet onto a web placed on a corrugated surface of a corrugated support having a corrugated surface on which a plurality of protrusions are formed, thereby entangling fibers contained in the web and forming the protrusions on the web, the uneven support body has a base plate that forms a surface of the uneven support body on which the web is placed, a plurality of the protrusions that are arranged on a surface of the base plate that corresponds to the uneven surface, and a plurality of through holes that penetrate the base plate in a thickness direction, the protrusions and the through holes being scattered on the uneven surface, The opening area of ​​the through hole on the uneven surface side is 3.5 mm ２ More than 20 mm ２ is as follows: The manufacturing method, wherein the thickness of the base plate is 2.5 mm or more.

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