JP7588472B2 - Top sheet for absorbent article and absorbent article including same - Google Patents

Description

The present invention relates to a top sheet for absorbent articles and an absorbent article equipped with the same.

Absorbent articles used to absorb fluids discharged from the body, such as sanitary napkins, incontinence pads, and panty liners, generally use a liquid-permeable sheet such as a nonwoven fabric as the top sheet that forms the skin-facing surface.

With the aim of improving the absorbency while improving the feel of the top sheet, Patent Document 1 discloses an absorbent article equipped with a top sheet having a first fiber layer containing water-retentive fibers and a second fiber layer adjacent to the non-skin side of the first fiber layer and containing hydrophobic fibers and water-retentive fibers. The document also discloses that the proportion of water-retentive fibers in the fibers constituting the first fiber layer is greater than the proportion of water-retentive fibers in the fibers constituting the second fiber layer, and that the proportion of water-retentive fibers in the second fiber layer is 50 to 90% by mass.

JP 2020-039570 A

The top sheet arranged in the absorbent article described in Patent Document 1 contains a high proportion of water-retentive fibers, so liquid discharged onto the top sheet is highly diffusible along the plane of the sheet, and the amount of liquid remaining on the sheet can be large. Patent Document 1 does not consider any solution to this problem.

Therefore, the object of the present invention is to provide a top sheet for absorbent articles that has a small liquid diffusion area and leaves little liquid behind on the sheet, and an absorbent article equipped with the top sheet.

The present invention comprises cotton,
A first surface and a second surface opposite the first surface,
The present invention provides a surface sheet for absorbent articles, in which, when the number of fiber fluffs on the first surface and the number of fiber fluffs on the second surface are measured by the following measurement method, the number of fiber fluffs on the second surface is greater than the number of fiber fluffs on the first surface.
<Measurement method>
(1) A piece measuring 20 cm square is cut out from the sheet to be measured, and the piece is folded in half at any position on the surface to be measured to obtain a measurement sample.
(2) The measurement sample is placed on a first mount, and a second mount having a 1 cm square hole is placed on the measurement sample so that the fold of the measurement sample can be seen through the hole.
(3) A 50 g weight is placed on each side of the second mount at a distance of 5 cm outward from the hole along the fold, and under this condition, the inside of the hole in the second mount is observed at 30x magnification using a microscope, and the number of fibers present above an imaginary line formed at a position moved parallel to and 0.2 mm upward from the fold is counted.
(4) The measurement in (3) above is carried out using three measurement samples, with three locations per measurement sample, and the arithmetic average value is regarded as the number of fuzz particles on the measurement surface.
(5) If a piece measuring 20 cm square cannot be cut out in (1) above, cut out three pieces measuring 5 cm square to use as measurement samples, and measure the number of fibers at any three positions for each measurement sample using the procedures in (2) and (3) above. The arithmetic average of the number of fibers at a total of nine positions is the number of fuzz on the surface to be measured.

The present invention also provides an absorbent article that includes a top sheet for an absorbent article, the top sheet being arranged so that a first surface side of the top sheet faces the body of a wearer.

The present invention provides a top sheet for absorbent articles that has a small liquid diffusion area and leaves little liquid behind on the sheet, and an absorbent article that includes the top sheet.

FIG. 1 is a cross-sectional view that illustrates one embodiment of the top sheet for absorbent articles of the present invention. 2(a) to (c) are schematic diagrams showing a method for measuring the number of fuzzed fibers in the topsheet for absorbent articles of the present invention. FIG. 3 is a cross-sectional view that illustrates a schematic view of another embodiment of the top sheet for absorbent articles of the present invention. FIG. 4 is a side view showing a schematic diagram of an embodiment of a manufacturing apparatus for manufacturing the topsheet for absorbent articles of the present invention.

The present invention will be described below based on preferred embodiments with reference to the drawings. The top sheet 1 for absorbent articles (hereinafter simply referred to as "top sheet 1") shown in FIG. 1 is a liquid-permeable sheet having a first surface F and a second surface R located on the opposite side of the first surface F. The top sheet 1 contains cotton 1a as its constituent fibers, and is formed by intertwining the constituent fibers. Typically, the top sheet 1 of the present invention is a spunlace nonwoven fabric.

The top sheet 1 is preferably used as a component of an absorbent article that absorbs bodily fluids such as urine and menstrual blood. The top sheet 1 is preferably configured so that the first side F is disposed on the skin-contacting side, which is the side that contacts the wearer's skin, and the second side R is disposed on the non-skin-contacting side, which is the side opposite to the skin-contacting side. Typically, the first side F is used as the liquid-receiving side, which is the side that first comes into contact with the top sheet 1 and excreted liquid, and the second side R is disposed in contact with a liquid-retentive absorbent.

The top sheet 1 has a different number of fluffs in the constituent fibers on each of its faces F and R. In particular, it is preferable that the number of fluffs Nf of the fibers on the first face F of the top sheet 1 is greater than the number of fluffs Nr of the fibers on the second face R of the top sheet 1. A top sheet 1 having such a configuration can be manufactured, for example, by the method described below.

The number of fiber fluffs Nf and Nr on each face F and R can be measured by the following measurement method. The following sampling and measurement are performed in an environment of 22±2° C. and 60±5% RH.
First, a piece measuring 20 cm square is cut out from the topsheet 1 to be measured using a sharp blade such as a razor. Then, as shown in Fig. 2(a), the piece is folded in half at an arbitrary position (in the direction of the arrow in Fig. 2(a)) so that the surface to be measured for the number of fuzz fibers faces outward, thereby forming a measurement sample 104.
Next, the measurement sample 104 is placed on a first mount 101 of A4 size and black, and further, as shown in Fig. 2(b), a second mount 102 of A4 size and black with a hole 107 of 1 cm square is placed on top of the measurement sample 104. At this time, as shown in Fig. 2(b), the measurement sample 104 is arranged so that the fold 105 of the measurement sample 104 is visible through the hole 107 of the second mount 102. For each mount 101, 102, for example, "Kenran (black) ream weight 265g" by Fuji Kyowa Paper Co., Ltd. can be used.

Thereafter, 50 g weights 10W are placed on both sides of the hole 107 at a distance of 5 cm outward along the fold 105 from the second mount 102 side, thereby completely folding the measurement sample 104. Then, as shown in Fig. 2(c), the inside of the hole 107 is observed at a magnification of 30 times using a microscope (for example, VHX-900, manufactured by Keyence Corporation), and the number N of fibers present above the imaginary line 108 formed at a position moved 0.2 mm upward in parallel from the fold 105 of the measurement sample 104 is measured.
Repeating the above procedure, three pieces are randomly cut out from each top sheet to be measured, and each is used as a measurement sample. The number of fibers N is measured at three arbitrary positions per measurement sample, and the arithmetic mean value of the number of fibers N at a total of nine positions is regarded as the "number of fiber fuzz" on the surface to be measured.
If it is not possible to cut out a piece measuring 20 cm square, three pieces measuring 5 cm square are cut out to serve as measurement samples, and the number N of fibers is measured at three arbitrary positions per measurement sample. The arithmetic mean value of the number N of fibers at a total of nine positions is regarded as the "number of fiber fuzz" on the surface to be measured.
The above-mentioned operation is performed on the surface of the slice corresponding to the first surface F and the surface of the slice corresponding to the second surface R, respectively, to obtain the number of fiber fluffs on the first surface F, Nf, and the number of fiber fluffs on the second surface R, Nr.

When the above-mentioned measurement method is adopted, the fewer the number of fiber fluffs Nf on the first surface F, the better, preferably 16 or less, more preferably 2 or less, and even more preferably 0, i.e., no fiber fluff on the first surface F.

Furthermore, under the same conditions, the number of fluffed fibers Nr of the constituent fibers on the second surface R is preferably 2 or more, more preferably 5 or more, and preferably 15 or less, more preferably 10 or less, provided that the number is greater than the number of fluffed fibers N1 of the constituent fibers on the first surface F.

Furthermore, under the same conditions, the ratio (Nf/Nr) of the number of fluffs Nf of the fibers on the first surface F to the number of fluffs Nr of the constituent fibers on the second surface R is preferably as low as possible, and is preferably 0.6 or less, more preferably 0.2 or less, and even more preferably 0 (zero).

The top sheet 1 having the above-mentioned configuration contains cotton, so it is easy to give the wearer of an absorbent article equipped with the top sheet 1 the softness of cotton fibers and the positive image of "gentleness" and "sense of security" that the wearer associates with cotton fibers. In addition, since the number of fluffs Nr of the constituent fibers on the second side R is greater than the number of fluffs Nf of the constituent fibers on the first side F, when the first side F is used as a liquid-receiving surface, the first side F and its vicinity have a high fiber density and a structure with high capillary force, making it easier to draw liquid into the top sheet. In addition, the second side R and its vicinity have a low fiber density and a structure with low capillary force compared to the first side F, so the absorbed liquid is less likely to diffuse in the sheet surface direction, and the liquid diffusion area is small. Furthermore, because the number of fuzzed fibers Nr on the second surface R is greater than the number of fuzzed fibers Nf on the first surface, the fuzzed fibers act as guides that facilitate the transfer of liquid absorbed in the top sheet 1 to the absorbent body or other member that is in contact with the second surface R, making it easier for the absorbed liquid to transfer to the liquid-retaining member such as the absorbent body. As a result, liquid is less likely to remain on the sheet, the liquid diffusion area is reduced, and the top sheet is pleasant to the touch.

As described above, the top sheet 1 may be configured to include cotton 1a as a constituent fiber. For example, the top sheet 1 may be configured to include only cotton 1a, or may include other fibers in addition to cotton 1a. From the viewpoint of obtaining a top sheet 1 that further reduces the amount of liquid remaining on the sheet and further reduces the liquid diffusion area, the top sheet 1 is preferably configured to include cotton 1a and a second fiber 2 other than cotton 1a (hereinafter, simply referred to as "second fiber 2") as constituent fibers, as shown in FIG. 3. Even in this case, it is preferable that each constituent fiber is kept in a sheet shape by intertwining. Note that the cotton 1a and the second fiber 2 shown in FIG. 3 are illustrated to have different fiber diameters, but this is shown only for the convenience of explaining the fibers and their arrangement, and the fiber diameters of both fibers may be the same or different.

Examples of the second fiber 2 include natural fibers, regenerated fibers, and synthetic fibers. Examples of natural fibers include cellulose fibers other than cotton, such as pulp. Examples of regenerated fibers include rayon and acetate fibers. Examples of synthetic fibers include thermoplastic fibers containing thermoplastic resins, and specific examples of thermoplastic resins include polyolefin resins such as polyethylene (PE) and polypropylene (PP), polyester resins such as polyethylene terephthalate (PET), polyamide resins, vinyl resins such as polyvinyl chloride and polystyrene, acrylic resins such as polyacrylic acid and polymethyl methacrylate, and fluororesins such as polyperfluoroethylene. These fibers can be used alone or in combination of two or more. Among these fibers, by using thermoplastic fibers as the second fiber 2, the fibers are less intertwined with each other than when cellulosic fibers such as natural fibers and regenerated fibers are used as the second fibers, so that fiber fluffing is more likely to occur on the sheet surface. When such a sheet is used as a liquid-receiving surface with the napped side of the fibers in contact with another component, the liquid is more likely to transfer to the other component. As a result, liquid is less likely to remain on the sheet, the liquid diffusion area is reduced, and the top sheet feels good against the skin.

When the top sheet 1 further contains the second fiber 2 in addition to the cotton 1a, it is preferable that, in a virtual plane parallel to the first surface F, the mass ratio of the cotton 1a decreases continuously, stepwise, or in a combination thereof from the first surface F to the second surface R when viewed from the first surface F along the thickness direction Z. In other words, the boundary between the fiber layer containing the cotton 1a and the fiber layer containing the second fiber 2 may be clear or unclear. The boundary between the fiber layer containing the cotton 1a and the fiber layer containing the second fiber 2 can be determined by dyeing the top sheet 1 with a fiber identification reagent (e.g., BOKENSTAIN II, manufactured by the Boken Quality Evaluation Organization, a general incorporated foundation) whose color changes depending on the type of fiber, and visually determining the area where the fiber composition ratio is different in the thickness direction Z from the color of the dyed fiber, and the border of the area can be determined as the boundary.

In detail, consider virtual dividing planes L1 and L2 that virtually divide the topsheet 1 into three equal parts in the thickness direction Z, and consider a first portion 10A including the first surface F, a second portion 10B including the second surface R, and a central portion 10C that is an area sandwiched between the virtual dividing planes L1 and L2 (see FIG. 3). In this case, it is preferable that the ratio A1 of the mass Wa of cotton 1a to the mass Wta of all fibers in the first portion 1A is higher than the ratio B1 of the mass Wb of cotton 1a to the mass Wtb of all fibers in the second portion 10B. With this configuration, the touch and flexibility of the sheet due to the texture of cotton are further improved, and the amount of residual liquid is further reduced, resulting in a topsheet 1 with an even smaller liquid diffusion area.

The mass and proportion of cotton 1a constituting the top sheet 1 can be measured by the following method. First, the top sheet 1 to be measured is divided into three equal parts in the thickness direction to obtain samples corresponding to the first portion 10A and the second portion 10B. These samples are immersed in an aqueous solution of 1000 ppm ascorbic acid/10 ppm riboflavin, and then exposed to sunlight to extract only the fiber components. The mass of these fiber components is measured and the masses Wta and Wtb of the total fibers in each portion 10A and 10B are taken as the masses Wta and Wtb of the total fibers in each portion 10A and 10B. Next, the fibers constituting each portion 10A and 10B are dyed with a fiber identification reagent (BOKENSTAIN II, manufactured by the Boken Quality Evaluation Organization, a general incorporated foundation), and only the fibers that have discolored to a grayish blue-green color are taken out. The discolored fibers are separated and dried one by one, and the total mass of the discolored fibers is measured for each portion 10A and 10B, and these are taken as the masses Wa and Wb of cotton 1a in each portion 10A and 10B. The percentage of the mass Wa of cotton 1a to the mass Wta of all fibers in the first region 10A, and the percentage of the mass Wb of cotton 1a to the mass Wtb of all fibers in the second region 10B are calculated, and the mass ratio A1 in the first region 10A and the mass ratio B1 in the second region 10B are calculated.

When the surface sheet 1 contains cotton 1a and the second fiber 2, the mass ratio A1 of cotton 1a to the mass Wta of all fibers in the first region 10A is preferably 50 mass% or more, more preferably 80 mass% or more, and particularly preferably 90 mass% or more and 100 mass% or less.
In addition, the mass ratio A2 of the second fibers 2 to the mass Wta of all fibers in the first portion 10A is preferably 50 mass% or less, more preferably 30 mass% or less, and particularly preferably 10 mass% or less, and 0 mass% or more.
Such a mass ratio makes it easier for the wearer of an absorbent article including the top sheet 1 to be given the positive images such as "gentleness" and "sense of security" that the wearer associates with cotton, and allows the high water absorbency of cotton 1a to be expressed.

The mass of the second fibers 2 in the first region 10A is calculated by subtracting the mass Wa of the cotton 1a from the mass Wta of all fibers in the region. The mass ratio of the second fibers 2 can be calculated as the percentage of the mass of the second fibers 2 relative to the mass Wta.

When the top sheet 1 includes cotton 1a and second fibers 2, the mass ratio B1 of cotton 1a to the mass Wtb of all fibers in the second portion 10B is preferably less than 50% by mass, more preferably 30% by mass or less, and preferably 0% by mass or more, and more preferably 10% by mass or more. This mass ratio reduces the liquid retention in the top sheet 1 and makes it easier to transfer the liquid to other members such as an absorbent, thereby further reducing the residual liquid in the sheet and the area where the liquid is spread.

When the top sheet 1 includes cotton 1a and second fiber 2, the mass ratio B2 of the second fiber 2 to the mass Wtb of all fibers in the second region 10B is preferably 50% by mass or more, more preferably 70% by mass or more, and preferably 100% by mass or less, more preferably 90% by mass or less. Such a mass ratio reduces the liquid retention in the top sheet 1 and increases the number of fibers that are fuzzed on the second surface R, making it easier to transfer the liquid to other members such as an absorbent, thereby further reducing the residual liquid and the liquid diffusion area in the sheet. This effect is particularly noticeable when thermoplastic fibers are used as the second fiber 2. The mass of the second fiber 2 in the second region 10B is calculated by subtracting the mass Wb of cotton 1a from the mass Wtb of all fibers in the same region. Then, the mass ratio B2 is calculated as the percentage of the mass of the second fiber 2 to the mass Wtb.

The top sheet 1 of the present invention can be suitably used as a component of an absorbent article. An absorbent article typically comprises a top sheet 1 and a back sheet, and can be used with an absorbent disposed between the top sheet 1 and the back sheet. Absorbent articles include, but are not limited to, incontinence pads, sanitary napkins, disposable diapers, etc., and broadly include articles used to absorb liquids discharged from the human body.

When the top sheet 1 of the present invention is used in an absorbent article, it is preferable that the top sheet 1 is arranged so that its first surface F constitutes the surface facing the skin of a wearer wearing the absorbent article when the absorbent article is worn in the correct position (hereinafter, this surface is also referred to as the "skin-facing surface"). It is also preferable that the top sheet 1 is arranged in a region where the absorbent article comes into direct contact with the wearer's skin, with the first surface F serving as the skin-facing surface.

The back sheet is a sheet that constitutes the surface side facing away from the skin of the wearer who wears the absorbent article. The back sheet used in the absorbent article can be any sheet that has been conventionally used in absorbent articles, without any particular restrictions. The back sheet can be the same as the top sheet, or it can be a resin film that is poorly permeable to liquids or water repellent, or a laminate of a resin film and a nonwoven fabric, etc.

The absorbent body used in absorbent articles has an absorbent core. The absorbent core is composed of, for example, a pile of hydrophilic fibers such as cellulose including pulp, a mixed pile of the hydrophilic fibers and a water-absorbent polymer, a pile of water-absorbent polymer, or the like. At least the skin-facing surface of the absorbent core may be covered with a liquid-permeable core wrap sheet, or the entire surface including the skin-facing surface and the non-skin-facing surface may be covered with the core wrap sheet. As the core wrap sheet, for example, tissue paper made of hydrophilic fibers or liquid-permeable nonwoven fabric can be used.

The fiber diameter of the cotton 1a used in the topsheet 1 is not particularly limited as long as it is one commonly used in the present technical field, and is preferably 10 μm or more, more preferably 20 μm or more, and preferably 50 μm or less, more preferably 45 μm or less. The fiber diameter of the cotton 1a fibers can be calculated as the arithmetic average value by measuring the maximum across length of the cross section of the fibers cut perpendicular to the fiber length direction for 10 fibers using a scanning electron microscope (DSC6200 manufactured by Seiko Instruments Inc.).
From the viewpoint of appropriately increasing the degree of entanglement of the fibers and appropriately controlling fiber fuzzing, the fiber length of the cotton 1a used in the topsheet 1 is preferably 10 mm or more, more preferably 20 mm or more, and preferably 50 mm or less, more preferably 45 mm or less. The fiber length of the cotton 1a fibers is measured using the above-mentioned scanning electron microscope for 10 fibers in their natural state, and the arithmetic average value is taken as the fiber length.

When the second fiber 2 is used, the fiber diameter of the second fiber 2 is not particularly limited as long as it is one that is commonly used in this technical field, but is preferably 0.5 dtex or more and preferably 5 dtex or less in fineness. The fiber diameter of the second fiber 2 can be calculated as a fineness expressed as the mass per a given fiber length.

The basis weight of the top sheet 1 can be appropriately changed depending on the type and application of the absorbent article used, but is preferably 20 g/ ^m2 or more, more preferably 25 g/m2 or ^more , and is preferably 45 g/m2 or ^less , more preferably 40 g/m2 or ^less .

The above describes the absorbent article topsheet of the present invention and the absorbent article comprising said sheet. Below, a preferred method for manufacturing the absorbent article topsheet of the present invention will be described. This manufacturing method can use, for example, the manufacturing apparatus 10 shown in FIG. 4. The manufacturing apparatus 10 comprises, in this order, a web forming section 20 and a hydroentanglement section 30 along the conveying direction MD. In the following description, an example will be described in which a web containing cotton 1a and a web containing second fibers 2 are formed separately.

The web forming section 20 includes carding machines 21A, 21B that produce fiber webs 21a, 21b to form the fiber aggregate that constitutes the top sheet 1, and guide rolls 23, 23 for the fiber webs 21a, 21b.

The water flow entanglement section 30 entangles each fiber web 21a, 21b with a water flow to form an entangled body 5 in which the constituent fibers are integrally entangled. The water flow entanglement section 30 includes a water flow nozzle 35 that sprays a water flow toward the fiber web 21a, and a support belt 36 made of an endless belt. The water flow nozzle 35 is located above the support belt 36, and is capable of spraying a high-pressure water flow across the entire width of the fiber webs 21a, 21b (direction perpendicular to the conveying direction MD). The support belt 36 is disposed opposite the water flow nozzle 35, and has a structure with holes in various patterns such as a lattice pattern to allow the sprayed water to pass through (not shown).

The method for manufacturing the topsheet 1 using the manufacturing device 10 shown in FIG. 4 is, for example, as follows. First, the fiber webs 21a, 21b are unwound from the carding machines 21A, 21B in the web forming section 20 via the guide rolls 23, 23, respectively. Through these unwound operations, the laminate 4 in which the fiber webs 21a, 21b are stacked is formed (lamination process).

The composition ratio of fibers in each fiber web 21a, 21b may be adjusted according to the composition of the desired top sheet 1. For example, the first fiber web 21a may be a web of only cotton 1a, or a web in which cotton 1a and the second fiber 2 are mixed in a predetermined ratio. The second fiber web 21b may be a web of only second fiber 2, or a web in which cotton 1a and the second fiber 2 are mixed in a predetermined ratio.

Next, in the water flow entanglement section 30, the laminate 4 is entangled by high-pressure water jets from the water flow nozzles 35 while being transported by the support belt 36 (entanglement process). Through the entanglement process, the constituent fibers of the fiber webs 21a and 21b that make up the laminate 4 are three-dimensionally entangled to form the entangled body 5.

In the entanglement process, the degree of entanglement of the constituent fibers can be adjusted by appropriately changing various conditions such as the pressure of the high-pressure water stream sprayed onto the laminate 4, the number of times the water stream is sprayed, the transport speed of the laminate 4, and the surface of the laminate 4 onto which the high-pressure water stream is sprayed. In general, lowering the pressure of the high-pressure water stream sprayed onto the laminate 4 or reducing the number of times the water stream is sprayed weakens the degree of entanglement of the constituent fibers. In addition, increasing the transport speed of the laminate 4 shortens the time the high-pressure water stream is sprayed at a specific position, thereby weakening the degree of entanglement of the constituent fibers. Furthermore, if the surface of the laminate 4 onto which the high-pressure water stream is sprayed is only one side, the degree of entanglement of the constituent fibers will be weakened. These conditions can be adjusted by changing equipment conditions such as the number of water flow nozzles 35 installed, the installation interval, nozzle diameter, or the interval between the water flow nozzles 35 and the support belt 36, or by changing conditions that can be easily changed artificially, such as control of the water pressure or conveying speed, or control of the surface to be sprayed.

In the case where the top sheet 1 of the present invention, which is a typical embodiment of the spunlace nonwoven fabric, is used on the skin-contacting side of an absorbent article, the first side F of the top sheet 1 constituting the skin-contacting side may cause fibers to fluff on the sheet surface due to unintentional weakening of the intertwining of fibers caused by friction with the wearer's skin or unintentional breakage of the constituent fibers of the top sheet 1 during use of the absorbent article, and this fluffing may cause unpleasant irritation to the wearer's skin. Therefore, it is preferable to entangle the fibers on the first side F of the top sheet 1 so as to increase the degree of intertwining, so that the fibers do not fluff even during use. On the other hand, the second side R of the top sheet 1 constituting the non-skin-contacting side is preferable in that, provided that the above-mentioned configuration of the first side F is satisfied, the constituent fibers are entangled so as to weaken the degree of intertwining, thereby maintaining the appropriate degree of fluffing of the fibers and making it easier to transfer liquid to other members through the fluffed fibers.

As with the top sheet 1 described above, in order to make the number of fiber fluffs different between the first side F and the second side R, it is possible to form the sheet by spraying a high-pressure water stream onto only one side of the laminate 4. It is also possible to form the sheet by reducing the number of times the water stream is sprayed. In this way, the resulting sheet maintains a strength sufficient for practical use, while preventing the fiber density within the sheet from becoming excessively high, and reducing liquid residue and liquid diffusion.

In detail, as shown in FIG. 4, the entanglement process is performed by spraying a high-pressure water stream from only one side, for example, the upper side, of the first fiber web 21a in the laminate 4. The high-pressure water stream is not sprayed from the other side.

When the high-pressure water stream is sprayed only on the top surface of the first fiber web 21a, the fibers on the surface sprayed with the high-pressure water stream become entangled and orient along the sheet surface direction as they are subjected to the resistance of the water stream, resulting in less fiber fuzzing. This surface is the surface intended to form the first surface F of the topsheet 1. On the other hand, the surface on the side not sprayed with the high-pressure water stream (the surface facing the support belt 36 in the figure) is less likely to be subjected to the resistance of the water stream, so fiber fuzzing is maintained to a certain extent. This surface is the surface intended to form the second surface R of the topsheet 1.

In this process, in the water flow entanglement section 30, for example, the width in the direction perpendicular to the conveying direction MD (hereinafter, this direction will also be simply referred to as the "perpendicular direction") is 500 mm, and two water flow nozzles 35 are installed, each having 600 nozzles with a diameter of 0.1 mm arranged at equal intervals along the perpendicular direction within that width, such that the interval between the water flow nozzles 35 along the conveying direction MD is 0.8 mm. The water pressure sprayed from the water flow nozzles 35 is preferably 2 MPa or more, more preferably 3 MPa or more, and preferably 10 MPa or less, more preferably 5 MPa or less.
The transport speed in the MD direction of the laminate 4 is preferably 3 m/min or more, more preferably 5 m/min or more, and is preferably 80 m/min or less, more preferably 30 m/min or less.
The entangling step set under the above-mentioned conditions is preferably carried out once or more, and preferably three or less times, on the same surface of the laminate 4 .
By setting such conditions, it is possible to more easily form a sheet that has sufficient strength to withstand practical use and in which the number of fiber fluffs on the first surface F and the second surface R are different.

After the entanglement process, the laminate 4 becomes an entangled body 5, in which the constituent fibers are three-dimensionally entangled and integrated. This entangled body 5 is a continuous sheet-like body. Since the high-pressure water stream is only sprayed onto one side of the entangled body 5, the surface 5F to which the high-pressure water stream is sprayed (the surface on the upper side of the paper of the entangled body 5 in Figure 4) has a small number of fiber fluffs. On the other hand, the surface 5R to which the high-pressure water stream is not sprayed (the surface on the lower side of the paper of the entangled body 5 in Figure 4) maintains a relatively high level of fiber fluffiness and has a large number of fiber fluffs.

Next, the interwoven body 5 is cut or otherwise shaped to the desired dimensions to obtain the top sheet 1. At this time, the top surface 5F of the interwoven body 5 coincides with the first surface F of the top sheet 1, and the bottom surface 5R of the interwoven body 5 coincides with the second surface R of the top sheet 1.

When the top sheet 1 is made of only cotton 1a, or when the cotton 1a and the second fiber 2 are each approximately uniformly present in the thickness direction Z, for example, only one carding machine is used, and a web of cotton 1a or a web in which cotton 1a and the second fiber 2 are approximately uniformly mixed is unwound from the carding machine and subjected to the above-mentioned entanglement process.

The present invention has been described above based on its preferred embodiment, but the present invention is not limited to the above embodiment. For example, the above-mentioned manufacturing method has been described as an embodiment using a fiber web, but it can be modified as appropriate as long as the effects of the present invention are achieved. For example, a laminate with various nonwoven fabrics as the upper layer and a fiber web as the lower layer may be formed, and a high-pressure water flow may be sprayed from the nonwoven fabric side to form the entangled body 5.

In addition, the surface sheet 1 in each embodiment is described as not having an uneven shape and each of the faces F and R being flat, but as long as the effects of the present invention are achieved, at least one of the faces may be unevenly shaped, for example by forming embossments in a scattered or continuous pattern.

The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples.

Example 1
A fiber web was formed using only cotton (manufactured by Marusan Sangyo Co., Ltd., model number: UDX-MS), and high-pressure water was sprayed twice onto only one side of the web to hydroentangle it, to obtain a topsheet 1 having a basis weight of 30 g/m ^2. The hydroentanglement conditions were as follows: water pressure was 3 MPa, and the web conveying speed was 5 m/min, under the arrangement conditions of the water flow nozzles 35 in the hydroentanglement section 30 described above.

Example 2
A first fiber web (basis weight 15 g/ ^m2 ) made of 100% cotton and a second fiber web (basis weight 15 g/m2) made of a mixture of 75% cotton and 25% thermoplastic fiber (manufactured by Daiwabo Polytech Co., Ltd., model number: SHW-15, raw material: concentric core-sheath composite heat-fusible fiber with a PET core and a PE sheath, fineness: ^2.4 dtex) were formed, and the first fiber web was laminated as the upper layer and the second fiber web was laminated as the lower layer. A high-pressure water stream was sprayed twice on only the surface side of the first fiber web of this laminate under the same conditions as in Example 1 to hydroentangle the first fiber web, thereby obtaining a surface sheet 1 with a basis weight of 30 g/ ^m2 .

Example 3
A topsheet 1 having a basis weight of 30 g/ ^m2 was obtained by hydroentangling in the same manner as in Example 2, except that a mixture of 50% by mass of cotton and 50% by mass of thermoplastic fiber was used as the second fiber web.

Example 4
A topsheet 1 having a basis weight of 30 g/ ^m2 was obtained by hydroentangling in the same manner as in Example 2, except that a mixture of 25% by mass of cotton and 75% by mass of thermoplastic fiber was used as the second fiber web.

Example 5
A topsheet 1 having a basis weight of 30 g/m ² was obtained by hydroentangling in the same manner as in Example 2, except that a second fiber web containing 100% by mass of thermoplastic fibers was used.

Comparative Example 1
A fiber web was formed using only cotton, and high-pressure water was sprayed onto each of both sides of the web four times for hydroentanglement, to obtain a topsheet 1 having a basis weight of 30 g/ ^m2 . The hydroentanglement conditions were the same as those in Example 1.

[Number of fiber fluffs on each side of the sheet]
For the topsheets 1 of the examples and comparative examples, the number of fiber fluffs on the first side F and the second side R was measured by the method described above. The first side F in the examples was the side sprayed with the water flow, and the first side F in the comparative examples was an arbitrary side. The results are shown in Table 1 below.

[Measurement of remaining liquid amount]
The topsheets 1 of the examples and comparative examples were arranged so that the first surface F faced outward to produce absorbent articles (sanitary napkins). The configuration of the absorbent article other than the topsheet 1 was the same as that of a sanitary napkin manufactured by Kao Corporation (Laurier F Shiawase Suhada Fluffy Type (registered trademark), 22.5 cm, manufactured in 2018).
This sanitary napkin was placed on a flat table with the topsheet 1 facing upward. An acrylic liquid injection plate, which was an integrally molded cylinder with a diameter of 10 mm and a height of 50 mm, was placed on top of the topsheet 1 with the liquid injection hole positioned at the center of the topsheet. In this state, 6 g of artificial blood was injected into the cylinder all at once. One minute after the injection, the liquid injection plate was removed, and the topsheet 1 was removed from the sanitary napkin and its mass was measured. The value obtained by subtracting the mass of the topsheet, which had been measured before injection, from the measured mass was taken as the remaining liquid amount (mg). The results are shown in Table 1 below.

The artificial blood used in the measurements was prepared from defibrinated horse blood manufactured by Japan Bio Test Laboratory Co., Ltd. When defibrinated horse blood is left to stand, the high viscosity parts (red blood cells, etc.) will settle and the low viscosity parts (plasma) will remain as the supernatant. The mixing ratio of these parts was adjusted so that the viscosity was 8.0 cP (25°C) to prepare the artificial blood. A TVB10 viscometer manufactured by Toki Sangyo Co., Ltd. was used for the adjustment. The condition was 30 rpm.

[Measurement of liquid diffusion area]
For the surface sheet 1 of the examples and comparative examples, a sample of 5 cm square was cut out, and 0.5 g of physiological saline containing 0.1 mass % of Blue No. 2 (indigo carmine, manufactured by Daiwa Kasei Co., Ltd.) was dropped onto the first surface F, and left to stand for 1 minute. After that, an OHP sheet (manufactured by Kokuyo Co., Ltd., recycled OHP film, A4 size, VF-1300N, transparent) was placed on the blue colored part, and the wet area was copied. The OHP sheet was then read with a scanner and imported into an image software (manufactured by Nippon Roper Co., Ltd., Image-Pro6.2J), and the area of the wet area was calculated. The measurement was performed three times, and the arithmetic average value was taken as the diffusion area (cm ² ). It can be evaluated that the smaller the diffusion area of the liquid, the lower the liquid diffusibility in the sheet. The results are shown in Table 1 below.

As shown in Table 1, the surface sheet 1 of each embodiment has a smaller amount of residual liquid and a smaller liquid diffusion area than the comparative example. In particular, as shown in Examples 2 to 5, this effect is more pronounced by using thermoplastic fibers as the second fibers 2 and increasing the mass ratio of the fibers on the second surface R side.

1: Surface sheet for absorbent article 1a: Cotton 2: Second fiber F: First surface R: Second surface Z: Thickness direction

Claims (5)

cotton and thermoplastic fibers,
A first surface and a second surface opposite the first surface,
A topsheet for absorbent articles, wherein when the number of fiber fluffs on a first surface and the number of fiber fluffs on a second surface are measured by the following measurement method, the number of fiber fluffs on the second surface is greater than the number of fiber fluffs on the first surface,
the top sheet is produced by processing the thermoplastic fibers in a carding machine;
When the surface sheet is virtually divided into three equal parts in the thickness direction,
a mass ratio of the cotton to a mass of all fibers in a portion including the first side is 90 mass% or more and 100 mass% or less, and a mass ratio of the thermoplastic fiber to a mass of all fibers in a portion including the first side is 0 mass% or more and 10 mass% or less,
a mass ratio of the cotton to a mass of all fibers in a portion including the second surface is less than 50 mass%, and a mass ratio of the thermoplastic fiber to a mass of all fibers in a portion including the second surface is 50 mass% or more;
The top sheet for absorbent articles is used so that the first surface is disposed on the skin contact side, which is the surface that contacts the skin of the wearer.
<Measurement method>
(1) A piece measuring 20 cm square is cut out from the sheet to be measured, and the piece is folded in half at any position on the surface to be measured to obtain a measurement sample.
(2) The measurement sample is placed on a first mount, and a second mount having a 1 cm square hole is placed on the measurement sample so that the fold of the measurement sample can be seen through the hole.
(3) A 50 g weight is placed on each side of the second mount at a distance of 5 cm outward from the hole along the fold, and under this condition, the inside of the hole in the second mount is observed at 30x magnification using a microscope, and the number of fibers present above an imaginary line formed at a position moved parallel to and 0.2 mm upward from the fold is counted.
(4) The measurement in (3) above is carried out using three measurement samples, with three locations per measurement sample, and the arithmetic average value is regarded as the number of fuzz particles on the measurement surface.
(5) If a piece measuring 20 cm square cannot be cut out in (1) above, cut out three pieces measuring 5 cm square to use as measurement samples, and measure the number of fibers at any three positions for each measurement sample using the procedures in (2) and (3) above. The arithmetic average of the number of fibers at a total of nine positions is the number of fuzz on the surface to be measured. cotton and thermoplastic fibers,
A first surface and a second surface opposite the first surface,
A topsheet for absorbent articles, wherein when the number of fiber fluffs on a first surface and the number of fiber fluffs on a second surface are measured by the following measurement method, the number of fiber fluffs on the second surface is greater than the number of fiber fluffs on the first surface,
The top sheet is obtained by hydroentangling a laminate of a cotton web and a cotton/thermoplastic fiber mixture web, or
The laminate is obtained by hydroentangling a web of only cotton and a web of only thermoplastic fibers,
When the surface sheet is virtually divided into three equal parts in the thickness direction,
a mass ratio of the cotton to a mass of all fibers in a portion including the first side is 90 mass% or more and 100 mass% or less, and a mass ratio of the thermoplastic fiber to a mass of all fibers in a portion including the first side is 0 mass% or more and 10 mass% or less,
a mass ratio of the cotton to a mass of all fibers in a portion including the second surface is less than 50 mass%, and a mass ratio of the thermoplastic fiber to a mass of all fibers in a portion including the second surface is 50 mass% or more;
The top sheet for absorbent articles is used so that the first surface is disposed on the skin contact side, which is the surface that contacts the skin of the wearer.
<Measurement method>
(1) A piece measuring 20 cm square is cut out from the sheet to be measured, and the piece is folded in half at any position on the surface to be measured to obtain a measurement sample.
(2) The measurement sample is placed on a first mount, and a second mount having a 1 cm square hole is placed on the measurement sample so that the fold of the measurement sample can be seen through the hole.
(3) A 50 g weight is placed on each side of the second mount at a distance of 5 cm outward from the hole along the fold, and under this condition, the inside of the hole in the second mount is observed at 30x magnification using a microscope, and the number of fibers present above an imaginary line formed at a position moved parallel to and 0.2 mm upward from the fold is counted.
(4) The measurement in (3) above is carried out using three measurement samples, with three locations per measurement sample, and the arithmetic average value is regarded as the number of fuzz particles on the measurement surface.
(5) If a piece measuring 20 cm square cannot be cut out in (1) above, cut out three pieces measuring 5 cm square to use as measurement samples, and measure the number of fibers at any three positions for each measurement sample using the procedures in (2) and (3) above. The arithmetic average of the number of fibers at a total of nine positions is the number of fuzz on the surface to be measured. 3. The topsheet for absorbent articles according to claim 1 or 2 , wherein the number of fuzzed fibers on the second surface is 2 or more. comprising cotton and a second fiber other than cotton,
4. The top sheet for absorbent articles according to claim 1, wherein, when the top sheet is virtually divided into three equal parts in the thickness direction, the mass ratio of the cotton to the mass of all fibers in a portion including a first surface is higher than the mass ratio of the cotton to the mass of all fibers in a portion including a second surface. The absorbent article comprises a top sheet for absorbent articles according to any one of claims 1 to 4 ,
The top sheet is disposed so that a first surface side thereof faces the body of a wearer.