JP7580428B2 - Composite sheet for absorbent articles - Google Patents

Description

The present invention relates to a composite sheet for absorbent articles.

In the case of composite sheets for absorbent articles, studies are being made to improve the texture. For example, Patent Document 1 discloses an absorbent article that includes a main body having a liquid-permeable top sheet, a liquid-impermeable back sheet, and an absorbent body interposed between the top sheet and the back sheet, and an exterior sheet that covers the back side of the main body, the exterior sheet being formed by laminating one or more sheets of nonwoven fabric, and the degree of twist of the outermost nonwoven fabric located on the outermost side is 3.8 gf·cm/cm or less. It is disclosed that the outermost nonwoven fabric is made of a single fiber of polypropylene and a core-sheath type composite fiber of polypropylene and polyethylene.

Patent Document 2 discloses an absorbent article having an absorbent main body having a longitudinal direction and a transverse direction and equipped with an absorbent core, and a pair of waist sections, the waist section having a skin-side sheet section arranged closest to the skin, in at least one of the pair of waist sections, the bending rigidity of the skin-side sheet section measured by the KES method is 0.0096 N·m ² /(m×10 ⁻⁴ ) or less, an inner layer sheet section is arranged on the non-skin side of the skin-side sheet section, the bending rigidity of the inner layer sheet section measured by the KES method is higher than the bending rigidity of the skin-side sheet section, and the inner layer sheet section is arranged on the skin side of the absorbent main body, straddling the longitudinal edge of the waist side of the absorbent main body. It is disclosed that the skin-side sheet section mainly contains polyethylene.

JP 2010-131167 A JP 2019-187744 A

When the outermost nonwoven fabric of Patent Document 1 is made of a single fiber of polypropylene, polypropylene is hard, so it is expected that there is a limit to how much the overall outer sheet consisting of the outermost nonwoven fabric and another nonwoven fabric can improve in terms of texture. When the outermost nonwoven fabric of Patent Document 1 is made of a core-sheath type composite fiber containing a core formed of polypropylene and a sheath formed of polyethylene, the outer sheet in which the outermost nonwoven fabric is bonded to another nonwoven fabric made of polypropylene has a problem that the bonding strength between the outermost nonwoven fabric made of composite fiber and the other nonwoven fabric is insufficient due to the large difference in melting points between polyethylene and polypropylene, resulting in poor compatibility, and the outermost nonwoven fabric and the other nonwoven fabric peeling off from each other when used repeatedly.

The skin-side sheet in Patent Document 2 mainly contains soft polyethylene, so there was concern that it would be difficult to provide the strength required for a composite sheet for absorbent articles and would be difficult to use repeatedly.

The objective of the present invention is to provide a composite sheet for absorbent articles that is highly durable while maintaining a pleasant feel against the skin.

The present invention relates to a composite sheet for absorbent articles having a first direction, a second direction, and a thickness direction that are mutually perpendicular, the composite sheet comprising, in order in the thickness direction, a first nonwoven fabric and a second nonwoven fabric, and further comprising a plurality of bonding portions in which the first nonwoven fabric and the second nonwoven fabric are thermally bonded to each other, the first nonwoven fabric having a first fiber layer and a second fiber layer disposed between the first fiber layer and the second nonwoven fabric, the first fiber layer comprising composite fibers, the composite fibers comprising, in cross section, a polypropylene-based resin portion comprising a polypropylene-based resin and a polyethylene-based resin portion comprising a polyethylene-based resin, the second fiber layer comprising a single fiber made of a polypropylene-based resin, and the second nonwoven fabric containing a polypropylene-based resin on the surface of the side in contact with the second fiber layer.

The composite sheet for absorbent articles according to the present invention is highly durable while maintaining a pleasant feel against the skin.

FIG. 2 is a plan view of a composite sheet according to an embodiment. FIG. 2 is a cross-sectional view showing a schematic state of the composite sheet according to the embodiment when it is stretched. FIG. 2 is a cross-sectional view showing a schematic state of the composite sheet according to the embodiment during shrinkage. FIG. 2 is a cross-sectional view of fibers of a first nonwoven fabric and a second nonwoven fabric according to the embodiment. FIG. 11 is a cross-sectional view of fibers of a first nonwoven fabric and a second nonwoven fabric according to a modified example of the embodiment. FIG. 1 is a perspective view showing an absorbent article using a composite sheet according to an embodiment. FIG. 13 is a plan view of a composite sheet according to a modified example (1). FIG. 11 is a cross-sectional view showing a schematic state of a composite sheet according to a modified example (2) when stretched.

The embodiments of the present invention relate to the following aspects:

[Aspect 1]
A composite sheet for an absorbent article, the composite sheet having a first direction, a second direction, and a thickness direction that are mutually perpendicular,
A first nonwoven fabric and a second nonwoven fabric are provided in this order in the thickness direction,
The first nonwoven fabric and the second nonwoven fabric are further provided with a plurality of bonding portions at which the first nonwoven fabric and the second nonwoven fabric are thermally bonded to each other,
The first nonwoven fabric has a first fiber layer and a second fiber layer disposed between the first fiber layer and the second nonwoven fabric,
the first fiber layer includes composite fibers, the composite fibers including, in a cross section, a polypropylene-based resin portion including a polypropylene-based resin and a polyethylene-based resin portion including a polyethylene-based resin;
the second fiber layer includes a single fiber made of a polypropylene-based resin,
A composite sheet, wherein the second nonwoven fabric contains a polypropylene-based resin on a surface thereof in contact with the second fiber layer.
The composite sheet includes the second fiber layer containing a single fiber made of a polypropylene-based resin, and therefore can have strength suitable for a composite sheet for use in the waist portion of an absorbent article.
The first fiber layer includes composite fibers including a polypropylene-based resin portion including a polypropylene-based resin and a polyethylene-based resin portion including a polyethylene-based resin, and therefore has excellent flexibility derived from the polyethylene-based resin. Since the first fiber layer is disposed on the surface of the composite sheet, the composite sheet has an excellent feel against the skin.
The bonding portion integrates the first fiber layer, the second fiber layer, and the second nonwoven fabric by thermal bonding. The first fiber layer and the second fiber layer contain the same type of polypropylene-based resin, and therefore have excellent compatibility and are bonded well. The second nonwoven fabric contains a polypropylene-based resin, which is the same type of resin as the single fiber contained in the second fiber layer, on the surface of the side in contact with the second fiber layer, and is therefore easily thermally bonded to the second fiber layer. Since the second fiber layer and the second nonwoven fabric are thermally bonded well, the composite sheet has excellent bonding strength between the first nonwoven fabric and the second nonwoven fabric, and peeling between the first nonwoven fabric and the second nonwoven fabric is suppressed when used repeatedly, resulting in excellent durability.
Therefore, the composite sheet is excellent in durability while maintaining a pleasant feel against the skin.

[Aspect 2]
2. The composite sheet of claim 1, wherein the second nonwoven fabric is an elastic nonwoven fabric that is stretchable in a first direction.
Since the composite sheet stretches in the first direction, it can be applied to, for example, a composite sheet for use around the waist of an absorbent article by arranging the first direction parallel to the waist direction of a wearer.
The first nonwoven fabric includes a highly flexible first fiber layer, and therefore easily shrinks in accordance with the shrinkage of the elastic nonwoven fabric (second nonwoven fabric).
The elastic nonwoven fabric contains a polypropylene-based resin, which is the same type of resin as the monofilament contained in the second fiber layer, on the surface in contact with the second fiber layer, and is therefore well thermally bonded to the second fiber layer, and therefore the composite sheet has excellent bonding strength between the first nonwoven fabric and the elastic nonwoven fabric (second nonwoven fabric).
Therefore, the composite sheet has excellent shrinkability and durability.

[Aspect 3]
A composite sheet according to claim 2, further comprising a third nonwoven fabric on the side of the second nonwoven fabric opposite to the side in contact with the first nonwoven fabric.
The composite sheet has a wider range of options for whether the first nonwoven fabric is on the skin side or not by providing a third nonwoven fabric suited to the application on the side of the second nonwoven fabric opposite to the side in contact with the first nonwoven fabric. Furthermore, the composite sheet has better durability because the mechanical strength of the composite sheet is increased by adding the third nonwoven fabric. Therefore, the composite sheet is more suitable as a composite sheet for the waist area of an absorbent article.

[Aspect 4]
2. The composite sheet of claim 1, comprising an elastic thread between the first nonwoven fabric and the second nonwoven fabric, the elastic thread stretching in a first direction.
Since the composite sheet stretches in a first direction, it can be applied to, for example, a composite sheet for use in the waist area of an absorbent article by arranging the first direction parallel to the waist area of a wearer.
The first nonwoven fabric includes a highly flexible first fiber layer, and therefore easily shrinks in accordance with the shrinkage of the elastic yarn.
In the composite sheet, a second nonwoven fabric is disposed on the opposite side of the first nonwoven fabric with the elastic yarn sandwiched therebetween, and the second nonwoven fabric is well thermally bonded to the second fiber layer. That is, the second fiber layer and the second nonwoven fabric are well thermally bonded with the elastic yarn sandwiched therebetween. Therefore, the composite sheet has excellent bonding strength between the first nonwoven fabric and the second nonwoven fabric.
Therefore, the composite sheet has excellent shrinkability and durability.

[Aspect 5]
The polypropylene-based resin contains a propylene-α-olefin random copolymer,
A composite sheet according to any one of Aspects 1 to 4, wherein the polyethylene-based resin includes an ethylene-based polymer.
The propylene-α-olefin random copolymer has a smaller difference in melting point with the polyethylene-based resin than polypropylene, and is therefore more easily thermally bonded to the polyethylene-based resin than polypropylene. Therefore, the fibers in the first fiber layer are thermally bonded to each other over a wider range at the joint. Therefore, the composite sheet has relatively little fuzzing due to the fibers in the first fiber layer arranged on the surface being thermally bonded to each other over a wider range, and can be used for a long time.

[Aspect 6]
A composite sheet according to aspect 5, wherein the melting point of the propylene-α-olefin random copolymer is 155° C. or less, and the melting point of the ethylene polymer is 95° C. or more and 125° C. or less.
When the melting points of the propylene-α-olefin random copolymer and the ethylene polymer are within the above ranges, the fibers in the first fiber layer can be thermally bonded more reliably over a wider range.

[Aspect 7]
A composite sheet according to any one of aspects 1 to 5, wherein the ratio of the polypropylene-based resin portion to the polyethylene-based resin portion is 70:30 to 10:90 (polypropylene-based resin portion: polyethylene-based resin portion) on a mass basis.
The first fiber layer contains a polyethylene-based resin portion, i.e., composite fibers containing a predetermined amount or more of polyethylene-based resin, so that the polyethylene-based resin is easily disposed on the surface of the first fiber layer. Since the first fiber layer is disposed on the surface side of the composite sheet, the composite sheet has an excellent feel against the skin.

[Aspect 8]
A composite sheet according to any one of Aspects 1 to 7, wherein the polyethylene resin portion is present on the fiber surface of the composite fiber.
The composite fiber has a polyethylene resin portion on the fiber surface. For example, the composite fiber is an eccentric core-sheath type in which the polypropylene resin portion is the core and the polyethylene resin portion is the sheath, and a part of the polypropylene resin portion is exposed from the polyethylene resin portion, or a side-by-side type. Since the polyethylene resin portion is present on the fiber surface, the composite fiber is highly flexible due to the polyethylene resin. Since the first fiber layer is disposed on the surface side of the composite sheet, the composite sheet has excellent texture.

[Aspect 9]
A composite sheet according to any one of Aspects 1 to 8, wherein a ratio of the first fiber layer to the second fiber layer is 33:67 to 67:33 (first fiber layer:second fiber layer) on a mass basis.
The first nonwoven fabric contains a second fiber layer made of a polypropylene-based resin in a predetermined amount or more. The second fiber layer is disposed in a position where it contacts the second nonwoven fabric, so that the second fiber layer is thermally bonded to the second nonwoven fabric more reliably. Therefore, the composite sheet has excellent bonding strength between the first nonwoven fabric and the second nonwoven fabric.

[Aspect 10]
A composite sheet according to any one of Aspects 1 to 9, wherein the polypropylene-based resin of the first fiber layer and the polypropylene-based resin of the second fiber layer are the same propylene-α-olefin random copolymer.
The propylene-α-olefin random copolymer has a smaller difference in melting point with the polyethylene-based resin than polypropylene, and is therefore more easily thermally bonded to the polyethylene-based resin than polypropylene. Therefore, the fibers in the first fiber layer are thermally bonded to each other over a wider range at the joint. Therefore, the composite sheet has relatively little fuzzing due to the fibers in the first fiber layer arranged on the surface being thermally bonded to each other over a wider range, and can be used for a long time.
Since the polypropylene-based resins of the first and second fiber layers are the same propylene-α-olefin random copolymer, they have excellent compatibility and are easily thermally bonded to each other over a wider range, and therefore the composite sheet has excellent bonding strength between the first and second fiber layers.

[Aspect 11]
a surface of the first fiber layer has a plurality of embossed bonding portions bonding the first fiber layer and the second fiber layer excluding the second nonwoven fabric;
A composite sheet according to any one of claims 1 to 10, wherein a total area of the plurality of bonded portions on the surface of the first fiber layer is smaller than a total area of the plurality of embossed bonded portions on the surface of the first fiber layer.
Since the total area of the multiple joints of the first nonwoven fabric is smaller than the total area of the multiple embossed joints, the first nonwoven fabric is easily separated from the second nonwoven fabric between the multiple joints and deforms in the thickness direction. Since the first nonwoven fabric is easily deformed in the thickness direction between the joints, when the composite sheet includes an elastic member (elastic nonwoven fabric or elastic thread), the second nonwoven fabric easily shrinks without being hindered by the first nonwoven fabric. Therefore, the composite sheet is easily deformed along the waist of the wearer, and has an excellent feel against the skin.

<Overall composition>
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the drawings are merely illustrative of an example of the embodiment, and the present invention is not limited to the embodiment shown in the drawings. FIG. 1 is a plan view of a composite sheet according to an embodiment. FIG. 2A is a cross-sectional view showing a composite sheet according to an embodiment when it is stretched. FIG. 2B is a cross-sectional view showing a composite sheet according to an embodiment when it is shrunk. FIG. 3A is a cross-sectional view of fibers of a first nonwoven fabric and a second nonwoven fabric according to an embodiment. The composite sheet 10A shown in FIG. 1 has a first direction W, a second direction L, and a thickness direction T (not shown in FIG. 1) that are perpendicular to each other. As shown in FIGS. 2A and 2B, the composite sheet 10A includes a first nonwoven fabric 11 and a second nonwoven fabric 14 in this order in the thickness direction T. When the composite sheet 10A is applied to a composite sheet for a waist portion of an absorbent article, the first nonwoven fabric 11 is disposed on the skin side and the second nonwoven fabric 14 is disposed on the non-skin side, and the first direction W is disposed so as to be approximately parallel to the waist of a wearer.

As shown in FIG. 1, the composite sheet 10A further includes a plurality of bonding portions 18 in which the first nonwoven fabric 11 and the second nonwoven fabric 14 are thermally bonded to each other. The thermal bonding is performed by using heat or ultrasonic waves to heat the first nonwoven fabric 11 and the second nonwoven fabric 14 to a temperature exceeding the melting point of the thermoplastic resin, thereby melting the first nonwoven fabric 11 and the second nonwoven fabric 14 and bonding them to each other.

The shape of the multiple joints 18 is a shape that is concave in the thickness direction T in a cross-sectional view, but the shape in a plan view is not particularly limited and may be, for example, linear or dot-like. The multiple joints 18 are concave in the thickness direction on at least one of the surface sides of the composite sheet 10A and the other surface side. The multiple joints 18 shown in FIG. 1 are dot-like in a plan view. The shape, size, and distance between the multiple joints 18 are not particularly limited and can be appropriately selected depending on the size and thickness of the composite sheet 10A. For example, the shape of each of the joints 18 as viewed from the thickness direction T may be a circle, or a polygon such as a triangle or a rectangle. The size of the joints 18 may be, for example, a diameter in the case of a circle, or a length of one side in the case of a rectangle, of 0.1 mm or more and 5.0 mm or less. The distance between the joints 18 may be 1 mm or more and 5 mm or less. The multiple joints 18 adjacent to each other in the first direction W may be shifted in the second direction L. The distance in the second direction L between the multiple joints 18 adjacent to each other in the first direction W is preferably 2.0 mm or more, and more preferably 3.7 mm or more. Each of the joints 18 may be arranged in a staggered pattern in the first direction W and the second direction L, as shown in FIG. 1.

The composite sheet 10A may further include a third nonwoven fabric 16. The third nonwoven fabric 16 is provided on the side of the second nonwoven fabric 14 opposite the side in contact with the first nonwoven fabric 11. The third nonwoven fabric 16 may be integrally thermally bonded to the first nonwoven fabric 11 and the second nonwoven fabric 14 at the bonding portion 18.

The thickness and basis weight of the composite sheet 10A are not particularly limited as long as they do not impair the effects of the present invention, and any thickness and basis weight can be adopted according to the desired application. The thickness of the composite sheet 10A when unstretched is, for example, preferably 1.0 mm or more and 3.5 mm or less, and more preferably 1.0 mm or more and 3.0 mm or less. The basis weight of the composite sheet 10A is, for example, preferably 60 g/ ^m2 or more and 150 g/m2 or ^less , and more preferably 70 g/m2 or ^more and 140 g/m2 or ^less .

The flexural rigidity in the CD direction of the composite sheet 10A in the second direction L as measured by the KES method is preferably 0.02 (N·m ² /(m×10 ^-4 )) or more and 0.38 (N·m ² /(m×10 ^-4 )) or less, preferably 0.02 (N·m ² /(m×10 ^-4 )) or more and 0.32 (N·m ² /(m×10 ^-4 )) or less, and more preferably 0.02 (N·m ² /(m×10 ^-4 )) or more and 0.20 (N·m ² /(m×10 ^-4 )) or less. By having a flexural rigidity in the second direction L as measured by the KES method of 0.38 (N·m ² /(m×10 ^-4 )) or less, the composite sheet 10A is highly flexible and has an excellent feel to the touch.

The breaking strength in the CD direction of the composite sheet 10A is not particularly limited as long as it can be used as a composite sheet for absorbent articles, and is preferably, for example, 14 (N/50 mm) to 75 (N/50 mm), more preferably 17 (N/50 mm) to 75 (N/50 mm), and even more preferably 20 (N/50 mm) to 75 (N/50 mm). The breaking strength is the maximum tensile load required to break the sample divided by the width of the sample.

The peel strength between the first and second nonwoven fabrics of the composite sheet 10A is preferably 1.0 (N/25 mm) or more, more preferably 1.4 (N/25 mm) or more, and even more preferably 1.5 (N/25 mm) or more.

(First nonwoven fabric)
The first nonwoven fabric 11 forms a surface that faces the wearer's skin when the absorbent article using the composite sheet 10A is worn. The first nonwoven fabric 11 has a first fiber layer 12 having a surface that faces the wearer's skin, and a second fiber layer 13 disposed between the first fiber layer 12 and a second nonwoven fabric 14.

The first fiber layer 12 and the second fiber layer 13 can be formed by a spunbond method, a card method, a meltblown method, an airlaid method, or the like, and are bonded to each other by embossing. In addition to the above-mentioned multiple bonding portions 18, the first nonwoven fabric 11 has multiple embossed bonding portions (not shown) formed by embossing on the surface, which are concave in the thickness direction T. At least one of the first surface and the other surface of the first nonwoven fabric 11 is concave in the thickness direction. It is preferable that the surface of the first nonwoven fabric 11 facing the first fiber layer 12 is concave in the thickness direction. It is preferable that the total area of the multiple bonding portions 18 in a plan view on the surface of the first nonwoven fabric 11 is smaller than the total area of the embossed bonding portions in a plan view on the surface of the first nonwoven fabric 11. The embossed bonding portions bond the first fiber layer 12 and the second fiber layer 13, excluding the second nonwoven fabric 14. That is, the embossed bonding portions do not bond the first nonwoven fabric 11 and the second nonwoven fabric 14. When the embossed joints are recessed in the thickness direction on the surface on the first fiber layer 12 side, it is preferable that the total area of the multiple joints 18 in a plan view on the surface of the first fiber layer 12 of the first nonwoven fabric 11 is smaller than the total area of the embossed joints in a plan view.

The ratio of the first fiber layer 12 to the second fiber layer 13 is preferably 33:67 to 67:33 (first fiber layer:second fiber layer) by mass, with the total of the first fiber layer 12 and the second fiber layer 13 being 100 parts by mass. By having the ratio of the first fiber layer 12 to the second fiber layer 13 within the above range, there is a tendency for the balance between strength and flexibility to be excellent.

(First fiber layer)
The first fiber layer 12 includes composite fibers. The composite fibers include, in cross section, a polypropylene-based resin portion (hereinafter referred to as a "PP resin portion") containing a polypropylene-based resin and a polyethylene-based resin portion (hereinafter referred to as a "PE resin portion") containing a polyethylene-based resin. The composite fibers may be, for example, sheath-core composite fibers having a PP resin portion as a core 20 and a PE resin portion as a sheath 22 as shown in FIG. 3A, or may be eccentric sheath-core composite fibers in which a part of the PP resin portion (core 20) is exposed from the PE resin portion (sheath 22) as shown in FIG. 3B. The composite fibers may be side-by-side composite fibers including a PP resin portion and a PE resin portion.

The ratio of the PP resin portion to the PE resin portion is preferably 70:30 to 10:90 (PP resin portion: PE resin portion) on a mass basis, with the total of the PP resin portion and the PE resin portion being 100 parts by mass. This ratio is more preferably 65:35 to 35:65, and even more preferably 65:35 to 55:45. The ratio of the PP resin portion to the PE resin portion in the composite fiber can be measured from the ratio of the integrated intensity of the hydrogen nuclei and carbon nuclei derived from the polyethylene resin and the integrated intensity of the hydrogen nuclei and carbon nuclei derived from the polypropylene resin using known nuclear magnetic resonance (NMR). The ratio of the PP resin portion to the PE resin portion in the composite fiber may be determined by a conventional method from the ¹³ C-NMR spectrum.

The average fiber diameter of the composite fiber is preferably 10 μm or more and 40 μm or less, more preferably 10 μm or more and 25 μm or less, even more preferably 12 μm or more and 20 μm or less, and particularly preferably 13 μm or more and 18 μm or less. When the average fiber diameter of the composite fiber is within the above range, it tends to have an excellent balance between strength and flexibility.

The thickness and basis weight of the first fiber layer 12 are not particularly limited as long as they do not impair the effects of the present invention, and any thickness and basis weight can be adopted according to the desired application. The thickness of the first fiber layer 12 is, for example, preferably 0.03 mm or more and 2.00 mm or less, and more preferably 0.05 mm or more and 1.00 mm or less. The basis weight of the first fiber layer 12 is, for example, preferably 3 g/m ² or more and 20 g/m ² or less, more preferably 4 g/m ² or more and 16 g/m ² or less, and even more preferably 5 g/m ² or more and 12 g/m ² or less.

(PP resin part)
The PP resin portion may contain a propylene-α-olefin random copolymer. The content of structural units derived from propylene in the propylene-α-olefin random copolymer is 50% by mass or more and less than 100% by mass, and from the viewpoint of achieving both flexibility and strength, it is preferably 70% by mass or more and 99% by mass or less, and more preferably 80% by mass or more and 98% by mass or less. The content of structural units derived from α-olefin in the propylene-α-olefin random copolymer is more than 0% by mass and 50% by mass or less, preferably 1% by mass or more and 30% by mass or less, and more preferably 2% by mass or more and 20% by mass or less.

The α-olefin in the propylene-α-olefin random copolymer is not particularly limited, and may be any α-olefin other than propylene. Examples of α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, and 4-methyl-1-hexene. Among these, ethylene is preferred as the α-olefin from the viewpoint of further improving flexibility.

The content of propylene-α-olefin random copolymer in the PP resin portion is preferably 10% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 99% by mass or more and 100% by mass or less.

Specific preferred examples of propylene-α-olefin random copolymers include propylene-1-butene random copolymers, propylene-ethylene random copolymers, and propylene-ethylene-1-butene random copolymers. From the viewpoint of achieving both flexibility and strength, a random copolymer of propylene and ethylene is more preferred.

To further improve strength, the PP resin portion may further contain propylene homopolymer or multiple types of propylene-α-olefin random copolymer.

The content of propylene homopolymer in the PP resin portion is preferably 1% by mass or more and 90% by mass or less, and more preferably 50% by mass or more and 80% by mass or less. When the PP resin portion contains propylene homopolymer within the above range, the content of propylene-α-olefin random copolymer is preferably an amount such that the sum of the propylene-α-olefin random copolymer and the propylene homopolymer is 100% by mass.

The content of structural units derived from propylene in the total resin components contained in the PP resin portion is preferably 90% by mass or more and 99.5% by mass or less, more preferably 93% by mass or more and 99% by mass or less, and even more preferably 95% by mass or more and 98% by mass or less.

The melting point of the propylene-α-olefin random copolymer is preferably 155°C or lower. When the PP resin portion contains only the propylene-α-olefin random copolymer as a resin component, the melting point of the propylene-α-olefin random copolymer is preferably 125°C or higher and 155°C or lower. In this specification, the "melting point" refers to the "peak top temperature" when measuring the endothermic behavior of the solid-to-liquid transition at a heating rate of 10°C/min using a differential scanning calorimeter.

The propylene-α-olefin random copolymer preferably has a melt flow rate (MFR, measurement conditions: 230°C, load 2.16 kg) measured according to a method conforming to ASTM standard D-1238 of 10 g/10 min or more and 100 g/10 min or more, and more preferably 15 g/10 min or more and 80 g/10 min or less. When the MFR of the propylene-α-olefin random copolymer is within the above range, it tends to have excellent flexibility.

(PE resin part)
The PE resin portion may contain an ethylene-based polymer. The PE resin portion has a density of 900 kg/m ³ or more and 945 kg/m ³ or less. The density of the PE resin portion is preferably 910 kg/m ³ or more and 940 kg/m ³ or less, more preferably 915 kg/m ³ or more and 940 kg/m ³ or less, and even more preferably 920 kg/m ³ or more and 940 kg/m ³ or less. When the density is within the above range, there is a tendency for the flexibility and strength to be excellent at the same time. The density of the PE resin portion can be adjusted by changing the density of the resin constituting the PE resin portion. The melting point of the ethylene-based polymer is about 95°C or more and 125°C or less.

The content of ethylene-derived structural units in the ethylene-based polymer is 50% by mass or more, preferably 70% by mass or more and 99.8% by mass or less, and more preferably 90% by mass or more and 99% by mass or less. The content of other structural units in the ethylene-based polymer is 0% by mass or more and 50% by mass or less, preferably 0.2% by mass or more and 30% by mass or less, and more preferably 1% by mass or more and 10% by mass or less. When the content of ethylene-derived structural units and/or other structural units in the ethylene-based polymer is within the above range, it tends to have excellent strength and flexibility.

Examples of monomers constituting other structural units include α-olefins. The α-olefins are not particularly limited as long as they are other than ethylene, and examples include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, and 4-methyl-1-hexene. Among these, 1-butene and 4-methyl-1-pentene are preferred as α-olefins from the viewpoint of achieving both flexibility and strength.

The ethylene-based polymer preferably contains an ethylene/α-olefin copolymer. The ethylene/α-olefin copolymer is preferably at least one selected from the group consisting of an ethylene/1-butene copolymer and an ethylene/4-methyl-1-pentene copolymer. When the ethylene-based polymer has the above-mentioned configuration, it tends to have excellent strength and flexibility.

The ethylene-based polymer preferably has an MFR (ASTM D-1238, 190°C, 2.16 kg load) of 10 g/10 min to 100 g/10 min, more preferably 15 g/10 min to 60 g/10 min, and even more preferably 20 g/10 min to 60 g/10 min. When the MFR of the ethylene-based polymer is within the above range, it tends to have excellent strength and flexibility.

The content of the ethylene polymer in the PE resin portion is preferably 10% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 99% by mass or more and 100% by mass or less. When the content of the ethylene polymer in the PE resin portion is within the above range, there is a tendency for the strength and flexibility to be excellent at the same time.

(hydrophilic agent)
The first fiber layer 12 preferably has a high hydrophilicity. When the composite fibers constituting the first fiber layer 12 are of an eccentric core-sheath type or a side-by-side type, a hydrophilic agent is preferably kneaded into the PP resin portion. In the case of the eccentric core-sheath type, a part of the core portion 20, which is the PP resin portion kneaded with the hydrophilic agent, is exposed from the sheath portion 22, so that the first fiber layer 12 has hydrophilicity.

Hydrophilic agents can be further classified into penetrating agents and wetting agents. The second nonwoven fabric 14 may contain both a penetrating agent and a wetting agent, or may contain no penetrating agent but a wetting agent. From the viewpoint of excellent hydrophilicity, it is preferable that the hydrophilic agent contains both a penetrating agent and a wetting agent.

The hydrophilic agent preferably contains at least one of a sulfonate and a sulfate salt as a penetrating agent. Examples of sulfonate include alkylbenzenesulfonate, alkylnaphthalenesulfonate, α-olefinsulfonate, and alkylsulfosuccinate. These sulfonate salts are preferably alkali metal salts. Examples of sulfate salts include higher alcohol sulfate salts and alkyl sulfate salts. These sulfate salts are preferably alkali metal salts. Among these, the hydrophilic agent preferably contains a sulfonate as a penetrating agent, and more preferably contains an alkali metal salt of sulfonic acid.

When the hydrophilic agent contains a wetting agent, the wetting agent is not particularly limited. For example, the hydrophilic agent may contain any of a cationic surfactant, an anionic surfactant, an amphoteric surfactant, and a nonionic surfactant as the wetting agent.

The content of the hydrophilic agent is preferably 0.01% by mass or more and 2.0% by mass or less, more preferably 0.05% by mass or more and 1.0% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less. An example of a method for kneading the hydrophilic agent into the raw resin material of the core-sheath type composite fiber is a method in which the above-mentioned hydrophilic agent is added to the raw resin material of the core portion 20 described above, and then the fiber is formed by spinning.

(Second fiber layer)
The second fiber layer 13 includes monofilaments made of a polypropylene resin. The average fiber diameter of the monofilaments is preferably 10 μm or more and 30 μm or less, more preferably 11 μm or more and 25 μm or less, and even more preferably 12 μm or more and 20 μm or less.

The second fiber layer 13 preferably contains 60% by mass or more, more preferably 75% by mass or more, and particularly preferably 95% by mass or more, of single fibers made of polypropylene-based resin.

The thickness and basis weight of the second fiber layer 13 are not particularly limited as long as they do not impair the effects of the present invention, and any thickness and basis weight can be adopted according to the desired application. The thickness of the second fiber layer 13 is preferably 0.03 mm or more and 2.00 mm or less, and more preferably 0.05 mm or more and 1.00 mm or less. The basis weight of the second fiber layer 13 is, for example, preferably 3 g/m ² or more and 20 g/m ² or less, more preferably 4 g/m ² or more and 16 g/m ² or less, and even more preferably 5 g/m ² or more and 12 g/m ² or less.

The polypropylene-based resin of the second fiber layer 13 may contain the above-mentioned propylene-α-olefin random copolymer that constitutes the first fiber layer 12.

(Second nonwoven fabric)
When an absorbent article using the composite sheet 10A is worn, the second nonwoven fabric 14 is disposed on the non-skin side of the wearer relative to the first nonwoven fabric 11. The second nonwoven fabric 14 according to this embodiment is an elastic nonwoven fabric that stretches in the first direction W.

The second nonwoven fabric 14 may be any nonwoven fabric, such as an air-through nonwoven fabric, a spunbond nonwoven fabric, a point-bond nonwoven fabric, a spunlace nonwoven fabric, a needle-punched nonwoven fabric, a meltblown nonwoven fabric, or a combination thereof (e.g., SMS, etc.). The second nonwoven fabric 14 may be, for example, a nonwoven fabric having thermoplastic elastomer fibers exhibiting approximately elasticity and thermoplastic resin fibers exhibiting approximately inelasticity, which has been subjected to an appropriate stretching process, such as a gear stretching process. That is, by performing such a stretching process, the approximately inelastic thermoplastic resin fibers contained in the nonwoven fabric are plastically deformed, or the junctions between the fibers are destroyed, etc., so that the nonwoven fabric can be changed into a structure that does not easily inhibit the approximately elastic stretching deformation of the thermoplastic elastomer fibers. In this way, the stretchability of the nonwoven fabric is expressed, and it becomes usable as an elastic nonwoven fabric.

Examples of substantially elastic thermoplastic elastomers include polyurethane-based elastomers, polystyrene-based elastomers, polyolefin-based elastomers, and polyamide-based elastomers. Examples of substantially inelastic thermoplastic resin fibers include polypropylene-based resins, such as polypropylene (PP), and may also include polyethylene (PE).

The second nonwoven fabric 14 has a polypropylene-based resin contained in the substantially inelastic thermoplastic resin fibers exposed on the surface in contact with the second fiber layer 13. The basis weight of the second nonwoven fabric 14 is not particularly limited, and may be, for example, 10 (g/ ^m2 ) or more and 80 (g/ ^m2 ) or less. The elongation ratio of the second nonwoven fabric 14 is not particularly limited, and may be, for example, 1.5 times or more and 3.5 times or less. The elongation ratio is the ratio of the length of the second nonwoven fabric 14 after elongation to the length of the second nonwoven fabric 14 when unstretched, which is taken as 1.

The thickness and basis weight of the second nonwoven fabric 14 are not particularly limited as long as they do not impair the effects of the present invention, and any thickness and basis weight can be adopted according to the desired application. The thickness of the second nonwoven fabric 14 is preferably 0.05 mm or more and 2.00 mm or less, and more preferably 0.10 mm or more and 1.50 mm or less. The basis weight of the second fiber layer 13 is, for example, preferably 10 g/m ² or more and 80 g/m ² or less, more preferably 12 g/m ² or more and 70 g/m ² or less, and even more preferably 14 g/m ² or more and 60 g/m ² or less.

(Third nonwoven fabric)
The third nonwoven fabric 16 forms a surface on the non-skin side of the wearer when the absorbent article using the composite sheet 10A is worn. The nonwoven fabric used as the third nonwoven fabric 16 can be any nonwoven fabric such as an air-through nonwoven fabric, a spunbond nonwoven fabric, a point-bond nonwoven fabric, a spunlace nonwoven fabric, a needle-punched nonwoven fabric, a melt-blown nonwoven fabric, or a combination thereof (e.g., SMS, etc.). The thickness and basis weight of the third nonwoven fabric 16 are not particularly limited as long as they do not impede the effects of the present invention, and any thickness and basis weight according to the desired application can be adopted. The thickness of the third nonwoven fabric 16 is preferably 0.05 mm or more and 2.00 mm or less, and more preferably 0.10 mm or more and 1.50 mm or less. The basis weight of the third nonwoven fabric 16 is, for example, preferably 8 g/m ² or more and 30 g/m 2 or ^less , more preferably 10 g/m ² or more and 25 g/m ² or less, and even more preferably 12 g/m ² or more and 20 g/m ² or less. The third nonwoven fabric 16 may be the same nonwoven fabric as the first nonwoven fabric 11 , or may be a nonwoven fabric different from the first nonwoven fabric 11 .

<Production Method>
In manufacturing the composite sheet 10A, first, the first nonwoven fabric 11, the second nonwoven fabric 14, and the third nonwoven fabric 16 are prepared. The first nonwoven fabric 11 is formed by stacking the first fiber layer 12 and the second fiber layer 13 in the thickness direction T and bonding them by embossing. A plurality of embossed bonding portions that are recessed in the thickness direction T are formed on the surface of the first nonwoven fabric 11 by the embossing.

Next, the first nonwoven fabric 11, the second nonwoven fabric 14, and the third nonwoven fabric 16 are stacked in order in the thickness direction T. In this case, the second nonwoven fabric 14 is in a state in which it has been stretched due to the speed difference between the supply speed and the winding speed after the gear stretching process. The first nonwoven fabric 11 is arranged so that the second fiber layer 13 is in contact with the second nonwoven fabric 14. The first nonwoven fabric 11, the second nonwoven fabric 14, and the third nonwoven fabric 16 are thermally bonded in a state in which they are stacked. For example, an ultrasonic horn and an anvil roll (not shown) may be used for thermal bonding. The ultrasonic horn generates ultrasonic vibrations on the outer circumferential surface. The anvil roll has multiple protrusions on the outer circumferential surface that protrude radially outward. The first nonwoven fabric 11, the second nonwoven fabric 14, and the third nonwoven fabric 16 are transported in an overlapping state between an ultrasonic horn and an anvil roll in the MD direction (W direction), which is the transport direction, and are sandwiched between the protrusions of the anvil roll and the ultrasonic horn to form multiple joints 18. The joints 18 have a shape that is concave in the thickness direction T due to ultrasonic compression. In this manner, a composite sheet 10A is formed. The composite sheet 10A has an embossed joint and a joint 18 on the surface of the first nonwoven fabric 11. The composite sheet 10A has a joint 18 on the surface of the third nonwoven fabric 16.

<Action and Effects>
Since the composite sheet 10A stretches in the first direction W, as shown in FIG. 4, it can be applied to a composite sheet for a waist circumference of an absorbent article by arranging the first direction W parallel to the waist circumference DW of a wearer. For example, a disposable diaper 1 as an absorbent article includes a crotch portion 2 that covers the crotch of a wearer and a waist circumference portion 3 that covers the waist circumference of the wearer. The waist circumference portion 3 is formed of the composite sheet 10A. The composite sheet 10A is arranged such that the first nonwoven fabric 11 is disposed on the skin side and the second nonwoven fabric 14 is disposed on the non-skin side, and the first direction W is parallel to the waist circumference DW of the wearer. When applied to a composite sheet for a waist circumference of a disposable diaper 1, the composite sheet 10A is stretched in the waist circumference direction DW and pulled up to be worn by a wearer. The composite sheet 10A shrinks to match the length of the waist circumference DW of the wearer with the first nonwoven fabric 11 in contact with the skin of the wearer.

The composite sheet 10A contains composite fibers that include a PP resin portion and a PE resin portion, and therefore has a first fiber layer 12 on the surface of the composite sheet 10A that is highly flexible due to the polyethylene resin. Therefore, the composite sheet 10A has an excellent feel to the touch.

The composite sheet 10A includes a second fiber layer 13 that includes a single fiber made of a polypropylene-based resin, which suppresses the decrease in mechanical strength caused by the first fiber layer 12 including a polyethylene-based resin. The breaking strength of the composite sheet 10A in the CD direction (L direction) is 14 (N/50 mm) or more, so that when applied to a composite sheet for the waist area of an absorbent article, the composite sheet is prevented from breaking due to the force pulling up the absorbent article when worn.

The second fiber layer 13 is in contact with the second nonwoven fabric 14 and is bonded to the second nonwoven fabric 14 by thermal bonding. Since the second fiber layer 13 contains a single fiber made of a polypropylene-based resin and the second nonwoven fabric 14 contains a polypropylene-based resin on the surface on the side in contact with the second fiber layer 13, a joint 18 in which the polypropylene-based resins are bonded to each other can be formed. The joint 18 in which the polypropylene-based resins are bonded to each other is highly compatible and does not contain a polyethylene-based resin, so that the joint is well thermally bonded. The first nonwoven fabric 11 and the second nonwoven fabric 14 have a joint 18 in which the polypropylene-based resins are bonded to each other, so that the joint strength is excellent. Since the composite sheet 10A has a peel strength of 1.0 (N/25 mm) or more, when applied to a composite sheet for the waist part of an absorbent article, peeling of the first nonwoven fabric 11 from the second nonwoven fabric 14 due to repeated use is suppressed. The second fiber layer 13 contains 60% by mass or more of single fibers made of polypropylene-based resin, which more reliably forms a joint 18 without the presence of polyethylene-based resin.

The composite sheet 10A has a first direction W, a second direction L, and a thickness direction T that are perpendicular to each other, and comprises, in order in the thickness direction T, a first nonwoven fabric 11 and a second nonwoven fabric 14, and further comprises a plurality of bonding portions 18 in which the first nonwoven fabric 11 and the second nonwoven fabric 14 are thermally bonded to each other. The first nonwoven fabric 11 has a first fiber layer 12 and a second fiber layer 13 arranged between the first fiber layer 12 and the second nonwoven fabric 14. The first fiber layer 12 contains composite fibers, and the composite fibers contain, in a cross section, a polypropylene-based resin portion containing a polypropylene-based resin and a polyethylene-based resin portion containing a polyethylene-based resin. The second fiber layer 13 contains a single fiber made of a polypropylene-based resin, and the second nonwoven fabric 14 contains a polypropylene-based resin on the surface on the side in contact with the second fiber layer 13.

The bonding portion 18 integrates the first fiber layer 12, the second fiber layer 13, and the second nonwoven fabric 14 by thermal bonding. The first fiber layer 12 and the second fiber layer 13 contain the same type of polypropylene resin, so they are highly compatible and well bonded. The second nonwoven fabric 14 contains a polypropylene resin, which is the same type of resin as the single fiber contained in the second fiber layer 13, on the surface of the side in contact with the second fiber layer 13, so it is easy to thermally bond with the second fiber layer 13. Since the second fiber layer 13 and the second nonwoven fabric 14 are well thermally bonded, the composite sheet 10A has excellent bonding strength between the first nonwoven fabric 11 and the second nonwoven fabric 14, and peeling between the first nonwoven fabric 11 and the second nonwoven fabric 14 is suppressed when used repeatedly, and has excellent durability. Therefore, the composite sheet 10A has excellent durability while maintaining a good feel.

The second nonwoven fabric 14 is preferably an elastic nonwoven fabric that can stretch in the first direction W. Since the composite sheet 10A stretches in the first direction W, it can be applied to, for example, a composite sheet for the waist part of an absorbent article by arranging the first direction W parallel to the waist of a wearer. The first nonwoven fabric 11 includes the first fiber layer 12, which is highly flexible, and therefore easily shrinks in accordance with the shrinkage of the second nonwoven fabric 14 (elastic nonwoven fabric). The second nonwoven fabric 14 (elastic nonwoven fabric) contains a polypropylene-based resin, which is the same type of resin as the single fiber contained in the second fiber layer 13, on the surface on the side in contact with the second fiber layer 13, and is therefore well thermally bonded to the second fiber layer 13. Therefore, the composite sheet 10A has excellent bonding strength between the first nonwoven fabric 11 and the second nonwoven fabric 14 (elastic nonwoven fabric). As a result, the composite sheet 10A has excellent shrinkability and durability.

The composite sheet 10A preferably includes a third nonwoven fabric 16 on the side of the second nonwoven fabric 14 opposite to the side in contact with the first nonwoven fabric 11. By providing the third nonwoven fabric 16 according to the application on the side of the second nonwoven fabric 14 opposite to the side in contact with the first nonwoven fabric 11, the composite sheet 10A has a wider range of options for whether the first nonwoven fabric 11 is on the skin side or not on the skin side. Furthermore, the addition of the third nonwoven fabric 16 increases the mechanical strength of the composite sheet 10A, so that the composite sheet 10A has superior durability. Therefore, the composite sheet 10A is more suitable as a composite sheet for the waist area of an absorbent article.

The polypropylene-based resin preferably contains a propylene-α-olefin random copolymer, and the polyethylene-based resin preferably contains an ethylene-based polymer. The propylene-α-olefin random copolymer has a smaller difference in melting point from the polyethylene-based resin than polypropylene, and is therefore more easily thermally bonded to the polyethylene-based resin than polypropylene. Therefore, the fibers of the first fiber layer 12 are thermally bonded over a wider range at the embossed joints and the joints 18. Therefore, the composite sheet 10A can be used for a long time because the fibers of the first fiber layer 12 arranged on the surface of the composite sheet 10A are thermally bonded over a wider range, and therefore fuzzing is relatively small.

It is preferable that the melting point of the propylene-α-olefin random copolymer is 155°C or less, and the melting point of the ethylene-based polymer is 95°C or more and 125°C or less. By having the melting points of the propylene-α-olefin random copolymer and the ethylene-based polymer each within the above range, the fibers of the first fiber layer 12 can be thermally bonded more reliably over a wider range.

The ratio of the PP resin portion to the PE resin portion is preferably 70:30 to 10:90 (polypropylene-based resin portion: polyethylene-based resin portion) by mass, with the total of the PP resin portion and the PE resin portion being 100 parts by mass. The first fiber layer 12 contains a polyethylene-based resin portion, i.e., composite fibers containing a predetermined amount or more of polyethylene-based resin, which makes it easier for the polyethylene-based resin to be disposed on the surface of the first fiber layer 12. Since the first fiber layer 12 is disposed on the surface side of the composite sheet 10A, the composite sheet 10A has an excellent feel to the touch.

The composite fiber preferably has the polyethylene resin portion on the fiber surface. For example, the composite fiber may be an eccentric core-sheath type in which the polypropylene resin portion is the core 20 and the polyethylene resin portion is the sheath 22, with a portion of the polypropylene resin portion exposed from the polyethylene resin portion, or a side-by-side type. Since the composite fiber has a polyethylene resin portion on the fiber surface, it is highly flexible due to the polyethylene resin. Since the first fiber layer 12 is disposed on the surface side of the composite sheet 10A, the composite sheet 10A has an excellent feel to the touch.

The ratio of the first fiber layer 12 to the second fiber layer 13 is preferably 33:67 to 67:33 (first fiber layer:second fiber layer) by mass, with the total of the first fiber layer 12 and the second fiber layer 13 being 100 parts by mass. The first nonwoven fabric 11 contains a predetermined amount or more of the second fiber layer 13 made of a polypropylene-based resin. The second fiber layer 13 is disposed in a position in contact with the second nonwoven fabric 14, so that it is thermally bonded to the second nonwoven fabric 14 more reliably. Therefore, the composite sheet 10A has excellent bonding strength between the first nonwoven fabric 11 and the second nonwoven fabric 14.

The polypropylene resin of the first fiber layer 12 and the polypropylene resin of the second fiber layer 13 are preferably the same propylene-α-olefin random copolymer. The propylene-α-olefin random copolymer has a lower melting point than polypropylene and a smaller difference in melting point from that of polyethylene resin, so it is easier to thermally bond with polyethylene resin than polypropylene. Therefore, at the embossed joint and the joint 18, the fibers of the first fiber layer 12 are thermally bonded to each other over a wider range. Therefore, the composite sheet 10A can be used for a long time because the fibers of the first fiber layer 12 arranged on the surface of the composite sheet 10A are thermally bonded to each other over a wider range, and therefore there is relatively little fluffing. Since the polypropylene resins of the first fiber layer 12 and the second fiber layer 13 are the same propylene-α-olefin random copolymer, they have excellent compatibility and are easier to thermally bond between the first fiber layer 12 and the second fiber layer 13 over a wider range. Therefore, the composite sheet 10A has excellent bonding strength between the first fiber layer 12 and the second fiber layer 13.

The composite sheet 10A has a plurality of embossed joints on the surface of the first fiber layer 12, which join the first fiber layer 12 and the second fiber layer 13, excluding the second nonwoven fabric 14, and the total area of the plurality of joints 18 on the surface of the first fiber layer 12 is preferably smaller than the total area of the plurality of embossed joints on the surface of the first fiber layer 12. Since the total area of the plurality of joints 18 is smaller than the total area of the plurality of embossed joints, the first nonwoven fabric 11 is easily deformed in the thickness direction T by separating from the second nonwoven fabric 14 between the plurality of joints 18. Since the first nonwoven fabric 11 is easily deformed in the thickness direction T between the joints 18, the second nonwoven fabric 14 easily shrinks without being hindered by the first nonwoven fabric 11. Therefore, the composite sheet 10A is easily deformed along the wearer's waistline, and has an excellent feel against the skin.

<Modification>
The present invention is not limited to the above embodiment, and may be modified as appropriate within the scope of the present invention. For example, in the above embodiment, the dot-like joints 18 are arranged in a lattice pattern, but the present invention is not limited to this. As shown in FIG. 5, in which the same components as in FIG. 1 are given the same reference numerals, they may be arranged in a lattice pattern. The joints 18 adjacent to each other in the first direction W shown in FIG. 5 are shifted by about 0.2 mm in the second direction L. The composite sheet 10B having the dot-like joints 18 shown in FIG. 5 can obtain the same effect as the above embodiment.

In the above embodiment, the second nonwoven fabric 14 is an elastic nonwoven fabric, but the present invention is not limited thereto. The composite sheet 10C shown in FIG. 6, in which the same components as those in FIG. 2A are denoted by the same reference numerals, includes a first nonwoven fabric 11, an elastic thread 24, and a second nonwoven fabric 26 in the thickness direction T. The elastic thread 24 can be a thermoplastic elastomer such as urethane or ethylene-vinyl acetate copolymer (EVA) molded into a thread shape. The second nonwoven fabric 26 contains a polypropylene resin on the surface of the first nonwoven fabric 11 that contacts the second fiber layer 13. The nonwoven fabric used as the second nonwoven fabric 26 can be any nonwoven fabric such as an air-through nonwoven fabric, a spunbond nonwoven fabric, a point-bond nonwoven fabric, a spunlace nonwoven fabric, a needle-punched nonwoven fabric, a meltblown nonwoven fabric, or a combination thereof (e.g., SMS, etc.). The thickness and basis weight of the second nonwoven fabric 26 are not particularly limited as long as they do not impede the effects of the present invention, and any thickness and basis weight according to the desired application can be adopted. The thickness of the second nonwoven fabric 26 is preferably 0.05 mm or more and 2.00 mm or less, more preferably 0.10 mm or more and 1.50 mm or less. The basis weight of the second nonwoven fabric is, for example, preferably 10 g/m ² or more and 30 g/m ² or less, more preferably 12 g/m ² or more and 25 g/m ² or less, and even more preferably 14 g/m ² or more and 20 g/m ² or less. The composite sheet 10C according to this modification is formed by thermally bonding the first nonwoven fabric 11 and the second nonwoven fabric 26 in a state in which the elastic thread 24 is disposed between them. The elastic thread 24 is bonded to the first nonwoven fabric 11 and the second nonwoven fabric 26 in a state in which it is stretched due to the speed difference between the supply speed and the winding speed.

The composite sheet 10C includes an elastic thread 24 that stretches in the first direction W between the first nonwoven fabric 11 and the second nonwoven fabric 26. Since the composite sheet 10C stretches in the first direction W, it can be applied to, for example, a composite sheet for the waist part of an absorbent article 1 by arranging the first direction W parallel to the waist of a wearer. The first nonwoven fabric 11 includes a first fiber layer 12 that is highly flexible, so it easily shrinks in accordance with the contraction of the elastic thread 24. The second nonwoven fabric 26 is arranged on the opposite side of the first nonwoven fabric 11 with the elastic thread 24 sandwiched therebetween, and the second nonwoven fabric 26 is well thermally bonded to the second fiber layer 13. That is, the second fiber layer 13 and the second nonwoven fabric 26 are well thermally bonded with the elastic thread 24 sandwiched between them. Therefore, the composite sheet 10C has excellent bonding strength between the first nonwoven fabric 11 and the second nonwoven fabric 26. As a result, the composite sheet 10C has excellent shrinkability and durability.

<Measurement method>
The method for measuring each of the values explained in the above embodiment will be described below.

(grammage)
First, one or more test pieces with a total area of 500 ( ^cm2 ) or more are cut out from the unstretched composite sheet to be used as samples. Next, the total weight of the samples is measured using a direct reading balance (e.g., electronic balance HF-300 manufactured by Kensei Kogyo Co., Ltd.). Finally, the weight per unit area of the sample (g/ ^m2 ) is calculated from the measured total weight and the total area of the samples, and this value is used as the basis weight of the composite sheet.

The basis weights of the first, second and third nonwoven fabrics are determined as follows: First, each material is separated from the composite sheet, and then one or more sample pieces are cut out from each material so that the total area is 500 ( ^cm2 ) or more when smoothed out. The total weight of each material is measured, and the weight per unit area (g/ ^m2 ) of each sample is calculated from each total weight and each total area, which is the basis weight of each material.

(Thickness)
The thickness is measured using a thickness measuring device, FS-60DS (presser foot diameter: 50.5 mm, measuring pressure: 0.3 KPa), manufactured by Daiei Scientific Instruments Manufacturing Co., Ltd.

(Bending rigidity according to KES method)
The bending stiffness according to the KES method is measured in the second direction of the composite sheet using a large bending tester, KES-FB2-L, manufactured by Kato Tech Co., Ltd. A sample having a length of 40 mm in the first direction and a length of 60 mm in the second direction is cut from the composite sheet.
The measurement conditions are as follows.
SENS: 4
SIZE: 4cm (set to the measurement width of the sample)
Mode: 1 cycle Bending curvature: 0.5 cm ^-1
B: K=0.1~0.3cm

(Breaking strength)
The breaking strength was measured using an autograph, AG-1, manufactured by Shimadzu Corporation. First, a sample was cut from the composite sheet in an elongated state without wrinkles, measuring 50 mm in the first direction and 70 mm in the second direction. The breaking strength of the composite sheet in the second direction was then measured with a chuck distance of 50 mm and a pulling speed of 500 mm/min. "N/50 mm" means the breaking strength (N) per 50 mm width.

(Average fiber diameter)
First, the first nonwoven fabric and the second nonwoven fabric were separated from the composite sheet, and a 10 mm x 10 mm sample was cut out from each nonwoven fabric and placed on a slide. Next, an appropriate amount of glycerin was dropped onto each sample so that the entire sample was soaked in glycerin, and a cover glass was placed on top of it. Next, the sample was observed at a magnification of 1000 times using a known optical microscope (e.g., KEYENCE VHC-100 Digital Microscope Lens VH-Z450), and the fiber diameter of the fiber exposed on the surface of the sample was measured at 50 points, and the average value was taken as the average fiber diameter.

(Peel Strength)
(1) A portion of the composite sheet including the joint (including the first nonwoven fabric and the second nonwoven fabric) is cut into a sample measuring 70 mm in the stretch direction × 25 mm in the non-stretch direction.
(2) Using a test machine for peel testing, the first nonwoven fabric and the second nonwoven fabric of the cut sample are peeled off in advance by 20 mm in the stretch direction L, and the end of the first nonwoven fabric and the end of the second nonwoven fabric are respectively held by two chucks provided in the test machine, with the distance (initial value) between the chucks when holding them being preset to 30 mm.
(3) Using a testing machine, the two chucks are pulled at a constant speed (e.g., 50 mm/min) so that the gap between the two chucks increases, and the first nonwoven fabric and the second nonwoven fabric at the joint are peeled off in a 180° direction while measuring the gap between the two chucks and the load F applied to the two chucks.
(4) The peel strength of the joint is measured based on the relationship between the load F applied between the two chucks and the distance Dm between the two chucks. The maximum value of the measured load F is taken as the peel strength (N/25 mm).

(Comparison of the area of the joint and embossed joint)
A sample measuring 10 mm x 10 mm is cut out from the nonwoven fabric. The sample is observed at a magnification of 100 times using an electron microscope, and the areas of the bonded portion and the embossed bonded portion on the surface of the sample are measured and compared.

The present invention will be explained below using examples, but the present invention is not limited to these examples.

(A) Sample A composite sheet was prepared comprising a first nonwoven fabric, an elastic nonwoven fabric as a second nonwoven fabric, and a third nonwoven fabric. The first nonwoven fabric was prepared by forming a first fiber layer made of eccentric core-sheath type composite fiber and a second fiber layer made of a single fiber by a spunbonding method, and embossing the first fiber layer and the second fiber layer were integrated. A propylene-α-olefin random copolymer (α-olefin: ethylene) was used as the polypropylene-based resin, and an ethylene-α-olefin copolymer (α-olefin: 1-butene) was used as the polyethylene-based resin. The elastic nonwoven fabric was a spunbonded nonwoven fabric containing polyurethane and polypropylene, and was the same for all samples. The third nonwoven fabric was a spunbonded nonwoven fabric comprising an eccentric core-sheath type composite fiber layer and a single fiber layer. The detailed configuration of each nonwoven fabric is as shown in Table 1. The ratio of the first fiber layer to the second fiber layer (first fiber layer:second fiber layer), relative to 100 parts by mass of the total of the first fiber layer and the second fiber layer, was 67:33 in Examples 1 to 3 and 33:67 in Examples 4 to 6.

The first nonwoven fabric, the elastic nonwoven fabric, and the third nonwoven fabric were layered in the thickness direction and thermally bonded using ultrasonic waves. For thermal bonding using ultrasonic waves, equipment manufactured by Herrmann Ultrasonics was used. The ultrasonic horns were 161 mm wide x 2, had a frequency of 20 KHz, and the pressure setting was 500 N. The anvil roll speed was 200 m/min, the elastic nonwoven fabric unwinding speed was 80 m/min, and the first nonwoven fabric and third nonwoven fabric unwinding speed was 199 m/min.

As reference examples, a composite sheet (Reference Example 1) was prepared that included a first nonwoven fabric that was a spunbond nonwoven fabric made of a single fiber, the above-mentioned elastic nonwoven fabric, and a third nonwoven fabric that was a spunbond nonwoven fabric made of a single fiber, and composite sheets (Reference Examples 2 and 3) were prepared that included a first nonwoven fabric that was a spunbond nonwoven fabric made of eccentric core-sheath composite fibers, the above-mentioned elastic nonwoven fabric, and a third nonwoven fabric that was a spunbond nonwoven fabric made of eccentric core-sheath composite fibers, and were thermally bonded using ultrasound under the same conditions as in the above examples to obtain a composite sheet.

(B) Results The composite sheets according to the Examples and Reference Examples were measured for breaking strength, bonding strength, and flexural rigidity in the CD direction. As shown in Table 1, Examples 1 to 6 had a first fiber layer containing composite fibers including a PP resin portion and a PE resin portion, so the flexural rigidity was 0.31 (N·m ² /(m×10 ^-4 )) or less, and had a second fiber layer containing a single fiber formed of a polypropylene resin, so the breaking strength was 17.39 N/50 mm or more. Furthermore, because the second fiber layer was thermally bonded to the elastic nonwoven fabric, a breaking strength of 1.47 N/mm or more was obtained.

In contrast, in Reference Example 1, the first nonwoven fabric was made of a single fiber of polypropylene, so the breaking strength and bonding strength in the CD direction were high, but the bending rigidity in the CD direction was also high. In Reference Examples 2 and 3, the first nonwoven fabric was made of a composite fiber containing a PP resin portion and a PE resin portion, and the elastic nonwoven fabric was thermally bonded, so the bonding strength was low.

Reference Signs List 1 Absorbent article 2 Crotch portion 3 Waist portion 10A Composite sheet 10B Composite sheet 10C Composite sheet 11 First nonwoven fabric 12 First fiber layer 13 Second fiber layer 14, 26 Second nonwoven fabric 16 Third nonwoven fabric 18 Bonding portion 20 Core portion 22 Sheath portion 24 Elastic yarn

Claims (11)

A composite sheet for an absorbent article, the composite sheet having a first direction, a second direction, and a thickness direction that are mutually perpendicular,
A first nonwoven fabric and a second nonwoven fabric are provided in this order in the thickness direction,
The first nonwoven fabric and the second nonwoven fabric are further provided with a plurality of bonding portions at which the first nonwoven fabric and the second nonwoven fabric are thermally bonded to each other,
the first nonwoven fabric has a first fiber layer and a second fiber layer disposed between the first fiber layer and the second nonwoven fabric and in contact with the second nonwoven fabric ;
the first fiber layer includes composite fibers, the composite fibers including, in a cross section, a polypropylene-based resin portion including a polypropylene-based resin and a polyethylene-based resin portion including a polyethylene-based resin;
the second fiber layer includes a single fiber made of a polypropylene-based resin,
A composite sheet, wherein the second nonwoven fabric contains a polypropylene-based resin on a surface thereof in contact with the second fiber layer. The composite sheet according to claim 1, wherein the second nonwoven fabric is an elastic nonwoven fabric that is stretchable in the first direction. The composite sheet according to claim 2, further comprising a third nonwoven fabric on the side of the second nonwoven fabric opposite the side in contact with the first nonwoven fabric. The composite sheet according to claim 1, comprising an elastic thread stretchable in the first direction between the first nonwoven fabric and the second nonwoven fabric. The polypropylene-based resin contains a propylene-α-olefin random copolymer,
The composite sheet according to claim 1 , wherein the polyethylene-based resin comprises an ethylene-based polymer. The composite sheet according to claim 5, wherein the melting point of the propylene-α-olefin random copolymer is 155°C or less, and the melting point of the ethylene polymer is 95°C or more and 125°C or less. The composite sheet according to claim 1, wherein the ratio of the polypropylene-based resin portion to the polyethylene-based resin portion is 70:30 to 10:90 (polypropylene-based resin portion: polyethylene-based resin portion) by mass. The composite sheet according to claim 1, wherein the polyethylene resin portion is present on the fiber surface of the composite fiber. The composite sheet according to claim 1, wherein the ratio of the first fiber layer to the second fiber layer is 33:67 to 67:33 (first fiber layer:second fiber layer) by mass. The composite sheet according to claim 1, wherein the polypropylene-based resin of the first fiber layer and the polypropylene-based resin of the second fiber layer are the same propylene-α-olefin random copolymer. a surface of the first fiber layer has a plurality of embossed bonding portions bonding the first fiber layer and the second fiber layer excluding the second nonwoven fabric;
The composite sheet of claim 1 , wherein a total area of the plurality of bonded portions on the surface of the first fibrous layer is smaller than a total area of the plurality of embossed bonded portions on the surface of the first fibrous layer.

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