JP7433583B2 - Nonwoven fabric for absorbent articles, top sheet for absorbent articles, and absorbent articles containing the same - Google Patents

Description

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

Nonwoven fabrics having a two-layer structure have been proposed as top sheets for absorbent articles such as disposable diapers, sanitary napkins, incontinence pads, and panty liners. For example, Patent Document 1 discloses a two-layer nonwoven fabric having a first fiber layer that touches the user's skin and a second fiber layer adjacent thereto, in which the fibers of the first fiber layer have a smaller specific fiber diameter. (11 to 18 μm), the fibers in the second fiber layer have a larger specific fiber diameter (19 to 31 μm), and the basis weights of the first fiber layer and the second fiber layer both have a specific value (7 We propose a top sheet for absorbent articles made of a nonwoven fabric with a weight of 30 g/m ² ). Patent Document 1 states that since the nonwoven fabric has such characteristics, it is possible to improve the feel of the top sheet and reduce the amount of wet back.

Furthermore, in Patent Document 1, the fibers of the first fiber layer and the second fiber layer are both made hydrophilic, and the fibers of the first fiber layer become more hydrophilic than the fibers of the second fiber layer by contact with water. It will be described that it is preferable to make the material hydrophilic so that the degree of oxidation tends to decrease because the amount of wet back can be further reduced.

Moreover, Patent Document 2 is made of a laminated nonwoven fabric having an upper layer disposed on the skin side and a lower layer disposed on the absorbent body side, and before liquid permeation, the lower layer has a higher or almost equal hydrophilicity than the upper layer. After permeation, we selected a hydrophilic oil agent whose water resistance is clearly higher than that of the hydrophilic oil agent used in the lower layer as the hydrophilic oil agent used in the upper layer. A top sheet of an absorbent article is proposed, which is characterized by a clearly increased degree of strength. Patent Document 2 discloses that according to the top sheet of the absorbent article, liquid permeability is maintained in a stable state when the absorbent article is used, and surface flow and wet back of liquids such as urine and menstrual blood are prevented. states that it can be prevented from being used for a long time.

Japanese Patent Application Publication No. 2004-166832 Japanese Patent Application Publication No. 2005-324010

In addition to texture and wet back amount, absorbent articles need to be improved in properties such as liquid absorption rate, diffusion length, repeated durability (of wet back amount, liquid absorption rate, and diffusion length), storage stability, and cost. It will be done. Furthermore, once diapers and the like get wet, they are not replaced immediately, so it is extremely important that they can withstand repeated excretion (that is, repeated durability).
Patent Document 1 states that it is preferable to make a two-layered nonwoven fabric hydrophilic, and that the degree of hydrophilicity of the fibers of the first fiber layer tends to decrease when they come into contact with water. However, Patent Document 1 does not specifically describe anything about the degree of hydrophilicity and its water resistance in its examples, nor does it describe anything about properties other than texture and wet back amount.

In addition, the nonwoven fabric and top sheet described in Patent Document 1 and Patent Document 2 are arranged on the skin side and constitute a surface that comes into contact with the wearer's skin during use (generally also referred to as a skin contact surface). and a fiber layer that constitutes the surface opposite to the skin-contacting surface and that does not come into contact with the wearer's skin during use and that faces the absorbent body. It is characterized by the fact that the strength of hydrophilicity (degree of hydrophilicity) and that the strength of hydrophilicity does not easily decrease even when it comes into contact with liquids, in other words, the durability against hydrophilic liquids differs between the upper and lower fiber layers. It is said that

In order to obtain such nonwoven fabrics and surface sheets, the synthetic fibers constituting these fiber layers must have a strong affinity for liquids (for example, hydrophilicity), and durability when in contact with liquids (such as hydrophilicity). A nonwoven fabric is manufactured by attaching a hydrophilizing agent (also referred to as a fiber treatment agent) to the surface of the fibers, taking into consideration the difficulty of falling off the fibers even when the fibers are exposed.

However, when a nonwoven fabric with a two-layer structure is manufactured, the nonwoven fabric is manufactured, stored, and shipped in a rolled form, and at this time, fibers with different properties are stored in close contact with each other. If the rolled state is kept in a roll for a long period of time or stored in a hot and humid environment, the hydrophilic agents may interact with each other in areas where fiber layers with different fiber treatment agents come into contact. If the absorbent product is made into an absorbent article, it may not be able to perform as designed.

Surprisingly, the present inventors have discovered a nonwoven fabric having at least a two-layer structure of a first fibrous layer and a second fibrous layer, in which both the first fibrous layer and the second fibrous layer each have a specific fineness. wherein the fiber diameter of the first fiber layer is smaller than the fiber diameter of the second fiber layer, and both the first fiber layer and the second fiber layer maintain a high degree of hydrophilicity even when in contact with water. , because both the first fiber layer and the second fiber layer have substantially the same hydrophilicity, the texture, wet back amount, liquid absorption time, diffusion length, (wet back amount, liquid absorption time, and It has been found that at least one selected from repeat durability (of diffusion length), storage stability, etc. is improved, and more preferably at least one selected from repeat durability of wet back amount, liquid absorption time, and diffusion length is improved. The present invention has been completed by discovering that one type can be improved.

That is, in one gist of the present invention,
A nonwoven fabric having a first fiber layer and a second fiber layer adjacent to the first fiber layer,
The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex,
The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex,
The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer,
The fibers forming the first fiber layer and the fibers forming the second fiber layer are both hydrophilic in that their high degree of hydrophilicity (degree of hydrophilicity) is maintained even when the fibers come into contact with water. treated (i.e., the degree of hydrophilicity of the fiber has water resistance), and its hydrophilicity (the degree of high hydrophilicity and its water resistance) are substantially the same,
A nonwoven fabric for an absorbent article is provided, in which the nonwoven fabric is arranged such that the first fiber layer faces a person's skin.

The affinity between the surface of a nonwoven fabric and water can be expressed by the magnitude of the contact angle formed between the surface of fibers constituting the nonwoven fabric and water droplets. That is, if the contact angle is small, the affinity (hydrophilicity) between the nonwoven fabric and the liquid is high, and if the contact angle is large, the affinity (hydrophilicity) is low. Furthermore, the durability against hydrophilic liquids can be expressed by the change in contact angle before and after the liquid passes through it.

Therefore, in another aspect, the present invention has the following aspects:
A nonwoven fabric having a first fiber layer and a second fiber layer adjacent to the first fiber layer,
The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex,
The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex,
The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer,
The contact angle (A1) of ion-exchanged water on the surface of the fibers forming the first fiber layer before contact with water, and the contact angle of ion-exchange water (A1) on the surface of the fibers forming the second fiber layer before contact with water. A2) satisfies the following (I),
(I): A1≦80°, A2≦80°, |A1-A2|<12
The contact angle (B1) of ion-exchanged water on the surface of the fibers forming the first fiber layer after contact with water, and the contact angle of ion-exchange water (B1) on the surface of the fibers forming the second fiber layer after contact with water. B2) satisfies the following (II),
(II): -5≦(B1-A1)<40°, -5≦(B2-A2)<40°
A nonwoven fabric for an absorbent article is provided, in which the nonwoven fabric is arranged such that a first fiber layer faces a person's skin.

Since the present invention has the above-mentioned characteristics, it is selected based on texture, wet back amount, liquid absorption time, diffusion length, repetition durability (of wet back amount, liquid absorption time, and diffusion length), storage stability, etc. At least one type is improved. More preferably, at least one selected from the wet back amount, liquid absorption time, and durability of repeated diffusion length is improved.

FIG. 1 schematically shows the contact angle between a water droplet and a fiber (surface). FIG. 2 schematically shows a stainless steel plate for attaching water droplets to a nonwoven fabric sample in order to measure the contact angle after water permeation.

The present invention provides a nonwoven fabric for absorbent articles.
Absorbent articles generally include a liquid-retentive absorbent core, a liquid-impermeable backsheet, and a liquid-permeable topsheet, with the backsheet disposed between the absorbent core and the topsheet. The nonwoven fabric for an absorbent article according to an embodiment of the present invention is arranged as a top sheet that comes into contact with the wearer's skin. As such backsheets and absorbers, those commonly used for absorbent articles can be used.
For example, a thermoplastic resin film with or without moisture permeability can be used as the backsheet. For example, as the absorbent material, it is possible to use an absorbent material in which pulp fibers, superabsorbent polymer particles, or a mixture thereof are wrapped or sandwiched between paper such as tissue paper.

The nonwoven fabric for absorbent articles of the form of the present invention is
A nonwoven fabric having at least two layers including a first fibrous layer and a second fibrous layer adjacent to the first fibrous layer,
The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex,
The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex,
The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer,
The fibers forming the first fibrous layer and the fibers forming the second fibrous layer both have hydrophilic properties such that their high degree of hydrophilicity is maintained even when the fibers come into contact with water. , their hydrophilicity is the same,
The nonwoven fabric is arranged so that the first fibrous layer faces the human skin, ie, faces the outside of the absorbent article.

The nonwoven fabric for absorbent articles according to the present invention has high hydrophilicity, which is the ease of compatibility with liquids containing water, on the surface of the fibers constituting the nonwoven fabric, and high hydrophilicity even when in contact with such liquids. The property of not easily decreasing can also be described as follows by using the contact angle between the fiber surface and water.

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

The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex, preferably 1.5 to 2.6 dtex, and more preferably 1.7 to 2.3 dtex.
The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex, preferably 2.0 to 5.0 dtex, and more preferably 2.6 to 4.0 dtex.
Furthermore, the fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer.
Therefore, in the present invention, thinner fibers are used in the first fiber layer facing the human skin, and thicker fibers are used in the second fiber layer facing the absorbent body.
The fibers of the first fiber layer facing the human skin have a specific fineness that is finer than the fibers of the second fiber layer, which is preferable because the texture and touch are improved.

It is preferable that all of the fibers forming the first fiber layer and the second fiber layer have a fiber fineness within the above range, but fibers outside the above range may be used as long as the desired effects of the present invention are not impaired. may be included.
The fiber diameter of the fibers forming the first fiber layer is preferably 10 to 20 μm, more preferably 12 to 19 μm, and even more preferably 14 to 18 μm.
The fiber diameter of the fibers forming the second fiber layer is preferably 13 to 28 μm, more preferably 15 to 26 μm, even more preferably 17 to 24 μm, and even more preferably 17 to 21 μm.

The fibers (raw materials or materials) of the first fiber layer are not particularly limited as long as the nonwoven fabric targeted by the present invention can be obtained.
The fibers of the first fibrous layer can include, for example, the following fibers: natural fibers such as cotton, silk and wool; viscose rayon, cupro, and solvent-spun cellulose fibers such as Lenzing Glyocel® and Regenerated fibers such as Tencel (registered trademark); polyolefin fibers, polyester fibers, polyamide fibers, (poly)acrylic fibers made of acrylonitrile, polycarbonate fibers, polyacetal fibers, polystyrene fibers, and cyclic polyolefin fibers Synthetic fibers such as fibers.
The fibers in the first fiber layer are not only fibers made of a single type of resin, but also composite fibers made of two or more types of resin (for example, concentric or eccentric core-sheath type composite fibers, sea-island type composite fibers). , side-by-side composite fibers) can also be used.
In addition, when natural fibers are included, their fineness or fiber diameter can be calculated according to the method according to JIS L 1019 7.4.1 Microneya.

As the fibers of the first fiber layer, synthetic fibers are preferred, and polyester fibers, polyolefin fibers, and combinations thereof are more preferred. The fibers of the first fiber layer may include synthetic fibers, recycled fibers and/or natural fibers as long as the nonwoven fabric targeted by the present invention can be obtained.
The fibers of the first fiber layer are, for example, polyester fibers such as polyethylene terephthalate; and polyethylene (high density polyethylene, low density polyethylene, linear low density polyethylene), polypropylene, ethylene-propylene copolymer, ethylene-butene. -Polyolefin fibers such as 1-propylene terpolymer; and fibers that are a combination thereof can be included.

It is more preferable that the polyethylene is high-density polyethylene because it can easily be crimped. In the present invention, a fiber treatment agent may be used to impart hydrophilic properties to the fibers as described below. If the fibers can be easily crimped, the fiber treatment agent may have less need to contain additional components to impart water repellency, for example, and may suppress unnecessary effects on liquid absorption properties.
These fibers can be used alone or in combination.

When two types of fibers are combined, the form of the combination is not particularly limited as long as the desired nonwoven fabric can be obtained, such as a simple mixture of each fiber, a concentric or eccentric core-sheath type composite fiber, etc. do not have.
Concentric or eccentric core-sheath type conjugate fibers are preferred, and concentric core-sheath type conjugate fibers are more preferred because the thickness of the first fiber layer can be reduced.
The thinner the nonwoven fabric, the shorter the distance to the absorbent body, which improves the mobility of the liquid, which can further improve the liquid absorption time and amount of wet back. Therefore, the first fiber layer should also be thinner. is preferred.
Even more preferred are concentric or eccentric core-sheath type composite fibers made of polyester resin and polyolefin resin. Particularly preferred is a core-sheath type composite fiber in which the core component is a polyester resin and the sheath component is a polyolefin resin.

The fibers of the first fiber layer preferably contain 50% by mass or more, more preferably 70% by mass or more of concentric core-sheath type composite fibers, and all the fibers forming the first fiber layer contain concentric core-sheath type composite fibers. Fibers are particularly preferred. When the fibers of the first fiber layer contain 50% by mass or more of concentric core-sheath type composite fibers, an increase in the thickness of the nonwoven fabric can be further suppressed.
The fibers of the first fiber layer may contain an additive such as titanium oxide in order to improve the texture and feel. Such additives are preferably contained in an amount of 0.1 to 10% by weight, more preferably 1 to 5% by weight, based on 100% by weight of the entire fiber including additives. Further, when the fibers of the first fiber layer are core-sheath type composite fibers, it is preferable that the additive is contained in a larger amount in the core component, and it is preferable that the additive is contained only in the core component. If additives are included in the sheath component, equipment for producing nonwoven fabrics etc. may be damaged.

In the case of a core-sheath type composite fiber, the composite ratio of the core component and the sheath component is preferably 80:20 to 40:60 in mass ratio, more preferably 70:30 to 50:50, and 65: More preferably, the ratio is 35 to 55:45. When the composite ratio is within this range, especially when the core component is larger in the composite ratio (mass ratio), it is preferable because the nonwoven fabric can have less unevenness in basis weight and texture.

The fibers (raw materials or materials) of the second fiber layer are not particularly limited as long as the nonwoven fabric targeted by the present invention can be obtained.
The fibers of the second fibrous layer can include, for example, the following fibers: natural fibers such as cotton, silk and wool; viscose rayon, cupro, and solvent-spun cellulose fibers such as Lenzing Glyocel® and Regenerated fibers such as Tencel (registered trademark); polyolefin fibers, polyester fibers, polyamide fibers, (poly)acrylic fibers made of acrylonitrile, polycarbonate fibers, polyacetal fibers, polystyrene fibers, and cyclic polyolefin fibers Synthetic fibers such as fibers.
The fibers in the second fiber layer are not only fibers made of a single type of resin, but also composite fibers made of two or more types of resin (for example, concentric or eccentric core-sheath type composite fibers, sea-island type composite fibers). , side-by-side composite fibers) can also be used.
In addition, when natural fibers are included, their fineness or fiber diameter can be calculated according to the method according to JIS L 1019 7.4.1 Microneya.

As the fibers of the second fiber layer, synthetic fibers are preferred, and polyester fibers, polyolefin fibers, and combinations thereof are more preferred. The fibers of the second fiber layer can include synthetic fibers, recycled fibers and/or natural fibers as long as the nonwoven fabric targeted by the present invention can be obtained.
The fibers of the second fiber layer are, for example, polyester fibers such as polyethylene terephthalate; and polyethylene (high density polyethylene, low density polyethylene, linear low density polyethylene), polypropylene, ethylene-propylene copolymer, ethylene-butene. -Polyolefin fibers such as 1-propylene terpolymer; and fibers that are a combination thereof can be included.

It is more preferable that the polyethylene is high-density polyethylene because it can easily be crimped. In the present invention, a fiber treatment agent may be used to impart hydrophilic properties to the fibers as described below. If the fibers can be easily crimped, the fiber treatment agent may have less need to contain additional components to impart water repellency, for example, and may suppress unnecessary effects on liquid absorption properties.
These fibers can be used alone or in combination.

When two types of fibers are combined, the form of the combination is not particularly limited as long as the desired nonwoven fabric can be obtained, such as a simple mixture of each fiber, a concentric or eccentric core-sheath type composite fiber, etc. do not have.
Concentric or eccentric core-sheath type conjugate fibers are preferred, and concentric core-sheath type conjugate fibers are more preferred because the thickness of the second fiber layer can be reduced.
The thinner the non-woven fabric is, the shorter the distance to the absorbent body, the better the mobility of the liquid, and the better the liquid absorption time and amount of wet back. Therefore, the second fiber layer should also be thinner. is preferred.
Even more preferred are concentric or eccentric core-sheath type composite fibers made of polyester resin and polyolefin resin. Particularly preferred is a core-sheath type composite fiber in which the core component is a polyester resin and the sheath component is a polyolefin resin.

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

In the case of a core-sheath type composite fiber, the composite ratio of the core component and the sheath component is preferably 80:20 to 40:60 in mass ratio, more preferably 70:30 to 50:50, and 65: More preferably, the ratio is 35 to 55:45. When the composite ratio is within this range, especially when the core component is larger in the composite ratio (mass ratio), it is more preferable because the nonwoven fabric can have less unevenness in basis weight and texture.

Further, the basis weight of the entire nonwoven fabric is preferably 10 to 80 g/m ² , more preferably 15 to 50 g/m ² , and still more preferably 17 to 40 g/m ² .
In the case of disposable diapers, the basis weight of the entire nonwoven fabric is preferably as low as possible in terms of cost, and in this case the basis weight is preferably 10 to 50 g/m ² , more preferably 15 to 40 g/m ² .

The thickness of the nonwoven fabric is preferably 0.2 to 3.0 mm, more preferably 0.3 to 1.5 mm, and even more preferably 0.35 to 0.8 mm. In the case of disposable diapers, the thickness of the nonwoven fabric should be as low as possible in terms of cost, and in that case the thickness is preferably 0.2 to 1.0 mm, and preferably 0.3 to 0.8 mm. More preferred.

The basis weight of the first fiber layer is preferably 3 to 40 g/m ² , more preferably 5 to 15 g/m ² .
The basis weight of the second fiber layer is preferably 3 to 40 g/m ² , more preferably 8 to 20 g/m ² .

The ratio of the basis weight of the second fiber layer to the basis weight of the first fiber layer (fabric weight of the second fiber layer/fabric weight of the first fiber layer) is preferably 0.8 to 3.0, and 1.0 to 2. It is more preferably .0, and even more preferably 1.3 to 1.7. In particular, when the basis weight of the first fiber layer having a smaller fiber diameter is smaller than the basis weight of the second fiber layer, that is, the ratio of the basis weight of the second fiber layer to the basis weight of the first fiber layer (the basis weight of the second fiber layer / When the basis weight of the first fiber layer is larger than 1, it is more preferable because better liquid absorption properties can be obtained while providing texture and touch.

Both the fibers forming the first fiber layer and the fibers forming the second fiber layer are given hydrophilic properties that maintain a high degree of hydrophilicity (degree of hydrophilicity) even when they come into contact with water. (i.e., the fibers are hydrophilic with water resistance).
"Hydrophilicity that maintains a high degree of hydrophilicity even when in contact with water" is preferably a water resistance index of 15 or less, preferably 14 or less, obtained by the water resistance index measurement method below. It is more preferable that the number is 10 or less, and particularly preferably 10 or less. It is considered that the smaller the water resistance index, the higher the hydrophilic water resistance.
When the water resistance index is 15 or less, the repeated liquid absorption property (durability of liquid absorption property), especially the repeated wet back property (durability of wet back) becomes better, which is more preferable.

In addition, "hydrophilicity that maintains a high degree of hydrophilicity even when it comes in contact with water" is determined by "first liquid absorption time (seconds)" and " Regarding the 3rd liquid absorption time (seconds), the value of the ratio of the 3rd liquid absorption time (seconds) to the 1st liquid absorption time (seconds) (3rd liquid absorption time (seconds) / 1st liquid absorption time (seconds)) It may also be expressed in terms of liquid absorption time (seconds). The value of such a ratio is preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. When the value of such a ratio is 30 or less, the repeated liquid absorption property (durability of liquid absorption property), especially the repeated wet back property (durability of wet back) becomes better, which is more preferable.

The hydrophilic water resistance (water resistance index) of the fiber treatment agent is evaluated as follows.
(1) Concentric core-sheath type composite fiber (fineness: 2.0 dtex, fiber length : 45 mm) (for example, NBF (registered trademark) product number (SH) manufactured by Daiwabo Polytec Co., Ltd.), 0.40% by mass of a fiber treatment agent was added, and the parallel card method and air-through method (heating temperature: 135 ° C., processing time: A nonwoven fabric sample (fabric weight: 20.0 g/m ² , dimensions: vertical 10.0 cm x horizontal 10.0 cm, thickness: 1.2 mm) was manufactured using Prepared.
The following items were also prepared.
Plate with injection barrel (Use the Strike-through plate described in NWSP 070.3.R0 (15) of EDANA Nonwovens Standard Procedures - Edition 2015)
0.90% saline (colored with blue dye)
Filter paper (trade name Lister Paper (Grade 989, 10cm x 10cm) manufactured by MEZGER inc.)

(2) The liquid absorption time of the nonwoven fabric sample was measured by the following method.
(i) Three sheets of filter paper were laminated, and a nonwoven fabric sample was laminated thereon. A plate with an injection barrel was placed on top of it.
(ii) 5.0 ml of physiological saline warmed to about 37° C. was injected from the tube. The time from injection until the physiological saline disappeared from the surface of the nonwoven fabric (the physiological saline was no longer confirmed as a liquid) was measured, and this was defined as the liquid absorption time.
(iii) After absorbing the liquid, it was allowed to stand still for 30 seconds, and then the above (ii) was repeated to perform measurements twice. The liquid absorption time was measured a total of three times.
(iv) Water resistance index was calculated using the following formula.
Formula: Water resistance index = 3rd liquid absorption time (seconds) - 1st liquid absorption time (seconds)

The "high degree of hydrophilicity" exhibited by the fibers of the first fiber layer and the fibers of the second fiber layer when wet is particularly limited as long as the nonwoven fabric for absorbent articles that is the object of the present invention can be obtained. There isn't. The degree of hydrophilicity during wetting is evaluated by the run-off evaluation method described below, and the sum of the 2nd to 5th run-off is preferably 9.0-30, more preferably 9.5-30. 20, particularly preferably 10.0 to 15.
When the sum of the second to fifth run-offs is 9.0 to 30, the repeated liquid absorption properties, especially the repeated wet back properties, become better, which is more preferable.

このような式によって得られた値（ランオフ指標）が、好ましくは１３．７～５５であり、より好ましくは１４．０～４０であり、特に好ましくは１４．５～３０である。このような式によって得られた値（ランオフ指標）が、１３．７～５５である場合、繰り返しの吸液特性、特に繰り返しのウェットバック特性が、より良好になり、より好ましい。 In addition, the "degree of high hydrophilicity" is the value (run-off index) obtained by the following formula for the values of the 1st to 5th run-off obtained by the same method as the calculation of the sum of the 2-5 run-offs. It may also be expressed as

The value obtained by such a formula (run-off index) is preferably 13.7 to 55, more preferably 14.0 to 40, particularly preferably 14.5 to 30. When the value obtained by such a formula (run-off index) is from 13.7 to 55, the repeated liquid absorption characteristics, especially the repeated wet back characteristics, are better, which is more preferable.

The degree of hydrophilicity of the fiber treatment agent was evaluated by measuring run-off as described below.
Concentric core-sheath type composite fiber (fineness: 2.0 dtex, fiber length: 45 mm) where the core is polyethylene terephthalate, the sheath is high-density polyethylene, and the composite ratio (core/sheath, mass ratio) is 60/40. (For example, NBF (registered trademark) product number (SH) manufactured by Daiwabo Polytec Co., Ltd.) was added with 0.40% by mass of a fiber treatment agent, and the parallel card method and air-through method (heating temperature: 135°C, processing time: 10 seconds, A nonwoven fabric sample (fabric weight: 20.0 g/m ² , dimensions: vertical 18.0 cm x horizontal 7.0 cm, thickness: 0.70 mm) was prepared using a wind speed of 1.0 m/s.

A triangular prism having a substantially right-angled isosceles triangle base was laid down on its side to prepare a support base whose slope made an angle of 45 degrees with the horizontal plane. On the slope, two filter papers (trade name Lister Paper (Grade 989, 27.5 cm x 14 cm) manufactured by MEZGER inc.) were laid one on top of the other, and the nonwoven fabric sample was placed and fixed thereon.

A total of 1.0 g of 0.90% saline (colored with blue dye) was dropped from a microtube pump or burette at a rate of 1.0 g/30 sec to a position 1 cm below the top edge of the nonwoven fabric. The mixture was added dropwise over 30 seconds. The position of the saline tip was measured when all the saline was absorbed into the nonwoven fabric and the saline droplets disappeared from the nonwoven surface. The distance between the position and the position where the physiological saline was dropped on the surface of the nonwoven fabric, that is, the longest distance that a droplet of physiological saline flowed on the surface of the nonwoven fabric was determined.

For the second run-off, use the nonwoven fabric sample used for the first run-off, and 30 seconds after the end of the first run-off measurement, perform the same procedure as the first run-off at the same position where the physiological saline was dropped. Physiological saline was dripped onto the surface of the nonwoven fabric, and the distance that the saline flowed on the surface of the nonwoven fabric was determined. For the third and subsequent run-offs, measurements were repeated in the same manner using the nonwoven fabric samples from the previous run-off.

Furthermore, the fibers forming the second fibrous layer are imparted with substantially the same hydrophilic properties as the fibers forming the first fibrous layer. Since the fibers of the first fibrous layer and the fibers of the second fibrous layer have such hydrophilic properties, the repeated liquid absorption properties, more specifically, are selected from the wetback amount, liquid absorption time, and diffusion length. At least one type of repeat durability can be further improved.
Furthermore, since the fibers forming the first fiber layer and the fibers forming the second fiber layer have substantially the same hydrophilicity, the hydrophilicity of the first fiber layer and the second fiber layer are mixed. This is preferable because the liquid absorption characteristics do not change.

In the nonwoven fabric for absorbent articles according to the present invention, the degree of hydrophilicity (degree of hydrophilicity or strength of hydrophilicity) of each of the first fiber layer and the second fiber layer, and the structure of each fiber layer. The hydrophilic water resistance (water resistance index, or the durability of the hydrophilic property of each fiber layer when it comes into contact with water) shown by the fiber treatment agent applied to the surface of the fiber It can be expressed using the angle (contact angle) between the surface and the surface of the water droplet attached thereto. The contact angle is measured by the method described below.

That is, the nonwoven fabric for absorbent articles of the form of the present invention is
The contact angle (A1) of ion-exchanged water on the surface of the fibers forming the first fiber layer before contact with water, and the contact angle of ion-exchange water (A1) on the surface of the fibers forming the second fiber layer before contact with water. A2) satisfies the following (I),
(I): A1≦80°, A2≦80°, |A1-A2|<12
The contact angle (B1) of ion-exchanged water on the surface of the fibers forming the first fiber layer after contact with water, and the contact angle of ion-exchange water (B1) on the surface of the fibers forming the second fiber layer after contact with water. B2) satisfies the following (II).
(II): -5≦(B1-A1)<40°, -5≦(B2-A2)<40°

In the nonwoven fabric for absorbent articles according to the embodiment of the present invention, the contact angle (A1) of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer before contact with water (before liquid permeation) and the formation of the second fiber layer. The contact angle (A2) of ion-exchanged water with respect to the fiber surface will be explained.
In A1 and A2, by spraying ion-exchanged water at about 20°C onto the surface of the fibers forming each fiber layer, minute droplets of the sprayed ion-exchanged water adhere to the fiber surface, and the surface of the droplets The angle between the fiber surface and the fiber surface.
A1 and A2 are hydrophilic properties on the surface of the fiber layer before receiving liquids such as urine and menstrual blood discharged from the wearer of the absorbent article (including humans and mammals) in the nonwoven fabric for absorbent articles according to the present invention. Indicates the height of sexuality.

In the nonwoven fabric for absorbent articles according to the present invention, both A1 and A2 are 80° or less (A1≦80°, A2≦80°).
Since A1 and A2 are both 80° or less, both the hydrophilicity of the first fiber layer and the hydrophilicity of the second fiber layer are sufficiently high, and when urine, menstrual blood, soft stool, etc. are excreted and come into contact with the nonwoven fabric. The fibers are easily compatible with the moisture contained in these liquids and discharged substances, and the nonwoven fabric can easily absorb these liquids and moisture instantly.
Both A1 and A2 are preferably 20° or more and 80° or less, more preferably 30° or more and 75° or less, particularly preferably 35° or more and 75° or less, and 40° or more and 70° or less. The following is most preferable.

In the nonwoven fabric for absorbent articles according to the embodiment of the present invention, the degree of hydrophilicity (degree of hydrophilicity) of the first fiber layer and the second fiber layer is approximately the same.
Therefore, in the nonwoven fabric for absorbent articles according to the embodiment of the present invention, the absolute value of the difference between A1 and A2 is less than 12 (|A1-A2|<12).
Since the absolute value of the difference between A1 and A2 is less than 12, the nonwoven fabric for absorbent articles of the form of the present invention has the strength of hydrophilicity (degree of hydrophilicity) exhibited by the first fiber layer before contact with water, The strength of hydrophilicity (degree of hydrophilicity) exhibited by the second fiber layer before contact with the first and second fiber layers is approximately the same.
That is, for example, the strength of the hydrophilicity of the fiber treatment agent used to treat the fibers constituting the first fiber layer is the same as the strength of the hydrophilicity of the fiber treatment agent used to treat the fibers constituting the second fiber layer. That's about it.
Since the absolute value of the difference between A1 and A2 is less than 12, the degree of hydrophilization of the first fiber layer and the degree of hydrophilization of the second fiber layer are about the same, and the compatibility with urine and menstrual blood is about the same. Since one layer has extremely high hydrophilicity compared to the other layer, it is difficult to easily retain liquids such as urine and menstrual blood.
The absolute value of the difference between A1 and A2 is preferably 10 or less, more preferably 8 or less, and particularly preferably 6 or less.

Next, in the nonwoven fabric for absorbent articles according to the embodiment of the present invention, the contact angle (B1) of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer after contact with water (after liquid permeation) and the contact angle (B1) of ion exchange water with respect to the surface of the fibers forming the first fiber layer after contact with water (after liquid permeation). The contact angle (B2) of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer will be explained.
B1 and B2 mean that 0.04 ml of ion-exchanged water at about 20°C is passed through the nonwoven fabric, the nonwoven fabric is air-dried, and then ion-exchanged water at about 20°C is applied to the surface of the nonwoven fabric in the area where the ion-exchanged water has passed. By spraying, minute droplets adhere to the fiber surface, and the angle between the surface of the droplet and the fiber surface is defined as the angle between the droplet surface and the fiber surface.
B1 and B2 are not particularly limited as long as the nonwoven fabric for absorbent articles of the form of the present invention can be obtained, but preferably less than 90°.
When B1 and B2 are less than 90°, the hydrophilicity of the first fiber layer and the second fiber layer is maintained to some extent, and urine and menstrual blood can be sufficiently absorbed even when repeatedly excreted. B1 and B2 are more preferably 30° or more and 85° or less, particularly preferably 40° or more and 80° or less, and most preferably 45° or more and 80° or less.

The absolute value of the difference between B1 and B2 is not particularly limited as long as the nonwoven fabric for absorbent articles of the form of the present invention can be obtained, but it is preferably less than 14.
When the absolute value of the difference between B1 and B2 is less than 14, the surface of the fibers forming each of the first fiber layer and the second fiber layer has high hydrophilicity even after contact with water (after liquid permeation). This means that the values are the same. That is, the hydrophilicity (degree of hydrophilicity) of the first fiber layer and the second fiber layer is the same, and the compatibility with urine and menstrual blood is the same even after passing through these liquids, One layer has extremely high hydrophilicity compared to the other layer, and it is difficult to easily retain liquids such as urine and menstrual blood.
The absolute value of the difference between B1 and B2 is more preferably 12 or less, particularly preferably 10 or less, and most preferably 8 or less.

In the nonwoven fabric for absorbent articles according to the present invention, the following relationship exists between the contact angles (A1, A2) before contact with water and the contact angles (B1 and B2) after contact with water.
-5≦(B1-A1)<40°, -5≦(B2-A2)<40°
Since B1-A1 and B2-A2 are within the above ranges, the durability of the hydrophilicity of the fiber surfaces forming the first fiber layer and the second fiber layer, that is, the water content of the fiber treatment agent applied to the fiber surfaces. It can be a fiber treatment agent that has appropriate durability against (for example, water contained in liquids such as urine and menstrual blood, and soft stools) and gradually dissolves into water little by little.
A fiber layer to which such a fiber treatment agent has been applied maintains a degree of hydrophilicity that allows water to absorb and pass through it multiple times, but as the degree of hydrophilicity gradually decreases, each fiber layer continues to retain water. It is thought that this makes it possible to suppress the amount of liquid remaining in the fiber layer returning to the surface of the nonwoven fabric (so-called wet back).

When B1-A1 and B2-A2 are smaller than -5°, the degree of hydrophilicity of the fiber layer after contact with water is too high, and the change in the degree of hydrophilicity is large, so the amount of liquid returned is It can increase.
If B1-A1 and B2-A2 are 40° or more, that is, if the degree of hydrophilicity is significantly reduced by contact with water, this fiber layer is a fiber whose degree of hydrophilicity is likely to decrease by contact with water. Not only that, but the fibrous layer also has a low degree of hydrophilicity after contact with water. Such a fiber layer has a low degree of hydrophilicity and water resistance, so the degree of hydrophilicity tends to decrease significantly when it comes into contact with water, and it is difficult to absorb and allow water (for example, urine, menstrual blood, etc.) to pass through it multiple times. This makes it easier for water (e.g. urine, menstrual blood, etc.) to leak.
B1-A1 and B2-A2 are preferably -3° or more and 35° or less, more preferably 0° or more and 30° or less, particularly preferably 3° or more and 25° or less, and 5° It is most preferable that the angle is greater than or equal to 20°.

In the nonwoven fabric for absorbent articles according to the present invention, the change in contact angle in the first fiber layer before and after contact with water (B1-A1) and the change in the contact angle in the second fiber layer before and after contact with water (B2-A1) It is preferable that A2) be approximately the same.
That is, it is preferable that the absolute value of (B1-A1)-(B2-A2) (|(B1-A1)-(B2-A2)|), which is the difference between B1-A1 and B2-A2, is 18 or less. .
The changes in the contact angle of the first fiber layer and the contact angle of the second fiber layer are the same before and after contact with water, so the durability of the hydrophilicity of the first fiber layer and the hydrophilicity of the second fiber layer are The water resistance (i.e., the durability of the fiber treatment agent attached to the surface of the fibers forming the first fiber layer against liquid, and the durability of the fiber treatment agent attached to the fibers forming the second fiber layer against water) is as follows: With similar strength, the degree of hydrophilicity due to fiber treatment agents can be reduced to the same extent by contact with water.
After contact with water, the degree of hydrophilicity (affinity for liquid) of either the first fiber layer or the second fiber layer is not extremely high or extremely low, so the amount of liquid returned is further reduced. It is thought that it is likely to decrease.
The absolute value of the difference between B1-A1 and B2-A2 ((B1-A1)-(B2-A2)) is more preferably 15 or less, particularly preferably 12 or less, and preferably 10 or less. and most preferred.

[Measurement of contact angle before liquid permeation]
The contact angle of water on the surface of the fibers forming the first fiber layer and the contact angle of water on the surface of the fibers forming the second fiber layer are determined by spraying ion-exchanged water onto the surface of each fiber layer to form each fiber layer. Measure the angle between the fiber surface and the surface of the water droplet.
The contact angle between water and the fiber surface can be measured by the following method.
A measuring unit attached to a microscope VHX-1000 manufactured by Keyence Corporation with a zoom lens (manufactured by Keyence Corporation, model number: VH-Z100R) is fixed in a horizontally tilted state. A measurement sample is prepared by cutting a nonwoven fabric containing fibers whose contact angle is to be measured into a size of 50 mm x 10 mm in length (MD direction) x width (CD direction). Test the measurement sample with the measurement surface facing upward and the CD direction of the nonwoven fabric perpendicular to the lens surface of the zoom lens (i.e., the observation direction is parallel to the CD direction). Place it on a stand and secure both ends with tape. Note that the observation direction (the direction in which the object is viewed through the zoom lens) is not particularly limited as long as it is selected so that the fibers extend in a direction perpendicular to the observation direction. Depending on the type of nonwoven fabric, the observation direction may be a direction that makes an angle of, for example, 45° with the CD direction of the nonwoven fabric.

Next, droplets of ion-exchanged water (water temperature about 20° C.) are sprayed onto the measurement sample using a sprayer that keeps the size of the mist as constant and fine as possible. Within 5 seconds after spraying, the water droplets on the fiber surface are observed using a zoom lens at a magnification of 50 to 1000 times, depending on the fiber diameter of the fiber being observed, and an image is captured. By repeating spraying and image capture, 20 images that clearly show the water droplets are obtained. From the images obtained, choose one in which the fibers are horizontal. This is due to the fact that the contact angle changes when the fibers are tilted. If the number of selected images is 10 or more, the contact angle is determined using those images. If the number of images in which the fibers are horizontal is less than 10, obtain 20 more images and select the image in which the fibers are horizontal. Repeat until the total number of images is 10 or more.

As shown in FIG. 1, the contact angle was determined by drawing a tangent to a water droplet at a location where the air-contacting surface of the water droplet contacts the fiber, and the angle between the tangent and the fiber. The contact angle is measured using image analysis processing software (for example, two-dimensional image analysis software "MicroMeasure" available from Scala Corporation), a protractor, or the like. The contact angle is measured in each selected image, and their average value (arithmetic mean value) is determined and used as the contact angle of the fiber to be measured.
The contact angle may not be measured using a nonwoven fabric, but may be measured by taking out the target constituent fibers from the measurement surface and spraying water droplets onto the constituent fibers.

When measuring the contact angle, pay attention to the following points.
(1) Measure the contact angle of a water droplet on the fiber. Do not measure the contact angle of water droplets hanging below the fibers or water droplets spanning two or more fibers.
(2) If the fiber has fine crimps such as a spiral shape, measure the fiber in a place where there are few crimps or stretch the fiber to eliminate the crimps.
(3) As described above, the contact angle measurement results are obtained by changing the measurement location or measurement sample, selecting 10 or more images in which the fibers are horizontal, and averaging the measurement values. If the degree of hydrophilicity of the fiber is high, the water droplet may move on the fiber (i.e. the shape of the water droplet may change) when measuring the contact angle. In that case, the "contact angle" is determined by taking into account the circumstances of the movement.
Less than 40% of the total number of measurements (total of measurement points where water droplets were attempted to be photographed, total of cases where the water droplet moved and cases where the water droplet did not move during photography) until the number of contact angle measurement points reached 20 points. When a water droplet moves, select 10 or more images where the fibers are horizontal and average the measured values to determine the contact angle.
If the water droplet moves 40% or more of the total number of measurements by the time the contact angle is measured at 20 points, the contact angle is determined to be 20° or less.

[Measurement of contact angle after liquid permeation]
The contact angle is measured in the same manner as the method for measuring the contact angle before liquid permeation described above, except that a nonwoven fabric sample for contact angle measurement is prepared as follows.

[Adjustment of nonwoven fabric sample]
A measurement sample is prepared by cutting the nonwoven fabric into a size of 22 cm in the vertical direction and 5 cm in the horizontal direction. Next, a stainless steel plate shown in FIG. 2 in which holes with a diameter of 15 mm are equally spaced (the distance between the centers of the holes is 20 mm) is prepared. Mark the four locations inside the holes of the plate with an oil-based marker pen. Place the plate on the measurement surface of the measurement sample. With the stainless steel plate placed on the measurement sample, pour 0.04ml of ion-exchanged water adjusted to approximately 20°C onto the measurement surface of the measurement sample located in the center of the hole in the stainless steel plate using a Komagome pipette or Drop using a buret. After dropping the ion-exchanged water, the ion-exchanged water of the measurement sample is absorbed. After the dropped water droplets disappear from the surface of the measurement sample, the measurement sample is dried in an atmosphere at 20 to 50°C. Note that after dropping water droplets on the measurement sample, when absorbing the water droplets, suck the remaining water droplets and force the moisture to be absorbed into the lower layer (second fiber layer, if there is one). Good too.

The dried measurement sample is cut along a straight line passing through points 1 and 2 in the hole of the stainless steel plate shown in FIG. Ion-exchanged water at about 20° C. is sprayed using the above-mentioned sprayer from above the cut surface of the measurement sample corresponding to the location where the ion-exchanged water has been dropped, and water droplets are attached to the fibers of the measurement sample.
Hereinafter, the contact angle after water permeation is measured by observing water droplets on the fibers of the measurement sample in the same manner as the method for measuring the contact angle before liquid permeation.

Preferably, the fibers of both the first fibrous layer and the second fibrous layer are treated with the same fiber treatment agent to impart substantially the same degree of hydrophilicity. Even if the fiber treatment agent comes into contact with water, it is preferable that it can maintain the same level of high hydrophilicity when wet and has the same level of hydrophilic water resistance.

Such fiber treatment agents include, for example, polyglycerin fatty acid esters, polyether-polyester block copolymers, polyether-modified silicones, fatty acid esters of ethylene oxide-added polyhydric alcohols, etc., which treat fibers even when in contact with water. Examples include substances that do not easily separate from the surface. For example, substantially the same degree of hydrophilicity can be imparted to the first fiber layer and the second fiber layer by applying such a fiber treatment agent to the surface of the fibers, and , can substantially maintain its hydrophilicity, ie, its hydrophilicity is substantially water resistant. The fibers may be treated with the fiber treatment agent either before or after the fibers form the fiber layer.

The above-mentioned fiber treatment agent is attached to the fibers of the first fiber layer and the fibers of the second fiber layer in an amount of 0.1 to 1.5% by mass, based on 100% by mass of the entire fibers including the fiber treatment agent, etc. It is preferable that the amount is 0.2 to 1.0% by mass, more preferably 0.25 to 0.8% by mass. It is preferable that a predetermined amount of the fiber treatment agent adheres to the fibers, since desired liquid absorption properties, particularly wet back properties, become better.

The first fibrous layer and the second fibrous layer used in the present invention can be manufactured using various fibrous web manufacturing methods. The manufacturing method is not particularly limited as long as the nonwoven fabric for absorbent articles that is the object of the present invention can be obtained. Examples of such manufacturing methods include card methods such as parallel web, cross web, crisscross web, semi-random web, and random web, and air lay method.

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

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

The nonwoven fabric for absorbent articles according to the present invention preferably has a strength at 10% elongation in the MD direction (machine direction) of 3.5 N/5 cm or more, more preferably 6.0 N/5 cm or more, It is more preferably 8.5 N/5 cm or more, and even more preferably 10.0 N/5 cm or more. Further, the strength at 20% elongation in the MD direction is preferably 8.0 N/5 cm or more, more preferably 10.0 N/5 cm or more, even more preferably 13.0 N/5 cm or more, and 15 It is even more preferable that it is .0 N/5 cm or more, and it is particularly preferable that it is 18.0 N/5 cm or more. When the strength at low elongation is within this range, the nonwoven fabric has good dimensional stability, the width of the nonwoven fabric is suppressed when processed into an absorbent article, and the processability of the nonwoven fabric is improved. In addition, from the viewpoint of the feel of the nonwoven fabric, such as drapability, the strength at 10% elongation in the MD direction is preferably 30.0 N/5 cm or less, preferably 25.0 N/5 cm or less, and 20.0 N/5 cm or less. More preferably, the length is 5 cm or less. The above strength is measured according to JIS L 1096 6.12.1 A method (strip method).

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

The present invention will be explained below using Examples and Comparative Examples, but these examples are for illustrating the present invention and are not intended to limit the present invention in any way.

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

The [fiber treatment agent (hydrophilic agent)] used to produce the nonwoven fabrics of Examples and Comparative Examples is shown below. The hydrophilicity and durability of the fiber treatment agent were evaluated as follows. The amount of the fiber treatment agent is approximately 0.40% by mass, based on the weight of the entire fiber including the fiber treatment agent and the like as 100%.
Fiber treatment agent A: A water-resistant, hydrophilic fiber treatment agent that contains C12 alkyl phosphate potassium salt and has water resistance. Fiber treatment agent B: Contains C12 alkyl phosphate potassium salt and has higher water resistance than fiber treatment agent A. Fiber treatment agent C: A water-resistant hydrophilic fiber treatment agent containing C12 alkyl phosphate potassium salt and having higher hydrophilicity than fiber treatment agent B. Fiber treatment agent D: C12 alkyl phosphate ester Hydrophilic fiber treatment agent that contains potassium salt and has no water resistance

[High hydrophilicity of fiber treatment agent during wetting (sum of values from 2 to 5 run-offs)]
The hydrophilicity level of the fiber treatment agents A to D during wetting was defined as the sum of the values obtained from 2 to 5 run-offs performed as described below. The smaller the number for each run-off, the higher the hydrophilicity, and the smaller the change in the number even if the number of run-offs increases, the higher the water resistance. As a result, it is considered that the smaller the sum of the values of 2 to 5 run-offs, the higher the hydrophilicity during wetting.

Concentric core-sheath type composite fiber (fineness: 2.0 dtex, fiber length: 45 mm) where the core is polyethylene terephthalate, the sheath is high-density polyethylene, and the composite ratio (core/sheath, mass ratio) is 60/40. (NBF (registered trademark) product number (SH) manufactured by Daiwabo Polytec Co., Ltd.) was added with 0.40% by mass of a fiber treatment agent, and the parallel card method and air through method (heating temperature: 135°C, processing time: 10 seconds, wind speed: 1.0 m/s), a nonwoven fabric sample (fabric weight: 20.0 g/m ² , dimensions: length 18.0 cm x width 7.0 cm, thickness: 0.70 mm) was prepared.

A triangular prism having a substantially right-angled isosceles triangle base was laid down on its side to prepare a support base whose slope made an angle of 45 degrees with the horizontal plane. On the slope, two filter papers (trade name Lister Paper (Grade 989, 27.5 cm x 14 cm) manufactured by MEZGER inc.) were laid one on top of the other, and the nonwoven fabric sample was placed and fixed thereon.

A total of 1.0 g of 0.90% saline (colored with blue dye) was dropped from a microtube pump or burette at a rate of 1.0 g/30 sec to a position 1 cm below the top edge of the nonwoven fabric. The mixture was added dropwise over 30 seconds. The position of the saline tip was measured when all the saline was absorbed into the nonwoven fabric and the saline droplets disappeared from the nonwoven surface. The distance between the position and the position where the physiological saline was dropped on the surface of the nonwoven fabric, that is, the longest distance that a droplet of physiological saline flowed on the surface of the nonwoven fabric was determined.

For the second run-off, use the nonwoven fabric sample used for the first run-off, and 30 seconds after the end of the first run-off measurement, perform the same procedure as the first run-off at the same position where the physiological saline was dropped. Physiological saline was dripped onto the surface of the nonwoven fabric, and the distance that the saline flowed on the surface of the nonwoven fabric was determined. For the third and subsequent run-offs, measurements were repeated in the same manner using the nonwoven fabric samples from the previous run-off.
The results are shown in Table 1.
It is thought that the hydrophilicity during wetting increases in the order of fiber treatment agents D, A, B, and C.

Furthermore, when the run-off index mentioned above was calculated, the numerical values were as follows.
Fiber treatment agent A: 19.5
Fiber treatment agent B: 14.9
Fiber treatment agent C: 13.6
Fiber treatment agent D: 61.4

[Water resistance of hydrophilicity of fiber treatment agent (water resistance index)]
The water resistance index of fiber treatment agents A to D was evaluated by the following method.
(1) Concentric core-sheath type composite fiber (fineness: 2.0 dtex, fiber length : 45 mm) (NBF (registered trademark) product number (SH) manufactured by Daiwabo Polytech Co., Ltd.), 0.40% by mass of a fiber treatment agent was added, and the parallel card method and air through method (heating temperature: 135 ° C., processing time: 10 seconds) , wind speed: 1.0 m/s), a nonwoven fabric sample (fabric weight: 20.0 g/m ² , dimensions: vertical 10.0 cm x horizontal 10.0 cm, thickness: 1.2 mm) was manufactured and prepared. .
The following items were also prepared.
Plate with injection barrel (Use the Strike-through plate described in NWSP 070.3.R0 (15) of EDANA Nonwovens Standard Procedures - Edition 2015)
0.90% saline (colored with blue dye)
Filter paper (trade name Lister Paper (Grade 989, 10cm x 10cm) manufactured by MEZGER inc.)

(2) Method The liquid absorption time was measured by the following method.
(i) Three sheets of filter paper were laminated, and a nonwoven fabric sample was laminated thereon. A plate with an injection barrel was placed on top of it.
(ii) 5.0 ml of physiological saline warmed to about 37° C. was injected from the tube. The time from injection until the physiological saline disappeared from the surface of the nonwoven fabric (the physiological saline was no longer confirmed as a liquid) was measured, and this was defined as the liquid absorption time.
(iii) After absorbing the liquid, it was allowed to stand still for 30 seconds, and then the above (ii) was repeated to perform measurements twice. The liquid absorption time was measured a total of three times.
(iv) Water resistance index was calculated using the following formula.
Formula: Water resistance index = 3rd liquid absorption time (seconds) - 1st liquid absorption time (seconds)

The water resistance index values of fiber treatment agents A to D were as follows.
Fiber treatment agent A: 6.2
Fiber treatment agent B: 1.0
Fiber treatment agent C: 1.0
Fiber treatment agent D: 49.0
It is considered that the smaller the water resistance index, the higher the water resistance.
It is thought that the water resistance increases in the order of fiber treatment agents D, A, B, and C (however, B and C are almost the same).

In addition, based on the liquid absorption time used to calculate the water resistance index above, the value of the ratio of the third liquid absorption time (seconds) to the first liquid absorption time (seconds) of fiber treatment agents A to D (third liquid absorption time) The liquid absorption time (seconds)/first liquid absorption time (seconds)) was as follows. It is considered that the smaller the value of this ratio, the higher the water resistance.
Fiber treatment agent A: 8.0
Fiber treatment agent B: 2.3
Fiber treatment agent C: 2.0
Fiber treatment agent D: 50.5

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

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

[Example 1]
Using Fiber 1 to which 0.40% by mass of fiber treatment agent A was applied, a first fibrous web serving as the first fibrous layer was manufactured using a parallel card machine. The basis weight of the first fibrous web was about 8 g/m ² .
A second fibrous web serving as a second fibrous layer was manufactured using Fiber 2 to which 0.4% by mass of fiber treatment agent A was applied using a parallel card machine. The basis weight of the second fibrous web was approximately 12 g/m ² .
The first fibrous web and the second fibrous web were overlapped and heat treated at 135° C. using a hot air penetration type heat treatment machine, and then integrated to obtain the nonwoven fabric of Example 1. The nonwoven fabric of Example 1 had a basis weight of 18.2 g/m ² and a thickness of 1.32 mm.

[Examples 2 to 4] and [Comparative Examples 4 to 5]
For Examples 2 to 4 and Comparative Examples 4 to 5, using the fibers and fiber treatment agents listed in Tables 2 to 3, and using the same method as the nonwoven fabric manufacturing method of Example 1 above, Examples were prepared. Nonwoven fabrics of Examples 2 to 4 and Comparative Examples 4 to 5 were obtained.

[Comparative Examples 1 to 3 and 6]
For Comparative Examples 1-3 and 6, the fabrication of the nonwoven fabric of Example 1 described above was performed using the fibers and fiber treatment agents listed in Table 3, except that the second fibrous web was not fabricated and laminated. Nonwoven fabrics of Comparative Examples 1 to 3 and 6 were obtained using a method similar to that described above.

Regarding the nonwoven fabrics of Examples and Comparative Examples thus obtained, liquid absorbent articles for evaluation were manufactured and their absorbency was evaluated.
[Manufacture of absorbent articles]
An absorbent article having a three-layer structure of top sheet/second sheet/absorbent body was taken out from a commercially available diaper (product name GOO.N (registered trademark) manufactured by Daio Paper Co., Ltd.). The top sheet was peeled off and removed from the absorbent article, and in place of the top sheet, the nonwoven fabrics of the above-mentioned Examples and Comparative Examples were laminated to obtain absorbent articles for evaluation. In addition, during lamination, the first fiber layer was arranged so as to face outward. Using this absorbent article for evaluation, the liquid absorption properties (wet back, liquid absorption time, and diffusion length) of the nonwoven fabrics of Examples and Comparative Examples were evaluated.

[Wet back]
The wet back properties of the nonwoven fabrics of Examples and Comparative Examples were evaluated by the following method.
(1) In order to measure the amount of wet back, the following articles were prepared.
Absorbent article for evaluation of the above-mentioned Examples and Comparative Examples Plate with injection tube (inner diameter of the bottom of the tube 2.5 cm)
0.90% saline (colored with blue dye)
Filter paper (ADVANTEC (registered trademark) No. 2 manufactured by Toyo Roshi Co., Ltd.) 10 cm x 10 cm
Weight (5kg) 10cm x 10cm

(2) Method The amount of wet back was measured according to the following procedure.
(i) The absorbent article for evaluation was arranged so that the nonwoven fabric (42 cm in length x 21 cm in width) faced upward, and a plate with an injection tube was placed thereon.
(ii) 50 ml of physiological saline warmed to about 37° C. was injected from the tube. It was left until the physiological saline was no longer visible on the surface of the nonwoven fabric (the physiological saline was no longer visible as a liquid).
(iii) The plate with injection barrel was removed and left to stand for 10 minutes.
(iv) Filter papers (30 sheets) whose mass had been measured in advance were placed on the nonwoven fabric, and a 5 kg weight was placed thereon for 20 seconds. Thereafter, the mass of the filter paper was measured. The difference between the mass of the filter paper before it is placed on the nonwoven fabric and the mass of the filter paper after it is placed on the nonwoven fabric and further on which a weight is placed corresponds to the amount of wet back.
(vi) Returning to (i) above, measurements were performed three times by repeating (i) to (iv). Wetback was evaluated a total of four times.

Three samples were prepared for one sample (nonwoven fabric). The average value of the wet back amount measured for each of the three samples was taken as the wet back amount of that sample.
The results are shown in Tables 2 and 3. The smaller the amount of water that seeps out of the nonwoven fabric, the more comfortable the human skin will be, so it is preferable that the wet back value is smaller.

[Liquid absorption time]
When measuring the wet back, the time from the injection of physiological saline until the physiological saline became invisible from the surface of the nonwoven fabric (the physiological saline was no longer confirmed as a liquid) was measured, and this was defined as the liquid absorption time.
The results are shown in Tables 2 and 3. It is preferable that the value of the liquid absorption time (seconds) is smaller, since the shorter the absorption time, the less the skin will become stuffy.

[Diffusion length]
When measuring the wet back, 5 minutes after injection of the physiological saline, the length of the absorbent article for evaluation in the vertical direction of absorbing the physiological saline was measured and defined as the diffusion length.
The results are shown in Tables 2 and 3. Since it is considered that the entire absorbent article can be used effectively, a larger value of the diffusion length (cm) is preferable.

Examples 1 and 4 are compared with Comparative Examples 1 and 3, respectively. It can be seen that when a single layer is laminated, the third or fourth wetback, that is, the repeated durability regarding the amount of wetback is improved.
Example 3 is compared with Comparative Example 2. It can be seen that when a single layer is made into a laminate, the repeated durability regarding the second to fourth liquid absorption times is greatly improved.
In Examples 1, 3 and 4 and Comparative Examples 1 to 3, fiber treatment agents A to C were used. All of the fiber treatment agents A to C have high hydrophilicity and high water resistance. It was found that when these fiber treatment agents of the Examples were used, repeat durability was improved by laminating a single layer.

Examples 1, 3 and 4 are compared with Comparative Example 4. In Examples 1, 3 to 4, fiber treatment agents A to C having high hydrophilicity and high water resistance were used in both the first fiber layer and the second fiber layer, and in Comparative Example 4, the first fiber treatment agent A to C having high hydrophilicity and high water resistance were used. Both the fiber layer and the second fiber layer use fiber treatment agent D, which has high hydrophilicity but low water resistance. It can be seen that when a fiber treatment agent having high hydrophilicity and high water resistance is used, the 3rd and 4th wetback, that is, the cyclic durability regarding the amount of wetback and the cyclic durability regarding the liquid absorption time are improved.

Incidentally, Comparative Example 4 will be compared with Comparative Example 6 just to be sure. In both cases, fiber treatment agent D, which has high hydrophilicity but low water resistance, is used. When fiber treatment agent D is used, when a single layer is made into a laminate structure, the liquid absorption time for the 3rd and 4th times is not much different, but the amount of wetback in the 3rd and 4th times is rather worsened, so when making a laminate structure, It can be seen that it is important to use a fiber treatment agent with high hydrophilicity and high water resistance.

Examples 1, 3 and 4 are compared with Comparative Example 5. Both the first fiber layer and the second fiber layer use fiber treatment agents A to C having high hydrophilicity and high water resistance. In Examples 1, 3 and 4, the fiber treatment agent used to treat the first fiber layer and the fiber treatment agent used to treat the second fiber layer were the same, but in Comparative Example 5, the fiber treatment agent used to treat the first fiber layer was the same. The fiber treatment agent and the fiber treatment agent used to treat the second fiber layer are different. In this case, no significant difference was observed regarding wet back and liquid absorption rate.

However, using different fiber treatment agents for the first fiber layer and the second fiber layer is more complicated than using the same fiber treatment agent, and increases costs. Furthermore, if the nonwoven fabric is wound into a roll and stored for a long time, especially in a high-temperature environment, the two types of fiber treatment agents may mix and may not exhibit the desired performance, so it is not necessary to use different fiber treatment agents. It is also possible that the benefits of differential hydrophilicity may be substantially eliminated.

Example 1 and Example 4 will be compared. It is better to use fiber treatment agent A (Example 1), which has high hydrophilicity and not too high water resistance, than to use fiber treatment agent C (Example 4) for the third or fourth time. It can be seen that the wet back is improved by repeating the process.

Note that the contact angle measurement results are substantially the same as the run-off measurement results.

The present invention provides a nonwoven fabric, a sheet for an absorbent article, and an absorbent article containing the same. They are preferably improved in at least one type selected from texture, wet back amount, liquid absorption time, diffusion length, repetition durability (of wet back amount, liquid absorption time, diffusion length), cost, storage stability, etc.

Claims (5)

A nonwoven fabric having a first fiber layer and a second fiber layer adjacent to the first fiber layer,
The fineness of the fibers forming the first fiber layer is 1.0 to 2.8 dtex,
The fineness of the fibers forming the second fiber layer is 1.7 to 5.6 dtex,
The fiber diameter of the fibers forming the first fiber layer is smaller than the fiber diameter of the fibers forming the second fiber layer,
All fibers forming the second fiber layer are concentric core-sheath type composite fibers,

The contact angle (A1) of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer before contact with water and the fiber forming the first fiber layer and the fiber forming the second fiber layer are The contact angle (A2) of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer is as follows (I)
(I): 40°≦A1≦80°, 40°≦A2≦80°, |A1-A2|<12
The same degree of hydrophilicity is imparted by satisfying

The contact angle (B1) of ion-exchanged water with respect to the surface of the fibers forming the first fiber layer after contact with water and the fibers forming the first fiber layer and the fibers forming the second fiber layer after contact with water are determined. The contact angle (B2) of ion-exchanged water with respect to the surface of the fibers forming the second fiber layer is as follows (II)
(II): 5≦(B1-A1)<30°, 5≦(B2-A2)<30°
The filling,
The contact angles (A1, A2) of the first fiber layer and the second fiber layer before contact with water, and the contact angles (B1, B2) of the first fiber layer and second fiber layer after contact with water, (B1 The absolute value of (B1-A1)-(B2-A2), which is the difference between -A1) and (B2-A2), is (III) below.
(III):|(B1-A1)-(B2-A2)|≦12
The fibers have hydrophilicity that maintains their high degree of hydrophilicity even when they come into contact with water, and their degree of hydrophilicity is the same;
A nonwoven fabric for absorbent articles, wherein the nonwoven fabric is arranged such that the first fiber layer faces human skin. The nonwoven fabric according to claim 1 , wherein the fibers forming the first fiber layer include concentric core-sheath composite fibers whose core component is polyester and whose sheath component is high-density polyethylene. 3. The method according to claim 1, wherein the ratio of the basis weight of the second fiber layer to the basis weight of the first fiber layer (fabric weight of the second fiber layer/fabric weight of the first fiber layer) is 0.8 to 3.0 . Non-woven fabric. A top sheet for an absorbent article, comprising the nonwoven fabric according to any one of claims 1 to 3 , wherein the first fiber layer is arranged to face human skin. An absorbent article comprising the top sheet according to claim 4 , wherein the first fibrous layer is arranged to face human skin.