JP7348460B2 - Surface sheet for absorbent articles, manufacturing method thereof, and absorbent articles - Google Patents

Description

The present invention relates to a topsheet for an absorbent article made of a hydroentangled nonwoven fabric made of 100% by mass of cellulose fibers, a method for producing the same, and an absorbent article.

Conventionally, nonwoven fabrics made of water-repellent synthetic fibers such as polyester fibers and polyolefin fibers that have been subjected to hydrophilic treatment have been widely used for surface sheets such as top sheets of absorbent products such as sanitary napkins and disposable diapers. was. In recent years, there has been an increasing demand for biodegradable and environmentally friendly materials, and the use of cellulose fibers has been proposed. For example, Patent Document 1 proposes a sanitary product in which the first layer includes synthetic fibers or hydrophobic cellulose fibers and the second layer includes artificial cellulose fibers. Further, Patent Document 2 proposes a nonwoven fabric for absorbent articles containing surface hydrophilic synthetic fibers and surface hydrophobic cellulose fibers.

Special Publication No. 2015-507977 Japanese Patent Application Publication No. 2017-179643

However, the nonwoven fabrics described in Patent Documents 1 and 2 still have the problem of containing synthetic fibers.

In order to solve the above conventional problems, the present invention provides a surface sheet for absorbent articles that is made of 100% by mass of cellulose fibers, has a soft texture and liquid permeability, has good liquid dispersibility, and has little liquid return. , a manufacturing method thereof, and an absorbent article.

The present invention is a surface sheet for an absorbent article composed of a hydroentangled nonwoven fabric, wherein the hydroentangled nonwoven fabric is composed of 100% by mass of cellulose fibers, and includes a first fiber layer disposed on the skin side during use, and a first fiber layer disposed on the skin side during use. a second fiber layer disposed in contact with one fiber layer, the first fiber layer contains 90% by mass or more of water-repellent cellulose fibers, and the second fiber layer contains 90% by mass or more of hydrophilic cellulose fibers. The fibers constituting the first fiber layer and the fibers constituting the second fiber layer are partially intertwined, and the water-repellent cellulose fibers have a crosslinking agent and a non-fluorinated water repellent bonded to the fiber surface. The present invention relates to a surface sheet for an absorbent article, wherein the hydrophilic cellulose fiber has a single fiber fineness of 0.5 dtex or more and 3.5 dtex or less.

The present invention also provides a method for manufacturing the topsheet for an absorbent article, comprising: a first fiber layer containing 90% by mass or more of water-repellent cellulose fibers; and a first fiber layer containing 90% by mass or more of hydrophilic cellulose fibers. The step of laminating two fiber layers, spraying a water jet on one or both sides of the obtained laminate to separate the fibers constituting the first fiber layer, the fibers constituting the second fiber layer, and the first fiber layer. The present invention relates to a method for manufacturing a topsheet for an absorbent article, which includes a step of partially hydroentangling the constituent fibers and the fibers constituent of the second fiber layer.

The present invention also relates to an absorbent article that includes the above-mentioned topsheet for an absorbent article and is used so that the first fiber layer is placed on the skin side.

According to the present invention, a top sheet for an absorbent article that is made of 100% by mass of cellulose fibers, has a soft texture, liquid permeability, good liquid dispersibility, and little liquid return, and an absorbent article containing the same. can be provided.
Further, according to the manufacturing method of the present invention, a top sheet for absorbent articles is obtained which is made of 100% by mass of cellulose fibers, has a soft texture and liquid permeability, has good liquid dispersibility, and has little liquid return. be able to.

The inventors of the present invention have made extensive studies to improve the liquid permeability and diffusivity of a top sheet for an absorbent article made of 100% by mass of cellulose fibers, and to reduce liquid return. As a result, it includes a first fiber layer that is placed on the skin side during use and a second fiber layer that is placed in contact with the first fiber layer, and the first fiber layer contains 90% by mass or more of water-repellent cellulose fibers. However, the second fiber layer contains 90% by mass or more of hydrophilic cellulose fibers, and the fibers constituting the first fiber layer and the fibers constituting the second fiber layer are partially entangled hydroentangled nonwoven fabrics that are absorbent. The surface sheet for the article is composed of cellulose fibers having a crosslinking agent and a non-fluorine water repellent bonded to the fiber surface as the water-repellent cellulose fibers, and the hydrophilic cellulose fibers having a single fiber fineness of 0. By using cellulose fibers with a density of 5 dtex or more and 3.5 dtex or less, it has a soft texture made of 100% by mass of cellulose fibers, has liquid permeability, has good liquid diffusivity, and absorbs with little liquid return. It has been found that a top sheet for sexual articles can be obtained.

In the present invention, hydrophilic cellulose fiber means that the sedimentation time is 60 seconds or less in a sedimentation test conducted according to JIS L 1097 7.1.3 (sedimentation method), and water-repellent cellulose fiber is , JIS L 1097 7.1.3 (sedimentation method) in a sedimentation test conducted in accordance with JIS L 1097 7.1.3 (sedimentation method), which means that the sedimentation time exceeds 60 seconds. In the following, unless otherwise indicated, the sedimentation time means the sedimentation time measured in a sedimentation test conducted according to JIS L 1097 7.1.3 (sedimentation method).

The topsheet for an absorbent article is made of a hydroentangled nonwoven fabric made of 100% by mass of cellulose fibers. This gives it a soft texture and is biodegradable, making it easy to dispose of and environmentally friendly. Furthermore, since cellulose fibers have excellent water absorption properties, they can easily exhibit a moisture absorption effect and can reduce the feeling of stuffiness.

The hydroentangled nonwoven fabric includes a first fiber layer that is placed on the skin side during use, and a second fiber layer that is placed in contact with the first fiber layer, and the first fiber layer contains 90 mass of water-repellent cellulose fibers. % or more, the second fiber layer contains hydrophilic cellulose fibers in an amount of 90% or more by mass, and the fibers constituting the first fiber layer and the fibers constituting the second fiber layer are partially intertwined. With this structure, when the first fiber layer comes into contact with liquid such as menstrual blood or urine, the liquid is gradually absorbed and passes through the first fiber layer, and the permeated liquid is absorbed into the second fiber layer. The liquid that has been diffused and diffused into the second fiber layer is prevented from returning.

Specifically, the first fiber layer may be composed of water-repellent cellulose fibers of 90% by mass or more and 100% by mass or less, and hydrophilic cellulose fibers of 0% by mass or more and 10% by mass or less, and 95% by mass of water-repellent cellulose fibers. % to 100% by mass, and 0 to 5% by mass of hydrophilic cellulose fibers. From the viewpoint of further reducing the liquid return rate, the first fiber layer is preferably composed of 100% by mass of water-repellent cellulose fibers.

The water-repellent cellulose fiber has a crosslinking agent and a non-fluorine water repellent bonded to the fiber surface. The water-repellent cellulose fibers may have a settling time of more than 60 seconds, but from the viewpoint of excellent water repellency, the settling time is preferably 2 minutes or more, more preferably 3 minutes or more, and 5 minutes or more. is even more preferable.

As the water-repellent cellulose fibers, cellulose fibers such as natural cellulose fibers and regenerated cellulose fibers having a crosslinking agent and a non-fluorine water repellent bonded to the fiber surface can be used as appropriate. Examples of natural cellulose fibers include cotton, hemp, and pulp. Examples of regenerated cellulose fibers include cellulose fibers regenerated by a viscose method such as rayon and polynosic, cellulose fibers regenerated by a copper ammonia method such as cupra, and purified cellulose fibers regenerated by a solvent spinning method such as lyocell. etc. Among them, the water-repellent cellulose fiber is recycled by the viscose method from the viewpoint of easy availability, low crystallinity, high official moisture content and water retention, high moisture absorption and desorption properties, and further reducing stuffiness. Preferably, the cellulose fibers are water-repellent regenerated cellulose fibers in which a cross-linking agent and a non-fluorine-based water repellent are bonded to the fiber surface of the cellulose fibers.

The regenerated cellulose fibers such as the rayon fibers more preferably contain a compound containing one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups. Incorporating a compound containing one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups into regenerated cellulose fibers such as rayon fibers, and bonding a crosslinking agent and a non-fluorine water repellent to the fiber surface. This increases the fixation of the non-fluorine water repellent agent on the fiber surface, resulting in better water repellency. In the following, unless otherwise specified, "a compound containing an acidic group" means a compound containing one or more acidic groups selected from the group consisting of a carboxyl group and a sulfonic acid group. When producing regenerated cellulose fibers, by spinning a spinning viscose solution prepared by mixing a compound containing an acidic group with a viscose stock solution, the compound containing an acidic group is kneaded into the fiber. Regenerated cellulose fibers can be impregnated with compounds containing acidic groups by immersing them in an aqueous solution containing compounds containing acidic groups, or by spraying or applying an aqueous solution containing compounds containing acidic groups to regenerated cellulose fibers. A compound containing an acidic group can be included in the regenerated cellulose fiber by attaching the compound containing an acidic group to the regenerated cellulose fiber. Among these, kneading is preferable because the compound containing acidic groups is uniformly mixed and dispersed throughout the surface and inside of the fiber, and the compound containing acidic group is difficult to fall off from the fiber. .

The carboxyl group-containing compound is not particularly limited, but is preferably a (meth)acrylic acid polymer, for example, from the viewpoint of easily imparting carboxyl groups to regenerated cellulose fibers. In the present invention, (meth)acrylic acid includes acrylic acid and methacrylic acid. The (meth)acrylic acid polymer may be a homopolymer of (meth)acrylic acid monomers or a copolymer of (meth)acrylic acid monomers and other monomers. It's okay. The carboxyl group-containing compound is more preferably one or more selected from the group consisting of polyacrylic acid and acrylic acid-maleic acid copolymer.

As the polyacrylic acid, it is preferable to use, for example, unneutralized polyacrylic acid, that is, H-type polyacrylic acid in which the carboxyl group of polyacrylic acid is in the H-type. Note that the H site of the carboxyl group of polyacrylic acid may be partially substituted with a metal ion such as Na or an ionic compound. In the following, unless otherwise specified, polyacrylic acid means an unneutralized product of polyacrylic acid. As the polyacrylic acid, a compound having a structure in which carboxyl groups are mainly attached to the main chain and in which the contribution of carboxyl groups to the molecular weight of the polymer is maximum can be used, for example, a compound with a theoretical amount of carboxyl groups of 72 g/mol It is preferable to use the above polyacrylic acid.

The acrylic acid-maleic acid copolymer contains an ethylenically unsaturated monomer containing at least one selected from the group consisting of acrylic acid and acrylates (hereinafter also referred to as acrylic acid monomer). , a polymer of ethylenically unsaturated monomers containing at least one selected from the group consisting of maleic acid, maleic acid salts and maleic anhydride (hereinafter also referred to as maleic acid monomers). Often, a polymer of ethylenically unsaturated monomers containing at least one member selected from the group consisting of acrylic acid and acrylates, and at least one member selected from the group consisting of maleic acid, maleate salts, and maleic anhydride. It may be. In addition, from the viewpoint of easily imparting carboxyl groups to fibers, the acrylic acid-maleic acid copolymer contains an ethylenically unsaturated monomer containing at least one selected from the group consisting of acrylic acid and acrylates, and maleic acid. A polymer of ethylenically unsaturated monomers containing at least one selected from the group consisting of acids and maleates, and/or at least one selected from the group consisting of acrylic acid and acrylates, and maleic acid. It is preferably a polymer of ethylenically unsaturated monomers containing at least one selected from the group consisting of maleate and maleate. In addition, if necessary, the acrylic acid-maleic acid polymer may be copolymerized with other monomers other than the acrylic acid monomer and the maleic acid monomer to the extent that the effects of the present invention are not impaired. It may be something that has been done. The other monomer may be, for example, an unsaturated monocarboxylic acid monomer.

The weight average molecular weight of the acrylic acid-maleic acid copolymer is preferably 5,000 or more and 500,000 or less, more preferably 6,000 or more and 250,000 or less, even more preferably 10,000 or more and 100,000 or less, and 30,000 or more and 80,000 or less. The following is particularly preferable. When the weight average molecular weight is within the above range, it is easy to knead into the regenerated cellulose, and the carboxyl group-containing compound is less likely to fall off or denature even when washed, dyed or washed.

The acrylic acid-maleic acid copolymer preferably contains 5% by mass or more and 95% by mass or less of maleic acid, more preferably 20% by mass or more and 80% by mass or less, and 30% by mass or more and 70% by mass or less. It is more preferable that the content is 40% by mass or more and 60% by mass or less. When the content of maleic acid in the acrylic acid-maleic acid copolymer is within the above range, carboxyl groups can be easily imparted to the regenerated cellulose fibers. When the same mass of acrylic acid-maleic acid copolymer is contained in the regenerated cellulose fiber, the amount of H-type carboxyl groups will be increased by including the acrylic acid-maleic acid copolymer with a high maleic acid ratio. Therefore, it is preferable.

In the present invention, the maleic acid ratio in the acrylic acid-maleic acid copolymer is measured and calculated as follows, assuming that the organic components in the acrylic acid-maleic acid copolymer are only acrylic acid and maleic acid. can do.
(1) Place about 4 to 5 mL of the sample (aqueous solution containing acrylic acid-maleic acid copolymer salt) into a glass vial, and heat and dry at 110° C. for 20 hours.
(2) Dissolve about 50 mg of the dry sample in about 0.7 mL of heavy water.
(3) Perform 1H-NMR analysis on the heavy water solution of the sample using an FT-NMR device (manufactured by JEOL Ltd., JMTC-300/54/SS). The composition ratio of the acrylic acid component (A) and the maleic acid component (M) is determined from the abundance ratio of the group carbon. The number of measurements is 16, and the average value is calculated.

The compound containing the sulfonic acid group is not particularly limited, but for example, naphthalene sulfonate, polystyrene sulfonate, phenol sulfonate, dihydroxydiphenyl sulfone, formalin condensate of hydroxyphenyl sulfone, etc. can be used.

In the regenerated cellulose fiber, the content of a compound containing one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups is, for example, 1% by mass or more and 35% by mass or less based on 100% by mass of cellulose. It is preferably 3% by mass or more and 30% by mass or less, and even more preferably 4% by mass or more and 25% by mass or less. In the regenerated cellulose fiber, if the content of the compound containing one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups is less than 1% by mass based on 100% by mass of cellulose, the effect of the acidic groups may be reduced. If the amount exceeds 35% by mass, the fiber strength may decrease and it may not be possible to form fine fibers.

In the regenerated cellulose fiber, the total amount of one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups is preferably 0.30 mmol/g or more and 1.60 mmol/g or less, more preferably 0.35 mmol. /g or more and 1.50 mmol/g or less, more preferably 0.40 mmol/g or more and 1.40 mmol/g or less. When the total amount of one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups is within the above-mentioned range, the effect of the acidic groups is likely to be exhibited. In the regenerated cellulose fibers, the acidic groups bond with isocyanate compounds, as described below, and even when the fiber surface is heated to a low temperature of 40°C or more and 110°C or less, the fiber surface of the non-fluorine water repellent is It has the effect of improving the fixing properties of regenerated cellulose fibers, as well as imparting ammonia deodorizing properties and pH buffering properties to the regenerated cellulose fibers. In the present invention, the total amount of one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups is measured and calculated as described below.

The non-fluorine water repellent is not particularly limited, but for example, a hydrocarbon water repellent is preferred. As the hydrocarbon water repellent, for example, a hydrocarbon water repellent made of a polymer containing a (meth)acrylic ester as a basic monomer unit in which the hydrocarbon group exists via an ester bond and has 12 or more carbon atoms. It is preferable to use a liquid solution. The number of carbon atoms in the hydrocarbon group is more preferably 24 or less, and even more preferably 21 or less. The hydrocarbon group may be linear or branched, saturated or unsaturated hydrocarbon, and further may have an alicyclic or aromatic ring. You may do so. Among these, those that are linear are preferable, and those that are linear alkyl groups are more preferable. In this specification, (meth)acrylic ester means acrylic ester and/or methacrylic ester.

The amount of the (meth)acrylic acid ester monomer is preferably 80% by mass or more and 100% by mass or less based on the total amount of monomer units constituting the polymer. Further, the weight average molecular weight of the hydrocarbon water repellent is preferably 100,000 or more, more preferably 500,000 or more. The hydrocarbon water repellent may be a copolymer of acrylic ester and methacrylic ester.

The hydrocarbon water repellent can be used as a water repellent composition in which hydrocarbon water repellent particles are dispersed in water. The water repellent composition may contain a surfactant and an organic solvent. As such a water repellent composition, for example, commercial products such as NeoSeed NR series (manufactured by NICCA CHEMICAL CO., LTD.) may be used.

In the water-repellent cellulose fiber such as the water-repellent regenerated cellulose fiber, the amount of the non-fluorine water repellent applied is preferably 0.1% by mass or more and 10% by mass or less based on 100% by mass of cellulose. , more preferably 0.2% by mass or more and 8% by mass or less, further preferably 0.3% by mass or more and 6% by mass or less, and even more preferably 0.5% by mass or more and 2% by mass or less. More preferred. When the amount of the non-fluorine water repellent applied is within the above range, the water repellency is good and the fibers are less likely to become rigid.

The non-fluorine water repellent may be used alone or in an appropriate combination of two or more.

The crosslinking agent is not particularly limited, but for example, it is preferable to use an isocyanate compound from the viewpoint of easily fixing the non-fluorine water repellent to the fiber surface. As the isocyanate compound, for example, a crosslinking agent such as a compound having an isocyanate group and a compound having a blocked isocyanate group can be used.

Examples of compounds having an isocyanate group include monoisocyanates such as butyl isocyanate, phenyl isocyanate, tolyl isocyanate, and naphthalene isocyanate, diisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, and hydrogenated diphenylmethane diisocyanate, and isocyanurate rings thereof. Examples include trimers and trimethylolpropane adducts.

Examples of the compound having a blocked isocyanate group include compounds obtained by protecting the isocyanate group of the above compound having an isocyanate group with a blocking agent. Blocking agents used at this time include organic blocking agents such as secondary or tertiary alcohols, active methylene compounds, phenols, oximes, and lactams, and bisulfite such as sodium bisulfite and potassium bisulfite. Examples include salt. In blocked isocyanate groups, highly reactive isocyanate groups are masked, and the blocks are usually dissociated by heat treatment at 120 to 180°C. Since it has one or more selected acidic groups, it is estimated that the blocks dissociate at a low temperature of 40° C. or higher and 110° C. or lower on the fiber surface. Therefore, the blocked isocyanate groups exist in a dissociated state on the surface of the water-repellent regenerated cellulose fiber.

In the water-repellent cellulose fiber such as the water-repellent regenerated cellulose fiber, the amount of the isocyanate compound attached is preferably, for example, 0.010% by mass or more and 5.0% by mass or less based on 100% by mass of cellulose. It is more preferably 0.020 mass% or more and 3.0 mass% or less, even more preferably 0.03 mass% or more and 2.0 mass% or less, and 0.05 mass% or more and 1.0 mass% or less. Even more preferably. When the amount of the non-fluorine water repellent applied is within the above range, the durability of water repellency (hereinafter also referred to as durable water repellency) will be good and the fibers will not easily become rigid.

The crosslinking agents such as the isocyanate compounds may be used alone or in an appropriate combination of two or more.

The mass ratio of the non-fluorine water repellent to the isocyanate compound (non-fluorine water repellent: isocyanate compound) is not particularly limited, but for example, from the viewpoint of improving water repellency and its durability, it is 3: The ratio is preferably 1 or more and 7:1 or less, more preferably 4:1 or more and 6:1 or less.

The water-repellent regenerated cellulose fibers are not particularly limited, but for example, a compound containing one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups is added to a viscose stock solution (raw material viscose) containing cellulose. A viscose liquid for spinning is prepared by mixing, the viscose liquid for spinning is extruded through a nozzle, and the viscose liquid is coagulated and regenerated to form a viscose rayon thread, and the viscose rayon thread is treated with an isocyanate compound and a non-fluorine water repellent. It can be produced by treating with a water-repellent treatment liquid containing a water-repellent agent and then heat-treating.

The raw material viscose may contain, for example, cellulose in a range of 7% by mass to 10% by mass, sodium hydroxide in a range of 5% by mass to 8% by mass, and carbon disulfide in a range of 2% by mass to 3.5% by mass. At this time, additives such as ethylenediaminetetraacetic acid (EDTA) and titanium dioxide may be used as necessary. The temperature of the raw material viscose is preferably kept at 18°C or higher and 23°C or lower.

The amount of the compound containing one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups may be 1% by mass or more and 35% by mass or less based on 100% by mass of cellulose in the raw material viscose. It is preferably 3% by mass or more and 30% by mass or less, and even more preferably 5% by mass or more and 25% by mass or less. Within the above range, a compound containing one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups can be effectively kneaded into the fibers while increasing the fiber strength.

The viscose rayon yarn can be produced using, for example, a normal circular nozzle. As the spinning nozzle, it is preferable to use a circular nozzle having a diameter of 0.05 mm or more and 0.12 mm or less and a hole number of 1000 or more and 20000 or less, although it depends on the desired production volume. Alternatively, a nozzle with an irregular cross section may be used. Using the spinning nozzle, the viscose liquid for spinning is extruded into a spinning bath to be spun and coagulated and regenerated. The spinning speed is preferably in the range of 30 m/min or more and 80 m/min or less. Further, the stretching ratio is preferably 39% or more and 55% or less. Here, the stretching ratio indicates how high the sliver speed after stretching is when the sliver speed before stretching is 100. In terms of magnification, before stretching it is 1, and after stretching it is 1.39 times or more and 1.55 times or less.

The spinning bath (Mueller bath) is, for example, a strong acid containing sulfuric acid of 95 g/L or more and 130 g/L or less, zinc sulfate of 10 g/L or more and 17 g/L or less, and sodium sulfate (Salt salt) of 290 g/L or more and 370 g/L or less. Preferably, a sex bath is used. A more preferable sulfuric acid concentration is 95 g/L or more and 120 g/L or less.

The viscose rayon yarn (regenerated cellulose fiber) obtained as described above is cut into a predetermined length and usually subjected to a scouring treatment. The scouring step can generally be performed in the order of hot water treatment, water washing, hydrosulfurization treatment (desulfurization), bleaching, pickling, and water washing. Note that bleaching and pickling may be omitted.

If necessary, the rayon fiber yarn after the scouring process may be subjected to a pH adjustment treatment to adjust the pH of the fiber to 7.0 or less. The pH adjustment process can be performed by immersing the fibers in a buffer solution with a pH of 6.0 or less. The bath ratio during immersion is not particularly limited, but is preferably 1:10 or more and 1:30 or less, more preferably 1:15 or more and 1:25 or less. The immersion time is not particularly limited, but is preferably 0.5 minutes or more and 50 minutes or less, more preferably 1 minute or more and 20 minutes or less. The pH adjusting buffer is not particularly limited, and for example, general buffer solutions such as acetic acid-sodium acetate buffer can be used, but it is preferable that the buffer solution contains sodium. . After being immersed in a pH adjusting buffer, it may be washed with water and then dried.

In the regenerated cellulose fiber (before water repellent finishing), the amount of H-type carboxyl groups and/or H-type sulfonic acid groups is preferably 0.20 mmol or more and 1.60 mmol/g or less, more preferably 0.30 mmol. /g or more and 1.50 mmol/g or less, more preferably 0.35 mmol/g or more and 1.40 mmol/g or less. Further, in the regenerated cellulose fiber, the amount of salt-type carboxyl groups and/or salt-type sulfonic acid groups is preferably 1.0 mmol/g or less, more preferably 0.35 mmol/g or less, and even more preferably It is 0.015 mmol/g or more and 0.20 mmol/g or less.

In the regenerated cellulose fiber (before water repellent finishing), the ratio of the amount of H-type carboxyl groups and/or H-type sulfonic acid groups to the total amount of carboxyl groups and/or sulfonic acid groups is 45% or more and 100% or less. It is preferably 80% or more and 98% or less, and even more preferably 90% or more and 95% or less. When the ratio of the amount of the H-type carboxyl group and/or the H-type sulfonic acid group is within the above-mentioned range, the carboxyl group and/or sulfonic acid group and the isocyanate group are likely to bond in the water repellent processing step described below, and The carboxyl group and/or sulfonic acid group acts as an acid catalyst, and the amine produced by the efficient reaction of the isocyanate group with water becomes more likely to undergo various side reactions, thereby improving durable water repellency.

After the scouring process, water repellent treatment is performed. First, the viscose rayon yarn is treated with a water repellent treatment solution containing a crosslinking agent such as an isocyanate compound and a non-fluorine water repellent to attach the isocyanate compound and the non-fluorine water repellent. The treatment method using the water-repellent treatment liquid is not particularly limited, and examples thereof include dipping, spraying, shower coating, and the like. The treatment with the water repellent treatment liquid is carried out under conditions where the moisture content of the viscose rayon yarn is 100% by mass or more and 180% by mass or less, from the viewpoint of easily adhering the isocyanate compound and the non-fluorine water repellent to the fibers. It is preferable to carry out under conditions where the moisture content is 120% by mass or more and 150% by mass or less.

In the water repellent treatment liquid, the non-fluorine water repellent and the isocyanate compound are dispersed in a solvent such as water. The concentration of the non-fluorine water repellent in the treatment liquid is not particularly limited, but is preferably 0.15% by mass or more and 40% by mass or less. More preferably, it is 0.35% by mass or more and 35% by mass or less. When the concentration of the treatment liquid is within the above range, it is easy to adjust the amount of the non-fluorinated water repellent and isocyanate compound attached, and the temperature of the fiber surface can be adjusted to a low temperature when solvents such as water are evaporated during heat treatment. Easy and desirable.

The amount of the non-fluorine water repellent used can be adjusted as appropriate depending on the degree of water repellency required, but the amount of the non-fluorine water repellent (as a water repellent) Even when a water repellent composition is used, it is preferable to adjust the content of non-fluorine water repellent (only non-fluorine water repellent) to 0.1% by mass or more and 10% by mass or less, and 0.2% by mass or more and 8.0% by mass or less. It is more preferable to adjust the amount to % by mass or less. When the amount of the non-fluorine water repellent applied is within the above range, water repellency can be easily imparted and the softness of the regenerated cellulose fibers can be maintained.

The amount of the isocyanate compound (for example, a crosslinking agent such as a compound having an isocyanate group and a compound having a blocked isocyanate group) to be used is not particularly limited, but from the viewpoint of easily maintaining the softness of the regenerated cellulose fiber, It is preferably 0.010% by mass or more and 5.0% by mass or less, and more preferably 0.02% by mass or more and 3.0% by mass or less, based on 100% by mass of the fibers.

In the water repellent treatment liquid, the mass ratio of the non-fluorinated water repellent to the isocyanate compound (non-fluorinated The ratio of fluorine water repellent to isocyanate compound is preferably 3:1 or more and 7:1 or less, more preferably 4:1 or more and 6:1 or less.

Next, by heat-treating the fibers, a non-fluorine water repellent is bonded to the fiber surface of the regenerated cellulose fibers using a crosslinking agent. The heat treatment is preferably performed under conditions such that the temperature of the fiber surface is 40° C. or higher and 110° C. or lower. A more preferable lower limit of the heat treatment temperature (actual temperature) is that the fiber surface is 50° C. or higher, and an even more preferable lower limit is that the fiber surface is 60° C. or higher. More preferably, the upper limit of the actual temperature is such that the fiber surface is less than 100°C, still more preferably 95°C or less, and still more preferably 90°C or less. When the heat treatment temperature is within the above range, the isocyanate compound and the non-fluorine water repellent are firmly bonded to the fibers, and deterioration of the fibers due to heat, such as yellowing of the fibers, can be suppressed. When the water-repellent treatment liquid contains water, the drying treatment performed to remove water can be heat treatment.

After the water repellent treatment, an oil agent may be applied as necessary to the extent that the water repellency is not impaired.

In the case of natural cellulose fibers, as in the case of regenerated cellulose fibers, a water repellent treatment may be performed after the refining process, and then an oil agent may be applied as necessary to the extent that the water repellency is not impaired. Alternatively, commercially available natural cellulose fibers may be used, subjected to water repellent treatment in the same manner as in the case of regenerated cellulose fibers, and then an oil agent may be applied as necessary to the extent that water repellency is not impaired.

The water-repellent regenerated cellulose fiber is not particularly limited, but preferably has a single fiber fineness of 0.3 dtex or more and 8.0 dtex or less, for example. More preferably, it is 0.6 dtex or more and 6.0 dtex or less, and still more preferably 0.7 dtex or more and 3.6 dtex or less. When the single fiber fineness is less than 0.3 dtex, single fiber breakage tends to occur during drawing. If the single fiber fineness exceeds 8.0 dtex, the regenerated state of the fibers tends to be poor, and the hue of the fibers may deteriorate.

The water-repellent regenerated cellulose fiber has a whiteness of Hw80 or more, and from the viewpoint of retaining the texture of cellulose, preferably Hw80 or more and Hw90 or less. In the case of general regenerated cellulose fibers, it is necessary to react with a crosslinking agent at 120°C or higher when applying water repellent treatment, and at 170°C or higher to improve water repellency durability. The temperature decreases significantly (Hw less than 80). In the present invention, since regenerated cellulose containing specific acidic groups is used, deterioration of cellulose can be suppressed, and as a result, whiteness tends to hardly decrease.

The water-repellent regenerated cellulose fiber preferably has a standard tensile strength (hereinafter also referred to as dry strength) of 1.5 cN/dtex or more and 3.0 cN/dtex or less, as measured according to JIS L 1015. More preferably, it is 1.7 cN/dtex or more and 2.7 cN/dtex or less. The tensile strength when wet (hereinafter also referred to as wet strength) is preferably 0.6 cN/dtex or more and 2.0 cN/dtex or less. More preferably, it is 0.8 cN/dtex or more and 1.8 cN/dtex or less.

The water-repellent regenerated cellulose fiber preferably has a standard elongation rate (hereinafter also referred to as dry elongation) of 15% or more and 25% or less, as measured according to JIS L 1015. More preferably, it is 16% or more and 24% or less. The elongation rate when wet (hereinafter also referred to as wet elongation) is preferably 15% or more and 40% or less. More preferably, it is 18% or more and 35% or less.

When the tensile strength and elongation rate are within the above ranges, spinnability is good and product strength tends to be good.

Normally, when applying water repellency to regenerated cellulose fibers, it is necessary to react with a crosslinking agent at 120°C or higher, and to improve water repellency durability, it is necessary to react with a crosslinking agent at 170°C or higher. As the water agent forms a film and cross-links strongly, the rigidity and strength of the entire fiber increases in standard conditions (dry state), but the strength of the cellulose itself decreases due to deterioration of the amorphous parts of cellulose due to heat. There is. Therefore, in addition to the strength of cellulose itself decreasing due to swelling due to water and cleavage of hydrogen bonds in amorphous portions, as in the case of humidity, the wet strength tends to decrease significantly due to the influence of deterioration due to heat. In the present invention, the cellulose has one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups, and can be treated with water repellency at a low temperature of 100°C or less, so the fibers are cross-linked. While the rigidity and strength of cellulose increases, there is less damage to the cellulose itself due to heat, and there is a tendency for the wet strength to decrease less.

The water-repellent regenerated cellulose fiber preferably has a standard apparent Young's modulus (hereinafter also referred to as dry Young's modulus (DY)) measured according to JIS L 1015 of 3500 MPa or more and 8500 MPa or less. More preferably, it is 4000 MPa or more and 8000 MPa or less. The apparent Young's modulus when wet (hereinafter also referred to as wet Young's modulus (WY)) is preferably 800 MPa or more and 1300 MPa or less. More preferably, it is 900 MPa or more and 1200 MPa or less. When the apparent Young's modulus is within the above range, appropriate stiffness can be imparted to the fiber while maintaining the softness of the fiber itself.

The ratio of wet/standard (wet/dry) in the apparent Young's modulus is expressed as a factor for firmly binding the water repellent while suppressing deterioration of cellulose itself, and is expressed by the following formula.
Wet and dry Young's modulus ratio = (WY/DY) x 100 (1)
The apparent Young's modulus indicates the initial tensile stiffness of the fiber, and the dry Young's modulus (DY) tends to increase due to the strength of the cellulose itself and the water repellent agent due to cross-linking. Young's modulus (WY) tends to decrease due to the swelling of cellulose due to water and the breaking of hydrogen bonds in the amorphous portion, which reduce the initial tensile stiffness, and the effect of deterioration of the amorphous portion due to heat. It is in. Therefore, as in the present invention, by suppressing the deterioration of cellulose, the decrease in WY is suppressed, and as a result, WY/DY tends to increase. WY/DY is preferably 12.0 or more. More preferably, it is 12.5 or more.

The hydrophilic cellulose fibers may have a settling time of 60 seconds or less, but from the viewpoint of excellent hydrophilicity, the settling time is preferably 50 seconds or less, more preferably 40 seconds or less, and 30 seconds or less. It is even more preferable.

As the hydrophilic cellulose fibers, natural cellulose fibers, regenerated cellulose fibers, purified cellulose fibers, etc. can be used as appropriate. Examples of natural cellulose fibers include cotton, silk, wool, hemp, and pulp. Examples of the regenerated cellulose fiber include rayon and cupro. Examples of purified cellulose fibers include Tencel and Lyocell. Among these, the hydrophilic cellulose fibers are preferably regenerated cellulose fibers from the viewpoint of easy availability and further reducing the feeling of stuffiness.

The fibers constituting the first fiber layer are not particularly limited, but, for example, it is preferable that each fiber has a single fiber fineness of 0.5 dtex or more and 6.0 dtex or less. From the viewpoint of making the texture smooth, the single fiber fineness is preferably 5.0 dtex or less, more preferably 4.0 dtex or less. From the viewpoint of increasing liquid permeability, the single fiber fineness is preferably 0.6 dtex or more, more preferably 0.8 dtex or more.

The fibers constituting the first fiber layer are not particularly limited, and the fiber length is preferably 1 mm or more and 100 mm or less. In particular, in the case of a carded web, the fiber length is preferably 25 mm or more and 100 mm or less, more preferably 30 mm or more and 80 mm or less, and even more preferably 30 mm or more and 60 mm or less, in consideration of card passability.

A fibrous web can be used as the first fibrous layer. Examples of the fibrous web include carded webs such as parallel webs, semi-random webs, random webs, cross webs, and criss-cross webs, air-laid webs, wet-laid webs, and the like. Since the topsheet for absorbent articles is required to have bulkiness, flexibility, a certain amount of voids between fibers, and an appropriate porosity, the fibrous web is preferably a carded web.

Although not particularly limited, the first fiber layer preferably has a basis weight of 5 g/m ² or more and 30 g/m 2 or less, more preferably 7 g/m ² or more and 25 g/m ² or less, from the viewpoint of improving the intertwining properties of the constituent fibers. m ² or less, more preferably 10 g/m ² or more and 20 g/m ² or less.

Specifically, the second fiber layer may consist of 90% by mass or more of hydrophilic cellulose fibers and 100% by mass or less, and 0% by mass or more of water-repellent cellulose fibers and 10% by mass or less, and 95% by mass or less of hydrophilic cellulose fibers. The water-repellent cellulose fiber may be comprised of 0 to 5 mass % of water-repellent cellulose fibers. The second fiber layer is preferably made of 100% by mass of hydrophilic cellulose fibers from the viewpoint of better liquid diffusivity. The hydrophilic cellulose fibers and water-repellent cellulose fibers are not particularly limited, and the hydrophilic cellulose fibers and water-repellent cellulose fibers described in the first fiber layer can be used as appropriate.

In the second fiber layer, the hydrophilic cellulose fiber has a single fiber fineness of 0.5 dtex or more and 3.5 dtex or less. As a result, the liquid that has passed through the first fiber layer is easily diffused in the second fiber layer, improving liquid diffusibility and improving liquid permeability. Preferably, the fibers constituting the second fiber layer all have a single fiber fineness of 0.5 dtex or more and 3.5 dtex or less. When the single fiber fineness of all the fibers constituting the second fiber layer is within the above range, liquid diffusivity is further improved. From the viewpoint of further improving liquid diffusivity, the fibers constituting the second fiber layer preferably have a single fiber fineness of 3.3 dtex or less, further preferably 2.0 dtex or less, and 1. It is even more preferably .5 dtex or less, and particularly preferably 1.1 dtex or less. From the viewpoint of further improving liquid permeability, it is more preferable that the single fiber fineness is 0.6 dtex or more.

The fibers constituting the second fiber layer are not particularly limited, and the fiber length is preferably 1 mm or more and 100 mm or less. In particular, in the case of a carded web, the fiber length is preferably 25 mm or more and 100 mm or less, more preferably 30 mm or more and 80 mm or less, and even more preferably 30 mm or more and 60 mm or less, in consideration of card passability.

A fibrous web can be used as the second fibrous layer. Examples of the fibrous web include carded webs such as parallel webs, semi-random webs, random webs, cross webs, and criss-cross webs, air-laid webs, wet-laid webs, and the like. Since the topsheet for absorbent articles is required to have bulkiness, flexibility, a certain amount of voids between fibers, and an appropriate porosity, the fibrous web is preferably a carded web.

Although not particularly limited, the second fiber layer preferably has a basis weight of 5 g/m ² or more and 30 g/m 2 or less, more preferably 7 g/m ² or more and 25 g/m ² or less, from the viewpoint of increasing the entanglement of the constituent fibers. m ² or less, more preferably 10 g/m ² or more and 20 g/m ² or less.

The fibers constituting the first fiber layer and the fibers constituting the second fiber layer are partially intertwined. Here, "partially entangled" means that the fibers constituting the first fiber layer and the fibers constituting the second fiber layer are the same as the first fiber layer and the second fiber in the thickness direction of the hydroentangled nonwoven fabric. This means that the layers are partially entangled at the interface. This increases liquid permeability and liquid diffusivity. In addition, the hydroentangled nonwoven fabric has a laminated structure of the first fiber layer and the second fiber layer, so that the effects of the respective fiber configurations of the first fiber layer and the second fiber layer are suitably exerted, and the first fiber layer Since the constituent fibers of the layer and the second fiber layer are partially intertwined at the interface between the two layers, a synergistic effect due to the fiber configurations of the first fiber layer and the second fiber layer can also be suitably exhibited.

The hydroentangled nonwoven fabric is, for example, a laminate obtained by laminating a first fiber layer containing 90% by mass or more of water-repellent cellulose fibers and a second fiber layer containing 90% by mass or more of hydrophilic cellulose fibers. Spray a water stream to partially entangle the fibers that make up the first fiber layer, the fibers that make up the second fiber layer, and the fibers that make up the first fiber layer and the fibers that make up the second fiber layer. It can be made by

The hydroentangling process involves partially entangling the fibers that make up the first fiber layer, the fibers that make up the second fiber layer, and the fibers that make up the first fiber layer and the fibers that make up the second fiber layer. The specific conditions are not particularly limited as long as it can be done.

The hydroentangling treatment can be carried out, for example, by placing the laminate on a support and spraying a water stream onto one or both sides of the laminate. There are no particular restrictions on the form of the support, and any known support may be used, but for example, the warp has a diameter of 0.05 mm or more and 1.5 mm or less, and the weft has a diameter of 0.05 mm or more and 1.5 mm. Hereinafter, a plain weave net having a mesh count of 5 or more and 110 or less can be used. A water flow with a water pressure of 1.0 MPa or more and 10.0 MPa or less is applied to one or both sides of the laminate from a nozzle in which orifices with a hole diameter of 0.05 mm or more and 0.5 mm or less are provided at intervals of 0.5 mm or more and 1.5 mm or less. Each can be injected once or more and four times or less. If the water pressure is less than 1.0 MPa, the fibers may not be sufficiently entangled with each other, and the obtained nonwoven fabric may easily become fluffy. When the water pressure exceeds 10.0 MPa, the intertwining of the fibers becomes too strong, and the texture of the nonwoven fabric may deteriorate. The water pressure is more preferably 1.5 MPa or more and 9.0 MPa or less, still more preferably 2.0 MPa or more and 7.0 MPa or less, and even more preferably 2.0 MPa or more and 6.0 MPa or less. The distance between the nozzle and the laminate may be, for example, 5 mm or more and 30 mm or less, or 7 mm or more and 20 mm or less.

Specifically, from the viewpoint of improving the uniformity of entanglement, first, the laminate is placed on a support, and a water stream with a water pressure of 1.0 MPa or more and 10.0 MPa or less is applied from the surface of the second fiber layer of the laminate. By injecting 1 to 4 times, the constituent fibers of the first fiber layer and the constituent fibers of the second fiber layer are entangled with each other, and the constituent fibers of the first fiber layer and the constituent fibers of the second fiber layer are intertwined with each other. The constituent fibers are partially entangled. Thereafter, if necessary, a water stream having a water pressure of 1.0 MPa or more and 10.0 MPa or less may be injected once or more and four times or less from the surface of the first fiber layer of the laminate. Thereafter, if necessary, a water stream having a water pressure of 1.0 MPa or more and 10.0 MPa or less may be injected once or more and four times or less from the surface of the second fiber layer of the laminate.

Next, the hydroentangled nonwoven fabric obtained by hydroentangling is dried. The drying process can be carried out using a contact type dryer (eg, iron type, roll type, etc.) or a non-contact type dryer (eg, hot air type, etc.). For example, drying is preferably performed at a temperature of 60°C or more and 180°C or less, more preferably 100°C or more and 170°C or less, and even more preferably 130°C or more and 160°C or less. Further, the drying time is not particularly limited, and may be, for example, 5 seconds or more and 5 minutes or less, 5 seconds or more and 1 minute or less, or 5 seconds or more and 20 seconds or less.

The hydroentangled nonwoven fabric preferably has a water absorption rate indicating liquid permeability of 30.0 seconds or less, more preferably 25.0 seconds or less, and even more preferably 20.0 seconds or less. The water absorption rate is measured as described below.

The hydroentangled nonwoven fabric preferably has a diffusion area exhibiting liquid diffusivity of 40.0 cm ² or more, more preferably 45.0 cm ² or more, and even more preferably 50.0 cm ² or more. Diffusion area is measured as described below.

The liquid return rate of the hydroentangled nonwoven fabric is preferably 12.0% or less, more preferably 10.0% or less, and even more preferably 8.0% or less. The liquid return rate is measured as described below.

The surface sheet for an absorbent article can be suitably used as a top sheet of an absorbent article. It can also be suitably used for a so-called second sheet located directly below the top sheet. By using the above-mentioned top sheet for an absorbent article as a top sheet and/or a second sheet, especially a top sheet, it is possible to provide a comfortable feeling to the user of the absorbent article.

Specifically, the surface sheet for absorbent articles is used for sanitary napkins, disposable diapers for infants, disposable diapers for adults, disposable diapers for animals including mammals, panty liners (vaginal discharge sheets), incontinence liners, etc. It can be preferably used as a top sheet (top sheet and/or second sheet) of various absorbent articles.

The absorbent article of the present invention is not particularly limited as long as it includes the above-mentioned top sheet for an absorbent article and has a first fiber layer disposed on the user's skin side. Examples include sanitary napkins, disposable diapers for infants, disposable diapers for adults, disposable diapers for animals including mammals, panty liners (vaginal discharge sheets), liners for incontinence, and the like.

Hereinafter, the present invention will be explained in more detail with reference to Examples. The present invention is not limited to the following examples.

First, the measurement methods used in Examples and Comparative Examples will be explained.

(Measurement of weight average molecular weight)
The weight average molecular weight (Mw) was determined by GPC (gel permeation chromatography) under the following conditions. When calculating the weight average molecular weight, the part having a molecular weight of 300 or more on the chart obtained by GPC was defined as a polymer.
Column: GF-7MHQ (manufactured by Showa Denko Co., Ltd.).
Mobile phase: Add pure water to 34.5 g of disodium hydrogen phosphate dodecahydrate and 46.2 g of sodium dihydrogen phosphate dihydrate (both reagent grade) to make a total amount of 5,000 g, and then Aqueous solution filtered through a 0.45 micron membrane filter.
Detector: UV 214 nm (manufactured by Nippon Waters Co., Ltd., Model 481).
Pump: L-7110 (manufactured by Hitachi, Ltd.).
Flow rate: 0.5mL/min.
Temperature: 35℃.
Calibration curve: Sodium polyacrylate standard sample (manufactured by Sowa Kagaku Co., Ltd.).

(Measurement of total amount of carboxyl groups)
(1) 1.2 g of a sample was immersed in 50 mL of a 1 mol/L hydrochloric acid aqueous solution (pH 0.1), stirred, and left for 5 minutes. Thereafter, the solution was stirred again to adjust the pH of the aqueous solution to 2.5. As a result, all carboxyl groups in the sample (fiber) exist as H-type. Next, the sample was washed with water and dried in a constant temperature blow dryer at 105° C. for 2 hours to make it completely dry. By washing the sample with water, all excess hydrochloric acid adhering to the fibers will be removed.
(2) 100 mL of ion-exchanged water, 0.4 g of sodium chloride, and 20 mL of a 0.1 mol/L aqueous sodium hydroxide solution were placed in a beaker.
(3) Precisely weigh 1 g of the sample prepared in (1) [W1 (g)], cut it into small pieces that will not wrap around the stirrer, put it in the beaker prepared in (2), and stir with a stirrer for 15 minutes. did. As a result, all carboxyl groups in the sample (fiber) are converted into salt forms. The stirred sample was filtered by suction. 60 mL of the filtrate was taken and titrated with a 0.1 mol/L aqueous hydrochloric acid solution using phenolphthalein as an indicator to give a titration amount of X1 (mL).
(4) The total amount of carboxyl groups Y (mmol/g) was calculated based on the following formula. Thus, the amount of sodium hydroxide determined by subtracting the remaining amount of sodium hydroxide from the total amount of sodium hydroxide corresponds to the total amount of carboxyl groups in the sample (fiber).
Total amount of carboxyl groups Y (mmol/g) = [[(0.1×20)-(0.1×X1)]×(120/60)]/W1

(Measurement of the amount of H-type carboxyl groups and the amount of salt-type carboxyl groups)
(1) The sample was washed with water and dried at 105° C. for 2 hours in a constant temperature blow dryer to dry completely.
(2) 100 mL of ion-exchanged water, 0.4 g of sodium chloride, and 20 mL of a 0.1 mol/L aqueous sodium hydroxide solution were placed in a beaker.
(3) 1 g of the sample was accurately weighed [W2 (g)], cut into pieces to a size that would not wrap around the stirrer, placed in the beaker prepared in (2), and stirred with a stirrer for 15 minutes. The stirred sample was filtered by suction. 60 mL of the filtrate was taken and titrated with a 0.1 mol/L aqueous hydrochloric acid solution using phenolphthalein as an indicator to give a titration amount of X2 (mL).
(4) Based on the following formula, the amount Z (mmol/g) of H-type carboxyl groups, the amount U (mmol/g) of salt-type carboxyl groups, the ratio (%) of the amount of H-type carboxyl groups, and the salt-type carboxyl groups The proportion (%) of the amount was calculated.
Amount of H-type carboxyl group Z (mmol/g) = [{(0.1×20)-(0.1×X2)]×(120/60)]/W2
Amount of salt-type carboxyl groups U (mmol/g) = Total amount of carboxyl groups Y (mmol/g) - Amount of H-type carboxyl groups Z (mmol/g)
Ratio (%) of the amount of H-type carboxyl group = {Amount Z of H-type carboxyl group (mmol/g)]
/{total amount of carboxyl groups Y (mmol/g)]×100
Ratio (%) of the amount of salt-type carboxyl groups = {Amount U of salt-type carboxyl groups (mmol/g)]
/{total amount of carboxyl groups Y (mmol/g)]×100

(Fiber whiteness)
The whiteness of the fibers was measured according to JIS Z 8722 using a "color difference meter CR-410" manufactured by Konica Minolta, Inc. Using the defined XYZ color system (Yxy color system) Y, x, y, the whiteness was calculated from the following formula.
Whiteness = (1-x-y) x Y/1.18 x y

(settling time)
According to JIS L 1907 7.1.3 (sedimentation method), the sedimentation time of cellulose fibers was measured according to the following procedure.
(1) 5g of fibers were collected and lightly defibrated by hand to obtain sample fibers.
(2) The sample fibers were floated on 1 L of water.
(3) The time required for the sample fibers to become wet and for all the sample fibers to settle was measured and defined as the settling time.

(liquid diffusivity)
0.5 mL of colored water (0.05 g of blue dye dissolved in 50 mL of water) was dropped from 1 cm above the surface of the first fiber layer of the hydroentangled nonwoven fabric, and completely penetrated. Since the trace of the water droplets passing through was circular, a square was drawn inscribed in the circle, and its area was measured and determined as the diffusion area. The larger the diffusion area, the better the liquid diffusibility.

(liquid permeability)
Peel off the top sheet from a commercially available diaper, place the hydroentangled nonwoven fabric on top of it with the first fiber layer side facing the skin, and place a transparent cylinder (height 10 cm, inner diameter 1.9 cm, outer diameter 2 .2 cm), put 10 g of colored water (0.05 g of blue dye dissolved in 50 mL of water) into the cylinder, and the colored water completely permeated the hydroentangled nonwoven fabric and was observed from the surface of the hydroentangled nonwoven fabric. The time until the water was absorbed was measured and defined as the water absorption rate. The faster the water absorption rate, the better the liquid permeability.

(liquid return rate)
After the liquid permeability test, a stack of 10 filter papers (manufactured by Toyo Roshi Co., Ltd., trade name ADVANTEC (registered trademark) No. 2, 10 cm x 10 cm) was weighed (W0) and placed on the hydroentangled nonwoven fabric. A 1 kg weight (shape: square, 10 cm x 10 cm) was placed on top and the weight was applied for 5 minutes. Thereafter, 10 stacked filter papers were weighed (W1), and the liquid return rate was calculated using the following formula. Note that the unit of W0 and W1 is g.
Liquid return rate (%) = (W1-W0)/10 (g) x 100

[Production example 1 of water-repellent regenerated cellulose fiber]
《Preparation of viscose liquid for spinning》
Aqueous solution of acrylic acid-maleic acid copolymer salt ("Aqualic TL400" manufactured by Nippon Shokubai Co., Ltd., an aqueous solution containing 40% by mass of sodium acrylic acid-maleic acid copolymer with a weight average molecular weight of 50,000, viscosity: 1990 mPa. s, the content of maleic acid in the sodium acrylic acid-maleic acid copolymer is 45% by mass), so that the acrylic acid-maleic acid copolymer salt is 5% by mass with respect to 100% by mass of cellulose, It was added to the raw material viscose and stirred and mixed using a mixer to prepare a viscose liquid for spinning. The temperature was kept at 20°C. The raw material viscose contained 8.5% by mass of cellulose, 5.7% by mass of sodium hydroxide, and 2.8% by mass of carbon disulfide. In addition, in the Examples and Comparative Examples, the viscosity was measured at 20° C. using a B-type viscometer manufactured by Tokyo Keiki Co., Ltd. Moreover, the weight average molecular weight of the compound containing a carboxyl group was measured and calculated as described below.
《Spinning process》
The obtained viscose liquid for spinning was spun by a two-bath tension spinning method at a spinning speed of 50 m/min and a drawing rate of 50% to obtain a viscose rayon yarn with a fineness of 1.4 dtex. As the first bath (spinning bath), a Mueller bath (50° C.) containing 100 g/L of sulfuric acid, 15 g/L of zinc sulfate, and 350 g/L of sodium sulfate was used. Further, a circular nozzle (pore diameter: 0.06 mm, number of holes: 4000) was used as a spinneret for discharging viscose.
《Scouring process》
The viscose rayon yarn obtained above was cut into fiber lengths of 40 mm, treated with hot water, washed with water, and desulfurized by showering with sodium hydrogen sulfide. The obtained treated cotton was washed again with water, bleached with sodium hypochlorite, pickled, and then washed with water. Thereafter, the fibers were squeezed using a compression roller so that the moisture content was 130%. In the regenerated cellulose fiber (before water-repellent finishing), the ratio of H-type carboxyl groups to the total amount of carboxyl groups was 94%, and the amount of H-type carboxyl groups was 0.53 mmol/g.
《Water repellent finishing》
First, a hydrocarbon water repellent composition (NeoSeed NR-158, manufactured by NICCA Chemical Co., Ltd.) was used as a non-fluorine water repellent, and a blocked isocyanate crosslinking agent (manufactured by NICCA Chemical Co., Ltd.) was used as an isocyanate compound. "NK Assist NY-30" (solid content concentration 40% by mass) was used to repel water by mixing the water repellent (water repellent particles): crosslinking agent (solid content) at a mass ratio of 5:1. A processing liquid was obtained. Next, the fibers obtained above with a moisture content of 130% were immersed in a water repellent treatment solution (50° C.) for 30 seconds. The bath ratio of fiber: water repellent treatment solution was 1:10. Thereafter, the fibers were squeezed using a compression roller so that the adhesion rate of the water repellent agent (solid content) to the fibers was 1% by mass, and then dried for 10 minutes in a dryer set at 100°C to obtain fiber A. Obtained. The actual temperature at this time was 85°C. The total amount of carboxyl groups in the obtained water-repellent regenerated cellulose fiber was 0.52 mmol/g.

The cellulose fibers used in Examples and Comparative Examples are as follows.
(1) Water-repellent cellulose fiber 1: Fiber A (water-repellent regenerated cellulose fiber), single fiber fineness 1.7 dtex, fiber length 40 mm, settling time longer than 5 minutes, whiteness Hw 84, dry strength 20.4 cN/dtex, wet Strength 1.13 cN/dtex, dry elongation 20.4%, wet elongation 26.7%, standard apparent Young's modulus 7040 MPa, wet apparent Young's modulus 1034 MPa, wet/dry Young's modulus ratio 14.7,
(2) Hydrophilic cellulose fiber 1: Rayon fiber, single fiber fineness 1.7 dtex, fiber length 40 mm, settling time 20.94 seconds (3) Hydrophilic cellulose fiber 3: Rayon fiber, single fiber fineness 1.4 dtex, fiber length 40 mm, settling time 20.31 seconds (4) Hydrophilic cellulose fiber 3: Rayon fiber, single fiber fineness 0.9 dtex, fiber length 40 mm, settling time 13.82 seconds

(Examples 1 to 3)
Using the water-repellent cellulose fiber 1, a fibrous web having a basis weight of 20 g/m ² was produced using a semi-random card machine and used as the first fibrous layer.
Using the hydrophilic cellulose fibers shown in Table 1, a fibrous web with a basis weight of 20 g/m ² was produced using a semi-random card machine and used as the second fibrous layer.
The first fiber layer was laminated on the second fiber layer, and the resulting laminate was subjected to hydroentanglement treatment. In the hydroentangling treatment, the laminate is placed on a 90-mesh plain weave support made of monofilament with a wire diameter of 0.132 mm, and a second A columnar water stream of 3 MPa is injected once from the surface of the fiber layer, then a columnar water stream of 5 MPa is injected once from the surface of the first fiber layer, and a columnar water stream of 5 MPa is further injected once from the surface of the second fiber layer. It was carried out. The speed of the support at this time was 4 m/min, and the distance between the nozzle and the laminate was 10 mm.
After hydroentangling, the surface of the first fiber layer of the laminate was dried by applying an iron at 150° C. for 10 seconds to obtain a hydroentangled nonwoven fabric.

(Comparative Examples 1-2)
A fibrous web having a basis weight of 40 g/m ² was produced using a semi-random card machine using the hydrophilic cellulose shown in Table 1 below.
A columnar water stream of 3 MPa is injected once from the first side of the fiber web, then a columnar water stream of 5 MPa is injected once from the second side, and a columnar water stream of 5 MPa is further injected once from the first side. The hydroentanglement treatment was carried out in the same manner as in Example 1 except for the following.
After hydroentangling, the first side of the fibrous web was dried by applying an iron at 150° C. for 10 seconds to obtain a hydroentangled nonwoven fabric.

(Comparative Examples 3-4)
Comparative Example 1 except that 50 parts by mass of water-repellent cellulose fiber 1 and 50 parts by mass of hydrophilic cellulose shown in Table 2 below were mixed to produce a fiber web with a basis weight of 40 g/m ² using a semi-random card machine. A hydroentangled nonwoven fabric was produced in the same manner.

(Comparative example 5)
Using water-repellent cellulose fiber 1, a fibrous web with a basis weight of 20 g/m ² was produced using a semi-random card machine, and a first hydroentangled nonwoven fabric was produced in the same manner as in Comparative Example 1, except that this fibrous web was used. Obtained.
A fibrous web with a basis weight of 20 g/m ² was produced using a semi-random card machine using the hydrophilic cellulose fiber 3, and a second hydroentangled nonwoven fabric was produced in the same manner as in Comparative Example 1, except that this fibrous web was used. Obtained.
The first hydroentangled nonwoven fabric was laminated on the second hydroentangled nonwoven fabric to obtain a laminated hydroentangled nonwoven fabric.

The liquid diffusivity, liquid permeability, and liquid return rate of the hydroentangled nonwoven fabrics of Examples and Comparative Examples were measured as described above, and the results are shown in Tables 1 and 2 below.

As can be seen from Table 1, in Examples 1 to 3, hydroentangled nonwoven fabrics (surface sheets for absorbent articles) having liquid permeability, good liquid diffusivity, and reduced liquid return rate were obtained. . In addition, the hydroentangled nonwoven fabrics of Examples 1 to 3 are composed of 100% by mass of cellulose fibers, so they have a soft texture and are environmentally friendly.

On the other hand, as can be seen from Table 2, the hydroentangled nonwoven fabrics made of hydrophilic cellulose fibers of Comparative Examples 1 and 2 had poor liquid diffusivity and high liquid return rates. Furthermore, the hydroentangled nonwoven fabrics prepared by blending water-repellent cellulose fibers and hydrophilic cellulose fibers of Comparative Examples 3 and 4 also had poor liquid diffusivity and high liquid return rates. In the laminated nonwoven fabric of Comparative Example 5 in which a hydroentangled nonwoven fabric made of water-repellent cellulose fiber 1 and a hydroentangled nonwoven fabric made of hydrophilic cellulose fiber 3 were laminated, water remained on the nonwoven fabric and did not absorb water.

The surface sheet for absorbent articles of the present invention can be used for various absorbent products such as sanitary napkins, disposable diapers for infants, disposable diapers for adults, disposable diapers for animals including mammals, panty liners (vaginal discharge sheets), and incontinence liners. It can be suitably used as a top sheet (top sheet and/or second sheet) of an article.

Claims (8)

A surface sheet for an absorbent article composed of a hydroentangled nonwoven fabric,
The hydroentangled nonwoven fabric is made of 100% by mass of cellulose fibers, and includes a first fiber layer that is placed on the skin side during use, and a second fiber layer that is placed in contact with the first fiber layer,
The first fibrous layer contains 90% by mass or more of water-repellent cellulose fibers, the second fibrous layer contains 90% by mass or more of hydrophilic cellulose fibers, and the fibers constituting the first fibrous layer and the second fibrous layer are The constituent fibers are partially intertwined,
The water-repellent cellulose fiber is a water-repellent regenerated cellulose fiber, and the water-repellent regenerated cellulose fiber contains one or more acidic groups selected from the group consisting of carboxyl groups and sulfonic acid groups kneaded into the fibers. Contains a compound, a crosslinking agent and a non-fluorine water repellent are bonded to the fiber surface,
A surface sheet for an absorbent article, wherein the hydrophilic cellulose fiber has a single fiber fineness of 0.5 dtex or more and 3.5 dtex or less. The topsheet for an absorbent article according to claim 1, wherein the non-fluorine water repellent is a hydrocarbon water repellent. The surface sheet for an absorbent article according to claim 2 , wherein the carboxyl group-containing compound is one or more selected from the group consisting of polyacrylic acid and acrylic acid-maleic acid copolymer. The surface sheet for a water-repellent absorbent article according to any one of claims 1 to 3 , wherein the water-repellent cellulose fiber has a whiteness of Hw80 or more. A method for producing a surface sheet for an absorbent article according to any one of claims 1 to 4 , comprising:
Laminating a first fiber layer containing 90% by mass or more of water-repellent cellulose fibers and a second fiber layer containing 90% by mass or more of hydrophilic cellulose fibers,
A water stream is sprayed on one or both sides of the obtained laminate to form the fibers constituting the first fiber layer, the fibers constituting the second fiber layer, and the fibers constituting the first fiber layer and the second fiber layer. 1. A method for producing a topsheet for an absorbent article, the method comprising a hydroentangling step of partially intertwining fibers. The production of a topsheet for an absorbent article according to claim 5 , wherein in the hydroentangling step, a water jet is jetted onto the surface of the second fiber layer of the laminate, and then a water jet is jetted onto the surface of the first fiber layer of the laminate. Method. An absorbent article comprising the topsheet for an absorbent article according to any one of claims 1 to 4 , wherein the first fiber layer is disposed on the user's skin side. The absorbent article according to claim 7 , wherein the absorbent article surface sheet is arranged as a top sheet.