JP6775051B2 - Absorbent article - Google Patents

Description

The present invention relates to absorbent articles.

Conventionally, an absorber containing water-absorbent resin particles has been used as an absorbent article for absorbing a liquid containing water as a main component such as urine. For example, Patent Document 1 below is a method for producing water-absorbent resin particles having a particle size preferably used for absorbent articles such as diapers, and Patent Document 2 is effective for containing body fluids such as urine. A method of using a hydrogel-absorbing polymer having specific salt water flow inducibility, performance under pressure, etc. as a specific absorbent member is disclosed.

Japanese Unexamined Patent Publication No. 6-345819 Special Table 9-510889 Gazette

In the absorbent article using the conventional absorbent body, there is room for improvement in terms of leakability that the liquid to be absorbed leaks to the outside of the absorbent article.

An object of the present invention is to provide an absorbent article in which liquid leakage is suppressed.

One aspect of the invention provides an absorbent article comprising a liquid impermeable sheet, an absorber, and a liquid permeable sheet. The liquid permeable sheet, the absorber and the liquid permeable sheet are arranged in this order. The absorber contains water-absorbent resin particles, and the 30-second value of the non-pressurized DW of the water-absorbent resin particles is 1.0 mL / g or more, and the measurement is performed in the order of i) and ii) below. The contact angle of the water-absorbent resin particles is 90 degrees or less.
i) At 25 ° C., spherical droplets corresponding to a diameter of 3.0 ± 0.1 mm of 25% by mass saline solution are dropped onto the surface of the layer made of water-absorbent resin particles, and the water-absorbent resin particles and the droplets are dropped. To make contact with.
ii) The contact angle of the droplet is measured 30 seconds after the droplet comes into contact with the surface.

The contact angle of the water-absorbent resin particles may be 70 degrees or less.

The liquid permeable sheet includes a thermal bond non-woven fabric, an air-through non-woven fabric, a resin bond non-woven fabric, a spun bond non-woven fabric, a melt blow non-woven fabric, an air-laid non-woven fabric, a spunlace non-woven fabric, a point-bond non-woven fabric, or a laminate of two or more kinds of non-woven fabrics selected from these. You can go out.

The absorber may further contain fibrous material. The absorbent article may further include a core wrap that at least covers the surface side of the absorber in contact with the liquid permeable sheet. The absorber may be adhered to a liquid permeable sheet. The water retention amount of the physiological saline of the water-absorbent resin particles may be 30 to 55 g / g.

According to the present invention, it is possible to provide an absorbent article in which liquid leakage is suppressed.

It is sectional drawing which shows an example of an absorbent article. It is the schematic which shows the measuring apparatus of the 30-second value of unpressurized DW. It is a schematic diagram which shows the method of evaluating the liquid leakage property of an absorbent article.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

In the present specification, "acrylic" and "methacryl" are collectively referred to as "(meth) acrylic". Similarly, "acrylate" and "methacrylate" are also referred to as "(meth) acrylate". In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range of one step can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range of another step. In the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. “A or B” may include either A or B, or both. "Water-soluble" means that it exhibits a solubility in water of 5% by mass or more at 25 ° C. The materials exemplified in the present specification may be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified.

Hereinafter, embodiments will be described in detail with reference to the drawings. In the following description, the same or corresponding parts will be designated by the same reference numerals, and duplicate description will be omitted. Further, unless otherwise specified, the positional relationship such as up, down, left, and right shall be based on the positional relationship shown in the drawings. Furthermore, the dimensional ratios in the drawings are not limited to the ratios shown.

FIG. 1 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in FIG. 1 includes an absorber 10, core wraps 20a and 20b for retaining the shape of the absorber, and a liquid permeable sheet 30 arranged on the outermost side on the side where the liquid to be absorbed enters. A liquid permeable sheet 40 is provided on the outermost side opposite to the side on which the liquid to be absorbed is infiltrated. Examples of the absorbent article 100 include diapers (for example, paper diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat pads, pet sheets, simple toilet materials, animal excrement treatment materials, and the like. Be done.

In the absorbent article 100, the liquid permeable sheet 40, the core wrap 20b, the absorbent body 10, the core wrap 20a, and the liquid permeable sheet 30 are laminated in this order. In FIG. 1, there is a portion shown so that there is a gap between the members, but the members may be in close contact with each other without the gap.

[Absorber]
The absorber 10 has a water-absorbent resin particle 10a and a fiber layer 10b containing a fibrous material. The water-absorbent resin particles 10a are dispersed in the fiber layer 10b. The absorber 10 is, for example, a mixture containing the water-absorbent resin particles 10a and the fibrous material 10b. The structure of the absorber 10 may be, for example, a structure in which the water-absorbent resin particles 10a and the fibrous material 10b are uniformly mixed, and the water-absorbent resin particles are formed between the fibrous material 10b formed in a sheet or layer. The configuration may be such that 10a is sandwiched, or other configurations may be used.

The mass ratio of the water-absorbent resin particles 10a in the absorber 10 is 2 to 100% by mass, 10 to 80% by mass, or 20 to 60% by mass with respect to the total of the water-absorbent resin particles 10a and the fibrous material 10b. Good.

The shape of the absorber 10 is not particularly limited and may be, for example, a sheet. The thickness of the absorber 10 (for example, the thickness of the sheet-shaped absorber) may be, for example, 0.1 to 20 mm or 0.3 to 15 mm.

The 30-second value of the non-pressurized DW of the water-absorbent resin particles 10a is 1.0 mL / g or more. The 30-second value of non-pressurized DW is 2.0 mL / g or more, 3.0 mL / g or more, 4.0 mL / g or more, 5.0 mL / g or more, from the viewpoint of further suppressing liquid leakage. It may be 6.0 mL / g or more, 7.0 mL / g or more, 8.0 mL / g or more, 9.0 mL / g or more, or 9.5 mL / g or more, 15 mL / g or less, 12 mL / g or less, Alternatively, it may be 10 mL / g or less. The 30-second value of the non-pressurized DW is a value measured by the measuring method described in Examples described later.

The contact angle of the water-absorbent resin particles 10a measured in the tests performed in the order of i) and ii) below is 90 degrees or less.
i) At 25 ° C., spherical droplets having a diameter of 3.0 ± 0.1 mm of 25% by mass saline solution are dropped onto the surface of the layer made of the water-absorbent resin particles 10a to form the water-absorbent resin particles 10a. Contact with droplets.
ii) The contact angle of the droplet is measured 30 seconds after the droplet comes into contact with the surface.

The contact angle may be 80 degrees or less, 70 degrees or less, 60 degrees or less, 50 degrees or less, or 40 degrees or less from the viewpoint of further suppressing liquid leakage. Further, the contact angle may be 0 degrees or more, may exceed 0 degrees, or may be 10 degrees or more, or 20 degrees or more.

The contact angle is a value measured according to JIS R 3257 (1999) "Wetting property test method for the surface of the base glass", and specifically, it is measured by the method described in Examples described later.

The water-absorbent resin particles 10a can have a high water-absorbing ability with respect to physiological saline. The water retention amount of the physiological saline of the water-absorbent resin particles 10a may be, for example, 20 to 60 g / g, 25 to 55 g / g, 30 to 55 g / g, 30 to 50 g / g, or 32 to 42 g / g. .. The water retention amount of the physiological saline of the water-absorbent resin particles 10a is measured by the method described in Examples described later.

Examples of the shape of the water-absorbent resin particles 10a include substantially spherical, crushed, and granular shapes. The medium particle diameter of the water-absorbent resin particles 10a may be 250 to 850 μm, 300 to 700 μm, or 300 to 600 μm. The water-absorbent resin particles 10a may have a desired particle size distribution at the time of being obtained by the production method described later, but the particle size distribution can be adjusted by performing an operation such as particle size adjustment using classification with a sieve. May be good.

The content of the water-absorbent resin particles 10a is 100 to 1000 g per square meter of the absorbent body 10 from the viewpoint that sufficient liquid absorption performance can be more easily obtained when the absorbent body 10 is used for the absorbent article 100 (that is,). It is preferably 100 to 1000 g / m ² ), more preferably 150 to 800 g / m ² , and even more preferably 200 to 700 g / m ² . From the viewpoint of exhibiting sufficient liquid absorption performance as the absorbent article 100 and particularly suppressing liquid leakage, the content of the water-absorbent resin particles 10a is preferably 100 g / m ² or more, and the occurrence of the gel blocking phenomenon occurs. The content of the water-absorbent resin particles 10a is preferably 1000 g / m ² or less from the viewpoint of suppressing, exhibiting the diffusion performance of the liquid as the absorbent article 100, and further improving the permeation rate of the liquid.

The water-absorbent resin particles 10a can contain, for example, a crosslinked polymer formed by polymerizing a monomer containing an ethylenically unsaturated monomer. The crosslinked polymer has a monomer unit derived from an ethylenically unsaturated monomer. Examples of the crosslinked polymer include a hydrolyzate of a starch-acrylonitrile graft copolymer, a neutralized product of a starch-acrylic acid graft polymer, a saponified product of a vinyl acetate-acrylic acid ester copolymer, and a polyacrylic acid moiety. Japanese products can be mentioned. Among these water-absorbent resins, the crosslinked polymer is preferably a partially neutralized polyacrylic acid from the viewpoint of production amount, production cost, water absorption performance, and the like.

The water-absorbent resin particles 10a can be produced by a method including a step of polymerizing a monomer containing an ethylenically unsaturated monomer. Examples of the polymerization method include a reverse phase suspension polymerization method, an aqueous solution polymerization method, a bulk polymerization method, and a precipitation polymerization method. Among these, the reverse phase suspension polymerization method or the aqueous solution polymerization method is preferable from the viewpoint of ensuring good water absorption characteristics of the obtained water-absorbent resin particles and facilitating control of the polymerization reaction. In the following, a reverse phase suspension polymerization method will be described as an example as a method for polymerizing an ethylenically unsaturated monomer.

The ethylenically unsaturated monomer is preferably water-soluble, for example, (meth) acrylic acid and a salt thereof, 2- (meth) acrylamide-2-methylpropanesulfonic acid and a salt thereof, (meth) acrylamide, N. , N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-diethylamino Examples thereof include propyl (meth) acrylate and diethylaminopropyl (meth) acrylamide. When the ethylenically unsaturated monomer has an amino group, the amino group may be quaternized. The ethylenically unsaturated monomer may be used alone or in combination of two or more. Functional groups such as the carboxyl group and amino group of the above-mentioned monomers can function as functional groups capable of cross-linking in the surface cross-linking step described later.

Among these, from the viewpoint of industrial availability, the ethylenically unsaturated monomer is selected from the group consisting of (meth) acrylic acid and its salts, acrylamide, methacrylamide, and N, N-dimethylacrylamide. It is preferable to contain at least one compound selected, and more preferably to contain at least one compound selected from the group consisting of (meth) acrylic acid and salts thereof, and acrylamide. From the viewpoint of further enhancing the water absorption property, the ethylenically unsaturated monomer further preferably contains at least one compound selected from the group consisting of (meth) acrylic acid and salts thereof.

The ethylenically unsaturated monomer is usually preferably used as an aqueous solution. The concentration of the ethylenically unsaturated monomer in the aqueous solution containing the ethylenically unsaturated monomer (hereinafter, simply referred to as “monomer aqueous solution”) is preferably 20% by mass or more and preferably 25 to 70% by mass. More preferably, 30 to 55% by mass is further preferable. Examples of the water used in the aqueous solution include tap water, distilled water, ion-exchanged water and the like.

As the monomer for obtaining the water-absorbent resin particles 10a, a monomer other than the above-mentioned ethylenically unsaturated monomer may be used. Such a monomer can be used, for example, by being mixed with an aqueous solution containing the above-mentioned ethylenically unsaturated monomer. The amount of the ethylenically unsaturated monomer used is preferably 70 to 100 mol% with respect to the total amount of the monomers. Above all, the ratio of (meth) acrylic acid and a salt thereof is more preferably 70 to 100 mol% with respect to the total amount of the monomers.

When the ethylenically unsaturated monomer has an acid group, the monomer aqueous solution may be used by neutralizing the acid group with an alkaline neutralizer. The degree of neutralization of the ethylenically unsaturated monomer by the alkaline neutralizing agent increases the osmotic pressure of the obtained water-absorbent resin particles and further enhances the water absorption characteristics (water retention amount, etc.). It is preferably 10 to 100 mol%, more preferably 50 to 90 mol%, and even more preferably 60 to 80 mol% of the acidic group in the weight. Examples of the alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide and potassium carbonate; ammonia and the like. The alkaline neutralizer may be used alone or in combination of two or more. The alkaline neutralizer may be used in the form of an aqueous solution to simplify the neutralization operation. Neutralization of the acid group of the ethylenically unsaturated monomer can be performed, for example, by adding an aqueous solution of sodium hydroxide, potassium hydroxide or the like to the above-mentioned monomer aqueous solution and mixing them.

In the reverse phase suspension polymerization method, the monomer aqueous solution is dispersed in a hydrocarbon dispersion medium in the presence of a surfactant, and the ethylenically unsaturated monomer is polymerized using a radical polymerization initiator or the like. Can be done. As the radical polymerization initiator, a water-soluble radical polymerization initiator can be used.

Examples of the surfactant include nonionic surfactants and anionic surfactants. As the nonionic surfactant, sorbitan fatty acid ester and (poly) glycerin fatty acid ester (“(poly)” means both with and without the prefix of “poly”. The same shall apply hereinafter. ), Sucrose fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene himashi Examples thereof include oil, polyoxyethylene cured castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, polyethylene glycol fatty acid ester and the like. Anionic surfactants include fatty acid salts, alkylbenzene sulfonates, alkylmethyl taurates, polyoxyethylene alkylphenyl ether sulfates, polyoxyethylene alkyl ether sulfonates, and polyoxyethylene alkyl ether phosphates. , And the phosphate ester of polyoxyethylene alkyl allyl ether and the like. The surfactant may be used alone or in combination of two or more.

From the viewpoint that the W / O type reverse phase suspension is in a good state, water-absorbent resin particles 10a having a suitable particle size can be easily obtained, and industrially available, the surfactant is a sorbitan fatty acid ester. , Polyglycerin fatty acid ester and sucrose fatty acid ester preferably contain at least one compound selected from the group. From the viewpoint that the water absorption characteristics of the obtained water-absorbent resin particles 10a are easily improved, the surfactant preferably contains a sucrose fatty acid ester, and more preferably a sucrose stearic acid ester.

The amount of the surfactant used is preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of the aqueous monomer solution from the viewpoint of obtaining a sufficient effect on the amount used and from the viewpoint of economic efficiency. .08 to 5 parts by mass is more preferable, and 0.1 to 3 parts by mass is further preferable.

In the reverse phase suspension polymerization, a polymer-based dispersant may be used in combination with the above-mentioned surfactant. Examples of the polymer dispersant include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride-modified EPDM (ethylene / propylene / diene / terpolymer), and maleic anhydride. Modified polybutadiene, maleic anhydride / ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, maleic anhydride / butadiene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer Examples thereof include coalescence, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymer, ethylene / acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose and the like. The polymer-based dispersant may be used alone or in combination of two or more. As the polymer-based dispersant, from the viewpoint of excellent dispersion stability of the monomer, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, and maleic anhydride / ethylene copolymer weight. Combined, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene / propylene copolymer At least one selected from the group consisting of coalescing is preferable.

The amount of the polymer-based dispersant used is preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of the monomer aqueous solution from the viewpoint of obtaining a sufficient effect on the amount used and from the viewpoint of economic efficiency. , 0.08 to 5 parts by mass, more preferably 0.1 to 3 parts by mass.

The hydrocarbon dispersion medium may contain at least one compound selected from the group consisting of chain aliphatic hydrocarbons having 6 to 8 carbon atoms and alicyclic hydrocarbons having 6 to 8 carbon atoms. As the hydrocarbon dispersion medium, a chain aliphatic hydrocarbon such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, n-octane; cyclohexane , Methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentane and other alicyclic hydrocarbons; benzene, Examples include aromatic hydrocarbons such as toluene and xylene. The hydrocarbon dispersion medium may be used alone or in combination of two or more.

From the viewpoint of industrial availability and stable quality, the hydrocarbon dispersion medium may contain at least one selected from the group consisting of n-heptane and cyclohexane. From the same viewpoint, as the mixture of the above-mentioned hydrocarbon dispersion medium, for example, commercially available ExxonHeptane (manufactured by ExxonMobil: containing 75 to 85% of n-heptane and isomeric hydrocarbons) is used. You may.

The amount of the hydrocarbon dispersion medium used is preferably 30 to 1000 parts by mass and 40 to 500 parts by mass with respect to 100 parts by mass of the monomer aqueous solution from the viewpoint of appropriately removing the heat of polymerization and easily controlling the polymerization temperature. Is more preferable, and 50 to 300 parts by mass is further preferable. When the amount of the hydrocarbon dispersion medium used is 30 parts by mass or more, the polymerization temperature tends to be easily controlled. When the amount of the hydrocarbon dispersion medium used is 1000 parts by mass or less, the productivity of polymerization tends to be improved, which is economical.

The radical polymerization initiator is preferably water-soluble, for example, persulfates such as potassium persulfate, ammonium persulfate, sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t. Peroxides such as -butylcumylperoxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, hydrogen peroxide; 2,2'-azobis (2-amidinopropane) ) 2 hydrochloride, 2,2'-azobis [2- (N-phenylamidino) propane] 2 hydrochloride, 2,2'-azobis [2- (N-allylamidino) propane] 2 hydrochloride, 2,2 '-Azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} Dihydrochloride, 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2'-azobis [2-methyl-N- (2-Hydroxyethyl) -propionamide], azo compounds such as 4,4'-azobis (4-cyanovaleric acid) and the like can be mentioned. The radical polymerization initiator may be used alone or in combination of two or more. Examples of the radical polymerization initiator include potassium persulfate, ammonium persulfate, sodium persulfate, 2,2'-azobis (2-amidinopropane) dihydrochloride, and 2,2'-azobis [2- (2-imidazolin-2-). Il) Propane] dihydrochloride and at least one selected from the group consisting of 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propan} 2 hydrochloride. Is preferable.

The amount of the radical polymerization initiator used may be 0.00005 to 0.01 mol per 1 mol of the ethylenically unsaturated monomer. When the amount of the radical polymerization initiator used is 0.00005 mol or more, the polymerization reaction does not require a long time and is efficient. When the amount of the radical polymerization initiator used is 0.01 mol or less, it is easy to suppress the occurrence of a rapid polymerization reaction.

The above-mentioned radical polymerization initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, and L-ascorbic acid.

At the time of the polymerization reaction, the aqueous monomer solution used for the polymerization may contain a chain transfer agent. Examples of the chain transfer agent include hypophosphates, thiols, thiolic acids, secondary alcohols, amines and the like.

In order to control the particle size of the water-absorbent resin particles 10a, the monomer aqueous solution used for the polymerization may contain a thickener. Examples of the thickener include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide and the like. If the stirring speed at the time of polymerization is the same, the higher the viscosity of the aqueous monomer solution, the larger the medium particle size of the obtained particles tends to be.

Cross-linking occurs by self-cross-linking during polymerization, but cross-linking may be further performed by using an internal cross-linking agent. When an internal cross-linking agent is used, it is easy to control the water absorption characteristics of the water-absorbent resin particles 10a. The internal cross-linking agent is usually added to the reaction solution during the polymerization reaction. Examples of the internal cross-linking agent include di or tri (meth) acrylic acid esters of polyols such as ethylene glycol, propylene glycol, trimethylpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; Unsaturated polyesters obtained by reacting polyols with unsaturated acids (maleic acid, fumaric acid, etc.); bis (meth) acrylamides such as N, N'-methylenebis (meth) acrylamide; polyepoxides and (meth) Di or tri (meth) acrylic acid esters obtained by reacting with acrylic acid; di (meth) obtained by reacting polyisocyanate (tolylene diisocyanate, hexamethylene diisocyanate, etc.) with hydroxyethyl (meth) acrylate. ) Acrylic acid carbamil esters; compounds having two or more polymerizable unsaturated groups such as allylated starch, allylated cellulose, diallyl phthalate, N, N', N "-triallyl isocyanurate, divinylbenzene; Poly such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, polyglycerol polyglycidyl ether, etc. Glycidyl compound; haloepoxy compound such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; 2 reactive functional groups such as isocyanate compound (2,4-tolylene diisocyanate, hexamethylene diisocyanate, etc.) Examples thereof include compounds having more than one. The internal cross-linking agent may be used alone or in combination of two or more. As the internal cross-linking agent, a polyglycidyl compound is preferable, and a diglycidyl ether compound is used. Is more preferable, and at least one selected from the group consisting of (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether is further preferable.

The amount of the internal cross-linking agent used is 1 mol of ethylenically unsaturated monomer from the viewpoint that the water-soluble property is suppressed by appropriately cross-linking the obtained polymer and a sufficient amount of water absorption can be easily obtained. It may be 0 mmol or more, 0.02 mmol or more, 0.03 mmol or more, 0.04 mmol or more, 0.05 mmol or more, or 0.1 mol or less. In particular, in the polymerization of multi-stage reverse phase suspension polymerization, when the amount of the internal cross-linking agent is 0.03 mmol or more per mol of the ethylenically unsaturated monomer, the amount of water retention and no pressurization It is easy to obtain water-absorbent resin particles suitable for DW.

An aqueous phase containing an ethylenically unsaturated monomer, a radical polymerization initiator, an internal cross-linking agent, etc., if necessary, and an oil containing a hydrocarbon-based dispersant, a surfactant, a polymer-based dispersant, etc., if necessary. Reversed phase suspension polymerization can be carried out in an aqueous system in oil by heating with stirring in a state where the phases are mixed.

When performing reverse phase suspension polymerization, a monomer aqueous solution containing an ethylenically unsaturated monomer is used as a hydrocarbon dispersion medium in the presence of a surfactant (and, if necessary, a polymer-based dispersant). Disperse in. At this time, before the start of the polymerization reaction, the timing of adding the surfactant, the polymer-based dispersant, etc. may be either before or after the addition of the monomer aqueous solution.

Among them, from the viewpoint of easily reducing the amount of the hydrocarbon dispersion medium remaining in the obtained water-absorbent resin particles 10a, the monomer aqueous solution is dispersed in the hydrocarbon dispersion medium in which the polymer-based dispersant is dispersed, and then the interface is formed. It is preferable to further disperse the activator before carrying out the polymerization.

Reverse-phase suspension polymerization can be carried out in one stage or in multiple stages of two or more stages. Reverse phase suspension polymerization is preferably carried out in 2 to 3 steps from the viewpoint of increasing productivity.

When reverse phase suspension polymerization is carried out in two or more stages, the reaction mixture obtained in the first step polymerization reaction after the first step reverse phase suspension polymerization is subjected to an ethylenically unsaturated single amount. The body may be added and mixed, and the reverse phase suspension polymerization of the second and subsequent steps may be carried out in the same manner as in the first step. In the reverse phase suspension polymerization in each stage of the second and subsequent stages, in addition to the ethylenically unsaturated monomer, the above-mentioned radical polymerization initiator and / or internal cross-linking agent is used in the reverse phase of each stage of the second and subsequent stages. Based on the amount of ethylenically unsaturated monomer added during suspension polymerization, reverse phase suspension polymerization is carried out by adding within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer. Is preferable. An internal cross-linking agent may be used in the reverse phase suspension polymerization in each of the second and subsequent stages, if necessary. When an internal cross-linking agent is used, it is added within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer based on the amount of the ethylenically unsaturated monomer provided in each stage, and the suspension is reversed. It is preferable to carry out turbid polymerization.

The temperature of the polymerization reaction varies depending on the radical polymerization initiator used, but by advancing the polymerization rapidly and shortening the polymerization time, the efficiency is improved and the heat of polymerization is easily removed to carry out the reaction smoothly. From the viewpoint, 20 to 150 ° C. is preferable, and 40 to 120 ° C. is more preferable. The reaction time is usually 0.5-4 hours. The completion of the polymerization reaction can be confirmed, for example, by stopping the temperature rise in the reaction system. As a result, the polymer of the ethylenically unsaturated monomer is usually obtained in the state of a hydrogel-like polymer.

After the polymerization, a cross-linking agent may be added to the obtained hydrogel polymer and heated to carry out the cross-linking after the polymerization. By performing cross-linking after polymerization, the degree of cross-linking of the hydrogel polymer can be increased, whereby the water-absorbing characteristics of the water-absorbent resin particles can be further improved.

Examples of the cross-linking agent for performing post-polymerization cross-linking include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; Compounds having two or more epoxy groups such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether; epichlorohydrin, epibromhydrin, α-methylepicrolhydrin, etc. Haloepoxy compounds; compounds having two or more isocyanate groups such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylenecarbonate; bis [N , N-di (β-hydroxyethyl)] hydroxyalkylamide compounds such as adipamide can be mentioned. Among these, polyglycidyl compounds such as (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and polyglycerol polyglycidyl ether are preferable. .. These cross-linking agents may be used alone or in combination of two or more.

The amount of the cross-linking agent used for the post-polymerization cross-linking is such that the obtained hydrogel-like polymer is appropriately cross-linked to exhibit suitable water absorption characteristics, and the amount is determined per mole of the ethylenically unsaturated monomer. It is preferably 0 to 0.03 mol, more preferably 0 to 0.01 mol, and even more preferably 0.00001 to 0.005 mol. When the amount of the cross-linking agent added is within the above range, it is easy to obtain water-absorbent resin particles having a suitable non-pressurized DW and contact angle.

The timing of adding the cross-linking after the polymerization may be after the polymerization of the ethylenically unsaturated monomer used for the polymerization, and in the case of the multi-stage polymerization, it is preferably added after the multi-stage polymerization. In consideration of heat generation during and after polymerization, retention due to process delay, system opening when a cross-linking agent is added, and fluctuation of water content due to addition of water due to addition of a cross-linking agent, the cross-linking agent for post-polymerization cross-linking From the viewpoint of water content (described later), it is preferable to add in the region of [water content ± 3% by mass immediately after polymerization].

Subsequently, drying is performed to remove water from the obtained hydrogel polymer. Drying gives polymer particles containing a polymer of ethylenically unsaturated monomers. As a drying method, for example, (a) a hydrogel-like polymer is dispersed in a hydrocarbon dispersion medium, and co-boiling distillation is performed by heating from the outside, and the hydrocarbon dispersion medium is refluxed to remove water. Examples thereof include (b) a method of taking out the hydrogel polymer by decantation and drying under reduced pressure, and (c) a method of filtering the hydrogel polymer with a filter and drying under reduced pressure. Above all, it is preferable to use the method (a) because of the simplicity in the manufacturing process.

The particle size of the water-absorbent resin particles can be adjusted by adjusting the rotation speed of the stirrer during the polymerization reaction, or by adding a flocculant into the system after the polymerization reaction or in the early stage of drying. By adding a flocculant, the particle size of the obtained water-absorbent resin particles can be increased. As the flocculant, an inorganic flocculant can be used. Examples of the inorganic flocculant (for example, powdered inorganic flocculant) include silica, zeolite, bentonite, aluminum oxide, talc, titanium dioxide, kaolin, clay, hydrotalcite and the like. From the viewpoint of excellent aggregating effect, the aggregating agent is preferably at least one selected from the group consisting of silica, aluminum oxide, talc and kaolin.

In the reverse phase suspension polymerization, as a method of adding the flocculant, the flocculant is previously dispersed in a hydrocarbon dispersion medium or water of the same type as that used in the polymerization, and then the hydrogel polymer is mixed under stirring. A method of mixing in a hydrocarbon dispersion medium containing the mixture is preferable.

The amount of the flocculant added is preferably 0.001 to 1 part by mass and 0.005 to 0.5 part by mass with respect to 100 parts by mass of the ethylenically unsaturated monomer used for the polymerization. Is more preferable, and 0.01 to 0.2 parts by mass is further preferable. When the amount of the flocculant added is within the above range, water-absorbent resin particles having the desired particle size distribution can be easily obtained.

In the production of the water-absorbent resin particles 10a, it is preferable that the surface portion of the hydrogel polymer is crosslinked (surface crosslinked) using a crosslinking agent in any of the drying step and subsequent steps. By performing surface cross-linking, it is easy to control the water absorption characteristics of the water-absorbent resin particles 10a. The surface cross-linking is preferably performed at a timing when the hydrogel polymer has a specific water content. The time of surface cross-linking is preferably when the water content of the hydrogel polymer is 5 to 50% by mass, more preferably 10 to 40% by mass, and even more preferably 15 to 35% by mass. The water content (mass%) of the hydrogel polymer is calculated by the following formula.
Moisture content = [Ww / (Ww + Ws)] x 100
Ww: Necessary when mixing a flocculant, a surface cross-linking agent, etc. to the amount obtained by subtracting the amount of water discharged to the outside of the system by the drying step from the amount of water contained in the monomer aqueous solution before polymerization in the entire polymerization step The amount of water in the hydrogel polymer to which the amount of water used is added.
Ws: A solid content calculated from the amount of materials such as an ethylenically unsaturated monomer, a cross-linking agent, and an initiator that constitute a hydrogel polymer.

Examples of the cross-linking agent (surface cross-linking agent) for performing surface cross-linking include compounds having two or more reactive functional groups. Examples of the cross-linking agent include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; (poly) ethylene glycol diglycidyl ether, Polyglycidyl compounds such as (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, trimethylpropan triglycidyl ether (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether; epichlorohydrin, epi Haloepoxy compounds such as bromhydrin and α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol, Oxetane compounds such as 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol; oxazoline such as 1,2-ethylenebisoxazoline Compounds: Carbonate compounds such as ethylene carbonate; Hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide may be mentioned. The cross-linking agent may be used alone or in combination of two or more. As the cross-linking agent, a polyglycidyl compound is preferable, and (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and polyglycerol poly At least one selected from the group consisting of glycidyl ether is more preferable.

The amount of the surface cross-linking agent used is usually 1 mol of ethylenically unsaturated monomer used for polymerization from the viewpoint of appropriately cross-linking the obtained hydrogel polymer to exhibit suitable water absorption characteristics. On the other hand, 0.00001 to 0.02 mol is preferable, 0.00005 to 0.01 mol is more preferable, and 0.0001 to 0.005 mol is further preferable. When the amount of the surface cross-linking agent added is within the above range, it is easy to obtain water-absorbent resin particles having a suitable non-pressurized DW and contact angle.

After surface cross-linking, water and a hydrocarbon dispersion medium are distilled off by a known method to obtain polymer particles which are surface-cross-linked dried products.

The water-absorbent resin particles 10a may be composed of only polymer particles, but further contain various additional components selected from, for example, a gel stabilizer, a metal chelating agent, a fluidity improver (lubricant), and the like. be able to. Additional components may be placed inside the polymer particles, on the surface of the polymer particles, or both. As the additional component, a fluidity improver (lubricant) is preferable, and inorganic particles are more preferable. Examples of the inorganic particles include silica particles such as amorphous silica.

The water-absorbent resin particles 10a may contain a plurality of inorganic particles arranged on the surface of the polymer particles. For example, by mixing the polymer particles and the inorganic particles, the inorganic particles can be arranged on the surface of the polymer particles. The inorganic particles may be silica particles such as amorphous silica. When the water-absorbent resin particles 10a contain inorganic particles arranged on the surface of the polymer particles, the ratio of the inorganic particles to the mass of the polymer particles is 0.2% by mass or more, 0.5% by mass or more, and 1. It may be 0% by mass or more, 1.5% by mass or more, 5.0% by mass or less, or 3.5% by mass or less. The inorganic particles here usually have a minute size as compared with the size of the polymer particles. For example, the average particle size of the inorganic particles may be 0.1 to 50 μm, 0.5 to 30 μm, or 1 to 20 μm. The average particle size here can be a value measured by a dynamic light scattering method or a laser diffraction / scattering method. When the amount of the inorganic particles added is within the above range, it is easy to obtain the water-absorbent resin particles 10a having suitable water-absorbing characteristics, particularly non-pressurized DW and contact angle.

One embodiment of the method for producing the water-absorbent resin particles 10a is a step of further evaluating the 30-second value and contact angle of the non-pressurized DW of the obtained water-absorbent resin particles 10a by the method according to the above-described embodiment. It may be included. For example, water-absorbent resin particles having a 30-second value of non-pressurized DW of 1.0 mL / g or more and a contact angle of 90 degrees or less measured by the above method may be selected. Thereby, the water-absorbent resin particles capable of suppressing the liquid leakage of the absorbent article can be produced more stably.

The liquid absorption performance of the absorbent article 100 is also affected by the water absorption performance of the water-absorbent resin particles 10a used. Therefore, the water-absorbent resin particles 10a have a 30-second value, contact angle, and liquid absorption capacity (water retention amount, load) of the non-pressurized DW of the water-absorbent resin particles 10a in consideration of the composition of each component of the absorbent article 100. It is preferable to select a material having a preferable range of water absorption performance, mass average particle size, etc. (represented by an index such as water absorption below).

(Fibrous material)
Examples of the fibrous material 10b include finely pulverized wood pulp; cotton; cotton linter; rayon; cellulosic fibers such as cellulose acetate; synthetic fibers such as polyamide, polyester and polyolefin; and a mixture of these fibers. The fibrous material 10b may be used alone or in combination of two or more. As the fibrous material 10b, hydrophilic fibers can be used.

The content of the fibrous material 10b is 50 to 800 g (that is, 50 to 800 g / g) per square meter of the absorber 10 from the viewpoint of obtaining sufficient liquid absorption performance even when the absorber 10 is used for the absorbent article 100. It is preferably m ² ), more preferably 100 to 600 g / m ² , and even more preferably 150 to 500 g / m ² . A fibrous material from the viewpoint of exhibiting sufficient liquid absorption performance as an absorbent article 100, particularly suppressing the occurrence of a gel blocking phenomenon, enhancing the liquid diffusion performance, and further enhancing the strength of the absorber 10 after absorption. The content of 10b is preferably 50 g or more (that is, 50 g / m ² or more) per square meter of the absorber 10, and the content of the fibrous material 10b is particularly from the viewpoint of suppressing reversion after liquid absorption. It is preferably 800 g or less (that is, 800 g / m ² or less) per square meter of the absorber 10.

In order to enhance the morphological retention of the absorber 10 before and during use, the fibers may be adhered to each other by adding an adhesive binder to the fibrous material 10b. Examples of the adhesive binder include heat-sealing synthetic fibers, hot melt adhesives, and adhesive emulsions. The adhesive binder may be used alone or in combination of two or more.

Examples of the heat-bondable synthetic fiber include a total fusion type binder such as polyethylene, polypropylene, and an ethylene-propylene copolymer; and a non-total fusion type binder having a side-by-side structure of polypropylene and polyethylene or a core-sheath structure. In the above-mentioned non-total fusion type binder, only the polyethylene portion can be heat-sealed.

Examples of the hot melt adhesive include ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, and styrene-ethylene-propylene-styrene block copolymer. , A mixture of a base polymer such as amorphous polypropylene and a tackifier, a plasticizer, an antioxidant and the like.

Adhesive emulsions include, for example, polymers of at least one monomer selected from the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene, and vinyl acetate.

(Additive)
The absorber 10 may further contain various additives such as inorganic powders, deodorants, pigments, dyes, fragrances, antibacterial agents, and adhesives that are usually used in the art. With these additives, various functions can be imparted to the absorber. Examples of the inorganic powder include silicon dioxide, zeolite, kaolin, clay and the like. When the water-absorbent resin particles 10a contain inorganic particles, the absorber 10 may contain inorganic powder in addition to the inorganic particles in the water-absorbent resin particles.

(Adhesion between liquid permeable sheet and absorber and / or core wrap)
In the absorbent article 100 including the core wrap 20a, the core wrap 20a may be adhered to the liquid permeable sheet 30. In this case, since the liquid is guided to the absorber 10 more smoothly, the absorbent article 100, which is more excellent in the effect of suppressing liquid leakage, can be obtained. The core wrap 20a is preferably adhered to at least the liquid permeable sheet 30, and more preferably the core wrap 20a is adhered to the absorber 10 in addition to being adhered to the liquid permeable sheet 30. ..

In the absorbent article 100 in which the absorbent body 10 is arranged so as to be in contact with the liquid permeable sheet 30, the absorbent body 10 may be adhered to the liquid permeable sheet 30. In this case, since the liquid is guided to the absorber 10 more smoothly, the absorbent article 100, which is more excellent in the effect of suppressing liquid leakage, can be obtained.

As a method of adhering the absorber 10 and / or the core wrap 20a to the liquid permeable sheet, for example, the hot melt adhesive is applied to the liquid permeable sheet 30 in a vertical stripe shape or a spiral shape at predetermined intervals in the width direction. Examples thereof include a method of applying and adhering to the above, a method of adhering using a water-soluble binder selected from starch, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone and other water-soluble polymers. When the absorber 10 contains the heat-sealing synthetic fiber, a method of adhering by heat-sealing may be adopted.

[Core Wrap]
The absorbent article 100 includes a core wrap 20a that covers the surface side of the absorbent body 10 in contact with the liquid permeable sheet 30, and a core wrap 20b that covers the surface side of the absorbent body 10 in contact with the liquid permeable sheet 40. In the absorbent article 100 provided with the core wraps 20a and 20b, the shape of the absorbent body 10 is maintained (the shape retention can be enhanced), so that the water-absorbent resin particles 10a and the like constituting the absorbent body 10 fall off and flow. Prevented or suppressed.

The core wrap 20a is arranged on one side of the absorber 10 (upper side of the absorber 10 in FIG. 1) in contact with the absorber 10. That is, the core wrap 20a covers at least the surface side of the absorber 10 in contact with the liquid permeable sheet 30. The core wrap 20b is arranged on the other side of the absorber 10 (lower side of the absorber 10 in FIG. 1) in contact with the absorber 10. That is, the core wrap 20b covers at least the surface side of the absorber 10 in contact with the liquid impermeable sheet 40. The absorber 10 is arranged between the core wrap 20a and the core wrap 20b. The core wrap 20a and the core wrap 20b have, for example, a main surface having the same size as the absorber 10.

Examples of the core wraps 20a and 20b include non-woven fabrics, woven fabrics, synthetic resin films having liquid permeation holes, net-like sheets having a mesh, and the like. From the viewpoint of economy, the core wraps 20a and 20b are preferably tissues made by wet-molding pulverized pulp.

[Liquid permeable sheet]
The liquid permeable sheet 30 is arranged on the outermost side on the side where the liquid to be absorbed enters. The liquid permeable sheet 30 is arranged on the core wrap 20a in contact with the core wrap 20a. The liquid permeable sheet 30 has, for example, a main surface wider than the main surface of the absorber 10, and the outer edge portion of the liquid permeable sheet 30 extends around the absorber 10 and the core wraps 20a and 20b. ing.

The liquid permeable sheet 30 may be a sheet formed of a resin or fiber usually used in the art. From the viewpoint of liquid permeability, flexibility and strength when used in an absorbent article, the liquid permeable sheet 30 is, for example, a polyolefin such as polyethylene (PE) and polypropylene (PP), polyethylene terephthalate (PET), or polytri. Polyesters such as methylene terephthalate (PTT) and polyethylene naphthalate (PEN), polyamides such as nylon, synthetic resins such as rayon, or synthetic fibers containing these synthetic resins may be contained, or cotton, silk, hemp. , Or a natural fiber containing pulp (cellulose). From the viewpoint of increasing the strength of the liquid permeable sheet 30, the liquid permeable sheet 30 may contain synthetic fibers. Synthetic fibers may be, in particular, polyolefin fibers, polyester fibers or combinations thereof. These materials may be used alone or in combination of two or more kinds of materials.

The liquid permeable sheet 30 may be a non-woven fabric, a porous sheet, or a combination thereof. Nonwoven fabric is a sheet that is entwined without weaving fibers. The non-woven fabric may be a non-woven fabric composed of short fibers (that is, staples) (short-fiber non-woven fabric) or a non-woven fabric composed of long fibers (that is, filaments) (long-fiber non-woven fabric). Staples are not limited to this, but generally may have a fiber length of several hundred mm or less.

The liquid permeable sheet 30 is selected from the group consisting of thermal bond non-woven fabric, air-through non-woven fabric, resin bond non-woven fabric, spun bond non-woven fabric, melt blow non-woven fabric, spun bond / melt blow / spun bond non-woven fabric, airlaid non-woven fabric, spun lace non-woven fabric, and point bond non-woven fabric. It may be at least one non-woven fabric, and is preferably at least one non-woven fabric selected from the group consisting of thermal bonded non-woven fabrics, air-through non-woven fabrics, spunbonded non-woven fabrics, and spunbond / melt blow / spunbonded non-woven fabrics.

The liquid permeable sheet 30 is a thermal bond non-woven fabric, an air-through non-woven fabric, a resin bond non-woven fabric, a spun-bond non-woven fabric, a melt blow non-woven fabric, an air-laid non-woven fabric, a spunlace non-woven fabric, a point bond non-woven fabric, or a laminate of two or more kinds of non-woven fabrics selected from these. It may be there. These non-woven fabrics can be, for example, those formed of the above-mentioned synthetic fibers or natural fibers. The laminate of two or more types of non-woven fabric may be, for example, a spunbond non-woven fabric, a melt-blow non-woven fabric, and a spunbond non-woven fabric, which are composite non-woven fabrics laminated in this order, such as spunbond / melt-blow / spunbond non-woven fabric. Among them, from the viewpoint of suppressing liquid leakage, a thermal bond non-woven fabric, an air-through non-woven fabric, a spunbond non-woven fabric, or a spunbond / melt blow / spunbond non-woven fabric is preferably used.

It is desirable that the non-woven fabric used as the liquid permeable sheet 30 has appropriate hydrophilicity from the viewpoint of the liquid absorption performance of the absorbent article. From this point of view, the liquid permeable sheet 30 is obtained by the pulp and paper test method No. It is preferable that the non-woven fabric has a hydrophilicity of 5 to 200 as measured according to the measuring method of 68 (2000). The hydrophilicity of the non-woven fabric is more preferably 10 to 150. Pulp and paper test method No. For details of 68, for example, WO2011 / 086843 can be referred to.

The non-woven fabric having hydrophilicity as described above may be formed of fibers showing appropriate hydrophilicity such as rayon fiber, or hydrophobic chemical fiber such as polyolefin fiber and polyester fiber may be made hydrophilic. It may be formed by the fibers obtained by the treatment. As a method for obtaining a non-woven fabric containing hydrophobic chemical fibers that have been hydrophobized, for example, a method for obtaining a non-woven fabric by a spunbond method using a mixture of hydrophobic chemical fibers and a hydrophilic agent, hydrophobic chemistry. Examples thereof include a method of accommodating a hydrophilic agent when producing a spunbonded nonwoven fabric from fibers, and a method of impregnating a spunbonded nonwoven fabric obtained by using hydrophobic chemical fibers with a hydrophilic agent. Examples of the hydrophilizing agent include anionic surfactants such as aliphatic sulfonates and higher alcohol sulfates, cationic surfactants such as quaternary ammonium salts, polyethylene glycol fatty acid esters, polyglycerin fatty acid esters, and sorbitan fatty acids. Nonionic surfactants such as esters, silicone-based surfactants such as polyoxyalkylene-modified silicones, and stain-releasing agents made of polyester-based, polyamide-based, acrylic-based, and urethane-based resins are used.

The liquid permeable sheet 30 is moderately bulky and has a basis weight from the viewpoint of imparting good liquid permeability, flexibility, strength and cushioning property to the absorbent article and from the viewpoint of accelerating the liquid penetration rate of the absorbent article. It is preferable that the non-woven fabric has a large weight. When the liquid permeable sheet 30 is a non-woven fabric, the basis weight of the liquid permeable sheet 30 is preferably 5 to 200 g / m ² , more preferably 8 to 150 g / m ² , and further preferably 10 to 100 g. / M ² , 15-60 g / m ² , or 20-30 g / m ² . When the liquid permeable sheet 30 is a non-woven fabric, the thickness of the liquid permeable sheet 30 is preferably 20 to 1400 μm, more preferably 50 to 1200 μm, and even more preferably 80 to 1000 μm.

[Liquid impermeable sheet]
The liquid permeable sheet 40 is arranged on the outermost side of the absorbent article 100 on the opposite side of the liquid permeable sheet 30. The liquid permeable sheet 40 is arranged under the core wrap 20b in contact with the core wrap 20b. The liquid impermeable sheet 40 has, for example, a main surface wider than the main surface of the absorber 10, and the outer edge portion of the liquid impermeable sheet 40 extends around the absorber 10 and the core wraps 20a and 20b. Exists. The liquid impermeable sheet 40 prevents the liquid absorbed by the absorber 10 from leaking to the outside from the liquid impermeable sheet 40 side.

The liquid impermeable sheet 40 includes a sheet made of a synthetic resin such as polyethylene, polypropylene, and polyvinyl chloride, and a spunbond / meltblow / spunbond (SMS) nonwoven fabric in which a water-resistant meltblown nonwoven fabric is sandwiched between high-strength spunbonded non-woven fabrics. Examples thereof include a sheet made of a non-woven fabric such as, and a sheet made of a composite material of these synthetic resins and a non-woven fabric (for example, spunbonded non-woven fabric, spunlaced non-woven fabric). The liquid impermeable sheet 40 is preferably breathable from the viewpoint of reducing stuffiness during wearing and reducing discomfort given to the wearer. As the liquid impermeable sheet 40, a sheet made of a synthetic resin mainly composed of a low density polyethylene (LDPE) resin can be used. From the viewpoint of ensuring flexibility so as not to impair the wearing feeling of the absorbent article, the liquid impermeable sheet 40 may be, for example, a sheet made of a synthetic resin having a basis weight of 10 to 50 g / m ² .

The magnitude relationship between the absorbent body 10, the core wraps 20a and 20b, the liquid permeable sheet 30, and the liquid permeable sheet 40 is not particularly limited, and is appropriately adjusted according to the use of the absorbent article and the like. Further, the method of retaining the shape of the absorber 10 by using the core wraps 20a and 20b is not particularly limited, and as shown in FIG. 1, the absorber may be wrapped by a plurality of core wraps, and the absorber is wrapped by one core wrap. It may be.

According to the present embodiment, it is possible to provide a liquid absorbing method using the water-absorbent resin particles, the absorbent body or the absorbent article according to the present embodiment. The liquid absorbing method according to the present embodiment includes a step of bringing the liquid to be absorbed into contact with the water-absorbent resin particles, the absorber or the absorbent article according to the present embodiment.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Manufacturing of water-absorbent resin particles>
[Manufacturing Example 1]
A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a volume of 2 L equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirring blade having four inclined paddle blades with a blade diameter of 5 cm in two stages as a stirrer. Got ready. To this flask, take 293 g of n-heptane as a hydrocarbon dispersion medium, add 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals Co., Ltd., High Wax 1105A) as a polymer-based dispersant, and stir. The temperature was raised to 80 ° C. to dissolve the dispersant, and then cooled to 50 ° C.

On the other hand, 92.0 g (1.03 mol) of an 80.5 mass% aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed in a beaker having an internal volume of 300 mL, and cooled from the outside by 20.9 mass. After 147.7 g of a% sodium hydroxide aqueous solution was added dropwise to neutralize 75 mol%, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HECAW-15F) was used as a thickener, and water-soluble radical polymerization was started. 0.092 g (0.339 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride as an agent, 0.018 g (0.068 mmol) of potassium persulfate, and ethylene glycol diglycidyl ether as an internal cross-linking agent. 0.010 g (0.057 mmol) was added and dissolved to prepare a first-stage aqueous solution.

Then, the aqueous solution prepared above was added to the separable flask, and after stirring for 10 minutes, sucrose stearic acid ester of HLB3 as a surfactant in 6.62 g of n-heptane (Mitsubishi Chemical Foods Co., Ltd., Ryo). A surfactant solution in which 0.736 g of Tosugar ester S-370) was heated and dissolved was further added, and the inside of the system was sufficiently replaced with nitrogen while stirring at a stirring speed of 550 rpm. The first-stage polymerized slurry solution was obtained by immersing in a water bath at ° C. to raise the temperature and performing polymerization for 60 minutes.

On the other hand, 128.8 g (1.43 mol) of an 80.5 mass% aqueous acrylic acid solution was taken as a water-soluble ethylenically unsaturated monomer in another beaker having an internal volume of 500 mL, and 27 mass% was cooled from the outside. After 159.0 g of an aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol%, 0.129 g (0) of 2,2'-azobis (2-amidinopropane) dihydrochloride salt as a water-soluble radical polymerization initiator. .475 mmol) and 0.026 g (0.095 mmol) of potassium persulfate were added and dissolved to prepare a second-stage aqueous solution.

After cooling the inside of the separable flask system to 25 ° C. while stirring at a stirring speed of 1000 rpm, the entire amount of the aqueous solution of the second stage is added to the polymerized slurry solution of the first stage. After replacing the inside of the system with nitrogen for 30 minutes, the flask was again immersed in a water bath at 70 ° C. to raise the temperature, and the polymerization reaction was carried out for 60 minutes. Then, 0.580 g (0.067 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added as a cross-linking agent for post-polymerization cross-linking to obtain a hydrogel polymer.

To the hydrogel polymer after the second stage polymerization, 0.265 g of a 45% by mass diethylenetriamine-5 sodium acetate aqueous solution was added with stirring. Then, the flask was immersed in an oil bath set at 125 ° C., and 238.5 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface cross-linking agent, and the flask was kept at 83 ° C. for 2 hours.

Then, n-heptane was evaporated at 125 ° C. and dried to obtain polymer particles (dried product). The polymer particles are passed through a sieve having an opening of 850 μm, and 0.2% by mass of amorphous silica (Oriental Silicas Corporation, Toxile NP-S) with respect to the mass of the polymer particles is mixed with the polymer particles. , 232.1 g of water-absorbent resin particles containing amorphous silica were obtained. The medium particle size of the water-absorbent resin particles was 396 μm.

[Manufacturing Example 2]
A water-absorbent resin in the same manner as in Production Example 1 except that 2.0% by mass of amorphous silica (Oriental Silicas Corporation, Toxile NP-S) was mixed with the polymer particles (dried product). 236.3 g of particles were obtained. The medium particle size of the water-absorbent resin particles was 393 μm.

[Manufacturing Example 3]
In the preparation of the first-stage aqueous solution, 0.0736 g (0.272 mmol) of potassium persulfate was used as the water-soluble radical polymerizer, and 2,2'-azobis (2-amidinopropane) dihydrochloride was used. Was not added, 0.090 g (0.334 mmol) of potassium persulfate was used as the water-soluble radical polymerization agent in the preparation of the aqueous solution in the second stage, and 2,2'-azobis (2-). Amidinopropane) dihydrochloride was not added, 247.9 g of water was extracted from the system by co-boiling distillation in the hydrogel polymer after the second stage polymerization, and the mass of the polymer particles. 231.0 g of water-absorbent resin particles were obtained in the same manner as in Production Example 1 except that 0.5% by mass of amorphous silica was mixed with the polymer particles. The medium particle size of the water-absorbent resin particles was 355 μm.

[Manufacturing Example 4]
In the preparation of the first-stage aqueous solution, 0.0736 g (0.272 mmol) of potassium persulfate was used as the water-soluble radical polymerizer, and 2,2'-azobis (2-amidinopropane) dihydrochloride was used. Was not added, 0.090 g (0.334 mmol) of potassium persulfate was used as the water-soluble radical polymerization agent in the preparation of the aqueous solution in the second stage, and 2,2'-azobis (2-). Amidinopropane) dihydrochloride was not added, 239.7 g of water was extracted from the system by co-boiling distillation in the hydrogel polymer after the second stage polymerization, and the polymer particles On the other hand, 229.2 g of water-absorbent resin particles were obtained in the same manner as in Production Example 1 except that 0.5% by mass of amorphous silica was mixed. The medium particle size of the water-absorbent resin particles was 377 μm.

[Manufacturing Example 5]
In the preparation of the first-stage aqueous solution, 0.0736 g (0.272 mmol) of potassium persulfate was used as the water-soluble radical polymerizer, and 2,2'-azobis (2-amidinopropane) dihydrochloride was used. In the preparation of the aqueous solution in the second stage, 0.090 g (0.334 mmol) of potassium persulfate and 2,2'-azobis (2-amidinopropane) 2 were used as the water-soluble radical polymerizer. No hydrochloride was added, 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether was used as the internal cross-linking agent, no cross-linking agent for post-polymerization cross-linking was added, and the second stage. In the hydrogel-like polymer after the polymerization of, 256.1 g of water was extracted from the system by co-boiling distillation, and 0.1% by mass of amorphous silica with respect to the mass of the polymer particles was added to the polymer particles. 230.8 g of water-absorbent resin particles were obtained in the same manner as in Production Example 1 except that they were mixed with. The medium particle size of the water-absorbent resin particles was 349 μm.

[Manufacturing Example 6]
Ethylene glycol diglycidyl ether 0.0046 g (0.026 mmol) was used as the internal cross-linking agent in the preparation of the first-stage aqueous liquid, and ethylene glycol was used as the internal cross-linking agent in the preparation of the second-stage aqueous liquid. Using 0.0116 g (0.067 mmol) of diglycidyl ether, no cross-linking agent was added after polymerization, and 219.2 g by co-boiling distillation in the hydrogel polymer after polymerization in the second stage. Water absorption was the same as in Production Example 1 except that the water was extracted from the system and 6.62 g (0.761 mmol) of a 2 mass% ethylene glycol diglycidyl ether aqueous solution was used as the surface cross-linking agent. 229.6 g of resin particles were obtained. The medium particle size of the water-absorbent resin particles was 356 μm.

[Manufacturing Example 7]
Ethylene glycol diglycidyl ether 0.0046 g (0.026 mmol) was used as the internal cross-linking agent in the preparation of the first-stage aqueous liquid, and ethylene glycol was used as the internal cross-linking agent in the preparation of the second-stage aqueous liquid. 0.0116 g (0.067 mmol) of diglycidyl ether, no cross-linking agent added after polymerization, and 234.2 g of water by co-boiling distillation in the hydrogel polymer after the second stage polymerization. 229.6 g of water-absorbent resin particles were obtained in the same manner as in Production Example 1 except that the particles were extracted from the system. The medium particle size of the water-absorbent resin particles was 355 μm.

<Making absorbents and absorbent articles>
(Example 1)
Using an airflow type mixer (Padformer manufactured by Otec Co., Ltd.), 10 g of water-absorbent resin particles and 9.5 g of crushed pulp obtained in Production Example 1 were uniformly mixed by air papermaking to obtain a size of 12 cm × 32 cm. A sheet-shaped absorber of a size was prepared. The water absorber was placed on a tissue paper (core wrap) having a basis weight of 16 g / m ^{2, and} the tissue paper (core wrap) and the air-through non-woven fabric (liquid permeable sheet), which is a short fiber non-woven fabric, were laminated in this order on the absorber. .. A load of 588 kPa was applied to this laminate for 30 seconds. Further, a polyethylene liquid permeable sheet having a size of 12 cm × 32 cm was attached to the surface opposite to the air-through non-woven fabric to prepare the absorbent article of Example 1. The basis weight of the air-through non-woven fabric used was 17 g / m ² .

<Examples 2 to 4>
The absorbent articles of Examples 2 to 4 were produced in the same manner as in Example 1 except that the water-absorbent resin particles were changed to the water-absorbent resin particles obtained in Production Examples 2 to 4.

<Example 5>
Same as in Example 1 except that an absorbent body was prepared using the water-absorbent resin particles obtained in Production Example 2 and an air-through non-woven fabric having a basis weight of 23 g / m ² was used as the liquid permeable top sheet. To prepare an absorbent article.

<Comparative Examples 1 to 3>
The absorbent articles of Comparative Examples 1 to 3 were produced in the same manner as in Example 1 except that the water-absorbent resin particles were changed to the water-absorbent resin particles obtained in Production Examples 5 to 7.

In the absorbent articles of Examples and Comparative Examples, the basis weight of the water-absorbent resin particles was 280 g / m ² , and the basis weight of the pulverized pulp (hydrophilic fiber) was 260 g / m ² . Table 1 shows the combinations of the water-absorbent resin particles and the liquid permeable sheet used in Examples and Comparative Examples.

<Measurement of saline retention>
A cotton bag (Membroad No. 60, width 100 mm x length 200 mm) weighing 2.0 g of water-absorbent resin particles was placed in a 500 mL beaker. Pour 500 g of 0.9 mass% sodium chloride aqueous solution (physiological saline) into a cotton bag containing water-absorbent resin particles at a time so that mamaco cannot be formed, tie the upper part of the cotton bag with a rubber ring, and let it stand for 30 minutes. The water-absorbent resin particles were swollen with. After 30 minutes, the cotton bag is dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set to have a centrifugal force of 167 G, and the cotton bag containing the swelling gel after dehydration. The mass Wa (g) of was measured. The same operation was performed without adding the water-absorbent resin particles, the empty mass Wb (g) of the cotton bag when wet was measured, and the amount of physiological saline water retained was calculated from the following formula.
Saline water retention (g / g) = [Wa-Wb] /2.0

<Medium particle size>
50 g of water-absorbent resin particles were used for measuring the medium particle size.

From the top, JIS standard sieves have a mesh size of 850 μm, a mesh size of 500 μm, a mesh size of 425 μm, a mesh size of 300 μm, a mesh size of 250 μm, a mesh size of 180 μm, a mesh size of 150 μm, and a sieve. Combined in the order of the saucer.

The water-absorbent resin particles were placed in the best combined sieve and shaken for 20 minutes using a low-tap shaker to classify. After classification, the mass of the water-absorbent resin particles remaining on each sieve was calculated as a mass percentage with respect to the total amount, and the particle size distribution was obtained. The relationship between the mesh size of the sieve and the integrated value of the mass percentage of the water-absorbent resin particles remaining on the sieve was plotted on a logarithmic probability paper by integrating the particle size distribution on the sieve in order from the one having the largest particle size. By connecting the plots on the probability paper with a straight line, the particle size corresponding to the cumulative mass percentage of 50% by mass was defined as the medium particle size.

<Measurement of 30-second value of unpressurized DW (DemandWetability)>
The non-pressurized DW of the water-absorbent resin particles was measured using the measuring device shown in FIG. The measurement was carried out 5 times for one type of water-absorbent resin particles, and the average value of the measured values at three points excluding the minimum value and the maximum value was obtained.
The measuring device has a burette portion 1, a conduit 5, a measuring table 13, a nylon mesh sheet 15, a frame 11, and a clamp 3. The burette portion 1 includes a burette tube 21 on which a scale is described, a rubber stopper 23 for sealing the upper opening of the burette tube 21, a cock 22 connected to the tip of the lower portion of the burette tube 21, and a lower portion of the burette tube 21. It has an air introduction pipe 25 and a cock 24 connected to the burette. The burette portion 1 is fixed by a clamp 3. The flat plate-shaped measuring table 13 has a through hole 13a having a diameter of 2 mm formed in the central portion thereof, and is supported by a frame 11 having a variable height. The through hole 13a of the measuring table 13 and the cock 22 of the burette portion 1 are connected by a conduit 5. The inner diameter of the conduit 5 is 6 mm.

The measurement was performed in an environment of a temperature of 25 ° C. and a humidity of 60 ± 10%. First, the cock 22 and the cock 24 of the burette portion 1 were closed, and 0.9 mass% saline solution 50 adjusted to 25 ° C. was put into the burette tube 21 through the opening at the upper part of the burette tube 21. The concentration of 0.9% by mass of the saline solution is a concentration based on the mass of the saline solution. After sealing the opening of the burette tube 21 with the rubber stopper 23, the cock 22 and the cock 24 were opened. The inside of the conduit 5 was filled with 0.9% by mass saline solution 50 to prevent bubbles from entering. The height of the measuring table 13 was adjusted so that the height of the water surface of the 0.9 mass% saline solution that reached the inside of the through hole 13a was the same as the height of the upper surface of the measuring table 13. After the adjustment, the height of the water surface of the 0.9 mass% saline solution 50 in the burette tube 21 was read by the scale of the burette tube 21, and the position was set as the zero point (reading value at 0 seconds).

A nylon mesh sheet 15 (100 mm × 100 mm, 250 mesh, thickness about 50 μm) was laid in the vicinity of the through hole 13 on the measuring table 13, and a cylinder having an inner diameter of 30 mm and a height of 20 mm was placed in the center thereof. 1.00 g of water-absorbent resin particles 10a were uniformly sprayed on this cylinder. Then, the cylinder was carefully removed to obtain a sample in which the water-absorbent resin particles 10a were dispersed in a circle in the central portion of the nylon mesh sheet 15. Next, the nylon mesh sheet 15 on which the water-absorbent resin particles 10a were placed was quickly moved so that the center thereof was at the position of the through hole 13a so that the water-absorbent resin particles 10a did not dissipate, and the measurement was started. .. The time when the air bubbles were first introduced from the air introduction pipe 25 into the burette pipe 21 was defined as the start of water absorption (0 seconds).

The amount of decrease in the 0.9% by mass saline solution 50 in the bullet tube 21 (that is, the amount of the 0.9% by mass saline solution absorbed by the water-absorbent resin particles 10a) is sequentially read in units of 0.1 mL, and the water-absorbent resin particles are read. The weight loss Wc (g) of 0.9 mass% saline solution 50 was read 30 seconds after the start of water absorption of 10a. From Wc, the 30-second value of non-pressurized DW was calculated by the following formula. The non-pressurized DW is the amount of water absorbed per 1.00 g of the water-absorbent resin particles 10a.
30-second value of non-pressurized DW (mL / g) = Wc / 1.00

<Measurement of contact angle>
The contact angle was measured in an environment with a temperature of 25 ° C. and a humidity of 60 ± 10%. A double-sided tape (Nichiban inner stack: 10 mm x 75 mm) was attached to a glass preparation (25 mm x 75 mm), and a tape with an exposed adhesive surface was prepared. First, 2.0 g of water-absorbent resin particles were uniformly sprayed on the double-sided tape attached to the preparation. Then, the preparation was erected vertically to remove excess water-absorbent resin particles, and a sample for measurement was prepared.

The contact angle meter (Kyowa Interface Science Co., Ltd .: Face s-150) consists of a sample mounting stage that can move up and down, a syringe section installed above it, and a scope section that allows horizontal observation of the stage. .. The contact angle was measured by the following procedure using such a contact angle meter.
First, a measurement sample was placed on the stage portion vertically below the syringe (capacity: 1 ml). Using the scope of the contact angle meter, a spherical droplet having a diameter of 3 mm in 25 mass% saline was prepared at the tip of the syringe. The diameter of the spherical droplet was allowed up to ± 0.1 mm. The stage was moved upwards and the prepared droplets were brought into contact with a place where the surface of the sample was smooth (at that point, t = 0 (seconds)). The angle of the straight line connecting the left and right end points and the apex of the contact surface between the saline solution droplet and the double-sided tape surface at t = 30 (seconds) with respect to the double-sided tape surface is read by the lens of the contact angle meter, and the angle is measured. It was set to θ / 2. The contact angle θ was obtained by doubling this. The measurement was repeated 5 times, and the average value was taken as the contact angle of the water-absorbent resin particles. The angle reading method conforms to JIS R 3257 (1999) "Wetting property test method for the surface of the base glass".

<Preparation of artificial urine>
Sodium chloride, calcium chloride and magnesium sulfate were dissolved in ion-exchanged water at the following concentrations. A small amount of Blue No. 1 was added to the obtained solution to obtain artificial urine colored blue. The obtained artificial urine was used as a test solution for evaluating leakability. The following concentrations are based on the total mass of artificial urine.
Artificial urine composition NaCl: 0.780% by mass
CaCl2: 0.022% by mass
00544: 0.038% by mass
Blue No. 1: 0.002% by mass

<Gradient absorption test>
FIG. 3 is a schematic view showing a method for evaluating the leakability of an absorbent article. Support plate 1 (acrylic resin plate here, hereinafter referred to as the inclined surface S ₁₎ of length 45cm having a flat main surface, and fixed by frame 41 in a state of being inclined 45 ± 2 degrees relative to the horizontal plane S ₀ .. In room temperature 25 ± 2 ° C., on the inclined surface S ₁ of the fixed support plate 1, the absorbent article 100 for testing, the longitudinal direction is adhered in a direction along the longitudinal direction of the support plate 1. Next, the dropping funnel 42, which was arranged vertically above the absorbent article, was adjusted to 25 ± 1 ° C. toward a position 8 cm above the center of the absorber in the absorbent article 100, so that the test solution 51 (artificial urine) Was dropped. 80 mL of the test solution was added dropwise at a rate of 8 mL / sec. The distance between the tip of the dropping funnel 42 and the absorbent article was 10 ± 1 mm. The test solution was repeatedly added under the same conditions at intervals of 10 minutes from the start of the first addition of the test solution, and the test solution was added until leakage was observed.

When the test liquid that was not absorbed by the absorbent article 100 leaked from the lower part of the support plate 1, the leaked test liquid was collected in a metal tray 44 arranged below the support plate 1. The weight (g) of the recovered test solution was measured by a balance 43, and the value was recorded as a leakage amount. By subtracting the leakage amount from the total input amount of the test solution, the absorption amount until the leakage occurred was calculated. It is judged that the larger this value is, the less likely it is that liquid will leak when worn.

From the results shown in Table 2, it can be said that the absorbent articles of Examples 1 to 5 are the absorbent articles in which the occurrence of leakage is suppressed as compared with the absorbent articles of Comparative Examples 1 to 3.

1 ... Burette part, 3 ... Clamp, 5 ... Conduit, 10 ... Absorbent, 10a ... Water-absorbent resin particles, 10b ... Fiber layer, 11 ... Stand, 13 ... Measuring table, 13a ... Through hole, 15 ... Nylon mesh sheet, 20a, 20b ... core wrap, 21 ... burette tube, 22 ... cock, 23 ... rubber stopper, 24 ... cock, 25 ... air introduction tube, 50 ... 0.9% by mass saline solution, 30 ... liquid permeable sheet, 40 ... liquid Impermeable sheet, 51 ... test solution, 100 ... absorbent article, S ₀ ... horizontal plane, S ₁ ... inclined surface, 100 ... absorbent article.

Claims (8)

An absorbent article comprising a liquid impermeable sheet, an absorbent body, and a liquid permeable sheet, wherein the liquid impermeable sheet, the absorbent body, and the liquid permeable sheet are arranged in this order.
The absorber contains water-absorbent resin particles and contains
Heavy the water absorbent resin particles, comprising a cross-linked polymer having a monomer unit derived from an ethylenically unsaturated monomer comprising at least one compound selected from the group consisting of (meth) acrylic acid and its salts Containing coalesced particles and silica particles disposed on the surface of the polymer particles ,
The ratio of (meth) acrylic acid and a salt thereof is 70 to 100 mol% with respect to the total amount of the monomer units in the crosslinked polymer.
The 30-second value of the non-pressurized DW of the water-absorbent resin particles is 1.0 mL / g or more.
The contact angle of the water-absorbent resin particles measured in the tests conducted in the order of i) and ii) below is 20 degrees or more and 80 degrees or less.
An absorbent article having a water retention capacity of 35 to 60 g / g.
i) At 25 ° C., spherical droplets having a diameter of 3.0 ± 0.1 mm of 25% by mass saline solution are dropped onto the surface of the layer composed of the water-absorbent resin particles to form the water-absorbent resin particles. The droplets are brought into contact with each other.
ii) The contact angle of the droplet is measured 30 seconds after the droplet comes into contact with the surface. The absorbent article according to claim 1, wherein the contact angle is 20 degrees or more and 70 degrees or less. The absorbent article according to claim 1 or 2, wherein the 30-second value of the non-pressurized DW is 3.0 mL / g or more. The liquid permeable sheet is a thermal bond non-woven fabric, an air-through non-woven fabric, a resin bond non-woven fabric, a spun-bond non-woven fabric, a melt blow non-woven fabric, an air-laid non-woven fabric, a spunlace non-woven fabric, a point-bond non-woven fabric, or a laminate of two or more kinds of non-woven fabrics selected from these. The absorbent article according to any one of claims 1 to 3, which comprises. The absorbent article according to any one of claims 1 to 4 , wherein the absorber further contains a fibrous substance. The absorbent article according to any one of claims 1 to 5 , further comprising a core wrap that covers at least the surface side of the absorbent body in contact with the liquid permeable sheet. The absorbent article of claim 6 , wherein the core wrap is adhered to the liquid permeable sheet. The absorber is arranged so as to be in contact with the liquid permeable sheet.
The absorbent article according to any one of claims 1 to 5 , wherein the absorbent body is adhered to the liquid permeable sheet.

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