WO2020218165A1

WO2020218165A1 - Water-absorbing resin particles, absorbent article, method for producing water-absorbing resin particles, and method for suppressing liquid leakage of absorbent article

Info

Publication number: WO2020218165A1
Application number: PCT/JP2020/016758
Authority: WO
Inventors: 志保岡澤
Original assignee: 住友精化株式会社
Priority date: 2019-04-23
Filing date: 2020-04-16
Publication date: 2020-10-29
Also published as: JP6889811B2; JPWO2020218165A1

Abstract

The present invention discloses water-absorbing resin particles in which the liquid permeation ratio A is greater than 0% and no greater than 60%. The liquid permeation ratio A is calculated according to the formula: liquid permeation ratio A (%)=(amount of water absorbed B (g/g)/amount of water absorbed C (g/g))×100. The amount of water absorbed B, once physiological saline supplied through a spun bond nonwoven textile is absorbed by 1.00 g of the water-absorbing resin particles according to the DW method without pressurization, is the mass of physiological saline per gram of water-absorbing resin particles absorbed by the water-absorbing resin particles up to five minutes from the start of absorption. The amount of water absorbed C, when 2.0 g of water-absorbing resins particles has swelled in 500 g of physiological saline over 60 minutes, is the mass of physiological saline per gram of water-absorbing resin particles absorbed.

Description

A method for producing water-absorbent resin particles, an absorbent article, a water-absorbent resin particle, and a method for suppressing liquid leakage of the absorbent article.

Method for producing water-absorbent resin particles, absorbent articles, water-absorbent resin particles, and method for suppressing liquid leakage of 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 Documents 1 to 3).

Japanese Unexamined Patent Publication No. 2010-116548 JP-A-2010-126552 Japanese Unexamined Patent Publication No. 2016-12127

The present invention provides water-absorbent resin particles in which liquid-absorbent resin particles are arranged inside a liquid-permeable sheet containing a spunbonded non-woven fabric and can suppress liquid leakage from the absorbent article, and an absorbent article using the same.

One aspect of the present invention is as follows:
Liquid permeation ratio A [%] = (water absorption B [g / g] / water absorption C [g / g]) × 100
The liquid permeation ratio A calculated by the above is more than 0% and 60% or less. The water absorption amount B is absorbed by the water-absorbent resin particles when 1.00 g of the water-absorbent resin particles absorb the physiological saline supplied through the spunbonded non-woven fabric by the DW method under no pressure. It is the mass of the physiological saline solution per 1 g of the water-absorbent resin particles that is absorbed within 5 minutes after the start of. The mass per unit area of the spunbonded non-woven fabric is 11 to 15 g / m ² . The water absorption amount C is the mass of the physiological saline solution per 1 g of the water-absorbent resin particles, which is absorbed when 2.0 g of the water-absorbent resin particles swells in 500 g of physiological saline solution over 60 minutes.

Another aspect of the present invention comprises a liquid impermeable sheet, an absorber, and a liquid permeable sheet, wherein the liquid impermeable sheet, the absorber and the liquid permeable sheet are arranged in this order. Regarding absorbent articles. The absorber contains the water-absorbent resin particles.

Yet another aspect of the present invention relates to a method for producing water-absorbent resin particles, which comprises a step of selecting water-absorbent resin particles having a liquid permeation ratio A of more than 0% and 60% or less.

Yet another aspect of the present invention is to suppress liquid leakage from the absorbent article containing the water-absorbent resin particles, which comprises setting the liquid permeation ratio A of the water-absorbent resin particles to be more than 0% and 60% or less. Regarding how to do it.

According to the present invention, there are provided a water-absorbent resin particle capable of suppressing liquid leakage from an absorbent article in which water-absorbent resin particles are arranged inside a liquid-permeable sheet containing a spunbonded nonwoven fabric, and an absorbent article using the same. Will be done.

It is a schematic diagram which shows the method of measuring the water absorption amount B. It is sectional drawing which shows one Embodiment of an absorbent article. It is a top view which shows an example of a stirring blade (a flat plate blade which has a slit in a flat plate part). It is a schematic diagram which shows the method of measuring the water absorption under load. It is a schematic diagram which shows the method of evaluating the leakability of an absorbent article.

Hereinafter, some embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

In this specification, "acrylic" and "methacryl" are collectively referred to as "(meth) acrylic". Similarly, "acrylate" and "methacrylate" are also referred to as "(meth) acrylate". "(Poly)" shall mean both with and without the "poly" prefix. 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.

The liquid permeation ratio A of the water-absorbent resin particles is calculated by the following formula. The water-absorbent resin particles according to one embodiment have a liquid permeation ratio A of more than 0% and 60% or less.
Liquid permeation ratio A [%] = (water absorption B [g / g] / water absorption C [g / g]) × 100
The water absorption amount B is determined by the water-absorbent resin particles starting to be absorbed when the physiological saline supplied via the spunbonded non-woven fabric is absorbed by 1.00 g of the water-absorbent resin particles by the DW method under no pressure. It is the mass of the physiological saline solution per 1 g of the water-absorbent resin particles that is absorbed until 5 minutes after that.

The spunbonded non-woven fabric used for measuring the water absorption amount B has a mass per unit area of 11 to 15 g / m ² . More specifically, the spunbonded non-woven fabric used for measuring the water absorption B is a non-woven fabric formed of polypropylene fibers that have been hydrophilized, and is composed of a spunbond layer, a melt blow layer, a melt blow layer, and a spunbond layer. It has a four-layer structure, and these are laminated in this order.

FIG. 1 is a schematic diagram showing a method of measuring the water absorption amount B. The measuring device shown in FIG. 1 has the same configuration as the device for measuring the non-pressurized DW value, and has a burette portion 2, a conduit 5, a measuring table 13, a spunbonded non-woven fabric 15, a frame 11, and a frame 11. It has a clamp 3. The burette portion 2 includes a burette tube 21 on which a scale is described, a rubber stopper 23 for sealing the opening at the upper part 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 2 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 2 are connected by a conduit 5. The inner diameter of the conduit 5 is 6 mm.

The water absorption amount B is measured by a method including the following steps in an environment of a temperature of 25 ° C. and a humidity of 50 ± 10%.
(1) The cock 22 and the cock 24 of the burette portion 2 are closed, and a physiological saline solution 50 (saline solution having a concentration of 0.9% by mass) at 25 ° C. is 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 physiological saline is a concentration based on the mass of the physiological saline.
(2) After sealing the opening of the burette tube 21 with the rubber stopper 23, the cock 22 and the cock 24 are opened. The inside of the conduit 5 is filled with saline 50 so that air bubbles do not enter.
(3) The height of the measuring table 13 is adjusted so that the height of the water surface of the physiological saline solution that has reached the inside of the through hole 13a is 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 physiological saline solution 50 in the burette tube 21 is read by the scale of the burette tube 21, and the position is set as the zero point (reading value at 0 seconds).
(4) A spunbonded non-woven fabric 15 is laid in the vicinity of the through hole 13a on the measuring table 13, and a cylinder having an inner diameter of 30 mm and a height of 20 mm is placed in the center thereof. 1.00 g of water-absorbent resin particles 10a are charged into this cylinder.
(5) Carefully remove the cylinder, and place the water-absorbent resin particles 10a in the circular region in the center of the spunbonded nonwoven fabric 15. Next, the spunbonded nonwoven fabric 15 on which the water-absorbent resin particles 10a are arranged is quickly moved so that the center thereof is at the position of the through hole 13a so that the water-absorbent resin particles 10a do not dissipate, and the measurement is started. The time when the air bubbles are first introduced from the air introduction pipe 25 into the burette pipe 21 is regarded as the start of water absorption (0 seconds).
(6) The decrease amount of the physiological saline solution 50 in the burette tube 21 (that is, the amount of the physiological saline solution absorbed by the water-absorbent resin particles 10a) is sequentially read in units of 0.1 mL. The weight loss Wc (g) of the physiological saline 50 5 minutes after the start of water absorption of the water-absorbent resin particles 10a is read. From the density of Wc and physiological saline (1.028 g / mL), the water absorption amount B is calculated by the following formula. The water absorption amount B is the mass per 1.00 g of the water-absorbent resin particles of the absorbed physiological saline.
Water absorption B [g / g] = Wc x 1.0028 / 1.00

The water absorption amount C is the mass of the physiological saline solution per 1 g of the water-absorbent resin particles, which is absorbed when 2.0 g of the water-absorbent resin particles swell in 500 g of physiological saline solution over 60 minutes. The water absorption amount C is measured by a method including the following steps in an environment of a temperature of 25 ° C. and a humidity of 50 ± 10%.
(1) 500 g of physiological saline (saline solution having a concentration of 0.9% by mass) is stirred at 600 rpm in a beaker having an internal volume of 500 mL, and 2.0 g of water-absorbent resin particles are dispersed therein.
(2) The physiological saline solution is left to stand for 60 minutes in a stirred state, whereby the water-absorbent resin particles are swollen.
(3) The swollen gel is taken out by filtration using a standard sieve having a mesh size of 75 μm.
(4) The sieve on which the removed swelling gel is placed is tilted so as to have an inclination angle of about 30 degrees with respect to the horizontal, and in that state, it is left for 30 minutes to remove excess water.
(5) The mass Wb (g) of the sieve on which the swollen gel is placed is measured. From Wb and the mass Wa (g) of the sieve measured in advance, the water absorption amount C is obtained by the following formula.
Water absorption C = (Wb-Wa) /2.0

The reason why the liquid permeation ratio A is moderately small is that the water-absorbent resin particles span as compared with the water absorption amount C when the water-absorbent resin particles sufficiently absorb the physiological saline by contact with an excessive amount of the physiological saline. It means that the amount of water absorption B when absorbing the physiological saline supplied through the bonded non-woven fabric is small. In the measurement of the water absorption amount B, the water absorption mode of the physiological saline tends to be significantly decelerated at a relatively early stage, and as a result, the water absorption amount B after 5 minutes may remain at a small value. The reason for this is not clear, but the present inventor speculates that in the combination of the spunbonded non-woven fabric and specific water-absorbent resin particles, the absorption of the liquid may unexpectedly become a moderately local absorption mode. ing. Therefore, the fact that the liquid permeation ratio A is as small as 60% or less means that the initial water absorption rate of the water-absorbent resin particles is higher than a certain level when the physiological saline is absorbed through the spunbonded non-woven fabric. It is considered that this contributes to the suppression of liquid leakage from the absorbent article in which the water-absorbent resin particles are arranged inside the liquid permeable sheet containing the spunbonded non-woven fabric.

From the viewpoint of suppressing liquid leakage, the liquid permeation ratio A may be 50% or less. The liquid permeation ratio A may be 1% or more, 5% or more, or 8% or more. The water absorption amount C may be 40 to 65 g / g.

The amount of water absorption of the water-absorbent resin particles with respect to physiological saline under a load of 2.07 kPa (hereinafter, may be referred to as "water absorption amount under load") may be 20 mL / g or more. When the amount of water absorption under load is large, high water absorption capacity can be maintained even under the load of the wearer of the absorbent article. From the same viewpoint, the water absorption amount of the water-absorbent resin particles under load may be 25 mL / g or more, 30 mL / g or more, 50 mL / g or less, or 45 mL / g or less.

The shape of the water-absorbent resin particles may be, for example, substantially spherical, crushed, or granular. The water-absorbent resin particles according to the present embodiment may be in a form in which fine particles (primary particles) are aggregated (secondary particles) in addition to a form in which each is composed of a single particle. The medium particle size of the water-absorbent resin particles may be 250 to 850 μm, 300 to 700 μm, or 300 to 600 μm. The water-absorbent resin particles may have a desired particle size distribution at the time of being obtained by the production method described later, but the particle size distribution may be adjusted by performing an operation such as particle size adjustment using classification by a sieve. Good.

The water-absorbent resin particles can include, 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.

The water-absorbent resin particles 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. From the viewpoint of ensuring good water absorption characteristics of the obtained water-absorbent resin particles and facilitating control of the polymerization reaction, a reverse phase suspension polymerization method or an aqueous solution polymerization method may be applied. 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 may be water-soluble. Examples of water-soluble ethylenically unsaturated monomers include (meth) acrylic acid and its salts, 2- (meth) acrylamide-2-methylpropanesulfonic acid and its salts, (meth) acrylamide, N, N-dimethyl. (Meta) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) Examples thereof include 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.

From the viewpoint of industrial availability, the ethylenically unsaturated monomer is at least one selected from the group consisting of (meth) acrylic acid and salts thereof, acrylamide, methacrylamide, and N, N-dimethylacrylamide. It may contain a compound of the species. The ethylenically unsaturated monomer may contain (meth) acrylic acid and a salt thereof, and at least one compound selected from the group consisting of acrylamide. From the viewpoint of further enhancing the water absorption property, the ethylenically unsaturated monomer may contain at least one compound selected from the group consisting of (meth) acrylic acid and salts thereof.

The ethylenically unsaturated monomer can be used in the polymerization reaction 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 20% by mass or more and the saturation concentration or less, 25 to 70% by mass, or 30. It may be up to 55% by mass. 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, 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 the total amount of the monomers (the total amount of the monomers for obtaining the water-absorbent resin particles. For example, the total amount of the monomers giving the structural unit of the crosslinked polymer. The same shall apply hereinafter). It may be 70 to 100 mol%, 80 to 100 mol%, 90 to 100 mol%, 95 to 100 mol%, or 100 mol%. The ratio of (meth) acrylic acid and its salt may be 70 to 100 mol%, 80 to 100 mol%, 90 to 100 mol%, 95 to 100 mol%, or 100 mol% with respect to the total amount of the monomer. It may be. "Ratio of (meth) acrylic acid and its salt" means the ratio of the total amount of (meth) acrylic acid and its salt.

When the ethylenically unsaturated monomer has an acid group, the acid group may be neutralized with an alkaline neutralizer, and then the monomer solution may be used in the polymerization reaction. The degree of neutralization of an ethylenically unsaturated monomer by an alkaline neutralizing agent increases the osmotic pressure of the obtained water-absorbent resin particles and further enhances the water absorption characteristics (water absorption amount, etc.). It may be 10-100 mol%, 50-90 mol%, or 60-80 mol% of the acidic group in the body. 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. Nonionic surfactants include sorbitan fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, and polyoxyethylene. Alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, Examples thereof include polyethylene glycol fatty acid ester. 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 having a suitable particle size can be easily obtained, and industrially available, the surfactant is a sorbitan fatty acid ester. It may contain at least one compound selected from the group consisting of polyglycerin fatty acid ester and sucrose fatty acid ester. From the viewpoint of easily improving the water absorption characteristics of the obtained water-absorbent resin particles, the surfactant may contain a sucrose fatty acid ester (for example, sucrose stearic acid ester).

The amount of the surfactant may be 0.05 to 10 parts by mass, 0.08 to 5 parts by mass, or 0.1 to 3 parts by mass with respect to 100 parts by mass of the monomer aqueous solution.

In 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. From the viewpoint of excellent dispersion stability of the monomer, the polymer-based dispersant includes maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, and maleic anhydride / ethylene copolymer. , Maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene / propylene copolymer It may be at least one selected from the group consisting of.

The amount of the polymer-based dispersant may be 0.05 to 10 parts by mass, 0.08 to 5 parts by mass, or 0.1 to 3 parts by mass with respect to 100 parts by mass of the monomer aqueous solution.

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 being industrially easily available and having 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, a commercially available exol heptane (manufactured by ExxonMobil: containing 75 to 85% of n-heptane and isomeric hydrocarbons) may be used. Good.

The amount of the hydrocarbon dispersion medium is 30 to 1000 parts by mass, 40 to 500 parts by mass, or 50 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. It may be up to 300 parts by mass. When the amount of the hydrocarbon dispersion medium is 30 parts by mass or more, the polymerization temperature tends to be easily controlled. When the amount of the hydrocarbon dispersion medium is 1000 parts by mass or less, the productivity of polymerization tends to be improved, which is economical.

The radical polymerization initiator may be water-soluble. Examples of water-soluble radical polymerization initiators are persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, and t-butyl cumylper. Peroxides such as oxides, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, hydrogen peroxide; 2,2'-azobis (2-amidinopropane) dihydrochloride , 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride, 2,2'-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2'-azobis [ 2- (2-Imidazolin-2-yl) propane] 2 hydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} 2 hydrochloride, 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2'-azobis [2-methyl-N- (2-hydroxy) Ethyl) -propionamide], azo compounds such as 4,4'-azobis (4-cyanovaleric acid) can be mentioned. The radical polymerization initiator may be used alone or in combination of two or more. The radical polymerization initiators are potassium persulfate, ammonium persulfate, sodium persulfate, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl). ) Propane] 2 hydrochloride and 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} 2 hydrochloride at least selected from the group. There may be.

The amount of the radical polymerization initiator 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 is 0.01 mol or less, it is easy to suppress the occurrence of a rapid polymerization reaction.

The exemplified 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 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, the monomer aqueous solution used for polymerization may contain a thickener. Examples of the thickener include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, 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 by self-cross-linking may occur 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. 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 compounds; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; 2 reactive functional groups such as isocyanate compounds (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. The internal cross-linking agent may be a polyglycidyl compound or diglycidyl. It may be an ether compound. The internal cross-linking agent comprises at least one selected from the group consisting of (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether. It may be.

The amount of the internal cross-linking agent is 0 per mol of the 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 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.

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.

From the viewpoint of easily reducing the amount of the hydrocarbon dispersion medium remaining in the obtained water-absorbent resin, the monomer aqueous solution is dispersed in the hydrocarbon dispersion medium in which the polymer-based dispersant is dispersed, and then the surfactant is further dispersed. It may be allowed to carry out polymerization.

Reverse phase suspension polymerization can be carried out in one stage or in multiple stages of two or more stages. Reversed phase suspension polymerization may be carried out in two or three stages from the viewpoint of increasing productivity.

When reverse phase suspension polymerization is carried out in two or more stages, an ethylenically unsaturated monomer is added to the reaction mixture obtained in the first step polymerization reaction after the first step reverse phase suspension polymerization is carried out. It 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 is used in the reverse phase suspension polymerization in each stage of the second and subsequent stages. Based on the amount of the ethylenically unsaturated monomer to be added, it may be added within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer to carry out reverse phase suspension polymerization. In the reverse phase suspension polymerization in each stage after the second stage, an internal cross-linking agent may be used 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. Muddy polymerization may be carried out.

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, it may be 20 to 150 ° C. or 40 to 120 ° C. 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 polymerization, cross-linking may be performed after polymerization by adding a cross-linking agent to the obtained hydrogel polymer and heating it. 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. Crosslinking agents for post-polymerization post-crosslinking are (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and polyglycerol polyglycidyl. It may be a polyglycidyl compound such as ether. These cross-linking agents may be used alone or in combination of two or more.

The amount of the cross-linking agent used for post-polymerization cross-linking is 1 mol of the water-soluble ethylenically unsaturated monomer from the viewpoint of appropriately cross-linking the obtained hydrogel-like polymer to exhibit suitable water absorption characteristics. It may be 0 to 0.03 mol, 0 to 0.01 mol, or 0.00001 to 0.005 mol.

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

Subsequently, water is removed from the obtained hydrogel polymer. Drying to remove water gives polymer particles containing a polymer of ethylenically unsaturated monomers. Examples of the drying method include (a) a method of removing water by co-boiling distillation in a state where the hydrogel polymer is dispersed in a hydrocarbon dispersion medium, and (b) taking out the hydrogel polymer by decantation and reducing the pressure. Examples thereof include a method of drying, and (c) a method of filtering the hydrogel polymer by a filter and drying under reduced pressure.

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 may be at least one selected from the group consisting of silica, aluminum oxide, talc and kaolin.

In reverse phase suspension polymerization, a coagulant is previously dispersed in a hydrocarbon dispersion medium of the same type as that used in the polymerization or water, and then this is placed in a hydrocarbon dispersion medium containing a hydrogel polymer under stirring. May be mixed with.

The amount of the flocculant is 0.001 to 1 part by mass, 0.005 to 0.5 part by mass, or 0.01 to 0.2 with respect to 100 parts by mass of the ethylenically unsaturated monomer used for the polymerization. It may be a mass part. When the amount of the flocculant is within these ranges, it is easy to obtain water-absorbent resin particles having a desired particle size distribution.

The polymerization reaction can be carried out using various stirrers having stirring blades. As the stirring blade, a flat plate blade, a lattice blade, a paddle blade, a propeller blade, an anchor blade, a turbine blade, a Faudler blade, a ribbon blade, a full zone blade, a max blend blade and the like can be used. The flat plate blade has a shaft (stirring shaft) and a flat plate portion (stirring portion) arranged around the shaft. Further, the flat plate portion may have a slit or the like. When a flat plate blade is used as the stirring blade, the uniformity of cross-linking of the polymer in the formed polymer particles tends to be high. The water-absorbent resin particles containing the polymer particles having high crosslink uniformity tend to exhibit a moderately low liquid permeation ratio A.

In the production of the water-absorbent resin particles, the surface portion of the hydrogel polymer may be crosslinked (surface crosslinked) using a crosslinking agent in any of the drying steps and subsequent steps. By performing surface cross-linking, it is easy to control the water absorption characteristics of the water-absorbent resin particles. The water content of the surface-crosslinked hydrogel polymer may be 5 to 50% by mass, 10 to 40% by mass, or 15 to 35% by mass. The water content (mass%) of the water-containing gel 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 water content of the hydrogel polymer calculated by adding the water content used according to.
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 surface cross-linking agents include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; (poly) ethylene glycol di Polyglycidyl compounds such as glycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, trimethylpropan triglycidyl ether (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether; epichlorohydre Haloepoxy compounds such as phosphorus, epibromhydrin and α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetane methanol, 3-ethyl-3- Oxetane compounds such as oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol; 1,2-ethylenebisoxazoline Oxazoline compounds such as; carbonate compounds such as ethylene carbonate; hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide can be mentioned. The surface cross-linking agent may be used alone or in combination of two or more. The surface cross-linking agent may be a polyglycidyl compound, and may be (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and It may contain at least one selected from the group consisting of polyglycerol polyglycidyl ether.

The amount of the surface cross-linking agent is 0.00001 to 0.02 mol, 0.00005 to 0.01 mol, or 0.0001 to 0.005 with respect to 1 mol of the ethylenically unsaturated monomer used for the polymerization. It may be a mole. When the amount of the surface cross-linking agent is 0.00001 mol or more, the cross-linking density on the surface portion of the water-absorbent resin particles is sufficiently increased, and the gel strength of the water-absorbent resin particles can be easily increased. When the amount of the surface cross-linking agent is 0.02 mol or less, it is easy to increase the water absorption amount of the water-absorbent resin particles.

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

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

The water-absorbent resin particles 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 include inorganic particles arranged on the surface of the polymer particles, the ratio of the amount of the inorganic particles to the mass of the polymer particles is 0.2% by mass or more, 0.5% by mass or more, 1 It may be 0.0% by mass or more, 1.5% by mass or more, 5.0% by mass or less, or 3.5% by mass or less. Water-absorbent resin particles containing a large amount of inorganic particles tend to exhibit a smaller liquid permeation ratio A. 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.

The absorber according to one embodiment contains the water-absorbent resin particles according to this embodiment. The absorber according to the present embodiment can contain a fibrous substance, for example, a mixture containing water-absorbent resin particles and the fibrous substance. The structure of the absorber may be, for example, a structure in which the water-absorbent resin particles and the fibrous material are uniformly mixed, and the water-absorbent resin particles are sandwiched between the fibrous material formed in a sheet or layer. It may be a configuration.

Examples of the fibrous material 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 average fiber length of the fibrous material is usually 0.1 to 10 mm and may be 0.5 to 5 mm. The fibrous material may be used alone or in combination of two or more. As the fibrous material, hydrophilic fibers can be used.

The mass ratio of the water-absorbent resin particles in the absorber may be 2 to 100% by mass, 10 to 90% by mass, or 20 to 80% by mass with respect to the total of the water-absorbent resin particles and the fibrous material.

In order to enhance the shape retention before and during use of the absorber, the fibers may be adhered to each other by adding an adhesive binder to the fibrous material. 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; a side-by-side of polypropylene and polyethylene, and a non-total fusion type binder having 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.

Examples of the adhesive emulsion include 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.

The absorber may contain an inorganic powder (for example, amorphous silica), a deodorant, an antibacterial agent, a fragrance, and the like. When the water-absorbent resin particles contain inorganic particles, the absorber may contain inorganic powder in addition to the inorganic particles in the water-absorbent resin particles.

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

The absorbent article according to one embodiment includes an absorber according to this embodiment. The absorbent article according to the present embodiment is a core wrap that retains the shape of the absorber; a liquid permeable sheet that is arranged on the outermost side of the side where the liquid to be absorbed enters; and the side where the liquid to be absorbed enters. Examples thereof include a liquid permeable sheet arranged on the outermost side on the opposite side. Absorbent articles 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. ..

FIG. 2 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in FIG. 2 includes an absorbent body 10, core wraps 20a and 20b, a liquid permeable sheet 30, and a liquid permeable sheet 40. 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. 2, 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.

The absorber 10 has a water-absorbent resin particle 10a according to the present embodiment and a fiber layer 10b containing a fibrous material. The water-absorbent resin particles 10a are dispersed in the fiber layer 10b.

The core wrap 20a is arranged on one side of the absorber 10 (upper side of the absorber 10 in FIG. 2) in contact with the absorber 10. The core wrap 20b is arranged on the other side of the absorber 10 (lower side of the absorber 10 in FIG. 2) in contact with the absorber 10. The absorber 10 is arranged between the core wrap 20a and the core wrap 20b. Examples of the core wraps 20a and 20b include tissue paper, non-woven fabric and the like. The core wrap 20a and the core wrap 20b have, for example, a main surface having the same size as the absorber 10.

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 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 permeable sheet 30 and the liquid permeable sheet 40 have, for example, a main surface wider than the main surface of the absorber 10, and the outer edges of the liquid permeable sheet 30 and the liquid permeable sheet 40 are It extends around the absorber 10 and the core wraps 20a, 20b.

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. The absorber 10 shown in FIG. 2 is held in shape by being sandwiched between two

core wraps

20a and 20b. The method of retaining the shape by the core wrap that retains the shape of the absorber is not limited to this, and for example, the absorber may be sandwiched between a single folded core wrap. The core wrap may form a bag and an absorber may be placed therein.

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 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. The liquid permeable sheet 30 may include a spunbonded non-woven fabric.

The liquid permeable sheet 30 is preferably a spunbonded non-woven fabric. The spunbonded non-woven fabric may be a single-layer spunbonded non-woven fabric, or may be a multi-layer laminated non-woven fabric having at least a single-layer spunbonded non-woven fabric as a spunbond layer. In the case of a laminated spunbonded non-woven fabric, one or both outermost layers are usually spunbond layers. Examples of the laminated structure of the spunbonded non-woven fabric of the laminated body include a spunbond layer / spunbond layer (SS non-woven fabric), a spunbond layer / melt blow layer / spunbond layer (SMS non-woven fabric), and a spunbond layer / melt blow layer / melt blow. Layer / spunbond layer (SMMS non-woven fabric) can be mentioned. In these laminated configurations, the layers are laminated in the order described.

The non-woven fabric used as the liquid permeable sheet 30 may have 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. A non-woven fabric having a hydrophilicity of 5 to 200 measured according to the measuring method of 68 (2000) may be used. The hydrophilicity of the non-woven fabric may be 10 to 150. Pulp and paper test method No. For details of 68, for example, WO2011 / 086843 can be referred to.

The hydrophilic non-woven fabric may be formed by containing fibers showing appropriate hydrophilicity such as rayon fibers, or hydrophobic chemical fibers such as polyolefin fibers and polyester fibers are hydrophilized. It may be formed by the obtained fibers. 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 may be a non-woven fabric having a large weight. The basis weight (mass per unit area) of the liquid permeable sheet 30 may be 5 to 200 g / m ² , 8 to 150 g / m ² , or 10 to 100 g / m ² . The thickness of the liquid permeable sheet 30 may be 20 to 1400 μm, 50 to 1200 μm, or 80 to 1000 μm.

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) non-woven fabric in which a water-resistant melt-blow non-woven fabric is sandwiched between high-strength spunbond 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 may have breathability from the viewpoint that stuffiness at the time of wearing is reduced and discomfort given to the wearer can be reduced. 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 absorbent article 100 is manufactured, for example, by a method comprising placing the absorber 10 between the core wraps 20a, 20b and placing them between the liquid permeable sheet 30 and the liquid impermeable sheet 40. Can be done. A laminate in which the liquid permeable sheet 40, the core wrap 20b, the absorber 10, the core wrap 20a, and the liquid permeable sheet 30 are laminated in this order is pressurized as necessary.

The absorber 10 is formed by mixing the water-absorbent resin particles 10a with the fibrous material. The water-absorbent resin particles having the liquid permeation ratio A of more than 0% and 60% or less may be selected and selectively used to form the absorber 10.

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.

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

1. 1. Preparation of water-absorbent resin particles Example 1
<First stage polymerization reaction>
A round-bottomed cylindrical separable flask having an inner diameter of 11 cm and an internal volume of 2 L equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer was prepared. A stirring blade 200 whose outline is shown in FIG. 3 was attached to the stirring machine. The stirring blade 200 includes a shaft 200a and a flat plate portion 200b. The flat plate portion 200b is welded to the shaft 200a and has a curved tip. The flat plate portion 200b is formed with four slits S extending along the axial direction of the shaft 200a. The four slits S are arranged in the width direction of the flat plate portion 200b. The width of the two inner slits S is 1 cm. The width of the two outer slits S is 0.5 cm. The length of the flat plate portion 200b is about 10 cm, and the width of the flat plate portion 200b is about 6 cm.

In the prepared separable flask, 293 g of n-heptane and 0.736 g of a dispersant (maleic anhydride-modified ethylene / propylene copolymer, manufactured by Mitsui Chemicals, Inc., high wax 1105A) were mixed. The dispersant was dissolved in n-heptane by heating the mixture in the separable flask to 80 ° C. while stirring with a stirrer. The formed reaction solution was cooled to 50 ° C.

92.0 g (1.03 mol) of an acrylic acid aqueous solution having a concentration of 80.5 mass% was placed in a beaker having an internal volume of 300 mL. While cooling the beaker from the outside, 147.7 g of a 20.9 mass% sodium hydroxide aqueous solution was added dropwise to the acrylic acid aqueous solution, thereby neutralizing 75 mol% of acrylic acid. 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HECAW-15F) as a thickener and 2,2'-azobis (2-amidinopropane) 2 as a water-soluble radical polymerization initiator in the neutralized acrylic acid aqueous solution. Dissolve these by adding 0.092 g (0.339 mmol) of hydrochloride, 0.0162 g (0.068 mmol) of sodium persulfate, and 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent. The first-stage monomer aqueous solution was prepared.

The first-stage monomer aqueous solution was added to the reaction solution in the separable flask described above, and the reaction solution was stirred for 10 minutes. Next, a surfactant solution containing 6.62 g of n-heptane and 0.736 g of sucrose stearic acid ester (HLB: 3, Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370) was added to the reaction solution, and the mixture was stirred. The inside of the system was sufficiently replaced with nitrogen while stirring the reaction solution at a blade rotation speed of 425 rpm. Then, the polymerization reaction was allowed to proceed over 60 minutes while heating the separable flask in a water bath at 70 ° C. By this polymerization reaction, a first-stage polymerization slurry liquid containing a hydrogel-like polymer was obtained.

<Second stage polymerization reaction>
128.8 g (1.44 mol) of an aqueous acrylic acid solution having a concentration of 80.5 mass% was placed in a beaker having an internal volume of 500 mL. While cooling the beaker from the outside, 159.0 g of a sodium hydroxide aqueous solution having a concentration of 27% by mass was added dropwise to the acrylic acid aqueous solution, thereby neutralizing 75 mol% of acrylic acid. Next, in an aqueous acrylic acid solution, 0.129 g (0.475 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride salt and 0.0226 g (0.095 mmol) of sodium persulfate as a water-soluble radical polymerization initiator. ) And 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent were added to dissolve them to prepare a second-stage monomer aqueous solution.

The first-stage polymerized slurry liquid in the separable flask was cooled to 25 ° C. while stirring at a stirring blade rotation speed of 650 rpm. The whole amount of the second-stage monomer aqueous solution was added thereto, and then the inside of the system was replaced with nitrogen over 30 minutes. Then, while heating the separable flask in a water bath at 70 ° C., the second-stage polymerization reaction was allowed to proceed over 60 minutes.

0.589 g of a 45% by mass diethylenetriamine-5 sodium acetate aqueous solution was added to the reaction solution after the second stage polymerization reaction under stirring. Then, a separable flask was immersed in an oil bath at 125 ° C., and 239.6 g of water was extracted from the system by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of an ethylene glycol diglycidyl ether aqueous solution having a concentration of 2% by mass was added to the reaction solution as a surface cross-linking agent, and the reaction solution was held at 83 ° C. for 2 hours to obtain a surface cross-linking agent. The cross-linking reaction was allowed to proceed.

From the reaction solution after the cross-linking reaction with the surface cross-linking agent, n-heptane was distilled off by heating at 125 ° C. to obtain a dried product of polymer particles. The obtained polymer particles were passed through a sieve having an opening of 850 μm. Then, 2.0% 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, and the water-absorbent resin particles 230 containing the amorphous silica are mixed. 5.5 g was obtained. The medium particle size of the obtained water-absorbent resin particles was 367 μm.

Example 2
The radical polymerization initiator used in the preparation of the aqueous solution in the first stage was changed to 0.0648 g (0.272 mmol) of sodium persulfate, and the amount of ethylene glycol diglycidyl ether added as an internal cross-linking agent was 0. Changed to 0156 g (0.090 mmol), changed the stirrer rotation speed at the time of nitrogen substitution to 350 rpm in the preparation of the first stage polymerization slurry liquid, and radical polymerization used in the preparation of the second stage aqueous liquid. The initiator was changed to 0.0907 g (0.381 mmol) of sodium persulfate, the amount of ethylene glycol diglycidyl ether added as an internal cross-linking agent was changed to 0.0129 g (0.074 mmol), and 235.3 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that the amount of water extracted to the outside of the system by co-boiling distillation was changed to 254.5 g. The medium particle size of the water-absorbent resin particles was 365 μm.

Example 3
A round-bottomed cylindrical separable flask having an inner diameter of 11 cm and an internal volume of 2 L equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer similar to that in Example 1 was prepared. In the prepared separable flask, 536.3 g of n-heptane and 1.237 g of a dispersant (Sorbitan monolaurate, manufactured by NOF CORPORATION, Nonion LP-20R, HLB value 8.6) were mixed. The dispersant was dissolved in n-heptane by heating the mixture in the separable flask to 50 ° C. while stirring with a stirrer. The formed reaction solution was cooled to 40 ° C.

103.1 g (1.15 mol) of an acrylic acid aqueous solution having a concentration of 80.5 mass% was placed in an Erlenmeyer flask having an internal volume of 500 mL. While cooling the Erlenmeyer flask with ice from the outside, 165.3 g of a 20.9 mass% sodium hydroxide aqueous solution was added dropwise to the acrylic acid aqueous solution, thereby neutralizing 75 mol% of acrylic acid. To the neutralized acrylic acid aqueous solution, 0.10 g (0.420 mmol) of sodium persulfate was added as a water-soluble radical polymerization initiator to obtain a monomer aqueous solution.

The prepared monomer aqueous solution was added to the above-mentioned reaction solution in the separable flask, and the inside of the flask was sufficiently replaced with nitrogen. Then, the separable flask was held in a water bath at 70 ° C. for 60 minutes while stirring the reaction solution at a rotation speed of the stirring blade of 300 rpm, whereby the polymerization reaction was allowed to proceed.

A dispersion containing 0.103 g of amorphous silica (Oriental Silicas Corporation, Toxile NP-S) and 100 g of n-heptane in the reaction solution while stirring the reaction solution after the polymerization reaction at a stirring blade rotation speed of 650 rpm. Was added, and stirring was continued for another 10 minutes. Then, the flask containing the reaction solution was immersed in an oil bath at 125 ° C., and 116.5 g of water was extracted from the system by azeotropic distillation of n-heptane and water. Subsequently, 9.28 g (1.07 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added to the reaction solution as a surface cross-linking agent, and the reaction solution was kept at an internal temperature of 83 ± 2 ° C. for 2 hours. The cross-linking reaction with the surface cross-linking agent was allowed to proceed.

N-heptane was distilled off from the reaction solution after the cross-linking reaction with the surface cross-linking agent to obtain a dried product of water-absorbent resin particles containing 0.1% by mass of silica amorphous silica. A dried product of the water-absorbent resin particles was passed through a sieve having an opening of 850 μm to obtain 96.5 g of the water-absorbent resin particles. The medium particle size of the obtained water-absorbent resin particles was 420 μm.

Comparative Example 1
The stirring blade was changed to one with a 4-blade inclined paddle blade with a blade diameter of 5 cm in two stages, and the radical polymerization initiator used in the preparation of the aqueous liquid in the first stage was 2,2'-azobis (2-amidino). Changed to 0.092 g (0.339 mmol) of propane) dihydrochloride and 0.018 g (0.068 mmol) of potassium persulfate, and the number of rotations of the stirrer at the time of nitrogen substitution in the preparation of the first-stage polymerized slurry Was changed to 550 rpm, and the radical polymerization initiator used in the preparation of the aqueous solution in the second stage was 0.129 g (0.475 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and excess. The change to 0.026 g (0.095 mmol) of potassium sulfate, and the change of the stirrer rotation speed when cooling the inside of the separable flask system to 25 ° C. to 1000 rpm after the preparation of the aqueous solution in the second stage. The amount of water extracted to the outside of the system by co-boiling distillation was changed to 239.2 g, and the amount of amorphous silica mixed with the polymer particles was changed to 0.2% by mass based on the mass of the polymer particles. 228.1 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except for the above. The medium particle size of the water-absorbent resin particles was 374 μm.

Comparative Example 2
The stirring blade was changed to one having a 4-blade inclined paddle blade with a blade diameter of 5 cm in two stages, and the radical polymerization initiator used in the preparation of the aqueous liquid in the first stage was 0.0736 g (0.272) of potassium persulfate. Millimole), the stirring speed at the time of nitrogen substitution was changed to 550 rpm in the preparation of the polymerized slurry liquid in the first stage, and the radical polymerization initiator used in the preparation of the aqueous liquid in the second stage was excessive. The change was made to 0.103 g (0.381 mmol) of potassium sulfate, and the number of revolutions of the stirrer when cooling the inside of the separable flask system to 25 ° C. was changed to 1000 rpm after the preparation of the aqueous solution in the second stage. The amount of water extracted to the outside of the system by radical polymerization was changed to 257.7 g, and the amount of amorphous silica mixed with the polymer particles was changed to 0.2% by mass based on the mass of the polymer particles. In the same manner as in Example 1, 228.0 g of water-absorbent resin particles were obtained. The medium particle size of the water-absorbent resin particles was 352 μm.

Comparative Example 3
The stirring blade was changed to one with a 4-blade inclined paddle blade with a blade diameter of 5 cm in two stages, and the radical polymerization initiator used in the preparation of the aqueous liquid in the first stage was 2,2'-azobis (2-amidino). Changed to 0.092 g (0.339 mmol) of propane) dihydrochloride and 0.018 g (0.068 mmol) of potassium persulfate, and added 0.0046 g (0) of ethylene glycol diglycidyl ether as an internal cross-linking agent. .026 mmol), the stirrer rotation speed at the time of nitrogen substitution was changed to 550 rpm in the preparation of the polymerization slurry liquid in the first stage, and the radical polymerization initiator used in the preparation of the aqueous liquid in the second stage. Was changed to 2,2'-azobis (2-amidinopropane) dihydrochloride 0.129 g (0.475 mmol) and potassium persulfate 0.026 g (0.095 mmol), and the second-stage aqueous solution. After the preparation of the above, the stirrer rotation speed when cooling the inside of the separable flask system to 25 ° C. was changed to 1000 rpm, and the amount of water extracted to the outside of the system by co-boiling distillation was changed to 216.7 g. In the same manner as in Example 1, 223.3 g of water-absorbent resin particles were obtained. The medium particle size of the water-absorbent resin particles was 345 μm.

Comparative Example 4
229.0 g of water-absorbent resin particles were obtained in the same manner as in Comparative Example 3 except that the amount of amorphous silica mixed with the polymer particles was changed to 0.2% by mass with respect to the mass of the polymer particles. .. The medium particle size of the water-absorbent resin particles was 348 μm.

2. Evaluation 2-1. Medium particle size 50 g of water-absorbent resin particles were used for measuring the medium particle size. The measurement was performed in an environment with a temperature of 25 ± 2 ° C. and a humidity of 50 ± 10%. 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. Water-absorbent resin particles were placed in the uppermost sieve and classified according to JIS Z 8815 (1994) using a low-tap shaker (manufactured by Iida Seisakusho Co., Ltd.). 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. By integrating the mass percentages of the water-absorbent resin particles remaining on the sieve in order from the larger particle size with respect to this particle size distribution, the opening of the sieve and the integrated value of the mass percentages of the water-absorbent resin particles remaining on the sieve are integrated. The relationship with is plotted on a logarithmic probability paper. 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.

2-2. Amount of water absorption under load The amount of water absorption of water-absorbent resin particles with respect to physiological saline under a load of 2.07 kPa was measured by measuring device Y shown in FIG. 4 under an environment of a temperature of 25 ° C. ± 2 ° C. and a humidity of 50 ± 10%. Measured using. The measuring device Y is composed of a burette unit 71, a conduit 72, a measuring table 73, and a measuring unit 74 placed on the measuring table 73. The burette portion 71 has a burette 71a extending in the vertical direction, a rubber stopper 71b arranged at the upper end of the burette 71a, a cock 71c arranged at the lower end of the burette 71a, and one end extending into the burette 71a in the vicinity of the cock 71c. It has an air introduction pipe 71d and a cock 71e arranged on the other end side of the air introduction pipe 71d. The conduit 72 is attached between the burette portion 71 and the measuring table 73. The inner diameter of the conduit 72 is 6 mm. A hole having a diameter of 2 mm is formed in the central portion of the measuring table 73, and the conduit 72 is connected to the hole. The measuring unit 74 has a cylinder 74a (made of acrylic resin (plexiglass)), a nylon mesh 74b adhered to the bottom of the cylinder 74a, and a weight 74c. The inner diameter of the cylinder 74a is 20 mm. The opening of the nylon mesh 74b is 75 μm (200 mesh). At the time of measurement, the water-absorbent resin particles 75 to be measured are uniformly sprinkled on the nylon mesh 74b. The diameter of the weight 74c is 19 mm, and the mass of the weight 74c is 59.8 g. The weight 74c is placed on the water-absorbent resin particles 75, and a load of 2.07 kPa can be applied to the water-absorbent resin particles 75.

After 0.100 g of the water-absorbent resin particles 75 were placed in the cylinder 74a of the measuring device Y, the weight 74c was placed and the measurement was started. Since the same volume of air as the physiological saline absorbed by the water-absorbent resin particles 75 is quickly and smoothly supplied to the inside of the burette 71a from the air introduction pipe, the water level of the physiological saline inside the burette 71a is reduced. However, the amount of physiological saline absorbed by the water-absorbent resin particles 75 is obtained. The scale of the burette 71a is engraved from top to bottom in 0 mL to 0.5 mL increments. As the water level of the physiological saline, the scale Va of the burette 71a before the start of water absorption and the scale Vb of the burette 71a 60 minutes after the start of water absorption are read, and the amount of water absorption under load (under a load of 2.07 kPa) is read from the following formula. The amount of water absorbed with respect to physiological saline) was calculated.
Water absorption under load [mL / g] = (Vb-Va) /0.1

2-3. Water absorption C
The water absorption amount C was measured in an environment of a temperature of 25 ± 2 ° C. and a humidity of 50 ± 10%. First, 500 g of physiological saline (saline with a concentration of 0.9% by mass) was weighed into a beaker having an internal volume of 500 mL. While stirring at 600 rpm, 2.0 g of water-absorbent resin particles were dispersed in physiological saline so as not to generate mamaco. The water-absorbent resin particles were sufficiently swollen by being left to stand for 60 minutes in a stirred state. The contents of the beaker were filtered using an open 75 μm standard sieve. The sieve on which the swelling gel was taken out was tilted so as to have an inclination angle of about 30 degrees with respect to the horizontal, and left in that state for 30 minutes to remove excess water. The mass Wb (g) of the sieve on which the swelling gel was placed was measured. From Wb and the mass Wa (g) of the sieve measured in advance, the water absorption amount C was determined by the following formula.
Water absorption C [g / g] = (Wb-Wa) /2.0

2-4. Water absorption B
Using the measuring device shown in FIG. 1, the water absorption amount B was measured in an environment of a temperature of 25 ± 2 ° C. and a humidity of 50 ± 10%. 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. First, the cock 22 and the cock 24 of the burette portion 2 were closed, and a physiological saline solution 50 (saline solution having a concentration of 0.9% by mass) adjusted to 25 ° C. was put into the burette tube 21 through the opening at the upper part of the burette tube 21. 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 physiological saline 50 to prevent air bubbles from entering. The height of the measuring table 13 was adjusted so that the height of the water surface of the physiological 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 physiological 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 spunbonded non-woven fabric (SMMS non-woven fabric, basis weight 13 g / m ² , manufactured by Toray Polytech (Nantong) Co., Ltd., LIVESEN (trade name), 1.6 Dtex) formed of hydrophilized polypropylene fibers was prepared. .. A spunbonded nonwoven fabric 15 having a size of 100 mm × 100 mm was laid in the vicinity of the through hole 13a 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 into the cylinder. Then, the cylinder was carefully removed, and the water-absorbent resin particles 10a were uniformly placed in the circular region in the center of the spunbonded nonwoven fabric 15. Next, the spunbonded nonwoven fabric 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 decrease amount of the physiological saline solution 50 in the bullet tube 21 (that is, the amount of the physiological saline solution absorbed by the water-absorbent resin particles 10a) is sequentially read in units of 0.1 mL, and calculated from the start of water absorption of the water-absorbent resin particles 10a. After 5 minutes, the weight loss Wc (mL) of the physiological saline 50 was read. From the density of Wc and physiological saline (1.028 g / mL), the water absorption amount B was determined by the following formula. The water absorption amount B is the mass per 1.00 g of the water-absorbent resin particles of the absorbed physiological saline.
Water absorption B [g / g] = Wc x 1.0028 / 1.00

2-5. Liquid permeation ratio A
From the water absorption amount B and the water absorption amount C, the liquid permeation ratio A was determined by the following formula.
Liquid permeation ratio A [%] = (water absorption amount B / water absorption amount C) x 100

2-6. Preparation of absorbent article and its evaluation Using an airflow type mixer (Padformer manufactured by Otec Co., Ltd.), 10.0 g of water-absorbent resin particles and 9.5 g of crushed pulp are uniformly mixed by air papermaking. A sheet-shaped absorber having a size of 32 cm × 12 cm was prepared. The top and bottom of the absorber were sandwiched between two spunbonded non-woven fabrics having the same size as the absorber. As the spunbonded non-woven fabric, the same spunbonded non-woven fabric as that used for measuring the water absorption amount B was used. In that state, a load of 588 kPa was applied to the whole for 30 seconds to obtain an absorber with a core wrap for testing as an absorbent article.

FIG. 5 is a schematic view showing a method for evaluating the leakability of an absorbent article. The support plate 1 of length 45cm having a flat inclined surface S ₁ (wherein the acrylic resin plate) was fixed by frame 41 in a state that is inclined 30 ± 2 degrees relative to the horizontal plane S _0. The surface of the support plate 1 was smooth, and the liquid did not stay or be absorbed by the support plate 1. Temperature 25 ± 2 ° C., under a humidity 50 ± 10% of the environment, on the inclined surface S ₁ of the fixed support plate 1, the upper end of the absorbent article 100 for testing, the longitudinal direction of the absorbent article 100 is supported It was attached with an adhesive tape so as to be oriented along the longitudinal direction of the plate 1. The lower end of the absorbent article 100 was not attached to the support plate 1. Next, a mark was marked at a position 8 cm above the center of the absorber in the absorbent article 100. The dropping funnel 42 had an inlet having an inner diameter of 3.4 mm. The dropping funnel 42 was fixed to the gantry 41 at a position where the tip of the insertion port was vertically above the mark and at a distance of 10 ± 1 mm. The throttle of the cock of the dropping funnel 42 was adjusted so that the liquid was poured at a rate of 3 mL / sec. A balance 43 was arranged below the support plate 1, and a metal tray 44 was placed on the balance 43.

After starting the balance 43 and correcting the display to zero, 80 mL of the test solution 55 (artificial urine) adjusted to 25 ± 1 ° C. was charged into the dropping funnel 42 at a time. The weight of the test solution that was dropped from the dropping funnel 42 and flowed down without being absorbed by the absorbent article 100 and entered the metal tray 44 was recorded as the first leakage amount [g]. At 10-minute intervals from the start of the first test solution injection, the second and third test solutions were added in the same manner as the first test solution, and the leakage amount [g] of each was recorded. It is judged that the smaller the value of the amount of leakage, the smaller the amount of liquid leakage when the absorbent article is worn. The artificial urine used as the test solution was prepared by mixing the following components.
-Ion-exchanged water: 5919.6 g
・ NaCl: 60.0 g
・ CaCl2 ・ H2O: 1.8g
-MgCl2.6H2O: 3.6g
・ Edible blue No. 1 (for coloring): 0.15 g
-Triton X-100 (1%) (octylphenol ethoxylate aqueous solution): 15.0 g

Table 1 shows the evaluation results. The absorbent article prepared by using the water-absorbent resin particles of the example in which the liquid permeation ratio A shows a specific value caused only a small amount of liquid leakage until the third test liquid injection in the leakability evaluation test. ..

1 ... Support plate, 2 ... Burette, 3 ... Clamp, 5 ... Conduit, 10 ... Absorber, 10a ... Water-absorbent resin particles, 10b ... Fiber layer, 11 ... Mount, 13 ... Measuring table, 13a ... Through hole, 15 ... spunbonded non-woven fabric, 20a ... core wrap, 20b ... core wrap, 21 ... burette tube, 22 ... cock, 23 ... rubber stopper, 24 ... cock, 25 ... air introduction tube, 30 ... liquid permeable sheet, 40 ... liquid impermeable Sheet, 41 ... gantry, 42 ... dripping funnel, 43 ... balance, 44 ... metal tray, 50 ... physiological saline, 71 ... burette, 71a ... burette, 71b ... rubber stopper, 71c ... cock, 71d ... air introduction pipe , 71e ... cock, 72 ... conduit, 73 ... measuring table, 74 ... measuring unit, 74a ... cylinder, 74b ... nylon mesh, 74c ... weight, 75 ... water-absorbent resin particles, 100 ... absorbent article, 200a ... shaft, 200b ... flat plate, S ... slit, S0 ... horizontal plane, S1 ... inclined surface, Y ... measuring device.

Claims

The following formula:
Liquid permeation ratio A [%] = (water absorption B [g / g] / water absorption C [g / g]) × 100
The water-absorbent resin particles having a liquid permeation ratio A calculated by the above method are more than 0% and 60% or less.
When the physiological saline supplied through the spunbonded non-woven fabric is absorbed by the water-absorbent resin particles of 1.00 g by the DW method under no pressure, the water-absorbent resin particles absorb the water-absorbent amount B. It is the mass of physiological saline per 1 g of the water-absorbent resin particles that is absorbed within 5 minutes after the start of.
The mass per unit area of the spunbonded non-woven fabric is 11 to 15 g / m 2 .
The water absorption amount C is the mass of the physiological saline solution per 1 g of the water-absorbent resin particles, which is absorbed when 2.0 g of the water-absorbent resin particles swells in 500 g of physiological saline solution over 60 minutes.
Water-absorbent resin particles.
The water-absorbent resin particle according to claim 1, wherein the water-absorbent resin particle has a water absorption amount of 20 mL / g or more with respect to a physiological saline solution under a load of 2.07 kPa.
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.
An absorbent article in which the absorber contains the water-absorbent resin particles according to claim 1 or 2.
The absorbent article according to claim 3, wherein the liquid permeable sheet contains a spunbonded non-woven fabric having a spunbond layer.
The absorbent article according to claim 4, wherein the spunbonded nonwoven fabric is a nonwoven fabric formed of hydrophilically treated polyolefin fibers.
The following formula:
Liquid permeation ratio A [%] = (water absorption B [g / g] / water absorption C [g / g]) × 100
Including a step of selecting water-absorbent resin particles having a liquid permeation ratio A of more than 0% and 60% or less calculated by
When the physiological saline supplied through the spunbonded non-woven fabric is absorbed by the water-absorbent resin particles of 1.00 g by the DW method under no pressure, the water-absorbent resin particles absorb the water-absorbent amount B. It is the mass of physiological saline per 1 g of the water-absorbent resin particles that is absorbed within 5 minutes after the start of.
The mass per unit area of the spunbonded non-woven fabric is 11 to 15 g / m 2 .
The water absorption amount C is the mass of the physiological saline solution per 1 g of the water-absorbent resin particles, which is absorbed when 2.0 g of the water-absorbent resin particles swells in 500 g of physiological saline solution over 60 minutes.
A method for producing water-absorbent resin particles.
The following formula:
Liquid permeation ratio A [%] = (water absorption B [g / g] / water absorption C [g / g]) × 100
A method for suppressing liquid leakage from an absorbent article containing water-absorbent resin particles, which comprises setting the liquid permeation ratio A of the water-absorbent resin particles to be more than 0% and 60% or less.
When the physiological saline supplied through the spunbonded non-woven fabric is absorbed by the water-absorbent resin particles of 1.00 g by the DW method under no pressure, the water-absorbent resin particles absorb the water-absorbent amount B. It is the mass of physiological saline per 1 g of the water-absorbent resin particles that is absorbed within 5 minutes after the start of.
The mass per unit area of the spunbonded non-woven fabric is 11 to 15 g / m 2 .
The water absorption amount C is the mass of the physiological saline solution per 1 g of the water-absorbent resin particles, which is absorbed when 2.0 g of the water-absorbent resin particles swells in 500 g of physiological saline solution over 60 minutes.
Method.