JP6775049B2 - Water-absorbent resin particles - Google Patents

Description

The present invention relates to water-absorbent resin particles.

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

Japanese Unexamined Patent Publication No. 6-345819 Special Table No. 09-510889

Usually, an absorber used for an absorbent article is required to absorb various liquids (urine, sweat, etc.) containing metal ions. Here, if the liquid provided to the absorber does not sufficiently permeate the absorber, the excess liquid may flow on the surface thereof and leak to the outside of the absorber. Therefore, it is necessary for the liquid containing metal ions to permeate the absorber at a sufficient speed, and it is required that a suitable permeation rate can be stably obtained regardless of the type of the liquid.

In an absorbent article using a conventional absorber, the liquid to be absorbed is not sufficiently absorbed by the absorber, and a phenomenon (liquid running) in which excess liquid flows on the surface of the absorber is likely to occur, and as a result, the liquid is absorbed. There was room for improvement in terms of leakability, which leaks out of the sex article.

An object of the present invention is to provide water-absorbent resin particles capable of suppressing liquid leakage.

One aspect of the present invention is that the 30-second value of unpressurized DW is 1.0 mL / g or more, and the contact angle measured in the tests performed in the order of i) and ii) below is 90 degrees or less. Provide some water-absorbent resin particles.
i) At 25 ° C., spherical droplets corresponding to a diameter of 3.0 ± 0.1 mm of 25% by mass saline solution are dropped onto the surface of the layer made of water-absorbent resin particles, and the water-absorbent resin particles and the droplets are dropped. To make contact with.
ii) The contact angle of the droplet is measured 30 seconds after the droplet comes into contact with the surface.

Since the water-absorbent resin particles have a 30-second value of non-pressurized DW and the contact angle within a predetermined range, liquid leakage can be suppressed. That is, the water-absorbent resin particles can effectively contribute to suppressing the occurrence of liquid leakage from the absorbent article. Here, the non-pressurized DW uses the physiological saline solution until a predetermined time elapses after the water-absorbent resin particles come into contact with the physiological saline solution (saline solution having a concentration of 0.9% by mass) under no pressure. It is the water absorption rate expressed by the amount absorbed. The non-pressurized DW is represented by the amount of absorption (mL) per 1 g of water-absorbent resin particles before absorption of physiological saline. The 30-second value of the non-pressurized DW means the amount of absorption 30 seconds after the water-absorbent resin particles come into contact with the physiological saline.

In the water-absorbent resin particles, the contact angle may be 70 degrees or less.

In the water-absorbent resin particles, the water retention amount of the physiological saline may be 20 to 60 g / g.

According to the present invention, it is possible to provide water-absorbent resin particles capable of suppressing liquid leakage.

It is the schematic which shows the measuring apparatus of the 30-second value of unpressurized DW. It is sectional drawing which shows an example of an absorbent article. It is the schematic which shows the measuring apparatus of the water absorption amount under the load of the water-absorbing resin particle.

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

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

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

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

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

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

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

The water absorption amount of the physiological saline under the load of the water-absorbent resin particles according to the present embodiment may be, for example, 10 to 40 mL / g, 15 to 35 mL / g, 20 to 30 mL / g, or 22 to 28 mL / g. .. As the water absorption amount of the physiological saline under the load, the water absorption amount (25 ° C.) at the load of 4.14 kPa can be used. The amount of water absorption can be measured by the method described in Examples described later.

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

The water-absorbent resin particles according to the present embodiment 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. Among these, the reverse phase suspension polymerization method or the aqueous solution polymerization method is preferable from the viewpoint of ensuring good water absorption characteristics of the obtained water-absorbent resin particles and facilitating control of the polymerization reaction. In the following, a reverse phase suspension polymerization method will be described as an example as a method for polymerizing an ethylenically unsaturated monomer.

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

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

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

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

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

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

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

From the viewpoint that the W / O type reverse phase suspension is in a good state, water-absorbent resin particles having a suitable particle size can be easily obtained, and industrially available, the surfactant is a sorbitan fatty acid ester. It is preferable to 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 preferably contains a sucrose fatty acid ester, and more preferably a sucrose stearic acid ester.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Among them, from the viewpoint of easily reducing the amount of the hydrocarbon dispersion medium remaining in the obtained water-absorbent resin, the surfactant is prepared after the monomer aqueous solution is dispersed in the hydrocarbon dispersion medium in which the polymer-based dispersant is dispersed. It is preferable to carry out the polymerization after further dispersing the above.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The water-absorbent resin particles according to the present embodiment may be composed of only polymer particles, and for example, a gel stabilizer and a metal chelating agent (ethylenediaminetetraacetic acid and a salt thereof, diethylenetriamine-5 acetic acid and a salt thereof, for example, diethylenetriamine). 5 Sodium acetate, etc.), and various additional components selected from fluidity improvers (lubricants) and the like can be further included. Additional components may be placed inside the polymer particles, on the surface of the polymer particles, or both. As the additional component, a fluidity improver (lubricant) is preferable, and inorganic particles are more preferable. Examples of the inorganic particles include silica particles such as amorphous silica.

The water-absorbent resin particles 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 inorganic particles to the mass of the polymer particles is 0.2% by mass or more, 0.5% by mass or more, 1.0. It may be 5% by mass or more, 1.5% by mass or more, 5.0% by mass or less, or 3.5% by mass or less. The inorganic particles here usually have a minute size as compared with the size of the polymer particles. For example, the average particle size of the inorganic particles may be 0.1 to 50 μm, 0.5 to 30 μm, or 1 to 20 μm. The average particle size here can be a value measured by a dynamic light scattering method or a laser diffraction / scattering method. When the amount of the inorganic particles added is within the above range, it is easy to obtain water-absorbent resin particles having suitable water-absorbing characteristics, particularly non-pressurized DW and contact angle.

One embodiment of the method for producing the water-absorbent resin particles may further include a step of evaluating the leakability of the obtained water-absorbent resin particles by the method according to the above-described embodiment. For example, the water-absorbent resin particles whose diffusion distance D measured value is smaller than the reference value (for example, 14 cm) may be selected. Thereby, the water-absorbent resin particles capable of suppressing the liquid leakage of the absorbent article can be produced more stably.

The 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 or another 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 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 80% by mass, or 20 to 60% by mass with respect to the total of the water-absorbent resin particles and the fibrous material.

In order to improve 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; and a non-total fusion type binder having a side-by-side structure of polypropylene and polyethylene or a core-sheath structure. In the above-mentioned non-total fusion type binder, only the polyethylene portion can be heat-sealed.

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

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

The absorber according to the present embodiment 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 according to the present embodiment 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 or 0.3 to 15 mm.

The absorbent article according to the present embodiment includes an absorbent body according to the present 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 tissues, non-woven fabrics 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. Examples of the liquid permeable sheet 30 include non-woven fabrics made of synthetic resins such as polyethylene, polypropylene, polyester and polyamide, and porous sheets. 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. Examples of the liquid impermeable sheet 40 include a sheet made of a synthetic resin such as polyethylene, polypropylene, and polyvinyl chloride, and a sheet made of a composite material of these synthetic resins and a non-woven fabric. 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. Further, the method of retaining the shape of the absorber 10 by using the core wraps 20a and 20b is not particularly limited, and as shown in FIG. 2, the absorber may be wrapped by a plurality of core wraps, and the absorber is wrapped by one core wrap. It may be.

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

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

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

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

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

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

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

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

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

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

[Example 3]
In the preparation of the first-stage aqueous solution, 0.0736 g (0.272 mmol) of potassium persulfate was used without using 2,2'-azobis (2-amidinopropane) dihydrochloride as the water-soluble radical polymerizer. 0.090 g of potassium persulfate (2) potassium persulfate (2) without using 2,2'-azobis (2-amidinopropane) dihydrochloride as the water-soluble radical polymerizer in the preparation of the aqueous solution in the second stage. 0.334 mmol) was used, 247.9 g of water was extracted from the system by co-boiling distillation in the hydrogel polymer after the second stage polymerization, and the mass of the polymer particles was increased. 231.0 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 0.5% by mass of amorphous silica was mixed with the polymer particles. The medium particle size of the water-absorbent resin particles was 355 μm.

[Example 4]
In the preparation of the aqueous solution in the first stage, 0.0736 g (0.272 mmol) of potassium persulfate was used without using 2,2'-azobis (2-amidinopropane) dihydrochloride as the water-soluble radical polymerizer. 0.090 g of potassium persulfate (2) potassium persulfate (2) without using 2,2'-azobis (2-amidinopropane) dihydrochloride as the water-soluble radical polymerizer in the preparation of the aqueous solution in the second stage. 0.334 mmol) was used, and 239.7 g of water was extracted from the system by co-boiling distillation in the hydrogel polymer after the second stage polymerization, and with respect to the polymer particles. , 229.2 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 0.5% by mass of amorphous silica was mixed. The medium particle size of the water-absorbent resin particles was 377 μm.

[Comparative Example 1]
In the preparation of the aqueous solution in the first stage, 0.0736 g (0.272 mmol) of potassium persulfate was used without using 2,2'-azobis (2-amidinopropane) dihydrochloride as the water-soluble radical polymerizer. In the preparation of the aqueous solution in the second stage, 0.090 g of potassium persulfate (2,2'-azobis (2-amidinopropane) dihydrochloride was not used as the water-soluble radical polymerization agent. 0.334 mmol) was used, 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether was used as the internal cross-linking agent, and no cross-linking agent for post-polymerization cross-linking was added. In the hydrogel polymer after the stage polymerization, 256.1 g of water was extracted out of the system by co-boiling distillation, and 0.1% by mass of amorphous silica was weighted with respect to the mass of the polymer particles. 230.8 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that they were mixed with the coalesced particles. The medium particle size of the water-absorbent resin particles was 349 μm.

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

[Comparative Example 3]
Ethylene glycol diglycidyl ether 0.0046 g (0.026 mmol) was used as the internal cross-linking agent in the preparation of the first-stage aqueous liquid, and ethylene glycol was used as the internal cross-linking agent in the preparation of the second-stage aqueous liquid. 0.0116 g (0.067 mmol) of diglycidyl ether, no cross-linking agent added after polymerization, and 234.2 g of water by co-boiling distillation in the hydrogel polymer after the second stage polymerization. 229.6 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that the particles were extracted from the system. The medium particle size of the water-absorbent resin particles was 355 μm.

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

<Amount of water absorption under load of water-absorbent resin particles>
The water absorption amount (room temperature, 25 ° C. ± 2 ° C.) of the physiological saline under the load (pressurization) of the water-absorbent resin particles was measured using the measuring device Y shown in FIG. The measuring device Y is composed of a burette unit 61, a conduit 62, a measuring table 63, and a measuring unit 64 placed on the measuring table 63. The burette portion 61 has a burette 61a extending in the vertical direction, a rubber stopper 61b arranged at the upper end of the burette 61a, a cock 61c arranged at the lower end of the burette 61a, and one end extending into the burette 61a in the vicinity of the cock 61c. It has an air introduction pipe 61d and a cock 61e arranged on the other end side of the air introduction pipe 61d. The conduit 62 is attached between the burette portion 61 and the measuring table 63. The inner diameter of the conduit 62 is 6 mm. A hole having a diameter of 2 mm is formed in the central portion of the measuring table 63, and the conduit 62 is connected to the hole. The measuring unit 64 has a cylinder 64a (made of acrylic resin (plexiglass)), a nylon mesh 64b adhered to the bottom of the cylinder 64a, and a weight 64c. The inner diameter of the cylinder 64a is 20 mm. The opening of the nylon mesh 64b is 75 μm (200 mesh). Then, at the time of measurement, the water-absorbent resin particles 65 to be measured are uniformly sprinkled on the nylon mesh 64b. The diameter of the weight 64c is 19 mm, and the mass of the weight 64c is 120 g. The weight 64c is placed on the water-absorbent resin particles 65, and a load of 4.14 kPa can be applied to the water-absorbent resin particles 65.

After 0.100 g of the water-absorbent resin particles 65 were placed in the cylinder 64a of the measuring device Y, the weight 64c was placed and the measurement was started. Since the same volume of air as the physiological saline absorbed by the water-absorbent resin particles 65 is quickly and smoothly supplied to the inside of the burette 61a from the air introduction pipe, the water level of the physiological saline inside the burette 61a is reduced. However, the amount of physiological saline absorbed by the water-absorbent resin particles 65 is obtained. The scale of the burette 61a is engraved from the top to the bottom in increments of 0 mL to 0.5 mL, and the scale Va of the burette 61a before the start of water absorption and the burette 61a 60 minutes after the start of water absorption are used as the water level of the physiological saline. The scale Vb of the above was read, and the amount of water absorption under load was calculated from the following formula. The results are shown in Table 1.
Water absorption under load [mL / g] = (Vb-Va) /0.1

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

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

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

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

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

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

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

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

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

<Inclination leak test>
(Preparation of artificial urine)
An artificial urine (test solution) was prepared by adding a small amount of Blue No. 1 to a solution prepared by mixing and dissolving the inorganic salt in ion-exchanged water so as to be present as described below. The following concentrations are based on the total mass of artificial urine.
Artificial urine composition NaCl: 0.780% by mass
CaCl ₂ : 0.022% by mass
0054 ₄ : 0.038% by mass
Blue No. 1: 0.002% by mass

(Evaluation of leakability)
The leakability of the water-absorbent resin particles was evaluated by the following procedures i), ii), iii), iv) and v).
i) A strip-shaped adhesive tape (manufactured by Diatex Co., Ltd., Piolan tape) having a length of 15 cm and a width of 5 cm is placed on a laboratory table with the adhesive side facing up, and the water-absorbent resin particles 3 are placed on the adhesive side. .0 g was evenly sprayed. A stainless steel roller (mass 4.0 kg, diameter 10.5 cm, width 6.0 cm) is placed on top of the sprayed water-absorbent resin particles, and the roller is reciprocated three times between both ends in the longitudinal direction of the adhesive tape. It was. As a result, a water-absorbing layer made of water-absorbent resin particles was formed on the adhesive surface of the adhesive tape.
ii) The adhesive tape was erected vertically to remove excess water-absorbent resin particles from the water-absorbent layer. The roller was placed on the water absorption layer again, and the adhesive tape was reciprocated three times between both ends in the longitudinal direction.
iii) In a room with a temperature of 25 ± 2 ° C., an acrylic resin plate having a rectangular flat main surface with a length of 30 cm and a width of 55 cm is arranged in a width direction parallel to a horizontal plane, and the main surface and the horizontal plane are 30 degrees. I fixed it to make it. An adhesive tape having a water absorbing layer formed on the main surface of the fixed acrylic plate was attached in a direction in which the water absorbing layer was exposed and the longitudinal direction thereof was perpendicular to the width direction of the acrylic resin plate.
iV) 0.25 mL of the test solution at a liquid temperature of 25 ° C. using a micropipette (Pipetteman Neo P1000N manufactured by MS Equipment Co., Ltd.) from a height of about 1 cm from the surface at a position about 1 cm from the upper end of the water absorption layer, 1 All were injected within seconds.
v) Thirty seconds after the start of injection of the test solution, the maximum value of the moving distance of the test solution injected into the water absorption layer was read and recorded as the diffusion distance D. The diffusion distance D is a distance on the main surface connecting the dropping point (injection point) and the longest reaching point with a straight line in the direction perpendicular to the short side horizontal plane of the acrylic resin plate. When the diffusion distance D was 14 cm or more, liquid leakage occurred.

From the results in Table 1, it was shown that the water-absorbent resin particles obtained in the examples can suppress liquid leakage as compared with the water-absorbent resin particles obtained in the comparative example.

1 ... Burette, 3 ... Clamp, 5 ... Conduit, 10 ... Absorber, 10a, 65 ... Water-absorbent resin particles, 10b ... Fiber layer, 11 ... Mount, 13 ... Measuring table, 13a ... Through hole, 15 ... Nylon mesh Sheet, 20a, 20b ... Core wrap, 21 ... Burette tube, 22 ... Cock, 23 ... Rubber stopper, 24 ... Cock, 25 ... Air introduction tube, 30 ... Liquid permeable sheet, 40 ... Liquid permeable sheet, 50 ... 0 .9 mass% saline, 61 ... burette, 61a ... burette, 61b ... rubber stopper, 61c ... cock, 61d ... air introduction pipe, 61e ... cock, 62 ... conduit, 63 ... measuring table, 64 ... measuring unit, 64a ... Cylindrical, 64b ... Nylon mesh, 64c ... Weight, 100 ... Absorbent article.

Claims (3)

Polymer particles containing a crosslinked polymer having a monomer unit derived from an ethylenically unsaturated monomer containing at least one compound selected from the group consisting of (meth) acrylic acid and a salt thereof, and the polymer. Including silica particles placed on the surface of the particles ,
The water-absorbent resin particles in which the ratio of (meth) acrylic acid and a salt thereof is 70 to 100 mol% with respect to the total amount of the monomer units in the crosslinked polymer.
The 30-second value of unpressurized DW is 1.0 mL / g or more.
The contact angle measured in the tests conducted in the order of i) and ii) below is 20 degrees or more and 80 degrees or less.
Water-absorbent resin particles having a water retention capacity of 35 to 60 g / g.
i) At 25 ° C., spherical droplets corresponding to a diameter of 3.0 ± 0.1 mm of 25% by mass saline solution are dropped onto the surface of the layer composed of the water-absorbent resin particles, and the water-absorbent resin particles and the above. Contact with droplets.
ii) The contact angle of the droplet is measured 30 seconds after the droplet comes into contact with the surface. The water-absorbent resin particle according to claim 1, wherein the contact angle is 20 degrees or more and 70 degrees or less. The water-absorbent resin particle according to claim 1 or 2, wherein the 30-second value of the non-pressurized DW is 3.0 mL / g or more.

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