JP6780047B2 - Water-absorbent resin particles, absorbers and absorbent articles - Google Patents

Description

The present invention relates to water-absorbent resin particles, absorbers and absorbent articles.

Conventionally, an absorber containing water-absorbent resin particles has been used as an absorbent article for absorbing a liquid (for example, urine) containing water as a main component. For example, Patent Documents 1 and 2 below disclose water-absorbent resin particles having a predetermined water absorption rate based on the conventional Vortex method at 600 rpm.

Japanese Unexamined Patent Publication No. 2013-132433 JP-A-2008-178667

If the liquid provided to the absorbent article does not sufficiently permeate the absorbent article, the excess liquid may flow on the surface of the absorbent article and leak to the outside of the absorbent article. Therefore, it is required that the liquid permeates the absorbent article at an excellent permeation rate.

One aspect of the present invention is to provide water-absorbent resin particles capable of obtaining an absorbent article having an excellent permeation rate. Another aspect of the present invention is to provide an absorber and an absorbent article using the water-absorbent resin particles.

The present inventor can obtain an excellent permeation rate when the water-absorbent resin particles are used in an absorbent article even when the water-absorbent resin particles are excellent in water absorption rate based on the conventional Vortex method at 600 rpm. After finding that it may be difficult, it was found that the water-absorbent resin particles having a suitable water absorption rate based on the low-speed flow Vortex method at 300 rpm are effective in obtaining an absorbent article having an excellent permeation rate. It was.

One aspect of the present invention provides water-absorbent resin particles having a water absorption rate of 10 to 50 seconds based on the Voltex method at 300 rpm.

According to the above-mentioned water-absorbent resin particles, an absorbent article having an excellent permeation rate can be obtained.

Another aspect of the present invention provides an absorber containing the above-mentioned water-absorbent resin particles.

Another aspect of the invention provides an absorbent article comprising the absorber described above.

According to one aspect of the present invention, it is possible to provide water-absorbent resin particles capable of obtaining an absorbent article having an excellent permeation rate. Further, according to another aspect of the present invention, it is possible to provide an absorber and an absorbent article using the water-absorbent resin particles. According to another aspect of the present invention, it is possible to provide application of resin particles, absorbers and absorbent articles to absorbents.

It is sectional drawing which shows an example of an absorbent article.

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

In the present specification, "acrylic" and "methacryl" are collectively referred to as "(meth) acrylic". Similarly, "acrylate" and "methacrylate" are also referred to as "(meth) acrylate". In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range of one step can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range of another step. In the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. "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. "Saline" refers to a 0.9% by mass sodium chloride aqueous solution.

In the water-absorbent resin particles according to the present embodiment, the water absorption rate based on the Vortex method (low-speed flow Vortex method) at a rotation speed of 300 rpm (rpm = min ^-1 ) is 10 to 50 seconds. According to such water-absorbent resin particles, an absorbent article having an excellent permeation rate can be obtained. Further, according to the water-absorbent resin particles according to the present embodiment, when the absorbent member is brought into contact with the liquid supply position of the absorbent article in a state where the liquid has penetrated into the absorbent article, the absorbent article permeates the absorbent article. The liquid is not easily absorbed by the absorbent member (that is, excellent quick-drying property is obtained).

The water absorption rate based on the conventional Vortex method of 600 rpm established by JIS in 1996 is useful as a simple index that can easily compare resins produced by various manufacturing methods in the water-absorbent resin industry where technological development has been diverse. Met. However, as the manufacturing method is further evolved or the water absorption characteristics are imparted by various modifiers, there are cases where the index is not sufficient for applications such as absorbent articles (for example, diapers). There is.

On the other hand, the inventors of the present invention not only measure the speed of contact and uptake of the liquid and the resin, but also the absorption capacity of the resin in order to converge the vortex generated by the flow of the liquid. It is presumed that the above is required, and that the characteristics such as the ease of block formation and gel strength (easiness of swelling) depending on the shape are comprehensively evaluated. On that basis, in recent water-absorbent resins, it was hypothesized that the degree of dynamic load could be improved as an index for absorbent articles, and a low-speed flow Vortex method at 300 rpm was found.

The water absorption speed based on the low-speed flow Voltex method of 300 rpm is based on the Japanese Industrial Standards JIS K 7224 (1996) disclosed in Patent Documents 1 and 2 above, except that the rotation speed of the conventional Voltex method was changed from 600 rpm to 300 rpm. It can be obtained based on the compliant Voltex method. As the water absorption rate based on the low-speed flow Vortex method at 300 rpm, the water absorption rate at 25 ° C. can be used. Specifically, 2.0 ± 0.002 g of water-absorbent resin particles was added to 50 ± 0.1 g of physiological saline stirred at 300 rpm, and after the addition of the water-absorbent resin particles, the vortex disappeared and the liquid level disappeared. The water absorption rate can be obtained as the time [seconds] until the particles become flat.

The water absorption rate based on the low-speed flow Vortex method at 300 rpm is preferably 48 seconds or less, 45 seconds or less, 42 seconds or less, or 41 seconds or less from the viewpoint of easily obtaining an excellent permeation rate and quick-drying property. The water absorption rate based on the low-speed flow Vortex method is 40 seconds or less, 39 seconds or less, 38 seconds or less, 37 seconds or less, 36 seconds or less, 35 seconds or less, 34 seconds or less, 33 seconds or less, or 32 seconds or less. Good. The water absorption rate based on the low-speed flow Vortex method is preferably 15 seconds or longer, 20 seconds or longer, 25 seconds or longer, or 30 seconds or longer from the viewpoint of easily avoiding gel blocking due to excessively fast absorption. The water absorption rate based on the low-speed flow Vortex method may be 32 seconds or longer, 34 seconds or longer, 35 seconds or longer, or 37 seconds or longer.

In the water-absorbent resin particles according to the present embodiment, the water absorption rate based on the conventional Voltex method at 600 rpm may be in the following range. The water absorption rate based on the conventional Voltex method may be 60 seconds or less, 55 seconds or less, 50 seconds or less, 48 seconds or less, 47 seconds or less, 46 seconds or less, or 45 seconds or less. The water absorption rate based on the conventional Voltex method may be 10 seconds or longer, 15 seconds or longer, 20 seconds or longer, 25 seconds or longer, 30 seconds or longer, 32 seconds or longer, or 34 seconds or longer. From these viewpoints, the water absorption rate based on the conventional Voltex method may be 10 to 60 seconds. The water absorption rate based on the conventional Vortex method can be obtained based on the Vortex method based on the Japanese Industrial Standards JIS K 7224 (1996). As the water absorption rate based on the conventional Voltex method, the water absorption rate at 25 ° C. can be used.

The ratio of the water absorption rate R _{slow fluid} (R _sf ) based on the low-speed flow Vortex method to the water absorption rate R _conventional (R _c ) based on the conventional Vortex method R _sf / R _c is a viewpoint that excellent permeation rate and quick-drying property can be easily obtained. Therefore, 1.30 or less, 1.29 or less, 1.25 or less, 1.20 or less, 1.15 or less, 1.10 or less, or 1.09 or less is preferable. The ratio R _sf / R _c is preferably 0.50 or more, 0.60 or more, 0.70 or more, or 0.75 or more from the viewpoint of easily avoiding gel blocking due to excessively fast absorption. From these viewpoints, the ratio R _sf / R _c is preferably 0.50 to 1.30. The ratio R _sf / R _c may be 1.08 or less, 1.05 or less, 1.00 or less, 0.95 or less, 0.93 or less, or 0.92 or less. The ratio R _sf / R _c may be 0.80 or more, 0.85 or more, or 0.90 or more.

The water-absorbent resin particles according to the present embodiment may be any water-absorbent resin particles as long as they can retain water, and the liquid to be absorbed may contain water. The water-absorbent resin particles according to the present embodiment are excellent in absorption of body fluids such as urine, sweat, and blood (for example, menstrual blood). The water-absorbent resin particles according to the present embodiment can be used as a constituent component of the absorber according to the present embodiment.

The water retention amount of the physiological saline of the water-absorbent resin particles according to the present embodiment is preferably in the following range. The amount of water retained is preferably 10 g / g or more, 15 g / g or more, 20 g / g or more, 25 g / g or more, or 30 g / g or more from the viewpoint of easily obtaining an excellent permeation rate and quick-drying property. The amount of water retained is 80 g / g or less, 75 g / g or less, 70 g / g or less, 65 g / g or less, 60 g / g or less, 55 g / g or less, 50 g / g from the viewpoint of easily obtaining excellent permeation rate and quick-drying property. Hereinafter, it is preferably 48 g / g or less, or 45 g / g or less. From these viewpoints, the water retention amount is preferably 10 to 80 g / g. The amount of water retained may be 32 g / g or more or 34 g / g or more. The water retention amount may be 43 g / g or less, 42 g / g or less, 40 g / g or less, or 39 g / g or less. The amount of water retained may be 30 to 40 g / g. As the water retention amount, the water retention amount at room temperature (25 ± 2 ° C.) can be used. The amount of water retained 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 obtained by polymerizing a monomer containing an ethylenically unsaturated monomer as polymer particles. That is, the water-absorbent resin particles according to the present embodiment can have a structural unit derived from an ethylenically unsaturated monomer. As the ethylenically unsaturated monomer, a water-soluble ethylenically unsaturated monomer can be used. 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 (water absorption rate, etc.) of the obtained water-absorbent resin particles and easy 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 preferably contains at least one compound selected, more preferably 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 characteristics (water absorption rate, water retention amount, etc.), the ethylenically unsaturated monomer further preferably contains at least one compound selected from the group consisting of (meth) acrylic acid and salts thereof. That is, the water-absorbent resin particles preferably have a structural unit derived from at least one selected from the group consisting of (meth) acrylic acid and salts thereof.

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.

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.

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 is ethylenic from the viewpoint of increasing the osmotic pressure of the obtained water-absorbent resin particles and further enhancing the water absorption characteristics (water retention amount, water absorption rate, 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 unsaturated monomer. 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. , 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 preferably contains at least one compound selected from the group consisting of polyglycerin fatty acid esters and sucrose fatty acid esters. From the viewpoint that an appropriate particle size distribution of the water-absorbent resin particles can be easily obtained, and from the viewpoint that the water absorption characteristics (water absorption rate, etc.) of the water-absorbent resin particles and the performance of the absorbent article using the same can be easily improved, the surfactant is used. , Sucrose fatty acid ester is preferably contained, and sucrose stearic acid ester is more preferable.

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.

The hydrocarbon dispersion medium may contain at least one selected from the group consisting of n-heptane and cyclohexane from the viewpoint of being industrially easily available and having stable quality. 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 400 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 0.05 to 10 mmol per mol of the ethylenically unsaturated monomer. When the amount of the radical polymerization initiator used is 0.05 mmol or more, the polymerization reaction does not require a long time and is efficient. When the amount of the radical polymerization initiator used is 10 mmol 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.

The monomer aqueous solution used for the polymerization may contain a thickener in order to control the particle size of the water-absorbent resin particles. 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 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 (water absorption rate, water retention amount, etc.) 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 from the viewpoint that excellent permeation rate and quick-drying property can be easily obtained, and the water-soluble property is suppressed by appropriately cross-linking the obtained polymer, so that a sufficient water absorption amount can be easily obtained. From the viewpoint, 30 mmol or less is preferable, 0.01 to 10 mmol is more preferable, 0.012 to 5 mmol is further preferable, and 0.015 to 1 mmol is particularly preferable, per 1 mol of the ethylenically unsaturated monomer. 0.02 to 0.1 mmol is highly preferred, and 0.025 to 0.06 mmol is very preferred.

An ethylenically unsaturated monomer, a radical polymerization initiator, a surfactant, a polymer-based dispersant, a hydrocarbon dispersion medium, etc. (if necessary, an internal cross-linking agent) are mixed and heated under stirring to obtain oil. Reversed phase suspension polymerization can be performed in a medium water system.

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 (more polymer-based dispersant if necessary). Disperse. 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 after the second stage, 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 in each stage after the second stage. 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.

After the polymerization, the obtained hydrogel polymer may be crosslinked by adding a crosslinking agent after the polymerization and heating. By performing cross-linking after the polymerization, the degree of cross-linking of the hydrogel polymer can be increased to further improve the water absorption characteristics (water absorption rate, water retention amount, etc.).

Examples of the post-polymerization 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. , (Poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, and other compounds having two or more epoxy groups; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepicrolhydrin; 2,4- Compounds having two or more isocyanate groups such as tolylene diisocyanate and hexamethylene diisocyanate; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylenecarbonate; bis [N, N-di (β-hydroxy) Ethyl)] 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. .. The cross-linking agent may be used alone or in combination of two or more.

The amount of the cross-linking agent after polymerization is preferably 30 mmol or less, more preferably 10 mmol or less per 1 mol of ethylenically unsaturated monomer, from the viewpoint that suitable water absorption characteristics (water absorption rate, water retention amount, etc.) can be easily obtained. , 0.01-5 mmol is more preferred, 0.012-1 mmol is particularly preferred, 0.015-0.1 mmol is very preferred, and 0.02-0.05 mmol is very preferred.

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

Subsequently, the polymer particles (for example, polymer particles having a structural unit derived from an ethylenically unsaturated monomer) are obtained by drying in order to remove water from the obtained hydrogel-like polymer. 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, more preferably 0.005 to 0.5 part by mass, based on 100 parts by mass of the ethylenically unsaturated monomer used for the polymerization. 01 to 0.2 parts by mass is more 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 water-absorbent resin particles, surface cross-linking of the surface portion (surface and vicinity of the surface) of the hydrogel polymer is performed using a surface cross-linking agent in the drying step (moisture removing step) or subsequent steps. Is preferable. By performing surface cross-linking, it is easy to control the water absorption characteristics (water absorption rate, water retention amount, etc.) 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 surface cross-linking agent include compounds having two or more reactive functional groups. Examples of the surface 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. , (Poly) Glycerin diglycidyl ether, (Poly) Glycerin triglycidyl ether, Trimethylol propantriglycidyl ether (Poly) propylene glycol Polyglycidyl ether, (Poly) Oxetane Polyglycidyl ether and other polyglycidyl compounds; Epichlorohydrin, Haloepoxy compounds such as epibromhydrin and α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylenediisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol , 3-butyl-3-oxetane methanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, 3-butyl-3-oxetaneethanol and other oxetane compounds; 1,2-ethylenebisoxazoline and the like. Examples thereof include oxazoline compounds; carbonate compounds such as ethylene carbonate; hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide. The surface cross-linking agent may be used alone or in combination of two or more. As the surface 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 are used. At least one selected from the group consisting of polyglycidyl ether is more preferable.

The amount of the surface cross-linking agent used is 0.01 to 20 mmol per 1 mol of the ethylenically unsaturated monomer used for polymerization from the viewpoint that suitable water absorption characteristics (water absorption rate, water retention amount, etc.) can be easily obtained. Is preferable, 0.05 to 10 mmol is more preferable, 0.1 to 5 mmol is further preferable, 0.15 to 1 mmol is particularly preferable, and 0.2 to 0.5 mmol is extremely preferable.

After surface cross-linking, polymer particles which are surface-cross-linked dried products can be obtained by distilling off water and a hydrocarbon dispersion medium by a known method, drying under heating and reduced pressure, and the like.

As described above, the polymer particles contained in the water-absorbent resin particles can be obtained by using an internal cross-linking agent used at the time of polymerization of the monomer, and are used after the polymerization of the internal cross-linking agent and the monomer. It can be obtained by using an external cross-linking agent (a post-polymerization cross-linking agent used after the polymerization of the monomer, and a surface cross-linking agent used in the post-polymerization drying step of the monomer or a subsequent step). The ratio of the amount of the external cross-linking agent used to the internal cross-linking agent (external cross-linking agent / internal cross-linking agent) is preferably 5 to 100, preferably 6 to 100, from the viewpoint that suitable water absorption characteristics (water absorption rate, water retention amount, etc.) can be easily obtained. 80 is more preferable, 8 to 60 is further preferable, 10 to 40 is particularly preferable, and 10 to 30 is extremely preferable. The water-absorbent resin particles may contain polymer particles which are a reaction product using an internal cross-linking agent, and may contain polymer particles which are a reaction product using an internal cross-linking agent and an external cross-linking agent. The ratio of the amount of the external cross-linking agent used to the internal cross-linking agent in the polymer particles is preferably in the above range.

In addition to the polymer particles, the water-absorbent resin particles according to the present embodiment include, for example, a gel stabilizer and a metal chelating agent (ethylenediaminetetraacetic acid and its salt, diethylenetriamine-5 acetic acid and its salt, for example, diethylenetriamine-5 sodium acetate and the like). , Additional components such as fluidity improver (lubricant) can be further included. Additional components may be located inside the polymer particles, on the surface of the polymer particles, or both.

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 content of the inorganic particles may be in the following range based on the total mass of the polymer particles. The content of the inorganic particles may be 0.05% by mass or more, 0.1% by mass or more, 0.15% by mass or more, or 0.2% by mass or more. The content of the inorganic particles may be 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, or 0.5% 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 can be measured by the pore electric resistance method or the laser diffraction / scattering method depending on the characteristics of the particles.

The absorber according to the present embodiment contains the water-absorbent resin particles according to the present embodiment. The absorber according to the present embodiment may 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.

In order to enhance the morphological 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 or core-sheath structure of polypropylene and polyethylene. 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 pigment, a dye, a fragrance, an adhesive and the like. When the water-absorbent resin particles contain inorganic particles, the absorber may contain an inorganic powder in addition to the inorganic particles in the water-absorbent resin particles.

The shape of the absorber according to the present embodiment may be, for example, a sheet shape. The thickness of the absorber (eg, the thickness of the sheet-like absorber) may be 0.1 to 20 mm or 0.3 to 15 mm.

The content of the water-absorbent resin particles in the absorber is 2 to 100% by mass, 10 to 80% by mass, or 20 to 20 to 100% by mass with respect to the total of the water-absorbent resin particles and the fibrous material from the viewpoint of easily obtaining sufficient water absorption performance. It may be 60% by mass.

The content of the water-absorbent resin particles in the absorber is preferably 100 to 1000 g, more preferably 150 to 800 g, and even more preferably 200 to 700 g per 1 m ^{2 of} the absorber from the viewpoint of easily obtaining sufficient water absorption performance. The content of the fibrous substance in the absorber is preferably 50 to 800 g, more preferably 100 to 600 g, and even more preferably 150 to 500 g per 1 m ^{2 of} the absorber from the viewpoint of easily obtaining sufficient water absorption performance.

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 and prevents the constituent members of the absorber from falling off or flowing; the liquid permeability arranged on the outermost side on the side where the liquid to be absorbed enters. Sheet; Examples thereof include a liquid permeable sheet arranged on the outermost side opposite to the side on which the liquid to be absorbed enters. Examples of absorbent articles include diapers (for example, paper diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat pads, pet sheets, toilet members, animal excrement treatment materials, and the like. ..

FIG. 1 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in FIG. 1 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. 1, there is a portion shown so that there is a gap between the members, but the members may be in close contact with each other without the gap.

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. 1) 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. 1) 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, woven fabrics, synthetic resin films having liquid permeation holes, net-like sheets having a mesh, 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. 1, the absorber may be wrapped by a plurality of core wraps, and the absorber is wrapped by one core wrap. It may be.

The absorber may be adhered to the top sheet. When the absorber is sandwiched or covered by the core wrap, it is preferable that at least the core wrap and the top sheet are adhered, and the core wrap and the top sheet are adhered and the core wrap and the absorber are adhered to each other. Is more preferable. As a method of adhering the absorber, a hot melt adhesive is applied to the top sheet at predetermined intervals in a striped shape, a spiral shape, etc. in the width direction and adhered; starch, carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, etc. Examples thereof include a method of adhering using a water-soluble binder such as a water-soluble polymer. Further, when the absorber contains heat-sealing synthetic fibers, a method of adhering by heat-sealing of the heat-sealing synthetic fibers may be adopted.

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.

According to the present embodiment, it is possible to provide a method for improving the permeation rate of an absorbent article, which is a method for improving the permeation rate using the water-absorbent resin particles, the absorber or the absorbent article according to the present embodiment. it can. According to the present embodiment, it is possible to provide a method for producing water-absorbent resin particles, which comprises a selection step of selecting water-absorbent resin particles based on a water-absorbing rate based on a low-speed flow Voltex method (Vortex method of 300 rpm). In the selection step, for example, the water-absorbent resin particles are selected based on whether or not the water absorption rate based on the low-speed flow Vortex method is 10 to 50 seconds.

Hereinafter, the contents of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Manufacturing of water-absorbent resin particles>
(Example 1)
Round bottom cylindrical separable flask with 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 (a stirrer blade having two stages of four inclined paddle blades with a blade diameter of 5 cm). Prepared. To this flask, 293 g of n-heptane is added as a hydrocarbon dispersion medium, and 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (manufactured by Mitsui Chemicals, Inc., High Wax 1105A) is added as a polymer-based dispersant. This gave the mixture. The dispersant was dissolved by heating the mixture to 80 ° C. with stirring, and then the mixture was cooled to 50 ° C.

Next, 92.0 g (acrylic acid: 1.03 mol) of an 80.5% by mass acrylic acid aqueous solution was added as a water-soluble ethylenically unsaturated monomer to a beaker having an internal volume of 300 mL. Subsequently, while cooling from the outside, 147.7 g of a 20.9 mass% sodium hydroxide aqueous solution was added dropwise into the beaker to neutralize 75 mol%. Then, 0.092 g of hydroxylethyl cellulose (manufactured by Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a water-soluble radical polymerization initiator, and ethylene as an internal cross-linking agent. An aqueous solution of the first stage was prepared by adding 0.010 g (0.057 mmol) of glycol diglycidyl ether and then dissolving the mixture.

Then, the above-mentioned aqueous solution of the first stage was added to the above-mentioned separable flask while stirring at a rotation speed of 550 rpm of the stirrer, and then the mixture was stirred for 10 minutes. Then, it was obtained by heating and dissolving 0.736 g of sucrose stearic acid ester (surfactant, manufactured by Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370, HLB value: 3) in 6.62 g of n-heptane. The detergent solution was added to the separable flask. Then, the inside of the system was sufficiently replaced with nitrogen while stirring at a stirring speed of 550 rpm. Then, the flask was immersed in a water bath at 70 ° C. to raise the temperature, and polymerization was carried out for 60 minutes to obtain a first-stage polymerization slurry solution.

Next, 128.8 g (acrylic acid: 1.43 mol) of an 80.5 mass% aqueous acrylic acid solution was added as a water-soluble ethylenically unsaturated monomer to another beaker having an internal volume of 500 mL. Subsequently, while cooling from the outside, 159.0 g of a 27 mass% sodium hydroxide aqueous solution was added dropwise into the beaker to neutralize 75 mol%. Then, 0.090 g (0.334 mmol) of potassium persulfate was added as a water-soluble radical polymerization initiator and then dissolved to prepare a second-stage aqueous solution.

Next, the inside of the separable flask described above was cooled to 25 ° C. while stirring at a rotation speed of 1000 rpm of the stirrer, and then the entire amount of the aqueous solution of the second stage described above was added to the polymerized slurry solution of the first stage described above. Was added to. Subsequently, 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 (ethylene glycol diglycidyl ether: 0.067 mmol) of 2% by mass of an ethylene glycol diglycidyl ether aqueous solution was added as a cross-linking agent after polymerization to obtain a second-stage hydrogel polymer. ..

To the hydrogel polymer of the second stage described above, 0.265 g of a 45% by mass diethylenetriamine-5 sodium acetate aqueous solution was added under stirring. Then, the flask was immersed in an oil bath set at 125 ° C., and 241.9 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (ethylene glycol diglycidyl ether: 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 mixture was held at 83 ° C. for 2 hours.

Then, n-heptane was evaporated at 125 ° C. and dried to obtain polymer particles (dried product). After passing the polymer particles through a sieve having an opening of 850 μm, 0.5% by mass of amorphous silica (Tokuseal NP-S manufactured by Oriental Silicas Corporation) is weighted based on the total mass of the polymer particles. By mixing with the coalesced particles, 229.2 g of water-absorbent resin particles containing amorphous silica were obtained. The medium particle size of the water-absorbent resin particles was 377 μm. In Example 1, the ratio of the amount of the external cross-linking agent used to the amount of the internal cross-linking agent used was 10.1 in terms of molar ratio.

(Example 2)
In the hydrogel polymer after the second stage polymerization, 231.0 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 247.9 g of water was extracted from the system by azeotropic distillation. Obtained. The medium particle size of the water-absorbent resin particles was 355 μm.

(Example 3)
In the preparation of the first-stage aqueous solution, 0.092 g (0.339 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.018 g of potassium persulfate (0.339 mmol) as a water-soluble radical polymerization initiator 0.068 mmol) and 0.0045 g (0.026 mmol) of ethylene glycol diglycidyl ether as the internal cross-linking agent were used, and as a water-soluble radical polymerization initiator in the preparation of the aqueous solution in the second stage. Using 0.129 g (0.475 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.026 g (0.095 mmol) of potassium persulfate, after the second stage polymerization. In the hydrogel polymer, 223.7 g of water was extracted from the system by radical polymerization, and 0.2% by mass of amorphous silica with respect to the mass of the polymer particles was mixed with the polymer particles. 229.6 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 346 μm. In Example 3, the ratio of the amount of the external cross-linking agent used to the amount of the internal cross-linking agent used was 22.1 in terms of molar ratio.

(Example 4)
In the hydrogel polymer after the second-stage polymerization, 230.1 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 256.1 g of water was extracted from the system by azeotropic distillation. Obtained. The medium particle size of the water-absorbent resin particles was 364 μm.

(Example 5)
In the hydrogel polymer after the second stage polymerization, 231.1 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 264.3 g of water was extracted from the system by azeotropic distillation. Obtained. The medium particle size of the water-absorbent resin particles was 361 μm.

(Example 6)
In the preparation of the aqueous solution in the first stage, 0.092 g (0.339 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.018 g of potassium persulfate (0.339 mmol) as water-soluble radical polymerization initiators were used. 0.068 mmol) was used and 0.0045 g (0.026 mmol) of ethylene glycol diglycidyl ether was used as the internal cross-linking agent; as a water-soluble radical polymerization initiator in the preparation of the aqueous solution in the second stage. 0.129 g (0.475 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.026 g (0.095 mmol) of potassium persulfate are used, and ethylene glycol diglycidyl ether is used as an internal cross-linking agent. 0.0117 g (0.067 mmol) was used; in the preparation of the hydrogel polymer, after the polymerization reaction was carried out for 60 minutes, 45% by mass of diethylenetriamine 5 sodium acetate was added without adding a cross-linking agent after the polymerization. 0.265 g of an aqueous solution was added; 217.8 g of water was extracted from the system by co-boiling distillation in the hydrogel polymer after the second stage polymerization; in the preparation of the polymer particles, n- Instead of evaporating heptane at 125 ° C., the highly water-absorbent resin hydrate obtained by removing the n-heptane phase from the reaction solution by filtration with a 38 μm sieve immediately after the surface cross-linking reaction was removed at 90 ° C. 230.5 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that the mixture was dried under heating and reduced pressure of 0.006 MPa with the vacuum dryer of the setting. The medium particle size of the water-absorbent resin particles was 367 μm. In Example 6, the ratio of the amount of the external cross-linking agent used to the amount of the internal cross-linking agent used was 5.5 in terms of molar ratio.

(Example 7)
In the preparation of the polymerized slurry liquid in the first stage, the rotation speed of the stirrer was changed to 500 rpm, and in the hydrogel polymer after the polymerization in the second stage, 256.1 g of water was removed by cobo distillation. Water-absorbent resin particles 230. In the same manner as in Example 1, except that the mixture was extracted into the polymer particles and 0.1% by mass of amorphous silica was mixed with the polymer particles with respect to the mass of the polymer particles. 8 g was obtained. The medium particle size of the water-absorbent resin particles was 349 μm.

(Comparative Example 1)
In the preparation of the aqueous solution in the second stage, 0.0117 g (0.067 mmol) of ethylene glycol diglycidyl ether was used as an internal cross-linking agent in addition to the water-soluble radical polymerization initiator to prepare a hydrogel polymer. In the above, after the polymerization reaction was carried out for 60 minutes, 0.265 g of a 45% by mass diethylenetriamine-5 sodium acetate aqueous solution of diethylenetriamine 5 sodium acetate was added without adding a cross-linking agent after the polymerization, and the hydrogel-like weight after the polymerization in the second stage. In the coalescence, except that 278.9 g of water was extracted from the system by co-boiling distillation and 0.2% by mass of amorphous silica with respect to the mass of the polymer particles was mixed with the polymer particles. , 230.8 g of water-absorbent resin particles were obtained in the same manner as in Example 1. In Comparative Example 1, the ratio of the amount of the external cross-linking agent used to the amount of the internal cross-linking agent used was 4.1 in terms of molar ratio.

(Comparative Example 2)
In the preparation of the first-stage aqueous solution, 0.092 g (0.339 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.018 g of potassium persulfate (0.339 mmol) as a water-soluble radical polymerization initiator 0.068 mmol) was used and 0.0045 g (0.026 mmol) of ethylene glycol diglycidyl ether was used as the internal cross-linking agent; as a water-soluble radical polymerization initiator in the preparation of the aqueous solution in the second stage. 2,2'-Azobis (2-amidinopropane) dihydrochloride 0.129 g (0.475 mmol) and potassium persulfate 0.026 g (0.095 mmol) are used, and ethylene glycol diglycidyl ether is used as an internal cross-linking agent. 0.0117 g (0.067 mmol) was used; in the preparation of the hydrogel polymer, after the polymerization reaction was carried out for 60 minutes, 45% by mass of diethylenetriamine 5 sodium acetate was added without adding a cross-linking agent after the polymerization. 0.265 g of an aqueous solution was added; 233.5 g of water was extracted from the system by co-boiling distillation in the hydrogel polymer after the second stage polymerization; 0 with respect to the mass of the polymer particles. .229.6 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that 2% by mass of amorphous silica was mixed with the polymer particles. In Comparative Example 2, the ratio of the amount of the external cross-linking agent used to the amount of the internal cross-linking agent used was 5.5 in terms of molar ratio.

(Comparative Example 3)
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 Comparative Example 2, except that 245.1 g of water was extracted from the system by azeotropic distillation. Obtained.

(Comparative Example 4)
Inner diameter 11 cm, contents equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirrer (a stirrer blade having two stages of four inclined paddle blades (surface treated with fluororesin) with a blade diameter of 5 cm). A round-bottomed cylindrical separable flask with a stack of 2 L and four side wall baffles (baffle width: 7 mm) was prepared. To this flask, 451.4 g of n-heptane as a hydrocarbon dispersion medium was added, and 1.288 g of sorbitan monolaurate (Nonion LP-20R, HLB value: 8.6, manufactured by NOF CORPORATION) was added as a surfactant. The mixture was obtained by addition. The sorbitan monolaurate was dissolved in n-heptane by heating the mixture to 50 ° C. while stirring at a stirring speed of 300 rpm, and then the mixture was cooled to 40 ° C.

Next, 92.0 g (acrylic acid: 1.03 mol) of an 80.5 mass% acrylic acid aqueous solution was placed in an Erlenmeyer flask having an internal volume of 500 mL. Subsequently, 147.7 g of a 20.9 mass% sodium hydroxide aqueous solution was added dropwise from the outside while cooling with ice to neutralize the acrylic acid, thereby obtaining an aqueous solution of a partially neutralized acrylic acid. Next, a monomer aqueous solution was prepared by adding 0.1012 g (0.374 mmol) of potassium persulfate as a water-soluble radical polymerization initiator to the acrylic acid partially neutralized aqueous solution and then dissolving the mixture.

After adding the above-mentioned aqueous monomer solution to the above-mentioned separable flask, the inside of the system was sufficiently replaced with nitrogen. Then, the flask was immersed in a water bath at 70 ° C. and held for 60 minutes to complete the polymerization while stirring at a rotation speed of 700 rpm of the stirrer to obtain a hydrogel polymer.

Then, while stirring at a stirring speed of 1000 rpm, amorphous silica (Oriental Silicas Corporation, oriental silicas corporation, etc.) was added to the polymer solution containing the produced hydrogel polymer, n-heptane and a surfactant as a powdery inorganic flocculant. A dispersion obtained by previously dispersing 0.092 g of Toxile NP-S) in 100 g of n-heptane was added and then mixed for 10 minutes. Then, the flask containing the reaction solution was immersed in an oil bath at 125 ° C., and 129.0 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.14 g (ethylene glycol diglycidyl ether: 0.475 mmol) of 2% by mass of an ethylene glycol diglycidyl ether aqueous solution was added as a surface cross-linking agent, and the mixture was maintained at an internal temperature of 83 ± 2 ° C. for 2 hours.

Then, water and n-heptane were evaporated at 120 ° C. and dried until almost no evaporation from the system was distilled off to obtain a dried product. The dried product was passed through a sieve having an opening of 850 μm to obtain 90.1 g of water-absorbent resin particles.

<Measurement of medium particle size>
The above-mentioned medium particle size of the water-absorbent resin particles was measured by the following procedure. That is, from the top, the JIS standard sieve has a mesh size of 600 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, and a mesh size of 150 μm. , And the saucer in that order. 50 g of water-absorbent resin particles were placed in the best combined sieve and shaken for 10 minutes using a low-tap shaker to classify. After classification, the mass of the 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 particles remaining on the sieve was plotted on a logarithmic probability paper by integrating on the sieve in order from the one having the largest particle size with respect to this particle size distribution. 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 obtained as the medium particle size.

<Water absorption rate of water-absorbent resin particles>
The water absorption rate of the physiological saline of the water-absorbent resin particles was measured by the following procedure based on the Vortex method. First, 50 ± 0.1 g of physiological saline adjusted to a temperature of 25 ± 0.2 ° C. in a constant temperature water tank was weighed in a beaker having an internal volume of 100 mL. Next, a vortex was generated by stirring at a rotation speed of 300 rpm (low-speed flow Vortex method) or 600 rpm (conventional Vortex method) using a magnetic stirrer bar (8 mmφ × 30 mm, without ring). 2.0 ± 0.002 g of water-absorbent resin particles were added to physiological saline at one time. The time [seconds] from the addition of the water-absorbent resin particles to the time when the vortex on the liquid surface converged was measured, and the time was obtained as the water absorption rate of the water-absorbent resin particles. The results are shown in Table 1.

<Amount of water retention of water-absorbent resin particles>
The water retention amount (room temperature, 25 ± 2 ° C.) of the physiological saline of the water-absorbent resin particles was measured by the following procedure. First, a cotton bag (Membroad No. 60, width 100 mm × length 200 mm) weighing 2.0 g of water-absorbent resin particles was placed in a beaker having an internal volume of 500 mL. After pouring 500 g of 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 band and let it stand for 30 minutes to swell the water-absorbent resin particles. I let you. After 30 minutes, the cotton bag was 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 then contained a swelling gel after dehydration. The mass Wa [g] of the cotton bag 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 water retention amount of the physiological saline of the water-absorbent resin particles was calculated from the following formula. The results are shown in Table 1.
Water retention [g / g] = (Wa-Wb) /2.0

<Making absorbent articles>
A sheet having a size of 40 cm × 12 cm by uniformly mixing 13.3 g of water-absorbent resin particles and 12.6 g of crushed pulp by air papermaking using an air flow type mixer (Padformer manufactured by Otec Co., Ltd.). A shape-like absorber was prepared. Next, with two sheets of tissue paper having a basis weight of 16 g / m ² having the same size as the sheet-shaped absorber sandwiching the upper and lower sides of the absorber, a load of 424 kPa is applied to the whole for 30 seconds and pressed. Obtained a laminate. Further, an absorbent article was prepared by arranging an air-through type porous liquid permeable sheet made of polyethylene-polypropylene having a basis weight of 22 g / m ² having the same size as the absorber on the upper surface of the laminate.

<Measurement of penetration time>
The absorbent article was placed on a horizontal table in a room at a temperature of 25 ± 2 ° C. Next, a liquid injection cylinder (cylinder with both ends open) having a capacity of 200 mL and having an inner diameter of 3 cm was placed in the center of the main surface of the absorbent article. Subsequently, 160 mL of physiological saline colored with a small amount of Blue No. 1 and adjusted to 25 ± 1 ° C. was charged into the cylinder at one time. Using a stopwatch, the time until the physiological saline completely disappeared from the cylinder was measured, and the time was obtained as the permeation time [seconds]. The results are shown in Table 1.

<Measurement of quick-drying>
The cylinder was removed after feeding the absorbent article with saline as in the above measurement of permeation time. Next, one minute after the start of supply of the physiological saline solution, 80 sheets of filter paper (75 g in total) having a basis weight of 94 g / m ^{2 and} 10 cm × 10 cm as an absorbent member were placed in the vicinity of the liquid supply position of the absorbent article. .. Further, a weight (bottom surface: 10 cm × 10 cm, mass: 2 kg) was placed on the filter paper. After loading with a weight for 1 minute, the mass of the filter paper was measured, and the amount of increase in mass was obtained as quick-drying [g]. The value of quick-drying is preferably small. The results are shown in Table 1.

According to Table 1, even when the water-absorbent resin particles have an excellent water absorption rate based on the conventional Vortex method at 600 rpm, an excellent permeation rate can be obtained when the water-absorbent resin particles are used for an absorbent article. It is confirmed that it may be difficult to do. Further, it is confirmed that adjusting the water absorption rate based on the low-speed flow Vortex method at 300 rpm is effective in obtaining an absorbent article having an excellent permeation rate.

10 ... Absorbent, 10a ... Water-absorbent resin particles, 10b ... Fiber layer, 20a, 20b ... Core wrap, 30 ... Liquid permeable sheet, 40 ... Liquid permeable sheet, 100 ... Absorbent article.

Claims (5)

Water-absorbent resin particles containing a crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer.
The ethylenically unsaturated monomer contains at least one compound selected from the group consisting of (meth) acrylic acid and a salt thereof.
The ratio of the (meth) acrylic acid and a salt thereof is 70 to 100 mol% with respect to the total amount of the monomers for obtaining the water-absorbent resin particles.
The amount of physiological saline retained is 32 to 80 g / g,
The water absorption rate of the physiological saline solution based on the Voltex method at 300 rpm is 35 to 50 seconds.
Absorption rate of physiological saline based on Vortex method 600rpm is Ri 40-60 Byodea,
Median particle diameter of Ru 250~377μm der, water absorbent resin particles. An absorber containing the water-absorbent resin particles according to claim 1. The absorber according to claim 2, wherein the content of the water-absorbent resin particles is 100 to 1000 g per 1 m ² of the absorber. An absorbent article comprising the absorber according to claim 2 or 3. The absorbent article according to claim 4, which is a diaper.

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