JP6752320B2 - Absorbent article and its manufacturing method - Google Patents

Description

The present invention relates to an absorbent article and a method for producing the same.

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 suitable for an absorbent article such as a diaper, and Patent Document 2 is effective for containing a body fluid 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. 06-345819 Special Table No. 09-510889

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

An object of the present invention is to provide an absorbent article in which liquid leakage is suppressed, and a method for producing the same.

One aspect of the invention provides an absorbent article comprising a liquid impermeable sheet, an absorber, and a liquid permeable sheet. The liquid permeable sheet, the absorber and the liquid permeable sheet are arranged in this order. The absorber contains water-absorbent resin particles.
Water absorption rate index I = (10 seconds value of non-pressurized DW) x 6 [mL / g],
When the water absorption rate index II = (3 minutes value of non-pressurized DW) / 3 [mL / g],
The following formula:
α = (I + II) / 2
The static suction index α of the water-absorbent resin particles calculated in 1 is 5.0 mL / g or more.

The non-pressurized DW is the amount of the water-absorbent resin particles that have absorbed the physiological saline solution within a predetermined time after the contact with the physiological saline solution (saline solution having a concentration of 0.9% by mass) under no pressurization. It is the water absorption rate represented by. 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 10-second value and the 3-minute value of the non-pressurized DW mean the amount of absorption 10 seconds and 3 minutes after the water-absorbent resin particles come into contact with the physiological saline solution, respectively. The water absorption rate indexes I and II correspond to the values obtained by converting the 10-second value and the 3-minute value of the non-pressurized DW into the water absorption rate per minute. The static suction index α corresponds to the average value of the water absorption rate indexes I and II, and a large static suction index α means that a relatively large water absorption rate is maintained for 10 seconds to 3 minutes. To do. According to the findings of the present inventor, the water-absorbent resin particles exhibiting a static suction index α of 5.0 mL / g or more can effectively suppress liquid leakage.

Another aspect of the invention provides a method of making an absorbent article. In the method according to the present invention, the water-absorbent resin particles having the static suction index α of 5.0 mL / g or more are selected, and the absorber containing the selected water-absorbent resin particles is liquid-impermeable. Includes placement between the sex sheet and the liquid permeable sheet. By this method, it is possible to produce an absorbent article in which the occurrence of liquid leakage is suppressed.

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

It is sectional drawing which shows one Embodiment of an absorbent article. It is a schematic diagram which shows an example of the measuring method of non-pressurized DW. It is a schematic diagram which shows the method of evaluating the liquid leakage property of an absorbent article.

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

In 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.

When the following water absorption rate indices I and II were obtained from the 10-second value and 3-minute value of the non-pressurized DW of the water-absorbent resin particles according to one embodiment,
Water absorption rate index I = (10 seconds value of non-pressurized DW) x 6 [mL / g]
Water absorption rate index II = (3 minutes value of non-pressurized DW) / 3 [mL / g]
The following formula:
α = (I + II) / 2
The static suction index α calculated in 1 is 5.0 mL / g or more. When the static suction index α is large, liquid leakage due to the water-absorbent resin particles tends to be suppressed more effectively. Static suction index α is 6.0 mL / g or more, 7.0 mL / g or more, 9.0 mL / g or more, 10 mL / g or more, 11 mL / g or more, 12 mL / g or more, 13 mL / g or more, 14 mL / g It may be more than or equal to 15 mL / g or more. The upper limit of the static suction index α is not particularly limited, but is usually 25 mL / g or less.

The water absorption rate index I may be 2 mL / g or more, or 30 mL / g or less. The water absorption rate index II may be 8 mL / g or more, or 30 mL / g or less. When the water absorption rate indexes I and II are within these numerical ranges, the static suction index α tends to be 5.0 mL / g.

The water-absorbent resin particles exhibiting a static suction index α of 5.0 mL / g or more can be obtained by, for example, attaching silica particles (for example, amorphous silica) to the polymer particles described later, and increasing the surface area of the water-absorbent resin particles. It can be obtained by adjusting the crosslink density in the surface layer of the water-absorbent resin particles, or by combining these.

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.

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, and the like. 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- Examples thereof include diethylaminopropyl (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 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 "monomeric 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 mixed with, for example, an aqueous solution containing the above-mentioned ethylenically unsaturated monomer and used. The amount of the ethylenically unsaturated monomer used is preferably 70 to 100 mol% with respect to the total amount of the monomer. 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 monomer.

When the ethylenically unsaturated monomer has an acid group, the aqueous monomer solution may be used by neutralizing the acid group with an alkaline neutralizer. The degree of neutralization of an ethylenically unsaturated monomer by an alkaline neutralizing agent increases the osmotic pressure of the obtained water-absorbent resin particles and further enhances the water absorption characteristics (water absorption 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 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, an aqueous monomer solution is dispersed in a hydrocarbon dispersion medium in the presence of a surfactant, and an 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 aqueous monomer 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. Hydrocarbon dispersion media include chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and 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. More preferably, 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, polyacrylic acid, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide and the like. If the stirring speed at the time of polymerization is the same, the higher the viscosity of the aqueous monomer solution, the larger the medium particle size of the obtained particles tends to be.

Cross-linking 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, or 0.05 mmol or more, or 0.15 mmol or less, or 0.10 mmol or less. Good. When the amount of the internal cross-linking agent is within these numerical ranges, it is easy to obtain water-absorbent resin particles having a static suction index α suitable for suppressing liquid leakage.

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. Reverse-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, the timing of adding the surfactant, the polymer-based dispersant, etc. may be either before or after the addition of the aqueous monomer solution, as long as it is before the start of the polymerization reaction.

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 is used in the reverse phase suspension polymerization in each stage of the second and subsequent stages. Based on the amount of ethylenically unsaturated monomer to be added, it is preferable to carry out reverse phase suspension polymerization by adding within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer. 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-ethylene bisoxazoline; carbonate compounds such as ethylene carbonate; 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 mol 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 used for cross-linking after polymerization is within the above range, water-absorbent resin particles having a large static suction index α can be easily obtained.

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 immediately after polymerization ± 3%].

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 the total amount of the ethylenically unsaturated monomer used for the polymerization from the viewpoint of appropriately cross-linking the obtained hydrogel polymer to exhibit suitable water absorption characteristics. With respect to 1 mol, 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 used is 0.00001 mol or more, the cross-linking density on the surface portion of the water-absorbent resin particles is sufficiently increased, and the gel strength of the water-absorbent resin particles can be easily increased. When the amount of the surface cross-linking agent used is 0.02 mol or less, the water-retaining ability of the water-absorbent resin particles can be easily enhanced. When the amount of the surface cross-linking agent is 0.0003 mol or less or 0.00025 mol or less with respect to 1 mol of the total amount of the ethylenically unsaturated monomer used for the polymerization, the static attraction coefficient α is 5. Water-absorbent resin particles of 0 mL / g or more are particularly easy to obtain.

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, but various additional particles selected from, for example, a gel stabilizer, a metal chelating agent, a fluidity improver (lubricant), and the like. Ingredients can be further included. Additional components may be placed inside the polymer particles, on the surface of the polymer particles, or both. 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.

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 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 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 absorber 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 placed 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. 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 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. The absorber 10 shown in FIG. 3 is held in shape by being sandwiched between two core wraps 20a and 20b. The method of retaining the shape by the core wrap that retains the shape of the absorber is not limited to this, and for example, the absorber may be sandwiched between a single folded core wrap. The core wrap may form a bag and an absorber may be placed therein.

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

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

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

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

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

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

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

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

The absorbent article 100 is manufactured, for example, by a method comprising placing the absorber 10 between the core wraps 20a, 20b and placing them between the liquid permeable sheet 30 and the liquid impermeable sheet 40. Can be done. A laminate in which the liquid permeable sheet 40, the core wrap 20b, the absorber 10, the core wrap 20a, and the liquid permeable sheet 30 are laminated in this order is pressurized as necessary.

The absorber 10 is formed by mixing the water-absorbent resin particles 10a with the fibrous material. The water-absorbent resin particles having the static suction index α of 5.0 mL / g or more may be selected and selectively used to form the absorber 10.

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

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

1. Fabrication of water-absorbent resin particles Production example 1
First-stage polymerization reaction A reflux cooler, 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, with an inner diameter of 11 cm and an internal volume of 2 L. A round-bottomed cylindrical separable flask was prepared. In this flask, 293 g of n-heptane and 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., High Wax 1105A) as a polymer-based dispersant were placed. The reaction solution in the flask was heated to 80 ° C. with stirring to dissolve the polymer-based dispersant in n-heptane. Then, the reaction solution was cooled to 50 ° C.

92.0 g (1.03 mol) of an acrylic acid aqueous solution having a concentration of 80.5 mass% was placed in a beaker having an internal volume of 300 mL. While cooling the beaker from the outside, 147.7 g of an aqueous sodium hydroxide solution having a concentration of 20.9% by mass was added dropwise to the aqueous acrylic acid solution, thereby neutralizing 75 mol% of acrylic acid. Next, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HECAW-15F) as a thickener and 2,2'-azobis (2-amidinopropane) dihydrochloride as a water-soluble radical polymerization initiator were added to an aqueous acrylic acid solution. The first step is to dissolve 0.092 g (0.339 mmol), 0.018 g (0.068 mmol) of potassium persulfate, and 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent. A monomer aqueous solution of the above was prepared.

The first-stage aqueous monomer solution was added to the above-mentioned reaction solution in the separable flask, and the reaction solution was stirred for 10 minutes. Next, a surfactant solution containing 6.62 g of n-heptane and 0.736 g of sucrose stearic acid ester (HLB: 3, Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370) was added to the reaction solution, and the mixture was stirred. The inside of the system was sufficiently replaced with nitrogen while stirring the reaction solution at a blade rotation speed of 550 rpm. Then, the polymerization reaction was allowed to proceed over 60 minutes while heating the separable flask in a water bath at 70 ° C. By this polymerization reaction, a first-stage polymerization slurry liquid containing a hydrogel-like polymer was obtained.

Second-stage polymerization reaction 128.8 g (1.43 mol) of an acrylic acid aqueous solution having a concentration of 80.5% by mass was placed in a beaker having an internal volume of 500 mL. While cooling the beaker from the outside, 159.0 g of a sodium hydroxide aqueous solution having a concentration of 27% by mass was added dropwise to the acrylic acid aqueous solution, thereby neutralizing 75 mol% of acrylic acid. Next, 0.129 g (0.475 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride and 0.026 g (0.095 mmol) of potassium persulfate were dissolved in an aqueous acrylic acid solution. A second-stage monomer aqueous solution was prepared.

The first-stage polymerized slurry liquid in the separable flask was cooled to 25 ° C. while stirring at a stirring blade rotation speed of 1000 rpm. The whole amount of the aqueous monomer solution of the second stage was added thereto, and then the inside of the system was replaced with nitrogen for 30 minutes. Then, the polymerization reaction was allowed to proceed over 60 minutes while heating the separable flask in a water bath at 70 ° C. As a cross-linking agent for post-polymerization cross-linking, 0.580 g (0.067 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added to obtain a hydrogel polymer.

To the reaction solution containing the hydrogel polymer, 0.265 g of an aqueous solution of diethylenetriamine-5 sodium acetate having a concentration of 45% by mass was added under 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 by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of an ethylene glycol diglycidyl ether aqueous solution having a concentration of 2% by mass was added to the reaction solution as a surface cross-linking agent, and the cross-linking reaction with the surface cross-linking agent was allowed to proceed at 83 ° C. for 2 hours. It was.

From the reaction solution after the surface cross-linking reaction, n-heptane was distilled off by heating at 125 ° C. to obtain polymer particles (dried product). The obtained polymer particles were passed through a sieve having an opening of 850 μm. Then, 0.2% by mass of amorphous silica (Oriental Silicas Corporation, Toxile NP-S) with respect to the mass of the polymer particles was mixed with the polymer particles, and the water-absorbent resin particles 232 containing the amorphous silica were mixed. .1 g was obtained. The medium particle size of the particles was 396 μm.

Production example 2
Water-absorbent resin particles containing amorphous silica are prepared in the same procedure as in Production Example 1 except that the amount of amorphous silica is changed to 2.0% by mass with respect to the mass of the polymer particles (dried product). 236.3 g was obtained. The medium particle size of the water-absorbent resin particles was 393 μm.

Production Example 3
The water-soluble radical polymerization initiator in the first-stage polymerization reaction was changed to 0.0736 g (0.272 mmol) of potassium persulfate, and 2,2'-azobis (2-amidinopropane) dihydrochloride was not added. That is, the water-soluble radical polymerization initiator in the second-stage polymerization reaction was changed to 0.090 g (0.334 mmol) of potassium persulfate, and 2,2'-azobis (2-amidinopropane) dihydrochloride was added. Polymer particles (dried products) were obtained in the same procedure as in Production Example 1 except that they were not present. The amount of water extracted from the reaction solution containing the hydrogel polymer by azeotropic distillation was 247.9 g.
Amorphous silica (Oriental Silicas Corporation, Toxile NP-S) in an amount of 0.5% by mass based on the mass of the polymer particles was mixed with the polymer particles to obtain 231.0 g of water-absorbent resin particles. The medium particle size of the water-absorbent resin particles was 355 μm.

Production Example 4
The water-soluble radical polymerization initiator in the first-stage polymerization reaction was changed to 0.0736 g (0.272 mmol) of potassium persulfate, and 2,2'-azobis (2-amidinopropane) dihydrochloride was not added. That is, the water-soluble radical polymerization initiator in the second-stage polymerization reaction was changed to 0.090 g (0.334 mmol) of potassium persulfate, and 2,2'-azobis (2-amidinopropane) dihydrochloride was added. Polymer particles (dried products) were obtained in the same procedure as in Production Example 1 except that they were not present. The amount of water extracted from the reaction solution containing the hydrogel polymer by azeotropic distillation was 239.7 g.
Amorphous silica (Oriental Silicas Corporation, Toxile NP-S) in an amount of 0.5% by mass based on the mass of the polymer particles was mixed with the polymer particles to obtain 229.2 g of water-absorbent resin particles. The medium particle size of the water-absorbent resin particles was 377 μm.

Production Example 5
The water-soluble radical polymerization initiator in the first-stage polymerization reaction was changed to 0.0736 g (0.272 mmol) of potassium persulfate, and 2,2'-azobis (2-amidinopropane) dihydrochloride was not added. That is, the water-soluble radical polymerization initiator in the second-stage polymerization reaction was changed to 0.090 g (0.334 mmol) of potassium persulfate, and 2,2'-azobis (2-amidinopropane) dihydrochloride was added. No, 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether was used as the internal cross-linking agent, no cross-linking agent for post-polymerization cross-linking was added, and after the second-stage polymerization. Production examples of the hydrogel polymer except that 256.1 g of water was extracted from the system by co-boiling distillation and 0.1% by mass of amorphous silica was mixed with the polymer particles. In the same manner as in No. 1, 230.8 g of water-absorbent resin particles were obtained. The medium particle size of the water-absorbent resin particles was 349 μm.

Production Example 6
The amount of ethylene glycol diglycidyl ether as an internal cross-linking agent in the first-stage polymerization reaction was changed to 0.0046 g (0.026 mmol), and ethylene was used as an internal cross-linking agent in the preparation of the second-stage aqueous solution. 0.0116 g (0.067 mmol) of glycol diglycidyl ether was used, no cross-linking agent was added for post-polymerization cross-linking, and co-boiling was performed in the second-stage post-polymerization hydrogel polymer. Manufactured except that 219.2 g of water was extracted from the system by distillation and the amount of ethylene glycol diglycidyl ether aqueous solution having a concentration of 2% by mass as a surface cross-linking agent was changed to 6.62 g (0.761 mmol). In the same procedure as in Example 1, 226.6 g of water-absorbent resin particles containing amorphous silica were obtained. The medium particle size of the water-absorbent resin particles was 356 μm.

Production Example 7
The amount of ethylene glycol diglycidyl ether as an internal cross-linking agent in the first-stage polymerization reaction was changed to 0.0046 g (0.026 mmol), and as an internal cross-linking agent in the preparation of the second-stage aqueous solution. 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether was used, no cross-linking agent was added for post-polymerization cross-linking, and both were used in the second-stage post-polymerization hydrogel polymer. 220.6 g of water-absorbent resin particles containing amorphous silica were obtained by the same procedure as in Production Example 1 except that 234.2 g of water was extracted from the system by boiling distillation. The medium particle size of the water-absorbent resin particles was 355 μm.

Production Example 8
The amount of ethylene glycol diglycidyl ether as an internal cross-linking agent in the first-stage polymerization reaction was changed to 0.0368 g (0.211 mmol). In the preparation of the second-stage aqueous solution, ethylene was used as an internal cross-linking agent. The use of 0.0515 g (0.296 mmol) of glycol diglycidyl ether, no addition of a cross-linking agent for post-polymerization cross-linking, and co-boiling in the second-stage post-polymerization hydrogel polymer. 222.2 g of water-absorbent resin particles containing amorphous silica were obtained by the same procedure as in Production Example 1 except that 286.9 g of water was extracted from the system by distillation. The medium particle size of the particles was 396 μm.

2. Evaluation 2-1. Amount of water retained in physiological saline A cotton bag (Membrod No. 60, width 100 mm x length 200 mm) weighing 2.0 g of water-absorbent resin particles was placed in a beaker containing 500 mL. Pour 500 g of 0.9 mass% sodium chloride aqueous solution (physiological saline) into a cotton bag containing water-absorbent resin particles at a time so that mamaco cannot be formed, tie the upper part of the cotton bag with a rubber ring, and let it stand for 30 minutes. The water-absorbent resin particles were swollen with. After 30 minutes, the cotton bag is dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set to have a centrifugal force of 167 G, and the cotton bag containing the swelling gel after dehydration. The mass Wa (g) of was measured. The same operation was performed without adding the water-absorbent resin particles, the empty mass Wb (g) of the cotton bag when wet was measured, and the amount of physiological saline water retained was calculated from the following formula.
Saline water retention (g / g) = [Wa-Wb] /2.0

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

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

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

2-2. Unpressurized DW
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 opening at the upper part of the burette tube 21, a cock 22 connected to the tip of the lower portion of the burette tube 21, and a lower portion of the burette tube 21. It has an air introduction pipe 25 and a cock 24 connected to the burette. The burette portion 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 13a on the measuring table 13, and a cylinder having an inner diameter of 30 mm and a height of 20 mm was placed in the center thereof. 1.00 g of water-absorbent resin particles 10a were uniformly sprayed 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. 10 seconds, 1 minute, 3 minutes, 5 minutes, and 10 minutes after the start of water absorption of 10a, the weight loss Wc (g) of 0.9% by mass saline solution was read. From Wc, the 10-second value, 1-minute value, 3-minute value, 5-minute value, and 10-minute value of the non-pressurized DW were obtained 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.
Unpressurized DW value (mL / g) = Wc / 1.00
The water absorption rate indexes I and II and the static suction index α were determined by the following formulas using the 10-second value and the 3-minute value of the non-pressurized DW.
Water absorption rate index I = (10 seconds value of non-pressurized DW) x 6 [mL / g]
Water absorption rate index II = (3 minutes value of non-pressurized DW) / 3 [mL / g]
α = (I + II) / 2

3. Absorbent article 3-1. Preparation of Absorbent and Absorbent Article <Example 1>
Using an air flow type mixer (Padformer manufactured by Otec Co., Ltd.), 10 g of water-absorbent resin particles and 9.5 g of crushed pulp obtained in Production Example 1 were uniformly mixed by air papermaking to obtain a size of 12 cm × 32 cm. A sheet-shaped absorber of a size was prepared. The water absorber was placed on a tissue paper (core wrap) having a basis weight of 16 g / m ^{2, and} the tissue paper (core wrap) and the air-through non-woven fabric (liquid permeable sheet), which is a short fiber non-woven fabric, were laminated in this order on the absorber. .. A load of 588 kPa was applied to this laminate for 30 seconds. Further, a polyethylene liquid permeable sheet having a size of 12 cm × 32 cm was attached to the surface opposite to the air-through non-woven fabric to prepare an absorbent article for testing. The basis weight of the air-through non-woven fabric used was 17 g / m ² .
In the absorbent article, the basis weight of the water-absorbent resin particles was 280 g / m ² , and the basis weight of the pulverized pulp (hydrophilic fiber) was 260 g / m ² .

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

<Comparative Examples 1 to 4>
The absorbent articles of Comparative Examples 5 to 8 were produced in the same manner as in Example 1 except that the water-absorbent resin particles were changed to the water-absorbent resin particles obtained in Production Examples 5 to 8.

Table 1 shows the performance of the water-absorbent resin particles and the water-absorbent resin particles used in Examples or Comparative Examples.

<Preparation of artificial urine>
Artificial urine was prepared by adding a small amount of Blue No. 1 to a solution prepared by blending and dissolving an 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

3-2. Gradient absorption test of water-absorbent article FIG. 3 is a schematic view showing a method for evaluating the leakability of an absorbent article. Support plate 1 (acrylic resin plate here, hereinafter referred to as the inclined surface S ₁₎ of length 45cm having a flat main surface, and fixed by frame 41 in a state of being inclined 45 ± 2 degrees relative to the horizontal plane S ₀ .. In room temperature 25 ± 2 ° C., on the inclined surface S ₁ of the fixed support plate 1, the absorbent article 100 for testing, the longitudinal direction is adhered in a direction along the longitudinal direction of the support plate 1. Next, the test solution 50 (artificial urine) adjusted to 25 ± 1 ° C. from the dropping funnel 42 arranged vertically above the absorbent article toward a position 8 cm above the center of the absorber in the absorbent article 100. Was dropped. 80 mL of the test solution was added dropwise at a rate of 8 mL / sec. The distance between the tip of the dropping funnel 42 and the absorbent article was 10 ± 1 mm. The test solution was repeatedly added under the same conditions at intervals of 10 minutes from the start of the first addition of the test solution, and the test solution was added until leakage was observed.

When the test liquid not absorbed by the absorbent article 100 leaked from the lower part of the support plate 1, the leaked test liquid was collected in a metal tray 44 arranged below the support plate 1. The weight (g) of the recovered test solution was measured by a balance 43, and the value was recorded as a leakage amount. By subtracting the leakage amount from the total input amount of the test solution, the absorption amount until the leakage occurred was calculated. It is judged that the larger this value is, the less likely it is that liquid will leak when worn. The measurement results are shown in Table 2.

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

Claims (4)

An absorbent article comprising a liquid impermeable sheet, an absorbent body, and a liquid permeable sheet, wherein the liquid impermeable sheet, the absorbent body, and the liquid permeable sheet are arranged in this order.
The absorber contains water-absorbent resin particles and contains
The weight of the water-absorbent resin 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. Containing coalesced particles and a plurality of inorganic particles arranged on the surface of the polymer particles.
The ratio of (meth) acrylic acid and a salt thereof is 70 to 100 mol% with respect to the total amount of the monomer units in the crosslinked polymer.
Water absorption rate index I = (10 seconds value of non-pressurized DW) x 6 [mL / g],
When the water absorption rate index II = (3 minutes value of non-pressurized DW) / 3 [mL / g],
The following formula:
α = (I + II) / 2
Der static suction index α is 5.0 mL / g or more of the water-absorbent resin particles in calculated is,
The water absorption rate index I of the water-absorbent resin particles is 2 mL / g or more.
The water absorption rate index II of the water-absorbent resin particles is 8 mL / g or more.
Absorbent article. The absorbent article according to claim 1, wherein the water-absorbent resin particles have a medium particle size of 250 to 850 μm . The absorbent article according to claim 1 or 2, wherein the inorganic particles are silica particles . Water absorption rate index I = (10 seconds value of non-pressurized DW) x 6 [mL / g],
When the water absorption rate index II = (3 minutes value of non-pressurized DW) / 3 [mL / g],
The following formula:
α = (I + II) / 2
To select water-absorbent resin particles having a static suction index α of 5.0 mL / g or more, a water absorption rate index I of 2 mL / g or more, and a water absorption rate index II of 8 mL / g or more. ,
The absorber containing the selected water-absorbent resin particles is placed between the liquid-impermeable sheet and the liquid-permeable sheet, and
Including
The weight of the water-absorbent resin 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. Containing coalesced particles and a plurality of inorganic particles arranged on the surface of the polymer particles.
The ratio of (meth) acrylic acid and a salt thereof is 70 to 100 mol% with respect to the total amount of the monomer units in the crosslinked polymer.
A method of manufacturing an absorbent article.

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