JP2016027845A - Water-absorbing resin, and absorbent article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-absorbent resin having a high diffusibility, when used in an absorber, against a liquid to be absorbed, while keeping a high water absorbility, and capable of reducing an inverse return amount, and an absorbent article using an absorber containing that water-absorbent resin.SOLUTION: A water-absorbing resin of the invention is the water-absorbing resin which is obtained by polymerizing a water-soluble ethylenic unsaturation monomer under the presence of an internal crosslinking agent and by performing an after cross linking the polymerized monomer with an after-crosslinking agent, and is characterized in that an absorber effective index number K expressed by formula (I) is 250 or more when a liquid flow test is performed by using said water-absorbing resin. The absorber effective index number K=a liquid flow quantity (g)×an artificial urine absorption magnification (g/g) - - - (I).SELECTED DRAWING: None

Description

  The present invention relates to a water-absorbent resin and an absorbent article, and more specifically, a water-absorbent resin constituting an absorbent body suitably used for sanitary materials such as paper diapers, sanitary napkins, incontinence pads, and the like. The present invention relates to an absorbent article.

  In recent years, water-absorbent resins have been widely used in the field of sanitary materials such as paper diapers, sanitary napkins, and incontinence pads.

  As such a water-absorbent resin, the acrylic acid partially neutralized salt polymer cross-linked product has excellent water absorption ability, and since it is easy to industrially obtain acrylic acid as a raw material, the quality is constant. In addition, since it can be produced at low cost and has many advantages such as being less susceptible to spoilage and deterioration, it is regarded as a preferred water-absorbing resin.

  On the other hand, absorbent articles such as paper diapers, sanitary napkins, and incontinence pads are mainly disposed in the center, and absorb and retain body fluids excreted from the body, such as urine and menstrual blood, It is composed of a liquid-permeable top sheet (top sheet) disposed on the side in contact with the liquid-impermeable back sheet (back sheet) disposed on the opposite side in contact with the body. Moreover, the absorber is comprised from hydrophilic fibers, such as a pulp, and water absorbing resin.

  In recent years, demands for thinner and lighter absorbent articles are increasing from the viewpoints of design, convenience in carrying, efficiency in distribution, and the like. Furthermore, from the viewpoint of environmental conservation, there is a need for a so-called eco-friendly orientation that effectively uses resources and avoids the use of natural materials that require a long period of growth, such as trees. Conventionally, as a method for thinning that is generally performed in absorbent articles, for example, reducing hydrophilic fibers such as pulverized pulp of wood, which is a role of fixing the water-absorbent resin in the absorbent body, There was a method of increasing the water-absorbing resin.

  An absorber using a low ratio of hydrophilic fibers and using a large amount of water-absorbing resin is preferable for thinning from the viewpoint of reducing bulky hydrophilic fibers and retaining liquid. However, when a load is applied to the absorbent body including the water-absorbent resin due to deformation, pressure, etc., such as when an infant wearing a thin absorbent article is sitting, the liquid to be absorbed is returned (liquid return). May not be sufficiently prevented. Furthermore, in the case of such an absorbent article, the absorbent article cannot withstand multiple urinations and may cause discomfort to the wearer.

  In addition, a large amount of water-absorbing resin becomes a soft gel due to absorption of liquid, and when a load is applied to this gel, so-called “gel blocking phenomenon” occurs, and the liquid diffusibility is remarkably lowered and absorbed. The body fluid penetration rate may be slow. This “gel blocking phenomenon” means that when a dense absorbent body absorbs a liquid, the water absorbent resin existing near the surface layer absorbs the liquid, and a soft gel is formed near the surface layer. This is a phenomenon in which the gel becomes dense and the penetration of the liquid into the absorber is prevented, and the water absorbent resin inside cannot absorb the liquid efficiently.

  Therefore, as a means of preventing problems that may occur when hydrophilic fibers are reduced and a large amount of water-absorbent resin has been used, for example, hydrogel absorbent weight having specific saline flow inductivity, performance under pressure, etc. A method using a coalescence (see Patent Document 1), a method using a water absorbent resin obtained by heat-treating a specific surface cross-linking agent to a specific water absorbent resin precursor (see Patent Document 2), and the like have been proposed.

  However, these methods do not necessarily satisfy the absorption performance as an absorber using a large amount of water-absorbent resin, and also tend to cause problems such as liquid leakage due to failure to capture the liquid to be absorbed. .

JP-T 09-510889 Japanese Patent Laid-Open No. 08-57311

  The present invention has been proposed in view of the above-described circumstances, and has a high diffusibility with respect to the liquid to be absorbed while reducing the amount of reversal while maintaining a high water absorption capacity when used in an absorber. It is an object of the present invention to provide an absorbent article using a water absorbent resin that can be produced and an absorbent body including the water absorbent resin.

  The inventors of the present invention have made extensive studies in order to solve the above-described problems. As a result, the water absorption is such that the absorbent effective index K expressed by the product of the liquid flow rate (g) calculated by performing a specific liquid flow test and the artificial urine absorption rate (g / g) is a predetermined value or more. In the evaluation of absorbent articles, it has been found that excellent absorbent performance can be obtained when an absorbent resin is used. That is, the present invention provides the following.

(1) The present invention is a water-absorbing resin obtained by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal cross-linking agent and post-crosslinking with a post-crosslinking agent, When the following liquid flow test is carried out using an absorbent, the absorbent effective index K represented by the formula (I) is 250 or more.
Absorber Effective Index K = Liquid Flow Rate (g) × Artificial Urine Absorption Rate (g / g) (I)
[Liquid flow test]
A non-woven fabric is placed on an acrylic plate, and 4.8 g of water-absorbing resin is uniformly sprayed, and then the non-woven fabric is placed from the top and sandwiched between them to make a measurement sample. Is placed so that the central part of the cylinder matches the central part of the measurement sample, 120 g of artificial urine with a liquid temperature of 25 ° C. is added at once from the cylindrical input part, and the artificial urine flowing out from the acrylic plate is weighed. Let it be the flow rate (g).

  (2) Moreover, this invention is the water-absorbent resin whose said artificial urine absorption capacity is 30.0 g / g or more in the invention which concerns on said (1).

  (3) Moreover, this invention is the water-absorbent resin whose said liquid flow amount is 5.0 g or more in the invention which concerns on said (1) or (2).

  (4) This invention is an absorptive article using the absorber containing the water absorbing resin in any one of said (1) thru | or (3).

  According to the present invention, when used in an absorbent body, a water-absorbing resin having high diffusibility with respect to the liquid to be absorbed and capable of reducing the amount of reversal while maintaining a high water-absorbing capacity, and the water-absorbing resin An absorptive article using an absorber containing it can be provided.

It is a schematic block diagram which shows the structure of the apparatus for measuring the water absorption ability of the physiological saline under the 4.14kPa load of a water absorbing resin. It is a schematic block diagram which shows the structure of the apparatus for measuring the liquid flow amount of a water absorbing resin.

  Hereinafter, the present invention will be described in detail.

<< 1. Water-absorbent resin >>
The water-absorbent resin according to the present invention has the following properties.

The water-absorbing resin according to the present invention is a water-absorbing resin obtained by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal cross-linking agent and post-crosslinking with a post-crosslinking agent, The absorber effective index K represented by I) is 250 or more.
Absorber Effective Index K = Liquid Flow Rate (g) × Artificial Urine Absorption Rate (g / g) (I)

[Liquid flow test]
In the liquid flow test, a non-woven fabric is placed on an acrylic plate, 4.8 g of water-absorbing resin is uniformly sprayed, and then the non-woven fabric is placed from the top to sandwich a measurement sample. Placed in the center of the cylinder so that the center of the cylinder coincides with the center of the sample to be measured, 120 g of artificial urine with a liquid temperature of 25 ° C. was poured at once from the cylinder-shaped feeding section, and the artificial plate flowed out of the acrylic board Urine is weighed to obtain the liquid flow rate (g).

  The absorbent effective index K of the water absorbent resin is preferably 300 or more, more preferably 350 or more, and further preferably 400 or more. The upper limit of the absorber effective index K is preferably 1000 or less.

  The water absorbent resin according to the present invention preferably has an artificial urine absorption capacity of 30.0 g / g or more. The artificial urine absorption capacity indicates the mass of artificial urine that can be absorbed by the water absorbent resin per unit mass, and represents the degree of absorption capacity of the liquid of the water absorbent resin. The artificial urine absorption rate is more preferably 32.0 g / g or more, further preferably 34.0 g / g or more, and further preferably 36.0 g / g or more. The upper limit of the artificial urine absorption capacity is preferably 60.0 g / g or less.

  Further, the water-absorbent resin according to the present invention preferably has a liquid flow amount of 5.0 g or more measured by the “liquid flow test” described above. As described above, the liquid flow amount is a measure indicating the diffusibility of the liquid charged into the absorber. The liquid flow amount is more preferably 6.0 g or more, further preferably 8.0 g or more, and still more preferably 10.0 g or more. Further, the upper limit value of the liquid flow rate is preferably 50.0 g / g or less.

  In the water absorbent resin according to the present invention, it is preferable that the water absorption capacity of physiological saline under a load of 4.14 kPa is 16 ml / g or more after 60 minutes from the start of water absorption. In general, in a water-absorbing resin that absorbs water slowly over a long period of time, for example, when pressure is applied to an absorbent body made of the water-absorbing resin (for example, an infant with a diaper using the absorbent body immediately after urination The amount of the liquid to be absorbed tends to increase when sitting). For example, when the higher physiological saline water absorption capacity under a load of 4.14 kPa is used as a sanitary material, the amount of return when the sanitary material is pressurized is reduced.

  It should be noted that the water absorption capacity of physiological saline under a load of 4.14 kPa is preferably 16 ml / g or more, more preferably 20 ml / g or more, and further preferably 24 ml / g after 60 minutes from the start of water absorption. That's it. Moreover, the water absorption capacity of physiological saline under a load of 4.14 kPa is preferably 50 ml / g or less, more preferably 40 ml / g or less after 60 minutes have elapsed since the start of water absorption.

  Further, the water-absorbent resin according to the present invention preferably has a median particle size of 200 to 600 μm, more preferably 250 to 500 μm, further preferably 300 to 450 μm, and 350 to 450 μm. It is even more preferable.

  In the water-absorbent resin according to the present invention, the mass ratio of particles of 150 to 850 μm in the total ratio is preferably 85% by mass or more, more preferably 90% by mass or more, and 95% by mass or more. More preferably. Moreover, it is preferable that the mass ratio of the particle | grains of 300-400 micrometers which occupies for the whole ratio is 20 mass% or more, and it is more preferable that it is 25 mass% or more.

  The particles of the water-absorbing resin may have a form (secondary particle) in which fine particles (primary particles) are aggregated in addition to a form of single particles. Examples of the shape of the primary particles include a substantially spherical shape, an irregular crushed shape, and a plate shape. In the case of primary particles produced by reversed-phase suspension polymerization, a substantially spherical single particle shape having a smooth surface shape such as a true spherical shape, an elliptical spherical shape, etc. can be mentioned. Since the surface shape is smooth, the fluidity as a powder is increased, and the aggregated particles are easily packed closely, so that they are not easily broken even under impact and have a high particle strength. Become.

  The above-mentioned water-absorbent resin has a liquid flow rate, an artificial urine absorption capacity, a physiological saline water absorption capacity under a load of 4.14 kPa, and a median particle diameter, all measured by the measurement methods described in the examples described later. can do.

  In addition, in order to provide various performances to the obtained water-absorbent resin, additives according to the purpose can be blended. Examples of such additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, radical chain inhibitors, antioxidants, antibacterial agents, and deodorants. For example, the fluidity of the water absorbent resin can be improved by adding 0.05 to 5 parts by mass of amorphous silica as an inorganic powder to 100 parts by mass of the water absorbent resin.

≪2. Manufacturing method of water absorbent resin >>
The water absorbent resin according to the present invention can be produced by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal crosslinking agent.

  As a polymerization method of the water-soluble ethylenically unsaturated monomer, a typical polymerization method such as an aqueous solution polymerization method, an emulsion polymerization method, a reverse phase suspension polymerization method, or the like is used. In the aqueous solution polymerization method, polymerization is performed by heating a water-soluble ethylenically unsaturated monomer aqueous solution while stirring as necessary. In the reverse phase suspension polymerization method, polymerization is performed by heating a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium with stirring. In the present invention, the reverse phase suspension polymerization method is preferred from the viewpoint of precise polymerization reaction control and wide particle size control.

  Regarding the water absorbent resin according to the present invention, an example of the production method will be described below.

  As a specific example of a method for producing a water-absorbent resin, a method for producing a water-absorbent resin by subjecting a water-soluble ethylenically unsaturated monomer to reverse phase suspension polymerization in a hydrocarbon dispersion medium, in the presence of an internal cross-linking agent. And a step of performing polymerization in the presence of at least an azo compound and a peroxide, and a step of performing post-crosslinking in the presence of a post-crosslinking agent on a hydrogel having an internal cross-linked structure obtained by polymerization. A method is mentioned.

<Polymerization process>
[Water-soluble ethylenically unsaturated monomer]
Examples of the water-soluble ethylenically unsaturated monomer include (meth) acrylic acid (in the present specification, “acryl” and “methacryl” are collectively referred to as “(meth) acryl”; the same shall apply hereinafter) and 2- (meth) acrylamide-2-methylpropanesulfonic acid and salts thereof; (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) Nonionic monomers such as acrylamide and polyethylene glycol mono (meth) acrylate; amino groups such as N, N-diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate and diethylaminopropyl (meth) acrylamide Examples thereof include unsaturated monomers and quaternized products thereof. Among these water-soluble ethylenically unsaturated monomers, (meth) acrylic acid or a salt thereof, (meth) acrylamide, and N, N-dimethylacrylamide are preferable from the viewpoint of industrial availability. , (Meth) acrylic acid and salts thereof are more preferred. In addition, these water-soluble ethylenically unsaturated monomers may be used independently and may be used in combination of 2 or more types.

  Among these, acrylic acid and its salts are widely used as raw materials for water-absorbing resins, and these acrylic acid partial neutralized salts are used by copolymerizing the other water-soluble ethylenically unsaturated monomers described above. In some cases. In this case, it is preferable that 70-100 mol% of acrylic acid partial neutralization salt is used as a main water-soluble ethylenically unsaturated monomer with respect to the total water-soluble ethylenically unsaturated monomer.

  The water-soluble ethylenically unsaturated monomer is preferably dispersed in a hydrocarbon dispersion medium in the form of an aqueous solution and subjected to reverse phase suspension polymerization. By making the water-soluble ethylenically unsaturated monomer into an aqueous solution, the dispersion efficiency in the hydrocarbon dispersion medium can be increased. The concentration of the water-soluble ethylenically unsaturated monomer in this aqueous solution is preferably in the range of 20% by mass to the saturated concentration or less. Moreover, as a density | concentration of a water-soluble ethylenically unsaturated monomer, it is more preferable that it is 55 mass% or less, It is further more preferable that it is 50 mass% or less, It is further more preferable that it is 45 mass% or less. On the other hand, the concentration of the water-soluble ethylenically unsaturated monomer is more preferably 25% by mass or more, further preferably 28% by mass or more, and further preferably 30% by mass or more.

  When the water-soluble ethylenically unsaturated monomer has an acid group such as (meth) acrylic acid or 2- (meth) acrylamido-2-methylpropanesulfonic acid, the acid group is previously alkaline if necessary. You may use what was neutralized with the neutralizing agent. Examples of such an alkaline neutralizer include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium hydroxide, and potassium carbonate; ammonia and the like. These alkaline neutralizers may be used in the form of an aqueous solution in order to simplify the neutralization operation. In addition, the alkaline neutralizer mentioned above may be used independently, and may be used in combination of 2 or more types.

  The degree of neutralization of the water-soluble ethylenically unsaturated monomer with the alkaline neutralizer is 10 to 100 mol% as the degree of neutralization for all acid groups of the water-soluble ethylenically unsaturated monomer. Is more preferable, 30 to 90 mol% is more preferable, 40 to 85 mol% is further preferable, and 50 to 80 mol% is still more preferable.

[Internal cross-linking agent]
Examples of the internal crosslinking agent include those capable of crosslinking the polymer of the water-soluble ethylenically unsaturated monomer to be used. For example, (poly) ethylene glycol [“(poly)” is prefixed with “poly”. It means the case with and without. The same shall apply hereinafter), (poly) propylene glycol, 1,4-butanediol, trimethylolpropane, diols such as (poly) glycerin, polyols such as triol, and (meth) acrylic acid, maleic acid, fumaric acid, etc. Unsaturated polyesters obtained by reacting with acids; bisacrylamides such as N, N-methylenebisacrylamide; di (meth) acrylates or tris obtained by reacting polyepoxides with (meth) acrylic acid (Meth) acrylic acid esters; di (meth) acrylic acid carbamyl esters obtained by reacting polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth) acrylate; allylated starch, allyl Cellulose, diallyl phthalate, N, Compounds having two or more polymerizable unsaturated groups such as', N ″ -triallyl isocyanate, divinylbenzene; (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl Polyglycidyl compounds such as diglycidyl compounds such as ether and triglycidyl compounds; Epihalohydrin compounds such as epichlorohydrin, epibromhydrin and α-methylepichlorohydrin; Reactivity of isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate Compound having two or more functional groups; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneeta And oxetane compounds such as 3-ethyl-3-oxetaneethanol and 3-butyl-3-oxetaneethanol. Among these internal crosslinking agents, polyglycidyl compounds are preferably used, diglycidyl ether compounds are more preferably used, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin. It is preferable to use diglycidyl ether. These internal crosslinking agents may be used alone or in combination of two or more.

  The amount of the internal crosslinking agent used is preferably 0.000001 to 0.02 mol, preferably 0.00001 to 0.01 mol, per 1 mol of the water-soluble ethylenically unsaturated monomer. More preferably, it is 0.00001-0.005 mol, and it is still more preferable that it is 0.00005-0.002 mol.

[Hydrocarbon dispersion medium]
Examples of the hydrocarbon dispersion medium include those having 6 to 8 carbon atoms such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane. Aliphatic hydrocarbons; alicyclic rings such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentane Aromatic hydrocarbons such as benzene, toluene and xylene. Among these hydrocarbon dispersion media, n-hexane, n-heptane, and cyclohexane are particularly preferably used because they are easily available industrially, have stable quality, and are inexpensive. These hydrocarbon dispersion media may be used alone or in combination of two or more. In addition, as an example of the mixture of the hydrocarbon dispersion medium, a suitable result can be obtained even if a commercially available product such as Exol heptane (ExxonMobil Corporation: containing 75 to 85% by mass of heptane and isomer hydrocarbon) is used. Can do.

  The amount of the hydrocarbon dispersion medium used is that from the viewpoint of uniformly dispersing the water-soluble ethylenically unsaturated monomer and facilitating control of the polymerization temperature, the first stage water-soluble ethylenically unsaturated monomer It is preferable that it is 100-1500 mass parts with respect to 100 mass parts, and it is more preferable that it is 200-1400 mass parts. As will be described later, the reverse-phase suspension polymerization is performed in one stage (single stage) or in multiple stages of two or more stages. The first stage polymerization described above is the first stage in single stage polymerization or multistage polymerization. (Hereinafter the same).

[Dispersion stabilizer]
(Surfactant)
In the reverse phase suspension polymerization, a dispersion stabilizer can be used in order to improve the dispersion stability of the water-soluble ethylenically unsaturated monomer in the hydrocarbon dispersion medium. As the dispersion stabilizer, a surfactant can be used.

  Examples of the surfactant include sucrose fatty acid ester, polyglycerin fatty acid ester, sorbitan 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 alkylphenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, Polyethylene glycol fatty acid ester, alkyl glucoside, N-alkyl gluconamides Polyoxyethylene fatty acid amides, polyoxyethylene alkyl amines, phosphoric esters of polyoxyethylene alkyl ethers, can be used phosphoric acid ester of polyoxyethylene alkyl aryl ether. Among these surfactants, sorbitan fatty acid ester, polyglycerin fatty acid ester, and sucrose fatty acid ester are preferably used from the viewpoint of dispersion stability of the monomer. These surfactants may be used alone or in combination of two or more.

  As the usage-amount of surfactant, it is preferable that it is 0.1-30 mass parts with respect to 100 mass parts of water-soluble ethylenically unsaturated monomers of the 1st step, and 0.3-20 More preferably, it is part by mass.

(Polymer dispersant)
Further, as the dispersion stabilizer used in the reverse phase suspension polymerization, a polymer dispersant may be used in combination with the above-described surfactant.

  Examples of the polymeric 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 anhydrous. Maleic acid-modified polybutadiene, maleic anhydride / ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, maleic anhydride / butadiene copolymer, polyethylene, polypropylene, ethylene / propylene Examples of the copolymer include oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymer, ethylene / acrylic acid copolymer, ethyl cellulose, and ethyl hydroxyethyl cellulose. Among these polymeric dispersants, in particular, from the viewpoint of dispersion stability of the monomer, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride / Ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymer It is preferable to use a polymer. These polymer dispersants may be used alone or in combination of two or more.

  The amount of the polymeric dispersant used is preferably 0.1 to 30 parts by mass with respect to 100 parts by mass of the first stage water-soluble ethylenically unsaturated monomer, and 0.3 to 20 More preferably, it is part by mass.

[Azo compounds and peroxides]
In the polymerization process, “in the presence of an azo compound and a peroxide” does not necessarily mean that the azo compound and the peroxide coexist at the start of the polymerization reaction. It means that the other compound is present while the monomer conversion by cleavage is less than 10%, but both of them coexist in the aqueous solution containing the monomer before the start of the polymerization reaction. Is preferred. In addition, the azo compound and the peroxide may be added to the polymerization reaction system through separate flow paths, or may be sequentially added to the polymerization reaction system through the same flow path. The form of the azo compound and peroxide used may be a powder or an aqueous solution.

(Azo compounds)
Examples of the azo compound include 1-{(1-cyano-1-methylethyl) azo} formamide, 2,2′-azobis [2- (N-phenylamidino) propane] dihydrochloride, 2,2 ′. -Azobis {2- [N- (4-chlorophenyl) amidino] propane} dihydrochloride, 2,2'-azobis {2- [N- (4-hydroxyphenyl) amidino] propane} dihydrochloride, 2,2 '-Azobis [2- (N-benzylamidino) propane] dihydrochloride, 2,2'-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2'-azobis (2-amidinopropane) ) Dihydrochloride, 2,2′-azobis {2- [N- (2-hydroxyethyl) amidino] propane} dihydrochloride, 2,2′-azobis [2- (5-methyl-2-imidazoline-2) -Yl) propane] dihydrochloric acid 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (4,5,6,7-tetrahydro-1H-1,3 -Diazepin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2, 2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane ], 2,2′-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2′-azobis {2-methyl-N- [1 , 1-Bis (hydroxymethyl) ethyl] propiona 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 2,2'-azobis (2-methylpropionamide) dihydrochloride, 4,4'-azobis- 4-cyanovaleric acid, 2,2′-azobis [2- (hydroxymethyl) propionitrile], 2,2′-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] An azo compound such as Among these, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} 2 Hydrochloride, 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate is preferred. These azo compounds may be used alone or in combination of two or more.

(Peroxide)
Examples of the peroxide include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t -Peroxides such as butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, and hydrogen peroxide. Among these peroxides, potassium persulfate, ammonium persulfate, sodium persulfate, and hydrogen peroxide are preferably used, and potassium persulfate, ammonium persulfate, and sodium persulfate are more preferably used. These peroxides may be used alone or in combination of two or more.

(Amount of azo compounds and peroxides used)
The amount of the azo compound and peroxide used is preferably 0.00005 mol or more, more preferably 0.0001 mol or more with respect to 1 mol of the water-soluble ethylenically unsaturated monomer. Moreover, it is preferable that it is 0.005 mol or less with respect to 1 mol of water-soluble ethylenically unsaturated monomers, and it is more preferable that it is 0.001 mol or less.

  The amount of the azo compound and peroxide used is preferably 40% by weight or more of the total amount of the azo compound and peroxide used, and preferably 50% by weight or more. It is more preferable to set it as a ratio, it is more preferable to set it as the ratio which is 60 mass% or more, and it is more preferable to set it as the ratio which is 70 mass% or more. On the other hand, the proportion of the azo compound is preferably 95% by mass or less, more preferably 90% by mass or less, of the total amount of the azo compound and peroxide used, more preferably 85% by mass or less. It is more preferable to set it as the ratio which is, and it is still more preferable to set it as the ratio which is 80 mass% or less. The mass ratio range (azo compound: peroxide) is preferably 8:12 to 19: 1.

[Other ingredients]
In the method for producing a water absorbent resin, reverse phase suspension polymerization may be carried out by adding other components to an aqueous solution containing a water-soluble ethylenically unsaturated monomer as desired. As other components, various additives such as a thickener and a chain transfer agent can be added.

(Thickener)
As an example, reverse phase suspension polymerization can be performed by adding a thickener to an aqueous solution containing a water-soluble ethylenically unsaturated monomer. By adjusting the aqueous solution viscosity by adding a thickener in this way, it is possible to control the median particle size obtained in the reverse phase suspension polymerization.

  Examples of the thickener include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, polyacrylic acid (partial) neutralized product, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol Polyvinyl pyrrolidone, polyethylene oxide, etc. can be used. In addition, if the stirring speed at the time of superposition | polymerization is the same, there exists a tendency for the median particle diameter of the particle | grains obtained to become large, so that the viscosity of water-soluble ethylenically unsaturated monomer aqueous solution is high.

[Reverse phase suspension polymerization]
In carrying out reverse phase suspension polymerization, for example, an aqueous monomer solution containing a water-soluble ethylenically unsaturated monomer is dispersed in a hydrocarbon dispersion medium in the presence of a dispersion stabilizer. At this time, before the polymerization reaction is started, the dispersion stabilizer (surfactant or polymer dispersant) may be added before or after the monomer aqueous solution is added.

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

  Such reverse phase suspension polymerization can be carried out in one stage or in multiple stages of two or more stages. Moreover, it is preferable to carry out in 2-3 steps from a viewpoint of improving productivity.

  When reverse-phase suspension polymerization is performed in two or more stages, water-soluble ethylenic unsaturation is performed on the reaction mixture obtained by the first-stage polymerization reaction after the first-stage reverse-phase suspension polymerization. Monomers may be added and mixed, and reverse phase suspension polymerization in the second and subsequent stages may be performed in the same manner as in the first stage. In the reverse phase suspension polymerization in each stage after the second stage, in addition to the water-soluble ethylenically unsaturated monomer, the internal crosslinking agent, the azo compound and the peroxide described above are added to each of the second stage and subsequent stages. Based on the amount of the water-soluble ethylenically unsaturated monomer added during the reverse phase suspension polymerization in the stage, it is added within the range of the molar ratio of each component to the water-soluble ethylenically unsaturated monomer described above. It is preferable to carry out reverse phase suspension polymerization. In the second and subsequent polymerizations, the polymerization is preferably performed in the presence of an azo compound and a peroxide.

  The reaction temperature of the polymerization reaction is 20 to 110 ° C. from the viewpoint of allowing the polymerization to proceed rapidly and shortening the polymerization time, thereby improving the economy and allowing the reaction to be smoothly performed by easily removing the heat of polymerization. It is preferable that it is 40-90 degreeC. The reaction time is preferably 0.5 to 4 hours.

<Post-crosslinking step>
Next, the water-absorbent resin according to the present invention is post-crosslinked with a post-crosslinking agent to a hydrous gel-like product having an internal cross-linked structure obtained by polymerizing a water-soluble ethylenically unsaturated monomer ( Obtained by post-crosslinking reaction). This post-crosslinking reaction is preferably performed in the presence of a post-crosslinking agent after the polymerization of the water-soluble ethylenically unsaturated monomer. Thus, after the polymerization, by performing a post-crosslinking reaction on the hydrogel having an internal cross-linked structure, the cross-linking density in the vicinity of the surface of the water-absorbent resin is increased, and the water absorption capacity under load, the water absorption speed, etc. It is possible to obtain a water-absorbent resin with improved performances.

  Examples of the post-crosslinking agent include compounds having two or more reactive functional groups. For example, polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, polyglycerin; (poly) ethylene glycol diglycidyl ether, (poly) Polyglycidyl compounds such as glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether; epichlorohydrin, epibromohydrin, α -Haloepoxy compounds such as methyl epichlorohydrin; isocyanates such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate Nate compounds; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, 3- Oxetane compounds such as butyl-3-oxetaneethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylene carbonate; hydroxyalkylamides such as bis [N, N-di (β-hydroxyethyl)] adipamide Compounds. Among these post-crosslinking agents, (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, (poly) propylene glycol polyglycidyl ether, ( Polyglycidyl compounds such as poly) glycerol polyglycidyl ether are preferred. These post-crosslinking agents may be used alone or in combination of two or more.

  The amount of the post-crosslinking agent used is preferably 0.00001 to 0.01 mol, preferably 0.00005 to 0.005 mol with respect to 1 mol of the total amount of the water-soluble ethylenically unsaturated monomer used for the polymerization. 005 mol is more preferable, and 0.0001 to 0.002 mol is more preferable.

  As a method for adding the post-crosslinking agent, the post-crosslinking agent may be added as it is or may be added as an aqueous solution, but if necessary, it may be added as a solution using a hydrophilic organic solvent as a solvent. Examples of the hydrophilic organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether, dioxane and tetrahydrofuran; N, N -Amides such as dimethylformamide; and sulfoxides such as dimethyl sulfoxide. These hydrophilic organic solvents may be used alone or in combination of two or more or as a mixed solvent with water.

  The post-crosslinking agent may be added after the polymerization reaction of the water-soluble ethylenically unsaturated monomer is almost completed. It is preferable to add in the presence of moisture in the range of 400 parts by mass, more preferably in the presence of moisture in the range of 5 to 200 parts by mass, and in the presence of moisture in the range of 10 to 100 parts by mass. Is more preferable, and it is still more preferable to add in the presence of water in the range of 20 to 60 parts by mass. The amount of moisture means the total amount of moisture contained in the polymerization reaction system and moisture used as necessary when adding the post-crosslinking agent.

  The reaction temperature in the post-crosslinking reaction is preferably 50 to 250 ° C, more preferably 60 to 180 ° C, still more preferably 60 to 140 ° C, and more preferably 70 to 120 ° C. Further preferred. Moreover, as reaction time of post-crosslinking reaction, it is preferable that it is 1 to 300 minutes, and it is more preferable that it is 5 to 200 minutes.

<Drying process>
After performing the above-described reverse phase suspension polymerization, a drying step of removing water, hydrocarbon dispersion medium, and the like by distillation by applying energy such as heat from the outside may be included. When dehydration is performed from a hydrous gel after reversed-phase suspension polymerization, water and the hydrocarbon dispersion medium are temporarily removed from the system by azeotropic distillation by heating the system in which the hydrogel is dispersed in the hydrocarbon dispersion medium. Distill off. At this time, if only the distilled hydrocarbon dispersion medium is returned to the system, continuous azeotropic distillation is possible. In that case, since the temperature in the system during drying is maintained below the azeotropic temperature with the hydrocarbon dispersion medium, it is preferable from the viewpoint that the resin is hardly deteriorated. Subsequently, water and hydrocarbon dispersion medium are distilled off to obtain water-absorbent resin particles. By controlling the treatment conditions of the drying step after the polymerization and adjusting the amount of dehydration, it is possible to control various performances of the resulting water-absorbent resin.

  In the drying step, the drying treatment by distillation may be performed under normal pressure or under reduced pressure. Moreover, you may carry out under airflow, such as nitrogen, from a viewpoint of improving drying efficiency. In the case where the drying treatment is performed under normal pressure, the drying temperature is preferably 70 to 250 ° C, more preferably 80 to 180 ° C, further preferably 80 to 140 ° C, 90 to More preferably, it is 130 degreeC. Moreover, when performing a drying process under reduced pressure, it is preferable that it is 40-160 degreeC as drying temperature, and it is more preferable that it is 50-110 degreeC.

  In addition, when the post-crosslinking step with the post-crosslinking agent is performed after the polymerization of the monomer by the reverse phase suspension polymerization, the drying step by distillation described above is performed after the completion of the cross-linking step. Or you may make it perform a post-crosslinking process and a drying process simultaneously.

  Moreover, you may add various additives, such as a chelating agent, a reducing agent, an oxidizing agent, an antibacterial agent, and a deodorizing agent after superposition | polymerization, during drying, or after drying with respect to a water absorbing resin as needed. .

≪3. Absorber, absorbent article >>
The water-absorbing resin according to the present invention constitutes an absorbent body used for sanitary materials such as sanitary goods and paper diapers, and is suitably used for absorbent articles including the absorbent body.

  Here, the absorbent body using the water absorbent resin is composed of, for example, a water absorbent resin and hydrophilic fibers. The structure of the absorber is a mixed dispersion obtained by mixing the water-absorbent resin and the hydrophilic fiber so as to have a uniform composition, and a sandwich in which the water-absorbent resin is sandwiched between layered hydrophilic fibers. Examples include a structure, a structure in which a water-absorbing resin and a hydrophilic fiber are wrapped with a tissue. The absorbent body may contain other components, for example, an adhesive binder such as a heat-fusible synthetic fiber, a hot melt adhesive, and an adhesive emulsion for enhancing the shape retention of the absorbent body. .

  As content of the water absorbing resin in an absorber, it is preferable that it is 5-95 mass%, It is more preferable that it is 20-90 mass%, It is more preferable that it is 30-80 mass%.

  Examples of hydrophilic fibers include cellulose fibers such as cotton-like pulp, mechanical pulp, chemical pulp, and semi-chemical pulp obtained from wood, synthetic cellulose fibers such as rayon and acetate, and polyamides, polyesters, and polyolefins that have been hydrophilized. Examples thereof include fibers made of resin.

  Further, by holding the absorbent body using the water absorbent resin between a liquid permeable sheet (top sheet) through which liquid can pass and a liquid impermeable sheet (back sheet) through which liquid cannot pass. It can be set as an absorbent article. The liquid permeable sheet is disposed on the side in contact with the body, and the liquid impermeable sheet is disposed on the opposite side in contact with the body.

  Examples of the liquid permeable sheet include air-through type, spun bond type, chemical bond type, needle punch type nonwoven fabrics and porous synthetic resin sheets made of fibers such as polyethylene, polypropylene, and polyester. Examples of the liquid impermeable sheet include synthetic resin films made of resins such as polyethylene, polypropylene, and polyvinyl chloride.

<< 4. Examples >>
EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated in detail, this invention is not limited at all by the following Examples.

<4-1. About Evaluation Test Method>
[Evaluation test of water-absorbent resin]
The water-absorbing resins obtained in the following Examples 1 to 4 and Comparative Examples 1 to 6 were subjected to various tests shown below and evaluated. Hereinafter, each evaluation test method will be described.

(1) Absorption capacity of physiological saline under load of 4.14 kPa Using measurement apparatus X schematically shown in FIG. 1, the absorption capacity of physiological saline under load of 4.14 kPa of water absorbent resin is measured. did.

  The measuring apparatus X shown in FIG. 1 includes a burette unit 1, a conduit 2, a measuring table 3, and a measuring unit 4 placed on the measuring table 3. In the burette unit 1, a rubber stopper 14 is connected to the upper part of the burette 10, an air introduction pipe 11 and a cock 12 are connected to the lower part, and a cock 13 is attached to the upper part of the air introduction pipe 11. A conduit 2 is attached from the burette unit 1 to the measuring table 3, and the diameter of the conduit 2 is 6 mm. A hole with a diameter of 2 mm is opened at the center of the measuring table 3 and the conduit 2 is connected. The measuring unit 4 includes a cylinder 40, a nylon mesh 41 attached to the bottom of the cylinder 40, and a weight 42. The inner diameter of the cylinder 40 is 2.0 cm. The nylon mesh 41 is formed to 200 mesh (aperture 75 μm). A predetermined amount of the water absorbent resin 5 is uniformly dispersed on the nylon mesh 41. The weight 42 has a diameter of 1.9 cm and a mass of 119.6 g. The weight 42 is placed on the water absorbent resin 5 so that a load of 4.14 kPa can be uniformly applied to the water absorbent resin 5.

  Using the measuring device X having such a configuration, first, the cock 12 and the cock 13 of the burette unit 1 are closed, and physiological saline adjusted to 25 ° C. is introduced from the upper part of the burette 10. Then, the cock 12 and the cock 13 of the burette part 1 were opened. Next, the height of the measurement table 3 was adjusted so that the tip of the conduit 2 at the center of the measurement table 3 and the air introduction port of the air introduction tube 11 had the same height.

  On the other hand, 0.10 g of the water absorbent resin 5 was uniformly spread on the nylon mesh 41 of the cylinder 40, and a weight 42 was placed on the water absorbent resin 5. The measuring unit 4 was placed so that the center of the measuring unit 4 coincided with the conduit port at the center of the measuring table 3.

  From the time when the water absorbent resin 5 started to absorb water, the decrease amount of physiological saline in the burette 10 (amount of physiological saline absorbed by the water absorbent resin 5) Wa (mL) was read. The water-absorbing capacity of the water-absorbent resin under a 4.14 kPa load after 60 minutes from the start of water absorption was determined by the following formula.

  4. Water absorption capacity of physiological saline under load of 14 kPa (mL / g) = Wa / 0.10 (g)

(2) Saline water absorption rate The saline water absorption rate was performed in a room adjusted to 25 ° C ± 1 ° C. A vortex was generated by stirring 50 ± 0.1 g of physiological saline adjusted to a temperature of 25 ± 0.2 ° C. in a constant temperature water bath at 600 rpm with a magnetic stirrer bar (no ring of 8 mmφ × 30 mm). 2.0 ± 0.002 g of the obtained water-absorbing resin is added to the physiological saline at once, and the time (seconds) from the addition of the water-absorbing resin until the vortex disappears and the liquid level becomes flat is obtained. The time was measured and the water absorption rate of the water absorbent resin was taken as the time.

(3) Median particle size (particle size distribution)
JIS standard sieve from above, sieve with an opening of 850 μm, sieve with an opening of 600 μm, sieve with an opening of 500 μm, sieve with an opening of 400 μm, sieve with an opening of 300 μm, sieve with an opening of 250 μm, sieve with an opening of 150 μm, and Combined in the order of the saucer.

  50g of water-absorbing resin was put on the combined uppermost sieve and classified by shaking for 20 minutes using a low-tap shaker. After classification, the mass of the water-absorbent resin remaining on each sieve was calculated as a mass percentage with respect to the total amount, and the particle size distribution was determined. With respect to this particle size distribution, the sieve screen was integrated in order from the largest particle size, and the relationship between the sieve opening and the integrated value of the mass percentage of the water absorbent resin remaining on the sieve was plotted on a logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle diameter corresponding to an integrated mass percentage of 50 mass% was defined as the median particle diameter.

  In addition, the mass ratio of 300-400 micrometers particle | grains which occupies for the ratio of the whole water-absorbing resin is a mass ratio of the water-absorbing resin which remained on the sieve of the 300 micrometers opening with respect to the whole in the above-mentioned measurement. Similarly, the mass ratio of the particles of 150 to 850 μm in the ratio of the entire water-absorbent resin is the sum of the mass ratio of the water-absorbent resin remaining on the sieves of 150 μm, 250 μm, 300 μm, 400 μm, 500 μm, and 600 μm. It is a thing.

(4) Preparation of artificial urine Artificial urine was prepared by adding a small amount of Blue No. 1 to ion-exchanged water that was mixed and dissolved in the presence of an inorganic salt as described below.
<Artificial urine composition>
NaCl: 0.780% by mass
CaCl ₂ : 0.022% by mass
MgSO ₄ : 0.038% by mass

(5) Artificial urine absorption capacity A cotton bag (Membroad No. 60, width 100 mm × length 200 mm) weighing 2.0 g of the water-absorbent resin was placed in a 500 mL beaker. Pour 500 g of the above artificial urine into a cotton bag containing a water-absorbent resin, stir the inside lightly so as not to make mamaco, tie the upper part of the cotton bag with a rubber band, and let it stand for 30 minutes. Freely swollen. After 30 minutes, the cotton bag containing the above water-absorbent resin was dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Centrifuge Co., Ltd., product number: H-122) set to have a centrifugal force of 167G. After removing the liquid, the mass Wb (g) of the cotton bag containing the swollen gel after dehydration was measured. After measurement, after removing the swollen gel, perform the same operation with only an empty cotton bag as the tare, measure the empty mass Wc (g) when wet, and calculate the artificial urine absorption rate from the following formula. Calculated to first place.

  Artificial urine absorption capacity (g / g) = [Wb−Wc] (g) / mass of water absorbent resin (g)

(6) Liquid flow amount The liquid flow test was performed using the apparatus Y shown in FIG. The apparatus Y includes a liquid collection tray 21 for “liquid flow amount”, a support base 22, an acrylic plate 23 for holding the sample, a measurement sample 30 comprising a water absorbent resin 5 sandwiched between the nonwoven fabrics 24A and 24B from above and below, And an acrylic plate 25 having a cylindrical inlet at the center.

First, a support base 22 made of SUS having a height of 10 cm was placed on a metal tray 21 having a depth of 30 cm and a depth of 5 cm. On top of that, a 16 cm × 12 cm acrylic plate 23 (thickness: 5 mm) was placed, and the level of the top of the acrylic plate 23 was confirmed with a leveler. A non-woven fabric 24B having the same size as the acrylic plate 23 (air-through porous liquid permeable sheet made of polyethylene-polypropylene having a basis weight of 22 g / m ² ) was placed thereon. A blank portion of 2 cm is provided from the four ends of the nonwoven fabric 24B, and 4.8 g of the water-absorbing resin 5 is uniformly sprayed on the inner portion (12 cm × 8 cm), and then the nonwoven fabric 24A having the same size is placed between the upper portions. A measurement sample 30 was prepared. At the top is a 48 cm × 28 cm acrylic plate 25 (mass: 840 g) having an inner diameter 3 cm and a height of 16.5 cm in the center, and the center of the cylinder matches the center of the measurement sample 30. I put it to do.

  120 g of artificial urine whose liquid temperature was adjusted to 25 ° C. was charged at once from the cylindrical charging portion 25a. Next, after the permeation is completed, it is confirmed that the flow of the artificial urine has stopped, the artificial urine that has flowed out of the acrylic plate 23 into the tray 21 is weighed, and the mass is the liquid flow rate (g). I asked to the rank.

[Evaluation test of absorbent body and absorbent article using water-absorbent resin]
(1) Preparation of absorber and absorbent article 12 g of water-absorbing resin and 12 g of pulverized pulp (Leonia Co., Ltd., Reiflock) are mixed uniformly by air paper making, thereby producing a sheet-like size of 40 cm × 12 cm. An absorbent core was produced. Next, with the top and bottom of the absorbent core being the same size as the absorbent core and sandwiched between two tissue papers having a basis weight of 16 g / m ² , a load of 196 kPa is applied to the whole for 30 seconds and pressing is performed. Thus, an absorber was produced. Furthermore, a polyethylene-polypropylene air-through porous liquid permeable sheet made of polyethylene-polypropylene having the same size as the absorber and having a basis weight of 22 g / m ² is disposed on the upper surface of the absorber, and the polyethylene liquid having the same size and the same basis weight. An impermeable sheet was disposed on the lower surface of the absorbent body, and the absorbent body was sandwiched to obtain an absorbent article.

(2) Penetration time of absorbent article Place the absorbent article on a horizontal table, place a measuring instrument equipped with a 3 cm inner diameter cylinder into the center of the absorbent article, and add 80 mL of artificial urine to it. The time until the artificial urine completely disappeared from the cylinder was measured using a stopwatch, and it was used as the first permeation time (second). Next, remove the cylinder, store the absorbent article as it is, and perform the same operation using the measuring instrument at the same position as the first time 30 minutes and 60 minutes after the start of the first artificial urine injection. The second and third permeation times (seconds) were measured. The total time for the first to third times was defined as the total penetration time. It can be said that the shorter the permeation time, the better the absorbent article.

(3) Amount of reversion 120 minutes after the start of the first test solution injection in the above-described measurement of the penetration time, a mass (Wd (g), about 50 g) is measured in the vicinity of the artificial urine input position on the absorbent article. A 10 cm square filter paper was placed, and a weight of 5 kg with a bottom surface of 10 cm × 10 cm was placed thereon. After loading for 5 minutes, the mass of the filter paper (We (g)) was measured, and the increased mass was taken as the reversal amount (g). In addition, it can be said that it is preferable as an absorbent article, so that the amount of reversion is small.

  Return amount (g) = We−Wd

(4) Diffusion length Within 5 minutes after the above measurement of the amount of reversion, the longitudinal dimension (cm) of the absorbent article into which the artificial urine permeated was measured. The numbers after the decimal point are rounded off.

<4-2. About Examples and Comparative Examples>
[Example 1]
As a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirrer, a 2-L round bottom cylindrical separable flask having an inner diameter of 110 mm and equipped with a stirring blade having two inclined paddle blades with a blade diameter of 50 mm in two stages. Got ready. In this flask, 300 g of n-heptane was taken as a hydrocarbon dispersion medium, 0.74 g of HLB3 sucrose stearate (Mitsubishi Chemical Foods, Ryoto Sugar Ester S-370) as a surfactant, and polymer dispersion 0.74 g of maleic anhydride-modified ethylene / propylene copolymer (Mitsui Chemicals, High Wax 1105A) was added as an agent, and the temperature was raised to 80 ° C. while stirring to dissolve the surfactant, and then up to 50 ° C. Cooled down.

  On the other hand, 92 g (1.02 mol) of 80% by mass acrylic acid aqueous solution was placed in a 500 mL Erlenmeyer flask, and 146.0 g of 21% by mass sodium hydroxide aqueous solution was added dropwise while cooling from the outside. After neutralization, 0.092 g of hydroxylethylcellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener and 2,2′-azobis (2-amidinopropane) dihydrochloride as an azo compound 092 g (0.339 mmol), potassium persulfate 0.037 g (0.136 mmol) as a peroxide, 0.0101 g (0.058 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent, and dissolved, An aqueous solution was prepared.

  Then, the rotation speed of the stirrer was set to 500 rpm, the monomer aqueous solution prepared as described above was added to the separable flask, the inside of the system was sufficiently replaced with nitrogen, and then the flask was immersed in a 70 ° C. water bath to raise the temperature. Then, polymerization was performed for 60 minutes to obtain a first stage polymerization slurry.

  On the other hand, 128.8 g (1.43 mol) of an 80% by weight acrylic acid aqueous solution was placed in another 500 mL Erlenmeyer flask, and 159.0 g of a 27% by weight sodium hydroxide aqueous solution was dropped while cooling from the outside. After neutralizing 75 mol%, 0.129 g (0.475 mmol) of 2,2′-azobis (2-amidinopropane) dihydrochloride as the azo compound and 0.052 g of potassium persulfate as the peroxide (0.191 mmol), 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent was added and dissolved to prepare a second-stage monomer aqueous solution.

  After changing the stirring rotation speed of the post-polymerization slurry to 1000 rpm, the inside of the above-described separable flask system is cooled to 25 ° C., and then the entire amount of the second-stage monomer aqueous solution is changed to the first-stage polymerization slurry liquid. After the addition and the inside of the system was sufficiently substituted with nitrogen, the flask was again immersed in a 70 ° C. water bath to raise the temperature, and the second stage polymerization was carried out for 30 minutes.

  After polymerization in the second stage, the temperature of the reaction solution was raised in an oil bath at 125 ° C., and 239 g of water was extracted out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. As a post-crosslinking agent, 4.42 g (0.51 mmol) of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was added and held at 80 ° C. for 2 hours. Thereafter, n-heptane was evaporated and dried to obtain a dried product. The dried product is mixed with 0.3% by mass of amorphous silica (Evonik Degussa Japan Co., Ltd., Carplex # 80), passed through a sieve having an opening of 1000 μm, and spherical particles are aggregated. 234.0 g of a water absorbent resin was obtained. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the obtained water-absorbent resin had a mass ratio of 150 to 850 μm particles in the total ratio of 95.5% by mass and a mass ratio of 300 to 400 μm particles of 25.0% by mass. . Moreover, the physiological saline water absorption speed of the obtained water-absorbent resin was 60 seconds.

[Example 2]
In Example 2, after the second stage polymerization, 242 g of water was withdrawn out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. The operation was performed to obtain 231.8 g of a water-absorbent resin having a secondary particle form in which spherical primary particles are aggregated. As a result, a water absorbent resin having a water retention capacity different from that of the water absorbent resin obtained in Example 1 was obtained. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the obtained water-absorbent resin had a mass ratio of 150 to 850 μm particles in the entire ratio of 96.6% by mass, and a mass ratio of particles of 300 to 400 μm was 27.6% by mass. . Moreover, the physiological saline water absorption speed of the obtained water-absorbing resin was 66 seconds.

[Example 3]
Example 3 was the same as Example 1 except that after the second stage polymerization, 236 g of water was withdrawn from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. The operation was performed to obtain 230.7 g of a water-absorbent resin having a form of secondary particles in which spherical primary particles were aggregated. As a result, a water absorbent resin having a water retention capacity different from that of the water absorbent resin obtained in Example 1 was obtained. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the obtained water-absorbent resin had a mass ratio of 150 to 850 μm particles in the total ratio of 96.3% by mass and a mass ratio of 300 to 400 μm particles of 25.3 mass%. . Moreover, the physiological saline water absorption speed of the obtained water-absorbent resin was 78 seconds.

[Example 4]
In Example 4, the stirring rotation speed during the first stage polymerization was changed to 550 rpm, and the 2 mass% aqueous solution of ethylene glycol diglycidyl ether was changed to 6.62 g as a post-crosslinking agent. The same operation was performed to obtain 231.4 g of a water absorbent resin having a form of secondary particles in which spherical primary particles were aggregated. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the obtained water-absorbent resin had a mass ratio of 150 to 850 μm particles in the total ratio of 97.4% by mass and a mass ratio of 300 to 400 μm particles of 42.1% by mass. . Moreover, the physiological saline water absorption speed of the obtained water-absorbent resin was 63 seconds.

[Comparative Example 1]
In Comparative Example 1, reverse-phase suspension polymerization was performed using only a peroxide alone to produce a water-absorbent resin.

  As a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirrer, a 2-L round bottom cylindrical separable flask having an inner diameter of 110 mm and equipped with a stirring blade having two inclined paddle blades with a blade diameter of 50 mm in two stages. Prepare and take 300 g of n-heptane as a hydrocarbon dispersion medium in this flask, 0.74 g of sucrose stearate ester of HLB3 (Mitsubishi Chemical Foods, Ryoto Sugar Ester S-370) as a surfactant, high After adding 0.74 g of maleic anhydride-modified ethylene / propylene copolymer (Mitsui Chemical Co., Ltd., High Wax 1105A) as a molecular dispersant, the temperature was raised to 80 ° C. with stirring, and the surfactant was dissolved. Cooled to 50 ° C.

  On the other hand, 92 g (1.02 mol) of 80% by mass acrylic acid aqueous solution was placed in a 500 mL Erlenmeyer flask, and 146.0 g of 21% by mass sodium hydroxide aqueous solution was added dropwise while cooling from the outside. After neutralization, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener, 0.074 g (0.274 mmol) of potassium persulfate, and ethylene glycol diglycidyl as an internal crosslinking agent 0.0184 g (0.1056 mmol) of ether was added and dissolved to prepare an aqueous monomer solution.

  Then, the monomer aqueous solution prepared as described above was added to the separable flask with the rotation speed of the stirrer being 500 rpm, and the inside of the system was sufficiently replaced with nitrogen, and then the flask was immersed in a 70 ° C. water bath and heated. The first-stage polymerization slurry was obtained by performing polymerization for 60 minutes.

  On the other hand, 128.8 g (1.43 mol) of an 80% by weight acrylic acid aqueous solution was placed in another 500 mL Erlenmeyer flask, and 159.0 g of a 27% by weight sodium hydroxide aqueous solution was dropped while cooling from the outside. After neutralization of 75 mol%, 0.104 g (0.382 mmol) of potassium persulfate and 0.0386 g (0.2218 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent were added and dissolved. A second stage monomer aqueous solution was prepared.

  After changing the stirring rotation speed of the post-polymerization slurry to 1000 rpm, the inside of the above-described separable flask system is cooled to 25 ° C., and then the entire amount of the second-stage monomer aqueous solution is changed to the first-stage polymerization slurry. After adding to the liquid and sufficiently replacing the system with nitrogen, the flask was again immersed in a 70 ° C. water bath to raise the temperature, and the second stage polymerization was carried out for 30 minutes.

  After polymerization in the second stage, the temperature of the reaction solution was raised in an oil bath at 125 ° C., and 273 g of water was extracted out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. As a post-crosslinking agent, 6.62 g (0.76 mmol) of a 2% by weight aqueous solution of ethylene glycol diglycidyl ether was added and held at 80 ° C. for 2 hours. Thereafter, n-heptane was evaporated and dried to obtain a dried product. 0.3% by mass of amorphous silica (Carplex # 80, manufactured by Evonik Degussa Japan Co., Ltd.) is mixed with this dried product, passed through a sieve having an opening of 1000 μm, and spherical particles are aggregated 231.2 g of a water absorbent resin was obtained. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the mass ratio of the 150-850 micrometers particle | grains which account for the obtained water absorbent resin was 97.0 mass%, and the mass ratio of the 300-400 micrometers particle | grain was 36.9 mass%. . Moreover, the physiological saline water absorption speed of the obtained water-absorbent resin was 41 seconds.

[Comparative Example 2]
In Comparative Example 2, the ethylene glycol diglycidyl ether added to the second stage monomer was changed to 0.0129 g, and the 2% by weight aqueous solution of ethylene glycol diglycidyl ether was changed to 4.42 g as a post-crosslinking agent. Except for the above, the same operation as in Comparative Example 1 was performed to obtain 232.9 g of a water absorbent resin having a form of secondary particles in which spherical primary particles were aggregated. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the obtained water-absorbent resin had a mass ratio of 150 to 850 μm particles in the total ratio of 96.4% by mass and a mass ratio of 300 to 400 μm particles of 35.7% by mass. . Moreover, the physiological saline water absorption speed of the obtained water-absorbent resin was 39 seconds.

[Comparative Example 3]
In Comparative Example 3, the ethylene glycol diglycidyl ether added to the first stage monomer was changed to 0.0101 g, and the stirring rotation speed during the first stage polymerization was changed to 550 rpm. Was polymerized. And the ethylene glycol diglycidyl ether added to the second-stage monomer was changed to 0.0116 g, and the 2% by weight aqueous solution of ethylene glycol diglycidyl ether was changed to 4.42 g as a post-crosslinking agent. The same operation as in Comparative Example 1 was performed to obtain 231.8 g of a water absorbent resin having the form of secondary particles in which spherical primary particles were aggregated. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the obtained water-absorbent resin had a mass ratio of 150 to 850 μm particles in the total ratio of 94.6% by mass and a mass ratio of 300 to 400 μm particles of 34.0% by mass. . Moreover, the physiological saline water absorption speed of the obtained water-absorbing resin was 35 seconds.

[Comparative Example 4]
In Comparative Example 4, ethylene glycol diglycidyl ether added to the first stage monomer was changed to 0.0156 g, and ethylene glycol diglycidyl ether added to the second stage monomer was changed to 0.0155 g. In the same manner as in Comparative Example 1 except that the 2 mass% aqueous solution of ethylene glycol diglycidyl ether was changed to 6.62 g as a post-crosslinking agent, the shape of secondary particles in which spherical primary particles were aggregated was changed. 231.4 g of a water absorbent resin was obtained. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the obtained water-absorbent resin had a mass ratio of 150 to 850 μm particles in the total ratio of 97.1% by mass, and a mass ratio of 300 to 400 μm particles of 35.9% by mass. . Moreover, the physiological saline water absorption speed | velocity of the obtained water absorbing resin was 40 second.

[Comparative Example 5]
In Comparative Example 5, the same operation as in Comparative Example 4 was performed except that the temperature in the separable flask before introducing the second-stage monomer aqueous solution was changed to 23 ° C., and spherical primary particles aggregated. 230.8 g of a water absorbent resin having the form of secondary particles was obtained. As a result, a water absorbent resin having a secondary particle diameter different from that of the water absorbent resin obtained in Comparative Example 4 was obtained. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the obtained water-absorbent resin had a mass ratio of 150 to 850 μm particles in the total ratio of 96.4% by mass and a mass ratio of 300 to 400 μm particles of 23.2% by mass. . Moreover, the physiological saline water absorption speed of the obtained water-absorbent resin was 51 seconds.

[Comparative Example 6]
In Comparative Example 6, ethylene glycol diglycidyl ether added to the first stage monomer was changed to 0.0092 g, and ethylene glycol diglycidyl ether added to the second stage monomer was changed to 0.0386 g. In the same manner as in Comparative Example 1 except that the 2 mass% aqueous solution of ethylene glycol diglycidyl ether was changed to 11.04 g as a post-crosslinking agent, the shape of secondary particles in which spherical primary particles were aggregated was changed. 231.0 g of a water absorbent resin was obtained. This water-absorbent resin was evaluated according to the various test methods described above.

  In addition, the obtained water-absorbent resin had a mass ratio of 150 to 850 μm particles in the total ratio of 92.9 mass% and a mass ratio of 300 to 400 μm particles of 36.6 mass%. . Moreover, the physiological saline water absorption speed of the obtained water-absorbent resin was 48 seconds.

<4-3. About evaluation results>
[Evaluation results of water absorbent resin]
Table 1 below shows the evaluation results of the water absorbent resin and the absorbent body formed using the water absorbent resin. Table 1 also shows the absorber effective index K represented by the following formula (I).
Absorber Effective Index K = Liquid Flow Rate (g) × Artificial Urine Absorption Rate (g / g) (I)

[Evaluation results of absorbent articles]
Next, in Table 2 below, regarding the absorbent articles produced using the water absorbent resins obtained in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, the artificial articles of the absorbent articles are shown. The measurement results of urine penetration time, amount of reversion, and diffusion length are shown.

X (Saline water absorption capacity under a load of 4.14 kPa) Measuring device Y (Liquid flow test) Measuring device 1 Burette part 2 Conduit 3 Measuring table 4 Measuring part 5 Water absorbing resin

Claims (4)

A water-absorbent resin obtained by polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal crosslinking agent and post-crosslinking with a post-crosslinking agent,
When the following liquid flow test is performed using the water absorbent resin, the absorbent effective index K represented by the formula (I) is 250 or more, and the water absorbent resin is characterized by the following.
Absorber Effective Index K = Liquid Flow Rate (g) × Artificial Urine Absorption Rate (g / g) (I)
[Liquid flow test]
A non-woven fabric is placed on an acrylic plate, and 4.8 g of water-absorbing resin is uniformly sprayed, and then the non-woven fabric is placed from the top and sandwiched between them to make a measurement sample. Is placed so that the central part of the cylinder matches the central part of the measurement sample, 120 g of artificial urine with a liquid temperature of 25 ° C. is added at once from the cylindrical input part, and the artificial urine flowing out from the acrylic plate is weighed. Let it be the flow rate (g).   The water absorbent resin according to claim 1, wherein the artificial urine absorption capacity is 30.0 g / g or more.   The water-absorbent resin according to claim 1 or 2, wherein the liquid flow amount is 5.0 g or more. An absorptive article using an absorber containing a water absorptive resin according to any one of claims 1 to 3.

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