JP7021300B2 - Absorber and absorbent article - Google Patents

Description

The present invention relates to an absorbent body and an absorbent article, and more particularly to an absorbent body preferably used for sanitary materials such as paper diapers, menstrual napkins, and incontinence pads, and an absorbent article using the same.

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

As such a water-absorbent resin, the crosslinked product of the partially neutralized salt polymer of acrylic acid has excellent water-absorbing ability, and the acrylic acid as a raw material thereof is easily industrially available, so that the quality is constant. Moreover, it is said to be a preferable water-absorbent resin because it can be manufactured at low cost and has many advantages such as resistance to decay and deterioration.

On the other hand, absorbent articles such as paper omelets, sanitary napkins, and incontinence pads are mainly placed in the center of the body as an absorber that absorbs and retains body fluids such as urine and menstrual blood excreted from the body. It is composed of a liquid-permeable front sheet (top sheet) arranged on the side in contact with the body and a liquid-impermeable back sheet (back sheet) arranged on the opposite side in contact with the body. Further, the absorber is composed of hydrophilic fibers such as pulp and a water-absorbent resin.

In recent years, there has been an increasing demand for thinner and lighter absorbent articles from the viewpoints of design, convenience at the time of carrying, efficiency at the time of distribution, and the like. Furthermore, from the viewpoint of environmental conservation, there is a growing need for so-called eco-friendly orientation, which makes effective use of resources and avoids the use of natural materials that require a long period of time to grow, such as trees. Conventionally, as a method for thinning generally performed in absorbent articles, for example, reducing hydrophilic fibers such as crushed wood pulp, which has a role of fixing the water-absorbent resin in the absorbent body, is used. There was a way to increase the water-absorbent resin.

An absorber having a low ratio of hydrophilic fibers and using a large amount of water-absorbent 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 containing the water-absorbent resin due to deformation, pressure, etc., such as when an infant wearing a thinned absorbent article sits down, the absorbed liquid reverts (returns). May not be fully prevented. Furthermore, in the case of such an absorbent article, it cannot withstand multiple urinations and may cause discomfort to the wearer.

In addition, a large amount of water-absorbent resin becomes a soft gel due to absorption of liquid, and when a load is applied to this gel, a so-called "gel blocking phenomenon" occurs, the liquid diffusivity is significantly reduced, and absorption is performed. The rate of penetration of body fluids may slow down. This "gel blocking phenomenon" is that when the absorbent body, which is densely packed with a large amount of water-absorbent resin, absorbs the liquid, the water-absorbent resin existing near the surface layer absorbs the liquid, and a soft gel is formed near the surface layer. When the gel becomes dense, the permeation of the liquid into the absorber is hindered, and the water-absorbent resin inside cannot absorb the liquid efficiently.

Therefore, as a means for reducing hydrophilic fibers and preventing problems that occur when a large amount of water-absorbent resin is used, for example, a hydrogel-absorbing polymer having specific saline flow inducibility, performance under pressure, etc. Proposed methods include 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 on a specific water-absorbent resin precursor (see Patent Document 2), and the like.

However, these methods do not always satisfy the absorption performance as an absorber using a large amount of water-absorbent resin, and also tend to cause a problem that the liquid to be absorbed cannot be captured and liquid leakage occurs. ..

Special Table No. 9-510889 Gazette Japanese Unexamined Patent Publication No. 8-57311

The present invention has been proposed in view of the above-mentioned circumstances, and is an absorber containing a water-absorbent resin which is excellent in water absorption performance and can improve the absorption performance under load when used as an absorber. And an absorbent article using the absorber.

The present inventors have made extensive studies to solve the above-mentioned problems. As a result, if an absorber containing a water-absorbent resin having an absorption capacity elasticity index expressed by the product of the storage elastic modulus of the water-absorbent resin and the centrifugal retention rate is equal to or higher than a predetermined value is used for the absorbent article, an excellent load is obtained. It was found that the absorption performance underneath was achieved. That is, the present invention provides the following.

(1) The present invention is an absorber containing a water-absorbent resin which is a polymer cross-linked product of a water-soluble ethylenically unsaturated monomer, an internal cross-linking agent, and a post-cross-linking agent, and hydrophilic fibers. The water-absorbent resin is an absorber that satisfies the following characteristics (A) to (D).
(A) The water absorption capacity of physiological saline under a load of 4.14 kPa is 16 mL / g or more, and (B) the mass ratio of particles of 150 to 850 μm to the entire water-absorbent resin is 85% by mass or more, and 300. The mass ratio of the particles having a size of ~ 400 μm is 20% by mass or more, (C) the tan δ measured by classifying the particles having a size of 300 to 400 μm of the water-absorbent resin is 2.00 × 10 ⁻² or less, and (D) the following formula (I). ) Has an absorption capacity elasticity index of 68,000 or more.
Absorption capacity elastic modulus = storage elastic modulus [Pa] x centrifugal retention rate [g / g] ... (I)

(2) Further, the present invention is an absorber having a storage elastic modulus of 1000 Pa or more and 10000 Pa or less in the invention according to the above (1).

(3) Further, the present invention is the absorber according to the invention (1) or (2), wherein the centrifugal retention rate is 30 g / g or more and 60 g / g or less.

(4) The present invention is an absorbent article using the absorber according to any one of (1) to (3) above.

The absorbent resin contained in the absorbent body according to the present invention can form a gel having excellent water absorption performance under a load and having appropriate elasticity when absorbing a liquid. Therefore, the absorbent article containing the absorber using the water-absorbent resin effectively suppresses the reversion of the absorbed liquid over time even when a load is applied due to deformation, pressure, etc., and under an excellent load. It is possible to demonstrate the absorption performance of.

It is a schematic block diagram which shows the structure of the apparatus for measuring the water absorption capacity of a physiological saline under a load of 4.14 kPa of a water-absorbent 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-absorbent resin according to the present invention has a physiological saline water-absorbing capacity of 16 mL / g or more under a load of 4.14 kPa, and the mass ratio of particles of 150 to 850 μm to the total ratio of the water-absorbent resin is 85% by mass. As described above, the mass ratio of the particles having a size of 300 to 400 μm is 20% by mass or more, and the absorption capacity elasticity index is 68,000 or more, which is represented by the following formula (I).
Absorption capacity elastic modulus = storage elastic modulus [Pa] x centrifugal retention rate [g / g] ... (I)

Regarding the particle size distribution of the water-absorbent resin, the mass ratio of the particles of 150 to 850 μm to the total ratio is 85% by mass or more, more preferably 90% by mass or more. Further, the mass ratio of the particles of 300 to 400 μm to the total ratio is 20% by mass or more, more preferably 25% by mass or more, and further preferably 30% by mass or more.

The particles of the water-absorbent resin may be in the form of agglomerated fine particles (primary particles) in addition to the form in which each is composed of a single particle. Examples of the shape of the primary particles include a substantially spherical shape, an amorphous crushed shape, and a plate shape. In the case of primary particles produced by reverse phase suspension polymerization, a substantially spherical single particle shape having a smooth surface shape such as a true spherical shape or an elliptical spherical shape can be mentioned. Is a water-absorbent resin with high particle strength, which has high fluidity as a powder due to its smooth surface shape and is not easily destroyed by impact because agglomerated particles are easily packed densely. Tends to be.

Further, the water-absorbent resin according to the present invention preferably has a medium particle size of 200 to 600 μm, more preferably 250 to 500 μm, and even more preferably 300 to 400 μm.

The water-absorbent resin according to the present invention is characterized in that, as described above, the absorption capacity elasticity index represented by the formula (I) is 68,000 or more. It has been found that if the water-absorbent resin has a higher index, the absorption performance (penetration rate, liquid reversion amount, etc.) of the absorbent article used for the resin under load is more excellent. The absorption capacity elasticity index is preferably 70,000 or more, more preferably 72,000 or more, and further preferably 74,000 or more. The absorption capacity elasticity index is preferably 200,000 or less, more preferably 150,000 or less, and even more preferably 100,000 or less.

Here, the "storage elastic modulus" is a numerical value measured by using a dynamic viscoelasticity measuring device for a swelling gel prepared by swelling a classified sample of a water-absorbent resin of 300 to 400 μm with physiological saline 50 times. To say. This storage elastic modulus is an index showing the ratio of strain to the stress of the gel, that is, the shape retention (difficulty of deformation) of the gel.

The "centrifugal retention rate" means that the water-absorbent resin sample is swollen (absorbed) with physiological saline under stirring for 60 minutes, dehydrated with a centrifugal force of 167 G for 1 minute, and then the water-absorbent resin has its own weight. It is a parameter showing how many times the swelling ratio can be maintained.

The water-absorbent resin according to the present invention has an absorption capacity elastic index represented by the formula (I) of 68,000 or more, and the water-absorbent resin having such properties has an appropriate centrifuge retention rate. By forming an elastic gel, it is possible to effectively suppress the reversion of the absorbed liquid over time due to deformation, pressure, or the like in the absorber using the gel. For example, when an absorbent article such as a disposable diaper is formed using this absorbent resin, it is extremely advantageous for multiple urinations, reduces discomfort to the wearer, and enables more comfortable use. In addition, the gel blocking phenomenon can be suppressed, and the absorption performance of the absorbent article under a load can be improved.

Further, the water-absorbent resin according to the present invention has a physiological saline water absorption capacity of 16 ml / g or more under a load of 4.14 kPa. Further, the physiological saline water absorption capacity under this 4.14 kPa load is preferably 18 ml / g or more, and more preferably 20 ml / g or more. The physiological saline water absorption capacity under a load of 4.14 kPa is preferably 50 ml / g or less, and more preferably 40 ml / g or less.

Further, in the water-absorbent resin according to the present invention, as described above, it is preferable that the tan δ measured by classifying particles having a size of 300 to 400 μm is 2.00 × 10 ⁻² or less. Here, the details of tan δ are described in, for example, “Polymer Viscoelasticity” (written by John D. Ferry, translated by Hiroshi Sobue, co-translated by Jokichi Murakami and Masao Takahashi, Tokyo Kagaku Dojin, published in October 1964). ..

Generally, in viscoelasticity evaluation, a polymer material is represented by a model consisting of an elastic component and a viscoelastic component, the elastic component is a component that converts impact energy into repulsive energy, and the latter converts impact energy into dissipated energy. It is a component to be converted. In the dynamic viscoelasticity measurement by vibration strain, the complex elastic modulus G ^* = G'+ iG'' (i is an imaginary unit) is physically shown. Here, G'(storage elastic modulus) and G'' (loss elastic modulus) represent the magnitudes of the elastic component and the viscous component of the polymer material, respectively. Then, tan δ (loss coefficient) = G'' / G'is an index of energy lost when the material is deformed.

In the water-absorbent resin according to the present invention, tan δ represented by “tan δ = loss elastic modulus / storage elastic modulus” is preferably 2.00 × ^10-2 or less, which means that a high storage elastic modulus is exhibited. However, it is also possible to suppress the gel blocking phenomenon that occurs when the liquid is absorbed. It is more preferable that tan δ is 1.00 × 10 ⁻² or more.

Further, the water-absorbent resin according to the present invention preferably has a storage elastic modulus of 1000 Pa or more, more preferably 1200 Pa or more, and further preferably 1500 Pa or more. The upper limit of the storage elastic modulus is preferably 10,000 Pa or less, more preferably 5000 Pa or less, further preferably 2500 Pa or less, and even more preferably 2000 Pa or less.

Further, the water-absorbent resin according to the present invention preferably has a centrifugal retention rate of 30 g / g or more. Centrifugal retention represents the degree of absorption capacity of the liquid of the water-absorbent resin. In the water-absorbent resin according to the present invention, the centrifugal retention rate is preferably 30 g / g or more, more preferably 36 g / g or more, still more preferably 38 g / g or more, still more preferably 40 g / g or more. The upper limit of the centrifugal retention rate is preferably about 60 g / g or less, more preferably 55 g / g or less, and even more preferably 50 g / g or less.

The above-mentioned water-absorbent resin has a centrifugal retention rate, a saline water absorption capacity under a load of 4.14 kPa, a medium particle size (particle size distribution), a storage elastic modulus, and a tan δ, all of which are described in Examples described later. It can be measured by the measuring method.

In addition, in order to impart various performances to the obtained water-absorbent resin, an additive suitable for the purpose can be added to prepare a water-absorbent resin composition. Examples of such additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, radical chain prohibiting agents, antioxidants, antibacterial agents, deodorants and the like. 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 cross-linking agent.

As a method for polymerizing the water-soluble ethylenically unsaturated monomer, a typical polymerization method such as an aqueous solution polymerization method, an emulsion polymerization method, or a reverse phase suspension polymerization method is used. In the aqueous solution polymerization method, polymerization is carried out by heating a water-soluble ethylenically unsaturated monomer aqueous solution with stirring as necessary. Further, in the reverse phase suspension polymerization method, polymerization is carried out by heating a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium under stirring. In the present invention, the reverse phase suspension polymerization method is preferable from the viewpoint of precise polymerization reaction control and control of a wide range of particle sizes.

An example of a method for producing the water-absorbent resin according to the present invention will be described below.

As a specific example of the method for producing a water-absorbent resin, in the method for producing a water-absorbent resin by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium, the presence of an internal cross-linking agent is used. It also has a step of performing polymerization in the presence of at least an azo compound and a peroxide, and a step of post-crosslinking the hydrogel-like substance having an internal crosslinked structure obtained by the polymerization with a post-crosslinking agent.

<Polymerization process>
[Water-soluble ethylenically unsaturated monomer]
Examples of the water-soluble ethylenically unsaturated monomer include (meth) acrylic acid (in the present specification, "acrylic" and "methacryl" are collectively referred to as "(meth) acrylic"; the same applies hereinafter) and. Salts; 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 contained therein and quaternized products thereof. Among these water-soluble ethylenically unsaturated monomers, (meth) acrylic acid or a salt thereof, (meth) acrylamide, N, N-dimethylacrylamide are preferable from the viewpoint of industrial availability. , (Meta) acrylic acid and salts thereof are more preferred. These water-soluble ethylenically unsaturated monomers may be used alone or in combination of two or more.

Among these, acrylic acid and its salts are widely used as raw materials for water-absorbent resins, and these partially neutralized acrylic acid salts are copolymerized with the other water-soluble ethylenically unsaturated monomers described above. In some cases. In this case, the acrylic acid partially neutralized salt is preferably used as the main water-soluble ethylenically unsaturated monomer in an amount of 70 to 100 mol% with respect to the total water-soluble ethylenically unsaturated monomer.

It is preferable that the water-soluble ethylenically unsaturated monomer is dispersed in a hydrocarbon dispersion medium in the state of an aqueous solution and subjected to reverse phase suspension polymerization. By using the water-soluble ethylenically unsaturated monomer as 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 saturation concentration or less. The concentration of the water-soluble ethylenically unsaturated monomer is more preferably 55% by mass or less, further preferably 50% by mass or less, and further preferably 45% by 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 and 2- (meth) acrylamide-2-methylpropanesulfonic acid, the acid group is previously alkaline if necessary. Those neutralized with a neutralizing agent may be used. Examples of such an alkaline neutralizer include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide and potassium carbonate; ammonia and the like. Further, these alkaline neutralizers may be used in the form of an aqueous solution in order to simplify the neutralization operation. The above-mentioned alkaline neutralizer may be used alone or in combination of two or more.

The degree of neutralization of the water-soluble ethylenically unsaturated monomer by the alkaline neutralizing agent shall be 10 to 100 mol% as the degree of neutralization with respect to all the 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 even more preferable.

[Internal cross-linking agent]
Examples of the internal cross-linking agent include those capable of cross-linking a polymer of a water-soluble ethylenically unsaturated monomer used, for example, (poly) ethylene glycol [“(poly)” is a prefix of “poly”. It means with and without. The same applies hereinafter], (poly) propylene glycol, 1,4-butanediol, trimethylolpropane, diols such as (poly) glycerin, polyols such as triol, and unsaturateds such as (meth) acrylic acid, maleic acid, and fumaric acid. Unsaturated polyesters obtained by reacting with an acid; bisacrylamides such as N, N-methylenebisacrylamide; di (meth) acrylic acid esters or tris obtained by reacting a polyepoxide with (meth) acrylic acid. (Meta) acrylic acid esters; Di (meth) acrylic acid carbamyl esters obtained by reacting polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth) acrylic acid; allylated starch, allyl. Compounds having two or more polymerizable unsaturated groups such as celluloseized cellulose, diallyl phthalate, N, N', N''-triallyl isocyanate, divinylbenzene; (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol di Diglycidyl compounds such as glycidyl ether, (poly) glycerin diglycidyl ether, polyglycidyl compounds such as triglycidyl compounds; epihalohydrin compounds such as epichlorohydrin, epibromhydrin, α-methylepicrolhydrin; 2,4-tolylene diisocyanate, hexamethylene. Compounds having two or more reactive functional groups such as isocyanate compounds such as diisocyanates; 3-methyl-3-oxetan methanol, 3-ethyl-3-oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3 Examples thereof include oxetane compounds such as oxetan ethanol, 3-ethyl-3-oxetan ethanol, and 3-butyl-3-oxetan ethanol. Among these internal cross-linking agents, it is preferable to use a polyglycidyl compound, more preferably a diglycidyl ether compound, and (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin. It is particularly preferable to use diglycidyl ether. These internal cross-linking agents may be used alone or in combination of two or more.

The amount of the internal cross-linking agent used is preferably 0.000001 to 0.02 mol, preferably 0.00001 to 0.01 mol, based on 1 mol of the water-soluble ethylenically unsaturated monomer. It is more preferably 0.00001 to 0.005 mol, still more preferably 0.00005 to 0.002 mol.

[Hydrocarbon dispersion medium]
Examples of the hydrocarbon dispersion medium include n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, n-octane and the like having 6 to 8 carbon atoms. Alicyclic hydrocarbons; alicyclics such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentane, etc. Group hydrocarbons; examples include aromatic hydrocarbons such as benzene, toluene and xylene. Among these hydrocarbon dispersion media, n-hexane, n-heptane, and cyclohexane are preferably used because they are industrially easily available, have stable quality, and are inexpensive. These hydrocarbon dispersion media may be used alone or in combination of two or more. As an example of the mixture of the hydrocarbon dispersion medium, a commercially available product such as ExxonMobil (manufactured by ExxonMobil: containing 75 to 85% by mass of hydrocarbon of heptane and its isomer) can also be used to obtain suitable results. be able to.

Regarding the amount of the hydrocarbon dispersion medium used, from the viewpoint of uniformly dispersing the water-soluble ethylenically unsaturated monomer and facilitating the control of the polymerization temperature, the first-stage water-soluble ethylenically unsaturated monomer is used. It is preferably 100 to 1500 parts by mass, more preferably 200 to 1400 parts by mass with respect to 100 parts by mass. As will be described later, the reverse phase suspension polymerization is carried out in one stage (single stage) or in multiple stages of two or more stages, and the above-mentioned first stage polymerization is the first stage in single stage polymerization or multi-stage polymerization. Means the polymerization reaction of (the same applies hereinafter).

[Dispersion stabilizer]
(Surfactant)
In the reverse phase suspension polymerization, a dispersion stabilizer can also 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, and polyoxyethylene. Alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, Use polyethylene glycol fatty acid ester, alkyl glucoside, N-alkyl glucon amide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, phosphoric acid ester of polyoxyethylene alkyl ether, phosphoric acid ester of polyoxyethylene alkyl allyl ether, etc. Can be done. Among these surfactants, it is particularly preferable to use sorbitan fatty acid ester, polyglycerin fatty acid ester, and sucrose fatty acid ester from the viewpoint of dispersion stability of the monomer. These surfactants may be used alone or in combination of two or more.

The amount of the surfactant used is preferably 0.1 to 30 parts by mass, preferably 0.3 to 20 parts by mass, based on 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage. It is more preferably by mass.

(Polymer dispersant)
Further, as the dispersion stabilizer used 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 / tarpolymer), 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 thereof include copolymers, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymers, ethylene / acrylic acid copolymers, ethyl cellulose, ethyl hydroxyethyl cellulose and the like. Among these polymer-based dispersants, in particular, from the viewpoint of the dispersion stability of the monomer, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride, and Ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene It is preferable to use a polymer. These polymer-based dispersants may be used alone or in combination of two or more.

The amount of the polymer-based dispersant used is preferably 0.1 to 30 parts by mass, preferably 0.3 to 20 parts by mass with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer in the first stage. It is more preferably by mass.

[Azo compounds and peroxides]
In one example of the method for producing a water-absorbent resin, reverse-phase suspension polymerization can be carried out on a water-soluble ethylenically unsaturated monomer in the presence of an azo compound and a peroxide.

Here, "in the presence of the azo compound and the peroxide" does not necessarily mean that the azo compound and the peroxide do not necessarily coexist at the start of the polymerization reaction (the time of radical cleavage of the compound). It means that the other compound is present while the conversion of one compound by radical cleavage is less than 10%, but both of them are contained in the aqueous solution containing the monomer before the start of the polymerization reaction. It is preferable that they coexist. Further, the azo compound and the peroxide may be added to the polymerization reaction system in separate flow paths, or may be sequentially added to the polymerization reaction system in the same flow path.

The form of the azo compound and the peroxide used may be a powder or an aqueous solution.

(Azo compound)
Specifically, examples of the azo compound include 1-{(1-cyano-1-methylethyl) azo} formamide, 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride, and the like. 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] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (4,5) , 6,7-Tetrahydro-1H-1,3-diazepine-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidine-) 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] propionamide}, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 2 , 2'-azobis (2-methylpropionamide) dihydrochloride, 4,4'-azobis-4-cyanovaleic 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] and the like. Among these, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} two Hydrochloride, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate makes it easy to adjust the polymerization reaction such as polymerization temperature, has a high centrifugation retention rate, and is loaded. It is particularly preferable from the viewpoint that a water-absorbent resin having a high water-absorbing ability underneath can be easily obtained. 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, dit-butyl peroxide, t-butyl cumyl peroxide, t. -Examples include peroxides such as butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, and hydrogen peroxide. Among these peroxides, potassium persulfate, ammonium persulfate, sodium persulfate, and hydrogen peroxide are preferably used from the viewpoint that a water-absorbent resin having a high storage elasticity can be easily obtained. Further, potassium persulfate, It is more preferable to use ammonium persulfate and sodium persulfate. These peroxides may be used alone or in combination of two or more.

(Amount and ratio of azo compounds and peroxides used)
The amount of the azo compound and the 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. Further, it is preferably 0.005 mol or less, more preferably 0.001 mol or less, with respect to 1 mol of the water-soluble ethylenically unsaturated monomer.

The ratio of the amount of the azo compound and the peroxide used is preferably 40% by mass or more, preferably 50% by mass or more of the total amount of the azo compound and the peroxide used. The ratio is more preferably 60% by mass or more, further preferably 70% by mass or more, and even more preferably 70% by 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, and 85% by mass or less of the total amount of the azo compound and peroxide used. It is more preferable that the ratio is 80% by mass or less, and it is even more preferable that the ratio is 80% by mass or less. The mass ratio range (azo compound: peroxide) is preferably 8:12 to 19: 1.

[Other ingredients]
In one example of this method for producing a water-absorbent resin, if desired, other components may be added to an aqueous solution containing a water-soluble ethylenically unsaturated monomer to carry out reverse-phase suspension polymerization. As other components, various additives such as thickeners and chain transfer agents can be added.

(Thickener)
As an example, in this method for producing a water-absorbent resin, a thickener may be added to an aqueous solution containing a water-soluble ethylenically unsaturated monomer to carry out polymerization. By adjusting the viscosity of the aqueous solution by adding a thickener in this way, it is possible to control the medium particle size obtained by the polymerization.

Specifically, examples of the thickener include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, polyacrylic acid (partially) neutralized product, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, and alginate. Sodium, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide and the like can be used. If the stirring speed at the time of polymerization is the same, the higher the viscosity of the water-soluble ethylenically unsaturated monomer aqueous solution, the larger the medium particle size of the obtained particles tends to be.

[Reverse phase suspension polymerization]
As an example of a method for producing a water-absorbent resin, a water-soluble ethylenically unsaturated monomer can be subjected to reverse-phase suspension polymerization. In performing reverse phase suspension polymerization, for example, a monomer aqueous solution containing a water-soluble ethylenically unsaturated monomer is used as a hydrocarbon dispersion medium in the presence of a surfactant and / or a polymer-based dispersant. Disperse. At this time, before the start of the polymerization reaction, the timing of adding the surfactant or the polymer-based dispersant may be either before or after the dispersion of the monomer aqueous solution.

Among them, from the viewpoint that the amount of the hydrocarbon dispersion medium remaining in the obtained water-absorbent resin can be easily reduced, after the monomer aqueous solution is dispersed in the hydrocarbon dispersion medium in which the polymer-based dispersant is dispersed, further It is preferable to add a surfactant and disperse the mixture before carrying out the polymerization.

It is possible to carry out such reverse phase suspension polymerization in one stage or in multiple stages of two or more stages. Further, from the viewpoint of increasing productivity, it is preferable to carry out in 2 to 3 steps.

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 water-soluble ethylenically unsaturated. The monomers may be added and mixed, and the reverse phase suspension polymerization of the second and subsequent stages may be carried out in the same manner as in the first stage. In the reverse phase suspension polymerization in each stage of the second and subsequent stages, in addition to the water-soluble ethylenically unsaturated monomer, an internal cross-linking agent and the above-mentioned azo compound and peroxide are used in each of the second and subsequent stages. Based on the amount of the water-soluble ethylenically unsaturated monomer added at the time of the reverse phase suspension polymerization in the stage, it is added within the range of the molar ratio of each component to the above-mentioned water-soluble ethylenically unsaturated monomer. It is preferable to carry out reverse phase suspension polymerization.

The reaction temperature of the polymerization reaction is 20 to 110 ° C. from the viewpoint of increasing the economic efficiency by rapidly advancing the polymerization and shortening the polymerization time, and easily removing the heat of polymerization to allow the reaction to proceed smoothly. It is preferably 40 to 90 ° C., and more preferably 40 to 90 ° C. The reaction time is preferably 0.5 to 4 hours.

<Post-crosslinking process>
Next, the water-absorbent resin according to the present invention is post-crosslinked with a post-crosslinking agent on a water-containing gel-like substance having an internal cross-linked structure obtained by polymerizing a water-soluble ethylenically unsaturated monomer ( It is obtained by post-crosslinking reaction). The post-crosslinking reaction is preferably carried out in the presence of a post-crosslinking agent after the polymerization of the water-soluble ethylenically unsaturated monomer. In this way, after the polymerization, by performing a post-crosslinking reaction on the water-containing gel-like material having an internal cross-linking structure, the cross-linking density near the surface of the water-absorbent resin is increased, and the water-absorbing ability and gel under load are increased. It is possible to obtain products with improved various performances such as elasticity.

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, epibromhydrin, α -Haloepoxy compounds such as methylepicrolhydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylenediisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanmethanol, 3-butyl-3-oxetanmethanol , 3-Methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, 3-butyl-3-oxetaneethanol and other oxetane compounds; 1,2-ethylenebisoxazoline and other oxazoline compounds; Examples thereof include hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide. 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, ( Poly) Polyglycidyl compounds such as glycerol polyglycidyl ethers are particularly 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, relative to 1 mol of the total amount of the water-soluble ethylenically unsaturated monomer used for the polymerization. It is more preferably 005 mol, and particularly preferably 0.0001 to 0.002 mol.

As a method for adding the post-crosslinking agent, the post-crosslinking agent may be added as it is or as an aqueous solution, or may be added as a solution using a hydrophilic organic solvent as a solvent, if necessary. 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. -Amids such as dimethylformamide; sulfoxides such as dimethylsulfoxide and the like can be mentioned. These hydrophilic organic solvents may be used alone, in combination of two or more, or as a mixed solvent with water.

The time for adding the post-crosslinking agent may be after almost all the polymerization reaction of the water-soluble ethylenically unsaturated monomer is completed, and 1 to 1 to 100 parts by mass of the water-soluble ethylenically unsaturated monomer. It is preferably added in the presence of water in the range of 400 parts by mass, more preferably in the presence of water in the range of 5 to 200 parts by mass, and added in the presence of water in the range of 10 to 100 parts by mass. Is more preferable, and it is even more preferable to add it in the presence of water in the range of 20 to 60 parts by mass. This makes it possible to enhance the water absorption capacity under load. The amount of water means the total amount of the water contained in the polymerization reaction system and the water 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, further preferably 60 to 140 ° C, and particularly preferably 70 to 120 ° C. preferable. The reaction time of the post-crosslinking reaction is preferably 1 to 300 minutes, more preferably 5 to 200 minutes.

<Drying process>
After the reverse phase suspension polymerization described above, a drying step of removing water, a hydrocarbon dispersion medium, etc. by distillation by applying energy such as heat from the outside may be included. When dehydrating from a hydrogel after reverse phase suspension polymerization, the water and the hydrocarbon dispersion medium are once removed from the system by co-boiling distillation by heating the system in which the hydrogel is dispersed in the hydrocarbon dispersion medium. Distill. At this time, if only the distilled hydrocarbon dispersion medium is returned into the system, continuous azeotropic distillation is possible. In that case, since the temperature in the system during drying is maintained below the azeotropic temperature of the hydrocarbon dispersion medium, it is preferable from the viewpoint that the resin is less likely to deteriorate. Subsequent distillation of water and the hydrocarbon dispersion medium gives water-absorbent resin particles. By controlling the treatment conditions in the drying step after the polymerization to adjust the amount of dehydration, it is possible to control the centrifugal retention rate of the obtained water-absorbent resin and the like.

In the drying step, the drying process by distillation may be performed under normal pressure or under reduced pressure. Further, from the viewpoint of increasing the drying efficiency, it may be performed under an air flow such as nitrogen. When 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, and 90 to 90 to. It is particularly preferable that the temperature is 130 ° C. When the drying treatment is performed under reduced pressure, the drying temperature is preferably 40 to 160 ° C, more preferably 50 to 110 ° C.

When the post-crosslinking step is carried out with a post-crosslinking agent after polymerizing the monomer by reverse phase suspension polymerization, the drying step by distillation described above is carried out after the completion of the post-crosslinking step. Alternatively, the post-crosslinking step and the drying step may be performed at the same time.

Further, if necessary, various additives such as a chelating agent, a reducing agent, an oxidizing agent, an antibacterial agent, and a deodorant may be added to the water-absorbent resin after polymerization, drying, or drying. ..

≪3. Absorber, absorbent article ≫
The water-absorbent resin according to the present invention constitutes an absorbent body used for sanitary materials such as paper diapers, menstrual napkins, and incontinence pads, and is suitably used for absorbent articles containing the absorbent body.

Here, the absorber 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 fibers so as to have a uniform composition, and a sandwich in which the water-absorbent resin is sandwiched between the layered hydrophilic fibers. Examples thereof include a structure, a structure in which a water-absorbent resin and a hydrophilic fiber are wrapped with a tissue, and the like. The absorber may contain other components, for example, an adhesive binder such as a heat-fusing synthetic fiber, a hot melt adhesive, or an adhesive emulsion for enhancing the shape retention of the absorber. ..

The content of the water-absorbent resin in the absorber is preferably 5 to 95% by mass, more preferably 20 to 90% by mass, and even more preferably 30 to 80% by mass. If the content of the water-absorbent resin is less than 5% by mass, the absorption capacity of the absorber becomes low, which may cause liquid leakage and reversion. On the other hand, if the content of the water-absorbent resin exceeds 95% by mass, the cost of the absorber becomes high and the feel of the absorber becomes hard.

As the hydrophilic fiber, synthesis of cellulose fiber such as cotton-like pulp obtained from wood, mechanical pulp, chemical pulp, semi-chemical pulp, artificial cellulose fiber such as rayon and acetate, hydrophilic treated polyamide, polyester, polyolefin and the like. Examples include fibers made of resin.

Further, by holding the absorber using the water-absorbent resin between the liquid permeable sheet (top sheet) through which the liquid can pass and the liquid permeable sheet (back sheet) through which the liquid cannot pass. , Can be an absorbent article. The liquid permeable sheet is placed on the side that comes into contact with the body, and the liquid permeable sheet is placed on the opposite side that comes into contact with the body.

Examples of the liquid permeable sheet include non-woven fabrics such as air-through type, spunbond type, chemical bond type and needle punch type, and porous synthetic resin sheets made of fibers such as polyethylene, polypropylene and polyester. Examples of the liquid impermeable sheet include a synthetic resin film made of a resin such as polyethylene, polypropylene, and polyvinyl chloride.

≪4. Example ≫
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples and the like.

<4-1. Evaluation test method>
[Evaluation test of water-absorbent resin]
The water-absorbent resins obtained in Examples 1 to 4 and Comparative Examples 1 to 3 below were subjected to various tests shown below and evaluated.

(1) Weigh 500 g of 0.9 mass% sodium chloride aqueous solution (physiological saline) in a beaker with a centrifugal retention rate of 500 mL, and stir at 600 r / min while producing 2.0 g of water-absorbent resin without generating mamaco. Dispersed like this. The water-absorbent resin was sufficiently swollen by leaving it to stand for 60 minutes in a stirred state. After that, it was poured into a cotton bag (Membroad No. 60, width 100 mm x length 200 mm), the upper part of the cotton bag was tied with a rubber bag, and a dehydrator set to have a centrifugal force of 167 G (manufactured by Domestic Centrifuge Co., Ltd., product number: The cotton bag was dehydrated for 1 minute using H-122), and the mass Wa (g) of the cotton bag containing the swollen gel after dehydration was measured. The same operation was performed without adding the water-absorbent resin, the empty mass Wb (g) of the cotton bag when wet was measured, and the centrifugal retention rate was calculated from the following formula.

Centrifugal retention (g / g) = [Wa-Wb] (g) / Mass of water-absorbent resin (g)

(2) Physiological saline water absorption capacity under a 4.14 kPa load The physiological saline water absorption capacity of the water-absorbent resin under a 4.14 kPa load was measured using the measuring device X whose schematic configuration was shown in FIG.

The measuring device X shown in FIG. 1 includes a burette unit 1, a duct 2, a measuring table 3, and a measuring unit 4 placed on the measuring table 3. In the burette portion 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 duct 2 is attached from the burette portion 1 to the measuring table 3, and the diameter of the duct 2 is 6 mm. A hole having a diameter of 2 mm is formed in the central portion of the measuring table 3, and the conduit 2 is connected to the hole. 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 in a 200 mesh (opening 75 μm). Then, a predetermined amount of the water-absorbent resin 5 is uniformly sprayed 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 portion 1 are closed, physiological saline adjusted to 25 ° C. is put in from the upper part of the burette 10, and the stopper on the upper part of the burette is used with the rubber stopper 14. After that, the cock 12 and the cock 13 of the burette part 1 were opened. Next, the height of the measuring table 3 was adjusted so that the tip of the conduit 2 at the center of the measuring table 3 and the air introduction port of the air introduction pipe 11 were at the same height.

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

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

4. Physiological saline water absorption capacity under 14 kPa load (mL / g) = Wc ÷ 0.10 (g)

(3) Storage modulus, loss modulus, and tanδ
The water-absorbent resin to be measured is adjusted to one that passes through a sieve with an opening of 400 μm and is held on a sieve with an opening of 300 μm, and the classified sample is swollen 50 times with physiological saline to form a 50-fold swollen gel. Made. Specifically, first, 49.0 g of physiological saline is weighed in a 100 mL beaker, a magnetic stirrer bar (8 mm φ × 30 mm without a ring) is put into the beaker, and a magnetic stirrer (manufactured by iuchi, HS-30D) is added. ), And the magnetic stirrer was adjusted to rotate at 600 r / min. Next, 1.0 g of the classified sample was put into a beaker being stirred, and stirring was continued until the rotating vortex disappeared and the liquid level became horizontal to prepare a 50-fold swollen gel. This 50-fold swelling gel was transferred to a centrifuge tube and degassed in a centrifuge (manufactured by Japan Centrifuge Co., Ltd., product number H-103NA SERIES) set to have a centrifugal force of 671 G over 4 minutes to prepare a measurement sample. ..

For the measurement, set the measurement sample prepared in the dynamic viscoelasticity measuring device Leometer (manufactured by TA Instruments Japan Co., Ltd., product number AR2000eZ), and store elastic modulus G'(Pa) and loss elastic modulus G. '' (Pa) frequency ω (rad / sec) dispersion was measured. A parallel plate having a diameter of 60 mm was used as the sample holder, and the distance between the plates was set to 3 mm. The thickness of the gel was 3000 μm. The measurement was performed at a measurement temperature of 25 ° C. under the conditions of frequency ω = 0.1 to 300 rad / sec and strain = 0.1% straight.

Then, the storage elastic modulus G'(Pa) and the loss elastic modulus G'' (Pa) at 10 rad / sec are obtained, and then the value of tan δ is calculated from the ratio of G'and G'' (G'' / G'). It was calculated and the value was taken as tan δ of the water-absorbent resin.

(4) Medium particle size (particle size distribution)
0.25 g of amorphous silica (Carplex # 80 manufactured by Evonik Degussa Japan Co., Ltd.) was mixed with 50 g of the water-absorbent resin as a lubricant. This was measured for medium particle size using the combination of sieves of the following [A].

[A] From the top of the JIS standard sieve, a sieve with an opening of 850 μm, a sieve with an opening of 600 μm, a sieve with an opening of 500 μm, a sieve with an opening of 400 μm, a sieve with an opening of 300 μm, a sieve with an opening of 250 μm, and a sieve with an opening of 150 μm. The sieve and the saucer were combined in this order.

The water-absorbent resin was put into the combined best sieve and shaken for 20 minutes using a low-tap type shaker to classify. 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 obtained. The relationship between the mesh size of the sieve 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 integrating the particles on the sieve in order from the one having the largest particle size with respect to this particle size distribution. By connecting the plots on the probability paper with a straight line, the particle size corresponding to the cumulative mass percentage of 50% by mass was defined as the medium particle size.

The abundance ratio of the water-absorbent resin having a particle size of 300 to 400 μm is the ratio of the water-absorbent resin remaining on the sieve having a 300 μm opening, and similarly, the presence of the water-absorbent resin having a particle size of 150 to 850 μm. The ratio is a value obtained by adding all the ratios of the water-absorbent resin remaining on the sieves of each opening of 150 μm, 250 μm, 300 μm, 400 μm, 500 μm, and 600 μm.

[Evaluation test of absorbent and absorbent articles using water-absorbent resin]
(1) Preparation of absorbent body and absorbent article By using 12 g of water-absorbent resin and 12 g of crushed pulp (Leonia's Reiflock) and uniformly mixing them by air papermaking, absorption in the form of a sheet having a size of 40 cm × 12 cm. A body core was made. Next, with the upper and lower sides of the absorber core sandwiched between two sheets of tissue paper having the same size as the absorber core and having a basis weight of 16 g / m ² , a load of 196 kPa is applied to the entire body and pressed for 30 seconds. As a result, an absorber was prepared. Further, on the upper surface of the absorber, a polyethylene-polypropylene air-through type porous liquid permeable sheet having the same size as the absorber and having a basis weight of 22 g / m ² is arranged, and a polyethylene liquid having the same size and the same basis weight is placed. By arranging the impermeable sheet on the lower surface of the absorber and sandwiching the absorber, an absorbent article (size: 40 × 12 cm) was obtained.

(2) Preparation of artificial urine As artificial urine, it is mixed and dissolved in ion-exchanged water so that NaCl: 0.780% by mass, CaCl ₂ : 0.022% by mass, and י ₄ : 0.038% by mass. , A small amount of Blue No. 1 was blended.

(3) Penetration speed An absorbent article was placed on a horizontal table. A measuring instrument having a mass of 2 kg and equipped with a liquid injection cylinder having an inner diameter of 3 cm was placed in the center of a plate having a bottom surface of 10 cm × 10 cm in the center of the absorbent article to put a load on the absorbent article. Next, 80 mL of artificial urine is poured into the cylinder at one time, and the time until the artificial urine completely disappears from the cylinder is measured using a stopwatch, and the first permeation rate (seconds) is used. did. Next, remove the cylinder, store the absorbent article as it is, and perform the same operation 30 minutes and 60 minutes after the start of the first artificial urine injection using the measuring instrument at the same position as the first time. The second and third permeation rates (seconds) were measured. The total of the first to third times was taken as the total permeation rate. It can be said that the shorter the permeation rate, the more preferable the absorbent article.

(4) Liquid reversion amount 120 minutes after the start of the first artificial urine injection in the above-mentioned measurement of the permeation rate, the mass (Wd (g), about 50 g) is measured in advance near the artificial urine injection position on the absorbent article. A 10 cm square filter paper was placed, and a weight with a bottom surface of 10 cm × 10 cm and a mass of 5 kg was placed on it. After loading for 5 minutes, the mass of the filter paper (We (g)) was measured, and the increased mass was taken as the amount of liquid reversion (g). It can be said that the smaller the amount of liquid reversion, the more preferable the absorbent article.
Liquid reversion amount (g) = We-Wd

<4-2. Examples and Comparative Examples>
[Example 1]
A round-bottomed cylindrical separable flask with an inner diameter of 110 mm and a capacity of 2 L, equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirring blade having four inclined paddle blades with a blade diameter of 50 mm in two stages as a stirrer. Got ready. In this flask, 300 g of n-heptane as a hydrocarbon dispersion medium is taken, 0.74 g of HLB3 sucrose stearic acid ester (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370) as a surfactant, and a polymer dispersant. Add 0.74 g of maleic anhydride-modified ethylene / propylene copolymer (Mitsui Chemicals Co., Ltd., High Wax 1105A), raise the temperature to 80 ° C with stirring to dissolve the surfactant, and then cool to 50 ° C. did.

On the other hand, 92 g (1.02 mol) of 80 mass% acrylic acid aqueous solution was taken in a 500 mL triangular flask, and 102.2 g of 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside to make 75 mol%. After neutralization, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener and 2,2'-azobis (2-amidinopropane) dihydrochloride as an azo compound 0. 092 g (0.339 mmol), potassium persulfate 0.037 g (0.137 mmol) as peroxide, ethylene glycol diglycidyl ether 0.010 g (0.058 mmol) as internal cross-linking agent, and ion exchange water 43.8 g Was added and dissolved to prepare an aqueous monomer solution.

Then, the aqueous monomer solution prepared as described above is added to the separable flask, the inside of the system is sufficiently replaced with nitrogen, the flask is immersed in a water bath at 70 ° C. to raise the temperature, and the polymerization is carried out for 60 minutes. The first-stage polymerized slurry liquid was obtained.

On the other hand, 128.8 g (1.43 mol) of an 80 mass% acrylic acid aqueous solution was taken in another 500 mL triangular flask, and 143.1 g of a 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside. After neutralization of 75 mol%, 0.129 g (0.475 mmol) of 2,2'-azobis (2-amidinopropane) dihydrochloride as an azo compound and 0.052 g of potassium persulfate as a peroxide. (0.191 mmol), 0.012 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent and 15.9 g of ion-exchanged water were added and dissolved to prepare a second-stage monomer aqueous solution.

After cooling the inside of the separable flask system to 25 ° C., the entire amount of the monomer aqueous solution of the second stage was added to the polymerization slurry liquid of the first stage, and the inside of the system was sufficiently replaced with nitrogen. The flask was again immersed in a water bath at 70 ° C. to raise the temperature, and the second-stage polymerization was carried out for 30 minutes.

After the second-stage polymerization, the reaction solution was heated in an oil bath at 125 ° C., and 236 g of water was extracted from 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 mass aqueous solution of ethylene glycol diglycidyl ether was added, and the mixture was kept at 80 ° C. for 2 hours. Then, n-heptane was evaporated and dried to obtain a dried product. This dried product was passed through a sieve having an opening of 1000 μm to obtain 234.1 g of a water-absorbent resin in the form of aggregated spherical particles. The water-absorbent resin thus obtained was evaluated according to the above-mentioned various test methods.

In the obtained water-absorbent resin, the mass ratio of the particles having a size of 150 to 850 μm was 94% by mass, and the mass ratio of the particles having a size of 300 to 400 μm was 36% by mass.

[Example 2]
In Example 2, the same as in Example 1 except that 239 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water after the second stage polymerization. did. As a result, 231.2 g of a water-absorbent resin having a different centrifugal retention rate and the like from the water-absorbent resin obtained in Example 1 was obtained. The water-absorbent resin thus obtained was evaluated according to the above-mentioned various test methods.

In the obtained water-absorbent resin, the mass ratio of the particles having a size of 150 to 850 μm was 92% by mass, and the mass ratio of the particles having a size of 300 to 400 μm was 32% by mass.

[Example 3]
In Example 3, the amount of ethylene glycol diglycidyl ether added as an internal cross-linking agent to be dissolved in the first-stage monomer aqueous solution was 0.020 g (0.116 mmol), and after the second-stage polymerization, n-heptane and water were added. The same procedure as in Example 1 was carried out except that 254 g of water was withdrawn from the system while refluxing n-heptane by co-boiling distillation with. As a result, 232.9 g of a water-absorbent resin having a different amount of the internal cross-linking agent from the water-absorbent resin obtained in Example 1 was obtained. The water-absorbent resin thus obtained was evaluated according to the above-mentioned various test methods.

In the obtained water-absorbent resin, the mass ratio of the particles having a size of 150 to 850 μm was 95% by mass, and the mass ratio of the particles having a size of 300 to 400 μm was 33% by mass.

[Example 4]
In Example 4, the same as in Example 3 except that 258 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water after the second stage polymerization. did. As a result, 226.0 g of a water-absorbent resin having a different centrifugal retention rate and the like from the water-absorbent resin obtained in Example 1 was obtained. The water-absorbent resin thus obtained was evaluated according to the above-mentioned various test methods.

In the obtained water-absorbent resin, the mass ratio of the particles having a size of 150 to 850 μm was 95% by mass, and the mass ratio of the particles having a size of 300 to 400 μm was 33% by mass.

[Comparative Example 1]
In Comparative Example 1, a round-bottomed cylinder having an inner diameter of 110 mm and a capacity of 2 L is provided with a reflux cooler, a dropping funnel, a nitrogen gas introduction pipe, and a stirring blade having four inclined paddle blades having a blade diameter of 50 mm in two stages as a stirrer. Prepare a type separable flask, take 300 g of n-heptane as a hydrocarbon dispersion medium in this flask, and use HLB3 sucrose stearic acid ester as a surfactant (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370). Add 0.74 g and 0.74 g of maleic anhydride-modified ethylene / propylene copolymer (Mitsui Chemicals Co., Ltd., High Wax 1105A) as a polymer dispersant, and raise the temperature to 80 ° C. with stirring to add a surfactant. After melting, it was cooled to 50 ° C.

On the other hand, 92 g (1.02 mol) of an 80 mass% acrylic acid aqueous solution was placed in a 500 mL triangular flask, and 102.2 g of a 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside to make 75 mol%. 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 as a peroxide, and an internal cross-linking agent. 0.010 g (0.058 mmol) of ethylene glycol diglycidyl ether and 43.8 g of ion-exchanged water were added and dissolved to prepare an aqueous monomer solution.

Then, the aqueous monomer solution prepared as described above is added to the separable flask, the inside of the system is sufficiently replaced with nitrogen, the flask is immersed in a water bath at 70 ° C. to raise the temperature, and the polymerization is carried out for 60 minutes. The first-stage polymerized slurry liquid was obtained.

On the other hand, 128.8 g (1.43 mol) of an 80 mass% acrylic acid aqueous solution was taken in another 500 mL triangular flask, and 143.1 g of a 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside. After neutralization of 75 mol%, 0.104 g (0.382 mmol) of potassium persulfate as a peroxide and 0.012 g (0.067 mmol) and 15.9 g of ethylene glycol diglycidyl ether as an internal cross-linking agent. Was added and dissolved to prepare a second-stage aqueous monomer solution.

After cooling the inside of the above-mentioned separable flask system to 25 ° C., the entire amount of the monomer aqueous solution of the second stage was added to the polymerization slurry liquid of the first stage, and the inside of the system was sufficiently replaced with nitrogen. After that, the flask was again immersed in a water bath at 70 ° C. to raise the temperature, and the second-stage polymerization was carried out for 30 minutes.

After the second stage polymerization, the reaction solution was heated in an oil bath at 125 ° C., and 257 g of water was extracted from 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 mass aqueous solution of ethylene glycol diglycidyl ether was added, and the mixture was kept at 80 ° C. for 2 hours. Then, n-heptane was evaporated and dried to obtain a dried product. This dried product was passed through a sieve having an opening of 1000 μm to obtain 228.2 g of a water-absorbent resin in the form of aggregated spherical particles. The water-absorbent resin thus obtained was evaluated according to the above-mentioned various test methods. In the obtained water-absorbent resin, the mass ratio of the particles having a size of 150 to 850 μm was 94% by mass, and the mass ratio of the particles having a size of 300 to 400 μm was 33% by mass.

[Comparative Example 2]
Comparative Example 2 is the same as in Comparative Example 1 except that 259 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water after the second stage polymerization. did. As a result, 228.2 g of a water-absorbent resin having a different centrifugal retention rate and the like from the water-absorbent resin obtained in Comparative Example 1 was obtained. The water-absorbent resin thus obtained was evaluated according to the above-mentioned various test methods.

In the obtained water-absorbent resin, the mass ratio of the particles having a size of 150 to 850 μm was 94% by mass, and the mass ratio of the particles having a size of 300 to 400 μm was 31% by mass.

[Comparative Example 3]
In Comparative Example 3, a water-absorbent resin to which a larger amount of cross-linking agent was added was obtained as compared with the water-absorbent resin obtained in Comparative Example 1.

Specifically, first, a reflux cooler, a dropping funnel, a nitrogen gas introduction pipe, and a 110 mm inner diameter, 2 L volume circle equipped with a stirring blade having four inclined paddle blades with a blade diameter of 50 mm in two stages as a stirrer. Prepare a bottom cylindrical separable flask, take 300 g of n-heptane as a hydrocarbon dispersion medium in this flask, and use HLB3 sucrose stearate as a surfactant (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S- 370) 0.74 g and 0.74 g of maleic anhydride-modified ethylene / propylene copolymer (Mitsui Chemicals Co., Ltd., High Wax 1105A) as a polymer-based dispersant are added, and the temperature is raised to 80 ° C. with stirring to make the interface. After dissolving the activator, it was cooled to 50 ° C.

On the other hand, 92 g (1.02 mol) of an 80 mass% acrylic acid aqueous solution was placed in a 500 mL triangular flask, and 102.2 g of a 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside to make 75 mol%. 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 as a peroxide, and an internal cross-linking agent. 0.018 g (0.106 mmol) of ethylene glycol diglycidyl ether and 43.8 g were added and dissolved to prepare an aqueous monomer solution.

Then, the aqueous monomer solution prepared as described above is added to the separable flask, the inside of the system is sufficiently replaced with nitrogen, the flask is immersed in a water bath at 70 ° C. to raise the temperature, and the polymerization is carried out for 60 minutes. The first-stage polymerized slurry liquid was obtained.

On the other hand, 128.8 g (1.43 mol) of an 80 mass% acrylic acid aqueous solution was taken in another 500 mL triangular flask, and 143.1 g of a 30 mass% sodium hydroxide aqueous solution was added dropwise while cooling from the outside. After neutralization of 75 mol%, 0.104 g (0.382 mmol) of potassium persulfate as a peroxide, 0.039 g (0.222 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent, and ion-exchanged water. 15.9 g was added and dissolved to prepare a second-stage aqueous monomer solution.

After cooling the inside of the above-mentioned separable flask system to 25 ° C., the entire amount of the monomer aqueous solution of the second stage was added to the polymerization slurry liquid of the first stage, and the inside of the system was sufficiently replaced with nitrogen. After that, the flask was again immersed in a water bath at 70 ° C. to raise the temperature, and the second-stage polymerization was carried out for 30 minutes.

After the second stage polymerization, the reaction solution was heated in an oil bath at 125 ° C., and 273 g of water was extracted from the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. As a post-crosslinking agent, 6.63 g (0.761 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether was added, and the mixture was kept at 80 ° C. for 2 hours. Then, n-heptane was evaporated and dried to obtain a dried product. This dried product was passed through a sieve having an opening of 1000 μm to obtain 231.2 g of a water-absorbent resin in the form of aggregated spherical particles. The water-absorbent resin thus obtained was evaluated according to the above-mentioned various test methods. In the obtained water-absorbent resin, the mass ratio of the particles having a size of 150 to 850 μm was 94% by mass, and the mass ratio of the particles having a size of 300 to 400 μm was 39% by mass.

<4-3. Evaluation results>
[Evaluation result of water-absorbent resin]
Table 1 below shows the evaluation results of the water-absorbent resin. In addition, this Table 1 also shows the absorption capacity elasticity index represented by the following formula (I).
Absorption capacity elastic modulus = storage elastic modulus [Pa] x centrifugal retention rate [g / g] ... (I)

As can be seen from the results shown in Table 1, the water-absorbent resins obtained in Examples 1 to 4 were water-absorbent resins having the desired performance.

[Evaluation results of absorbent articles]
Next, in Table 2 below, with respect to the absorbent articles prepared using the water-absorbent resins obtained in Examples 1 to 3 and Comparative Examples 1 and 3 described above, the permeation rate of artificial urine of the absorbent articles is shown. , Liquid reversion amount, diffusion length measurement results are shown.

As shown in the results of Table 2, the absorbent articles using the water-absorbent resin having an absorption capacity elasticity index of 68,000 or more obtained in Examples 1 to 3 are the water-absorbent resin obtained in Comparative Example. It was demonstrated that the permeation rate and the amount of liquid reversion, which are the absorption performance under load, are superior to those of the absorbent article prepared by using.

X Measuring device 1 Burette part 2 Conduit 3 Measuring table 4 Measuring part 5 Water-absorbent resin

Claims (4)

A water-absorbent resin that is a cross-linked product of a polymer of a water-soluble ethylenically unsaturated monomer, an internal cross-linking agent, and a post-cross-linking agent.
The water-soluble ethylenically unsaturated monomer is (meth) acrylic acid and / or a salt thereof.
The internal cross-linking agent is a polyglycidyl compound and is
The post-crosslinking agent is a polyglycidyl compound and
A water-absorbent resin in which the water-absorbent resin satisfies the following characteristics (A) to ( E ).
(A) Physiological saline water absorption capacity under a load of 4.14 kPa is 16 mL / g or more,
(B) The mass ratio of the particles of 150 to 850 μm to the entire water-absorbent resin is 85% by mass or more, and the mass ratio of the particles of 300 to 400 μm is 20% by mass or more.
(C) The tan δ measured by classifying 300 to 400 μm particles of the water-absorbent resin is 2.00 × 10 ⁻² or less,
(D) The absorption capacity elasticity index represented by the following formula (I) is 68,000 or more and 74400 or less,
(E) The centrifugal retention rate of the water-absorbent resin is 50 g / g or less .
Absorption capacity elastic modulus = storage elastic modulus [Pa] x centrifugal retention rate [g / g] ... (I)
[Measurement method of tan δ above]
First, 49.0 g of physiological saline is weighed in a 100 mL beaker, a magnetic stirrer bar is put into the beaker, the magnetic stirrer is placed on the magnetic stirrer, and the magnetic stirrer is adjusted to rotate at 600 r / min. Next, 1.0 g of the classified sample is put into a beaker being stirred, and stirring is continued until the rotating vortex disappears and the liquid level becomes horizontal to prepare a 50-fold swollen gel. The 50-fold swelling gel is transferred to a centrifuge tube and degassed in a centrifuge set to have a centrifugal force of 671 G for 4 minutes to obtain a measurement sample.
Next, the measurement sample is set in the dynamic viscoelasticity measuring device leometer. A parallel plate with a diameter of 60 mm is used as a sample holder, the distance between the plates is 3 mm, the gel thickness is 3000 μm, the measurement temperature is 25 ° C, the frequency is in the range of 0.1 to 300 rad / sec, and the strain is 0.1% stretch. Measure the storage modulus and loss modulus with. Of these, the ratio of the storage elastic modulus to the loss elastic modulus (loss elastic modulus / storage elastic modulus) at 10 rad / sec is defined as tan δ.
[Measuring method of storage elastic modulus]
First, 49.0 g of physiological saline is weighed in a 100 mL beaker, a magnetic stirrer bar is put into the beaker, the magnetic stirrer is placed on the magnetic stirrer, and the magnetic stirrer is adjusted to rotate at 600 r / min. Next, 1.0 g of the classified sample is put into a beaker being stirred, and stirring is continued until the rotating vortex disappears and the liquid level becomes horizontal to prepare a 50-fold swollen gel. The 50-fold swelling gel is transferred to a centrifuge tube and degassed in a centrifuge set to have a centrifugal force of 671 G for 4 minutes to obtain a measurement sample.
Next, the measurement sample is set in the dynamic viscoelasticity measuring device leometer. A parallel plate with a diameter of 60 mm is used as a sample holder, the distance between the plates is 3 mm, the gel thickness is 3000 μm, the measurement temperature is 25 ° C, the frequency is in the range of 0.1 to 300 rad / sec, and the strain is 0.1% straight. Measure the storage modulus with. Of these, the storage elastic modulus at 10 rad / sec is used in the above equation (I).
[Measuring method of centrifugal retention rate]
While stirring 500 g of 0.9 mass% sodium chloride aqueous solution (physiological saline), 2.0 g of water-absorbent resin was dispersed and left for 60 minutes, then poured into a cotton bag and the centrifugal force was 167 G using a dehydrator. Dehydrate for 1 minute under the conditions of the above, and measure the mass Wa (g) of the cotton bag containing the swollen gel after dehydration. Further, the same operation is performed without adding the water-absorbent resin, and the empty mass Wb (g) of the cotton bag when wet is measured. The centrifugal retention rate is calculated from the following equation (II).
Centrifugal retention (g / g) = [Wa-Wb] (g) / Mass of water-absorbent resin (g) ... (I)
I)
[Measuring method of physiological saline water absorption capacity under the above 4.14 kPa load]
After spraying 0.10 g of the water-absorbent resin inside a cylinder with an inner diameter of 2.0 cm to which a 200-mesh nylon mesh is attached to the bottom, a weight is placed on the water-absorbent resin and a load of 4.14 kPa is applied. Add. A cylinder is placed on the hole of a measuring table having a hole having a diameter of 2 mm so that the center of the cylinder coincides with the hole, and the hole is provided with an air inlet and a burette containing physiological saline. Are connected via a conduit and arranged so that the tip of the conduit in the measuring table and the air inlet are at the same height. The burette and the air inlet were opened to start water absorption of the water-absorbent resin, and the decrease amount Wc (mL) of the physiological saline solution was measured 60 minutes after the start, and the load was 4.14 kPa from the following formula (III). Calculate the saline water absorption capacity below.
4. Physiological saline water absorption capacity under a load of 14 kPa (mL / g) = Wc ÷ 0.10 (g) ・ ・ ・ (III) The water-absorbent resin according to claim 1, wherein the storage elastic modulus is 1000 Pa or more and 10000 Pa or less. The water-absorbent resin according to claim 1 or 2, wherein the centrifugal retention rate is 30 g / g or more . An absorbent article using an absorber containing the water-absorbent resin according to any one of claims 1 to 3.

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