JP2020121089A - Water absorption resin particle - Google Patents

Abstract

To provide a water absorption resin particle which, when used in a sanitary article, quickly provides dry feeling after absorbing water.SOLUTION: A water absorption resin particle has an artificial urine liquid permeation rate of 1.0 g/min or more in 10 times swelling, and a contact angle measured in a test carried out in the followings i) and ii) in this order is 70 degrees or less: i) at 25°C, a spherical type droplet corresponding to a diameter 3.0±0.1 mm of 25 mass % saline solution is dropped onto a surface of a layer composed of water absorption resin particles, to bring the droplet into contact with the water absorption resin particle, and ii) a contact angle of the droplet is measured at the moment when 30 seconds have passed since the droplet came into contact with the surface.SELECTED DRAWING: None

Description

The present invention relates to water absorbent resin particles.

Water-absorbent resins are used in the field of hygiene products. Specifically, it is used as a material for an absorber included in absorbent articles such as diapers. For example, Patent Document 1 discloses a water-absorbent resin particle having a specific absorption rate pattern measured by the DW method and a method for producing the same, and an absorbent article to which the water-absorbent resin particle is applied has an uneven absorption rate. It is described that it is excellent in absorption amount and absorption rate.

JP, 2014-5472, A

Since absorbent articles such as diapers are used by directly touching the skin, moisture does not remain on the surface of the absorbent article after absorbing the liquid, and it may dry quickly and give a dry feel. preferable. However, the water-absorbent resin particles that provide an absorbent article having such properties sufficiently have not been obtained.

It is an object of the present invention to provide water-absorbent resin particles which, when used as a hygiene product, can provide a more dry feel after absorbing water.

The water-absorbent resin particles of the present invention have an artificial urine flow rate of 1.0 g/min or more when swollen 10 times, and have a contact angle measured in a test conducted in the order of i) and ii) below. It is 70 degrees or less.
i) At 25° C., spherical droplets corresponding to a diameter of 3.0±0.1 mm of 25% by mass saline solution are dropped on the surface of the layer formed of the water-absorbent resin particles, and the water-absorbent resin particles and the above Contact with the droplet.
ii) The contact angle of the droplet is measured 30 seconds after the droplet contacts the surface.

The water absorbent resin particles may have a water retention capacity of physiological saline of 20 to 60 g/g.

The water-absorbent resin particles may have a saline water absorption of 15 ml/g or more under a load of 4.14 kPa.

INDUSTRIAL APPLICABILITY The present invention provides water-absorbent resin particles which, when used as a hygiene product, can provide a quicker and more dry feel after absorbing water.

It is sectional drawing which shows an example of an absorbent article. It is a schematic diagram showing a measuring device of artificial urine permeation rate at the time of 10 times swelling. It is a schematic diagram showing a measuring device of water absorption under load.

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

In the present specification, “acrylic” and “methacrylic” are collectively referred to as “(meth)acrylic”. "Acrylate" and "methacrylate" are also referred to as "(meth)acrylate". In the numerical ranges described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range of a certain stage can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range of another stage. In the numerical range described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. “Water-soluble” means exhibiting a solubility of 5% by mass or more in water at 25° C. The materials exemplified in this specification may be used alone or in combination of two or more kinds. The content of each component in the composition means the total amount of the plurality of substances present in the composition, unless a plurality of substances corresponding to each component are present in the composition, unless otherwise specified.

The water absorbent resin particles according to the present embodiment have an artificial urine flow rate of 1.0 g/min or more when swollen 10 times. The artificial urine permeation rate during 10-fold swelling may be 1.5 g/min or more, 2.0 g/min or more, or 3.0 g/min or more from the viewpoint of further enhancing the effect of the present invention. The artificial urine permeation rate during 10-fold swelling may be 35.0 g/min or less, and is preferably 30.0 g/min or less. The artificial urine flow rate at the time of 10-fold swelling may be 20.0 g/min or less, 15.0 g/min or less, or 12.5 g/min or less. The artificial urine permeation rate during 10-fold swelling is defined as the value measured by the method described in Examples below. In addition, in this specification, artificial urine is 0.780 mass% sodium chloride, 0.022 mass% calcium chloride, 0.038 mass% magnesium sulfate, and 0.002 mass% blue No. 1 , And water.

The water-absorbent resin particles according to the present embodiment have a contact angle of 70 degrees or less measured in the tests performed in the order i) and ii) below.
i) At 25° C., spherical droplets corresponding to a diameter of 3.0±0.1 mm of 25% by mass saline solution are dropped on the surface of the layer formed of the water-absorbent resin particles, and the water-absorbent resin particles and the above Contact with the droplet.
ii) The contact angle of the droplet is measured 30 seconds after the droplet contacts the surface.

The contact angle may be 65 degrees or less, 55 degrees or less, or 45 degrees or less from the viewpoint of further enhancing the effect of the present invention. The contact angle may be 0 degree or more, may exceed 0 degree, may be 10 degrees or more, or may be 20 degrees or more. The contact angle is preferably 30 degrees or more.

The contact angle is a value measured according to JIS R 3257 (1999) “Test method for wettability of substrate glass surface”, and specifically, it is measured by a method described in Examples described later.

The water-absorbent resin particles according to the present embodiment have a rapid artificial urine flow rate during 10-fold swelling and the contact angle is within a predetermined range, so that when used as a hygiene product, water is absorbed rapidly after water absorption. In the surface of the absorbent article, a dry and dry feeling can be obtained at an early stage. The water-absorbent resin particles according to the present embodiment have sufficiently high hydrophilicity on the particle surface and excellent wettability, and therefore have excellent water drawing force into the inside of the particles.

The water-absorbent resin particles according to this embodiment can have a high water-absorbing ability with respect to physiological saline. The water retention capacity of the physiological saline of the water absorbent resin particles according to the present embodiment is, for example, 20 to 60 g/g, 25 to 55 g/g, 25 to 50 g/g, 25 to 45 g/g, 30 to 45 g/g, Or it may be 32-42 g/g. The water retention capacity of the physiological saline is measured by the method described in Examples described later.

The water absorption amount of the physiological saline solution under the load of 4.14 kPa (0.6 psi) (water absorption amount under load) of the water absorbent resin particles according to the present embodiment may be, for example, 15 ml/g or more, and 18 ml/g or more. , Or 20 ml/g or more. The physiological saline water absorption under a load of 4.14 kPa may be, for example, 35 ml/g or less, or 30 ml/g or less. The water absorption of physiological saline under a load of 4.14 kPa is measured by the method described in Examples below.

Examples of the shape of the water absorbent resin particles according to the present embodiment include a substantially spherical shape, a crushed shape, and a granular shape. The median particle diameter of the water absorbent resin particles according to the present embodiment may be 250 to 850 μm, 300 to 700 μm, or 300 to 600 μm. The water-absorbent resin particles according to the present embodiment may have a desired particle size distribution at the time when the polymer particles are obtained by the production method described below, but an operation such as particle size adjustment using classification with a sieve is performed. The particle size distribution may be adjusted accordingly.

The physiological saline water absorption rate of the water absorbent resin particles according to the present embodiment may be, for example, 20 to 80 seconds, 25 to 70 seconds, or 30 to 60 seconds. The physiological saline absorption rate is measured by the following method. In a room adjusted to 25°C ± 1°C, 50 ± 0.1 g of physiological saline in a 100 ml beaker was adjusted to a temperature of 25 ± 0.2°C in a constant temperature water bath, and then a magnetic stirrer bar (8 mmφ) was used. A vortex is generated by stirring at 600 rpm with (30 mm, no ring). 2.0±0.002 g of the water-absorbent resin particles were added at once to the physiological saline solution, and the time (seconds) from the addition of the water-absorbent resin particles until the vortex disappeared and the liquid surface became flat was measured. Then, the time is defined as the physiological saline water absorption rate of the water absorbent resin particles.

The water absorbent resin particles according to the present embodiment can include, for example, a crosslinked polymer formed by polymerization of a monomer containing an ethylenically unsaturated monomer. The crosslinked polymer has a monomer unit derived from an ethylenically unsaturated monomer. That is, the water absorbent resin particles according to the present embodiment can have a structural unit derived from an ethylenically unsaturated monomer.

Examples of the method for polymerizing the above-mentioned monomer include a reverse phase suspension polymerization method, an aqueous solution polymerization method, a bulk polymerization method, a precipitation polymerization method and the like. Among these, the reverse phase suspension polymerization method or the aqueous solution polymerization method is preferable from the viewpoints of ensuring good water absorption characteristics of the water-absorbent resin particles obtained and controlling the polymerization reaction easily. In the following, the reverse phase suspension polymerization method will be described as an example of the method for polymerizing the ethylenically unsaturated monomer.

The ethylenically unsaturated monomer is preferably water-soluble, and examples thereof include (meth)acrylic acid and salts thereof, 2-(meth)acrylamide-2-methylpropanesulfonic acid and salts thereof, (meth)acrylamide, N. , N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, polyethylene glycol mono(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylamino Examples include propyl (meth)acrylate and diethylaminopropyl (meth)acrylamide. When the ethylenically unsaturated monomer contains an amino group, the amino group may be quaternized. A functional group such as a carboxyl group and an amino group possessed by the above-mentioned monomer can function as a functional group capable of being crosslinked in the surface crosslinking step described later. These ethylenically unsaturated monomers may be used alone or in combination of two or more.

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

As the monomer, some monomers other than the above ethylenically unsaturated monomer may be used. Such a monomer can be used, for example, as a mixture with an aqueous solution containing the ethylenically unsaturated monomer. The amount of the ethylenically unsaturated monomer used is preferably 70 to 100 mol% with respect to the total amount of the monomers. Above all, (meth)acrylic acid and salts thereof are more preferably 70 to 100 mol% with respect to the total amount of the monomers.

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

When the ethylenically unsaturated monomer used contains an acid group, the aqueous monomer solution may be used after neutralizing the acid group with an alkaline neutralizing agent. In the ethylenically unsaturated monomer, the degree of neutralization with an alkaline neutralizing agent increases the osmotic pressure of the water-absorbent resin particles to be obtained, and from the viewpoint of further enhancing water absorption properties such as water retention, the ethylenically unsaturated monomer is used. It is 10 to 100 mol%, preferably 50 to 90 mol%, and more preferably 60 to 80 mol% of the acidic groups in the body. Examples of the alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium hydroxide and potassium carbonate; ammonia and the like. These alkaline neutralizing agents may be used in the form of an aqueous solution in order to simplify the neutralizing operation. The above alkaline neutralizing agents may be used alone or in combination of two or more. The acid group of the ethylenically unsaturated monomer can be neutralized by, for example, dropping an aqueous solution of sodium hydroxide, potassium hydroxide or the like into the aqueous monomer solution and mixing them.

In the reverse phase suspension polymerization method, an aqueous monomer solution is dispersed in a hydrocarbon dispersion medium in the presence of a surfactant, and a radical polymerization initiator or the like is used to polymerize an ethylenically unsaturated monomer. Done.

Examples of the surfactant include nonionic surfactants and anionic surfactants. Examples of nonionic surfactants include sorbitan fatty acid ester and (poly)glycerin fatty acid ester (“(poly)” means both with and without the prefix “poly”. The same), sucrose fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene 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 and the like can be mentioned. Examples of the anionic surfactant include fatty acid salts, alkylbenzene sulfonates, alkylmethyl taurates, polyoxyethylene alkylphenyl ether sulfates, polyoxyethylene alkyl ether sulfonates, and polyoxyethylene alkyl ether phosphorus. Examples thereof include acid esters and phosphoric acid esters of polyoxyethylene alkyl allyl ether. Among these, the surfactant is a sorbitan from the viewpoint that the W/O type reverse phase suspension is in a good state, the water-absorbent resin particles are easily obtained with a suitable particle size, and are industrially easily available. It is preferable to contain at least one compound selected from the group consisting of fatty acid ester, polyglycerin fatty acid ester, and sucrose fatty acid ester. Furthermore, it is more preferable that the surfactant contains a sucrose fatty acid ester, from the viewpoint that the water absorbing properties of the water absorbent resin particles obtained are improved. These surfactants may be used alone or in combination of two or more.

The amount of the surfactant is preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of the aqueous ethylenically unsaturated monomer solution, from the viewpoint of sufficiently obtaining the effect on the amount used and being economical. , 0.08 to 5 parts by mass, more preferably 0.1 to 3 parts by mass.

Moreover, you may use together a polymeric dispersant with the above-mentioned 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 thereof include copolymers, oxidized polyethylene, oxidized polypropylene, oxidized ethylene/propylene copolymers, ethylene/acrylic acid copolymers, 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 polymeric dispersants may be used alone or in combination of two or more.

The amount of the polymeric dispersant is 0.05 to 10 parts by mass with respect to 100 parts by mass of the aqueous ethylenically unsaturated monomer solution, from the viewpoint of sufficiently obtaining the effect on the amount used and being economical. Is more preferable, 0.08 to 5 parts by mass is more preferable, and 0.1 to 3 parts by mass is still more preferable.

The radical polymerization initiator is preferably water-soluble, and examples thereof 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-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, and peroxides such as hydrogen peroxide; 2,2'-azobis(2-amidino) Propane) dihydrochloride, 2,2′-azobis[2-(N-phenylamidino)propane] dihydrochloride, 2,2′-azobis[2-(N-allylamidino)propane] dihydrochloride, 2, 2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane } Dihydrochloride, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N] -(2-hydroxyethyl)-propionamide], 4,4′-azobis(4-cyanovaleric acid), and other azo compounds. Among these, potassium persulfate, ammonium persulfate, sodium persulfate, 2,2′-azobis(2-amidinopropane) dihydrochloride, 2,2′-azobis[2-(2-imidazolin-2-yl)propane ] Dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride is preferred. These radical polymerization initiators may be used alone or in combination of two or more kinds.

The amount of the radical polymerization initiator used may be 0.00005 to 0.01 mol with respect to 1 mol of the ethylenically unsaturated monomer. When the amount of the radical polymerization initiator used is 0.00005 mol or more, the polymerization reaction does not require a long time and is efficient. When the amount used is 0.01 mol or less, a rapid polymerization reaction tends not to occur.

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

At the time of the polymerization reaction, a chain transfer agent may be included in the ethylenically unsaturated monomer aqueous solution used for the polymerization. Examples of the chain transfer agent include hypophosphites, thiols, thiolic acids, secondary alcohols, amines and the like.

Further, in order to control the particle diameter of the water absorbent resin particles, a thickener may be included in the ethylenically unsaturated monomer aqueous solution used for polymerization.

As the thickener, for example, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, etc. may be used. You can If the stirring speed during polymerization is the same, the higher the viscosity of the aqueous ethylenically unsaturated monomer solution, the larger the median particle size of the particles obtained.

The hydrocarbon dispersion medium may contain at least one compound selected from the group consisting of a chain aliphatic hydrocarbon having 6 to 8 carbon atoms and an alicyclic hydrocarbon having 6 to 8 carbon atoms. Examples of the hydrocarbon dispersion medium include chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane. Alicyclic hydrocarbon such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentane; Examples thereof include aromatic hydrocarbons such as benzene, toluene and xylene. These hydrocarbon dispersion media may be used alone or in combination of two or more. From the viewpoint of industrial availability and stable quality, the hydrocarbon dispersion medium may contain n-heptane, cyclohexane, or both of them. From the same viewpoint, as the mixture of the hydrocarbon dispersion medium, for example, commercially available exol heptane (manufactured by Exxon Mobil: n-heptane and 75 to 85% of isomer hydrocarbons) may be used. Good.

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

Normally, internal cross-linking occurs due to self-crosslinking during polymerization, but the water-absorbing properties of the water-absorbent resin particles may be controlled by further using an internal cross-linking agent. Examples of the internal crosslinking agent used include di- or tri(meth)acrylic acid esters of polyols such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol and polyglycerin; Unsaturated polyesters obtained by reacting the above polyols with unsaturated acids such as maleic acid and fumaric acid; bis(meth)acrylamides such as N,N'-methylenebis(meth)acrylamide; polyepoxides and (meth) Di or tri(meth)acrylic acid esters obtained by reacting with acrylic acid; Di(meth) obtained by reacting polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth)acrylate Acrylic acid carbamyl esters; compounds having two or more polymerizable unsaturated groups such as allylated starch, allylated cellulose, diallyl phthalate, N,N′,N″-triallyl isocyanurate, and divinylbenzene; ) Polyglycidyl such as ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, (poly)propylene glycol polyglycidyl ether, polyglycerol polyglycidyl ether Compounds; haloepoxy compounds such as epichlorohydrin, epibromhydrin and α-methylepichlorohydrin; compounds having two or more reactive functional groups such as isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate. .. Among these internal cross-linking agents, it is preferable to use a polyglycidyl compound, more preferably to use a diglycidyl ether compound, (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, (poly)glycerin. It is particularly preferred to use diglycidyl ether. These cross-linking agents may be used alone or in combination of two or more.

The amount of the internal cross-linking agent is such that the water-soluble property is suppressed by the resulting polymer being appropriately cross-linked, and from the viewpoint of showing a sufficient water absorption amount, per 1 mol of the ethylenically unsaturated monomer, The amount is preferably 0 to 0.03 mol, more preferably 0.00001 to 0.01 mol, and further preferably 0.00002 to 0.005 mol.

An ethylenically unsaturated monomer, a radical polymerization initiator, an aqueous phase containing components such as an internal crosslinking agent, if necessary, a hydrocarbon-based dispersion medium, a surfactant, and if necessary, a polymer-based dispersant, etc. Reverse phase suspension polymerization can be carried out in a water-in-oil system by mixing with an oil phase containing components and heating with stirring.

When performing reverse phase suspension polymerization, a monomer aqueous solution containing an ethylenically unsaturated monomer is dispersed in a hydrocarbon dispersion medium in the presence of a surfactant and, if necessary, a polymer dispersant. Let At this time, as long as the polymerization reaction is not started, the surfactant or the polymeric dispersant may be added either before or after the addition of the aqueous monomer solution.

Among them, from the viewpoint of easily reducing the amount of hydrocarbon dispersion medium remaining in the resulting 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. In addition, it is preferable to carry out in 2 to 3 steps from the viewpoint of improving productivity.

When performing reverse phase suspension polymerization in multiple stages of two or more stages, after performing the first stage reverse phase suspension polymerization, the reaction mixture obtained in the first stage polymerization reaction is mixed with an ethylenically unsaturated monomer. The body 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 the second and subsequent stages, in addition to the ethylenically unsaturated monomer, the above radical polymerization initiator and internal crosslinking agent are used in the reverse phase suspension in the second and subsequent stages. On the basis of the amount of ethylenically unsaturated monomer added during the polymerization, it is possible to perform the reverse phase suspension polymerization by adding within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer. preferable. In the reverse phase suspension polymerization in the second and subsequent stages, an internal cross-linking agent may be used if necessary. When an internal cross-linking agent is used, it is added within the range of the molar ratio of each component to the above-mentioned ethylenically unsaturated monomer based on the amount of ethylenically unsaturated monomer to be supplied to each stage, and the reverse phase suspension is added. It is preferable to carry out turbid polymerization.

The temperature of the polymerization reaction varies depending on the radical polymerization initiator used, but it promotes the polymerization rapidly and shortens the polymerization time to improve the economical efficiency and easily remove the heat of polymerization to smoothly carry out the reaction. From a viewpoint, 20-150 degreeC is preferable and 40-120 degreeC is more preferable. The reaction time is usually 0.5 to 4 hours. The completion of the polymerization reaction can be confirmed by, for example, stopping the temperature rise in the reaction system. Thereby, the polymer of the ethylenically unsaturated monomer is usually obtained in a hydrogel state.

After the polymerization, a cross-linking agent may be added to the obtained hydrous gel-like polymer and heated to perform cross-linking after the polymerization. By carrying out cross-linking after the polymerization, the degree of cross-linking of the hydrogel polymer can be increased and the water absorption property can be improved more preferably.

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

The amount of the cross-linking agent used for post-polymerization cross-linking is, from the viewpoint that the resulting water-containing gel polymer exhibits suitable water absorption properties by being appropriately cross-linked, per 1 mol of the ethylenically unsaturated monomer, The amount is preferably 0 to 0.03 mol, more preferably 0 to 0.01 mol, and further preferably 0.00001 to 0.005 mol. When the addition amount of the cross-linking agent is within the above range, water-absorbent resin particles having suitable liquid permeability are easily obtained.

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

Subsequently, in order to remove water from the obtained hydrous gel polymer, drying is performed. By drying, polymer particles containing a polymer of an ethylenically unsaturated monomer are obtained. As a drying method, for example, (a) the above hydrogel polymer is dispersed in a hydrocarbon dispersion medium, and azeotropic distillation is performed by externally heating the mixture to reflux the hydrocarbon dispersion medium to remove water. Method, (b) a method of taking out the hydrous gel-like polymer by decantation and drying under reduced pressure, and (c) a method of separating the hydrous gel-like polymer by filtration and drying under reduced pressure. Above all, it is preferable to use the method (a) because it is easy in the manufacturing process.

The particle diameter of the water-absorbent resin particles can be controlled, for example, by adjusting the rotation speed of the stirrer during the polymerization reaction, or after the polymerization reaction or at the beginning of drying, adding a powdered inorganic coagulant to the system. Can be done by By adding the aggregating agent, the particle diameter of the water-absorbent resin particles obtained can be increased. Examples of the powdery inorganic coagulant include silica, zeolite, bentonite, aluminum oxide, talc, titanium dioxide, kaolin, clay, hydrotalcite, and the like. Among them, silica, aluminum oxide, talc or from the viewpoint of coagulation effect. Kaolin is preferred.

In the inverse suspension polymerization, as a method for adding the powdery inorganic coagulant, the powdered inorganic coagulant is previously dispersed in a hydrocarbon dispersion medium or water of the same kind as that used in the polymerization, and then stirred. A method of mixing in a hydrocarbon dispersion medium containing a hydrogel is preferable.

In the production of the water-absorbent resin particles according to the present embodiment, in the drying step or any of the subsequent steps, the surface portion of the hydrogel polymer may be cross-linked (surface cross-linking) using a cross-linking agent. preferable. The surface cross-linking is preferably performed at a timing when the hydrogel polymer has a specific water content. The time of surface cross-linking is preferably a time when the water content of the hydrogel polymer is 5 to 50 mass %, more preferably 10 to 40 mass %, and further preferably 15 to 35 mass %.

The water content (mass %) of the water-containing gel polymer is calculated by the following formula.
Moisture content=[Ww/(Ww+Ws)]×100
Ww: When mixing the powdered inorganic coagulant, surface cross-linking agent, etc. to the amount obtained by subtracting the amount of water discharged to the outside of the system in the drying step from the amount of water contained in the aqueous liquid before the polymerization in the entire polymerization step Water content of the water-containing gel-like polymer with the water content used as needed.
Ws: Solid content calculated from the charged amounts of materials such as an ethylenically unsaturated monomer, a cross-linking agent, and an initiator that compose the hydrogel polymer.

Examples of the surface cross-linking agent for surface cross-linking include compounds having two or more reactive functional groups. Examples thereof include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol and polyglycerin; (poly)ethylene glycol diglycidyl ether, Polyglycidyl compounds such as (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, trimethylolpropane triglycidyl ether (poly)propylene glycol polyglycidyl ether, (poly)glycerol polyglycidyl ether; epichlorohydrin, epibromhydrin , Haloepoxy compounds such as α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3- Oxetane compounds such as oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; ethylene carbonate, etc. Carbonate compounds; hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]adipamide. Among these, polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and polyglycerol polyglycidyl ether are more preferable. preferable. These surface cross-linking agents may be used alone or in combination of two or more.

The amount of the surface cross-linking agent is usually 1 mol of the ethylenically unsaturated monomer used for the polymerization, from the viewpoint that the resulting water-containing gel polymer is appropriately cross-linked so as to exhibit suitable water absorbing properties. On the other hand, the ratio is 0.00001 to 0.02 mol, preferably 0.00005 to 0.01 mol, and more preferably 0.0001 to 0.005 mol.

From the viewpoint of sufficiently increasing the crosslink density in the surface portion of the polymer particles and increasing the gel strength of the water absorbent resin particles, the amount of the surface crosslinking agent used is preferably 0.00001 mol or more. Further, it is preferably 0.02 mol or less from the viewpoint of increasing the water retention capacity of the water-absorbent resin particles while increasing the water absorption amount of the saline solution under load.

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

The polymer particles have a ratio of the amount of the external cross-linking agent to the amount of the internal cross-linking agent (hereinafter, also referred to as “crosslinking ratio”) of 6 or more from the viewpoint of enhancing the liquid permeability and adjusting the contact angle to a suitable range. It is preferably 8 or more, more preferably 10 or more. The crosslinking ratio may be, for example, 100 or less, 80 or less, 60 or less, 40 or less, 30 or less, 20 or less or 15 or less. The amount of the internal cross-linking agent is the total amount (mmol) of the internal cross-linking agent added once or a plurality of times, and the amount of the external cross-linking agent is the total amount of the post-polymerization cross-linking agent and the surface cross-linking agent (mmol). ).

Although the water-absorbent resin particles according to the present embodiment may be composed of only polymer particles, for example, inorganic powder, a surfactant, an oxidizing agent, a reducing agent, a metal chelating agent (ethylenediaminetetraacetic acid and its salt, diethylenetriamine). 5 acetic acid and its salts, such as diethylenetriamine pentaacetic acid 5 sodium), radical chain inhibitors, antioxidants, antibacterial agents, deodorants, gel stabilizers, fluidity improvers (lubricants), etc. Ingredients may further be included. The additional components can be located within the polymer particles, on the surface of the polymer particles, or both. As the additional component, a fluidity improver (lubricant) is preferable, and among them, inorganic particles are more preferable. Examples of the inorganic particles include silica particles such as amorphous silica. For example, by adding 0.05 to 5 parts by mass of amorphous silica as inorganic particles to 100 parts by mass of polymer particles, the fluidity of the water absorbent resin particles can be improved. The water absorbent resin particles according to the present embodiment preferably do not contain non-porous spherical silicon oxide.

The water absorbent resin particles may include a plurality of inorganic particles arranged on the surface of the polymer particles. For example, the inorganic particles can be arranged on the surface of the polymer particles by mixing the polymer particles and the inorganic particles. The inorganic particles may be silica particles such as amorphous silica. When the water-absorbent resin particles include the inorganic particles arranged on the surface of the polymer particles, the ratio of the inorganic particles to the mass of the polymer particles is 0.2% by mass or more, 0.5% by mass or more, 1.0 It may be at least mass%, or at least 1.5 mass%, may be at most 5.0 mass%, or may be at most 3.5 mass%. The inorganic particles here usually have a minute size as compared with the size of the polymer particles. For example, the average particle size of the inorganic particles may be 0.1 to 50 μm, 0.5 to 30 μm, or 1 to 20 μm. The average particle diameter here can be a value measured by a dynamic light scattering method or a laser diffraction/scattering method. When the addition amount of the inorganic particles is within the above range, it is easy to obtain water-absorbent resin particles having good water-absorbing properties.

The water-absorbent resin particles according to the present embodiment are excellent in absorbability of body fluids such as urine and blood, for example, disposable diapers, sanitary napkins, sanitary products such as tampons, pet sheets, toilet compositions for dogs or cats, etc. It can be applied to the field of animal excrement disposal materials.

The water absorbent resin particles according to the present embodiment can be suitably used for an absorber. The absorber according to the present embodiment includes water absorbent resin particles. The absorber may further comprise fibrous material, for example.

The mass ratio of the water-absorbent resin particles in the absorber may be 2% to 100%, preferably 10% to 80%, and preferably 20% to the total amount of the water-absorbent resin particles and the fibrous material. It is more preferably 70%. The structure of the absorbent body may be, for example, a form in which the water-absorbent resin particles and the fibrous substance are uniformly mixed, and the water-absorbent resin particles are sandwiched between the fibrous substances formed into a sheet or layer. It may be in any form, or in any other form.

Examples of the fibrous material include finely pulverized wood pulp, cellulosic fibers such as cotton, cotton linter, rayon and cellulose acetate, and synthetic fibers such as polyamide, polyester and polyolefin. The fibrous material may be a mixture of the above fibers.

The fibers may be bonded to each other by adding an adhesive binder to the fibrous material in order to improve shape retention before and during use of the absorbent body. Examples of the adhesive binder include heat-fusible synthetic fibers, hot melt adhesives and adhesive emulsions.

Examples of the heat-fusible synthetic fiber include a fully-meltable binder such as polyethylene, polypropylene, and an ethylene-propylene copolymer, and a non-fully-meltable binder having a side-by-side polypropylene-polyethylene or core-sheath structure. In the non-total melting type binder, only the polyethylene portion is heat-sealed. Examples of hot melt adhesives include ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-ethylene-propylene-styrene block copolymer. , A blend of a base polymer such as amorphous polypropylene and a tackifier, a plasticizer, an antioxidant and the like.

Examples of the adhesive emulsion include a polymer of at least one monomer selected from the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene, and vinyl acetate. To be These adhesive binders may be used alone or in combination of two or more.

The absorber according to this embodiment may further contain an inorganic powder (for example, amorphous silica), a deodorant, an antibacterial agent, a fragrance, or the like. When the water-absorbent resin particles include inorganic particles, the absorber may include inorganic powder in addition to the inorganic particles in the water-absorbent resin particles.

The shape of the absorber according to the present embodiment is not particularly limited, and may be, for example, a sheet shape. The thickness of the absorber (for example, the thickness of the sheet-shaped absorber) may be, for example, 0.1 to 20 mm and 0.3 to 15 mm.

The said absorber can be conveniently used for an absorbent article. The absorbent article according to the present embodiment includes the absorber according to the present embodiment. The absorbent article according to the present embodiment includes a core wrap that retains the shape of an absorbent body; a liquid permeable sheet that is arranged at the outermost side of a side into which a liquid to be absorbed enters; a side into which a liquid to be absorbed enters. A liquid impermeable sheet or the like arranged on the outermost side on the opposite side can be used. Examples of absorbent articles include diapers (eg, paper diapers), toilet training pants, incontinence pads, hygiene products (sanitary napkins, tampons, etc.), sweat pads, pet sheets, simple toilet parts, animal excrement disposal materials, etc. ..

FIG. 1 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in FIG. 1 includes an absorber 10, core wraps 20a and 20b, a liquid permeable sheet 30, and a liquid impermeable sheet 40. In the absorbent article 100, the liquid impermeable sheet 40, the core wrap 20b, the absorber 10, the core wrap 20a, and the liquid permeable sheet 30 are laminated in this order. In FIG. 1, there is a portion where there is a gap between the members, but the members may be in close contact with each other without the gap.

The absorber 10 includes the water-absorbent resin particles 10a according to the present embodiment and a fiber layer 10b containing a fibrous material. The water absorbent resin particles 10a are dispersed in the fiber layer 10b.

The core wrap 20a is arranged on one surface side of the absorbent body 10 (the upper side of the absorbent body 10 in FIG. 1) while being in contact with the absorbent body 10. The core wrap 20b is arranged on the other surface side of the absorbent body 10 (below the absorbent body 10 in FIG. 1) while being in contact with the absorbent body 10. The absorber 10 is arranged between the core wrap 20a and the core wrap 20b. Examples of the core wraps 20a and 20b include tissues and non-woven fabrics. The core wrap 20a and the core wrap 20b have, for example, a main surface having the same size as the absorber 10.

The liquid permeable sheet 30 is arranged on the outermost side on the side where the liquid to be absorbed enters. The liquid permeable sheet 30 is arranged on the core wrap 20a while being in contact with the core wrap 20a. Examples of the liquid permeable sheet 30 include a nonwoven fabric made of a synthetic resin such as polyethylene, polypropylene, polyester and polyamide, and a porous sheet. The liquid impermeable sheet 40 is arranged on the outermost side of the absorbent article 100 on the side opposite to the liquid permeable sheet 30. The liquid-impermeable sheet 40 is arranged below the core wrap 20b while being in contact with the core wrap 20b. Examples of the liquid impermeable sheet 40 include a sheet made of a synthetic resin such as polyethylene, polypropylene and polyvinyl chloride, and a sheet made of a composite material of these synthetic resins and a non-woven fabric. The liquid permeable sheet 30 and the liquid impermeable sheet 40 have, for example, a main surface wider than the main surface of the absorber 10, and the outer edge portions of the liquid permeable sheet 30 and the liquid impermeable sheet 40 are It extends around the absorber 10 and the core wraps 20a, 20b.

The size relationship among the absorber 10, the core wraps 20a and 20b, the liquid permeable sheet 30, and the liquid impermeable sheet 40 is not particularly limited, and is appropriately adjusted according to the application of the absorbent article and the like. The method of retaining the shape of the absorbent core 10 using the core wraps 20a and 20b is not particularly limited, and the absorbent core may be wrapped with a plurality of core wraps as shown in FIG. 1, and the absorbent core may be wrapped with one core wrap. But it's okay.

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

<Production of water absorbent resin particles>
[Example 1]
A reflux condenser, a dropping funnel, a nitrogen gas introducing tube, and a stirrer equipped with a 2 L round bottom cylindrical separable flask having an inner diameter of 11 cm and equipped with stirring blades having two stages of four inclined paddle blades with a blade diameter of 5 cm Got ready. To this flask was added 293 g of n-heptane as a hydrocarbon dispersion medium, and 0.736 g of a maleic anhydride-modified ethylene/propylene copolymer (Mitsui Chemicals, Inc., Hiwax 1105A) as a polymer dispersant. The reaction liquid in the flask was heated to 80° C. with stirring to dissolve the polymer dispersant. Then, the reaction solution was cooled to 50°C.

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

The prepared aqueous solution was added to the reaction solution in the separable flask and stirred for 10 minutes. Next, a surfactant solution prepared by dissolving 0.736 g of sucrose stearate (HLB:3, Mitsubishi Chemical Foods Corporation, Ryoto Sugar Ester S-370) as a surfactant in 6.62 g of n-heptane was heated. It was further added to the reaction solution, and the system was sufficiently replaced with nitrogen while stirring at a rotation speed of the stirrer of 550 rpm. Then, the flask was immersed in a water bath at 70° C., the temperature was raised, and polymerization was carried out for 60 minutes to obtain a first stage polymerization slurry liquid.

On the other hand, in another beaker with an internal volume of 500 ml, 128.8 g (1.43 mol) of an 80.5 mass% acrylic acid aqueous solution as an ethylenically unsaturated monomer was taken, and while cooling from the outside, 27 mass% of water was added. 159.0 g of an aqueous sodium oxide solution was added dropwise to neutralize 75 mol%. Thereafter, 0.12 g (0.475 mmol) of 2,2′-azobis(2-amidinopropane) dihydrochloride as a radical polymerization initiator and 0.026 g (0.095 mmol) of potassium persulfate were added and dissolved. A second stage aqueous solution was prepared.

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

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

Then, n-heptane was evaporated at 125° C. and dried to obtain polymer particles (dry product). The polymer particles were passed through a sieve with an opening of 850 μm, and 0.2% by mass of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) was mixed with the polymer particles based on the mass of the polymer particles. 232.1 g of water-absorbent resin particles containing amorphous silica was obtained. The median particle diameter of the water-absorbent resin particles was 396 μm, and the water absorption rate of physiological saline was 39 seconds. The ratio of the amount of external crosslinking agent to the amount of internal crosslinking agent (crosslinking ratio) was 10.1. The internal crosslinking agent amount is the total amount (mmole) of the internal crosslinking agent added once or twice, and the external crosslinking agent amount is the total amount of the post-polymerization crosslinking agent amount and the surface crosslinking agent amount (mmol). ).

[Example 2]
236.3 g of water-absorbent resin particles was obtained in the same manner as in Example 1 except that the amount of the amorphous silica mixed with the polymer particles (dry product) was changed to 2.0% by mass. The median particle diameter of the water absorbent resin particles was 393 μm, and the water absorption rate of physiological saline was 38 seconds. The crosslinking ratio was 10.1.

[Example 3]
In the preparation of the first-stage aqueous liquid, the amount of potassium persulfate as a radical polymerization initiator was changed to 0.0736 g (0.272 mmol), 2,2′-azobis(2-amidinopropane) 2 No hydrochloric acid salt was added, the amount of potassium persulfate as a radical polymerization initiator was changed to 0.090 g (0.334 mmol) in the preparation of the second-stage aqueous liquid, 2,2′- Azobis(2-amidinopropane) dihydrochloride was not added, and in the reaction liquid containing the hydrogel polymer after the second-stage polymerization, the amount of water extracted out of the system by azeotropic distillation was adjusted to 247.9 g. 231.0 g of water-absorbent resin particles was obtained in the same manner as in Example 1 except that the content was changed and the amount of the amorphous silica mixed with the polymer particles was changed to 0.5% by mass. The median particle diameter of the water-absorbent resin particles was 355 μm, and the water absorption rate of physiological saline was 37 seconds. The crosslinking ratio was 10.1.

[Example 4]
In the preparation of the first-stage aqueous liquid, the amount of potassium persulfate as a radical polymerization initiator was changed to 0.0736 g (0.272 mmol), 2,2′-azobis(2-amidinopropane) 2 No hydrochloric acid salt was added, the amount of potassium persulfate as a radical polymerization initiator was changed to 0.090 g (0.334 mmol) in the preparation of the second-stage aqueous liquid, 2,2′- Azobis(2-amidinopropane) dihydrochloride was not added, and in the reaction liquid containing the hydrogel polymer after the second-stage polymerization, the amount of water taken out of the system by azeotropic distillation was 239.7 g. 229.2 g of water-absorbent resin particles was obtained in the same manner as in Example 1 except that the content of the amorphous silica was changed to 0.5% by mass, and the content of the amorphous silica was changed to 0.5% by mass. The median particle diameter of the water-absorbent resin particles was 377 μm, and the water absorption rate of physiological saline was 40 seconds. The crosslinking ratio was 10.1.

[Example 5]
In the preparation of the first-stage aqueous liquid, the amount of ethylene glycol diglycidyl ether as an internal cross-linking agent was changed to 0.0046 g (0.026 mmol), and the second-stage water-containing gel-like weight after polymerization was changed. In the reaction liquid containing the coalescence, the amount of water extracted to the outside of the system by azeotropic distillation was changed to 219.2 g, and the amount of 2% by mass ethylene glycol diglycidyl ether aqueous solution as a surface crosslinking agent was 6.62 g. 229.6 g of water-absorbent resin particles was obtained in the same manner as in Example 1 except that the content was changed to (0.761 mmol). The median particle diameter of the water-absorbent resin particles was 356 μm, and the water absorption rate of physiological saline was 56 seconds. The crosslinking ratio was 31.8.

[Comparative Example 1]
In the preparation of the first-stage aqueous liquid, the amount of ethylene glycol diglycidyl ether as an internal cross-linking agent was changed to 0.0046 g (0.026 mmol). 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as a cross-linking agent was added, no cross-linking agent for post-polymerization cross-linking was added, and water content after the second-stage polymerization 229.6 g of water-absorbent resin particles was obtained in the same manner as in Example 1 except that the amount of water extracted from the system by azeotropic distillation was changed to 234.2 g in the reaction solution containing the gelled polymer. .. The median particle diameter of the water-absorbent resin particles was 355 μm, and the water absorption rate of physiological saline was 48 seconds. The crosslinking ratio was 5.5.

[Comparative example 2]
In the preparation of the first-stage aqueous liquid, the amount of ethylene glycol diglycidyl ether as an internal cross-linking agent was changed to 0.0368 g (0.211 mmol). The amount of ethylene glycol diglycidyl ether as a cross-linking agent was changed to 0.0515 g (0.296 mmol), no cross-linking agent for post-polymerization cross-linking was added, and after the second-stage polymerization 222.2 g of water-absorbent resin particles were obtained in the same manner as in Example 1 except that the amount of water extracted by azeotropic distillation was changed to 286.9 g. The median particle diameter of the particles was 396 μm, and the water absorption rate of physiological saline was 67 seconds. The crosslinking ratio was 1.0.

[Comparative Example 3]
A reflux condenser, a dropping funnel, a nitrogen gas introducing tube, and a stirrer equipped with a 2 L round bottom cylindrical separable flask having an inner diameter of 11 cm and equipped with stirring blades having two stages of four inclined paddle blades with a blade diameter of 5 cm Got ready. In this flask, 281 g of cyclohexane as a hydrocarbon dispersion medium was taken, 0.564 g of ethyl cellulose (Aqualon N100 manufactured by Ashland) was added, and nitrogen gas was blown into the system while stirring while the rotation speed of the stirrer was 700 rpm to dissolve dissolved oxygen. , And the flask was immersed in a water bath at 80° C. to raise the temperature to 75° C.

On the other hand, in a beaker having an internal volume of 300 ml, 92.0 g (1.28 mol) of 100% acrylic acid was taken as an ethylenically unsaturated monomer, and while cooling from the outside, 142.0 g of a 27 mass% sodium hydroxide aqueous solution was added. After dripping to neutralize 75 mol%, a solution of 0.184 g (0.681 mmol) of potassium persulfate dissolved in 14.8 g of water as a radical polymerization initiator was added and dissolved, followed by nitrogen gas. Was blown in to remove oxygen remaining in the aqueous solution to prepare a monomer aqueous solution.

The prepared monomer aqueous solution was dropped into the separable flask system using a tube pump over 1 hour to carry out a polymerization reaction. After the polymerization, the flask was immersed in an oil bath set at 125°C while stirring with the number of revolutions of the stirrer being 1000 rpm, and 107.2 g of water was added to the system by azeotropic distillation of cyclohexane and water while refluxing the cyclohexane. I pulled it out.

After that, 0.036 g (0.176 mmol) of polyglycerol polyglycidyl ether (Denacol EX-512, manufactured by Nagase Kasei Co., Ltd.) as a surface crosslinking agent was dissolved and added to 3.61 g of water and heated in an oil bath. While reacting at 75 to 80°C for 1 hour. Immediately after the reaction, the cyclohexane phase was filtered off with a 38 μm sieve to remove the water-absorbent resin hydrate.

The water-absorbent resin hydrate was heated to 0.006 MPa and dried under reduced pressure in a vacuum dryer set at 90° C. to obtain polymer particles. These were passed through a sieve with an opening of 850 μm, and 0.5% by mass of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) was added to the polymer particles based on the mass of the polymer particles (dry product). By mixing, 105.1 g of water-absorbent resin particles containing amorphous silica was obtained. The median particle diameter of the water-absorbent resin particles was 310 μm, and the water absorption rate of physiological saline was 78 seconds. The crosslinking ratio could not be calculated because the internal crosslinking agent was not used.

Regarding the obtained water-absorbent resin particles, the contact angle, the artificial urine permeation rate at the time of 10 times swelling, the physiological saline water absorption under load, the physiological saline retention capacity, the medium particle size, and the surface are measured by the following methods. The dryness index and water absorption rate were evaluated.

<Measurement of contact angle>
The contact angle was measured under the environment of a temperature of 25° C. and a relative humidity of 60±10%. A double-sided tape (Nichiban inner stack: 10 mm×75 mm) was attached to a glass slide (25 mm×75 mm) to prepare an adhesive surface exposed. First, 2.0 g of the water-absorbent resin particles were uniformly dispersed on the double-sided tape attached to the above-mentioned preparation. Then, the preparation was set up vertically to remove excess water-absorbent resin particles to prepare a measurement sample.

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

<Preparation of artificial urine>
Artificial urine (test solution) was prepared by blending ion-exchanged water so that an inorganic salt was present as described below and dissolving it, and further blending a small amount of Blue No. 1. The following concentrations are based on the total mass of artificial urine.
Artificial urine composition NaCl: 0.780 mass%
CaCl ₂ : 0.022 mass%
MgSO _4: 0.038 wt%
Blue No. 1: 0.002 mass%

<Measurement of artificial urine flow rate when swelling 10 times>
(A) Installation of measuring device As the measuring device, the one whose schematic configuration is shown in FIG. 2 was used. The measurement part is the same as the cylindrical container (A) 61 made of an acrylic resin having an inner diameter of 19 mm, an outer diameter of 25 mm, a height of 120 mm, and a weight of about 30 g, to which a nylon mesh sheet (250 mesh) 64 is adhered. Of the acrylic resin cylindrical container (B) 62 having an inner diameter of 26 mm, an outer diameter of 40 mm, and a height of 140 mm, and the swollen water-absorbent resin particles 10a. ) Can move up and down inside the cylindrical container (A) without resistance. The dish 66 has an inner diameter of about 70 mm.

(B) Measurement of liquid passing rate The measurement was performed at room temperature of about 25°C. Into the cylindrical container (B) 62, 0.20 g of water-absorbent resin particles was uniformly placed, and the cylindrical container (A) 61 was inserted from above to form a measuring section. The mesh side of the measurement part was immersed in a petri dish having an inner diameter of 30 mm containing 1.8 g of artificial urine and allowed to swell for 10 minutes to swell the water-absorbent resin particles 10 times.

The mass (Wa) was measured with a dried wire mesh 67 of 1.4 mm (100 mm×100 mm) placed on an empty petri dish 66. Next, a measuring section containing the swollen water-absorbent resin particles 10a was placed on the center of the wire net 67. Next, 20 g of artificial urine was added from the upper part of the cylindrical container (A) 61, and at the same time, a stopwatch was started. After 30 seconds from the introduction of artificial urine, the measuring section containing the water-absorbent resin particles 10a was removed from the wire net 67, and the swollen water-absorbent resin particles 10a passed through 30 seconds (0.5 minutes) after the introduction. Then, the total mass (Wb) of the petri dish 66 containing the artificial urine 65 that flowed out and the wire net 67 was measured, and the artificial urine flow rate (g/min) was determined by the following formula. The results are shown in Table 1.
Artificial urine flow rate (g/min)=(Wb-Wa)/0.5

<Measurement of water absorption of physiological saline under a load of 4.14 kPa>
The physiological saline water absorption under a load of 4.14 kPa (water absorption under load) was measured using a measuring device schematically shown in FIG. The measurement was performed twice for one type of water-absorbent resin particle, and the average value was obtained. The measuring device includes a buret unit 1, a clamp 3, a conduit 5, a pedestal 11, a measuring table 13, and a measuring unit 4 placed on the measuring table 13. The burette part 1 includes a burette tube 21 with graduations, a rubber stopper 23 that tightly plugs the upper opening of the burette tube 21, a cock 22 connected to the lower end of the burette tube 21, and a lower portion of the burette tube 21. It has an air introduction pipe 25 and a cock 24 connected to each other. The bullet part 1 is fixed by a clamp 3. The flat plate-shaped measuring table 13 has a through hole 13a having a diameter of 2 mm formed in the center thereof, and is supported by a gantry 11 having a variable height. The through hole 13 a of the measuring table 13 and the cock 22 of the buret part 1 are connected by the conduit 5. The inner diameter of the conduit 5 is 6 mm.

The measuring unit 4 has a cylinder 31 made of Plexiglas, a polyamide mesh 32 adhered to one opening of the cylinder 31, and a weight 33 movable in the cylinder 31 in the vertical direction. The cylinder 31 is placed on the measuring table 13 via the polyamide mesh 32. The inner diameter of the cylinder 31 is 20 mm. The openings of the polyamide mesh 32 are 75 μm (200 mesh). The weight 33 has a diameter of 19 mm and a mass of 119.6 g, and it is possible to apply a load of 4.14 kPa (0.6 psi) to the water-absorbent resin particles 10a uniformly arranged on the polyamide mesh 32 as described later. it can.

The measurement of the physiological saline absorption capacity under a load of 4.14 kPa by the measuring device shown in FIG. 3 was performed in a room at 25° C. First, the cock 22 and the cock 24 of the buret part 1 were closed, and 0.9% by mass physiological saline adjusted to 25° C. was put into the buret tube 21 through the opening in the upper part of the buret tube 21. Next, the upper opening of the burette tube 21 was sealed with the rubber stopper 23, and then the cock 22 and the cock 24 were opened. The inside of the conduit 5 was filled with 0.9 mass% saline solution 50 to prevent air bubbles from entering. The height of the measuring table 13 was adjusted such that the height of the water surface of the 0.9 mass% saline solution that reached the through hole 13a was the same as the height of the upper surface of the measuring table 13. After the adjustment, the height of the water surface of the 0.9 mass% saline solution 50 in the burette pipe 21 was read on the scale of the burette pipe 21, and the position was set as the zero point (reading value at 0 second).

In the measurement unit 4, 0.10 g of the water-absorbent resin particles 10a are uniformly arranged on the polyamide mesh 32 in the cylinder 31, and the weight 33 is arranged on the water-absorbent resin particles 10a. It was installed so as to coincide with the conduit port at the center of the measuring table 13. Reduced amount of physiological saline in the buret tube 21 60 minutes after the water absorbent resin particles 10a start absorbing the physiological saline from the conduit 5 (that is, the amount of physiological saline absorbed by the water absorbent resin particles 10a) Wc (ml) was read and the water absorption capacity of physiological saline under a load of 4.14 kPa of the water absorbent resin particles 10a was calculated by the following formula. The results are shown in Table 1.
4. Saline water absorption capacity under a load of 4.14 kPa (ml/g)=Wc (ml)/mass of water-absorbent resin particles (g)

<Measurement of water retention capacity of saline>
A cotton bag (Membroad No. 60, width 100 mm×length 200 mm) in which 2.0 g of the water-absorbent resin particles was weighed out was placed in a 500 ml beaker. In a cotton bag containing water-absorbent resin particles, pour 500 g of 0.9 mass% sodium chloride aqueous solution (physiological saline solution) at a time so that mamako cannot be caught, tie the upper part of the cotton bag with a rubber band, and let it stand for 30 minutes. The water-absorbent resin particles were swollen with. The cotton bag after 30 minutes has been dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set to have a centrifugal force of 167 G, and a cotton bag containing the swollen gel after dehydration. The mass Wd (g) of was measured. The same operation was performed without adding the water-absorbent resin particles, and the empty mass We(g) of the cotton bag when wet was measured, and the water retention capacity of the physiological saline was calculated from the following formula. The results are shown in Table 1.
Saline water retention capacity (g/g)=[Wd-We]/2.0

<Measurement of medium particle size (particle size distribution)>
50 g of the water absorbent resin particles were used for measuring the median particle size (particle size distribution). From the JIS standard sieve, a sieve having an opening of 850 μm, a sieve having an opening of 500 μm, a sieve having an opening of 425 μm, a sieve having an opening of 300 μm, a sieve having an opening of 250 μm, a sieve having an opening of 180 μm, a sieve having an opening of 150 μm, and Combined in the order of the saucers.

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

<Measurement of physiological saline absorption rate>
Weigh 50±0.1 g of 0.9% NaCl aqueous solution adjusted to a temperature of 25±0.2° C. in a constant temperature water tank into a 100 ml beaker and stir with a magnetic stirrer bar (8 mmφ×30 mm ring is not used). A vortex was generated at a rotation speed of 600 rpm. 2.0±0.002 g of the water-absorbent resin particles were added to the 0.9% NaCl aqueous solution at once, and the time (seconds) from the addition of the water-absorbent resin particles to the point when the vortex of the liquid surface converges The measurement was performed, and the time was taken as the water absorption rate of the water absorbent resin particles. This water absorption rate is also referred to as the Vortex method or vortex time.

<Corneometer measurement>
[Production of absorbent article]
A sheet having a size of 40 cm×12 cm is obtained by uniformly mixing 13.3 g of water-absorbent resin particles and 12.9 g of crushed pulp by air-papermaking using an air flow type mixing device (Pad former, manufactured by Autech Co., Ltd.). A shaped absorber was prepared. Next, pressing with applying a load of 588 kPa to the entire body for 30 seconds while sandwiching the top and bottom of the absorbent core with two pieces of tissue paper having the same size as the absorbent core and having a basis weight of 16 g/m ² as core wraps. To obtain a laminated body. Furthermore, an air-through type porous liquid permeable sheet made of polyethylene-polypropylene having a basis weight of 22 g/m ² and having the same size as the absorbent body is arranged on the upper surface of the laminate, and further has the same size as the absorbent body. An absorbent article was produced by sticking the polyethylene liquid-impermeable sheet having the above to the surface opposite to the air-through type porous liquid-permeable sheet.

[Corneometer measurement]
Corneometer measurement is a method of measuring the amount of water on the surface of an object based on a capacitance measuring method. In the capacitance measuring method, the amount of water can be measured by utilizing the fact that the permittivity of water and the permittivity of other substances have a significant difference. In the Corneometer measurement, the water content is represented by an index of 0 to 120.

160 ml of 0.9 mass% physiological saline (25° C.) was prepared in a 200 ml graduated cylinder, and was poured into the center of the absorbent article using a liquid charging cylinder having an opening with an inner diameter of 3 cm. The moment when it was charged was 0 minutes. The water content index after a predetermined time was measured using a Corneometer (CM825, manufactured by Courage+Khazaka). Specifically, the measurement probe (49 mm ² ) attached to the Corneometer was pressed against the center of the absorbent article, and the amount of water on the surface of the absorbent article at 1 minute and 1.5 minutes after the physiological saline was added. The index was measured at constant force (1N±10%). The measurement was performed in an environment of 25±1° C. and a relative humidity of 50±5%.

In the Corneometer measurement of the absorbent article, when the measurement point of the absorbent article is touched with a finger, the finger gets wet when the water content index exceeds 100, and the finger has a water content index of about 50 to 60. Although it did not get wet, it felt a little water, and when the water content index was 10 or less, no water was felt at all.

The surface dryness index was calculated from the obtained measured values by the following formula. The index is an index of how quickly the surface of the physiological saline solution dries quickly within 30 seconds after the physiological saline solution has penetrated into the absorbent article for one minute, and the lower the value, the more preferable. The results are shown in Table 2. The absorbent articles using the water-absorbent resin particles of the examples were shown to have a sufficiently low surface dryness index.
Surface dryness index=(water content index 1.5 minutes after liquid addition/water content index 1 minute after liquid addition)×100

DESCRIPTION OF SYMBOLS 1... Burette part, 3... Clamp, 4... Measuring part, 5... Conduit, 10... Absorber, 10a... Water absorbent resin particle, 10b... Fiber layer, 11... Stand, 13... Measuring stand, 13a... Through hole, 20a , 20b... Core wrap, 21... Burette tube, 22... Cock, 23... Rubber stopper, 24... Cock, 25... Air introduction tube, 30... Liquid permeable sheet, 31... Cylinder, 32... Polyamide mesh, 33... Weight, 40 ... Liquid impermeable sheet, 61... Cylindrical container (A), 62... Cylindrical container (B), 63, 64... Nylon mesh sheet, 65... Artificial urine, 66... Petri dish, 67... Wire mesh, 100... Absorbent Goods.

[ Reference Example 1 ]
In the preparation of the first-stage aqueous liquid, the amount of potassium persulfate as a radical polymerization initiator was changed to 0.0736 g (0.272 mmol), 2,2′-azobis(2-amidinopropane) 2 No hydrochloric acid salt was added, the amount of potassium persulfate as a radical polymerization initiator was changed to 0.090 g (0.334 mmol) in the preparation of the second-stage aqueous liquid, 2,2′- Azobis(2-amidinopropane) dihydrochloride was not added, and in the reaction liquid containing the hydrogel polymer after the second-stage polymerization, the amount of water taken out of the system by azeotropic distillation was 239.7 g. 229.2 g of water-absorbent resin particles was obtained in the same manner as in Example 1 except that the content of the amorphous silica was changed to 0.5% by mass and the amount of the amorphous silica mixed with the polymer particles was changed to 0.5% by mass. The median particle diameter of the water-absorbent resin particles was 377 μm, and the water absorption rate of physiological saline was 40 seconds. The crosslinking ratio was 10.1.

[ Reference Example 2 ]
In the preparation of the first-stage aqueous liquid, the amount of ethylene glycol diglycidyl ether as an internal cross-linking agent was changed to 0.0046 g (0.026 mmol), and the second-stage water-containing gel-like weight after polymerization was changed. In the reaction liquid containing the coalescence, the amount of water extracted to the outside of the system by azeotropic distillation was changed to 219.2 g, and the amount of 2% by mass ethylene glycol diglycidyl ether aqueous solution as a surface crosslinking agent was 6.62 g. 229.6 g of water-absorbent resin particles was obtained in the same manner as in Example 1 except that the content was changed to (0.761 mmol). The median particle diameter of the water-absorbent resin particles was 356 μm, and the water absorption rate of physiological saline was 56 seconds. The crosslinking ratio was 31.8.

Claims (3)

A water absorbent resin having an artificial urine permeation rate of 10 g/min at a swelling of 10 times or more and a contact angle of 70 degrees or less measured in the tests conducted in the order of i) and ii) below. particle.
i) At 25° C., spherical droplets having a diameter of 3.0±0.1 mm of 25% by mass saline solution are dropped on the surface of the layer formed of the water-absorbent resin particles, and the water-absorbent resin particles and the Contact with the droplet.
ii) The contact angle of the droplet is measured 30 seconds after the droplet contacts the surface. The water absorbent resin particles according to claim 1, wherein the water retention capacity of physiological saline is 20 to 60 g/g. The water-absorbent resin particle according to claim 1 or 2, which has a water absorption of physiological saline of 15 ml/g or more under a load of 4.14 kPa.

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