WO2021049487A1

WO2021049487A1 - Water absorbent resin particles, absorbent article, and production method for water absorbent resin particles

Info

Publication number: WO2021049487A1
Application number: PCT/JP2020/033951
Authority: WO
Inventors: 河原　徹
Original assignee: 住友精化株式会社
Priority date: 2019-09-09
Filing date: 2020-09-08
Publication date: 2021-03-18
Also published as: JPWO2021049487A1

Abstract

The present invention discloses water absorbent resin particles 10a comprising polymer particles having a surface cross-linked by a surface-crosslinking agent. The ratio A/B is 21 or less where A is the static water absorption rate [seconds] of the water absorbent resin particles and B is the dynamic water absorption rate [seconds] of the water absorbent resin particles. The static water absorption rate is the time required for 1.00 g of the water absorbent resin particles to absorb 25 ml of physiological saline solution from the start of absorption in a DW test under no pressure. The dynamic water absorption rate is the water absorption rate measured by a Vortex test.

Description

Method for producing water-absorbent resin particles, absorbent articles, and water-absorbent resin particles

The present invention relates to water-absorbent resin particles, absorbent articles, and a method for producing water-absorbent resin particles.

The polymer particles constituting the water-absorbent resin particles may be surface-crosslinked by various surface-crosslinking agents (for example, Patent Document 1).

Japanese Patent No. 4810635

In absorbent articles such as diapers, it may be necessary to quickly allow the liquid to penetrate into the curved sheet-shaped absorbent body. Therefore, the present invention provides water-absorbent resin particles that enable the sheet-shaped absorber to absorb water at a sufficiently high permeation rate even in a curved state.

One aspect of the present invention provides water-absorbent resin particles containing polymer particles surface-crosslinked by a surface-crosslinking agent. When the static water absorption rate of the water-absorbent resin particles is A [seconds] and the dynamic water absorption rate of the water-absorbent resin particles is B [seconds], the A / B is 21 or less. The static water absorption rate is such that when the water-absorbent resin particles of 1.00 g are absorbed with physiological saline by the non-pressurized DW method, the water-absorbent resin particles have 25 mL of physiological saline after the absorption is started. It is the time to absorb water. The dynamic water absorption rate is the water absorption rate measured by the Vortex method.

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

According to the findings of the present inventor, the ratio of the water absorption rate when statically absorbing water in a non-pressurized state to the water absorption rate when dynamically absorbing water in a fluid state is a liquid to a curved absorber. Correlates with the permeation rate of. In particular, when the ratio A / B of the static water absorption rate A to the dynamic water absorption rate B is 21 or less, the permeation rate of the liquid into the curved absorber can be remarkably improved.

Yet another aspect of the present invention provides a method of producing water-absorbent resin particles. The method comprises a step of surface cross-linking the polymer particles by heating a reaction mixture containing the polymer particles and an aqueous solution of a surface cross-linking agent containing water and a surface cross-linking agent. X and Y are the following formulas:
X = (mass of water in the reaction mixture) / (mass of the surface cross-linking agent in the reaction mixture)
Y = (dry mass of the polymer particles in the reaction mixture) / (mass of the surface cross-linking agent in the reaction mixture)
X × Y is 11000 or less when it is a value calculated by.

It is considered that the surface cross-linking of the polymer particles forms a layer (surface cross-linking layer) in which the cross-linking density of the polymer constituting the polymer particles is increased on the surface layer of the polymer particles. The above X and Y are considered to be related to the efficiency of the surface cross-linking reaction on the surface layer of the polymer particles. When the value of X is small, the phenomenon that the surface cross-linking agent reacts with water in the reaction mixture can be suppressed, so that the surface cross-linking of the polymer particles can be efficiently performed and the cross-linking density of the surface can be increased. It is thought that it can be done. When the value of Y is small, it is considered that a stronger surface cross-linking layer is formed because the surface cross-linking agent is larger than that of the polymer particles. Therefore, the polymer particles surface-crosslinked under the condition that X × Y is 110,000 or less tend to have a strong surface-crosslinked layer with a high crosslink density. If the surface crosslinked layer is strong, the water-absorbent resin after swelling is less likely to be crushed, so that gel blocking is less likely to occur. If gel blocking is unlikely to occur, the static water absorption rate becomes relatively high, and as a result, the ratio A / B of the static water absorption rate A to the dynamic water absorption rate B is considered to be small.

According to the present invention, there is provided water-absorbent resin particles capable of absorbing water at a sufficiently high permeation rate even when the sheet-shaped absorber is in a curved state.

It is sectional drawing which shows one Embodiment of an absorbent article. It is a schematic diagram which shows the method of measuring the static water absorption rate of a water-absorbing resin particle. It is a schematic diagram which shows the method of the water absorption test for evaluating the permeation rate of the liquid into a curved absorber.

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

In this specification, "(meth) acrylic" means both acrylic and methacrylic. Similarly, "acrylate" and "methacrylate" are also referred to as "(meth) acrylate". The same is true for other similar terms. "(Poly)" shall mean both with and without the "poly" prefix. In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range of one step can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range of another step. In the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. "Water-soluble" means that it exhibits a solubility in water of 5% by mass or more at 25 ° C. The materials exemplified in the present specification may be used alone or in combination of two or more.

(Water-absorbent resin particles)
The water-absorbent resin particles according to the embodiment include polymer particles surface-crosslinked by a surface-crosslinking agent. When the static water absorption rate of the water-absorbent resin particles is A [seconds] and the dynamic water absorption rate of the water-absorbent resin particles is B [seconds], the A / B is 21 or less.

The static water absorption rate is such that when 1.00 g of water-absorbent resin particles absorb physiological saline by the non-pressurized DW method, the water-absorbent resin particles start absorbing 25 mL of physiological saline after the absorption is started. It is the time to absorb. In the non-pressurized DW method, water-absorbent resin particles are placed on a liquid-permeable sheet (mesh sheet) placed on a measuring table having a through hole, and a physiological saline solution supplied from the through hole without pressurization. Is a water absorption test in which water-absorbent resin particles absorb the water. Normally, the inner diameter of the through hole is 2 mm. The amount of the water-absorbent resin particles used in the test is 1.00 ± 0.01 g, and this amount of the water-absorbent resin particles is uniformly arranged in a circular region having a diameter of 30 mm centered on the position directly above the through hole. Will be done. The measurement of the static water absorption rate by the non-pressurized DW method is performed in an environment of a temperature of 25 ° C. ± 2 ° C. and a humidity of 50 ± 10%. The physiological saline solution is an aqueous solution containing 0.9% by mass of salt based on the volume (mL) of the physiological saline solution. Other details of the test conditions will be described in Examples described later.

The dynamic water absorption rate is the time required to completely absorb and eliminate the vortex after adding 2.00 g of water-absorbent resin particles to 50 mL of physiological saline, which is measured by the Vortex method. The water absorption test by the Vortex method can be performed by measuring the time until the vortex disappears using an instrument according to the method specified in JIS K7224: 1996. Put 50 mL of physiological saline in a glass beaker with a capacity of 100 mL and stir at 600 ± 10 rpm. From the time when 2.0 g of the finely weighed water-absorbent resin particles were placed in this beaker, the time until the physiological saline was absorbed by the water-absorbent resin particles and the vortex due to stirring disappeared was measured, and the time [seconds] was moved. It is a measured value of the target water absorption rate. Other details of the test conditions will be described in Examples described later.

According to the findings of the present inventors, when the A / B is small, the curved absorber tends to absorb water at a faster permeation rate. In particular, when the A / B is 21 or less, an absorber having a sufficiently fast permeation rate can be obtained. From the same viewpoint, the A / B may be 19 or less, 17 or less, 15 or less, or 12 or less. The lower limit of A / B is not particularly limited, but may be, for example, 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. A / B may be 19 or less and 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more, and 17 or less and 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. Often, 15 or less may be 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more, and 12 or less may be 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more.

The static water absorption rate A may be 50 seconds or more, 100 seconds or more, 150 seconds or more, 200 seconds or more, 250 seconds or more, or 300 seconds or more, 2000 seconds or less, 1800 seconds or less, 1600 seconds or less, 1500. It may be less than a second or less than 1400 seconds. The static water absorption rate A may be 50 seconds or more and 2000 seconds or less, 1800 seconds or less, 1600 seconds or less, 1500 seconds or less, or 1400 seconds or less, and 100 seconds or more and 2000 seconds or less, 1800 seconds or less, 1600. Seconds or less, 1500 seconds or less, or 1400 seconds or less, 150 seconds or more, 2000 seconds or less, 1800 seconds or less, 1600 seconds or less, 1500 seconds or less, or 1400 seconds or less, 200 seconds or more 2000 seconds or less, 1800 seconds or less, 1600 seconds or less, 1500 seconds or less, or 1400 seconds or less, 250 seconds or more and 2000 seconds or less, 1800 seconds or less, 1600 seconds or less, 1500 seconds or less, or 1400 seconds It may be 250 seconds or more and 2000 seconds or less, 1800 seconds or less, 1600 seconds or less, 1500 seconds or less, or 1400 seconds or less, and 300 seconds or more and 2000 seconds or less, 1800 seconds or less, 1600. It may be seconds or less, 1500 seconds or less, or 1400 seconds or less. The dynamic water absorption rate B may be 20 seconds or more, 30 seconds or more, 40 seconds or more, 50 seconds or more, or 60 seconds or more, 120 seconds or less, 110 seconds or less, 100 seconds or less, 90 seconds or less, 80. It may be less than a second or less than 70 seconds. The dynamic water absorption rate B may be 20 seconds or more and 120 seconds or less, 110 seconds or less, 100 seconds or less, 90 seconds or less, 80 seconds or less, or 70 seconds or less, and 30 seconds or more and 120 seconds or less, 110. It may be seconds or less, 100 seconds or less, 90 seconds or less, 80 seconds or less, or 70 seconds or less, 40 seconds or more and 120 seconds or less, 110 seconds or less, 100 seconds or less, 90 seconds or less, 80 seconds or less, or It may be 70 seconds or less, 50 seconds or more and 120 seconds or less, 110 seconds or less, 100 seconds or less, 90 seconds or less, 80 seconds or less, or 70 seconds or less, 60 seconds or more and 120 seconds or less. , 110 seconds or less, 100 seconds or less, 90 seconds or less, 80 seconds or less, or 70 seconds or less. When the static water absorption rate A and the dynamic water absorption rate B are within these ranges, a better permeation rate tends to be exhibited.

The amount of water absorption of the water-absorbent resin particles with respect to physiological saline may be 30 g / g or more, 35 g / g or more, 40 g / g or more, or 45 g / g or more, 80 g / g or less, 75 g / g or less, 70 g. It may be / g or less, 65 g / g or less, 60 g / g or less, or 55 g / g or less. When the water absorption amount of the water-absorbent resin particles is within these ranges, a better permeation rate tends to be exhibited. The amount of water-absorbent resin particles retained in physiological saline can be measured by the method described in Examples described later.

The medium particle size of the water-absorbent resin particles (or polymer particles) may be 100 to 800 μm, 150 to 700 μm, 200 to 600 μm, or 250 to 500 μm. The medium particle size can be measured by the following method. From the top of the JIS standard sieve, a sieve with a mesh size of 600 μm, a sieve with a mesh size of 500 μm, a sieve with a mesh size of 425 μm, a sieve with a mesh size of 300 μm, a sieve with a mesh size of 250 μm, a sieve with a mesh size of 180 μm, a sieve with a mesh size of 150 μm, and , Combine in the order of the saucer. 50 g of water-absorbent resin particles are placed in the best combined sieve, and the mixture is classified according to JIS Z8815 (1994) using a low-tap shaker (manufactured by Iida Seisakusho Co., Ltd.). After classification, the mass of the particles remaining on each sieve is calculated as a mass percentage with respect to the total amount to obtain the particle size distribution. The relationship between the mesh size of the sieve and the integrated value of the mass percentage of the particles remaining on the sieve is plotted on the 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 is obtained as the medium particle size.

The shape of the water-absorbent resin particles (or polymer particles) is not particularly limited, and may be, for example, substantially spherical, crushed, or granular, and particles in which primary particles having these shapes are aggregated are formed. May be good.

The polymer particles may be water-absorbent particles containing a polymer containing an ethylenically unsaturated monomer as a monomer unit. The ethylenically unsaturated monomer may be a water-soluble monomer, and examples thereof include (meth) acrylic acid and salts thereof, 2- (meth) acrylamide-2-methylpropanesulfonic acid and its salts. Salt, (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-diethylaminopropyl (meth) acrylate, and diethylaminopropyl (meth) acrylamide. The ethylenically unsaturated monomer may be used alone or in combination of two or more. The proportion of the polymer containing the ethylenically unsaturated monomer as a monomer unit in the polymer particles is 50 to 100% by mass, 60 to 100% by mass, and 70 to 100% by mass based on the mass of the polymer particles. , Or 80 to 100% by mass. The polymer particles may be particles containing a (meth) acrylic acid-based polymer containing at least one of (meth) acrylic acid or (meth) acrylate as a monomer unit. The total ratio of the monomer units derived from (meth) acrylic acid or (meth) acrylate in the (meth) acrylic acid-based polymer may be 90 to 100% by mass based on the mass of the polymer. Good.

Of the polymer particles, at least the polymer in the surface layer portion is crosslinked by the reaction with the surface cross-linking agent. The surface cross-linking agent may be, for example, a compound having two or more functional groups (reactive functional groups) having reactivity with a functional group derived from an ethylenically unsaturated monomer. Examples of the surface cross-linking agent include alkylene carbonate compounds such as ethylene carbonate and propylene carbonate; polyols such as 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol and polyglycerin; Polyglycidyl compounds such as (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether; epichlorohydrin, epibrom Haloepoxy compounds such as hydrin and α-methylepicrolhydrin; compounds having two or more reactive functional groups such as isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetane methanol, 3 -Oxetane compounds such as ethyl-3-oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol; 1, Examples thereof include oxazoline compounds such as 2-ethylenebisoxazoline; and hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide. The surface cross-linking agent may contain an alkylene carbonate compound. The ratio of the alkylene carbonate compound in the surface cross-linking agent is 50 to 100% by mass, 60 to 100% by mass, 70 to 100% by mass, 80 to 100% by mass, or 90 to 100% by mass based on the total mass of the surface cross-linking agent. It may be.

Even inside the polymer particles, the polymer may be internally crosslinked by self-crosslinking, cross-linking by reaction with an internal cross-linking agent, or both.

The internal cross-linking agent is, for example, a compound having two or more polymerizable unsaturated groups, a compound having two or more reactive functional groups having reactivity with a functional group of an ethylenically unsaturated monomer, or a compound thereof. It can contain one or more compounds, including combinations.

As an example of a compound having two or more polymerizable unsaturated groups, (poly) ethylene glycol (in this specification, for example, "polyethylene glycol" and "ethylene glycol" are collectively referred to as "(poly) ethylene glycol". Di or tri (meth) acrylic acid esters of polyols such as (poly) propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and (poly) glycerin; Unsaturated polyesters obtained by reacting with unsaturated acids such as maleic acid and fumaric acid; bisacrylamides such as N, N'-methylenebis (meth) acrylamide; by reacting polyepoxide with (meth) acrylic acid. Di or tri (meth) acrylic acid esters obtained; di (meth) acrylic acid carbamil esters obtained by reacting polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth) acrylic acid; Alylated starch; allylated cellulose; diallyl phthalate; N, N', N''-triallyl isocyanurate; divinylbenzene.

Examples of compounds having two or more reactive functional groups include glycidyl group-containing compounds such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether; (poly). ) Ethylene glycol, (poly) propylene glycol, (poly) glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, glycidyl (meth) acrylate.

The polymer particles may contain a certain amount of water in addition to the polymer of the ethylenically unsaturated monomer, and may further contain various additional components therein. Examples of additional ingredients include gel stabilizers, metal chelating agents.

The water-absorbent resin particles may further contain inorganic particles adhering to the surface of the polymer particles. Examples of the inorganic particles include silica particles such as amorphous silica. The amount of inorganic particles adhering to the surface of the polymer particles is 0.05% by mass or more, 0.1% by mass or more, 0.15% by mass or more, or 0.2% by mass based on the mass of the polymer particles. % Or more, 5.0% by mass or less, 3.0% by mass or less, 1.0% by mass or less, 0.5% by mass or less, or 0.3% by mass or less. The average particle size of the inorganic particles may be 0.1 to 50 μm, 0.5 to 30 μm, or 1 to 20 μm. The average particle size can be measured by the pore electric resistance method or the laser diffraction / scattering method depending on the characteristics of the particles.

(Method of manufacturing water-absorbent resin particles)
The water-absorbent resin particles according to the above-exemplified embodiment surface-crosslink the polymer particles by heating, for example, a reaction mixture containing the polymer particles and an aqueous solution of a surface-crosslinking agent containing water and a surface-crosslinking agent. It can be manufactured by a method comprising a step. In this method, X and Y are the following formulas:
X = (mass of water in reaction mixture) / (mass of surface cross-linking agent in reaction mixture)
Y = (dry mass of polymer particles in the reaction mixture) / (mass of surface cross-linking agent in the reaction mixture)
Water absorption in which the above-mentioned A / B is appropriately controlled by adjusting the amount ratio of the polymer particles, the surface cross-linking agent, and water so that X × Y becomes 11000 or less when it is the value calculated by. Sex resin particles can be easily obtained.

The mass of water in the reaction mixture is the total mass including not only the amount of water in the aqueous surface cross-linking agent solution but also the amount of water contained in the polymer particles subjected to surface cross-linking. The dry mass of the polymer particles is the mass obtained by subtracting the amount of water contained in the polymer particles from the mass of the polymer particles subjected to surface cross-linking. The water content in the polymer particles based on the mass of the polymer particles (hereinafter referred to as "moisture content of the polymer particles") is measured, and the value is used to determine the water content in the polymer particles. And the dry mass of the polymer particles can be calculated by the following formula.
Moisture content in polymer particles (g) = mass of polymer particles x water content of polymer particles / 100
Dry mass (g) of polymer particles = mass of polymer particles x (100-moisture content of polymer particles) / 100

The water content of the polymer particles can be determined from the change in mass when the water content is removed by heating the polymer particles at 105 ° C. for 2 hours. The water content of the polymer particles mixed with the surface cross-linking agent aqueous solution and subjected to surface cross-linking may be, for example, 30% by mass or less, or 15% by mass or less, and 0% by mass or more, 2% by mass or more, 4 It may be 5% by mass or more, or 6% by mass or more.

X / Y may be 10,000 or less, 9000 or less, 8000 or less, or 7000 or less, and may be 50 or more, or 100 or more. X / Y may be 10,000 or less and 50 or more or 100 or more, 9000 or less and 50 or more or 100 or more, 8000 or less and 50 or more or 100 or more, and 7000 or less. It may be 50 or more or 100 or more. X may be 1 or more, 2 or more, or 3 or more, and may be 50 or less, 40 or less, 30 or less, or 20 or less. X may be 1 or more and 50 or less, 40 or less, 30 or less, or 20 or less, 2 or more and 50 or less, 40 or less, 30 or less, or 20 or less, and 3 or more and 50 or less. , 40 or less, 30 or less, or 20 or less. Y may be 10 or more, 20 or more, or 30 or more, and may be 250 or less, or 200 or less. Y may be 10 or more and 250 or less, or 200 or less, 20 or more and 250 or less, or 200 or less, and 30 or more and 250 or less, or 200 or less.

The surface cross-linking agent aqueous solution contains water and a surface cross-linking agent dissolved in water. The aqueous surface cross-linking agent solution may further contain a hydrophilic organic solvent. The organic solvent may be, for example, an alcohol such as 2-propanol, ethanol, methanol, ethylene glycol, or propylene glycol. The contents of water and the surface cross-linking agent in the surface cross-linking agent aqueous solution, and the mixing ratio of the surface cross-linking agent aqueous solution to the polymer particles can be adjusted so that X × Y is in an appropriate range. The ratio of water to the total amount of water and the organic solvent is 100% by mass or less, and may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, and 90% by mass or more.

The polymer particles can be surface-crosslinked by mixing the polymer particles and the aqueous surface cross-linking agent solution and heating the reaction mixture formed with stirring, if necessary. The heating temperature for surface cross-linking may be appropriately adjusted so that the surface cross-linking proceeds, for example, 70 to 300 ° C., 100 to 270 ° C., 120 to 250 ° C., 150 to 220 ° C., or 170 to 200 ° C. You may. The reaction time for surface cross-linking may be, for example, 1 to 200 minutes, 10 to 100 minutes, 20 to 80 minutes, 30 to 70 minutes, 40 to 60 minutes, or 5 to 100 minutes. The surface cross-linking step may be carried out twice or more.

The polymer particles to be subjected to surface cross-linking can be obtained, for example, by a method including a step of polymerizing a monomer containing an ethylenically unsaturated monomer. The polymerization method of the monomer can be selected from, for example, a reverse phase suspension polymerization method, an aqueous solution polymerization method, a bulk polymerization method, and a precipitation polymerization method. Internally crosslinked polymer particles may be obtained by polymerizing an ethylenically unsaturated monomer in the presence of an internal crosslinking agent. Polymer particles containing inorganic particles may be obtained by polymerizing an ethylenically unsaturated monomer in the presence of inorganic particles such as silica. A part or all of the ethylene-based unsaturated monomer may form a salt such as an alkali metal salt.

In the case of the aqueous solution polymerization method, for example, the ethylenically unsaturated monomer is polymerized in a monomer aqueous solution containing an ethylenically unsaturated monomer and water to form a hydrogel polymer containing the polymer. The polymer particles before surface cross-linking can be obtained by a method including the above and drying of the hydrogel polymer. When a lumpy hydrogel polymer is formed, it may be coarsely crushed and the crude product of the hydrogel polymer may be dried. The hydrogel polymer or a crude product thereof may be dried and then pulverized, or the particles obtained by pulverization may be classified. The polymer particles to be subjected to surface cross-linking may be dried coarsely crushed products or particles obtained by further pulverizing the coarsely crushed products. The polymer particles obtained by pulverizing the coarsely crushed product may be classified, the particle size of the polymer particles may be adjusted as necessary, and then subjected to surface cross-linking.

The concentration of the ethylenically unsaturated monomer in the aqueous monomer solution may be 20% by mass or more and less than the saturated concentration, 25 to 70% by mass, or 30 to 50% by mass based on the mass of the aqueous monomer solution. Good.

The monomer aqueous solution may further contain a polymerization initiator. The polymerization initiator may be a photopolymerization initiator or a thermal radical polymerization initiator, or may be a water-soluble thermal radical polymerization initiator. The thermally radically polymerizable compound may be an azo compound, a peroxide, or a combination thereof. The amount of the polymerization initiator may be 0.00005 to 0.01 mol per 1 mol of the ethylenically unsaturated monomer.

The monomer aqueous solution may further contain the above-mentioned internal cross-linking agent. The amount of the internal cross-linking agent is 0 mmol or more, 0.001 mmol or more, 0.01 mmol or more, 0.015 mmol or more, or 0.020 mmol or more with respect to 1 mol of the ethylenically unsaturated monomer. It may be 2 mmol or less, 1 mmol or less, 0.5 mmol or less, or 0.1 mmol or less. If necessary, the aqueous monomer solution may further contain other additives such as a chain transfer agent and a thickener.

The polymerization temperature varies depending on the polymerization initiator used, but may be, for example, 0 to 130 ° C. or 10 to 110 ° C. The polymerization time may be 1 to 200 minutes or 5 to 100 minutes.

The water content of the hydrogel polymer formed by polymerization (water content based on the mass of the hydrogel polymer) is 30 to 80% by mass, 40 to 75% by mass, or 50 to 70% by mass. May be.

When a lumpy hydrogel polymer is coarsely crushed, the coarsely crushed product obtained by the coarse crushing may be in the form of particles or may have an elongated shape such that particles are connected. The minimum width of the pyroclastic material may be, for example, about 0.1 to 15 mm or 1.0 to 10 mm. The maximum width of the pyroclastic material may be about 0.1 to 200 mm or 1.0 to 150 mm. Examples of devices for crushing include kneaders (eg, pressurized kneaders, double-armed kneaders, etc.), meat choppers, cutter mills, and pharmacomills. If necessary, the lumpy hydrogel polymer may be cut before coarse crushing.

The hydrogel polymer or its crude product is dried mainly to remove water. The drying method may be a general method such as natural drying, heat drying, and vacuum drying. By further pulverizing the dried hydrogel polymer or a crude product thereof and classifying the obtained particles as necessary, polymer particles having an appropriate particle size can be obtained. The crushing method is not particularly limited, and for example, a roller mill (roll mill), a stamp mill, a jet mill, a high-speed rotary crusher (hammer mill, pin mill, rotor beater mill, etc.), or a container-driven mill (rotary mill, vibration mill, etc.). , Planet mill, etc.) can be applied. The classification method is also not particularly limited, and for example, a method using a vibrating sieve, a rotary shifter, a cylindrical stirring sieve, a blower shifter, or a low-tap type shaker can be applied.

In the case of the reverse phase suspension polymerization method, for example, an interface between a hydrocarbon dispersion medium and a monomer aqueous solution containing an ethylenically unsaturated monomer, a radical polymerization initiator, water, etc. dispersed in the hydrocarbon dispersion medium. In a suspension containing an activator, an ethylenically unsaturated monomer is polymerized to form a particulate hydrogel polymer containing the polymer, and hydrocarbon dispersion from the suspension. Polymer particles to be subjected to surface cross-linking can be obtained by methods including removing the medium and water.

The hydrocarbon dispersion medium may contain at least one compound selected from the group consisting of chain aliphatic hydrocarbons having 6 to 8 carbon atoms and alicyclic hydrocarbons having 6 to 8 carbon atoms. Hydrocarbon dispersion media include chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane; cyclohexane. , Methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentane and other alicyclic hydrocarbons; benzene, Examples include aromatic hydrocarbons such as toluene and xylene. The hydrocarbon dispersion medium may be used alone or in combination of two or more. The amount of the hydrocarbon dispersion medium may be 30 to 1000 parts by mass, 40 to 500 parts by mass, or 50 to 300 parts by mass with respect to 100 parts by mass of the aqueous monomer solution containing the monomer.

Examples of thermal radical polymerization initiators include persulfates, peroxides, and azo compounds. The amount of the radical polymerization initiator may be 0.00005 to 0.01 mol per 1 mol of the ethylenically unsaturated monomer.

The suspension for reverse phase suspension polymerization may further contain the above-mentioned internal cross-linking agent. The internal cross-linking agent is usually added to a monomer aqueous solution containing an ethylene-based unsaturated monomer. The amount of the internal cross-linking agent is 0 mmol or more, 0.001 mmol or more, 0.01 mmol or more, 0.015 mmol or more, or 0.020 mmol or more with respect to 1 mol of the ethylenically unsaturated monomer. It may be 2 mmol or less, 1 mmol or less, 0.5 mmol or less, or 0.1 mmol or less.

Suspensions for reverse phase suspension polymerization usually further contain a surfactant. The surfactant may be a nonionic surfactant, an anionic surfactant or the like. 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 applies hereinafter.), Sucrose fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxy. Examples thereof include ethylene castor oil, polyoxyethylene cured castor oil, alkylallyl formaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, polyethylene glycol fatty acid ester and the like. Examples of anionic surfactants include fatty acid salts, alkylbenzene sulfonates, alkylmethyl taur phosphates, polyoxyethylene alkylphenyl ether sulfates, polyoxyethylene alkyl ether sulfonates, and phosphorus in polyoxyethylene alkyl ethers. Examples thereof include acid esters and phosphoric acid esters of polyoxyethylene alkyl allyl ethers. The surfactant may be used alone or in combination of two or more. The amount of the surfactant may be 0.05 to 10 parts by mass, 0.08 to 5 parts by mass, or 0.1 to 3 parts by mass with respect to 100 parts by mass of the aqueous monomer solution.

The suspension for reverse phase suspension polymerization may further contain a polymer-based residual agent. Examples of polymer dispersants 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, ethyl hydroxyethyl cellulose and the like. The polymer-based dispersant may be used alone or in combination of two or more. The amount of the polymer-based dispersant may be 0.05 to 10 parts by mass, 0.08 to 5 parts by mass, or 0.1 to 3 parts by mass with respect to 100 parts by mass of the aqueous monomer solution.

The suspension for reverse phase suspension polymerization may contain other components such as a chain transfer agent and a thickener, if necessary. The temperature of the polymerization reaction varies depending on the radical polymerization initiator used, but may be, for example, 20 to 150 ° C. or 40 to 120 ° C. The reaction time is usually 0.5-4 hours. The reverse phase suspension polymerization may be carried out in a plurality of times.

By removing the hydrocarbon dispersion medium and water from the suspension containing the hydrogel polymer and the hydrocarbon dispersion medium, the polymer particles before surface cross-linking can be obtained. For example, azeotropic distillation, decantation, filtration, vacuum drying, or a combination thereof can remove the hydrocarbon dispersion medium and water. Water, hydrocarbon dispersion medium, or both may remain to some extent in the polymer particles before surface cross-linking.

Water and hydrocarbon dispersion medium are removed from the polymer particles after surface cross-linking, if necessary. The polymer particles after surface cross-linking may be further treated by drying, grinding, classification or a combination thereof.

The method for producing the water-absorbent resin particles may further include a step of adhering the above-mentioned inorganic particles to the surface of the polymer particles after surface cross-linking.

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

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

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

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

The magnitude relationship between the absorbent body 10, the core wraps 20a and 20b, the liquid permeable sheet 30, and the liquid permeable sheet 40 is not particularly limited, and is appropriately adjusted according to the use of the absorbent article and the like. Further, the method of retaining the shape of the absorber 10 using the core wraps 20a and 20b is not particularly limited, and as shown in FIG. 1, the absorber may be wrapped by a plurality of core wraps, and the absorber is wrapped by one core wrap. But it may be.

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

1. 1. Water-absorbent resin particles (Example 1)
Polymer particles (before surface cross-linking)
A round-bottomed cylindrical separable flask having an inner diameter of 11 cm and a volume of 2 L equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction pipe, and a stirring blade having two stages of four inclined paddle blades having a blade diameter of 5 cm was prepared. In this separable flask, 293 g of n-heptane and 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (manufactured by Mitsui Chemicals, Inc., High Wax 1105A) as a polymer-based dispersant were placed and mixed. The dispersant was dissolved in n-heptane by raising the temperature to 80 ° C. while stirring the mixture in the separable flask with a stirrer. The formed solution was cooled to 50 ° C.

In a beaker with a capacity of 300 mL, 92.0 g (1.03 mol) of an 80.5 mass% acrylic acid aqueous solution as a water-soluble ethylenically unsaturated monomer was placed, and 20.9 mass% of water was cooled from the outside. 75 mol% of acrylic acid was neutralized by dropping 147.7 g of an aqueous sodium oxide solution into a beaker. Then, 0.092 g of hydroxylethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a radical polymerization initiator, and ethylene glycol as an internal cross-linking agent. By adding 0.010 g (0.057 mmol) of diglycidyl ether and dissolving them, the first-stage monomer aqueous solution was prepared.

The first-stage monomer aqueous solution was added to the n-heptane solution containing the dispersant in the separable flask, and the formed reaction solution was stirred for 10 minutes. A surfactant solution in which 0.736 g of sucrose stearic acid ester (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370, HLB: 3), which is a surfactant, is dissolved in 6.62 g of n-heptane is dissolved therein. Further, the inside of the system was sufficiently replaced with nitrogen while stirring the reaction solution at a rotation speed of the stirrer of 550 rpm. Then, the separable flask was immersed in a water bath at 70 ° C. to raise the temperature of the reaction solution, and the polymerization reaction was allowed to proceed for 60 minutes to obtain a first-stage polymerized slurry solution.

128.8 g (1.44 mol) of an acrylic acid aqueous solution having a concentration of 80.5 mass% was placed in another beaker having a capacity of 500 mL. 75 mol% of acrylic acid was neutralized by dropping 159.0 g of a sodium hydroxide aqueous solution having a concentration of 27% by mass while cooling from the outside. To the neutralized acrylic acid aqueous solution, 0.103 g (0.381 mmol) of potassium persulfate as a radical polymerization initiator and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal cross-linking agent were added. By dissolving these, a second-stage monomer aqueous solution was prepared.

The first-stage polymerized slurry solution in the separable flask was cooled to 25 ° C. while stirring at a stirring speed of 1000 rpm, and the entire amount of the second-stage monomer aqueous solution was added thereto. After replacing the inside of the separable flask with nitrogen for 30 minutes, the separable flask is immersed again in a water bath at 70 ° C. to raise the temperature of the reaction solution, and the second-stage polymerization reaction for 60 minutes causes a hydrogel-like weight. I got a coalescence.

0.589 g of a 45% by mass diethylenetriamine-5 sodium acetate aqueous solution was added to the hydrogel polymer after the second stage polymerization under stirring. Then, the separable flask was immersed in an oil bath set at 125 ° C., and 234.2 g of water was extracted from the system by azeotropic distillation of n-heptane and water and reflux dehydration. Subsequently, n-heptane and water were further removed by drying at 125 ° C. to obtain a dried product of the polymer particles.

The above operation was performed again to obtain a dried product of polymer particles. This was mixed with the polymer particles obtained for the first time, and all the polymer particles were passed through a sieve having an opening of 850 μm. After passing through the sieve, the amount of polymer particles recovered was 505.2 g, and the medium particle size thereof was 352 μm. The obtained polymer particles were subjected to surface cross-linking to obtain water-absorbent resin particles.

30 g of surface-crosslinked polymer particles were placed in a round-bottomed cylindrical separable flask having an inner diameter of 11 cm equipped with a fluororesin-made anchor-shaped stirring blade. While stirring the polymer particles in the separable flask at 300 rpm, a surface cross-linking agent aqueous solution, which is a mixture of 0.75 g (8.517 mmol) of ethylene carbonate as a surface cross-linking agent and 0.75 g of water, is passed therethrough. Dropped with a tool pipette. Then, the separable flask was immersed in an oil bath set at 200 ° C., and the reaction mixture was heated for 40 minutes with stirring to proceed the surface cross-linking reaction with ethylene carbonate.

After the classification and silica addition reaction mixture was cooled to room temperature, the polymer particles were passed through a sieve having an opening of 850 μm to obtain polymer particles. Amorphous silica (Oriental Silicas Corporation, Toxile NP-S) in an amount of 0.1% by mass based on the mass of the polymer particles is mixed with the polymer particles to obtain water-absorbent resin particles containing the amorphous silica. It was.

(Example 2)
Water-absorbent resin particles were obtained in the same manner as in Example 1 except that the aqueous surface cross-linking agent was changed to a mixture of 0.30 g (3.407 mmol) of ethylene carbonate and 0.30 g of water.

(Example 3)
Water-absorbent resin particles were obtained in the same manner as in Example 1 except that the aqueous surface cross-linking agent was changed to a mixture of 0.45 g (5.110 mmol) of ethylene carbonate and 1.80 g of water.

(Example 4)
Water-absorbent resin particles were obtained in the same manner as in Example 1 except that the aqueous surface cross-linking agent was changed to a mixture of 0.30 g (3.407 mmol) of ethylene carbonate and 1.20 g of water.

(Example 5)
Water-absorbent resin particles were obtained in the same manner as in Example 1 except that the aqueous surface cross-linking agent was changed to a mixture of 0.21 g (2.385 mmol) of ethylene carbonate and 1.89 g of water.

(Example 6)
Water-absorbent resin particles were obtained in the same manner as in Example 1 except that the aqueous surface cross-linking agent was changed to a mixture of 0.30 g (3.407 mmol) of ethylene carbonate and 2.70 g of water.

(Example 7)
Water-absorbent resin particles were obtained in the same manner as in Example 1 except that the aqueous surface cross-linking agent was changed to a mixture of 0.18 g (2.044 mmol) of ethylene carbonate and 3.42 g of water.

(Example 8)
Water-absorbent resin particles were obtained in the same manner as in Example 1 except that the aqueous surface cross-linking agent was changed to a mixture of 0.15 g (1.703 mmol) of ethylene carbonate and 2.85 g of water.

(Comparative Example 1)
Water-absorbent resin particles were obtained in the same manner as in Example 1 except that the aqueous surface cross-linking agent was changed to a mixture of 0.15 g (1.703 mmol) of ethylene carbonate and 7.35 g of water.

(Comparative Example 2)
Water-absorbent resin particles were obtained in the same manner as in Example 1 except that the aqueous surface cross-linking agent was changed to a mixture of 0.12 g (1.363 mmol) of ethylene carbonate and 5.88 g of water.

(Comparative Example 3)
A hydrogel-like polymer was obtained by the same first-stage and second-stage polymerization reactions as in Example 1 except that the temperature was changed to 31 ° C. when the entire amount of the second-stage aqueous solution was added. It was. To the obtained hydrogel polymer, 0.589 g of a 45% by mass diethylenetriamine-5 sodium acetate aqueous solution was added under stirring. Then, the separable flask was immersed in an oil bath set at 125 ° C., and 275.8 g of water was extracted from the system by azeotropic distillation of n-heptane and water. The mass of the polymer particles containing water in the separable flask was 257.2 g.

Subsequently, 4.42 g (0.507 mmol) of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added to the separable flask as a surface cross-linking agent. Surface cross-linking with ethylene glycol diglycidyl ether was promoted by holding the reaction mixture in the separable flask at 83 ° C. for 2 hours.

After surface cross-linking, n-heptane was evaporated by heating at 125 ° C. to obtain a dried product of surface-cross-linked polymer particles. The polymer particles are passed through a sieve having an opening of 850 μm, and 0.1% by mass of amorphous silica (Oriental Silicas Corporation, Toxile NP-S) with respect to the mass of the polymer particles is mixed with the polymer particles. , 233.0 g of water-absorbent resin particles containing amorphous silica were obtained. The medium particle size of the water-absorbent resin particles was 128 μm.

2. Surface cross-linking X, Y
1.00 g of polymer particle powder to be subjected to surface cross-linking is placed in an aluminum foil case having a constant amount (W1 (g)) in advance, and the total mass W2 (g) of the aluminum foil case and the polymer particles is precisely weighed. did. Subsequently, the polymer particles contained in the aluminum foil case were dried for 2 hours in a hot air dryer (manufactured by ADVANTEC, model: FV-320) in which the internal temperature was set to 105 ° C. The dried polymer particles were allowed to cool to room temperature in a desiccator. Then, the total mass W3 (g) of the aluminum foil and the dried polymer particles was measured. From the following formula, the water content of the polymer particles (water content based on the mass of the polymer particles) was calculated.
Moisture content (mass%) of polymer particles = [{(W2-W1)-(W3-W1)} / (W2-W1)] × 100

Using the calculated water content, the amount of water (g) in the polymer particles subjected to surface cross-linking in each Example or Comparative Example and the mass of the polymer particles excluding water (drying of the polymer particles). The mass, g) was determined.
Moisture content in polymer particles (g) = mass of polymer particles (g) x water content of polymer particles / 100
Dry mass of polymer particles (g) = mass of polymer particles (g) x (100-moisture content of polymer particles) / 100

X and Y were obtained by the following formula, and X × Y was further calculated. The obtained values are shown in Table 1.
X = (mass of water in reaction mixture (g)) / (mass of surface cross-linking agent in reaction mixture (g))
Y = (dry mass (g) of polymer particles in the reaction mixture) / (mass (g) of surface cross-linking agent in the reaction mixture)
Here, the mass of water in the reaction mixture was the total mass of water in the polymer particles and water in the aqueous surface cross-linking agent solution.

2. Evaluation of water-absorbent resin particles 2-1. Water absorption (saline)
500 g of physiological saline was weighed in a beaker having a capacity of 500 mL. There, 2.0 g of water-absorbent resin particles were dispersed so as not to generate mamaco while stirring at 600 rpm using a stirrer bar (8 mmφ × 30 mm, without ring). It was left in that state for 60 minutes to sufficiently swell the water-absorbent resin particles. Subsequently, the contents in the beaker were filtered using a standard sieve having a mesh size of 75 μm (mass Wa (g)). Excess water was filtered off from the swollen gel on the sieve by leaving the sieve tilted at an inclination angle of about 30 degrees with respect to the horizontal for 30 minutes. Then, the total mass Wb (g) of the sieve and the swollen gel on the sieve was measured. The amount of water absorption of physiological saline was determined by the following formula.
Water absorption of saline [g / g] = (Wb-Wa) /2.0

2-2. Static water absorption rate A
The static water absorption rate A was measured using the measuring device by the non-pressurized DW method shown in FIG. The measurement was carried out 5 times for one type of water-absorbent resin particles, and the average value of the measured values at three points excluding the minimum value and the maximum value was obtained.

The measuring device shown in FIG. 2 has a burette portion 1, a conduit 5, a measuring table 13, a nylon mesh sheet 15, a frame 11, and a clamp 3. The burette portion 1 includes a burette tube 21 on which a scale is described, a rubber stopper 23 for sealing the opening at the upper part of the burette tube 21, a cock 22 connected to the tip of the lower portion of the burette tube 21, and a lower portion of the burette tube 21. It has an air introduction pipe 25 and a cock 24 connected to the burette. The burette portion 1 is fixed by a clamp 3. The flat plate-shaped measuring table 13 has a circular through hole 13a having a diameter of 2 mm formed in the central portion thereof, and is supported by a frame 11 having a variable height. The through hole 13a of the measuring table 13 and the cock 22 of the burette portion 1 are connected by a conduit 5. The inner diameter of the conduit 5 is 6 mm.

The measurement was performed in an environment with a temperature of 25 ° C and a humidity of 60 ± 10%. First, the cock 22 and the cock 24 of the burette portion 1 were closed, and the physiological saline 50 adjusted to 25 ° C. was put into the burette tube 21 through the opening at the upper part of the burette tube 21. After sealing the opening of the burette tube 21 with the rubber stopper 23, the cock 22 and the cock 24 were opened. The inside of the conduit 5 was filled with physiological saline 50 to prevent air bubbles from entering. The height of the measuring table 13 was adjusted so that the height of the water surface of the physiological saline solution that reached the inside of the through hole 13a was the same as the height of the upper surface of the measuring table 13. After the adjustment, the height of the water surface of the physiological saline solution 50 in the burette tube 21 was read by the scale of the burette tube 21, and the position was set as the zero point (reading value at 0 seconds).

A nylon mesh sheet 15 (100 mm × 100 mm, 250 mesh, thickness about 50 μm) was laid in the vicinity of the through hole 13a on the measuring table 13, and a cylinder having an inner diameter of 30 mm and a height of 20 mm was placed in the center thereof. 1.00 g of water-absorbent resin particles 10a were uniformly sprayed in this cylinder. Then, the cylinder was carefully removed to obtain a sample in which the water-absorbent resin particles 10a were dispersed in a circle in the central portion of the nylon mesh sheet 15. Next, the nylon mesh sheet 15 on which the water-absorbent resin particles 10a were placed was quickly moved so that the center thereof was at the position of the through hole 13a so that the water-absorbent resin particles 10a did not dissipate, and the measurement was started. .. The time when the air bubbles were first introduced from the air introduction pipe 25 into the burette pipe 21 was defined as the start of water absorption (0 seconds). The time from the start of absorption until the water-absorbent resin particles 10a absorbed 25 mL of physiological saline 50 was recorded as the static water absorption rate A [seconds].

2-2. Dynamic water absorption rate B
The dynamic water absorption rate B of the water-absorbent resin particles with respect to physiological saline was measured by the following procedure based on the Vortex method. First, 50 ± 0.1 mL of physiological saline adjusted to a temperature of 25 ± 0.2 ° C. in a constant temperature water tank was weighed in a beaker having a capacity of 100 mL. Next, a vortex was generated by stirring at 600 rpm using a magnetic stirrer bar (8 mmφ × 30 mm, without ring). 2.0 ± 0.002 g of water-absorbent resin particles were added to physiological saline at one time. The time [seconds] from the addition of the water-absorbent resin particles to the time when the vortex on the liquid surface converged was measured. The measurement was performed 5 times for one type of water-absorbent resin particles, and the average value of the measured values at three points excluding the minimum value and the maximum value was recorded as the dynamic water absorption rate B of the water-absorbent resin particles.

3. 3. Preparation of absorbent articles and their evaluation 3-1. Preparation of absorbent article 40 cm x 10 cm by uniformly mixing 10.0 g of water-absorbent resin particles and 10.0 g of crushed pulp by air papermaking using a flow-type mixer (Padformer manufactured by Otec Co., Ltd.). A sheet-shaped absorber of the size of 1 was prepared. The absorber was sandwiched from above and below with two sheets of tissue paper (core wrap) having the same size as the absorber and having a basis weight of 16 g / m ² , and in that state, the whole was pressed with a load of 141 kPa for 30 seconds. A polyethylene-polypropylene air-through porous liquid permeable sheet having the same size as the absorber and having a basis weight of 22 g / m ² is placed on the upper surface of the tissue paper to form a tissue paper / absorber / tissue paper / air-through porous sheet. An evaluation absorbent article having a laminated structure of liquid permeable sheets was obtained.

3-2. Water absorption test Put 60 g of sodium chloride, 1.8 g of calcium chloride dihydrate, 3.6 g of magnesium chloride hexahydrate and an appropriate amount of distilled water in a container with a capacity of 10 L, and completely dissolve each metal salt compound in water. It was. 0.02 g of polyoxyethylene nonylphenyl ether was added to the obtained solution, and distilled water was added to adjust the total mass of the aqueous solution to 6000 g. Subsequently, it was colored with 0.15 g of Blue No. 1 to obtain a test solution (artificial urine).

FIG. 3 is a schematic diagram showing a method of a water absorption test for evaluating the permeation rate of the liquid into the curved absorber. The water absorption test was conducted in an environment with a temperature of 25 ± 2 ° C. and a humidity of 50% ± 10%. The U-shaped instrument 52 shown in FIG. 3 is a molded body made of acrylic resin having a curved surface 52a having a U-shaped cross section having an opening at the upper side. The curved surface 52a has an opening width w of 22 cm, a depth d of 18.5 cm, and a depth of 10 cm. A liquid permeable sheet 53 (polyethylene film) was placed on the curved surface 52a. The evaluation absorbent article 100'was placed on the liquid impermeable sheet 53 so that the central portion thereof was located at the deepest part of the curved surface 52a. A liquid injection cylinder 54 having a capacity of 100 mL and having an inner diameter of 3 cm was fixed to the center of the evaluation absorbent article 100'. 80 mL of the test liquid 51 was charged into the liquid charging cylinder 54 at a rate of 10 mL / sec using a dropping funnel. The time from the time when the test liquid 51 first reached the evaluation absorbent article 100'to the time when the test liquid 51 completely disappeared from the liquid charging cylinder 54 was defined as the first permeation time (seconds). After the test liquid 51 completely disappeared from the inside of the cylinder 54, the cylinder 54 was removed from the water-absorbent article 100'for evaluation. This series of operations of adding the test solution 51 was performed twice more at 10-minute intervals, for a total of three times. The total time of each permeation time for 3 injections was recorded.

As shown in Table 2, it was confirmed that the evaluation absorbent articles containing the absorbent resin particles of each example showed a short permeation time and could absorb water at a high water absorption rate even in a curved state.

1 ... Burette part, 3 ... Clamp, 5 ... Conduit, 10 ... Absorbent, 10a ... Water-absorbent resin particles, 10b ... Fiber layer, 11 ... Stand, 13 ... Measuring table, 13a ... Through hole, 15 ... Nylon mesh sheet, 20a, 20b ... core wrap, 21 ... burette tube, 22, 24 ... cock, 23 ... rubber stopper, 25 ... air introduction tube, 30 ... liquid permeable sheet, 40, 53 ... liquid permeable sheet, 51 ... test solution, 52 ... U-shaped instrument, 52a ... Curved surface, 54 ... Liquid injection cylinder, 100 ... Absorbent article.

Claims

Water-absorbent resin particles containing polymer particles surface-crosslinked by a surface-crosslinking agent.
When the static water absorption rate of the water-absorbent resin particles is A [seconds] and the dynamic water absorption rate of the water-absorbent resin particles is B [seconds], the A / B is 21 or less.
When the water-absorbent resin particles having a static water absorption rate of 1.00 g were absorbed with physiological saline by the non-pressurized DW method, the water-absorbent resin particles were physiologically 25 mL after the absorption was started. It is the time it takes to absorb the saline solution.
The dynamic water absorption rate is the water absorption rate measured by the Vortex method.
Water-absorbent resin particles.
The water-absorbent resin particle according to claim 1, wherein the polymer particles contain a poly (meth) acrylic acid-based polymer having at least one of (meth) acrylic acid or a salt thereof as a monomer unit.
The water-absorbent resin particles according to claim 1 or 2, wherein the surface cross-linking agent contains an alkylene carbonate compound.
An absorbent article comprising an absorber containing the water-absorbent resin particles according to any one of claims 1 to 3.
A step of surface cross-linking the polymer particles by heating a reaction mixture containing the polymer particles and an aqueous solution of a surface cross-linking agent containing water and a surface cross-linking agent is provided.
X and Y are the following formulas:
X = (mass of water in the reaction mixture) / (mass of the surface cross-linking agent in the reaction mixture)
Y = (dry mass of the polymer particles in the reaction mixture) / (mass of the surface cross-linking agent in the reaction mixture)
X × Y is 11000 or less when it is a value calculated by
A method for producing water-absorbent resin particles.
The method according to claim 5, wherein Y is 200 or less.
The fifth or six claim, wherein the polymer particles containing 20% by mass or less of water based on the mass of the polymer particles are mixed with the surface cross-linking agent aqueous solution to form the reaction mixture. Method.
The invention according to any one of claims 5 to 7, wherein the polymer particles contain a poly (meth) acrylic acid-based polymer having at least one of (meth) acrylic acid or a salt thereof as a monomer unit. the method of.
The method according to any one of claims 5 to 8, wherein the surface cross-linking agent contains an alkylene carbonate compound.