JP2024027100A - water absorbent resin particles - Google Patents

Abstract

An object of the present invention is to provide water-absorbing resin particles that can provide an absorbent article with excellent surface drying properties after water absorption and less unevenness in surface drying properties depending on location. [Solution] A crosslinked polymer (A) whose surface has a structure crosslinked with a surface crosslinking agent (C) containing a polyvalent metal salt (c1) and a polyvalent glycidyl compound (c2), the following (1) ) to (3). (1) Weight average particle diameter is 250 to 600 μm (2) Absorption rate (seconds) by Vortex method is 30 to 70 seconds (3) Absorption amount after 1 minute by Demand Wettability method is 3 to 15 ml/g [Selection diagram] Figure 1

Description

The present invention relates to water-absorbing resin particles.

BACKGROUND ART Absorbent articles such as paper diapers, sanitary napkins, and incontinence pads use water-absorbing resin particles whose main raw materials are hydrophilic fibers such as pulp and acrylic acid (salt) as absorbents. In recent years, consumers have tended to seek greater comfort, and there is an increasing demand for absorbent articles whose surfaces do not become damp when water is absorbed (hereinafter also referred to as surface dryness).

In recent years, from the viewpoint of improving QOL and sustainability, the demand for absorbent articles has shifted to lighter and thinner ones, and as a result, there has been a desire to reduce the amount of hydrophilic fibers used. Therefore, water-absorbing resin particles have come to play the roles of high initial absorption rate and liquid diffusivity, which have traditionally been played by hydrophilic fibers. In addition, in order to improve the surface dryness of the absorbent body, it is strongly desired that the water-absorbing resin particles not only have a high water-absorbing speed but also have a fast liquid withdrawal rate from the surface nonwoven fabric used in absorbent articles. (For example, cited document 1).

International Publication No. 2020/137241

However, conventional absorbent articles using water-absorbing resin particles not only lack surface dryness after water absorption, but also have large variations in surface dryness depending on location.

An object of the present invention is to provide water-absorbing resin particles that have excellent surface drying properties after water absorption and can provide absorbent articles with less unevenness in surface drying properties depending on location.

The present invention
One or more monomers (A1) selected from the group consisting of a water-soluble unsaturated monocarboxylic acid (a1) and its salt, and a monomer (a2) that becomes the water-soluble unsaturated monocarboxylic acid (a1) upon hydrolysis; , a water-soluble unsaturated dicarboxylic acid (a3) and its salt, and one or more monomers (A2) selected from the group consisting of a monomer (a4) that becomes the water-soluble unsaturated dicarboxylic acid (a3) upon hydrolysis; A crosslinked polymer having a structure having an internal crosslinking agent (b) as a structural unit and whose surface is crosslinked with a surface crosslinking agent (C) containing a polyvalent metal salt (c1) and a polyvalent glycidyl compound (c2). These are water-absorbing resin particles containing aggregate (A) and satisfying the following (1) to (3).
(1) Weight average particle diameter is 250 to 600 μm
(2) Absorption rate (seconds) by Vortex method is 30 to 70 seconds (3) Absorption amount after 1 minute by Demand Wettability method is 3 to 15 ml/g

According to the water-absorbing resin particles of the present invention, it is possible to obtain an absorbent article that has excellent surface drying properties after water absorption and less unevenness in surface drying properties depending on location.

1 is a diagram schematically showing an apparatus for measuring absorption amount by a demand wettability method.

<Water-absorbing resin particles>
The water-absorbing resin particles of this embodiment are
One or more monomers (A1) selected from the group consisting of a water-soluble unsaturated monocarboxylic acid (a1) and its salt, and a monomer (a2) that becomes the water-soluble unsaturated monocarboxylic acid (a1) upon hydrolysis; , a water-soluble unsaturated dicarboxylic acid (a3) and its salt, and one or more monomers (A2) selected from the group consisting of a monomer (a4) that becomes the water-soluble unsaturated dicarboxylic acid (a3) upon hydrolysis; A crosslinked polymer having a structure having an internal crosslinking agent (b) as a structural unit and whose surface is crosslinked with a surface crosslinking agent (C) containing a polyvalent metal salt (c1) and a polyvalent glycidyl compound (c2). Contains coalescence (A) and satisfies the following (1) to (3).
(1) Weight average particle diameter is 250 to 600 μm
(2) Absorption rate (seconds) by Vortex method is 30 to 70 seconds (3) Absorption amount after 1 minute by Demand Wettability method is 3 to 15 ml/g

[Crosslinked polymer (A)]
[Monomer (A1)]
(Water-soluble unsaturated monocarboxylic acid (a1) and its salt)
The water-soluble unsaturated monocarboxylic acid (a1) can be used without particular limitation as long as it is a water-soluble unsaturated monocarboxylic acid. The water-soluble unsaturated monocarboxylic acid (a1) is preferably at least one selected from the group consisting of acrylic acid, methacrylic acid, and crotonic acid from the viewpoint of water absorption performance when crosslinked and ease of availability. , acrylic acid, and methacrylic acid are more preferred.

Examples of the salts of the water-soluble unsaturated monocarboxylic acid (a1) include alkali metal (lithium, sodium, potassium, etc.) salts, alkaline earth metal (magnesium, calcium, etc.) salts, and ammonium (NH ₄ ) salts. . Among these salts, from the viewpoint of absorption performance and the like, alkali metal salts and ammonium salts are preferred, alkali metal salts are more preferred, and sodium salts are particularly preferred.

(Monomer (a2))
The monomer (a2) which becomes the water-soluble unsaturated monocarboxylic acid (a1) by hydrolysis can be used together with or instead of the water-soluble unsaturated monocarboxylic acid (a1). The monomer (a2) is not particularly limited, and examples include monomers having one hydrolyzable substituent that becomes a carboxy group upon hydrolysis. The hydrolyzable substituent includes a group containing an acid anhydride (1,3-oxo-1-oxapropylene group, -COO-CO-), a group containing an ester bond (alkyloxycarbonyl, vinyloxycarbonyl, allyl), and a group containing an ester bond (alkyloxycarbonyl, vinyloxycarbonyl, allyl). Examples include oxycarbonyl or propenyloxycarbonyl, -COOR) and cyano group. Note that R is an alkyl group having 1 to 3 carbon atoms (methyl, ethyl, and propyl), vinyl, allyl, and propenyl.

In addition, in this specification, water-soluble means that at least 5g is dissolved in 100g of water at 25°C. Moreover, the hydrolyzability of the monomer (a2) means the property of being hydrolyzed by the action of water and, if necessary, a catalyst (acid, base, etc.) and becoming water-soluble. The monomer (a2) may be hydrolyzed during the polymerization, after the polymerization, or both, but from the viewpoint of the absorption performance of the resulting water-absorbing resin particles, it is preferably after the polymerization.

[Monomer (A2)]
(Water-soluble unsaturated dicarboxylic acid (a3) and its salt)
The water-soluble unsaturated dicarboxylic acid (a3) can be used without particular limitation as long as it is a water-soluble unsaturated dicarboxylic acid. The water-soluble unsaturated dicarboxylic acid (a3) is composed of maleic acid, fumaric acid, methylenesuccinic acid, and citraconic acid from the viewpoint of reactivity with the water-soluble unsaturated monocarboxylic acid (a1) and ease of availability. One or more selected from the group is preferred, and methylene succinic acid is more preferred.

Examples of the salt of the water-soluble unsaturated dicarboxylic acid (a3) include alkali metal (lithium, sodium, potassium, etc.) salts, alkaline earth metal (magnesium, calcium, etc.) salts, and ammonium (NH ₄ ) salts. Among these salts, from the viewpoint of absorption performance and the like, alkali metal salts and ammonium salts are preferred, alkali metal salts are more preferred, and sodium salts are particularly preferred.

(Monomer (a4))
A monomer (a4) that becomes the water-soluble unsaturated dicarboxylic acid (a3) by hydrolysis can be used together with or instead of the water-soluble unsaturated dicarboxylic acid (a3). The monomer (a4) is not particularly limited, and examples include monomers having at least one of the hydrolyzable substituents.

The monomer (a4) may be hydrolyzed during the polymerization, after the polymerization, or both, but from the viewpoint of the absorption performance of the resulting water-absorbing resin particles, it is preferably after the polymerization.

At least one of the monomer (A1) and the monomer (A2) preferably has ^{a 14} C/C of 1.2×10 ⁻¹² to 1.0×10 ⁻¹⁶ as measured by carbon radiocarbon dating. is preferably 1.5×10 ⁻¹² to 1.2×10 ⁻¹⁴ . Specifically, the radiocarbon age of carbon can be determined by measuring the concentration of carbon-14 in the sample and calculating backward using the content ratio of carbon-14 in the atmosphere (107pMC (percent modern carbon)) as an index. The proportion of carbon-14 among the included carbons can be determined. The sample (water-absorbing resin particles) is made by converting the constituent carbon into _CO2 , or converting the obtained _CO2 into graphite (C), and then applying it to an accelerator mass spectrometer (AMS) using a standard material (for example, NIST in the United States). It can be determined by comparing and measuring the carbon-14 content with respect to (oxalic acid).

In the radiocarbon dating method, carbon that existed as carbon dioxide in the atmosphere is taken into plants, and radiocarbon (i.e., carbon that is present in plant-derived raw materials synthesized from the plants) Carbon-14) is measured. Since there are almost no carbon-14 atoms remaining in fossil raw materials such as petroleum, we measured the concentration of carbon-14 in the target sample and determined the content ratio of carbon-14 in the atmosphere (107 pMC (percent modern carbon)). By calculating backward using this as an index, it is possible to determine the proportion of biomass-derived carbon in the carbon contained in the sample.

Furthermore, by measuring the carbon stable isotope ratio (δ ¹³ C), it is also possible to identify the origin of the raw material. Carbon stable isotope ratio (δ ¹³ C) is the three types of isotopes of carbon atoms that exist in nature (abundance ratio ¹² C: ¹³ C: ¹⁴ C = 98.9: 1.11: 1.2 × 10 ^-12 units; %), refers to the ratio of ¹³ C to ¹² C, and the carbon stable isotope ratio is expressed as a deviation from a standard substance, and refers to the value (δ value) defined by the following formula.
δ ¹³ C(‰)=[(δ ¹³ C/δ ¹² C) _sample /( ¹³ C/ ¹² C) _PDB -1.0]×1000

Here, [( ¹³ C/ ¹² C) _sample ] represents the stable isotope ratio of the measurement sample, and [( ¹³ C/ ¹² C) _PDB ] represents the stable isotope ratio of the standard material. PDB is an abbreviation of "Pee Dee Belemnite", which refers to a fossil of a floeite made of calcium carbonate (the standard material is a fossil of a floe excavated from the PeeDee layer in South Carolina), and has ^{a 13} C/ ¹² C ratio. It is used as a standard body. Moreover, the "carbon stable isotope ratio (δ ¹³ C)" is measured by accelerator mass spectrometry (AMS method). In addition, since standard materials are rare, it is also possible to use working standards whose stable isotope ratios with respect to the standard materials are known.

At least one of the monomer (A1) and the monomer (A2) preferably has a carbon stable isotope ratio (δ ¹³ C) of -60‰ to -5‰, more preferably -50‰ to -10‰.

The ratio of the weight of the monomer (A1) to the weight of the monomer (A2) in the crosslinked polymer (A) (weight of the monomer (A1)/weight of the monomer (A2)) is the water absorption under load. From the viewpoint of performance improvement and environmental conservation, it is preferably 1/99 to 99/1, more preferably 5/95 to 99/1, even more preferably 5/95 to 90/10, and particularly preferably 30/70. ~80/20.

In addition to the monomer (A1) and the monomer (A2), other vinyl monomers (A3) copolymerizable with these may be used as the constituent units of the crosslinked polymer (A). The vinyl monomer (A3) may be used alone or in combination of two or more.

The vinyl monomer (A3) is not particularly limited, and may be a hydrophobic vinyl monomer disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553, paragraph 0025 of Japanese Patent Application Publication No. 2003-165883, and Hydrophobic vinyl monomers such as the vinyl monomers disclosed in paragraph 0058 of Publication No. 2005-75982 can be used, and specifically, for example, the following vinyl monomers (i) to (iii) can be used.
(i) Aromatic ethylenic monomers having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, and halogen substituted products of styrene such as vinylnaphthalene and dichlorostyrene.
(ii) Aliphatic ethylenic monomers having 2 to 20 carbon atoms Alkenes (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.); and alkadienes (butadiene, isoprene, etc.).
(iii) Alicyclic ethylenic monomers having 5 to 15 carbon atoms, monoethylenically unsaturated monomers (pinene, limonene, indene, etc.); and polyethylenic vinyl monomers [cyclopentadiene, bicyclopentadiene, ethylidene norbornene, etc.].

The content (mol%) of the vinyl monomer (A3) units is preferably 0 to 5 based on the total number of moles of the monomer (A1) units and the monomer (A2) units from the viewpoint of absorption performance etc. More preferably, it is 0 to 3, particularly preferably 0 to 2, particularly preferably 0 to 1.5, and from the viewpoint of absorption performance, etc., the content of the vinyl monomer (A3) unit is preferably 0 mol%. Most preferred.

[Internal crosslinking agent (b)]
The internal crosslinking agent (b) is not particularly limited and is known in the art (for example, a crosslinking agent having two or more ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 3648553, a water-soluble substituent and Crosslinking agent having at least one reactive functional group and at least one ethylenically unsaturated group, and crosslinking agent having at least two functional groups capable of reacting with a water-soluble substituent, JP 2003-165883A A crosslinking agent having two or more ethylenically unsaturated groups, a crosslinking agent having an ethylenically unsaturated group and a reactive functional group, and a crosslinking agent having two or more reactive substituents disclosed in paragraphs 0028 to 0031 of the publication Crosslinking agents, crosslinkable vinyl monomers disclosed in paragraph 0059 of JP-A No. 2005-75982 and cross-linkable vinyl monomers disclosed in paragraphs 0015 to 0016 of JP-A No. 2005-95759, etc. Can be used.

The internal crosslinking agent (b) is preferably a crosslinking agent having two or more ethylenically unsaturated groups, and from the viewpoint of reactivity with monomers and water absorption characteristics, a polyvalent (meth) having two or more ethylenically unsaturated groups. ) Allyl compounds and acrylamide compounds are more preferred, and poly(meth)allyl ethers of polyhydric alcohols such as alkylene glycol, trimethylolpropane, glycerin, pentaerythritol and sorbitol, tetraallyloxyethane, and Selected from the group consisting of polyvalent (meth)allyl compounds such as triallylisocyanurate, N,N'-methylenebisacrylamide, N,N'-methylenebismethacrylamide, and compounds represented by the following general formula (1) One or more types are more preferred. The internal crosslinking agent (b) may be used alone or in combination of two or more. From the viewpoint of reactivity, balance of water retention and absorption under load, it is more preferable to use N,N'-methylenebisacrylamide and a compound represented by the following general formula (1).

[In general formula (1), R ¹ and R ² are each independently a hydrogen atom or a methyl group. X ¹ is an n-valent organic group having an aliphatic group having 1 or more carbon atoms and may contain a nitrogen atom, an oxygen atom, or a sulfur atom, and the aliphatic group may be linear or branched. may have. n is an integer from 2 to 6. ]

Examples of commercially available compounds represented by the general formula (1) include methylene bisacrylamide and FOM-03006, FOM-03007, FOM-03008, and FOM-03009 manufactured by Fuji Film Corporation.

The content (mol%) of the internal crosslinking agent (b) in the crosslinked polymer (A) is determined by the total number of moles of the monomer (A1) units and the monomer (A2) units, etc. from the viewpoint of absorption performance, etc. When using the vinyl monomer (A3), it is preferably 0.001 to 5, more preferably 0.005 to 3, particularly preferably 0.005 to 5, based on the total number of moles of (A1) to (A3). It is 1.

[Surface crosslinking agent (C)]
The water-absorbing resin particles have a structure in which the surface of the crosslinked polymer (A) is crosslinked with a surface crosslinking agent (C) containing a polyvalent metal salt (c1) and a polyvalent glycidyl compound (c2). By crosslinking the surface of the crosslinked polymer (A) with the surface crosslinking agent (C), the gel strength of the water absorbent resin particles can be improved, and by suppressing blocking, homogeneous water absorbent resin particles can be obtained. The resulting water-absorbing resin particles can be used to obtain absorbent articles with less unevenness in surface dryness depending on location.

Examples of the polyvalent metal salt (c1) include inorganic acid salts of zirconium, aluminum, or titanium, and examples of the inorganic acid forming the polyvalent metal salt (c1) include sulfuric acid, hydrochloric acid, nitric acid, and hydrobromic acid. , hydroiodic acid and phosphoric acid. Examples of inorganic acid salts of zirconium include zirconium sulfate and zirconium chloride, and examples of inorganic acid salts of aluminum include aluminum sulfate, aluminum chloride, aluminum nitrate, ammonium aluminum sulfate, potassium aluminum sulfate, and sodium aluminum sulfate. Examples of inorganic acid salts of titanium include titanium sulfate, titanium chloride, and titanium nitrate. Among these, from the viewpoint of availability and solubility, inorganic acid salts of aluminum and inorganic acid salts of titanium are preferred, and aluminum sulfate, aluminum chloride, potassium aluminum sulfate, and sodium aluminum sulfate are more preferred, and particularly preferred are aluminum sulfate, aluminum chloride, potassium aluminum sulfate, and sodium aluminum sulfate. are aluminum sulfate and sodium aluminum sulfate, most preferably sodium aluminum sulfate.

By using the polyvalent metal salt (c1) and the polyvalent glycidyl compound (c2), at least a part of the surface of the crosslinked polymer (A) is mixed with the polyvalent metal salt (c1) and the polyvalent glycidyl compound (c2). The water-absorbent resin particles are coated with glycidyl compound (c2), and the breakage resistance and blocking resistance of the water-absorbent resin particles are improved, resulting in homogeneous water-absorbent resin particles with less unevenness in surface dryness depending on location. This results in water-absorbing resin particles that can be used to obtain sexual products. Each of the polyvalent metal salt (c1) and the polyvalent glycidyl compound (c2) may be used alone, or two or more thereof may be used in combination.

The amount (wt%) of the polyvalent metal salt (c1) is preferably 0.05 to 5 based on the weight of the solid content of the water-absorbing resin particles from the viewpoint of breakage resistance and blocking resistance. More preferably 0.1 to 3, particularly preferably 0.2 to 2. In this specification, the solid content of water-absorbing resin particles is determined by heating and drying 5 g of water-absorbing resin particles at 150°C for 15 minutes using an infrared moisture meter (manufactured by Kett Scientific Research Institute, FD-230). It can be determined using the following formula using the water content measured as follows.
Solid weight of water-absorbing resin particles (g) = weight of water-absorbing resin particles (g) x {100-water content (%)}/100

Examples of the polyglycidyl compound (c2) include polyglycidyl ethers of polyhydric alcohols such as ethylene glycol diglycidyl ether, glycerin triglycidyl ether, and sorbitol polyglycidyl ether, and the valence of the polyhydric alcohol depends on the absorption performance. From the viewpoint of absorption performance, it is divalent to octavalent, more preferably divalent to trivalent, and the number of glycidyl groups per molecule is preferably from 2 to 10, more preferably from 2 to 4 from the viewpoint of absorption performance. The polyvalent glycidyl compound (c2) may be used alone or in combination of two or more.

The amount (wt%) of the polyvalent glycidyl compound (c2) used is preferably 0.001 to 3 based on the weight of the solid content of the water-absorbing resin particles from the viewpoint of breakage resistance and blocking resistance. More preferably 0.005 to 2, particularly preferably 0.01 to 1, and most preferably 0.01 to 0.50.

The surface crosslinking agent (C) may contain a known surface crosslinking agent other than the polyvalent metal salt (c1) and the polyvalent glycidyl compound (c2). Known surface crosslinking agents include polyvalent amines, polyaziridine compounds, and polyisocyanate compounds described in JP-A-59-189103, and JP-A-58-180233 and JP-A-61-16903. Polyhydric alcohols described in Japanese Patent Application Laid-open Nos. 61-211305 and 61-252212, alkylene carbonates described in Japanese Patent Application Publication No. 5-508425, and JP-A No. 11-240959. Organic surface crosslinking agents such as polyvalent oxazoline compounds described in the above publication can be used.

The water-absorbing resin particles may contain other components to some extent as long as their performance is not impaired. Other examples of the other components include anionic water-insoluble silicon-containing fine particles (D) (described later), polyhydric alcohol (E) (described later), preservatives, fungicides, ultraviolet absorbers, antioxidants, Examples include coloring agents, fragrances, deodorants, liquid permeability improvers, and organic fibrous materials. The amount thereof is preferably 5% by weight or less based on the weight of the water-absorbing resin particles.

[Anionic water-insoluble silicon-containing fine particles (D)]
The water-absorbing resin particles may contain anionic water-insoluble silicon-containing fine particles (D) (hereinafter also simply referred to as silicon-containing fine particles (D)). By mixing the silicon-containing fine particles (D) with the water-absorbing resin particles, the moisture absorption blocking resistance is improved when fine powder is generated, and the incidence of defects during the absorbent article production process is reduced, which is preferable.

Examples of the silicon-containing fine particles (D) include colloidal silica, fumed silica, polysilicic acid, polyaluminum silicate, smectite, vermiculite, and montmorillonite. Among these silicon-containing fine particles (D), colloidal silica and fumed silica are preferred from the viewpoint of uniformity of adhesion to the surface of water-absorbing resin particles and moisture absorption blocking resistance. The silicon-containing fine particles (D) may be used alone or in combination of two or more.

The silicon-containing fine particles (D) are preferably spherical or amorphous particles with an average primary particle size of 1 to 100 nm from the viewpoint of moisture absorption and blocking resistance, and spherical or amorphous particles with an average primary particle size of 10 to 25 nm. More preferably, they are particles.

The content (wt%) of the silicon-containing fine particles (D) in the solid content of the water-absorbing resin particles is preferably 0.10 to 0.80, more preferably 0.20 from the viewpoint of moisture absorption blocking resistance. -0.60, particularly preferably 0.25-0.40.

[Polyhydric alcohol (E)]
The water-absorbing resin particles may contain a polyhydric alcohol (E) having 4 or less carbon atoms. Containing the polyhydric alcohol (E) in the water-absorbing resin particles has the advantage of contributing to prevention of breakage of the water-absorbing resin particles and stability against changes over time.

Examples of the polyhydric alcohol (E) include ethylene glycol, propylene glycol, 1,3-propanediol, glycerin, and 1,4-butanediol. Among these polyhydric alcohols (E), propylene glycol is preferred from the viewpoint of absorption characteristics and safety when remaining. The polyhydric alcohol (E) may be used alone or in combination of two or more.

The content (wt%) of the polyhydric alcohol (E) in the solid content of the water-absorbing resin particles is not particularly limited as it can be varied depending on crosslinking conditions, target performance, etc. From the viewpoint of absorption performance of the resin particles, it is preferably 5 or less, more preferably 3.0 or less, particularly preferably 1.5 or less.

From the viewpoint of water absorption performance, the water absorbent resin particles preferably contain at least one typical element selected from the group consisting of iodine, tellurium, antimony, and bismuth as the other component. When the water-absorbing resin particles contain the typical element, the content (wt%) of the typical element in the solid content of the water-absorbing resin particles is preferably 0.0005 to 0.1 from the viewpoint of water absorption performance. , 0.001 to 0.05 are more preferable.

The water-absorbing resin particles have a weight average particle diameter of 250 to 600 μm, preferably 300 to 500 μm, and more preferably 300 to 450 μm, from the viewpoint of water absorption performance and the like. In addition, in this specification, the weight average particle diameter is measured by the method described in Examples.

There is no particular limitation on the shape of the water-absorbing resin composition, and examples thereof include particles such as amorphous crushed particles, scale-shaped particles, pearl-shaped particles, and rice grain-shaped particles. Among these, amorphous crushed particles are preferable from the viewpoint of good entanglement with fibrous materials for use in disposable diapers, etc., and no fear of falling off from the fibrous materials.

The water-absorbing resin particles have an absorption rate (seconds) measured by the Vortex method of 30 to 70 seconds, preferably 30 to 55 seconds, and more preferably 30 to 45 seconds, from the viewpoint of surface drying properties of the absorbent body. In this specification, the absorption rate (seconds) by the Vortex method is measured by the method described in Examples.

The water-absorbing resin particles have an absorption amount of 3 to 15 ml/g after 1 minute in the Demand Wettability method, preferably 10 to 15 ml/g, from the viewpoint of surface drying properties of the absorbent body. In this specification, the amount of absorption after 1 minute in the Demand Wettability method is measured by the method described in Examples.

<Method for producing water-absorbing resin particles>
The method for producing water absorbent resin particles of the present embodiment is the method for producing the water absorbent resin particles, comprising:
a polymerization step of obtaining a hydrogel containing the crosslinked polymer (A);
a drying step of drying the hydrogel;
and a surface crosslinking step of surface crosslinking the crosslinked polymer (A) with the surface crosslinking agent (C) diluted with the polyhydric alcohol (E).

According to the method for producing water-absorbing resin particles of the present embodiment, it is possible to produce water-absorbing resin particles that can produce absorbent articles that have excellent surface drying properties after water absorption and less unevenness in surface drying properties depending on location. can.

[Polymerization process]
In the polymerization step, a monomer composition containing at least the monomer (A1), the monomer (A2), and the internal crosslinking agent (b) is polymerized to obtain a hydrogel containing the crosslinked polymer (A). It is a process. The polymerization step is preferably a step of polymerizing the monomer composition in the presence of a chelating agent (F) to obtain a hydrogel containing the crosslinked polymer (A). Examples of the polymerization method of the monomer composition include known solution polymerization and known reverse phase suspension polymerization.

The monomer (A1) and the monomer (A2) in the polymerization step are preferably neutralized, and the degree of neutralization (number of moles) relative to the total of the monomer (A1) and monomer (A2) during polymerization is: It is preferably 1 to 80%, more preferably 1 to 50%, particularly preferably 5 to 40%. Within this range, the obtained polymer has a high molecular weight, so water absorption performance under load is good, and the miscibility of the monomer (A1) and the monomer (A2) is improved. , good handling. Here, the degree of neutralization is (number of moles of added base)/(number of moles of carboxylic acid in the monomer), and since monomer (A1) is monocarboxylic acid and monomer (A2) is dicarboxylic acid, neutralization is It is a value calculated by: degree of compatibility (%) = number of moles of added base/(number of moles of monomer (A1) + number of moles of monomer (A2) x 2).

As the base for neutralization, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal carbonates such as sodium carbonate, sodium bicarbonate, and potassium carbonate can usually be used.

Among the methods for polymerizing the monomer composition, the solution polymerization method is preferred, and the aqueous solution polymerization method is particularly preferred because it does not require the use of organic solvents and is advantageous in terms of production cost. The aqueous adiabatic polymerization method is most preferable because water-absorbing resin particles with a large amount of water and a small amount of water-soluble components can be obtained, and temperature control during polymerization is not necessary.

When the monomer composition is polymerized by aqueous solution polymerization, a mixed solvent containing water and an organic solvent can be used, and examples of the organic solvent include methanol, ethanol, acetone, methyl ethyl ketone, N,N-dimethylformamide, Dimethyl sulfoxide and mixtures of two or more thereof are included. When the monomer composition is polymerized by aqueous solution polymerization, the amount (wt%) of the organic solvent used is preferably 40 or less, more preferably 30 or less, based on the weight of water.

When using a catalyst for polymerization, conventionally known radical polymerization catalysts can be used, such as azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid, and 2,2'-azobis(2-amidinopropane) hydrochloride]. , 2,2'-azobis(2-methylpropionamidine) dihydrochloride aqueous solution, etc.], inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [peroxide benzoyl, di-t-butyl peroxide, cumene hydroperoxide, succinic acid peroxide and di(2-ethoxyethyl) peroxydicarbonate, etc.] and redox catalysts (alkali metal sulfites or bisulfites, ammonium sulfite, and combinations of reducing agents such as ammonium bisulfite and ascorbic acid with oxidizing agents such as alkali metal persulfates, ammonium persulfates, hydrogen peroxide, and organic peroxides. These catalysts may be used alone or in combination of two or more thereof.

In addition, for the purpose of promoting the polymerization reaction, iron salts (iron (II) chloride, iron (III) chloride, iron (II) sulfate, iron (III) nitrate, iron (III) phosphate, iron (II) phosphate, and their hydrates, etc.) and copper salts ((copper(I) chloride, copper(II) chloride, copper(I) sulfate, copper(I) nitrate, and their hydrates, etc.)), etc. It may be added, and preferably contains an iron salt. The presence of iron ions is preferable because it promotes the cleavage of the peroxide used as an initiator and improves the polymerization reaction rate.

The amount (wt%) of the radical polymerization catalyst to be used is based on the total weight of monomer (A1) and monomer (A2), and (A1) to (A3) when using other vinyl monomer (A3). It is preferably from .0005 to 5, more preferably from 0.001 to 2.

At the time of polymerization, a polymerization control agent such as a chain transfer agent may be used in combination as necessary, and specific examples thereof include sodium hypophosphite, sodium phosphite, alkyl mercaptan, alkyl halide, and thiocarbonyl compounds. etc. These polymerization control agents may be used alone or in combination of two or more thereof.

The amount (wt%) of the polymerization control agent to be used is based on the total weight of monomer (A1) and monomer (A2), and (A1) to (A3) when using other vinyl monomers (A3). It is preferably from .0005 to 5, more preferably from 0.001 to 2.

When the monomer composition is polymerized in the presence of the chelating agent (F), the chelating agent (F) may be added to the monomer composition, and the monomer (A1) and the monomer It may be added to either or both of the monomers before mixing with (A2) to form a monomer composition. From the viewpoint of stability of the monomer (A2), it is preferable that the monomer (A2) and the chelating agent (F) are mixed and then mixed with the monomer (A1).

Examples of the chelating agent (F) include ethylenediamine-N,N'-disuccinic acid (EDDS), nitrilotriacetic acid (NTA), tetrasodium L-glutamic acid diacetate (GLDA4Na), and hydroxyethyliminodiacetic acid (HIDA). ), hydroxyethylethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethyliminodiacetic acid (HIDA), ethylenediaminedipropionic acid (EDDP), hydroxyiminodisuccinic acid (HIDS) , ethylenediaminetetramethylenephosphonic acid (EDTMP), triethylenetetraminehexaacetic acid (TTHA), ethylenediaminedisuccinic acid (EDDS), etc., and preferably ethylenediamine-N,N'-disuccinic acid, nitrilotriacetic acid (NTA). , L-glutamic acid diacetic acid tetrasodium (GLDA・4Na), and hydroxyethyliminodiacetic acid.

The ratio (ppm) of the added weight of the chelating agent (F) is the total weight of the monomer (A1) and the monomer (A2), or (A1) to (A3) when using other vinyl monomers (A3). is preferably 0.1 to 1000, more preferably 1 to 1000, particularly preferably 1 to 500, based on the total weight of. Within this range, the amount of iron that acts as a catalyst on the initiator in the polymerization system is appropriate, so that the strength of the gel produced is further improved.

In the polymerization step, when using the iron salt, a monomer composition containing the monomer (A1), the monomer (A2), and the internal crosslinking agent (b) is added in the presence of the chelating agent (F). It is preferable to polymerize with Iron ions lead to decomposition of the resin, inhibition of radical polymerization, and changes in the resin over time. On the other hand, if iron ions are completely inactivated during polymerization, the polymerization will not proceed and a water-absorbing resin will not be obtained. When iron ions and the chelating agent (F) coexist in the polymerization system, the chelating agent (F) binds to the iron ions and suppresses the influence of the iron ions, thereby increasing the monomer (A1) and monomer (A2). The polymerization reaction can proceed favorably.

When the chelating agent (F) is used simultaneously with an iron salt, the amount (number of moles) of the chelating agent (F) added is 1 to 300 times the number of moles of iron ions (Fe ³⁺ ) in the polymerization solution. The amount is preferably 1 to 150 times, particularly preferably 1 to 50 times. Within this range, the amount of iron that acts as a catalyst on the initiator in the polymerization system is appropriate, so that the strength of the gel produced is further improved.

The crosslinked polymer (A) is a monomer composition containing the monomer (A1), the monomer (A2), and the internal crosslinking agent (b), an organic iodine compound, an organic tellurium compound, an organic antimony compound, and an organic By polymerizing in the presence of at least one type of organic typical element compound selected from the group consisting of bismuth compounds, it is possible to improve the gel strength during water absorption, the absorption amount under load, and the gel passing rate.

The organic iodine compound, the organic tellurium compound, the organic antimony compound, and the organic bismuth compound are not limited as long as they are organic typical element compounds that act as dormant species in radical polymerization, and include those described as dormant species in WO2011/016166. Organic iodine compounds, organic tellurium compounds described in WO2004/014848, organic antimony compounds described in WO2006/001496, organic bismuth compounds described in WO2006/062255, and the like can be used. Among these, organic typical element compounds are preferred from the viewpoint of reactivity. These organic typical element compounds may be used alone or in combination of two or more.

When a suspension polymerization method or a reverse-phase suspension polymerization method is used as the polymerization method, the polymerization may be carried out in the presence of a conventionally known dispersant or surfactant, if necessary. Furthermore, in the case of reverse phase suspension polymerization, polymerization can be carried out using conventionally known hydrocarbon solvents such as xylene, n-hexane, and n-heptane.

The amount of the organic main element compound to be used is preferably determined based on the weight of the monomer (A1) and the monomer (A2) from the viewpoint of improving gel strength during water absorption, absorption amount under load, and gel passing rate. The amount is 0.0005 to 0.1% by weight, more preferably 0.005 to 0.05% by weight.

When a suspension polymerization method or a reverse-phase suspension polymerization method is used as the polymerization method, the polymerization may be carried out in the presence of a conventionally known dispersant or surfactant, if necessary. Furthermore, in the case of reverse phase suspension polymerization, polymerization can be carried out using conventionally known hydrocarbon solvents such as xylene, n-hexane, and n-heptane.

The polymerization initiation temperature can be adjusted as appropriate depending on the type of catalyst used, but from the viewpoint of polymerization reactivity, it is preferably 0 to 100°C, more preferably 2 to 80°C, and from the viewpoint of polymerization reactivity and absorption performance. The temperature is particularly preferably 5 to 60°C.

When using a solvent (organic solvent, water, etc.) for polymerization, it is preferable to distill off the solvent after polymerization. When the solvent contains an organic solvent, the content (wt%) of the organic solvent after distillation is preferably 0 to 10, more preferably 0 to 5, particularly 0 to 5, based on the weight of the crosslinked polymer (A). Preferably it is 0-3, most preferably 0-1. Within this range, the absorption performance of the water-absorbing resin particles becomes even better.

When the solvent contains water, the water content (wt%) after distillation is preferably 0 to 20, more preferably 1 to 10, particularly preferably 2 to 9, based on the weight of the crosslinked polymer (A). Most preferably it is 3-8. Within this range, the absorption performance will be even better.

The content of the organic solvent and the moisture content were determined using an infrared moisture meter [JE400 manufactured by KETT Co., Ltd.: 120±5℃, 30 minutes, atmospheric humidity before heating 50±10%RH, lamp specifications 100V, 40W. ] is determined from the weight loss of the measurement sample when heated.

A hydrogel-like material (hereinafter also referred to as hydrogel) in which the crosslinked polymer (A) contains water can be obtained by the polymerization method described above.

[Shredding process]
The method for producing water-absorbing resin particles of the present embodiment may include a shredding step of shredding the hydrogel, if necessary. The size of the gel after shredding (longest diameter) is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, particularly preferably 1 mm to 1 cm. Within this range, the drying properties in the drying step will be even better.

Shredding can be performed by a known method, using a shredding device (for example, a Bex mill, a rubber chopper, a Pharma mill, a mincer, an impact crusher, a roll crusher), or the like. Further, if necessary, the hydrogel polymer obtained as described above can be mixed with an alkali to neutralize it. The degree of neutralization of acid groups is preferably 50 to 80 mol%. If the degree of neutralization is less than 50 mol%, the resulting hydrogel polymer will have high stickiness, and workability during production and use may deteriorate. Furthermore, the water retention amount of the obtained water-absorbing resin particles may decrease. On the other hand, if the degree of neutralization exceeds 80%, the pH of the resulting resin may become high and there may be concerns about safety for human skin.

In addition, neutralization may be carried out at any stage after the polymerization of the crosslinked polymer (A) in the production of the water-absorbing resin particles, and for example, a method such as neutralization in the state of a hydrogel is preferable. Illustrated as an example.

As the base for neutralization, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal carbonates such as sodium carbonate, sodium bicarbonate, and potassium carbonate can usually be used.

[Drying process]
The method for producing water-absorbing resin particles of the present embodiment includes a drying step of drying the hydrogel to obtain a water-absorbing resin composition in which the solvent (including water) in the hydrogel is distilled off.

In the drying step, methods for distilling off the solvent in the hydrogel include a method of distilling off (drying) with hot air at a temperature of 80 to 230°C, a thin film drying method using a drum dryer heated to 100 to 230°C, etc. , (heat) vacuum drying method, freeze drying method, infrared ray drying method, decantation, filtration, etc. can be applied.

[Crushing process]
The method for producing water-absorbing resin particles of the present embodiment includes a pulverizing step of pulverizing the water-absorbing resin composition obtained in the drying step to obtain water-absorbing resin particles containing the crosslinked polymer (A). It's okay.

In the pulverizing step, there is no particular limitation on the method of pulverizing the water-absorbing resin composition containing the crosslinked polymer (A), and a pulverizing device (for example, a hammer-type pulverizer, an impact-type pulverizer, a roll-type pulverizer) is used. Machines such as pulverizers and Schette airflow pulverizers can be used. The particle size of the obtained water-absorbing resin particles can be adjusted by sieving or the like, if necessary.

[Surface crosslinking process]
The method for producing water absorbent resin particles of the present embodiment includes a surface crosslinking step of surface crosslinking the crosslinked polymer (A) with the surface crosslinking agent (C) diluted with the polyhydric alcohol (E). The water-absorbing resin particles obtained through the surface crosslinking step have a structure in which the surface of the crosslinked polymer (A) is crosslinked with the surface crosslinking agent (C). When surface crosslinking the crosslinked polymer (A) with the surface crosslinking agent (C), uniformity of surface crosslinking can be achieved by diluting the surface crosslinking agent (C) with the polyhydric alcohol (E). water-absorbing resin particles that improve the breakage resistance and blocking resistance of the water-absorbing resin particles, yielding homogeneous water-absorbing resin particles, and producing absorbent articles with less unevenness in surface dryness depending on location. becomes.

The surface crosslinking of the crosslinked polymer (A) can be carried out by mixing the crosslinked polymer (A) and the surface crosslinking agent (C) diluted with the polyhydric alcohol (E) and heating the mixture. can. The method for mixing the crosslinked polymer (A), the surface crosslinking agent (C), and the polyhydric alcohol (E) includes a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, and a nauta. Mold mixer, double-arm kneader, fluid mixer, V-type mixer, mincing mixer, ribbon mixer, fluid mixer, air flow mixer, rotating disc mixer, conical blender, roll mixer, etc. A method of homogeneously mixing the crosslinked polymer (A), the surface crosslinking agent (C), and the polyhydric alcohol (E) using a mixing device mentioned above may be mentioned.

The temperature at which the crosslinked polymer (A) and the surface crosslinking agent (C) diluted with the polyhydric alcohol (E) are mixed is not particularly limited, but is preferably 10 to 150°C, more preferably 20°C. -100°C, particularly preferably 25-80°C.

After mixing the crosslinked polymer (A) and the surface crosslinking agent (C) diluted with the polyhydric alcohol (E), heat treatment is performed. The heating temperature is preferably 100 to 180°C, more preferably 110 to 170°C, particularly preferably 120 to 160°C from the viewpoint of breakage resistance of the water absorbent resin particles. Heating at a temperature of 180° C. or lower allows indirect heating using steam and is advantageous in terms of equipment, whereas heating at a temperature of less than 100° C. may result in poor absorption performance. Further, the heating time can be appropriately set depending on the heating temperature, but from the viewpoint of absorption performance, it is preferably 5 to 60 minutes, more preferably 10 to 40 minutes.

After the surface of the crosslinked polymer (A) is crosslinked with the surface crosslinking agent (C), it is sieved if necessary to adjust the particle size.

[Silicon-containing fine particles (D) addition step]
The method for producing water-absorbing resin particles of the present embodiment may include a silicon-containing fine particle (D) addition step of adding the silicon-containing fine particle (D). The timing of adding the silicon-containing fine particles (D) is not particularly limited, but the silicon-containing fine particles (D) present on the surface can suppress coalescence of fine powder generated from water-absorbing resin particles. Therefore, it is preferable to add it in a step after the polymerization step, and it is particularly preferable to add it in a step after the surface crosslinking step.

The method for mixing the silicon-containing fine particles (D) includes a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a flexomix, a Nauta mixer, a double-arm kneader, a fluid mixer, Examples include a method of uniformly mixing using known mixing devices such as a V-type mixer, a mince mixer, a ribbon-type mixer, a fluidized mixer, an air-flow mixer, a rotating disc mixer, a conical blender, and a roll mixer. It will be done.

When mixing the silicon-containing fine particles (D), it is preferable to add the silicon-containing fine particles (D) to the water-absorbing resin particles while stirring them. The silicon-containing fine particles (D) may be added simultaneously with water and/or a solvent. When the silicon-containing fine particles (D) are added simultaneously with water and/or a solvent, a dispersion of the silicon-containing fine particles (D) in water and/or a solvent can be added, and from the viewpoint of workability etc. It is preferable to add a dispersion liquid, and it is more preferable to add an aqueous dispersion liquid. When adding a dispersion liquid, it is preferably added by spraying or dropping.

When using the dispersion of the silicon-containing fine particles (D), the content of the silicon-containing fine particles (D) contained in the dispersion is preferably 5 to 70% by weight, more preferably 5% to 70% by weight based on the total weight of the dispersion. is 10 to 60% by weight.

As the dispersion of the silicon-containing fine particles (D), a dispersion obtained by directly granulating raw materials by reacting them in water and/or a solvent by a conventionally known method may be used, or a dispersion obtained by directly granulating the fine particles in water and/or a solvent may be used. Alternatively, a dispersion obtained by mechanically dispersing it in a solvent may be used.

From the viewpoint of stability of the dispersion, it is preferable to use a dispersion obtained by reacting raw materials in water and/or a solvent and directly granulating them. The dispersion of the silicon-containing fine particles (D) can be obtained commercially as an aqueous colloid liquid (sol).

Note that the dispersion liquid may contain additives such as arbitrary stabilizers as necessary. Examples of stabilizers include commercially available surfactants and dispersants, commercially available acid compounds [phosphoric acid (salts), boric acid (salts), alkali metals (salts) and alkaline earth metals (salts), hydroxycarbonate] acids (salts), fatty acids (salts), etc.].

The temperature at which the water-absorbing resin particles and the silicon-containing fine particles (D) are mixed is preferably 10 to 150°C, more preferably 20 to 100°C, particularly preferably 25 to 80°C, from the viewpoint of absorption performance. be. Further, the heating time can be appropriately set depending on the heating temperature, but from the viewpoint of economic efficiency, it is preferably 5 to 60 minutes, and more preferably 10 to 40 minutes.

<Absorber>
An absorbent body can be obtained using the water-absorbing resin particles. As the absorbent body, the water-absorbing resin particles may be used alone or together with other materials to form an absorbent body. Examples of the other materials include fibrous materials. The structure and manufacturing method of the absorber when used with a fibrous material are the same as those known (Japanese Patent Laid-Open Nos. 2003-225565, 2006-131767, and 2005-097569, etc.). be.

Preferred as the fibrous material are cellulose fibers, organic synthetic fibers, and mixtures of cellulose fibers and organic synthetic fibers.

Examples of cellulose fibers include natural fibers such as fluff pulp, and cellulose chemical fibers such as viscose rayon, acetate, and cupro. The raw materials (softwood, hardwood, etc.), manufacturing method (chemical pulp, semi-chemical pulp, mechanical pulp, CTMP, etc.), bleaching method, etc. of this cellulosic natural fiber are not particularly limited.

Examples of organic synthetic fibers include polypropylene fibers, polyethylene fibers, polyamide fibers, polyacrylonitrile fibers, polyester fibers, polyvinyl alcohol fibers, polyurethane fibers, and heat-fusible composite fibers (the above-mentioned fibers with different melting points). Examples include fibers in which at least two of the above fibers are combined into a sheath-core type, eccentric type, parallel type, etc., fibers in which at least two of the above fibers are blended, and fibers in which the surface layer of the above fibers is modified.

Among these fibrous materials, preferred are cellulose natural fibers, polypropylene fibers, polyethylene fibers, polyester fibers, heat-fusible composite fibers, and mixed fibers thereof, and more preferred are Fluff pulp, heat-fusible conjugate fibers, and mixed fibers thereof are used because they have excellent shape retention properties after water absorption.

There are no particular limitations on the length and thickness of the fibrous material, and it can be suitably used as long as the length is in the range of 1 to 200 mm and the thickness is in the range of 0.1 to 100 deniers. The shape is not particularly limited as long as it is fibrous, and examples thereof include a thin cylinder, a split yarn, a staple, a filament, and a web.

When the water-absorbing resin particles are used as an absorber together with a fibrous material, the weight ratio of the water-absorbing resin particles to the fibers (weight of water-absorbing resin particles/weight of fibrous material) is 40/60 to 90/10. The ratio is preferably 70/30 to 80/20.

<Absorbent article>
An absorbent article can be obtained using the water absorbent resin particles. Specifically, the above absorber is used. Absorbent products are not only used for sanitary products such as disposable diapers and sanitary napkins, but also for absorbing various aqueous liquids in various industrial fields such as anti-condensation agents, water retention agents for agriculture and gardening, waste blood solidifying agents, and disposable body warmers. It can be applied to various uses such as a retention agent and a gelling agent. The manufacturing method of the absorbent article is the same as the known method (described in JP-A No. 2003-225565, JP-A No. 2006-131767, JP-A No. 2005-097569, etc.).

The present invention will be further explained below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Unless otherwise specified, parts are parts by weight and percentages are percentages by weight. The water-absorbing resin particles were evaluated in a room at 25±2° C. and 50±5 RH% by the following method. In addition, water-absorbing resin particles that were allowed to stand for 24 hours in a room at 25 ± 2°C and 50 ± 5 RH% after production to have a water content of 3% by weight were used for each measurement, and the 0.9% by weight used in the measurement was used for each measurement. The temperature of physiological saline was adjusted in advance to 25°C±2°C before use.

<Method for measuring water retention amount for 0.9% by weight physiological saline>
Put 1.00 g of the measurement sample into a tea bag (length 20 cm, width 10 cm) made of nylon mesh with an opening of 63 μm (JIS Z8801-1:2006), and add it to 1,000 ml of physiological saline (salt concentration 0.9%). After being immersed in water for 1 hour without stirring, the sample was taken out and hung for 15 minutes to drain. Thereafter, each tea bag was placed in a centrifuge, centrifuged at 150 G for 90 seconds to remove excess physiological saline, the weight (h1) including the tea bag was measured, and the water retention amount was determined from the following formula. Note that the temperature of the physiological saline used and the measurement atmosphere was 25°C±2°C.
Water retention amount (g/g) = (h1) - (h2)
Note that (h2) is the weight of the tea bag measured in the same manner as above in the case where there is no measurement sample.

<Method for measuring absorption under load for 0.9% by weight physiological saline>
Measurement using a standard sieve in a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) with a nylon mesh with an opening of 63 μm (JIS Z8801-1:2006) attached to the bottom, and sieved into a range of 250 to 500 μm. Weigh 0.16 g of the sample, arrange the cylindrical plastic tube vertically on the nylon net so that the sample has an almost uniform thickness, and place a weight (weight: 310.6 g, external) on the sample. Diameter: 24.5mm). After weighing the entire weight (M1) of this cylindrical plastic tube, place the cylindrical plastic tube containing the measurement sample and weight in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline (salt concentration 0.9%). Stand the tube vertically, immerse it with the nylon mesh side facing down, and let it stand for 60 minutes. After 60 minutes, remove the cylindrical plastic tube from the Petri dish, tilt it diagonally, collect the water that has adhered to the bottom in one place, and let it drip as water droplets to remove excess water. The weight (M2) of the entire cylindrical plastic tube was measured, and the amount of absorption under load was determined from the following equation. Note that the temperature of the physiological saline used and the measurement atmosphere was 25°C±2°C.
Absorption amount under load (g/g) = {(M2)-(M1)}/0.16

<Method for measuring weight average particle diameter>
Using a low-tap test sieve shaker and a standard sieve (JIS Z8801-1:2006), the method described in Perry's Chemical Engineers Handbook, 6th edition (McGraw-Hill Books Company, 1984, p. 21) It was measured with That is, JIS standard sieves are assembled in the order of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 μm and 45 μm, and a saucer from the top, and approximately 50 g of the particles to be measured are placed on the top sieve. and shaken for 5 minutes using a low-tap test sieve shaker. The weight of the measured particles on each sieve and saucer is weighed, and the weight fraction of the particles on each sieve is determined by taking the total as 100% by weight. ), the vertical axis is weight fraction}, a line was drawn connecting each point, the particle diameter corresponding to a weight fraction of 50% by weight was determined, and this was taken as the weight average particle diameter.

<Method for measuring absorption rate measured by Vortex test>
Required for 2.000 g of the absorbent resin granule composition to absorb 50 g of physiological saline that is stirred at 600 revolutions per minute in a 100 ml tall beaker with a flat bottom as specified in JIS R 3503. The time (unit: seconds) was measured in accordance with JIS K7224-1996, and was taken as the absorption rate measured by the Vortex test.

<Method for measuring absorption amount after 1 minute in Demand Wettability method (DW method)>
The test was conducted indoors at 25° C. and 50% humidity using the apparatus shown in FIG. The measuring device shown in FIG. 1 consists of a burette part (2) {scale capacity 50 ml, length 86 cm, inner diameter 1.05 cm}, a conduit {inner diameter 7 mm}, and a measuring table (6). The burette part (2) is connected to a rubber stopper (1) at the top, an intake introduction pipe (9) {tip inner diameter 3 mm} and a cock (7) at the bottom, and the upper part of the intake introduction pipe (9) is connected to the cock (7). There is a cook (8). A conduit is attached from the burette part (2) to the measurement stand (6). A hole with a diameter of 3 mm is opened in the center of the measuring table (6) as a physiological saline supply part, and a conduit is connected to the hole.

Using a measuring device with this configuration, first close the cock (7) of the buret part (2) and the cock (8) of the air introduction tube (9), and then add a predetermined amount of physiological saline (salt water) adjusted to 25°C. 0.9% by weight) from the top of the burette part (2), plug the top of the burette with the rubber stopper (1), and then close the cock (7) of the burette part (2) and the cock of the air introduction pipe (9). I opened (8). Next, after wiping off the physiological saline that overflowed onto the measuring table (6), the top surface of the measuring table (6) and the surface of the saline coming out from the conduit port in the center of the measuring table (6) are connected. The height of the measurement stand (6) was adjusted so that the heights were the same. While wiping off the physiological saline from the physiological saline supply section, the water level of the physiological saline in the burette section (2) was adjusted to the top of the burette section (2) scale (0 ml line).

Next, close the cock (7) of the burette part (2) and the cock (8) of the air introduction tube (9), and place the plain-woven nylon mesh ( 5) (opening 63 μm, 5 cm x 5 cm), and then on top of this plain-woven nylon mesh (5), 0.50 g was placed in an area of 2.7 cm in diameter around the physiological saline supply part of the measuring table (6). absorbent resin particles (4) were uniformly dispersed. Thereafter, the cock (7) of the burette part (2) and the cock (8) of the air introduction pipe (9) were opened.

When the absorbent resin particles (4) begin to absorb water and the first bubble introduced from the air introduction tube (9) reaches the water surface of the physiological saline in the burette part (2) (buret part (2) The measurement start time is the time when the water level of the physiological saline in the buret part (2) has dropped (the time when the water level of the physiological saline in the buret part (2) has fallen), and the measurement is continuously carried out. The amount of saline solution M (ml) was read. The amount of absorption of the absorbent resin particles (4) one minute after the start of water absorption was determined using the following formula.
Absorption amount (ml/g) in Demand Wettability method = M÷0.50

<Surface dryness evaluation by SDME method>
The water absorbent resin particles (50 parts by weight) according to Examples 1 to 23 and Comparative Examples 1 to 3 were each adhered to fluff pulp (50 parts by weight) to create an absorbent body, which was cut into a rectangle of 10 cm x 40 cm. Above and below it, water-absorbing paper (basis weight 15.5 g/m ² , manufactured by Advantech, Filter Paper No. 2) of the same size as the absorbent body (10 cm x 40 cm) is layered, and then a polyethylene sheet (polyethylene film manufactured by Tamapoly, Inc.) is layered. An evaluation disposable diaper according to each example was prepared by sandwiching the diaper with a nonwoven fabric (Basic weight: 20 g/m ² , Eltas Guard manufactured by Asahi Kasei Corporation). Each evaluation paper diaper heated at 80°C for 2 hours was placed on the detector of a Surface Dryness Measurement Equipment tester (manufactured by WK system, hereinafter referred to as the SDME tester), and a 100% dryness value was set. Calibrated. Each evaluated disposable diaper was then soaked in artificial urine (0.03% by weight potassium chloride, 0.08% by weight magnesium sulfate, 0.8% by weight sodium chloride, and 99.09% by weight deionized water) for 60 minutes. After that, it was placed on the calibrated SDME detector, and a 0% dryness value was set. Next, a metal ring (inner diameter 70 mm, length 50 mm) was set in the center of each evaluation disposable diaper, and 80 ml of artificial urine was injected into the inside of the metal ring. When confirmation could no longer be made, the metal ring was immediately removed. After removing the metal ring, we placed detectors at three locations in total: the center of each evaluation disposable diaper and two locations 10 cm apart on the left and right in the longitudinal direction of each evaluation diaper, and measured the dryness value from the start of the measurement. The value was read after 5 minutes. The dryness value at the center was defined as the surface dryness value (SD1-1), and the dryness values at the remaining two locations were defined as the surface dryness value (SD1-2) and the surface dryness value (SD1-3). Note that the artificial urine, measurement atmosphere, and leaving atmosphere were 25±5° C. and 65±10% RH.

<Example 1>
Acrylic acid (A1-1) (Mitsubishi Chemical) 240 parts, methylene succinic acid (A2-1) (Fuso Chemical) 60 parts, internal crosslinking agent (b-1) N,N'-methylenebisacrylamide 0. 9 parts and 623 parts of deionized water were kept at 5°C while stirring and mixing. After nitrogen was introduced into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 15 parts of a 2% aqueous 2,2'-azobis(2-methylpropionamidine) dihydrochloride solution, 1 part of a 1% aqueous hydrogen peroxide solution. 2 parts, 2.3 parts of 2% aqueous ascorbic acid solution, 0.6 parts of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) aqueous solution, and 0.4 part of 0.03% aqueous iron sulfate heptahydrate solution. part was added and mixed to initiate polymerization. After the temperature of the mixture reached 70°C, a hydrogel was obtained by polymerizing at 70±2°C for about 5 hours.

Next, 500 parts of this water-containing gel was shredded using a mincing machine (12VR-400K manufactured by ROYAL, perforated plate diameter 8 mm), and 128 parts of a 48.5% sodium hydroxide aqueous solution was added to mix and neutralize. A Japanese gel (degree of neutralization: 72%) was obtained. Furthermore, the neutralized hydrogel was dried for 50 minutes in a ventilation dryer {150° C., wind speed 2 m/sec} to obtain a dried product. The dried product was pulverized for 3 minutes using a juicer mixer (OSTERIZER BLENDER manufactured by Oster), and then sieved to remove particles remaining on a 710 μm sieve and particles passing through a 150 μm sieve, and crosslinked. A polymer (A-1) was obtained.

Then, 100 parts of the obtained crosslinked polymer (A-1) was stirred at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and 0.0. 2 parts of polyhydric alcohol (E), 2 parts of propylene glycol as polyvalent metal salt (c1), 1.2 parts of sodium aluminum sulfate dodecahydrate as polyvalent metal salt (c1), and 2.5 parts of water. After uniformly mixing, the mixture was heated at 140° C. for 40 minutes to obtain amorphous crushed water-absorbing resin particles (P-1).

<Example 2>
In Example 1, except that 0.6 parts of 0.1% ethylenediamine-N,N'-disuccinic acid (EDDS) was changed to 0.6 parts of 0.1% nitrilotriacetic acid (c-1) aqueous solution. After obtaining a cross-linked polymer (A-2) in the same manner as in Example 1, 100 parts of the cross-linked polymer (A-2) was stirred at high speed (high-speed stirring turbulizer made by Hosokawa Micron: 2000 rpm) and 0.2 parts of ethylene glycol diglycidyl ether as the valent glycidyl compound (c2), 2 parts of propylene glycol as the polyhydric alcohol (E), 1.2 parts of sodium aluminum sulfate dodecahydrate as the polyvalent metal salt (c1), and A liquid mixture containing 2.5 parts of water was added, mixed uniformly, and then heated at 140° C. for 40 minutes to obtain irregularly shaped crushed water absorbent resin particles (P-2).

<Example 3>
In Example 1, 0.6 parts aqueous solution of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) was mixed with 0.6 parts aqueous solution of 0.1% by weight L-glutamic acid diacetic acid tetrasodium (GLDA 4Na). A crosslinked polymer (A-3) was obtained in the same manner as in Example 1, except that 100 parts of the crosslinked polymer (A-3) was stirred at high speed (Hosokawa Micron high speed stirring turbulizer: 0.2 parts of ethylene glycol diglycidyl ether as the polyvalent glycidyl compound (c2), 2 parts of propylene glycol as the polyhydric alcohol (E), and 12 parts of sodium aluminum sulfate as the polyvalent metal salt (c1). Add a mixed solution of 1.2 parts of hydroxide and 2.5 parts of water, mix uniformly, and then heat at 140°C for 40 minutes to obtain irregularly shaped crushed water-absorbing resin particles (P-3). I got it.

<Example 4>
In Example 1, except that 0.6 parts of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) aqueous solution was changed to 0.6 parts of 0.1% by weight hydroxyethyliminodiacetic acid (HIDA) aqueous solution. After obtaining a crosslinked polymer (A-4) in the same manner as in Example 1, 100 parts of the crosslinked polymer (A-4) was stirred at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). Meanwhile, 0.2 parts of ethylene glycol diglycidyl ether as the polyvalent glycidyl compound (c2), 2 parts of propylene glycol as the polyhydric alcohol (E), and 1.2 parts of sodium aluminum sulfate dodecahydrate as the polyvalent metal salt (c1). A mixed solution of 2.5 parts of water and 2.5 parts of water was added, mixed uniformly, and heated at 140° C. for 40 minutes to obtain irregularly shaped crushed water absorbent resin particles (P-4).

<Example 5>
A crosslinked polymer (A-5 ), 100 parts of the crosslinked polymer (A-5) was stirred at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm) to obtain ethylene glycol diglycidyl ether 0 as a polyvalent glycidyl compound (c2). .2 parts, 2 parts of propylene glycol as the polyhydric alcohol (E), 1.2 parts of sodium aluminum sulfate dodecahydrate as the polyvalent metal salt (c1), and 2.5 parts of water were added. After uniformly mixing, the mixture was heated at 140° C. for 40 minutes to obtain amorphous crushed water-absorbing resin particles (P-5).

<Example 6>
Acrylic acid (A1-1) (Mitsubishi Chemical) 240 parts, methylene succinic acid (A2-1) (Fuso Chemical) 60 parts, internal crosslinking agent (b-1) N,N'-methylenebisacrylamide 0. 9 parts of 2-methyl-2-iodopropionitrile (manufactured by TCI) and 623 parts of deionized water were kept at 5°C while stirring and mixing. After nitrogen was introduced into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 15 parts of a 2% aqueous 2,2'-azobis(2-methylpropionamidine) dihydrochloride solution, 1 part of a 1% aqueous hydrogen peroxide solution. 2 parts, 2.3 parts of 2% aqueous ascorbic acid solution, 0.6 parts of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS), and 0.4 parts of 0.03% aqueous iron sulfate heptahydrate solution. After the temperature of the mixture, which was added and mixed to initiate polymerization, reached 70°C, the mixture was polymerized at 70±2°C for about 5 hours to obtain a hydrogel.

Next, while shredding 500 parts of this hydrous gel using a mincing machine (12VR-400K manufactured by ROYAL), 128 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the gel. degree: 72%). Furthermore, the neutralized hydrogel was dried for 50 minutes in a ventilation dryer {150° C., wind speed 2 m/sec} to obtain a dried product. The dried product was pulverized for 3 minutes using a juicer mixer (OSTERIZER BLENDER manufactured by Oster), and then sieved to remove particles remaining on a 710 μm sieve and particles passing through a 150 μm sieve, and crosslinked. A polymer (A-6) was obtained.

Then, 100 parts of the obtained crosslinked polymer (A-6) was stirred at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm) to add 0.0% of ethylene glycol diglycidyl ether as a polyvalent glycidyl compound (c2). 2 parts of polyhydric alcohol (E), 2 parts of propylene glycol as polyvalent metal salt (c1), 1.2 parts of sodium aluminum sulfate dodecahydrate as polyvalent metal salt (c1), and 2.5 parts of water. After uniformly mixing, the mixture was heated at 140° C. for 40 minutes to obtain amorphous crushed water-absorbing resin particles (P-6).

<Example 7>
In Example 6, except that 0.6 parts of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) aqueous solution was changed to 0.6 parts of 0.1% by weight nitrilotriacetic acid (c-1) aqueous solution. After obtaining a crosslinked polymer (A-7) in the same manner as in Example 6, 100 parts of the crosslinked polymer (A-7) was stirred at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). 0.2 parts of ethylene glycol diglycidyl ether as the polyvalent glycidyl compound (c2), 2 parts of propylene glycol as the polyhydric alcohol having 4 or less carbon atoms (E), and sodium aluminum sulfate 12 water as the polyvalent metal salt (c1). Add a mixed solution of 1.2 parts of hydrate and 2.5 parts of water, mix uniformly, and heat at 140°C for 40 minutes to obtain irregularly shaped crushed water-absorbing resin particles (P-7). I got it.

<Example 8>
In Example 6, 0.6 parts aqueous solution of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) was mixed with 0.6 parts aqueous solution of 0.1% by weight L-glutamic acid diacetic acid tetrasodium (GLDA 4Na). A crosslinked polymer (A-8) was obtained in the same manner as in Example 6, except that 100 parts of the crosslinked polymer (A-8) was stirred at high speed (Hosokawa Micron high speed stirring turbulizer: 0.2 parts of ethylene glycol diglycidyl ether as the polyvalent glycidyl compound (c2), 2 parts of propylene glycol as the polyhydric alcohol (E), and 12 parts of sodium aluminum sulfate as the polyvalent metal salt (c1). Add a mixed solution of 1.2 parts of hydrate and 2.5 parts of water, mix uniformly, and heat at 140°C for 40 minutes to obtain irregularly shaped crushed water-absorbing resin particles (P-8). I got it.

<Example 9>
In Example 6, except that 0.6 parts of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) aqueous solution was changed to 0.6 parts of 0.1% by weight hydroxyethyliminodiacetic acid (HIDA) aqueous solution. After obtaining a crosslinked polymer (A-9) in the same manner as in Example 6, 100 parts of the crosslinked polymer (A-9) was stirred at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm). Meanwhile, 0.2 parts of ethylene glycol diglycidyl ether as the polyvalent glycidyl compound (c2), 2 parts of propylene glycol as the polyhydric alcohol (E), and 1.2 parts of sodium aluminum sulfate dodecahydrate as the polyvalent metal salt (c1). A mixed solution of 2.5 parts of water and 2.5 parts of water was added, mixed uniformly, and then heated at 140° C. for 40 minutes to obtain irregularly pulverized water-absorbing resin particles (P-9).

<Example 10>
Acrylic acid (A1-1) (Mitsubishi Chemical) 240 parts, methylene succinic acid (A2-1) (Fuso Chemical) 60 parts, 48.5% sodium hydroxide aqueous solution 37.1 parts, internal crosslinking agent (b -1) 0.9 part of N,N'-methylenebisacrylamide and 623 parts of deionized water were kept at 5°C while stirring and mixing. After nitrogen was introduced into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 15 parts of a 2% aqueous 2,2'-azobis(2-methylpropionamidine) dihydrochloride solution, 1 part of a 1% aqueous hydrogen peroxide solution. 2 parts, 2.3 parts of 2% aqueous ascorbic acid solution, 0.6 parts of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) aqueous solution, and 0.4 part of 0.03% aqueous iron sulfate heptahydrate solution. part was added and mixed to initiate polymerization. After the temperature of the mixture reached 70°C, a hydrogel was obtained by polymerizing at 70±2°C for about 5 hours.

Next, 500 parts of this water-containing gel was shredded using a mincing machine (12VR-400K manufactured by ROYAL), and 107 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the gel. degree: 72%). Furthermore, the neutralized hydrogel was dried for 50 minutes in a ventilation dryer {150° C., wind speed 2 m/sec} to obtain a dried product. The dried product was pulverized for 3 minutes using a juicer mixer (OSTERIZER BLENDER manufactured by Oster), and then sieved to remove particles remaining on a 710 μm sieve and particles passing through a 150 μm sieve, and crosslinked. A polymer (A-10) was obtained.

Then, 100 parts of the obtained crosslinked polymer (A-10) was stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and 0.0% of ethylene glycol diglycidyl ether was added as a polyvalent glycidyl compound (c2). 2 parts of polyhydric alcohol (E), 2 parts of propylene glycol as polyvalent metal salt (c1), 1.2 parts of sodium aluminum sulfate dodecahydrate as polyvalent metal salt (c1), and 2.5 parts of water. After uniformly mixing, the mixture was heated at 140° C. for 40 minutes to obtain amorphous crushed water absorbent resin particles (P-10).

<Example 11>
In Example 10, except that 0.6 parts of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) aqueous solution was changed to 0.6 parts of 0.1% by weight nitrilotriacetic acid (c-1) aqueous solution. After obtaining a crosslinked polymer (A-11) in the same manner as in Example 10, 100 parts of the crosslinked polymer (A-11) was stirred at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). Meanwhile, 0.2 parts of ethylene glycol diglycidyl ether as the polyvalent glycidyl compound (c2), 2 parts of propylene glycol as the polyhydric alcohol (E), and 1.2 parts of sodium aluminum sulfate dodecahydrate as the polyvalent metal salt (c1). A mixed solution of 2.5 parts of water and 2.5 parts of water was added, mixed uniformly, and then heated at 140° C. for 40 minutes to obtain irregularly pulverized water-absorbing resin particles (P-11).

<Example 12>
In Example 10, 0.6 parts of a 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) aqueous solution was mixed with 0.6 parts of 0.1% by weight L-glutamate diacetic acid tetrasodium (GLDA 4Na). After obtaining a crosslinked polymer (A-12) in the same manner as in Example 19, except for changing the 2000 rpm), 0.2 parts of ethylene glycol diglycidyl ether as the polyvalent glycidyl compound (c2), 2 parts of propylene glycol as the polyhydric alcohol (E), and sodium aluminum sulfate decahydrate as the polyvalent metal salt (c1). Add a mixture of 1.2 parts of solids and 2.5 parts of water, mix uniformly, and heat at 140°C for 40 minutes to form irregularly shaped crushed water absorbent resin particles (P-12). Obtained.

<Example 13>
In Example 10, except that 0.6 parts of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS) aqueous solution was changed to 0.6 parts of 0.1% by weight hydroxyethyliminodiacetic acid (HIDA) aqueous solution. After obtaining a crosslinked polymer (A-13) in the same manner as in Example 10, 100 parts of the crosslinked polymer (A-13) was stirred at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). Meanwhile, 0.2 parts of ethylene glycol diglycidyl ether as the polyvalent glycidyl compound (c2), 2 parts of propylene glycol as the polyhydric alcohol (E), and 1.2 parts of sodium aluminum sulfate dodecahydrate as the polyvalent metal salt (c1). A mixed solution of 2.5 parts of water and 2.5 parts of water was added, mixed uniformly, and then heated at 140° C. for 40 minutes to obtain irregularly pulverized water-absorbing resin particles (P-13).

<Example 14>
In Example 12, amorphous crushed water absorbent resin particles (P-14 ) was obtained.

<Example 15>
In Example 12, amorphous crushed water absorbent resin particles (P-15 ) was obtained.

<Example 16>
While stirring 100 parts of the crosslinked polymer (A-10) obtained in Example 10 at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm), ethylene glycol diglycidyl ether was added as a polyvalent glycidyl compound (c2). 0.2 parts, 2 parts of propylene glycol as the polyhydric alcohol (E), 1.2 parts of sodium aluminum sulfate dodecahydrate as the polyvalent metal salt (c1), Klebosol 30 cal 25 (AZ Materials Co., Ltd.) as the silicon-containing fine particles (D). A mixture of 1.0 part of colloidal silica manufactured by Co., Ltd. (average primary particle size 25 nm) and 2.5 parts of water was added and mixed uniformly, heated at 140° C. for 40 minutes, and cooled to room temperature. Next, 0.2 part of silica (Aerosil 200 manufactured by Aerosil Co., Ltd., average primary particle diameter 12 nm) as silicon-containing fine particles (D) was added and uniformly mixed while stirring at high speed (High speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). Thereafter, it was heated at 80° C. for 30 minutes to obtain irregularly pulverized water-absorbing resin particles (P-15).

<Example 17>
In Example 16, 1.0 parts of Klebosol30cal25 (colloidal silica manufactured by AZ Materials) was changed to 3.0 parts, and 0.2 parts of silica (Aerosil 200 manufactured by Aerosil, average primary particle size 12 nm) was not added. In the same manner as in Example 16, amorphous crushed water-absorbing resin particles (P-17) were obtained.

<Example 18>
In Example 16, 1.0 part of Klebosol30cal25 (colloidal silica manufactured by AZ Materials) was not added, and 0.2 parts of silica (Aerosil 200 manufactured by Aerosil, average primary particle size 12 nm) was changed to 1.0 parts. In the same manner as in Example 16, amorphous crushed water-absorbing resin particles (P-18) were obtained.

<Example 19>
Amorphous crushed water-absorbing resin particles (P-19) were obtained in the same manner as in Example 12, except that 0.2 part of ethylene glycol diglycidyl ether was changed to 0.35 part.

<Example 20>
Amorphous crushed water-absorbing resin particles (P-20) were obtained in the same manner as in Example 12, except that 0.2 part of ethylene glycol diglycidyl ether was changed to 0.01 part.

<Example 21>
Amorphous crushed water absorbent resin particles (P-21) were obtained in the same manner as in Example 12, except that 1.2 parts of sodium aluminum sulfate dodecahydrate was changed to 0.1 part. Ta.

<Example 22>
In Example 12, amorphous crushed water-absorbing resin particles (P-22) were obtained in the same manner as in Example 16, except that 1.2 parts of sodium aluminum sulfate dodecahydrate was changed to 5.0 parts. Ta.

<Example 23>
Acrylic acid (A1-1) (Mitsubishi Chemical) 90 parts, methylene succinic acid (A2-1) (Fuso Chemical) 210 parts, 48.5% sodium hydroxide aqueous solution 129.9 parts, internal crosslinking agent (b -1) 0.9 part of N,N'-methylenebisacrylamide and 556 parts of deionized water were kept at 5°C while stirring and mixing. After nitrogen was introduced into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 15 parts of a 2% aqueous 2,2'-azobis(2-methylpropionamidine) dihydrochloride solution, 1 part of a 1% aqueous hydrogen peroxide solution. 2 parts, 2.3 parts of 2% aqueous ascorbic acid solution, 0.6 parts of 0.1% by weight ethylenediamine-N,N'-disuccinic acid (EDDS), and 0.4 parts of 0.03% aqueous iron sulfate heptahydrate solution. were added and mixed to initiate polymerization. After the temperature of the mixture reached 70°C, a hydrogel was obtained by polymerizing at 70±2°C for about 5 hours.

Next, 500 parts of this water-containing gel was shredded using a mincing machine (12VR-400K manufactured by ROYAL), and 40.1 parts of a 48.5% sodium hydroxide aqueous solution was added to mix and neutralize it, and the neutralized gel ( Neutralization degree: 72%) was obtained. Furthermore, the neutralized hydrogel was dried for 50 minutes in a ventilation dryer {150° C., wind speed 2 m/sec} to obtain a dried product. The dried product was pulverized for 3 minutes using a juicer mixer (OSTERIZER BLENDER manufactured by Oster), and then sieved to remove particles remaining on a 710 μm sieve and particles passing through a 150 μm sieve, and crosslinked. A polymer (A-11) was obtained.

Then, 100 parts of the obtained crosslinked polymer (A-11) was stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron, rotation speed: 2000 rpm), and 0.0% of ethylene glycol diglycidyl ether was added as a polyvalent glycidyl compound (c2). 2 parts of polyhydric alcohol (E), 2 parts of propylene glycol as polyvalent metal salt (c1), 1.2 parts of sodium aluminum sulfate dodecahydrate as polyvalent metal salt (c1), and 2.5 parts of water. After uniformly mixing, the mixture was heated at 140° C. for 40 minutes to obtain irregularly-shaped crushed water-absorbing resin particles (P-23).

<Example 24>
In Example 23, the particle size distribution of the particles remaining on the 710 μm sieve and the particles passing through the 150 μm sieve was changed so that the weight average particle diameter was 250 μm. In the same manner as in Example 23, amorphous crushed water-absorbing resin particles (P-24) were obtained.

<Example 25>
In Example 23, the particle size distribution of the particles that remained on the 710 μm sieve and the particles that passed through the 150 μm sieve was changed so that the weight average particle diameter was adjusted to 300 μm. In the same manner as in Example 23, amorphous crushed water-absorbing resin particles (P-25) were obtained.

<Example 26>
In Example 23, the particle size distribution of the particles remaining on the 710 μm sieve and the particles passing through the 150 μm sieve was changed, and the weight average particle diameter was adjusted to 450 μm. In the same manner as in Example 23, amorphous crushed water absorbent resin particles (P-26) were obtained.

<Example 27>
In Example 23, the particle size distribution of the particles remaining on the 710 μm sieve and the particles passing through the 150 μm sieve was changed, and the weight average particle diameter was adjusted to 600 μm. In the same manner as in Example 23, amorphous crushed water-absorbing resin particles (P-27) were obtained.

<Comparative example 1>
Amorphous crushed water-absorbing resin particles (R-1) were obtained in the same manner as in Example 1, except that 1.2 parts of sodium aluminum sulfate dodecahydrate was not added.

<Comparative example 2>
Amorphous crushed water-absorbing resin particles (R-2) were obtained in the same manner as in Example 8, except that 1.2 parts of sodium aluminum sulfate dodecahydrate was not added.

<Comparative example 3>
In Example 16, irregularly pulverized water-absorbing resin particles (R-3) were obtained in the same manner as in Example 8, except that 1.2 parts of sodium aluminum sulfate dodecahydrate was not added.

<Comparative example 4>
Stir 155 parts of acrylic acid (A1-1) (manufactured by Mitsubishi Chemical), 0.5 part of internal crosslinking agent (b-1) {pentaerythritol triallyl ether, manufactured by Daiso Corporation}, and 340.39 parts of deionized water. - Maintained at 3°C while mixing. After nitrogen was introduced into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 0.6 parts of a 1% aqueous hydrogen peroxide solution, 1.2 parts of a 2% aqueous ascorbic acid solution, and 2% 2,2'-azobis[ 2.3 parts of an aqueous solution of 2-methyl-N-(2-hydroxyethyl)-propionamide was added and mixed to initiate polymerization. After the temperature of the mixture reached 90°C, a hydrogel was obtained by polymerizing at 90±2°C for about 5 hours.

Next, 500 parts of this water-containing gel was shredded with a mincing machine (12VR-400K manufactured by ROYAL, perforated plate diameter 8 mm) at a gel temperature of 90°C, and 128 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed. A neutralized gel was obtained. Further, the neutralized hydrogel was dried for 50 minutes in a ventilation dryer {150° C., wind speed 2 m/sec} to obtain a dried product. The dried product was pulverized for 3 minutes using a juicer mixer (OSTERIZER BLENDER manufactured by Oster), and then sieved to remove particles remaining on a 710 μm sieve and particles passing through a 150 μm sieve, and crosslinked. A polymer (A-12) was obtained.

Next, 100 parts of the obtained crosslinked polymer (A-12) was stirred at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm), and 0.0% of ethylene glycol diglycidyl ether as a surface crosslinking agent was added thereto. 2 parts of propylene glycol, 5 parts of water, and 0.8 parts of propylene glycol, 1.6 parts of water, and a polyvalent metal salt (c1) of sodium aluminum sulfate hexahydrate (Fujifilm Wa A mixed solution containing 0.3 part of Hikari Pure Chemical Industries, Ltd.) was added at the same time, mixed uniformly, and heated at 130° C. for 30 minutes to obtain irregularly shaped crushed water absorbent resin particles (R-4).

Table 1 shows the evaluation results for each example and comparative example.

From the results in Table 1, it can be seen that the water absorbent resin particles of the present invention have more homogeneous surface drying properties than the water absorbent resin particles of Comparative Examples 1 to 4.

Since the water-absorbing resin particles of the present invention have homogeneous water-absorbing properties, they can be preferably applied to an absorbent body containing water-absorbing resin particles and a fibrous material, and absorbent articles comprising this absorbent body (disposable diapers) , sanitary napkins, medical blood preservation agents, etc.). In addition, pet urine absorbents, urine gelling agents for portable toilets, freshness preservation agents for fruits and vegetables, drip absorbers for meat and seafood, ice packs, disposable body warmers, gelling agents for batteries, water retention agents for plants and soil, and condensation. It can also be used in various applications such as preventive agents, water-stopping agents, packing agents, and artificial snow.

1 Rubber stopper 2 Buret part 3 Physiological saline 4 Absorbent resin particles 5 Plain weave nylon mesh 6 Measuring table 7 Cock 8 Cock 9 Intake introduction pipe

Claims (5)

One or more monomers (A1) selected from the group consisting of a water-soluble unsaturated monocarboxylic acid (a1) and its salt, and a monomer (a2) that becomes the water-soluble unsaturated monocarboxylic acid (a1) upon hydrolysis; , one or more monomers (A2) selected from the group consisting of a water-soluble unsaturated dicarboxylic acid (a3) and its salt, and a monomer (a4) that becomes the water-soluble unsaturated dicarboxylic acid (a3) upon hydrolysis; A cross-linked polymer having a structure in which the internal cross-linking agent (b) is a structural unit, and the surface is cross-linked with a surface cross-linking agent (C) containing a polyvalent metal salt (c1) and a polyvalent glycidyl compound (c2). Water-absorbing resin particles containing aggregate (A) and satisfying the following (1) to (3).
(1) Weight average particle diameter is 250 to 600 μm
(2) Absorption rate (seconds) by Vortex method is 30 to 70 seconds (3) Absorption amount after 1 minute by Demand Wettability method is 3 to 15 ml/g The water-absorbing resin particles according to claim 1, wherein the water-absorbing resin particles have an irregularly crushed shape. An absorbent body comprising the water-absorbing resin particles according to claim 1 or 2. An absorbent article comprising the absorbent body according to claim 3. A method for producing water-absorbing resin particles according to claim 1 or 2, comprising:
a polymerization step of obtaining a hydrogel containing the crosslinked polymer (A);
a drying step of drying the hydrogel;
A method for producing water absorbent resin particles, comprising a surface crosslinking step of surface crosslinking the crosslinked polymer (A) with the surface crosslinking agent (C) diluted with a polyhydric alcohol having 4 or less carbon atoms (E).