JP2023147658A - Method of manufacturing water-absorbent resin composition, water-absorbent resin composition, absorber using the same, and absorbent article - Google Patents

Abstract

To provide a method for manufacturing a water-absorbent resin composition whose water absorption performance under load is comparable to that of a water absorbent resin composition composed solely of a petrochemical-derived monomer, namely acrylic acid, while using a plant-derived raw material with low polymerization reactivity.SOLUTION: A water-absorbent resin composition contains a crosslinked polymer (A) having as its constituent units: one or more monomers (A1) selected from the group consisting of water-soluble unsaturated monocarboxylic acids (a1) and salts thereof; one or more monomers (A2) selected from the group consisting of water-soluble unsaturated dicarboxylic acids (a3) and salts thereof; and a crosslinking agent (b). A method of manufacturing the water-absorbent resin composition has: a polymerization step of polymerizing a monomer composition containing the monomers (A1), the monomers (A2) and the crosslinking agent (b) in the presence of a chelating agent (c) to obtain a hydrous gel containing the crosslinked polymer (A); and a drying step of drying the hydrous gel.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a water absorbent resin composition, a water absorbent resin composition, an absorbent body using the same, and an absorbent article.

The water-absorbing resin composition is a resin that can absorb several tens to several thousand times its own weight of water, and for example, polyacrylic acid-based absorbent resin compositions are known. These water-absorbing resin compositions are widely used in disposable sanitary products due to their high water-absorbing properties. However, with conventional water-absorbing resin compositions, there are problems with the way sanitary products containing them are disposed of from the perspective of environmental impact, and it has been pointed out that the method of disposing of them in an incinerator causes global warming. There is. Under these circumstances, there is a strong demand for water-absorbing resin compositions using plant-derived raw materials from the viewpoint of carbon neutrality and the like.

By using plant-derived materials as raw materials for the water-absorbing resin composition, the amount of acrylic acid derived from petrification in the water-absorbing resin composition can be reduced. In addition, by using plant-derived raw materials in the production of water-absorbing resin compositions, carbon dioxide emissions are generated during the production of acrylic acid (during oil drilling, propylene production by naphtha cracking, and synthesis of acrolein and acrylic acid from propylene). It is expected that this will lead to a reduction in the amount. As a means for obtaining a water absorbent resin composition using plant-derived raw materials, there is a method of radically polymerizing a plant-derived raw material and acrylic acid to form a copolymer (for example, Patent Documents 1 and 2).

China Patent Application Publication No. 103183764 US Patent Application Publication No. 9109059

However, when producing homopolymers from plant-derived raw materials known as monomers with double bonds such as maleic acid, itaconic acid, and fumaric acid, the molecular weight becomes extremely small. Even in systems where polyacrylic acid is used, the molecular weight tends to be smaller than that of polyacrylic acid. As a result, there is a problem that the gel strength of the water-absorbing resin composition decreases, and the water-absorbing performance under load decreases.

The object of the present invention is to create a water-absorbing resin composition that uses plant-derived raw materials with low polymerization reactivity, but whose water-absorbing performance under load is comparable to that of a water-absorbing resin composition made only of petrification-derived monomers, that is, acrylic acid. The present invention provides a method for producing a composition, a water absorbent resin composition, an absorbent body using the same, and an absorbent article.

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 method for producing a water absorbent resin composition containing a crosslinked polymer (A) having as a structural unit a crosslinking agent (b),
A monomer composition containing the monomer (A1), the monomer (A2), and the crosslinking agent (b) is used as a chelating agent (c) having a logarithmic value of the chelate stability constant for Fe ³⁺ at pH 4 of 6.5 to 12. A polymerization step of obtaining a hydrogel containing the crosslinked polymer (A) by polymerizing in the presence of
The present invention provides a method for producing a water-absorbing resin composition, a water-absorbing resin composition, an absorbent body using the same, and an absorbent article, which comprises a drying step of drying the hydrogel.

According to the present invention, a water-absorbing resin whose water-absorbing performance under load is comparable to that of a water-absorbing resin composition made only of a petrification-derived monomer, that is, acrylic acid, while using a plant-derived raw material with low polymerization reactivity. A method for producing a composition, a water absorbent resin composition, an absorbent body using the same, and an absorbent article can be provided. The reason why the present invention has such an effect is not clear, but it is thought to be as follows.

As a result of research, the present inventors found that the very small molecular weight of homopolymers of plant-derived raw materials and copolymers of plant-derived raw materials and acrylic acid, which is a petrochemical-derived raw material, is due to the presence of trace amounts in the polymerization reaction system. We obtained knowledge that this is due to the influence of iron ions. This is because the reactivity of water-soluble unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, which are plant-derived raw materials and known as monomers with double bonds, is much lower than that of acrylic acid. It is presumed that the radical reaction is inhibited and the polymerization reaction is stopped midway, thereby lowering the molecular weight of the polymer containing the plant-derived raw material. In the method for producing a water-absorbing resin composition of the present invention, the chelating agent (c) binds to iron ions in the polymerization system and suppresses the influence of the iron ions, so that homopolymers of plant-derived raw materials and plant-derived It is presumed that the reduction in the molecular weight of the copolymer of the raw material and acrylic acid, which is a petrification-derived raw material, can be suppressed.

FIG. 2 is a diagram schematically showing a cross section of a filtration cylindrical tube for measuring liquid permeability of a water absorbent resin composition. FIG. 2 is a perspective view schematically showing a pressurizing shaft and a weight for measuring liquid permeability of a water-absorbing resin composition.

<Method for manufacturing water absorbent resin composition>
The method for producing the water absorbent resin composition of this embodiment is as follows:
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 method for producing a water absorbent resin composition containing a crosslinked polymer (A) having as a structural unit a crosslinking agent (b),
A monomer composition containing the monomer (A1), the monomer (A2), and the crosslinking agent (b) is used as a chelating agent (c) having a logarithmic value of the chelate stability constant for Fe ³⁺ at pH 4 of 6.5 to 12. A polymerization step of obtaining a hydrogel containing the crosslinked polymer (A) by polymerizing in the presence of
and a drying step of drying the hydrogel.
According to the method for producing a water-absorbing resin composition of the present embodiment, a water-absorbing resin whose water-absorbing performance under load is made only of a monomer derived from petrification, that is, acrylic acid, while using plant-derived raw materials with low polymerization reactivity. It is possible to provide a water-absorbing resin composition that is comparable to that of the present invention.

[Water absorbent resin composition]
[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 polymerization, after polymerization, or both, but from the viewpoint of the absorption performance of the resulting water-absorbing resin composition, it is preferably after 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 composition, 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 composition) is prepared 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) to obtain a standard substance (for example, the US It can be determined by comparatively measuring the carbon-14 content with respect to NIST 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 amount of the monomer (A1) to the amount of the monomer (A2) in the crosslinked polymer (A) (amount of the monomer (A1)/amount of the monomer (A2)) is determined by the load. From the viewpoint of improving the water absorption performance below and protecting the environment, the ratio is preferably 1/99 to 99/1, more preferably 5/95 to 99/1, and still more preferably 5/95 to 90/10.

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.

(Crosslinking agent (b))
The crosslinking agent (b) is not particularly limited and is known (for example, a crosslinking agent having two or more ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 3648553, which reacts with a water-soluble substituent). A crosslinking agent having at least one functional group capable of reacting with a water-soluble substituent and at least one ethylenically unsaturated group, and a crosslinking agent having at least two functional groups capable of reacting with a water-soluble substituent, JP-A-2003-165883 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. A crosslinking agent such as a crosslinking vinyl monomer disclosed in paragraph 0059 of JP-A No. 2005-75982 and a cross-linking vinyl monomer disclosed in paragraphs 0015 to 0016 of JP-A No. 2005-95759 is used. can.

The 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. One or more selected from the group consisting of allyl compounds and acrylamide compounds are more preferable, and poly(meth)allyl ethers of polyhydric alcohols such as alkylene glycol, trimethylolpropane, glycerin, pentaerythritol and sorbitol, tetraallyloxyethane, and 1 selected from the group consisting of polyvalent (meth)allyl compounds such as allyl isocyanurate, N,N'-methylenebisacrylamide, N,N'-methylenebismethacrylamide, and compounds represented by the following general formula (1) It is more preferable to use more than one species. The 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 2 or more carbon atoms and may contain a nitrogen atom, an oxygen atom, or a sulfur atom; may have. n is an integer from 2 to 6. ]

In the general formula (1), R ¹ and R ² are each independently a hydrogen atom or a methyl group. R ¹ and R ² are preferably hydrogen atoms from the viewpoint of good polymerization reactivity.

X ¹ is an n-valent organic group that has an aliphatic group having 2 or more carbon atoms and may contain a nitrogen atom, an oxygen atom, or a sulfur atom. The aliphatic group may be linear or branched.

The number of carbon atoms in the aliphatic group is 2 or more, preferably 30 or less, more preferably 15 or less from the viewpoint of absorption performance and the like.

In the organic group, the aliphatic group is selected from -O- and -NX ² - (where X ² is a hydrogen atom, an alkyl group, or a (meth)acryloyl group) from the viewpoint of absorption performance etc. Preferably, they are connected via at least one selected divalent linking group. The linking group is preferably one or more selected from -O- and -NX ² - (where X ² is a (meth)acryloyl group) from the viewpoint of absorption performance and the like. The number of the linking groups is preferably 1 to 4, more preferably 1 to 3, from the viewpoint of absorption performance and the like.

In the general formula (1), n is an integer from 2 to 6, and is preferably an integer from 2 to 4 from the viewpoint of absorption performance and the like.

When n is 2 in the general formula (1), the X ¹ is preferably an organic group represented by the following general formula (b1) or the following general formula (b2) from the viewpoint of absorption performance and the like.

[In the general formula (b1), R ³ is an alkylene group having 1 to 6 carbon atoms, R ⁴ is a hydrogen atom or a methyl group, x is an integer of 2 to 4, and r is an integer of 1 to 6. and R ⁵ is a single bond or an alkylene group having 1 to 6 carbon atoms. ]

[R ⁶ is an alkylene group having 1 to 3 carbon atoms, y is an integer of 2 to 4, s is an integer of 1 to 6, and R ⁷ is a single bond or an alkylene group having 1 to 3 carbon atoms. be. ]

In the general formula (b1), R ³ is an alkylene group having 1 to 6 carbon atoms, preferably an alkylene group having 1 to 3 carbon atoms, and more preferably an ethylene group, from the viewpoint of easy availability of raw materials.

In the general formula (b1), R ⁴ is a hydrogen atom or a methyl group, preferably a hydrogen atom, from the viewpoint of good polymerization reactivity.

In the general formula (b1), x is an integer of 2 to 4, preferably 2 or 3, and more preferably 2, from the viewpoint of availability of raw materials.

In the general formula (b1), r is an integer from 1 to 6, preferably 1 or 2, from the viewpoint of availability of raw materials.

In the general formula (b1), R ⁵ is a single bond or an alkylene group having 1 to 6 carbon atoms, and a single bond is preferable from the viewpoint of availability of raw materials.

In the general formula (b2), R ⁶ is an alkylene group having 1 to 3 carbon atoms, preferably an alkylene group having 2 or 3 carbon atoms, and more preferably a propylene group, from the viewpoint of availability of raw materials.

In the general formula (b2), y is an integer from 2 to 4, preferably 2, from the viewpoint of availability of raw materials.

In the general formula (b2), s is an integer of 1 to 6, preferably 2 to 5, and more preferably 3 or 4, from the viewpoint of availability of raw materials.

In the general formula (b2), R ⁷ is a single bond or an alkylene group having 1 to 3 carbon atoms, preferably a methylene group, from the viewpoint of availability of raw materials.

In the general formula (1), when the X ¹ is an organic group represented by the general formula (b1), a specific example of the crosslinking agent (b) is represented by the following general formula (b1-1). Examples include a crosslinking agent (b1-1) and a crosslinking agent (b1-2) represented by the following general formula (b1-2).

In the general formula (1), when the X ¹ is an organic group represented by the general formula (b2), a specific example of the crosslinking agent (b) is represented by the general formula (b2-1) below. A crosslinking agent (b2-1), a crosslinking agent (b2-2) represented by the following general formula (b2-2), a crosslinking agent (b2-3) represented by the following general formula (b2-3), and the following general A crosslinking agent (b2-4) represented by the formula (b2-4), a crosslinking agent (b2-5) represented by the following general formula (b2-5), and a crosslinking agent represented by the following general formula (b2-6) (b2-6) and the like.

When n is 4 in the general formula (1), the X ¹ is preferably an organic group represented by the following general formula (b3) from the viewpoint of absorption performance and the like.

In the general formula (b3), R ⁸ is a single bond or an alkylene group having 1 to 3 carbon atoms, preferably an alkylene group having 1 or 2 carbon atoms, and more preferably a methylene group, from the viewpoint of availability of raw materials. preferable.

In the general formula (b3), z is an integer of 2 to 4, preferably 2 or 3, and more preferably 2, from the viewpoint of availability of raw materials.

In the general formula (b3), t is an integer of 1 to 6, preferably an integer of 1 to 4, and more preferably 1, from the viewpoint of availability of raw materials.

In the general formula (b3), R ⁹ is a single bond or an alkylene group having 1 to 3 carbon atoms, preferably an alkylene group having 1 or 2 carbon atoms, and more preferably a methylene group, from the viewpoint of availability of raw materials. preferable.

In the general formula (1), when the X ¹ is an organic group represented by the general formula (b3), a specific example of the crosslinking agent (b) is represented by the following general formula (b3-1). Examples include a crosslinking agent (b3-2) and a crosslinking agent (b3-2) represented by the following general formula (b3-2).

Examples of commercially available crosslinking agents (b) include FOM-03006, FOM-03007, FOM-03008, and FOM-03009 (all manufactured by Fuji Film Corporation).

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

[Chelating agent (c)]
The water-absorbing resin composition contains a chelating agent (c) having a logarithm value of a chelate stability constant for Fe ³⁺ at pH 4 of 6.5 to 12.

Note that the chelate stability constant can be determined by the following formula.
Chelate stability constant = [ML _n ]/([M] [L] ⁿ )
In the above formula, [M] means the metal ion concentration, [L] the complex concentration, [ML _n ] the chelate complex, and n the number of complexes that react with the metal ion.

Examples of the chelating agent (c) include ethylenediamine-N,N'-disuccinic acid (EDDS), nitrilotriacetic acid (NTA), tetrasodium L-glutamic acid diacetate (GLDA・4Na), 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 content (molar ratio) of the chelating agent (c) in the water-absorbing resin composition is 0.1 to 1000 parts with respect to 1000000 parts of the total amount of the monomer (A1) unit and monomer (A2) unit. is preferable, more preferably 0.2 to 500, particularly preferably 0.2 to 200. 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 content (substance amount) of the chelating agent (c) in the water-absorbent resin composition is preferably 1 to 100 times the iron ion (Fe ³⁺ ) in the water-absorbent resin composition, more preferably 1 -50, particularly preferably 1-20. 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 water-absorbing resin composition preferably has a structure in which the surface of the crosslinked polymer (A) is crosslinked with a surface crosslinking agent (d). By crosslinking the surface of the crosslinked polymer (A), the gel strength of the water absorbent resin composition can be improved, and the desired water retention amount and absorption amount under load of the water absorbent resin composition are satisfied. I can do it. The surface crosslinking agent (d) can be either inorganic or organic. As the surface crosslinking agent (d), publicly known (polyvalent glycidyl compounds, polyvalent amines, polyvalent aziridine compounds, polyvalent isocyanate compounds, etc. described in JP-A-59-189103, JP-A-58-180233) and the polyhydric alcohols described in JP-A-61-16903, the silane coupling agents described in JP-A-61-211305 and JP-A-61-252212, and the silane coupling agents described in JP-A-5-508425. Organic surface crosslinking agents such as alkylene carbonate, polyvalent oxazoline compounds described in JP-A-11-240959, etc.) can be used. Among these surface crosslinking agents, from the viewpoint of economy and absorption characteristics, one or more selected from the group consisting of polyvalent glycidyl compounds, polyhydric alcohols, and polyvalent amines are preferred, and more preferred are polyvalent glycidyl compounds and polyvalent amines. One or more types selected from the group consisting of polyhydric alcohols, particularly preferably one or more types selected from the group consisting of polyvalent glycidyl compounds, most preferably ethylene glycol diglycidyl ether. One type of surface crosslinking agent (d) may be used alone, or two or more types may be used in combination.

The water-absorbing resin composition may contain a certain amount of other components such as a residual solvent and a residual crosslinking component within a range that does not impair its performance.

In the water-absorbing resin composition, the other components are preferably selected from the group consisting of iodine, tellurium, antimony, and bismuth, from the viewpoint of improving gel strength during water absorption, absorption amount under load, and gel passing rate. It may contain at least one typical element. When the water-absorbing resin composition contains the typical element, the content of the typical element in the water-absorbing resin composition is determined from the viewpoint of improving the gel strength during water absorption, the absorption amount under load, and the gel passing rate. , preferably 0.0005 to 0.1% by weight, more preferably 0.001 to 0.05% by weight. The water-absorbing resin composition containing the representative element is prepared by combining a monomer composition containing the monomer (A1), the monomer (A2), and the crosslinking agent (b) in the presence of the organic representative element compound described below. It can be obtained by polymerizing and drying the obtained hydrogel.

Other examples of the other ingredients include preservatives, fungicides, antibacterial agents, antioxidants, ultraviolet absorbers, antioxidants, colorants, fragrances, deodorants, liquid permeability improvers, and inorganic substances. Examples include powders and organic fibrous materials. The amount thereof is usually 5% by weight or less based on the weight of the water absorbent resin composition.

Although the shape of the water-absorbing resin composition is not particularly limited, a particulate shape is preferable from the viewpoint of improving absorption performance. The weight average particle diameter (μm) of the particulate water-absorbing resin composition (hereinafter also referred to as water-absorbing resin particles) is 250 to 600, preferably 300 to 500, more preferably 340 to 460. If the weight average particle diameter is less than 250 μm, the liquid passing performance will deteriorate, and if it exceeds 600 μm, the absorption rate will deteriorate, so within this range, the absorption performance will be even better.

The weight average particle diameter was determined using a low-tap test sieve shaker and a standard sieve (JISZ8801-1:2006), according to Perry's Chemical Engineers Handbook, 6th edition (McGraw-Hill Books Company, 1984). (page 21). That is, JIS standard sieves are assembled in the following order from the top: 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. Approximately 50 g of the particles to be measured are placed in the top sieve and shaken for 5 minutes using a low-tap test sieve shaker. Weigh the particles to be measured on each sieve and saucer, take the total as 100% by weight, determine the weight fraction of particles on each sieve, and compare this value with logarithmic probability paper [the horizontal axis is the sieve opening (particle diameter ), the vertical axis is the weight fraction], a line is drawn connecting each point, the particle diameter corresponding to a weight fraction of 50% by weight is determined, and this is defined as the weight average particle diameter.

The smaller the content of fine powder contained in the water-absorbing resin particles, the better the liquid passing performance. %) is 3 or less, preferably 1 or less. The weight proportion of water-absorbing resin particles having a particle diameter of less than 150 μm can be determined using the graph created when determining the weight average particle diameter described above.

There is no particular limitation on the shape of the water-absorbing resin particles, and examples thereof include amorphous crushed shapes, flaky shapes, pearl shapes, and rice grain shapes. 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.

[Polymerization process]
By polymerizing a monomer composition containing the monomer (A1), the monomer (A2), and the crosslinking agent (b) in the presence of the chelating agent (c), iron ions in the polymerization system are chelated. , the reaction can proceed efficiently and it becomes easier to obtain a high molecular weight crosslinked polymer. Examples of the polymerization method of the monomer composition include known solution polymerization and known reverse phase suspension polymerization.

Iron ions have the effect of promoting the cleavage of peroxide-based initiators and decomposition of resin in water-absorbing resin compositions, leading to inhibition of radical polymerization and deterioration of resin over time. If it is inactivated, polymerization will not proceed and a water-absorbing resin will not be obtained. Furthermore, if the amount of active iron ions that do not form a chelate with the chelating agent in the polymerization system is less than 1 ppb, the amount of radicals supplied will be too low and ultra-high molecular weight components will be produced, impairing water absorption. Therefore, the amount of active iron ions is preferably controlled within the range of 1 ppb to 1 ppm relative to the polymerization solution.

The chelating agent (c) may be added either before or after mixing the monomer (A1) and the monomer (A2). Alternatively, the monomers may be mixed after being added to either or both of the respective monomers. From the viewpoint of stability of monomer (A2), it is preferable to mix (A2) and chelating agent (c) and then mix with monomer (A1).

The amount (ppm) of the chelating agent (c) to be added is the total amount of the monomer (A1) and the monomer (A2), and when using other vinyl monomers (A3), the amount of (A1) to (A3). Based on the total amount, it is preferably from 0.1 to 1000, more preferably from 1 to 1000, particularly preferably from 1 to 500. 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 amount of the chelating agent (c) added (substance amount) is preferably 1 to 300 times, more preferably 1 to 150 times, particularly preferably 5 to 80 times the amount of iron ions (Fe ³⁺ ) in the polymerization solution. be. 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 degree of neutralization (number of moles) relative to the total of monomer (A1) and monomer (A2) during polymerization 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 preferred because it yields a water-absorbing resin composition with a large amount of water and a small amount of water-soluble components, and there is no need to control the temperature during polymerization.

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.

The monomer composition containing monomers (A1), (A2) and crosslinking agent (b) during polymerization, and the polymerization solution containing the chelating agent (c) preferably have a pH range of 1 to 10. , more preferably 1-7, still more preferably 1-5. Within this range, the polymerization reaction will proceed efficiently and the required water absorption performance will be easily obtained.

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]. etc.], inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinic acid peroxide, etc. oxide and di(2-ethoxyethyl) peroxydicarbonate, etc.) and redox catalysts (alkali metal sulfite or bisulfite, ammonium sulfite, ammonium bisulfite, and reducing agents such as ascorbic acid and alkali metal persulfates, ammonium persulfate, hydrogen peroxide, and a combination with an oxidizing agent such as an organic peroxide), and the like. 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. These catalysts that may be added may be used alone, or two or more of these may be used in combination.

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.

The crosslinked polymer (A) is a monomer composition containing the monomer (A1), the monomer (A2), and the crosslinking agent (b), an organic iodine compound, an organic tellurium compound, an organic antimony compound, and an organic bismuth compound. By polymerizing in the presence of at least one type of organic typical element compound selected from the group consisting of compounds, it is possible to improve the gel strength during water absorption, the amount of absorption 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 them, from the viewpoint of reactivity, organic typical element compounds represented by the following general formula (2) are preferred. These organic typical element compounds may be used alone or in combination of two or more.

In the general formula (2), R ¹⁰ and R ¹¹ each independently represent a hydrogen atom, a saturated hydrocarbon group having 1 to 7 carbon atoms, at least one non-addition polymerizable double bond, or at least one non-addition polymerizable triple bond. R 12 is a monovalent group having 1 to 7 carbon atoms, and R ¹² is an m-valent saturated hydrocarbon group having 1 to 6 carbon atoms, or at least one non-addition polymerizable double bond, or at least one non-addition polymerizable double bond. It is an m-valent group having 2 to 12 carbon atoms and having an addition polymerizable triple bond, provided that at least one of R ¹⁰ to R ¹² in one molecule is the corresponding non-addition polymerizable double bond. A group having a double bond or at least one non-addition polymerizable triple bond, m is an integer of 1 to 3, and when m is 1, R ¹⁰ and R ¹¹ may be bonded to each other, ³ is a monovalent organic typical element group having a tellurium element, an antimony element, or a bismuth element, or an iodo group. In this specification, non-addition polymerizable double bonds (hereinafter also simply referred to as non-polymerizable double bonds) and non-addition polymerizable triple bonds (hereinafter also simply referred to as non-polymerizable triple bonds) refer to unsaturated bonds. These are bonds excluding addition-polymerizable unsaturated bonds (addition-polymerizable carbon-carbon double bonds and addition-polymerizable carbon-carbon triple bonds, respectively), and non-addition-polymerizable double bonds and non-addition-polymerizable Triple bonds include carbon-oxygen double bonds contained in carbonyl groups, carbon-nitrogen triple bonds contained in nitrile groups, carbon-carbon double bonds constituting aromatic hydrocarbons, and oxygen constituting heteroaromatic compounds. - Nitrogen double bonds and carbon-nitrogen double bonds, etc., among which carbon-oxygen double bonds contained in carbonyl groups, carbon-nitrogen triple bonds contained in nitrile groups, and carbon constituting aromatic hydrocarbons. - Carbon double bonds are preferred.

When R ¹⁰ and R ¹¹ are saturated hydrocarbon groups having 1 to 7 carbon atoms, the saturated hydrocarbon groups having 1 to 7 carbon atoms include linear saturated hydrocarbon groups having 1 to 7 carbon atoms (methyl group, ethyl group, group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, etc.) and branched saturated hydrocarbon groups having 1 to 7 carbon atoms (i-propyl group, isobutyl group, s-butyl group, t -butyl group, isopentyl group, neopentyl group, t-pentyl group, 1-methylbutyl group, isohexyl group, s-hexyl group, t-hexyl group, neohexyl group, heptyl group, etc.). Among these, from the viewpoint of solubility and polymerizability, linear saturated hydrocarbon groups having 1 to 5 carbon atoms are preferred, and linear saturated hydrocarbon groups having 1 to 3 carbon atoms are more preferred.

When R ¹⁰ and R ¹¹ are monovalent groups having 1 to 7 carbon atoms and having at least one non-polymerizable double bond or at least one non-polymerizable triple bond, preferred groups include carboxy (salt) groups. (1 carbon number, carbon-oxygen double bond), phenyl group (6 carbon numbers, non-polymerizable carbon-carbon double bond), cyano group (1 carbon number, carbon-nitrogen triple bond), cyanomethyl group (carbon number 2, carbon-nitrogen triple bond), cyanoethyl group (3 carbon atoms, carbon-nitrogen triple bond), cyanopropyl group (4 carbon atoms, carbon-nitrogen triple bond), cyanobutyl group (5 carbon atoms, carbon-nitrogen triple bond) ), cyanopentyl group (6 carbon atoms, carbon-nitrogen triple bond), cyanohexyl group (7 carbon atoms, carbon-nitrogen triple bond), carboxymethyl group (2 carbon atoms, carbon-oxygen double bond), carboxyethyl group (3 carbon atoms, carbon-oxygen double bond), carboxypropyl group (4 carbon atoms, carbon-oxygen double bond), carboxybutyl group (5 carbon atoms, carbon-oxygen double bond), carboxypentyl group ( 6 carbon atoms, carbon-oxygen double bond), carboxyhexyl group (7 carbon atoms, carbon-oxygen double bond), benzyl group (7 carbon atoms, non-polymerizable carbon-carbon double bond), methoxycarbonyl group ( 2 carbon atoms, carbon-oxygen double bond), ethoxycarbonyl group (3 carbon atoms, carbon-oxygen double bond), propyloxycarbonyl group (4 carbon atoms, carbon-oxygen double bond), butyloxycarbonyl group ( 5 carbon atoms, carbon-oxygen double bond), pentyloxycarbonyl group (6 carbon atoms, carbon-oxygen double bond), hexyloxycarbonyl group (7 carbon atoms, carbon-oxygen double bond), hydroxyethoxycarbonyl group (3 carbon atoms, carbon-oxygen double bond), hydroxypropyloxycarbonyl group (4 carbon atoms, carbon-oxygen double bond), hydroxybutyloxycarbonyl group (5 carbon atoms, carbon-oxygen double bond), hydroxy Examples include pentyloxycarbonyl group (carbon number 6, carbon-oxygen double bond) and hydroxyhexyloxycarbonyl group (carbon number 7, carbon-oxygen double bond), and more preferably carboxy (salt) group, cyano group, carboxymethyl group, and carboxyethyl group. Examples of the salt include alkali metal (lithium, sodium, potassium, etc.) salts, alkaline earth metal (magnesium, calcium, etc.) salts, ammonium (NH ₄ ) salts, and the like. 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.

R ¹² is an m-valent saturated hydrocarbon group having 1 to 7 carbon atoms or an m-valent group having 2 to 12 carbon atoms and having at least one non-polymerizable double bond or at least one non-polymerizable triple bond; , m is an integer from 1 to 3.

Among the m-valent saturated hydrocarbon groups having 1 to 7 carbon atoms represented by R ¹² , monovalent saturated hydrocarbon groups having 1 to 7 carbon atoms include linear saturated hydrocarbon groups having 1 to 7 carbon atoms; (methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, heptyl group, etc.) and branched saturated hydrocarbon groups having 1 to 7 carbon atoms (i-propyl group, isobutyl group, etc.) group, s-butyl group, t-butyl group, isopentyl group, neopentyl group, t-pentyl group, 1-methylbutyl group, isohexyl group, s-hexyl group, t-hexyl group, neohexyl group, isoheptyl group, etc. It will be done. Among the m-valent saturated hydrocarbon groups having 1 to 7 carbon atoms represented by R ¹² , the divalent saturated hydrocarbon groups having 1 to 7 carbon atoms include divalent linear saturated hydrocarbon groups having 1 to 7 carbon atoms. Hydrocarbon groups (methylene group, ethylene group, propylene group, butylene group, pentene group, hexene group, heptene group, etc.) and divalent branched saturated hydrocarbon groups having 1 to 7 carbon atoms (isopropylene group, isobutylene group, s -butylene group, t-butylene group, isopentylene group, neopentylene group, t-pentylene group, 1-methylbutylene group, isohexylene group, s-hexylene group, t-hexylene group, neohexylene group, isoheptylene group, etc.). Among the m-valent saturated hydrocarbon groups having 1 to 7 carbon atoms represented by R ¹² , examples of the trivalent saturated hydrocarbon group having 1 to 7 carbon atoms include a methine group. Among the m-valent saturated hydrocarbon groups having 1 to 7 carbon atoms represented by R ¹² , methyl, methylene, and methine groups are preferred, and methyl and methylene groups are more preferred.

Among the m-valent groups in which R ¹² has at least one non-polymerizable double bond or at least one non-polymerizable triple bond and has 2 to 12 carbon atoms, monovalent groups include R ¹⁰ and R ¹¹ The same groups as the exemplified groups are mentioned, and preferred ones are also the same. When R ¹² is a divalent group having from 2 to 12 carbon atoms and having at least one non-polymerizable double bond or at least one non-polymerizable triple bond, preferred groups include a benzenediyl group (a carbon number of 6 , non-polymerizable carbon-carbon double bond), 1-methoxycarbonyl-carbonyloxyethyleneoxycarbonyl group (carbon number 6, oxygen-oxygen double bond) and carbonyloxyethylene carbonyl group (carbon number 4, oxygen-oxygen double bond) double bonds), etc. When R ¹² is a trivalent group having from 2 to 12 carbon atoms and having at least one non-polymerizable double bond or at least one non-polymerizable triple bond, it is preferably a benzenetriyl group (a carbon number 6, non-polymerizable carbon-carbon double bond) and 2-carbonyloxy-carbonyloxypropylene carbonyl group (5 carbon atoms, oxygen-oxygen double bond).

When m is 1, R ¹⁰ and R ¹¹ may be bonded to each other, and preferable groups having a ring structure formed by bonding R ¹⁰ and R ¹¹ to each other include γ-butyrolactonyl group and Examples include fluorenyl group. Note that a group in which R ¹⁰ and R ¹¹ are bonded to each other to form a ring structure includes a carbon atom to which R ¹⁰ and R ¹¹ are bonded in the ring structure.

X ³ is a monovalent organic typical element group having a tellurium element, an antimony element, or a bismuth element, or an iodo group, and preferable examples thereof include a methyltellanyl group, a dimethylstivanyl group, a dimethylbismutanyl group, and an iodo group. Among them, methyltellanyl group and iodo group are more preferable, and iodo group is most preferable.

Examples of organic typical element compounds represented by the general formula (2) include 2-iodopropionitrile, 2-methyl-2-iodopropionitrile, α-iodobenzyl cyanide, 2-iodopropionic acid amide, and ethyl -2-Methyl-2-iodo-propinate, methyl 2-methyl-iodopropionate, propyl 2-methyl-iodopropionate, butyl 2-methyl-iodopropionate, pentyl 2-methyl-iodopropionate, 2-methyl - Hydroxyethyl iodopropionate, 2-methyl-2-iodo-propionic acid (salt), 2-iodopropionic acid (salt), 2-iodoacetic acid (salt), methyl 2-iodoacetate, ethyl 2-iodoacetate, Ethyl 2-iodopentanoate, methyl 2-iodopentanoate, 2-iodopentanoic acid (salt), 2-iodohexanoic acid (salt), 2-iodoheptanoic acid (salt), diethyl 2,5-diiodoadipate , 2,5-diiodoadipic acid (salt), dimethyl 2,6-diiodo-heptanedioate, 2,6-diiodo-heptanedioic acid (salt), α-iodo-γ-butyrolactone, 2-iodoacetophenone, Benzyl iodide, 2-iodo-2-phenylacetic acid (salt), methyl 2-iodo-2-phenylacetate, ethyl 2-iodo-2-phenylacetate, 1,4-bis(1'-iodoethyl)benzene, ethylene Glycol bis(2-methyl-2-iodo-propinate), tris(2-methyl-iodopropionic acid) glycerol, 1,3,5-tris(1'-iodoethylbenzene), ethylene glycol bis(2-iodo-2 2-methyl-2-iodopropionitrile, ethyl-2-methyl-2-iodo-propinate, 2-methyl-2-iodo-propionic acid (salt), and the like. ), 2-iodoacetic acid (salt), methyl 2-iodoacetate, diethyl 2,5-diiodoadipate, 2,5-diiodoadipate, ethylene glycol bis(2-methyl-2-iodo-propinate), Ethylene glycol bis(2-iodo-2phenylacetate) is mentioned.

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 from 0 to 10, more preferably from 0 to 5, particularly preferably from 0 to 5, based on the weight of the crosslinked polymer (A). is from 0 to 3, most preferably from 0 to 1. Within this range, the absorption performance of the water-absorbing resin composition becomes 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.

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.

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.

The hydrogel may be neutralized with a base. 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 resulting water absorbent resin composition may be reduced. 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, in the production of the water-absorbent resin composition, neutralization may be carried out during polymerization or at any stage after the polymerization of the crosslinked polymer (A), and it may be carried out in two or more steps. Neutralization may also be carried out. For example, a method of neutralizing in a hydrogel state is exemplified as a preferable example.

[Shredding process]
The method for producing a water-absorbing resin composition 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.

[Drying process]
The method for producing a water-absorbent resin composition of the present embodiment includes drying the hydrogel, distilling off the solvent (including water) in the hydrogel, and producing the water-absorbent resin containing the crosslinked polymer (A). It has a drying process to obtain.

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 a water-absorbing resin composition of the present embodiment includes a pulverizing step of pulverizing the water-absorbing resin obtained in the drying step to obtain particulate water-absorbing resin containing the crosslinked polymer (A). You may do so.

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

[Surface crosslinking process]
When the surface of the crosslinked polymer (A) is crosslinked with the surface crosslinking agent (d), the method for producing a water absorbent resin composition of the present embodiment includes the crosslinked polymer (A) obtained in the drying step. ) includes a surface crosslinking step of surface crosslinking the water absorbent resin containing the water absorbent resin.

The amount (wt%) of the surface crosslinking agent (d) to be used is not particularly limited, as it can be varied depending on the type of surface crosslinking agent, conditions for crosslinking, target performance, etc., but from the viewpoint of absorption characteristics, etc. Based on the weight of the crosslinked polymer (A), it is preferably 0.001 to 3, more preferably 0.005 to 2, particularly preferably 0.01 to 1.5.

Surface crosslinking of the crosslinked polymer (A) can be carried out by mixing a water absorbent resin containing the crosslinked polymer (A) and a surface crosslinking agent (d) and heating the mixture. Methods for mixing the water absorbent resin containing the crosslinked polymer (A) and the surface crosslinking agent (d) include a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, Mixing equipment such as double-arm kneader, fluid mixer, V-type mixer, mincing mixer, ribbon mixer, fluid mixer, airflow mixer, rotating disc mixer, conical blender, and roll mixer. A method of homogeneously mixing a water-absorbing resin containing a crosslinked polymer (A) and a surface crosslinking agent (d) using a surface crosslinking agent (d) can be mentioned. At this time, the surface crosslinking agent (d) may be used after being diluted with water and/or any solvent.

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

After mixing the crosslinked polymer (A) and the surface crosslinking agent (d), a heat treatment is usually performed. The heating temperature is preferably 100 to 180°C, more preferably 110 to 175°C, particularly preferably 120 to 170°C from the viewpoint of breakage resistance of the water absorbent resin. 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. It is also possible to further surface crosslink the water-absorbing resin obtained by surface crosslinking using a surface crosslinking agent of the same type or a different type from the surface crosslinking agent used initially.

After the surface of the crosslinked polymer (A) is crosslinked with the surface crosslinking agent (d), it is sieved if necessary to adjust the particle size. The average particle diameter of the obtained particles is preferably 100 to 600 μm, more preferably 200 to 500 μm. The content of fine particles is preferably small, the content of particles of 100 μm or less is preferably 3% by weight or less, and the content of particles of 150 μm or less is more preferably 3% by weight or less.

In the method for producing a water absorbent resin composition of the present embodiment, the plant-derived raw material may be added after the polymerization step. The method of adding the plant-derived raw material is not particularly limited, and includes a method of kneading it with the hydrogel, a method of adding the plant-derived raw material and shredding the hydrogel in the shredding process, and a method of adding the water-absorbing resin obtained in the drying process. Examples include a method of kneading a plant-derived raw material and a method of mixing a crosslinked polymer (A), a surface crosslinking agent (d), and a plant-derived raw material in a surface crosslinking step. From the viewpoint of absorption performance and productivity, it is preferable to add the water-containing gel particles obtained in the shredding step and/or the gel shredding step during the drying step.

Plant-derived raw materials include the water-soluble unsaturated dicarboxylic acid (a3) and its salts, as well as oils and fats, proteins, fibers, extracts, saccharides, and the like. Among these, from the viewpoint of water absorption performance, oils and fats, fibers, and sugars are preferred, and more preferably fibers and sugars with a carbon stable isotope ratio (δ ¹³ C) of -60‰ to -5‰, And if ^{the 14} C/C measured by carbon radiocarbon dating satisfies 1.2×10 ^-12 to 1.0×10 ^-16 , some or all of it can be chemically modified. or a mixture thereof.

Examples of the fats and oils include soybean oil, coconut oil, palm oil, palm kernel oil, corn oil, olive oil, safflower oil, safflower oil, cottonseed oil, rapeseed oil, castor oil, and sesame oil.

Examples of fibers include vegetable fibers such as kenaf, jute hemp, manila hemp, sisal hemp, gampi, kozo, banana, pineapple, coconut palm, corn, sugarcane, bagasse, palm, papyrus, reed, Examples include fibers of various plants such as esparto, Sabai grass, wheat, rice, bamboo, conifers such as cedar and cypress, broad-leaved trees, and cotton.

Examples of sugars include fructose, glucose, lactose, maltose, galactose, sucrose, starch, cellulose, and cellulose derivatives.

The method for kneading the hydrogel or water-absorbent resin and the plant-derived raw material includes a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, a double-arm kneader, and a fluidized kneader. There is a method of uniform mixing using mixing equipment such as a mixer, V-type mixer, mincing mixer, ribbon mixer, fluid mixer, airflow mixer, rotating disk mixer, conical blender, and roll mixer. Can be mentioned.

Furthermore, at any stage, water, preservatives, fungicides, antibacterial agents, antioxidants, ultraviolet absorbers, antioxidants, colorants, fragrances, deodorants, liquid permeability improvers, inorganic powders and Organic fibrous materials and the like can be added, and the amount thereof is usually 5% by weight or less based on the weight of the water-absorbing resin composition. Further, it may have a foamed structure, or may be granulated or molded, if necessary.

The content of the crosslinked polymer (A) in the water absorbent resin composition is preferably 50 to 99.5% by weight, more preferably 60 to 99% by weight. When the content of the crosslinked polymer is 50% or more, a water absorbent resin composition having sufficient water retention ability can be obtained.

The water retention amount (g/g) of the water absorbent resin composition can be measured by the method described below, and from the viewpoint of absorption amount, it is preferably 10 or more, more preferably 15 or more, and particularly preferably 18 or more. . Further, from the viewpoint of stickiness, the upper limit is preferably 60 or less, more preferably 55 or less, and particularly preferably 50 or less. The amount of water retained can be adjusted as appropriate by adjusting the amounts (wt%) of the crosslinking agent (b) and surface crosslinking agent (d).

The gel passing rate (ml/min) of the water absorbent resin composition can be measured by the method described below, and is preferably 3 to 300, more preferably 5 to 200, from the viewpoint of diaper absorption rate. Particularly preferably, it is 10-180. It is empirically known that the gel passing rate is in conflict with the water retention amount, and there are cases where a high water retention amount is required and cases where a high gel passing rate is required depending on the configuration of the diaper.

The absorption amount under load (g/g) of the water-absorbing resin composition can be measured by the method described below, and is preferably 11 or more from the viewpoint of the absorption amount of a diaper under load, and 13 or more is further preferred. It is preferably 16 or more, particularly preferably. It has been empirically known that the amount of absorption under load is contradictory to the amount of water retained, and depending on the configuration of the diaper, there are cases where a high water retention amount is required and cases where a high gel passing rate is required.

<Absorber>
An absorbent body can be obtained using the water absorbent resin composition. As the absorbent body, the water-absorbing resin composition 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 composition. Specifically, the above absorber is used. Absorbent products include not only sanitary products such as disposable diapers and sanitary napkins, but also anti-condensation agents, water retention agents for agriculture and gardening, residual soil solidification materials, disaster sandbags, waste blood solidification agents, disposable body warmers, ice packs, and alkaline batteries. It can be used for various purposes such as absorbing various aqueous liquids, holding agent, gelling agent, etc. in various industrial fields such as cosmetics, pet sheets, and cat litter. The manufacturing method of the absorbent article is the same as known methods (those 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. Hereinafter, parts refer to parts by weight, and % refers to % by weight, unless otherwise specified. The water retention capacity of the water-absorbent resin in physiological saline, the absorption capacity under load, the gel passing rate, and the pH of the polymerization solution were measured by the following methods.

<How to measure water retention amount>
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>
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 a 250 to 500 μm mesh were sieved using a 30 mesh sieve and a 60 mesh sieve. Weigh 0.16 g of the measurement sample that has been sieved into a wide area, arrange the cylindrical plastic tube vertically on the nylon net so that the measurement sample has an approximately uniform thickness, and place a weight (weight: 206.2g, outer diameter: 24.5mm) was loaded. 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%). The tube was immersed in an upright vertical position with the nylon mesh side facing down, and left to 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 drops 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 formula. 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

<Measurement method of liquid permeability>
Measurement was performed using the equipment shown in FIGS. 1 and 2 by the following operations.
Swelling gel particles 2 were prepared by immersing 0.32 g of the measurement sample in 150 ml of physiological saline 1 (salt concentration 0.9%) for 30 minutes. A vertical cylinder 3 (diameter (inner diameter) 25.4 mm, length 40 cm) has scale lines 4 and 5 at 60 ml and 40 ml positions from the bottom, respectively. } is placed in a filtration cylindrical tube that has a wire mesh 6 (opening 106 μm, JIS Z8801-1:2006) and a cock 7 that can be opened and closed (inner diameter of the liquid passage part 5 mm), with the cock 7 closed. After the prepared swollen gel particles 2 are transferred together with physiological saline, a circular wire mesh 8 (opening 150 μm, diameter 25 mm) is placed on top of the swollen gel particles 2 with a pressure shaft 9 (heavy weight) connected perpendicularly to the surface of the wire mesh. A weight 10 (88.5 g) was placed on the pressure shaft 9, and the weight was left standing for 1 minute. Next, open the cock 7, measure the time (T1; seconds) required for the liquid level in the filtration cylindrical tube to go from 60ml scale line 4 to 40ml scale line 5, and calculate the gel flow rate (ml/min) using the following formula. The liquid permeability was evaluated by determining.
Gel flow rate (ml/min) = 20ml x 60/(T1-T2)
Note that the temperature of the physiological saline used and the measurement atmosphere was 25° C.±2° C., and T2 is the time measured by the same operation as above for the case where there is no measurement sample.

<Method for measuring pH of polymerization solution>
To measure the pH of the polymerization solution, draw out about 20 ml of the homogeneous polymerization solution from the reaction system into a polycup, and use a desktop pH meter (model number F-71S, Horiba, Ltd.) calibrated with calibration solutions of pH = 4, 7, and 9. It was measured by dipping it into an electrode manufactured by the company. The liquid temperature at this time was 25°C±2.

<Example 1>
Acrylic acid (A1-1) (Mitsubishi Chemical) 240 parts, methylene succinic acid (A2-1) (Fuso Chemical) 60 parts, 48.5% sodium hydroxide aqueous solution 38.1 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. Add and mix 2 parts, 2.3 parts of 2% ascorbic acid aqueous solution, 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1), and 0.4 parts of 0.03% iron sulfate heptahydrate aqueous solution. 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 with a juicer mixer (OSTERIZER BLENDER, manufactured by Oster), and then sieved to adjust the particle size to an opening of 710 to 150 μm to obtain a crosslinked polymer (A-1).

Next, 100 parts of the obtained crosslinked polymer (A-1) was stirred at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm), and 0.0% of ethylene glycol diglycidyl ether was added as the surface crosslinking agent (d). 2 parts of propylene glycol, and 2.5 parts of water were added, mixed uniformly, and heated at 140°C for 40 minutes to form the water-absorbing resin particles (P-1) of the present invention. Obtained.

<Example 2>
The water-absorbing resin particles (P-2) of the present invention were prepared in the same manner as in Example 1, except that 0.6 parts of the 0.1% nitrilotriacetic acid aqueous solution (c-1) was changed to 6 parts. I got it.

<Example 3>
In Example 1, except that 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was changed to 0.6 parts of 0.1% L-glutamic acid diacetic acid/tetrasodium aqueous solution (c-2). The water absorbent resin particles (P-3) of the present invention were obtained in the same manner as in Example 1.

<Example 4>
Example 1 except that 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was changed to 6 parts of L-glutamic acid diacetic acid tetrasodium aqueous solution (c-2). In the same manner, water absorbent resin particles (P-4) of the present invention were obtained.

<Example 5>
In Example 1, except that 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was changed to 0.6 parts of 0.1% hydroxyethyliminodiacetic acid aqueous solution (c-3). Water absorbent resin particles (P-5) of the present invention were obtained in the same manner as in Example 1.

<Example 6>
Example 1 except that in Example 1, 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was changed to 6 parts of 0.1% hydroxyethyliminodiacetic acid aqueous solution (c-3). In the same manner as above, water absorbent resin particles (P-6) of the present invention were obtained.

<Example 7>
Example 1 except that 0.2 parts of ethylene glycol diglycidyl ether was changed to 0.25 parts, 2 parts of propylene glycol was changed to 2.5 parts, and 2.5 parts of water was changed to 3.1 parts. In the same manner as above, water absorbent resin particles (P-7) of the present invention were obtained.

<Example 8>
In Example 1, except that 623 parts of deionized water was changed to 623 parts of industrial water (containing 40 ppb of iron ions (Fe ³⁺ )) and 0.4 part of 0.03% iron sulfate heptahydrate aqueous solution was not added. In the same manner, water absorbent resin particles (P-8) of the present invention were obtained.

<Example 9>
In Example 1, 210 parts of 240 parts of acrylic acid (A1-1) (manufactured by Mitsubishi Chemical), 90 parts of 60 parts of methylene succinic acid (A2-1) (manufactured by Fuso Chemical Industries), and 0.1% nitrile 30 parts of 0.6 parts of acetic acid aqueous solution (c-1), 57.1 parts of 48.5% sodium hydroxide aqueous solution for the polymerization process, and 107 parts of 48.5% sodium hydroxide aqueous solution for the mincing and shredding process. Except for this, water absorbent resin particles (P-9) of the present invention were obtained in the same manner as in Example 1.

<Example 10>
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. Add and mix 2 parts, 2.3 parts of 2% ascorbic acid aqueous solution, 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1), and 0.4 parts of 0.03% iron sulfate heptahydrate aqueous solution. 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 129 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 using a juicer mixer (OSTERIZER BLENDER, manufactured by Oster), and then sieved to adjust the particle size to an opening of 710 to 150 μm to obtain a crosslinked polymer (A-2).

Next, 100 parts of the obtained crosslinked polymer (A-1) was stirred at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm), and 0.0% of ethylene glycol diglycidyl ether was added as the surface crosslinking agent (d). 2 parts of propylene glycol, and 2.5 parts of water were added, mixed uniformly, and heated at 140°C for 40 minutes to form water-absorbing resin particles (P-10) of the present invention. Obtained.

<Comparative example 1>
Comparative water-absorbing resin particles (R-1) were prepared in the same manner as in Example 1, except that 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was not added. I got it.

<Comparative example 2>
In Example 1, 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was added to 30 parts of 0.1% tetrasodium 3-hydroxy-2,2'-iminodisuccinate aqueous solution (c-4). Comparative water absorbent resin particles (R-2) were obtained in the same manner as in Example 1 except for the following changes.

<Comparative example 3>
Example 1 except that in Example 1, 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was changed to 30 parts of 0.1% ethylenediaminetetramethylenephosphonic acid aqueous solution (c-5). Comparative water absorbent resin particles (R-3) were obtained in the same manner as above.

<Comparative example 4>
Example 1 except that 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was changed to 30 parts of 0.1% ethylenediaminetetraacetic acid disodium aqueous solution (c-6). Comparative water absorbent resin particles (R-4) were obtained in the same manner as above.

<Comparative example 5>
In Example 1, 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was changed to 30 parts of 0.1% triethylenetetraminehexaacetic acid hexasodium aqueous solution (c-7). Comparative water absorbent resin particles (R-5) were obtained in the same manner as in Example 1.

<Comparative example 6>
Same as Example 1 except that 0.6 parts of 0.1% nitrilotriacetic acid aqueous solution (c-1) was changed to 30 parts of 0.1% diethylenetriaminepentaacetic acid aqueous solution (c-8). Then, water absorbent resin particles (R-6) for comparison were obtained.

The evaluation results are shown in Table 1.

Note that the chelate stability constant can be determined by the following formula.
Chelate stability constant = [ML _n ]/([M] [L] ⁿ )
In the above formula, [M] means the metal ion concentration, [L] the complex concentration, [ML _n ] the chelate complex concentration , and n the number of complexes that react with the metal ion.

Claims (10)

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 method for producing a water absorbent resin composition containing a crosslinked polymer (A) having as a structural unit a crosslinking agent (b),
A monomer composition containing the monomer (A1), the monomer (A2), and the crosslinking agent (b) is used as a chelating agent (c) having a logarithmic value of the chelate stability constant for Fe ³⁺ at pH 4 of 6.5 to 12. A polymerization step of obtaining a hydrogel containing the crosslinked polymer (A) by polymerizing in the presence of
A method for producing a water absorbent resin composition, comprising a drying step of drying the hydrogel. 2. The chelating agent (c) is one or more selected from ethylenediamine-N,N'-disuccinic acid, nitrilotriacetic acid, tetrasodium L-glutamic acid diacetate, and hydroxyethyliminodiacetic acid. A method for producing a water-absorbing resin composition. Claim 1 or 2, wherein the monomer (A2) is one or more water-soluble unsaturated dicarboxylic acids (a3) selected from the group consisting of maleic acid, fumaric acid, methylene succinic acid, and citraconic acid, and salts thereof. A method for producing a water-absorbing resin composition according to . The method for producing a water absorbent resin composition according to any one of claims 1 to 3, wherein the crosslinking agent (b) is an acrylamide compound. The method for producing a water-absorbing resin composition according to any one of claims 1 to 4, wherein in the polymerization step, the pH of the polymerization solution of the monomer composition is in the range of 1 to 10. 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 water-absorbing resin composition containing a crosslinking agent (b) and a crosslinked polymer (A) having as a constituent unit,
A water-absorbing resin composition further comprising a chelating agent (c) having a logarithmic value of a chelate stability constant for Fe ³⁺ at pH 4 of 6.5 to 12. The ratio of the amount of the monomer (A1) to the amount of the monomer (A2) in the crosslinked polymer (A) (amount of the monomer (A1)/amount of the monomer (A2)) is 1. The water-absorbing resin composition according to claim 6, which has a molecular weight of /99 to 99/1. The water-absorbing resin composition according to claim 6 or 7, wherein the water-absorbing resin composition is in the form of particles. An absorbent body comprising the water absorbent resin composition according to any one of claims 6 to 8. An absorbent article comprising the absorbent body according to claim 9.