JP7130887B1 - Method for producing water absorbent resin composition, water absorbent resin composition, absorbent body using the same, and absorbent article - Google Patents

Abstract

[Problem] To provide a water-absorbing resin composition that uses a plant-derived raw material with low polymerization reactivity and has a water-absorbing performance under load equivalent to that of a water-absorbing resin composition that consists only of a petrochemical-derived monomer, that is, acrylic acid. Provide a manufacturing method. SOLUTION: One or more monomers (A1) selected from the group consisting of water-soluble unsaturated monocarboxylic acids (a1) and salts thereof, and water-soluble unsaturated dicarboxylic acids (a3) selected from the group consisting of salts thereof A method for producing a water-absorbent resin composition containing a crosslinked polymer (A) having, as structural units, one or more monomers (A2) and a crosslinking agent (b), wherein the monomer (A1) and a polymerization step of obtaining a hydrous gel containing the crosslinked polymer (A) by polymerizing a monomer composition containing the monomer (A2) and the crosslinking agent (b) in the presence of a chelating agent (c); A method for producing a water absorbent resin composition, comprising a drying step of drying the hydrous gel. [Selection drawing] Fig. 1

Description

TECHNICAL FIELD 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.

A water-absorbent resin composition is a resin capable of absorbing water several tens to several thousand times its own weight, and for example, a polyacrylic acid-based absorbent resin composition is known. These water-absorbing resin compositions are widely used in disposable sanitary products due to their high water-absorbing properties. However, it has been pointed out that conventional water-absorbing resin compositions are problematic from the viewpoint of environmental load in the disposal method of sanitary goods containing them, and that the method of disposal in an incinerator causes global warming. there is Under such circumstances, there is a strong demand for a water-absorbing resin composition using a plant-derived raw material from the viewpoint of carbon neutrality and the like.

By using a plant-derived raw material for the water-absorbing resin composition, the amount of petrochemical-derived acrylic acid used in the water-absorbing resin composition can be reduced. In addition, by using plant-derived raw materials for the production of the water absorbent resin composition, carbon dioxide emissions generated during acrylic acid production (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 of waste. As means for obtaining a water absorbent resin composition using a plant-derived raw material, 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).

Chinese Patent Application Publication No. 103183764 U.S. Patent Application Publication No. 9109059

However, when homopolymers are produced with maleic acid, itaconic acid, fumaric acid, etc., which are known to be plant-derived raw materials with double bonds, the molecular weight becomes very small, and these plant-derived raw materials are copolymerized with acrylic acid. The molecular weight tends to be smaller than that of polyacrylic acid even in systems where As a result, there is a problem that the gel strength of the water-absorbent resin composition is lowered, and the water absorption performance under load is lowered.

An object of the present invention is to provide a water-absorbent resin having a water-absorbent performance under load equivalent to that of a water-absorbent resin composition composed only of a petrochemical-derived monomer, that is, acrylic acid, while using a plant-derived raw material with low polymerization reactivity. An object of the present invention is to provide 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 water-soluble unsaturated monocarboxylic acids (a1) and salts thereof, and monomers (a2) that become the water-soluble unsaturated monocarboxylic acids (a1) by hydrolysis; , one or more monomers (A2) selected from the group consisting of a water-soluble unsaturated dicarboxylic acid (a3) and a salt thereof, and a monomer (a4) that becomes the water-soluble unsaturated dicarboxylic acid (a3) by hydrolysis; A method for producing a water-absorbing resin composition containing a cross-linked polymer (A) having a cross-linking agent (b) as a structural unit, wherein the monomer (A1) and the monomer (A2) and the cross-linking agent (b ) in the presence of a chelating agent (c) having a ^chelate stability constant logarithm value of 7 or more in at least one of pH 1 to 6 to form the crosslinked polymer (A ) and a polymerization step of obtaining a hydrous gel containing
A method for producing a water-absorbent resin composition, a water-absorbent resin composition, an absorbent body using the same, and an absorbent article, each comprising a drying step of drying the water-containing gel.

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

As a result of research, the present inventors found that the molecular weight of a homopolymer of a plant-derived raw material or a copolymer of a plant-derived raw material and a petrochemical-derived raw material of acrylic acid becomes extremely small only in a very small amount in the polymerization reaction system. The knowledge that it is the influence of iron ion was obtained. 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 are known as monomers with double bonds, is much lower than that of acrylic acid. It is presumed that the molecular weight of the polymer containing the plant-derived raw material is lowered by inhibiting the radical reaction and stopping the polymerization reaction in the middle. 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, suppressing the influence of the iron ions, thereby making homopolymers of plant-derived raw materials and plant-derived It is presumed that the decrease in the molecular weight of the copolymer of the raw material and acrylic acid, which is a petrochemical-derived raw material, can be suppressed.

The figure which represented typically the cross section of the filtration cylindrical tube for measuring the liquid permeability of a water-absorbent-resin composition. FIG. 3 is a perspective view schematically showing a pressurizing shaft and a weight for measuring the liquid permeability of the water absorbent resin composition.

<Method for producing water absorbent resin composition>
The method for producing the water absorbent resin composition of the present embodiment includes:
one or more monomers (A1) selected from the group consisting of water-soluble unsaturated monocarboxylic acids (a1) and salts thereof, and monomers (a2) that become the water-soluble unsaturated monocarboxylic acids (a1) by hydrolysis; , one or more monomers (A2) selected from the group consisting of a water-soluble unsaturated dicarboxylic acid (a3) and a salt thereof, and a monomer (a4) that becomes the water-soluble unsaturated dicarboxylic acid (a3) by hydrolysis; A method for producing a water-absorbing resin composition containing a cross-linked polymer (A) having a cross-linking agent (b) as a structural unit, wherein the monomer (A1) and the monomer (A2) and the cross-linking agent (b ) in the presence of a chelating agent (c) having a ^chelate stability constant logarithm value of 7 or more in at least one of pH 1 to 6 to form the crosslinked polymer (A ) and a polymerization step of obtaining a hydrous gel containing
and a drying step of drying the hydrous gel.
According to the method for producing a water-absorbing resin composition of the present embodiment, while using a plant-derived raw material with low polymerization reactivity, the water-absorbing performance under load is a petrochemical-derived monomer, that is, a water-absorbing resin composed only of acrylic acid. It is possible to provide a water absorbent resin composition that is comparable to the composition.

[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 and availability when crosslinked. , acrylic acid, and methacrylic acid are more preferred.

Examples of the salt 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, alkali metal salts and ammonium salts are preferable, alkali metal salts are more preferable, and sodium salts are particularly preferable, from the viewpoint of absorption performance and the like.

(monomer (a2))
The monomer (a2) that 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 a monomer having one hydrolyzable substituent that becomes a carboxy group by hydrolysis can be exemplified. Examples of the hydrolyzable substituent include acid anhydride-containing groups (1,3-oxo-1-oxapropylene group, -COO-CO-), ester bond-containing groups (alkyloxycarbonyl, vinyloxycarbonyl, allyl oxycarbonyl or propenyloxycarbonyl, —COOR), cyano group and the like. R is an alkyl group having 1 to 3 carbon atoms (methyl, ethyl and propyl), vinyl, allyl and propenyl.

In this specification, the term "water-soluble" means that at least 5 g of the substance dissolves in 100 g of water at 25°C. Further, 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.) to become water-soluble. The hydrolysis of the monomer (a2) may be carried out during polymerization, after polymerization, or both of them, but from the viewpoint of the absorption performance of the resulting water-absorbent resin composition, it is preferably carried out after polymerization.

[Monomer (A2)]
(Water-soluble unsaturated dicarboxylic acid (a3) and salts thereof)
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) consists of maleic acid, fumaric acid, methylenesuccinic acid, and citraconic acid from the viewpoint of reactivity with the water-soluble unsaturated monocarboxylic acid (a1) and availability. One or more selected from the group is preferable, and methylenesuccinic acid is more preferable.

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, alkali metal salts and ammonium salts are preferable, alkali metal salts are more preferable, and sodium salts are particularly preferable, from the viewpoint of absorption performance and the like.

(Monomer (a4))
The 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 thereof include monomers having at least one hydrolyzable substituent.

Hydrolysis of the monomer (a4) may be carried out during polymerization, after polymerization, or at both of these times, but is preferably carried out after polymerization from the viewpoint of the absorption performance of the resulting water-absorbent resin composition.

At least one of the monomer (A1) and the monomer (A2) has a ¹⁴ C/C measured by carbon radiocarbon dating of 1.2×10 ⁻¹² to 1.0×10 ⁻¹⁶ , preferably is preferably 1.5×10 ⁻¹² to 1.2×10 ⁻¹⁴ . Specifically, the radiocarbon age of carbon is measured by measuring the concentration of carbon-14 in the sample, and calculating back using the content ratio of carbon-14 in the atmosphere (107pMC (percent modern carbon)) as an index. The percentage of carbon-14 among the carbons contained can be determined. The sample (water-absorbing resin composition) is converted to CO ₂ from the constituent carbon, or the obtained CO ₂ is further converted to graphite (C), and then subjected to an accelerator mass spectrometer (AMS) and subjected to a standard substance (for example, the United States It can be determined by comparatively measuring the content of carbon-14 with respect to NIST oxalic acid).

In the radiocarbon dating method of carbon, the carbon that existed as carbon dioxide in the atmosphere is incorporated into plants, and radiocarbon, which is carbon present in plant-derived raw materials synthesized using the plants as raw materials (i.e., Carbon 14) is measured. Then, since almost no carbon-14 atoms remain in fossil raw materials such as petroleum, the concentration of carbon-14 in the target sample is measured, and the content of carbon-14 in the atmosphere (107pMC (percent modern carbon)) By calculating back using as an index, the ratio of biomass-derived carbon in the carbon contained in the sample can be obtained.

It is also possible to identify the origin of the raw material by measuring the stable carbon isotope ratio (δ ¹³ C). The stable carbon isotope ratio (δ ¹³ C) refers to 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 x 10 ⁻¹² units; %), the ratio of ¹³ C to ¹² C, and the stable carbon isotope ratio is expressed as a deviation from a standard substance and refers to a 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 substance. PDB is an abbreviation for "Pee Dee Belemnite" and means a fossil of a pilaster made of calcium carbonate (as a reference material, a fossil of a pilaster excavated from the PeeDee Formation in South Carolina), and has a ¹³ C/ ¹² C ratio. used as a standard body for In addition, the "stable carbon isotope ratio (δ ¹³ C)" is measured by accelerator mass spectrometry (AMS method; Accelerator Mass Spectrometry). Since standard substances are scarce, a working standard with a known stable isotope ratio to the standard substance can also be used.

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

The ratio of the substance amount of the monomer (A1) to the substance amount of the monomer (A2) in the crosslinked polymer (A) (substance amount of the monomer (A1)/substance amount of the monomer (A2)) is the load From the viewpoints of improving water absorption performance under low temperature conditions 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), another vinyl monomer (A3) copolymerizable therewith can be used as the structural unit of the crosslinked polymer (A). One of the vinyl monomers (A3) may be used alone, or two or more of them may be used in combination.

The vinyl monomer (A3) is not particularly limited, and is known (for example, hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553; 2005-75982, paragraph 0058) can be used, and specifically, vinyl monomers (i) to (iii) below can be used.
(i) Aromatic ethylenic monomer having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, vinylnaphthalene, and halogen-substituted styrene such as 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) C5-C15 alicyclic ethylenic monomers monoethylenically unsaturated monomers (pinene, limonene, indene, etc.); and polyethylene vinyl monomers [cyclopentadiene, bicyclopentadiene, ethylidenenorbornene, etc.], and the like.

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

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

The cross-linking agent (b) is preferably a cross-linking agent having two or more ethylenically unsaturated groups, and from the viewpoint of reactivity with monomers and water absorption properties, polyvalent (meta) having two or more ethylenically unsaturated groups More preferably one or more selected from the group consisting of allyl compounds and acrylamide compounds, poly (meth) allyl ethers of polyhydric alcohols such as alkylene glycol, trimethylolpropane, glycerin, pentaerythritol and sorbitol, tetraallyloxyethane and tri 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) Species or more are more preferred. The said crosslinking agent (b) may be used individually by 1 type, or may use 2 or more types together. N,N'-methylenebisacrylamide and a compound represented by the following general formula (1) are more preferably used from the viewpoint of reactivity and balance between water retention capacity and absorption capacity under load.

［一般式（１）中、Ｒ^１およびＲ^２はそれぞれ独立に水素原子又はメチル基である。Ｘ^１は、炭素数２以上の脂肪族基を有し、窒素原子、酸素原子、又は硫黄原子を含んでもよいｎ価の有機基であり、前記脂肪族基は直鎖であっても分岐を有していてもよい。ｎは２から６の整数である。］

[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 optionally containing 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; ]

In 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 having an aliphatic group having 2 or more carbon atoms and optionally containing 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, from the viewpoint of absorption performance, etc., the aliphatic group is from —O— and —NX ² — (wherein X ² is a hydrogen atom, an alkyl group, or a (meth)acryloyl group). It is preferable to connect 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 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 of 2 to 6, and preferably an integer of 2 to 4 from the viewpoint of absorption performance and the like.

When n is 2 in the general formula (1), 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.

［一般式（ｂ１）において、Ｒ^３は炭素数１～６のアルキレン基であり、Ｒ^４は水素原子又はメチル基であり、ｘは２～４の整数であり、ｒは１～６の整数であり、Ｒ^５は単結合または炭素数１～６のアルキレン基である。］

[In 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は炭素数１～３のアルキレン基であり、ｙは２～４の整数であり、ｓは１～６の整数であり、Ｒ^７は単結合または炭素数１～３のアルキレン基である。］

[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 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 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, more preferably 2, from the viewpoint of availability of raw materials.

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

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

In 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 of 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, more preferably 3 or 4, from the viewpoint of availability of raw materials.

In 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 X ¹ is an organic group represented by the general formula (b1), a specific example of the cross-linking agent (b) is represented by the following general formula (b1-1) Cross-linking agents (b1-1), cross-linking agents (b1-2) represented by the following general formula (b1-2), and the like.

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

When n is 4 in the general formula (1), 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, 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, 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, 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, more preferably a methylene group, from the viewpoint of availability of raw materials. preferable.

In the general formula (1), when X ¹ is an organic group represented by the general formula (b3), a specific example of the cross-linking agent (b) is represented by the following general formula (b3-1). Cross-linking agents (b3-2) and cross-linking agents (b3-2) represented by the following general formula (b3-2) are included.

Examples of commercially available products of the cross-linking agent (b) include FOM-03006, FOM-03007, FOM-03008, and FOM-03009 (all manufactured by FUJIFILM Corporation).

The content (mol%) of the cross-linking agent (b) in the cross-linked polymer (A) is, from the viewpoint of absorption performance, etc., the total number of moles of the monomer (A1) units and the monomer (A2) units, other When the 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). is.

[Chelating agent (c)]
The water-absorbent resin composition contains a chelating agent (c) having a logarithm of a chelate stability constant with respect to Fe ³⁺ of 7 or more at least at pH 1-6.

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

From the viewpoint of reactivity during polymerization, the chelating agent (c) preferably has a logarithm of the chelate stability constant with respect to Fe ³⁺ of 7 or more and 16 or less, more preferably 13, at least at pH 1 to 6. 20 or less.

Examples of the chelating agent (c) include ethylenediamine-N,N'-disuccinic acid (EDDS), nitrilotriacetic acid (NTA), L-glutamic acid diacetic acid tetrasodium (GLDA 4Na), 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., preferably ethylenediamine-N,N'-disuccinic acid, nitrilotriacetic acid (NTA) , tetrasodium L-glutamic acid diacetate (GLDA.4Na), and hydroxyethyliminodiacetic acid.

The content (weight ratio) of the chelating agent (c) in the water absorbent resin composition is 0.1 to 1,000 parts per 1,000,000 parts of the total substance amount of the monomer (A1) unit and the monomer (A2) unit. is preferred, more preferably 1-500, and particularly preferably 5-200. Within this range, the amount of iron acting as a catalyst for the initiator in the polymerization system is appropriate, so that the strength of the resulting gel is further improved.

The content (ppm) of the chelating agent (c) in the water absorbent resin composition is 0.1-1000, preferably 1-500, more preferably 5-200. Within this range, the absorption performance under load is improved by improving the gel strength. The content of the chelating agent (c) can be measured by the method described below.

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 to 50, particularly preferably 1 to 20. Within this range, the amount of iron acting as a catalyst for the initiator in the polymerization system is appropriate, so that the strength of the resulting gel is further improved.

The water absorbent resin composition preferably has a structure in which the surface of the crosslinked polymer (A) is crosslinked by the surface crosslinking agent (d). By cross-linking the surface of the crosslinked polymer (A), the gel strength of the water-absorbing resin composition can be improved, and the water-absorbing resin composition satisfies the desired water retention capacity and absorption capacity under load. can be done. The surface cross-linking agent (d) can be inorganic or organic. As the surface cross-linking agent (d), known (polyvalent glycidyl compounds, polyvalent amines, polyvalent aziridine compounds and polyvalent isocyanate compounds described in JP-A-59-189103, etc., JP-A-58-180233 And the polyhydric alcohol of JP-A-61-16903, the silane coupling agent described in JP-A-61-211305 and JP-A-61-252212, the JP-A-5-508425 described Organic surface cross-linking agents such as alkylene carbonates and polyvalent oxazoline compounds described in JP-A-11-240959 can be used. Among these surface cross-linking agents, one or more selected from the group consisting of polyhydric glycidyl compounds, polyhydric alcohols and polyhydric amines are preferred from the viewpoint of economy and absorption characteristics, and more preferred are polyhydric glycidyl compounds and One or more selected from the group consisting of polyhydric alcohols, particularly preferably one or more selected from the group consisting of polyhydric glycidyl compounds, most preferably ethylene glycol diglycidyl ether. The surface cross-linking agent (d) may be used alone or in combination of two or more.

The water-absorbing resin composition may contain other components such as residual solvent and residual cross-linking components to the extent that the performance of the composition is not impaired.

In the water-absorbent resin composition, the other component is preferably selected from the group consisting of iodine, tellurium, antimony, and bismuth, from the viewpoint of improving gel strength, absorption under load, and gel flow rate at the time of water absorption. At least one type of typical element may be included. When the water-absorbent resin composition contains the typical element, the content of the typical element in the water-absorbent resin composition is adjusted from the viewpoint of improving the gel strength, the absorption amount under load, and the gel liquid permeation rate at the time of water absorption. , preferably 0.0005 to 0.1% by weight, more preferably 0.001 to 0.05% by weight. The water-absorbing resin composition containing the main group element is prepared by adding a monomer composition containing the monomer (A1) and the monomer (A2) and the cross-linking agent (b) in the presence of the organic main group element compound described later. It can be obtained by polymerizing and drying the resulting hydrous gel.

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

Although the shape of the water absorbent resin composition is not particularly limited, it is preferably particulate from the viewpoint of improving the absorption performance. The particulate water absorbent resin composition (hereinafter also referred to as water absorbent resin particles) has a weight average particle diameter (μm) of 250-600, preferably 300-500, more preferably 340-460. When the weight-average particle size is less than 250 µm, the liquid permeability deteriorates, and when it exceeds 600 µm, the absorption speed deteriorates.

In addition, the weight average particle size was measured using a low-tap test sieve shaker and a standard sieve (JISZ8801-1:2006), Perry's Chemical Engineers Handbook 6th Edition (McGraw-Hill Book Company, 1984, page 21). That is, JIS standard sieves 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 are combined in this order from the top. About 50 g of the particles to be measured are placed in the top sieve and shaken for 5 minutes with a Rotap test sieve shaker. The weight of the particles to be measured on each sieve and the tray is weighed, the total is 100% by weight, and the weight fraction of the particles on each sieve is obtained. ) and the weight fraction on the vertical axis], draw a line connecting the points, determine the particle diameter corresponding to a weight fraction of 50% by weight, and take this as the weight average particle diameter.

Since the smaller the content of the fine powder contained in the water absorbent resin particles, the better the liquid permeability, the weight ratio (weight %) is 3 or less, preferably 1 or less. The weight ratio of the water-absorbing resin particles having a particle size of less than 150 μm can be determined using the graph created when determining the weight average particle size.

The shape of the water-absorbent resin particles is not particularly limited, and examples thereof include irregularly pulverized shape, scaly shape, pearl shape, rice grain shape, and the like. Of these, irregularly crushed forms are preferred from the viewpoints of good entanglement with fibrous materials for use in paper diapers and the like, and no fear of falling off from fibrous materials.

[Polymerization process]
A monomer composition containing the monomers (A1) and (A2) and the crosslinking agent (b) is polymerized in the presence of the chelating agent (c) to chelate iron ions in the polymerization system. , the reaction can proceed efficiently, making it easier to obtain a high-molecular-weight crosslinked polymer. Examples of the method for polymerizing the monomer composition include known solution polymerization and known reversed-phase suspension polymerization.

Iron ions have the effect of promoting the cleavage of the peroxide initiator and the decomposition of the resin in the water-absorbing resin composition. If it is inactivated, the polymerization will not proceed and the water absorbent resin will not be obtained. Further, when the amount of active iron ions that do not form a chelate with the chelating agent in the polymerization system is 1 ppb or less, the amount of radicals supplied is too low to produce an ultrahigh molecular weight component, impairing water absorption. Therefore, the amount of active iron ions is preferably controlled within the range of 1 ppb to 1 ppm with respect to the polymerization solution.

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

The amount (ppm) of the chelating agent (c) added is the total amount of the monomer (A1) and the monomer (A2). Based on the total amount, it is preferably 0.1-1000, more preferably 1-1000, particularly preferably 1-500. Within this range, the amount of iron acting as a catalyst for the initiator in the polymerization system is appropriate, so that the strength of the resulting gel is further improved.

The addition amount (substance amount) of the chelating agent (c) 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 acting as a catalyst for the initiator in the polymerization system is appropriate, so that the strength of the resulting gel is further improved.

The degree of neutralization (number of moles) relative to the sum of the monomers (A1) and (A2) during polymerization is preferably 1 to 80%, more preferably 1 to 50%, and particularly preferably 5 to 40%. Within this range, the obtained polymer is obtained as a high-molecular weight body, so that the 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 monomer), and since monomer (A1) is a monocarboxylic acid and monomer (A2) is a dicarboxylic acid, Addition degree (%) = number of moles of added base/(number of moles of monomer (A1) + number of moles of monomer (A2) x 2).

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

Of the methods for polymerizing the monomer composition, preferred is the solution polymerization method, and particularly preferred is the aqueous solution polymerization method because it does not require the use of an organic solvent or the like and is advantageous in terms of production cost. The aqueous solution adiabatic polymerization method is most preferable because it provides a water-absorbent resin composition containing a large amount of water and a small amount of water-soluble components, and does not require temperature control 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 the organic solvent includes methanol, ethanol, acetone, methyl ethyl ketone, N,N-dimethylformamide, Dimethylsulfoxide and mixtures of two or more thereof are included. When the monomer composition is polymerized by aqueous solution polymerization, the amount (% by weight) of the organic solvent used is preferably 40 or less, more preferably 30 or less based on the weight of water.

The pH range of the monomer composition containing the monomers (A1) and (A2) and the cross-linking agent (b) and the polymerization solution containing the chelating agent (c) at the time of polymerization is preferably 1 to 10. , more preferably 1-7, more preferably 1-6. Within this range, the polymerization reaction proceeds efficiently, and the required water absorption performance can be easily obtained.

When a catalyst is used for polymerization, conventionally known radical polymerization catalysts can be used, for example, azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid and 2,2′-azobis(2-amidinopropane) hydrochloride etc.], inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate and sodium persulfate, etc.), organic peroxides [benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, persuccinic acid oxide and di(2-ethoxyethyl) peroxydicarbonate, etc.] and redox catalysts (alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite and reducing agents such as ascorbic acid and alkali metal persulfates, ammonium persulfate, hydrogen peroxide, organic peroxide, etc.), and the like. For the purpose of promoting the polymerization reaction, iron salts (iron chloride (II), 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 which may be added may be used alone, or two or more thereof may be used in combination.

The amount (% by weight) of the radical polymerization catalyst used is 0 based on the total weight of the monomers (A1) and (A2), and (A1) to (A3) when another vinyl monomer (A3) is used. 0.0005 to 5 is preferred, and 0.001 to 2 is more preferred.

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

The amount (% by weight) of the polymerization control agent used is 0, based on the total weight of the monomers (A1) and (A2), and (A1) to (A3) when another vinyl monomer (A3) is used. 0.0005 to 5 is preferred, and 0.001 to 2 is more preferred.

The crosslinked polymer (A) is a monomer composition containing the monomers (A1) and (A2) and the crosslinking agent (b), and By polymerizing in the presence of at least one organic main group element compound selected from the group consisting of compounds, gel strength, absorption under load and gel permeation rate upon water absorption can be improved.

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 main group element compounds that act as dormant species for radical polymerization, and are 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, an organic main group element compound represented by the following general formula (2) is preferable. These organic main group element compounds may be used alone or in combination of two or more.

In the general formula (2), R ¹⁰ and R ¹¹ are each independently a hydrogen atom, a saturated hydrocarbon group having 1 to 7 carbon atoms, or at least one non-addition polymerizable double bond or at least one non-addition polymerizable triple is a monovalent group having 1 to 7 carbon atoms and having a bond, 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- an m-valent group having 2 to 12 carbon atoms and 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 divalent 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 main group element group containing tellurium, antimony or bismuth or an iodine group. In the present specification, non-addition polymerizable double bond (hereinafter also simply referred to as non-polymerizable double bond) and non-addition polymerizable triple bond (hereinafter simply referred to as non-polymerizable triple bond) means an unsaturated bond Of these, the bonds excluding addition-polymerizable unsaturated bonds (addition-polymerizable carbon-carbon double bonds and addition-polymerizable carbon-carbon triple bonds, respectively), non-addition-polymerizable double bonds and non-addition-polymerizable As the triple bond, the carbon-oxygen double bond contained in the carbonyl group, the carbon-nitrogen triple bond contained in the nitrile group, the carbon-carbon double bond that constitutes the aromatic hydrocarbon, and the oxygen that constitutes the heteroaromatic compound -Nitrogen double bonds and carbon-nitrogen double bonds, among others, carbon-oxygen double bonds contained in carbonyl groups, carbon-nitrogen triple bonds contained in nitrile groups and carbons 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, n-propyl group, n-butyl group, n-pentyl group and n-hexyl group) 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 them, straight-chain saturated hydrocarbon groups having 1 to 5 carbon atoms are preferable, and straight-chain saturated hydrocarbon groups having 1 to 3 carbon atoms are more preferable from the viewpoint of solubility and polymerizability.

When R ¹⁰ and R ¹¹ are C 1-7 monovalent groups having at least one non-polymerizable double bond or at least one non-polymerizable triple bond, preferred groups are carboxy (salt) groups. (carbon number 1, carbon-oxygen double bond), phenyl group (carbon number 6, non-polymerizable carbon-carbon double bond), cyano group (carbon number 1, 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 (C3, carbon-oxygen double bond), hydroxypropyloxycarbonyl group (4 carbons, carbon-oxygen double bond), hydroxybutyloxycarbonyl group (5 carbons, carbon-oxygen double bond), hydroxy Examples include a pentyloxycarbonyl group (6 carbon atoms, carbon-oxygen double bond) and a hydroxyhexyloxycarbonyl group (7 carbon atoms, carbon-oxygen double bond), and more preferably a carboxy (salt) group, cyano group, carboxymethyl group, and carboxyethyl group. Examples of salts 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, alkali metal salts and ammonium salts are preferable, alkali metal salts are more preferable, and sodium salts are particularly preferable, from the viewpoint of absorption performance and the like.

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 , the monovalent saturated hydrocarbon group having 1 to 7 carbon atoms is a linear saturated hydrocarbon group 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.). be done. Among the m-valent saturated hydrocarbon groups having 1 to 7 carbon atoms represented by R ¹² , the divalent saturated hydrocarbon group having 1 to 7 carbon atoms is a linear saturated divalent hydrocarbon group 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 , trivalent saturated hydrocarbon groups having 1 to 7 carbon atoms include a methine group and the like. Of the m-valent saturated hydrocarbon groups having 1 to 7 carbon atoms represented by R ¹² , methyl group, methylene group and methine group are preferred, and methyl group and methylene group are more preferred.

Among m-valent groups in which R ¹² has 2 to 12 carbon atoms and at least one non-polymerizable double bond or at least one non-polymerizable triple bond, the monovalent groups include R ¹⁰ and R ¹¹ Examples include the same groups as the exemplified groups, and preferred ones are also the same. When R ¹² is a divalent group having 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 (6 carbon atoms , non-polymerizable carbon-carbon double bond), 1-methoxycarbonyl-carbonyloxyethyleneoxycarbonyl group (6 carbon atoms, oxygen-oxygen double bond) and carbonyloxyethylenecarbonyl group (4 carbon atoms, oxygen-oxygen two double bond) and the like. When R ¹² is a trivalent group having 2 to 12 carbon atoms having at least one non-polymerizable double bond or at least one non-polymerizable triple bond, it is preferably a benzenetriyl group (having 6, non-polymerizable carbon-carbon double bond) and 2-carbonyloxy-carbonyloxypropylenecarbonyl group (5 carbon atoms, oxygen-oxygen double bond).

When m is 1, R ¹⁰ and R ¹¹ may be bonded to each other, and preferred groups having a ring structure formed by bonding R ¹⁰ and R ¹¹ are γ-butyrolactonyl and A fluorenyl group and the like can be mentioned. The group in which R ¹⁰ and R ¹¹ are bonded together to form a ring structure includes the carbon atom to which R ¹⁰ and R ¹¹ are bonded in the ring structure.

X3 is a monovalent organic main group element group containing tellurium ^, antimony or bismuth or an iodine group, preferably methyltheranyl, dimethylstivanyl, dimethylbismutanyl and iodine. Among them, a methylteranyl group and an iodo group are more preferred, and an iodo group is most preferred.

Examples of the organic main element compound represented by the general formula (2) include 2-iodopropionitrile, 2-methyl-2-iodopropionitrile, α-iodobenzyl cyanide, 2-iodopropionamide, ethyl -2-methyl-2-iodo-propionate, methyl 2-methyl-iodopropionate, 2-methyl-propyl iodopropionate, butyl 2-methyl-iodopropionate, 2-methyl-pentyl 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-diiodoadipate (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-iodopropionate), tris(2-methyl-iodopropionate) glycerol, 1,3,5-tris(1′-iodoethylbenzene), ethylene glycol bis(2-iodo-2 phenyl acetate), etc. Among them, 2-methyl-2-iodopropionitrile, ethyl-2-methyl-2-iodo-propionate, 2-methyl-2-iodo-propionic acid (salt ), 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) can be mentioned.

The amount of the organic main group element compound used is preferably 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 employed as the polymerization method, polymerization may be carried out in the presence of a conventionally known dispersant or surfactant, if necessary. In the case of the reversed-phase suspension polymerization method, the polymerization can be carried out using conventionally known hydrocarbon solvents such as xylene, normal hexane and normal heptane.

The polymerization initiation temperature can be appropriately adjusted 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., from the viewpoint of polymerization reactivity and absorption performance. is particularly preferably 5 to 60°C.

When a solvent (organic solvent, water, etc.) is used for polymerization, it is preferred to distill off the solvent after polymerization. When the solvent contains an organic solvent, the content (% by weight) of the organic solvent after distillation is preferably 0 to 10, more preferably 0 to 5, particularly preferably 0 to 5, based on the weight of the crosslinked polymer (A). is 0-3, most preferably 0-1. Within this range, the absorption performance of the water absorbent resin composition is further improved.

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

When the solvent contains water, the water content (% by weight) 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 3-8. Within this range, the absorption performance is further improved.

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

The hydrous gel 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 hydrous gel polymer will have high adhesiveness, and workability during production and use may deteriorate. Furthermore, the water-retaining capacity of the obtained water-absorbent resin composition may decrease. On the other hand, if the degree of neutralization exceeds 80%, the resulting resin will have a high pH and may be unsafe for human skin.

In the production of the water-absorbing resin composition, neutralization may be carried out during polymerization, or may be carried out at any stage after polymerization of the crosslinked polymer (A), and may be divided into two or more steps. neutralization may be carried out. For example, a method of neutralizing in the state of hydrous gel is exemplified as a preferable example.

[Shredding process]
The method for producing the water-absorbing resin composition of the present embodiment may have a shredding step of shredding the hydrous gel, if necessary. The size (maximum diameter) of the gel after shredding 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 property in the drying process is further improved.

Shredding can be performed by a known method, and can be performed using a shredding device (eg, Vex mill, rubber chopper, farmer mill, mincing machine, impact pulverizer, roll pulverizer) and the like.

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

In the drying step, the method of distilling off the solvent in the hydrous gel includes a method of distilling (drying) with hot air at a temperature of 80 to 230 ° C., and a thin film drying method using a drum dryer or the like heated to 100 to 230 ° C. , (heating) vacuum drying method, freeze drying method, infrared drying method, decantation, filtration, and the like can be applied.

[Pulverization process]
The method for producing a water absorbent resin composition of the present embodiment includes a pulverizing step of pulverizing the water absorbent resin obtained in the drying step to obtain a particulate water absorbent resin containing the crosslinked polymer (A). You may have

In the pulverization step, the method for pulverizing the water-absorbent resin containing the crosslinked polymer (A) is not particularly limited, and pulverization equipment (e.g., hammer pulverizer, impact pulverizer, roll pulverizer and A jet stream pulverizer) or the like can be used. The pulverized crosslinked polymer (A) can be adjusted in particle size by sieving or the like, if necessary.

[Surface cross-linking step]
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 ) has a surface cross-linking step of surface cross-linking the water absorbent resin containing.

The amount (% by weight) of the surface cross-linking agent (d) used is not particularly limited because it can be varied depending on the type of the surface cross-linking agent, cross-linking conditions, target performance, etc., but is not particularly limited from the viewpoint of absorption characteristics and the like. Therefore, it is preferably 0.001 to 3, more preferably 0.005 to 2, and particularly preferably 0.01 to 1.5, based on the weight of the crosslinked polymer (A).

The surface cross-linking of the cross-linked polymer (A) can be carried out by mixing the water absorbent resin containing the cross-linked polymer (A) and the surface cross-linking agent (d) and heating the mixture. The method for mixing the water absorbent resin containing the crosslinked polymer (A) and the surface cross-linking agent (d) includes a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, Mixing equipment such as twin-arm kneaders, fluidized mixers, V-shaped mixers, mincing mixers, ribbon mixers, fluidized mixers, airflow mixers, rotating disk mixers, conical blenders and roll mixers. A method of uniformly mixing the water-absorbing resin containing the crosslinked polymer (A) and the surface cross-linking agent (d) using a cross-linked polymer (A). At this time, the surface cross-linking agent (d) may be diluted with water and/or any solvent before use.

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

After mixing the crosslinked polymer (A) and the surface cross-linking agent (d), 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 breaking resistance of the water absorbent resin. Heating at 180° C. or less enables indirect heating using steam, which is advantageous in terms of facilities. Heating temperatures below 100° C. may result in poor absorption performance. 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 that is the same as or different from the surface-crosslinking agent used first.

After cross-linking the surface of the cross-linked polymer (A) with the surface-cross-linking agent (d), the particle size is adjusted by sieving if necessary. The average particle size of the obtained particles is preferably 100-600 μm, more preferably 200-500 μm. The content of fine particles is preferably as small as possible, 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 the 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 with the hydrous gel, a method of shredding the hydrous gel by adding the plant-derived raw material in the shredding step, and a water-absorbing resin obtained in the drying step. and a method of kneading a plant-derived raw material, and a method of mixing a cross-linked polymer (A), a surface cross-linking agent (d), and a plant-derived raw material in the surface cross-linking 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 salts thereof, as well as oils and fats, proteins, fibers, extracts, sugars, and the like. Among these, fats and oils, fibers, and sugars are preferred from the viewpoint of water absorption performance, and fibers and sugars are more preferred, and the stable carbon isotope ratio (δ ¹³ C) is from −60‰ to −5‰, And if the ¹⁴ C/C measured by the carbon radiocarbon dating method satisfies 1.2×10 ⁻¹² to 1.0×10 ⁻¹⁶ , part or all of it is chemically modified or a mixture thereof.

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, sesame oil, and the like.

Fibers include vegetable fibers, and vegetable fibers include kenaf, jute hemp, manila hemp, sisal hemp, ganpi, kozo, banana, pineapple, coconut palm, corn, sugar cane, bagasse, palm, papyrus, reed, Coniferous trees such as esparto, surviving grass, barley, rice, bamboo, cedar and cypress, broad-leaved trees, and fibers of various plants such as cotton.

Sugars include fructose, glucose, lactose, maltose, galactose, sucrose, starch, cellulose, cellulose derivatives and the like.

Methods for kneading the hydrous gel or water absorbent resin and the plant-derived raw material include a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, a double-arm kneader, and a fluid type. Uniform mixing using mixing equipment such as mixers, V-type mixers, mincing mixers, ribbon mixers, fluidized mixers, airflow mixers, rotating disk mixers, conical blenders and roll mixers. mentioned.

Furthermore, at any stage, water, preservatives, antifungal agents, antibacterial agents, antioxidants, ultraviolet absorbers, antioxidants, coloring agents, fragrances, deodorants, liquid permeability improvers, inorganic powders and An organic fibrous material or the like can be added, and the amount thereof is usually 5% by weight or less based on the weight of the water absorbent resin composition. Moreover, if necessary, it may have a foamed structure, and may be granulated or molded.

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, it is possible to obtain a water absorbent resin composition having sufficient water retention capacity.

The water retention capacity (g/g) of the water absorbent resin composition can be measured by the method described later, and is preferably 10 or more, more preferably 15 or more, and particularly preferably 18 or more from the viewpoint of absorption capacity. . Moreover, the upper limit is preferably 60 or less, more preferably 55 or less, and particularly preferably 50 or less, from the viewpoint of stickiness. The amount of water retention can be appropriately adjusted by the amount (% by weight) of the cross-linking agent (b) and the surface cross-linking agent (d) used.

The gel permeation rate (ml/min) of the water absorbent resin composition can be measured by the method described later, and is preferably 5 to 300, more preferably 10 to 200, from the viewpoint of diaper absorption rate. 15-180 is particularly preferred. It is empirically known that the gel permeation rate conflicts with the water retention capacity, and there are cases where a high water retention capacity is required and there are cases where a high gel permeation rate is required depending on the configuration of the diaper.

The absorbency under load (g/g) of the water-absorbent resin composition can be measured by the method described later, and is preferably 11 or more, and more preferably 13 or more, from the viewpoint of the diaper absorbency under load. It is preferably 16 or more, particularly preferably 16 or more. It is empirically known that the absorbency under load conflicts with the water retention capacity, and there are cases where a high water retention capacity is required and cases where a high gel permeation rate is required depending on the configuration of the diaper.

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

Cellulose fibers, organic synthetic fibers, and mixtures of cellulosic fibers and organic synthetic fibers are preferable as the fibrous material.

Examples of cellulosic fibers include natural fibers such as fluff pulp, and chemical cellulosic fibers such as bicose rayon, acetate and cupra. The raw material (softwood, hardwood, etc.), manufacturing method (chemical pulp, semi-chemical pulp, mechanical pulp, CTMP, etc.), bleaching method, and the like of this cellulose-based 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 fibers having different melting points). (sheath-and-core type, eccentric type, side-by-side type, etc.), fibers obtained by blending at least two of the above fibers, and fibers obtained by modifying the surface layer of the above fibers.

Among these fibrous materials, cellulosic natural fibers, polypropylene fibers, polyethylene fibers, polyester fibers, heat-fusible conjugate fibers and mixed fibers thereof are preferred, and more preferred are fluff pulp, heat-fusible conjugate fibers and mixed fibers thereof in that they are excellent in shape retention after water absorption by the water absorbing agent.

The length and thickness of the above-mentioned fibrous material are not particularly limited, and a length of 1 to 200 mm and a thickness of 0.1 to 100 denier can be suitably used. The shape is not particularly limited as long as it is fibrous, and examples include a thin cylindrical shape, a split yarn shape, a staple shape, a filament shape, a web shape, and the like.

When the water absorbent resin particles are used as an absorber together with fibrous materials, the weight ratio of the water absorbent resin particles and fibers (weight of water absorbent resin particles/weight of fibrous materials) is 40/60 to 90/10. It is preferably 70/30 to 80/20, more preferably 70/30 to 80/20.

<Absorbent article>
An absorbent article can be obtained using the water absorbent resin composition. Specifically, the absorber described above is used. Absorbent products include not only sanitary products such as paper diapers and sanitary napkins, but also anti-condensation agents, water retention agents for agriculture and gardening, soil solidification agents, disaster sandbags, waste blood solidification agents, disposable body warmers, refrigerants, and alkaline batteries. It can be used for various purposes such as absorption of various aqueous liquids, retention agent use, and gelling agent use in various industrial fields such as cosmetics, pet sheets, and cat litter. The manufacturing method of the absorbent article and the like are the same as those known (described in JP-A-2003-225565, JP-A-2006-131767, JP-A-2005-097569, etc.).

EXAMPLES The present invention will be further described with reference to Examples and Comparative Examples below, but the present invention is not limited to these. Hereinafter, unless otherwise specified, parts indicate parts by weight and % indicates % by weight. The water retention capacity of the water-absorbent resin in physiological saline, the absorption capacity under load, the gel permeation rate, the content of the chelating agent, and the pH of the polymerization solution were measured by the following methods.

<Method for measuring water retention>
Put 1.00 g of the measurement sample in a tea bag (20 cm long, 10 cm wide) made of nylon mesh with an opening of 63 μm (JIS Z8801-1: 2006), and put it in 1,000 ml of physiological saline (salt concentration 0.9%). After being immersed for 1 hour without stirring, it was taken out and hung for 15 minutes to drain. After that, the whole tea bag was placed in a centrifuge and dehydrated by centrifugation at 150 G for 90 seconds to remove excess physiological saline. The physiological saline used and the temperature of the measurement atmosphere were 25°C ± 2°C.
Water retention amount (g/g) = (h1) - (h2)
In addition, (h2) is the weight of the tea bag measured by the same operation as above without the measurement sample.

<Method for measuring absorption under load>
In a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) with a mesh opening of 63 μm (JIS Z8801-1: 2006) attached to the bottom, 250 to 500 μm using a 30 mesh sieve and a 60 mesh sieve. Weigh 0.16 g of the measurement sample sieved to the range, vertical the cylindrical plastic tube, arrange the measurement sample on the nylon mesh so that the thickness is almost uniform, and put a weight (weight: 206.2 g, outer diameter: 24.5 mm,) was placed. After measuring the weight (M1) of the entire cylindrical plastic tube, a cylindrical plastic tube containing a measurement sample and a weight in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline (salt concentration 0.9%) The tube was placed vertically, immersed with the nylon mesh side down, and allowed to stand for 60 minutes. After 60 minutes, the cylindrical plastic tube was pulled up from the petri dish, tilted to collect the water adhering to the bottom in one place, and dripped down to remove excess water. The weight (M2) of the entire cylindrical plastic tube was weighed, and the absorption under load was obtained from the following formula. The physiological saline used and the temperature of the measurement atmosphere were 25°C ± 2°C.
Absorption under load (g/g) = {(M2) - (M1)}/0.16

<Method for measuring liquid permeability>
It was measured by the following operation using the instrument shown in FIGS.
Swollen 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 positions 60 ml and 40 ml from the bottom, respectively. } at the bottom of the filtration cylindrical tube having a wire mesh 6 (opening 106 μm, JIS Z8801-1: 2006) and a freely openable and closable cock 7 (inner diameter of the liquid passing part 5 mm), with the cock 7 closed, After transferring the prepared swollen gel particles 2 together with a physiological saline solution, a circular wire mesh 8 (opening 150 μm, diameter 25 mm) was placed on the swollen gel particles 2, and a pressurizing shaft 9 (heavy weight) was attached perpendicularly to the surface of the wire mesh. 22 g in length and 47 cm in length) was placed so that the wire mesh and the swollen gel particles were in contact with each other, and a weight 10 (88.5 g) was placed on the pressure shaft 9 and allowed to stand for 1 minute. Subsequently, open the cock 7, measure the time (T1; seconds) required for the liquid level in the filtration cylindrical tube to change from the 60 ml scale line 4 to the 40 ml scale line 5, and use the following formula to obtain the gel flow rate (ml / min). was obtained to evaluate the liquid permeability.
Gel permeation rate (ml / min) = 20ml × 60 / (T1-T2)
The physiological saline used and the temperature of the measurement atmosphere were set at 25° C.±2° C., and T2 is the time measured by the same operation as above without the measurement sample.

<Method for measuring content of chelating agent>
The water-absorbing resin composition was classified with a JIS standard sieve with an opening of 150 μm, and the material not passing through the sieve (on product/particle size of 150 μm or more and less than 850 μm) was freeze-pulverized to a particle size of 100 μm or less. 6 g of this water-absorbent resin composition was added to 18 g of a mixed solvent of water/methanol=1/1 (w/w) and stirred at room temperature for 3 hours to extract the chelating agent into the mixed solvent (stirring rotation speed : 500±50 rpm). Thereafter, the swollen gel and the supernatant were roughly separated by decantation, and the resulting supernatant was centrifuged at 2000 rpm for 5 minutes to obtain an extract. After that, the obtained filtrate is passed through a filter for HPLC sample pretreatment (Chromatodisc 25A/aqueous type, pore size; 0.45 μm/manufactured by Kurashiki Spinning Co., Ltd.), and subjected to liquid chromatography mass spectrometry (LC/MS). was used to measure the content of the chelating agent in the filtrate. The content of the chelating agent in the water-absorbent resin composition is determined by taking into consideration the dilution ratio of the water-absorbent resin composition with respect to the water/methanol mixed solvent, using the calibration curve obtained by measuring the monomer standard solution of known concentration as an external standard. I asked. Measurement conditions by liquid chromatography mass spectrometry (LC/MS) are as follows.
<<Eluent>>; Mixed solution of 1920 ml of 0.01 mol/L ammonium acetate aqueous solution and 1080 ml of methanol for LC/MS <<Column>>; Inert Sustain (2 μm) (manufactured by GL Sciences)
<<Column temperature>>; 40±2°C
<<Flow rate>>; 0.2 ml/min
<Detector>; MS (ESI)

<Method for measuring pH of polymerization solution>
In measuring the pH of the polymerization solution, about 20 ml of the homogenized polymerization solution was extracted from the reaction system into a plastic cup, and a desk-top pH meter (model number F-71S, HORIBA, Ltd.) calibrated with pH = 4, 7, and 9 calibration solutions. (manufactured). The liquid temperature at this time was 25° C.±2.

<Example 1>
Acrylic acid (A1-1) (manufactured by Mitsubishi Chemical) 240 parts, methylene succinic acid (A2-1) (manufactured by Fuso Chemical Industry) 60 parts, 48.5% sodium hydroxide aqueous solution 38.1 parts, internal cross-linking agent (b -1) 0.9 parts of N,N'-methylenebisacrylamide and 623 parts of deionized water were kept at 5°C while stirring and mixing. Nitrogen was introduced into this mixture to reduce the dissolved oxygen content to 1 ppm or less. 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 are added and mixed. to initiate polymerization. After the temperature of the mixture reached 70° C., polymerization was carried out at 70±2° C. for about 5 hours to obtain a hydrous gel.

Next, while chopping 500 parts of this hydrous gel with a mincing machine (12VR-400K manufactured by ROYAL), 107 parts of a 48.5% sodium hydroxide aqueous solution is added and mixed and neutralized, resulting in a neutralized gel (neutralized degree: 72%). Further, the neutralized water-containing gel was dried for 50 minutes in a ventilated dryer {150° C., wind speed 2 m/sec} to obtain a dry product. The dried product was pulverized with a juicer mixer (Osterizer Blender manufactured by Oster), sieved, and adjusted to a particle size range of 710 to 150 μm in opening to obtain a crosslinked polymer (A-1).

Then, 100 parts of the obtained crosslinked polymer (A-1) was stirred at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron Corporation: 2000 rpm) while adding 0.00 of ethylene glycol diglycidyl ether as a surface cross-linking agent (d). 2 parts of propylene glycol, and 2.5 parts of water are added to a mixed liquid, mixed uniformly, and then heated at 140° C. for 40 minutes to obtain the water absorbent 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. got

<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 diacetic acid/tetrasodium aqueous solution (c-2). obtained water-absorbing resin particles (P-3) of the present invention in the same manner as in Example 1.

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

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

<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 to 2.5 parts, and 2.5 parts of water to 3.1 parts in Example 1. Water-absorbing resin particles (P-7) of the present invention were obtained in the same manner as above.

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

<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 Industry), and 0.1% nitrilo3 30 parts of 0.6 parts of acetic acid aqueous solution (c-1), 57.1 parts of 48.5% sodium hydroxide aqueous solution in the polymerization step, and 107 parts of 48.5% sodium hydroxide aqueous solution in the minced shredding step. Water-absorbent resin particles (P-9) of the present invention were obtained in the same manner as in Example 1, except for the above.

<Example 10>
240 parts of acrylic acid (A1-1) (manufactured by Mitsubishi Chemical), 60 parts of methylene succinic acid (A2-1) (manufactured by Fuso Chemical Industry), internal cross-linking agent (b-1) N,N'-methylenebisacrylamide 0.00 9 parts and 623 parts of deionized water were kept at 5° C. while stirring and mixing. Nitrogen was introduced into this mixture to reduce the dissolved oxygen content to 1 ppm or less. 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 are added and mixed. to initiate polymerization. After the temperature of the mixture reached 70° C., polymerization was carried out at 70±2° C. for about 5 hours to obtain a hydrous gel.

Next, while chopping 500 parts of this water-containing gel with a mincing machine (12VR-400K manufactured by ROYAL), 128 parts of a 48.5% sodium hydroxide aqueous solution is added and mixed and neutralized, resulting in a neutralized gel (neutralized degree: 72%). Further, the neutralized water-containing gel was dried for 50 minutes in a ventilated dryer {150° C., wind speed 2 m/sec} to obtain a dry product. The dried product was pulverized with a juicer mixer (Osterizer Blender manufactured by Oster), sieved, and adjusted to a particle size range of 710 to 150 μm in opening to obtain a crosslinked polymer (A-2).

Then, 100 parts of the obtained crosslinked polymer (A-1) was stirred at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron Corporation: 2000 rpm) while adding 0.00 of ethylene glycol diglycidyl ether as a surface cross-linking agent (d). 2 parts of propylene glycol, and 2.5 parts of water are added to a mixed liquid, mixed uniformly, and then heated at 140° C. for 40 minutes to obtain the water absorbent resin particles (P-10) of the present invention. Obtained.

<Comparative Example 1>
Comparative water-absorbent resin particles (R-1) 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 not added. got

<Comparative Example 2>
Acrylic acid (A1-1) (manufactured by Mitsubishi Chemical) 240 parts, methylene succinic acid (A2-1) (manufactured by Fuso Chemical Industry) 60 parts, 48.5% sodium hydroxide aqueous solution 255.4 parts, internal cross-linking agent (b -1) 0.9 parts of N,N'-methylenebisacrylamide and 419 parts of deionized water were kept at 5°C while stirring and mixing. Nitrogen was introduced into this mixture to reduce the dissolved oxygen content to 1 ppm or less. 2 parts, 2.3 parts of 2% ascorbic acid aqueous solution, 30 parts of 0.1% hydroxyethyliminodiacetic acid (HIDA) and 0.4 parts of 0.03% iron sulfate heptahydrate aqueous solution are added and mixed to polymerize. was started. After the temperature of the mixture reached 70° C., polymerization was carried out at 70±2° C. for about 5 hours to obtain a hydrous gel.

Next, 500 parts of this water-containing gel was chopped and mixed with a mincing machine (12VR-400K manufactured by ROYAL) to obtain a neutralized gel (degree of neutralization: 72%). Further, the hydrous gel was dried for 50 minutes in a ventilation dryer {150° C., wind speed 2 m/sec} to obtain a dry product. The dried product was pulverized with a juicer mixer (Osterizer Blender manufactured by Oster), sieved, and adjusted to a particle size range of 710 to 150 μm in opening to obtain a crosslinked polymer (A-3).

Then, 100 parts of the obtained crosslinked polymer (A-3) was stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron Co., Ltd.: rotation speed 2000 rpm), and ethylene glycol diglycidyl ether as a surface cross-linking agent (d) was added to 0. .2 parts, 2 parts of propylene glycol, and 2.5 parts of water are added to a mixed liquid, mixed uniformly, and then heated at 140° C. for 40 minutes to obtain water-absorbent resin particles for comparison (R-2). got

<Comparative Example 3>
300 parts of acrylic acid (A1-1) (manufactured by Mitsubishi Chemical), 0.9 parts of N,N'-methylenebisacrylamide as an internal cross-linking agent (b-1) and 623 parts of deionized water were heated to 5°C while stirring and mixing. kept. After flowing nitrogen into this mixture to make the dissolved oxygen content 1 ppm or less, 2% 2,2'-azobis(2-methylpropionamidine) dihydrochloride aqueous solution, 1.2 parts of 1% hydrogen peroxide aqueous solution , 2.3 parts of a 2% ascorbic acid aqueous solution, and 0.4 parts of a 0.03% iron sulfate heptahydrate aqueous solution were added and mixed to initiate polymerization. After the temperature of the mixture reached 90° C., polymerization was carried out at 90±2° C. for about 5 hours to obtain a hydrous gel.

Next, 129.2 parts of a 48.5% sodium hydroxide aqueous solution is added and mixed while shredding 500 parts of this hydrous gel with a mincing machine (12VR-400K manufactured by ROYAL), and the neutralized gel (degree of neutralization: 72 %) was obtained. Further, the hydrous gel was dried for 50 minutes in a ventilation dryer {150° C., wind speed 2 m/sec} to obtain a dry body. The dried product was pulverized with a juicer mixer (Osterizer Blender manufactured by Oster), sieved, and adjusted to a particle size range of 710 to 150 μm in opening to obtain a crosslinked polymer (A-4).

Then, 100 parts of the obtained crosslinked polymer (A-4) was stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron Co., Ltd.: rotation speed 2000 rpm), and ethylene glycol diglycidyl ether as a surface cross-linking agent (d) was added to 0. .2 parts, 2 parts of propylene glycol, and 2.5 parts of water are added to a mixed liquid, mixed uniformly, and then heated at 140° C. for 40 minutes to obtain water-absorbing resin particles for comparison (R-3). got

Table 1 shows the evaluation results.

Claims (10)

one or more monomers (A1) selected from the group consisting of water-soluble unsaturated monocarboxylic acids (a1) and salts thereof, and monomers (a2) that become the water-soluble unsaturated monocarboxylic acids (a1) by hydrolysis; , one or more monomers (A2) selected from the group consisting of a water-soluble unsaturated dicarboxylic acid (a3) and a salt thereof, and a monomer (a4) that becomes the water-soluble unsaturated dicarboxylic acid (a3) by hydrolysis; A method for producing a water-absorbing resin composition containing a cross-linked polymer (A) having a cross-linking agent (b) as a structural unit, wherein the monomer (A1) and the monomer (A2) and the cross-linking agent (b ) , iron ions (Fe ³⁺ ) and a chelating agent (c) having a logarithm value of the chelate stability constant for the iron ions ( Fe ³⁺ ) of 7 or more at least at pH 1 to 6 A polymerization step of obtaining a hydrous gel containing the crosslinked polymer (A) by polymerizing in the presence of
and a drying step of drying the hydrous gel ,
In the polymerization step, the addition amount (ppm) of the chelating agent (c) with respect to the total amount of the monomer (A1) and the monomer (A2) in the polymerization solution is 0.1 to 1000, and A method for producing a water-absorbing resin composition, wherein the amount (substance amount) of the chelating agent (c) added is 1 to 300 times the substance amount of the iron ion (Fe ³⁺ ). 2. The method for producing a water absorbent resin composition according to claim 1, wherein the logarithmic value of the chelating agent (c) is 16 or less. 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, methylenesuccinic acid and citraconic acid, and salts thereof. A method for producing the water absorbent resin composition according to . The method for producing a water absorbent resin composition according to any one of claims 1 to 3, wherein the cross-linking agent (b) is an acrylamide compound. The method for producing a water absorbent resin composition according to any one of claims 1 to 4, wherein in the polymerization step, the pH range of the polymerized solution of the monomer composition is 1 to 10. one or more monomers (A1) selected from the group consisting of water-soluble unsaturated monocarboxylic acids (a1) and salts thereof, and monomers (a2) that become the water-soluble unsaturated monocarboxylic acids (a1) by hydrolysis; , one or more monomers (A2) selected from the group consisting of a water-soluble unsaturated dicarboxylic acid (a3) and a salt thereof, and a monomer (a4) that becomes the water-soluble unsaturated dicarboxylic acid (a3) by hydrolysis; A water-absorbing resin composition containing a cross-linked polymer (A) having a cross-linking agent (b) as a structural unit,
Furthermore, it contains a chelating agent (c) whose logarithm value of the chelate stability constant for Fe ³⁺ is 7 or more in at least one of pH 1 to 6,
The content of the chelating agent (c) in the water absorbent resin composition is 0.1 to 1000 parts by weight with respect to the total 1000000 parts by weight of the substance amount of the monomer (A1) unit and the monomer (A2) unit. A water absorbent resin composition. The ratio of the substance amount of the monomer (A1) to the substance amount of the monomer (A2) in the crosslinked polymer (A) (substance amount of the monomer (A1)/substance amount of the monomer (A2)) is 1 /99 to 99/1, the water absorbent resin composition according to claim 6. The water absorbent resin composition according to claim 6 or 7, wherein the water absorbent resin composition is particulate. 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 .

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