HK1056183B - Crosslinked polymer, process for producing the same, absorbent structure, and absorbable article - Google Patents

Description

Crosslinked polymer, method for producing same, absorbent structure, and absorbent article

Technical Field

The present invention relates to a crosslinked polymer, a method for producing the same, an absorbent structure, and an absorbent article. More particularly, it relates to a crosslinked polymer which is excellent in water retention and absorption under load, a method for producing the same, an absorbent structure, and an absorbent article.

Background

Conventionally, crosslinked polymers used in absorbent articles such as disposable diapers are desired to have a large water retention amount and a large absorption amount under load, and to be improved by various methods. As a method for increasing the water retention amount, a method of using a chain transfer agent such as a thiol compound has been proposed in addition to optimizing the amount of a polymerization initiator, polymerization temperature, polymerization concentration, etc. (JP-A-3-179008). In addition, as a method for improving the absorption performance under load, a method of treating the vicinity of the surface of polymer particles in a large number has been proposed (japanese patent No. 267529, EPA618005, etc.).

However, these methods cannot satisfy both the water retention property of the crosslinked polymer and the absorption property under load at the same time because of the imbalance in properties, and therefore, when used in an absorbent article, the absorption property is not sufficient, and further improvement is desired. The present inventors have conducted extensive studies to obtain a crosslinked polymer which exhibits excellent absorption properties when used in an absorbent article, and as a result, have completed the present invention.

Disclosure of Invention

The present invention aims to provide a crosslinked polymer which satisfies both of water retention properties and absorption properties under load, and a method for producing the same. It is also an object of the present invention to provide an absorbent structure and an absorbent article which exhibit excellent absorption properties when the crosslinked polymer of the present invention is applied to sanitary articles such as a sanitary napkin.

That is, the present invention is the following inventions (I) to (IV).

(I) A crosslinked polymer (A) comprising, as essential constituent units, (a) one or more vinyl monomers selected from water-soluble vinyl monomers and/or vinyl monomers (a) which are water-soluble by hydrolysis and (b) a crosslinking agent, and (c) the following components;

①(X)≥33g/g

②(Y)≥25g/g

③(Y)≥-0.54(X)+42

[ wherein (X) is the water retention capacity after 1 hour of absorption of physiological saline; (Y) is at 60g/cm²Under the load of (1), the amount of absorption after 1 hour of absorption of physiological saline solution]

(II) a process for producing a crosslinked polymer, which comprises polymerizing a monomer (a) selected from water-soluble vinyl monomers and/or one or more vinyl monomers (a) which are hydrolyzed to be water-soluble, optionally together with another vinyl monomer (A3) and a first crosslinking agent (b1) in the presence of a water and one or more initiators (c) selected from azo initiators, peroxide initiators, redox initiators and organic halide initiators to obtain a crosslinked polymer (A2), and then surface-crosslinking the crosslinked polymer (A2) with the second crosslinking agent (b 2);

(III) an absorbent structure (C) comprising the crosslinked polymer (A) and a fibrous material (B) as a base material, wherein the amount of the crosslinked polymer (A) is 30 to 95 wt% based on the weight of the absorbent structure (C);

(IV) an absorbent article comprising the absorbent structure (C), a liquid-permeable sheet, and a breathable back sheet.

Detailed Description

(crosslinked Polymer and Process for producing the same)

In the present invention, the water-soluble vinyl monomer and/or the vinyl monomer (a) which becomes water-soluble by hydrolysis are not particularly limited, but examples of the water-soluble monomer (a1) include vinyl monomers having at least one acid group and/or salt-forming group thereof [ carboxylic acid (salt) group, sulfonic acid (salt) group, sulfuric acid (salt) group, phosphoric acid (salt) group, etc. ], hydrophilic groups such as hydroxyl group, amide group, amino group, quaternary ammonium salt group, etc., and can be classified into anionic, nonionic, cationic, etc., and examples thereof include the following compounds.

(i) Anionic or anionically polymerizable vinyl monomers

(i-1) As the monomer having a carboxylic acid group, there may be mentioned carboxylic acids having 3 to 30 carbon atoms, such as unsaturated monocarboxylic acids, for example: (meth) acrylic acid, crotonic acid, cinnamic acid, and the like; unsaturated dicarboxylic acids, such as: maleic acid, fumaric acid, citraconic acid, itaconic acid, and the like; monoalkyl (1 to 8 carbon atoms) esters of the above unsaturated dicarboxylic acids, such as: carboxyl group-containing vinyl monomers such as monobutyl maleate, monobutyl fumarate, monoethyl carbitol maleate, monoethyl carbitol fumarate, monobutyl citraconate, and monoethyl glycol itaconate, and combinations of two or more thereof.

(i-2) examples of the vinyl monomer having a sulfonic acid group include aliphatic or aromatic vinylsulfonic acids having 2 to 30 carbon atoms, such as vinylsulfonic acid, (meth) allylsulfonic acid; styrene sulfonic acid, alpha-methyl styrene sulfonic acid; (meth) acryloylalkylsulfonic acids [ (meth) acryloyloxypropylsulfonic acid, 2-hydroxy-3- (meth) acryloyloxypropylsulfonic acid, 2- (meth) acryloylamino-2, 2-dimethylethanesulfonic acid, 3- (meth) -acryloyloxyethanesulfonic acid, 2- (meth) -acrylamide-2-methylpropanesulfonic acid, 3- (meth) -acrylamide-2-hydroxypropanesulfonic acid ]; and alkyl (C3-C18) esters of (meth) allylsulfosuccinic acid.

(i-3) examples of the vinyl monomer having a sulfate group or a sulfate ester include a sulfate ester of hydroxyalkyl (having 2 to 6 carbon atoms) meth (acrylate [ (sulfuric acid ester of hydroxyethyl meth) acrylate ], etc.); a poly (n-2-30) oxyalkylene group (alkylene group has 2-4 carbon atoms and may be singly, randomly or blockwise) a sulfuric acid ester of a mono (meth) acrylate [ e.g., a sulfuric acid ester of poly (n-5-15) oxypropylene monomethacrylate ]; and other compounds represented by the following general formulae (1), (2) and (3).

CH₂＝CHCH₂OCH₂CH[O(AO)_nSO₃H]-CH₂O-Ar-R (1)

CH₃CH＝CH-Ar[O(AO)_nSO₃H]-R (2)

CH₂＝CHCH₂OCH₂(OH)CHCH₂OCOCH(SO₃H)-CH₂COOR’ (3)

In the general formulas (1) to (3), R represents an alkyl group having 1 to 15 carbon atoms; r' represents an alkyl group having 1 to 15 carbon atoms which may be substituted with a fluorine atom; a represents an alkylene group having 2 to 4 carbon atoms, and when n is greater than 1, A may be the same or different, and when they are different, it may be a random polymerization or a block polymerization; ar represents a benzene ring; n represents an integer of 1 to 50.

(i-4) examples of the vinyl monomer having a phosphonic acid group include a phosphonic acid monoester of hydroxyalkyl (carbon number 2 to 6) ester (meth) acrylate [ e.g., hydroxyethyl (meth) acrylate monophosphonate ], a phosphoric acid diester of hydroxyalkyl (carbon number 2 to 6) ester (meth) acrylate [ e.g., phenyl-2-acryloyloxyethylphosphonate ], and an alkyl (carbon number 2 to 6) phosphonic acid (meth) acrylate [ e.g., 2-acryloyloxyethylphosphonic acid ].

(i-5) examples of the salts of the above-mentioned (i-1) to (i-4) include alkali metal salts (sodium salt, potassium salt), alkaline earth metal salts (calcium salt, magnesium salt), ammonium salts [ ammonium, tetraalkyl (having 1 to 8 carbon atoms) ammonium, e.g., tetraoctylammonium ], organic amine salts { alkanolamine having 2 to 8 carbon atoms, polyalkylene (having 1 to 8 carbon atoms) polyamine (having 2 to 10 amino groups) or derivatives thereof [ alkylate having 1 to 8 carbon atoms, oxyalkylene adduct having 2 to 12 carbon atoms (1 to 30 mol), etc. ], lower alkylamine having 1 to 4 carbon atoms, etc. ].

(ii) Nonionic monomer

(ii-1) examples of the vinyl monomer having a hydroxyl group include monoethylenically unsaturated alcohols [ e.g., (meth) allyl alcohol ], monoethylenically unsaturated esters or ethers of 2-to 6-membered or higher-membered polyhydric alcohols (e.g., alkylene glycols having 2 to 20 carbon atoms, glycerin, polyalkylene (having 2 to 4 carbon atoms) glycols (having a molecular weight of 106 to 2000), etc. [ e.g., (meth) hydroxyethyl acrylate, hydroxypropyl (meth) acrylate, triethylene glycol (meth) acrylate, and polyethylene glycol propylene glycol mono (meth) acrylate (random or block copolymerization) (the hydroxyl group at the terminal may be etherified, or esterified) ].

(ii-2) examples of the vinyl monomer having an amide group include (meth) acrylamide, N-alkyl (C1-8) (meth) acrylamide [ e.g., N-methacrylamide ], N-dialkyl (C1-8) acrylamide [ e.g., N-dimethylacrylamide, N-di-N- (or iso-) butylacrylamide, etc. ], N-hydroxyalkyl (C1-8) (meth) acrylamide [ e.g., N-methylol (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, etc. ]; n, N-dihydroxyalkyl (C1-C8) (meth) acrylamide [ e.g., N-dihydroxyethyl (meth) acrylamide ], vinyl lactams [ e.g., N-vinylpyrrolidone ], and the like.

(iii) Cationic or cationized vinyl monomer

(iii-1) examples of the vinyl polymerizable monomer having an amino group include, for example, an amino group-containing ester of a monoethylenically unsaturated monomer or a dicarboxylic acid, such as dialkyl (1 to 8 carbon atoms) amino (2 to 10 carbon atoms) alkyl (meth) acrylate, dihydroxyalkyl (1 to 8 carbon atoms) aminoalkyl (2 to 10 carbon atoms) ester, and morpholinoalkyl (1 to 8 carbon atoms) ester [ e.g., dimethylaminoethyl (meth) acrylate, diethylamino (meth) acrylate, morpholinoethyl (meth) acrylate, and dimethylaminoethyl fumarate ]; an amino group-containing amide containing a monoethylenically unsaturated mono-or di-carboxylic acid, such as monoalkyl (having 2 to 10 carbon atoms) (meth) acrylamide [ e.g., dimethylaminoethyl (meth) acrylamide, diethylaminoethyl (meth) acrylamide, etc. ]; heterocyclic vinyl compounds [ e.g., vinyl pyridines such as 2-vinylpyridine, 4-vinylpyridine and N-vinylpyridine, N-vinylimidazole, etc. ], diallylamine, etc.

(iii-2) examples of the vinyl monomer having a quaternary ammonium group include quaternary ammonium compounds of vinyl polymerizable monomers having a tertiary amino group (the vinyl polymerizable monomer having a tertiary amino group is quaternized with an alkylating agent having 1 to 8 carbon atoms such as methyl chloride, dimethyl sulfate, benzyl chloride, dimethyl carbonate, and other quaternizing agents), such as trimethylaminoethyl (meth) acrylate hydrochloride, methyldiethylaminoethylmethacrylate pyrosulfite, trimethylaminoethyl (meth) acrylamide hydrochloride, and dimethyldiethylbenzylamine methyl (meth) acrylamide hydrochloride.

Examples of the water-soluble vinyl monomer (a2) formed by hydrolysis include monomers having at least one hydrolyzable group [ acid anhydride, lower alkyl (having 1 to 3 carbon atoms) ester group, nitrile group, and the like]The vinyl monomer of (1). Examples of the vinyl monomer having an acid anhydride group include vinyl monomers having 4 to 20 carbon atoms such as maleic anhydride, itaconic anhydride, and citraconic anhydride; as the monomer having an ester group, for example, a lower alkyl group (C) of a monoethylenically unsaturated carboxylic acid₁～C₃) Esters [ e.g. methyl (meth) acrylate, ethyl (meth) acrylate, etc. ]]Esters of monoethylenically unsaturated alcohols [ e.g., vinyl acetate, (meth) allyl acetate, and the like]. Examples of the vinyl monomer having a nitrile group include (meth) acrylonitrile. The hydrolysis of these vinyl monomers (a2) may occur during the polymerization or may occur during the polymerizationLater, the salts formed, usually by hydrolysis, are water soluble. The salt is the same as the salt described in the above salt-forming group.

Among these, the vinyl monomer (a) is preferably a water-soluble vinyl monomer (a 1). More preferred are vinyl monomers having a carboxylic acid (salt) group, a sulfonic acid (salt) group, and an amide group, and particularly preferred are (meth) acrylic acid (salt) and (meth) acrylamide. These vinyl monomers (a) may be used alone or in combination of two or more kinds as required.

The polymerization may be carried out using other vinyl monomers (a3) copolymerizable with the above vinyl monomers (a1) and (a2) at the same time. Examples of the other vinyl monomer (a3) copolymerizable with (a1) and (a2) include, but are not limited to, hydrophobic vinyl monomers.

Examples of the vinyl monomer (a3) include the following vinyl monomers (i) to (iv).

(i) An aromatic vinyl monomer having 8 to 30 carbon atoms;

styrenes such as styrene, α -methylstyrene, vinyltoluene, and hydroxystyrene, vinylnaphthalenes, and halogenated styrenes such as dichlorostyrene;

(ii) an aliphatic vinyl monomer having 2 to 20 carbon atoms;

olefins [ e.g., ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene ], dienes [ e.g., butadiene, isoprene ], etc.;

(iii) an alicyclic ethylenic monomer having 5 to 15 carbon atoms;

monoethylenically unsaturated monomers [ pinene, limonene, indene, etc. ], polyethylenically vinyl polymerized monomers [ cyclopentadiene, dicyclopentadiene, ethylidene norbornene, etc. ], and the like;

(iv) an alkyl (meth) acrylate having an alkyl group having 4 to 50 carbon atoms: n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, eicosyl (meth) acrylate, and the like;

the amount of the vinyl monomer (a3) used is preferably 0 to 50% by weight, more preferably 0 to 25% by weight, based on the amount of the vinyl monomer (a).

In the present invention, as the crosslinking agent (b), there are a first crosslinking agent (b1) used together at the time of polymerization of the vinyl monomer (a) and a surface crosslinking agent (second crosslinking agent) (b2) which crosslinks the dried and pulverized particles and the particle surface after polymerization, if necessary. Examples of the first crosslinking agent (b1) include a crosslinking agent having two or more ethylenically unsaturated groups, a crosslinking agent having at least one functional group reactive with the functional group of the vinyl monomer (a) and having at least one ethylenically unsaturated group, a crosslinking agent having at least two or more functional groups reactive with the functional group of the vinyl monomer (a), and the like.

(i) Examples of the crosslinking agent having two or more unsaturated groups include N, N' -methylene (meth) acrylamide, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, glycerol di or tri (meth) acrylate, trimethylolpropane triacrylate, triallylamine, triallylcyanurate, triallylisocyanurate, tetraallyloxyethane, pentaerythritol triallylether, and the like.

(ii) Examples of the crosslinking agent having at least one functional group reactive with a functional group (for example, a carboxyl group) of the vinyl monomer (a) and having at least one ethylenically unsaturated group include crosslinking agents having at least one functional group reactive with a carboxylic acid (salt) group, a hydroxyl group, an amino group, and the like and having at least one ethylenically unsaturated group, and examples thereof include ethylenically unsaturated groups having an epoxy group such as glycidyl (meth) acrylate, and ethylenically unsaturated groups having a hydroxyl group such as N-methylol (meth) acrylamide and hydroxyethyl (meth) acrylate.

(iii) Examples of the crosslinking agent having at least two functional groups reactive with the functional groups of the vinyl monomer (a) include a crosslinking agent having at least two functional groups reactive with a carboxylic acid (salt) group, a hydroxyl group, an amino group, and the like, and examples thereof include glycidyl ether compounds having 2 to 10 epoxy groups in one molecule [ e.g., ethylene glycol diglycidyl ether, glycerol-1, 3-diglycidyl ether, glycerol triglycidyl ether, polyethylene glycol (polymerization degree of 2 to 100) diglycidyl ether, and polyglycerol (polymerization degree of 2 to 100) polyglycidyl ether ]; a binary to twenty-membered polyhydric alcohol compound [ glycerin, ethylene glycol, polyethylene glycol (polymerization degree 2-100), etc. ]; a binary to twenty-membered polyamine compound (ethylenediamine, diethylenetriamine, etc.); polyamine resins having a molecular weight of 200 to 500,000 (e.g., polyamide polyamine epichlorohydrin resins, etc.), alkylene carbonates [ e.g., ethylene carbonate ], ethyleneimine compounds, and polyimine compounds. These crosslinking agents may be used alone or in combination of two or more.

The amount of the first crosslinking agent (b1) used is preferably 0.001 to 5.0% by weight, more preferably 0.002 to 2% by weight, and particularly preferably 0.003 to 1.6% by weight, based on the weight of the vinyl monomer (a) or the total weight of the vinyl monomer (a) and the vinyl monomer (a 3). When the amount of the first crosslinking agent (b1) is 0.001 wt% or more, the water retention/absorption ability is good, and when the amount is 5.0 wt% or less, the crosslinking is not so strong and the water retention/absorption ability is not lowered.

The method for polymerizing the crosslinked polymer (a) in the present invention is not particularly limited as long as the crosslinked polymer (a) can exhibit the above-mentioned various properties, and various conventionally known methods can be used, and examples thereof include solution polymerization, emulsion polymerization, suspension polymerization, reversed-phase suspension polymerization, thin-film polymerization, and spray polymerization using an initiator. Examples of the polymerization control method include an adiabatic polymerization method, a temperature-controlled polymerization method, and an isothermal polymerization method. When the suspension polymerization method or the reversed-phase suspension polymerization method is used as the polymerization method, the polymerization may be carried out in the presence of a conventionally known dispersant, protective colloid, surfactant, or two or more thereof, as required. In the case of reversed-phase suspension polymerization, polymerization is carried out using a conventionally known solvent such as cyclohexane, n-hexane, n-heptane, xylene, etc. The solution polymerization method using a polymerization initiator is preferable, and the aqueous solution polymerization method which is advantageous in terms of production cost without using an organic solvent is particularly preferable.

The polymerization initiator (c) is not particularly limited as long as it is an azo initiator, a peroxide initiator, a redox initiator or an organic halide initiator, and various known initiators can be used. The following examples are specifically mentioned.

(i) Examples of the azo initiator include azobisisobutyronitrile, azobiscyanovaleric acid and salts thereof, 2 '-azobis (2-amidinopropane) hydrochloride, and 2, 2' -azobis (2-methyl-N-2-hydroxyethyl) propionamide;

(ii) examples of the peroxide initiator include inorganic peroxides [ e.g., hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate ], organic peroxides [ e.g., benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinic peroxide, and bis (2-ethoxyethyl) peroxydicarbonate ];

(iii) examples of the redox initiator include a combination of a reducing agent such as alkali metal sulfite or bisulfite, ammonium sulfite, ammonium bisulfite, ferrous chloride, ferrous sulfate, or ascorbic acid, and an oxidizing agent such as alkali metal persulfate, ammonium persulfate, hydrogen peroxide, or organic peroxide;

(iv) examples of the halogen in the organic halide initiator include fluorine, chlorine, bromine, and iodine.

The organic halide is not particularly limited, but from the viewpoint of polymerizability, an organic halide having 1 to 10 or more halogen atoms and 1 to 15 or more carbon atoms in the alkyl halide, the halide of alkylphenyl ketone, the halide of alkyl halide of alkyl carboxylate, or the halide of alkyl carboxylate is preferable. More preferably, it is carbon tetrachloride, trichlorobromomethane, trichloroiodomethane, dichloromethylphenylketone, 1-bromo-1-methylethylcarboxylic acid, or an alkyl 1-bromo-1-methylacetate in which the alkyl group has 1 to 8 carbon atoms (for example, methyl 1-bromo-1-methylacetate, ethyl 1-bromo-1-methylacetate, octyl 1-bromo-1-methylacetate, or lauryl 1-bromo-1-methylacetate). Particularly preferred are dichloromethyl phenyl ketone and alkyl 1-bromo-1-methylacetate in which the alkyl group has 1 to 8 carbon atoms.

These polymerization initiators may be used alone or in combination of two or more. It is preferable to use azo type initiators, redox type initiators and a combination thereof.

The amount of the polymerization initiator (c) used is preferably 0.005 to 0.5% by weight, more preferably 0.007 to 0.4% by weight, and particularly preferably 0.009 to 0.3% by weight, based on the total weight of the vinyl monomer (a) and the crosslinking agent (b) or the total weight of the vinyl monomer (a), the vinyl monomer (a3), and the crosslinking agent (b).

In order to make the crosslinked polymer (A) of the present invention exhibit the above-mentioned various properties, it is necessary to increase the molecular weight of the crosslinked polymer (A), and therefore, for example, the crosslinked polymer (A) can be treated by the following methods (i) to (iii). These methods may also be used in combination.

Polymerizing a polymerization solution in which the total weight of the vinyl monomer (a) and the crosslinking agent (b) or the concentration of the total weight of the vinyl monomer (a), the vinyl monomer (a3) and the crosslinking agent (b) (all vinyl monomers) is 20% by weight or less;

② the polymerization liquid is preferably at least 70% by weight, more preferably at least 80% by weight, and the polymerization is carried out at a polymerization temperature of 60 ℃ or lower, preferably at a constant temperature within a temperature control range of. + -. 5 ℃ or more preferably. + -. 2 ℃. The majority of the total ethylene monomers, which accounts for 70% by weight or more, are subjected to constant-temperature polymerization at a temperature of 60 ℃ or less.

③ polymerization is carried out in the presence of a complex (d) comprising a metal element (d1) and an anionic or neutral molecular ligand (d 2).

The crosslinked polymer (A) of the present invention is particularly preferably a crosslinked polymer obtained from (c).

The complex (d) is a complex composed of a metal element (d1) and an anionic or neutral molecular ligand (d2), and has a structure in which the metal element (d1) is surrounded by the anionic or neutral molecular ligand (d 2).

The metal element (d1) is not particularly limited as long as it is a metal element, and examples thereof include group IA element metals (lithium, sodium, potassium, cesium, etc.), group IB element metals (copper, silver, gold, etc.), group IIA element metals (magnesium, calcium, barium, etc.), group IIIA element metals (scandium, yttrium, etc.), group IIIB element metals (aluminum, gallium, indium, thallium, etc.), group IVA element metals (titanium, zirconium, hafnium, etc.), group IVB element metals (tin, zinc, etc.), group VA element metals (vanadium, niobium, tantalum, etc.), group VB element metals (antimony, bismuth, etc.), group VIA element metals (chromium, molybdenum, tungsten, etc.), group VIB element metals (tellurium, polonium, etc.), group VIIA element metals (manganese, technetium, rhenium, etc.), group VIII element metals (iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, platinum, etc.), lanthanide metals (lanthanum, cerium, etc.), lanthanum, etc.), lanthanide metals, Actinide metals (actinium, thorium, etc.). From the viewpoint of polymerizability of the vinyl monomer, metals of group IB, group IIIA, group IVA, group VA, group VIA, group VIIA, group VIII and lanthanoid series are preferable, metals of group IB, group VIII and lanthanoid series are more preferable, and metals of group IB and group VIII of 4 to 6 periods are particularly preferable. From the viewpoint of ease of handling, most preferable are group VIII element metals of period 5 (ruthenium, rhodium, palladium).

The metal element (d1) is usually present in cationic form, but forms other than cationic, such as the neutral form of iron pentacarbonyl, are also possible.

The anionic or neutral molecular ligand (d2) is not particularly limited as long as it is an anionic or neutral molecular ligand, and examples thereof include (i) anions selected from atoms such as hydrogen and halogen; ② compounds having one or more atoms selected from nitrogen, oxygen, phosphorus, sulfur and the like; ③ one or more than two of conjugated systems.

Specific examples thereof include the following compounds.

Anions selected from atoms such as hydrogen, halogen and the like;

anions of hydrogen, fluorine, chlorine, bromine, iodine;

② as having selected from nitrogen, oxygen, phosphorus, sulfur atoms and more than one compounds, can cite the following compounds. Preferred are compounds having a molecular weight of 1,000 or less (when there are two or more coordination possibilities, which of the possible ligands is to be classified).

(1) A tertiary phosphine compound having 1 to 4 or more phosphorus atoms and 3 to 42 or more carbon atoms;

trimethylphosphine, triethylphosphine, diethylphenylphosphine, triphenylphosphine (hereinafter referred to as PPh3), o-phenylenedi (diphenylphosphine), o-phenylenedi (dimethylphosphine), o-phenylenedi (diethylphosphine), o-phenylenedi (ethylphenylphosphine), 1, 2-bis (diphenylphosphino) ethane, 1, 2-bis (dimethylphosphino) ethane (hereinafter referred to as dppe), 1, 2-bis (diethylphosphino) ethane, 1, 2-bis (ethylphenylphosphino) ethane, 1, 2-bis (diphenylphosphino) methane (hereinafter referred to as dppm), 1, 2-bis (dimethylphosphino) methane, 1, 2-bis (diethylphosphino) methane, 1, 2-bis (ethylphenylphosphino) methane, tris (diphenylphosphinoethyl) phosphine, tris (diethylphosphinoethyl) phosphine, tris (dimethylphosphinoethyl) phosphine, Tris (ethylphenylphosphinoethyl) phosphine, and the like;

(2) ammonia or an amine having 1 to 4 or more nitrogen atoms and 0 to 4 or more carbon atoms;

(2-1) the number of nitrogen atoms is 1; for example, pyridine (hereinafter referred to as py), diethylamine, salicylamine, aminoethylselenol, 2-hydroxy-6-methylpyridine, 2-diethylaminoethanol, bis (2-aminoethyl) amine, ethanolamine, 2-aminoethanol, β -aminopropionic acid, 2-hydroxy-6-methylpyridine, 3-salicylidene-1-aminopropanol, 2-pyrrolidone, 8-hydroxyquinoline, salicylaldimine, α -methylpyridine, etc.;

(2-2) the number of nitrogen atoms is 2; ethylenediamine (hereinafter referred to as en), propylenediamine, trimethylenediamine, 1, 2-cyclohexyldiamine, N-diethylethylenediamine, N-dimethylethylenediamine, salicylideneethylenediamine, N-ethylsalicylaldolamine, di (benzoylacetone) ethylenediamine, 1, 2-diamino-1, 1 ' -dimethylmethane, 2 ' -bipyridine (hereinafter referred to as bpy), 2 ' -bipyridine-3-yne, 2 ' -bipyridine-N, N ' -dioxide, dicyanodiimide, (aminoiminomethyl) urea, [ (2-aminoethyl) amino ] -1-propanol, 2- [ (3-aminopropyl) amino ] ethanol, N-2- [2- (diethylamino) ethyl ] -3-amino-1-propanol, tris [2- (methylamino) ethyl ] amine, imidazole, N, N '-bissalicylidene trimethylene diamine, 4, 6, 6-trimethyl-3, 7-diazepin-3-ene-1, 9-diol, N, N, N' -tetramethylethylenediamine, 1, 8-naphthyridine, etc.;

(2-3) the number of nitrogen atoms is 3 or more; diethylenetriamine, triethylenetetramine, tetraethylpentylamine, N, N '-bis (aminobenzylidene) ethylenediamine, tris [2- (methylamino) ethyl ] amine aminopyridine, 1, 3-bis [ bis (2-pyridylethyl) aminomethyl ] benzene, 4-dimethylamino-2, 3-dimethyl-1-phenyl-5-pyrazoline, biguanide, imidodicarbonimidic diamide, biuret, carbamoylguanidine, phthalocyanine, N, N, N', N '-tetrakis (2-aminoethyl) ethylenediamine, 1, 2, 3-triaminopropane, tris (2-benzimidazolyl) amine, tetrakis (2-pyridylmethyl) ethylenediamine, 2', 2 "-terpyridine, 1, 4, 7, 10-tetraazadecane, 1, 4, 8, 11-tetraazaundecane, 1, 5, 8, 12-tetraazadodecane, 1, 4, 8, 11-tetraazacyclotetradecane, ethylenebis (biguanide), tetraphenylhematoporphyrin, tris (2-pyridylmethyl) amine, histidine, and the like;

(3) a carbonyl group-containing compound having 1 to 3 or more carbonyl groups and 3 to 40 or more carbon atoms (excluding carboxylic acids);

ethyl acetoacetate, acetylacetone (hereinafter referred to as acac), 2, 4-pentanedione, bis (acetylacetone), 3-methylpentane-2, 4-dione, 1-phenyl-1, 3-butanedione, 3-phenylpentane-2, 4-dione, 1, 3-diphenyl-1, 3-propanedione, 1-phenyl-1, 3, 5-hexanetrione, 5 '- (1, 2-ethanediyldiazone) bis (1-phenyl-1, 3-hexanedione), trifluoroacetylacetone, hexafluoroacetylacetone, benzyldibenzoylmethane, asparagines benzoylacetone, 4' - (1, 2-ethanediyldiazone) bis (2-pentanone), dipivaloylmethane, and the like;

(4) carboxylic acids having 1 to 4 or more carboxylic acid groups and 2 to 20 or more carbon atoms;

oxalic acid, malic acid, salicylic acid, phthalic acid, nicotinic acid, picolinic acid, aspartic acid, benzoylpyruvic acid, ethylenediamine diacetic acid, nitrilotriacetic acid, N' - (2-hydroxyethyl) -ethylenediamine triacetic acid, propylenediamine tetraacetic acid, ethylenediamine tetraacetic acid, trans-1, 2-cyclohexanediamine tetraacetic acid, trans-1, 2- (cyclohexanediazone) tetraacetic acid, (1, 2-ethanediyldiazone) tetraacetic acid, ethylenediamine tetrapropionic acid, glycine, N-methylglycine, glycylglycine, glycylglycylglycylglycylglycylglycylglycylglycine, salicylideneglycine, iminodiacetic acid, methyliminodiacetic acid, N-diethylselenyldicarbamic acid, methionine, proline, sarcosine, xanthic acid, and the like;

(5) oximes having an oxime number of 1 to 4 or more and a carbon number of 2 to 20 or more;

dimethylglyoxime, 3- (2-aminoethylimino) -2-butanone oxime, benzylmethylglyoxime, 2, 6-diacetylpyridine dioxime, 2-pyridylacetaldoxime, 3-phenylimino-2-butanone oxime, salicylaldoxime, and the like;

(6) phenols having 1 to 4 or more phenols and 6 to 30 or more carbon atoms;

catechol, 1, 2-benzenediol, 1, 3-bis [ bis (2-pyridylethyl) aminomethyl ] phenol, 2, 6-bis [ bis (2-pyridylethyl) aminomethyl ] -4-phenol, 1-nitroso-2-naphthol, and the like;

(7) ethers having 1 to 8 or more ether groups and 4 to 30 or more carbon atoms;

tetrahydrofuran, 1, 4-dioxane, tetrahydrofuran, 1, 4, 7, 10-tetraoxa-cyclotetradecane, 1, 4, 7, 10, 13-pentaoxa-cyclopentadecane, 1, 4, 7, 10, 13, 16-hexaoxa-cyclooctadecane, 4, 7, 13, 16-tetraoxa-1, 10-diaza-cyclooctadecane, 4, 7, 13, 18-tetraoxa-1, 10-diazacyclo [8, 5, 5] eicosane, 2, 3-benzo-1, 4, 7, 10, 13-pentaoxa-cyclopenta-2-ene, 4, 7, 13, 16, 21-pentaoxa-1, 10-diazacyclo [8, 5, 5] tricosane, scirpenin, nigericin, etc.;

(8) a sulfur compound having 1 to 4 or more sulfur atoms and 2 to 40 or more carbon atoms;

diethyldimercaptocarbamic acid, ethylmercaptoacetic acid, ethylenedimercaptoacetic acid, ethylenethiourea, phenyldimercaptoacetic acid, dimercaptobenzoic acid, 1, 2-aminoethanethiol, diphenylthiocarbazone, dimethyl sulfoxide, 2, 4-pentanedithiol, 2, 7, 7-tetramethyl-3, 6-thiaoctane, 2-imidazolidinethione, dimethyldimercaptocarbamic acid, thiourea, cysteine, maleonitrile dithiol, 1, 4, 8, 11-tetrathia-decane, and the like;

(9) an amide compound having 1 to 3 or more amide groups and 3 to 54 or more carbon atoms;

diazoamide, N-dimethylacetamide, N-dimethylformamide, hexamethylphosphoric triamide, diphenylphosphinic amide, aminoacetamide, oxamide, valinomycin, phthalimide, succinimide, valinomycin, and the like;

(10) n-oxide compounds having 1 to 3 or more N-oxide groups and 6 to 20 or more carbon atoms;

α -methylpyridine-N-oxide, γ -methylpyridine-N-oxide, pyridine-N-oxide, etc.;

(11) others;

nitrogen molecule, water, carbon monoxide, urea, salicylaldehyde, N-nitrosophenylhydroxylamine acid and the like.

③ the conjugated compound having 2 to 10 or more unsaturated groups and 4 to 14 or more carbon atoms, the following compounds may be mentioned.

1, 5-cyclooctadiene (hereinafter referred to as cod), 1, 3, 5, 7-cyclooctatetraene, cyclopentadiene, pentamethylcyclopentadiene, tropolone, 1, 10-phenanthroline, etc.;

from the viewpoint of vinyl polymerizability, a compound containing a halogen (fluorine, chlorine, bromine, iodine) ion and a phosphorus atom is preferable, and a compound containing an anion selected from chlorine, bromine, iodine and the like atoms and a tertiary phosphine is more preferable.

The complex (d) is usually synthesized by mixing a salt of a metal element (d1) (e.g., a metal halide) and an anion or neutral molecular ligand (d2) at room temperature. In addition, there is also a case where the objective complex is reproduced after another intermediate complex is formed. The salt of the metal element (d1) and the anionic or neutral molecular ligand (d2) may be dissolved in the aqueous solution/solvent solution as they are or separately and then mixed, or may be mixed in the aqueous solution/solvent solution. If necessary, the temperature may be increased to 30 to 200 ℃. When a substance to be removed is produced, it can be removed by reducing the pressure. The resulting complex (d) may be removed as it is or as crystals, or may be purified and reused. Examples of the solvent used herein include alcohol solvents (methanol and ethanol), ketone solvents (acetone and methyl ethyl ketone), amide solvents (N, N-dimethylformamide and N-methylpyrrolidone), sulfone solvents (dimethyl sulfoxide and the like), and mixtures of two or more of these solvents.

Complexes (d) are very numerous compounds, but can be used, for example, in the context of the Angew. chem. int. ed. Engl., 12, 57 (1973); chem. educ., 50, 343 (1973); accts. chem. research, 3, 105 (1970); rev, 73, 487 (1973); Interscience-Wilry (1968); chem.soc.rev., 4, 27 (1975); examples of the synthetic methods include methods described in basic inorganic chemistry (Japanese edition, F.A. コツトン, and G. ゥイルキンソン, Pefeng corporation) and inorganic compound complex dictionary (Japanese edition, Zhongsheng よし, lecture corporation).

The form of the coordination is not particularly limited, and may be a terminal coordination (e.g., triphenylphosphine as a ligand), a 2-coordination (e.g., ethylenediamine as a ligand), a 3-6 coordination (e.g., terpyridine as a ligand), or the like. Usually in a complex coordination state. The complex (d) is usually a non-electrolytic complex having no charge, but may be an electrolytic complex having a charge, such as a cationic complex or an anionic complex.

Specific examples of the complex (d) include the following.

Specific examples thereof include:

(1) in the case where the metal element (d1) is a group IB metal element,

[Cu(CH₃)(PPh₃)]、[Cu₂Cl(cod)₂]、[Ag(py)₂]Cl、[Ag(py)₄]Cl、[Ag(py)₄]Cl₂、[AuCl(PPh₃)]、[AuCl₃(PPh₃)]、[Au(dppe)]cl, etc.;

(2) in the case where the metal element (d1) is a 4-period group VIII metal element,

[FeCl₂(bpy)₂]、[FeCl₂(bpy)₂]Cl、[FeCl(H)CO(PPh₃)₃]、[FeCl(H)(dppe)₂]、[FeCl₃(NO)(PPh₃)₂]、[FeCl₂(PPh₃)₃]、[FeCl₂(PPh₃)₄]、[Fe(CN)₂(bpy)₂]、[Fe(CO)₂(PPh₃)₃]、[Fe(H)₂(N₂)(PPh₃)₃]、[Co₂Cl₂(cod)₂]、[CoCl(CO)(PPh₃)₂]、[CoCl(PPh₃)₃]、[CoGl(O₂)(PPh₃)₃]、[CoCl₃(py)₃]、[Co(cod)₂]Cl、[Co(H)(CO)(PPh₃)₃]、[Ni(acac)Cl(PPh₃)]、[NiBr(CH₃){P(C₂H₅)₃}₂]、[NiBr(NH₃)₃]、[Ni(CH₃)Cl(cod)]、[Ni(C₂H₅)(cod)]Cl、[Ni(CH₃)(PPh₃)]、[Ni₂Cl₂(acac)₂]、[NiCl₂(bpy)]、[NiCl₂(cod)]、[Ni₂Cl₂(dppm)]、[NiCl₂(en)]、[NiCl₂(NH₃)(PPh₃)]、[NiCl₂(PPh₃)]、[Ni₂Cl₄(PPh₃)₂]、[Ni(PPh₃)₄]、[Ni(py)₄]Cl₂、[Ni(SO₃)(H₂O)₃]、[Ni(SO₃)(NH₃)₃]etc.;

(3) in the case where the metal element (d1) is a group VIII metal element of period 5,

[Rh₂Cl₂(cod)₂]、[RhCl(CO)(PPh₃)₂]、[RhCl(PPh₃)₃]、[RhCl(O₂)(PPh₃)₃]、[RhCl₃(py)₃]、[Rh(cod)₂]Cl、[Rh(H)(CO)(PPh₃)₃]、[RuCl₂(bpy)₂]、[RuCl₂(bpy)₂]Cl、[RuCl(H)(CO)(PPh₃)₃]、[RuCl(H)(dppe)₂]、[RuCl₃(NO)(PPh₃)₂]、[RuCl₂(PPh₃)₃]、[RuCl₂(PPh₃)₄]、[Ru(CN)₂(bpy)₂]、[Ru(CO)₂(PPh₃)₃]、[Ru(H)₂(N)₂(PPh₃)₃]、[Pd(acac)Cl(PPh₃)]、[PdBr(CH₃){P(C₂H₅)₃}₂]、[PdBr(NH₃)₃]、[Pd(CH₃)Cl(cod)]、[Pd(C₂H₅)(cod)]Cl、[Pd(CH₃)(PPh₃)]、[Pd₂Cl₂(acac)₂]、[PdCl₂(bpy)]、[PdCl₂(cod)]、[Pd₂Cl₂(dppm)]、[PdCl₂(en)]、[PdCl₂(NH₃)(PPh₃)]、[PdCl₂(PPh₃)]、[Pd₂Cl₄(PPh₃)₂]、[Pd(PPh₃)₄]、[Pd(py)₄]Cl₂、[Pd(SO₃)(H₂O)₃]、[Pd(SO₃)(NH₃)₃]etc.;

(4) in the case where the metal element (d1) is a metal element of group VIII of period 6,

[OsCl₂(bpy)2]、[OsCl₂(bpy)₂]Cl、[OsCl(H)(CO)(PPh₃)₃]、[OsCl(H)(dppe)₂]、[OsCl₃(NO)(PPh₃)₂]、[OsCl₂(PPh₃)₃]、[OsCl₂(PPh₃)₄]、[Os(CN)₂(bpy)₂]、[Os(CO)₂(PPh₃)₃]、[Os(H)₂(N₂)(PPh₃)₃]、[Ir₂Cl₂(cod)₂]、[IrCl(CO)(PPh₃)₂]、[IrCl(PPh₃)₃]、[IrCl(O₂)(PPh₃)₃]、[IrCl₃(py)₃]、[Ir(cod)₂]Cl、[Ir(H)(CO)(PPh₃)₃]、[Pt(acac)Cl(PPh₃)]、[PtBr(CH₃){P(C₂H₅)₃}₂]、[PtBr(NH₃)₃]、[Pt(CH₃)Cl(cod)]、[Pt(C₂H₅)(cod)]Cl、[Pt(CH₃)(PPh₃)]、[Pt₂Cl₂(acac)₂]、[PtCl₂(bpy)]、[PtCl₂(cod)]、[Pt₂Cl₂(dppm)]、[PtCl₂(en)]、[PtCl₂(NH₃)(PPh₃)]、[PtCl₂(PPh₃)]、[Pt₂Cl₄(PPh₃)₂]、[Pt(PPh₃)₄]、[Pt(py)₄]Cl₂、[Pt(SO₃)(H₂O)₃]、[Pt(SO₃)(NH₃)₃]etc.;

however, the compounds in the above-mentioned range are suitable for use without being limited thereto.

Preferred is [ RuCl ]₂(PPh₃)₃]、[RuCl₂(PPh₃)₄]、[Pd₂Cl₂(dppm)]、[RhCl(CO)(PPh₃)₂]、[RhCl(PPh₃)₃]And the like, 5-cycle complex of a ligand such as an anion of a group VIII metal element (ruthenium, rhodium, palladium) and an atom selected from chlorine, bromine, iodine and the like, a tertiary phosphine compound and the like.

From the viewpoint of polymerizability and workability, the complex (d) is preferably a complex dissolved in water or a water-soluble organic solvent. Examples of the water-soluble organic solvent include the same solvents as used for the synthesis of the complex (d).

The weight of the complex (d) is preferably 0.005ppm to 2% by weight and the amount of the metal element (d1) is preferably 0.001ppm to 1% by weight based on the total weight of the vinyl monomer (a) and the crosslinking agent (b) or the total weight of the vinyl monomer (a), the vinyl monomer (a3) and the crosslinking agent (b). More preferably, the amount of the complex (d) is 0.01ppm to 1% by weight, the amount of the metal element (d1) is 0.005ppm to 0.5% by weight, particularly preferably, the amount of the complex (d) is 0.02ppm to 0.6% by weight, and the amount of the metal element (d1) is 0.01ppm to 0.3% by weight.

When the amount of the complex (d) is 0.005ppm to 2% by weight and the amount of the complex (d1) is 0.001ppm to 1% by weight, the ethylene monomer exhibits sufficient polymerization rate and is excellent in productivity while exhibiting the performance as an absorbent article.

When the solubility of the complex (d) in the aqueous polymerization solution is low, the vinyl monomer (a) can be polymerized by dissolving or dispersing it in the aqueous polymerization solution using a water-soluble organic solvent and a surfactant at the same time.

In the present invention, it is preferable that at least one kind of ethylene monomer which is water-soluble and/or becomes water-soluble by hydrolysis is polymerized in the presence of water. The polymerization concentration, that is, the concentration of all the vinyl monomers [ the total weight of the vinyl monomers (a) and (b) or the total weight of the vinyl monomers (a), the vinyl monomers (a3), and (b) ] in the polymerization liquid is preferably 10 to 45% by weight, more preferably 12 to 40% by weight, and particularly preferably 15 to 35% by weight, based on the total weight of the polymerization liquid. When the total concentration of the vinyl monomer is 10% by weight or more, it is effective to have a sufficient concentration for use after polymerization. When the concentration is 45% by weight or less, the molecular weight of the polymer obtained by using the complex (d) is not too low, side reactions such as self-crosslinking do not occur, the molecular weight distribution of the main chain is relatively narrow, and the obtained polymer can exhibit the characteristics such as absorption capacity under the above-mentioned water retention capacity and load. The amount of water is preferably 90 to 55 wt% based on the total weight. When the weight of water is 90% by weight or less, it is effective to have a sufficient concentration for use after polymerization. When the amount is 55% by weight or more, the molecular weight of the main chain of the resulting polymer is not too low, and side reactions such as self-crosslinking do not occur, and the molecular weight distribution is narrow, whereby various characteristics of the present invention can be exhibited.

In the polymerization of the vinyl monomer (a) and the crosslinking agent (b) of the present invention, the polymerization temperature, time and other polymerization conditions are not particularly limited as long as the various characteristics of the present invention can be exhibited, and the polymerization can be carried out under known conditions, and for example, the polymerization initiation temperature may be changed depending on the kind of the polymerization initiator used, and is usually-5 to 90 ℃ and preferably 2 to 70 ℃. Further, whether or not a chain transfer agent (for example, isopropyl alcohol, a thiol chain transfer agent, sodium hypophosphite, or the like) is added is not particularly limited.

The polymerization may be carried out in the presence of a grafting base. Examples of the graft base include natural sugars such as starch and cellulose, modified products thereof, and water-soluble or water-dispersible synthetic resins such as polyoxyalkylene, polyvinyl alcohol, poly (meth) acrylate, and polyester.

The crosslinked polymer obtained is kneaded and crosslinked with the crosslinking agent (iii) and a polyvalent metal compound (calcium chloride, magnesium sulfate, aluminum sulfate, etc.) which forms ionic crosslinking, if necessary, in a state of containing a hydrogel. This relatively uniform crosslinking makes it possible to produce a crosslinked polymer having a high gel strength and containing a small amount of water-soluble components.

The hydrogel-like polymer of the crosslinked polymer thus obtained is dried and then pulverized, and if necessary, the crosslinked copolymer (a) is obtained by surface-crosslinking the crosslinked polymer obtained by adjusting the particle size in the vicinity of the surface thereof with a crosslinking agent (second crosslinking agent), whereby the excellent performance of the absorbent article of the present invention can be further improved.

The drying method may be a method of drying with hot air at a temperature of 80 to 230 ℃ or a film drying method using a drum dryer heated to 100 to 230 ℃, (heating) reduced pressure drying method, freeze drying method, infrared drying method, or the like.

The method of pulverization is not particularly limited, and a conventional apparatus such as a hammer mill, an impact mill, a roll mill, or an air jet mill can be used. The resultant pulverized material was sieved as necessary to adjust the particle size. The shape of the crosslinked polymer after pulverization is not particularly limited, and examples thereof include irregular crushed shapes, scaly shapes, bead shapes, rice grain shapes, and cut shapes. In the use of a disposable diaper or the like, it is preferable to use an irregularly crushed shape because the entanglement with the fibrous material is good and there is no fear of falling off from the fibrous material.

The weight average particle diameter of the crosslinked polymer obtained is preferably 100 to 800 μm, more preferably 200 to 500 μm, and the weight average particle diameter of the crosslinked polymer is preferably 95% by weight or more in the range of 100 to 850 μm, and a pulverized product can be used. It is preferable to use particles having a small content of fine particles, and the content of particles having a particle size of 100 μm or less is preferably 3% or less, more preferably 3% or less, and the content of particles having a particle size of 150 μm or less is more preferably 3% or less. The weight average particle diameter is a graph obtained by plotting the distribution of the particle sizes of the water-absorbent resin on paper, and the particle size at 50% of the total weight is determined as the weight average particle diameter by plotting the particle size on the horizontal axis and the content logarithmic probability on the basis of the weight on the vertical axis.

As a method for surface crosslinking of the crosslinked polymer, a conventionally known method can be used, and for example, a method in which a mixed solution of the second crosslinking agent (b2), water, and an organic solvent is mixed with the crosslinked polymer and then reacted by heating can be exemplified.

The second crosslinking agent (b2) may be the same as or different from the first crosslinking agent, and is preferably a crosslinking agent having an acid group such as a carboxyl group (iii) and/or at least two functional groups reactive with a base thereof. Particularly preferred are glycidyl ether compounds, polyamide-based resins, and ethyleneimine compounds, from the viewpoint of surface crosslinking at relatively low temperatures.

The amount of the second crosslinking agent (b2) is preferably 0.001 to 7.0% by weight, more preferably 0.002 to 5.0% by weight, particularly preferably 0.003 to 4.0% by weight, based on the weight of the vinyl monomer (a) or the total weight of the vinyl monomer (a) and the vinyl monomer (a 3). When the amount of the second crosslinking agent (b2) used is 0.001 wt% or more, the surface crosslinking degree is sufficient, and the absorption amount under load is increased. On the other hand, when the amount of the second crosslinking agent (b2) is 7.0 wt% or less, the degree of crosslinking on the surface is not excessive, and the water retention amount is not decreased.

The amount of water used in the surface crosslinking is preferably 1 to 10%, more preferably 2 to 7%, based on the weight of the crosslinked polymer, and in the case where the amount of water used is 1% or more, the second crosslinking agent (b2) can sufficiently penetrate into the interior of the particles of the crosslinked polymer and absorb an amount under load, particularly under high load (e.g., 60 kg/cm)²) The absorption amount of (2) has a good effect of improving. When the amount of water used is 10% or less, the second crosslinking agent (b2) is addedThe crosslinked polymer does not excessively penetrate into the interior, and it is considered that the absorption capacity can be increased under load, and the problem of the so-called large reduction in water retention capacity does not occur.

In the present invention, as the type of the organic solvent used together with water, a conventionally known hydrophilic solvent can be used, and it can be appropriately selected in consideration of suitability of the second crosslinking agent (b2) for penetrating into the crosslinked polymer, reactivity of the second crosslinking agent (b2), and the like. Preferably, the solvent is a hydrophilic organic solvent such as methanol or diethylene glycol dissolved in water. These solvents may be used alone or in combination of two or more.

The amount of the solvent to be used may vary depending on the kind of the solvent, but is preferably 1 to 10% by weight based on the crosslinked polymer. The ratio of the solvent to water may be arbitrarily changed, and is preferably 20 to 80% by weight, more preferably 30 to 70% by weight.

The second crosslinking agent (b2) is added to the crosslinked polymer in a mixed solution of water and a solvent by a conventionally known method, mixed, and then subjected to a heating reaction. The reaction temperature is preferably 80 to 200 ℃, more preferably 100 to 160 ℃. The reaction time varies depending on the reaction temperature, and is preferably 3 to 60 minutes, more preferably 5 to 40 minutes.

The particulate crosslinked polymer (a) obtained by surface crosslinking in this way can be additionally surface-crosslinked with the same second crosslinking agent (b2) or with a second crosslinking agent (b2) different from that used in (a).

The particle size of the crosslinked polymer (A) obtained by surface crosslinking in this manner is adjusted by a sieve as necessary. The weight average particle diameter of the obtained (A) is almost unchanged, preferably 100 to 800 μm, more preferably 200 to 500 μm, and 95 wt% or more of particles in the range of 100 to 850 μm among the pulverized particles that can be used. The content of fine particles is preferably small, and the content of particles having a particle size of 100 μm or less is preferably 3% or less, more preferably 3% or less, and the content of particles having a particle size of 150 μm or less is more preferably 3% or less.

Such a surface-crosslinked polymer not only has excellent absorption properties under a load under normal pressure, but also has a large gel strength.

The crosslinked polymer (A) of the present invention is obtained by polymerizing the vinyl monomer (a) and, if necessary, the vinyl monomer (A3) and the first crosslinking agent (b1) in the presence of at least one initiator (c) selected from the group consisting of azo-type initiators, peroxide initiators, redox-type initiators and organic halide initiators and water, to obtain a crosslinked polymer (A2) which is more preferably surface-crosslinked with the second crosslinking agent (b 2).

The crosslinked polymer of the present invention thus obtained satisfies the following conditions (i) to (iii).

①(X)≥33g/g

②(Y)≥25g/g

③(Y)≥-0.54(X)+42

[ wherein (X) represents the water retention in physiological saline after 1 hour of absorption; (Y) is at 60g/cm²Under a load of (1), the amount of absorption of physiological saline solution after 1 hour of absorption]。

The condition (i) relates to the water retention of the crosslinked polymer, and the condition (ii) relates to the absorption capacity under a high load, and if these conditions are not satisfied, the water retention is too small, or the absorption capacity under a load is small, so that the performance as an absorbent article is low, and in particular, in the case of being applied to a thin absorbent article, a problem of liquid leakage occurs. The condition (c) indicates a balance between the water retention amount of the crosslinked polymer and the amount absorbed under a high load, and if the condition (c) is not satisfied, an absorbent article having excellent absorption properties cannot be obtained.

When the above conditions are satisfied, the absorbent article is found to have excellent properties.

The gel elasticity of the crosslinked polymer (A) which swells 40 times with physiological saline is preferably 3,000N/m²Above, more preferably 4,000N/m²Above, especially preferredIs selected from 5,000 to 200,000N/m²Most preferably 6,000 to 180,000N/m²。

When the gel elasticity value is 3,000N/m²In the above case, when a shearing force is applied to the water-absorbent gel, the gel is hardly deformed or broken, and when an absorbent article using a crosslinked polymer is used for a long period of time, repeated absorption performance is not lowered, and a dry feeling and leakage do not occur.

When the crosslinked polymer (A) of the present invention is used in an absorbent structure or an absorbent article, the water content is preferably 2 to 10% by weight, more preferably 3 to 8% by weight, the degree of dusting is preferably 0 to 50cpm, more preferably 0 to 30pcm, the average particle diameter is preferably 200 to 500 μm, and the moisture absorption blocking ratio after standing for 3 hours at 40 ℃ and 80% relative humidity is preferably 0 to 50%, more preferably 0 to 20%, from the viewpoint of handling, texture, hand feeling, moisture resistance, and the like.

The water content can be measured by the weight loss rate of the crosslinked polymer (A) of the present invention after drying at 125 ℃ for 1 hour.

The dust emission degree was measured using a 1L suction bottle, a suction port, and a digital dust meter (manufactured by Takeda scientific Co., Ltd.). The suction inlet of the suction bottle and the suction inlet of the digital dust meter (manufactured by Kashisha scientific Co., Ltd.) had an inner diameter of 7mm, and they were connected by a glass tube having a length of 10cm, and 20g of the crosslinked polymer powder was put into the suction bottle from the upper port of the suction bottle using a rotor. The number of dust generation from the falling crosslinked polymer powder in 1 minute was measured by a digital dust meter, and this value was taken as the degree of dust generation (in cpm).

In the present invention, a surfactant, a preservative (a preservative such as salicylic acid, sorbic acid, dehydroacetic acid, menadione, etc., a bactericide such as chloramine B, nitrofurazone, etc.), a fungicide (butyl paraben, etc.), an antibacterial agent (alkyldimethylbenzylammonium chloride, chlorohexidine Gluconate, etc.), an antioxidant, an ultraviolet absorber, a colorant (an inorganic pigment such as titanium oxide, iron oxide, etc., an organic pigment such as azolakebase, benzophenones, cyanine, etc., a dye such as aniline black, aniline, etc.), an aromatic agent (a natural perfume such as musk, rosin oil, terpene, etc., menthol, citral, p-methylacetophenone, florale, etc.), a deodorizing agent (zeolite, silica sand, flavonoid, cyclodextrin, etc.), a preservative, a bactericide such as chloramine B, nitrofurazone, etc.), a fungicide (butyl paraben, etc.), an antibacterial agent (an alkyldimethylbenzylammonium chloride, a chlorohexidine Gluconate, etc.), an antioxidant, an ultraviolet absorber, an organic, Inorganic powders, organic fibrous materials, and the like. The amount thereof used varies depending on the purpose, but is preferably 0 to 20% by weight, more preferably 0 to 18% by weight, based on the weight of the crosslinked polymer (A).

Examples of the surfactant include anionic, nonionic, cationic and amphoteric surfactants, and one or two or more of them can be used in combination, for example, as described in USP-4331447.

Examples of the anionic surfactant include carboxylic acids and salts of hydrocarbon ethers having 8 to 24 carbon atoms, [ sodium polyoxyethylene (degree of polymerization: 1 to 100) lauryl ether acetate, disodium polyoxyethylene (degree of polymerization: 1 to 100) lauryl sulfonate ], salts of hydrocarbon sulfates having 8 to 24 carbon atoms, [ sodium lauryl sulfate, sodium polyoxyethylene (degree of polymerization: 1 to 100) lauryl sulfate, triethylamine polyoxyethylene (degree of polymerization: 1 to 100) lauryl sulfate, sodium polyoxyethylene (degree of polymerization: 1 to 100) sodium coconut fatty acid monoethanolamide sulfate ], hydrocarbon sulfonates having 8 to 24 carbon atoms [ sodium dodecylbenzenesulfonate, etc. ], salts of hydrocarbon phosphates having 8 to 24 carbon atoms [ sodium lauryl phosphate, sodium polyoxyethylene (degree of polymerization: 1 to 100) lauryl ether phosphate, etc. ], salts of fatty acids [ sodium laurate, sodium laureth phosphate, etc. ], salts of hydrocarbon phosphates having 8 to 24 carbon atoms [ sodium laureth phosphate, sodium laureth, Triethanolamine laurate, etc.), acetylated amino acid salts [ sodium coconut fatty acid methyl taurate, sodium coconut fatty acid sarcosinate, coconut fatty acid sarcosine triethanolamine salt, N-coconut fatty acid acetyl-L-glutamic acid triethanolamine salt, N-coconut fatty acid-L-sodium glutamate, lauroyl- β -alanine sodium, etc. ], and other [ polyoxyethylene sulfosuccinate (disodium lauroyl ethanolamine having a polymerization degree of 1 to 100, etc. ].

Specific examples of the nonionic surfactant include adducts (degree of polymerization: 1 to 100) of aliphatic alcohol (having 8 to 24 carbon atoms) oxyalkylene (having 2 to 8 carbon atoms) [ polyoxyethylene lauryl (degree of polymerization: 20) adducts, polyoxyethylene oleyl (degree of polymerization: 10) adducts, polyoxyethylene cetyl (degree of polymerization: 35) adducts ], polyoxyalkylene (having 2 to 8 carbon atoms and having 1 to 100 degree of polymerization) higher fatty acid (having 8 to 24 carbon atoms) [ polyoxyalkylene monostearate (degree of polymerization: 20) ester, polyoxyalkylene distearate (degree of polymerization: 30) ester ], polyhydric alcohol (having 2 to 10 or more carbon atoms) fatty acid (having 8 to 24 carbon atoms) [ glyceryl monostearate, ethylene glycol monostearate, (mono/di) sorbitan laurate, (mono/di) sorbitan palmitate, sorbitan monopalmitate, sorbitan monolaurate, and sorbitan monolaurate, (mono/di) sorbitan stearate, (mono/di) sorbitan oleate, (mono/di) sorbitan cocoate, etc. ], polyoxyalkylene (having 2 to 8 carbon atoms and a polymerization degree of 1 to 100) polyol (2 to 10 or more) higher fatty acid ester [ polyoxyethylene (polymerization degree of 10) (mono/di) sorbitan laurate, polyoxyethylene (polymerization degree of 20) (mono/di) sorbitan palmitate, polyoxyethylene (polymerization degree of 15) (mono/di) sorbitan stearate, polyoxyethylene (polymerization degree of 10) (mono/di) sorbitan laurate, polyoxyethylene (polymerization degree of 25) (mono/di) laurate, polyoxyethylene (polymerization degree of 50) (mono/di) stearate, polyoxyethylene (polymerization degree of 18) (mono/di) oleate, polyoxyethylene (polymerization degree of 10) (mono/di) oleate, polyoxyethylene (polymerization degree of 25) (mono/di) laurate, polyoxyethylene (polymerization degree of 50) (mono/di) stearate, polyoxyethylene (polymerization degree of 18) (mono/di) oleate, polyoxyethylene (di) stearate, polyoxyethylene (polymerization degree of 10) (mono/di) laurate, polyoxyethylene (mono/di) oleate, polyoxyethylene (di, Examples of the alkyl group include glycidyl alcohol, polyoxyethylene (polymerization degree of 50) dioleic acid methyl glucoside, etc.), fatty acid alkanolamide [ 1: 1 coconut oil fatty acid diethanolamide, 1: 1 lauric acid diethanolamide, etc. ], polyoxyalkylene (having 2 to 8 carbon atoms and a polymerization degree of 100) alkyl (having 1 to 22 carbon atoms) phenyl ether (polyoxyethylene (polymerization degree of 20) nonylphenol ether, etc.), polyoxyalkylene (having 2 to 8 carbon atoms and a polymerization degree of 1 to 100) alkyl (having 8 to 24 carbon atoms) amino ether or alkyl (having 8 to 24 carbon atoms) dialkyl (having 1 to 6 carbon atoms) amine oxide [ lauryldimethylamine oxide ], polydimethylcyclohexane polyoxyethylene adduct, polyoxyethylene-polyoxypropylene block polymer (weight average molecular weight of 150 to 10,000), and the like.

Examples of the cationic surfactant include quaternary ammonium salt type [ stearyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, distearyl dimethyl ammonium chloride, lanolin fatty acid aminopropyl ethyl dimethyl ammonium ethyl sulfate, etc. ], amine salt type [ stearic acid diethylaminoethyl amide lactate, dilaurylamine hydrochloride, oleylamine lactate, etc. ].

Examples of the amphoteric surfactant include betaine-type amphoteric surfactants [ such as cocamidopropyl dimethylamino acetic acid betaine, lauryl dimethyl glycine betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolium betaine, lauryl hydroxysulfobetaine, and lauramidoethyl hydroxyethyl carboxymethyl betaine hydroxypropyl sodium phosphate ], and amino acid-type amphoteric surfactants [ such as sodium β -laurylaminopropionate ].

Examples of the antioxidant include hindered phenol-based antioxidants such as triethylene glycol bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate ], 1, 6-hexanediol bis [3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], octadecyl 3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate and diethyl 3, 5-di-tert-butyl-4-hydroxybenzylphosphate, amine-based antioxidants such as n-butylamine, triethylamine and diethylaminomethyl methacrylate, and two or more of these can be used in combination.

Examples of the ultraviolet absorber include benzotriazole-based ultraviolet absorbers such as 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- (3, 5-di-t-butyl-2-hydroxyphenyl) -5-chlorobenzotriazole and 2- (3, 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, triazine-based ultraviolet absorbers such as 2- (4, 6-diphenyl-1, 3, 5-triazin-2-yl) -5- [ (hexyl) oxy ] -phenol, benzophenone-based ultraviolet absorbers such as 2-hydroxy-4-n-octyloxybenzophenone, and the like, Oxalic acid phenylamine-based ultraviolet absorbers such as 2-ethoxy-2' -ethyl oxalic acid phenylaniline, and two or more of them are used simultaneously.

Examples of the inorganic powder include calcium carbonate, kaolin, talc, mica powder, bentonite, clay, diatomaceous earth, asbestos powder, glass fiber, carbon fiber, glass powder, glass bead, silicone rubber bead, coal powder, metal powder, ceramic powder, silica, zeolite, slate powder, and the like. The form thereof may be arbitrary, and the average particle diameter is preferably from 0.1 μm to 1 mm.

Examples of the pigment include carbon black, titanium oxide, red iron oxide, red lead, red parr, and deep blue.

Examples of the organic fibrous material include natural fibers [ e.g., cellulose-based natural fibers (e.g., cotton, sawdust, and grass), peat, wool, microfibril, and bacterial cellulose ], rayon (e.g., cellulose-based fibers such as rayon and acetate), synthetic fibers (e.g., polyamide, polyester, and acrylic fibers), pulp [ e.g., mechanical pulp (e.g., wood pulp made of logs, caustic soda pulp, sulfate pulp, nitrate pulp, and chloride pulp), semi-mechanical pulp, and recycled pulp (e.g., recycled pulp produced by mechanically crushing or pulverizing old paper once the pulp is formed into paper) ], and the like.

(absorbent Structure and absorbent article)

The crosslinked polymer of the present invention is particularly excellent in the balance between the water retention capacity and the absorption capacity under load, and therefore, is suitable for various absorbent structures (C) and absorbent articles (D), and can provide articles excellent in absorption performance.

As a method for suitably using the crosslinked polymer (a) in the absorbent structure (C), there is, for example, a method for forming an article from the crosslinked polymer (a) and the fibrous material (B) as a base material.

Examples thereof include:

(1) dispersing a crosslinked polymer in a granular form between fibrous layers of pulp and heat-fusible fibers arranged in layers;

(2) mixing a fibrous material comprising pulp, a heat-fusible fiber, etc. with a crosslinked polymer;

(3) an absorbent structure is obtained by using two or more sheets of absorbent paper or nonwoven fabric, optionally together with a fibrous material, in a layered state with a crosslinked polymer.

Examples of the fibrous material (B) include various flocculent pulps, cotton pulps, and fibrous materials used in absorbent products at present, and there are no particular limitations on the raw material (coniferous or broadleaf), the production method [ chemical pulping, semi-chemical pulping, or pre-heated wood chip chemical groundwood pulping (CTMP) ], the bleaching method, and the like.

In addition to the organic fibrous materials, the fibrous materials may be a combination of water-insoluble synthetic fibers and the above-mentioned flocculent pulp or cotton-like pulp, if necessary. Examples of the synthetic fibers include polyolefin fibers (e.g., polyethylene fibers and polypropylene fibers), polyester fibers (e.g., PET fibers), polyolefin-polyester composite fibers, polyamide fibers, and acrylic fibers.

The length and thickness of the fibrous material (B) are not particularly limited, but the length is usually 1 to 200mm, and the thickness is preferably 0.1 to 100 denier.

The shape is not particularly limited as long as it is fibrous, and examples thereof include a net shape, a thin cylindrical shape, a split tear-off filament shape, a short filament shape, and a long filament shape.

The amount of the crosslinked polymer (a) to be added to the absorbent structure (C) may be varied depending on the type and size of the absorbent structure and the intended absorption performance, and is preferably 30 to 95% by weight, more preferably 40 to 95% by weight, based on the amount of the absorbent structure (C).

The absorbent article of the present invention is preferably an absorbent article (D) comprising an absorbent structure (C), a liquid-permeable sheet, and a breathable back sheet, more preferably an absorbent article (D) as a sanitary product, and particularly preferably a paper diaper having a surface dryness value of 50% or more, more preferably 55% or more, as measured by the following SDME method.

Examples

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto. In the present invention, the water retention capacity, the absorption capacity under pressure, the gel elasticity and the moisture absorption blocking rate are measured by the following methods. In the following, unless otherwise specified,% represents% by weight.

< Water Retention amount >

A "teabag" bag made of a 250-mesh nylon net (20 cm in length and 10cm in width) was charged with 1.00G of a crosslinked polymer, placed in 1,000cc of a physiological saline solution (0.9% salt concentration) and soaked for 1 hour without stirring, then hung for 15 minutes to drain water, and the bag was put into a centrifuge together and dehydrated at 150G for 90 seconds to remove the remaining water. The amount of water retained was determined as the weight gain after centrifugation. Further, the temperature of the physiological saline used and the measurement temperature were both 25 ℃.

< absorption under load >

A250 mesh nylon net was tightly attached to a cylindrical plastic tube (inner diameter 30mm, height 60mm) on the bottom surface, 0.10g of a crosslinked polymer was added and homogenized, a weight of 30mm outer diameter was placed on the resin, and 60g/cm was applied²The load of (2).

A glass dish (diameter 12cm) was placed with 60mL of physiological saline, and the nylon mesh side of a plastic tube filled with a crosslinked polymer was soaked from below and left to stand. The weight increase of the crosslinked polymer due to absorption of physiological saline after 1 hour was measured, and the value of 10 times thereof was defined as 60g/cm²The absorption of the load under the conditions. The temperature of the physiological saline used and the measurement temperature were both 25 ℃.

< gel elasticity value >

A40-fold swollen gel was obtained by allowing 1.00g of the crosslinked polymer to absorb 40mL of physiological saline. 40mL of physiological saline was added to a 100mL beaker. A3 cm stirring piece was placed on a magnetic stirrer, and the stirring piece was rotated in the center of the beaker. After the liquid was confirmed to form a stable vortex by rotating at 600. + -. 10rpm, 1.00g of the crosslinked polymer powder was added at a time, the rotation was stopped in the middle, and the sample was left for 3 hours to obtain a swollen gel.

0.200g of the swollen gel was placed in the middle of a support table of a rheometer (manufactured by SHAN electric Co., Ltd., クリ - プメ - タ -RE-33005) and flattened. Then, a stress of 30g (P: 30 × 98/S) was applied to the upper surface of the swollen gel, and the deformation ratio (H: height at compression/initial height) when compressed by a cylinder was obtained. The cross-sectional area of the gel at this time [ S ═ sample volume/(initial height-height at compression) ], was measured, and the gel elasticity value was determined by the following equation.

Gel elasticity value (N/m)²)＝P/H

The temperature of the physiological saline solution used, the temperature at the time of producing the swollen gel, and the measurement temperature were all 25 ℃.

< moisture absorption blocking Rate >

10g of the crosslinked polymer powder was uniformly placed in a dish made of alumina having a diameter of 5cm, and allowed to stand in a constant temperature bath at 40 ℃ and a relative humidity of 80% for 3 hours. The weight of the crosslinked polymer after standing for 3 hours was measured, and then lightly sieved through a 12-mesh wire net, and the weight of a powder of the crosslinked polymer which was not allowed to pass through the 12-mesh screen due to agglomeration by moisture absorption was measured, and the moisture-absorption agglomeration rate was determined by the following formula.

Moisture absorption blocking ratio (weight of crosslinked polymer remaining on 12 mesh net after standing for 3 hours/total weight of crosslinked polymer after standing for 3 hours) × 100

Example 1

77g of sodium acrylate, 22.85g of acrylic acid, 0.15g of N, N' -methylenebisacrylamide, 293g of deionized water, and 0.001g of dichlorotris (triphenylphosphine) ruthenium were charged into a glass reactor having a capacity of 1L, and the contents were kept at 3 ℃ while being stirred and mixed.

After nitrogen gas was passed through the contents to make the dissolved oxygen content lower than 1ppm, 0.3g of a 1% aqueous hydrogen peroxide solution, 0.8g of a 0.2% aqueous ascorbic acid solution and 0.8g of a 2% 2, 2' -azobis (2-amidinopropane) dihydrochloride aqueous solution were added and mixed to start polymerization, and the temperature reached 69 ℃ after 1.5 hours, and the temperature was maintained, thereby obtaining a hydrogel-containing polymer complex (A-1) after 5 hours of polymerization in total after the start.

The aqueous gel of (A-1) thus obtained was cut in an internal mixer and then dried on an air-permeable belt dryer at 135 ℃ and an air speed of 2.0 m/sec.

The dried product obtained was pulverized and adjusted to a particle size of 30 to 60 mesh, 100g of this powder was added to a 10% water/methanol mixed solution of 2g of ethylene glycol diglycidyl ether (water/methanol: 70/30) under high-speed stirring, and mixed, and heated at 140 ℃ for 30 minutes to crosslink, thereby obtaining a crosslinked polymer (1).

The particle size distribution and evaluation results of this crosslinked polymer (1) are shown in Table 1. The water content of the crosslinked polymer was 4% and the degree of dusting was 10 cpm.

Example 2

A glass reactor having a capacity of 1L was charged with 81.7g of acrylic acid, 0.15g of N, N' -methylenebisacrylamide, 241g of deionized water, and 0.001g of dichlorotris (triphenylphosphine) ruthenium, and the contents were kept at 3 ℃ while stirring and mixing.

After nitrogen gas was passed through the contents to make the dissolved oxygen content lower than 1ppm, 0.3g of a 1% aqueous hydrogen peroxide solution, 0.8g of a 0.2% aqueous ascorbic acid solution and 0.8g of a 2% 2, 2' -azobis (2-amidinopropane) dihydrochloride aqueous solution were added and mixed to start polymerization, and the temperature reached 74 ℃ after 1.5 hours, and the temperature was maintained, whereby a hydrogel-like polymer was obtained after 5 hours of polymerization in total after the start.

After the hydrogel polymer was cut in an internal mixer, 109.1g of a 30% aqueous solution of sodium hydroxide was added thereto, followed by kneading to obtain a 72% carboxylic acid-neutralized hydrogel (A-2).

The aqueous gel (A-2) was dried on an air-permeable belt dryer at 140 ℃ and an air speed of 2.0 m/sec.

The dried product obtained was pulverized and adjusted to a particle size of 30 to 60 mesh, 100g of this powder was added to a 10% water/methanol mixed solution of 2g of ethylene glycol diglycidyl ether (water/methanol: 70/30) under high-speed stirring, and mixed, and heated at 140 ℃ for 30 minutes to crosslink, thereby obtaining a crosslinked polymer (2).

The particle size distribution and evaluation results of this crosslinked polymer (2) are shown in Table 1. The crosslinked polymer (2) had a water content of 5% and a dust generation degree of 11 cpm.

Example 3

77g of sodium acrylate, 22.6g of acrylic acid, 0.4g of pentaerythritol triallyl ether, 293g of deionized water, and 0.001g of dichlorotris (triphenylphosphine) ruthenium were charged into a glass reactor having a capacity of 1 liter, and the contents were kept at 3 ℃ while being mixed with stirring.

After nitrogen gas was passed through the contents to make the dissolved oxygen content lower than 1ppm, 0.3g of a 1% aqueous hydrogen peroxide solution, 0.8g of a 0.2% aqueous ascorbic acid solution and 0.8g of a 2% 2, 2' -azobis (2-amidinopropane) dihydrochloride aqueous solution were added and mixed to start polymerization, and the temperature reached 69 ℃ after 1.5 hours, and the temperature was maintained, thereby obtaining a hydrogel-containing polymer complex (A-3) after 5 hours of polymerization in total after the start.

The aqueous gel of (A-3) thus obtained was cut in an internal mixer and then dried on an air-permeable belt dryer at 135 ℃ and an air speed of 2.0 m/sec.

The dried product obtained was pulverized and adjusted to a particle size of 30 to 60 mesh, 100g of this powder was added to a 10% water/methanol mixed solution of 2g of ethylene glycol diglycidyl ether (water/methanol: 70/30) under high-speed stirring, and mixed, and heated at 140 ℃ for 30 minutes to crosslink, thereby obtaining a crosslinked polymer (3).

The particle size distribution and evaluation results of this crosslinked polymer (3) are shown in Table 1. The crosslinked polymer (3) had a water content of 4% and a dust generation degree of 15 cpm.

Example 4

A glass reactor having a capacity of 1L was charged with 81.7g of acrylic acid, 0.4g of pentaerythritol triallyl ether, 241g of deionized water, and 0.001g of dichlorotris (triphenylphosphine) ruthenium, and the contents were kept at 3 ℃ while being stirred and mixed.

After nitrogen gas was passed through the contents to make the dissolved oxygen content lower than 1ppm, 0.3g of a 1% aqueous hydrogen peroxide solution, 0.8g of a 0.2% aqueous ascorbic acid solution and 0.8g of a 2% 2, 2' -azobis (2-amidinopropane) dihydrochloride aqueous solution were added and mixed to start polymerization, and the temperature reached 74 ℃ after 1.5 hours, and the temperature was maintained, whereby a hydrogel-like polymer was obtained after 5 hours of polymerization in total after the start.

After the hydrogel polymer was cut in an internal mixer, 109.1g of a 30% aqueous solution of sodium hydroxide was added thereto, followed by kneading to obtain a 72% carboxylic acid-neutralized hydrogel (A-4).

The aqueous gel (A-4) was dried on an air-permeable belt dryer at 140 ℃ and an air speed of 2.0 m/sec.

The dried product thus obtained was pulverized and adjusted to a particle size of 30 to 60 mesh, and 100g of this powder was added to and mixed with 2g of a 10% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol: 70/30) under high-speed stirring, and heated at 140 ℃ for 30 minutes to crosslink the mixture, thereby obtaining a crosslinked polymer (4).

The particle size distribution and evaluation results of this crosslinked polymer (4) are shown in Table 1. The crosslinked polymer (4) had a water content of 6% and a dust generation degree of 20 cpm.

Example 5

A surface-crosslinked polymer (5) was obtained in the same manner as in example 1 except that in example 1, 0.17g of ethylene glycol diglycidyl ether was used in place of 0.15g of N, N' -methylenebisacrylamide.

The particle size distribution and evaluation results of this crosslinked polymer (5) are shown in Table 1. The crosslinked polymer (5) had a water content of 8% and a dust generation degree of 9 cpm.

Example 6

A surface-crosslinked polymer (6) was obtained in the same manner as in example 2 except that in example 2, 0.3g of a 1% aqueous solution of potassium persulfate was used in place of 0.3g of a 1% aqueous solution of hydrogen peroxide.

The particle size distribution and evaluation results of this crosslinked polymer (6) are shown in Table 2. The crosslinked polymer (6) had a water content of 6% and a dust generation degree of 18 cpm.

Reference 1

In example 4, the same procedure as in example 4 was repeated except that 0.5g of pentaerythritol triallyl ether was used instead of 0.4g of pentaerythritol triallyl ether, 375g of deionized water was used instead of 241g of deionized water, 1.0g of a 2% aqueous solution of 2, 2 '-azobis (2-amidinopropane) dihydrochloride was used instead of 0.8g of 2, 2' -azobis (2-amidinopropane) dihydrochloride solution, and dichlorotris (triphenylphosphine) ruthenium was not used, to obtain a surface-crosslinked-type crosslinked polymer (7).

The particle size distribution and evaluation results of this crosslinked polymer (7) are shown in Table 2. The crosslinked polymer (7) had a water content of 8% and a dust generation degree of 18 cpm.

Reference 2

In a 500mL four-necked round-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen introduction tube, 121.2g of cyclohexane was charged, 0.9g of glycidyl monostearate was added and dissolved, and then nitrogen was introduced to blow out dissolved oxygen. In a 300mL Erlenmeyer flask, a mixture of 45g of acrylic acid and 6.4g of water was added under ice cooling to a 25% aqueous solution of 70.0g of sodium hydroxide to neutralize 70% of the carboxyl groups. Then, 0.033g of N, N '-methylenebisacrylamide as a crosslinking agent, 0.0546g of sodium hypophosphite as a water-soluble chain transfer agent, and 0.0313g of 2, 2' -azobis (2-amidinopropane) dihydrochloride as a polymerization initiator were added and dissolved. The contents of this 300mL conical flask were added to the contents of the above four-necked round-bottomed flask, and polymerization was carried out for 2 hours while stirring and dispersing the mixture, and raising the internal temperature of the flask in an oil bath with bubbling of nitrogen gas, and maintaining the internal temperature at 60 ℃. After 2 hours, the content was that the crosslinked polymer swollen with water was dispersed in cyclohexane in the form of slurry. Then, the temperature of the oil bath was raised, and the water content of the swollen crosslinked polymer was dehydrated to 20% by azeotropy with cyclohexane in the flask. After dehydration the stirring was stopped and the swollen polymer particles settled to the bottom of the round bottom flask and were easily separated by decantation for cyclohexane compatibility. And (3) transferring the separated swelling polymer to a decompression dryer, and drying at 80-90 ℃ to remove attached cyclohexane and water to obtain the coarse granular crosslinked polymer. 30g of this was stirred at a high speed, and simultaneously, 0.6g of a 10% water/methanol mixed solution of ethylene glycol diglycidyl ether (water/methanol: 70/30) was added and mixed, and heated at 140 ℃ for 30 minutes to crosslink, thereby obtaining a surface-crosslinked polymer (8).

The particle size distribution and evaluation results of this crosslinked polymer (8) are shown in Table 2. The crosslinked polymer (8) had a water content of 5% and a dust generation degree of 18 cpm.

Comparative example 1

77g of sodium acrylate, 22.7g of acrylic acid, 0.3g of N, N' -methylenebisacrylamide and 295g of deionized water were charged into a 1L glass reactor, and stirred and mixed while maintaining the temperature of the contents at 3 ℃.

After nitrogen gas was introduced into the contents to make the dissolved oxygen content lower than 0.3ppm, 1g of a 1% aqueous solution of hydrogen peroxide, 1.2g of a 0.2% aqueous solution of ascorbic acid and 2.8g of a 2% aqueous solution of 2, 2' -azobis (2-amidinopropane) dihydrochloride were added and mixed, and polymerization was started, and 1.5 hours later, 70 ℃ was reached, the temperature was maintained, and polymerization was started for about 5 hours in total to obtain a water-containing gel-like polymer complex (a-1).

The resulting aqueous gel (A-1) was cut in an internal mixer and then dried on an air-permeable belt dryer at 135 ℃ and an air speed of 2.0 m/sec.

The resulting dried product was pulverized, and the particle size was adjusted to 30 to 60 mesh, 100g of this powder was added to a 10% water/methanol mixed solution of 1g of ethylene glycol diglycidyl ether (water/methanol: 70/30) under stirring and mixed, and heated at 140 ℃ for 30 minutes to crosslink, to obtain a comparative crosslinked polymer (1').

The particle size distribution of this comparative crosslinked polymer (1') and the evaluation results are shown in Table 2.

Comparative example 2

A1L glass reactor was charged with 81.7g of acrylic acid, 0.2g of N, N' -methylenebisacrylamide and 241g of deionized water, and the mixture was stirred and mixed while maintaining the temperature of the contents at 3 ℃.

After nitrogen gas was introduced into the contents to make the dissolved oxygen content lower than 0.3ppm, 1g of a 1% aqueous solution of hydrogen peroxide, 1.2g of a 0.2% aqueous solution of ascorbic acid and 0.8g of a 2% aqueous solution of 2, 2' -azobis (2-amidinopropane) dihydrochloride were added and mixed to start polymerization, and 1.5 hours later, the temperature was changed to 75 ℃ and the temperature was maintained, and polymerization was started for about 5 hours in total to obtain a hydrogel-containing polymer.

This hydrogel was cut in an internal mixer, and 109g of a 30% aqueous solution of sodium hydroxide was added thereto and kneaded to neutralize 71 mol% of carboxyl groups, thereby obtaining hydrogel (A-2).

The (A-2) was dried on an air-permeable belt dryer at 140 ℃ and an air speed of 2.0 m/sec.

The resulting dried product was pulverized, and the particle size was adjusted to 30 to 60 mesh, 100g of this powder was added to a 10% water/methanol mixed solution of 1g of ethylene glycol diglycidyl ether (water/methanol: 70/30) under stirring and mixed, and heated at 140 ℃ for 30 minutes to crosslink, to obtain a comparative crosslinked polymer (2').

The particle size distribution of this comparative crosslinked polymer (2') and the evaluation results are shown in Table 2.

< evaluation of paper diaper >

Absorbent structures were produced using the crosslinked polymers (1) to (6) of the present invention and the comparative crosslinked polymers (1 ') and (2'), and the absorbent capacity under load, the absorption rate under load, the spreading area under load, the surface dry feel, and the SDME surface dryness values of the paper diapers produced by the following methods were measured by the following methods. In the following, the% are all weight% unless otherwise specified.

< absorption under load >

A plexiglass plate (weight: 0.5kg) having a cylinder (inner diameter: 3cm, length: 20cm) at the center and having the same size as the area of the diaper (140 mm. times.360 mm) was placed on the diaper, and a load of 20kg (total weight: 20.5kg) was uniformly applied to the plexiglass plate. The cylinder was filled with 80mL of artificial urine. After 5 minutes, 80mL of artificial urine was again injected. Also after 5 minutes a third 80mL artificial urine injection was made, followed by another 5 minutes. The load and the plexiglass plate were removed and at the same time the artificial urine not absorbed by the diaper was removed, and the weight (Wg) of the wet specimen was measured. W is the amount of absorption under load.

< absorption Rate under load >

A plexiglass plate (weight: 0.5kg) having a cylinder (inner diameter: 3cm, length: 20cm) at the center and having the same size as the area of the diaper (140 mm. times.360 mm) was placed on the diaper, and a load of 20kg (total weight: 20.5kg) was uniformly applied to the plexiglass plate. The cylinder was filled with 80mL of artificial urine (colored with blue ink). After 10 minutes, 80mL of artificial urine was again injected. A third injection of 80mL artificial urine was also made after 10 minutes. The absorption time of these three times was measured as the absorption rate under load.

< diffusion area under load >

After the third absorption rate was measured, the area of the artificial urine spread in the direction of the absorption plane was defined as the spread area under load.

< feeling of surface drying >

After the spread area was measured, the surface dryness of the model diaper was judged by a 10-person evaluation group by finger contact, and evaluated in the following three cases. The average of 10 persons was determined as the surface dryness.

O: good dry feeling

And (delta): slightly moist but satisfactory level of dry feel in use

X: lack of dry feeling, wet state, or no dry feeling, wet state

< dryness number by SDME measurement >

The dryness value obtained by the SDME measurement was measured by using an SDME (surface dryness measuring device) tester (manufactured by WK System Co., Ltd.) in the following order.

The SDME tester was calibrated by placing the detector of the SDME tester on a very wet diaper and setting the dryness to 0, and then placing the detector of the SDME tester on a dry diaper and setting the dryness to 100.

Then, a metal ring (diameter: 70mm) was placed in the middle of the diaper to be measured, and 80mL of artificial urine was injected. Immediately after the injection, the metal ring was removed and the measurement was started in the middle of the diaper with the SDME tester. After the start of the measurement, the value after 5 minutes was taken as the dryness value of SDME.

Examples 9 to 16

100 parts of flocculent pulp and 100 parts of the crosslinked polymers (1) to (6) of the present invention obtained in examples 1 to 8 were mixed in an air-flow mixing apparatus and uniformly laminated so that the weight per unit area of the mixture was about 400g/cm²At a rate of 5kg/cm²The pressure in (2) was increased for 30 seconds to obtain absorbent structures (B1) to (B8) of examples 9 to 16.

Example 17

After 50 parts of a flocculent pulp layer was formed, 100 parts of the crosslinked polymer (2) obtained in example 2 was uniformly dispersed thereon, and a 50 parts flocculent pulp layer was laid thereon to form a sandwich structure at 5kg/cm²The load of (2) was applied for 30 seconds to obtain an absorbent structure (C2).

Comparative examples 3 and 4

100 parts of fluffed pulp and the comparative crosslinked polymers (1 ') and (2') obtained in comparative examples 1 and 2 were mixed in an air-flow mixer and uniformly laminated so that the weight per unit area of the mixture was about 400g/cm²At a rate of 5kg/cm²The load of (3) was applied for 30 seconds, thereby obtaining comparative absorbent structures (B1 ') and (B2') of comparative examples 3 and 4.

< test example >

The absorbent structures obtained in examples 9 to 16 and 17 and comparative examples 3 and 4 were cut into a rectangular shape of 14cm × 36cm, and water-absorbent papers (weight per unit area of 15.5 g/m) having the same size as the absorbent structure were disposed on the upper and lower surfaces of the absorbent structure²) A polyethylene sheet used in a commercially available disposable diaper was placed on the back surface of the diaper, and a nonwoven fabric (20.0 g/m in basis weight) was formed²) And then disposed on the surface to produce a disposable diaper. The evaluation results of the absorption capacity under load, the absorption speed under load, the spreading area under load, the surface dry feeling, the surface dryness value of SDME, and the like of these paper diapers are shown in table 3.

Industrial applicability

The crosslinked polymer of the present invention exhibits the following effects.

The balance of water retention performance and absorption performance under load is excellent, and dry and comfortable hand feeling is displayed after water absorption;

② the crosslinked polymer of the invention has not only excellent absorption properties but also excellent characteristics that it is hardly precipitated even when absorbed liquid is under pressure when used in sanitary goods such as disposable diapers and sanitary napkins.

Examples of the sanitary products include paper diapers (e.g., children's paper diapers and adult paper diapers), sanitary napkins (e.g., sanitary napkins), paper towels, pads (e.g., pads for incontinent persons and surgical pads), and pet diapers (e.g., sheets for absorbing pet urine).

The component (A) of the present invention is useful not only for the above-mentioned sanitary products but also for various applications such as urine gelling agents for portable toilets, fresh fruit preservatives, drip absorbents for meat, fish and shrimp and the like, cold-keeping agents, disposable bosom ovens, gelling agents for batteries, water-retaining agents for plants and soil, anti-dewing agents, waterproofing materials and sealing materials, artificial snow and the like.

TABLE 1

		Examples
							1	2	3	4	5
		Particle size (%)	850 to 710 μm above 850 μm, 710 to 500 μm, 500 to 300 μm, 300 to 150 μm and less than 150 μm	0.00.19.356.622.41.6	0.00.114.956.626.61.8	0.00.119.357.522.01.1						0.00.118.155.322.42.1	0.00.115.256.426.51.8
Average particle diameter (μm)							363	365	362	354	364
		Gel elasticity value (N/m)2)		13,000	14,000	12,000						13,000	13,000
Moisture absorption blocking ratio (%)							18	19	19	20	19
		Water retention (g/g)		36	36	35						35	36
Condition (1)							Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of
		60g/cm2Absorbency under load (g/g)		26	27	25						26	26
Condition 2							Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of
		Condition (c)		Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of						Satisfy the requirement of	Satisfy the requirement of

TABLE 2

		Examples	Reference to		Comparative example
							6	1	2	1	2
		Particle size (%)	850 to 710 μm above 850 μm, 710 to 500 μm, 500 to 300 μm, 300 to 150 μm and less than 150 μm	0.00.114.856.726.51.9	0.00.118.155.322.42.1	0.60.14.883.710.60.3						0.00.116.157.524.32.1	0.00.120.259.619.11.0
Average particle diameter (μm)							363	354	363	350	366
		Gel elasticity value (N/m)2)		13,000	11,000	10,000						10,000	9,000
Moisture absorption blocking ratio (%)							19	20	19	61	62
		Water retention (g/g)		35	35	36						35	35
Condition (1)							Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of
		60g/cm2Absorbency under load (g/g)		25	23	22						21	20
Condition 2							Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of
		Condition (c)		Satisfy the requirement of	Satisfy the requirement of	Satisfy the requirement of						Not meet the requirements of	Not meet the requirements of

TABLE 3

		Absorbent structure for use in paper diaper	Properties of paper diaper
								Absorbency under load (g/sheet)	Absorption Rate under load (seconds)	Diffusion area under load (cm)2)	Feeling of surface dryness	SDME surface dryness (%)
			Examples	9	B1	287	355						444	○	75
10	B2	266						362	437	○	65
				11	B3	272	341					450	○	70
12	B4	259						353	458	○	62
				13	B5	263	341					440	○	68
14	B6	277						344	445	○	71
				15	B7	251	365					440	○	60
16	B8	247						380	441	○	57
				17	C2	303	321					427	○	80
Comparative example	3	B1’						225	397	382	△				43
			4	B2’	218	411	390					△	36

Claims (27)

1. A crosslinked polymer (A) characterized in that: the water-soluble vinyl monomer comprises one or more vinyl monomers (a) selected from water-soluble vinyl monomers and/or water-soluble monomers obtained by hydrolysis and a crosslinking agent (b) as essential components, and has the following conditions:

①(X)≥33g/g

②(Y)≥25g/g

③(Y)≥-0.54(X)+42

wherein (X) is the water retention after 1 hour of absorption of physiological saline; (Y) is at 60g/cm²Under the load of (1), to the physiologyThe amount of saline absorbed 1 hour later.

2. The crosslinked polymer of claim 1, wherein: the crosslinked polymer (A) having absorbed therein a physiological saline solution is swollen by a gel of 40 times and has a gel elasticity value of 3,000N/m²Or more.

3. The crosslinked polymer of claim 1, wherein: wherein the vinyl monomer (a) is a water-soluble vinyl monomer (a1) having at least one hydrophilic group selected from the group consisting of carboxylic acid and/or carboxylic acid salt groups, sulfonic acid and/or sulfonic acid salt groups, sulfuric acid and/or sulfuric acid salt groups, phosphoric acid and/or phosphoric acid salt groups, hydroxyl groups, amine groups, amino groups, and quaternary ammonium salt groups, and/or a vinyl monomer (a2) having at least one hydrolyzable group selected from the group consisting of acid anhydride groups, lower alkyl ester groups having 1 to 3 carbon atoms, and nitrile groups, which is hydrolyzed to become water-soluble.

4. The crosslinked polymer of claim 1, wherein: the crosslinked polymer (A) is obtained by polymerizing the vinyl monomer (a) and the first crosslinking agent (b1), or the vinyl monomer (a) and other one or more other vinyl monomers (A3) selected from the group consisting of aromatic vinyl monomers having 8 to 30 carbon atoms, aliphatic vinyl monomers having 2 to 20 carbon atoms, alicyclic vinyl monomers having 5 to 15 carbon atoms, alkyl (meth) acrylates having alkyl groups having 4 to 50 carbon atoms, and the first crosslinking agent (b1) in the presence of water and one or more initiators (c) selected from the group consisting of azo initiators, peroxide initiators, redox initiators, and organic halide initiators, to obtain a crosslinked polymer (A2), and surface-crosslinking the crosslinked polymer (A2) with the second crosslinking agent (b2), thereby obtaining the crosslinked polymer (A).

5. The crosslinked polymer of claim 4, wherein: wherein the amount of the first crosslinking agent (b1) is 0.001 to 5.0% by weight based on the weight of the ethylene monomer (a) or the total weight of the ethylene monomer (a) and the ethylene monomer (a 3).

6. The crosslinked polymer of claim 4, wherein: wherein the amount of the second crosslinking agent (b2) is 0.001 to 7.0% by weight based on the weight of the ethylene monomer (a) or the total weight of the ethylene monomer (a) and the ethylene monomer (a 3).

7. The crosslinked polymer of claim 1, wherein: wherein the crosslinked polymer (A) is obtained by polymerizing a polymerization solution having a total weight and concentration of the vinyl monomer (a) and the crosslinking agent (b) of 20% or less by weight.

8. The crosslinked polymer of claim 1, wherein: wherein the crosslinked polymer (A) is obtained by polymerizing at a polymerization temperature of 60 ℃ or less and within a temperature control range of. + -. 5 ℃.

9. The crosslinked polymer of claim 1 or 4, wherein: wherein the crosslinked polymer (A) is obtained by polymerizing in the presence of a complex compound (d) formed from a metal element (d1) and an anionic or neutral molecular ligand (d 2).

10. The crosslinked polymer of claim 9, wherein: wherein the metal element (d1) is selected from long periodic table of group IB and periodic table of group VIII.

11. The crosslinked polymer of claim 9, wherein: wherein the complex compound (d) is present in an amount of 0.005ppm to 2% by weight and the metal element (d1) is present in an amount of 0.001ppm to 1% by weight, based on the total weight of the vinyl monomer (a) and the crosslinking agent (b) or the total weight of the vinyl monomer (a), the vinyl monomer (a3) and the crosslinking agent (b).

12. The crosslinked polymer of claim 9, wherein: wherein the anionic or neutral molecular ligand (d2) is one or more selected from the following (1) to (3):

(1) an anion selected from hydrogen, halogen atoms;

(2) a compound having one or more atoms selected from nitrogen, oxygen, phosphorus, and sulfur;

(3) a conjugated compound.

13. The crosslinked polymer of claim 9, wherein: wherein said metallic element (d1) is an element selected from group VIII of period 5 and said anionic or neutral molecular ligand (d2) is a halide ion and/or a tertiary phosphine compound.

14. The crosslinked polymer of claim 1, wherein: wherein the crosslinked polymer (A) has a water content of 2 to 10% by weight, a dust generation degree of 0 to 50cpm, an average particle diameter of 200 to 500 μm, and a blocking rate of 0 to 50% after standing for 3 hours at 40 ℃ and 80% relative humidity

15. The crosslinked polymer of claim 1, wherein: wherein the crosslinked polymer (A) contains one or more additives (e) selected from surfactants, preservatives, mildewcides, antibacterial agents, antioxidants, ultraviolet absorbers, pigments, dyes, fragrances, deodorizers, inorganic powders and organic fibrous materials.

16. A process for producing a crosslinked polymer (A) according to claim 4, which comprises: wherein the crosslinked polymer (a) is obtained by polymerizing one or more vinyl monomers (a) selected from water-soluble vinyl monomers and/or vinyl monomers (a) which are water-soluble by hydrolysis, optionally adding another vinyl monomer (A3), and the first crosslinking agent (b1) in the presence of one or more initiators (c) selected from azo initiators, peroxide initiators, redox initiators, and organic halide initiators, and water, and the second crosslinking agent (b2) is surface-crosslinked with the second crosslinking agent (b 539b 2).

17. The method for producing a crosslinked polymer according to claim 16, wherein: wherein the polymerization is carried out in the presence of the complex compound (d) formed by the metal element (d1) and the anionic or neutral molecular ligand (d 2).

18. The method for producing a crosslinked polymer according to claim 17, wherein: wherein the metal element (d1) is a metal element selected from group IB and group 4-6 period VIII of the periodic Table of the elements.

19. The method for producing a crosslinked polymer according to claim 17, wherein: wherein the anionic or neutral molecular ligand (d2) is one or more selected from the following (1) to (3):

(1) an anion selected from hydrogen, halogen atoms;

(2) a compound having one or more atoms selected from nitrogen, oxygen, phosphorus, and sulfur;

(3) a conjugated compound.

20. The method for producing a crosslinked polymer according to claim 17, wherein: wherein said metallic element (d1) is an element selected from group VIII of period 5 and said anionic or neutral molecular ligand (d2) is a halide ion and/or a tertiary phosphine compound.

21. The method for producing a crosslinked polymer according to claim 17, wherein: wherein the amount of the first crosslinking agent (b1) is 0.001 to 5.0% by weight based on the weight of the ethylene monomer (a) or the total weight of the ethylene monomer (a) and the ethylene monomer (a 3).

22. The method for producing a crosslinked polymer according to claim 17, wherein: wherein the amount of the second crosslinking agent (b2) is 0.001 to 7.0% by weight based on the weight of the ethylene monomer (a) or the total weight of the ethylene monomer (a) and the ethylene monomer (a 3).

23. The method for producing a crosslinked polymer according to claim 17, wherein: wherein the amount of the initiator (c) is 0.005 to 0.5% by weight based on the total weight of the vinyl monomer (a) and the crosslinking agent (b) or the total weight of the vinyl monomer (a), the vinyl monomer (a3) and the crosslinking agent (b).

24. An absorbent structure (C) comprising the crosslinked polymer (A) according to claim 1 and a fibrous material (B) as a base material, characterized in that: the amount of the crosslinked polymer (A) is 30 to 95% by weight of the absorbent structure (C).

25. An absorbent article comprising the absorbent structure (C) according to claim 24, a liquid-permeable sheet and a breathable backsheet.

26. The absorbent article of claim 25, wherein: comprises a paper diaper, a sanitary towel, a cushion, a paper towel and a pet sheet.

27. The paper diaper of claim 26 wherein the surface dryness value is 50% or greater as measured by the SDME method.