JP2001200006A - Preparation method of water absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water absorbing resin as particles, which has a great water retention amount, a little content of a water-soluble component, and a relationship between the water retention amount and water absorption amount under a load, and particularly, has a balance at a high level of the water absorption amount under the heavy load. SOLUTION: In a preparation method of the water absorbing resin comprising radical-polymerizing at least one radical polymerizable monomer which is a water-soluble and/or becomes water-soluble by a hydrolysis and a crosslinking agent in the presence of water, the method is characterised by polymerizing the reactants together with at least one compound (C) selected among a benzotriazole series compound, a benzophenone series compound, a triazine series compound, a hindered amine series compound, and a hindered phenol series compound. Further, according to a surface crosslinking of the resulting water absorption resin as the partilces, the absorption performance under the load is improved while holding high water retention amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water-absorbent resin having excellent absorption performance and a water-absorbent resin. More specifically, the present invention relates to a surface-crosslinked water-absorbing resin having excellent water retention performance, a small amount of water-soluble components, and excellent absorption performance under load, and a method for producing the same.

[0002]

The water-absorbing resin used in absorbent articles such as disposable diapers has a large water retention capacity and an absorption capacity under a load such as a state in which the weight of the wearer is added. It is demanded that the water retention and the water retention are balanced and at a high level. As a way to increase water retention,
Although it is a common practice to reduce the amount of the cross-linking agent (b) to be used, a chain transfer agent such as a thiol compound may be used for aqueous polymerization of a monomer aqueous solution containing a radical polymerizable monomer and a cross-linking agent. (JP-A-3-179008) has been proposed. On the other hand, as a method for improving the absorption performance under load, many so-called surface cross-linking methods of further cross-linking the vicinity of the surface of the water-absorbent resin particles with a cross-linking agent have been proposed (for example, Patent Nos. 2675729 and EPA618005). .

[0003]

However, although the conventional method using a chain transfer agent has a certain effect on the improvement of water retention, it has a drawback that the amount of water-soluble components as low molecular weight components increases. was there. Further, when the water-absorbent resin particles obtained by the method using the conventional chain transfer agent are further surface-crosslinked, they can be applied under a relatively low load (for example, 2
With respect to the absorption performance at a load of 0 g / cm 2, a certain improvement in performance is recognized, but under a high load (for example, 60 g / cm 2).
g / cm <2> load) is insufficient, and the amount of water-soluble components cannot be reduced. When the amount of the water-soluble component is large, the dry feeling of the water-absorbing gel required for an absorbent article such as a disposable diaper decreases, and the water-absorbing gels are apt to cause gel blocking, which is not preferable. On the other hand, in the method of surface-crosslinking a normal water-absorbent resin without using a chain transfer agent, there is a problem that although the absorption performance under load is improved, the water retention is greatly reduced by the surface crosslinking. In the past, since paper diapers for infants were the main use of water-absorbent resin, water-absorbent resins as described above could be used, but as the application of water-absorbent resins to adult paper diapers progressed, The emergence of a water-absorbent resin at a high level is desired in which the ability to efficiently retain water in a large amount of urine and the ability to absorb it under a high load, such as when the weight of an adult is added, are balanced. .

[0004]

Means for Solving the Problems The present inventors have excellent water retention performance, have a small amount of water-soluble components, and have a high level of balance between water retention and absorption under load, especially absorption under high load. As a result of intensive studies to obtain a superabsorbent water-absorbent resin, the present invention has been achieved.

That is, the present invention relates to a water-absorbent resin which is obtained by radically polymerizing one or more kinds of radically polymerizable monomers (a) which become water-soluble and / or water-soluble by hydrolysis and a crosslinking agent (b) in the presence of water. In the manufacturing method, benzotriazole-based compound, benzophenone-based compound, benzoate-based compound, triazine-based compound, hindered amine-based compound,
A process for producing a water-absorbent resin (A1), wherein polymerization is carried out in the presence of at least one compound (c) selected from hindered phenolic compounds; and the particulate water-absorbent resin (A1) Is a method for producing a water-absorbent resin (A2) in which the surface is cross-linked with a cross-linking agent (d).

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as the radical polymerizable monomer (a), a water-soluble radical polymerizable monomer (a1) or a radical polymerizable monomer (a2) which becomes water-soluble by hydrolysis is used. it can. Examples of the water-soluble radical polymerizable monomer (a1) include at least one carboxylic acid (salt) group, sulfonic acid (salt) group, phosphoric acid (salt) group, hydroxyl group, amide group, amino group, quaternary ammonium base, and the like. And a radical polymerizable monomer having a hydrophilic group.

Examples of the monomer having a carboxylic acid (salt) group include (meth) acrylic acid, (anhydride) maleic acid, monoalkyl maleate, fumaric acid, monoalkyl fumarate, crotonic acid, itaconic acid,
Carboxyl group-containing vinyl monomers such as itaconic acid monoalkyl ester, itaconic acid glycol monoether, citraconic acid, citraconic acid monoalkyl ester, and cinnamic acid; and alkali metal salts (sodium salt, potassium salt, etc.) and alkaline earth thereof Metal salt (calcium salt, magnesium salt, etc.), amine salt, ammonium salt and the like can be mentioned. Examples of the monomer having a sulfonic acid (salt) group include aliphatic or aromatic vinyl sulfonic acids (salts) [for example, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, (meth) acryl sulfonic acids (sulfopropyl ( Meth) acrylates,
2-hydroxy-3- (meth) acryloxypropylsulfonic acid and the like, and salts thereof (alkali metal salt, ammonium salt, amine salt and the like). Examples of the monomer having a phosphoric acid (salt) group include (meth)
Hydroxyalkyl acrylate monoester [eg, 2-hydroxyethyl (meth) acryloyl phosphate, phenyl-2-acryloyloxyethyl phosphate, etc.], alkyl phosphonic acid (meth) acrylate [eg, 2-acryloyloxyethyl phosphonic acid] (Salt) and the like].

Examples of the monomer having a hydroxyl group include monoethylenically unsaturated alcohols such as (meth) allyl alcohol and the like; and monoethylenically unsaturated alcohols such as alkylene glycol, glycerin and polyoxyalkylene glycol. Ester or ether [e.g., hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, triethylene glycol (meth) acrylate, poly-oxyethylene-oxypropylene (random or block) glycol mono (meth) allyl ether (terminal (Hydroxy groups may be etherified or esterified)
Etc.]. Examples of the monomer having an amide group include (meth) acrylamide, N-alkyl (meth) acrylamide (eg, N-methylacrylamide), N, N′-dialkylacrylamide [eg, N, N′-dimethylacrylamide, N,
N′-di-n- or i-propylacrylamide, etc.), N-hydroxyalkyl (meth) acrylamide [for example, N-methylol (meth) acrylamide, N
-Hydroxyethyl (meth) acrylamide and the like];
N, N′-dihydroxy (meth) acrylamide [eg, N, N′-dihydroxyethyl (meth) acrylamide], vinyllactams [eg, N-vinylpyrrolidone] and the like. Examples of the monomer having an amino group include, for example, an amino group-containing ester of monoethylenically unsaturated mono- or di-carboxylic acid, dialkylaminoalkyl ester, dihydroxyalkylaminoalkyl ester, morpholinoalkyl ester and the like [for example, dimethylaminoethyl ( Meth) acrylate, diethylamino (meth) acrylate, morpholinoethyl (meth) acrylate, dimethylaminoethyl fumarate, etc.], heterocyclic vinyl compound [for example, 2
-Vinylpyridine, 4-vinylpyridine, vinylpyridines such as N-vinylpyridine, N-vinylimidazole, etc.]. Examples of the monomer having a quaternary ammonium group include tertiary amine groups such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylamide, diethylaminoethyl (meth) acrylamide, and diallylamine. And a quaternized vinyl monomer (containing a quaternizing agent using a quaternizing agent such as methyl chloride, dimethyl sulfate, benzyl chloride, and dimethyl carbonate).

The radically polymerizable monomer (a2) which becomes water-soluble by hydrolysis includes a monomer having at least one hydrolyzable group (ester group, nitrile group, amide group, etc.). Examples of the monomer having an ester group include lower alkyl (C1-C3) esters of monoethylenically unsaturated carboxylic acids [eg, methyl (meth) acrylate, ethyl (meth) acrylate,
2-ethylhexyl (meth) acrylate, etc.], and esters of monoethylenically unsaturated alcohol [for example, vinyl acetate, (meth) allyl acetate, etc.]. Examples of the monomer having a nitrile group include (meth) acrylonitrile and the like. Among these, a water-soluble radically polymerizable monomer (a1) is preferred.
More preferred are monomers having a carboxylic acid (salt) group, and particularly preferred are acrylic acid and / or acrylate. These radical polymerizable monomers (a)
May be used alone or, if necessary, in combination of two or more.

In the present invention, the radically polymerizable monomer (a) is radically polymerized in the presence of water. Polymerization concentration,
That is, the concentration of (a) in the polymerization solution is usually 20 to 45% by mass, preferably 25% by mass, based on the total mass of the polymerization solution.
-40 mass%, particularly preferably 25-35 mass%. When the concentration of (a) is less than 20% by mass, it takes a long time to evaporate water after polymerization, that is, to dry, so that productivity is deteriorated. On the other hand, if it exceeds 45% by mass, the molecular weight of the obtained polymer will be low, especially in adiabatic polymerization,
When a side reaction such as self-crosslinking occurs, the resulting water-absorbent resin is undesirably reduced in water retention and increased in water-soluble product.

The radical polymerizable monomer (a1) containing an acid group can be used as a water-soluble salt, and examples of the salt include alkali metal salts (salts such as sodium, potassium and lithium) and alkaline earth metal salts. (Salts such as calcium and magnesium), ammonium salts and amine salts (salts of alkylamines such as methylamine and trimethylamine; salts of alkanolamines such as triethanolamine and diethanolamine) and two or more of these. Preferred among these are the sodium and potassium salts. When an acid type monomer is selected as (a1) and polymerization is performed without neutralization at the monomer stage, the polymerization is neutralized with an alkaline substance (eg, sodium hydroxide, calcium hydroxide, sodium carbonate, etc.). The degree of neutralization is usually 50 to 9 of acid groups in the polymer.
0 mol%, preferably 60 to 80 mol%. When the degree of neutralization is less than 50 mol%, the resulting hydrogel polymer has high tackiness, and it is difficult to produce a water-absorbent resin with good workability. Furthermore, the water retention of the resulting water-absorbent resin is also reduced. On the other hand, when the degree of neutralization exceeds 90%, the pH of the obtained polymer increases, and there is a concern about safety on human skin. Further, partial neutralization (eg, 10 to 30 mol% neutralization) may be performed at the stage of the monomer aqueous solution, and further additional neutralization may be performed in the state of a hydrogel polymer as a polymerization product. Preferably, an acid-type radical polymerizable monomer (for example, acrylic acid) is polymerized from the viewpoint that a water-absorbent resin having a high molecular weight, a small amount of water-soluble components, and a large water retention capacity is obtained. This is a method in which a hydrogel polymer is formed by immersion and then neutralized.

In the present invention, as the crosslinking agent (b),
Compound (b) having two or more radically polymerizable double bonds
1) having at least one functional group reactive with the functional group of the radical polymerizable monomer (a), and
A compound (b2) having two radically polymerizable double bonds,
The compound (b3) having two or more functional groups capable of reacting with the functional group of the radically polymerizable monomer (a) is exemplified. 2
Compound having at least two radical polymerizable double bonds (b
Examples of 1) include bis (meth) acrylamides such as N, N'-methylenebisacrylamide; (poly)
Poly- (meth) acrylates or poly (meth) allyl ethers of polyhydric alcohols such as alkylene glycol, trimethylolpropane, glycerin, pentaerythritol and sorbitol; divinyl compounds such as divinylbenzene; tetraallyloxyethane, pentaerythritol triallyl ether And allyloxyalkanes.

A compound (b) having at least one functional group reactive with the functional group of the radically polymerizable monomer (a) and having at least one radically polymerizable double bond
2) includes a carboxylic acid (salt) group, a hydroxyl group,
Examples thereof include radical polymerizable compounds having a functional group capable of reacting with an amino group and the like. For example, radical polymerizable monomers having a hydroxyl group such as hydroxyethyl (meth) acrylate and N-methylol (meth) acrylamide, and glycidyl (meth) Examples include radical polymerizable monomers having an epoxy group such as acrylate.

The compound (b3) having two or more functional groups capable of reacting with the functional group of the radical polymerizable monomer (a) includes a functional group capable of reacting with a carboxylic acid (salt) group, a hydroxyl group, an amino group and the like. Glyoxal; polycarboxylic acids such as phthalic acid and adipic acid; polyhydric alcohols such as (poly) alkylene glycol, glycerin and sorbitol; (poly) alkylene polyamines such as ethylenediamine; Examples thereof include polyglycidyl ethers of polyhydric alcohols such as ethylene glycol diglycidyl ether, glycerin triglycidyl ether, and sorbitol polyglycidyl ether. Among these, a compound (b1) having two or more radically polymerizable double bonds is preferable, and N, N′-methylenebisacrylamide, trimethylolpropane triacrylate, pentaerythritol triallyl ether, Tetraallyloxyethane. These crosslinking agents (b) may be used alone or in combination of two or more as necessary.

The amount of the crosslinking agent (b) used is usually from 0.001 to 5 based on the mass of the radical polymerizable monomer (a).
%, Preferably 0.01 to 2% by mass.
When the amount of (b) is less than 0.001%, the obtained resin has a low gel strength at the time of water absorption and becomes a sol, resulting in poor productivity and a large amount of water-soluble components. On the other hand, if it exceeds 5% by mass, on the contrary, the gel strength becomes too large, and the water retention capacity decreases.

In the present invention, a benzotriazole compound, a benzophenone compound, a triazine compound,
It is an essential condition that polymerization is carried out in the presence of at least one compound (c) selected from a hindered amine compound and a hindered phenol compound.

Examples of the benzotriazole compound (c1) include, for example, hydroxyphenylbenzotriazole
[Hydroxyphenylbenzotriazole, 2- (5-
Methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α'dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3,5-di-t-butyl) -2-hydroxyphenyl) benzotriazole, 2- (3-t-butyl-
5-methyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3,5-di-t-butyl-2)
-Hydroxyphenyl) -5-crylibenzotriazole, 2- (3,5-di-t-amyl-2-hydroxyphenyl) benzotriazole, 2- (2'-hydroxy-5'-t-octylphenyl) benzotriazole And condensates (molecular weight 300 or more) of methyl-3- [5-t-butyl-3- (2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate and polyethylene glycol. Examples of the benzophenone-based compound (c2) include 2-hydroxy-4-n-octyloxybenzophenone and the like. Examples of the triazine-based compound (c3) include 2
-(4,6-diphenyl-1,3,5-triazine-2
-Yl) -5-[(hexyl) oxy] -phenol,
2,4,6-Triphenoxy-sym-triazine and the like.

Examples of the hindered amine compound (c4) include, for example, a polycondensate of dimethyl-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine (molecular weight: 1000) And poly [{6- (1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl}.
｛(2,2,6,6-tetramethyl-4-piperidyl)
Imino {hexamethylene} (2,2,6,6-tetramethyl-4-piperidyl) imino}] (molecular weight 1000 or more), N, N′-bis (3-aminopropyl) ethylenediamine-2,4-bis [ N-butyl-N- (1,2,
2,6,6-pentamethyl-4-piperidyl) amino]
-6-chloro-1,3,5-triazine condensate (molecular weight 1000 or more), bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,
6,6-pentamethyl-4-piperidinyl) sebacate, bis (1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, 2- (3,5-
Di-tert-butyl-4-hydroxybenzyl) -2-n-
Bis (1,2,2,6,6-pentamethyl-4-piperidyl) butylmalonate and the like.

As the hindered phenol compound (c5), for example, triethylene glycol-bis [3-
(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythr Lityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3-
(3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N′-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamide), 1, 3,5-trimethyl-2,4,6-
Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, 2,4-di-t-butylphenyl-
3,5-Di-t-butyl-4-hydroxybenzoate, calcium bis (3,5-di-t-butyl-4-hydroxybenzylphosphonate) calcium and the like.
Among these, preferred are a benzotriazole compound (c1), a hindered amine compound (c4) and a hindered phenol compound (c6), and particularly preferred are a benzotriazole compound (c1).
It is.

The amount of the compound (c) used is usually from 0.001 to 1 based on the mass of the radically polymerizable monomer (a).
%, Preferably 0.002 to 0.5%. If the amount used is less than 0.001%, the effect of using (c), that is, the effect of improving the water retention amount of the water absorbent resin (A1) will be insufficient. On the other hand, if it exceeds 1%, the polymerization rate of the radically polymerizable monomer (a) may not be sufficiently increased, or the polymerization rate may be reduced, and it is necessary to lengthen the polymerization time or the aging time. It is not preferable because the property deteriorates. When the solubility of the compound (c) in the aqueous polymerization liquid is low, the polymerization can be carried out by dissolving or dispersing the compound (c) in the aqueous polymerization liquid together with a surfactant or the like.

In the present invention, polymerization can be carried out in the presence of a graft substrate. As this graft substrate,
Examples include conventionally known natural polysaccharides such as starch and cellulose or modified products thereof, polyalkylene oxide, polyvinyl alcohol, and water-soluble polyester resins.
The weight average molecular weight of the graft substrate is usually 5,000 or more, preferably 10,000 or more. Molecular weight 500
If it is less than 0, the effect of increasing the molecular weight by grafting, that is, the effect of increasing the water retention by increasing the molecular weight, is small. The amount of the graft substrate to be used is generally 0 to 20% by mass, preferably 0.5 to 10% by mass, especially 1 to 5% by mass based on the mass of the radically polymerizable monomer (a). When the use amount of the graft substrate exceeds 20% by mass, the water-absorbing resin obtained has a low water retention. The graft substrate is usually used by dissolving or dispersing it in an aqueous polymerization solution containing the radically polymerizable monomer (a). Preferably, it is dissolved in an aqueous polymerization solution.

The polymerization method in the present invention may be any of the conventionally known methods carried out in the presence of water, for example, an aqueous solution polymerization method using a radical polymerization initiator, a suspension polymerization method,
A reverse phase suspension polymerization method and the like can be mentioned. In addition, a method of polymerizing with a photoinitiator, or a method of irradiating radiation, an electron beam, ultraviolet light, or the like to start polymerization may be used. Among these, the aqueous solution polymerization method is preferred because it is not necessary to use an organic solvent or the like and is advantageous in terms of production cost. In particular, a large amount of water retention, and a water-absorbent resin having a small amount of water-soluble components can be obtained, and temperature control during polymerization is unnecessary,
Aqueous adiabatic polymerization is preferred.

As the polymerization initiator used in the polymerization using the radical polymerization initiator, conventionally known initiators can be used. For example, azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid, 2,2'-azobis (2-amidinopropane) hydrochloride, etc.], inorganic peroxides [hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.], organic peroxides [benzoyl peroxide, t- Butyl hydroperoxide, di-t-butyl peroxide, cumene hydroperoxide, succinic peroxide, di (2-ethoxyethyl) peroxydicarbonate, etc.] and a redox catalyst [alkali metal sulfite or bisulfite,
Composed of a combination of a reducing agent such as ammonium sulfite, ammonium bisulfite, or ascorbic acid and an oxidizing agent such as an alkali metal persulfate, ammonium persulfate, hydrogen peroxide, or an organic peroxide]. These polymerization initiators may be used alone, or two or more of these may be used in combination. Preferred combinations of the polymerization initiator include a redox catalyst and an azo compound, a redox catalyst and an organic peroxide, and a combination of the redox catalyst and an azo catalyst having a 10-hour half-life temperature different from each other.

The amount of the radical polymerization initiator used is usually 0.0005 to 5%, preferably 0.001 to 2%, based on the mass of the radical polymerizable monomer (a). The other polymerization conditions are not particularly limited. For example, the polymerization initiation temperature can be variously changed depending on the type of the polymerization initiator used, but is usually -5 ° C to 90 ° C, preferably 2 ° C to 70 ° C. .

The polymerization is carried out in the presence of water, but may be carried out in the presence of water and an organic solvent if necessary. Examples of the solvent include methanol, ethanol, acetone, methyl ethyl ketone, N, N-dimethylformamide, dimethyl sulfoxide, and a mixture of two or more thereof. It is 40% or less, preferably 30% or less. When a suspension polymerization method or a reversed-phase suspension polymerization method is used as the polymerization method, the polymerization is carried out, if necessary, in the presence of a conventionally known dispersant, protective colloid or surfactant. In the case of the reverse phase suspension polymerization method, polymerization is carried out using a conventionally known solvent such as cyclohexane, normal hexane, normal heptane and xylene.

In the present invention, if necessary, a compound (eg, ethylene glycol diglycidyl ether) having at least two groups capable of reacting the obtained neutralized crosslinked polymer with a carboxylic acid (salt) group in a hydrogel state And other polyglycidyl compounds such as ethylene glycol, diethylene glycol, glycerin, etc., (poly) alkylene polyamines such as ethylene diamine, and polyvalent metal compounds capable of forming ionic crosslinks) for further crosslinking. Can also. By this relatively uniform crosslinking, a water-absorbent resin having high gel strength and a small amount of water-soluble components can be produced.

In the present invention, the obtained hydrogel polymer is heated, dried and pulverized, and then, if necessary, the particle size is adjusted to obtain a particulate water-absorbent resin (A1). How to dry
A method of drying with hot air at a temperature of 80 to 230 ° C.,
Conventional methods such as a thin film drying method using a drum dryer heated to 230 ° C., a (heating) reduced pressure drying method, a freeze drying method, and a drying method using infrared rays may be used.

There is no particular limitation on the pulverizing method, and a usual apparatus such as a hammer type pulverizer, an impact type pulverizer, a roll type pulverizer and a shet air flow type pulverizer can be used. The obtained pulverized product is sieved as necessary to adjust the particle size. The average particle size of the obtained water-absorbent resin (A1) is usually 100 to 700.
μm, preferably 200 to 600 μm;
A powder crushed so that particles having a size of 850 μm are 95% by mass or more can be used. The content of the fine particles is preferably as small as possible, and the content of particles having a particle size of 100 μm or less is usually 3% or less, and the content of particles having a particle size of 150 μm or less is preferably 3% or less. The shape of the water-absorbent resin (A1) is not particularly limited, and examples thereof include irregularly crushed, scaly, pearl, rice, and granulated shapes. An amorphous crushed shape is preferred in that it is well entangled with fibrous materials for use in disposable diapers and there is no fear of falling off from the fibrous materials.

The water-absorbent resin (A1) obtained by the method of the present invention has a water retention of 40 g / g or more in physiological saline and a water-soluble component content of 10% or less after extraction with physiological saline for 3 hours. Preferably, the amount of water retained in physiological saline is 45 g / g or more, and the amount of water-soluble components after extraction with physiological saline for 3 hours is 8% or less. In addition, the amount of water retention and the amount of water-soluble components are measured by the methods described below.

In the present invention, the resulting water-absorbent resin (A
The effect of the present invention can be further improved by cross-linking the surface of 1). As a method for surface-crosslinking the water-absorbent resin (A1), a conventionally known method, for example, a mixed solution of a crosslinking agent (d), water and an organic solvent is mixed with (A1),
A method of causing a heat reaction is exemplified. As the cross-linking agent (d), a known cross-linking agent which has been conventionally used can be applied. As a specific example, two epoxy groups are contained in one molecule.
Polyglycidyl ether compound having 10 [ethylene glycol diglycidyl ether, glycerin-1,3
-Diglycidyl ether, glycerin triglycidyl ether, polyethylene glycol (degree of polymerization 2 to 100)
Diglycidyl ether, polyglycerol (polymerization degree 2
100) polyglycidyl ether and the like]; divalent to 20-valent polyol compound [glycerin, ethylene glycol,
Polyethylene glycol (degree of polymerization: 2 to 100)];
Polyamine compound having a valence of 20 to 20 (ethylenediamine, diethylenetriamine, etc.); molecular weight of 200 to 500,00
And polyamine epichlorohydrin resin (polyamide epichlorohydrin resin and polyamine epichlorohydrin resin), alkylene carbonate [ethylene carbonate and the like], aziridine compound, polyimine compound and the like. Among these, polyglycidyl ether compounds, polyamine resins and aziridine compounds are preferable because they can cause surface crosslinking at a relatively low temperature.

The amount of the cross-linking agent (d) used is usually 0.005 to 5% based on the weight of (A1), preferably
It is 0.01 to 2%, particularly preferably 0.05 to 1%. When the amount of the crosslinking agent (d) used is less than 0.005% by mass, the degree of surface crosslinking is insufficient, and the effect of improving the absorption under load is insufficient. On the other hand, when the use amount of (d) exceeds 5% by mass, the degree of cross-linking of the surface becomes excessive, and the water retention amount decreases. The amount of water used at the time of surface crosslinking is usually 1 to 10%, preferably 2 to 7%, based on the mass of the water-absorbent resin (A1). When the amount of water used is less than 1%, the penetration of the crosslinking agent (d) into the inside of the particles of (A1) becomes insufficient, and the amount of absorption under a load, particularly under a high load (for example, 60 g / cm 2). The effect of increasing the amount becomes poor. On the other hand, if water usage exceeds 10%,
The penetration of the crosslinking agent (d) into (A1) becomes excessive, and although the amount of absorption under load is improved, there is a problem that the water retention is reduced. In the present invention, as the type of the organic solvent used in combination with water, a conventionally known solvent can be used, and the degree of penetration of the crosslinking agent (d) into (A1) and the reaction of the crosslinking agent (d) It can be appropriately selected in consideration of properties and the like. Preferred are water-soluble hydrophilic organic solvents such as methanol and diethylene glycol. Such solvents may be used alone or in combination of two or more. The amount of the solvent used can be variously changed depending on the type of the solvent, but is usually 1 to 10% based on the mass of the water-absorbent resin (A1).
The ratio of the solvent to water can be arbitrarily changed, and is usually 20 to 80%, preferably 30 to 70% on a mass basis.

A mixed solution of a crosslinking agent (d), water and a solvent is added to (A1) by a conventionally known method and mixed, followed by a heating reaction. The reaction temperature is usually 80 to 200 ° C, preferably,
100-160 ° C. The reaction time can be changed depending on the reaction temperature, but is usually 3 to 60 minutes, preferably 5 to 40 minutes. The particulate water-absorbent resin (A2) obtained by surface cross-linking in this manner can be further subjected to additional surface cross-linking with the same type of cross-linking agent or a cross-linking agent different from that used in (A2). . The particulate water-absorbent resin (A2) obtained by surface cross-linking in this manner is sieved, if necessary, to adjust the particle size. The average particle size of the obtained (A2) is usually 100 to 800 μm, preferably 200 to 600 μm.
95% by mass of particles in the range of 100 to 850 μm.
A material pulverized so as to be as described above 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 usually 3% or less, preferably 150 μm or less.
The content of particles of m or less is 3% or less.

The surface-crosslinked particulate water-absorbent resin (A2) of the present invention satisfies the following requirements. Absorption amount for physiological saline under a load of 30 g / g or more under a load of 20 g / cm2 is at least 25 g / g. Absorption amount of physiological saline under a load of 40 g / cm2 is at least 20 g / g, 60 g / cm2. Absorption amount to physiological saline under load is 15 g / g or more, and water-soluble component amount after extraction with physiological saline for 3 hours is 1
0% or less. Preferably, it is a water-absorbing agent which satisfies the following requirements of physiological saline. 'Water holding capacity for physiological saline is 35 g / g or more.' Absorption under 20 g / cm 2 load is 30 g / g or more. 'Absorption under 40 g / cm 2 load is 25 g / g or more.' Absorption under 60 g / cm 2 load. The amount is 20 g / g or more, and the amount of water-soluble components after extraction with physiological saline for 3 hours is 8% or less. In addition, the amount of water retention, the amount of absorption under load, and the amount of water-soluble components are measured by the methods described below. The coexistence of the compound (c) during the polymerization enhances the absorption performance and reduces the amount of the water-soluble component. The reason why the compound (c) stabilizes the growing radical during the polymerization and stops the termination reaction It is presumed that a high molecular weight polymer can be obtained by suppression. Furthermore, it is presumed that it also functions to suppress self-crosslinking based on chain transfer of growing radicals. As a result, it is considered that the absorption performance was improved by increasing the molecular weight and suppressing self-crosslinking, and the amount of the water-soluble component that was a low molecular weight product was reduced.

In the present invention, a preservative, a fungicide, an antibacterial agent, a colorant,
Fragrance, deodorant, residual monomer reducing agent (sodium sulfite,
Cysteine, Michael additive, etc.), moisture absorption blocking agent (silica, silicone oil, etc.), fluidity imparting agent (silica, talc, etc.), pH adjuster (fumaric acid, maleic acid, etc.), inorganic powder, organic fiber The amount is usually 5% or less, preferably 2% or less, based on the mass of the obtained water-absorbent resin (A1) or (A2). If necessary, a treatment for forming a foamed structure may be performed at any stage in the method of the present invention, and granulation or molding may be performed. Due to the above effects, the water-absorbent resin obtained by the method of the present invention includes disposable disposable diapers (such as children's disposable diapers and adult disposable diapers), sanitary napkins, incontinent pads, breast milk pads, surgical underpads, Hygiene and medical supplies such as puerperal mats and dressings for wound protection. Further, it is suitable for various household and industrial absorbent sheets (for example, pet urine absorbent sheet, freshness retaining sheet, drip absorbent sheet, rice seedling raising sheet, concrete curing sheet, water running prevention sheet for cables, etc.). Can be used.

[0035]

The present invention will be further described below with reference to examples, but the present invention is not limited to these examples. Hereinafter, unless otherwise specified,% indicates mass%. In addition, water retention, 20
The amount of absorption and the amount of water-soluble component under a load of g / cm2, 40 g / cm2, and 60 g / cm2 are measured by the following methods. <Water retention> Water-absorbent resin was placed in a tea bag (length 20 cm, width 10 cm) made of a 250 mesh nylon net.
000 g and physiological saline (NaCl concentration 0.90%
Immersed in an ion exchange aqueous solution for 60 minutes, suspended for 15 minutes, drained, placed in a centrifugal dehydrator together with the tea bag, and centrifuged at 250 G for 90 seconds to remove excess water. The increased mass after the centrifugal dehydration was measured and defined as the water retention. <Absorption under load> A plastic cylinder with a 250 mesh nylon mesh attached to the bottom surface (inner diameter 25 mm, height 30 m)
m) into 0.160 g of a water-absorbent resin, and evenly
On this water-absorbent resin is placed a weight of 100 g that moves up and down smoothly in the cylinder with an outer diameter of 25 mm. The load at this time corresponds to about 20 g / cm2. A plastic cylinder containing a water-absorbent resin and a weight is immersed in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline with the nylon mesh side facing down, and allowed to stand. The mass of the water-absorbent resin increased by absorbing the physiological saline was measured after 60 minutes, and the value was measured as 1 g of the water-absorbing agent.
The amount of absorption under a load of 20 g / cm @ 2 was converted to a value per unit. The absorption amounts under a load of 40 g / cm 2 and 60 g / cm 2 were 200 g and 300 g of the same outer diameter, respectively.
Is determined by performing the same measurement using a weight of

<Amount of Water-Soluble Component> In a 300 ml beaker, 1.00 g of the water-absorbent resin is accurately measured, and physiological saline is added to 250 g, followed by stirring for 3 hours to extract a water-soluble component. 20 ml of the filtrate filtered using filter paper is diluted with 30 ml of ion-exchanged water to obtain a measurement solution. The measurement solution is first titrated to pH 10 with a 1 / 50N aqueous KOH solution, and then the pH is adjusted with a 1 / 20N aqueous HCl solution.
Titrate to 2.7. Based on the amounts of the two kinds of titrants required for the titration at this time, the amounts of polyacrylic acid and salts thereof were calculated in consideration of the molecular weight and concentration, and the mass% per 1 g of the water-absorbent resin was determined. The amount of the water-soluble component was used.

Example 1 Water-absorbent resin (A1) 200 g of acrylic acid, methyl-3- [5-t-butyl-
0.1 g of a condensate of 3- (2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate and polyethylene glycol (molecular weight: about 300), and pentaerythritol triallyl ether 0.6 as a crosslinking agent
g and ion-exchanged water (515 g) were mixed to prepare a polymerization aqueous solution, and this solution was placed in a polymerization tank capable of adiabatic polymerization. By introducing nitrogen gas into the solution, the amount of dissolved oxygen in the solution was set to 0.2 ppm, and the solution temperature was set to 5 ° C. To this polymerization solution, 10 g of a 0.1% aqueous hydrogen peroxide solution, 5 g of a 0.1% aqueous ascorbic acid solution, and 10 g of a 1% aqueous solution of V-50 (azo catalyst manufactured by Wako Pure Chemical Industries) were added (concentration of acrylic acid: 2
5%). After about 20 minutes, a temperature rise indicating the start of polymerization was confirmed, and after about 2.5 hours, the temperature reached the maximum, and a hydrogel polymer was obtained. After aging at the same temperature for 5 hours, 160 parts of a 50% aqueous NaOH solution was added while the hydrogel polymer was broken into small pieces using a meat chopper, and about 72 mol% of carboxyl groups in the polymer were added. Was converted to a sodium salt. The neutralized hydrogel polymer was supplied using a ventilated hot air drier (manufactured by Inoue Kinzoku) at a supply air temperature of 150 ° C. and an air velocity of 1.5.
When dried under aeration at 25 m / sec for 25 minutes, a dried product having a water content of 4% was obtained. The dried product is pulverized with a household mixer, sieved, and a 22-mesh wire mesh (opening diameter: 710 μm)
m) and a wire mesh of 119 mesh (opening diameter: 125
μm) to obtain a water-absorbent resin (a). The water-absorbent resin (a) had an average particle size of 380 microns and contained 0.8% of fine particles of 150 microns or less. Table 1 shows the performance evaluation results of the water absorbent resin (a).

Example 2 <Water-absorbent resin (A1)> In Example 1, methyl-3- [5-t-butyl-3
-(2H-Benzotriazol-2-yl) -4-hydroxyphenyl] propionate and polyethylene glycol instead of bis (1,2,2,6,6-
A water-absorbent resin (b) was obtained in the same manner as in Example 1 except that the same amount of (pentamethyl-4-piperidinyl) sebacate was used. Table 1 shows the performance evaluation results of the water absorbent resin (b).

Example 3 <Water-absorbent resin (A1)> In Example 1, methyl-3- [5-t-butyl-3
-(2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate and polyethylene glycol instead of pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-) [Hydroxyphenyl) propionate] was used in the same manner as in Example 1 except that 0.2 g of [hydroxyphenyl) propionate] was used to obtain a water-absorbing resin (C). Table 1 shows the performance evaluation results of the water absorbent resin (c).

Example 4 <Water-absorbing resin (A1)> Acrylic acid (200 g) and water (410 g) were mixed, and the mixture was cooled externally so that the solution temperature did not exceed 35 ° C.
About 72 mol% of acrylic acid was neutralized by gradually adding 160 g of a 50% aqueous NaOH solution. Then, methyl-3-
[5-t-butyl-3- (2H-benzotriazole-
2-yl) -4-hydroxyphenyl] propionate and polyethylene glycol 0.1 g, 10 g of ethylene glycol diglycidyl ether as a crosslinking agent
% Aqueous solution was added and mixed, and the solution temperature was adjusted to 5 ° C. This solution was charged into a polymerization apparatus capable of adiabatic polymerization, and nitrogen was introduced into the solution to adjust the amount of dissolved oxygen in the polymerization liquid to 0.2 ppm. 10 g of a 0.1% aqueous hydrogen peroxide solution, 5 g of a 0.1% ascorbic acid aqueous solution,
10 g of a 1% V-50 aqueous solution was added. Hereinafter, Example 1
A water-absorbent resin (d) was obtained in the same manner as in Example 1, except that the hydrogel polymer obtained in the above was not neutralized.
Table 1 shows the performance evaluation results of the water absorbent resin (d).

Comparative Example 1 <Comparative Example of Water Absorbent Resin (A1)> In Example 1, methyl-3- [5-t-butyl-3
-(2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate and a polyethylene glycol were not used, and a comparative water-absorbent resin (1) was obtained in the same manner as in Example 1. Table 1 shows the performance evaluation results of the comparative water absorbent resin (1).

Comparative Example 2 <Comparative Example of Water Absorbent Resin (A1)> In Example 1, methyl-3- [5-t-butyl-3
-(2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate and polyethylene glycol instead of the condensate were used except that 0.02 g of sodium hypophosphite monohydrate was used as a chain transfer agent. A comparative water absorbent resin (2) was obtained in the same manner as in Example 1. Table 1 shows the performance evaluation results of the comparative water absorbent resin (2).

Comparative Example 3 <Comparative Example of Water Absorbent Resin (A1)> In Example 4, methyl-3- [5-t-butyl-3
-(2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate and a comparative water-absorbent resin (3) were obtained in the same manner as in Example 4 except that a condensate of polyethylene glycol was not used. Table 1 shows the performance evaluation results of the comparative water absorbent resin (3).

Example 5 <Water-absorbent resin (A2)> A solution consisting of 0.2 g of ethylene glycol diglycidyl ether, 3 g of water and 7 g of methanol was sprayed and mixed while stirring 100 g of the water-absorbent resin (a). , 140
A heating reaction was performed at 40 ° C. for 40 minutes to obtain a water-absorbing resin (e).
Table 2 shows the performance evaluation results of the obtained water-absorbent resin (e).

Examples 6 to 8 <Water-absorbent resin (A2)> The procedure of Example 5 was repeated except that the water-absorbent resins (b) to (d) were used in place of the water-absorbent resin (a). Similarly, water-absorbing resins (f) to (h) were obtained. Table 2 shows the performance evaluation results of the obtained water absorbent resins (f) to (h).

Comparative Examples 4 to 6 <Comparative Examples of Water Absorbent Resin (A2)> In Example 5, except that the comparative water absorbent resins (1) to (3) were used in place of the water absorbent resin (A). In the same manner as in Example 5, comparative water absorbent resins (4) to (6) were obtained. Table 2 shows the performance evaluation results of the obtained comparative water absorbent resins (4) to (6).

[0047]

[Table 1]

[0048]

[Table 2] * Absorption under load 20: Absorption under load of 20 g / cm2 Absorption under load 40: Absorption under load of 40 g / cm2 Absorption under load 60: Absorption under load of 60 g / cm2

[0049]

Industrial Applicability In a process for producing a water-absorbing resin in which a radical polymerizable monomer (a) and a crosslinking agent (b) are radically polymerized in the presence of water, a benzotriazole compound, a benzophenone compound, a benzoate compound, a triazine compound are used. By polymerizing at least one compound selected from the group consisting of a hindered amine compound and a hindered phenol compound, a water-absorbent resin (A1) having a large water retention and a small amount of a water-soluble component can be obtained. . Furthermore, a water-absorbing resin having such characteristics can be manufactured with high productivity. In addition, the water-absorbing resin (A
The particulate water-absorbent resin (A2) obtained by surface-crosslinking the particles of 1) maintains a high water retention and exhibits high absorption performance even under a load. Has a good balance. Especially 60g / cm2
The feature is that it has excellent absorption performance under high load. Further, the generation of a water-soluble component which is a low molecular polymer is small.

Claims (7)

[Claims] 1. A method for producing a water-absorbent resin in which one or more radically polymerizable monomers (a) which become water-soluble and / or water-soluble by hydrolysis and a crosslinking agent (b) are radically polymerized in the presence of water. A water-absorbent resin (A1) characterized in that polymerization is carried out in the presence of at least one compound (c) selected from a benzotriazole compound, a benzophenone compound, a triazine compound, a hindered amine compound, and a hindered phenol compound. ) Manufacturing method. 2. The method according to claim 1, wherein the amount of (c) is 0.001 to 1% by mass based on the amount of (a). 3. The method according to claim 1, wherein the main component of the radically polymerizable monomer (a) is acrylic acid and / or acrylate. 4. The obtained water-absorbent resin (A1) has a water retention capacity in physiological saline of 40 g / g or more, and an amount of water-soluble components after extraction with physiological saline for 3 hours is 10% or less on a mass basis. The production method according to any one of claims 1 to 3. 5. A process for producing a water-absorbent resin (A2), wherein the particulate water-absorbent resin (A1) obtained by the process according to claim 1 is surface-crosslinked with a crosslinking agent (d). 6. The method according to claim 5, wherein the crosslinking agent (d) is a polyglycidyl compound. 7. A particulate water-absorbing resin obtained by the production method according to claim 5 and satisfying the following requirements. The water retention capacity for physiological saline is 30 g / g or more, the absorption capacity for physiological saline under a load of 20 g / cm 2 is 25 g / g or more, and the absorption capacity for physiological saline under a load of 40 g / cm 2 is 20 g / g or more, 60 g / g Absorbed amount to physiological saline under a load of 15 cm / g or more under a load of 2 cm2, water-soluble component amount after extraction with physiological saline for 3 hours was 1
0% or less.