JPH11315148A - Production of water absorbing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an absorbent having excellent urine resistance free from deterioration with time in absorbing urine, by mixing a specific water absorbing resin with a prescribed surface crosslinking agent and an ion sequestering agent. SOLUTION: (A) A carboxyl group-containing water absorbing resin (e.g. a crosslinked body of a polyacrylic acid part-neutralized substance) being a resin to form a hydrogel by absorbing a large amount of water in water in an amount of 100 pts.wt. (solid content) is mixed with (B) 0.01-10 pts.wt., preferably 0.05-5 pts.wt. of a surface crosslinking agent (e.g. ethylene glycol diglycidyl ether) capable of being reacted with the carboxyl group of the component A, (C) an ion sequestering agent (e.g. diethylenetriaminopentaacetate) being an amino carboxylic acid (salt) preferably containing >=3 carboxyl groups and optionally (D) 0.01-10 pts.wt., preferably 0.5-3 pts.wt. of water to give the objective absorbent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a water absorbing agent. More specifically, the present invention relates to a method for producing a water-absorbing agent that causes less deterioration during urine absorption.

[0002]

2. Description of the Related Art In recent years, sanitary materials such as disposable diapers, sanitary napkins, so-called incontinence pads, and the like, have been designed to absorb bodily fluids such as urine and menstrual blood.
Water-absorbing resins (water-absorbing agents) are widely used. Examples of such a water-absorbent resin include, for example, a hydrolyzate of a starch-acrylonitrile graft polymer (JP-B-49-4).
No. 3395), neutralized starch-acrylic acid graft polymer (JP-A-51-125468), vinyl acetate-
Saponified acrylate copolymer (Japanese Patent Laid-Open No. 52-1982)
No. 14689), a hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer (JP-B-53-15).
No. 959) or cross-linked products thereof, self-cross-linked sodium polyacrylate obtained by reversed-phase suspension polymerization (JP-A-53-46389), and cross-linked polyacrylic acid partially neutralized product (JP-A-55-549). -84304) and the like.

[0003] Desirable characteristics of such a water-absorbent resin include a high absorption capacity when contacted with an aqueous liquid, an excellent absorption rate, liquid permeability, a gel strength of a swollen gel, and the ability of water to be absorbed from a substrate containing an aqueous liquid. For example, there is a suction force for raising. However, the relationship between these properties does not necessarily indicate a positive correlation, and for example, there is a problem that the higher the absorption capacity, the lower the physical properties such as liquid permeability, gel strength, and absorption rate. .

As a method for improving the water absorbing properties of such a water-absorbent resin in a well-balanced manner, a technique of crosslinking the surface of the water-absorbent resin near its surface is known, and various methods have been proposed so far. For example, a method using a polyhydric alcohol as a crosslinking agent (JP-A-58-180233 and JP-A-61-180233)
-16903), a method using a polyvalent glycidyl compound, a polyvalent aziridine compound, a polyvalent amine compound, and a polyvalent isocyanate compound (JP-A-59-189103), and a method using a polyvalent metal (JP-A-51-136588). Nos. 61-257235 and 62-7745) and a method using a monoepoxy compound (JP-A-61-98121).
), A method using an epoxy compound and a hydroxy compound (Japanese Patent Application Laid-Open No. 2-132103), a method using an alkylene carbonate (DE-4020780), and the like.

[0005] However, although the surface treatment has improved the balance of various properties of water absorption, the use of the water-absorbent resin in the absorbent for the diaper deteriorates the water-absorbent resin with time, and lowers the liquid permeability. There was a problem that gel strength was reduced and urine leaked from the diaper. Deterioration of the water-absorbent resin occurs from the surface of the water-absorbent resin, solubilities are eluted, and liquid permeability and gel strength are reduced. It is considered that such deterioration of the water absorbent resin is caused by a trace amount of metal ions and L-ascorbic acid contained in urine.

[0006]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for producing a water-absorbing agent which exhibits little deterioration over time when urine is absorbed and has excellent urine resistance.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, by mixing a water-absorbing resin having a carboxyl group with a surface crosslinking agent capable of reacting with the carboxyl group, It has been found that the above-mentioned problems can be solved by using a specific additive in the production of, and the present invention has been completed.

That is, the method for producing a water-absorbing agent of the present invention comprises mixing a water-absorbing resin having a carboxyl group with a surface crosslinking agent capable of reacting with the carboxyl group and an ion-blocking agent.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The water-absorbing resin that can be used in the present invention is one that absorbs a large amount of water in water to form a hydrogel, and needs to have a carboxyl group. Examples of such a water-absorbing resin include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylonitrile graft polymer, a hydrolyzate of a starch-acrylic acid graft polymer, and vinyl acetate-acrylate copolymer. Examples thereof include a combined saponified product, a hydrolyzed product of an acrylonitrile copolymer or an acrylamide copolymer, a crosslinked product thereof, a crosslinked polyvinyl alcohol saponified product containing a carboxyl group, and a crosslinked isobutylene-maleic anhydride copolymer.

Such water-absorbing resins are generally unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, β-hydroxyacrylic acid, β-acryloxypropion. It can be obtained by polymerizing a monomer component essentially containing at least one selected from acids and neutralized products thereof. Preferred monomer components are acrylic acid, methacrylic acid and their alkali metal salts such as lithium, sodium and potassium or ammonium salts.

The water-absorbing resin which can be used in the present invention may be polymerized by using another monomer in combination with the above unsaturated carboxylic acid, if necessary. Specifically, anionic compounds such as 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, and styrenesulfonic acid Monomers and their alkali metal salts such as lithium, sodium and potassium, and ammonium salts; (meth) acrylamide, N-substituted (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, Nonionic hydrophilic group-containing monomers such as methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, N-vinylpyrrolidone, and N-vinylacetamide; N, N-dimethylaminoethyl (meth) acrylate; N-dimethyl Minopuropiru (meth) acrylate, N, N-dimethylaminopropyl (meth) and an amino group-containing unsaturated monomers and quaternized products thereof and the like of acrylamide. In addition, in an amount that does not extremely impair the hydrophilicity of the obtained water-absorbent resin, for example, acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, vinyl acetate, and propion A hydrophobic monomer such as vinyl acid may be used.

The amount of carboxyl groups in the water-absorbing resin is not particularly limited, but it is preferable that the carboxyl groups are present in an amount of 0.01 equivalent or more per 100 g of the water-absorbing resin. For example, the ratio of unneutralized polyacrylic acid is 1 to 6
It is preferably in the range of 0 mol%, more preferably in the range of 10 to 50 mol%. In addition, the water-absorbent resin was copolymerized or reacted with a very small amount of an internal cross-linking agent having two or more polymerizable unsaturated groups or two or more reactive groups than a self-cross-linking type resin not using a cross-linking agent. Things are desirable. For example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate , Trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, N, N'-methylenebis (meth) acrylamide, triallyl isocyanurate, cyanuric Triallyl acid, trimethylolpropane di (meth) allyl ether, triallylamine, tetraallyloxyethane, glycerol propoxy Compound having two or more ethylenically unsaturated groups in one molecule, such as a triacrylate, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerine,
Polyglycerin, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl alcohol, diethanolamine, tridiethanolamine, polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbit, sorbitan, Polyhydric alcohols such as glucose, mannitol, mannitan, sucrose, glucose; polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether and glycerin triglycidyl ether; epichlorohydrin, α-methylchlorohydrin Haloepoxy compounds such as glutaraldehyde and glyoxal; polyamines such as ethylenediamine; calcium hydroxide , Calcium chloride, calcium carbonate, calcium oxide, magnesium borax, magnesium oxide, aluminum chloride, zinc chloride, nickel chloride, etc., hydroxides, halides and carbonates of metals of Groups 2A, 3B and 8 of the periodic table , Oxides, borates such as borax, and polyvalent metal compounds such as aluminum isopropylate. One or more of these can be used in consideration of reactivity, but it is most preferable to use a compound having two or more ethylenically unsaturated groups in one molecule as a crosslinking agent. The amount of the crosslinking agent used is 0.005 to 2 mol%, more preferably 0.01 to 1 mol%, based on the monomer component.

In the polymerization, starch, cellulose and derivatives thereof; polyacrylic acid (salt), crosslinked polyacrylic acid (salt), hydrophilic polymers such as polyvinylpyrrolidone and polyvinyl alcohol; hypophosphorous acid (salt) , A chain transfer agent such as a long-chain alkyl mercaptan; a surfactant; a foaming agent such as a carbonate, dry ice, and an azo compound.

When the above monomers are polymerized to obtain the water-absorbent resin of the present invention, bulk polymerization or precipitation polymerization can be performed, but from the viewpoint of performance and ease of polymerization control, simple polymerization is required. It is preferable to carry out aqueous solution polymerization or reverse phase suspension polymerization using the monomer as an aqueous solution. The aqueous solution concentration at that time is usually 1
It is from 0% by weight to a saturated concentration, preferably from 20 to 40% by weight. The hydrogel obtained after the polymerization can be neutralized with an alkali.

The shape of the water-absorbent resin particles obtained by these polymerization methods can be variously used in the present invention, such as irregularly crushed, spherical, fibrous, rod-like, substantially spherical, and scale-like shapes. The water-absorbent resin used in the present invention has a water content (based on wet weight)
However, for example, 1 to 50%, preferably 1 to 20%, more preferably 1 to 10% can be handled as a powder. When the water content exceeds 50%, the surface cross-linking agent penetrates too much into the water absorbent resin, so that not only the absorption capacity is reduced but also the absorption characteristics under pressure may not be improved.

In the present invention, for example, the water-absorbing resin having a carboxyl group obtained as described above is mixed with an ion-sequestering agent and a surface cross-linking agent capable of reacting with the carboxyl group to thereby improve urine resistance. Excellent water-absorbing agent can be obtained. Examples of the ion sequestering agent used in the present invention include the following compounds. (1) aminocarboxylic acid and its salt, (2) citric acid monoalkylamide and citric acid monoalkenylamide and salts thereof, (3) malonic acid monoalkylamide and malonic acid monoalkenylamide and salts thereof, (4 )
Monoalkyl phosphates and monoalkenyl phosphates and salts thereof, (5) N-acylated glutamic acid and N-acylated aspartic acid and salts thereof,
(6) β-diketone derivative, (7) tropolone derivative,
(8) Organic phosphate compounds.

(1) As aminocarboxylic acids and salts thereof, aminocarboxylic acids having three or more carboxyl groups and salts thereof are preferable from the viewpoint of ion-blocking ability. In particular,
Nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol diethyletherdiaminetetraacetic acid, ethylenediaminetetrapropionic acid, N -Alkyl-N'-carboxymethylaspartic acid, N-
Alkenyl N'-carboxymethyl aspartic acid,
And their alkali metal salts, alkaline earth metal salts, ammonium salts or amine salts.

(2) Citric acid monoalkylamide and citric acid monoalkenylamide and salts thereof are obtained, for example, by dehydration condensation of alcohol and citric acid. (3) Malonic acid monoalkylamide, malonic acid monoalkenylamide and salts thereof can be obtained, for example, by adding an α-olefin to methyl malonate and then hydrolyzing it.

(4) Examples of the monoalkyl phosphate, monoalkenyl phosphate and salts thereof include lauryl phosphoric acid and stearyl phosphoric acid. (5) Examples of N-acylated glutamic acid, N-acylated aspartic acid and salts thereof include Amisoft HS-11 and GS-1 which are commercially available from Ajinomoto Co., Inc.
1 and the like.

(6) Examples of the β-diketone derivative include acetylacetone and benzoylacetone. (7) Examples of tropolone derivatives include tropolone, β-thiaprisin, and γ-thiaprisin. (8) Examples of the organic phosphoric acid compound include ethylidenephosphonic acid; 1-hydroxyethylidene-1,1-diphosphonic acid; aminotrimethylenephosphonic acid; ethylenediaminetetra (methylenephosphonic acid); and diethylenetriaminepenta (methylenephosphonic acid). Particularly preferred is 1-hydroxyethylidene-
1,1-diphosphonic acid; ethylenediaminetetra (methylenephosphonic acid); diethylenetriaminepenta (methylenephosphonic acid). Preferred as salts are N
Examples thereof include alkali metal salts such as a salt and K salt, ammonium salt, and amine salt. These compounds are known as a kind of sequestering agent.

Among these ion sequestering agents, preferred are aminocarboxylic acids having three or more carboxyl groups and salts thereof. Among them, diethylenetriaminepentaacetic acid,
Triethylenetetraaminehexaacetic acid, cyclohexane-1,2-diaminotetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid and salts thereof are most preferred in view of urine resistance.

In the present invention, the amount of the ion sequestering agent to be used varies depending on the surface cross-linking agent used for cross-linking near the surface.
The range is from 0001 to 10 parts by weight, preferably from 0.0002 to 5 parts by weight. If the amount used exceeds 10 parts by weight, not only the effect corresponding to the use cannot be obtained, but it becomes uneconomical, but also problems such as a decrease in the absorption amount occur. Also, 0.000
If the amount is less than 1 part by weight, the effect of improving urine resistance cannot be obtained.

Examples of the surface crosslinking agent which can be used in the present invention and which can react with a carboxyl group include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, and dipropylene. Glycol, 2,3,4-trimethyl-1,
3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedi Methanol, 1,2-cyclohexanediol,
Polyhydric alcohol compounds such as trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol, sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl Epoxy compounds such as ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylene Imine, polyamide poly Polyvalent amine compounds such as amine, epichlorohydrin, epibromohydrin, haloepoxy compounds such as α- methyl epichlorohydrin; condensates of the polyvalent amine compound and the haloepoxy compound; 2,4
Polyvalent isocyanate compounds such as tolylene diisocyanate and hexamethylene diisocyanate; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; γ
Silane coupling agents such as glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane; 1,3-dioxolan-2-one, 4-methyl-
1,3-dioxolan-2-one, 4,5-dimethyl-
1,3-dioxolan-2-one, 4,4-dimethyl-
1,3-dioxolan-2-one, 4-ethyl-1,3
-Dioxolan-2-one, 4-hydroxymethyl-
1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, Alkylene carbonate compounds such as 1,3-dioxoban-2-one; zinc, calcium, magnesium,
Hydroxides such as aluminum and polyvalent metal compounds such as chlorides; and the like, but are not particularly limited.

Among the surface cross-linking agents exemplified above, polyhydric alcohol compounds, epoxy compounds, polyamine compounds, condensates of polyamine compounds and haloepoxy compounds, and alkylene carbonate compounds are more preferable. These surface cross-linking agents may be used alone or in combination of two or more. When two or more types of surface cross-linking agents are used in combination, a water-absorbing agent having even more excellent water-absorbing properties is obtained by combining the first surface cross-linking agent and the second surface cross-linking agent having different solubility parameters (SP values). be able to. The above-mentioned solubility parameter is a value generally used as a factor indicating the breadth of a compound.

The first surface cross-linking agent is a compound capable of reacting with a carboxyl group of the water-absorbing resin and having a solubility parameter of 12.5 (cal / cm ³ ) ^1/2 or more.
For example, ethylene glycol, propylene glycol, glycerin, ethylene carbonate, propylene carbonate, etc. are applicable. The second surface cross-linking agent is a compound having a solubility parameter of less than 12.5 (cal / cm ³ ) ^{1/2 which} can react with a carboxyl group of the water-absorbing resin, for example, glycerol polyglycidyl ether,
(Poly) glycerol polyglycidyl ether, ethylene glycol diglycidyl ether, 1,3-butadiol, trimethylolpropane, 1,3-propanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1, 4-butanediol and the like correspond.

The amount of the surface cross-linking agent used with respect to the water-absorbent resin depends on the combination of the water-absorbent resin and the surface cross-linking agent, but is preferably 0.1 to 100 parts by weight of the dry water-absorbent resin.
005 to 10 parts by weight, more preferably 0.05
It may be within the range of 5 to 5 parts by weight. By using the surface cross-linking agent within the above range, the water absorbing properties for body fluids (aqueous liquids) such as urine, sweat, menstrual blood, etc. can be further improved. If the amount of the surface cross-linking agent used is less than 0.005 parts by weight, the cross-linking density in the vicinity of the surface of the water-absorbent resin cannot be increased. If the amount of the surface cross-linking agent is more than 5 parts by weight, the surface cross-linking agent becomes excessive, which is uneconomical and may make it difficult to control the cross-linking density to an appropriate value.

In the present invention, it is preferable to use water when mixing the water absorbing resin with the ion-sequestering agent and the surface cross-linking agent. In the present invention, the amount of water used varies depending on the type, particle size, and water content of the water-absorbent resin, but based on 100 parts by weight of the solid content of the water-absorbent resin, 0.5 to 10 parts by weight, preferably It is in the range of 0.5 to 3 parts by weight. If the amount of water used exceeds 10 parts by weight, the absorption capacity may decrease. If the amount is less than 0.5 part by weight, it becomes difficult to fix the ion-sequestering agent on the surface of the water-absorbing resin, and it may not be possible to improve urine resistance.

The addition of the ion sequestering agent is not limited to the above method. As described above, a specific aminocarboxylic acid can be obtained by mixing a surface cross-linking agent with a water-absorbent resin before surface cross-linking to perform a surface treatment, or adding water to a specific cross-linked water-absorbent resin and granulating the water-absorbent resin. An ion sequestering agent selected from acids can be fixed on the surface of the water-absorbing resin. Since the deterioration of the water-absorbent resin occurs from the resin surface, it is preferable that the ion-sequestering agent is disposed near the surface of the water-absorbent resin. When polymerizing a water-soluble monomer capable of forming a water-absorbing resin, it is also possible to add the ion sequestering agent, but when the polymerization of the monomer in the presence of the ion sequestering agent, the monomer Polymerization may be inhibited, and a water-absorbent resin having excellent absorption performance may not be obtained. Further, the ion sequestering agent may deactivate the ion sequestering ability during the polymerization.

In the present invention, a hydrophilic organic solvent may be used when mixing the water absorbing resin with the ion-sequestering agent and the surface cross-linking agent. Examples of the hydrophilic organic solvent used include lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, and t-butyl alcohol; ketones such as acetone; dioxane, alkoxy (poly) ethylene glycol And ethers such as tetrahydrofuran; amides such as N, N-dimethylformamide; and sulfoxides such as dimethylsulfoxide. The amount of the organic solvent used depends on the type and particle size of the water-absorbing resin,
It is in the range of 0 to 10 parts by weight, preferably 0.1 to 5 parts by weight based on parts by weight.

In the present invention, the water-absorbing resin, the ion-sequestering agent, and the surface cross-linking agent may be mixed in a state where the water-absorbing resin is dispersed in an organic solvent such as cyclohexane or pentane. In order to maximize the effect, the following methods (1) to (4) are preferably exemplified. (1) A method in which an ion-sequestering agent containing water and / or a hydrophilic organic solvent as necessary and a surface cross-linking agent are mixed in advance, and then the mixture is sprayed or dropped on a water-absorbent resin.

(2) A method in which an ion-sequestering agent or an aqueous solution of an ion-sequestering agent is previously mixed with a water-absorbing resin, and then, if necessary, a surface crosslinking agent containing water and / or a hydrophilic organic solvent is sprayed or dropped. (3) After spraying or dripping and mixing a surface cross-linking agent containing water and / or a hydrophilic organic solvent to the water-absorbing resin as necessary,
Then, a method of mixing an ion sequestering agent or an aqueous solution of the ion sequestering agent.

(4) If necessary, a surface cross-linking agent containing water and / or a hydrophilic organic solvent and an additive are added using two nozzles or the like.
A method of simultaneously spraying or dripping and mixing the water absorbent resin. Further, as described above, for mixing the ion-sequestering agent and the surface cross-linking agent into the water-absorbing resin, it is preferable to mix them as a solution using water or a hydrophilic organic solvent. By mixing the ion-sequestering agent and the water-absorbing resin in the presence of water, the ion-sequestering agent can be fixed in the vicinity of the surface of the water-absorbing resin. Elution can be prevented. When water is used for mixing, a water-insoluble fine particle powder and a surfactant may coexist.

The preferred mixing device used for the mixing is
It is necessary to be able to produce large mixing forces to ensure uniform mixing. Examples of the mixing device that can be used in the present invention include, for example, a cylindrical mixer, a double-walled conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluid mixer. Furnace rotary desk mixer, air flow mixer, double arm kneader, internal mixer,
A pulverizing kneader, a rotary mixer, a screw type extruder and the like are suitable.

In the present invention, after the water-absorbing resin is mixed with the ion-sequestering agent and the surface cross-linking agent, preferably, the on-sequestering agent and the surface cross-linking agent are preliminarily mixed, added to the water-absorbing resin, and further heated. Is performed to crosslink the vicinity of the surface of the water absorbent resin. When performing the heat treatment in the present invention, the treatment temperature is preferably in the range of 80 to 250 ° C, and 100 to 230 ° C.
Is more preferred. When the heating temperature is lower than 80 ° C., the heat treatment takes a long time and not only causes a decrease in productivity,
Uniform cross-linking is not achieved, and there is a possibility that a desired water-absorbing agent having high water-absorbing properties under pressure and under control of elution of soluble components may not be obtained.

The heat treatment can be carried out using a usual dryer or a heating furnace, and includes a groove type mixing dryer, a rotary dryer, a desk dryer, a fluidized bed dryer, a flash dryer and an infrared dryer. Is exemplified. By crosslinking the vicinity of the surface of the water-absorbent resin as described above, it is possible to prevent the soluble component from being eluted from inside the water-absorbent resin. However, when absorbing urine or the like containing L-ascorbic acid, the water-absorbent resin is mixed with trace amounts of iron, copper, or other heavy metal ions mixed in the production process or the diaper production process or contained in the urine. Due to the action of L-ascorbic acid, the main chain or the crosslinked structure is cut and deteriorated with time. In particular, the vicinity of the surface of the water-absorbent resin is susceptible to deterioration, and the elution of soluble components cannot be suppressed. For this reason, the water-absorbing resin decreases its absorption ability over time during urine absorption. The present invention, by mixing a surface treatment agent and an ion sequestering agent in the water-absorbing resin, deterioration of the water-absorbing resin,
In particular, it suppresses deterioration near the surface and suppresses elution of soluble components.

After the heat treatment, the heated product is optionally sieved with a sieve to obtain the water absorbing agent of the present invention. The water absorbing agent of the present invention includes not only single particles but also granules thereof. In addition to the above water-absorbing agents, if necessary, deodorants, antibacterial agents, fragrances, various inorganic powders, foaming agents, pigments, dyes, hydrophilic short fibers, plasticizers, adhesives, surfactants, fertilizers , An oxidizing agent, a reducing agent, water, salts and the like may be added to impart various functions to the water absorbing agent.

Examples of the inorganic powder include substances inert to aqueous liquids and the like, for example, fine particles of various inorganic compounds and fine particles of clay minerals. The inorganic powder preferably has an appropriate affinity for water and is insoluble or hardly soluble in water. Specifically, for example, metal oxides such as silicon dioxide and titanium oxide, silicic acids (salts) such as natural zeolite and synthetic zeolite, kaolin, talc, clay,
Bentonite and the like can be mentioned. Among them, silicon dioxide and silicic acid (salt) are more preferable, and silicon dioxide and silicic acid (salt) having an average particle diameter of 200 μm or less as measured by the Coulter counter method are more preferable.

The amount of the inorganic powder used for the water-absorbing resin is as follows:
Although it depends on the combination of the water-absorbent resin and the inorganic powder,
The amount may be in the range of 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the water absorbent resin. The mixing method of the water-absorbent resin and the inorganic powder,
There is no particular limitation, and for example, a dry blending method, a wet mixing method, or the like can be employed. However, it is preferable to employ a dry blending method.

The water-absorbing agent thus obtained is made into an absorbent article by combining (combining) it with a fibrous material such as pulp. Examples of the absorbent articles include sanitary materials (body fluid absorbing articles) such as disposable diapers, sanitary napkins, incontinence pads, wound protecting materials, wound healing materials, etc .; absorbent articles such as urine for pets; building materials and water retaining materials for soil. Materials for civil engineering and construction such as waterproofing materials, waterproofing materials, packing materials, gel blisters, etc .; Food products such as drip absorbing materials, freshness preserving materials, cooling materials, etc .; Various industrial products such as oil / water separating materials, dew condensation preventing materials, coagulating materials Agricultural and horticultural articles such as water retention materials such as plants and soil; and the like, but are not particularly limited. In addition, for example, a disposable diaper is formed by laminating a back sheet (back surface material) made of a liquid-impermeable material, the above-described water-absorbing composition, and a top sheet (surface material) made of a liquid-permeable material in this order. It is formed by fixing to each other and attaching a gather (elastic portion) or a so-called tape fastener to the laminate. Further, the disposable diaper also includes pants with a disposable diaper used when disciplining urination and defecation for infants.

[0040]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited only to these Examples. Further,% in Examples and Comparative Examples means% by weight unless otherwise specified, and parts means parts by weight. The water absorption of the water absorbing agent, the water absorption capacity under load, the soluble component elution amount, and the soluble component elution amount in artificial urine were measured by the following methods. (1) Water absorption of water-absorbing agent 0.2 g of water-absorbing resin is added to a tea bag type bag (6 cm × 6 c
m), the opening was heat-sealed, and then immersed in physiological saline. After 60 minutes, the tea bag bag was lifted up, drained at 250 G for 3 minutes using a centrifuge, and then the weight W ₁ (g) of the bag was measured. The same operation was performed without using a water-absorbing resin, and the weight W ₀ (g) at that time was measured. And these weights W ₁ , W ₀
Then, the water absorption (g / g) was calculated according to the following equation.

Water absorption (g / g) = (W ₁ −W ₀ ) / weight of water-absorbent resin (g) (2) Water absorption under load The water absorption under load was determined using the measuring apparatus shown in FIG. .
As shown in FIG. 1, the measuring device includes a balance 1, a container 2 having a predetermined capacity placed on the balance 1, an outside air suction pipe sheet 3,
It comprises a conduit 4, a glass filter 6, and a measuring section 5 mounted on the glass filter 6. The container 2 has an opening 2a on the top and an opening 2b on the side. Opening 2
a is fitted with an outside air suction pipe 3 and has an opening 2b.
Is provided with a conduit 4. The container 2 contains a predetermined amount of a 0.9% by weight aqueous solution of sodium chloride (hereinafter referred to as physiological saline) 12. The lower end of the outside air suction pipe 3 is submerged in a physiological saline solution 12. The outside air suction pipe 3 is provided to keep the pressure in the container 2 at substantially the atmospheric pressure. The above glass filter 6 has a diameter of 55 m.
m. Container 2 and glass filter 6
Are connected to each other by a conduit 4 made of silicone resin. Further, the position and height of the glass filter 6 with respect to the container 2 are fixed. The above measuring unit 5
Has a filter paper 7, a support cylinder 9, a wire mesh 10 attached to the bottom of the support cylinder 9, and a weight 11. The measuring section 5 has a filter paper 7 and a support cylinder 9 (that is, a wire mesh 10) placed on a glass filter 6 in this order. The wire mesh 10 is made of stainless steel, and the size of the mesh is 400 mesh. The height of the upper surface of the wire mesh 10, that is, the height of the contact surface between the wire mesh 10 and the water absorbing agent 15 is set to be equal to the height of the lower end surface 3 a of the outside air suction pipe 3. Wire mesh 1
A predetermined amount of the water-absorbing agent is evenly sprayed on zero. Weight 1
1 is 0.7 ps with respect to the wire net 10, that is, the water absorbing agent 15.
The weight is adjusted so that the load i can be applied uniformly.

The water absorption capacity under load was measured using the measuring apparatus having the above-mentioned configuration. The measuring method will be described below. A predetermined amount of physiological saline 12 is put in the container 2. A predetermined preparation operation such as fitting the external suction pipe 3 into the container 2 was performed. Next, the filter paper 7 was placed on the glass filter 6. Also,
In parallel with the placement, 0.9 g of the water-absorbing agent was evenly sprayed inside the support cylinder 9, that is, on the wire mesh 10, and the weight 11 was placed on the water-absorbing agent 15. Next, the wire mesh 1 is placed on the filter paper 7.
0, that is, the support cylinder 9 on which the water-absorbing agent 15 and the weight 11 were placed was placed so that the center part thereof coincided with the center part of the glass filter 6. Next, the supporting cylinder 9 is placed on the filter paper 7.
The weight of the physiological saline absorbed by the water-absorbing agent 15 was determined from the measured value of the balance 1 over a period of 60 minutes from when the sample was placed. The same operation was performed without using the water-absorbing agent 15, and the weight of physiological saline other than the water-absorbing agent, for example, absorbed by the filter paper 7 or the like was obtained from the measured value of the balance 1, and this was used as a blank value. The water absorption capacity under load was determined by the following equation. Water absorption capacity under load (g / g) = (water absorption after 60 minutes-blank value) / weight of water absorbing agent (3) Dissolution amount of soluble component of water absorbing agent In a 100 ml beaker, 1 g of the water absorbing agent and 25 ml of artificial urine
Swelled, covered and left at 37 ° C. for 16 hours. The swollen gel was then dispersed in 975 ml of deionized water, stirred for 1 hour, and filtered through filter paper. The obtained filtrate was titrated by colloid titration to determine the soluble component elution amount (%) of the water absorbing agent.

The composition of the artificial urine is shown below. Urea 1.9% Sodium chloride 0.8% Magnesium chloride 0.1% Calcium chloride 0.1% (4) Degradation of water-absorbing agent in artificial urine Elution amount of soluble component In a 100 ml beaker, 1 g of water-absorbing agent is Swelled in 25 ml of artificial urine containing 0.005% ascorbic acid, 37
Leave at 16 ° C. for 16 hours. Then swelled gel 975m
1 l of deionized water, and the eluted soluble matter was rinsed with deionized water. After stirring for 1 hour, the mixture was filtered through filter paper, and the obtained filtrate was titrated by colloid titration to determine the amount (%) of the soluble soluble component degraded by the water-absorbing agent.

Reference Example 1 A mixture of 67.0 parts of a 37% aqueous solution of sodium acrylate, 10.2 parts of acrylic acid, 0.079 part of polyethylene glycol diacrylate (average number of polyethylene oxide units: 8) and 22.0 parts of water were mixed. An aqueous monomer solution was prepared. Nitrogen was blown into the aqueous solution in the vat to reduce the dissolved oxygen in the solution to 0.1 ppm or less.

Subsequently, the temperature of the aqueous solution was adjusted to 18 ° C. in a nitrogen atmosphere, and then 0.16 parts of a 5% aqueous solution of sodium persulfate and 0.16 parts of a 5% aqueous solution of 2,2′-azobis (2-amidinopropane) hydrochloride were added. , 0.55 parts of a 0.5% aqueous L-ascorbic acid solution and 0.17 parts of a 0.35% aqueous hydrogen peroxide solution were sequentially added dropwise with stirring. Polymerization started immediately after the dropwise addition of hydrogen peroxide, and after 10 minutes, the temperature of the monomer reached the peak temperature. The peak temperature was 85 ° C. Subsequently, the vat was immersed in a hot water bath at 80 ° C. and aged for 10 minutes.

The obtained transparent hydrogel was crushed with a meat chopper and then dried at 180 ° C. for 30 minutes. The dried product is pulverized with a pulverizer and passed through a 500 μm sieve to 105 μm.
The material remaining on the sieve was classified to obtain a water-absorbent resin (A). (Example 1) To 100 parts of the water-absorbent resin (A) obtained in Reference Example 1, pentasodium diethylenetriaminepentaacetate was added in an amount of 0.1%.
001 parts, ethylene glycol diglycidyl ether 0.05 parts, propylene glycol 1 part, water 3 parts and isopropyl alcohol 1 part
Heat treatment was performed at 80 ° C. for 40 minutes to obtain a water absorbing agent. Table 1 shows the performance evaluation results of the obtained water absorbing agent.

Example 2 A water-absorbing agent of the present invention was obtained in the same manner as in Example 1 except that 0.01 parts of disodium triethylenetriaminepentaacetate was used. Table 1 shows the performance evaluation results of the obtained water absorbing agent. (Example 3) A water-absorbing agent of the present invention was obtained in the same manner as in Example 1 except that 0.1 parts of pentasodium diethylenetriaminepentaacetate was used. Table 1 shows the performance evaluation results of the obtained water absorbing agent.

Example 4 The water-absorbing agent of the present invention was prepared in the same manner as in Example 1 except that 0.01 parts of trisodium triethylenetetraamine hexaacetate was used instead of pentasodium diethylenetriaminepentaacetate. I got Table 1 shows the performance evaluation results of the obtained water absorbing agent.

Example 5 A water absorbing agent of the present invention was obtained in the same manner as in Example 1 except that 0.01 parts of cyclohexanediaminetetraacetic acid was used instead of pentasodium diethylenetriaminepentaacetic acid. Table 1 shows the performance evaluation results of the obtained water absorbing agent. Comparative Example 1 A comparative water-absorbing agent was obtained in the same manner as in Example 1, except that pentasodium diethylenetriaminepentaacetate was not added. Table 1 shows the performance evaluation results of the obtained comparative water absorbing agent.

Reference Example 2 81.8 parts of a 38% aqueous solution of sodium acrylate, 7.7 parts of acrylic acid, 0.038 part of trimethylolpropane triacrylate and 9.8 parts of water
The parts were mixed to prepare an aqueous monomer solution. In a double bowl type kneader equipped with a jacket, nitrogen was blown into the aqueous solution to remove dissolved oxygen in the solution. Subsequently, the temperature of the aqueous monomer solution was adjusted to 22 ° C.

Next, 0.60 parts of a 10% aqueous sodium persulfate solution and 0.30 parts of a 0.1% L-ascorbic acid aqueous solution were added with stirring. One minute after the addition, the aqueous monomer solution began to become cloudy and the temperature began to rise. After 20 minutes, the peak temperature was reached, and the mixture was aged for 20 minutes with further stirring. The peak temperature was 96 ° C. After aging, the obtained gel was taken out and dried at 170 ° C. for 65 minutes. The dried polymer is pulverized and sieved with an 850 μm sieve to obtain a water-absorbent resin (B).
I got

(Example 6) 100 parts of the water-absorbent resin (B) obtained in Reference Example 2 was composed of 0.001 part of cyclohexanediaminetetraacetic acid, 0.5 part of ethylene carbonate, 3 parts of water and 3 parts of isopropyl alcohol. The liquids were mixed, and the resulting mixture was heated at 190 ° C. for 50 minutes to obtain a water absorbing agent. Table 1 shows the performance evaluation results of the obtained water absorbing agent.

Example 7 A water-absorbing agent of the present invention was obtained in the same manner as in Example 6, except that 0.5 parts of 1,4-butanediol was used instead of ethylene carbonate. Table 1 shows the performance evaluation results of the obtained water absorbing agent. (Comparative Example 2) A comparative water absorbing agent was obtained in the same manner as in Example 6, except that cyclohexanediaminetetraacetic acid was not added. Table 1 shows the performance evaluation results of the obtained comparative water absorbing agent.

Comparative Example 3 Example 7 was repeated except that cyclohexanediaminetetraacetic acid was not used.
In the same manner as in the above, a comparative water-absorbing agent was obtained. Table 1 shows the performance evaluation results of the obtained comparative water absorbing agent.

[0055]

[Table 1]

[0056]

According to the production method of the present invention, it is possible to easily obtain a water-absorbing agent with little deterioration over time due to urine and little elution components.

[Brief description of the drawings]

FIG. 1 is an apparatus for measuring a water absorption capacity under load.

[Explanation of symbols]

 Reference Signs List 1 balance 2 container 2a top opening 2b side opening 3 outside air suction pipe sheet 4 conduit 5 measuring unit 6 glass filter 7 filter paper 9 support cylinder 10 wire mesh 11 weight 12 physiological saline 15 water absorbing agent

Claims (4)

[Claims] 1. A water-absorbing resin having a carboxyl group,
A method for producing a water absorbing agent, comprising mixing a surface crosslinking agent capable of reacting with the carboxyl group and an ion sequestering agent. 2. 0.01 to 10 parts by weight of a surface cross-linking agent and 0.0001 of an ion sequestering agent with respect to 100 parts by weight of a water-absorbent resin.
The method for producing a water-absorbing agent according to claim 1, wherein 10 to 10 parts by weight is blended. 3. 0.01 parts by weight based on 100 parts by weight of the water absorbent resin.
The method for producing a water-absorbing agent according to claim 1 or 2, wherein water is further mixed at a ratio of 10 to 10 parts by weight. 4. The method for producing a water absorbing agent according to claim 1, further comprising a step of heating the mixture at 80 to 250 ° C.