JPH11315147A - Production of water absorbing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an absorbent having excellent urine resistance, causing slight deterioration of a water absorbing resin with time in absorbing urine. SOLUTION: A monomer component essentially containing an unsaturated carboxylic acid is polymerized in the presence of an internal crosslinked agent to give a water absorbing resin, which is crosslinked in the vicinity of its surface. The crosslinked water absorbing resin is mixed with water and an ion sequestering agent and granulated. Preferably, 100 pts.wt. of the crosslinked water absorbing resin is mixed with 0.1-20 pts.wt. of water and 0.0001-10 pts.wt. of the ion sequestering agent to give the objective absorbent. sequestering.

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.

On the other hand, the water-absorbing resin is in powder form,
It may contain fine powder having a particle size of μm or less, and it is known that granulation is performed by adding water in order to improve the handling property and the liquid permeability in a diaper. Granulation can prevent powdering and improve fluidity during moisture absorption. However, when water is added to the surface-crosslinked water-absorbent resin and granulated, there is a problem that the surface crosslinked layer is easily broken. In particular, the water-absorbent resin having a high absorption capacity under pressure, which has been desired in recent years, prevents the dissolution of soluble components by crosslinking the vicinity of the surface of the water-absorbent resin having a high water absorption capacity. -When the surface crosslinked layer is deteriorated by ascorbic acid or the like, elution of soluble components cannot be suppressed. Therefore, when used for a diaper, there is a problem that liquid permeability is reduced and gel strength is reduced, and urine leaks from the diaper.

[0007]

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.

[0008]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, they have been obtained by polymerizing a monomer component essentially containing an unsaturated carboxylic acid in the presence of an internal crosslinking agent. After cross-linking the vicinity of the surface of the water-absorbent resin, it has been found that the above problem can be solved by adding an ion-sequestering agent when granulating the cross-linked water-absorbent resin with water. Reached.

Therefore, in the method for producing a water-absorbing agent of the present invention, the vicinity of the surface of a water-absorbing resin obtained by polymerizing a monomer component essentially containing an unsaturated carboxylic acid in the presence of an internal crosslinking agent is subjected to a crosslinking treatment. Thereafter, the method includes adding water and an ion sequestering agent to the crosslinked water-absorbent resin and granulating the water-absorbent resin.

[0010]

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 absorbs a large amount of water in water to form a hydrogel, and preferably has 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. Combined saponified product, acrylonitrile copolymer or acrylamide copolymer hydrolyzate or cross-linked thereof,
Carboxyl group-containing crosslinked polyvinyl alcohol saponified product, crosslinked isobutylene-maleic anhydride copolymer and the like can be mentioned.

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 that 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, may be mentioned N- dimethylaminopropyl (meth) acrylamide, an amino group-containing unsaturated monomers and quaternized products thereof and the like the like. Further, the amount of the obtained water-absorbent resin may be, for example, methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) in an amount that does not extremely impair the hydrophilicity of the water-absorbent resin.
Acrylic esters such as acrylates, vinyl acetate,
A hydrophobic monomer such as vinyl propionate may be used.

The amount of the carboxyl group contained in the water-absorbing resin is not particularly limited, but it is preferable that the carboxyl group is 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. Use things. 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 easy control of polymerization, 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 obtained by these polymerization methods can be preferably 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 (for example, on a wet basis) of 1 to 50%, preferably 1 to 20%, more preferably 1 to 10%, and can be handled as a powder. If the water content exceeds 50%, the surface cross-linking agent permeates too far into the interior,
It may be difficult to obtain a water-absorbing resin having excellent water-absorbing performance.

In the present invention, the surface of the water-absorbent resin is subjected to a surface cross-linking treatment with a surface cross-linking agent having two or more functional groups capable of reacting with a functional group such as a carboxyl group of the water-absorbent resin. Examples of the surface crosslinking agent capable of reacting with a carboxyl group that can be used in the present invention include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, , 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
-Cyclohexanedimethanol, 1,2-cyclohexanediol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene,
Oxyethylene-oxypropylene block copolymer,
Polyhydric alcohol compounds such as pentaerythritol and sorbitol; ethylene glycol diglycidyl ether;
Polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether,
Epoxy compounds such as polypropylene glycol diglycidyl ether and glycidol; polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine and polyamidepolyamine; epichlorohydrin, epibromohydrin , Α-
Haloepoxy compounds such as methyl epichlorohydrin; condensates of the above polyvalent amine compounds and the above haloepoxy compounds; polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate, hexamethylene diisocyanate;
Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane; 1,3-dioxolan-2-one,
-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-dioxane-
Alkylene carbonate compounds such as 2-one and 1,3-dioxoban-2-one; hydroxides such as zinc, calcium, magnesium, and aluminum; and polyvalent metal compounds such as chlorides; and the like, but are not particularly limited. Not something.

Among the surface cross-linking agents exemplified above, polyhydric alcohol compounds, epoxy compounds, polyvalent amine compounds, condensates of polyvalent amine 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 the 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 capable of reacting with a carboxyl group of the water-absorbing resin and having a solubility parameter of less than 12.5 (cal / cm ³ ) ^1/2 , for example, glycerol polyglycidyl ether,
(Poly) glycerol polyglycidyl ether, ethylene glycol diglycidyl ether, 1,3-butanediol, trimethylolpropane, 1,3-propanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, , 4-butanediol and the like.

The amount of the surface cross-linking agent used with respect to the water-absorbing resin depends on the combination of the water-absorbing resin and the surface cross-linking agent.
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, when mixing the water-absorbing resin and the surface crosslinking agent, it is preferable to use water. 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 0.5 ~
The range is 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 may be difficult to obtain a water-absorbing resin having a high absorption capacity under pressure.

In the present invention, when mixing the water-absorbing resin and the surface crosslinking agent, a hydrophilic organic solvent may be used.
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, but is usually in the range of 0 to 10 parts by weight, preferably 0.1 to 5 parts by weight, per 100 parts by weight of the water-absorbing resin.

In the present invention, the water-absorbing resin and the surface cross-linking agent are mixed in a state in which the water-absorbing resin is dispersed in an organic solvent such as cyclohexane or pentane. After previously mixing the mixed solvent and the surface crosslinking agent, the mixture can be sprayed or dropped onto the water-absorbent resin. Suitable mixing devices used for the mixing need 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. A furnace rotary desk mixer, an air flow mixer, a double arm kneader, an internal mixer, a pulverizing kneader, a rotary mixer, a screw extruder and the like are suitable.

When performing the heat treatment in the present invention, the treatment temperature is preferably in the range of 80 to 250 ° C. When the heating temperature is lower than 80 ° C., the heat treatment takes a long time to cause a decrease in productivity, and also, uniform cross-linking is not achieved, and the objective of the present invention is to suppress the dissolution of soluble components and to absorb water under pressure. There is a possibility that a water absorbing agent having high characteristics may not be obtained. The heat treatment can be performed using a normal dryer or a heating furnace, and examples thereof include a groove-type mixing dryer, a rotary dryer, a desk dryer, a fluidized-bed dryer, a gas-flow dryer, and an infrared dryer. .

The water-absorbing resin obtained by the surface cross-linking treatment as described above has a 0.9% by weight aqueous solution of sodium chloride (physiological saline) under a load of 0.7 psi having an absorption capacity under pressure of 20 (g / g) or more. , Preferably 22 (g / g)
As described above, more preferably 24 (g / g) or more of the water-absorbent resin is preferably used for granulation described below. 20 absorption capacity under pressure
If it is lower than (g / g), sufficient water absorption performance cannot be exhibited in the diaper.

Examples of the ion sequestering agent used in the present invention include the following compounds. (1) aminocarboxylic acid and its salt; (2) polycarboxylic acid and its derivative; (3) (poly) phosphoric acid and its derivative; (4) N-acylated glutamic acid and N-acylated aspartic acid and their Salts, (5) β-diketone derivatives, (6) tropolone derivatives, (7) organophosphate compounds.

(1) Aminocarboxylic acids and salts thereof include dihydroxyethylglycine, iminodiacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, 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'-carboxymethyl aspartic acid,
N-Alkenyl-N'-carboxymethyl aspartic acid and alkali metal, alkaline earth metal, ammonium or amine salts thereof. Among them, aminocarboxylic acids having three or more carboxyl groups and salts thereof are preferred from the viewpoint of ion sequestering ability.

(2) Polycarboxylic acids and derivatives thereof include succinic acid, polyacrylic acid, monoalkylamide citrate, monoalkenylamide citrate, monoalkylamide malonate, monoalkenylamide malonate, and alkalis thereof. Metal salts, alkaline earth metal salts, ammonium salts or amine salts are mentioned. (3) (Poly) phosphoric acid and its derivatives include hexametaphosphoric acid, metaphosphoric acid, tripolyphosphoric acid, alkyl phosphate, alkenyl phosphate and alkali metal salts, alkaline earth metal salts, ammonium salts or amine salts thereof. Is mentioned.

(4) N-acylated glutamic acid and N-
Acylated aspartic acid and salts thereof include, for example, Amisoft HS-1 commercially available from Ajinomoto Co., Inc.
1 and GS-11. (5) Examples of the β-diketone derivative include acetylacetone, benzoylacetone and the like.

(6) Examples of the tropolone derivative include tropolone, β-thiaprisin, γ-thiaprisin and the like. (7) 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 used is usually 0.1 to 100 parts by weight of the solid content of the water absorbent resin.
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.

In the present invention, water and the above-mentioned ion-sequestering agent are added to the water-absorbing resin which has been subjected to the surface cross-linking treatment in advance by using the above-mentioned surface cross-linking treatment agent, and the water-absorbing resin is used as a binder. The particles are combined and granulated to obtain a water absorbing agent having excellent urine resistance. The water-absorbent resin is obtained by subjecting a water-absorbent resin obtained by polymerizing a monomer component essentially containing an unsaturated carboxylic acid in the presence of an internal cross-linking agent to a cross-linking treatment in the vicinity of the surface. By using an internal crosslinking agent,
When the swollen gel is exposed to a deteriorating atmosphere, the elution of soluble components from the inside of the gel can be suppressed. The average particle size of the water-absorbent resin is increased by the granulation, and the moisture-absorbing fluidity is also improved so that the resin can be easily handled. The amount of water to be added is in the range of 0.1 to 20 parts by weight, preferably 0.1 to 10 parts by weight, more preferably 0.5 to 4 parts by weight, based on 100 parts by weight of the water absorbent resin. Range. If the amount of water is less than 0.1 part by weight, it becomes difficult to granulate the water-absorbent resin particles. Further, the ion sequestering agent cannot be fixed near the surface of the water-absorbing resin. On the other hand, if the amount of water is more than 20 parts by weight, the water-absorbent resin swells to the inside to form a gel. The layer may be broken.

The method of granulation with the addition of the ion sequestering agent is not particularly limited. In addition to the above-mentioned methods, for example, a method of adding the ion sequestering agent to the water-absorbent resin and then adding water to granulate the mixture may be mentioned. Can be A hydrophilic organic solvent such as methanol, ethanol, or isopropyl alcohol can be used in combination to improve the mixing properties of the ion-sequestering agent and water with the water-absorbing resin. Further, a surfactant or inorganic fine particles such as silica and titanium oxide may be added in advance or simultaneously.

As described above, the addition of the ion sequestering agent
This is performed when water is added to perform granulation after a cross-linking treatment is performed on the vicinity of the surface of the water absorbent resin. Thereby, the ion sequestering agent can be fixed to the surface of the water absorbent resin. Since the deterioration of the water-absorbent resin occurs from the resin surface, the ion-sequestering agent is disposed near the surface of the water-absorbent resin. When adding the ion sequestering agent when polymerizing a water-soluble monomer capable of forming a water-absorbing resin, polymerization of the monomer is inhibited when polymerization of the monomer is performed in the presence of the ion sequestering agent. Therefore, there is a possibility that a water-absorbent resin having excellent absorption performance may not be obtained. Further, during the polymerization, the ion sequestering agent may deactivate the ion sequestering ability and the chelating ability.

In addition to the above water absorbing agent, if necessary,
Adds deodorant, antibacterial agent, fragrance, various inorganic powders, foaming agent, pigment, dye, hydrophilic short fiber, plasticizer, adhesive, surfactant, fertilizer, oxidizing agent, reducing agent, water, salts, etc. Then, various functions may be imparted 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. Specific examples include metal oxides such as silicon dioxide and titanium oxide, silicic acids (salts) such as natural zeolites and synthetic zeolites, kaolin, talc, clay, bentonite and the like. 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-absorbent 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.

[0039]

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 amount of water-soluble components, and the amount of soluble components eluted 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 absorbing resin (g) (2) Elution amount of soluble component of water absorbing agent In a 100 ml beaker, 1 g of the water absorbing agent was added to 25 ml of artificial urine.
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% (3) Degradation of water-absorbing agent Elution amount of soluble component In a 100 ml beaker, 1 g of water-absorbing agent was added to 0.005 L-ascorbic acid. Swelled in 25 ml of artificial urine containing
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. (4) Absorption capacity under load The water absorption capacity under load was determined using the measuring device 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 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 (5) Average particle size of water absorbing agent 850 μm, 600 μm, 500 μm, 425 of water absorbing agent
μm, 300 μm, 220 μm, 150 μm, 105 μ
After sieving and classification using a sieve of m, the residual percentage R was plotted on logarithmic establishment paper, and the particle size corresponding to R = 50% was defined as the average particle size.

(Reference Example 1) 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. under 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 resulting 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.
Were classified into those remaining on the sieve. To 100 parts of the classified product, a composition liquid consisting of 0.05 parts of ethylene glycol diglycidyl ether, 1 part of propylene glycol, 3 parts of water and 1 part of isopropyl alcohol was mixed, and treated at 180 ° C. for 40 minutes to obtain a water absorbent resin (A ) Got.

Example 1 100 parts of the water-absorbent resin (A) was prepared by adding 0.005 sodium diethylenetriaminepentaacetic acid to 0.005 parts.
1 part and a mixture of 3 parts of water are sprayed and granulated.
Drying at 0 ° C. gave a water-absorbing agent. Table 1 shows the evaluation results of the obtained water absorbing agent (1). (Example 2) Example 1 was the same as Example 1 except that 0.1 part of pentasodium diethylenetriaminepentaacetate was added.
In the same manner as in the above, a water absorbing agent of the present invention was obtained. Table 1 shows the evaluation results of the obtained water absorbing agent (2).

Example 3 The water-absorbing agent of the present invention was prepared in the same manner as in Example 1 except that 0.001 part of trisodium triethylenetetraaminehexaacetate was used instead of pentasodium diethylenetriaminepentaacetate. Obtained. Table 1 shows the evaluation results of the obtained water absorbing agent (3).

Comparative Example 1 The water-absorbing resin (A) was used as it was as a comparative water-absorbing agent (1). Table 1 shows the performance evaluation results of the comparative water absorbing agent (1). Comparative Example 2 A comparative water-absorbing agent was obtained in the same manner as in Example 1 except that 3 parts of water were mixed. Table 1 shows the performance evaluation results of the obtained comparative water-absorbing agent (2).

[0049]

[Table 1]

[0050]

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-absorbent resin obtained by polymerizing a monomer component essentially containing an unsaturated carboxylic acid in the presence of an internal cross-linking agent is subjected to a cross-linking treatment in the vicinity of the surface, and then the cross-linked water-absorbent resin is obtained. A method for producing a water-absorbing agent, comprising adding water and an ion-sequestering agent to the mixture and granulating the mixture. 2. 0.1 to 20 parts by weight of water and 100.01 parts by weight of an ion-sequestering agent per 100 parts by weight of a crosslinked 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. The method for producing a water-absorbing agent according to claim 1, wherein the water content (on a wet basis) of the crosslinked water-absorbing resin is 20% by weight or less. 4. The crosslinked water-absorbent resin has an absorption capacity under load of at least 20 (g / g).
The method for producing a water-absorbing agent according to any one of the above.