JP2000007790A - Preparation of water-absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve excellent water absorption under atmospheric pressure or an elevated pressure and excellently small time-dependence of water absorption during operation by adding a chelating agent when recycling a gelled or fine polymer which generates in a preparation process of a water-absorbing resin. SOLUTION: This water-absorbing resin is required to have a carboxy group so that the resin absorbs a lot of water in water to form a hydrogel and such an example is a partially neutralized crosslinked polyacrylic acid or the like. A content of the carboxy group is not limited but is preferably not less than 0.01 equivalent per 100 g of the water-absorbing resin. The water-absorbing resin is preferably a resin on which an extremely small amount of an intra- crosslinking agent containing not less than 2 polymerizable unsaturated groups or not less than 2 reactive groups is made to copolymerize or react rather than a resin which is self-crosslinkable without use of a crosslinking agent. A chelating agent to be used is an aminocarboxylic acid or the like and the amount thereof is 0.0001-10 pts.wt. per 100 pts.wt. of a product to be recycled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a water absorbent resin. More specifically, the present invention relates to a method for producing a water-absorbent resin which is excellent in water absorbency under normal pressure and pressure and has a small decrease in water absorbance with time.

[0002]

2. Description of the Related Art In recent years, for the purpose of absorbing body fluid, a water-absorbent resin has been widely used as one of constituent materials of sanitary materials such as disposable diapers, sanitary napkins and incontinence pads.

[0003] As such a water-absorbing resin, for example,
Hydrolyzate of starch-acrylonitrile graft polymer (JP-B-49-43395) and neutralized product of starch-acrylic acid graft polymer (JP-A-51-125468)
No.), saponified vinyl acetate-acrylate copolymer (JP-A-52-14689), hydrolyzate of acrylonitrile copolymer or acrylamide copolymer (JP-B-53-15959), or a mixture thereof. Cross-linked product, self-cross-linked sodium polyacrylate obtained by reverse phase suspension polymerization (JP-A-53-46389), cross-linked polyacrylic acid partially neutralized product (JP-A-55-84304)
No.) etc. are known.

[0004] Desirable characteristics of such a water-absorbent resin include a high absorption capacity when contacted with an aqueous liquid, an excellent absorption rate, a 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. .

[0005] 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 vicinity of the surface of the water-absorbent resin is known, and various methods have been proposed so far.

For example, a method using a polyhydric alcohol as a surface cross-linking agent (JP-A-58-180233, JP-A-61-16903), polyhydric glycidyl compounds, polyhydric aziridine compounds, polyhydric amine compounds, Method using a polyvalent isocyanate compound (JP-A-59-189103)
No.), a method using a polyvalent metal (JP-A-51-13658)
No. 8, No. 61-257235, No. 62-7745
No.), a method using a monoepoxy compound (Japanese Unexamined Patent Publication No.
98121), a method using an epoxy compound and a hydroxy compound (JP-A-2-132103), and a method using an alkylene carbonate (DE-4020780).
No.) etc. are known.

[0007] In the above surface cross-linking, it is important to improve the properties of the water-absorbing resin from which more uniform cross-linking can be obtained. Therefore, it is known that the surface cross-linking agent is diluted with an organic solvent and mixed with the water-absorbent resin, or a water-absorbent resin having a sharp particle size distribution is used.

The water-absorbent resin is obtained by removing a polymer such as fine powder of the water-absorbent resin in the pulverizing / classifying step. Although the removed polymer can be discarded, it is desirable to recycle and reuse it in consideration of resource saving and environmental impact.

[0009] However, it has become apparent that when the above-mentioned polymer is recycled, the properties of the water-absorbent resin obtained and the stability over time during swelling decrease. In particular, when the fine powder of the water-absorbent resin is recycled, not only does the water-absorbency under normal pressure or pressure decrease, but when used as an absorbent for diapers, the gel deteriorates with time, and the liquid permeability and water-absorbency decrease. The problem became clear.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a water-absorbent resin which is excellent in water absorbency under normal pressure or under pressure, and which is excellent in stability over time when absorbing water.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that a chelating agent is used when recycling polymers such as gels and fine powders generated in the process of producing a water absorbent resin. It has been found that the above-mentioned problems can be solved by using the same, and the present invention has been achieved.

Accordingly, the present invention provides a method for producing a water-absorbent resin, comprising: a step of extracting at least a part of a raw material or a polymer; and a step of extracting at least a part of the extracted raw material or a polymer and a chelating agent before the extracting step. And a method for producing a water-absorbing resin.

The present invention also provides a composition comprising a water-absorbing resin having a particle size of 300 μm or less and a chelating agent.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described 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 must 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 or a crosslinked product thereof, a carboxyl group-containing crosslinked polyvinyl alcohol modified product, a crosslinked isobutylene-maleic anhydride copolymer, and the like.

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-mentioned 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 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%.

Further, the water-absorbing resin is preferably two or more polymerizable unsaturated groups or 2
It is desirable that a very small amount of an internal crosslinking agent having at least two reactive groups be copolymerized or reacted. 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, triallyl cyanurate, trimethylolpropanedi (meth) allyl ether, triallylamine, tetraallyloxyethane, glycerolpropoxytriacrylate, etc. Compounds having two or more saturated groups; ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, 1,4-butanediol, 1,5-
Pentanediol, 1,6-hexanediol, neopentyl alcohol, diethanolamine, tridiethanolamine, polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbit, sorbitan, glucose, mannitol, mannitol, sucrose,
Polyhydric alcohols such as glucose; polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether and glycerin triglycidyl ether; haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; glutaraldehyde, glyoxal Polyamines such as ethylenediamine; calcium hydroxide;
Periodic Table 2A for calcium chloride, calcium carbonate, calcium oxide, magnesium borax chloride, magnesium oxide, aluminum chloride, zinc chloride, nickel chloride, etc.
Hydroxides, halides, carbonates, 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 0.0
It is from 0.05 to 2 mol%, more preferably from 0.01 to 1 mol%.

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 polymerizing the above-mentioned monomer, bulk polymerization or precipitation polymerization can be performed. However, from the viewpoint of performance and easy control of polymerization, the monomer is used as an aqueous solution, and aqueous polymerization or reverse polymerization is performed. It is preferred to carry out phase suspension polymerization. The concentration of the aqueous solution at that time is usually from 10% 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 may be various, such as irregularly crushed, spherical, fibrous, rod-like, substantially spherical, and scale-like shapes.

In the process of producing a water-absorbent resin in the present invention, for example, in the case of aqueous solution polymerization, the preparation of an aqueous monomer solution
A series of steps such as polymerization, granulation of gel, drying, pulverization, classification (1), mixing of a surface treating agent, surface cross-linking treatment, and classification (2) may be mentioned. Examples of the raw materials and the polymer taken out in these steps include the following. Monomers and water in the polymerization process. A gel that adheres to a container or a granulation device in a gel granulation step or a gel that has not been granulated. Monomers, water and undried products in the drying process. Fine powder and coarse particles of the water absorbent resin in the classification (1) step. A solvent generated in the surface cross-linking treatment step when a solvent is used as the surface treatment agent. Examples of the water-absorbent resin of the product in the classification (2) step and fine powder and coarse particles other than the resin. In the case of reverse phase suspension polymerization, a solvent such as cyclohexane or hexane or a surfactant may be used in addition to the above product.

In the present invention, when the above-mentioned monomer is subjected to aqueous polymerization, it is generally from 10% by weight to a saturated concentration, preferably 20% by weight.
A 水溶液 40% by weight aqueous monomer solution is prepared and then polymerized. Examples of the polymerization method include a method of performing polymerization in a twin bowl type kneader with stirring as necessary, a method of performing cast polymerization in a container, a method of (continuously) standing polymerization on a driving belt, and the like. . As the temperature of the aqueous monomer solution increases during the polymerization, water and the monomer may adhere to the wall surface of the polymerization vessel or may be discharged out of the system. These water and monomer are recovered and can be added to the monomer aqueous solution preparation step and the polymerization step.

In order to dry the hydrogel obtained in the above polymerization step, it is desirable that the hydrogel is reduced to a predetermined particle size. The granulation of the hydrous gel can be performed at the time of polymerization by performing polymerization while stirring with a double bowl type kneader or the like, or by extruding the gel after polymerization from a die using a meat chopper or the like. Further, it can be made finer by a cutting mill or the like. The particle size of the finely-divided gel can be appropriately set depending on the capacity of the dryer and the like, but is generally preferably in the range of 0.1 to 10 mm. If the gel is finer than 0.1 mm, the obtained water-absorbent resin may have low physical properties. If it is larger than 10 mm, drying may be difficult.

In the grain refinement step, coarse gels larger than 10 mm and fine gels smaller than 0.1 mm can be formed. These polymers can be taken out and added to, for example, an aqueous monomer solution or a polymer gel.

The gel finely divided in the above-mentioned fine-graining step is dried in the drying step. As a drying method, for example, a hot air dryer, a flash dryer, a fluidized bed dryer, a drum dryer,
Microwaves, far infrared rays, and the like can be used. The drying temperature is 120 ° C. or higher, preferably 150 to 250 ° C.
And more preferably in the range of 160 ° C to 220 ° C. If the drying temperature is lower than 120 ° C., it takes too much time for drying, and furthermore, it is liable to be deteriorated because it is heated for a long time in a state of a hydrogel. The monomer or water taken out in the drying step can be added to the aqueous monomer solution or the polymerization step.

In the drying step, not only dried products but also undried products can be produced. The undried material may stop the pulverizer in the pulverization process, or reduce the water absorption performance when mixed with the product without being pulverized. The undried material is taken out during or after drying, and can be added to, for example, a drying step or a polymerization step.

The hydrogel dried in the drying step is pulverized to a predetermined particle size in a pulverizing / classifying step. The particle size can be appropriately set according to the use of the obtained water-absorbent resin, but is 1 mm or less, preferably 0.85 mm or less when used for diapers and napkins. Further, in order to improve the working environment when manufacturing diapers and napkins, and to sufficiently exhibit water absorption performance in diapers and napkins, 10
Fine powder of 5 μm or less, preferably fine powder of 212 μm or less,
More preferably, fine powder having a size of 300 μm or less is preferably removed by classification.

The fine powder taken out in the above-mentioned pulverization / classification step can be added to, for example, an aqueous monomer solution, a polymerization step or a drying step and recycled.

As a method for recycling the polymer taken out, particularly the fine powder, the following method is exemplified.

(A) A method in which the removed polymer, particularly fine powder, is added to the aqueous monomer solution, and polymerization is performed in the presence of a polymer such as fine powder. The amount of the polymer to be recycled is not particularly limited, but is generally in the range of 0.1 to 100 parts by weight, preferably 0.1 to 50 parts by weight, per 100 parts by weight of the monomer. If the recycled amount of the polymer exceeds 100 parts by weight, the water absorption capacity of the resulting water-absorbent resin may be reduced, or the residual monomer may be increased. When the fine powder is recycled, it can be added in powder form, added by forming an aqueous gel by adding an aqueous liquid, or added by dispersing in an organic solvent.

(B) A method in which the removed polymer, particularly fine powder, is added to an aqueous monomer solution or hydrogel during polymerization.
The polymer can be added during the period from the start of the polymerization and the increase in the viscosity of the aqueous monomer solution to the end of the polymerization of the monomer. The polymer can be added while stirring the aqueous monomer solution or hydrogel, or can be added substantially in a static state. The amount of the polymer to be recycled is not particularly limited, but is generally in the range of 0.1 to 100 parts by weight, preferably 0.1 to 50 parts by weight, per 100 parts by weight of the monomer. If the recycled amount of the polymer exceeds 100 parts by weight, the water absorption capacity of the resulting water-absorbent resin may be reduced, or the residual monomer may be increased. The fine powder can be added in powder form, added by forming an aqueous gel by adding an aqueous liquid, or added by dispersing in an organic solvent. An initiator can be added together with the fines.

(C) adding fine powder to the hydrogel after polymerization,
A method of mixing and drying after mixing as necessary. It can be sprayed on the surface of the hydrogel or added to the hydrogel before mixing, kneading and drying. After adding the fine powder to the hydrogel, the gel can be extruded from a perforated plate or the like and then dried. The amount of the fine powder to be added is not particularly limited, but is generally in the range of 0.1 to 100 parts by weight, preferably in the range of 0.1 to 50 parts by weight, per 100 parts by weight of the monomer. If the recycle amount of the fine powder exceeds 100 parts by weight, the water absorption capacity of the obtained water-absorbent resin may decrease or the residual monomer may increase. The fine powder can be added in powder form, added by forming an aqueous gel by adding an aqueous liquid, or added by dispersing in an organic solvent.

(D) A method in which an aqueous liquid is added to the polymer, particularly fine powder, taken out to form a hydrogel and then dried.
Examples of the aqueous liquid to be added to the fine powder include water, a mixed liquid of water and a hydrophilic organic solvent, and the like. The temperature of the aqueous liquid is 0
The temperature is in the range of 100 ° C, preferably 40 to 95 ° C. The ratio of the aqueous liquid and the fine powder is 5 to 100 parts by weight of the fine powder.
1000 parts by weight, preferably 10 to 400 parts by weight.
It is in the range of parts by weight. If the amount of the aqueous liquid is less than 5 parts by weight, the water-containing gel tends to return to the original fine powder after drying. When the amount of the aqueous liquid is more than 1000 parts by weight, it takes too much time for drying. An initiator, a surfactant, and the like can be added to the aqueous liquid.

The fine powder of the water-absorbing resin, particularly the fine powder having a size of 300 μm or less, especially the fine powder of the irregularly shaped water-absorbing resin has a large surface area, and is liable to be deteriorated in a water-containing state. A composition comprising a water-absorbing resin and a chelating agent which has passed through a 300 μm sieve becomes a hydrogel having excellent stability over time in a hydrous state.

Examples of the chelating agent usable in the present invention include the following compounds.

(1) aminocarboxylic acids and salts thereof,
(2) Citric acid monoalkylamide and citric acid monoalkenylamide and salts thereof, (3) Malonic acid monoalkylamide and malonic acid monoalkenylamide and salts thereof, (4) Monoalkyl phosphate and monoalkenyl phosphorus Acid esters and their salts, (5) N-
Acylated glutamic acid and N-acylated aspartic acid and salts thereof, (6) β-diketone derivative, (7) tropolone derivative, (8) polycarboxylic acid, (9) polyphosphoric acid.

(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) Monoalkyl phosphates and monoalkenyl phosphates and salts thereof include lauryl phosphate, stearyl phosphate and the like.

(5) 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.

(6) Examples of β-diketone derivatives include acetylacetone and benzoylacetone.

(7) Examples of the tropolone derivative include tropolone, β-thiaprisin, γ-thiaprisin and the like.

(8) Examples of the polycarboxylic acids and salts thereof include citric acid, succinic acid, tartaric acid, malic acid, gluconic acid, polyacrylic acid, and lithium, sodium, potassium, calcium, ammonium salts thereof. .

(9) Polyphosphoric acid and salts thereof include:
Examples thereof include metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, hexametaphosphoric acid, and lithium, sodium, potassium, calcium, and ammonium salts thereof.

Among these chelating agents, aminocarboxylic acids having three or more carboxyl groups and salts thereof are preferred. Particularly preferred are diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid and salts thereof.

The chelating agent is used in an amount of 0.1 to 100 parts by weight of a product to be recycled, for example, 100 parts by weight of a fine powder of a water absorbent resin.
0001 to 10 parts by weight, preferably 0.0
002 to 1 part by weight. When the use amount of the chelating agent exceeds 10 parts by weight, not only the effect corresponding to the use is not obtained but it becomes uneconomical, but also a problem such as a decrease in the absorption amount occurs. If the amount is less than 0.0001 part by weight, the effect of improving urine resistance cannot be obtained.

As a method of adding a chelating agent, a method of adding a chelating agent to a polymer such as fine powder of a water-absorbing resin, and then adding a mixture of the polymer and the chelating agent to an aqueous monomer solution or a polymer gel. A method in which a polymer such as fine powder of a water-absorbent resin is added to an aqueous monomer solution or a polymer gel and then a chelating agent is added; A method of adding a polymer such as fine powder of a water-absorbent resin and a chelating agent together to a monomer aqueous solution or a polymer gel;
A method of adding an aqueous liquid after adding a chelating agent to a polymer such as fine powder of a water absorbent resin; a method of adding an chelating agent after adding an aqueous liquid to a polymer; a method of combining a polymer, a chelating agent and water together A method of mixing and the like can be mentioned.

The water-absorbent resin of the present invention can be cross-linked in the vicinity of its surface using a surface cross-linking agent having two or more functional groups capable of reacting with the functional groups of the water-absorbent resin.

Examples of the surface crosslinking agent include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, 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.

Of the above surface crosslinking agents, polyhydric alcohol compounds, epoxy compounds, polyamine compounds, condensates of polyamine compounds and haloepoxy compounds, and alkylene carbonate compounds are more preferable.

These surface crosslinking agents may be used alone or in combination of two or more. When two or more surface crosslinking agents are used in combination, the solubility parameter (S
By combining the first surface cross-linking agent and the second surface cross-linking agent having different P values), it is possible to obtain a water-absorbing resin having even more excellent water-absorbing properties. 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 that can react with a carboxyl group of the water-absorbing resin, for example, ethylene glycol diglycidyl ether, , 4-butanediol and the like.

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, etc., but may be 0.1 to 100 parts by weight of the water-absorbent resin in a dry state.
Within the range of 01 to 10 parts by weight, more preferably 0.05 to 5 parts by weight.
It may be within the range of 3 parts by weight. By using the surface cross-linking agent in the above range, the water absorbing property 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 0.01 parts by weight, the cross-linking density in the vicinity of the surface of the water-absorbent resin can hardly 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. The amount of water used varies depending on the type, particle size, and water content of the water-absorbent resin, but is preferably 0.1 to 100 parts by weight of the solid content of the water-absorbent resin.
It is in the range of 5 to 10 parts by weight, preferably 0.5 to 3 parts by weight. If the amount of water used exceeds 10% by weight, the absorption capacity may decrease. If the amount is less than 0.5% by weight, it may be difficult to form a surface crosslinked layer having a sufficient thickness near the surface.

When mixing the water-absorbing resin and the surface crosslinking agent, a hydrophilic organic solvent may be used. As the hydrophilic organic solvent used, methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol,
Lower alcohols such as butyl alcohol, isobutyl alcohol and t-butyl alcohol; ketones such as acetone; ethers such as dioxane, alkoxy (poly) ethylene glycol and tetrahydrofuran; amides such as N, N-dimethylformamide; dimethyl And sulfoxides such as sulfoxide. 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.

A suitable mixing device used for mixing the surface cross-linking agent and the water-absorbing resin needs to be capable of producing a large mixing force 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.

After mixing the water absorbent resin with the surface crosslinking agent,
Further, by performing a heat treatment, the vicinity of the surface of the water absorbent resin can be crosslinked.

When performing the heat treatment, the treatment temperature is 80 to 3
A range of 00 ° C. is preferred. If the heating temperature is less than 80 ° C,
Not only does the heat treatment take a long time to cause a decrease in productivity, but also uniform crosslinking is not achieved, and a water-absorbent resin having high water-absorbing properties under pressure and under suppression of dissolution of the soluble component aimed at by the present invention can be obtained. There is a risk of disappearing.

The heat treatment can be performed using a usual dryer or heating furnace, and includes a groove-type mixing dryer, a rotary dryer, a disk dryer, a fluidized-bed dryer, a gas-flow dryer, and an infrared dryer. Is exemplified.

After the heat treatment, the heated product is optionally sieved with a sieve to obtain the water-absorbent resin of the present invention. The water-absorbent resin of the present invention includes not only single particles but also granules thereof. In addition to the above water-absorbing resin, if necessary, a deodorant,
Antibacterial agents, fragrances, various inorganic powders, foaming agents, pigments, dyes,
A hydrophilic short fiber, a plasticizer, a pressure-sensitive adhesive, a surfactant, a fertilizer, an oxidizing agent, a reducing agent, water, salts, and the like may be added, thereby imparting various functions to the water-absorbing resin.

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-absorbent resin is made into an absorbent article by, for example, compounding (combining) with a fibrous material such as pulp.

Examples of the absorbent articles include sanitary materials (body fluid absorbent articles) such as disposable diapers, sanitary napkins, incontinence pads, wound protection materials, wound healing materials, etc .; absorbent articles such as urine for pets; Materials for civil engineering and construction such as water retention materials, water stop materials, packing materials, gel blisters, etc .; Food products such as drip absorbents, freshness retention materials, cold insulation materials; oil / water separation materials, dew condensation prevention materials,
Various industrial articles such as coagulants; agricultural and horticultural articles such as water retention materials such as plants and soil; and the like 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.

[0068]

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.

(1) Absorption of water-absorbent resin 0.2 g of water-absorbent resin was added to a tea bag type bag (6 cm × 6 c
m), the opening was heat-sealed, and then immersed in artificial urine. After 60 minutes, the tea bag bag was pulled out and drained at 250 G for 3 minutes using a centrifuge, and then the weight W1 (g) of the bag was measured. Further, the same operation was performed without using the water-absorbing resin, and the weight W ₀ at that time was obtained.
(G) was measured. Then, the water absorption (g / g) was calculated from the weights W ₁ and W ₀ according to the following equation.

Absorbed amount (g / g) = (W ₁ −W ₀ ) / weight of water-absorbent resin (g) The composition of artificial urine is shown below.

Urea 1.9% Sodium chloride 0.8% Magnesium chloride 0.1% Calcium chloride 0.1% (2) Absorption capacity under load The water absorption capacity 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 absorbent resin 15 is set to be equal to the height of the lower end surface 3 a of the outside air suction pipe 3. A predetermined amount of a water-absorbent resin is evenly spread on the wire mesh 10. The weight of the weight 11 is adjusted so that a load of 0.7 psi can be uniformly applied to the wire net 10, that is, the water absorbent resin 15.

The water absorption capacity under load was measured using the measuring device 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, filter paper 7 is placed on glass filter 6.
Was placed. Further, in parallel with the placing, inside the support cylinder 9,
That is, 0.9 g of the water-absorbent resin was evenly sprayed on the wire mesh 10, and the weight 11 was placed on the water-absorbent resin 15. Next, on the filter paper 7, the wire cylinder 10, that is, the support cylinder 9 on which the water-absorbent resin 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, after the support cylinder 9 is placed on the filter paper 7,
Over time, the weight of the physiological saline absorbed by the water-absorbent resin 15 was determined from the measured value of the balance 1. Also,
The same operation was performed without using the water-absorbent resin 15, and the weight of physiological saline absorbed by, for example, the filter paper 7 and the like other than the water-absorbent resin 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-absorbent resin (3) Amount of soluble component eluted from water-absorbent resin 1 g of water-absorbent resin in a 100 ml beaker The artificial urine 25
ml, swelled 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 absorbent resin.

(4) Degradation of Water Absorbent Resin Amount of soluble component eluted In a 100 ml beaker, 1 g of water absorbent resin was swollen in 25 ml of artificial urine containing 0.005% L-ascorbic acid,
Capped and left at 37 ° C. for 16 hours. The swollen gel was then dispersed in 975 ml of deionized water and the eluted solubles were rinsed with deionized water. After stirring for 1 hour, the mixture was filtered with a filter paper, and the obtained filtrate was titrated by colloid titration to determine the amount (%) of a soluble soluble component of the water-absorbent resin that was degraded.

Reference Example 1 39.3 parts of acrylic acid, 257.7 parts of a 37% by weight aqueous solution of sodium acrylate, polyethylene glycol diacrylate (average number of polyethylene glycol units: 8)
0.46 parts and 148.5 parts of water were mixed to prepare an aqueous monomer solution. Nitrogen gas was blown into this aqueous monomer solution to remove dissolved oxygen.

Subsequently, the monomer aqueous solution was charged into a jacketed double bowl type kneader, and the temperature of the monomer aqueous solution was maintained at 25 ° C.

Then, while rotating a kneader blade at 40 rpm under a nitrogen stream, 0.4 part of a 20% by weight aqueous sodium persulfate solution as a polymerization initiator and 10% by weight of 2.2%
1.6 parts of '-azobis (2-amidinopropane) hydrochloride aqueous solution, 0.1% by weight of L-ascorbic acid aqueous solution 0.7
And 0.4 part of a 0.35% aqueous hydrogen peroxide solution were added to initiate polymerization. After confirming the initiation of polymerization by the turbidity of the aqueous monomer solution, the blade was stopped when the temperature (internal temperature) of the aqueous monomer solution rose to 30 ° C. It was left standing until the internal temperature reached 60 ° C. while removing heat with a jacket. When the internal temperature exceeded 60 ° C., the blade was rotated, the generated gel was pulverized into particles, and polymerization was further performed so that the maximum internal temperature was 77 ° C.

Next, the obtained gel was sieved with a 10 mm-wide saw blade. The gel that passed through the mushroom was dried at 180 ° C. for 40 minutes. The dried product is pulverized with a roll mill and then 850 μm.
A 150 μm sieve passed through a sieve of m was collected to obtain a water-absorbent resin (A).

To 100 parts of the water-absorbent resin (A), a composition solution composed 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 heat-treated at 180 ° C. for 40 minutes. ,
A water absorbing resin (B) was obtained.

Example 1 In Reference Example 1, 50 parts by weight of the water-absorbent resin fine powder passed through a 150 μm sieve was added with diethylenetriaminepentaacetic acid
50 parts by weight of hot water containing 0.002 parts of sodium at a temperature of 80 ° C. were mixed with stirring. 180 of the resulting mixture
It dried at 40 degreeC for 40 minutes. The dried product was pulverized by a roll mill, and then a 150 μm sieve was collected through a 850 μm sieve to obtain a water-absorbent resin (C). Subsequently, 10 parts of the water absorbent resin (C) and 90 parts of the water absorbent resin (A) were mixed.
100 parts of this mixture was mixed with a composition solution composed of 0.05 parts of ethylene glycol diglycidyl ether, 1 part of propylene glycol, 3 parts of water and 1 part of isopropyl alcohol, and heat-treated at 180 ° C. for 40 minutes to obtain a water-absorbent solution of the present invention. Resin (1) was obtained.

Comparative Example 1 A comparative water absorbent resin (1) was obtained in the same manner as in Example 1 except that pentasodium diethylenetriaminepentaacetate was not used.

Example 2 10 parts of the fine powder obtained in Reference Example 1 and passed through a 150 μm sieve, and 0.001 part of pentasodium diethylenetriaminepentaacetate were separately polymerized in the same manner as in Reference Example 1 and added to the gel after completion of the polymerization. Then, the mixture was stirred and mixed in the kneader.

Subsequently, the gel was taken out of the kneader and sieved with a 10 mm-wide saw. Gel that has passed through the snowboard
It was dried at 80 ° C. for 40 minutes. The dried product was pulverized by a roll mill, and then a 150 μm sieve was passed through an 850 μm sieve.

To 100 parts of the pulverized / classified product, a composition liquid comprising 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 heat-treated at 180 ° C. for 40 minutes.
The water-absorbent resin (2) of the present invention was obtained.

Comparative Example 2 A comparative water absorbent resin (2) was obtained in the same manner as in Example 2 except that pentasodium diethylenetriaminepentaacetate was not used.

Example 3 In Example 2, 150 μm obtained in Reference Example 1 was used.
10 parts of fine powder, 0.001 part of pentasodium diethylenetriaminepentaacetate and 0.001 part of polymerized gel passed through a sieve having a diameter of 13 mm were passed through a meat chopper having a perforated plate having a hole having a diameter of 13 mm to mix the polymerized gel and fine powder. .

Subsequently, the mixed gel was dried at 180 ° C. for 40 minutes. The dried product is pulverized with a roll mill, and then 850
A 150 μm sieve was collected through a μm sieve.

To 100 parts of the pulverized / classified product, a composition liquid comprising 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 heat-treated at 180 ° C. for 40 minutes.
The water-absorbent resin (3) of the present invention was obtained.

Comparative Example 3 A comparative water absorbent resin (3) was obtained in the same manner as in Example 3 except that pentasodium diethylenetriaminepentaacetate was not used.

[0091]

[Table 1]

[0092]

According to the present invention, the use of a chelating agent when recycling raw materials and polymers removed in the process of manufacturing a water-absorbent resin prevents the physical properties of the obtained water-absorbent resin from deteriorating. be able to. Above all, by recycling the fine powder of the water-absorbing resin in the presence of the chelating agent, a water-absorbing resin with improved urine resistance can be obtained.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Balance 2 Container 2a Top opening 2b Side opening 3 Open air suction pipe sheet 4 Conduit 5 Measuring part 6 Glass filter 7 Filter paper 9 Support cylinder 10 Wire net 11 Weight 12 Physiological saline 15 Water absorbing resin

Claims (5)

[Claims] In a method for producing a water-absorbent resin, a step of extracting at least a part of a raw material or a polymer, and adding at least a part of the extracted raw material or a polymer and a chelating agent to a step prior to the extracting step. And a method for producing a water-absorbent resin. 2. A method of adding the removed polymer to an aqueous solution of a monomer capable of forming a water-absorbing resin, during the polymerization of the monomer, or to a hydrogel obtained by polymerizing the monomer. 2. The method for producing a water-absorbent resin according to claim 1, wherein: 3. The method for producing a water-absorbent resin according to claim 1, further comprising a step of adding an aqueous liquid to the polymer taken out. 4. The method for producing a water-absorbent resin according to claim 1, wherein the polymer taken out is a fine powder of a water-absorbent resin having a particle diameter passing through a 300 μm sieve. 5. A composition comprising a water absorbing resin having a particle size of 300 μm or less and a chelating agent.