JP2002212301A - Water absorbent and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water absorbent excellent in water absorption rate under pressurization or no pressurization, highly safe for the skin and the like and suitable for medical supplies, and to provide a method for producing the absorbent. SOLUTION: This water absorbent comprises a water absorbent resin powder (A) whose surface is at least partially covered with a coating film comprising an adduct of a polyamine compound (B) and an olefinic double bond-bearing compound (C). The other objective method for producing the water absorbent comprises adding the polyamine and the olefinic double bond-bearing compound (C) to the water absorbent resin powder (A) and making an addition reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a water-absorbing agent excellent in water absorption capacity under pressure and under no pressure and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, sanitary materials such as disposable diapers and sanitary napkins, so-called incontinence pads, have been used as constituent materials thereof.
Water absorbing resin (water absorbing agent) for the purpose of absorbing body fluid
Is widely used. Conventionally, as a water-absorbing resin, for example, a crosslinked product of partially neutralized polyacrylic acid, starch-
Hydrolysis product of acrylic acid graft polymer, vinyl acetate-
A saponified acrylate copolymer, a hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer, a crosslinked product thereof, a crosslinked product of a cationic monomer, and the like are known.

Since the water-absorbing resin used for such a sanitary material actually needs to withstand a load and absorb urine and the like, the absorption capacity under no pressure (the amount of absorption under no load) is simply measured. ) As well as excellent absorption capacity under pressure (absorption under load). In the conventional water-absorbing resin, it is effective to increase the degree of crosslinking in order to improve the absorption capacity under pressure. However, for example, by increasing the amount of the copolymerizable crosslinking agent used,
If the degree of cross-linking (internal cross-link density) is increased uniformly, the absorption capacity under pressure is improved, but the absorption capacity under no pressure is reduced, and eventually the absorption capacity under pressure is improved. There are also limitations.

As a method for solving this problem, the degree of crosslinking inside the water-absorbent resin is reduced to maintain the water absorption capacity under no pressure, and at the same time, for example, at least two functional groups which react with the carboxylic acid of the water-absorbent resin are provided. A so-called surface cross-linking method has been proposed in which the cross-linking agent is used to cross-link the vicinity of the surface of the water-absorbent resin particles to increase the degree of cross-linking. However, in the conventional surface cross-linking method, when performing surface cross-linking, the cross-linking agent may penetrate relatively deeply into the water-absorbent resin particles, and as a result, even though the cross-linking is not as uniform as the internal cross-linking (internal cross-linking). Because of cross-linking, it was not possible to sufficiently prevent a decrease in water absorption capacity under no pressure.

[0005] Therefore, as an improvement of the above-mentioned surface cross-linking method, a water-absorbent resin hydrate containing a certain amount of water is used.
A predetermined amount of a hydrophilic polymer having a reactive group and a cross-linking agent having two or more functional groups capable of reacting with the reactive group are added and mixed, and the mixture is heated and reacted to form a hydrophilic polymer near the surface of the water absorbent resin. A method for forming a partially crosslinked coating is reported in Japanese Patent Application Laid-Open No. 8-53550. According to this method, in order to efficiently coat the hydrophilic polymer, it is necessary to contain a certain amount or more of water in the water-absorbent resin, but when the water content of the water-absorbent resin at the time of surface crosslinking is large, Water absorption capacity under no pressure,
The water absorption capacity under pressure tends to decrease, and satisfactory performance has not been obtained. In addition, according to the above method, a glycidyl compound is used as a cross-linking agent. However, since the glycidyl compound has relatively strong skin irritation, if it remains, the glycidyl compound absorbs water from sanitary materials that may come into direct contact with the skin. When used as an agent, there was a problem that safety was concerned.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a water-absorbing agent which is excellent in hygroscopicity under pressure and under no pressure, has high safety to skin and the like, and is suitable for sanitary materials, and a method for producing the same. Is to provide.

[0007]

Means for Solving the Problems The present inventor has made intensive studies to achieve the above object. As a result, it has been found that a coating film covering the water-absorbent resin particles (A) can be formed by an addition reaction between the polyamine compound (B) and the compound (C) having an olefinic double bond, and the present invention Was completed.

That is, in the water absorbing agent of the present invention, the compound (C) in which at least a part of the surface of the water absorbing resin particles (A) has an olefinic double bond of the polyvalent amine compound (B).
Coated with a coating film composed of an adduct to the polymer.

In the method for producing a water-absorbing agent of the present invention, a polyvalent amine compound (B) and a compound having an olefinic double bond (C) are added to the water-absorbing resin particles (A), followed by an addition reaction.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The water-absorbing agent of the present invention comprises water-absorbing resin particles (A)
Of the water-absorbent resin particles (A) by adding a polyamine compound (B) and a compound (C) having an olefinic double bond to the water-absorbent resin particles (A). More specifically, the water-absorbing agent of the present invention provides at least a part of the surface of the water-absorbent resin particles (A) by an addition reaction between the polyvalent amine compound (B) and the compound (C), preferably a Michael addition reaction. It is obtained by forming a coating film to cover.

The water-absorbent resin particles (A) in the present invention are a water-swellable, water-insoluble crosslinked polymer, and the water-absorbent agent in the present invention means that the water-absorbent resin is a main component (preferably, It refers to a modified (preferably surface-modified) water-absorbent resin having a content of 80% by weight or more, more preferably 90% by weight or more. In the present invention, particles of a conventionally used water-absorbing resin can be used, for example,
A conventionally known cross-linked polymer (water-absorbing resin) which absorbs a large amount of water of 50 to 1000 times in ion-exchanged water and forms an anionic, nonionic or cationic hydrogel, or as required, Drying the polymer,
Those obtained by usually pulverizing before and / or after drying may be mentioned. Further, the water-insoluble crosslinked polymer of the present invention means that an uncrosslinked water-soluble component in the water absorbent resin is preferably 40% by weight or less, more preferably 25% by weight or less, and still more preferably 20% by weight or less. %, Still more preferably 15% by weight or less, particularly preferably 10% by weight or less.

Specific examples of the water-absorbent 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, Saponified vinyl acetate-acrylic ester copolymer, hydrolyzed acrylonitrile copolymer or acrylamide copolymer or cross-linked products thereof, carboxyl group-containing cross-linked polyvinyl alcohol-modified product, cross-linked isobutylene-maleic anhydride copolymer, etc. Or one or more of these.

Among the above water-absorbing resins, one having a carboxyl group or a mixture thereof is preferable. Typically, a monomer component containing acrylic acid and / or a salt thereof (neutralized product) as a main component is used. Polymer obtained by polymerization and cross-linking (cross-linked water-swellable polyacrylic acid (salt))
It is. As the salt of acrylic acid, sodium salt,
Examples thereof include alkali metal salts such as potassium salts and lithium salts, ammonium salts, amine salts and the like. As such a water-absorbent resin, as constituent units, acrylic acid 0 mol% to 50 mol% and acrylate 100 mol%
To 50 mol% (the total amount of both is 100 mol%), preferably 10 mol% to 40 mol% of acrylic acid and 90 mol% to 60 mol% of acrylate (however, both Is more preferably 100 mol%). Further, the neutralization of the crosslinked polymer for forming the salt may be performed in a monomer state before polymerization, or may be performed in a polymer state during or after polymerization, or Although it may be used in combination, the neutralization in the polymer state has the advantage that the soluble component is reduced, but the neutralization requires a considerably long time,
From the viewpoint of production cost, it is preferable to neutralize the monomer before polymerization.

As a monomer component for obtaining a polymer which is a main component of the preferred water-absorbing resin, if necessary,
A monomer other than the acrylic acid (salt) may be contained. The monomer other than acrylic acid (salt) is not particularly limited, but specifically, for example, methacrylic acid, maleic acid, vinylsulfonic acid, styrenesulfonic acid, 2- (meth) acrylamide- Anionic unsaturated monomers such as 2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) Acrylamide, Nn-propyl (meth) acrylamide, N
-Isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate N, N-dimethylaminoethyl (meth) acrylate, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine, N-vinylacetamide and the like; , N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and cationic unsaturated monomers such as quaternary salts thereof. Body, and the like. These monomers may be used alone or as a mixture of two or more. In the case where a monomer other than the acrylic acid (salt) is used, the monomer other than the acrylic acid (salt) is preferably used with respect to the total amount of acrylic acid and its salt used as a main component. Is preferably at most 30 mol%, more preferably at most 10 mol%. By using a monomer other than the acrylic acid (salt) in this ratio,
The absorption properties of the finally obtained water absorbing agent are further improved, and at the same time, the water absorbing agent can be obtained at a lower cost.

When polymerizing the monomer component in order to obtain a polymer which is a main component of the preferred water-absorbing resin, bulk polymerization or precipitation polymerization can be performed.
From the viewpoint of performance and ease of polymerization control, and from the viewpoint of liquid permeability of the swollen gel, aqueous solution polymerization or reversed-phase suspension polymerization by using the monomer component as an aqueous solution is preferable, and aqueous solution polymerization is particularly preferable. When the monomer component is used as an aqueous solution, the concentration of all monomers in the aqueous solution (hereinafter, referred to as an aqueous monomer solution) is not particularly limited, but is 10% by weight to 70% by weight. In the range of 20% by weight to 60% by weight.
More preferably, it is in the range of weight%. In addition, when performing aqueous solution polymerization, a solvent other than water may be used in combination, if necessary, and the type of the solvent used in combination is not particularly limited.

As a method of aqueous solution polymerization, the aqueous monomer solution is polymerized while crushing the obtained hydrogel in a double-arm kneader, or the aqueous monomer solution is supplied in a predetermined container or on a driven belt. And a method of pulverizing a gel obtained by polymerization with a meat chopper or the like.

When the polymerization is started, for example, potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide,
It is possible to use a radical polymerization initiator such as 2,2'-azobis (2-amidinopropane) dihydrochloride or a photopolymerization initiator such as 2-hydroxy-2-methyl-1-phenyl-propan-1-one. it can. The amount of these polymerization initiators used is usually 0.001 to 2 mol%, preferably 0.01 to 2 mol%.
It is good to be 0.1 mol%. If the amount of the polymerization initiator is less than 0.001 mol%, unreacted monomers increase, and the amount of residual monomers in the obtained polymer is undesirably increased. On the other hand, the amount of the polymerization initiator used is 2 mol%.
If it exceeds, the amount of water-soluble components in the obtained polymer increases, which may not be preferable.

When the polymerization is initiated, a redox initiator may be used by further using a reducing agent which promotes the decomposition of the polymerization initiator and combining the two. Examples of the reducing agent include (bis) sulfurous acid (salt) such as sodium sulfite and sodium hydrogen sulfite;
-Ascorbic acid (salt), reducing metals (salts) such as ferrous salt, amines, etc., are not particularly limited.

When the polymerization is started, the polymerization reaction may be started by irradiating the reaction system with an active energy ray such as radiation, an electron beam, or an ultraviolet ray, or at the same time, the polymerization initiator is used in combination. You can also.

The reaction temperature in the polymerization reaction is as follows:
Although not particularly limited, a range of 15 to 130 ° C is preferable, and a range of 20 to 110 ° C is more preferable.
Also, the reaction time is not particularly limited, and may be appropriately set according to the type of the monomer component and the polymerization initiator, the reaction temperature, and the like.

The water-absorbing resin may be a self-crosslinking resin which does not use a crosslinking agent.
Those obtained by copolymerizing or reacting an internal crosslinking agent having two or more polymerizable unsaturated groups or two or more reactive groups are more preferable.

Specific examples of the internal crosslinking agent include, for example,
N, N'-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, glycerin tri (meth) acrylate, glycerin Acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly ) Ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, Serine, pentaerythritol, ethylene diamine, ethylene carbonate, propylene carbonate, polyethylene imine, glycidyl (meth)
Acrylate and the like can be mentioned. These internal crosslinking agents may be used alone, or two or more of them may be used as a mixture. The use amount of these internal crosslinking agents is preferably in the range of 0.005 to 2 mol%, and more preferably in the range of 0.02 to 0.5 mol%, based on the monomer component. More preferably, 0.04 to 0.2 mol%
It is more preferable to be within the range. If the amount of the internal cross-linking agent is less than 0.005 mol% or more than 2 mol%, sufficient absorption characteristics may not be obtained. When introducing a cross-linked structure into the polymer using the internal cross-linking agent, the internal cross-linking agent, before the polymerization of the monomer component, or during the polymerization, or after the polymerization, or after the neutralization, the reaction system What is necessary is just to add it. Also,
The internal cross-linking agent may be added to the reaction system all at once or in portions. When using at least one or two or more internal crosslinking agents, a compound having two or more polymerizable unsaturated groups is indispensable at the time of polymerization in consideration of the absorption characteristics of the water absorbing agent finally obtained. Is preferably used.

In the above polymerization, various foaming agents such as carbonic acid (hydrogen) salt, carbon dioxide, azo compound, and inert organic solvent; starch / cellulose; starch / cellulose derivatives; polyvinyl alcohol; A hydrophilic polymer such as a crosslinked product of acrylic acid (salt) and polyacrylic acid (salt); various surfactants; a chelating agent; a chain transfer agent such as hypophosphorous acid (salt);

When the water-absorbent resin is obtained by the above-mentioned aqueous solution polymerization and is in a gel state, that is, when it is a hydrogel cross-linked polymer, it is dried if necessary, before drying and / or
Or, it may be pulverized later to obtain the water-absorbing resin particles (A).

As the water-absorbent resin particles (A) in the present invention, an uncrosslinked water-soluble component in the water-absorbent resin is preferably 20% by weight or less, more preferably 15% by weight or less, further preferably 12% by weight. %, Particularly preferably 10% by weight or less.

The water content of the water-absorbent resin particles (A) in the present invention is not particularly limited, but is preferably 0.1% by weight.
Not less than 40% by weight, more preferably not less than 0.2% by weight and not more than 20% by weight, more preferably not less than 0.5% by weight and not more than 1% by weight.
The content is preferably 0% by weight or less, most preferably 7% by weight or less.

The shape of the water-absorbent resin particles (A) of the present invention is as follows:
It is not particularly limited, and may be, for example, any of a spherical shape, a scaly shape, and an irregular shape. The size of the water-absorbent resin particles (A) is usually 10 μm to 1500 μm, preferably 10 μm to 1500 μm, which is determined by reading the value obtained by classifying with a sieve and plotting on a log probability paper.
μm to 1000 μm, more preferably 50 μm to 800
μm, more preferably more than 75 μm and not more than 700 μm, particularly preferably more than 150 μm and not more than 600 μm.

Examples of the polyamine compound (B) include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, lysine, and polyethyleneimine.
Examples include polyallylamine, polyvinylamine, and polylysine. Further, a block copolymer of polyethyleneimine-polyethyleneglycol, a product obtained by reacting acrylic acid with some amino groups of polyethyleneimine, and the like can be mentioned. These may be used alone or in combination of two or more. These polyamine compounds include 1
Having a primary, secondary, or tertiary amino group;
Those having a secondary amino group are preferred.

The polyvalent amine compound (B) has a molecular weight of 6
0 to 200,000, preferably 600 to 1
More preferably, it is 00,000. When the molecular weight of the polyvalent amine compound (B) is less than 60, the reaction becomes uneven and the physical properties are hardly improved.
If it exceeds 0, it is not preferable because the handleability is poor. In the present invention, the amount of the polyvalent amine compound (B) used is preferably in the range of 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, based on the water-absorbent resin particles (A). Preferably, the range is 0.1 to 3% by weight.
When the amount of the polyvalent amine compound (B) is less than 0.01% by weight, the water absorbing properties such as the absorption capacity under pressure of the water absorbing agent are not improved. The water absorption capacity tends to decrease, and it is uneconomical.

The compound (C) having an olefinic double bond has an α, β-unsaturated group, preferably has an α, β-unsaturated conjugated group, and more preferably has an α, β-unsaturated conjugated group.
-A compound having an unsaturated carbonyl group is preferable because an addition reaction is likely to occur. The α, β-unsaturated carbonyl group is not particularly limited.
(Meth) acryloyl group, α, β-unsaturated amide group and the like. As such a compound having an α, β-unsaturated carbonyl group, a mono- or polyfunctional compound is used. Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, butyl acrylate, ethylene glycol Di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, dipropylene glycol di (meth)
Acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 2-hydroxy-1,3-dimethacryloxypropane, 2,2-bis [4- (methacryloxyethoxy) phenyl] propane, 1,3-butylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolpropane tri (meth) acrylate, Glycerin tri (meth) acrylate, glycerin acrylate methacrylate, tetramethylolmethanetetraacrylate, methylenebisacrylamide, (meth) acrylamide and the like can be mentioned.

In the present invention, the amount of the compound (C) having an olefinic double bond is preferably 0.05 to 10% by weight based on the water-absorbent resin particles (A). If the amount of the compound (C) is less than 0.05% by weight, the surface of the water-absorbent resin particles is not sufficiently crosslinked, so that the water absorption capacity under pressure is not improved. The water absorption capacity under pressure tends to decrease, and it is uneconomical.

In the present invention, the ratio between the polyamine compound (B) and the compound (C) is such that the polyamine compound (B) / compound (C) (weight ratio) = 100/1 to 1 /
It is preferably 50, more preferably 50/1 to 1.
The ratio is preferably 1/20, more preferably 20/1 to 1/10. If the ratio is outside the above range, sufficient crosslinking by the addition reaction cannot be obtained, and the physical properties may not be improved.

In the present invention, the polyhydric amine compound (B) and the compound (C) having an olefinic double bond are added to the water-absorbent resin particles (A), and the mixture is subjected to an addition reaction. And Michael addition reaction. In the addition reaction, a catalyst may be added to accelerate the reaction, or pressure may be applied.

Further, a coating film covering at least a part of the surface of the water-absorbent resin particles (A) is formed by the addition reaction, preferably the Michael addition reaction. At this time,
Although the addition reaction may occur uniformly inside the particles, it is preferable that the reaction occurs on or near the surface of the water-absorbent resin particles (A). In addition, specifically, the surface or the vicinity thereof is a portion where the depth (thickness) from the particle surface to the inside in the particle size of the water-absorbent resin particles (A) is preferably 以下 or less of the particle size. Yes,
More preferably 1/3 or less, further preferably 1/10
The following is the part. Further, the thickness of the coating film is determined by the compound (B) added to the water-absorbent resin particles (A),
It can be controlled by the addition amount and composition of (C) and the water content of the water-absorbent resin particles (A). For example, the addition amount of the polyamine compound (B) or the compound (C) having an olefinic double bond is reduced, and when water is added as described later, the water amount is reduced. The thickness of the coating film can be reduced by increasing the molecular weight of the divalent amine compound (B), reducing the water content of the water-absorbent resin particles (A), and the like.

In the present invention, an addition reaction, preferably a Michael addition reaction, is performed. However, since the progress of the Michael addition reaction between the polyamine compound (B) and the compound (C) is extremely fast, water absorption When mixing the polyvalent amine compound (B) and the compound (C) with the conductive resin particles (A), it is preferable to mix the three components as quickly as possible. As a method of mixing the water-absorbent resin particles (A), the polyvalent amine compound (B) and the compound (C), for example,
(B) and (C) are mixed, and the mixture is immediately sprayed or dropped on the water-absorbent resin particles (A).
Alternatively, there is a method of mixing the three at the same time so as to be quickly uniform, but the method is not limited thereto. The coating film formed by the addition reaction is a film made of an adduct of a polyamine compound (B) and a compound (C) having an olefinic double bond.

When the polyamine compound (B) and the compound (C) are mixed with the water-absorbent resin particles (A), water may be further added. At this time, the amount of water used varies depending on the type, particle size and water content of the water-absorbent resin particles (A). -10 parts by weight, preferably 0.1
It is preferred that the content be in the range of 3 to 3 parts by weight. If the amount of water used exceeds 10% by weight, the water absorption capacity may decrease, while if it is less than 0.05% by weight, the water absorption capacity under pressure may not be able to be improved. When water is used, the timing of its addition depends on the surface treatment agent (polyamine compound (B) and compound (C)).
Is dissolved in water, so that an aqueous solution thereof is added, or water is separately added simultaneously with the addition of the surface treatment agent, or water is separately added after the addition of the surface treatment agent,
Is preferred. When water is used, water-insoluble fine particle powder and a surfactant may be used together.

When mixing the polyvalent amine compound (B) and the compound (C) with the water-absorbent resin particles (A), a hydrophilic organic solvent may be further added. Examples of the hydrophilic organic solvent include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, t-butyl alcohol, and propylene glycol; ketones such as acetone; dioxane and alkoxy (poly) Ethers such as ethylene glycol and tetrahydrofuran; amides such as N, N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. When an organic solvent is added, the amount used depends on the type and particle size of the water-absorbent resin particles (A), but is usually 0 to 10 parts by weight, preferably 0 to 10 parts by weight, per 100 parts by weight of the water-absorbent resin particles (A). ~ 5 parts by weight, more preferably 0.1 ~
The range is preferably 5 parts by weight. When an organic solvent is used, the addition time is determined by dissolving the surface treating agent (polyamine compound (B) and compound (C)) in a mixture of water and an organic solvent, and adding the mixture. It is preferable that the organic solvent be separately added simultaneously with the addition of the surface treatment agent, or that an organic solvent be separately added after the addition of the surface treatment agent.

In the present invention, the polyamine compound (B) and the compound (C) are used as surface treatment agents. In addition to these, for example, ethylene glycol, 1,4 -Butanediol, 1,6-
Polyhydric alcohols such as hexanediol, propylene glycol and glycerin; alkylene carbonate compounds such as ethylene carbonate and propylene carbonate;
Conventionally used surface treatment agents such as polyvalent epoxy compounds such as (poly) ethylene glycol diglycidyl ether; polyvalent amine compounds such as ethylenediamine and polyethyleneimine; polyvalent metals such as aluminum sulfate and (poly) aluminum chloride; May be.

The device used for the mixing is preferably one capable of producing a large mixing force to ensure uniform mixing. For example, a cylindrical mixer, a double-walled conical mixer,
High-speed stirrer, V-shaped mixer, ribbon-type mixer, screw-type mixer, fluid-type furnace rotary disk-type mixer, air-flow-type mixer, double-arm kneader, internal mixer, pulverization-type kneader, rotation A type mixer, a screw type extruder and the like are preferable.

The processing time for the addition reaction of the water-absorbent resin particles (A) by mixing the polyvalent amine compound (B) with the compound (C) and, if necessary, water and / or an organic solvent is as follows: 1 minute to 180 minutes is preferable, 3 minutes to 120 minutes is more preferable, and 5 minutes to 100 minutes is further preferable. The treatment temperature at that time is preferably in the range of room temperature (normal temperature) to 180 ° C, more preferably in the range of room temperature (normal temperature) to 120 ° C.

The water-absorbing agent of the present invention obtained as described above has at least a part of the surface of the water-absorbing resin particles (A),
It is obtained by coating with a coating film comprising an adduct of a polyvalent amine compound (B) and a compound (C) having an olefinic double bond, preferably a Michael adduct.
In the present invention, it is sufficient that at least a part of the surface of the water-absorbent resin particles (A) is covered with the coating film. As described above, it is more preferable that the entire surface of the water-absorbent resin particles (A) is covered. Also,
In the present invention, the coating film is formed by, for example, an amidation reaction between an amino group remaining in the adduct and a carboxylic acid of the water-absorbent resin particles (A), an ionic bond, or the like. ) And partial bonding (crosslinking)
It does not matter.

The thickness of the coating film composed of an adduct of the polyamine compound (B) and the compound (C) is preferably 0.02 to 20% of the particle size of the water-absorbing resin particles. When the thickness of the coating film is less than 0.02%,
Water absorption properties such as water absorption under pressure are not improved, while 20%
When it exceeds, the water absorption capacity under no pressure tends to be extremely reduced. In order to set the thickness of the coating film in the above range, the amount of water in the surface treatment solution (mixed solution of the polyvalent amine compound (B) and the compound (C)) and the amount of water or a solvent such as a hydrophilic organic solvent are used. In the above range. Further, the weight average particle diameter of the water absorbing agent of the present invention covered with the coating film,
Preferably it is 150-600 micrometers, More preferably, it is 300-600 micrometers.

Since the water-absorbing agent of the present invention has a structure in which the water-absorbing resin particles are coated with a coating film, the water-absorbing agent is excellent in both the water absorption capacity under pressure and the water absorption capacity under no pressure. For example, the water-absorbing agent of the present invention has a water absorption capacity of 20 g / g or more under an applied pressure of 2.07 kPa, which is a pressurized amount in consideration of the weight of an infant in an absorbent article such as a diaper,
More preferably, it is 25 g / g or more.
The water absorption capacity under a pressure of 4.83 kPa is preferably 10 g / g or more, more preferably 17 g / g or more. The water absorption capacity under no pressure is preferably 25 g /
g or more, more preferably 30 g / g or more. Also,
The water-soluble content of the water-absorbing agent of the present invention is 40% by weight or less, preferably 25% by weight or less, more preferably 15% by weight or less,
More preferably, it is at most 10% by weight. The weight average particle size is in the above range.

In addition, the water-absorbing agent of the present invention does not require a material having strong skin irritation, such as a glycidyl compound.
It has high safety to skin and the like, and can be suitably used as a sanitary material.

[0046]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Various properties of the obtained water absorbing agent were measured by the following methods.

(Water absorption capacity under no pressure) 0.20 g of a water absorbing agent is uniformly placed in a nonwoven bag (60 mm × 60 mm).
It was immersed in 0.9% by weight physiological saline at 5 ° C. After 60 minutes, the bag is lifted and 250 × 9.81 using a centrifuge.
After draining for 3 minutes at m / sec ² (250G),
The weight W1 (g) of the bag was measured. The same operation was performed without using a water absorbing agent, and the weight W0 (g) at that time was measured. From these W1 and W0, the water absorption capacity under no pressure (g / g) was calculated according to the following equation.

Water absorption capacity under no pressure (g / g) = [(W1 (g) -W0 (g)) / weight of water absorbing agent (g)]-1 (water absorption capacity under pressure) Plastic support cylinder with inner diameter of 60 mm A 400-mesh stainless steel wire mesh (mesh size 38 μm) was fused to the bottom of
Is spread evenly, and 2.07 k
The piston and the load are adjusted so that a load of Pa or 4.83 kPa can be applied uniformly, the outer diameter is slightly smaller than 60 mm, no gap is formed on the wall surface with the supporting cylinder, and the vertical movement is not hindered. Are placed in this order,
The weight Wa (g) of this set of measuring devices was measured.

A diameter 9 mm is placed inside a 150 mm diameter petri dish.
Place a 0 mm glass filter and add 0.9 wt% saline to the same level as the glass filter. A filter paper having a diameter of 90 mm is placed thereon, so that the entire surface is wetted, and excess liquid is removed.

The above set of measuring devices is placed on the wet filter paper to absorb the liquid under load. One hour later, the set of measuring devices is lifted, and its weight Wb (g) is measured. And
From Wa and Wb, the water absorption capacity under pressure (g /
g) was calculated.

Water absorption capacity under pressure (g / g) = (Wb (g) −Wa (g)) / weight of water-absorbing agent ((0.9) g) Reference example 1-Content having two sigma-type blades In a reactor formed by attaching a 10-liter jacketed stainless-steel double-arm kneader with a lid, 5500 g of an aqueous solution of sodium acrylate having a neutralization ratio of 75 mol% (monomer concentration: 33% by weight) was mixed with polyethylene. To a reaction solution in which 4.99 g of glycol diacrylate (average number of repeating ethylene glycol units was 9) was dissolved, 2.5 g of sodium persulfate and L
When 0.05 g of ascorbic acid was added with stirring, polymerization started after about 1 minute. Then, polymerization was performed at 30 to 80 ° C. while pulverizing the generated gel, and the hydrogel crosslinked polymer (1) was taken out 60 minutes after the polymerization started.

The obtained hydrogel crosslinked polymer (1) was
The diameter was subdivided to about 5 mm or less. This finely divided hydrogel crosslinked polymer (1) was spread on a 50-mesh (mesh opening: 300 μm) wire mesh, dried with hot air at 150 ° C. for 90 minutes, and then dried. 1.0mm / 0.45mm /
(0.25 mm) to obtain a water-absorbent resin.
The obtained water-absorbent resin is passed through a JIS standard sieve (mesh opening 500
(μm, 300 μm) and classified to a particle size of 500 to 300 μm to obtain water-absorbent resin particles (1).

Reference Example 2 In a reaction vessel equipped with a stainless steel vat and a thermometer and a lid, 2,000 g of an aqueous solution of sodium acrylate having a neutralization ratio of 65 mol% (monomer concentration: 35% by weight) was mixed with polyethylene. To a reaction solution in which 1.97 g of glycol diacrylate (average repeating unit of ethylene glycol unit was 9) was dissolved, 3.24 g of a 5% by weight aqueous solution of sodium persulfate and 2.92 g of a 0.5% by weight aqueous solution of L-ascorbic acid were added.
5% by weight of 2,2'-azobis (2-amidinopropane)
3.24 g of an aqueous solution of dihydrochloride (trade name: V-50, manufactured by Wako Pure Chemical Industries, Ltd.), 3.3 aqueous solution of 0.35% by weight of hydrogen peroxide 3.3
4 g was added with stirring and the reaction solution was degassed with nitrogen, and polymerization started about 1 minute later. Then, the polymerization was carried out while cooling the lower surface of the reaction vessel to 10 ° C., and the exothermic peak temperature (82 ° C.) was reached 10 minutes after the polymerization started.
Then, after heating the lower surface of the reactor at 60 ° C. for 20 minutes,
The hydrogel crosslinked polymer (2) was taken out.

The obtained hydrogel crosslinked polymer (2) was pulverized with a meat chopper (Hiraga Seisakusho Co., Ltd., two blades, die diameter: 9.5 mm) so that the gel diameter became about 5 mm or less. The pulverized hydrogel crosslinked polymer (2) is spread on a 50-mesh (mesh opening: 300 μm) wire mesh and dried with hot air at 170 ° C. for 40 minutes. (Miyako Bussan) to obtain a water-absorbent resin. The obtained water absorbent resin is JIS
The mixture was sieved with a standard sieve (500 μm or 300 μm), and classified to a particle size of 500 to 300 μm to obtain water-absorbent resin particles (2).

Reference Example 3 In a reaction vessel equipped with a stainless steel vat and a thermometer and a lid, 2,000 g of an aqueous solution of sodium acrylate having a neutralization ratio of 70 mol% (monomer concentration: 39% by weight) was mixed with polyethylene. In a reaction solution in which 4.33 g of glycol diacrylate (average repeating unit of ethylene glycol unit was 9) was dissolved, 5.33 g of a 20% by weight aqueous sodium persulfate solution and 3.20 g of a 0.5% by weight aqueous L-ascorbic acid solution were added.
Was added with stirring, and the reaction solution was degassed with nitrogen.
After about 4 minutes, polymerization started. Then, the polymerization was carried out while cooling the lower surface of the reaction vessel to 15 ° C., and the peak temperature of the heat generation (93 ° C.) was reached 16 minutes after the polymerization started. Thereafter, the lower surface of the reactor was heated at 80 ° C. for 20 minutes, and then the hydrogel crosslinked polymer (3) was taken out.

The obtained hydrogel crosslinked polymer (3) was pulverized with a meat chopper (Hiraga Seisakusho Co., Ltd., 2 blades, die diameter 16 mm) so that the gel diameter was about 5 mm or less. This ground hydrogel crosslinked polymer (3)
Spread on a 50 mesh (mesh size 300 μm) wire mesh,
After drying with hot air at 170 ° C. for 40 minutes, the dried product is pulverized with a desktop dual-purpose pulverizer FDS type (manufactured by Miyako Bussan Co., Ltd.),
A water-absorbing resin was obtained. The obtained water-absorbent resin is sieved with a JIS standard sieve (850 μm, 150 μm), 85
The particles were classified into particle sizes of 0 to 150 μm, and the weight average particle size (D
₅₀ ) to obtain water-absorbent resin particles (3) having a size of 450 μm.

Example 1 Polyethyleneimine (trade name “Epomin S” manufactured by Nippon Shokubai)
P-006 ": molecular weight 600:" SP-00 "in the table
6 ". ) 0.5 part by weight and polyethylene glycol diacrylate (an average repeating unit of ethylene glycol unit is 9: abbreviated as "PEGDA" in the table) 2.6
Immediately after mixing with 100 parts by weight, 100 parts by weight of the water-absorbent resin particles (1) obtained in Reference Example 1 were added. further,
2.0 parts by weight of water was added and mixed to obtain a water absorbing agent (1).
Table 1 shows the water absorption capacity under no pressure and the water absorption capacity under pressure of the obtained water absorbing agent (1).

Example 2 Polyethyleneimine (trade name "Epomin S" manufactured by Nippon Shokubai)
P-200 ": molecular weight 10,000: In the table," SP-
200 ". ), And 6.0 parts by weight of a 50% by weight aqueous solution of methyl acrylate (abbreviated as “MA” in the table).
Immediately after mixing with a mixture of 0.27 parts by weight and 2.0 parts by weight of isopropyl alcohol, 100 parts by weight of the water-absorbent resin particles (1) obtained in Reference Example 1 were added and mixed.
Heat for 1 hour in a hot-air dryer at 80 ° C to absorb water (2)
I got Table 1 shows the water absorption capacity under no pressure and the water absorption capacity under pressure of the obtained water absorbing agent (2).

Example 3 Polyethyleneimine (trade name "Epomin S" manufactured by Nippon Shokubai)
P-006 ": molecular weight 600:" SP-00 "in the table
6 ". ) 0.5 part by weight and polyethylene glycol diacrylate (an average repeating unit of ethylene glycol unit is 9: abbreviated as "PEGDA" in the table) 2.6
Immediately after mixing with 100 parts by weight, 100 parts by weight of the water absorbent resin particles (2) obtained in Reference Example 2 were added. further,
2.0 parts by weight of water was added and mixed to obtain a water absorbing agent (3).
Table 1 shows the water absorption capacity under no pressure and the water absorption capacity under pressure of the obtained water absorbing agent (3).

Example 4 Polyethyleneimine (trade name “Epomin S” manufactured by Nippon Shokubai)
P-006 ": molecular weight 600:" SP-00 "in the table
6 ". ) 0.5 part by weight and polyethylene glycol diacrylate (an average repeating unit of ethylene glycol unit is 9: abbreviated as "PEGDA" in the table) 2.6
Immediately after mixing with 100 parts by weight, 100 parts by weight of the water-absorbent resin particles (3) obtained in Reference Example 3 were added. further,
2.0 parts by weight of water was added and mixed to obtain a water absorbing agent (4).
Table 1 shows the water absorption capacity under no pressure and the water absorption capacity under pressure of the obtained water absorbing agent (4).

Comparative Example 1 Using the water-absorbent resin particles (1) obtained in Reference Example 1 as a comparative water-absorbing agent (1), the water absorption capacity under no pressure and the water absorption capacity under pressure were measured. Table 1 shows the results.

Comparative Example 2 Polyethyleneimine (trade name “Epomin S” manufactured by Nippon Shokubai)
P-006 ": molecular weight 600:" SP-00 "in the table
6 ". 100 parts by weight of the water-absorbent resin particles (1) obtained in Reference Example 1 were added to 0.5 part by weight, and 2.0 parts by weight of water were further added and mixed to obtain a comparative water-absorbing agent (2).
I got Table 1 shows the water absorption capacity under no pressure and the water absorption capacity under pressure of the obtained comparative water-absorbing agent (2).

Comparative Example 3 Polyethylene glycol diacrylate (average repeating unit of ethylene glycol unit is 9: in the table, "PEGD
A ". ) To 2.6 parts by weight, 100 parts by weight of the water-absorbent resin particles (1) obtained in Reference Example 1 were added and mixed, and 2.0 parts by weight of water were further added and mixed to obtain a comparative water-absorbing agent (3)
I got Table 1 shows the water absorption capacity under no pressure and the water absorption capacity under pressure of the obtained comparative water-absorbing agent (3).

Comparative Example 4 The water-absorbent resin particles (1) 12 obtained in Reference Example 1 were placed in a 1 L four-necked flask equipped with a stirrer, a condenser, and a dropping funnel.
5 g, 400 ml of cyclohexane, and 0.625 g of ethylcellulose (trade name “ethylcellulose N-100” manufactured by Hercules) were heated to 75 to 80 ° C., 37.5 g of ion-exchanged water was added, and the mixture was refluxed for 30 minutes. And stirred. Then, polyethyleneimine (trade name "Epomin SP-006" manufactured by Nippon Shokubai): molecular weight 60
0: Abbreviated as "SP-006" in the table. ) A solution prepared by dissolving 0.25 g in 5 g of water was added, and the mixture was stirred at 75 to 80 ° C for 15 minutes. Next, as a crosslinking agent, polyglycerol polyglycidyl ether (manufactured by Nagase Kasei Kogyo Co., Ltd., trade name "Denacol EX-512"): In the table, "EX-5"
12 ". ) A solution prepared by dissolving 0.102 g in 4 g of water was added, and the mixture was stirred at 75 to 80 ° C for 1 hour under reflux. The generated gel was separated and dried under reduced pressure to obtain a comparative water absorbing agent (4). Table 1 shows the water absorption capacity under no pressure and the water absorption capacity under pressure of the obtained comparative water-absorbing agent (4).

Comparative Example 5 Water-absorbent resin particles (4) sufficiently dried under reduced pressure in a 1 L four-necked flask equipped with a stirrer, a condenser, and a dropping funnel
(Nippon Shokubai, product name "AQUALIC CA-W4") 1
25 g, 400 ml of cyclohexane, and 0.625 g of ethyl cellulose (trade name “ethyl cellulose N-100” manufactured by Hercules, Inc.) were charged at 75 to 80 ° C.
Then, 37.5 g of ion-exchanged water was added, and the mixture was stirred under reflux for 30 minutes. Then, polyethyleneimine (trade name "Epomin SP-006" manufactured by Nippon Shokubai): molecular weight 6
00: Abbreviated as "SP-006" in the table. ) 0.25g
Was dissolved in 5 g of water, and added at 75 to 80 ° C. for 15 minutes.
Stirred for minutes. Next, as a crosslinking agent, polyglycerol polyglycidyl ether (manufactured by Nagase Kasei Kogyo Co., Ltd.)
Product name “Denacol EX-512”: “EX-
512 ". ) A solution prepared by dissolving 0.102 g in 4 g of water was added, and the mixture was stirred at 75 to 80 ° C for 1 hour under reflux.
The generated gel was separated and dried under reduced pressure to obtain a comparative water absorbing agent (5). Table 1 shows the water absorption capacity under no pressure and the water absorption capacity under pressure of the obtained comparative water-absorbing agent (5).

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[Table 1]

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According to the present invention, it is possible to provide a water-absorbing agent which is excellent in hygroscopicity under pressurized and non-pressurized conditions, has high safety to skin and the like, and is suitable for sanitary materials, and a method for producing the same. .

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) A61F 13/53 C08L 29:04 Z B01J 20/26 33:00 20/30 A61F 13/18 307B // C08L 29:04 A41B 13/02 D 33:00 F term (reference) 3B029 BA18 4C003 AA24 GA02 4C098 AA09 CC03 DD05 DD06 DD13 DD24 DD25 DD26 DD27 DD28 DD30 4F070 AA03 AA26 AA29 AA32 AA33 AA35 AA37 AB08 AC83 AC84 CB05 DC03 DC17 AB AC27D AE06B BA09 BA38 CA43 DA12 DA13 EA05 FA07 FA37

Claims (4)

[Claims] At least a part of the surface of the water-absorbent resin particles (A) is covered with a coating film comprising an adduct of a polyvalent amine compound (B) and a compound (C) having an olefinic double bond. A water absorbing agent. 2. The water-absorbing agent according to claim 1, wherein the compound (C) having an olefinic double bond is a compound having an α, β-unsaturated conjugated group. 3. The water absorption capacity under pressure of 2.07 kPa is 20 g /
The water-absorbing agent according to claim 1, which is not less than g. 4. A method for producing a water-absorbing agent, comprising adding a polyamine compound (B) and a compound (C) having an olefinic double bond to a water-absorbent resin particle (A), followed by an addition reaction.