JP2003105092A - Water-absorbing agent and its manufacturing method, and hygienic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-absorbing agent excellent in the amounts of absorption per unit absorbent magnification under non-pressure, and under pressure and a balance of flow inductivity of a physiological salt solution as well as a method for manufacturing the water-absorbing agent for a short time, having a small deflection value of the flow inductivity of the physiological salt solution in every lot when manufacturing or in each lot and having a stable physical property. SOLUTION: One of manufacturing methods of the water-absorbing agent comprises: mixing (a) a water-absorbable resin powder containing an acidic group with (b1) a non-crosslinking water-soluble inorganic base and/or (b2) a pH buffer of a non-reductive alkali metal salt and (c1) a dehydrating reactive crosslinking agent which may be reactive with the acidic group; and a crosslinking treatment of (a) the water-absorbable resin powder.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water absorbing agent and a method for producing the same. More specifically, the present invention is a water-absorbing agent obtained by modifying a water-absorbent resin with a crosslinking agent, wherein the water-absorbing agent exhibits a high absorption capacity under no pressure or under pressure, and a higher physiological saline flow conductivity. Agent and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, sanitary materials such as disposable diapers, sanitary napkins and so-called incontinence pads have been used as constituent materials thereof.
BACKGROUND ART Water-absorbent resins (water-absorbing agents) for the purpose of absorbing body fluids are widely used. Examples of the water absorbent resin include crosslinked polyacrylic acid partially neutralized products and starch-
Hydrolyzate of acrylic acid graft polymer, vinyl acetate-
Known are saponified acrylic ester copolymers, hydrolyzed products of acrylonitrile copolymers or acrylamide copolymers or crosslinked products thereof, and crosslinked polymers of cationic monomers.

The properties which the above-mentioned water-absorbent resin should have are conventionally a superior amount of absorbed liquid, a water-absorption rate, a gel strength, a gel permeability, and a substrate containing an aqueous liquid when contacted with an aqueous liquid such as a body fluid. The suction power to suck up water from the water is being advocated.
And conventionally, having a plurality of these characteristics, when used in sanitary materials such as disposable diapers and sanitary napkins,
Various water-absorbent resins (water-absorbing agents) exhibiting excellent performance (absorption characteristics) have been proposed. For example, as a method for improving a well-balanced absorption characteristics such as absorption capacity without load and absorption capacity under load of a water absorbent resin, a technique of crosslinking the vicinity of the surface of the water absorbent resin is known, and various methods have been known so far. Is disclosed.

As an example thereof, a method using a polyhydric alcohol (JP-A-58-180233 and JP-A-61-1)
6903), polyhydric glycidyl compounds, polyhydric aziridine compounds, polyhydric amine compounds, polyhydric isocyanate compounds (JP-A-59-189103), and glyoxal (JP-A-52-11).
7393), a method using a polyvalent metal (JP-A-51)
-136588, JP-A-61-257235, JP-A-62-7745), a method using a silane coupling agent (JP-A-61-211305,
JP-A 61-252212, JP-A 61-264
006), a method using alkylene carbonate (German Patent No. 4020780), and a method using polyvalent heterocyclic carbonate (JP-A-11-31521).
6), a method using oxazolidinone (WO99 / 42)
494), a method using a polyvalent oxazolidinone (WO99 / 43720), a method using oxazine (WO00 / 31153), a method using an oxazoline compound (JP2000-197818A) and the like are known. There is.

Further, there is also known a method of using additives (inert mixing aid, acid catalyst, base) for further improving the performance when improving the absorption characteristics by the above crosslinking agent. That is, as a method (1) using an inert mixing aid as an additive, a method in which an inert inorganic powder is present (Japanese Patent Laid-Open Nos. 60-163956 and 60-2558).
14), a method in which water containing a salt and / or hydroxide of a polyvalent metal is present (JP-A-62-7745), and a method in which a dihydric alcohol is present (JP-A 1-2).
92004), a method in which water and an ether compound are present (JP-A-2-153903), a method in which a water-soluble polymer is present (JP-A-3-126730), an alkylene oxide adduct of a monohydric alcohol,
Method of allowing monovalent salt of organic acid or lactam to be present (Japanese Patent Publication No. 6-74331, JP-A-7-33818).
Japanese Laid-Open Patent Publication No. 2004-242242, and a method for allowing a monovalent metal salt to exist (WO98 / 4).
9221), a method of allowing a cation to exist (WO0
0/53664 and WO00 / 53644) are known.

Further, as a method (2) using an acid catalyst as an additive, a method in which phosphoric acid is present (WO94 / 1)
5651), a method of allowing an inorganic acid or an organic acid to exist (JP-A-7-278225), and the like. In addition, as a method (3) using a base as an additive, a method in which a water-soluble alkali compound is present (Japanese Patent Laid-Open No. 6-58242)
-298841) and the like are also known. These (1),
The presence of the additive used in the methods (2) and (3) together with the cross-linking agent can improve the balance of the absorption characteristics of the water-absorbing agent to some extent as compared with the case of using the cross-linking agent alone, but it is still sufficient. It was hard to say.

That is, in the case of the additive (inert mixing aid) used in the method (1), when the water-absorbent resin used contains a large amount of fine powder, it acts as a mixing aid. Although the effect appears, on the other hand, the presence of the cross-linking agent shows almost no improvement in the absorption property due to excessive reduction of the permeability of the cross-linking agent into the water-absorbent resin powder or inhibition of the cross-linking reaction. There was also a problem that the amount of used was increased, the reaction time was prolonged, and the reaction temperature had to be raised. With the additive (acid catalyst) used in the method of (2), the effect as a catalyst for promoting the reaction of the crosslinking agent can be expected, but if an amount for obtaining a certain effect is added, the pH of the crosslinking agent solution becomes In the case of an extreme decrease and in the case of a partially neutralized water-absorbing resin containing an acid group, surface acidification particularly occurs and it becomes difficult to control the permeability of the crosslinking agent. Further, acidification of the surface is not preferable because it tends to increase the adhesiveness between particles of the water absorbent resin and lead to the formation of aggregates. As a result, there is a problem in that a desired crosslinking density of the surface layer of the water absorbent resin particles cannot be obtained and it is difficult to obtain a material having satisfactory performance.

In the method (3), a compound (polyvalent metal salt, polyepoxy compound, polyaziridinyl compound, polyisocyanate compound) having two or more functional groups capable of easily reacting with an additive (base) and a carboxyl group is used. The surface cross-linking by the combination of the above is disclosed to improve the gel strength and the absorption capacity under load at a relatively low load (20 g / cm ² ). However, the method of JP-A-6-298841 is still insufficient for improving the mixing property of the surface cross-linking agent and the physical properties of the water-absorbent resin.
It was difficult to improve the absorbency against pressure (AAP) under a high load (4.83 kPa, about 50 g / cm ² ) (all will be described later).

Further, as a typical water-absorbent resin, an acrylic acid-based water-absorbent resin composed of a partially neutralized salt of acrylic acid is mentioned from the viewpoint of its high physical properties and cost. As a method for producing such an acrylic acid-based water-absorbent resin, a method of polymerizing acrylic acid and its salt neutralized in advance to a predetermined neutralization rate (hereinafter, referred to as neutralization polymerization method) and unneutralized to low Two methods are generally performed: a method of polymerizing neutralizing acrylic acid and then post-neutralizing the polymer gel (hereinafter referred to as an acid-type polymerization method). Compared to the neutralization polymerization method, the latter acid-type polymerization method tends to give a water-absorbing resin with a low absorption content at a high absorption capacity, but it uniformly neutralizes the hydrogel crosslinked polymer after polymerization. This requires a long time and is technically very difficult, and the neutralization ratio of the individual particles of the water-absorbent resin powder obtained may be non-uniform. In such a case, although the water-absorbent resin of the acid polymerization method has a high absorption capacity and a low soluble content, sufficient performance of the water-absorbing agent cannot be obtained even if the surface cross-linking treatment is performed. -10173 (European Patent Publication 08)
82502A1).

That is, conventionally, in the case of surface-crosslinking a water-absorbent resin, the required surface-crosslinking treatment differs depending on the difference in neutralization rate. If the desired performance of the water absorbing agent is not obtained,
In particular, when the neutralization ratio of individual particles of the water-absorbent resin powder is mixed in various ways, the desired performance of the water-absorbing agent may not be obtained. As described above, the surface cross-linking treatment cannot be uniformly performed by the conventional techniques, and as a result, various physical properties of the resulting water absorbent resin (CRC, A
The balance of AP, SFC, etc., especially SFC) became poor, and the SFC varied. For this reason,
For example, lot variations in the performance of diapers and large differences in performance among a single diaper have occurred.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above conventional problems. That is, the subject of the present invention, during the cross-linking treatment, does not inhibit the cross-linking reaction while showing the effect as a mixing aid, in some cases also has the effect as a reaction catalyst, and partially neutralized and polymerized water-absorbing resin. Another object of the present invention is to provide a method for producing a water-absorbing agent that can exhibit uniform surface cross-linking, regardless of the difference in the neutralization ratio and the uniformity of the neutralization ratio resulting from the post-neutralization operation of acid-type polymerization.
Furthermore, the object of the present invention is not only excellent absorption balance without load, absorption capacity under load, excellent balance of physiological saline flow inducibility, but also for each lot at the time of production, or the value of physiological saline flow inductivity in each lot. Another object of the present invention is to provide a method and a water absorbing agent for producing a water absorbing agent having small physical fluctuations (variation) and having stable physical properties in a short time.

[0012]

Means for Solving the Problems The inventors of the present invention have made earnest studies on a water absorbing agent having excellent absorption characteristics, and as a result, the above problems can be solved by using a specific additive together with a specific cross-linking agent of a water absorbent resin. The present invention has been completed and the present invention has been completed. That is, the water absorbing agent according to the present invention is a particulate water absorbing agent whose main component is a water absorbing resin having a crosslinked structure obtained by polymerizing an unsaturated monomer component, and the particulate water absorbing agent is particles. Particles having a diameter of less than 850 μm and 150 μm or more containing 90% by weight or more of all particles, and having a particle diameter of less than 850 μm and 600 μm or more (A1), a particle diameter of 600 μm
Below 500 μm (A2), particle size is 500
Particles (A3) smaller than 300 μm and smaller than 300 μm, particle size 3
The present invention relates to a water-absorbing agent, which contains at least two kinds selected from particles (A4) having a particle size of less than 00 μm and a size of 150 μm or more, and further satisfying the following physical properties.

No pressure on 0.90 wt% saline
Under 30 minutes absorption capacity (CRC) of 31 g / g or more.
6 at 4.83 kPa against 0.90 wt% saline
The absorbency against pressure (AAP) at 0 minutes is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20
(Unit: 10^-7× cm ³× s × g^-1)that's all. The following formula
The SFC change index defined in (1) is 0 to 25%.   SFC change index (%) = [(standard deviation of SFC of particles A1 to A4) / (particles SFC of whole water absorbent)] × 100 (1) Further, another water absorbing agent according to the present invention comprises an unsaturated monomer component.
Main component is a water-absorbent resin having a cross-linked structure obtained by polymerization
And a particulate water absorbing agent, wherein the particulate water absorbing agent is a particle
All particles with a diameter of less than 850 μm and 150 μm or more
90% by weight or more and the particle size is less than 850 μm
Particle size of 600 μm or more (A1), particle size of 600 μm
Below 500 μm (A2), particle size is 500
Particles (A3) smaller than 300 μm and smaller than 300 μm, particle size 3
Select from particles (A4) of less than 00 μm and 150 μm or more
It contains at least two or more of the
The present invention relates to a water absorbing agent characterized by being added.

No pressure on 0.90% by weight saline
Under 30 minutes absorption capacity (CRC) of 31 g / g or more.
6 at 4.83 kPa against 0.90 wt% saline
The absorbency against pressure (AAP) at 0 minutes is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20
(Unit: 10^-7× cm ³× s × g^-1)that's all. The following formula
The SFC variation coefficient defined in (2) is 0 to 0.25.   SFC coefficient of variation = (standard deviation of SFC of particles A1 to A4) / (from particles A1 A4 SFC average) (2) Furthermore, another water absorbing agent according to the present invention is an unsaturated monomer composition.
Mainly water-absorbing resin having a cross-linked structure obtained by polymerizing
A particulate water absorbing agent as a component, wherein the particulate water absorbing agent
Are particles with a particle size of less than 850 μm and 150 μm or more.
Includes 90% by weight or more of all particles and has a particle size of 850μ
Particles (A1) having a particle size of less than 600 m and 600 μm or more, and a particle diameter of 60
Particles (A2) having a particle size of less than 0 μm and 500 μm or more, and a particle size of
Particles less than 500 μm and 300 μm or more (A3), particles
Particles with a diameter of less than 300 μm and 150 μm or more (A4)
At least two or more selected from the following, and further
A continuously produced water-absorbing agent characterized by satisfying
Concerned.

No pressure on 0.90 wt% saline
Under 30 minutes absorption capacity (CRC) of 31 g / g or more.
6 at 4.83 kPa against 0.90 wt% saline
The absorbency against pressure (AAP) at 0 minutes is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20
(Unit: 10^-7× cm ³× s × g^-1)that's all. The following formula
The continuous production system SFC standard deviation specified in (4) is 5.0
Less than.   SFC standard deviation of continuous production system = standard deviation of SFC of each lot (4) (However, CRC, AAP, and SFC are Lot averages.
Each Lot is 20 kg or more. Lot number is 10 or more. ) Furthermore, another water absorbing agent according to the present invention is an acid group-containing monomer.
Obtained by polymerizing the monomer containing (salt) and further neutralizing
A particulate water-absorbing agent obtained by surface-crosslinking a water-absorbing resin,
The neutralization index of the particulate water absorbing agent or water absorbing resin is 15 or more.
And with 0.90% by weight physiological saline solution after surface crosslinking.
Absorption capacity under pressure (AA) for 60 minutes at 4.83 kPa
P) is 20 (g / g) or more.

Further, in the method for producing a water-absorbing agent according to the present invention, the water-absorbent resin powder (a) containing an acid group is added to the non-crosslinkable water-soluble inorganic base (b1) and / or the non-reducing alkali metal salt. A pH buffering agent (b2) and a dehydration-reactive crosslinking agent (c1) capable of reacting with the acid group are mixed, and the water-absorbent resin powder (a) is subjected to a crosslinking treatment. Furthermore, another method for producing a water-absorbing agent according to the present invention is that it contains an acid group and has a weight average particle size of 300 to 600 μm and a particle size of 150 μm.
Water-absorbent resin powder (a
1) A non-crosslinkable water-soluble inorganic base (b1) and / or a non-reducing alkali metal salt pH buffer (b2), and a crosslinking agent (c) capable of reacting with the acid group are mixed, The water absorbent resin powder (a1) is subjected to a crosslinking treatment.

Further, the sanitary material of the present invention contains the water absorbing agent of the present invention.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. In the following description, the water-absorbing agent in the present invention is a water-absorbing resin having a crosslinked structure (hereinafter, simply referred to as water-absorbing resin) as a main component (preferably 50 to 100% by weight, more preferably 8).
The water-absorbent resin is further modified with a crosslinking agent (preferably surface-modified, especially surface-crosslinked), and is referred to as a water-absorbing agent. (Method for producing water-absorbent resin) In the present invention, the acid group-containing water-absorbent resin powder is hereinafter referred to as water-absorbent resin powder (a),
Among the water-absorbent resin powders (a), those whose particle size is further controlled, for example, a weight average particle diameter of 300 to 600 μm
A fine powder having a particle size of m of 150 μm or less and 10% by weight or less is referred to as a water absorbent resin powder (a1).

The water-absorbent resin of the present invention is a conventionally known water-absorbent resin, for example, in ion-exchanged water, it is essentially 5 times or more, preferably 50 to 1000 times, its own weight. Absorbs water, anionic,
It is a conventionally known cross-linked polymer which forms a nonionic or cationic water-insoluble hydrogel. These are generally particulate water-absorbing agents whose main component is a water-absorbing resin having a crosslinked structure obtained by polymerizing an unsaturated monomer component (preferably an acid group-containing unsaturated monomer). That is, it is obtained by polymerizing in a state of a monomer solution, optionally drying the polymer, and usually pulverizing before and / or after drying. As such a water-absorbent resin, a polyacrylic acid partially neutralized polymer, a hydrolyzate of a starch-acrylonitrile graft polymer, a starch-acrylic acid graft polymer, a saponified product of a vinyl acetate-acrylic acid ester copolymer. , Acrylonitrile copolymer or acrylamide copolymer hydrolyzate, or crosslinked products thereof, carboxyl group-containing crosslinked polyvinyl alcohol modified product, crosslinked isobutylene-maleic anhydride copolymer, etc. it can.

These water-absorbent resins may be used alone or as a mixture. Among them, acid-group-containing water-absorbent resins, and further, carboxyl-group-containing water-absorbent resins which are carboxylic acids or salts thereof, or their mixtures. A mixture is preferable, typically a polymer obtained by polymerizing and crosslinking a monomer having acrylic acid and / or its salt (neutralized product) as a main component, that is, a polyacrylic containing a graft component if necessary. The acid salt cross-linked polymer is the main component. Further, it is essential that the water absorbent resin is water-swellable and water-insoluble, and the uncrosslinked water-soluble component (water-soluble polymer) in the water absorbent resin is preferably 50% by weight or less, It is preferably 25% by weight or less, more preferably 20% by weight or less, even more preferably 15% by weight or less, particularly preferably 10% by weight or less.

Examples of the acrylic acid salt include alkali metal salts of acrylic acid such as sodium, potassium and lithium,
Examples thereof include ammonium salts and amine salts. The water-absorbent resin has 0 to 50 mol% acrylic acid and 100 to 50 mol% acrylate as its constituent units.
(However, the total amount of both is 100 mol% or less) is preferable, and acrylic acid is 10 to 40 mol%.
And those having an acrylic acid salt in the range of 90 to 60 mol% (however, the total amount of both is 100 mol% or less) are more preferable. The molar ratio of this acid and salt is called the neutralization rate. Neutralization of the water absorbent resin for forming the salt may be carried out in a monomer state before the polymerization, or may be carried out in the polymer state during the polymerization or after the polymerization, or they may be used in combination. May be.

In general, when the unneutralized or low-neutralized monomer is polymerized and neutralized in a polymer state (acid type polymerization method), a water-absorbent resin having a high absorption capacity and a low solubility is used. Although it tends to be obtained, a considerable amount of labor, equipment and time are required to uniformly neutralize the individual particles of the water absorbent resin (JP-A-10-1017).
No. 3). However, by using the method of the present invention, regardless of the neutralization state of the water-absorbent resin or the production method, all the water-absorbent resin can be satisfactorily used for surface cross-linking and the like. It is possible to greatly improve the physical properties and productivity. The monomer for obtaining the water absorbent resin used in the present invention may contain a monomer other than the above acrylic acid (salt), if necessary. The monomer other than acrylic acid (salt) is not particularly limited, and 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, methoxy polyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinyl pyridine, N-vinyl pyrrolidone, N-acryloyl piperidine, N-acryloyl pyrrolidine, N-vinyl acetamide Hydrophilic group-containing unsaturated monomer; N,
N-dimethylaminoethyl (meth) acrylate, N,
N-diethylaminoethyl (meth) acrylate, N,
N-dimethylaminopropyl (meth) acrylate,
Examples include N, N-dimethylaminopropyl (meth) acrylamide, and cationic unsaturated monomers such as quaternary salts thereof. These monomers may be used alone,
Two or more kinds may be appropriately mixed and used.

In the present invention, when a monomer other than acrylic acid (salt) is used, the amount of the monomer other than acrylic acid (salt) is the total amount of acrylic acid and its salt used as the main components. On the other hand, the proportion is preferably 30 mol% or less, more preferably 10 mol% or less. By using the monomers other than the acrylic acid (salt) in the above ratio,
The absorption characteristics of the finally obtained water-absorbent resin (water-absorbing agent) are further improved, and the water-absorbent resin (water-absorbing agent) can be obtained at a lower cost. When polymerizing the above monomers to obtain the water absorbent resin used in the present invention,
It is possible to perform bulk polymerization or precipitation polymerization, but from the viewpoints of performance, ease of control of polymerization, and absorption characteristics of swollen gel, aqueous polymerization or reverse phase suspension by using the above monomer as an aqueous solution. It is preferable to carry out turbid polymerization. When the above monomer is used as an aqueous solution, the concentration of the monomer in the aqueous solution (hereinafter referred to as “monomer aqueous solution”) depends on the temperature of the aqueous solution and the monomer and is not particularly limited. But 1
It is preferably in the range of 0 to 70% by weight, and 20 to 60% by weight.
Is more preferable. Moreover, when performing the aqueous solution polymerization, a solvent other than water may be used in combination as necessary, and the type of the solvent used in combination is not particularly limited.

The aqueous solution is polymerized by crushing the resulting hydrogel in a dual-arm kneader, or by supplying the monomer aqueous solution into a predetermined container or a driving belt. The method of pulverizing the gel obtained by polymerization with a meat chopper or the like can be mentioned. When initiating the above polymerization, for example, potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, etc. Radical polymerization initiator or 2
-Hydroxy-2-methyl-1-phenyl-propane-
A photopolymerization initiator such as 1-one can be used.

Further, a reducing agent that accelerates the decomposition of these polymerization initiators may be used in combination, and a combination of both may be used as a redox type initiator. Examples of the reducing agent include (bis) sulfite (salt) such as sodium sulfite and sodium bisulfite, L-ascorbic acid (salt), reducing metal (salt) such as ferrous salt, amines and the like. However, it is not particularly limited. The amount of these polymerization initiators used is usually 0.001 to 2 mol%, preferably 0.01 to 0.1 mol%. If the amount of these polymerization initiators used is less than 0.001 mol%, the amount of unreacted monomers increases, and therefore the amount of residual monomers in the resulting water absorbent resin or water absorbent increases. Not preferable. On the other hand, if the amount of these polymerization initiators used exceeds 2 mol%, the amount of water-soluble components in the resulting water-absorbent resin or water-absorbing agent increases, which is not preferable in some cases.

The polymerization reaction may be initiated by irradiating the reaction system with active energy rays such as radiation, electron beams, and ultraviolet rays, or the above polymerization initiator may be used in combination. The reaction temperature in the above polymerization reaction is not particularly limited, but is preferably in the range of 15 to 130 ° C, more preferably in the range of 20 to 120 ° C. Further, the reaction time and the polymerization pressure are not particularly limited, and may be appropriately set depending on the types of the monomer and the polymerization initiator, the reaction temperature and the like. The water-absorbent resin may be a self-crosslinking resin that does not use a crosslinking agent, but a crosslinker having two or more polymerizable unsaturated groups or two or more reactive groups in one molecule. Those obtained by copolymerizing or reacting an agent (internal cross-linking agent of water absorbent resin) are more preferable.

Specific examples of these internal crosslinking agents 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, triallyl amine, poly (meth) allyloxy alkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol,
Propylene glycol, glycerin, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, glycidyl (meth) acrylate, and the like may be used alone or in combination of two or more as appropriate. You may use it. Further, these internal cross-linking agents may be added to the reaction system all at once or may be added in portions. In the case of using at least one kind or two or more kinds of internal cross-linking agents, a compound having two or more polymerizable unsaturated groups in consideration of absorption characteristics of the finally obtained water-absorbent resin or water-absorbent agent. Is preferably used as an essential component during polymerization.

The amount of these internal crosslinking agents used is preferably 0.001 to 2 with respect to the above-mentioned monomers (excluding the crosslinking agent).
Mol%, more preferably 0.005 to 0.5 mol%, further preferably 0.01 to 0.2 mol%, and particularly preferably 0.03 to 0.15 mol%. When the amount of the internal cross-linking agent used is less than 0.001 mol% or more than 2 mol%, sufficient absorption characteristics may not be obtained. When the crosslinked structure is introduced into the polymer using the internal crosslinking agent, the internal crosslinking agent is added to the reaction system before or during the polymerization of the monomer, after the polymerization, or after the neutralization. You can do it like this.

In the above polymerization, the reaction system contains hydrophilic polymers such as starch / cellulose, derivatives of starch / cellulose, polyvinyl alcohol, polyacrylic acid (salt), crosslinked polyacrylic acid (salt) 0 to hydrophilic polymer. Various foaming agents such as carbonic acid (hydrogen) salts, carbon dioxide, azo compounds, inert organic solvents of 50% by weight (relative to monomer) and other 0 to 10% by weight; various surfactants; chelating agents; A chain transfer agent such as phosphorous acid (salt) may be added. When the cross-linked polymer is obtained by aqueous solution polymerization and is in a gel form, that is, when it is a hydrogel cross-linked polymer, the cross-linked polymer is optionally dried and before and / or after drying. It is usually pulverized to obtain a water absorbent resin. Also, the drying is usually from 60 ° C
It is carried out in a temperature range of 250 ° C, preferably 100 ° C to 220 ° C, more preferably 120 ° C to 200 ° C. The drying time depends on the surface area of the polymer, the water content, and the type of dryer, and is selected so as to obtain the desired water content.

The water content of the water-absorbent resin or water-absorbent agent that can be used in the present invention (specified by the amount of water contained in the water-absorbent resin or water-absorbent agent / measured by the loss on drying for 3 hours at 180 ° C.) is not particularly limited. Is a powder showing fluidity even at room temperature from the viewpoint of physical properties of the water-absorbing agent obtained, and more preferably 0.2 to 30.
%, More preferably 0.3 to 15% by weight, and particularly preferably 0.5 to 10% by weight in a powder state. As the water-absorbent resin that can be used in the production method of the present invention, powdery ones can be mentioned. As the particles of the water-absorbent resin, those having a gel-like average particle diameter of more than 1000 μm obtained by the polymerization reaction before drying and pulverization can be used, but usually they do not become powders, so they are (preferably) dried and pulverized if necessary. -By classification, the powder particle size is adjusted according to the purpose.

The particle size of the water-absorbent resin powder or water-absorbing agent is
Weight average particle diameter is 10 to 2000 μm, preferably 10
0 to 1000 μm, more preferably 200 to 700 μm
m, more preferably 300 to 600 μm, and particularly preferably 400 to 550 μm. More preferably, water-absorbent resin powder or fine powder in water-absorbing agent (for example, 100 μm or less, preferably 150 μm or less)
It is preferable that the amount of fine powder is less, specifically 10% by weight
It is preferably 5% by weight or less, more preferably 1% by weight or less. The water-absorbent resin powder and the water-absorbing agent are preferably substantially 1000 μm or more, more preferably 850
Particles having a size of μm or more are 5% by weight or less, and further 1% by weight or less.

The particle shape of the water-absorbent resin or water-absorbing agent thus obtained is not particularly limited, such as spherical shape, crushed shape, and indefinite shape, but indefinite crushed shape obtained through the crushing process. What can be used preferably. Further, its bulk specific gravity (defined by JIS K-3362) is preferably 0.40 to 0.80 g / ml, more preferably 0.50 to 0.75 g / ml, and further preferably from the viewpoint of excellent physical properties of the water absorbing agent. It is in the range of 0.60 to 0.73 g / ml. The water-absorbent resin obtained by the above method usually has a saturated absorption capacity of about 10 to 100 g / g for physiological saline under no pressure, and physical properties such as this absorption capacity are appropriately adjusted according to the purpose. To be done.

(Water-soluble inorganic base (b1)) In the present invention, a non-crosslinkable water-soluble inorganic base (b1), that is, preferably an alkali metal, is added to the water-absorbent resin powder (a) or (a1). Water-soluble inorganic base (b1) selected from the group consisting of salts, ammonium salts, alkali metal hydroxides, ammonia or hydroxides thereof (hereinafter referred to as water-soluble inorganic base (b1)), and / or A non-reducing alkali metal salt pH buffer (b2) and a crosslinking agent (c) or a dehydration-reactive crosslinking agent (c1) are added, and the water-soluble inorganic base (b1) will be described below.

That is, in the present invention, the water-soluble inorganic base is
OH from water or the base by dissociation in aqueous solution ^-
And an inorganic compound (including carbonate and bicarbonate) that neutralizes an acid group to produce a salt. The water-soluble inorganic base (b1) used in the present invention is preferably selected from the group consisting of alkali metal salts, ammonium salts, alkali metal hydroxides, and ammonia or its hydroxides, which are usually It is a substantially non-crosslinkable water-soluble inorganic base. (Note that examples of the water-soluble inorganic base crosslinkable to the acid group-containing water-absorbent resin include hydroxides of polyvalent metals typified by calcium hydroxide and aluminum hydroxide. Valent metals are not included in the water-soluble inorganic base of the present invention).

As the water-soluble inorganic base (b1), it is essential that it is water-soluble from the viewpoint of the physical properties of the resulting water-absorbing agent, and usually 5 g or more, preferably 20 g per 100 g of room temperature water.
Or more, more preferably 50 g or more, still more preferably 1
A substance having a solubility of at least 00 g is used. In the present invention, a combination of a water-insoluble inorganic base, an organic base and a crosslinkable inorganic base (hydroxide of a polyvalent metal) is not excluded, but a non-crosslinkable water-soluble inorganic base (b1) is not used. The physical properties of the obtained water absorbing agent are low. Specifically, a water-soluble inorganic base (b
Examples of 1) include carbonate compounds containing alkali metal salts and / or ammonium salts such as lithium carbonate, sodium carbonate, potassium carbonate, sodium potassium carbonate, cesium carbonate, rubidim carbonate, and ammonium carbonate, and hydrates thereof (decahydrate salt, Heptahydrate, monopentahydrate, monohydrate, etc.), lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, cesium bicarbonate, rubidium bicarbonate, ammonium bicarbonate and other heavy metals containing and / or ammonium. Carbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, rubidium hydroxide, ammonium hydroxide, hydroxide compounds containing alkali metals and ammonium such as water glass, disodium hydrogen phosphate, dipotassium hydrogen phosphate , 2 lithium hydrogen phosphate, 2 rubidium hydrogen phosphate, 2 hydrogen hydrogen phosphate Hydrogen phosphate compounds, sodium sesquicarbonate, such um _{(Na 2 CO 3 · NaHCO 3} · 2H 2 O)
And the like, and two or more of them may be mixed or used in combination. In addition, these water-soluble inorganic bases (b
Although 1) is purchased, preserved or used as a powder, a hydrate thereof, a pellet or an aqueous solution, its form is not limited.

Among the water-soluble inorganic bases (b1), an alkali metal salt is preferable, a lithium salt, a sodium salt or a potassium salt is more preferable, and a sodium salt is more preferable in view of physical properties and solubility. Further, among the compounds (b1), from the viewpoint of physical properties, carbonate / hydrogen carbonate / hydroxide is preferably used, more preferably hydroxide and / or hydrogen carbonate, and particularly preferably hydroxide is used. That is, specifically, as the water-soluble inorganic base (b1), sodium hydrogen carbonate and / or sodium hydroxide is preferably used, and more preferably sodium hydroxide is used. The amount of the water-soluble inorganic base (b1) used in the present invention is 0.001 to 10 with respect to 100 parts by weight of the water-absorbent resin when not used in combination with the non-reducing alkali metal salt pH buffer (b2) described below. The content is preferably within the range of parts by weight, more preferably within the range of 0.01 to 5 parts by weight, and even more preferably within the range of 0.01 to 2 parts by weight. By using within the above range, the absorption characteristics for body fluid (aqueous liquid) such as urine, sweat and menstrual blood can be further improved. If the amount used is less than 0.001 part by weight, the neutralization rate of the functional groups in the vicinity of the surface of the water absorbent resin cannot be adjusted appropriately and the absorption characteristics may not be improved. When the amount of the water-soluble inorganic base (b1) used is more than 10 parts by weight, it becomes excessive, which is uneconomical and may not improve the absorption capacity.

When the water-soluble inorganic base (b1) is used in combination with the non-reducing alkali metal salt pH buffer (b2) described later, the total amount of the water-soluble inorganic base (b1) and the non-reducing alkali metal salt pH buffer (b2) is 0.001 to 100 parts by weight of the organic resin
The range of 10 parts by weight is preferable, the range of 0.01 to 5 parts by weight is more preferable, and the range of 0.01 to 2 is more preferable.
The range is parts by weight. However, when the water-soluble inorganic base (b1) and the non-reducing alkali metal salt pH buffer (b2) described later are used in combination in the present invention, at least one of the functions (b1) and (b2) Are appropriately used in combination.
Although the mechanism for improving the absorption characteristics is not clear, the following two reasons ((1) formation of uniform surface cross-linking layer by uniformization of surface neutralization ratio, (2) optimization of mixing and permeation by change of salt concentration )It is estimated to be.

That is, as the reason (1), in general, in the water-absorbent resin powder, regardless of whether or not post-neutralization after polymerization (the above-mentioned neutralization polymerization method or acid-type polymerization method), one particle of the water-absorbent resin powder is generally used. The neutralization rate of the particles and the neutralization rate of the surface of the powder are minutely different even for the same single powder.In the conventional surface treatment, the crosslinking reaction of the powder and the mixing of the crosslinking agent are caused by these reasons. Was uneven, and the physical properties were deteriorated. Therefore, in the present invention, by using the water-soluble inorganic base (b1) in combination with the crosslinking agent (c), the neutralization rate of each particle of the water-absorbent resin powder and the minute surface neutralization of one particle of the powder can be obtained. By eliminating the difference in the ratio, the neutralization ratio of the carboxyl groups in the vicinity of the surface involved in cross-linking could be uniformly optimized, and as a result, it became possible to carry out uniform surface cross-linking. For example, a water absorbing agent obtained from a polyacrylic acid-based water-absorbing resin neutralized by 70 mol% and 0.01-2 parts by weight of sodium hydroxide is 0.025-
The neutralization ratio of the water absorbing agent is increased in the range of 5 mol%, and the neutralization ratio is selectively high near the surface of the particles. Furthermore, it is speculated that the water-soluble inorganic base (b1) of the present invention also acts as a reaction catalyst for the cross-linking agent due to the improved absorption characteristics.

Further, as the reason (2), the water-soluble inorganic base (b1) is used to improve the mixing property by controlling the permeation into the water absorbent resin due to the high salt concentration in the crosslinking agent solution when the crosslinking agent is mixed. However, after mixing, it neutralizes with the carboxyl groups of the water-absorbent resin to form alkali metal salts and ammonium salts, which disappears from the solution of the cross-linking agent, so that it functions to promote penetration of the cross-linking agent. Presumed. With conventional additives (hydrophilic organic solvents such as isopropanol),
Permeation into the water-absorbent resin derived from an inert organic solvent is controlled and the mixing property is improved, but even after mixing, the organic solvent remains in the cross-linking agent solution and prevents the cross-linking agent from penetrating inside the surface. Presumed to be.

Further, unlike the water-soluble inorganic base (b1),
When a polyvalent metal salt such as aluminum is used, it is presumed that the crosslinking reaction due to the polyvalent metal ion proceeds and the absorption capacity under no pressure or under pressure is reduced. Further, the cross-linking by polyvalent metal ions is very weak because it forms an ionic bond, and in the water swollen state, the polyvalent metal ions move to the inside of the particles to form cross-links, which may further lower the physical properties. Guessed. It is presumed that the water-soluble inorganic base (b1) of the present application has improved the conventional drawbacks such as the insufficient thickness of the crosslinked layer of the water-absorbing agent and the deterioration of the physical properties, which are caused by the above phenomena. It is also presumed that by using the dehydration-reactive crosslinking agent (c1), the water generated from the dehydration-crosslinking reaction further penetrates the crosslinking agent into the vicinity of the surface, and the thickness of the crosslinking layer is further increased.

(Non-reducing alkali metal salt pH buffer (b
2)) In the present invention, a non-crosslinkable water-soluble inorganic base (b) is added to the water-absorbent resin powder (a) or (a1).
1), that is, a water-soluble inorganic base (b1) selected from the group consisting of an alkali metal salt, an ammonium salt, an alkali metal hydroxide, ammonia or a hydroxide thereof, and / or a non-reducing alkali metal Salt p
The H buffer (b2) and the crosslinking agent (c) or the dehydration-reactive crosslinking agent (c1) are added, but the non-reducing alkali metal salt pH buffer (b2) will be described below.

Non-reducing alkali metal salt p in the present invention
The H buffer (b2) maintains an almost constant hydrogen ion concentration even when the addition of acid or base to some extent disappears in the solution, and is essentially non-reducing, preferably non-oxidizing alkali. A metal salt is used (for example, in the case of an alkali metal salt pH buffer containing phosphorus or sulfur, if the oxidation number of the phosphorus atom is + 5 / the oxidation number of the sulfur atom is +6, the pH buffer is a non-oxidizing non-reducing agent). Shows sex). If the pH buffer has a reducing property or is not an alkali metal salt, it may hinder the crosslinking, and the object of the present invention cannot be sufficiently achieved. The present invention applies an alkali metal salt that acts as a pH buffer, and is made from a combination of various acids, bases, or salts. Further, the molecular weight of the pH buffering agent is 50 to 10 because of its miscibility and permeability to the water absorbent resin.
00, further 60 to 800, especially 70 to 500 are used.

The alkali metal salt which functions as the pH buffer (b2) in the present invention is typically one or more of hydrogen carbonate, dihydrogen phosphate and hydrogen phosphate. . Specific examples include partial alkalis of inorganic polybasic acids such as sodium hydrogen carbonate, potassium hydrogen carbonate, lithium hydrogen carbonate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate. Metal salts; Organic polyvalent carboxylic acids such as potassium dihydrogen citrate, sodium dihydrogen citrate, disodium hydrogen citrate, dipotassium hydrogen citrate, sodium hydrogen tartrate, potassium hydrogen tartrate, monosodium fumarate, potassium hydrogen phthalate Partial alkali metal salts, particularly sodium or potassium salts, and further lithium salts can be mentioned.

In addition to the above pH buffer (b2),
The pH buffer (b2) prepared from a combination of various acids, bases or salts as used in the present invention is a buffer typically formed from a combination of compounds used in preparing a conventionally known buffer solution. An agent is illustrated. The buffer solution is a solution of a buffer, particularly an aqueous solution of a salt of a weak acid and a strong base, a salt of a strong acid and a weak base, or a mixture of those salts. In the case of a water-absorbent resin containing an acid group such as a carboxyl group, a buffer is preferably used as a mixture of salts consisting of a weak acid and a strong base, and more preferably an inorganic salt is used.

As a concrete example, a combination of the compounds used in the buffer solution described in Chemical Handbook (edited by The Chemical Society of Japan, II-355, 356) can be mentioned as the buffer agent. For example, Clark-Lubs buffer (potassium chloride / hydrochloric acid; pH 1.0 to 2.2, potassium hydrogen phthalate / hydrochloric acid; pH 2.2 to 3.8, potassium hydrogen phthalate / sodium hydroxide; pH 4.0 to 4.0). 6.2, potassium dihydrogen phosphate / sodium hydroxide; pH 5.8 to 8.0,
Boric acid / potassium chloride / sodium hydroxide; pH 7.8
~ 10.0), Sφrensen's buffer (glycine +
Sodium chloride / hydrochloric acid; pH 1.1 to 4.6, glycine + sodium chloride / hydrochloric acid; pH 8.6 to 13.0, sodium citrate / hydrochloric acid; pH 1.1 to 4.9, sodium citrate / sodium hydroxide; pH 5.0 to 6.7,
Sodium tetraborate / hydrochloric acid; pH 7.6 to 9.2, sodium tetraborate / sodium hydroxide; pH 9.3 to 1
2.4, potassium dihydrogen phosphate / disodium hydrogen phosphate; pH 5.3-8.0, Kolthoff buffer (potassium citrate / citric acid; pH 2.2-3.6)
Potassium dihydrogen citrate / hydrochloric acid; pH 2.2-3.6,
Potassium dihydrogen citrate / sodium hydroxide; pH 3.
8-6.0, succinic acid / sodium tetraborate; pH 3.
0-5.8, potassium dihydrogen citrate / sodium tetraborate; pH 3.8-6.0, potassium dihydrogen phosphate / sodium tetraborate; pH 5.8-9.2, sodium tetraborate / carbonic acid Sodium; pH 9.2 to 11.0, hydrochloric acid / sodium carbonate; pH 10.2 to 11.2, disodium hydrogen phosphate / sodium hydroxide; pH 11.0-1
2.0), Michaelis buffer (tartaric acid / sodium tartrate; pH 1.4-4.5, lactic acid / sodium lactate; pH 2.3-5.3, acetic acid / sodium acetate; p.
H3.2-6.2, potassium dihydrogen phosphate / disodium hydrogen phosphate; pH 5.2-8.3, sodium diethyl barbiturate + sodium acetate / hydrochloric acid; pH 2.6-
9.2, Sodium diethyl barbiturate / hydrochloric acid; pH
6.8 to 9.6, N, N-dimethylglycine sodium salt / hydrochloric acid; pH 8.6 to 10.6), Mcilvain
broad buffer of e (disodium hydrogen phosphate / citric acid;
pH 2.2-8.0), Britton-Robins
on wide range buffer (citric acid + potassium dihydrogen phosphate +
Boric acid + diethyl barbituric acid / trisodium phosphate), Carmody's broad buffer (boric acid + citric acid / trisodium phosphate; pH 2.0-12.0), Go
mori buffer (2,4,6-trimethylpyridine /
Hydrochloric acid; pH 6.4 to 8.4, tris (hydroxymethyl) aminomethane / hydrochloric acid; pH 7.2 to 9.1, 2-amino-2-methyl-1,3-propanediol / hydrochloric acid;
pH 7.8-9.7), Tr of Bates-Power
is buffer (tris (hydroxymethyl) aminomethane / hydrochloric acid; pH 7.0 to 9.0), Delory-Kin
g buffer (carbonate / bicarbonate; pH 9.2-10.
7), and the like. And p of the buffer used
The H and the concentration depend on the neutralization ratio of the water absorbent resin and the type of the surface cross-linking agent to be used, but the pH of the surface cross-linking agent solution is preferably in the range of 1.5 to 10.0 by adding a buffering agent. Adjusted to.

Among the above, partially neutralized salts of inorganic polybasic acids are preferable from the viewpoints of performance, stability, use in one-component system, cost, etc., and partially alkali metal neutralized salts of phosphoric acid and carbonic acid are preferable. More preferable. The above pH buffer (b2) in the present invention
When not used in combination with the above-mentioned water-soluble inorganic base (b1), the amount of is preferably in the range of 0.005 to 10 parts by weight with respect to 100 parts by weight of the solid content of the water absorbent resin, and 0.05
It is more preferably in the range of 5 parts by weight. By using within the above range, the absorption characteristics for body fluid (aqueous liquid) such as urine, sweat and menstrual blood can be further improved.
If the amount used is less than 0.005 parts by weight, the neutralization rate of the functional groups near the surface of the water absorbent resin cannot be adjusted appropriately,
Absorption characteristics may not be improved. pH buffer (b2)
If the amount used is greater than 10 parts by weight, the additive becomes excessive, which is uneconomical and may not improve the absorption capacity.

When the non-reducing alkali metal salt pH buffer (b2) is used in combination with the above-mentioned water-soluble inorganic base (b1), the total amount of the water-soluble inorganic bases (b1) is 0.001-1 with respect to 100 parts by weight of the organic resin
The range of 0 parts by weight is preferable, the range of 0.01 to 5 parts by weight is more preferable, and the range of 0.01 to 2 parts by weight is more preferable. However, in the present invention, when the water-soluble inorganic base (b1) and the non-reducing alkali metal salt pH buffer (b2) are used in combination, (b1) and (b2) are at least in the range where they function. Used as appropriate. The mechanism for improving the absorption characteristics is not clear, but it is also presumed to be the following two reasons ((1) uniformization of surface neutralization rate, and (2) optimization of mixing and permeation by changing salt concentration).

That is, as the reason (1), in the water-absorbent resin powder, each particle of the water-absorbent resin powder is irrespective of the presence or absence of post-neutralization after polymerization (the above-mentioned neutralization polymerization method or acid-type polymerization method). The neutralization ratio of the powder and the neutralization ratio of the powder surface are minutely different even for the same single powder, resulting in non-uniformity in the powder cross-linking reaction and mixing of the cross-linking agent, resulting in poor physical properties. In addition, by using the pH buffering agent (a) of the present invention together with the crosslinking agent (b), the neutralization ratio of each particle of the water-absorbent resin powder and the minute surface neutralization of one particle of the powder can be obtained. In order to eliminate the difference in the rate, regardless of the neutralization rate of the water-absorbent resin powder or the neutralization index described later, in the present invention, the neutralization rate of the carboxyl groups near the surface involved in crosslinking is uniform. This is probably because it can be optimized. As a result, the pH buffering agent of the present invention acts as a mixing aid without hindering the penetration of the crosslinking agent into the water-absorbent resin powder, and also acts as a reaction catalyst of the crosslinking agent. It is presumed that this is due to the improved characteristics.

Further, as the reason (2), since the pH buffering agent such as hydrogen carbonate exists as an alkali metal salt in the cross-linking agent solution when the cross-linking agent is mixed, it permeates the water-absorbent resin derived from a high salt concentration. Is controlled to improve the mixing property.
Since the alkali metal salt of the H buffer disappears from the solution of the cross-linking agent, it is presumed that the salt that inhibits the permeation of the cross-linking agent disappears after the mixing and acts to promote the permeation of the cross-linking agent. This is because with conventional additives (hydrophilic organic solvents such as isopropanol), penetration into the water-absorbent resin derived from an inert organic solvent is controlled and mixing is improved, but even after mixing, the organic solvent remains a crosslinking agent solution. It is presumed that the pH buffer agent of the present application has improved the conventional drawback that the residual water remains inside and the penetration of the crosslinking agent into the surface is impeded, and the thickness of the crosslinking layer of the water absorbing agent is insufficient.

(Crosslinking Agent (c) and Mixture and Crosslinking Treatment) In the present invention, the crosslinking agent (c) capable of reacting with an acid group is preferably a surface crosslinking agent, and further a dehydration-reactive crosslinking agent (c1). Is preferably used. In the present invention, the dehydration reactivity means that the functional group of the water absorbent resin (particularly the functional group near the surface) and the cross-linking agent undergo a dehydration reaction, preferably dehydration esterification and / or dehydration amidation, and more preferably, It is a cross-linking agent that cross-links by dehydration esterification. Specifically, when the water absorbent resin contains a carboxyl group, a hydroxyl group-containing cross-linking agent such as a polyhydric alcohol, an amino group-containing cross-linking agent such as a polyvalent amine, further, an alkylene carbonate or mono, di or poly Oxazolidinone compounds;
A cyclic cross-linking agent such as an oxetane compound such as 3-methyl-3-oxetane methanol, which produces a hydroxyl group or an amino group in association with the ring-opening reaction of the cyclic cross-linking agent, and the hydroxyl group or the amino group undergoes a cross-linking reaction reaction. An example of the crosslinking agent (c1) that exhibits dehydration reactivity is a cyclic crosslinking agent that does. One kind or two or more kinds of the dehydration-reactive crosslinking agent (c1) is used, and a non-dehydration-reactive crosslinking agent such as a polyvalent metal may be used in combination.

Specifically, the dehydration-reactive crosslinking agent (c1) that can be used in the present invention is not particularly limited as long as it is a crosslinking agent capable of reacting with the functional group of the water-absorbent resin, and it is usually used for the above purpose. It is a known cross-linking agent (surface cross-linking agent). For example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol,
Tetraethylene glycol, polyethylene glycol,
Dipropylene glycol, polypropylene glycol,
1,3-propanediol, 2,2,4-trimethyl-
1,3-pentanediol, glycerin, diglycerin, polyglycerin, 2-butene-1,4-diol,
1,4-butanediol, 1,5-pentanediol,
1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol, sorbitol, etc. Polyhydric alcohol compounds; ethylenediamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyamide polyamines, polyallylamine, polyethyleneimine and other polyvalent amine compounds, and condensation products of these polyvalent amines with haloepoxy compounds; 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-
Alkylene carbonate compounds such as dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one and 1,3-dioxopan-2-one And a polyvalent alkylene carbonate compound such as ethylene glycol bis (4-methylene-1,3-dioxolan-2-one) ether;
Examples thereof include mono-, di- or poly-oxazolidinone compounds; oxetane compounds such as 3-methyl-3-oxetane methanol and polyvalent oxetane compounds;

Among these dehydration-reactive crosslinking agents, at least one selected from polyhydric alcohols, alkylene carbonates, oxazolidinone compounds and (polyhydric) oxetane compounds is preferable, and at least polyhydric alcohols are particularly preferable. As the crosslinking agent (c), in addition to these dehydration-reactive crosslinking agents (c1), ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether are further added. Epoxy compounds such as ether, polyethylene diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol, γ-glycidoxypropyltrimethoxysilane; polyhydric compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate Isocyanate compounds; Polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; γ-glycidoxypropyltrimethoxysilane, γ- Silane coupling agents such as amino propyl trimethoxy silane; 2,2
Bishydroxymethylbutanol-tris [3- (1-
Examples thereof include polyvalent aziridine compounds such as aziridinyl) propionate] and polyvalent metals such as beryllium, magnesium, calcium, strontium, zinc, aluminum, iron, chromium, manganese, titanium and zirconium.

In the present invention, the dehydration-reactive crosslinking agent (c
1) and 1 at a weight average particle diameter of 300 to 600 μm
Water-absorbent resin powder (a1) containing 10% by weight or less of fine powder of 50 μm or less and / or 15 when the particle diameter is less than 850 μm.
Particles having a particle size of 0 μm or more in an amount of 90% by weight or more of all particles, and having a particle size of less than 850 μm, 600 μm or more (A1), a particle size of less than 600 μm and 500 μm or more (A2), a particle size of less than 500 μm. Particles of 300 μm or more (A3), 150 μ if the particle size is less than 300 μm
When not using both of the water-absorbent resin powders containing at least two kinds selected from m or more particles (A4), the water-absorbing agent generally obtained has low physical properties, preferably the dehydration-reactive crosslinking agent (c1), Also, both the water absorbent resin powder (a1) having the specific particle size are used in the present invention.

In the present invention, the water-absorbent resin powder (a) or (a1), a water-soluble inorganic base (b1) and / or a non-reducing alkali metal salt pH buffer (b2), and a crosslinking agent (c). Alternatively, when (c1) is mixed, it is preferable to use water. At this time, the amount of water used is usually 0.5 to 20 parts by weight, preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the water absorbent resin, although it depends on the water content of the water absorbent resin used. The range is parts by weight. If the amount of water used exceeds 20 parts by weight, the absorption capacity may decrease. If the amount is less than 0.5 part by weight, the effect is less likely to be exhibited, and the absorption capacity under load may not be improved.

In the present invention, the water-absorbent resin powder (a) or (a1), the water-soluble inorganic base (b1) and / or the non-reducing alkali metal salt pH buffer (b).
When 2) and the crosslinking agent (c) or (c1) are mixed, a hydrophilic organic solvent may be used. Examples of the hydrophilic organic solvent used include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol and t-butyl alcohol; ketones such as acetone and methyl ethyl ketone; dioxane and alkoxy (poly) ethylene. Ethers such as glycol and tetrahydrofuran; amides such as ε-caprolactam and N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide; ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene Pyrene glycol, glycerin, polyglycerin, glycerophosphoric acid, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1 , 2-Cyclohexanedimethanol, 1,2-
Examples thereof include polyhydric alcohols such as cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol.

The amount of the hydrophilic organic solvent used varies depending on the kind and particle size of the water absorbent resin, but is usually 0 to 10 parts by weight, preferably 0 to 5 parts by weight with respect to 100 parts by weight of the water absorbent resin.
Parts by weight, more preferably 0 to 3 parts by weight. When the amount of the hydrophilic organic solvent used is 10 parts by weight or more, the solubility of the above-mentioned additive may be lowered and the absorption property may not be improved. The polyhydric alcohol may be reacted with a water-absorbent resin as a cross-linking agent depending on reaction conditions (heating temperature, time, water content, etc.), may be used as a solvent without reaction, or may be used together. May be. Further, in the present invention, the water absorbent resin powder (a) or (a1), the additive (b1) and / or the non-reducing alkali metal salt pH buffer (b2), and the cross-linking agent (c) or (c1). When mixed with), a surfactant or an inert inorganic fine particle powder may be used as a substance other than water or a hydrophilic organic solvent within a range that does not impair the effects of the present invention. Surfactants and inert inorganic fine particle powders used are described in US Pat.
4459, European Patent No. 827753, European Patent No. 349240, European Patent No. 761241 and the like.

In the present invention, the water-absorbent resin powder (a) or (a1) and the above water-soluble inorganic base (b1) and / or non-reducing alkali metal salt pH buffer (b)
2) and the mixing of the cross-linking agent (c) or (c1),
The water-absorbent resin may be dispersed in a hydrophilic organic solvent or an organic solvent such as cyclohexane or pentane, but water, a cross-linking agent, and a mixture of additives may be added several times. The mixing method is not particularly limited.
In addition, the water-soluble inorganic base (b1) and / or the non-reducing alkali metal salt pH buffer (b2), and the cross-linking agent (c) or (c1), and water or hydrophilic organic used as necessary. The solvent, the inorganic powder and the like may be mixed separately with respect to the water absorbent resin, may be mixed at once, or may be mixed in several times, but are preferably water-soluble inorganic bases. (B1) and / or a non-reducing alkali metal salt pH buffer (b2) and a cross-linking agent (c) or (c1) are mixed in advance and then added to the water-absorbent resin, at which time a water-soluble inorganic base ( It is more preferable that b1) and / or the non-reducing alkali metal salt pH buffer (b2) and the cross-linking agent (c) or (c1) be an aqueous solution. The temperature of the aqueous solution at this time is 0 ° C to the boiling point, preferably 5 to 50 ° C, and more preferably 10 to 30 ° C from the viewpoint of the mixing property and the stability. The temperature of the water-absorbent resin powder (a) or (a1) before mixing is preferably in the range of 0 to 80 ° C, more preferably 40 to 70 ° C from the viewpoint of mixability.

Furthermore, in the present invention, among various mixing methods, water and / or a hydrophilic organic solvent, if necessary, a water-soluble inorganic base (b1) and / or a non-reducing alkali metal salt pH buffer (b2) are used. ), And the cross-linking agent (c) or (c1) are mixed in advance, and then the aqueous solution thereof is preferably sprayed or added dropwise to the water-absorbent resin powder (a), more preferably sprayed. The size of the sprayed droplets is preferably 300 μm or less, and is 200
It is more preferably not more than μm. Further, upon mixing, a water-insoluble fine particle powder and a surfactant may coexist as long as the effects of the present invention are not impaired.

A suitable mixing apparatus used for the above mixing is
It is necessary to be able to produce a large mixing force to ensure uniform mixing. Examples of the mixing device that can be used in the present invention include a cylindrical mixer, a double-walled cone mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a flow mixer. A mold furnace rotary disk type mixer, an air flow type mixer, a double arm type kneader, an internal mixer, a crushing type kneader, a rotary type mixer, a screw type extruder and the like are suitable. In the method for producing a water-absorbing agent of the present invention, a water-soluble inorganic base (b1) and / or a non-reducing alkali metal salt pH is added to the water-absorbent resin powder (a) or (a1).
Buffering agent (b2) and cross-linking agent (c) or (c1)
And the water-absorbent resin powder (a) or (a1)
Is crosslinked.

In the method for producing a water-absorbing agent of the present invention, preferably, the water-absorbent resin powder (a) or (a1) is mixed with a water-soluble inorganic base (b1) and / or a non-reducing alkali metal salt pH buffer ( After b2) and the cross-linking agent (c) or (c1) are mixed, a heat treatment is performed when the vicinity of the surface of the water absorbent resin is cross-linked. When the heat treatment is performed in the present invention, the treatment time is preferably 1 minute to 180 minutes, and 3 minutes to 1 minute.
20 minutes is more preferable, and 5 minutes to 100 minutes is further preferable. The heat treatment temperature (specified by heat medium temperature or material temperature) is preferably in the range of 100 to 250 ° C, and 140 to 240 ° C.
Is more preferable, the range of 150 to 230 ° C is further preferable, and the range of 160 to 220 ° C is even more preferable. If the heating temperature is lower than 100 ° C, not only the heat treatment and the dehydration reaction take time to cause a decrease in productivity, but also uniform cross-linking cannot be achieved and an excellent water absorbing agent may not be obtained. If the treatment temperature exceeds 250 ° C., the water absorbing agent obtained may be damaged, and it may be difficult to obtain a product having excellent physical properties.

The heat treatment can be carried out by using an ordinary dryer or a heating furnace, and a groove type mixing dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an air flow type dryer, and an infrared dryer are used. It is illustrated. In the method for producing a water absorbing agent according to the present invention, further, if necessary, a deodorant, an antibacterial agent, a fragrance, an inorganic powder such as silicon dioxide or titanium oxide, a foaming agent, a pigment, a dye, a hydrophilic short Fiber, plasticizer, adhesive, surfactant, fertilizer, oxidizer, reducing agent, water, salt,
Add chelating agents, bactericides, hydrophilic polymers such as polyethylene glycol and polyethyleneimine, hydrophobic polymers such as paraffin, thermoplastic resins such as polyethylene and polypropylene, and thermosetting resins such as polyester resin and urea resin. For example, the step of imparting various functions to the water absorbing agent or the water absorbing resin may be included. The amount of these additives used is 0 to 10 parts by weight, preferably 0 to 1 part by weight, based on 100 parts by weight of the water absorbing agent.

The cationic polymer compound used in the water-absorbing agent of the present invention can improve the fixing property of the water-absorbing agent to the sanitary material, etc., and preferably has a weight average molecular weight of 2000 or more, more preferably 5000 or more, and most preferably. Has a weight average molecular weight of 10,000 or more. Also, the amount used is
Preferably 0.01 to 1 per 100 parts by weight of the water-absorbent resin
The amount is 0 parts by weight, more preferably 0.05 to 5 parts by weight, still more preferably 0.1 to 3 parts by weight. The mixture of the cationic polymer compounds is added alone or as a solution (aqueous solution), preferably after surface cross-linking. Specific examples of the cationic polymer compound include polyethyleneimine,
Examples thereof include polyvinylamine, polyallylamine, condensates of polyamidoamine and epichlorohydrin, polyamidines, partial hydrolysates of poly (N-vinylformaldehyde), and salts thereof.

By using the water-insoluble fine particles, it is possible to further improve the liquid permeability of the water absorbing agent and the blocking resistance when absorbing moisture. The fine particles used are preferably 10 μm.
m or less, further 1 μm or less, particularly 0.1 μm or less, inorganic or organic water-insoluble fine particles are used, and specifically, silicon oxide (trade name, Aerosil, manufactured by Nippon Aerosil Co., Ltd.), titanium oxide, aluminum oxide, etc. Is used. For mixing, powder mixing (Dry-Blend) or slurry mixing is used, and the amount thereof is 10 parts by weight or less, more preferably 0.001 to 5 parts by weight, preferably 0.01 parts by weight based on 100 parts by weight of the water absorbing agent. ~ 2 parts by weight are used.

(Water Absorbing Agent and Sanitary Material Using the Water Absorbing Agent) In the present invention, preferably, the water-absorbent resin powder (a) or (a1) contains a water-soluble inorganic base (b1) and / or a non-reducing alkali. By mixing the metal salt pH buffer (b2) and the cross-linking agent (c) or (c1) and subjecting the water-absorbent resin powder (a) or (a1) to a cross-linking treatment, the above-mentioned effects of the present invention can be obtained. Provided is a novel water absorbing agent having high physical properties. The water absorbing agent according to the present invention is preferably a particulate water absorbing agent containing a water absorbing resin having a crosslinked structure obtained by polymerizing an unsaturated monomer component as a main component.

(1) Water Absorbent Obtained in Acid Polymerization The water absorbent of the present invention is preferably a monomer containing an acid group-containing monomer (salt) when a water absorbent resin is obtained by acid polymerization. Is a water-absorbing agent obtained by surface-crosslinking a water-absorbent resin obtained by polymerizing and then neutralizing. More preferably, the water-absorbent resin obtained by the above-mentioned neutralization has a neutralization index of 15 or more, further preferably 17 or more, particularly preferably 20 or more. Further, the neutralization index of the surface-crosslinked water-absorbing agent is preferably 15 or more, more preferably 17 or more, and particularly preferably 20 or more. When the neutralization index is lowered in order to enhance the surface cross-linking effect, it takes a long time and complicated steps to neutralize, but in the present invention, excellent surface cross-linking can be easily achieved even with non-uniform neutralization.

Conventionally, a water-absorbent resin obtained by polymerizing a monomer containing an acid group-containing monomer (salt) and then post-neutralizing the water-absorbent resin has a high absorption capacity and a low soluble content. Due to the uneven neutralization of the resin, it was generally difficult to improve the absorption capacity under pressure. In order to solve such a problem, Japanese Patent Laid-Open No. 10-10
In 1735 (European Patent Publication 0882502), a technique is known in which the difference in neutralization ratio (neutralization index) of each particle of the water absorbent resin is highly controlled. Such a method of controlling the neutralization index is a water-absorbent resin having a low soluble content obtained by polymerizing a monomer containing an acid group-containing monomer (salt) and further post-neutralizing the monomer. Although it achieves a high absorption capacity under pressure, it requires much labor to control the neutralization index. However, the alkali metal pH buffer agent (b
The method of the present invention using 2) is highly preferable because it does not require a high degree of control of the neutralization index and gives a high absorption capacity under pressure even with simple and non-uniform post-neutralization. Note that, of course, the present invention is limited to a water-absorbing resin having a low soluble content by an acid-type polymerization method, which is obtained by polymerizing a monomer containing an acid group-containing monomer (salt) and further post-neutralizing it. However, as shown in Examples and the like which will be described later, it is also suitably applied to a water-absorbent resin obtained by a neutralization polymerization method that does not include a post-neutralization step.

(2) Novel Water-Absorbing Agent Having Five Physical Properties Also, the water-absorbing agent of the present invention preferably has the following physical properties, including the case where acid polymerization is not carried out. In addition to particle size, CRC, AAP, SFC, SFC change index, SFC variation coefficient, SF
A novel water-absorbing agent having one or more, preferably two or more, more preferably three or more, particularly preferably four or more) such as C fluctuation rate, continuous production system SFC standard deviation, surface layer soluble content, etc. . (A) Particle Size The average particle size and bulk specific gravity of the water absorbing agent according to the present invention are in the range of the water absorbent resin, that is, the weight average particle size of 300 to 6
It is preferable that the fine powder having a size of 00 μm and 150 μm or less is 10% by weight or less. It is more preferably 5% by weight or less, further preferably 3% by weight or less, and particularly 2% by weight or less.

The water absorbing agent according to the present invention has a particle size of 850.
90% by weight of all particles below 150 μm and below 150 μm
Including the above, and 600 μm when the particle size is less than 850 μm
The above particles (A1) having a particle size of less than 600 μm are 500
3 μm or more particles (A2) with a particle size of less than 500 μm
It contains at least two types selected from particles (A3) having a particle size of 00 μm or more and particles (A4) having a particle size of less than 300 μm and having a particle size of 150 μm or more, more preferably 3 types or more, and further preferably 4 types. The water-absorbing agent according to the present invention preferably contains particles having a particle size of less than 850 μm and 150 μm or more in an amount of 95% by weight or more, more preferably 97% by weight or more, and further preferably 98% by weight or more. By controlling to such a specific particle size, high physical properties are achieved in the sanitary material.

The water-absorbing agent according to the present invention preferably contains 0.1% by weight of each of the four particles A1 to A4.
The above content is included, more preferably 1% by weight or more, and further preferably 3% by weight or more. In this case, the upper limit is not particularly limited, but preferably, the four types of particles A1 to A4 are each 99% by weight or less, more preferably 90% by weight or less, and further preferably 80% by weight or less. By containing each particle size in a certain amount or more, the water absorption rate depending on the surface area of the particle is controlled in a well-balanced manner. (B) CRC The water-absorbing agent according to the present invention has an absorption capacity (Centrifu) of 0.90% by weight physiological saline for 30 minutes under no pressure.
ge Retention Capacity / CR
C) is preferably 31 g / g or more. When the CRC is 31 g / g or more, it is possible to obtain a sanitary material that is critically excellent in absorbing sanitary materials using a water-absorbing agent, and can achieve a compact sanitary material. (Which means a body fluid absorbent containing other water absorbing materials such as fibers). The CRC is more preferably 32 g / g or more, further preferably 33 g / g or more, even more preferably 34 g / g or more, particularly preferably 35 g / g or more, and particularly preferably 36 g / g or more. If the absorption capacity for 30 minutes under a non-pressurized condition against 0.90% by weight physiological saline solution is smaller than 31 g / g, the total amount of urine that can be absorbed by the water absorbing body will be small, and the urine absorbed by the water absorbing body will be diaper. The return to the surface is very large.
Furthermore, when trying to maintain the amount of urine that the water absorbent body requires, the amount of water absorbent used in the water absorbent body increases, which makes the sanitary material bulky and heavy, which leads to an increase in the cost of the water absorbent body. Is not preferable.

(C) AAP The water-absorbing agent according to the present invention has a absorbency against pressure (Ab) under pressure of 0.90% by weight physiological saline for 60 minutes at 4.83 kPa.
sorbency Against Pressure
/ AAP) is preferably 20 g / g or more. A
When AP is 20 g / g or more, when the water absorbing agent of the present invention is used for a part of the water absorbent body of the paper diaper, the effect of preventing the urine absorbed in the water absorbent body from returning to the surface of the diaper is very large. Become. The absorbency against pressure of 0.90 wt% physiological saline for 60 minutes at 4.83 kPa is more preferably 22 g / g or more, still more preferably 24 g / g or more, even more preferably 25 g / g or more, and particularly preferably It is 26 g / g, particularly preferably 27 g / g or more. 4.83 kP against 0.90 wt% saline
If the absorbency against pressure for 60 minutes under a is less than 20 g / g, it is not preferable because the effect of preventing the urine absorbed by the water absorber from returning to the surface of the diaper becomes extremely small.

(D) SFC The water-absorbing agent according to the present invention has a 0.69% by weight physiological saline flow conductivity (SFC) of 20 (unit: 10 ^-7 × cm ³ × s).
It is preferably not less than × g ⁻¹ ). SFC has a very large effect on the liquid permeability after swelling of the water absorbing agent obtained in the present invention. That is, for example, when the water absorbent of the present invention is used for a part of the water absorbent body of a paper diaper, the liquid permeability is improved, the liquid absorbent is sufficiently spread over the water absorbent body, the liquid absorption amount is increased, and the liquid leaks. The effect of preventing is significantly improved.
The SFC is more preferably 25 (unit: 10 ^-7 × cm ³
× s × g ⁻¹ ) or more, more preferably 30 (unit: 10)
^-7 × cm ³ × s × g ^-1 ) or more, and even more preferably 3
5 (unit: 10 ⁻⁷ × cm ³ × s × g ⁻¹ ) or more, particularly preferably 40 (unit: 10 ⁻⁷ × cm ³ × s × g ⁻¹ ) or more,
Particularly preferably 50 (unit: 10 ⁻⁷ × cm ³ × s ×)
g ^-1 ) or more. SFC is 20 (unit: 10 ^-7 x cm
^If it is smaller than ³ × s × g ⁻¹ ), for example, the liquid permeability when used for a water absorbent body of a paper diaper is lowered, the liquid is localized in the water absorbent body, the liquid absorption amount is decreased, and the liquid leaks. Is increased, and the performance as a water absorber is significantly reduced, which is not preferable.

That is, the water absorbing agent of the present invention preferably has the following three physical properties in a well-balanced manner in addition to the particle size for use in sanitary materials. That is, CRC, AAP,
It has been found that the high physical properties of one or two SFCs alone are not well suited for hygiene materials. These three physical properties are suitably applied not only to the water-absorbing agent having a specific neutralization index obtained by acid polymerization but also to a water-absorbing resin prepared by a neutralization polymerization method which does not include a post-neutralization step. Absorption capacity (CRC) of 0.90% by weight physiological saline for 30 minutes under no pressure of 31 g /
g or more.

4.8 to 0.90 wt% saline
Water absorption capacity under pressure (AAP) at 3 kPa is 24 g / g or less
Up. 0.69 wt% saline flow conductivity (SFC)
20 (Unit: 10^-7× cm ³× s × g^-1)that's all. (E) SFC change index In addition, the present inventors have found that the conventional physical properties of the entire particle (bulk) are
Water-absorbent resin (water-absorbing agent) particles that have been evaluated and managed
Physical properties of water-absorbent resin (water-absorbing agent) particles by particle size
Are different, and the difference in physical properties depending on the particle size is a hygienic material
I found the fact that the physical property deterioration in. Hygiene
Microscopically, the water-absorbent agent particles contained in the material vary in particle size.
The physical properties of individual hygiene materials due to their particle size
And the difference in the physical properties of the sanitary materials
It is presumed to cause deterioration of physical properties.

Therefore, the inventors of the present invention provide a water-absorbing agent having a small difference in physical properties depending on the particle size, particularly a small variation in SFC between particle sizes. The water absorbing agent according to the present invention preferably has an SFC change index defined by the following formula (1) of 0 to 25%. SFC change index (%) = [(standard deviation of SFC of particles A1 to A4) / (SFC of the entire particulate water-absorbing agent)] × 100 (1) In this SFC change index and the SFC variation coefficient described later,
The standard deviation of the SFC of the particles A1 to A4 is that the water-absorbing agent particles are classified to obtain 2 to 4 types of particles existing in the water-absorbing agent among the particles A1 to A4, and then, for each obtained particle size. SFC is measured once, and 2 to 4 types of SFC are measured.
Calculated by calculating the standard deviation from the values. Also, from 2
The average value is similarly calculated from the four types of SFC values.

This SFC change index is the SFC for each grain size.
Of the SFC change index of 0 to 25%, the water absorbent body has more uniform liquid permeability, the liquid is easily dispersed throughout the water absorbent body, and the leakage of the liquid is prevented. It will be effective. The SFC change index is more preferably 0 to 23%, further preferably 0 to 20%, even more preferably 0 to 18%, particularly preferably 0 to 15%,
It is particularly preferably 0 to 10%. When the SFC change index is larger than 25%, for example, when a water absorbing agent is used in the water absorbent body of the paper diaper, the liquid absorbing characteristics of the water absorbent body vary, and it becomes difficult to disperse the liquid in the entire water absorbent body. It is not preferable in terms of generation and reduction of the amount of liquid absorbed by the water absorber.

(F) SFC coefficient of variation The water-absorbing agent according to the present invention has S defined by the following formula (2).
The FC variation coefficient is preferably 0 to 0.25. SFC coefficient of variation = (standard deviation of SFC of particles A1 to A4) / (average value of SFC of particles A1 to A4) (2) This SFC coefficient of variation and the following SFC coefficient of variation are also similar to the difference in SFC for each particle size. Represents a small amount, SFC coefficient of variation is 0
Since it becomes ~ 0.25, each particle size (for example, A1
To A4), the degree of SFC variation decreases,
For example, in the case of producing a water absorbent body of a paper diaper using the water absorbent of the present invention, the liquid permeability in the water absorbent body becomes uniform, and even if each of the water absorbent bodies is compared, there is no variation in the performance of the paper diaper, It is possible to manufacture a stable-quality disposable diaper. The SFC coefficient of variation is more preferably 0 to 0.23,
It is more preferably 0 to 0.20, even more preferably 0 to 0.18, particularly preferably 0 to 0.15, and particularly more preferably 0 to 0.10. The SFC coefficient of variation is 0.
When it is larger than 25 and / or the SFC fluctuation rate is less than 0.65, the liquid permeability of the sanitary material (especially disposable diaper) using the water absorbing agent becomes uneven in the water absorbing body and Even if they are compared with each other, there is a large variation in the performance of the diaper, which is not preferable because it is impossible to manufacture a diaper of stable quality.

(G) SFC fluctuation rate In other words, the water absorbing agent according to the present invention preferably has an SFC fluctuation rate defined by the following formula (3) of 0.65 to 1.00. SFC fluctuation rate = (minimum SFC among SFCs of particles A1 to A4) / (maximum SFC among SFCs of particles A1 to A4) Is preferably 0.70 to 1.00, more preferably 0.75 to 1.00, and particularly preferably 0.8.
It is 0 to 1.00.

(H) Surface Layer Soluble Content The water absorbing agent of the present invention preferably has a surface layer soluble content of 6.0% by weight or less (relative to the water absorbing agent). The surface layer soluble content is preferably 5.5% by weight or less, more preferably 5.
It is 0% by weight or less, more preferably 4.5% by weight or less, and particularly preferably 4.0% by weight or less. The surface soluble content defined by the measuring method of the present application is a soluble content corresponding to actual use in sanitary materials, and is more excellent in water absorption capacity in sanitary materials. That is, conventionally, measurement of water-soluble components (US Re 3264)
9 and EDANA method, etc.) are known, but due to long-term measurement with an excess liquid, an excess amount of soluble components that is considered to be eluted in actual use is used. I found out that I was measuring. It was then found that the method of the present invention is the most modeled for practical use in sanitary materials.

(I) Continuous Production System SFC Standard Deviation The water absorbing agent of the present invention preferably has a continuous production system SFC standard deviation of 5.0 or less defined by the following formula (4). SFC standard deviation of continuous production system = standard deviation of SFC of each lot (4) (However, each lot is 20 kg or more. The number of lots is 10 or more.) The above continuous production system is one line, 24 hours or more, or 10 t The above shows that the water absorbing agent is continuously produced. Further, polymerization, which is a basic step of the method for producing the water absorbing agent,
Drying, crushing, surface treatment, etc. may be continuous or batch type in a continuous production system (for example, continuous polymerization and batch polymerization in the polymerization step), but the interval between each step is 24 hours or less. The time is preferably 12 hours or less, more preferably 6 hours or less, and particularly preferably 3 hours or less.

Each Lot is preferably 20 kg to 100
t, more preferably 0.1t to 50t, still more preferably 0.5t to 25t. The Lot number is preferably 2
0 or more, more preferably 30 or more, and further preferably 5
It is 0 or more, particularly preferably 100 or more. This continuous production system SFC standard deviation is L for each continuous production of water absorbing agent.
Represents the dispersion of the SOT value of ot, and is a continuous production SFC
When the standard deviation is 5.0 or less, the variation in SFC for each Lot becomes small, and for example, when a water absorbent body of a paper diaper is manufactured using the water absorbent of the present invention, a stable quality diaper can be manufactured. Becomes The continuous production system SFC standard deviation is more preferably 4.5 or less, still more preferably 4.3 or less, even more preferably 4.0 or less, particularly preferably 3.5 or less, particularly preferably 3.0 or less, Most preferably, it is 2.5 or less. If the SFC standard deviation of the continuous production system is larger than 5.0, it is not preferable because it is impossible to manufacture a disposable diaper with stable quality.

When the water absorbing agent is used as a sanitary material, the above-mentioned various physical properties are important physical properties that correlate with the results of actual use (absorption amount of diaper, leakage, etc.), and the water absorbing agent of the present invention is It is particularly excellent in the above various physical properties. These measuring methods are described in the examples. The water absorbing agent according to the present invention,
It is preferable to have the various characteristics described above, and particularly preferable configurations include the above formulas (1), (2), and (4).
Any one or more of the above, more preferably two or more, and even more preferably all three are water-absorbing agents. That is,
The water absorbing agent according to the present invention is a particulate water absorbing agent whose main component is a water absorbing resin having a crosslinked structure obtained by polymerizing an unsaturated monomer component, and the particulate water absorbing agent has a particle diameter of 8
If the particle size is less than 50 μm and more than 150 μm, 90% by weight or more of all the particles are contained, and the particle size is less than 850 μm, 600
5 μm or more particles (A1) with particle size less than 600 μm
Particles with a size of 00 μm or more (A2), particles with a particle size of less than 500 μm and 300 μm or more (A3), a particle size of 300 μm
The water-absorbing agent is characterized by containing at least two kinds selected from particles (A4) having a particle size of 150 μm or less and further satisfying the following physical properties.

No pressure on 0.90% by weight physiological saline
Under 30 minutes absorption capacity (CRC) of 31 g / g or more.
6 at 4.83 kPa against 0.90 wt% saline
The absorbency against pressure (AAP) at 0 minutes is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20
(Unit: 10^-7× cm ³× s × g^-1)that's all. The following formula
The SFC change index defined in (1) is 0 to 25%.   SFC change index (%) = [(standard deviation of SFC of particles A1 to A4) / (particles SFC of whole water absorbent)] × 100 (1) Further, another water absorbing agent according to the present invention is an unsaturated monomer component.
Mainly composed of water-absorbing resin with cross-linked structure obtained by polymerizing
Particulate water absorbing agent, wherein the particulate water absorbing agent is
All particles with a particle size of less than 850 μm and 150 μm or more
90% by weight or more of the particles and particle size of 850 μm
Particles with a size of 600 μm or more (A1), particle size 600 μm
particles (A2) having a particle size of less than 500 μm and a particle size of 50 or more
Particles (A3) having a particle size of less than 0 μm and 300 μm or more, and a particle size of
Select from particles (A4) smaller than 300 μm and larger than 150 μm
Including at least 2 kinds of
It is a water-absorbing agent characterized by satisfying.

No pressurization against 0.90 wt% saline
Under 30 minutes absorption capacity (CRC) of 31 g / g or more.
6 at 4.83 kPa against 0.90 wt% saline
The absorbency against pressure (AAP) at 0 minutes is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20
(Unit: 10^-7× cm ³× s × g^-1)that's all. The following formula
The SFC variation coefficient defined in (2) is 0 to 0.25.   SFC coefficient of variation = (standard deviation of SFC of particles A1 to A4) / (from particles A1 A4 SFC average) (2) Further, still another water absorbing agent according to the present invention is an unsaturated monomer.
Water absorbent resin having a crosslinked structure obtained by polymerizing body components
A particulate water-absorbing agent containing as a main component, the particulate water-absorbing agent
The agent is particles with a particle size of less than 850 μm and 150 μm or more.
Containing 90% by weight or more of all particles and having a particle size of 850
Particles of less than μm and 600 μm or more (A1) with a particle size of 6
Particles (A2) smaller than 00 μm and 500 μm or more, particle diameter
Particles less than 500 μm and 300 μm or more (A3), particles
Particles with a diameter of less than 300 μm and 150 μm or more (A4)
Including at least two or more selected from
It is a water absorbing agent characterized by satisfying physical properties.

No pressurization against 0.90 wt% saline
Under 30 minutes absorption capacity (CRC) of 31 g / g or more.
6 at 4.83 kPa against 0.90 wt% saline
The absorbency against pressure (AAP) at 0 minutes is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20
(Unit: 10^-7× cm ³× s × g^-1)that's all. The following formula
The continuous production system SFC standard deviation specified in (4) is 5.0
Less than.   SFC standard deviation of continuous production system = standard deviation of SFC of each lot (4) (However, CRC, AAP, and SFC are Lot averages.
Each Lot is 20 kg or more. Lot number is 10 or more. ) Still another water absorbing agent according to the present invention is an acid group-containing monomer.
Obtained by polymerizing the monomer containing (salt) and further neutralizing
A particulate water-absorbing agent obtained by surface-crosslinking a water-absorbing resin,
The neutralization index of the particulate water absorbing agent or water absorbing resin is 15 or more.
And with 0.90% by weight physiological saline solution after surface crosslinking.
Absorption capacity under pressure (AA) for 60 minutes at 4.83 kPa
P) is 20 (g / g) or more,
It is a liquid medicine.

In the above water absorbing agent, CRC, AAP, S
FC, SFC change index, SFC variation coefficient and the like are preferably in the above-mentioned ranges, and the novel water-absorbing agent of the present invention can be obtained, for example, by the above-mentioned method for producing the water-absorbing agent of the present invention. The water-absorbing agent of the present invention has extremely high CRC, AAP and SFC and maintains a good balance of high physical properties. Furthermore, since the change in physical properties for each particle size is unprecedented, it has high physical properties under any sanitary material usage conditions. It is an excellent water absorbing agent.
According to the present invention, it is possible to easily produce a water-absorbing agent having good absorption characteristics with excellent balance of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity. It is widely used in water retention agents, industrial water retention agents, moisture absorbents, dehumidifiers, building materials, etc., and the water absorbents are particularly preferably used for sanitary materials for absorbing feces, urine or blood, such as paper diapers and sanitary napkins. To be Furthermore, since the water absorbing agent of the present invention is excellent in various physical properties in a well-balanced manner, sanitary materials generally have a high concentration as the concentration of the water absorbing agent (weight ratio of the water absorbing agent to the total of the water absorbing agent and the fiber base material), for example, 30 to 100 weight. %, Preferably 40 to 100% by weight, more preferably 50 to 95% by weight. Further, the structure of the water absorber in the sanitary material is not particularly limited as long as it is a structure used for general water-absorbing articles, and for example, a water-absorbing agent is arranged between hydrophilic fiber materials formed into a sheet shape, so-called Examples thereof include a water absorbent having a sandwich structure and a water absorbent having a so-called blend structure formed by molding a mixture of a hydrophilic fiber material and a water absorbent.

[0086]

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. The various properties of the water absorbent resin or the water absorbent were measured by the following methods. In the case of a water absorbent used as a final product such as a sanitary material, the water absorbent absorbs moisture, so the water absorbent is appropriately separated from the final product and dried under reduced pressure and low temperature (for example, 1 mmHg or less, 60 ° C or less). Measurement for 12 hours). The water content of the water-absorbent resins used in the examples and comparative examples of the present invention was 6% by weight or less.

Further, in the case of measuring SFC for each particle size in (4) described later, in the water absorbent used as the final product such as sanitary material, the SFC is measured after the above operation, but the water absorption before use is When measuring a water-absorbing agent manufactured in a laboratory, in order to correlate with the damage of actual production or actual use, the water-absorbing agent after mechanical damage described in (5) below is used. SFC, SFC before classification
Shall be measured. (1) Absorption capacity under no pressure (absorption capacity / CRC for 30 minutes under no pressure against 0.90% by weight physiological saline / CRC) Under conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH%, a water absorbent resin or A non-woven bag (60 g) containing 0.20 g of water absorbent
(mm × 60 mm) and uniformly sealed, and then immersed in 0.9 wt% physiological saline at room temperature. After 30 minutes, the bag was pulled up and drained at 250 G for 3 minutes using a centrifuge (manufactured by Kokusan Co., Ltd., centrifuge: model H-122), and then the weight W1 (g) of the bag was measured. In addition, the same operation is performed without using a water absorbent resin or a water absorbent,
The weight W0 (g) at that time was measured. And these W
From 1, W0, absorption capacity without load (g /
g) was calculated.

Absorption capacity without load (g / g) = (W1
(G) -W0 (g)) / weight of water-absorbent resin or water-absorbing agent (g) (2) absorbency against load (absorbance ratio under load at 0.93 wt% physiological saline at 4.83 kPa for 60 minutes / AA
P) A stainless steel 400-mesh wire mesh (mesh size 38 μm) is fused to the bottom of a plastic support cylinder having an inner diameter of 60 mm, and the metal mesh is placed on the net under the conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH%. 0.90 g of the water-absorbing agent was evenly dispersed on the water-absorbing agent, and on top of that, 4.83 kPa (0.7 ps.
The piston and the load, which are adjusted so that the load of i) can be uniformly applied, have an outer diameter slightly smaller than 60 mm, do not create a gap with the supporting cylinder, and do not hinder the vertical movement, and the load are placed in this order. However, the weight Wa of this set of measuring devices
(G) was measured.

Inside a Petri dish with a diameter of 150 mm, a diameter of 9
Place a 0 mm glass filter (manufactured by Mutual Rikagaku Glass Co., Ltd., pore diameter: 100 to 120 μm),
0.90 wt% saline (20-25 ° C) was added to the same level as the upper surface of the glass filter. On top of that, a piece of filter paper with a diameter of 90 mm (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No.
2), thickness 0.26 mm, retained particle diameter 5 μm),
All surfaces were allowed to wet and excess liquid was removed. The complete set of the above measuring devices was placed on the wet filter paper to absorb the liquid under load. After 1 hour, the set of measuring devices was lifted and the weight Wb (g) was measured. Then, the absorption capacity under pressure (g / g) was calculated from Wa and Wb according to the following formula.

Absorption capacity under pressure (g / g) = (Wa (g)
-Wb (g)) / weight of water absorbing agent ((0.9) g) (3) Weight average particle diameter Water-absorbent resin powder or water absorbing agent is opened at 850 μm, 60
0 μm, 500 μm, 425 μm, 300 μm, 212
JIS such as μm, 150 μm, 106 μm, 75 μm
After sieving with a standard sieve, the residual percentage R was plotted on a log probability paper. As a result, the weight average particle diameter (D50)
Read. Sieving and SF by particle size described later
The classification method when measuring C is as follows: Water absorbing resin powder or water absorbing agent 10.0 g, room temperature (20 to 25 ° C.), humidity 50R
Under the condition of H%, openings 850 μm, 600 μm, 50
It was charged in a 0 μm, 300 μm, and 150 μm JIS standard sieve (THE IIDA TESTING SIEVE: diameter 8 cm), and a vibration classifier (IIDA SIEVE
SHAKER, TYPE: ES-65 type, SER. N
o. According to 0501), classification was performed for 10 minutes.

(4) 0.69% by weight physiological saline flow conductivity (SFC) The physiological saline flow conductivity of SF 9-509591 (SF)
C) It carried out according to the test. Using the apparatus shown in FIG. 1, a water absorbent (0.900 g) uniformly placed in the container 40 was pressurized in artificial urine (1) under a pressure of 0.3 psi (2.07 kPa).
Swell for 60 minutes, record the height of the gel layer of gel 44,
Then, under pressure of 0.3 psi (2.07 kPa), 0.6
9% by weight physiological saline solution 33 is added to the tank 31 at a constant hydrostatic pressure.
The gel layer swollen from is passed through. This SFC test was performed at room temperature (20 to 25 ° C.). Using a computer and a balance, record the amount of liquid passing through the gel layer at intervals of 20 seconds for 10 minutes as a function of time. The flow rate F _s (t) through the swollen gel 44 (mainly between particles) is determined in g / s by dividing the weight gain (g) by the time increment (s). The time required to obtain a constant hydrostatic pressure and a stable flow velocity is t _s
And using only the data obtained between t _s and 10 minutes for the flow velocity calculation, and using the flow velocity obtained between t _s and 10 minutes, the value of F _s (t = 0), that is, the gel layer Calculate the initial flow velocity through. F _s (t = 0) is calculated by extrapolating the result of the least squares method of F _s (t) versus time to t = 0.

Saline flow conductivity = (F _s (t = 0) × L ₀ ) / (ρ × A × ΔP) = (F _s (t = 0) × L ₀ ) / 139506 where F _s (T = 0): Flow rate in g / s L ₀ : Height of gel layer in cm: ρ: Density of NaCl solution (1.003 g / cm ³ ) A: Area of gel layer upper side in cell 41 (28.27c
m ² ) ΔP: hydrostatic pressure applied to the gel layer (4920 dyne / cm
² ) and the unit of SFC value is (10 ^-7 × cm ³ × s × g ^-1 )
Is.

In the apparatus shown in FIG. 1, a glass tube 32 is inserted into a tank 31, and a lower end of the glass tube 32 contains 0.69% by weight physiological saline solution 33 in a swelling gel 44 in a cell 41. It was placed so that it could be maintained at a height of 5 cm above the bottom. The 0.69 wt% physiological saline solution 33 in the tank 31 was supplied to the cell 41 through the L-shaped tube 34 with a cock. A container 48 for collecting the passed liquid is arranged below the cell 41, and the collection container 48 is a precision balance 49.
Was installed on top of. The inner diameter of the cell 41 is 6 cm, and No. A 400 stainless wire gauze (opening 38 μm) 42 was installed. There was a hole 47 in the lower part of the piston 46 sufficient for the liquid to pass through, and a glass filter 45 with good permeability was attached to the bottom so that the water absorbing agent or its swelling gel would not enter the hole 47. The cell 41 was placed on a table on which the cell was placed, and the surface of the table that was in contact with the cell was placed on a metal wire mesh 43 made of stainless steel that does not prevent liquid permeation.

The artificial urine (1) contains 0.25 g of calcium chloride dihydrate, 2.0 g of potassium chloride, 0.50 g of magnesium chloride hexahydrate, 2.0 g of sodium sulfate and 0 ammonium dihydrogen phosphate. 0.85 g, diammonium hydrogen phosphate 0.15 g, and pure water 994.25 g were added. (5) Mechanical damage test Glass container shown in Fig. 2 (mayonnaise bottle manufactured by Yamamura Glass Co., Ltd.,
Product name: A-29) 30 g of water absorbing agent and glass beads (soda lime glass beads for precision fractionation filling with a ball diameter of about 6 mm)
10g was put. This was sandwiched and fixed between the clamps provided in the disperser (No. 488 test disperser manufactured by Toyo Seiki Seisakusho Co., Ltd.) shown in FIG. 3, and vibration at a vibration speed of 750 cpm was applied at 100 V / 60 Hz for 10 minutes. This allows
The container fixed to the disperser tilts 12.5 ° to the left and right (25 ° in total) with respect to the mounting surface of the clamp in the disperser, and at the same time, moves 8 mm forward and backward.
By vibrating (16 mm in total), the water absorbent inside the container is impacted. The above-mentioned impact is a force empirically determined as representative of the impact force that the water-absorbing agent receives during the manufacturing process of the water-absorbing agent, but it can be widely applied to transportation after manufacturing and damage during manufacturing of the water-absorbing body. Is. In the present invention, when mechanical damage is caused, it is particularly assumed that the water absorbing agent is manufactured and the water absorbing body is manufactured. further,
The SFC change index, the SFC variation coefficient, and the SFC variation rate are indexes for measuring the variation in the performance of the water absorbing agent inside the water absorbing body. Therefore, when measuring the physical properties by particle size, all water-absorbing agents manufactured on a laboratory scale (the amount of water-absorbing agent obtained in one manufacturing step is 20 kg or less) must be subjected to the above mechanical damage. .

(6) Weigh 184.3 g of 0.9 wt% physiological saline solution (physiological saline) in a plastic container with a capacity of 250 ml of soluble component (water-soluble component), and absorb water into the aqueous solution. Add 1.00g of resin
The soluble matter in the resin was extracted by stirring for a time. A piece of filter paper (ADVANTEC Toyo Co., Ltd.,
Product name: (JIS P 3801, No. 2), thickness 0.
50.0 g of the filtrate obtained by filtering using 26 mm and a retained particle diameter of 5 μm) was used as a measurement solution. First, use only physiological saline, and then add 0.1N Na.
Titrate with an aqueous OH solution to pH 10, then 0.1
Titration with an aqueous solution of N HCl to pH 2.7 was carried out to obtain a blank titer ([bNaOH] ml, [bHCl] ml).

By performing the same titration operation on the measurement solution, the titration amount ([NaOH] ml, [HCl] m
l) was determined. For example, in the case of a water-absorbent resin consisting of a known amount of acrylic acid and its sodium salt, based on the average molecular weight of the monomer and the titration amount obtained by the above operation, the soluble content in the water-absorbent resin is calculated by the following formula: Can be calculated by When the amount is unknown, the average molecular weight of the monomer is calculated using the neutralization rate obtained by titration. Soluble content (% by weight) = 0.1 x (average molecular weight) x 184.3 x 100 x ([HC1]-[bHCl]) / 1000 / 1.0 / 50.0 Neutralization rate (mol%) = (1-([NaOH]-[bNaOH]) / ([HC1]-[bHCl])) * 100 (7) Amount of surface layer soluble component (water soluble component) 250 ml in a plastic container with a lid of 0 100 g of a 50% by weight physiological saline solution was weighed, 0.50 g of a water absorbing agent was added to the aqueous solution, and the surface soluble component in the water absorbing agent was extracted for 1 hour. In this extraction operation, stirring is performed only for the purpose of dispersing the water absorbing agent in the initial stage and homogenizing the final liquid, and is not performed except for the above. Specifically, the surface soluble component is extracted by standing and stirred for 1 minute before and after the extraction (stirring speed: 400 rpm, stirrer: Teflon (registered trademark)).
(2.5 cm). Add this extract to 1 sheet of filter paper (A
DVANTEC Toyo Co., Ltd., product name: (JIS P 3
801, No. 2), thickness 0.26 mm, retained particle size 5
of the filtrate obtained by filtering
0.0 g was measured and used as a measurement solution.

First, only 0.5 wt% NaCl aqueous solution was titrated to pH 10 with 0.1 N NaOH aqueous solution, and then 0.1 N HCl aqueous solution was added to pH 2.
Titrate up to 7 and titrate the air ([bNaOH] ml, [bH]
Cl] ml) was obtained. By performing the same titration operation on the measurement solution, the titration amount ([NaOH] ml, [HC
l] ml) was determined. For example, in the case of a water absorbing agent consisting of a known amount of acrylic acid and its sodium salt, based on the average molecular weight of the monomer and the titration amount obtained by the above operation, the surface layer soluble content in the water absorbing agent is calculated by the following formula. It can be calculated. When the amount is unknown, the average molecular weight of the monomer is calculated using the neutralization rate obtained by titration.

Soluble content in surface layer (% by weight) = 0.1 × (average molecular weight) × 100 × 100 × ([HC1]-[bHCl]) / 1000 / 0.5 / 50.0 Neutralization rate (mol %) = (1-([NaOH]-[bNaOH]) / ([HC1]-[bHCl])) * 100 (8) Neutralization index JP-A-10-101735 and its claim 3 (European Patent Publication). The neutralization index of the water-absorbent resin powder and the water-absorbing agent was determined according to No. 0882502 and claims 2 to 4 thereof.

That is, 300 to 600 by JIS standard sieve
Particles of water-absorbent resin powder or water-absorbent agent classified to μm 20
20 grains x 20 mm with a cover glass attached
Place in a 1.6 mm thick plastic plate with the openings in and add 0.2 ml deionized water. Furthermore, Blumthymol Blue (BTB) is added to the swollen gel.
0.1 wt% ethanol solution and methyl red (MR)
0.05 ml of a 1.5: 1 mixed solution with a 0.1 wt% ethanol solution was added with a microsyringe, and the coloring of 200 particles was observed with a pH indicator. Thus, from the average neutralization rate of the water-absorbing resin or the water-absorbing agent, the number of particles (some out of 200) that were non-uniformly neutralized over 20 mol% was determined, and The number was determined as the neutralization index (first neutralization index / claim 3 in the above patent). Of course, the larger the neutralization index, the more uneven the neutralization of the water absorbent resin powder. See the above patent for details.

Reference Example 1 Production of Water-Absorbent Resin Powder (A) / Neutralization Polymerization Reaction formed by attaching a stainless steel double-arm kneader with a jacket having two sigma type blades and an internal volume of 10 liters with a lid. In a vessel, 5500 g of an aqueous solution of sodium acrylate having a neutralization ratio of 75 mol% (monomer concentration 38% by weight, average molecular weight of the monomer 88.5) was added with 3.70 g of polyethylene glycol diacrylate (n = 9). It was made to melt | dissolve and it was set as the reaction liquid. Next, this reaction liquid was degassed for 30 minutes under a nitrogen gas atmosphere. Subsequently, 28.3 g of a 10 wt% sodium persulfate aqueous solution and 2.1 g of a 1 wt% L-ascorbic acid aqueous solution were added to the reaction solution with stirring, and polymerization started after about 1 minute. Then, while pulverizing the generated gel, polymerization was carried out at 20 to 95 ° C., and 30 minutes after the polymerization was started, the hydrogel crosslinked polymer (1) was taken out.

The obtained water-containing gel-like crosslinked polymer (1) is
The diameter was subdivided into about 5 mm or less. The finely divided hydrogel crosslinked polymer (1) was spread on a wire mesh of 50 mesh (opening 300 μm) and dried at 150 ° C. for 90 minutes with hot air. Then, it is crushed using a roll mill and further classified by a JIS standard sieve having openings of 850 μm and 106 μm, so that most of the particles are 850 μm to 106 μm.
Water-absorbent resin powder (A) in the range of m was obtained. The absorption capacity of the obtained water-absorbent resin powder (A) under no pressure was 49 (g
/ G), the soluble content is 23% by weight, and the weight average particle diameter (D5
0) was 97% by weight of the water absorbent resin powder in the range of 330 μm and 850 μm to 150 μm.

Reference Example 2 Production of Water-Absorbent Resin Powder (B) / Neutralization Polymerization Reaction formed by attaching a cap to a stainless steel double-arm kneader with a jacket having two internal sigma type blades and an internal volume of 10 liters. In a container, to 5500 g of an aqueous solution of sodium acrylate having a neutralization rate of 71 mol% (monomer concentration 41% by weight, average molecular weight of monomer 87.7) was added 8.05 g of polyethylene glycol diacrylate (n = 9). It was made to melt | dissolve and it was set as the reaction liquid. Next, this reaction liquid was degassed for 30 minutes under a nitrogen gas atmosphere. Subsequently, 30.8 g of a 10 wt% sodium persulfate aqueous solution and 2.57 g of a 1 wt% L-ascorbic acid aqueous solution were added to the reaction solution with stirring, and polymerization started after about 1 minute. Then, while crushing the generated gel, polymerization is performed at 20 to 95 ° C.,
30 minutes after the initiation of polymerization, a hydrogel crosslinked polymer (2)
Took out.

The resulting hydrogel-like crosslinked polymer (2) is
The diameter was subdivided into about 5 mm or less. The hydrous gel-like crosslinked polymer (2) that had been subdivided was spread on a 50-mesh (mesh opening 300 μm) wire net and dried with hot air at 180 ° C. for 50 minutes. Then, it was pulverized using a roll mill and further classified by a JIS standard sieve having an opening of 850 μm to obtain a water-absorbent resin powder (B) having most of the particles in a range of 850 μm or less. The water-absorbent resin powder (B) thus obtained had an absorption capacity without load of 36 (g / g), a soluble content of 10% by weight, and a weight average particle diameter (D50) of 450 μm and 850 μm.
The water absorbent resin powder in the range of m to 150 μm was 97% by weight.

(Reference Example 3): Production example of water-absorbent resin powder (C) / neutralization polymerization Polymerization and drying were carried out in the same manner as in Reference Example 2 except that 5.01 g of polyethylene glycol diacrylate was used. Then, pulverization and classification were performed to obtain a water absorbent resin powder (C). The water-absorbent resin powder (C) thus obtained had an absorption capacity without load of 39 (g / g), a soluble content of 13% by weight, and a weight average particle diameter (D50) of 450 μm and 850 μm.
97% by weight of water absorbent resin powder in the range of up to 150 μm
Met. (Reference Example 4): Production example of water-absorbent resin powder (D) / neutralization polymerization Polymerization, drying, and pulverization were performed in the same manner as in Reference Example 2 except that 5.01 g of polyethylene glycol diacrylate was used. I went. The obtained pulverized product was further classified by a JIS standard sieve having openings of 600 μm and 300 μm to obtain a water absorbent resin powder (D) in the range of 600 μm to 300 μm. The water-absorbent resin powder (D) thus obtained had an absorption capacity without load of 40 (g / g), a soluble content of 9% by weight, and a weight average particle diameter (D50) of 450 μm.
Met.

(Example 1): Crosslinking treatment of water-absorbent resin powder (A) / with water-soluble inorganic base 100 g of the water-absorbent resin powder (A) obtained in Reference Example 1 was mixed with ethylene glycol diglycidyl ether (Denacol E).
X-810, manufactured by Nagase Kasei Co., Ltd., 0.027 g, 0.9 g of propylene glycol, 2.7 g of water, and 0.18 g of sodium hydrogencarbonate were mixed, and then the mixture was mixed at 210 ° C. Water-absorbing agent (1) was obtained by heating for 35 minutes. Obtained water absorbing agent (1)
Table 1 also shows the results of measuring the absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity.

(Example 2): Cross-linking treatment of water-absorbent resin powder (A) / with water-soluble inorganic base The same as in Example 1 except that 0.09 g of sodium carbonate was used instead of sodium hydrogen carbonate. Thus, a water absorbing agent (2) was obtained. Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity. (Comparative Example 1): Cross-linking treatment of water-absorbent resin powder (A) / without water-soluble inorganic base A water absorbent (1) for water was obtained. Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity.

(Comparative Example 2): Cross-linking treatment of water-absorbent resin powder (A) / without water-soluble inorganic base In the same manner as in Example 1, except that sodium hydrogen carbonate was not used, a comparative water-absorbing agent (2) Got Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity. (Example 3): Crosslinking treatment of water-absorbent resin powder (B) / with water-soluble inorganic base 100 g of water-absorbent resin powder (B) obtained in Reference Example 2 with 0.384 g of 1,4-butanediol and propylene glycol After mixing a surface treatment agent consisting of a mixture of 0.6 g, water 3.28 g, and 24% by weight aqueous sodium hydroxide solution 0.3 g (solid content 0.072 g), the mixture was added to 21
By heat treatment at 2 ° C for 30 minutes, the water absorbing agent (3)
Got The resulting water-absorbing agent (3) was also in the form of powder, and its absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity were measured. The results are shown in Table 1.

(Comparative Example 3): Cross-linking treatment of water-absorbent resin powder (B) / without water-soluble inorganic base In the same manner as in Example 3, except that a 24 wt% sodium hydroxide aqueous solution was not used, comparative water-absorbing Agent (3)
Got Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity. (Example 4): Crosslinking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base 100 g of water-absorbent resin powder (C) obtained in Reference Example 3 with 0.384 g of 1,4-butanediol and propylene glycol After mixing a surface treatment agent consisting of a mixed solution of 0.6 g, water 3.28 g, and sodium hydrogencarbonate 0.24 g, the mixture was heated at 212 ° C. for 40 minutes to obtain a water absorbing agent (4). . The water-absorbing agent (4) obtained was also in the form of powder, and its absorption capacity without load, absorption capacity under load,
The results of measuring the saline flow conductivity are shown in Table 1.

(Example 5): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base In the same manner as in Example 4 except that sodium hydrogen carbonate was used instead of 0.12 g of sodium carbonate. Thus, a water absorbing agent (5) was obtained. Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity. (Example 6): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base In Example 4, instead of using sodium hydrogencarbonate, 0.3 g of 24 wt% sodium hydroxide aqueous solution (solid content: 0. A water absorbing agent (6) was obtained in the same manner except that (072 g) was used. Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity.

(Comparative Example 4): Crosslinking treatment of water-absorbent resin powder (C) / without water-soluble inorganic base In the same manner as in Example 4, except that sodium hydrogencarbonate was not used, a comparative water-absorbing agent (4) Got Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity. (Example 7): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base A water absorbing agent (7) was obtained in the same manner as in Example 4, except that the heat treatment time was 30 minutes. Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity.

(Example 8): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base In the same manner as in Example 7, except that 0.12 g of sodium carbonate was used instead of sodium hydrogen carbonate. Thus, a water absorbing agent (8) was obtained. Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity. (Example 9): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base In Example 7, instead of using sodium hydrogencarbonate, 0.3 g of 24 wt% sodium hydroxide aqueous solution (solid content: 0. A water absorbing agent (9) was obtained in the same manner except that (072 g) was used. Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity. The surface layer soluble content of the water absorbing agent (9) was 3.8% by weight.

(Comparative Example 5): Crosslinking treatment of water-absorbent resin powder (C) / without water-soluble inorganic base In the same manner as in Example 7 except that sodium hydrogen carbonate was not used, a comparative water-absorbing agent (5) was obtained. Got Table 1 shows the results of measurement of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity. The surface soluble content of the comparative water absorbent (5) was 6.5% by weight. (Comparative Example 6): Crosslinking treatment of water-absorbent resin powder (C) / without water-soluble inorganic base In Example 9, instead of the 24 wt% sodium hydroxide aqueous solution, aluminum sulfate 14 to 18 was used according to WO00 / 53664. A comparative water absorbing agent (6) was obtained in the same manner except that 0.455 g of the hydrate was used. The results are shown in Table 1.

(Example 10): Crosslinking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base 100 g of the water-absorbent resin powder (C) obtained in Reference Example 3 was supplemented with ethylene glycol diglycidyl ether (Denacol E).
X-810, manufactured by Nagase Kasei Co., Ltd., 0.784 g, water 4.0 g, and a surface treatment agent composed of a mixed solution of 24% by weight aqueous sodium hydroxide solution 0.5 g (solid content 0.12 g) were mixed. Then, the mixture was heat-treated at 212 ° C. for 40 minutes to obtain a water absorbing agent (10). The water absorbing agent (10) obtained was also in powder form, and the results are shown in Table 1. (Comparative Example 7): Crosslinking treatment of water-absorbent resin powder (C) / without water-soluble inorganic base In the same manner as in Example 10, except that a 24 wt% sodium hydroxide aqueous solution was not used, a comparative water-absorbing agent (7) was used. ) Got. The results are shown in Table 1.

(Example 11): Crosslinking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base 3 to 100 g of water-absorbent resin powder (C) obtained in Reference Example 3
-Ethyl-3-oxetane methanol 0.4 g, water 3.
0 g, and a 24 wt% sodium hydroxide aqueous solution 0.3
After mixing a surface treatment agent consisting of a mixed liquid of g (solid content 0.072 g), the mixture was heat-treated at 212 ° C. for 40 minutes to obtain a water absorbing agent (11). The water absorbing agent (11) obtained was also in the form of powder, and the results are shown in Table 1. (Comparative Example 8): Cross-linking treatment of water-absorbent resin powder (C) / without water-soluble inorganic base In the same manner as in Example 11 except that the 24 wt% sodium hydroxide aqueous solution was not used, a comparative water-absorbing agent (8 ) Got. The results are shown in Table 1.

(Example 12): Crosslinking treatment of water-absorbent resin powder (C) / with pH buffer agent 100 g of the water-absorbent resin powder (C) obtained in Reference Example 3 was supplemented with ethylene glycol diglycidyl ether (Denacol E).
X-810, manufactured by Nagase Kasei) 0.15 g, propylene glycol 1.0 g, water 5.0 g, and a surface treatment agent consisting of a mixed solution of sodium dihydrogen phosphate dihydrate 0.5 g, and then mixed. The mixture was heat-treated at 150 ° C. for 30 minutes to obtain a water absorbing agent (12). The water absorbing agent (12) obtained was also in the form of powder, and the results are shown in Table 1. (Comparative Example 9): Crosslinking treatment / pH of water absorbent resin powder (C)
No buffering agent In the same manner as in Example 12 except that sodium dihydrogen phosphate dihydrate was not used, a comparative water absorbing agent (9)
Got The results are shown in Table 1.

(Example 13): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base In Example 9, the water absorbing agent (1
3) was obtained. The above water-absorbing agent (13) was subjected to the above mechanical damage for 10 minutes, and then the absorption capacity without load, the absorption capacity under load, and the physiological saline flow conductivity were measured. The results are shown in Table 2. Further, the water absorbent (13) thus obtained was passed through a JIS standard sieve (opening 850 μ).
m, 600 μm, 500 μm, 300 μm, 150 μ
m) sieve, 600 μm less than 850 μm, respectively
5 or more particles (13-a) having a particle diameter of less than 600 μm
Particles (13-b) of 00 μm or more, particle diameter of 500 μm
Less than 300 μm particles (13-c), particle size 3
Particles (13-d) of less than 00 μm and 150 μm or more were obtained. The obtained water absorbing agents (13-a), (13-b), (1
The results of measuring 3-c) and (13-d) are shown in Table 2. Table 3 shows the results of calculating the SFC change index, the SFC variation coefficient, and the SFC variation rate.

(Example 14): Crosslinking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base In Example 9, the water absorbing agent (14) was prepared in the same manner except that the heating time was 20 minutes. Got The above water-absorbing agent (14) was subjected to the above mechanical damage for 10 minutes, and the water-absorbing agent (14) obtained was measured. The results are shown in Table 2. Further, the water absorbing agent (14) thus obtained was passed through a JIS standard sieve (openings 850 μm, 600 μm, 500 μm, 3
00μm, 150μm), 850μ each
particles having a diameter of less than 600 μm and more than 600 μm (14-a), particles having a diameter of less than 600 μm and having a diameter of more than 500 μm (14-b),
Particles with a particle size of less than 500 μm and 300 μm or more (14
-C), particles (14-d) having a particle size of less than 300 m and 150 m or more were obtained. The resulting water absorbing agent (14-a),
The results of measuring (14-b), (14-c) and (14-d) are shown in Table 2. Table 3 shows the results of calculating the SFC change index, the SFC variation coefficient, and the SFC variation rate.

(Comparative Example 10): Cross-linking treatment of water-absorbent resin powder (C) / without water-soluble inorganic base In Comparative Example 5, a similar water-absorbing agent (10) was obtained by the same method. After mechanically damaging the obtained comparative water-absorbing agent (10) for 10 minutes, the absorption capacity without load, the absorption capacity under load, and the physiological saline flow conductivity of the obtained comparative water-absorbing agent (10) were measured. The measured results are shown in Table 2. Further, the obtained water absorbent for comparison (10) was passed through a JIS standard sieve (opening 850 μm, 600 μm, 500 μm, 300
, 150 μm), and particles (10-a) having a particle size of less than 850 μm and 600 μm or more, and a particle diameter of 60, respectively.
Particles of less than 0 μm and more than 500 μm (10-b), particles of less than 500 μm and more than 300 μm (10-b).
c), particles (10-d) having a particle diameter of less than 300 μm and 150 μm or more were obtained. The obtained comparative water-absorbing agent (10-
The results of measuring a), (10-b), (10-c), and (10-d) are shown in Table 2. Also, SFC change index, S
The results of calculating the FC variation coefficient and the SFC variation rate are shown in Table 3.

(Comparative Example 11): Commercially available water-absorbing agent Pumpers Acitve marketed in Germany
The water absorbing agent was taken out from the diaper of Fit (P & G, purchased on December 5, 2001) to obtain a comparative water absorbing agent (11). The results of measuring the absorption capacity without load, the absorption capacity under load, and the physiological saline flow conductivity of the resulting comparative water-absorbing agent (11) are shown in Table 2. Further obtained comparative water-absorbing agent (1
1), JIS standard sieve (opening 850, 600, 5
00, 300, 150 μm), 85 respectively
Particles of less than 0 μm and 600 μm or more (11-a), particles of less than 600 μm and 500 μm or more (11-a)
b), particles (11-c) having a particle size of less than 500 μm and 300 μm or more, and particles (11-d) having a particle size of less than 300 μm and 150 μm or more were obtained. The resulting water absorbing agent (11-
The results of measuring a), (11-b), (11-c), and (11-d) are shown in Table 2. Also, SFC change index, S
The results of calculating the FC variation coefficient and the SFC variation rate are shown in Table 3.

(Comparative Example 12): Commercially available water absorbing agent "Pampers Sarasara Care" (P
A water absorbing agent was taken out from a diaper manufactured by & G Co., Ltd. (purchased in December 1997) and used as a comparative water absorbing agent (12). Table 2 shows the results of measuring the absorption capacity without load, the absorption capacity under load, and the physiological saline flow conductivity of the comparative water absorbent (12). Further, the obtained comparative water-absorbing agent (12) is sieved with a JIS standard sieve (mesh size 850, 600, 500, 300, 150 μm), and particles of less than 850 μm and 600 μm or more (12-a) and a particle diameter of 600 μm, respectively. Less than 500μ
m or more particles (12-b), particle size less than 500 μm and 300 μm or more particles (12-c), particle size 300 μm
Particles (12-d) having a particle size of less than m and a size of 150 μm or more were obtained. The resulting water absorbing agents (12-a), (12-b), (12-
Table 2 shows the results of measuring the absorption capacity without load, the absorption capacity under load, and the physiological saline flow conductivity of c) and (12-d). Table 3 shows the results of calculating the SFC change index, the SFC variation coefficient, and the SFC variation rate.

(Example 15): Crosslinking treatment of water-absorbent resin powder (D) / with water-soluble inorganic base 100 g of water-absorbent resin powder (D) obtained in Reference Example 4 with 0.384 g of 1,4-butanediol , A propylene glycol (0.6 g), water (3.28 g), and a 24 wt% sodium hydroxide aqueous solution (0.3 g, solid content 0.072 g) were mixed, and then the mixture was mixed with 21
By heat treatment at 2 ° C. for 20 minutes, a water absorbing agent (1
5) was obtained. The water-absorbing agent (15) obtained was subjected to the above mechanical damage for 10 minutes, and the water-absorbing agent (15) obtained was measured. The results are shown in Table 2. Further, the water absorbent (15) obtained was passed through a JIS standard sieve (opening 850 μm, 6
00μm, 500μm, 300μm, 150μm), 500μm when the particle size is less than 600μm, respectively
3 or more particles (15-b) having a particle diameter of less than 500 μm
Particles (15-c) having a size of 00 μm or more were obtained. The results of measuring the obtained water absorbing agents (15-b) and (15-c) are shown in Table 2. Also, SFC change index, SFC variation coefficient, SF
The results of calculating the C fluctuation rate are shown in Table 3.

(Example 16): Water-absorbing resin powder (D) was subjected to a crosslinking treatment / with a water-soluble inorganic base. It was After applying the above mechanical damage to the obtained water absorbing agent (16) for 10 minutes,
The results of measuring the water absorbent (16) thus obtained are shown in Table 2. Further, the water-absorbing agent (16) obtained was passed through a JIS standard sieve (opening 850 μm, 600 μm, 500 μm, 30
0 μm, 150 μm), and the particle size is 6
Particles smaller than 00 μm and larger than 500 μm (16-b), particles smaller than 500 μm and larger than 300 μm (16-b)
c) was obtained. The resulting water absorbing agent (16-b), (16-
The results of measuring c) are shown in Table 2. Table 3 shows the results of calculating the SFC change index, the SFC variation coefficient, and the SFC variation rate.

(Comparative Examples 13 to 16): Commercially available water absorbing agent As a water absorbing agent (water absorbing resin) actually used, 200
The water-absorbent resin was taken out from a commercially available diaper in 1 year and used as comparative water-absorbing agents (13) to (16). Comparative water absorbent (13)
Table 4 shows the results of measuring the absorption capacity without load, the absorption capacity under load, and the physiological saline flow conductivity of (16). Reference Example 5: Production of Water-Absorbent Resin Powder (E) / Post-Neutralization by Acid Type Polymerization 252.2 g of acrylic acid in a 2 L plastic container,
N, N'-methylenebisacrylamide 1.1 g, water 9
98.4g was mixed and it was set as the reaction liquid. Next, this reaction liquid was degassed for 30 minutes under a nitrogen gas atmosphere. Subsequently, in the reaction solution, 5.1 g of 2,2′-azobis (2-amidinopropane) dihydrochloride of 15% by weight, 0.63 g of 10% by weight L-ascorbic acid aqueous solution, and 7% by weight of hydrogen peroxide aqueous solution were added. Polymerization was initiated by adding 6 g. Polymerization was carried out at 16 to 74 ° C., and 3 hours after the polymerization was initiated, the hydrogel crosslinked polymer (5) was taken out. The polymer (5) obtained was cut into squares of about 5 cm, and 1000 g thereof was mixed with 15.0 g of a 48% by weight aqueous sodium hydroxide solution at a neutralization ratio of 65 mol%, and the die diameter 9.5
Milled gel was obtained by passing through a mm meat chopper. The resulting crushed gel is 50 mesh (opening 30
It was spread on a wire mesh of 0 μm) and dried with hot air at 170 ° C. for 40 minutes. Then, it was pulverized using a roll mill, and further classified by a JIS standard mesh having openings of 500 μm and 300 μm to obtain a water-absorbent resin powder (E) in which most of the particles were in the range of 500 μm to 300 μm. The absorption capacity of the obtained water-absorbent resin powder (E) under no pressure was 49 (g / g),
The soluble content was 6% by weight.

Further, in order to examine the uniformity of the neutralization ratio of the obtained particles, 200 particles were swollen, and the pH was further adjusted.
A 0.1 wt% ethanol solution of indicators bromothymol blue and methyl red was added, and the neutralization index (claim 3 of JP-A-10-101735) was measured. As a result, 200 particles of the water-absorbent resin powders (A), (F) and (G) obtained from the neutralization polymerization obtained in Reference Examples 1, 6 and 7 were uniformly yellow (neutralization index). Of the water-absorbent resin powder (E) is mixed with particles that develop various colors from dark green to red, and the neutralization rate of each particle is extremely uneven (medium). The sum index was 15 or more).

Reference Example 6 Production Example of Water-Absorbent Resin Powder (F) / Neutralization Polymerization In Reference Example 1, the monomer concentration is 39% by weight, the neutralization rate is 71 mol%, and polyethylene glycol diacrylate 9 is used. Polymerization in the same manner as in Reference Example 1 except that the amount was changed to 0.6 g,
It was dried and ground. The obtained pulverized product was further classified by a JIS standard sieve having openings of 500 μm and 300 μm to obtain a water absorbent resin powder (F) in which most of the particles were in the range of 500 μm to 300 μm. The absorption capacity of the obtained water-absorbent resin powder (F) without load was 32 (g / g),
The soluble content was 10% by weight. Reference Example 7: Production Example of Water-Absorbent Resin Powder (G) / Neutralization Polymerization In Reference Example 1, the monomer concentration is 41% by weight, the neutralization rate is 71 mol%, polyethylene glycol diacrylate 5.47 g, Aqueous sodium persulfate solution 30.8 g, L-
2.57 g of ascorbic acid aqueous solution, hot air drying temperature 180
Polymerization, drying and pulverization were carried out in the same manner as in Reference Example 1 except that the temperature was changed to 50 ° C. and the hot air drying time was changed to 50 minutes. The resulting pulverized product was further classified with a JIS standard sieve having an opening of 850 μm to obtain a water absorbent resin powder (G) in which most of the particles were in the range of 850 μm or less.

The water-absorbent resin powder (G) thus obtained had an absorption capacity without load of 38 (g / g) and a soluble content of 13% by weight.
The weight average particle diameter (D50) was 400 μm. (Example 17): Crosslinking treatment of water-absorbent resin powder (E) / p
With H buffering agent 100 g of the water-absorbent resin powder (E) obtained in Reference Example 5 was mixed with ethylene glycol diglycidyl ether (Denacol E
X-810, Nagase Kasei Co., Ltd. 0.5 g, propylene glycol 1.0 g, neutral phosphate pH standard solution (potassium dihydrogen phosphate / disodium hydrogen phosphate; pH)
6.86) 6.0 g and a surface treatment agent consisting of 1.0 g of isopropyl alcohol were mixed, and then the mixture was heat-treated at 120 ° C. for 30 minutes to obtain a water absorbing agent (17). The resulting water absorbing agent (17) was also in the form of powder, and the results of measuring the absorption capacity without load and the absorption capacity under load are shown in Table 5.

(Comparative Example 17): Cross-linking treatment of water-absorbent resin powder (E) / no pH buffering agent The same as in Example 17 except that 6.0 g of water was used in place of the neutral phosphate pH standard solution. A water absorbent for comparison (17) was obtained. The absorption capacity without load and the absorption capacity under load were measured, and the results are shown in Table 5. (Example 18): Crosslinking treatment of water-absorbent resin powder (F) / p
With H buffering agent 100 g of the water-absorbent resin powder (F) obtained in Reference Example 6, 0.32 g of 1,4-butanediol, 0.5 g of propylene glycol, 2.73 g of water, sodium dihydrogen phosphate dihydrate After mixing a surface treating agent consisting of 1.2 g of the mixed liquid, the mixture was heat-treated at 197 ° C. for 10 minutes to obtain a water absorbing agent (18). The water absorbing agent (18) obtained was also in the form of powder, and the results of measuring the absorption capacity without load and the absorption capacity under load are shown in Table 5.

(Comparative Example 18): Cross-linking treatment of water-absorbent resin powder (F) / without pH buffer In Example 18, phosphoric acid (85% by weight) was used in place of sodium dihydrogen phosphate dihydrate. A comparative water absorbing agent (18) was obtained in the same manner except that 6 g was used. The results of measuring the absorption capacity without load and the absorption capacity under load are shown in Table 5. (Comparative Example 19): Crosslinking treatment of water-absorbent resin powder (F) / p
No H-buffering agent In the same manner as in Example 18, except that sodium dihydrogen phosphate dihydrate was not used, a comparative water-absorbing agent (19)
Got The results of measuring the absorption capacity without load and the absorption capacity under load are shown in Table 5.

(Example 19): Crosslinking treatment of water-absorbent resin powder (G) / with pH buffering agent 100 g of the water-absorbent resin powder (G) obtained in Reference Example 7, 0.32 g of 1,4-butanediol, After mixing a surface treatment agent solution consisting of a mixed solution of 0.5 g of propylene glycol, 2.73 g of water, and 0.2 g of sodium hydrogencarbonate, the mixture was heated at 212 ° C. for 25 minutes to give a water absorbing agent (19). Got The results of measuring the absorption capacity without load and the absorption capacity under load are shown in Table 5. (Example 20): Cross-linking treatment of water-absorbent resin powder (G) / p
With H buffering agent 100 g of the water-absorbent resin powder (G) obtained in Reference Example 7 was mixed with 0.34 g of 1,4-butanediol, 0.5 g of propylene glycol, 2.73 g of water, and 0.24 g of potassium hydrogencarbonate. After mixing the surface treating agent solution consisting of a liquid, the mixture was heat-treated at 212 ° C. for 25 minutes to obtain a water absorbing agent (20). The results of measuring the absorption capacity without load and the absorption capacity under load are shown in Table 5.

(Comparative Example 20): Cross-linking treatment of water-absorbent resin powder (G) / without pH buffering agent In the same manner as in Example 19 except that sodium hydrogen carbonate was not used, a comparative water-absorbing agent (20) was obtained. It was The results of measuring the absorption capacity without load and the absorption capacity under load are shown in Table 5. (Example 21): A continuous production system in which 71 mol% of the partially neutralized sodium acrylate and polyethylene glycol diacrylate (n = 9) were continuously polymerized in an aqueous solution at a ratio of Reference Example 3 (belt retention time: About 30 minutes, thickness: about 25 mm), the resulting hydrogel crosslinked polymer of the water-absorbent resin is roughly crushed into particles with a meat chopper, which is spread thinly on a perforated plate of a band dryer and placed. It was continuously hot-air dried at 180 ° C. for 30 minutes. A block-shaped dry polymer was obtained at the dryer outlet. The dried polymer was taken out and disintegrated at the same time, and the resulting particulate dry product was subjected to a three-stage roll granulator (roll gap 1.0 mm / 0.55 mm / from the top at 1000 kg / h).
0.42 mm) was continuously fed to pulverize. The obtained powder of the particulate water-absorbing resin at about 60 ° C. was meshed with 85
Classify with a sieving device having a 0 μm sieve mesh, and
Water-absorbent resin powder (H) having a weight% of less than 850 μm and a size of 150 μm or more (average particle diameter: 430 to 460)
μm) was obtained. The average absorption capacity (CRC) of the obtained water-absorbent resin powder (H) under no pressure was 40 g / g, and the average amount of soluble components was 11% by weight. The physical properties of the CRC and the soluble content are average values measured every 2 hours (2000 kg / lot).

Further, the water-absorbent resin powder (H) was mixed with a high-speed continuous mixer (Turbulizer / 1000 rpm) for 10 times.
The water-absorbent resin powder (H) was continuously supplied at a rate of 00 kg / h, and 1,4-butanediol / propylene glycol / water / 24% sodium hydroxide aqueous solution = 0.384 /
An aqueous surface cross-linking agent solution consisting of 0.63 / 3.39 / 0.3 (wt% / powder) was sprayed and mixed with a spray to form droplets of about 200 μm. The mixture obtained is then added to 19
A water-absorbing agent powder was obtained by continuously performing heat treatment with a paddle dryer at 5 ° C. for 40 minutes. Further, the obtained water-absorbing agent powder was classified by a sieving device having a sieving mesh with a mesh opening of 850 μm to obtain a water-absorbing agent (21) having 90% by weight or more of particles having a size of less than 850 μm and 150 μm or more.

The above-mentioned series of steps (polymerization, drying, pulverization, heat treatment) are continuously carried out for 24 hours and every 2 hours (200
Physical properties of water absorbing agent at 0 kg / lot) (lot number: 11 points)
As a result of measurement, the average value of absorption capacity without load was 31.
1 g / g, the average value of absorption capacity under pressure is 25.5 g /
g, the average value of physiological saline flow conductivity is 30 (SFC value for each lot: 32, 32, 28, 28, 30, 27, 2
7, 32, 31, 32, 28), and the standard deviation value of the SFC was 2.1. (Example 22): Continuous production system A continuous production was carried out in the same manner as in Example 21 except that 24 hours was changed to 10 days to obtain a water absorbing agent (22). As a result of measuring the physical properties (Lot number: 110 points) of the water-absorbing agent every 2 hours (2000 kg / lot), the average absorption capacity without load was 31.3 g / g, and the average absorption capacity under load. Is 25.2 g / g, the average value of physiological saline flow inducibility is 30 (SFC value for each Lot is omitted), and its S
The FC standard deviation value was 3.9.

(Comparative Example 21): Continuous production system Continuous production was carried out in the same manner as in Example 21, except that the 24% aqueous sodium hydroxide solution was not used, to obtain a comparative water absorbing agent (21). Every 2 hours (2000 kg /
As a result of measuring the physical properties of the water absorbing agent (Lot number: 11 points), the average value of the absorption capacity without load was 31.1 g /
g, the average value of the absorption capacity under pressure is 24.2 g / g, and the average value of the physiological saline flow conductivity is 20 (SFC for each lot.
Value of: 26, 17, 11, 17, 17, 18, 20, 1
7, 16, 28, 28), and the standard deviation value of the SFC was 5.5.

The water absorbing agents (21) and (22) described in Examples 21 and 22 have a smaller standard deviation of SFC than the comparative water absorbing agent (21) described in Comparative Example 21. In case of continuously producing the water absorbing agent of the invention, defective products (low S
(FC products, etc.) does not occur, and variation in quality (SFC) is reduced.

[0135]

[Table 1]

[0136]

[Table 2]

[0137]

[Table 3]

The water-absorbing agents (1) and (2) described in Examples 1 and 2 have a larger absorption capacity under load than the comparative surface-absorbing water-absorbing agents (1) and (2). Excellent balance between absorption capacity without load and absorption capacity under load. Compared with the comparative water-absorbing agent (3) described in Comparative Example 3, the water-absorbing agent (3) described in Example 3 had three types of absorption capacity without load, absorption capacity under load, and saline flow conductivity. Good balance. Furthermore, the water-absorbing agents (4), (5), and (6) described in Example 4 and Example 5 and Example 6 were compared with the comparative water-absorbing agent (4) described in Comparative Example 4 in that no addition was required. The absorption capacity under pressure is almost the same, but the physiological saline flow conductivity is high.

Similarly, in the water absorbing agents (7), (8) and (9) described in Examples 7 and 8 and 9,
Compared with the comparative water-absorbing agent (5) and the comparative water-absorbing agent (6) described in Comparative Examples 5 and 6, the absorption capacity without load was almost the same, but the absorption capacity under load and the saline flow rate were almost the same. Inducibility shows a high value. Further, the water-absorbing agents (10), (11) described in Examples 10, 11 and 12
(12) is compared with the comparative water-absorbing agents (7), (8) and (9) described in Comparative Example 7, Comparative Example 8 and Comparative Example 9, respectively,
The absorption capacity without load is almost the same, but the physiological saline flow conductivity shows a high value.

The water absorbing agents (13) and (14) described in Examples 13 and 14 were the same as Comparative Example 10 and Comparative Example 11, respectively.
And the comparative water-absorbing agent (10) and (1
Compared with 1) and (12), SFC change index and SFC
The coefficient of variation is small, the SFC variation rate is large, and variations in SFC are reduced in both cases. In addition, Example 15
And the water absorbing agents (15), (16) described in Example 16
However, the SFC change index and SFC fluctuation index are small,
The FC fluctuation rate is large, and the variation in SFC is reduced in both cases. As described above, the water-absorbing agent produced by the method of the present invention is excellent in the three balances of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity, and has good performance. Furthermore, since there is little variation in SFC for each particle size, it is a very excellent water absorbing agent for stabilizing the performance of the diaper.

[0141]

[Table 4]

Comparative water-absorbing agents (13), (14) described in Comparative Examples 13, 14, 14, 15 and 16,
In each of (15) and (16), the three balances of absorption capacity without load, absorption capacity under load, and physiological saline flow conductivity were poor.

[0143]

[Table 5]

The water-absorbing agent (17) described in Example 17 is superior to the comparative water-absorbing agent (17) described in Comparative Example 17 in the balance between the absorption capacity without load and the absorption capacity under load and the total thereof. . Further, the water-absorbing agent (18) described in Example 18 was similar to the water-absorbing agent for comparison (18) described in Comparative Example 18 to which phosphoric acid was added, similarly, the crosslinking reaction proceeded in a short time of 10 minutes, and The absorption capacity under load is the same, but the absorption capacity under load shows a high value. Furthermore, with respect to the comparative water-absorbing agent (19) described in Comparative Example 19 to which nothing was added, a sufficient crosslinking reaction did not proceed in a short time of 10 minutes, and a decrease in absorption capacity without load was hardly seen. The absorption capacity under load is also low.

As described above, the water absorbing agent produced by the method of the present invention is excellent in the balance between the absorption capacity without load and the absorption capacity under load and the total thereof, and has good performance even in a short reaction time. .

[0146]

EFFECTS OF THE INVENTION According to the present invention, during the cross-linking treatment, while exhibiting the effect as a mixing aid, it does not hinder the cross-linking reaction and, in some cases, also has the effect as a reaction catalyst, and is partially neutralized and polymerized. Uniform surface cross-linking can be expressed regardless of the difference in the neutralization ratio of the water-absorbent resin and the uniformity of the neutralization ratio resulting from the post-neutralization operation of acid-type polymerization. Absorption capacity without load and absorption capacity under load In addition to having excellent balance of physiological saline flow conductivity, a water absorbent with stable physical properties for a short time with little fluctuation (variation) in the value of physiological saline flow conductivity during manufacturing lots or within each lot The method and the water absorbing agent can be provided.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a measuring device used for measurement of saline flow conductivity.

FIG. 2 is a schematic side view (a) and a schematic plan view (b) of a glass container used for a mechanical damage test.

FIG. 3 is a schematic view of a disperser used for a mechanical damage test.

[Explanation of symbols]

31 tanks 32 glass tubes 33 0.69 wt% sodium chloride aqueous solution 34 L-shaped tube with cock 35 cook 40 containers 41 cells 42 stainless steel wire mesh 43 stainless steel wire mesh 44 Swelling gel 45 glass filter 46 pistons 47 Hole in the piston 48 Collection container 49 Precision balance 51 glass containers 52 Disperser 53 Upper clamp 54 Lower clamp

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08J 3/24 C08L 101/14 C08K 3/00 C09K 3/00 N C08L 101/02 A61F 13/18 307A 101 / 14 A41B 13/02 D C09K 3/00 (72) Inventor Yasuhiro Fujita 1 992 Nishikioki, Hamaji-ku, Himeji-shi, Hyogo Prefecture Nihon Shatai Co., Ltd. (72) Inventor Makoto Nagasawa 992 Nishiki-oki, Akiho, Aboshi-ku, Himeji-shi, Hyogo Prefecture No. 1 NIPPON SHOKUBAI Co., Ltd. (72) Inventor Shigeru SAKAMOTO No. 992 Nishikioki, Akihama, Himeji-shi, Hyogo Prefecture No. 1 NIPPON SHOKUBAI Co., Ltd. (72) Inventor Dairoku Yoritomo 1 share at 992 West Okihama, Aboshi-ku, Himeji-shi, Hyogo Prefecture Company Nippon Shokubai (72) Inventor Katsuyuki Wada 1 992, Nishikioki, Kamahama-ku, Himeji-shi, Hyogo Prefecture Nihon Shokubai Co., Ltd. (7 2) Inventor Shinichi Fujino 1 at 992 Nishikioki, Akihama, Aboshi-ku, Himeji-shi, Hyogo Prefecture, inside Nippon Shokubai Co., Ltd. (72) Inventor, Toshinori Kitayama 1 at 992, Offshore, Kohama, Aboshi-ku, Himeji-shi, Hyogo Prefecture (72) Invention Person Hitoichi Kazuto Hyogo Prefecture Himeji City Aboshi Ward Nishihama-ji, 992, Nishioki Oki F-term (reference) 3B029 BA18 4C003 AA23 4C098 AA09 CC02 DD05 DD24 DD27 DD30 4F070 AA29 AB01 AB13 AC14 AC36 AE08 DB06 DC07 DC11 DC16 4J002 4J002 BG10W GD03

Claims (19)

[Claims] 1. Crosslinking obtained by polymerizing an unsaturated monomer component
A particulate water-absorbing agent whose main component is a water-absorbing resin having a structure
There The particulate water-absorbing agent has a particle size of less than 850 μm and is 150
90% by weight or more of all particles having a particle size of μm or more, and
Particles with a particle size of less than 850 μm and 600 μm or more (A
1), particles having a particle size of less than 600 μm and 500 μm or more
(A2), the particle size is less than 500 μm and 300 μm or more
Particles (A3) having a particle size of less than 300 μm and 150 μm or more
Contains at least two kinds selected from the above particles (A4)
See Further, a water absorbing agent characterized by satisfying the following physical properties.
30 minutes under no pressure to 0.90 wt% saline
Absorption capacity (CRC) of 31 g / g or more. 0.90% by weight
Suction under pressure for 60 minutes at 4.83 kPa against physiological saline
The collection ratio (AAP) is 24 g / g or more. 0.69% by weight raw
The saline flow conductivity (SFC) is 20 (unit: 10^-7×
cm ³× s × g^-1)that's all. S defined by the following formula (1)
FC change index is 0 to 25%.   SFC change index (%) = [(standard deviation of SFC of particles A1 to A4) / (particles SFC of whole water absorbent)] × 100 (1) 2. The particle size distribution of the water absorbing agent is from particles A1 to A
The water absorbing agent according to claim 1, wherein the water absorbing agent contains 0.1% by weight or more of 4 respectively. 3. The water absorbing agent according to claim 1, wherein the SFC variation coefficient defined by the following formula (2) is 0 to 0.25. SFC coefficient of variation = (standard deviation of SFC of particles A1 to A4) / (average value of SFC of particles A1 to A4) (2) 4. The water absorbing agent according to claim 1, wherein the SFC fluctuation rate defined by the following formula (3) is 0.65 to 1.00. SFC fluctuation rate = (the smallest SFC among the SFCs of particles A1 to A4) / (the largest SFC among the SFCs of particles A1 to A4) (3) 5. The water absorbing agent according to any one of claims 1 to 4, wherein the water absorbing agent further contains a cationic polymer compound and / or water-insoluble fine particles. 6. Crosslinking obtained by polymerizing an unsaturated monomer component
A particulate water-absorbing agent whose main component is a water-absorbing resin having a structure
There The particulate water-absorbing agent has a particle size of less than 850 μm and is 150
90% by weight or more of all particles having a particle size of μm or more, and
Particles with a particle size of less than 850 μm and 600 μm or more (A
1), particles having a particle size of less than 600 μm and 500 μm or more
(A2), the particle size is less than 500 μm and 300 μm or more
Particles (A3) having a particle size of less than 300 μm and 150 μm or more
Contains at least two kinds selected from the above particles (A4)
See Further, a water absorbing agent characterized by satisfying the following physical properties.
30 minutes under no pressure to 0.90 wt% saline
Absorption capacity (CRC) of 31 g / g or more. 0.90% by weight
Suction under pressure for 60 minutes at 4.83 kPa against physiological saline
The collection ratio (AAP) is 24 g / g or more. 0.69% by weight raw
The saline flow conductivity (SFC) is 20 (unit: 10^-7×
cm ³× s × g^-1)that's all. S defined by the following formula (2)
FC coefficient of variation is 0 to 0.25.   SFC coefficient of variation = (standard deviation of SFC of particles A1 to A4) / (from particles A1 A4 SFC average) (2) 7. Crosslinking obtained by polymerizing an unsaturated monomer component
A particulate water-absorbing agent whose main component is a water-absorbing resin having a structure
There The particulate water-absorbing agent has a particle size of less than 850 μm and is 150
90% by weight or more of all particles having a particle size of μm or more, and
Particles with a particle size of less than 850 μm and 600 μm or more (A
1), particles having a particle size of less than 600 μm and 500 μm or more
(A2), the particle size is less than 500 μm and 300 μm or more
Particles (A3) having a particle size of less than 300 μm and 150 μm or more
Contains at least two kinds selected from the above particles (A4)
See Furthermore, continuous production characterized by satisfying the following physical properties
Water absorbent. No addition to 0.90 wt% saline
Absorption capacity (CRC) for 30 minutes under pressure is 31 g / g or more.
6 at 4.83 kPa against 0.90 wt% saline
The absorbency against pressure (AAP) at 0 minutes is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20
(Unit: 10^-7× cm ³× s × g^-1)that's all. The following formula
The continuous production system SFC standard deviation specified in (4) is 5.0
Less than.   SFC standard deviation of continuous production system = standard deviation of SFC of each lot (4) (However, CRC, AAP, and SFC are Lot averages.
Each Lot is 20 kg or more. Lot number is 10 or more. ) 8. A particulate water-absorbing agent obtained by polymerizing a monomer containing an acid group-containing monomer (salt), and further post-neutralizing the resulting water-absorbent resin, which is surface-crosslinked. Absorption capacity under pressure (AA) for 60 minutes at a neutralization index of the water-absorbing agent or water-absorbent resin of 15 or more, and after surface cross-linking to 0.90% by weight physiological saline at 4.83 kPa.
P) is 20 (g / g) or more, Water-absorbing agent characterized by the above-mentioned. 9. A water-absorbent resin powder (a) containing an acid group, a non-crosslinkable water-soluble inorganic base (b1) and / or a non-reducing alkali metal salt pH buffer (b2), and the acid. A method for producing a water-absorbing agent, which comprises mixing a dehydration-reactive crosslinking agent (c1) capable of reacting with a group and subjecting the water-absorbent resin powder (a) to a crosslinking treatment. 10. A weight average particle diameter of 300 containing an acid group.
-600 μm and fine particles of 150 μm or less in the water absorbent resin powder (a1) containing 10% by weight or less of the non-crosslinkable water-soluble inorganic base (b1) and / or non-reducing alkali metal salt p
A method for producing a water-absorbing agent, which comprises mixing the H-buffering agent (b2) and a crosslinking agent (c) capable of reacting with the acid group, and subjecting the water-absorbent resin powder (a1) to a crosslinking treatment. 11. The water-absorbent resin powder (a) is a fine powder having a weight average particle diameter of 300 to 600 μm and 150 μm or less.
The method for producing a water absorbing agent according to claim 9, wherein the water absorbing resin powder (a1) is 0% by weight or less. 12. The method according to claim 9, wherein the water-soluble inorganic base (b1) is at least one selected from the group consisting of alkali metal salts, ammonium salts, alkali metal hydroxides, ammonia and hydroxides thereof. 11. The method for producing a water absorbent according to any one of 11 to 11. 13. The alkali metal salt pH buffer (b2)
Is an inorganic salt consisting of a weak acid and a strong base, The method for producing a water absorbing agent according to any one of claims 9 to 12. 14. The alkali metal salt pH buffering agent (b2).
Is a partially alkali metal neutralized salt of a polybasic acid, The method for producing a water absorbent according to any one of claims 9 to 13. 15. The production of a water absorbing agent according to claim 9, wherein the crosslinking agent (c) or the dehydration-reactive crosslinking agent (c1) is a polyhydric alcohol compound. Method. 16. The water-soluble inorganic base (b1) and / or the cross-linking agent (c) or the dehydration-reactive cross-linking agent (c1).
Alternatively, a non-reducing alkali metal salt pH buffer (b2) is mixed in advance to form an aqueous solution, and then the aqueous solution is spray-added to the water absorbent resin powder (a) or (a1). 16. The method for producing the water absorbent according to any one of 1 to 15. 17. The method for producing a water absorbing agent according to claim 9, wherein the crosslinking treatment is performed by heat treatment at 140 to 240 ° C. 18. A water absorbing agent obtained by the method according to any one of claims 9 to 17. 19. A sanitary material comprising the water absorbing agent according to any one of claims 1 to 8 and claim 18.