JPH1160975A - Pressure-resistant water-absorbing resin, paper diaper using the same and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-absorbing resin remarkably excellent in affinity for aqueous liquid and remarkably improved in water absorbing rate and water- absorbing magnification without pressure and under pressure, compared with that of conventional resin and provide a method for producing the resin and obtain paper diaper using the resin. SOLUTION: In this pressure-resistant water-absorbing resin, water absorption magnification under pressure to artificial urine under 50 g/cm<2> load is >=30 g/g and pressure-resistant water absorption ratio defined by a ratio of water absorption magnification under high pressure to artificial urine under 100 g/cm<2> load to water absorption magnification under pressure is >=0.6. This method for producing the water-absorbing resin comprises adding a compound having plural functional groups capable of reacting with COOR to a water-absorbing crosslinked polymer containing >=12 mmol COOR (R is hydrogen atom, metal atom or ammonium) and having <0.5 molar ratio of COOH/COOR and heating these compounds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a disposable diaper having excellent pressure resistance and a water-absorbing resin having excellent pressure resistance. Further, the present invention relates to a water-absorbent resin which has remarkably excellent affinity for an aqueous liquid and has a remarkably improved water absorption rate and a water absorption ratio under no pressure and under pressure as compared with conventional ones, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a water-absorbing resin has been developed which absorbs water of several tens to several hundreds times its own weight. It is variously used in applications requiring water absorption and water retention, such as in the field of foods, such as the field of food such as maintaining freshness, and in the field of industry such as prevention of dew condensation and cooling materials.

Examples of such a water-absorbing resin include a hydrolyzate of a starch-acrylonitrile graft polymer, a neutralized product of a starch-acrylic acid graft polymer, a saponified product of a vinyl acetate-acrylate copolymer, and acrylonitrile. A hydrolyzate of a copolymer or a crosslinked product thereof, a hydrolyzate of an acrylamide copolymer or a crosslinked product thereof, a self-crosslinked polyacrylate, a partially neutralized polyacrylate crosslinked product, and the like are known.

[0004] The required properties of the water-absorbent resin differ depending on the application. For example, the properties desired for a water-absorbent resin for sanitary materials such as disposable diapers include a high water absorption ratio under pressure to an aqueous liquid, High water absorption speed, high liquid permeability and the like can be mentioned. For example, European Patent 443627 discloses a water-absorbing structure using a water-absorbing resin excellent in water absorption capacity under pressure and absorption rate at a concentration of 60% by weight or more. However, the characteristics of the water absorption capacity and the absorption rate do not always show a positive correlation, and in particular, the water absorption capacity under pressure and the water absorption rate are contrary to each other. Therefore, at the same time these two
It is difficult to improve one property.

[0005] For example, as an attempt to increase the water absorption rate of a water absorbent resin, there is a method of increasing the surface area. Attempts have been made to reduce the particle size of the water-absorbent resin or to make it into a granular or scaly shape. However, when the particle size of the water-absorbent resin is generally reduced to increase the surface area, the physical strength and the voids between the particles after swelling due to water absorption are reduced, so that the water absorption ratio under pressure or under non-pressure is conversely reduced.

On the other hand, the molecular chains in the vicinity of the surface of the water-absorbent resin are crosslinked to increase the crosslink density of the surface layer, and voids are provided between the particles for allowing liquid to move when the polymer absorbs water and swells.
Accordingly, there is a technique that does not reduce the water absorption capacity even when the water absorbing resin is pressurized. However, in general, the size of the surface area is contradictory to the water absorption capacity under pressure, and when the surface area of the particles is increased, it becomes difficult to uniformly mix the crosslinking agent, so that uniform surface crosslinking becomes difficult. Until now, most of the improvements aimed at increasing the water absorption capacity of a water-absorbent resin under pressure and at the same time improving the water absorption rate have been due to a combination of the above two methods (increase in surface area and crosslinking near the surface). . Unfortunately, however, these two characteristics are contradictory as described above, and at present, satisfactory results have not been obtained due to technical limitations.

In recent years, a porous polymer using a foaming agent or the like has been proposed as a method of improving the surface area without reducing the particle diameter in order to overcome the technical limit, and a technique of crosslinking the vicinity of the surface has been proposed. Proposed. As such a method, for example, a method of polymerizing an aqueous solution of 70 mol% neutralized sodium polyacrylate in the presence of a crosslinking agent and a carbonate as a foaming agent, and subjecting the obtained polymer to a cross-linking treatment in the vicinity of the surface ( U.S. Pat. No. 5,314,420, JP-A-7-18
No. 5331), a method of polymerizing a 70 mol% neutralized potassium polyacrylate aqueous solution or ammonium salt aqueous solution in the presence of a crosslinking agent and a carbonate as a foaming agent, and subjecting the obtained polymer to a crosslinking treatment in the vicinity of the surface (particularly, Table Hei 8-509521
No., EP 0707603, WO9502002
), A method of polymerizing an aqueous solution of partially neutralized sodium acrylate while dispersing a solid blowing agent, and subjecting the resulting polymer to a cross-linking treatment in the vicinity of the surface (WO9617884, EP 7444).
No. 35) In addition to foaming, a method of cross-linking the vicinity of the surface of a superficially porous sodium acrylate polymer obtained by reverse phase suspension polymerization in the presence of a specific surfactant (European Patent No. 06)
95762) and the like.

Indeed, the method of crosslinking the vicinity of the surface of a porous polymer using these foaming agents improved the water absorption capacity and the water absorption rate under pressure. However,
Also in these methods, when the cross-linking treatment is performed near the surface of the porous polymer, if the surface cross-linking density is increased to increase the water absorption under pressure, it is difficult to control the cross-linking density of the porous polymer due to its structure. Therefore, the hydrophilicity of the surface decreases.
As a result, even if a porous polymer is used, there has been a problem that the water absorption rate eventually decreases.

On the other hand, it is known to use a water-absorbent resin having a high water absorption capacity under pressure (under load) for a disposable diaper.
10 g / cm ² as a load for measuring water absorption ratio, which indicates physical properties suitable for practical use in diapers and the like (Japanese Patent Application Laid-Open No. 60-1354)
No. 32), 0.3 psi (about 20 g / cm ² , EP 0339461), 50 g / cm ² (JP-A-63-9)
9861), 63000 dynes / cm ² (about 50 g /
cm ² , Tokuhyo Hei 8-509522), 60 g / cm ²
(Japanese Patent Publication No. Hei 8-509521, European Patent 0707603)
No.), a total amount of a minimum of 0.01 to 0.7 psi (a total amount of about 0.7 g / cm ² to a maximum of 63 g / cm ² , JP-A-6-254118, US Pat. No. 5,601,542);
0.6 to 1 psi (about 43 g / cm ^{2 to} about 71
g / cm ² , Japanese Patent Publication No. Hei 8-510484) and the like, and these water-absorbing resins are disclosed. Among these conventional water-absorbing resins, the highest water absorption capacity under pressure is 25.9 g at 1 psi (about 71 g / cm ² ).
/ G of absorbent resin (Experimental Example 6e of Japanese Patent Publication No. 9-501975) or 1.7 psi (about 121 g / cm ² ).
water-absorbing resin exhibiting a water absorption capacity of 0.1 ml / g (European Patent 033
No. 9461, Table B).

However, these water-absorbing resins exhibit a water absorption capacity under pressure of 30 g / g or more under relatively low pressure.
In general, as the load increases, the water absorption capacity under pressure greatly decreases (see JP-A-6-254118, JP-T-Hei-8-5-5).
No. 09521, FIG. 1 of JP-T-Hei 8-510484, and Table B of EP 0339461. For example, load 0.3p
When increasing from si to 0.6 psi, the water absorption capacity under pressure often drops significantly to less than half. In addition, when the surface area of the resin is increased to achieve a high water absorption rate for these resins, 100 g / cm ² (about 1.4 ps)
Under the load of i), less than 10 g / g, at most 20 g / g
It showed less than g absorption capacity.

As described above, unfortunately, the conventional technologies sufficiently meet the market needs of a high water absorption ratio under high pressure and a water absorption rate under higher pressure, which are necessary for improving the performance of disposable diapers. Absent. For this reason, there is still no water-absorbing resin in which the water absorption capacity under pressure and the water absorption speed are well balanced.

Further, in a disposable diaper or the like, since the baby constantly moves around, the load is not constant, and even with a water-absorbing resin exhibiting a high water absorption capacity under pressure, the water-absorbing ability against pressure may not be constant. For this reason, the expected load from the baby's general weight (around 10 kg), at most 1
Simply showing a high water absorption capacity under pressure with respect to 0 to several tens g / cm ² does not always work satisfactorily even if the water-absorbent resin is incorporated into an actual diaper, and good results cannot be obtained with a disposable diaper. Conceivable. Therefore, even if the water-absorbing resin is evaluated or screened based on the water absorption under pressure measured by simply changing the load (10 to several tens of g / cm ² ) as in the related art, even if it is actually used in a diaper or the like, It is not an indicator of water-absorbing resin. As a final evaluation of the water-absorbent resin used in the diaper, it is not enough to measure only the physical properties of the water-absorbent resin such as the water absorption capacity under pressure, and in the end, it takes enormous cost, time and effort to create the diaper. In fact, it is necessary to do a monitor test.

Under such circumstances, the known technology can simultaneously satisfy both the water absorption ratio under pressure and the water absorption speed at a level close to the technical limit at an extremely high level. A water absorbing resin is desired. Further, a water-absorbing resin having a large water absorption capacity under pressure is desired even though the surface area of the particles is large. Also, 1
Even under a high pressure of 00 g / cm ^2, a pressure-resistant water-absorbing resin exhibiting a high water absorption capacity not seen in conventional water-absorbing resins, exhibiting a small decrease in water absorption capacity due to an increase in pressure, and exhibiting an excellent water absorption capacity is desired. It is.

Further, a paper diaper which exhibits a high water absorption capacity even when the baby moves around and the load constantly fluctuates and which has a small amount of leakage and a large absorption amount is desired. In measuring the physical properties of the water-absorbent resin, a parameter of the water-absorbent resin that is correlated with the actual use of the diaper is desired.

In addition, there is a demand for a method of producing a water-absorbent resin having a large water absorption capacity under no pressure and under pressure and a high water absorption rate under no pressure and under pressure.

[0016]

The present inventors have achieved a water-absorbent resin obtained by subjecting a water-absorbent crosslinked polymer having a specific range of -COOR and -COOH / -COOR molar ratio to surface cross-linking to achieve the above object. The inventors have found that the present invention can be performed and completed the present invention. Hereinafter, -COOR (R is a hydrogen atom, a metal atom or ammonium) is simply described as -COOR.

That is, according to the present invention, -COOR is 12 mmol
/ G or more, and the -COOH / -COOR molar ratio is 0.
An object of the present invention is to provide a water-absorbent resin obtained by adding a compound having a plurality of functional groups capable of reacting with -COOR to a water-absorbent crosslinked polymer of less than 5. Further, the vicinity of the surface is subjected to a crosslinking treatment with a compound having a plurality of functional groups capable of reacting with -COOR, containing -COOR of 12 mmol / g or more, and -COOR.
The present invention provides a water-absorbent resin having an OH / -COOR molar ratio of less than 0.5. In addition, the BET specific surface area is 0.03 m
² / g or more, and in which high absorbency against pressure for artificial urine under a load of 100 g / cm ² to provide 25 g / cm ² by weight of the water absorbing resin.

Further, a compound having a plurality of functional groups capable of reacting with -COOR is added to a water-absorbent crosslinked polymer containing -COOR of 12 mmol / g or more and having a -COOH / -COOR molar ratio of less than 0.5. It is intended to provide the above water-absorbent resin. Further, the present invention provides the above water-absorbent resin, wherein the fine powder having a water-absorbent resin content of 150 μm or less is 10% by weight or less. Also, 50g / cm
Water absorption capacity under pressure for artificial urine under load of ² is 30 g
/ G or more, and a pressure-resistant water-absorbent resin having a pressure-resistant water absorption ratio of 0.6 or more, which is defined by the ratio of the water absorption capacity under high pressure to artificial urine under a load of 100 g / cm ² , relative to the water absorption capacity under pressure. Is provided.

Further, the water absorption under pressure for artificial urine under a load of 50 g / cm ² is 30 g / g or more, and the water absorption under high pressure for artificial urine under a load of 100 g / cm ^{2 is} the same as that of the above. An object of the present invention is to provide a disposable diaper using a pressure-resistant water-absorbing resin having a pressure-resistant water-absorbing ratio defined by a ratio to a reduction water-absorption ratio of 0.6 or more.

In addition, a compound having a plurality of functional groups capable of reacting with -COOR is added to a water-absorbing crosslinked polymer containing -COOR of 12 mmol / g or more and having a -COOH / -COOR molar ratio of less than 0.5. And a method for producing a water-absorbent resin characterized by heating. Further, the compound is a covalent crosslinking agent, and the water absorbing capacity of the water-absorbing crosslinked polymer under no load is reduced to 0.9 to 0.3 times before crosslinking by the covalent crosslinking agent. The above-mentioned production method is provided. Hereinafter, the present invention will be described in detail.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Water-absorbent crosslinked polymer The water-absorbent crosslinked polymer used in the present invention is -COOR 1
It contains 2 mmol / g or more, and the -COOH / -COOR molar ratio is less than 0.5.

Examples of the metal atom R include alkali metals such as lithium, sodium, potassium, rubidium and cesium; alkaline earth metals such as beryllium, magnesium and calcium; transition metals such as zinc; and metals such as aluminum. And ammonium for ammonium (N
In addition to H ₄ ), primary ammonium such as monoethanolammonium and methylammonium; secondary ammonium such as diethanolammonium and dimethylammonium; tertiary ammonium such as triethanolammonium and triethylammonium; and quaternary ammonium such as tetramethylammonium Is included. R in the present invention
Are preferably a hydrogen atom, an alkali metal atom and ammonium (NH ₄ ), and more preferably a hydrogen atom or a lithium atom, a sodium atom and an ammonium (N
H ₄ ). R contained in the water-absorbent crosslinked polymer may include two or more types in addition to one type described above.

The reason that -COOR is contained in an amount of 12 mmol / g or more is that this value becomes a dominant factor in the water absorption capacity and the water absorption rate under pressure, and the pressure-resistant water absorption is excellent in the water absorption capacity under pressure and under high pressure. This is because it has been found that a conductive resin can be obtained. The amount of -COOR is based on the amount of the carboxyl group (-COO) contained in the unit weight of the water-absorbent crosslinked polymer.
OH) and the total amount of -COOR neutralized therefrom. If the -COOH / -COOR molar ratio is less than 0.5, not only safety but also various physical properties such as a water absorption rate and a water absorption capacity under pressure may be poor, which is not preferable. Therefore, -C
With a water-absorbent crosslinked polymer having an OOR of less than 12 mmol / g, a water-absorbent resin with improved water-absorbing properties, which is the object of the present invention and in which the water absorption capacity under pressure and the water absorption rate are balanced, cannot be obtained.

Here, the amount of -COOR of the water-absorbent crosslinked polymer is determined by the amount of -COR per monomer constituting the unit amount of the water-absorbent resin.
It can be theoretically calculated using the amount of OOR. For example, -COOR of a polymer (molecular weight 94 g / mol) in which the carboxyl group of an acrylic acid homopolymer is 100% neutralized with sodium hydroxide is 1/94 (g / mol) = 10.6 mm.
ol / g. When R is an n-valent metal (M), -COOR can be expressed as -COO (M) _{1 / n,} and the -COOR amount can be calculated in the same manner as described above. When the water-absorbent crosslinked polymer contains a monomer or polymer that does not contain -COOR, for example, starch, PVA, a surfactant, or the like, the correction may be appropriately made.

On the other hand, the amount of -COOR of the water-absorbent crosslinked polymer is determined, for example, by a known analysis such as neutralization titration, NMR, elemental analysis, or fluorescent X-ray analysis using sodium polyacrylate having a known amount of -COOR as a standard. It can be measured by the method. In general, the water-absorbent resin contains less than 10% by weight of water in the resin, so that the amount of -COOR needs to be appropriately corrected in order to calculate the amount of -COOR. It is also possible to use a commercially available product, but most of the commercially available products are partially neutralized sodium polyacrylate (-COOR = about 11 mmo).
l / g) or partially neutralized potassium polyacrylate (-COO
R = about 10 mmol / g), and in the present invention, -COO
It is essential to further increase the content of R.

(2) Method for producing water-absorbent crosslinked polymer The water-absorbent crosslinked polymer used in the present invention comprises the following (i)
It is obtained by the method of (ii), (iii) or (iv), preferably by the method of (i), (ii) or (iii). (I) It contains a copolymerizable crosslinking agent, and after polymerization, -COOR is 1
-COO containing 2 mmol / g or more and prepared in advance so that the -COOH / -COOR molar ratio is less than 0.5
A method in which an aqueous R-containing monomer solution is polymerized, and the obtained hydrogel polymer is dried and optionally pulverized to obtain a water-absorbent crosslinked polymer.

(Ii) When an aqueous solution of a carboxyl group-containing monomer containing a copolymerizable crosslinking agent is polymerized and 50 mol% or more of the carboxyl group after polymerization is post-neutralized, -C in the polymer is used.
A method of neutralizing with a salt so that the OOR becomes 12 mmol / g or more, drying the obtained hydrogel polymer, and pulverizing as necessary to obtain a water-absorbent crosslinked polymer. (Iii) polymerizing a -COOR-containing monomer aqueous solution prepared beforehand so as to contain -COOR of 12 mmol / g or more after polymerization and to have a -COOH / -COOR molar ratio of less than 0.5, and thereafter -COOR A method of reacting a compound having a plurality of functional groups capable of reacting with a polymer with the polymer to introduce a crosslinked structure into the polymer, and drying the polymer, if necessary, to obtain a water-absorbing crosslinked polymer. (Iv) After saponification of the polymer, -COOR was added at 12 mmol /
g or more of a carboxyl group-containing monomer ester compound prepared in advance to contain at least 12 g / COOR of the polymer before or after crosslinking,
A method of saponifying so that a -COOH / -COOR molar ratio is less than 0.5. Salts that can be used to neutralize the polymer or monomer include various aqueous solutions such as lithium hydroxide, sodium hydroxide, potassium hydroxide and calcium hydroxide, inorganic amines such as hydroxylamine, and monoethanolamine. And organic amines such as diethanolamine and triethanolamine.

In addition, the resulting water-absorbent crosslinked polymer is
Containing at least 12 mmol / g of -COOR;
As long as the / -COOR molar ratio satisfies the condition of less than 0.5, the step of neutralizing the carboxyl group and the introduction of the crosslinked structure may be carried out before, after or during the polymerization. .

As more specific embodiments for synthesizing the preferred water-absorbent crosslinked polymer of the present invention, for example,
Any of the following methods (A) to (E), preferably, any of the methods (A) to (D) can be exemplified. In order to improve the surface area of the water-absorbing resin in the present invention, preferably, any one of the methods (a) to (c),
In particular, in order to obtain a water-absorbent resin having a large surface area and a small amount of fine powder, foam polymerization according to (b) is preferred.

(A) An aqueous lithium acrylate solution containing a copolymerizable crosslinkable monomer and having a degree of neutralization in the range of 50 to 100 mol% is dispersed in an inert gas bubble in the presence of a polymerization initiator. Method of polymerizing in a hot state. (B) the degree of neutralization containing the copolymerizable crosslinking monomer is 50 to 10;
A method of polymerizing an aqueous solution of lithium acrylate in the range of 0 mol% in a state where bubbles of an inert gas are dispersed in the presence of a polymerization initiator and a surfactant. (C) the degree of neutralization containing the copolymerizable crosslinking monomer is 50 to 10;
A method in which an aqueous solution of lithium acrylate in the range of 0 mol% is subjected to reverse phase suspension polymerization in an organic solvent in the presence of a polymerization initiator and a surfactant. (D) Acrylic acid aqueous solution containing a copolymerizable crosslinkable monomer is polymerized in the presence of a polymerization initiator, and after polymerization, lithium carbonate or lithium hydroxide aqueous solution is added, and 5
A method of neutralizing 0 to 100 mol%. (E) Acrylic acid ester is polymerized, further saponified before or after crosslinking, and ion-exchanged if necessary to obtain -CO
A method for obtaining a lithium polyacrylate having an OH / -COOR molar ratio in a range of less than 0.5.

(A) -COOR-containing monomer The carboxyl group-containing monomer used to obtain the water-absorbent crosslinked polymer used in the present invention includes maleic acid,
Examples thereof include fumaric acid, itaconic acid, mesaconic acid, citraconic acid, and acrylic acid. In addition to one of these, two or more of these can be used in combination. The above-mentioned metal salts and the like correspond to the monomer containing a salt of a carboxyl group. Furthermore, if a water-absorbing crosslinked polymer containing -COOR of 12 mmol / g or more and a -COOH / -COOR molar ratio of less than 0.5 can be obtained, a copolymer with these monomers other than the above monomers may be used. It is also possible to appropriately use other polymerizable monomers in combination.

As such a monomer, for example, 2-
(Meth) acryloylethanesulfonic acid, 2- (meth)
Sulfonic acid group-containing monomers such as acryloylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid, and styrenesulfonic acid, and alkali metal salts and ammonium salts thereof such as lithium, sodium, and potassium. ; (Meth) acrylamide, N
-Substituted (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, N-vinylpyrrolidone, N-vinylacetamide and the like A nonionic hydrophilic group-containing monomer of N;
N-dimethylaminoethyl (meth) acrylate, N,
N-dimethylaminopropyl (meth) acrylate,
Amino group-containing unsaturated monomers such as N, N-dimethylaminopropyl (meth) acrylamide and quaternary compounds thereof;
Specific examples thereof include acrylic esters such as methyl (meth) acrylate, ethyl (meth) acrylate and butyl (meth) acrylate, and hydrophobic monomers such as vinyl acetate and vinyl propionate.

(B) Copolymerizable crosslinkable monomer In producing the water-absorbent crosslinked polymer used in the present invention,
A copolymerizable crosslinking monomer is used. Preferred copolymerizable crosslinking monomers include, for example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol di (meth) acrylate.
Acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate,
Trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, N, N'-methylenebis (meth) acrylamide, triallyl isocyanurate, trimethylol Examples thereof include propane di (meth) allyl ether, triallylamine, tetraallyloxyethane, and glycerol propoxy triacrylate, and one or more of these may be used in combination.

The preferred amount of the copolymerizable crosslinkable monomer is in the range of 0 to 2 parts by weight, preferably 0.001 to 1 part by weight, per 100 parts by weight of the -COOR-containing monomer. When the amount of the copolymerizable crosslinkable monomer is less than 0.001 part by weight, the proportion of the water-soluble component in the obtained water-absorbent crosslinked polymer increases, and therefore, it is not possible to secure sufficient water absorption and water absorption rate under pressure. There is. On the other hand, when the amount of the copolymerizable crosslinkable monomer exceeds 2 parts by weight, the crosslink density becomes too high, and the water absorption capacity of the resulting water-absorbent crosslinked polymer may be insufficient.

(C) Polymerization initiator In synthesizing the water-absorbing crosslinked polymer of the present invention,
Examples of the polymerization initiator that can be preferably used include, for example, 2,2.
Azo compounds such as 2'-azobis (2-amidinopropane) dihydrochloride; ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, benzoyl peroxide, cumene hydroperoxide, di-t-butyl peroxide, etc. And redox initiators obtained by combining the above-mentioned peroxides with reducing agents such as sulfites, bisulfites, thiosulfates, formamidinesulfinic acid, and ascorbic acid. These polymerization initiators may be used alone or in combination of two or more.

The amount of the polymerization initiator to be used for the carboxyl group or its salt-containing monomer depends on the combination of the monomer and the polymerization initiator and the like. 0.001 for
The range is preferably from 5 to 5 parts by weight, more preferably from 0.01 to 1 part by weight. The amount of the polymerization initiator used is 0.00
If the amount is less than 1 part by weight, the amount of unreacted monomer increases,
Accordingly, the amount of residual monomers in the obtained water-absorbent crosslinked polymer increases, which is not preferable. On the other hand, when the amount of the polymerization initiator exceeds 5 parts by weight, it is not preferable because control of polymerization becomes difficult and the amount of water-soluble components in the obtained water-absorbent crosslinked polymer increases.

The temperature at the start of polymerization depends on the type of polymerization initiator used, but is preferably in the range of 0 to 70 ° C.
More preferably, it is in the range of 0 to 65 ° C. The polymerization temperature during the reaction is preferably in the range of 20 to 110 ° C.,
More preferably, the temperature is in the range of -90 ° C. When the temperature at the start of polymerization or the polymerization temperature during the reaction is out of the above range,
(I) The amount of the residual monomer in the obtained water-absorbent crosslinked polymer increases, and (ii) excessive self-crosslinking reaction proceeds to lower the water absorbency of the water-absorbent crosslinked polymer. There is a risk.

(D) Surfactant In order to synthesize the preferred water-absorbent crosslinked polymer of the present invention by the methods (b) and (c) described above, examples of the surfactant used if necessary include, for example, , Anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants and the like.

Specific examples of the anionic surfactant used include fatty acid salts such as mixed fatty acid sodium soap, semi-hardened tallow fatty acid sodium soap, sodium stearate soap, potassium oleate soap and castor oil potassium soap; lauryl sulfate Alkyl sulfates such as sodium, higher alcohol sodium sulfate, sodium lauryl sulfate, and triethanolamine lauryl sulfate; alkyl benzene sulfonates such as sodium dodecylbenzene sulfonate; alkyl naphthalene sulfonates such as sodium alkyl naphthalene sulfonate; dialkyl Alkyl sulfosuccinates such as sodium sulfosuccinate; alkyl diphenyl ether disulfonates such as sodium alkyl diphenyl ether disulfonate: alkyl Alkyl phosphates such as potassium;
Sodium polyoxyethylene lauryl ether sulfate,
Sodium polyoxyethylene alkyl ether sulfate,
Polyoxyethylene alkyl (or alkylallyl) sulfate salts such as polyoxyethylene alkyl ether triethanolamine sulfate and sodium polyoxyethylene alkyl phenyl ether sulfate; special reactive anionic surfactant; special carboxylic acid surfactant; β A sodium salt of a naphthalenesulfonic acid formalin condensate,
Naphthalenesulfonic acid formalin condensate such as sodium salt of special aromatic sulfonic acid formalin condensate; special polycarboxylic acid type polymer surfactant; polyoxyethylene alkyl phosphate;

Examples of the nonionic surfactant used include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene higher alcohol ether and the like. Polyoxyethylene alkyl aryl ethers such as alkyl ether and polyoxyethylene nonylphenyl ether; sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, sorbitan sesquiole Sorbitan fatty acid esters such as ate and sorbitan distearate; polyoxyethylene sorbitan monolaurate, polyoxo Sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate,
Polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate; polyoxy such as polyoxyethylene sorbite tetraoleate Ethylene sorbitol fatty acid ester; glycerol monostearate,
Glycerin fatty acid esters such as glycerol monooleate and self-emulsifying glycerol monostearate: polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, and polyethylene glycol monooleate; poly Oxyethylene alkylamine; polyoxyethylene hydrogenated castor oil; alkyl alkanolamide and the like.

As the cationic surfactant and the double-sided surfactant used, coconut amine acetate,
Alkylamine salts such as stearylamine acetate; quaternary ammonium salts such as lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, distearyldimethylammonium chloride, alkylbenzyldimethylammonium chloride; laurylbetaine, stearylbetaine, lauryl Alkyl betaines such as carboxymethylhydroxyethyl imidazolinium betaine; and amine oxides such as lauryl dimethylamine oxide. By using a cationic surfactant, antibacterial properties can be imparted to the resulting water-absorbent resin.

Further, as other surfactants, there are fluorine surfactants. By using the fluorine-based surfactant, bubbles of the inert gas can be stably dispersed in the aqueous monomer solution for a long time. For example, a perfluoroalkyl group is obtained by replacing the hydrogen of the lipophilic group of a general surfactant with fluorine, and has a significantly higher surface activity.

(E) Polymerization method In the present invention, the polymerization methods more preferably adopted to remarkably improve the water absorption rate are the above-mentioned polymerization methods (a) to (b), that is, if necessary, the above-mentioned surfactant is used. In this method, foam polymerization of the monomer is performed in a state where bubbles are dispersed in an aqueous monomer solution. The volume of the aqueous monomer solution in which the bubbles are dispersed at that time is 1.02 times or more, preferably 1.08 times or more, and more preferably 1.11 times or more of the non-dispersed state. This is because the water absorption rate of the obtained water-absorbent resin can be drastically increased within this range.

(F) Water-Absorbent Crosslinked Polymer In the present invention, a water-absorbent crosslinked polymer containing -COOR of 12 mmol / g or more and having a -COOH / -COOR molar ratio of less than 0.5 includes, for example, neutralized Degree is 50-10
Lithium polymaleate crosslinked product in the range of 0 mol%, ammonium polymaleate crosslinked product, sodium polymaleate crosslinked product, potassium polymaleate crosslinked product in the range of neutralization degree of 50-66.4 mol%, neutralization degree of 50- Polymaleic acid salts such as crosslinked lithium polyfumarate, crosslinked ammonium polyfumarate, crosslinked sodium polyfumarate, crosslinked potassium polyfumarate having a degree of neutralization in the range of 50 to 66.4 mol% in the range of 100 mol%; Lithium polyitaconate crosslinked product, ammonium polyitaconate crosslinked product having a degree of stiffness in the range of 50 to 100 mol%, and a degree of neutralization of 5
Crosslinked sodium polyitaconate in the range of 0 to 83.2 mol%, crosslinked lithium polymesaconate, crosslinked ammonium polymesaconate in the range of neutralization degree of 50 to 100 mol%, neutralization degree of 50 to 83.2 mol % Polymesaconate crosslinked product in the range of 50% to 100% by mole
Lithium polycitraconic acid crosslinked product, ammonium polycitraconic acid crosslinked product, crosslinked sodium polycitraconic acid having a degree of neutralization of 50 to 83.2 mol%, polyacrylic acid having a degree of neutralization of 50 to 100 mol% Lithium oxide crosslinked bodies can be exemplified.

Among the above-mentioned water-absorbent crosslinked polymers, ammonium salts are sometimes decomposed and released upon heating, so that preferred water-absorbent crosslinked polymers have a degree of neutralization of 50 to 50.
A crosslinked lithium polymaleate in the range of 100 mol%,
Crosslinked sodium polymaleate, neutralization degree 50 to 6
A potassium polymaleate crosslinked product in the range of 6.4 mol%,
Crosslinked lithium polyfumarate and sodium polyfumarate having a degree of neutralization in the range of 50 to 100 mol%, crosslinked potassium potassium fumarate having a degree of neutralization in the range of 50 to 66.4 mol%, and a degree of neutralization of 50 to 100 mol% Lithium polyitaconate crosslinked product in the range of 100 mol%, neutralization degree of polysodium polyitaconate in the range of 50 to 83.2 mol%, neutralization degree of 50
Lithium polymesaconate crosslinked product having a degree of neutralization of 50 to 83.2 mol%, lithium polycitraconic acid crosslinked product having a neutralization degree of 50 to 100 mol%. Body, degree of neutralization is 50
It is at least one selected from a crosslinked product of sodium polycitraconic acid in the range of 83.2 mol% and a crosslinked lithium lithium acrylate having a degree of neutralization of 50 to 100 mol%.

More preferred crosslinked water-absorbing polymers are a crosslinked lithium maleate, a crosslinked sodium polymaleate having a degree of neutralization of 50 to 100 mol%,
A crosslinked lithium polyfumarate or sodium polyfumarate having a degree of neutralization in the range of 50 to 100 mol%, a crosslinked lithium polyitaconate having a degree of neutralization in the range of 50 to 100 mol%, or a neutralization degree of 50 to 83. Crosslinked sodium polyitaconate in the range of 2 mol%, neutralization degree of 50 to 100 mol%
Lithium mesaconate crosslinked product having a degree of neutralization of 50
Sodium polymesaconate crosslinked product having a degree of neutralization of 50 to 83.2 mol%, neutralization degree of 50 to 83.2 mol%
And at least one selected from a crosslinked lithium polyacrylate having a degree of neutralization of 50 to 100 mol%, and most preferably a polystyrene having a degree of neutralization of 50 to 100 mol%. It is a crosslinked lithium acrylate.

The water-absorbent crosslinked polymer which can be used in the present invention contains at least 12 mmol / g of -COOR and satisfies the condition of a water-absorbent crosslinked polymer having a -COOH / -COOR molar ratio of less than 0.5. Then, in the cross-linked body exemplified above, for example, a plurality of kinds of alkali metal salts used for neutralizing a carboxyl group such as a combination of a lithium salt and a sodium salt may be used in combination.

(G) Drying Method The hydrogel polymer obtained during the polymerization reaction or after the completion of the polymerization reaction may have a thickness of about 0.1 mm to about 50 mm by a predetermined method.
It is possible to obtain a water-absorbent crosslinked polymer suitable for the present invention by crushing into pieces of about mm and drying. The drying temperature is
Although not particularly limited, for example, 100 to 25
The temperature may be in the range of 0 ° C, more preferably in the range of 120 to 200 ° C. The drying time is appropriately determined and is not particularly limited, but is preferably about 10 seconds to 5 hours, and more preferably about 1 minute to 2 hours.

The drying methods include heating drying, hot air drying, vacuum drying, infrared drying, microwave drying, drum dryer drying, azeotropic dehydration with a hydrophobic organic solvent,
Various methods such as high-humidity drying using high-temperature steam can be adopted, and there is no particular limitation.

The preferred water-absorbent crosslinked polymer according to the present invention is porous and has pores having an average pore diameter in the range of 10 to 500 μm, more preferably 20 to 400 μm. The average pore diameter can be determined by performing an image analysis of a cross section of the dried water-absorbent crosslinked polymer by an electron microscope. Such a porous polymer can be polymerized by foam polymerization such as (a) and (b) above.

(I) Shape and BE of water-absorbent crosslinked polymer
T Specific Surface Area The water-absorbent crosslinked polymer that can be used in the present invention may be of any shape such as fibrous, spherical, granular, scaly, porous, crushed, etc. Is considered, the preferred shape is 10 to 1000 μm
Spherical or porous particles having an average particle diameter of More preferably, the average particle size is 100 to 600 μm
In the form of particles having a particle size of

The BET specific surface area of the particles is 0.035 m
² / g or more, preferably 0.040M ² / g or more, more preferably 0.05 m ² / g or more, more preferably 0.
It is at least 08 m ² / g, particularly preferably at least 0.10 m ² / g. In the present invention, the surface area may be increased by reducing the particle diameter or by foaming polymerization. However, in order to reduce fine powder having a particle size of 150 μm or less, foaming polymerization is preferred. The amount of fine powder having a particle size of 150 μm or less is preferably 20% by weight or less, more preferably 10% by weight or less,
It is even more preferably at most 5% by weight. In addition, the measurement of the BET specific surface area of the present invention is based on the method described in the measurement items and the measurement method in Examples described later.

(3) Water Absorbent Resin The present invention shows an improvement in water absorption capacity under high pressure against artificial urine under a load of 100 g / cm ² , and a high pressure absorption capacity with little decrease in water absorption capacity under load due to the load. Water absorbent resin,
It has been found that it is suitable for disposable diapers. Therefore, from the viewpoint of obtaining such a water-absorbent resin, as a compound having a plurality of functional groups capable of reacting with -COOR, a covalent crosslinker is essentially used, and the covalent crosslinker is used to form a water-absorbent crosslinked polymer. It is preferable to reduce the water absorption ratio to 0.9 to 0.3 times before crosslinking under no load.
When the decrease in water absorption capacity under no load is less than 0.9 times that before surface crosslinking before crosslinking, -COOR is 12 mmol /
g or more, and the molar ratio of -COOH / -COOR is 0.5
Less than 100 g / cm ²
This is because there is little improvement in the water absorption capacity under pressure with respect to artificial urine under a load, and the pressure-resistant water absorption ratio may be low.
Further, when the decrease in the water absorption capacity under no load is reduced to 0.3 times or less before cross-linking, not only is the water absorption capacity disadvantageous, but also the water absorption rate may be inferior. Therefore, in obtaining the pressure-resistant water-absorbent resin of the present invention, the water absorption ratio under no load in the range of 0.9 to 0.3 times before surface crosslinking,
More preferably, the type and amount of the following surface cross-linking agent, heating temperature and time are adjusted so as to be in the range of 0.85 to 0.5 times, and more preferably in the range of 0.8 to 0.6 times. I just need. In addition, the water absorption capacity of the present invention depends on the method described in the measurement items and the measurement method in the examples described later.

(A) Compound having a plurality of functional groups capable of reacting with -COOR The water-absorbing resin of the present invention is subjected to a crosslinking treatment with a compound having a plurality of functional groups capable of reacting with -COOR in the vicinity of the surface with a surface crosslinking agent. Is preferred. The degree of crosslinking treatment near the surface can be confirmed by observing the cross section of the resin by a known method such as IR. Although there is no particular limitation on the crosslinking method, a preferred production method is -COOR of 12 mm.
ol / g or more and a compound having a plurality of functional groups capable of reacting with -COOR as a surface cross-linking agent in 100 parts by weight of a water-absorbing cross-linked polymer having a -COOH / -COOR molar ratio of less than 0.5. A method of adding 10 to 10 parts by weight and heating can be employed.

Examples of the compound having a plurality of functional groups capable of reacting with -COOR which can be suitably used in the present invention include, for example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, Polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4 -Butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol,
Polyhydric alcohol compounds such as 1,2-cyclohexanediol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol Diglycidyl ether, glycerol polyglycidyl ether,
Epoxy compounds such as diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, Polyamine compound of polyamide polyamine; Haloepoxy compound such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; Condensate of the above polyamine compound and the above haloepoxy compound; 2,4-tolylene Polyvalent isocyanate compounds such as isocyanate and hexamethylene diisocyanate; polyvalent oxazolyl such as 1,2-ethylenebisoxazoline Compounds; .gamma.-glycidoxypropyltrimethoxysilane, .gamma.-aminopropyl silane coupling agent such as trimethoxysilane, 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolane -2
-One, 4,5-dimethyl-1,3-dioxolan-2
-One, 4,4-dimethyl-1,3-dioxolan-2
-One, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2
-One, 1,3-dioxan-2-one, 4-methyl-
1,3-dioxan-2-one, 4,6-dimethyl-
Alkylene carbonate compounds such as 1,3-dioxan-2-one and 1,3-dioxolan-2-one; polyvalent metal salts such as aluminum chloride and aluminum sulfate; and the like, but are not particularly limited.

Among the compounds having a plurality of functional groups capable of reacting with -COOR as exemplified above, polyhydric alcohol compounds, epoxy compounds, polyvalent amine compounds, condensates of polyvalent amine compounds and haloepoxy compounds, and alkylene carbonate compounds Is more preferred. As a result, 100 g
/ Absorption of artificial urine under a high load under a load of / cm ^2, a high pressure absorption ratio with a small decrease in the water absorption under pressure due to the load, and a surface area of 0.03 g / m 2.
This is because a pressure-resistant water-absorbent resin having a water absorption capacity as large as ² or more and having a high water absorption capacity under high pressure can be obtained, and the water-absorbent resin can be suitably used for a disposable diaper. In the present invention, as a surface crosslinking agent,
A covalent crosslinking agent capable of covalently bonding with -COOR in the water-absorbent resin is preferable, and among them, at least one selected from a polyhydric alcohol compound, an epoxy compound, a polyamine compound, and an alkylene carbonate compound is preferable. Used.

These compounds having a plurality of functional groups capable of reacting with -COOR may be used alone or in combination of two or more. When two or more compounds having a plurality of functional groups capable of reacting with -COOR are used in combination, solubility parameters (SP values) exemplified in U.S. Pat. No. 5,422,405 are different from each other. By combining a compound having a plurality of functional groups capable of reacting with -COOR, such as a combination with a second surface cross-linking agent, a water-absorbing resin having even more excellent water-absorbing properties can be obtained. The solubility parameter is a value generally used as a factor representing the characteristics of a compound.

In the present invention, the above-mentioned solubility parameters are compared with the polymer handbook, 3rd edition (WILEY INTE
RSCIENCE published by) 527 pp solubility parameter of the solvent pp ~539 δ (cal ^/ cm ³⁾ and applying a ^half value. Further, regarding the solubility parameter of the solvent not described in the above-mentioned page, the aggregation equation of Hoy described in page 525 is substituted for Small's equation described in page 524 of the polymer handbook. The derived value will be applied.

First, as the first surface crosslinking agent, a solubility parameter capable of reacting with a functional group of the polymer and having a solubility parameter of 12.5 is used.
(Cal / cm ³ ) ^1/2 or more compounds are preferable, and 1
Compounds having a ratio of 3.0 (cal / cm ³ ) ^1/2 or more are more preferable. Specifically, for example, ethylene glycol, propylene glycol, glycerin, pentaerythritol, sorbitol, ethylene carbonate (1,3-dioxolan-2-one), propylene carbonate (4
-Methyl-1,3-dioxolan-2-one) and the like, but are not limited to these compounds. The first surface crosslinking agent may use only one of these,
As appropriate, two or more kinds may be used as a mixture.

As the second surface cross-linking agent, a solubility parameter capable of reacting with the functional group of the polymer and having a solubility parameter of 12.5 is used.
(Cal / cm ³ ) A compound of less than ^1/2 is preferable,
9.5 (cal / cm ³ ) ^{1/2 to} 12.0 (cal / cm ³ )
Compounds in the range of cm ³ ) ^1/2 are more preferred. Specifically, for example, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,5-hexane Diol, trimethylolpropane, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and the like, but are limited to these compounds. It is not something to be done. The second surface crosslinking agent may use only one of these,
Two or more kinds may be used as a mixture.

The amount of the compound having a plurality of functional groups capable of reacting with —COOR to the water-absorbent crosslinked polymer is preferably 0.001 to 100 parts by weight of the water-absorbent crosslinked polymer.
The range may be from 10 to 10 parts by weight, more preferably from 0.01 to 5 parts by weight. In addition, even when the first surface cross-linking agent and the second surface cross-linking agent are used in combination, the total amount thereof can be appropriately selected depending on the type of the cross-linking agent to be used, the combination thereof, and the like, The amount is preferably in the range of 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the solid content. -COOR
If the amount of the compound having a plurality of functional groups capable of reacting with the above is within the above range, the crosslink density near the surface of the obtained water-absorbent resin can be made higher than that inside, whereby the load depends on the magnitude of the load. Thus, a water-absorbent resin having excellent absorption characteristics under pressure can be obtained. The amount of the crosslinking agent used is 0.0
If the amount is less than 01 parts by weight, the crosslinking density in the vicinity of the surface of the obtained water-absorbent resin can hardly be increased, and the effect of improving the absorption characteristics under pressure may not be sufficiently obtained.
On the other hand, when the amount of the crosslinking agent exceeds 10 parts by weight, the added crosslinking agent is not efficiently used and becomes uneconomical. In addition, it may be difficult to control the crosslinking density to an appropriate value in forming an optimal crosslinking structure in the water-absorbing resin. Further, the amount of the surface cross-linking agent tends to be excessive, it is difficult to control the cross-linking density to an appropriate value, and the water absorption capacity may be excessively lowered, which is not preferable. Further, there is a possibility that the amount of -COOR in the water-absorbent resin is significantly reduced.

This makes it possible to further improve the balance of the water absorption characteristics with respect to body fluids (aqueous liquids) such as urine, sweat, menstrual blood and the like.

(B) Method of adding surface cross-linking agent: -COOR of the present invention having an improved -COOR amount is added to 12 m
The method for adding a compound having a plurality of functional groups capable of reacting with -COOR to a water-absorbent crosslinked polymer containing at least mol / g and having a -COOH / -COOR molar ratio of less than 0.5 includes, for example, the following: The methods (i) to (iv) are used.

(I) A method of mixing a water-absorbent crosslinked polymer with a compound having a plurality of functional groups capable of reacting with —COOR without using a solvent.

(Ii) After dispersing the water-absorbent crosslinked polymer in a hydrophobic solvent such as cyclohexane or pentane,
A method in which a compound having a plurality of functional groups capable of reacting with R is dissolved in an aqueous solvent or a hydrophobic solvent and mixed.

(Iii) A method in which a compound having a plurality of functional groups capable of reacting with -COOR is dissolved or dispersed in a hydrophilic solvent, and then the solution or dispersion is sprayed or dropped onto the water-absorbing crosslinked polymer and mixed. .

(Iv) A method in which a compound having a plurality of functional groups capable of reacting with -COOR is added to a water-absorbent crosslinked polymer whose water content is adjusted to a specific range.

Among the above, the preferred method in the present invention is (iii) after dissolving or dispersing a compound having a plurality of functional groups capable of reacting with -COOR in a hydrophilic solvent, and then subjecting the solution or dispersion to water absorption. This is a method of mixing by spraying or dropping on the crosslinked polymer.

As the hydrophilic solvent in the above (iii), water or an organic solvent soluble in water and water (hydrophilic solvent)
Mixtures with are preferred.

Examples of the organic solvent include, for example, methyl alcohol, ethyl alcohol, n
-Propyl alcohol, iso-propyl alcohol,
n-butyl alcohol, iso-butyl alcohol, t
Lower alcohols such as -butyl alcohol; ketones such as acetone; ethers such as dioxane, ethylene oxide (EO) adduct of monohydric alcohol, and tetrahydrofuran; amides such as N, N-dimethylformamide and ε-caprolactam; And sulfoxides such as sulfoxide. These organic solvents may be used alone or in combination of two or more.

The above water-absorbent crosslinked polymer and -COOR
The amount of the hydrophilic solvent to be used for the compound having a plurality of functional groups capable of reacting with the water-absorbing cross-linked polymer or the compound having a plurality of functional groups capable of reacting with -COOR, a combination of the hydrophilic solvent, etc. 200 parts by weight or less, more preferably 0.001 to 5 parts by weight, based on 100 parts by weight of the crosslinked polymer.
It may be in the range of 0 parts by weight, more preferably in the range of 0.1 to 50 parts by weight, particularly preferably in the range of 0.5 to 30 parts by weight.

The mixing apparatus used for mixing the water-absorbent crosslinked polymer and the solution containing a compound having a plurality of functional groups capable of reacting with —COOR requires a large mixing force to uniformly and surely mix the two. It is preferable to have.
Examples of the above mixing device include a cylindrical mixer, a double-walled conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a fluidized furnace rotary desk type. Mixers, air-flow mixers, double-arm kneaders, internal mixers, pulverizing kneaders, rotary mixers, screw-type extruders and the like are preferred.

(C) Heating Method In order to increase the crosslink density near the surface of the water-absorbent crosslinked polymer of the present invention, after adding a compound having a plurality of functional groups capable of reacting with -COOR to the water-absorbent crosslinked polymer, Heat. The heating temperature may be appropriately selected according to the desired crosslinking density, etc., but the preferred heating temperature is in the range of 40 to 250 ° C., and more preferably in the range of 80 to 220 ° C.
The reaction time may be appropriately selected from 1 to 120 minutes, preferably from 3 to 60 minutes.

In the present invention, -COOR is contained as a base polymer in an amount of 12 mmol / g or more.
By using a water-absorbing crosslinked polymer having an H / -COOR molar ratio of less than 0.5, a conventional 70 mol% neutralized sodium polyacrylate crosslinked product (-COOR: 11.4 mmol /
Compared with g), the reaction time can be significantly shortened or the reaction temperature can be lowered.

(D) BET Specific Surface Area and Particle Size The water-absorbent resin of the present invention has a BET specific surface area of 0.03 m ^2.
/ G or more, more preferably 0.035 m ² / g or more, further preferably large specific surface area of 0.04 m ² / g or more. In addition, the absorbent resin of the present invention simultaneously
The water absorption capacity under high pressure with respect to artificial urine under a load of 00 g / cm ² is 25 g / g or more, more preferably 28 g / g or more, and most preferably 30 g / g or more. This is because such a novel water-absorbent resin is extremely effective for disposable diapers.

The water-absorbent resin of the present invention has a particle size of 15
The amount of the fine powder of 0 μm or less is also preferably 20% by weight or less,
More preferably, it is reduced to 10% by weight or less, particularly preferably to 5% by weight or less. In addition, the measurement of the amount of fine powder of the present invention is based on the method described in the measurement items and measurement methods in Examples described later. Such a water-absorbent resin having a large surface area and a small amount of fine powder can be obtained by the above-mentioned foam polymerization.

A method of reducing the particle size of the water-absorbing resin in order to improve the water-absorbing speed has been known. However, fine powder having a particle size of 150 μm or less is 20% by weight, and 3% or less.
If it exceeds 0% by weight, not only diaper leakage due to clogging of the swollen gel is caused, but also uniform surface cross-linking becomes difficult, so that the water absorption capacity under pressure is reduced. As a method of increasing the surface area without reducing the particle size of the water-absorbent resin, a method of using a foamed water-absorbent resin has also been proposed. If emphasis is placed on the water absorption capacity under pressure, it is necessary to form a high surface cross-linking density, and the hydrophilicity of the surface of the porous polymer, for which it is difficult to control the cross-linking density, is reduced. However, problems such as a decrease in the water absorption rate due to surface cross-linking have arisen. That is, in the present invention, the surface area and the water absorption capacity under pressure, in particular, the properties opposite to the water absorption capacity under high pressure, are different from those of the present invention. Surprisingly, even when the surface area is improved by reducing the particle diameter or foaming the particles, the water absorption capacity under a high pressure shows an extremely high value of 22 g / g or more. It provides a new water-absorbing resin.

(4) Pressure-resistant water-absorbent resin The pressure-resistant water-absorbent resin of the present invention has a water absorption capacity of 35 g / g or more under no pressure and a water absorption capacity of 30 g / g under pressure (50 g / cm ² ). g or more, preferably more than 33 g / g, and the water absorption capacity under high pressure (100 g / cm ² ) is more than 22 g / g, and the water absorption capacity after 5 minutes (50 g / cm ² )
cm ² ) is greater than 25 g / g, and the water absorption rate is 20 seconds or less. For this reason, it is a pressure-resistant water-absorbing resin that has an excellent balance between the water absorption capacity and the water absorption rate under extremely high pressure. As such a pressure-resistant water-absorbing resin,
There is the above water-absorbing resin.

The water-resistant water-absorbent resin of the present invention has a water-soluble component content of 25% by weight or less, preferably 15% by weight or less, more preferably 10% by weight or less. In addition, the amount of the water-soluble component of the present invention depends on the method described in the measurement items and the measurement method in Examples described later.

(5) Pressure-resistant water absorption ratio In the present invention, the pressure-resistant water absorption ratio is defined as (water absorption ratio under pressure to artificial urine under a load of 50 g / cm ² ) / (100 g / cm 2).
⁽² ) water absorption ratio under high pressure with respect to artificial urine under a load of ² ). This pressure-resistant water absorption ratio is a new parameter for evaluating the suitability of the water-absorbing resin for the disposable diaper.

The pressure-resistant water-absorbent resin of the present invention is 50 g / c
absorbency against pressure for artificial urine under a load of m ² is 30
g / g or more, more preferably 35 g / g or more, and the pressure-resistant water absorption ratio defined by the ratio of the water absorption capacity under high pressure to the artificial urine under the load of 100 g / cm ² is 0. 0.6 or more, preferably 0.7 or more, more preferably 0.75 or more, and particularly preferably 0.1 or more.
It shows an extremely high breakdown voltage ratio of 8 or more. For example, in Example 2 of the present invention described later, a load (pressure) having a pressure resistance ratio of 0.82 is used.
Shows extremely stable water absorption capacity against changes.

In the case of a water-absorbing resin having a water absorption capacity under pressure of less than 30 g / g for artificial urine under a load of 50 g / cm ^2, a water absorption capacity under high pressure for artificial urine under a load of 100 g / cm ² Are also low at the same time, but since both are low, the decrease with respect to the increase in the load is reduced, and as a result, the pressure absorption ratio may be 0.7 or more (for example, Comparative Examples 1 to 3 of the present invention described later). But 50g / cm
Water absorption capacity under pressure for artificial urine under load of ² is 30 g
A water-absorbent resin less than 1 g / g is a water-absorbent resin that cannot withstand the load of a normal baby, and does not achieve the object of the present invention at all.

That is, the load expected from the baby's general weight (about 10 kg), at most 10 to several tens g / c
Simply exhibiting a high water absorption capacity under pressure with respect to m ² does not always work satisfactorily even if the water absorbent resin is actually incorporated into a diaper. On the other hand, the pressure-resistant water-absorbent resin of the present invention has a conventional water-absorbent resin having a low pressure-resistant water absorption ratio (about 0.5) and a water absorption capacity under pressure against artificial urine under a low load of 50 g / cm ² ( (About several tens g / g), and is suitable for a disposable diaper in which the load around movement changes.

In other words, although many water-absorbing trees having a simply higher water absorption capacity under pressure have been proposed in the past, 10 to several tens of cubs expected from the general weight of a baby (about 10 kg).
Assuming that the water absorption capacity under load with respect to a load of g / cm ² is a parameter, even if a water absorbent resin having such a parameter is actually used for a diaper, it does not always work satisfactorily. Also, of the conventional water-absorbing resins, under pressure (50 g / c
m ² ) having a water absorption capacity of 30 g / g or more has recently been proposed.
The water absorption capacity of 00 g / cm ² ) is at most 18 g / g, which is extremely insufficient as a water-absorbing resin. On the other hand, the parameter of the pressure-resistant water-absorbent resin of the present invention is to decrease the water absorption capacity under pressure in a region exceeding the load expected from the body weight, that is, (addition to artificial urine under a load of 50 g / cm ² ). It is a pressure-resistant water absorption ratio determined by (water absorption capacity under pressure) / (water absorption capacity under high pressure for artificial urine under a load of 100 g / cm ² ), and is extremely important as a parameter for a disposable diaper. Furthermore, even if the water absorption capacity under pressure (50 g / cm ² ) of the conventional water-absorbing resin shows 30 g / g or more, the reduction in water absorption capacity with an increase in load (pressure) is large, specifically, 100 g / g. / Cm ² shows a low value of less than 0.6 as the pressure-resistant water absorption ratio defined by the ratio of the water absorption capacity under high pressure to artificial urine under a load of / cm ^{2 and} the water absorption capacity under pressure. A conventional water-absorbent resin having a pressure-resistant water absorption ratio of less than 0.6 has sufficient performance as a disposable diaper even if the water absorption ratio under pressure to artificial urine under a load of 50 g / cm ² is 30 g / g or more. What was not shown was revealed by our monitor test.

(6) Additives The water-absorbing resin and the pressure-resistant water-absorbing resin of the present invention may further contain, if necessary, an antibacterial agent, a deodorant, a fragrance, various inorganic powders, a foaming agent, a pigment, a dye, a hydrophilic material. Adds various functions to the water-absorbent resin and the pressure-resistant absorbent resin by adding water-soluble short fibers, plasticizers, adhesives, surfactants, dyes, oxidizing agents, reducing agents, water, salts, etc. Can be.

Examples of the inorganic powder include substances inert to aqueous liquids and the like, for example, fine particles of various inorganic compounds and fine particles of clay minerals. The inorganic powder preferably has an appropriate affinity for water and is insoluble or hardly soluble in water. Specifically, for example, metal oxides such as silicon dioxide and titanium oxide, silicic acids (salts) such as natural zeolite and synthetic zeolite, kaolin, talc, clay,
Bentonite and the like can be mentioned. Among them, silicon dioxide and silicic acid (salt) are more preferable, and silicon dioxide and silicic acid (salt) having an average particle diameter of 200 μm or less, preferably 20 μm or less, further preferably 2 μm or less are particularly preferable.

The amount of the inorganic powder used in the water-absorbent resin and the pressure-resistant water-absorbent resin of the present invention depends on the combination of the (pressure-resistant) water-absorbent resin and the inorganic powder. The amount may be within the range of 0.001 to 10 parts by weight, more preferably within the range of 0.01 to 5 parts by weight, based on part by weight. (Pressure resistance) The method of mixing the water-absorbing resin and the inorganic powder is not particularly limited, and for example, a dry blending method, a wet mixing method, or the like can be employed, but a dry blending method is preferred.

(7) Use (a) Water Absorbent Article The water absorbent resin and the pressure-resistant water absorbent resin of the present invention are made into a water absorbent article by, for example, compounding (combining) with a fibrous material such as pulp. . Examples of the water-absorbing articles include sanitary materials (body fluid-absorbing articles) such as disposable diapers, sanitary napkins, incontinence pads, wound protection materials, wound healing materials, etc .; absorbent articles such as urine for pets; Materials for civil engineering and construction such as water materials, packing materials, gel blisters, etc .; Food products such as drip absorbents, freshness preserving materials, and cold insulators; Agricultural and horticultural products such as water retention materials such as soil and soil;
There is no particular limitation.

(B) Disposable diaper The disposable diaper using the water-absorbent resin or the pressure-resistant water-absorbent resin of the present invention includes, for example, a back sheet (back material) made of a liquid-impermeable material, a water-absorbent resin of the present invention, and a fiber. A core layer (absorber) containing a porous material and a top sheet (surface material) made of a liquid-permeable material are laminated in this order and fixed to each other. It is formed by attaching a fastener or the like. In addition, the disposable diaper also includes pants with a disposable diaper used when disciplining infants for urination and defecation. Since the absorbent resin of the present invention has a high pressure-resistant water absorption ratio, it can be used as a high-concentration core (water-absorbent resin / (fiber substrate + water-absorbent resin) wt / wt) in a disposable diaper,
Its concentration is 30-100% core, more preferably 40%.
It has a core of 95%, in particular a core of 50 to 90%, whereby a thin diaper can be obtained.

[0090]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the scope of the present invention is not limited to these Examples. Further,% in Examples and Comparative Examples means% by weight unless otherwise specified, and parts means parts by weight.

(Measurement Items and Measurement Methods) The water absorption rate, water absorption capacity, water absorption capacity under pressure, and the amount of water-soluble components of the water-absorbent crosslinked polymer and the (pressure-resistant) water-absorbent resin were measured by the following methods. Hereinafter, the names of the pressure-resistant water-absorbent resin and the water-absorbent resin are collectively referred to as a water-absorbent resin.

(1) Water absorption rate of water-absorbent crosslinked polymer and water-absorbent resin First, 600 to 700 ppm of sodium cation, 65 to 75 ppm of calcium cation, 55 to 6
5 ppm magnesium cation, 1100 ppm to 1
200 ppm potassium cation, 240 ppm-28
0 ppm phosphorus, 450 ppm to 500 ppm sulfur,
1100 ppm to 1300 ppm chlorine, and 130
An aqueous solution containing 0 to 1400 ppm of sulfate groups was prepared and used as artificial urine.

A water-absorbent crosslinked polymer or 1.00 g of a water-absorbent resin was placed in a bottomed cylindrical polypropylene cup having an inner diameter of 50 mm and a height of 70 mm. Next, 15 g of artificial urine was poured into the cup. And, from the point of pouring artificial urine,
The time until the artificial urine was completely absorbed by the water-absorbent resin or the water-absorbent crosslinked polymer and disappeared was measured. The measurement is repeated three times, and the average value is determined by the water absorption rate (second).
And

(2) Water absorption capacity of water-absorbent cross-linked polymer and water-absorbent resin under no load 0.200 g of water-absorbent cross-linked polymer or water-absorbent resin is uniformly placed in a tea bag-type bag (6 cm × 6 cm), and opened. After heat sealing the part, it was immersed in artificial urine. After 60 minutes, pull up the tea bag bag and use a centrifuge to remove the bag.
After draining at 50G for 3 minutes, the weight W of the bag
₁ (g) was measured. The same operation was performed without using the water-absorbing crosslinked polymer or the water-absorbing resin, and the weight W ₀ (g) was measured. And these weights W ₁ and W
_{From 0} , the water absorption capacity (g / g) was calculated according to the following equation a.

[0095]

Formula a: Water absorption capacity under no load (g / g) = (W ₁
-W ₀ ) /0.200 (3) Amount of water-soluble component in water-absorbent crosslinked polymer and water-absorbent resin
After dispersing in 0 ml of deionized water and stirring for 16 hours,
The swollen crosslinked gel was filtered with filter paper. Then, the amount of the water-soluble polymer in the obtained filtrate, that is, the amount of the water-soluble component was titrated by colloid titration to determine the amount (% by weight) of the water-soluble component in the water-absorbent crosslinked polymer or the water-absorbent resin.

(4) Average particle size of water-absorbent crosslinked polymer The average particle size is as follows:
JIS of (μm, 300μm, 150μm, 106μm)
After sieving and classifying the water-absorbent crosslinked polymer using a standard sieve, the residual percentage R was plotted on log probability paper, and the particle size corresponding to R = 50% was defined as the average particle size.

(5) Specific surface area of water-absorbent crosslinked polymer and water-absorbent resin Specific surface area of water-absorbent crosslinked polymer and water-absorbent resin is
It was determined by the "BET one-point method (Braunauer-Emmett-Teller adsorption method)". As the measuring device, "specimen fully automatic specific surface area measuring device 4-sorb U1" (manufactured by Yuasa Ionics Co., Ltd.) was used. First, a water-absorbing cross-linked polymer (JIS
A particle size range of 600 to 300 μm was collected by a standard sieve, and this was used as a sample.
cm ³ of microcell (TYPE: QS-400) placed in the sample containing the micro-cell in a nitrogen gas stream 150
The sample was heated to ℃ to sufficiently deaerate and dehydrate the sample. Then, the sample-containing microcell was cooled to -200 ° C. in a mixed gas flow of helium gas and 0.1% krypton gas.
And the mixed gas was adsorbed to the sample until equilibrium. Thereafter, the temperature of the microcell containing the sample was returned to room temperature, the mixed gas was desorbed from the sample, and the specific surface area of the water-absorbent crosslinked polymer was determined from the amount of the desorbed krypton mixed gas. In addition, the adsorption-desorption process of the microcell containing the sample is performed in 3 steps.
The specific surface area (m ² / g) of the water-absorbent crosslinked polymer was determined from the average amount.

(6) Bulk specific gravity of water-absorbent crosslinked polymer An apparent density measuring device (according to JIS K3362 6.2) is placed horizontally on a stable table, and the water-absorbent crosslinked polymer 10
0.0 g is put into an upper funnel of an apparent density measuring instrument, and is freely dropped into a 100 ml acrylic resin cup (conforming to JIS K3366.2) having a known weight (g) of 100 ml in internal volume. Of the dropped water-absorbent crosslinked polymer, the portion raised from the cup was gently ground with a glass rod, and then the weight (g) of the polymer-filled cup was measured in 0.01 g units to obtain 100 ml. Weight (g) of the water-absorbent crosslinked polymer per unit was determined, and this was used as the capacity of the cup (100 ml).
To obtain a bulk specific gravity (g / ml).

(7) Water Absorption Ratio of Water Absorbent Resin Under Pressure and High Pressure First, a measuring device used for measuring the water absorption ratio under pressure will be briefly described with reference to FIG.

As shown in FIG. 1, the measuring device is a balance 1
And a container 2 having a predetermined capacity mounted on the balance 1, an outside air suction pipe 3, a conduit 4, a glass filter 6, and a measuring unit 5 mounted on the glass filter 6. I have. The container 2 has an opening 2a at the top and an opening 2b at the side surface thereof.
The outside air suction pipe 3 is fitted into the opening a, and the conduit 4 is attached to the opening 2b. The container 2 contains a predetermined amount of artificial urine 11. The lower end of the outside air suction pipe 3 is submerged in the artificial urine 11. The above glass filter 6 is formed to have a diameter of 70 mm. And container 2
And the glass filter 6 are in communication with each other by a conduit 4. The upper part of the glass filter 6 is fixed at a position slightly higher than the lower end of the outside air suction pipe 3.

The measuring section 5 includes a filter paper 7 and a support cylinder 8.
And a wire mesh 9 attached to the bottom of the support cylinder 8, and a weight 10. Then, the measuring unit 5 places the filter paper 7 and the support cylinder 8 (that is, the wire mesh 9) on the glass filter 6 in this order, and places the weight 10 inside the support cylinder 8, that is, on the wire mesh 9. It has been. Support cylinder 8
Has an inner diameter of 60 mm. The wire mesh 9 is made of stainless steel and is formed in a 400 mesh (mesh size 38 μm). Then, a predetermined amount of the water-absorbing resin is evenly spread on the wire mesh 9. The weight 10
The weight is adjusted so that a load of 50 g / cm ² or 100 g / cm ² can be uniformly applied to the wire mesh 9, that is, the water absorbent resin.

The water absorption capacity under pressure was measured using the measuring apparatus having the above-mentioned structure. The measuring method will be described below.

First, predetermined preparation operations such as putting a predetermined amount of artificial urine 11 into the container 2 and fitting the outside air suction pipe 3 into the container 2 were performed. Next, filter paper 7 is placed on glass filter 6.
Was placed. On the other hand, in parallel with these placing operations, 0.9 g of the water-absorbing resin was evenly spread inside the support cylinder, that is, on the wire mesh 9, and the weight 10 was placed on the water-absorbing resin. Next, the supporting cylinder 8 on which the wire mesh 9, that is, the water-absorbent resin and the weight 10 was placed, was placed on the filter paper 7. And
The weight W of the artificial urine 11 absorbed by the water-absorbing resin for 60 minutes from the time when the support cylinder 8 is placed on the filter paper 7
₂ (g) was measured using the balance 1. Then, the weight W ₂ of the above according to the following formula b, calculates the water absorption capacity under a load after 60 minutes from the absorption initiation (g / g), under pressure (5
0 g / cm ² ) and a water absorption capacity (g / g) under high pressure (100 g / cm ² ).

[0104]

## EQU2 ## Formula b; water absorption capacity under pressure (g / g) = weight W ₂
(G) / Weight (g) of water-absorbent resin Since the measurement can be performed with time, in the present invention, as a measure of the water absorption rate under pressure, the pressure after 5 minutes (50 g / cm ² ) Of water absorption (g / g) was also determined.

(8) Water absorption ratio under pressure The water absorption ratio under pressure (g / g) 60 minutes after the start of absorption determined in the water absorption ratio under pressure of the water-absorbent resin in (7) above.
g) and the water absorption capacity under high pressure (g / g), the pressure-resistant water absorption ratio was determined according to the following equation c.

[0106]

## EQU3 ## Equation c: Water absorption ratio under pressure = (water absorption ratio under high pressure) /
(Water absorption capacity under pressure) (9) Fine powder amount After shrinking 10 g of the obtained water-absorbent resin, JIS150
The particles were classified with a μm standard comb, and the ratio (% by weight) to the total amount of the passing amount was defined as the fine powder amount.

(Reference Example 1) 23.94 parts of an aqueous solution of lithium acrylate having 18.01 parts of acrylic acid and a concentration of 25% by weight
Partially neutralized aqueous solution of lithium acrylate (concentration: 30% by weight, neutralization degree: 75%), in which 0.0231 part (0.015% by mole of monomer) of N, N'-methylenebisacrylamide as a crosslinking agent was uniformly dissolved. Mol%) and degassed with nitrogen gas. Thereafter, 1.2 parts of a 10% by weight aqueous solution of sodium persulfate was further added thereto. Next, in a 4-neck separable flask having a volume of 1 L and having a nitrogen atmosphere, equipped with a stirring blade, a thermometer, a cooling tube, and a dropping funnel,
700 parts of cyclohexane as a dispersion solvent and a surfactant sorbitan monostearate (trade name Span-6)
0, manufactured by Kao Corporation). afterwards,
The monomer aqueous solution was uniformly dispersed in cyclohexane by adding a partially neutralized lithium acrylate aqueous solution prepared in advance under stirring. After the monomer aqueous solution was stably dispersed, the temperature of the cyclohexane phase was raised to 60 ° C. by a water bath to initiate reverse phase suspension polymerization. After about 30 minutes, the polymerization reached the peak temperature (about 65 ° C.), and the polymerization was continued for another hour. Water was removed by azeotropic dehydration from the dispersion obtained by dispersing the spherical water-containing crosslinked polymer thus obtained, and the obtained dry polymer was separated from cyclohexane by filtration. The spherical dry polymer thus obtained was washed with 200 ml of methanol at about 50 ° C., and this operation was repeated three times to remove the surfactant on the surface. Finally, the polymer was dried under reduced pressure at 70 ° C. for one day. By doing so, the -COO of the present invention
R containing 13.1 mmol / g, -COOH / -CO
A water-absorbing crosslinked polymer (1) having an OR molar ratio of 0.25 was obtained. The obtained water-absorbent crosslinked polymer (1) had a water absorption capacity and a water-soluble component amount of 64.8 (g / g) and 15.8% by weight, respectively.

Reference Example 2 Monohydrate 4 of lithium hydroxide
2 parts, 96 parts of acrylic acid, polyethylene glycol (n
= 8) 0.649 parts of diacrylate, polyoxyethylene sorbitan monostearate (trade name: Leodol Super TW-S120, manufactured by Kao Corporation) 0.047
And a monomer aqueous solution containing 268 parts of pure water. After degassing the monomer aqueous solution with nitrogen, the monomer aqueous solution is cooled to a temperature of 22 ° C., and nitrogen gas bubbles are stably generated and dispersed in the monomer aqueous solution, and the volume thereof is the volume of the bubble non-dispersed state. 1.33 parts of a 10% aqueous solution of sodium persulfate and 0.67 parts of a 1% aqueous solution of L-ascorbic acid were added while stirring at a high speed to 1.08 times. Approximately 3 minutes after the addition of the polymerization initiator, the aqueous monomer solution gelled, so stirring was stopped and the polymerization was allowed to proceed as it was. About 35 minutes after the addition of the polymerization initiator, the polymerization temperature reached the peak of 78 ° C, and after the peak, the reaction system was heated in a 90 ° C hot water bath for 1 hour to complete the polymerization. The sponge-like hydrogel polymer containing a large amount of air bubbles obtained in this manner was cut into dice of about 10 mm with scissors, and then dried in a hot air drier at 160 ° C. for 90 minutes. 11. The dried product is pulverized by a tabletop pulverizer, and the material having passed through a sieve having an opening of 850 μm is fractionated to obtain an average particle size of 280 μm and -COOR of 12.
A water-absorbent crosslinked polymer (2) containing 9 mmol / g and having a -COOH / -COOR molar ratio of 0.25 was obtained. The obtained water-absorbent crosslinked polymer (2) had a water absorption capacity, a water absorption rate, a water-soluble component amount, a bulk specific gravity, and a specific surface area of 51.0 (g /
g), 14 seconds, 9.1% by weight, 0.1 (g / ml),
0.1375 (m ² / g).

Reference Example 3 Monohydrate 4 of lithium hydroxide
2 parts, 96 parts of acrylic acid, polyethylene glycol (n
= 8) 0.5192 parts of diacrylate, polyoxyethylene sorbitan monostearate (trade name: LEODOL SUPER TW-S120, manufactured by Kao Corporation) 0.01
And a monomer aqueous solution containing 282 parts of pure water. After degassing the monomer aqueous solution with nitrogen, the monomer aqueous solution is cooled to a temperature of 12 ° C., and bubbles of nitrogen gas are stably generated and dispersed in the monomer aqueous solution, and the volume thereof is the volume of the bubble non-dispersed state. 1.33 parts of a 10% 2,2′-azobis (2-methylpropionamidine) dihydrochloride aqueous solution and a 10% sodium persulfate aqueous solution 0.67 while stirring at a high speed to 1.05 times.
Parts, 0.93 part of a 0.1% aqueous hydrogen peroxide solution, and 0.1 part.
1.99 parts of a 1% L-ascorbic acid aqueous solution was added.
Approximately 1 minute after the addition of the polymerization initiator, the aqueous monomer solution gelled, so stirring was stopped and the polymerization was allowed to proceed as it was. About 40 minutes after the addition of the polymerization initiator, the polymerization temperature reached a peak of 54 ° C., and after the peak, the reaction system was heated in a hot water bath at 69 ° C. for 20 minutes to complete the polymerization. The thus obtained sponge-like hydrogel polymer containing a large amount of air bubbles is cut using a mini slicer (manufactured by Asahi Sangyo Co., Ltd.), and then cut into 15 pieces.
Drying was performed in a hot air dryer at 0 ° C. for 60 minutes. The dried product is pulverized with a tabletop pulverizer, and the material having passed through the sieve having an opening of 850 μm is fractionated to have an average particle diameter of 310 μm and a -COOR of 12.9 m.
mol / g, and a water-absorbent crosslinked polymer (3) having a molar ratio of -COOH / -COOR of 0.25 was obtained. The water-absorbing magnification, water-absorbing speed, water-soluble component amount, bulk specific gravity, and specific surface area of the obtained water-absorbent crosslinked polymer (3) were each 61.4 (g / g).
g), 18 seconds, 8.8% by weight, 0.26 (g / ml),
0.043 (m ² / g).

Reference Example 4 Monohydrate 4 of lithium hydroxide
2 parts, 96 parts of acrylic acid, polyethylene glycol (n
= 8) 0.389 parts of diacrylate, polyoxyethylene sorbitan monostearate (trade name: Reodol Super TW-S120, manufactured by Kao Corporation) 0.012
And a monomer aqueous solution containing 268 parts of pure water. After degassing the monomer aqueous solution with nitrogen, the monomer aqueous solution is cooled to a temperature of 24 ° C., and nitrogen gas bubbles are stably generated and dispersed in the monomer aqueous solution, and the volume thereof is the volume of the bubble non-dispersed state. 1.33 parts of a 10% aqueous solution of sodium persulfate and 0.67 parts of a 1% aqueous solution of L-ascorbic acid were added while stirring at a high speed to 1.07 times. Approximately 2 minutes after the addition of the polymerization initiator, the aqueous monomer solution gelled, so the stirring was stopped and the polymerization was allowed to proceed as it was. About 45 minutes after the addition of the polymerization initiator, the polymerization temperature reached a peak of 73 ° C., and after the peak, the reaction system was heated in a hot water bath at 80 ° C. for 30 minutes to complete the polymerization. The sponge-like hydrogel polymer containing a large amount of air bubbles obtained in this manner was cut into dice of about 20 mm with scissors, and then dried in a hot-air dryer at 160 ° C. for 60 minutes. The dried product is pulverized with a tabletop pulverizer, and the material having passed through a sieve having an opening of 850 μm is fractionated to obtain an average particle diameter of 310 μm and -COOR of 1
A water-absorbent crosslinked polymer (4) containing 2.9 mmol / g and having a -COOH / -COOR molar ratio of 0.25 was obtained. The obtained water-absorbent crosslinked polymer (4) had a water absorption capacity, water absorption rate, water-soluble component amount, bulk specific gravity, and specific surface area of 62.1, respectively.
(G / g), 13 seconds, 14.4% by weight, 0.098 (g
/ Ml) and 0.1615 (m ² / g).

Reference Example 5 Lithium Hydroxide Monohydrate 4
2 parts, 96 parts of acrylic acid, polyethylene glycol (n
= 8) A monomer aqueous solution containing 0.389 parts of diacrylate and 268 parts of pure water was prepared. After degassing the monomer aqueous solution with nitrogen, the monomer aqueous solution is cooled to a temperature of 24 ° C., and nitrogen gas bubbles are stably generated and dispersed in the monomer aqueous solution under a nitrogen stream, and the volume is non-bubble dispersed. 1.33 parts of a 10% aqueous solution of sodium persulfate and 0.6% of a 1% aqueous solution of L-ascorbic acid were stirred at a high speed to 1.03 times the volume of the state.
7 parts were added. Approximately 2 minutes after the addition of the polymerization initiator, the aqueous monomer solution gelled, so the stirring was stopped and the polymerization was allowed to proceed as it was. About 40 minutes after the addition of the polymerization initiator, the polymerization temperature reached a peak of 75 ° C, and after the peak, the reaction system was heated in a hot water bath at 80 ° C for 30 minutes to complete the polymerization. The sponge-like hydrogel polymer containing air bubbles obtained in this manner was cut into about 5 mm dice with scissors, and then dried in a hot air drier at 160 ° C. for 120 minutes. The dried product is pulverized by a tabletop pulverizer, and the material having passed through the sieve having an opening of 850 μm is fractionated, and the average particle diameter is 390 μm, and -COOR is 12.9 mmol.
/ G and a molar ratio of -COOH / -COOR of 0.25
Water-absorbent crosslinked polymer (5) was obtained. Water absorption capacity, water absorption rate, amount of water-soluble component of the obtained water-absorbent crosslinked polymer (5),
The bulk specific gravity and the specific surface area are 57.1 (g / g) and 21 respectively.
Second, 13.5% by weight, 0.296 (g / ml), 0.0
371 (m ² / g).

Reference Example 6 45.21 parts of acrylic acid, 495.69 parts of a 30% by weight aqueous solution of lithium acrylate,
Crosslinking agent N, N'-methylenebisacrylamide 0.30
95 parts (based on 0.08 mol% of monomer), ion-exchanged water 2
An aqueous solution of partially neutralized lithium acrylate obtained by uniformly mixing 54.42 parts was placed in a cylindrical container and degassed with nitrogen gas. Next, while maintaining the partially neutralized lithium acrylate aqueous solution at 14 ° C., a 10% by weight aqueous solution 2 of 2,2′-azobis (2-amidinopropane) dihydrochloride (trade name: V-50, manufactured by Wako Pure Chemical Industries, Ltd.) 0.5 parts, 1.25 parts of a 10% by weight aqueous solution of sodium persulfate, 0.35 parts of hydrogen peroxide
1.1 parts by weight of an aqueous solution of L-ascorbic acid
When 1.76 parts by weight of a 1% by weight aqueous solution was added and mixed as a polymerization initiator, polymerization was started in about 1 minute, and then, adiabatic polymerization was continued for 1.5 hours. Further, the obtained hydrogel polymer was taken out of the reaction vessel, placed in a kneader having a jacket at 70 ° C., and the hydrogel was cut into about 1 to 5 mm by stirring the blade for 15 minutes. It was dried with a hot air drier for 1 hour. The obtained dried product is pulverized with a tabletop pulverizer and passed through a JIS standard sieve to obtain 60%.
A portion having a particle diameter of 0 to 300 μm is fractionated and -COOR is set to 1
A water-absorbent crosslinked polymer (6) containing 3.1 mmol / g and having a -COOH / -COOR molar ratio of 0.25 was obtained. The water absorbing capacity of the water absorbent crosslinked polymer (6) thus obtained was 7
1.2 (g / g) and the amount of water-soluble components was 18.2% by weight.

(Reference Example 7) 160.00 parts of acrylic acid,
An acrylic acid aqueous solution obtained by uniformly mixing 622.5 parts of ion-exchanged water and 0.342 parts of N, N'-methylenebisacrylamide was placed in a cylindrical container, and degassed with nitrogen gas. Next, 2,2′-azobis (2-amidinopropane)
5% by weight of hydrochloride (trade name V-50, manufactured by Wako Pure Chemical Industries)
9.60 parts of an aqueous solution, 4.57 parts of a 3.5% by weight aqueous solution of hydrogen peroxide, and 1% by weight of an aqueous solution of L-ascorbic acid
When 00 parts were added and mixed as a polymerization initiator, the polymerization was started in about 1 minute, and then the adiabatic polymerization was continued for 1.5 hours. Further, the obtained hydrogel polymer was taken out of the reaction vessel, placed in a kneader having a jacket at 70 ° C., and the blade was stirred for 20 minutes to reduce the hydrogel to about 1%.
It was cut to ５5 mm. The carboxyl groups in the cut hydrogel were converted to a 3.48% aqueous solution of lithium hydroxide 1144.9.
And neutralized uniformly using phenolphthalein as an indicator until coloration of phenolphthalein was not completely observed. Further, the hydrogel after neutralization is mixed with 160
After drying for 1 hour with a hot-air dryer at ℃, further pulverized with a tabletop pulverizer and passed through a JIS standard sieve to 600-300 μm
Of the particle diameter of -COOR was 12.9 mmol
/ G and a molar ratio of -COOH / -COOR of 0.25
Water-absorbent crosslinked polymer (7) was obtained. The water absorption capacity of the water-absorbent crosslinked polymer (7) thus obtained was 75.0 (g / g).
g), the amount of water-soluble components was 9.1% by weight.

Reference Example 8 Monohydrate 4 of lithium hydroxide
2 parts, 96 parts of acrylic acid, polyethylene glycol (n
= 8) A monomer aqueous solution containing 0.389 parts of diacrylate and 268 parts of pure water was prepared. After degassing the monomer aqueous solution with nitrogen, the monomer aqueous solution is cooled to a temperature of 24 ° C., and nitrogen gas bubbles are stably generated and dispersed in the monomer aqueous solution under a nitrogen stream, and the volume is non-bubble dispersed. 1.33 parts of a 10% aqueous sodium persulfate solution and 0.6% of a 1% aqueous L-ascorbic acid solution were stirred at a high speed to 1.05 times the volume of the state.
7 parts were added. Approximately 3 minutes after the addition of the polymerization initiator, the aqueous monomer solution gelled, so stirring was stopped and the polymerization was allowed to proceed as it was. About 33 minutes after the addition of the polymerization initiator, the polymerization temperature reached the peak temperature of 70 ° C., and after the peak, the reaction system was heated in a hot water bath at 80 ° C. for 30 minutes to complete the polymerization. The sponge-like hydrogel polymer containing a large amount of air bubbles obtained in this manner is cut into approximately 5 mm dice with scissors.
Drying was performed in a hot air dryer at 60 ° C. for 120 minutes. The dried product is pulverized with a tabletop pulverizer, and the material having passed through a JIS standard sieve having an opening of 850 μm is fractionated to have an average particle diameter of 350 μm,
R containing 12.9 mmol / g, -COOH / -CO
The water absorption capacity, water absorption rate, water-soluble component amount, bulk specific gravity, and specific surface area of the water-absorbent crosslinked polymer (8) having an OR molar ratio of 0.25 are 59.4 (g / g), 16 seconds, and 24.0, respectively. %, 0.198 (g / ml), 0.0509 (m ² /
g).

Example 1 Water-absorbing crosslinked polymer (1) 10
0 part, 0.03 part of ethylene glycol diglycidyl diether, 1 part of propylene glycol, 3 parts of pure water
Parts, an aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 2 parts of isopropanol is added,
The mixture was heated at 150 ° C. for 10 minutes to obtain a water-absorbent resin (1) of the present invention whose surface was crosslinked. Water absorption rate, water absorption capacity, water-soluble component amount, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained water-absorbent resin (1) of the present invention, 5 The water absorption capacity under pressure after minutes is 15 seconds, 42.2 (g / g), 1
5.0% by weight, 43.2 (g / g), 31.6 (g / g)
g) and 29.9 (g / g). The results are shown in Table 1 together with the BET specific surface area and the amount of fine powder.

(Example 2) Water-absorbing crosslinked polymer (2) 10
-COO consisting of 0.25 part of ethylene glycol diglycidyl ether, 2.5 parts of propylene glycol, 7.5 parts of pure water and 7.5 parts of isopropanol with respect to 0 parts.
An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with R was added, and the mixture was heated at 150 ° C. for 10 minutes to obtain a water-absorbent resin (2) of the present invention in which the surface was crosslinked. Water absorption rate, water absorption capacity, amount of water-soluble component, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained water-absorbent resin (2) of the present invention, 5 The water absorption capacity under pressure after minutes is 6 seconds and 36.0 (g, respectively).
/ G), 8.2% by weight, 34.9 (g / g), 28.5
(G / g) and 31.1 (g / g).

(Example 3) Water-absorbing crosslinked polymer (3) 10
With respect to 0 parts, 0.3 parts of ethylene glycol diglycidyl ether, 3 parts of propylene glycol, 9 parts of pure water,
An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 9 parts of isopropanol was added, and 15
The mixture was heated at 0 ° C. for 10 minutes to obtain a water-absorbent resin (3) of the present invention whose surface was crosslinked. Water absorption rate, water absorption capacity, amount of water-soluble component, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained water absorbent resin (3) of the present invention, 5 The water absorption capacity under pressure after minutes is 11 seconds, 40.0 (g / g), and 7, respectively.
9% by weight, 38.5 (g / g), 29.4 (g / g),
33.3 (g / g).

Example 4 Water-absorbent crosslinked polymer (3) 10
With respect to 0 parts, 0.3 parts of ethylene glycol diglycidyl ether, 3 parts of propylene glycol, 9 parts of pure water,
An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 9 parts of isopropanol was added, and 18
The mixture was heated at 5 ° C. for 5 minutes to obtain a water-absorbent resin (4) of the present invention whose surface was crosslinked. Water absorption rate, water absorption capacity, amount of water-soluble components, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained water-absorbent resin (4) of the present invention, 5 The water absorption capacity under pressure after minutes was 12 seconds, 41.2 (g / g) and 7, respectively.
2% by weight, 39.3 (g / g), 30.1 (g / g),
30.0 (g / g).

Example 5 Water-absorbing crosslinked polymer (4) 10
0 parts, 0.4 parts of ethylene glycol diglycidyl ether, 4 parts of propylene glycol, 12 parts of pure water
, An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 12 parts of isopropanol is added, heated at 150 ° C for 5 minutes, and the surface of the water-absorbent resin of the present invention is crosslinked. (5) was obtained. Water absorption rate, water absorption capacity, water-soluble component amount, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained water-absorbent resin (5) of the present invention, 5 The absorption capacity under pressure after minutes is 6 seconds, 38.3 (g / g), 1
3.4% by weight, 35.0 (g / g), 26.9 (g / g)
g) 31.0 (g / g).

Example 6 Water Absorbent Crosslinked Polymer (5) 10
With respect to 0 parts, 0.3 parts of ethylene glycol diglycidyl ether, 3 parts of propylene glycol, 9 parts of pure water,
An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 9 parts of isopropanol was added, and 15
The mixture was heated at 0 ° C. for 5 minutes to obtain a water-absorbent resin (6) of the present invention whose surface was crosslinked. Water absorption rate, water absorption capacity, water-soluble component amount, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained water-absorbent resin (6) of the present invention, 5 The absorption capacity under pressure after 1 minute was 14 seconds, 40.0 (g / g), 1
2.5% by weight, 35.0 (g / g), 26.0 (g / g)
g) and 25.7 (g / g).

Example 7 Water-absorbing crosslinked polymer (6) 10
0 part, ethylene glycol diglycidyl ether 0.05 part, propylene glycol 1 part, pure water 3
Parts, an aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 3 parts of isopropanol is added,
The mixture was heated at 185 ° C. for 10 minutes to obtain a water-absorbent resin (7) of the present invention whose surface was crosslinked. Water absorption rate, water absorption capacity, amount of water-soluble component, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained water-absorbent resin (7) of the present invention, 5 The absorption capacity under pressure after 42 minutes was 42 seconds, 60.0 (g / g), 1
6.2% by weight, 38.5 (g / g), 28.1 (g / g)
g) and 19.0 (g / g).

(Example 8) Water-absorbing crosslinked polymer (7) 10
0 part, ethylene glycol diglycidyl ether 0.05 part, propylene glycol 1 part, pure water 3
Parts, an aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 3 parts of isopropanol is added,
The resultant was heated at 185 ° C. for 60 minutes to obtain a water-absorbent resin (8) of the present invention whose surface was crosslinked. Water absorption rate, water absorption capacity, amount of water-soluble component, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained water-absorbent resin (8) of the present invention, 5 The water absorption capacity under pressure after minutes was 44 seconds, 59.7 (g / g), respectively.
7.0% by weight, 34.8 (g / g), 25.4 (g / g)
g) and 16.0 (g / g).

Example 9 Water-absorbing crosslinked polymer (8) 10
With respect to 0 parts, 0.3 parts of ethylene glycol diglycidyl ether, 3 parts of propylene glycol, 9 parts of pure water,
An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 9 parts of isopropanol was added, and 15
The mixture was heated at 0 ° C. for 10 minutes to obtain a water-absorbent resin (9) of the present invention whose surface was crosslinked. Water absorption rate, water absorption capacity, amount of water-soluble components, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained water-absorbent resin (9) of the present invention, 5 The absorption capacity under pressure after 10 minutes is 10 seconds, 40.0 (g / g), 2
2.8% by weight, 30.0 (g / g), 23.0 (g / g)
g) and 26.4 (g / g).

Comparative Example 1 96.00 parts of acrylic acid, 65.24 parts of potassium hydroxide having a purity of 86%, 0.5192 parts of polyethylene glycol (n = 8) diacrylate,
A monomer aqueous solution containing 397.06 parts of ion-exchanged water was prepared. After degassing the monomer aqueous solution with nitrogen, the monomer aqueous solution is cooled to a temperature of 14 ° C., and nitrogen gas bubbles are stably generated and dispersed in the monomer aqueous solution under a nitrogen stream, and the volume is non-bubble dispersed. While stirring so that the volume of the state becomes 1.02 times,
1.33 parts of a 10% by weight aqueous solution of 2'-azobis (2-amidinopropane) dihydrochloride (trade name: V-50, manufactured by Wako Pure Chemical Industries, Ltd.) and 0.13% by weight of a 10% by weight aqueous solution of sodium persulfate.
67 parts, 1.99% by weight of a 0.1% aqueous solution of hydrogen peroxide
Part, 0.1% by weight aqueous solution of L-ascorbic acid 0.93
Was added and mixed as a polymerization initiator, and polymerization was started in about 1 minute. Thereafter, static adiabatic polymerization was continued for 1.5 hours. The obtained hydrogel polymer containing bubbles was taken out of the reaction vessel, and the hydrogel was cut into about 1 to 5 mm.
It was dried for 1 hour with a hot air dryer at 0 ° C. The obtained dried product is pulverized with a tabletop pulverizer, and is JIS having an opening of 850 μm.
By passing through a standard sieve, an average particle diameter of 360 μm
Containing 9.82 mmol of COOR, -COOH / -C
A porous comparative water-absorbent crosslinked polymer (1) having an OOR molar ratio of 0.25 was obtained. Comparative Water Absorbent Crosslinked Polymer Obtained (1)
Absorption capacity, water absorption rate, and water-soluble component amount of
0.4 (g / g), 22 seconds, 25.7% by weight.

Comparative water-absorbent crosslinked polymer (1): 100 parts by weight: ethylene glycol diglycidyl ether ether
An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 3 parts, 3 parts of propylene glycol, 9 parts of pure water, and 9 parts of isopropanol was added.
By heating for 0 minutes, a comparative water-absorbent resin (1) whose surface was crosslinked was obtained. Comparative water-absorbing resin obtained (1)
Water absorption rate, water absorption capacity, amount of water-soluble components,
g / cm ² ), under high pressure (100 g / c
m ² ) The water absorption capacity under pressure after 5 minutes is 23 seconds, 40.0 (g / g), 24.0% by weight, 2
3.0 (g / g), 18.6 (g / g), 10.0 (g)
/ G).

Comparative Example 2 96.00 parts of acrylic acid, 2
A monomer aqueous solution containing 58.62 parts of a 9% aqueous ammonia solution, 0.5192 parts of polyethylene glycol (n = 8) diacrylate, and 193.58 parts of ion-exchanged water was prepared. After degassing the monomer aqueous solution with nitrogen, the monomer aqueous solution is cooled to a temperature of 14 ° C., and nitrogen gas bubbles are stably generated and dispersed in the monomer aqueous solution under a nitrogen stream, and the volume is non-bubble dispersed. While stirring so that the volume of the state becomes 1.02 times,
1.33 parts of a 10% by weight aqueous solution of 2'-azobis (2-amidinopropane) dihydrochloride (trade name: V-50, manufactured by Wako Pure Chemical Industries, Ltd.) and 0.13% by weight of a 10% by weight aqueous solution of sodium persulfate.
67 parts, 1.99% by weight of a 0.1% aqueous solution of hydrogen peroxide
Part, 0.1% by weight aqueous solution of L-ascorbic acid 0.93
Was added and mixed as a polymerization initiator, and polymerization was started in about 1 minute. Thereafter, static adiabatic polymerization was continued for 1.5 hours. The obtained hydrogel polymer containing bubbles was taken out of the reaction vessel, and the hydrogel was cut into about 1 to 5 mm.
It was dried for 1 hour with a hot air dryer at 0 ° C. The obtained dried product is pulverized with a tabletop pulverizer, and is JIS having an opening of 850 μm.
By passing through a standard sieve, an average particle size of 290 μm
Containing 11.7 mmol of COOR, -COOH / -C
A porous comparative water-absorbent crosslinked polymer (2) having an OOR molar ratio of 0.25 was obtained. The obtained comparative water-absorbent crosslinked polymer (2)
Absorption capacity, water absorption rate, and water-soluble component amount are 5
7.2 (g / g), 22 seconds, 17.4% by weight.

The comparative water-absorbent crosslinked polymer (2) was charged with 100 parts of ethylene glycol diglycidyl ether in a proportion of 100 parts.
An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR, consisting of 3 parts, 3 parts of propylene glycol, 9 parts of pure water, and 9 parts of isopropanol, was added.
After heating for 0 minutes, a comparative water-absorbent resin (2) whose surface was crosslinked was obtained. Comparative water-absorbing resin obtained (2)
Water absorption rate, water absorption capacity, amount of water-soluble components,
g / cm ² ), under high pressure (100 g / c
m ² ) The water absorption capacity under pressure after 5 minutes was 25 seconds, 37.2 (g / g), 17.1% by weight,
9.3 (g / g), 17.7 (g / g), 11.3 (g
/ G).

(Comparative Example 3) 40 parts of sodium hydroxide, 96 parts of acrylic acid, 0.5192 parts of polyethylene glycol (n = 8) diacrylate, polyoxyethylene sorbitan monostearate (trade name: Reodol Super TW-S120) , Kao Corporation) 0.01 parts, pure water 3
An aqueous monomer solution containing 50 parts was prepared. After degassing the monomer aqueous solution with nitrogen, the monomer aqueous solution is cooled to a temperature of 12 ° C., and bubbles of nitrogen gas are stably generated and dispersed in the monomer aqueous solution, and the volume thereof is the volume of the bubble non-dispersed state. 10% by weight aqueous solution of 2,2′-azobis (2-methylpropionamidine) dihydrochloride while stirring at a high speed to 1.04 times.
33 parts, 10% by weight aqueous solution of sodium persulfate 0.67
Parts, 0.93 part of a 0.1% aqueous hydrogen peroxide solution, and 0.1 part.
1.99 parts of a 1% L-ascorbic acid aqueous solution was added.
Approximately 2 minutes after the addition of the polymerization initiator, the aqueous monomer solution gelled, so the stirring was stopped and the polymerization was allowed to proceed as it was. After the polymerization temperature peak, the reaction system was heated in a hot water bath at 69 ° C. for 20 minutes to complete the polymerization. The resulting sponge-like hydrogel polymer containing air bubbles therein was cut using scissors, and then dried in a hot-air dryer at 150 ° C. for 60 minutes. The dried product is pulverized with a desktop pulverizer and the opening is 850 μm
Is passed through a sieve to obtain an average particle size of 290 μm, -COO
R containing 11.1 mmol or more, -COOH / -CO
A water-absorbent crosslinked polymer (3) having an OR molar ratio of 0.25 was obtained. Water absorption capacity of the obtained comparative water-absorbent crosslinked polymer (3),
The water absorption rate, the water-soluble component amount, and the bulk specific gravity are each 57.3.
(G / g), 20 seconds, 19.6% by weight, 0.27 (g / g
ml).

The comparative water-absorbent crosslinked polymer (3) was added to 100 parts of ethylene glycol diglycidyl diether 0.1 part.
An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 3 parts, 3 parts of propylene glycol, 9 parts of pure water, and 9 parts of isopropanol was added.
After heating for 0 minutes, a comparative water-absorbent resin (3) whose surface was crosslinked was obtained. Comparative water-absorbing resin obtained (3)
Water absorption rate, water absorption capacity, amount of water-soluble components,
g / cm ² ), under high pressure (100 g / c
m ² ), the water absorption capacity under pressure after 5 minutes was 19 seconds, 41.5 (g / g), 18.8% by weight, 2
8.0 (g / g), 19.8 (g / g), 9.8 (g / g)
g).

(Comparative Example 4) Partially neutralized sodium acrylate having a neutralization ratio of 75 mol% was placed in a reactor equipped with a jacket and a double-arm stainless steel kneader having a capacity of 10 L and having two sigma-type blades and having a capacity of 75 mol%. 3367% by weight aqueous solution of salt 5367
g, polyethylene glycol (n
= 8) A reaction solution prepared by dissolving 4.73 g of diacrylate was charged. Next, the inside of the reactor was purged with nitrogen while maintaining the temperature of the reaction solution at 26 ° C. Next, 12 g of a 20% by weight aqueous solution of sodium persulfate as a polymerization initiator was added to the reaction solution while stirring the kneader blade,
10 g of a 1% by weight aqueous solution of L-ascorbic acid was added, and polymerization was carried out while crushing the gel for 60 minutes.

Thereafter, this polymer was dried, pulverized and classified with an 850 μm sieve in the same manner as in Example 1 to obtain a comparative water-absorbent crosslinked polymer (4). The water content was 6% by weight. The water absorption capacity, water-soluble component amount, and bulk specific gravity of the obtained comparative water-absorbent crosslinked polymer (4) were 51.3, respectively.
(G / g), 20 seconds, 12.6% by weight, 0.68 (g / g)
ml).

Next, the comparative water-absorbent resin crosslinked polymer (4)
To 100 parts, an aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 0.03 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol, 3 parts of pure water, and 2 parts of isopropanol was added. Heated at 185 ° C. for 40 minutes, containing 11.4 mmol of —COOR, the surface of which has been cross-linked,
A comparative water absorbent resin (4) having a COOH / -COOR molar ratio of 0.25 was obtained. The water absorption rate, water absorption capacity, water-soluble component amount, and pressure (50 g / c) of the obtained comparative water-absorbent resin (4)
m ² ), the water absorption capacity under high pressure (100 g / cm ² ), and the water absorption capacity under pressure after 5 minutes are 40
Sec, 41.0 (g / g), 11.3% by weight, 34.0
(G / g), 17.4 (g / g), 19.8 (g / g)
Met.

Comparative Example 5 In Comparative Example 4, the concentration of 5367 g of the aqueous monomer solution used for polymerization was set to 38% by weight.
The same operation as in Comparative Example 4 was carried out except that 2.51 g of trimethylolpropane triacrylate was used as the internal crosslinking agent, to obtain a water-absorbent crosslinked polymer (5). The water content is 6
% By weight. The obtained comparative water-absorbent crosslinked polymer (5)
Has a water absorption capacity, water-soluble component amount and bulk specific gravity of 44.
0 (g / g), 12.5% by weight, 0.69 (g / ml)
Met.

Next, the comparative water-absorbent resin crosslinked polymer (5)
An aqueous liquid containing a compound having a plurality of functional groups capable of reacting with -COOR consisting of 0.5 part of glycerin, 2 parts of isopropanol, and 1 part of water was added to 100 parts, and heated at 205 ° C. for 30 minutes. Cross-linked near the surface,-
Containing 11.4 mmol of COOR, -COOH / -C
A comparative water absorbent resin (5) having an OOR molar ratio of 0.25 was obtained. Water absorption rate, water absorption capacity, water-soluble component amount, water absorption capacity under pressure (50 g / cm ² ), water absorption capacity under high pressure (100 g / cm ² ) of the obtained comparative water-absorbent resin (5), after 5 minutes Are 40.0 seconds and 36.
0 (g / g), 11.9% by weight, 30.0 (g / g),
It was 15.5 (g / g) and 17.8 (g / g).

(Comparative Example 6) As a water-absorbent resin which is a commercial product and exhibits high magnification under pressure, A-COOR having about 11 mmol of A
SAP2300 (trade name; crosslinked product of sodium polyacrylate manufactured by Chemdahl) was used as a comparative water-absorbent resin (6). Water absorption speed, water absorption ratio of comparative water absorbent resin (6),
The amount of the water-soluble component, the water absorption under pressure (50 g / cm ² ), the water absorption under high pressure (100 g / cm ² ), and the water absorption under pressure after 5 minutes are 45 seconds and 38.7 g / cm, respectively.
g, 6.0% by weight, 32.0 g / g, 18.3 g / g,
It was 19.3 g / g.

(Example 10) -C obtained in Example 9
OOH / -COOR = 0.25 and -COOR is 12
50 parts by weight of a pressure-resistant water-absorbent resin (9) containing at least 50 mmol / g and having a water absorption capacity under pressure of 30.0 (g / g) at 50 g / cm ² and a pressure-resistant water absorption ratio of 0.76; 50 parts by weight of the pulp were dry mixed using a mixer. Next, the obtained mixture was subjected to 400 mesh (mesh size 3).
8 μm) by air-milling on a wire screen formed using a batch-type air-milling apparatus.
It was formed into a web having a size of mm × 400 mm. Further, by pressing this web at a pressure of 2 (kg / cm ² ) for 5 seconds, a basis weight of about 0.047 (g / cm ² ) was obtained.
Was obtained.

Subsequently, a back sheet (liquid-impermeable sheet) made of liquid-impermeable polypropylene and having a so-called leg gather, the above-described absorber, and a top sheet made of liquid-permeable polypropylene (liquid-permeable polypropylene) Sheets) were adhered to each other in this order using a double-sided tape, and two so-called tape fasteners were attached to the adhered product to obtain a disposable diaper (1) using a pressure-resistant water-absorbent resin. The weight of this disposable diaper (1) is 46
g.

(Comparative Example 7) In Example 10, instead of the water-absorbing resin (9) having a pressure-resistant and water-absorbing ratio of 0.76 obtained in Example 9, the same water absorption under pressure as the water-absorbing resin (9) was used. 30
g / g) obtained in Comparative Example 5 having a pressure-resistant water absorption ratio of 0.52.
Water absorbent resin for comparison (5) (-COOH / -COOR =
Except for using 0.25 and -COOR of less than 12 mmol / g), a comparative absorbent article was obtained in the same manner as in Example 10. The comparative absorbent article (1) weighs 46 g.
Met.

(Example 11) A disposable diaper (1) using a water-absorbent resin (9) obtained in Example 10 and having a water absorption capacity under pressure (30 g / g) and a pressure-resistant water absorption ratio of 0.76, and a comparison The comparative disposable diaper (1) obtained in Example 7 using the pressure-resistant water-absorbent resin (9) having a water absorption capacity under pressure (30 g / g) and a pressure-resistant water absorption ratio of 0.52 was obtained by an employee of Nippon Shokubai Co., Ltd. I did a monitor test on an actual baby for one week. As a result, the disposable diaper (1) using the pressure-resistant water-absorbent resin was excellent in the amount of leakage and the amount of urine absorption. Thus, it was found that even with the same water absorption capacity under pressure (30 g / g), in the case of a water-absorbent resin having a low pressure-resistant water absorption ratio (0.76 vs. 0.52), no good paper diaper was given.

Example 12 Water Absorption Ratio Under Pressure and High Pressure of the Absorbent for Diapers 50 parts by weight of the water-absorbent resin and 50 parts by weight of pulp were dry-mixed using a mixer. The resulting mixture is then added to 4
A web having a size of 120 mm × 400 mm was formed on a wire screen having a size of 00 mesh (mesh size: 38 μm) by air forming using a batch type air forming apparatus. Further, the web is subjected to a pressure of 2 (k
g / cm ² ) for 5 seconds to obtain an absorbent having a basis weight of about 0.047 (g / cm ² ). This absorber was cut out into a circular shape having a diameter of 60 mm, and molded to obtain an evaluation sample of an absorbent for diapers. Using this evaluation sample, the water absorption capacity under pressure and under high pressure of the absorber was measured.

As the measuring device used for measuring the water absorption capacity under high pressure of the absorber, the same device as that used for measuring the water absorption capacity of the water absorbent resin under pressure was used. Except setting, it measured by the same method.

The absorption capacity under pressure (50 kg / cm ² ) and high absorption capacity under high pressure (100 kg / cm ² ) of the absorbent were measured for 60 minutes from the start of absorption, as in the measurement of the water-absorbent resin. from the weight _{W 3} of artificial urine 11,
According to the following equation, the water absorption capacity under pressure and high pressure 60 minutes after the start of absorption was calculated, and the water absorption capacity under pressure and high pressure of the absorber was determined.

[0143]

## EQU4 ## Water absorption capacity under pressure and high pressure of the absorber = weight of artificial urine absorbed by the sample for evaluation (W ₃ g) / weight of sample for evaluation (W ₄ g) Obtained in Examples 1 to 8 Also, -COOH / -COOR =
The water absorption capacity under pressure and under high pressure of the absorbent article for diapers using water-absorbing resins (1) to (8) having 0.25 and containing -COOR of 12 mmol / g or more were measured. Table 2 shows the results.

(Comparative Example 8) In Example 12, -CO
OH / -COOR = 0.25 and -COOR is 12 m
-COOH / -COO obtained in Comparative Examples 1 to 5 instead of the water-absorbing resins (1) to (8) containing at least mol / g.
A diaper absorbent was obtained in the same manner as in Example 12 except that the comparative water-absorbent resins (1) to (5) having R = 0.25 and -COOR of less than 12 mmol / g were obtained, and under pressure. And the water absorption capacity under high pressure was measured. Table 2 shows the results.

[0145]

[Table 1]

[0146]

[Table 2]

[0147]

The water-absorbent resin or pressure-resistant water-absorbent resin of the present invention has the following excellent effects (1) to (5).

(1) In the production of an absorbent resin, the reactivity with a compound having a plurality of functional groups capable of reacting with -COOR existing near the surface of the polymer without being affected by the shape of the base polymer may be increased. As a result, the heat treatment time for the surface crosslinking treatment can be shortened without being affected by the shape.

(2) Even with the porous base polymer, the affinity with the aqueous liquid after the surface cross-linking treatment does not decrease, and as a result,
The rate of water absorption can be significantly increased.

(3) It is possible to obtain a water-absorbent resin which is excellent in balance between the water absorption ratio under pressure and the water absorption speed and has dramatically improved water absorption characteristics.

(4) Even under a load of 100 g / cm ² , it exhibits a high water absorption ratio under pressure, which is not seen in conventional water-absorbent resins, and exhibits a large load increase from 50 g / cm ² to 100 g / cm ² . A novel pressure-resistant water-absorbing resin is obtained in which the absorption capacity is small and the absorption capacity is excellent under any load.

(5) The water absorption under pressure for artificial urine under a load of 50 g / cm ² is 30 g / g or more, and the water absorption under high load for artificial urine under a load of 100 g / cm ² is the above-mentioned. There is provided a disposable diaper using a pressure-resistant water-absorbent resin having a pressure-resistant water absorption ratio of 0.6 or more, which is defined by a ratio to a water absorption capacity under pressure. Thereby, even when the baby moves constantly and the load is not constant, a diaper having a high water absorption capacity under pressure and having a small amount of leakage and a large absorption amount is provided. Further, the concentration of the water-absorbing resin in the core (absorber) can be increased, and a thin diaper can be obtained.

(6) Although the specific surface area is as large as 0.03 m ² / g or more, the water absorption capacity under high pressure is 22
g / g high water-absorbent resin was obtained for the first time, and such a novel water-absorbent resin was found to be extremely effective for diapers. Preferably, the amount of fine powder having a particle size of 150 μm or less is reduced to preferably 20% by weight or less, more preferably 10% by weight. The water-absorbent resin having a large surface area and a small amount of fine powder is obtained by the above-described foaming.

That is, in the present invention, the base polymer contains -COOR of 12 mmol / g or more, and -COOH
By using a water-absorbing crosslinked polymer having a / -COOR molar ratio of less than 0.5, the water absorption rate was significantly increased without lowering the water absorption rate even after the secondary crosslinking treatment near the surface.

Further, with the water-absorbent crosslinkable polymer of -COOR in the specific range, the secondary cross-linking time is remarkably shortened without being affected by the shape such as spherical, crushed, scaly, and porous. At the same time, a water-absorbing resin was obtained in which the water absorption rate and the water absorption rate under no pressure and under pressure were significantly improved in a well-balanced manner as compared with the conventional one.

Further, in the present invention, as the base polymer,
Polymers having a specific range of -COOR, i.e. -C
OOR containing 12 mmol / g or more, -COOH /-
The water-absorbent crosslinked polymer having a COOR molar ratio of less than 0.5 is further surface-crosslinked with a covalent crosslinking agent, and the water-absorbing capacity of the obtained water-absorbent resin under no load is set at 0.1 before the crosslinking. 9 to 0.3 times, whereby, for the first time, even under a load of 100 g / cm ^2, a high water absorption capacity under pressure not seen in the conventional water-absorbing resin is exhibited, and 50 g / cm 2
^Even with a large load increase from ² to 100 g / cm ² , the absorption capacity is extremely low, that is, the pressure-resistant water absorption ratio is high,
A novel pressure-resistant water-absorbent resin showing excellent absorption under any load was obtained.

Further, even when the paper diaper using the pressure-resistant water-absorbent resin and the like constantly moved and the load was not constant, a diaper having a high water absorption capacity under pressure and a large amount of absorption with little leakage was obtained.

That is, 50 g / c conventionally proposed.
It is defined not only by the water absorption capacity under pressure for artificial urine under a load of m ² , but also by the ratio of the water absorption capacity under high pressure to artificial urine under a load of 100 g / cm ² with respect to the water absorption capacity under pressure, that is, , (Pressure absorption capacity for artificial urine under a load of 100 g / cm ² ) / (pressure absorption capacity for artificial urine under a load of 50 g / cm ² ) Is important as an index of the water-absorbing resin. Conventionally, it has been known that the water absorption capacity under pressure is reduced by an increase in load, but it is important that the stability of the water absorption capacity at a specific pressure (100 g / cm ² and 50 g / cm ² ) is important for a diaper. It has been found that this gives the parameters of the water-absorbent resin that can be used in disposable diapers. Further, in the present invention, a water-absorbing resin having a high water absorption capacity under high pressure of 23 g / g is obtained for the first time despite the large BET specific surface area of 0.3 m ² / g or more. It has been found to be extremely effective in disposable diapers. In the present invention, it has been found that the parameters of such a water-absorbent resin are well correlated with the results of actual use in diapers (diaper-monitoring results).

[Brief description of the drawings]

FIG. 1 is an apparatus for measuring a water absorption capacity under pressure used in the present invention.

[Explanation of symbols]

 1. Balance 2. Container 3. 3. Outside air intake pipe Conduit 5. Measurement unit 6. Glass filter 7. Filter paper 8. Support cylinder 9. Wire mesh 10. Weight 11. Artificial urine 2a. Opening 2b. Aperture

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshimasa Kitayama 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo 1

Claims (9)

[Claims] Claims: 1. Contains -COOR (R is a hydrogen atom, a metal atom or ammonium) in an amount of 12 mmol / g or more,
A water-absorbent resin obtained by adding a compound having a plurality of functional groups capable of reacting with -COOR to a water-absorbent crosslinked polymer having a -COOH / -COOR molar ratio of less than 0.5. 2. The surface vicinity is cross-linked with a compound having a plurality of functional groups capable of reacting with -COOR (R is a hydrogen atom, a metal atom or ammonium).
Containing at least 12 mmol / g of -COOH / -COO
A water-absorbing resin having an R molar ratio of less than 0.5. 3. A water-absorbent resin having a BET specific surface area of 0.03 m ² / g or more and a water absorption capacity under artificial high urine under a load of 100 g / cm ² under high pressure of 25 g / cm ² or more. 4. Contains -COOR (R is a hydrogen atom, a metal atom or ammonium) in an amount of 12 mmol / g or more,
The water-absorbent resin according to claim 3, wherein a compound having a plurality of functional groups capable of reacting with -COOR is added to a water-absorbent crosslinked polymer having a -COOH / -COOR molar ratio of less than 0.5. 5. The water-absorbent resin according to claim 3, wherein a fine powder having a size of 150 μm or less is 10% by weight or less.
Or the water absorbent resin according to 4. 6. The water absorption capacity under pressure to artificial urine under a load of 50 g / cm ² is 30 g / g or more, and 10
A pressure-resistant water-absorbent resin having a pressure-resistant water-absorption ratio of 0.6 or more, which is defined by the ratio of the high water absorption ratio under artificial pressure to the artificial urine under a load of 0 g / cm ² with respect to the water absorption ratio under pressure. 7. The water absorption capacity under pressure to artificial urine under a load of 50 g / cm ² is 30 g / g or more, and
A disposable diaper using a pressure-resistant water-absorbent resin having a pressure-resistant water-absorbing ratio of 0.6 or more, which is defined by the ratio of the water absorption capacity under high pressure to artificial urine under a load of 0 g / cm ² with respect to the water absorption capacity under pressure. 8. It contains -COOR (R is a hydrogen atom, a metal atom or ammonium) in an amount of 12 mmol / g or more,
A method for producing a water-absorbent resin, comprising adding a compound having a plurality of functional groups capable of reacting with -COOR to a water-absorbent crosslinked polymer having a -COOH / -COOR molar ratio of less than 0.5, and heating. 9. The method according to claim 1, wherein the compound is a covalent crosslinker.
9. The method according to claim 8, wherein the water-absorbing capacity of the water-absorbent crosslinked polymer under no load is reduced to 0.9 to 0.3 times that before crosslinking by a covalent crosslinker.