JP2022016990A - Water-absorbing resin crosslinker composition - Google Patents

Abstract

To provide a crosslinker for producing a water absorber that keeps high FSC and CRC and achieves water absorption power while, simultaneously, achieving improved AUL and reduced amounts of backflow.SOLUTION: A water-absorbing resin crosslinker composition contains a crosslinker having reactivity with a polyacrylic acid (salt)-based water-absorbing resin and a water dissolution rate of 95% or less, and a solvent mixture of water and a hydrophilic solvent having a higher boiling point than that of water.SELECTED DRAWING: None

Description

INDUSTRIAL APPLICABILITY According to the present invention, a water-absorbent resin crosslink capable of producing a water-absorbing agent having a high free swelling ratio (FSC), a centrifuge holding capacity (CRC), and a weighted absorption multiple (AUL) and a low reversion amount. It relates to a water absorbent composed of an agent composition and a water-absorbent resin crosslinked with the water-absorbent resin cross-linking agent composition.

Water-absorbent resins are widely used in various fields such as sanitary products, foods, agriculture and forestry, civil engineering, etc., but they are widely used in sanitary products such as disposable diapers and sanitary napkins by taking advantage of their water-absorbing power. Examples of the water-absorbent resin used in such hygiene products include partially neutralized salts of polyacrylic acid and polymethacrylic acid. Water-absorbent resins used in sanitary products such as disposable diapers are required to have high water-absorbing capacity not only under normal pressure but also under body pressure (under pressure).

As one of the technical means capable of solving the above problems, a method of cross-linking the surface of the water-absorbent resin particles with a cross-linking agent is known. In such a surface cross-linking method, the surface layer of the water-absorbent resin particles having a carboxylic acid group and / or a carboxylic acid base is cross-linked by a cross-linking agent, while the cross-linking inside the water-absorbent resin particles is suppressed in order to maintain the water absorption capacity. Therefore, a water-absorbing agent having a high water-absorbing rate is obtained.

As the surface cross-linking agent, for example, an epoxy compound such as ethylene glycol diglycidyl ether (Patent Document 1) and a polyhydric alcohol compound such as ethylene glycol and propylene glycol (Patent Document 2) are known.

Japanese Unexamined Patent Publication No. 2017-185485 Japanese Unexamined Patent Publication No. 61-16903

In the water-absorbing material obtained by surface cross-linking with a conventional cross-linking agent, the free swelling ratio (FSC) and the centrifuge holding capacity (CRC) decrease when the water absorption material is designed to have a high absorption double amount (AUL) under weight. There was a tendency to do. On the contrary, when the FSC and CRC are increased and the water absorption capacity is improved, the AUL tends to decrease and the amount of reversion tends to increase. An object of the present invention is to provide a cross-linking agent for producing a water-absorbing agent that maintains high FSC and CRC, improves water absorption capacity, and at the same time improves AUL and reduces the amount of reversion.

The present inventors set the water content of the cross-linking agent to a certain level or less, and surface-crosslink the cross-linking agent using a cross-linking agent composition in which the cross-linking agent is dissolved in water and a hydrophilic solvent having a boiling point higher than that of water to absorb water. The present invention has been completed by finding that the strength of surface cross-linking of a resin can be improved.

That is, the present invention comprises a cross-linking agent having reactivity with a polyacrylic acid (salt) -based water-absorbent resin and having a water content of 95% or less, water, and a hydrophilic solvent having a boiling point higher than that of water. The present invention relates to a water-absorbent resin cross-linking agent composition containing a mixed solvent of.

The content of the hydrophilic solvent in the mixed solvent is preferably 5 to 60% by weight.

The water content of the cross-linking agent is preferably 20 to 95%.

The cross-linking agent is preferably an epoxy compound.

The epoxy compound preferably contains an ester bond.

The hydrophilic solvent is preferably propylene glycol.

The present invention also relates to a water-absorbent agent containing a polyacrylic acid (salt) -based water-absorbent resin surface-crosslinked with the water-absorbent resin cross-linking agent composition.

The CRC (centrifugal retention capacity) of the saline solution is preferably 5 to 50 g / g.

The water-absorbent resin cross-linking agent composition of the present invention improves FSC and CRC by improving the uniformity of surface cross-linking of the water-absorbent resin, and at the same time, improves AUL and reduces the amount of reversion under pressure. can.

<< Water-absorbent resin cross-linking agent composition >>
The water-absorbent resin cross-linking agent composition of the present invention can react with a polyacrylic acid (salt) -based water-absorbent resin, a cross-linking agent having a water content of 95% or less, and water and hydrophilicity having a higher boiling point than water. It is characterized by containing a mixed solvent with a sex solvent.

<Crosslinking agent>
The cross-linking agent used in the present invention is characterized by having reactivity with a polyacrylic acid (salt) -based water-absorbent resin and having a water content of 95% or less. The reactivity with a polyacrylic acid (salt) -based water-absorbent resin refers to the activity of reacting with two carboxylic acid groups and / or carboxylic acid bases of a polyacrylic acid (salt) -based resin to crosslink both.

The cross-linking agent is not particularly limited as long as it has reactivity with a polyacrylic acid (salt) -based water-absorbent resin and has a water content of 95% or less. Examples of such a cross-linking agent include an epoxy compound, a polyvalent amine compound, a polyisocyanate compound, an alkylene carbonate compound, a haloepoxy compound, a halohydrin compound, a polyvalent oxazoline compound, a silane coupling agent, a polyvalent metal compound and the like. Can be done. Only one kind of these cross-linking agents may be used, or two or more kinds thereof may be used in combination.

Examples of the epoxy compound include succinic acid glycidyl ester, adipic acid glycidyl ester, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, and polyglycerol poly. Examples thereof include glycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidol. Among these, sorbitol polyglycidyl ether, diglycerol polyglycidyl ether, and succinic acid diglycidyl ester, which can easily adjust the water content, are preferable. Among them, an epoxy compound containing an ester bond is preferable, and a succinic acid glycidyl ester is more preferable, from the viewpoint of having a high affinity with a polyacrylic acid (salt) -based water-absorbent resin and a wide allowable range of crosslinking conditions.

Examples of the polyvalent amine compound include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and inorganic salts or organic salts (azitinium salts, etc.) of these polyvalent amine compounds. Can be done.

Examples of the polyisocyanate compound include 2,4-tolylene diisocyanate and hexamethylene diisocyanate, and examples of the multivalent oxazoline compound include 1,2-ethylene bisoxazoline.

Examples of the alkylene carbonate compound include 1,3-dioxolane-2-one, 4-methyl-1,3-dioxolane-2-one, 4,5-dimethyl-1,3-dioxolane-2-one, and 4, , 4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxane- Examples thereof include 2-on, 4-methyl-1,3-dioxane-2-one, 4,6-dimethyl-1,3-dioxane-2-one and the like.

Examples of the haloepoxy compound include epichlorohydrin, epibromohydrin, α-methylepichlorohydrin and its polyvalent amine adduct (eg, Kaimen (registered trademark) manufactured by Hercules). ..

Other known cross-linking agents include silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane, and hydroxides such as zinc, calcium, magnesium, aluminum, iron and zirconium. And polyvalent metal compounds such as chloride can also be used.

The water content of the cross-linking agent means the dissolution rate when 10 parts by weight of the cross-linking agent is dissolved in 90 parts by weight of water at 25 ° C. The water content of the cross-linking agent used in the present invention is 95% or less, preferably 20 to 95%, more preferably 25 to 80%. The above-mentioned cross-linking agent may be used in combination of two or more kinds, and when two or more kinds are used in combination, the water content of the mixture may be 95% or less. For example, ethylene glycol diglycidyl ether alone has a water content of more than 95%, whereas a mixture of ethylene glycol diglycidyl ether and succinic acid glycidyl ester in a weight ratio of 2: 1 has a water content of 95%. Can be suitably used in the composition of. Examples of such a mixture of cross-linking agents include ethylene glycol diglycidyl ether and trimethylolpropane polyglycidyl ether, glycerol polyglycidyl ether and sorbitol polyglycidyl ether, glycerol polyglycidyl ether and succinic acid glycidyl ester, and the like. ..

By using a cross-linking agent composition consisting of a cross-linking agent having a water content of 95% or less and a mixed solvent of water and a water-soluble solvent having a boiling point higher than that of water, until the water evaporates during cross-linking by heating. Crosslinking proceeds while the component dissolved in water is preferentially impregnated with the water-absorbent resin, and a first crosslinked layer is formed on the surface. Furthermore, when the amount of water is low and the hydrophilic solvent is rich, the water-insoluble component is dissolved in the hydrophilic solvent, impregnated with the polyacrylic acid (salt) -based water-absorbent resin, and inside the first crosslinked layer. The cross-linking proceeds at, and a second cross-linking layer is formed. As a result, a uniform cross-linked layer is formed at an appropriate depth as a whole, the cross-linking density inside the water-absorbent resin does not become too high, the swellability increases, and the FSC becomes high. Further, the two uniform crosslinked layers increase the strength of the water-absorbent resin, improve CRC and AUL, and decrease the amount of reversion. When the water content of the cross-linking agent exceeds 95%, the cross-linking agent is consumed by the internal cross-linking, the cross-linking on the surface becomes insufficient, and the strength tends not to be improved.

The content of the cross-linking agent in the water-absorbent resin cross-linking agent composition is preferably 0.01 to 20% by weight, more preferably 0.02 to 10% by weight, still more preferably 0.05 to 5% by weight. If it exceeds 20% by weight, the cross-linking agent composition does not uniformly adhere to the resin surface when added to the polyacrylic acid (salt) -based water-absorbent resin, and the cross-linking tends to be non-uniform, 0.01 % by weight. If it is less than, the polyacrylic acid (salt) -based water-absorbent resin tends to aggregate due to the mixed solvent, and the cross-linking tends to be non-uniform.

<Mixed solvent>
In the present invention, as the mixed solvent, a mixture of water and a hydrophilic solvent having a boiling point higher than that of water is used. The boiling point of the hydrophilic solvent is preferably 130 ° C. or higher, more preferably 150 ° C. or higher, and even more preferably 180 ° C. or higher. The upper limit of the boiling point is not particularly limited, but is preferably 300 ° C. or lower, more preferably 250 ° C. or lower, and even more preferably 200 ° C. or lower.

The hydrophilic solvent is not particularly limited, but one that is inert to the polyacrylic acid (salt) -based water-absorbent resin is preferable. For example, polyhydric alcohols such as propylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerin, diacetin, triacetin and the like. Glycerin acetates, methyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, alkylene glycol alkyl ethers such as jigglyme; alkylene glycol monoalkyl ether acetates such as butyl cellosolve acetate and propylene glycol monomethyl ether acetate; ε-caprolactam, N, N- Amidos such as dimethylformamide; sulfoxides such as dimethylsulfoxside and the like can be mentioned. Among these, polyhydric alcohols and alkylene glycol alkyl ethers are preferable, and propylene glycol, propylene glycol monomethyl ether and the like are more preferable, from the viewpoint of affinity with water-insoluble components in the cross-linking agent and polyacrylic acid. These hydrophilic solvents may be used alone or in combination of two or more.

In the mixed solvent, the content of the hydrophilic solvent is preferably 5 to 60% by weight, more preferably 10 to 50% by weight. The content of the mixed solvent in the entire water-absorbent resin cross-linking agent composition is preferably 80 to 99.99% by weight, more preferably 90 to 99.98% by weight, still more preferably 95 to 99.95% by weight.

<Arbitrary ingredient>
The water-absorbent resin cross-linking agent composition of the present invention may optionally contain other components in addition to the cross-linking agent and the mixed solvent. Examples of other components include surfactants, polyvalent metal salts, organic acids and / or inorganic acids and the like.

The surfactant is not particularly limited as long as it is inert to the polyacrylic acid (salt) -based water-absorbent resin, and for example, sorbitan monolaurate, sodium laurate, polyoxyethylene lauryl ether sulfate, and acyl. Examples thereof include glutamate, sodium lauroylmethylalanine, and sodium dodecyl sulfate. These surfactants may be used alone or in combination of two or more.

The polyvalent metal salt is not particularly limited as long as it is inactive against a polyacrylic acid (salt) -based water-absorbent resin, and examples thereof include aluminum sulfate, calcium phosphate, calcium sulfate, and barium sulfate. These polyvalent metal salts may be used alone or in combination of two or more.

The organic acid and / or the inorganic acid is not particularly limited as long as it is inert to the polyacrylic acid (salt) -based water-absorbent resin, and is, for example, lactic acid, citric acid, p-toluenesulfonic acid, phosphoric acid, and the like. Examples thereof include sulfuric acid, sulfonic acid, and hydrochloric acid. These organic acids and / or inorganic acids may be used alone or in combination of two or more.

<< Water Absorbent >>
The water-absorbent agent of the present invention is characterized by containing a polyacrylic acid (salt) -based water-absorbent resin surface-crosslinked with the above-mentioned water-absorbent resin cross-linking agent composition.

<Water-absorbent resin>
Examples of the polyacrylic acid (salt) -based water-absorbent resin used in the present invention include a cross-linked product of a partially neutralized polyacrylic acid, a self-crosslinked polyacrylic acid partially neutralized product, and a starch-acrylic acid graft polymer.

The main building blocks of water-absorbent resin are acrylic acid and acrylate. It is preferable that acrylic acid is 10 to 40 mol% and acrylic acid salt is 90 to 60 mol% in the total amount of acrylic acid and acrylic acid salt. Examples of the salt of acrylic acid include sodium salt, potassium salt, ammonium salt and the like, and sodium salt is particularly preferable.

When obtaining the water-absorbent resin, a monomer other than acrylic acid (salt) may be used in combination, if necessary. Examples of the monomer other than acrylic acid (salt) include methacrylic acid, maleic acid, vinyl sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, and 2- (meth) acryloylethane. Anionic unsaturated monomers such as sulfonic acid, 2- (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, metaacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N- Isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, Nonionic hydrophilic group-containing unsaturated monomers such as vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidin, N-acryloylpyrrolidine; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl ( Examples include cationic unsaturated monomers such as meth) acrylates, N, N-dimethylaminopropyl (meth) acrylates, N, N-dimethylaminopropyl (meth) acrylamides, and quaternary salts thereof. These may be used alone or may use two or more kinds.

When a monomer other than acrylic acid (salt) is used, the amount used is preferably 30 mol% or less, more preferably 10 mol% or less, based on the total amount of acrylic acid (salt) used as the main component. By using it in this range, the water-absorbing property of the obtained water-absorbent resin is further improved, and the water-absorbent resin can be obtained at a lower cost.

At the time of producing the water-absorbent resin, the water-absorbent resin can be crosslinked by polymerizing the structural unit of the water-absorbent resin in the presence of an internal cross-linking agent. Further, the water-absorbent resin can be crosslinked by adding an internal cross-linking agent after the polymerization of the constituent units of the water-absorbent resin. As an internal cross-linking agent, polyethylene glycol di (meth) acrylate, N, N-methylenebis (meth) acrylamide, polypropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate. , Ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene. Glycer diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylene diamine, ethylene carbonate, propylene carbonate, polyethylene imine, and glycidyl (meth) acrylate. Only one kind of these internal cross-linking agents may be used, or two or more kinds thereof may be used in combination.

The method and shape of the water-absorbent resin are not particularly limited, but for example, a reverse-phase suspension polymerization method, pearl-like water-absorbent resin particles obtained by the method, an aqueous solution polymerization method, and a dried product after the polymerization are pulverized. Examples thereof include lint-like, lump-like, rock-like, granular, and amorphous water-absorbent resins.

When surface cross-linking of a water-absorbent resin with the water-absorbent resin cross-linking agent composition of the present invention, the amount of the water-absorbent resin cross-linking agent composition used is 0.001 to 10 with respect to 100 parts by weight of the water-absorbent resin. The amount to be parts by weight is preferable, the amount to be 0.005 to 5 parts by weight is more preferable, and the amount to be 0.01 to 3 parts by weight is further preferable. If the amount of the cross-linking agent used is less than 0.001 part by weight with respect to 100 parts by weight of the water-absorbent resin, the cross-linking of the water-absorbent resin cannot be effectively performed, and a sufficient effect of improving water absorption under pressure can be obtained. If it exceeds 10 parts by weight, the crosslink density may become too high, and the water absorption capacity and water absorption rate of the obtained water absorbent may decrease.

The water-absorbent resin cross-linking agent composition and the water-absorbent resin are, for example, a cylindrical mixer, a V-shaped mixer, a ribbon-type mixer, and a screw type after spraying the water-absorbent resin cross-linking agent composition onto the water-absorbent resin. It is appropriate to mix by a known method using a mixer, a double-armed mixer, a pulverized kneader or the like. At this time, a surfactant can be added as needed.

When cross-linking the water-absorbent resin, a mixed solvent consisting of water, a hydrophilic solvent or a mixture thereof may be added, if necessary. Examples of such a hydrophilic solvent include hydrophilic solvents similar to those contained in the water-absorbent resin cross-linking agent composition. These hydrophilic solvents may be one kind or a mixed solvent of two or more kinds.

The heating temperature at the time of surface cross-linking may be appropriately changed depending on the type of the water-absorbent resin and the like, but is usually 40 ° C to 250 ° C. When the heating temperature is within the above range, the surface of the water-absorbent resin is uniformly crosslinked without deterioration of the water-absorbent resin, and the balance between the water absorption ratio under normal pressure and the water absorption ratio under pressure is excellent, and the water absorption capacity is high. A high water absorption agent can be obtained. The heating time may be appropriately adjusted depending on the type of the water-absorbent resin and the like, but is usually 0.2 hours to 3 hours.

Further, the water absorbent is a disinfectant, a deodorant, an antibacterial agent, a fragrance, various inorganic powders, a foaming agent, a pigment, a dye, a hydrophilic short fiber, a fertilizer, an oxidizing agent, and a reducing agent for the purpose of imparting various functions. It may contain other additives such as agents, water, and salts. The amount of these other additives added is appropriately selected by those skilled in the art. Further, these other additives may be added to the water-absorbent resin cross-linking agent composition and then mixed with the water-absorbent resin, or may be added separately from the water-absorbent resin cross-linking agent composition.

<Physical characteristics of absorbent>
CRC (Centrifugation Capacity) absorbs physiological saline (0.9% sodium chloride aqueous solution) without applying a load to the water absorbent, and then centrifuges at 150 G to drain water and then absorbs water. , Obtained by measurement by the method described in Examples. The water absorbing agent of the present invention preferably has a CRC of 5 to 50 g / g, more preferably 25 to 40 g / g.

AUL (water absorption ratio under pressure) is determined by measuring the absorbability of physiological saline when a load is applied to the water absorbing agent by the method described in Examples. The water absorbing agent of the present invention preferably has an AUL of 10 to 30 g / g, more preferably 11 to 25 g / g.

FSC (free swelling ratio) is determined by measuring the absorbability of physiological saline when no load is applied to the water absorbing agent by the method described in Examples. The water absorbing agent of the present invention preferably has an FSC of 30 to 100 g / g, more preferably 40 to 70 g / g.

<< Hygiene products >>
The water-absorbing agent of the present invention can be suitably used for sanitary products such as disposable diapers and sanitary products. Examples of hygienic products include a back sheet, an absorber, and a laminated body in which a top sheet is laminated in this order. The absorber contains the water-absorbing agent of the present invention, and may contain water-absorbing paper or pulp if necessary.

<Physical characteristics of hygiene products>
The absorption amount is determined by measuring the amount of the water-absorbent resin / pulp mixed absorber prepared from the water-absorbent resin and pulp that has absorbed the physiological saline by the method described in Examples.

As for the water retention amount, the water absorption after the water-absorbent resin / pulp mixed absorber prepared from the water-absorbent resin and the pulp absorbs the physiological saline and then drains by centrifugation at 150 G, according to the method described in the example. Obtained by measurement.

The water absorption rate is determined by measuring the time required for the water-absorbent resin / pulp mixed absorber prepared from the water-absorbent resin and pulp to completely absorb 80 g of physiological saline by the method described in Examples.

The amount of reversion is determined by placing the filter paper on the water-absorbent resin / pulp mixed absorber after measuring the absorption rate, and applying a load of 3.5 kg from the filter paper for 3 minutes. The amount is determined by measuring by the method described in Examples.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the following examples. Hereinafter, "part" or "%" means "part by weight" or "% by weight", respectively, unless otherwise specified.

(1) Materials used 1. Raw material monomer for water-absorbent resin Acrylic acid (manufactured by Mitsubishi Chemical Corporation)
2. 2. Internal cross-linking agent Pentaerythritol triallyl ether (manufactured by Daiso Co., Ltd.)
3. 3. Polymerization initiator / hydrogen peroxide solution (manufactured by Hodogaya Chemical Co., Ltd.)
・ Ascorbic acid (made by Marubeni Chemix)
・ 2,2'-Azobis [2-methyl-N- (2-hydroxyethyl) -propionamide] (Fujifilm Wako Pure Chemical Industries, Ltd.)
4. Neutralizer Sodium hydroxide (Tosoh Corporation)
5. Surface cross-linking agent / ethylene glycol diglycidyl ether (manufactured by Nagase ChemteX, EX-810, solubility in propylene glycol 100%, water content 100%)
-Succinic acid glycidyl ester (manufactured by Nagase ChemteX, GSR-105, solubility in propylene glycol 100%, water content 70%)
-Sorbitol polyglycidyl ether (manufactured by Nagase ChemteX, EX-614B, solubility in propylene glycol 100%, water content 94%)
-Diglycerol polyglycidyl ether (manufactured by Nagase ChemteX, EX-421, solubility in propylene glycol 100%, water content 88%)
-Trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX, EX-321, solubility in propylene glycol 100%, water content 27%)
6. Hydrophilic solvent Propylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

(2) Polymerization of water-absorbent resin and internal cross-linking 155 parts by mass (2.15 mol) of acrylic acid, 0.6225 parts by mass (0.0024 mol) of pentaerythritol triallyl ether as an internal cross-linking agent, and deionized water. 340.27 parts by mass was kept at 1 ° C. while stirring and mixing. After influxing nitrogen into this mixture to reduce the amount of dissolved oxygen to 0.1 ppm or less, 0.31 parts by mass of a 1% by mass aqueous hydrogen peroxide solution and 1.1625 parts by mass of a 1% by mass aqueous solution of ascorbic acid and 0.5% by mass. % 2,2'-Azobis [2-methyl-N- (2-hydroxyethyl) -propionamide] aqueous solution 2.325 parts by mass was added and mixed to initiate polymerization. After the temperature of the mixture reached 85 ° C., a hydrogel was obtained by polymerizing at 85 ± 2 ° C. for about 10 hours. Next, while shredding 502.27 parts by mass of this hydrous gel with a mincing machine (“12VR-400K” manufactured by ROYAL), 128.42 parts by mass of a 48.5 mass% sodium hydroxide aqueous solution was added and mixed. Further, 3 parts by mass of a 1% by mass aqueous solution of ethylene glycol diglycidyl ether was added and mixed to obtain a shredded gel. Further, the shredded gel was dried with a ventilation type band dryer {200 ° C., wind speed 5 m / sec} to obtain a dried product. The dried product was pulverized with a juicer mixer (“OSTERIZERBLENDER” manufactured by Oster), and then adjusted to a particle size of 150 μm to 710 μm using a sieve with an opening of 150 μm and 710 μm to obtain dried product particles.

(3) Surface cross-linking (Examples 1 to 4, Comparative Example 1)
The cross-linking agent, water, and hydrophilic solvent shown in Table 1 were mixed to prepare a water-absorbent resin cross-linking agent composition. 6 parts by weight of each water-absorbent resin cross-linking agent composition was sprayed onto 100 parts by weight of the water-absorbent resin after the polymerization and internal cross-linking, and the mixture was sufficiently mixed. The mixture was heated at 120 ° C. for 30 minutes to obtain a surface crosslinked water absorbent. Table 1 shows the measurement results of AUL, FSC, and CRC of this water absorbing agent.

(4) Production of disposable diapers A 40 cm × 12 cm water absorbent / pulp mixed absorber was prepared by mixing 10 g of a water absorbent and 10 g of crushed wood pulp with a batch type air paper machine. The upper and lower parts of the water-absorbent / pulp mixed absorber were sandwiched between tissue papers and pressed 10 times with a 15 kg roller to obtain an absorbent layer. The absorbent layer was sandwiched between a thermal bond non-woven fabric (18 gsm) and a polyethylene sheet, and the periphery was fixed with a gum tape to prepare a disposable diaper sample.

(5) Evaluation of physical properties of water-absorbing agent (5-1) AUL (double amount of absorption under weight)
The measurement sample was sieved in the range of 250 to 500 μm using a 30 mesh sieve and a 60 mesh sieve. 0.16 g of the sieved measurement sample was weighed in a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) having a nylon net having an opening of 63 μm (JIS Z8801-1: 2006) attached to the bottom surface. After arranging the cylindrical plastic tube vertically on a nylon net so that the measurement sample has almost uniform thickness, place a weight (weight: 310.6 g, outer diameter: 24.5 mm) on the measurement sample. rice field. After weighing the entire weight (M1) of this cylindrical plastic tube, the measurement sample and the cylindrical plastic tube containing the weight are placed vertically in a petri dish containing 60 ml of physiological saline (salt concentration 0.9% by weight). It was soaked upright with the nylon mesh side facing down and left to stand for 60 minutes. After 60 minutes, the cylindrical plastic tube was pulled up from the petri dish, tilted diagonally, and the water adhering to the bottom was collected in one place and dropped as water droplets to remove excess water, and then the measurement sample and weight were contained. The weight (M2) of the entire cylindrical plastic tube was weighed, and the absorption double amount under pressure was calculated from the following formula. The temperature of the physiological saline used and the measurement atmosphere was 25 ° C ± 2 ° C.
AUL (g / g) = {(M2)-(M1)} /0.16

(5-2) FSC (free swelling ratio)
Put 1.00 g of the measurement sample in a tea bag (length 20 cm, width 10 cm) made of a nylon net with an opening of 63 μm (JIS Z8801-1: 2006), and put 1,000 ml of physiological saline (salt concentration 0.9% by weight). After immersing the sample in it for 1 hour without stirring, it was hung for 15 minutes and drained. The weight (h1) including the tea bag was measured, and the water retention amount was calculated from the following formula. The temperature of the physiological saline used and the measurement atmosphere was 25 ° C ± 2 ° C.
FSC (g / g) = (h1)-(h2)
Note that (h2) is the weight of the tea bag measured by the same operation as above when there is no measurement sample.

(5-3) CRC (centrifugal force holding capacity)
After measuring the FSC, put the tea bag in a centrifuge, dehydrate it centrifugally at 150 G for 90 seconds to remove excess physiological saline, measure the weight (h3) including the tea bag, and calculate the water retention amount from the following formula. rice field.
CRC (g / g) = (h3)-(h4)
Note that (h4) is the weight of the tea bag measured by the same operation as above when there is no measurement sample.

(6) Evaluation of physical properties of disposable diapers (6-1) Absorption amount The disposable diapers prepared in (4) were immersed in 10,000 ml of physiological saline (salt concentration 0.9% by weight) for 1 hour without stirring, and then 15 I hung it for a minute and drained it. The weight (h5) was measured and the absorption amount was calculated from the following formula. The temperature of the physiological saline used and the measurement atmosphere was 25 ° C ± 2 ° C.
Absorption amount (g / sheet) = (h5)-(h6)
Note that (h6) is the weight of the disposable diaper before immersion.

(6-2) Water retention amount After the absorption amount test, the mixture was placed in a centrifuge and centrifugally dehydrated at 150 G for 90 seconds to remove excess physiological saline, and the weight (h7) was measured to determine the water retention amount from the following equation. ..
Water retention (g / sheet) = (h7)-(h6)

(6-3) Place the paper diaper created in (4) on a horizontal surface with the top sheet facing up, place a stainless steel plate with a measuring tube (weight 200 g) on the center part, and put it in the cylinder in the center. Pour 80 g of physiological saline (salt concentration 0.9% by weight) into the pan at once. The time required for the physiological saline solution in the cylinder to be absorbed into the disposable diaper is measured and used as the water absorption rate.

(6-4) After the reversion amount absorption rate test, leave it for 5 minutes, remove the stainless steel plate with a cylinder for measurement, put about 20 g of filter paper (weigh accurately to make W1 g), and further 3. Place a 5 kg weight and pressurize for 3 minutes. After 3 minutes, the filter paper is removed and its weight is measured (W2g). The amount of reversion is calculated by the following formula.
Reversion amount (g) = W2-W1

The operations of (6-3) and (6-4) are repeated twice more, and the measurement is performed three times in total. In the measurement of the amount of reversion, the filter paper used for the second measurement is about 30 g, and the filter paper used for the third measurement is about 40 g.

In Comparative Example 1, since the water content of the cross-linking agent used exceeded 95%, the amount of reversion of the disposable diaper increased in the second and third times. In Example 1, the FSC and CRC could be improved while the AUL was equivalent to that of Comparative Example 1. Further, in Examples 2 to 4, the AUL was improved as compared with the Comparative Example, and the FSC and CRC could also be improved. Further, in Examples 1 to 4, the absorption amount, the water retention amount, and the absorption rate of the disposable diapers were improved to be equal to or higher than those of Comparative Example 1, and the amount of reversion could be significantly reduced.

Claims (8)

A cross-linking agent that has reactivity with a polyacrylic acid (salt) -based water-absorbent resin and has a water content of 95% or less, and
A water-absorbent resin cross-linking agent composition comprising a mixed solvent of water and a hydrophilic solvent having a boiling point higher than that of water. The water-absorbent resin cross-linking agent composition according to claim 1, wherein the content of the hydrophilic solvent in the mixed solvent is 5 to 60% by weight. The water-absorbent resin cross-linking agent composition according to claim 1 or 2, wherein the water content of the cross-linking agent is 20 to 95%. The water-absorbent resin cross-linking agent composition according to any one of claims 1 to 3, wherein the cross-linking agent is an epoxy compound. The water-absorbent resin cross-linking agent composition according to claim 4, wherein the epoxy compound contains an ester bond. The water-absorbent resin cross-linking agent composition according to any one of claims 1 to 5, wherein the hydrophilic solvent is propylene glycol. A water-absorbent agent containing a polyacrylic acid (salt) -based water-absorbent resin surface-crosslinked with the water-absorbent resin cross-linking agent composition according to any one of claims 1 to 6. The water absorbing agent according to claim 7, wherein the CRC (centrifugal force holding capacity) of the physiological saline solution is 5 to 50 g / g.