WO2020059762A1 - Method for producing particulate water-absorbing agent and particulate water-absorbing agent - Google Patents

Abstract

Provided are a method for producing a particulate water-absorbing agent and a particulate water-absorbing agent, the particulate water-absorbing agent combining excellent moisture-absorbing fluidity, high absorption capacity under pressure, and high liquid permeability under pressure. The present invention addresses the problem of providing a method for producing a particulate water-absorbing agent, the method including: a step for adding a surface treatment liquid containing a surface cross-linking agent and cationic colloidal silica to the water-absorbing resin; and a surface cross-linking step including a heat treatment step for heat-treating the water-absorbing resin to which the surface treatment liquid is added.

Description

Method for producing particulate water absorbing agent and particulate water absorbing agent

The present invention relates to a method for producing a particulate water absorbing agent and a particulate water absorbing agent. More specifically, excellent moisture absorption fluidity, high absorption capacity under pressure, and a method for producing a particulate water absorbing agent having both high liquid permeability under pressure, and excellent moisture absorption fluidity, high absorption capacity under pressure, and The present invention relates to a particulate water absorbing agent having high liquid permeability under pressure.

2. Description of the Related Art For hygienic materials such as disposable diapers, sanitary napkins and so-called incontinence pads, a particulate water-absorbing agent comprising a water-absorbing resin is widely used for the purpose of absorbing body fluids.

In recent years, these sanitary materials have been advanced in function. The water-absorbing resin has not only a water absorption capacity but also liquid permeability, absorption capacity under pressure, suction, anti-caching (powder flow under high humidity). Sex; functions such as Blocking @ Rato (BR) are also required. Therefore, by adding a minor additive such as water-insoluble inorganic particles or a water-soluble polyvalent metal salt to the water-absorbing resin, and particularly by coating the surface of the water-absorbing resin with the minor additive, the production process of the particulate water-absorbing agent Research and development have been carried out to improve the mixing properties of the treating agents to prevent aggregation of the water-absorbing resin, and to add various functions to the obtained particulate water-absorbing agent.

For example, Patent Document 1 discloses surface cross-linking of a water-absorbing resin in the presence of water-insoluble inorganic fine particles. Patent Documents 2 and 3 disclose a water-absorbing resin containing water-insoluble inorganic fine particles and a water-soluble polyvalent metal salt. Patent Document 4 discloses a method of realizing a water-absorbing polymer having excellent absorption capacity, retention and permeability under pressure by using a chemical crosslinking agent and a dispersed colloidal inorganic compound (colloidal silica) on an untreated absorbent polymer structure. A method of heating after contacting an aqueous solution containing

Patent Document 5 discloses a method for realizing absorbent resin particles which can maintain good absorption characteristics even when used for a long time when applied to an absorbent article. A method is disclosed in which spherical single particles and a binder are mixed and, if necessary, heat-treated to produce absorbent resin particles.

Patent Document 6 discloses a technique of mixing colloidal silica and a non-polymeric water-soluble saturated aliphatic compound having a boiling point of 100 ° C. or higher after surface crosslinking. Patent Document 7 discloses a technique of adding a hydrophilic organic solvent and an inorganic sol to water-absorbent resin particles. Patent Document 8 discloses a technique for drying a mixture of a superabsorbent resin powder, an inorganic substance powder, and an inorganic sol. Patent Documents 9 and 10 disclose water-absorbent resins containing water-insoluble non-porous spherical single particles having an average particle diameter of 1 to 50 nm.

Patent Documents 11 to 15 disclose a water-absorbing resin containing inorganic fine particles and defined by specific parameters (EFFC, AAP, CRC, SFC, gel strength, etc.) and surface crosslinking in the presence of inorganic fine particles as a method for producing the same. ing.

U.S. Pat. No. 4,758,617 WO2007 / 116777 International Publication WO2010 / 149735 Japanese Unexamined Patent Publication "Tokuyo 2006-503948" Japanese Unexamined Patent Publication "JP 2008-297512 A" Japanese Patent Laid-Open Publication "JP-A No. 2015-016450" Japanese Unexamined Patent Publication "JP-A-06-016822" Japanese Unexamined Patent Publication "JP-A-2001-137704" International Publication WO02 / 005949 Japanese Unexamined Patent Publication "JP-A-2003-17642" International Publication WO2017 / 155197 International Publication WO2017 / 155196 International Publication WO2017 / 171208 International Publication WO2018 / 110760 International Publication WO2018 / 110758

However, in general, the properties of the water-absorbent resin are often contradictory, and additives such as water-insoluble inorganic particles and water-soluble polyvalent metal salts are added to the water-absorbent resin for liquid permeability, absorption capacity under pressure, and suction. In this method, one performance can be improved, but the other performance is reduced. All of the prior arts described in Patent Documents 1 to 15 described above are not sufficient in that they provide a particulate water-absorbing agent having both excellent moisture absorption fluidity, high absorption capacity under pressure, and high liquid permeability under pressure. Did not.

Furthermore, the addition of water-insoluble inorganic particles has a problem that the absorption capacity under pressure of the particulate water absorbing agent is greatly reduced. In addition, the particulate water-absorbing agent containing additives such as water-insoluble inorganic particles and water-soluble polyvalent metal salts can be used in sanitary articles such as diapers by increasing chargeability or decreasing powder fluidity. When used, a problem that the quantitative supply of the particulate water-absorbing agent is reduced in a manufacturing process of a sanitary article or the like, and a problem that a return amount (Re-Wet) of the sanitary article such as a diaper in actual use increases. And so on.

An object of one embodiment of the present invention is to provide a method for producing a particulate water-absorbing agent and a particulate water-absorbing agent having excellent moisture absorption fluidity, high absorption capacity under pressure, and high liquid permeability under pressure.

解決 In order to solve the above problems, the present invention includes the following inventions [1] to [11].

[1] A method for producing a particulate water-absorbing agent, comprising a surface cross-linking step of surface-cross-linking a water-absorbent resin using a surface cross-linking agent. A surface treatment liquid adding step, and a heat treatment step of heating the water-absorbent resin to which the surface treatment liquid is added, wherein the surface treatment liquid contains the surface cross-linking agent and cationic colloidal silica, The manufacturing method, wherein the heat treatment step is performed at a temperature higher than 150 ° C. and equal to or lower than 250 ° C.

[2] The production method according to [1], wherein the amount of the cationic colloidal silica used is 1% by mass to 10,000% by mass with respect to the amount of the surface cross-linking agent used as a solid content.

[3] The method according to [1] or [2], wherein the amount of the cationic colloidal silica used is 0.001% by mass to 10% by mass based on the amount of the water-absorbent resin in solid content. Production method. [4] The method according to any one of [1] to [3], wherein the surface crosslinking agent is at least one selected from the group consisting of polyhydric alcohol compounds, alkylene carbonates, and epoxy compounds.

[5] The production method according to any one of [1] to [4], including a rewetting step of adding 1% by mass to 20% by mass of water to the water-absorbent resin after surface crosslinking.

[6] The production method according to any one of [1] to [5], further comprising a fine powder recycling step.

[7] including a first classification step of the water-absorbent resin before surface cross-linking and / or a second classification step after surface cross-linking, wherein the fine powder after classification is granulated and recycled before the drying step; [6] The production method described in 1.

[8] A particulate water-absorbing agent containing a surface-crosslinked water-absorbing resin and cationic silicon dioxide particles, having a moisture-absorbing fluidity of 50% by weight or less (further 30% by weight or less), and AAP ( 0.7 psi) is 20 (g / g) or more.

[9] The particulate water-absorbing agent according to [8], wherein the liquid permeability under pressure is 10 (g / g) or more.

[10] The particulate water-absorbing agent according to [8] or [9], wherein the content of the cationic silicon dioxide particles is 0.001% by mass to 10% by mass based on the particulate water-absorbing agent.

[11] The particulate water-absorbing agent according to any one of [8] to [10], wherein the water content is 1% to 20%.

According to one embodiment of the present invention, it is possible to provide a method for producing a particulate water-absorbing agent and a particulate water-absorbing agent having excellent moisture absorption fluidity, high absorption capacity under pressure, and high liquid permeability under pressure.

Also, by using such a particulate water-absorbing agent, it is possible to provide a sanitary material such as a disposable diaper, a sanitary napkin, and a so-called incontinence pad, which has a high liquid intake speed and a reduced liquid return amount.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to this, and various changes can be made within the described range. The present invention is also applicable to embodiments obtained by appropriately combining technical means disclosed in different embodiments. Included in the technical scope. In this specification, "A to B" representing a numerical range means "A or more and B or less" unless otherwise specified.

[1] Method for producing particulate water-absorbing agent A method for producing a particulate water-absorbing agent according to one embodiment of the present invention includes a surface crosslinking step of surface-crosslinking a water-absorbing resin using a surface crosslinking agent. A method for producing an agent, wherein the surface cross-linking step includes a surface treatment liquid adding step of adding a surface treatment liquid to the water absorbent resin, and a heat treatment of heating the water absorbent resin to which the surface treatment liquid is added. Wherein the surface treatment liquid comprises the surface cross-linking agent and cationic colloidal silica, and the heat treatment step is performed at a temperature higher than 150 ° C. and 250 ° C. or lower.

(1-1) Surface Cross-linking Step The method for producing a particulate water-absorbing agent according to one embodiment of the present invention includes a surface cross-linking step of surface-cross-linking a water-absorbing resin using a surface cross-linking agent. The surface cross-linking step is a step of cross-linking the surface of the water-absorbent resin by reacting the water-absorbent resin with a surface cross-linking agent capable of reacting with a functional group of the water-absorbent resin. By cross-linking the surface of the water-absorbent resin, the cross-link density in the vicinity of the surface of the water-absorbent resin can be made higher than the cross-link density in the inside. This makes it possible to obtain a water-absorbing resin having excellent water-absorbing properties such as absorption capacity under pressure.

(1-1-1) Water-absorbing resin In the method for producing a particulate water-absorbing agent according to one embodiment of the present invention, “water-absorbing resin” means a water-swellable, water-insoluble polymer gelling agent. In addition, "water swellability" means that the CRC (centrifuge retention capacity) specified by EDANA method ERT441.2-02 is 5 g / g or more, and "water insoluble" means EDANA method ERT470. It means that the Ext (water-soluble content) defined in 2-02 is 0 to 50% by mass.

Here, "EDANA" is an abbreviation of the European Nonwovens Industry Association (European Disposables and Nonwovens Associations), and "ERT" is a European standard (almost global standard) water-absorbing resin measurement method (EDANA Recommended Test Methods). It is an abbreviation. In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured based on the original ERT (revised in 2002 / known literature).

CRC (centrifuge retention capacity) specified in ERT441.2-02 is an abbreviation of centrifuge retention capacity (centrifuge retention capacity), and the water absorption capacity of a particulate water-absorbing agent or water-absorbent resin under no pressure (“water absorption capacity”). Magnification "). Specifically, 0.2 g of the particulate water-absorbing agent or the water-absorbing resin is put in a nonwoven bag, and then immersed in a large excess of 0.90% by mass aqueous sodium chloride solution for 30 minutes to allow free swelling. Water absorption capacity (unit: g / g) after draining with a centrifuge (250 G).

ＥExt (water-soluble component) defined in ERT470.2-02 is an abbreviation of Extractables and means the water-soluble component (amount of water-soluble component) of the particulate water-absorbing agent or the water-absorbing resin. Specifically, 1.0 g of a particulate water-absorbing agent or a water-absorbing resin is added to 200 ml of a 0.90 mass% aqueous sodium chloride solution, and the amount of the dissolved polymer (unit: mass%) after stirring at 500 rpm for 16 hours is described. Say. The measurement of the amount of dissolved polymer is performed using pH titration.

The water-absorbent resin can be appropriately designed according to its use, and is not particularly limited, but is preferably a hydrophilic cross-linked polymer obtained by cross-linking and polymerizing an unsaturated monomer having a carboxyl group. The water-absorbent resin is not limited to a form in which the total amount (100% by mass) is a polymer, and a water-absorbent resin composition containing an additive and the like within a range satisfying the physical properties (CRC, Ext). It may be.

Further, the water-absorbent resin in one embodiment of the present invention is not limited to the water-absorbent resin powder before surface crosslinking, but may be an intermediate in the process of producing the water-absorbent resin (for example, a hydrogel crosslinked polymer after polymerization, And a water-absorbent resin after surface cross-linking), and together with the water-absorbent resin composition, all of them are collectively referred to as "water-absorbent resin". The shape of the water-absorbent resin may be a sheet, a fiber, a film, a particle, a gel, or the like. In the present invention, the particulate water-absorbent resin is preferable. Here, in the present specification, “particulate” means having the form of a particle, and the particle refers to a solid or liquid granular small object having a measurable size. The term “particulate” is intended to include irregularly crushed, spherical, rod-like, substantially spherical, and flat shapes.

Examples of the water absorbing resin include polyacrylic acid (salt) resin, polysulfonic acid (salt) resin, maleic anhydride (salt) resin, polyacrylamide resin, polyvinyl alcohol resin, polyethylene oxide resin, and polyasparagine. Acid (salt) -based resins, polyglutamic acid (salt) -based resins, polyalginic acid (salt) -based resins, starch-based resins, and cellulose-based resins are preferred, and polyacrylic acid (salt) -based resins are preferably used.

The “polyacrylic acid (salt) -based resin” is a polymer containing acrylic acid and / or a salt thereof (hereinafter, referred to as “acrylic acid (salt)”) as a main component as a repeating unit, and a graft component as an optional component. Refers to coalescence. Polyacrylic acid may be obtained by hydrolysis of polyacrylamide or polyacrylonitrile, but is preferably obtained by polymerization of acrylic acid (salt).

Here, the “main component” means that the used amount (content) of acrylic acid (salt) is usually 50 mol% to 100 mol% based on the whole monomer (excluding the internal crosslinking agent) used for polymerization. %, Preferably 70 mol% to 100 mol%, more preferably 90 mol% to 100 mol%, and still more preferably substantially 100 mol%.

(1-1-2) Particulate water absorbent In the method for producing a particulate water absorbent according to one embodiment of the present invention, “particulate water absorbent” means a particulate water absorbent. Further, “water absorbing agent” means an aqueous liquid absorbing gelling agent containing a water absorbing resin as a main component.

The “aqueous liquid” may include water, and is not particularly limited. The aqueous liquid is not limited to water, and includes urine, blood, sweat, feces, waste liquid, moisture, steam, ice, a mixture of water and an organic solvent and / or an inorganic solvent, rainwater, and groundwater. The aqueous liquid preferably includes urine, menstrual blood, sweat, and other body fluids.

粒子 The particulate water-absorbing agent according to one embodiment of the present invention is suitably used as a sanitary material for absorbing an aqueous liquid. The water absorbing resin is contained as a main component in the particulate water absorbing agent. That is, the water-absorbing resin is preferably 60% by mass to 100% by mass, more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, particularly preferably 90% by mass in the particulate water-absorbing agent. % By mass to 100% by mass. The particulate water absorbing agent optionally contains other additives. The preferred water content of the particulate water-absorbing agent is 0.2% to 30% by mass. That is, a water-absorbing resin composition in which these components are integrated is also included in the category of the particulate water-absorbing agent.

The upper limit of the water-absorbing resin in the particulate water-absorbing agent is 99.999% by mass, further 99% by mass, further 97% by mass, particularly about 95% by mass and 90% by mass, preferably other than the water-absorbing resin. Further contains about 0 to 10% by mass of a component, particularly, for example, water and an additive described below (cationic silicon dioxide fine particles).

(1-1-3) Surface Treatment Liquid Addition Step The surface crosslinking step in one embodiment of the present invention includes a surface treatment liquid addition step of adding a surface treatment liquid to the water-absorbent resin. The surface treatment liquid contains the surface cross-linking agent and cationic colloidal silica. In the method for producing a particulate water-absorbing agent according to one embodiment of the present invention, the surface crosslinking agent and the cationic colloidal silica are added to the water-absorbing resin in one liquid. Particles having excellent moisture absorption fluidity, high absorption capacity under pressure, and high liquid permeability under pressure when added to the water-absorbent resin in the state where these are mixed in the surface treatment liquid (one liquid). Water absorbent can be obtained.

(Surface cross-linking agent)
As the surface cross-linking agent, a compound having a functional group capable of reacting with a plurality of functional groups (eg, a COOH group) of the water absorbent resin is used. The number of functional groups in the surface cross-linking agent is not limited to plural, and any compound capable of cross-linking with a carboxyl group such as ethylene carbonate to generate a functional group OH may be used as long as it is a compound that cross-links the surface of the water-absorbing resin. The valent metal cation may be used, that is, the surface cross-linking agent may be a compound having one functional group capable of reacting with a plurality of functional groups of the water-absorbing resin, and is not particularly limited. As the surface crosslinking agent that can be used in one embodiment of the present invention, various organic surface crosslinking agents or inorganic surface crosslinking agents can be exemplified. Among them, an organic surface cross-linking agent is more preferable. Examples of the organic surface cross-linking agent include polyhydric alcohol compounds, epoxy compounds, polyamine compounds, condensates of polyamine compounds and haloepoxy compounds, oxazoline compounds, monooxazolidinone compounds, dioxazolidinone compounds, polyoxazolidinone compounds, and polyhydric compounds. It is preferable to use one or a combination of two or more selected from metal salts and alkylene carbonate compounds.

In the present invention, the water-absorbing resin is mixed with a surface cross-linking agent (more preferably an organic surface cross-linking agent, more preferably a water-soluble organic surface cross-linking agent) in a surface treatment liquid containing the cationic colloidal silica. It has been found that by performing (one-liquid mixing), the mixing property is improved and the physical properties are improved as compared with the case where the surface cross-linking agent and the cationic colloidal silica are individually mixed with the water-absorbing resin (two-liquid mixing). .

As the organic surface cross-linking agent, for example, the surface cross-linking agents disclosed in U.S. Pat. Nos. 6,228,930, 6,071,976 and 6,254,990 can be used. That is, as the organic surface crosslinking agent, more specifically, monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentane Polyhydric alcohol compounds such as diol, 1,6-hexanediol and 1,2-cyclohexanedimethanol; epoxy compounds such as ethylene glycol diglycidyl ether and glycidol; ethylenediamine, diethylenetriamine, Polyvalent amine compounds such as ethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine and polyamidepolyamine; haloepoxy compounds such as epichlorohydrin, epibromhydrin and α-methylepichlorohydrin; polyvalent amine compounds And a haloepoxy compound; an oxazolidinone compound such as 2-oxazolidinone; and an alkylene carbonate compound such as ethylene carbonate.

の う ち Among these surface cross-linking agents, one or more selected from a polyhydric alcohol compound, an alkylene carbonate, and an epoxy compound are more preferable from the viewpoint that the obtained particulate water-absorbing agent is excellent in moisture absorption fluidity and absorption capacity under pressure. Further, one or more, more preferably two or more selected from a polyhydric alcohol compound and an alkylene carbonate are preferred. When a plurality of surface cross-linking agents (particularly organic surface cross-linking agents) are used in combination, it is preferable that the polyhydric alcohol compound and the alkylene carbonate are the main components, and the total amount of the polyhydric alcohol compound and the alkylene carbonate is the surface cross-linking agent. The content of the (particularly, organic surface crosslinking agent) is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and further preferably 90 to 100% by weight. When the concentration of the cationic colloidal silica is reduced, the effect of the dispersant is reduced, and aggregation and precipitation tend to occur easily. However, it was found that by using these surface cross-linking agents, aggregation and precipitation of colloidal silica did not occur contrary to the prediction, and a particulate water absorbing agent could be stably produced. In addition, it has been found that the obtained particulate water-absorbing agent is excellent in moisture absorption fluidity and absorption capacity under pressure. Accordingly, it is not necessary to add an additive in a later step to impart moisture absorption fluidity, so that manufacturing equipment can be simplified.

The amount of the surface cross-linking agent used depends on the type of the surface cross-linking agent to be used and the combination of the water-absorbing resin and the surface cross-linking agent. 10% by mass is preferable, 0.01% by mass to 5% by mass is more preferable, 0.05% by mass to 2% by mass is more preferable, and 0.1% by mass to 1% by mass (furthermore, 0.2% by mass is As described above, 0.3% by mass or more, for example, 0.4 to 1% by mass) is particularly preferable. When the amount of the surface cross-linking agent is 0.001% by mass or more, the absorption capacity under pressure (AAP) and the liquid permeability under pressure (PDAUP) are preferably improved. When the amount of the surface cross-linking agent used is 10% by mass or less, it is preferable because the cost can be suppressed and the surface cross-linking agent does not remain.

(Cationic colloidal silica)
The “cationic colloidal silica” used in one embodiment of the present invention may be any cationic colloidal silica. More preferably, the cationic colloidal silica is a colloidal silica having a positive zeta potential and usually in the range of +60 mV or less, preferably in the range of +5 mV to +55 mV. Here, the cation is preferably a polyvalent metal cation, more preferably a divalent to tetravalent polyvalent metal cation, still more preferably a trivalent or tetravalent polyvalent metal cation, and particularly preferably an aluminum cation. The cationic colloidal silica is preferably a colloidal silica modified or modified with these cations.

"Colloidal silica" refers to a colloidal solution in which silicon dioxide particles are dispersed in a dispersion medium. The dispersion medium is water, an organic solvent, or a mixture of water and an organic solvent. Colloidal silica can be a colloidal solution in which silicon dioxide particles are dispersed in water. Colloidal silica, particularly the cationic colloidal silica used in one embodiment of the present invention, can be stably dispersed only with water as a dispersion medium, but when mixed with a water absorbent resin, an organic solvent and an organic surface cross-linking agent are used. In particular, water-soluble organic solvents and water-soluble organic surface crosslinking agents are used. Here, “water-soluble” means that the degree of solvation in water (100 g / 25 ° C.) is 1 g or more. More preferably, the water-soluble organic solvent and the water-soluble organic surface cross-linking agent having the solubility of 10 g or more, more preferably 50 g or more, are used with colloidal silica and mixed with the water-absorbing resin.

有機 Examples of the organic solvent include methanol and ethylene glycol. As the organic solvent, an organic substance (for example, a polyhydric alcohol or an alkylene carbonate, that is, the organic surface cross-linking agent) that can act as a surface cross-linking agent for the water absorbent resin may be used. In the mixture of water, the organic solvent, and the organic surface cross-linking agent, the content ratio of water, the organic solvent, and the organic surface cross-linking agent is not particularly limited. The mass ratio of the crosslinking agent is preferably from 99: 1 to 1: 1 and more preferably from 90: 1 to 10: 1. From the viewpoint of the dispersibility of colloidal silica, the organic solvent is more preferably also an organic surface cross-linking agent.

比 べ Compared to the case of using powdered silica, the use of colloidal silica is preferable because the performance of the obtained particulate water-absorbing agent is stabilized. That is, it is possible to obtain the effect that the moisture absorption fluidity and the absorption capacity under pressure of the obtained particulate water absorbing agent do not change. It is considered that this effect is obtained because, for example, the average particle diameter fluctuates due to the collapse of the powdered silica in the production process, whereas the colloidal silica does not collapse in the production process.

Further, as a problem of the conventional additives such as water-insoluble inorganic particles, there is a problem that the absorption capacity under pressure of the particulate water-absorbing agent is greatly reduced. In addition, when the water absorbing agent containing water-insoluble inorganic particles and an additive such as a water-soluble polyvalent metal salt is used for a diaper or the like, the chargeability of the water absorbing agent is increased or the powder fluidity is reduced. There were problems such as a decrease in the quantitative supply of the particulate water-absorbing agent in the process and the like, and a problem of an increase in the amount of return (Re-Wet) when the diaper was actually used. However, according to an embodiment of the present invention, such a problem is solved or improved. The electrification of the particulate water-absorbing agent (water-absorbing resin) may cause the particulate water-absorbing agent (water-absorbing resin) to adhere to pipes or devices during transportation or mixing, and the particulate water-absorbing agent (water-absorbing resin) may be attached. This may reduce the uniform mixing property and transportability of the (water-absorbent resin), and as a result, the productivity and physical properties of the final product (eg, disposable diaper) using the particulate water-absorbing agent (water-absorbent resin) may be deteriorated. Is not preferred.

The average particle size of the silicon dioxide particles contained in the cationic colloidal silica is not particularly limited, but is preferably 1 nm to 100 nm, more preferably 1 nm to 80 nm, further preferably 5 nm to 60 nm, and particularly preferably. Is 5 nm to 50 nm. When the average particle diameter of the silicon dioxide particles contained in the cationic colloidal silica is in the above range, adhesion between particles of the particulate water-absorbing agent after the addition of the cationic colloidal silica can be suppressed, so that the particulate water absorption The agent has improved moisture absorption and fluidity.

平均 The average particle size of the silicon dioxide particles contained in the cationic colloidal silica may be measured by a conventionally known method. For example, a method of actually measuring the longest diameter and the shortest diameter of individual particles of 100 or more silicon dioxide particles from an image of 50,000 times with a transmission electron microscope and taking the average as the particle diameter, and calculating the average value Can be mentioned. The average particle diameter of the silicon dioxide particles can also be measured using a scattering particle size distribution analyzer using dynamic light scattering or laser diffraction. When a commercially available cationic colloidal silica is used, its catalog value can be used instead.

The pH of the cationic colloidal silica is preferably from 1.2 to 4.8, more preferably from 1.5 to 4.8 as an aqueous solution before being mixed with the organic solvent, from the viewpoint of improving the moisture absorption and fluidity of the water absorbing agent. 4.5, and more preferably 2 to 4.

The specific surface area of the silicon dioxide particles contained in the cationic colloidal silica is not particularly limited, from the viewpoint of improving the absorption under load of the particulate water-absorbing agent, preferably ^{50m 2 / g ~ 400m 2 /} g, It is more preferably from 75 m ² / g to 350 m ² / g, and still more preferably from 100 m ² / g to 300 m ² / g.

方法 A method for obtaining the cationic colloidal silica is not particularly limited, and examples thereof include a method for cationizing colloidal silica. Examples of the method of cationizing colloidal silica include a method of reacting a compound of a polyvalent metal ion such as an aluminum ion with the colloidal silica and coating the surface of the colloidal silica with aluminum ions. Alternatively, the colloidal silica may be modified into cationic colloidal silica by adding a silane coupling agent having an amino group to the surface of the colloidal silica.

カ チ オ ン The cationic colloidal silica is more preferably cationic colloidal silica in which the surface of silicon dioxide particles is coated with aluminum ions. The method for producing such a cationic colloidal silica is not particularly limited, and examples thereof include a method described in JP-A-2-172812.

市 販 As the colloidal silica used for the cationization, a commercial product can be easily obtained. Commercially available products include Snowtex ST-XS, Snowtex ST-OXS, Snowtex ST-NXS, Snowtex ST-CXS, Snowtex ST-S, Snowtex manufactured by Nissan Chemical Industries, Ltd. Tex ST-OS, Snowtex ST-NS, Snowtex ST-30, Snowtex ST-O, Snowtex ST-N, Snowtex ST-C, Snowtex ST-AK, Snowtex ST-50, Snowtex ST -O-40, Snowtex ST-N-40, Snowtex ST-CM, Snowtex ST-20L, Snowtex ST-OL, Snowtex ST-AK-L, Snowtex ST-XL, Snowtex ST-YL , Snowtex ST-OYL, Snowtex ST AK-YL, Snowtex ST-ZL, Snowtex MP-1040, Snowtex MP-2040, Snowtex MP-3040, Snowtex MP-4540M; Klebosol (registered trademark, hereinafter the same) manufactured by AZ Electronic Materials Co., Ltd. 20H12;

The amount of the cationic colloidal silica used is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 5% by mass, and more preferably 0.01% by mass to 5% by mass, based on the amount of the water-absorbing resin used. 1% by mass to 3% by mass is more preferable, and 0.2% by mass to 2% by mass is particularly preferable. When the amount of the cationic colloidal silica used is 0.001% by mass or more as a solid content, it is preferable from the viewpoint of imparting moisture absorption fluidity. When the amount of the cationic colloidal silica used is 10% by mass or less in terms of solid content, the amount of the cationic colloidal silica is not excessively added, and the added amount functions properly.

(Solvent or dispersion medium)
The surface treatment liquid includes the surface cross-linking agent and the cationic colloidal silica, and may further include a solvent or a dispersion medium (hereinafter, the solvent or the dispersion medium is simply referred to as a “solvent”).

The solvent may be the same as or different from the dispersion medium contained in the cationic colloidal silica.

The solvent is water, an organic solvent, or a mixture of water and an organic solvent. The solvent is more preferably water or a mixture of water and an organic solvent from the viewpoint of mixing with the water-absorbing resin.

The organic solvent is more preferably a water-soluble organic solvent. Examples of the water-soluble organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol and t-butyl alcohol; ketones such as acetone; dioxane, tetrahydrofuran And ethers such as methoxy (poly) ethylene glycol; amides such as ε-caprolactam and N, N-dimethylformamide; and sulfoxides such as dimethylsulfoxide. Among them, the organic solvent is more preferably a lower alcohol. Alternatively, the organic solvent can be replaced with the surface crosslinking agent described above.

When water is contained in the surface treatment liquid, the amount of water contained depends on the water content of the water-absorbing resin used, but is usually 0.1% by mass to 20% by mass relative to the water-absorbing resin. It is preferably from 0.5% by mass to 15% by mass, more preferably from 1% by mass to 10% by mass. In addition, the amount of water contained in the surface treatment liquid refers to the total amount of water including the water contained in the cationic colloidal silica when the cationic colloidal silica contains water.

When the surface treatment liquid contains an organic solvent, the amount of the organic solvent is usually preferably 10% by mass or less, and more preferably 0.1% by mass to 5% by mass, based on the water-absorbing resin. Is more preferable. In addition, the amount of the organic solvent contained in the surface treatment liquid refers to the total amount of the organic solvent including the organic solvent contained in the cationic colloidal silica when the cationic colloidal silica contains the organic solvent. The total amount of the organic solvent mentioned here does not include the amount of the surface crosslinking agent.

The amount of the surface cross-linking agent contained in the surface treatment liquid is preferably 0.1% by mass to 50% by mass, more preferably 1% by mass to 30% by mass, and still more preferably the total amount of the surface treatment solution. It is 2% by mass to 10% by mass. When the amount of the surface cross-linking agent contained in the surface treatment liquid is within the above range, the absorption capacity under pressure and the liquid permeability under pressure are preferably improved.

Further, the solid content of the cationic colloidal silica contained in the surface treatment liquid is preferably 1% by mass to 50% by mass, more preferably 3% by mass to 30% by mass, and more preferably 3% by mass to 30% by mass, based on the total amount of the surface treatment solution. It is preferably from 5% by mass to 10% by mass. It is preferable that the solid content of colloidal silica as a surface cross-linking agent contained in the surface treatment liquid is within the above range, since silicon dioxide particles do not aggregate and precipitate.

The surface treatment liquid may further include a third substance such as a mixing aid. Examples of the mixing aid include a surfactant, a water-soluble polymer, a water-soluble organic solvent, a water-soluble inorganic compound, an inorganic acid (salt), and an organic acid (salt). These mixing aids may be used alone or in the form of a mixture of two or more.

The amount of the cationic colloidal silica used is preferably from 1% by mass to 10,000% by mass, more preferably from 10% by mass to 1,000% by mass, and still more preferably from 20% by mass, based on the amount of the surface cross-linking agent used. % By mass to 500% by mass. When the ratio of the amount of the cationic colloidal silica to the amount of the surface cross-linking agent used is within the above range, it is preferable because the moisture absorption fluidity, and the absorption capacity under pressure, or the liquid permeability under pressure can be compatible. .

(Preparation of surface treatment liquid)
In one embodiment of the present invention, the surface treatment liquid uniformly mixes the surface cross-linking agent, the cationic colloidal silica, and the solvent as required (if the mixed liquid is not separated, it may be dissolved. (A homogeneous liquid or a cloudy dispersion).

方法 The method of uniformly mixing the surface cross-linking agent, the cationic colloidal silica, and the solvent, if necessary, is not particularly limited, and a conventionally known method can be appropriately used.

表面 In the surface cross-linking step in one embodiment of the present invention, a surface treatment solution prepared by previously mixing the surface cross-linking agent and the cationic colloidal silica is added to the water-absorbent resin. It is preferable that the surface cross-linking agent and the cationic colloidal silica are uniformly mixed at the time when the addition of the surface treatment liquid to the water absorbent resin is started. This allows the surface cross-linking agent and the cationic silicon dioxide particles to be uniformly present on the surface of the water-absorbent resin to which the surface treatment liquid has been added. Therefore, a particulate water-absorbing agent having both excellent moisture-absorbing fluidity (for example, BR described below), high absorption capacity under pressure (for example, AAP described below), and high liquid permeability under pressure (for example, PDAUP described later) is obtained. be able to.

(Method of adding surface treatment liquid)
The addition of the surface treatment liquid can be performed by various methods. For example, when the water-absorbent resin is obtained by aqueous solution polymerization, a method of drop-mixing the surface treatment liquid with the water-absorbent resin during or after the drying step, a method of spray-mixing, and the like can be used. When adding by a spraying method, the size of the sprayed droplet is preferably 0.1 μm to 300 μm as an average droplet diameter, more preferably 1 μm to 200 μm.

(4) As a mixing device used when mixing the water-absorbing resin and the surface treatment liquid, a device having a large mixing force is preferable in order to uniformly and surely mix them. Examples of such a 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 double-arm kneader, A pulverizing kneader, a rotary mixer, an airflow mixer, a turbulizer, a batch-type Ladyge mixer, a continuous Ladyge mixer, and the like can be suitably used.

(1-1-4) Heat Treatment Step The surface cross-linking step in one embodiment of the present invention includes a heat treatment step of heating the water-absorbent resin to which the surface treatment liquid has been added.

加熱 In the step of adding the surface treatment liquid, a heat treatment is performed after the surface treatment liquid and the water-absorbing resin are mixed. In the heat treatment, the temperature of the water-absorbent resin or the temperature of the heating medium used for the heat treatment is higher than 150 ° C. and 250 ° C. or lower, more preferably 160 ° C. to 240 ° C., further preferably 170 ° C. to 230 ° C., and particularly preferably 180 ° C. ２２０220 ° C. The heating time of the heat treatment is preferably 1 minute to 2 hours, more preferably 5 minutes to 1.5 hours, further preferably 10 minutes to 1.4 hours, and particularly preferably 20 minutes to 1 hour. If the heating temperature is higher than 150 ° C., sufficient physical properties can be obtained. If the heating temperature is 250 ° C. or lower, not only the control of surface cross-linking is easy, but also the problem of thermal deterioration and coloring of the water-absorbent resin itself does not easily occur. . In particular, in one embodiment of the present invention, as the surface cross-linking agent, a cross-linking agent that undergoes dehydration esterification with a carboxyl group, which is a functional group of the water-absorbent resin, particularly a polyhydric alcohol or alkylene carbonate (carbonate of polyhydric alcohol) Esters). In such an embodiment, the water-absorbent resin is surface-crosslinked by a dehydration esterification reaction with a functional group (acid group, particularly carboxyl group) of the water-absorbent resin at a high temperature of more than 150 ° C. and 250 ° C. or less.

When heating the mixture of the surface treatment liquid and the water-absorbing resin, the mixture may be heated in a stationary state, or may be heated using a mixing means such as stirring, but over the entire mixture. From the viewpoint of uniform heating, heating under stirring and mixing is preferable. Among them, a batch paddle mixer and a continuous paddle mixer are more preferable, and a continuous paddle mixer is more preferable.

(1-2) Method for Producing Water Absorbent Resin Used in Surface Crosslinking Step The water absorbent resin used in the surface crosslinking step in one embodiment of the present invention is preferably an unsaturated monomer in the presence of an internal crosslinking agent. Obtained by polymerizing the body. The method for producing a water-absorbent resin subjected to the surface crosslinking step may include the following steps. Therefore, the method for producing a particulate water-absorbing agent according to one embodiment of the present invention may further include the following steps.

(1-2-1) Polymerization Step The polymerization step is a step of polymerizing an unsaturated monomer to obtain a hydrogel crosslinked polymer (hereinafter, referred to as “hydrogel”).

When a polyacrylic acid (salt) resin is used as the water-absorbing resin, for example, acrylic acid (salt) may be used as a main component as an unsaturated monomer. A monomer (hereinafter, referred to as “another monomer”) may be used as a copolymer component.

Examples of the other monomer include, but are not limited to, methacrylic acid, (anhydride) maleic acid, fumaric acid, crotonic acid, itaconic acid, vinylsulfonic acid, and 2- (meth) acrylamide. 2-methylpropanesulfonic acid, (meth) acryloxyalkanesulfonic acid and its alkali metal salt or ammonium salt, N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth) acrylamide, N-isopropyl (meth) acrylamide, Water-soluble or hydrophobic compounds such as N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, isobutylene and lauryl (meth) acrylate Saturated monomer It can be mentioned.

The amount of the other monomer described above is 0 to 50 mol%, preferably 0 to 30 mol%, more preferably 0 to 10 mol%, and more preferably 0 to 50 mol%, based on the total number of moles of the unsaturated monomer. Preferably it is 0 to 5 mol%.

When the unsaturated monomer (including the other monomers described above) is an acid group-containing monomer, the salt of the unsaturated monomer may be an alkali metal salt, an alkaline earth metal salt or An ammonium salt may be used. Among these, it is preferable to use a sodium salt and a potassium salt. Further, the neutralization ratio is preferably from 50 mol% to 100 mol%, more preferably from 60 mol% to 90 mol%, further preferably from 70 mol% to 80 mol%.

(Internal crosslinking agent)
In the method for producing a water-absorbent resin subjected to the surface cross-linking step, it is preferable to use a cross-linking agent (hereinafter, referred to as “internal cross-linking agent”) from the viewpoint of the water-absorbing performance of the obtained water-absorbent resin. The internal crosslinking agent is not particularly limited, for example, a polymerizable crosslinking agent that reacts with a double bond of a monomer, a reactive crosslinking agent that reacts with a carboxyl group of a monomer, or a crosslinking agent that has these properties. And the like.

Examples of the internal crosslinking agent include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and trimethylolpropane tri (meth) acrylate. Glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (Meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol Lumpur, propylene glycol, glycerol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethylene imine, and glycidyl (meth) acrylate.

は These internal cross-linking agents may be used alone or in a combination of two or more. Further, the internal crosslinking agent may be added to the reaction system all at once, or may be added in portions. Further, it is preferable to use an internal crosslinking agent having two or more polymerizable unsaturated groups at the time of polymerization in consideration of the water absorbing performance of the finally obtained water-absorbing resin composition.

The amount of the internal crosslinking agent to be used is preferably 0.001 mol% to 5 mol%, more preferably 0.001 mol% to 3 mol%, based on the monomer excluding the crosslinking agent, from the viewpoint of obtaining good physical properties of the water absorbent resin. Mol% is more preferable, and 0.001 to 2 mol% is particularly preferable. When the use amount of the internal crosslinking agent exceeds 5 mol%, physical properties such as the water absorption capacity of the water absorbent resin may be reduced. If the amount of the polymerization initiator is less than 0.001 mol%, the water solubility of the water-absorbing resin may increase.

(Polymerization initiator)
The polymerization initiator used in the polymerization step is appropriately selected depending on the polymerization mode, and is not particularly limited. Examples thereof include, for example, a photolytic polymerization initiator, a thermal decomposition polymerization initiator, and a redox polymerization initiator. it can.

Examples of the photolytic polymerization initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, and azo compounds. Examples of the thermal decomposition type polymerization initiator include, for example, persulfates (sodium persulfate, potassium persulfate, ammonium persulfate), peroxides (hydrogen peroxide, t-butyl peroxide, methyl ethyl ketone peroxide), azo compounds (2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, and the like). Examples of the redox polymerization initiator include a system in which a persulfate or a peroxide is combined with a reducing compound such as L-ascorbic acid or sodium bisulfite. In addition, a combination of a photodecomposition type initiator and a thermal decomposition type polymerization initiator can also be mentioned as a preferable embodiment.

使用 The use amount of these polymerization initiators is preferably from 0.001 mol% to 2 mol%, more preferably from 0.01 mol% to 0.1 mol%, based on the monomers. When the amount of the polymerization initiator used is 0.001 mol% or more, there is no possibility that the amount of the residual monomer is increased. When the amount of the polymerization initiator used does not exceed 2 mol%, the control of polymerization does not become difficult.

(Polymerization method)
The polymerization method applied in this step is not particularly limited, but is preferably gas phase spray polymerization, gas phase droplet polymerization, aqueous solution polymerization, and reverse phase suspension from the viewpoints of water absorption properties and ease of polymerization control. Polymerization, more preferably aqueous solution polymerization, and reverse phase suspension polymerization, further preferably aqueous solution polymerization. Among them, continuous aqueous polymerization is particularly preferable, and any of continuous belt polymerization and continuous kneader polymerization is applied.

As a specific polymerization mode, continuous belt polymerization is described in U.S. Patent Nos. 4,893,999 and 6,241,928 and U.S. Patent Application Publication No. 2005/0215734, and continuous kneader polymerization is described in U.S. Patent Nos. 6,987,151 and 6,710,141. , Respectively. By employing these continuous aqueous polymerization methods, the production efficiency of the water-absorbing resin is improved.

When an unsaturated monomer is polymerized in an aqueous solution, the concentration of the monomer in the aqueous solution is determined by the temperature of the aqueous solution and the type of the monomer, and is not particularly limited. Is preferably, and more preferably 20% by mass to 60% by mass.

重合 The polymerization of the unsaturated monomer is started by adding a polymerization initiator, irradiating an active energy ray such as an ultraviolet ray, an electron beam or a γ ray, or a combination thereof. The reaction temperature in the polymerization reaction may be appropriately selected according to the type of the polymerization initiator and the active energy ray used, and is not particularly limited, but is preferably from 15 ° C to 130 ° C, more preferably from 20 ° C to 120 ° C. preferable. By being in the preferred range described above, the amount of the residual monomer in the obtained water-absorbent resin is increased, and the self-crosslinking reaction does not excessively proceed, and there is no possibility that the water-absorbing performance of the water-absorbent resin is reduced. .

In addition, the reversed-phase suspension polymerization is a method of performing polymerization by suspending an aqueous monomer solution in a hydrophobic organic solvent, for example, US Pat. Nos. 4,093,776, 4,667,323, 4,446,261, Nos. 4,683,274 and 5,244,735.

In addition, aqueous solution polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. For example, U.S. Pat. Nos. 4,625,001, 4,873,299, 4,286,082, 4,9773632, and No. 4,985,518, No. 5,124,416, No. 5,250,640, No. 5,264,495, No. 5,145,906, No. 5,380,808, etc., and European Patent Nos. 0811636, 09555086, and 0922717. . In addition, a solvent other than water may be used in combination, if necessary, and its type is not particularly limited.

Therefore, a water-absorbing resin can be obtained by applying an unsaturated monomer, a polymerization initiator, and the like to the polymerization methods disclosed in the respective patent documents.

(1-2-2) Gel Pulverizing Step The gel pulverizing step is a step of subdividing the hydrogel during or after the polymerization to obtain a particulate hydrogel. This step is referred to as “gel pulverization” to be distinguished from “pulverization” of a pulverization step and a classification step described later. In this step, the hydrogel is subdivided into a size that is about a fraction of the original size.

ゲ ル The gel crushing device used in the present gel crushing step is not particularly limited as long as the polymer obtained by polymerization can be finely divided, and various devices and methods can be suitably used.

When the polymerization step is kneader polymerization, the polymerization step and the gel pulverization step are performed simultaneously. Further, when a particulate hydrogel is directly obtained in the polymerization process such as gas phase polymerization or reverse phase suspension polymerization, the gel pulverizing step may not be performed.

(1-2-3) Drying Step The drying step is a step of drying the particulate hydrogel obtained in the polymerization step or the gel pulverizing step to obtain a dried polymer. The drying method in this step is not particularly limited, but may be heat drying, hot air drying, reduced pressure drying, infrared drying, microwave drying, azeotropic dehydration with a hydrophobic organic solvent, and high humidity using high-temperature steam. Various drying methods such as drying are employed.

条件 The conditions such as the drying temperature and the drying time are not particularly limited, and various methods and conditions can be suitably combined.

樹脂 The resin solid content after drying is preferably 80% by mass or more, more preferably 85% by mass to 99% by mass, and still more preferably 90% by mass to 98% by mass.

(1-2-4) Pulverizing Step and Classifying Step This step is a step of pulverizing and classifying the dried polymer obtained in the drying step to obtain a water-absorbent resin adjusted to a predetermined range of particle size. is there. The gel pulverizing step differs from the gel pulverizing step in that the resin solid content at the time of pulverization, in particular, the object to be pulverized has undergone a drying step (preferably, drying to the resin solid content). Further, the water-absorbing resin particles obtained after the pulverizing step may be referred to as a pulverized product.

乾燥 The dried polymer obtained in the drying step can be directly subjected to a surface cross-linking step, but it is preferable to control the particle size to a specific particle size in order to improve physical properties in the surface cross-linking step. The particle size control is not limited to the main pulverization step and the classification step, but can be appropriately performed in the polymerization step, the fine powder recovery step, the granulation step, and the like.

The pulverizer that can be used in the pulverization step is not particularly limited, and includes, for example, a vibration mill, a roll granulator, a knuckle-type pulverizer, a roll mill, a high-speed rotary pulverizer (pin mill, hammer mill, screw mill), and a cylinder. Mixer and the like. Among them, it is preferable to use a multi-stage roll mill or roll granulator from the viewpoint of particle size control.

で は In the classification step, the classification operation is preferably performed before the surface crosslinking step (first classification step), but the classification operation (second classification step) may be further performed after the surface crosslinking. Note that the first classification step and the second classification step in the present invention are not limited to classification at one place (in other words, one time point) or classification by one classifier. The classifying step includes a classifying step (first classifying step) at one or more places and / or a plurality of classifiers before surface crosslinking, and a classifying step at one or more places and / or a plurality of classifiers after the surface crosslinking. This is a general term for (second classification step). The classification operation can be performed by a known method, and is not particularly limited. In the case of sieving using a sieve, classification is performed as follows. That is, when the particle size distribution of the water-absorbent resin particles is set to 150 μm to 850 μm, for example, first, the pulverized material is sieved with a sieve having an aperture of 850 μm, and the pulverized material that has passed through the sieve has an aperture of 150 μm or 150 μm. Further sieve through a sieve (eg, 200 μm). Then, the pulverized material remaining on the sieve having an opening of 150 μm or the like becomes water-absorbent resin particles having a desired particle size distribution. In addition to the sieve classification, various classifiers such as airflow classification can be used. Fine powder having a particle size smaller than the target particle size (for example, a product passed through a 150 μm sieve) may be discarded after being removed, may be used for other purposes, or may be recycled. The fine powder is more preferably recycled, more preferably recycled before the drying step, and particularly preferably recycled from the polymerization step to the drying step.

The particle size of the water-absorbing resin particles before surface cross-linking, the water-absorbing resin particles after surface cross-linking, and the particulate water-absorbing agent (final product) is appropriately set depending on the purpose, but the particles having a particle size of 150 μm to 850 μm are It is preferably set to 90% by mass or more, more preferably 95% by mass or more, further preferably 98% by mass or more, and the average particle size (defined by sieving classification) is preferably 200 μm to 600 μm, more preferably 250 μm to 500 μm, Preferably, it is set to about 300 μm to 450 μm. The particle size and the particle size can be measured, for example, by the classification method described in EP1594556B1.

(1-3) Step After Surface Cross-Linking Step The water-absorbing resin after surface cross-linking obtained in the surface cross-linking step in one embodiment of the present invention can be used as it is as a particulate water absorbing agent. Alternatively, the water-absorbing resin after the surface cross-linking can be converted into a particulate water-absorbing agent through the following steps for further improving physical properties or recycling. Therefore, the method for producing a particulate water-absorbing agent according to one embodiment of the present invention may further include the following steps.

(1-3-1) Additive Addition Step This step is a step of adding an additive in order to impart various functions to the water-absorbent resin after surface crosslinking, and is composed of one or more steps. The additives may include additives such as inorganic fine particles, surfactants, fragrances, foaming agents, pigments, dyes, and fertilizers to impart or enhance functions. The additional function is not particularly limited, and includes, for example, functions such as transportability, liquid permeability, moisture absorption fluidity, urine resistance, antibacterial property, deodorant performance, and dust amount reduction of the water-absorbent resin composition.

量 Unless otherwise specified, the amount of the additive is less than 10% by mass, preferably less than 5% by mass, and more preferably less than 1% by mass based on the water-absorbent resin after surface crosslinking. In addition, these additives may be performed simultaneously with the surface crosslinking step or in a separate step.

(1-3-2) Rewetting Step This step is a step of adding water in order to adjust the water content of the water-absorbent resin after the surface crosslinking, or to add the additive as an aqueous solution or slurry. . When the additive is added as an aqueous solution or slurry, the additive adding step and this step are performed simultaneously.

水性 By adding water, the water-absorbent resin swells again with water. For this reason, this step is referred to as a “rewetting step”. In this step, the amount of water to be added is not particularly limited, but is preferably from 1% by mass to 20% by mass, and more preferably from 1% by mass to 10% by mass. The lower limit of the added amount of water is more preferably 2% by mass or more, further preferably 3% by mass or more, 4% by mass or more, 5% by mass or more, and 6% by mass or more.

る こ と It is preferable that the amount of water to be added is within the above-mentioned range, since adhesion in the production process and a decrease in absorption performance can be suppressed.

In one embodiment of the present invention, the water-absorbing resin after the surface cross-linking by the cross-linking reaction performed at the above-mentioned heating time in the surface cross-linking step at 150 ° C. to 250 ° C., preferably the dehydration esterification reaction, is substantially dried. State (water content 1% by mass or less, further less than 1% (defined by loss on drying at 180 ° C.)). In the present step, the dried surface-crosslinked water-absorbent resin is preferably re-wetted to be a water-absorbent resin having a certain water content or a particulate water-absorbing agent. The water content of the re-wetted water-absorbent resin or particulate water-absorbing agent is preferably 1 to 20% by mass (furthermore, more than 1%, particularly 1.5% or more), more preferably 2 to 15% by mass, and still more preferably. Is 3 to 12% by mass, particularly preferably 4 to 12% by mass, and 5 to 12% by mass. The particulate water-absorbing agent obtained in the re-wetting step is resistant to mechanical damage, has good initial liquid familiarity, and has a low chargeability, so that it is excellent in handleability.

(1-3-3) Fine powder removal step In this step, when a classification step (second classification step) is further included after the surface crosslinking step, the classification step can pass through a classification net having an aperture of 150 μm. This indicates a step of removing at least a part of the water absorbent resin. The mesh size of the classification network used in this step is preferably 300 μm or less, more preferably 260 μm or less, further preferably 210 μm or less, and most preferably 180 μm or less. The proportion of the water-absorbent resin that can pass through the classifier with a mesh size of 150 μm to be removed is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, based on the water-absorbent resin after surface crosslinking. , Most preferably 1.0% by mass or more. The removed “water-absorbent resin containing particles that can pass through a 150 μm mesh” is preferably water (and / or more preferably after being mixed with the fine particles removed before the surface crosslinking step). Aqueous solution) and granulated and recycled to the drying step.

(1-3-4) Fine powder recycling step The fine powder removed in the classification step before the surface crosslinking (first classification step) and / or the classification step after the surface crosslinking (second classification step) is an object of the present invention. Is preferably recycled in order to solve the above problem more suitably. The fine powder is recycled before the drying step, and more preferably, at one or more points in the polymerization step to the drying step. The fine powder to be recycled preferably contains 70 to 100% by mass of particles having a particle size specified by JIS standard sieves of less than 200 μm, more preferably less than 150 μm. It is further preferable that the recycled fine powder contains the particles having a particle size of less than 200 μm, more preferably less than 150 μm, in an amount of 80 to 100% by mass. The problem of the present invention is more preferably solved by recycling such fine powder, and the water absorption rate (for example, Vortex described later) is also improved as compared with the case where fine powder is removed and not recycled. For recycling of the fine powder, the dried fine powder may be recycled as it is to a monomer mixture before and / or during polymerization or a mixture of hydrogel / monomer during polymerization, and a gel crushing step after polymerization and / or drying. It may be recycled to the process. Alternatively, the dried fine powder may be granulated and / or gelled with water and recycled. In such a case, a binder and / or a mixing aid (agglomeration inhibitor) may be added during granulation. Examples of the binder include water, a hydrophilic polymer or a hydrophobic polymer, an organic crosslinking agent (which can also be used for surface crosslinking) or an inorganic crosslinking agent, and a polyhydric alcohol. Among them, water is preferable, and further, other binders can be used in combination. The binder may be a liquid (solution) or a powder binder such as a hydrophilic polymer or a hydrophobic polymer.
Water in the binder used for recycling the fine powder is preferably 0 to 300% by mass (0 is unused), more preferably 1 to 200% by mass, and still more preferably 10 to 150% by mass based on the dry fine powder. is there. Water may contain other additives and binders as necessary. The water is not limited to liquid water, but may be gaseous water (steam). The water, its solution, and its dispersion may be heated or cooled as necessary from the viewpoint of granulation and mixing properties, and from the melting point to the boiling point, more preferably from 0 to 100 ° C, further preferably from 20 to 100 ° C. Water at 60 ° C to 100 ° C, its solution, and its dispersion.

In one embodiment of the present invention, the amount of the fine powder to be recycled is 0 to 40% by mass (0 is unused), more preferably 5 to 35% by mass, and still more preferably the amount of the water-absorbing resin in the obtained particulate water-absorbing agent. Is from 10 to 30% by mass. In such a range, a more excellent particulate water-absorbing agent can be obtained. Here, the amount of the fine powder to be recycled is, for example, 5 to 35% by mass (furthermore, 10 to 30% by mass), and 65 to 95% by mass (70 to 90% by mass) of the remaining water absorbent resin in the obtained particulate water absorbing agent. ) Can be non-recyclable particles. When fine powder granulation is performed in the fine powder recycling step, the particulate water-absorbing agent is composed of granulated particles (recycled fine particles; for example, granules of fine powder having a size of 150 μm or less and 850 to 150 μm) and primary particles (non-recycled particles). For example, particles having a particle size of 850 to 150 μm), and such a particulate water-absorbing agent more suitably solves the problem of the present invention.

[2] Particulate water-absorbing agent The particulate water-absorbing agent according to one embodiment of the present invention is a surface-crosslinked particulate water-absorbing agent containing a water-absorbing resin and silicon dioxide particles, and has a moisture-absorbing fluidity of 50. % By mass, more preferably 30% by mass or less. The silicon dioxide particles are cationic.

The “particulate water-absorbing agent”, “water-absorbing resin”, “silicon dioxide particles”, “surface cross-linking”, “fine powder recycling”, and “moisture content” are as described in the above [1]. The method for producing the particulate water-absorbing agent according to one embodiment of the present invention is not limited to this, but it can be produced by the method described in the above [1].

The term "moisture-absorbing fluidity" refers to an index for evaluating blocking, caking, and fluidity as a powder when the particulate water-absorbing agent is left for 1 hour in an atmosphere at a temperature of 25 ° C and a relative humidity of 90% RH. It is described as “moisture-absorbing fluidity (BR: Blocking Ratio)” or “moisture-absorbing blocking ratio”. The details of the method for calculating the hygroscopic fluidity will be described in Examples, but the outline is as follows.

After classifying the particulate water-absorbing agent using a sieve, the mass (W1) (unit; g) of the particulate water-absorbing agent remaining on the sieve and the mass (W2) (unit) of the particulate water-absorbing agent passed through the sieve. g) is measured and calculated according to the following equation.
Moisture absorption fluidity (BR) = {W1 / (W1 + W2)} × 100
The moisture-absorbing fluidity of the particulate water-absorbing agent according to one embodiment of the present invention may be 50% by mass or less, more preferably 40% by mass, and particularly preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably. It is at most 10% by mass, most preferably 0. The lower limit of the hygroscopic fluidity is 0. When the moisture absorption fluidity (BR) is 30% by mass or less, it is possible to prevent the water-absorbent resin from blocking, and thus it can be suitably used for manufacturing sanitary articles such as diapers.

In addition, the absorption capacity under pressure (AAP: Absorption Against Pressure) 0.7 psi (AAP 0.7) of the particulate water-absorbing agent according to one embodiment of the present invention is preferably 20 g / g or more, more preferably 21 g / g or more. , More preferably at least 22 g / g, most preferably at least 23 g / g. The upper limit is not particularly limited, but is preferably 30 g / g or less.

When the absorption capacity under pressure of the particulate water-absorbing agent is within the above range, the amount of liquid returned when pressure is applied to the absorbent containing the particulate water-absorbing agent (usually referred to as “Re-Wet”). Since it does not increase too much, it can be suitably used as an absorbent for sanitary articles such as disposable diapers.

The liquid permeability under pressure (PDAUP: Permeability Dependent Absorption Under Pressure) of the particulate water-absorbing agent according to one embodiment of the present invention is preferably 6 g / g or more, more preferably 7 g / g or more, and still more preferably 8 g / g. Above, particularly preferably 9 g / g or more, most preferably 10 g / g or more. The upper limit is preferably as high as possible, but is usually about 25 g / g, and more preferably about 20 g / g.

"Liquidity under pressure" is the absorption capacity under pressure under the condition where the water permeability of the swollen gel is a controlling factor, and is measured by the method described in Examples. Liquid permeability under pressure is an index for evaluating the liquid intake speed and return amount of the absorbent when the particulate water-absorbing agent is used as an absorbent for a sanitary article. When the liquid permeability under pressure of the particulate water-absorbing agent is within the above range, the liquid intake speed of the absorber using the particulate water-absorbing agent is high, and the return amount is reduced.

The CRC (centrifuge retention capacity) of the particulate water-absorbing agent according to one embodiment of the present invention may be 5 g / g or more, but is usually 20 to 60 g / g, more preferably 25 to 45 g / g, and even more. The order is 30 g / g to 50 g / g, more preferably 31 g / g to 45 g / g, still more preferably 32 g / g to 40 g / g, particularly preferably 33 g / g to 39 g / g, and most preferably 34 g / g. g to 38 g / g.

場合 When the CRC is less than 5 g / g, the amount of absorption is small and it is not suitable as an absorbent for sanitary articles such as disposable diapers. On the other hand, if the CRC exceeds 70 g / g, the rate of absorbing bodily fluids such as urine and blood decreases, so that it is not suitable for use in high absorption rate type disposable diapers. The CRC can be controlled by an internal crosslinking agent, a surface crosslinking agent, and the like.

The water absorption rate (Vortex (30 ° C.)) of the particulate water-absorbing agent according to one embodiment of the present invention is 60 seconds or less, further 55 seconds or less, 50 seconds or less, 45 seconds or less, 40 seconds or less, 35 seconds or less, 30 seconds or less. It is preferable in the order of seconds or less. The lower limit of the water absorption rate (Vortex) may be 1 second, more preferably 5 seconds, and especially 10 seconds. If the water absorption rate is in such a range, a more excellent sanitary material can be provided. Generally, a particulate water absorbing agent having a high water absorption rate has a high moisture absorption rate, and thus tends to block under high humidity. However, the particulate water absorbing agent according to one embodiment of the present invention does not have such a problem.

The content of the recycled fine powder of the particulate water-absorbing agent according to one embodiment of the present invention (particularly the finely-granulated product) is 0 to 40% by mass of the amount of the water-absorbing resin in the particulate water-absorbing agent (0 is unused). , More preferably 5 to 35% by mass, and still more preferably 10 to 30% by mass. With such a content, a more excellent particulate water absorbing agent can be provided. Specifically, the fine powder can be reduced by such a content, and further, the chargeability is reduced, and a more excellent particulate water absorbing agent can be provided. The low chargeability and high moisture absorption fluidity (BR) of the particulate water-absorbing agent improve the handleability of the particulate water-absorbing agent in actual use, and for example, the particulate water-absorbing agent in the manufacture of sanitary articles such as disposable diapers. Handling, especially in the production of absorbent layers for sanitary articles such as disposable diapers by mixing a particulate water-absorbing agent and pulp, in any use environment (for example, changes in temperature and humidity, changes in the amount of water conveyed due to changes in the transport amount) ), It is possible to provide an excellent particulate water-absorbing agent that can maintain uniform mixing properties and uniform transportability of the particulate water-absorbing agent in actual use. In addition to high AAP and liquid permeability under pressure, due to uniform mixing and uniform transport in actual use, the particulate water absorbing agent is used as the final consumable material (typically, the absorption of a mixture of the particulate water absorbing agent and pulp. Since it is contained uniformly and stably in a sanitary article such as a disposable diaper including a layer, it exhibits superior performance as a final water-absorbing agent as compared with a particulate water-absorbing agent having the same AAP or the like.

[3] Use of particulate water-absorbing agent The use of the particulate water-absorbing agent according to one embodiment of the present invention is not particularly limited, but is preferably used for absorbent articles of sanitary articles such as disposable diapers, sanitary napkins, incontinence pads, and the like. No. In particular, it can be used as an absorbent for sanitary articles containing a high concentration of particulate water-absorbing agent, which has problems such as a low liquid intake speed and a large amount of return. The particulate water-absorbing agent having a high moisture absorption fluidity (BR), a high AAP, and a high liquid permeability under pressure (PDAUP), and more preferably a predetermined water content and / or a predetermined fine powder recovery amount is preferable. As described above, a superior performance can be exhibited in the final consumption material as compared with the water-absorbent resin having the same AAP or the like.

吸収 In addition, an absorbent material such as pulp fiber can be used as the absorbent in addition to the particulate water absorbing agent. In this case, the content (core concentration) of the particulate water-absorbing agent in the absorber is preferably 30 to 100% by mass, more preferably 40 to 100% by mass, still more preferably 50 to 100% by mass, and still more preferably. Is from 60 to 100% by weight, particularly preferably from 70 to 100% by weight, most preferably from 75 to 95% by weight.

The particulate water-absorbing agent according to one embodiment of the present invention exhibits high fluidity at high moisture absorption (that is, low BR: {Blocking} Ratio) even under high temperature and high humidity. Regardless of the change in humidity, the final consumption material (for example, a disposable diaper) can be stably produced, so that air conditioning in an expensive use environment (for example, in a factory) is unnecessary.

Hereinafter, the present invention will be described based on examples, but the present invention is not construed as being limited to the examples. Unless otherwise specified, various physical properties described in the present specification and Examples were determined at room temperature (20 ° C. to 25 ° C.) and a humidity of 50% RH according to the EDANA method and the following measurement methods. Furthermore, the electric devices presented in the examples and comparative examples used a power supply of 200 V or 100 V, 60 Hz. In addition, "liter" is described as "L" for convenience.

[Measurement method of physical properties]
(1) CRC (centrifuge holding capacity)
CRC was measured according to the EDANA method (ERT441.2-02).

(2) Ext (water soluble)
Ext was measured according to the EDANA method (ERT 470.2-02).

(3) AAP 0.7 (absorption capacity under pressure)
The measurement of AAP (water absorption capacity under pressure) is performed according to EDANA NWSP 242.0. Performed according to R2 (15). Specifically, 0.900 g of the particulate water-absorbing agent was weighed, and a 0.9% by mass aqueous sodium chloride solution was swelled under a load of 4.83 kPa (0.7 psi, 49 (g / cm ² )) for 1 hour. The water absorption capacity (AAP 0.7 (g / g)) after this was measured.

(4) BR (moisture absorption fluidity)
After uniformly dispersing 2 g of the particulate water-absorbing agent or the water-absorbing resin in an aluminum cup having a diameter of 52 mm, a constant-temperature and constant-humidity device (PLATINOUSLUCIFERPL-2G; manufactured by TABIESPEC) at a temperature of 25 ° C and a relative humidity of 90 ± 5% RH ) For 1 hour. After one hour, the particulate water-absorbing agent or water-absorbing resin contained in the aluminum cup is gently transferred onto a JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80 mm) having a mesh size of 2000 μm (JIS 8.6 mesh). Using a low tap type sieve shaker (ES-65 type sieve shaker manufactured by Iida Seisakusho Co., Ltd .; rotational speed 230 rpm, impact number 130 rpm) at room temperature (20 ° C. to 25 ° C.) and relative humidity 50% RH. Classification was performed for 5 seconds. The mass (W1 [g]) of the particulate water-absorbing agent or the water-absorbing resin remaining on the JIS standard sieve and the mass (W2 [g]) of the particulate water-absorbing agent or the water-absorbing resin passed through the JIS standard sieve were measured. Then, BR was calculated according to the following equation.
BR (mass%) = {W1 / (W1 + W2)} × 100
In addition, the lower the value of BR, the better the moisture absorption fluidity.

(5) PDAUP (liquid permeability under pressure)
The measurement of PDAUP (liquid permeability under pressure) is performed according to EDANA NWSP 243.0. Performed according to R2 (15). Specifically, 5.00 g of the particulate water-absorbing agent was weighed, and a 0.9% by mass aqueous sodium chloride solution was swelled under a load of 4.83 kPa (0.7 psi, 49 (g / cm ² )) for 1 hour. After that, the water absorption capacity (PDAUP (g / g)) was measured.

(6) Chargeability 10 g of the particulate water-absorbing agent is put in a plastic bag with a chuck (Unipack E-4: manufactured by Japan: 140 mm × 100 mm × 0.04 mm), and after closing the chuck, the bag is strongly pushed up and down for 1 minute. Shook. The state of adhesion of the particulate water-absorbing agent to the inside of the plastic bag was visually observed and evaluated according to the following criteria.

(Evaluation criteria)
：: The particulate water absorbing agent hardly adheres to the inside of the plastic bag.
Δ: A very small portion of the particulate water-absorbing agent adheres to the inside of the plastic bag.
×: Most of the particulate water-absorbing agent adheres to the inside of the plastic bag.

(7) Water absorption speed (Vortex)
50 ml of physiological saline adjusted to a liquid temperature of 30 ° C. was measured in a 100 ml beaker, and 2.0 g of a particulate water-absorbing agent was added while stirring at 600 rpm with a cylindrical stirrer having a length of 40 mm and a thickness of 8 mm, The absorption rate (seconds) was measured. The end point is based on the standard described in JIS K 7224-1996 “Explanation of test method for water absorption rate of superabsorbent resin”, and the particulate water-absorbing agent absorbs physiological saline and covers the stirrer chip with the test solution. The time until was measured as the absorption rate (seconds).
(8) Water content 1.000 g of the particulate water-absorbing agent is evenly spread on an aluminum plate having a diameter of 60 mm, and the inside is heated to 180 ° C. in a windless drier (EYELA natural open NDO-450, manufactured by Tokyo Rika Kikai Co., Ltd.). The drying loss (mass%) after heating and drying for 3 hours was defined as the water content.

(9) Impact resistance test An impact resistance test of the particulate water absorbing agent was performed by shaking 10 g of the particulate water absorbing agent with a paint shaker for 10 minutes according to EP0812873. The decrease in AAP (g / g) and the increase in fines (increase in 150 μm pass-through) before and after impact were measured.

(10) Absorbent preparation test (under dehumidification and high humidity conditions)
In a room at a constant temperature and humidity (80% Rh at a temperature of 30 ° C. and 40% Rh at a temperature of 25 ° C.), an absorber was produced by the following method. That is, first, 50 parts by mass of the particulate absorbent and 50 parts by mass of the ground wood pulp were humidified for 10 seconds by an ultrasonic humidifier using a mixer, and then the particulate absorbent and the ground wood pulp were mixed. Next, the obtained mixture was air-formed on a wire screen formed into a 400 mesh (mesh size of 38 μm) using a batch-type air-forming device to form a web having a size of 120 mm × 400 mm. . Further, the web was pressed at a pressure of 2 kg / cm ² (196.14 kPa) for 1 minute to obtain an absorbent having a basis weight of about 0.047 g / cm ² .

Here, 80% Rh at a temperature of 30 ° C. is set to a high humidity condition (model in a rainy day in a factory without air conditioning), and 40% Rh at a temperature of 25 ° C. is set to a dehumidifying condition (model of a factory with air conditioning).
(11) Return amount of absorber (Re-Wet)
An aqueous solution having the composition of 1.9% by weight of urea, 0.8% by weight of NaCl, 0.1% by weight of CaCl _{2 and} 0.1% by weight of MgSO ₄ (the remainder being water), that is, artificial urine (25 ° C.) Prepared.

Then, a load of 50 g / cm ² (4.9 kPa) is uniformly applied to the entirety of the absorber obtained in the above (10), and a cylinder having a diameter of 30 mm and a height of 120 mm is applied to the center of the absorber. And the cylinder was set upright. Then, 50 g of artificial urine at 25 ° C. was poured into the cylinder quickly (at once), and then the same artificial urine was injected twice more at 50-minute intervals. Thirty minutes after the third artificial urine injection, the load was removed from the absorber, and a paper towel (made by Oji Paper Co., Ltd., kitchen towel extra dry cut to 120 mm x 450 mm and stacked 30 sheets) was placed on the absorber. Then, a load of 50 g / cm ² (4.9 kPa) was applied thereto and left for 1 minute. The amount of liquid absorbed by the paper towel was determined by measuring the change in the mass of the paper towel, and this was defined as the return amount (g).

(12) Uniformity of the absorber After measuring the return amount (Re-Wet) of the absorber in the above (11), the deviation of the swelling gel of the water-absorbent resin in the absorber was visually observed, and the following criteria were used. Was used to evaluate the uniformity of the absorber.

(Evaluation criteria)
：: Swelled gel particles of the water-absorbent resin are uniformly present.
Δ: Segregation of swollen gel particles and mottled portions are observed in a part.
×: Segregation or spots of swollen gel particles are observed in the whole or in many areas.

(13) Gel deterioration fluidity test 95 g of urea, 40 g of sodium chloride, 5 g of magnesium sulfate, 5 g of calcium chloride, and 4855 g of ion-exchanged water were mixed, and the content of L-ascorbic acid was adjusted to 0.005% by mass. To make artificial urine. 2 g of the particulate water-absorbing agent was placed in a 120-ml polypropylene container (with an inner diameter of 54 mm) with a lid, and the artificial urine was added to absorb the particulate water-absorbing agent. As a result, a hydrogel was obtained in which the particulate water-absorbing agent swelled 25-fold. This hydrogel was left in an atmosphere at a temperature of 37 ° C. and a relative humidity of 90%. After 16 hours and 20 hours, the container was tilted at 90 °, and the gel was degraded based on the distance that the hydrogel under the container moved for 1 minute.

(Evaluation methods)
：: The gel does not flow even when the container is turned sideways.
Δ: Deformation occurs when the container is turned sideways.
×: The container is deformed when it is turned sideways, and reaches the end of the container.

[Production Example 1]
In a polypropylene container having an inner diameter of 80 mm and a capacity of 1 liter covered with styrene foam as a heat insulating material, 291 g of acrylic acid and 0.43 g of polyethylene glycol diacrylate (molecular weight 523) as an internal crosslinking agent (unsaturated monomer containing carboxyl group) 0.02 mol% based on the body), 1.80 g of a 1.0 mass% aqueous solution of diethylenetriaminepentaacetic acid / pentasodium, and 3.60 g of a 1.0 mass% acrylic acid solution of IRGACURE (registered trademark) 184 were charged and mixed. Thus, a solution (A) was prepared. A solution (B) was prepared by separately mixing 247 g of a 48.5% by mass aqueous sodium hydroxide solution and 255 g of ion-exchanged water adjusted to 50 ° C. 800 r.m. using a magnetic stirrer having a length of 5 cm. p. m. While stirring the solution (A) at, the solution (B) was quickly added to the solution (A) and mixed to obtain a monomer aqueous solution (C). The temperature of the aqueous monomer solution (C) rose to about 100 ° C. due to the heat of neutralization and the heat of dissolution. The neutralization ratio of acrylic acid was 73.5 mol%.

Next, 1.8 g of a 3% by mass aqueous solution of sodium persulfate was added to the aqueous monomer solution (C), and the mixture was stirred for about 1 second. The mixture was poured into a vat-type container in an open system. The mixture was poured into a stainless steel vat-shaped container and irradiated with ultraviolet rays.

重合 The polymerization started shortly after the mixture was poured into the vat-type container, and the polymerization mixture reached a peak temperature within about 1 minute. After 3 minutes, irradiation with ultraviolet rays was stopped, and the hydrogel, which was a polymer, was taken out. Note that these series of operations were performed in a system opened to the atmosphere.

The obtained hydrogel was pulverized with a meat chopper (MEAT-CHOPPER TYPE: 12VR-400KSOX Iizuka Kogyo Co., Ltd., die hole diameter: 6.4 mm, number of holes: 38, die thickness 8 mm) to obtain finely divided particles. A hydrogel was obtained.

(5) The finely divided particulate hydrogel was spread on a 50-mesh (mesh size: 300 μm) wire mesh and dried at 180 ° C. with hot air. The obtained dried product is pulverized by a roll mill, and further classified by a JIS standard sieve having an opening of 850 μm and an opening of 150 μm to obtain irregularly-crushed water-absorbing resin particles (solid content: 96% by mass). (A) was obtained. The CRC (absorbency against pressure) of the water-absorbent resin particles (a) was 47.3 g / g.

[Production Example 2] Granulation of fine powder When obtaining water-absorbent resin particles (a) of 850 to 150 μm in Production Example 1, 100 parts by mass of water-absorbent resin fine powder removed by a JIS standard sieve of a 150 μm mesh. Then, 100 parts by mass of hot water at 60 ° C. were mixed in a Loedige mixer for about 1 minute to obtain a hydrogel fine powder having a particle size of about 1 to 2 mm. The obtained hydrogel fine powder was dried for about 30 minutes with a 170 ° C. hot drier. The obtained dried granules were pulverized with a roll mill and classified by sieving at 850 to 150 μm to obtain 850 to 150 μm water absorbent resin fine powder granules (a1).

[Production Example 3]
By mixing 80 parts by mass of the water-absorbent resin particles (a) and 20 parts by mass of the water-absorbent resin fine powder granules (a1), finely-recycled water-absorbent resin particles (b) (850 to 150 μm) were obtained.

[Example 1]
3.3 g of cationic colloidal silica (trade name: Klebosol 30CAL25 30% aqueous solution, manufactured by AZ Electronic Material / silicon dioxide fine particles containing aluminum cation), 0.5 g of 1,3-propanediol, 1 g of methanol, and 3 g of pure water Was uniformly mixed in a polypropylene container to prepare a surface treatment liquid (1).

(4) The surface treatment liquid (1) was uniformly mixed with 100 g of the irregularly shaped water-absorbent resin particles (a) obtained in Production Example 1. Then, the obtained mixture was heat-treated at 200 ° C. for 40 minutes. The heated product was cooled, and classified with a JIS standard sieve having openings of 850 μm and 150 μm to obtain surface-crosslinked water-absorbent resin particles (1). The water-absorbent resin particles (1) containing 0.99% by mass of the cationic silicon dioxide fine particles (based on the water-absorbent resin, 0.99 rounded off and equivalent to 1% by mass) were mixed with the particulate water-absorbing agent (1). did.

[Example 2]
3.3 g of cationic colloidal silica (trade name: Klebosol 30CAL25 30% aqueous solution, manufactured by AZ Electronic Material Co., Ltd./fine particles of silicon dioxide containing aluminum cation), 0.03 g of ethylene glycol diglycidyl ether, 0.3 g of ethylene carbonate, and propylene A surface treatment liquid (2) was prepared by uniformly mixing 0.5 g of glycol and 2 g of pure water in a polypropylene container.

(4) The surface treatment liquid (2) was uniformly mixed with 100 g of the irregularly shaped water-absorbent resin particles (a) obtained in Production Example 1. Then, the obtained mixture was heat-treated at 190 ° C. for 40 minutes. The heated product was cooled and classified with a JIS standard sieve having openings of 850 μm and 150 μm to obtain surface-crosslinked water-absorbent resin particles (2). The water-absorbing resin particles (2) containing the cationic silicon dioxide fine particles were used as a particulate water-absorbing agent (2).

[Comparative Example 1]
According to Comparative Example 10 of Patent Document 6 (Japanese Patent Application Laid-Open No. 2015-16450), 3.3 g of cationic colloidal silica (trade name: Klebosol 30CAL25 30% aqueous solution, manufactured by AZ Electronic Material Co., Ltd./aluminum cation-containing silicon dioxide fine particles) A surface treatment liquid (3) was prepared by uniformly mixing 0.015 g of ethylene glycol diglycidyl ether, 1 g of propylene glycol, and 0.7 g of pure water in a polypropylene container.

(4) The surface treatment liquid (3) was uniformly mixed with 100 g of the irregularly shaped water-absorbent resin particles (a) obtained in Production Example 1. Thereafter, according to Comparative Example 10 of Patent Document 6, the obtained mixture was subjected to a heat treatment at 100 ° C. for 45 minutes. The heated product was cooled and classified with a JIS standard sieve having openings of 850 μm and 150 μm to obtain surface-crosslinked comparative water-absorbent resin particles (1). The comparative water-absorbing resin particles (1) containing the cationic silicon dioxide fine particles were used as comparative particulate water-absorbing agents (1).

[Comparative Example 2]
In Examples 1 and 2 and Comparative Example 1, the surface treatment liquid containing cationic colloidal silica and an organic surface cross-linking agent (water-soluble organic substance) was mixed with the water-absorbing resin. The cationic colloidal silica was added without being mixed with the surface crosslinking agent (water-soluble organic substance).

That is, 100 g of the amorphous water-absorbent resin particles (a) obtained in Production Example 1 was added to a cationic colloidal silica (trade name: Klebosol 30 CAL 25 30% aqueous solution, AZ Electronic Material Co., Ltd./aluminum cation-containing silicon dioxide fine particles) ) 3.3 g were added and mixed. Then, a surface cross-linking agent solution (0.5 g of 1,3-propanediol, 1 g of methanol and 3 g of pure water) was added to the obtained mixture (a mixture of the water-absorbent resin and the cationic colloidal silica) ( 1) was mixed uniformly.

Thereafter, the obtained mixture (a mixture of the water-absorbent resin, the surface crosslinking agent solution, and the cationic colloidal silica) was subjected to a heat treatment at 200 ° C for 40 minutes in the same manner as in Example 1. The heated product was cooled, and classified with a JIS standard sieve having openings of 850 μm and 150 μm to obtain surface-crosslinked comparative water-absorbent resin particles (2). The comparative water-absorbing resin particles (2) containing the cationic silicon dioxide fine particles were used as comparative particulate water-absorbing agents (2).

[Comparative Example 3]
To 100 g of the irregularly shaped water-absorbent resin particles (a) obtained in Production Example 1, 0.5 g of 1,3-propanediol as in Comparative Example 2, 1 g of methanol, and 3 g of pure water were mixed. The surface crosslinking agent solution (1) was uniformly mixed. Then, cationic colloidal silica (trade name: 30% aqueous solution of Klebosol 30CAL25, manufactured by AZ Electronic Material / aluminum cation-containing silicon dioxide fine particles) is added to the obtained mixture (mixture of the water-absorbing resin and the aqueous solution of the surface crosslinking agent). 3 g were added and mixed.

Thereafter, the obtained mixture (a mixture of the water-absorbent resin, the surface crosslinking agent solution, and the cationic colloidal silica) was subjected to a heat treatment at 200 ° C for 40 minutes in the same manner as in Example 1. The heated product was cooled and classified with JIS standard sieves having openings of 850 μm and 150 μm to obtain surface-crosslinked comparative water-absorbent resin particles (3). The comparative water-absorbing resin particles (3) containing the cationic silicon dioxide fine particles were used as comparative particulate water-absorbing agents (3).

[Comparative Example 4]
In Example 1, a surface crosslinking agent solution (2) (1,3-propanediol) having the same composition as the surface treatment liquid (1) except that cationic colloidal silica was not added instead of the surface treatment liquid (1) Surface cross-linking was carried out with the surface cross-linking agent solution (2) in the same manner as in Example 1 except that 0.5 g, 1 g of methanol, and 3 g of pure water were mixed. Comparative water-absorbing resin particles (4) were obtained. This comparative water-absorbing resin particle (4) was used as a comparative particulate water-absorbing agent (4).

[Comparative Example 5]
In Example 1, 3.3 g of anionic colloidal silica (trade name: Klebosol 30B25, 30% aqueous solution, manufactured by AZ Electronic Material) was added instead of the cationic colloidal silica in place of the surface treatment liquid (1). Except for this, a surface-crosslinked comparative water-absorbent resin particle (5) was obtained in the same manner as in Example 1 except that a surface treatment liquid (4) having the same composition as the surface treatment liquid (1) was added. The comparative water-absorbing resin particles (5) containing the anionic silicon dioxide fine particles were used as comparative particulate water-absorbing agents (5).

[Comparative Example 6]
In Example 1, instead of the surface treatment liquid (1), 1 g of powdered silica (trade name: Aerosil 200CF, manufactured by Nippon Aerosil Co., Ltd.) was used instead of the cationic colloidal silica, and the surface treatment liquid (5) was used. Was prepared in the same manner as in Example 1, except that the powdered silica was not uniformly mixed with the surface treatment liquid (5), and the comparative water-absorbing resin particles (corresponding to the comparative particulate water-absorbing agent (6)) Was not obtained.

[Comparative Example 7]
In Comparative Example 7, cationic colloidal silica was mixed with propylene glycol after surface cross-linking according to Patent Document 6 (Japanese Patent Application Laid-Open No. 2015-16450) which discloses that colloidal silica and an organic solvent were added after surface cross-linking. .

That is, based on the comparative particulate particulate water-absorbing agent (4) obtained by surface crosslinking (without addition of colloidal silica) of Comparative Example 4, 100 parts by mass of cationic colloidal silica (trade name: Klebosol) according to Patent Document 3.3 parts by mass of 30 CAL 25% 30% aqueous solution, manufactured by AZ Electronic Material / silicon dioxide fine particles containing aluminum cations, 1 g of propylene glycol, and 0.7 g of pure water were uniformly mixed and prepared in a polypropylene container. The liquid was added to obtain comparative water absorbent resin particles (7). The comparative water-absorbing resin particles (7) containing the cationic silicon dioxide fine particles were used as comparative particulate water-absorbing agents (7).

[Comparative Example 8]
1 mass of powdered silica (trade name: Aerosil 200CF, manufactured by Nippon Aerosil Co., Ltd.) with respect to 100 mass parts of the comparative particulate water-absorbing agent (4) obtained by surface crosslinking (without addition of colloidal silica) of Comparative Example 4. The resulting mixture was added to obtain comparative water-absorbent resin particles (8). The comparative water-absorbing resin particles (8) containing the silicon dioxide fine particles were used as comparative particulate water-absorbing agents (8).

[Comparative Example 9]
Comparative water-absorbing resin particles (9) were obtained in the same manner as in Example 1 except that the surface crosslinking temperature was changed from 200 ° C. to 140 ° C. The comparative water-absorbing resin particles (9) containing the cationic silicon dioxide fine particles were used as comparative particulate water-absorbing agents (9).

[Comparative Example 10]
Comparative water-absorbing resin particles (10) were obtained in the same manner as in Example 2, except that the surface crosslinking temperature was changed from 200 ° C to 140 ° C. The comparative water-absorbing resin particles (10) containing the cationic silicon dioxide fine particles were used as comparative particulate water-absorbing agents (10).

[Example 3]
In Example 1, 3.3 g of cationic colloidal silica (trade name: Klebosol 30CAL25 30% aqueous solution, manufactured by AZ Electronic Material / aluminum cation-containing silicon dioxide fine particles) (corresponding to 1% by mass with respect to water-absorbent resin / 0.99%) (Rounded off) was changed to 5 g of cationic colloidal silica (trade name: Snowtex ST-K: particle diameter 12 μm, 20% aqueous solution), and cationic colloidal silica / 1,3-propanediol was used in the same manner as in Example 1. /Methanol/water=1/0.5/1/5.3 (mass ratio; water-absorbent resin 100) to prepare a surface treatment liquid (6). A particulate water-absorbing agent (3) was obtained by performing the same operation as in Example 1 except that the surface treatment liquid (6) was used instead of the surface treatment liquid (1).

[Example 4]
In Example 1 (1% by mass of cationic colloidal silica (based on the water-absorbing resin)), the same cationic colloidal silica (trade name: Klebosol 30CAL25) was used, and the amount of the cationic colloidal silica used was 0.6 g (solid content). To 0.18% by mass (based on the water-absorbing resin), and cationic colloidal silica / 1,3-propanediol / methanol / water = 0.18 / 0.5 / 1 / 5.3 (mass ratio) A surface treatment liquid (7) comprising the water-absorbent resin 100) was prepared. A particulate water absorbing agent (4) was obtained by performing the same operation as in Example 1 except that the surface treatment liquid (7) was used instead of the surface treatment liquid (1).

[Example 5]
In Example 1 (1% by mass of cationic colloidal silica (based on the water-absorbing resin)), the same cationic colloidal silica (trade name: Klebosol 30CAL25) was used, and the amount of cationic colloidal silica used was changed to 2.5 in solid content. % By mass (to water-absorbent resin), cationic colloidal silica / 1,3-propanediol / methanol / water = 2.5 / 0.5 / 1 / 5.3 (mass ratio; water-absorbent resin) A surface treatment liquid (8) consisting of 100) was prepared. A particulate water absorbing agent (5) was obtained by performing the same operation as in Example 1 except that the surface treatment liquid (8) was used instead of the surface treatment liquid (1).

[Example 6]
In Example 1 (0.5% by mass of the surface crosslinking agent 1,3-propanediol (based on the water-absorbing resin)), the amount of the surface crosslinking agent 1,3-propanediol was changed to 1.1% by mass. A surface treatment liquid (9) composed of cationic colloidal silica / 1,3-propanediol / methanol / water = 1 / 1.1 / 0.5 / 5.3 (mass ratio; water absorbent resin 100) was prepared. . In this embodiment, the amount of the cationic colloidal silica used is 91% by mass based on the amount of the surface crosslinking agent used. A particulate water absorbing agent (6) was obtained by performing the same operation as in Example 1 except that the surface treatment liquid (9) was used instead of the surface treatment liquid (1).

[Example 7]
In Example 1 (0.5% by mass of the surface crosslinking agent 1,3-propanediol (based on the water-absorbing resin)), the amount of the surface crosslinking agent 1,3-propanediol used was changed to 0.3% by mass. A surface treatment liquid (10) composed of cationic colloidal silica / 1,3-propanediol / methanol / water = 1 / 0.3 / 0.5 / 5.3 (mass ratio; water-absorbent resin 100) was prepared. . In this example, the amount of the cationic colloidal silica used was 333% by mass based on the amount of the surface crosslinking agent used. A particulate water-absorbing agent (7) was obtained by performing the same operation as in Example 1 except that the surface treatment liquid (10) was used instead of the surface treatment liquid (1).

Example 8
A particulate water-absorbing agent (8) was obtained by performing the same operation as in Example 1 except that the surface crosslinking temperature was changed to 225 ° C. in Example 1 (surface crosslinking temperature: 200 ° C.).

[Example 9]
A particulate water-absorbing agent (9) was obtained in the same manner as in Example 1 except that the surface crosslinking temperature was changed to 175 ° C in Example 1 (surface crosslinking temperature: 200 ° C).

[Example 10]
5 parts by mass of water was sprayed on 100 parts by mass of the particulate water-absorbing agent (1) obtained in Example 1, and mixed for about 1 minute in a Loedige mixer (a type manufactured by Loedige; T5R). The obtained particulate water-absorbing agent was passed through an 850 μm sieve to obtain a re-wetted particulate water-absorbing agent (10) (water content: about 4%).

[Example 11]
By performing the same operation as in Example 10 except that the particulate water absorbing agent (2) obtained in Example 2 was used instead of the particulate water absorbing agent (1) obtained in Example 1, A wet particulate water-absorbing agent (11) (moisture content about 4%) was obtained.

[Example 12]
By performing the same operation as in Example 1 except that the water-absorbing resin particles (a) were changed to the water-absorbing resin particles (b) in Example 1, the finely-granulated material (about (20% by mass) was obtained.

[Example 13] Recycling of fine powder The same operation as in Example 2 was carried out except that the water-absorbing resin particles (a) were changed to the water-absorbing resin particles (b) in Example 2, thereby obtaining a fine powder in the fine powder recycling step. A particulate water-absorbing agent (13) containing the resulting finely-pulverized granules (about 20% by mass) was obtained.

[Example 14]
To 100 parts by mass of the particulate water-absorbing agent (12) obtained in Example 12, 7 parts by mass of water was sprayed and mixed in the Loedige mixer of Example 7 for about 1 minute. The obtained particulate water-absorbing agent was passed through an 850 μm sieve to obtain a re-wetted particulate water-absorbing agent (14) (water content: about 7%).

[Example 15]
To 100 parts by mass of the particulate water-absorbing agent (13) obtained in Example 13, 7 parts by mass of water was sprayed and mixed in the Loedige mixer of Example 7 for about 1 minute. The obtained particulate water-absorbing agent was passed through an 850 μm sieve to obtain a re-wetted particulate water-absorbing agent (15) (water content: about 7%).

[Example 16]
In Example 1 (1% by mass of cationic colloidal silica (based on the water-absorbing resin)), the same cationic colloidal silica (trade name: Klebosol 30CAL25) was used, and the amount of the cationic colloidal silica used was 2.0 g (solid content). To 0.6 mass% (based on water-absorbing resin), and cationic colloidal silica / propanediol / methanol / water = 0.6 / 0.5 / 1 / 5.3 (mass ratio; water-absorbing resin) A surface treatment liquid (11) composed of the resin 100) was prepared. A particulate water absorbing agent (16) was obtained by performing the same operation as in Example 1 except that the surface treatment liquid (11) was used instead of the surface treatment liquid (1).

For the particulate water absorbing agents (1) to (16) and the comparative particulate water absorbing agents (1) to (10) (the comparative particulate water absorbing agent (6) was not obtained by aggregation), CRC, AAP0.7, B . R. , PDAUP, water absorption rate (Vortex) and water content were measured and are summarized in Table 1.

In addition, for the particulate water-absorbing agents (1) to (2) and (10) to (16), the chargeability, the decrease in AAP and the increase in fine powder before and after impact were measured, and are shown in Table 2.

　（まとめ）
　実施例１及び２（架橋温度２００℃、１９０℃）と、比較例１（同１００℃）、比較例９（同１４０℃）及び比較例１０（１４０℃）との対比から、カチオン性コロイダイルシリカを含む表面処理液による低温表面処理ではＡＡＰ及びＰＤＡＵＰが低いことが示された。これにより、カチオン性コロイダイルシリカを含む表面処理液による表面架橋には高温表面架橋（１５０℃を超え２５０℃以下）が重要であることが分かる。

(Summary)
From the comparison between Examples 1 and 2 (crosslinking temperature 200 ° C, 190 ° C) and Comparative Example 1 (100 ° C), Comparative Example 9 (140 ° C) and Comparative Example 10 (140 ° C), cationic colloidal It was shown that AAP and PDAUP were low in low-temperature surface treatment using a surface treatment solution containing silica. This indicates that high-temperature surface cross-linking (more than 150 ° C. and not more than 250 ° C.) is important for surface cross-linking with a surface treatment solution containing cationic colloidal silica.

From the comparison between Example 1 (crosslinking temperature: 200 ° C.), Example 8 (225 ° C.), and Example 9 (175 ° C.), the temperature of the surface treatment with the surface treatment solution containing cationic colloidal silica was 180 to 230. It turns out that C is more preferable.

From the comparison between Examples 1 and 2 and Comparative Examples 2 and 3, it is understood that batch addition with a surface cross-linking agent is important for the addition of cationic colloidal silica.
From comparison between Examples 1 and 2 and Comparative Examples 4 and 5, it is understood that cationic colloidal silica is important for anti-caching (BR).

対 From the comparison between Examples 1 and 2 and Comparative Example 6, it can be seen that powdered silica cannot obtain a particulate water-absorbing agent due to severe aggregation at the time of mixing the surface crosslinking agent solution.

From the comparison between Examples 1 and 2 and Comparative Example 7 (corresponding to Patent Document 6 / post-addition of cationic colloidal silica), AAP, PDAUP, and Anti-Caking (BR) are greatly improved in the method according to the present invention. You can see that

対 From the comparison between Examples 1 and 2 and Comparative Example 8, it can be seen that AAP and PDAUP are greatly reduced by the subsequent addition of powdered silica.

From the comparison between Example 1 and Example 12 (with fine powder recycling) and the comparison between Example 2 and Example 13 (with fine powder recycling), the water absorption rate (Vortex) is improved by including fine powder recycling (in any case). From 50 seconds to 44 seconds).

From Table 2, comparison between Example 1 and Example 10 (rewetting), comparison between Example 2 and Example 11 (rewetting), comparison between Example 12 and Example 14 (rewetting), and From the comparison between Example 13 and Example 15 (rewetting), by rewetting the particulate water-absorbing material, the chargeability is reduced, and the reduction in AAP and the generation of fine powder after impact are reduced, and the impact resistance is stabilized. It can be seen that the properties are improved.

対 Comparing Example 1 and Example 3, it can be seen that the same effect is exhibited even when the type (maker) of the cationic colloidal silica is changed.

Although not described in the table, it was confirmed that the particulate water-absorbing agent of the example exhibited excellent gel stability also in the aforementioned (13) Gel deterioration fluidity test.

The particulate water-absorbing agents (1) to (3) obtained in Examples 1 to 3, and the comparative particulate water-absorbing agents (1) to (3), (9) obtained in Comparative Examples 1 to 3, 9 and 10, and Using (10), an absorber was produced under a high humidity condition and a dehumidification condition, and the uniformity and the return amount of the obtained absorber were measured. Table 3 summarizes the measurement results of the absorber manufactured under high humidity conditions.

　（まとめ）
　表３に示す「吸収体の均一性」は、高湿条件下（３０℃＊８０％Ｒｈ）で作製した吸収体の、膨潤後の吸水性樹脂の偏りを目視で確認した結果である。また、表３に示す「戻り量（Ｒｅ－Ｗｅｔ）」は、高湿条件下で作製した吸収体の戻り量を測定した結果である。
カチオン性コロイダイルシリカを含み、吸湿流動性が３０質量％以下、ＡＡＰ（０．７ｐｓｉ）が２０（ｇ／ｇ）以上である粒子状吸水剤は、高湿条件下でも除湿条件でも均一に吸水性樹脂が混合された吸収体が製造できるだけでなく、ＡＡＰが高い吸水性樹脂が均一に混合されているため、吸収体としての戻り量（Ｒｅ－Ｗｅｔ）（ｇ）も低減できる。

(Summary)
The “uniformity of the absorber” shown in Table 3 is a result of visually confirming the unevenness of the water-absorbent resin after swelling of the absorber manufactured under a high humidity condition (30 ° C. * 80% Rh). The “return amount (Re-Wet)” shown in Table 3 is a result of measuring the return amount of the absorber manufactured under high humidity conditions.
A particulate water-absorbing agent containing cationic colloidal silica, having a moisture-absorbing fluidity of 30% by mass or less, and an AAP (0.7 psi) of 20 (g / g) or more, absorbs water uniformly under both high-humidity conditions and dehumidifying conditions. Not only can an absorbent body mixed with a water-soluble resin be produced, but also a water-absorbent resin with a high AAP is uniformly mixed, so that the amount of re-wet (g) as an absorber can be reduced.

Such a particulate water-absorbing agent can handle a water-absorbing resin without dehumidifying a diaper manufacturing process or a plant regardless of changes in the use environment such as temperature and humidity. Disposable diapers containing resin).

粒子 The particulate water-absorbing agent produced by the method of the present invention has excellent moisture absorption fluidity (BR), high absorption capacity under pressure (AAP), and high liquid permeability under pressure (PDUP). By using such a particulate water-absorbing agent, it is possible to provide a sanitary material such as a disposable diaper, a sanitary napkin, and a so-called incontinence pad, which has a high liquid intake speed and a reduced amount of liquid return.

Claims (11)

A method for producing a particulate water-absorbing agent, comprising a surface cross-linking step of surface-cross-linking the water-absorbent resin using a surface cross-linking agent,
The surface crosslinking step includes a surface treatment liquid addition step of adding a surface treatment liquid to the water absorbent resin, and a heat treatment step of heat treating the water absorbent resin to which the surface treatment liquid is added,
The production method, wherein the surface treatment liquid includes the surface cross-linking agent and cationic colloidal silica, and the heat treatment step is performed at a temperature higher than 150 ° C and 250 ° C or lower. 製造 The production method according to claim 1, wherein the amount of the cationic colloidal silica used is 1% by mass to 10,000% by mass based on the amount of the surface cross-linking agent used in solid content. The production method according to claim 1, wherein the amount of the cationic colloidal silica used is 0.001% by mass to 10% by mass, based on the amount of the water-absorbent resin, as solids. The method according to any one of claims 1 to 3, wherein the surface crosslinking agent is at least one selected from the group consisting of a polyhydric alcohol compound, an alkylene carbonate, and an epoxy compound. The production method according to any one of claims 1 to 4, further comprising a rewet step of adding 1% by mass to 20% by mass of water to the water-absorbent resin after the surface crosslinking. (6) The production method according to any one of (1) to (5), further comprising a fine powder recycling step. 7. The method according to claim 6, comprising a first classification step of the water-absorbent resin before surface crosslinking and / or a second classification step after surface crosslinking, wherein the fine powder after classification is granulated and recycled before the drying step. Production method. A surface-crosslinked water-absorbent resin, comprising cationic silicon dioxide particles, a particulate water-absorbing agent,
A particulate water absorbing agent having a moisture absorption fluidity of 50% by mass or less and an AAP (0.7 psi) of 20 (g / g) or more. The particulate water-absorbing agent according to claim 8, wherein the liquid permeability under pressure is 10 (g / g) or more. 10. The particulate water-absorbing agent according to claim 8, wherein the content of the cationic silicon dioxide particles is 0.001% by mass to 10% by mass based on the particulate water-absorbing agent. The particulate water-absorbing agent according to any one of claims 8 to 10, wherein the water content is 1% to 20%.