JP2022011517A - Method for producing water absorbent - Google Patents

Abstract

To provide means whereby: even if a water-absorbing resin is recovered, a resultant water absorbent does not show a decrease in water absorption ratios under/not under pressure.SOLUTION: A method for producing a water absorbent includes adding a water-absorbing resin solution, obtained from a water-absorbing resin and an alkali aqueous solution, to a water absorbent production process.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a water absorbing agent.

A water-absorbent resin (SAP / SuperAbsorbentPolymer) is a water-swellable water-insoluble polymer gelling agent, which is an absorbent article such as a disposable diaper or a sanitary napkin, a water-retaining agent for agriculture and horticulture, a water-stopping agent for industrial use, and the like. , Is widely used in various fields.

Many monomers and hydrophilic polymers are used as raw materials for the water-absorbent resin, but from the viewpoint of water-absorbing performance, the main component is a polymer composed of an acid group-containing unsaturated monomer. Water-absorbent resin is the most industrially produced.

The water-absorbent resin is required to have various functions (higher physical properties) as the performance of paper diapers, which is the main use, is improved. In particular, the non-pressurized water absorption ratio and the pressurized water absorption ratio are very important as basic physical properties.

Such a water-absorbent resin can have various shapes such as a sheet shape, a fibrous shape, and a film shape, but is generally used as a powder-like or particle-like water-absorbent agent.

Examples of a method for producing a powdery or particulate water-absorbing agent include an aqueous solution polymerization method and a reverse phase suspension polymerization method. In particular, in the aqueous solution polymerization method in which polymerization is carried out using a monomer aqueous solution, usually, in order to finally obtain a particulate water-absorbent resin, a polymerization step of polymerizing an acid group-containing unsaturated monomer aqueous solution is performed. Gel crushing (fine granulation) step to crush the obtained hydrogel polymer, drying step to dry the crushed gel, crushing step to crush the dried product, classification step to adjust the crushed product to an appropriate particle size range, classification. Many manufacturing steps such as a surface cross-linking step of treating the water-absorbent resin powder with a surface cross-linking agent are required.

In such a manufacturing process, unnecessary water-absorbent resin such as fine powder and non-standard products is generated. For example, the amount of fine powder generated reaches 10 to several tens of mass% (for example, 20 to 30% by mass) of the total production amount. Unnecessary water-absorbent resin is removed during the manufacturing process, but the disposal of the removed water-absorbent resin is costly, so the water-absorbency removed in the process before the classification process, especially in the process before the drying process. The resin is collected and reused. So far, many studies have been made on the recovery and reuse of water-absorbent resins.

In Patent Document 1, fine powder of a water-absorbent resin is dispersed in acrylic acid to obtain a dispersion liquid, and then the dispersion liquid is added to a monomer aqueous solution to reuse the fine powder.

Further, in Patent Document 2, after treating the fine powder of the water-absorbent resin with an alkaline substance, the treated product is added to the monomer aqueous solution to reuse the fine powder. According to Patent Document 2, by performing the step, the water-absorbent resin obtained has an improved absorption capacity for holding a liquid in a state where no load is applied. The treatment with an alkaline substance referred to in Patent Document 2 states that "by spraying or dropping, the fine powder is evenly distributed on the fine powder of the highly absorbent polymer", and the form of the fine powder is maintained even by the treatment.

Further, as a method for recovering fine powder, there is a method of granulating and recovering fine powder. When the fine powder is granulated, if the strength of the fine powder granulated product is insufficient, for example, the fine powder is generated again in the drying step, the crushing step and the classification step, and as a result, it is generated in the entire manufacturing process. Increases the amount of fine powder. So far, various proposals have been made to improve the strength of the finely divided granulated product. For example, Patent Document 3 proposes, for example, a method of firmly binding fine powders to each other by gelling the fine powders with a large amount of warm water.

Special Table No. 5-508674 Gazette Japanese Patent Publication No. 2012-506462 Japanese Unexamined Patent Publication No. 11-106514

According to the description of Patent Document 2, the process improves the water absorption ratio (CRC) of the water-absorbent resin obtained under no pressure as compared with the case where the untreated fine powder is added, but it is improved. There is still room for. Furthermore, it is also an important issue to suppress a decrease in the water absorption ratio under pressure, which is the same basic physical property as the water absorption ratio under no pressure.

On the other hand, the polymer constituting the water-absorbent resin is produced by adding an acid group-containing unsaturated monomer such as acrylic acid together with a polymerization initiator and the like and polymerizing by heating. At this time, there is a problem that not a little acid group-containing unsaturated monomer component used as a raw material remains in the polymer reaction product after the polymer is produced (problem of residual monomer). This is not preferable from the viewpoint of the productivity and performance of the polymer. Further, especially in applications in which it comes into contact with the human body, it is required to reduce the toxicity and irritation caused by the residual monomer as much as possible. However, when the water-absorbent resin obtained by the conventional fine powder recovery method such as the fine powder recovery method by granulation is reused, the residual monomer of the obtained water-absorbent resin tends to increase.

An object of the present invention is a method for producing a water-absorbing agent, which suppresses a decrease in the non-pressurized water-absorbing ratio and the pressurized water-absorbing ratio of the obtained water-absorbing agent even when the water-absorbing resin such as fine powder is recovered and reused. Is to provide.

Another object of the present invention is to provide a method for producing a water absorbing agent, which reduces the amount of residual monomers in the product.

The present invention is characterized in that a water-absorbent resin solution obtained by a water-absorbent resin and an alkaline agent is added to the process of manufacturing the water-absorbent agent.

According to the method for producing a water-absorbent agent of the present invention, even when a water-absorbent resin such as fine powder is recovered and reused, a decrease in the water absorption ratio of the obtained water-absorbent agent under no pressure is suppressed. Further, according to the method for producing a water-absorbing agent of the present invention, the amount of residual monomers of the obtained water-absorbing agent is reduced.

The present invention will be described in detail below. It is possible to do. Further, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the claims. Other embodiments obtained by appropriately combining the technical means disclosed for each of the plurality of embodiments are also included in the technical scope of the present invention.
[1] Definition of terms [1-1] "Water-absorbent resin"
The "water-absorbent resin" in the present invention refers to a water-swellable water-insoluble polymer gelling agent, and refers to a resin that satisfies the following physical properties. That is, as water swelling property, NWSP 241.0. The CRC (centrifugal force holding capacity) defined by R2 (15) (NWSP will be described later) is 5 g / g or more, and NWSP 270.0. Refers to a polymer gelling agent having an Ext (water-soluble content) of 50% by mass or less as defined by R2 (15).

The water-absorbent resin can be designed according to its use and purpose, and is not particularly limited, but is preferably a hydrophilic crosslinked polymer obtained by cross-linking and polymerizing an unsaturated monomer having a carboxyl group. Further, the total amount is not limited to the form of a crosslinked polymer, and a composition containing an additive or the like may be used.

The "water-absorbent resin" in the present invention may be surface-crosslinked (also known as post-crosslinked; secondary crosslinked) or may not be surface-crosslinked. In the present invention, the water-absorbent resin for which the predetermined surface cross-linking treatment has been completed may be separately referred to as a surface-crosslinked water-absorbent resin.

[1-2] "Poly (meth) acrylic acid (salt)"
The "poly (meth) acrylic acid (salt)" in the present invention refers to poly (meth) acrylic acid and / or a salt thereof, and (meth) acrylic acid and / or a salt thereof as a main component (hereinafter, "(meth) acrylic acid (meth)". ) Acrylic acid (salt) ”) as a repeating unit, and means a crosslinked polymer containing a graft component as an optional component.

The above-mentioned "main component" means that the amount (content) of (meth) acrylic acid (salt) used is preferably 50 mol% to 100 mol%, more preferably 50 mol% to 100 mol%, based on the total amount of the monomer used for the polymerization. It means that it is 70 mol% to 100 mol%, more preferably 90 mol% to 100 mol%, and particularly preferably substantially 100 mol%.

Here, the poly (meth) acrylic acid (salt) may be unneutralized, but is preferably a partially neutralized or completely neutralized poly (meth) acrylate, more preferably a monovalent salt. It is more preferably an alkali metal salt or an ammonium salt, still more preferably an alkali metal salt, and particularly preferably a sodium salt.

(1-3) "Water absorbent"
The "water-absorbing agent" in the present invention means an absorbent gelling agent for an aqueous liquid containing a water-absorbent resin as a main component. The water-absorbing agent according to the present invention is suitably used as a sanitary material for absorbing an aqueous liquid. The water-absorbent resin of the present invention preferably contains 60 to 100% by mass, 70 to 100% by mass, 80 to 100% by mass, and 90 to 100% by mass, and various additives described later as other components. May include. That is, the water-absorbent resin composition in which these components are integrated is also in the category of the water-absorbent agent of the present invention. The water-absorbent agent of the present invention may be referred to as a water-absorbent resin, a water-absorbent resin powder, and water-absorbent resin particles. In particular, in the definition of the following evaluation method, when the water-absorbing agent is evaluated, the water-absorbent resin is defined by replacing it with the water-absorbing agent.

[1-3] Definition of evaluation method "NWSP" stands for "Non-Woven Standard Procedures-Edition 2015" and represents EDANA (European Disposables And Nonwovens Association, European Nonwoven Fabric Industry Association) and INDA (European Nonwoven Fabric Industry Association). The Nonwoven Fabric Industry Association) has jointly issued a unified evaluation method for non-woven fabrics and their products in the United States and Europe, and indicates a standard measurement method for water-absorbent resins. Unless otherwise specified, in the present invention, the physical properties of the water-absorbent resin are measured in accordance with "Non-Woven Standard Procedures-Edition 2015". For evaluation methods not described in NWSP, measurement is performed by the methods and conditions described in Examples.

[1-3-1] "CRC" (NWSP 241.0.R2 (15))
"CRC" is an abbreviation for Centrifuge Retention Capacity (centrifugator holding capacity), and means a water absorption ratio (sometimes referred to as a "water absorption ratio") of a water-absorbent resin under no pressure. Specifically, 0.2 g of a water-absorbent resin is placed in a bag made of a non-woven fabric, and then immersed in a large excess of 0.9 mass% sodium chloride aqueous solution for 30 minutes for free swelling, and then a centrifuge (250 G). ) For 3 minutes, the water absorption ratio (unit: g / g) after draining. For the hydrous gel after polymerization and / or gel pulverization, 0.4 g of hydrogel is used, the measurement time is changed to 24 hours, and the solid content is corrected to obtain CRC.

[1-3-2] "PSD" (NWSP 220.0.R2 (15))
"PSD" is an abbreviation for Particle Size Division, and means the particle size distribution of the water-absorbent resin measured by sieving classification. The mass average particle size (D50) and the logarithmic standard deviation (σζ) of the particle size distribution are the (3) mass average particle size (D50) and the logarithmic standard deviation of the particle size distribution of columns 27 to 28 of US Pat. No. 7,638,570. It is measured by a vibration classifier (power supply 60 Hz) in the same manner as described.

[1-3-3] "AAP" (NWSP 242.0.R2 (15))
"AAP" is an abbreviation for AbsorptionAgainstPressure, and means the water absorption ratio under pressure of the water-absorbent resin. Specifically, it refers to the water absorption ratio (unit: g / g) measured under the conditions described in the examples.

[1-3-4] "ResidalMonomers" (NWSP 210.0.R2 (15))
"Residal Monomers" means the ratio (unit: ppm) of the mass of the monomer (monomer) remaining in the water-absorbent resin (hereinafter referred to as "residual monomer") to the mass of the water-absorbent resin. Specifically, 1.0 g of a water-absorbent resin is added to 200 ml of a 0.9 mass% sodium chloride aqueous solution, and the amount of the monomer eluted after stirring for 1 hour is measured by using high performance liquid chromatography. The residual monomer of the hydrous gel is the ratio (unit) of the mass of the residual monomer obtained by measuring by the method described later after performing a polymerization termination operation such as forced cooling to the mass of the resin solid content of the hydrogel. ; Mass%).

[1-3-5] "Vortex"
"Vortex" in the present invention is an index showing the water absorption rate of the water-absorbent resin, and is required for 2.0 g of the water-absorbent resin to absorb 50 ml of a 0.9% by mass sodium chloride aqueous solution to a predetermined state. It means time (unit; seconds).

[1-4] Others In the present specification, "XY" indicating a range means "X or more and Y or less". Unless otherwise specified, "t (ton)", which is a unit of mass, means "Metericton", and "ppm" means "mass ppm" or "weight ppm". Further, "mass" and "weight", "mass part" and "weight part", and "mass%" and "weight%" are treated as synonyms, respectively. Further, "-acid (salt)" means "-acid and / or a salt thereof", and "(meth) acrylic" means "acrylic and / or methacrylic".
[2] Method for producing a water-absorbent agent In the production method according to the present invention, a water-absorbent resin solution obtained by a water-absorbent resin and an alkaline agent is obtained, and the water-absorbent resin solution is added to the process for producing a water-absorbent tree. It is a method for manufacturing an agent. Hereinafter, the water-absorbent resin mixed with the alkaline agent is also referred to as water-absorbent resin A.

The water-absorbent agent obtained by such a production method can suppress deterioration of the basic physical properties of CRC and AAP even when the recovered water-absorbent resin is reused during the production process of the water-absorbent agent. In the water-absorbent resin solution, the water-absorbent resin A does not exist in the form of powder or gel, but exists as a dissolved water-absorbent resin. By the form in which the water-absorbent resin is dissolved, the water-absorbent resin A becomes a soluble component derived from the raw material monomer and / or the raw material monomer, and by using the dissolved solution in the manufacturing process of the water-absorbent agent, the water-absorbent resin A becomes a soluble component. It becomes possible to incorporate (react) into the water-absorbent resin by heating in the process. Therefore, it is considered that the deterioration of the physical properties of the obtained water-absorbing agent is suppressed.

In addition, the residual monomer tends to increase in the water-absorbing agent obtained by the conventional method of collecting and reusing the fine powder, such as a method of granulating and reusing the recovered fine powder. When the water-absorbent resin is reused during the process of the water-absorbent resin by a conventional method (fine powder granulation, etc.), the reused water-absorbent resin captures the monomer from the surrounding monomer aqueous solution or water-containing gel, and simply It is considered that this is because the reactivity of the weight is lowered, which leads to an increase in the amount of residual monomer in the final product. On the other hand, when the water-absorbent resin solution obtained by the water-absorbent resin A and the alkaline agent is reused in the process of the water-absorbent resin as in the present invention, not only does it not capture the surrounding monomers, but also the water-absorbent resin. The residual monomer originally contained in A can also react with the surrounding unreacted parts (monomer, initiator, etc.) by heating in the process, so it is considered to be effective in reducing the amount of residual monomer. Be done. As shown in Examples described later, the amount of residual monomers is reduced in Examples as compared with Reference Examples in which the water-absorbent resin A is not added during the production process. This effect suggests that the water-absorbent resin solution has a new function as an additive in the production of the water-absorbent agent.

Further, according to the above-mentioned production method, the alkaline agent in the water-absorbent resin solution polymerizes the acid group-containing unsaturated monomer or the acid group-containing unsaturated monomer to the acid group in the polymer. It can act as a neutralizer. Therefore, even if the water-absorbent resin solution is added during the manufacturing process, the effect on the physical properties of the water-absorbent resin is small.

The above estimation does not limit the technical scope of the present invention.

The addition of the water-absorbent resin solution is added to any of the manufacturing steps of the water-absorbent agent. In other words, the water-absorbent resin solution is used as a part of the raw material of the water-absorbing agent.

Specifically, the water-absorbent resin solution is preferably added to any one or more of the following production steps (1) to (5).
(1) Preparation step of monomeric aqueous solution (form 1),
(2) Polymerization step (form 2),
(3) Gel crushing step (form 3)
(4) Fine powder granulation process (form 4)
(5) Surface cross-linking step (form 5).

More preferably, the solution is added to one or more of the manufacturing steps (1), (2) and (3) because the effects of the present invention are further exhibited.

More preferably, the water-absorbent resin solution is added to the production step (1) because the water absorption rate of the obtained water-absorbent agent is improved.

Hereinafter, each step will be described in detail.

[2-1] Water-absorbent resin solution preparation step This step is a step of mixing a water-absorbent resin, an alkaline agent, and if necessary, water to obtain a water-absorbent resin solution. The water-absorbent resin mixed with the alkaline agent is also referred to as water-absorbent resin A.

The dissolution liquid refers to a state in which almost all of the water-absorbent resin is dissolved in the aqueous solution of the alkaline agent, and it can be visually determined whether or not the water-absorbent resin is dissolved. That is, when the liquid is visually confirmed, it refers to a state in which no precipitate or suspended matter is present and the solution is uniform. More specifically, the amount of insoluble content remaining on the sieve when filtered using a sieve having a nominal opening of 850 μm according to JIS Z 8801-1: 2019 is 10% by weight or less based on the weight of the solution. ..

The method for obtaining the water-absorbent resin solution is not particularly limited, and when the water-absorbent resin has a high water content (for example, a water-containing gel), an alkaline agent described later may be directly mixed with the water-absorbent resin. As a preferred embodiment, a water-absorbent resin solution and an aqueous solution of an alkaline agent (hereinafter referred to as an alkaline aqueous solution) can be mixed to obtain a water-absorbent resin solution.

The method of mixing the water-absorbent resin with the alkaline aqueous solution is not particularly limited, and a method of gradually adding the water-absorbent resin while stirring the alkaline aqueous solution; a method of gradually adding the alkaline aqueous solution while stirring the water-absorbent resin; etc. Either method may be used. Further, the water-absorbent resin may be swollen with a certain amount of water or an alkaline aqueous solution before being added to the alkaline aqueous solution.

The amount (solid content) of the water-absorbent resin A added to the alkaline aqueous solution is not particularly limited, but the alkaline aqueous solution 100 is considered in consideration of the solubility of the water-absorbent resin A in the alkaline aqueous solution and the recovery efficiency of the water-absorbent resin A. It is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 3 parts by mass with respect to parts by mass.

The liquid temperature of the alkaline aqueous solution when the water-absorbent resin A is added is not particularly limited, and is about 5 to 100 ° C. The higher the temperature, the better the solubility of the water-absorbent resin. Therefore, the temperature of the alkaline aqueous solution is preferably 15 ° C. or higher, more preferably 20 ° C. or higher. Further, considering the heat of neutralization, the upper limit is preferably 100 ° C. or lower, more preferably 80 ° C. or lower. In order to control the temperature to the above temperature, the alkaline aqueous solution may be appropriately cooled and heated.

Further, when the water-absorbent resin A is mixed with the alkaline aqueous solution, the dissolution of the water-absorbent resin is promoted by irradiating with UV light or ultrasonic waves. Further, the dissolution of the water-absorbent resin is promoted by using an oxidizing agent such as hydrogen peroxide solution in combination.

The alkaline agent may be a compound that is water-soluble and shows alkalinity when made into an aqueous solution, and is, for example, a hydroxide of an alkali metal such as sodium hydroxide, ammonium hydroxide, potassium hydroxide, or lithium hydroxide. Inorganic alkaline agents such as hydroxides of alkaline earth metals such as calcium hydroxide and magnesium hydroxide; monomethylamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, DBU (1,8-diazabicyclo [5] , 4,0] -7-Undecene), DBN (1,5-diazabicyclo [4,3,0] -5-nonen), Tetramethylammonium Hydroxide, Tetraethylammonium Hydroxide, Tetrapropylammonium Hydroxide, Tetrabutyl Preferable examples include organic alkaline agents such as ammonium hydroxide and triethylbutylammonium hydroxide. From the viewpoint of sufficiently dissolving the water-absorbent resin A, an alkaline agent that exhibits strong alkalinity when made into an aqueous solution is preferable, and an inorganic alkaline agent is preferable. Specifically, an alkaline agent having a pH of 10 or more with an alkaline aqueous solution is preferable. Among these, an alkali metal hydroxide is preferable, sodium hydroxide and / or potassium hydroxide is more preferable, and sodium hydroxide is even more preferable. By using the above-mentioned alkali metal hydroxide as an alkaline agent, it can be suitably used as a neutralizing agent for obtaining an acid group-containing unsaturated monomer (salt) which is a main raw material of a water-absorbent resin. These alkaline agents can be used alone or in combination of two or more. Further, from the viewpoint of the performance of the obtained water-absorbent resin, the alkaline agent is used as a neutralizing agent for an acid group-containing unsaturated monomer and / or a polymer obtained by polymerizing the monomer, which will be described later. It is preferably the same as the basic substance.

The concentration of the alkaline agent in the aqueous alkaline solution is preferably 1% by mass or more from the viewpoint of sufficiently advancing the neutralization of the acid group-containing unsaturated monomer / the polymer polymerized from the monomer. It is more preferably 5% by mass or more, and considering the solubility of the water-absorbent resin A, it is preferably 50% by mass or less, and preferably 30% by mass or less. The concentration of the alkaline agent in the alkaline aqueous solution is preferably 1 to 50% by mass, more preferably 5 to 30% by mass. The pH of the alkaline aqueous solution is preferably 10 or more, more preferably 12 or more.

As the water used for the alkaline aqueous solution, for example, deionized water (ion exchanged water), pure water, ultrapure water, distilled water and the like can be used, but deionized water (ion exchanged water) is preferable.

The alkaline aqueous solution may contain a small amount of a hydrophilic solvent. Examples of the hydrophilic solvent include alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol and t-butyl alcohol. The solvent used in combination is used in an amount of, for example, 0 to 10% by mass with respect to water. From the viewpoint of recovery efficiency of the water-absorbent resin A, water and / or a hydrophilic solvent may be distilled off after the water-absorbent resin A is dissolved in an alkaline aqueous solution.

The method for obtaining the water-absorbent resin A is not particularly limited. The water-absorbent resin A may be obtained in the manufacturing process of the water-absorbing agent of the present invention, or may be obtained in another manufacturing process of the water-absorbing resin and the water-absorbing agent different from the present invention. Further, the water-absorbent resin of a commercially available product or an in-stock product may be used as the water-absorbent resin A. The water-absorbent resin A may be produced so as to have the physical properties and / or the particle size described later according to a known production method (for example, a method for producing a water-absorbing agent described later) and production conditions. For example, the water-absorbent resin A may be obtained by aqueous solution polymerization or reverse phase suspension polymerization. Examples of the water-absorbent resin A include fine powder formed in the manufacturing process, a final product, and an absorbent resin taken out from a commercially available diaper. The shape of the water-absorbent resin A is not particularly limited, and examples thereof include an amorphous crushed shape, a spherical shape, a sausage shape, a granulated shape thereof, and a broccoli shape. Further, the water-absorbent resin A may be in the form of a gel by absorbing water, and contains an intermediate product obtained in a known manufacturing process of the water-absorbent resin, and is not limited to the definition of the water-absorbent resin in [1-1]. .. For example, when the device to which the water-absorbent resin is attached, which is used in the manufacturing process of the water-absorbent agent, is washed with water or the like, the gel-like water-absorbent resin A can be obtained. Further, when the water-containing gel adhering to the belt during continuous belt polymerization, which will be described later, is washed with water, a gel-like water-absorbent resin A can be obtained. In addition, a gelled water-absorbent resin A can be obtained from used diapers.

The monomer composition used for the polymer constituting the water-absorbent resin A is preferably the same as the monomer composition constituting the polymer contained in the water-absorbent resin produced in the present invention. Therefore, the water-absorbent resin A is mainly composed of a polymer obtained by polymerizing an acid group-containing unsaturated monomer (salt) (preferably a polymer obtained by polymerizing (meth) acrylic acid (salt)). It is preferably a water-absorbent resin. Here, the main component means that it is 50 mol% or more in the water-absorbent resin (upper limit 100 mol%), preferably 70 mol% to 100 mol%, and more preferably 90 mol% to 100 mol%. be. The acid group in the acid group-containing unsaturated monomer is not particularly limited, and examples and suitable forms are the same as those of the acid group-containing unsaturated monomer described in the column of the monomer aqueous solution preparation step described later. be.

The polymer obtained by polymerizing the acid group-containing unsaturated monomer (salt) may be unneutralized or neutralized. It is preferably a partially or completely neutralized poly (meth) acrylic acid (salt) -based polymer. A poly (meth) acrylic acid (salt) -based polymer neutralized with an alkali metal salt or an ammonium salt, more preferably an alkali metal salt, and particularly preferably a sodium salt. Here, the poly (meth) acrylic acid (salt) -based polymer refers to a polymer in which the main component of the monomer mixture used in the polymerization is (meth) acrylic acid. Here, the main component means that the content is 50 mol% or more (upper limit 100 mol%) in the monomer mixture used in the polymerization, preferably 70 mol% to 100 mol%, and more preferably 90. It is from mol% to 100 mol%.

The neutralization rate of the polymer obtained by polymerizing the acid group-containing unsaturated monomer (salt) is appropriately adjusted by a known method, but is preferably 40 mol% or more, more preferably 40 mol% to 80 mol. %, More preferably 45 mol% to 78 mol%, particularly preferably 50 mol% to 75 mol%.

The polymer obtained by polymerizing the acid group-containing unsaturated monomer (salt) is preferably a crosslinked polymer crosslinked by an internal crosslinking agent as described in the column of the method for producing a water absorbing agent below. That is, preferably, the water-absorbent resin A contains a crosslinked polymer obtained by polymerizing an acid group-containing unsaturated monomer (salt). As described below, in order to improve the physical properties of the water-absorbent resin, an internal cross-linking agent is often used to form a cross-linked polymer when the acid group-containing unsaturated monomer is polymerized. Fine powder or the like generated during the production of the water-absorbent resin containing the internally crosslinked crosslinked polymer may be recovered. In this way, the present invention is used when recovering the water-absorbent resin containing the internally crosslinked crosslinked polymer. By uniformly treating with an alkaline agent as in the above, the water absorption rate of the obtained water-absorbent resin is improved. The crosslinked chain is cleaved by mixing the internally crosslinked polymer with an alkaline aqueous solution. By forming the polymer in a chain form in this way, especially when it is contained in the monomer aqueous solution, the thickening effect of the monomer aqueous solution is exhibited as described below, and the water absorption rate of the obtained water absorbing agent is further increased. It is thought to improve. From the above viewpoint, the internal cross-linking agent is preferably a compound having an ester bond in the molecule or forming an ester bond by a cross-linking polymerization reaction. More preferably, the internal cross-linking agent is a compound having an ester bond in the molecule, and more preferably a (meth) acrylate compound. The type, amount, etc. of the internal cross-linking agent used in producing the cross-linked polymer, and suitable forms thereof are the same as those described in the column of the preparation step of the monomer aqueous solution of the water-absorbent resin below. Is.

Further, the polymer obtained by polymerizing the acid group-containing unsaturated monomer (salt) may or may not be subjected to the surface crosslinking described in the column of the surface crosslinking step of the water-absorbent resin below. For example, the water-absorbent resin powder (such water-absorbent resin powder) removed during the recovery of the water-containing gel-like water-absorbent resin before the drying step or during the classification step after the drying step and before the surface cross-linking is referred to as a base polymer. If the water-absorbent resin powder removed during the classification step after the surface cross-linking is recovered, the surface cross-linking is performed. Surface crosslinked water-absorbent resin powder. The types of the surface cross-linking agent, the amount of the surface cross-linking agent used, the method of the surface cross-linking, and the suitable forms thereof are the same as those described in the column of the surface cross-linking step of the water-absorbent resin below. From the viewpoint of reducing the residual monomer, a so-called base polymer that does not undergo surface cross-linking of the acid group-containing unsaturated monomer (salt) may be used as the water-absorbent resin A. Further, the base polymer may be a base polymer before the classification or sizing step, or may be a base polymer after the classification or sizing step.

From the viewpoint of fluidity and mixability, the solid content of the water-absorbent resin A as a powder is preferably 75% by mass or more, more preferably 80% by mass or more, still more preferably 85% by mass or more. The upper limit is not particularly limited, but the solid content ratio is usually 99.9% by mass or less, preferably 99.5% by mass or less. The method for measuring the solid content of the water-absorbent resin will be described later in Examples.

The CRC (centrifugal force holding capacity) of the water-absorbent resin A is preferably 5 g / g or more, more preferably 10 g / g or more, still more preferably 15 g / g or more, particularly preferably 15 g / g or more in terms of solid content. Is 18 g / g or more. When the CRC is within the above range, the dissolution rate can be improved and the process efficiency can be improved. The upper limit of the CRC of the water-absorbent resin A is not particularly limited, but is, for example, 80 g / g or less.

The water-absorbent resin A may contain the additives described in the step of adding water or other additives of the water-absorbent resin described later. That is, the water-absorbent resin A is not limited to the form in which 100% is a polymer, and the water-absorbent resin A may contain water or other trace components (eg, inorganic fine particles) which are auxiliary raw materials of the water-absorbent resin powder. ..

Preferably, the water-absorbent resin A is a classification step or a granulation step (drying step, a classification step after a crushing step, a surface cross-linking step) (after an optional additive addition step) carried out in a known water-absorbent resin manufacturing step. ), Unnecessary water-absorbent resin powder (for example, coarse particles (mass average particle diameter of 850 μm or more) and its crushed material, fine powder having a mass average particle diameter of 150 μm or less, etc. It is a water-absorbent resin powder (for example, non-standard water-absorbent resin powder) removed out of the desired physical properties, and more preferably fine powder. That is, the fine powder removed in the classification step is collected and recovered. It is preferable that the water-absorbent resin powder is used in this step.

The fine powder is a particulate or powdery water-absorbent resin. It is known that in powdery or particulate water-absorbent resins, the water-absorbing performance, handleability, and usability vary depending on the particle size, particle size distribution, and the like. Therefore, there is a demand for a powdery or particulate water-absorbent resin in which the particle size and particle size distribution are appropriately controlled. In particular, in the use of sanitary products such as disposable diapers, a water-absorbent resin powder having a low content of fine powder (for example, a particle size distribution of 850 to 150 μm) is preferable from the viewpoint of water absorption ratio under pressure and liquid permeability. Therefore, the fine powder may be removed by an operation such as classification. Since it is not preferable to dispose of the fine powder thus removed from the viewpoint of cost, it is preferable to recycle the fine powder during the process, and the method of the present invention can be applied at that time.

As the fine powder applicable as the water-absorbent resin A of the present invention, the mass average particle size (D50) by sieving is preferably less than 150 μm, more preferably 10 to 150 μm, and further preferably 20 to 140 μm. The proportion of particles having a particle diameter of less than 150 μm (JIS standard sieve mesh permeability of 150 μm) contained in the fine powder is preferably 70% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. Yes, ideally 100% by mass.

[2-2] Production step of crosslinked polymer using acid group-containing unsaturated monomer In the production process of crosslinked polymer, the water-absorbent resin solution obtained in [2-1] (hereinafter, simply dissolved) A liquid) may be added, and the embodiment is suitable.

When the solution is added in the step of producing the crosslinked polymer, it can be carried out in any one of the steps of preparing the aqueous monomer solution (form 1) and the polymerization step (form 2), or both steps.

In the first and second forms, the timing of adding the solution is different. In any form, the alkaline agent in the solution may be used as an acid group-containing unsaturated monomer or an acid group-containing unsaturated monomer polymerized as an acid group neutralizing agent in a polymer. It works. That is, the water-absorbent resin solution is used as a part of the raw material of the water-absorbing agent. Further, the solution is added either before the start of the polymerization reaction, during the polymerization reaction, or after the completion of the polymerization reaction. When it is used as a neutralizing agent in the case of multi-step neutralization, it may be used at any timing, but it is preferably used as a neutralizing agent in the first neutralization.

Hereinafter, preferred embodiments will be described in detail.

[2-2-1: Preparation step of monomeric aqueous solution]
This is a step of preparing an aqueous solution containing an acid group-containing unsaturated monomer as a main component (hereinafter referred to as “monomer aqueous solution”). A monomer slurry liquid (dispersion liquid exceeding the saturation concentration of the monomer) may be used as long as the water absorption performance of the obtained water-absorbing agent does not deteriorate, but in this section, such a liquid cannot be used for convenience. The slurry liquid is also included in the monomer aqueous solution.

Further, the above-mentioned "main component" means that the amount (content) of the acid group-containing unsaturated monomer used is the entire monomer (excluding the internal cross-linking agent) subjected to the polymerization reaction of the water-absorbent resin. It means that it is usually 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more (upper limit is 100 mol%).

The acid group in the acid group-containing unsaturated monomer is not particularly limited, and examples thereof include a carboxyl group, a sulfone group, and a phosphoric acid group. Examples of this acid group-containing unsaturated monomer include (meth) acrylic acid, (anhydrous) maleic acid, itaconic acid, silicic acid, vinyl sulfonic acid, allyltoluene sulfonic acid, vinyl toluene sulfonic acid, and styrene sulfonic acid. , 2- (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloyloxyethanesulfonic acid, 2- (meth) acryloyloxypropanesulfonic acid, 2-hydroxyethyl (meth) acryloyl phosphate and the like. Be done. From the viewpoint of water absorption performance, (meth) acrylic acid, (maleic anhydride) maleic acid, itaconic acid, and cinnamic acid are preferable, and (meth) acrylic acid is more preferable.

It is preferable that a part or all of the acid groups contained in the acid group-containing unsaturated monomer contained in the aqueous monomer solution are neutralized. Examples of the salt of the acid group-containing unsaturated monomer include salts with inorganic cations such as alkali metal salts, alkaline earth metal salts, and ammonium salts, and basic substances such as amine-based organic compounds having amino groups and imino groups. It is appropriately selected from the salts of and used. Among them, a salt with a monovalent cation is more preferable, at least one selected from an alkali metal salt, an ammonium salt and an amine salt is more preferable, and an alkali metal salt is further preferable. Among the alkali metal salts, at least one selected from sodium salt, lithium salt, and potassium salt is more preferable, and sodium salt is particularly preferable.

The neutralizing agent used to neutralize the acid group-containing unsaturated monomer is not particularly limited, but may be a salt containing a cation constituting the salt of the acid group-containing insoluble monomer. Generally, an inorganic salt such as sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium carbonate, or a basic substance such as an amine-based organic compound having an amino group or an imino group is appropriately selected and used. Two or more basic substances may be used in combination as a neutralizing agent. The monomer in the present invention is a concept containing a neutralizing salt unless otherwise specified.

In the first form, by mixing the water-absorbent resin solution with the aqueous monomer solution, the solution also serves as a neutralizing agent for the acid group-containing unsaturated monomer.

From the viewpoint of water absorption performance, the number of moles of the neutralizing salt (hereinafter referred to as "neutralization rate") with respect to the total number of moles of the acid group-containing unsaturated monomer and its neutralizing salt is finally preferable. Is adjusted to be 40 mol% or more, more preferably 40 mol% to 80 mol%, still more preferably 45 mol% to 78 mol%, and particularly preferably 50 mol% to 75 mol%. The preferred range of the neutralization rate is the same for post-neutralization (neutralization in a hydrogel polymer).

As a method for adjusting the neutralization rate, a neutralizing salt of the acid group-containing unsaturated monomer obtained by mixing an acid group-containing unsaturated monomer and a water-absorbent resin solution and an acid group-containing insoluble mixture are used. Method of mixing the monomer and the acid group; a method of adding a water-absorbent resin solution and / or a known neutralizing agent to the acid group-containing unsaturated monomer; water absorption to the acid group-containing unsaturated monomer. A method of adding a known neutralizing agent after adding a resin dissolving solution; an acid group-containing unsaturated substance adjusted to a predetermined neutralization rate in advance using a water-absorbent resin dissolving solution as all or part of the neutralizing agent. A method using a partially neutralized salt of the monomer (that is, a mixture of an acid group-containing unsaturated monomer and the neutralized salt thereof); and the like can be mentioned. Moreover, you may combine these methods.

The neutralization rate may be adjusted before the start of the polymerization reaction of the acid group-containing unsaturated monomer (the embodiment of Form 1), or may be performed during the polymerization reaction of the acid group-containing unsaturated monomer. This may be performed on the hydrogel-like crosslinked polymer obtained after the completion of the polymerization reaction of the acid group-containing unsaturated monomer (post-neutralization, embodiment 2). Further, the neutralization rate may be adjusted by selecting one of the steps before the start of the polymerization reaction, during the polymerization reaction, or after the completion of the polymerization reaction, or the neutralization rate may be adjusted in a plurality of steps. That is, the neutralizing agent may be added once or in multiple steps (for example, two-step neutralization). Two-step neutralization involves adding a neutralizing agent over two steps. In any of the embodiments, if the water-absorbent resin solution is used as all or part of the neutralizing agent of the acid group-containing unsaturated monomer or its polymer, it is included in the scope of the present invention.

The monomer aqueous solution may contain a monomer other than the acid group-containing unsaturated monomer.

The monomer other than the acid group-containing unsaturated monomer may be a compound that can be polymerized to become a water-absorbent resin. For example, amide group-containing unsaturated monomers such as (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide; N, N-dimethylaminoethyl (meth) acrylate, N, N. -Amino group-containing unsaturated monomer such as dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide; mercapto group-containing unsaturated monomer; phenolic hydroxyl group-containing unsaturated monomer; Examples thereof include lactam group-containing unsaturated monomers such as N-vinylpyrrolidone.

Monomer concentration in the monomer aqueous solution (= total monomer amount / (total monomer amount + total polymerization solvent amount (usually water)), where the monomer is an acid group-containing unsaturated monomer (Including monomers other than) is preferably 10% by mass to 90% by mass, more preferably 20% by mass to 80% by mass, still more preferably 30% by mass or more, from the viewpoint of physical properties and productivity of the water-absorbent resin. It is 70% by mass, particularly preferably 40% by mass to 60% by mass. Hereinafter, the monomer concentration may be referred to as “monomer concentration”.

A polymerization inhibitor, an internal cross-linking agent, or the like may be added to the monomer aqueous solution prepared in this step. As described above, a form containing an internal cross-linking agent is suitable.

-Polymerization inhibitor The monomer used for polymerization preferably contains a small amount of a polymerization inhibitor from the viewpoint of polymerization stability. A preferred polymerization inhibitor is p-methoxyphenol. The amount of the polymerization inhibitor contained in the monomer (particularly acrylic acid and its salt) is usually 1 ppm to 250 ppm, preferably 10 ppm to 160 ppm, and more preferably 20 ppm to 80 ppm.

-Internal cross-linking agent The internal cross-linking agent adjusts the water absorption performance of the obtained water-absorbent resin, the gel strength at the time of water absorption, and the like.

The internal cross-linking agent may have a total of two or more unsaturated bonds or reactive functional groups in one molecule. For example, as an internal cross-linking agent having a plurality of polymerizable unsaturated groups (which can be copolymerized with a monomer) in the molecule, N, N-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, ( Poly) Propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, glycerin (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, tri. Allyl cyanurate, triallyl isocyanurate, triallyl phosphate, trimethylolpropane di (meth) allyl ether, poly (meth) allyl ether of polyols having 2 to 10 carbon atoms, pentaerythritol triallyl ether, tetraallyloxyetane, etc. Can be mentioned. Triallylamine, polyaryloxyalkane, (poly) ethylene glycol diglycidyl ether, as an internal cross-linking agent having a plurality of reactive functional groups (which can react with a monomer functional group (eg, carboxy group)) in the molecule, Examples thereof include glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine and the like (here, ethylene carbonate and the like). Cyclic carbonate is a cross-linking agent that further produces functional group OH by reaction with a carboxyl group). Further, examples of the internal cross-linking agent having a polymerizable unsaturated group and a reactive functional group in the molecule include glycidyl (meth) acrylate and the like. Of these, two or more may be used in combination.

Among these internal cross-linking agents, from the viewpoint of the effect of the present invention, a compound having a plurality of polymerization unsaturated groups in the molecule is preferable, and a compound having a (poly) alkylene structural unit in the molecule is more preferable. , More preferably a compound having a polyethylene glycol structural unit, and particularly preferably an acrylate compound having a polyethylene glycol structural unit. In the water-containing gel obtained by using these internal cross-linking agents, the effect that the water absorption ratio can be easily improved by drying can be obtained.

The amount of the internal cross-linking agent used is appropriately set according to the type of the monomer and the internal cross-linking agent and the like. From the viewpoint of the gel strength of the obtained water-absorbent resin, it is preferably 0.001 mol% or more, more preferably 0.005 mol% or more, still more preferably 0.01 mol% or more with respect to the monomer. Further, from the viewpoint of improving the water absorption performance of the water-absorbent resin, it is preferably 5 mol% or less, more preferably 2 mol% or less. It is not necessary to use the internal cross-linking agent under the polymerization conditions in which the self-cross-linking reaction of the monomer is effective.

When the internal cross-linking agent is added, the time for adding the internal cross-linking agent to the acid group-containing monomer is not particularly limited, and the internal cross-linking agent may be added at any time as long as it is before the start of polymerization. For example, in the case of the polymerization form 1, it may be before or after the addition of the solution.

-Other substances To the extent that the object of the present invention is achieved, the substances exemplified below (hereinafter referred to as "other substances") can be added to the aqueous monomer solution.

Specific examples of other substances include chain transfer agents such as thiols, thiolic acids, secondary alcohols, amines and hypophosphites; foaming agents such as carbonates, bicarbonates, azo compounds and bubbles; ethylenediamine. Chelating agents such as tetra (methylenephosphinic acid) and its metal salt, ethylenediamine 4acetic acid and its metal salt, diethylenetriamine-5acetic acid and its metal salt; polyacrylic acid (salt) and crosslinked products thereof (for example, fine powder consisting of water-absorbent resin) ), Distillates, celluloses, starch-cellulose derivatives, hydrophilic polymers such as polyvinyl alcohol, and the like. Other substances may be used alone or in combination of two or more.

The amount of the other substance used is not particularly limited, but the total concentration of the other substance is preferably 10% by mass or less, more preferably 0.001% by mass to 5% by mass, particularly preferably the monomer. Is 0.01% by mass to 1% by mass.

(Dissolved oxygen amount)
It is also preferable to reduce the dissolved oxygen in the aqueous monomer solution before polymerization by raising the temperature or replacing it with an inert gas. For example, the dissolved oxygen is preferably reduced to 5 ppm or less, more preferably 3 ppm or less, and particularly preferably 1 ppm or less.

In addition, bubbles (particularly the above-mentioned inert gas) can be dispersed in the monomer aqueous solution. In this case, foam polymerization occurs in the polymerization reaction.

(Form 1)
In the first form, the water-absorbent resin A is added in the step of preparing the monomer aqueous solution. That is, a monomer aqueous solution containing a water-absorbent resin solution and an acid group-containing unsaturated monomer is obtained, and the acid group-containing unsaturated monomer is polymerized in the next step using the monomer aqueous solution. conduct.

In the first embodiment, by adding the water-absorbent resin solution to the monomer aqueous solution, the viscosity of the aqueous solution is increased by the polymer component derived from the water-absorbent resin A contained in the solution. Due to such an increase in viscosity, it becomes difficult for bubbles generated during polymerization to escape, and the surface area of the obtained water-absorbent resin increases. Therefore, the water absorption rate of the water-absorbent resin is further improved.

In the first form, the solution and the acid group-containing unsaturated monomer are mixed to form an aqueous monomer solution. Here, the mixed form is a form in which an acid group-containing unsaturated monomer and a solution are collectively added and mixed; after forming an acid group-containing unsaturated monomer aqueous solution, the acid group-containing unsaturated single amount is used. A form in which a solution is added to an aqueous solution of a body; and the like can be mentioned. In the case of adding the solution to the acid group-containing unsaturated monomer aqueous solution after forming the acid group-containing unsaturated monomer aqueous solution, the entire amount of the solution was added to the acid group-containing unsaturated monomer aqueous solution. Later, the polymerization may be started, or the polymerization may be carried out while continuously supplying the acid group-containing unsaturated monomer aqueous solution and the solution separately. It is preferable that the aqueous solution of the unsaturated monomer containing an acid group and the solution are continuously supplied separately and sufficiently mixed by, for example, line mixing, and then polymerized. Further, an aqueous neutralizing agent solution is added to the acid group-containing unsaturated monomer solution in advance to form an acid group-containing unsaturated monomer aqueous solution, and then a solution is added to the acid group-containing unsaturated monomer aqueous solution. You may.

The amount of the solution to be added to the acid group-containing monomer is appropriately set in consideration of the degree of neutralization, the influence of physical properties on the obtained water-absorbent resin, recovery efficiency, etc., and is, for example, 100 parts by mass of acrylic acid. On the other hand, it is 1 to 400 parts by mass.

The liquid temperature of the alkaline aqueous solution when the solution is added to the monomer aqueous solution is preferably 5 to 100 ° C, more preferably 10 to 60 ° C, and even more preferably 15 to 40 ° C.

[2-2-2: Polymerization step]
This step is a step of polymerizing the monomer aqueous solution and then neutralizing it in some cases to obtain a hydrogel-like polymer (hereinafter, may be referred to as “hydrogen gel”).

The polymerization can be carried out by adding a polymerization initiator. As the polymerization initiator, the monomer aqueous solution may contain a polymerization initiator. The polymerization initiator is appropriately selected depending on the polymerization form and the like, and is not particularly limited. Examples thereof include a redox-based polymerization initiator using a reducing agent in combination. Specifically, one or more of the polymerization initiators disclosed in US Pat. No. 7,265,190 are used. From the viewpoint of the handleability of the polymerization initiator and the physical properties of the water-absorbent resin, a peroxide or an azo compound is preferably used, more preferably a peroxide, and still more preferably a persulfate.

The amount of the polymerization initiator used is preferably 0.001 mol% to 1 mol%, more preferably 0.001 mol% to 0.5 mol%, based on the monomer. When redox polymerization is performed, if necessary, the amount of the reducing agent used in combination with the oxidizing agent is preferably 0.0001 mol% to 0.02 mol% with respect to the monomer.

In addition to the method of carrying out the polymerization reaction by adding the above-mentioned polymerization initiator, there is a method of irradiating with active energy rays such as radiation, electron beam, and ultraviolet rays. Further, after adding the polymerization initiator, irradiation with active energy rays may be used in combination.

The polymerization form is not particularly limited. From the viewpoint of water absorption performance and ease of polymerization control, it is preferable to use droplet polymerization in a gas phase, aqueous solution polymerization, or reverse phase suspension polymerization (here, droplet polymerization in a hydrophobic organic solvent is also an example of reverse phase suspension. ), More preferably, aqueous solution polymerization, reverse phase suspension polymerization, and even more preferably aqueous solution polymerization. For details of the reverse phase suspension polymerization, reference can be made to Japanese Patent No. 4969778 [0016] to [0033], specifically, Example 1. Among them, continuous aqueous solution polymerization is particularly preferable, and examples thereof include continuous belt polymerization and continuous kneader polymerization. By adopting continuous aqueous solution polymerization, the production efficiency of the water-absorbent resin is improved.

Moreover, "high temperature start polymerization" and "high concentration polymerization" are mentioned as a preferable form of aqueous solution polymerization. The "high temperature start polymerization" means that the temperature of the aqueous monomer solution is preferably 30 ° C. or higher, more preferably 35 ° C. or higher, further preferably 40 ° C. or higher, and particularly preferably 50 ° C. or higher (upper limit is the boiling point). The term "high-concentration polymerization" means that the monomer concentration is preferably 30% by mass or more, more preferably 35% by mass or more, still more preferably 40% by mass or more, and particularly preferably 45% by mass or more. It refers to a form in which polymerization is carried out at (the upper limit is the saturation concentration). These polymerization forms can also be used in combination.

In the droplet polymerization in the gas phase, the polymerization can be carried out in an air atmosphere, but from the viewpoint of the color tone of the obtained water-absorbent resin, the polymerization should be carried out in an inert gas atmosphere such as nitrogen or argon. Is preferable. In this case, for example, it is preferable to control the oxygen concentration in the gas phase to 1 volume% or less.

By polymerizing the acid group-containing unsaturated monomer, a hydrogel-like polymer (hereinafter, also simply referred to as a hydrogel) can be obtained.

(Form 2)
In form 2, the solution is added in the polymerization step. Here, the timing of adding the solution is not particularly limited, but it is preferable to add the water-absorbent resin solution to the hydrogel (that is, before the drying treatment step). Specifically, a form in which a water-absorbent resin solution is added during the polymerization of a monomer aqueous solution containing an acid group-containing unsaturated monomer (specifically, polymerization and gel such as continuous kneader polymerization). A form in which a water-absorbent resin solution is added in the gel crushing step during the polymerization step, such as when crushing is performed at the same time); A form in which a water-absorbent resin solution is added; and the like. The amount of the water-absorbent resin solution added to the water-containing gel polymer is appropriately set in consideration of the degree of neutralization, the influence of physical properties on the obtained water-absorbent resin, the recovery efficiency, and the like. It is 1 to 100 parts by mass with respect to 100 parts by mass of the polymer.

[2-3] Gel crushing step In this step, the hydrogel-like polymer obtained in the above polymerization step is pulverized at the same time as and / or after the polymerization to form a particulate hydrogel-like crosslinked polymer (hereinafter, “particles”). It is a step of obtaining a state-hydrated gel ”). This step may be carried out twice or more in order to obtain a particulate hydrogel having a predetermined particle size. Further, when a particulate hydrogel having a desired particle size can be obtained in the polymerization step, such as reverse phase suspension polymerization or vapor phase polymerization, this step may not be carried out. If necessary, after the polymerization step and before the gel crushing step, the hydrogel-like crosslinked polymer is cut or coarsely crushed to a size that can be put into the gel crushing apparatus by using a roller cutter, a guillotine cutter, or the like. A shredding step may be carried out. In particular, when the polymerization step is belt polymerization and a sheet-shaped or block-shaped hydrogel is obtained, it is preferable to carry out the shredding step.

(Form 3)
The water-absorbent resin solution of the present invention may be added at the same time as the gel crushing step (form 3). Before the gel crushing step, the water-absorbent resin solution may be added in the shredding step of cutting or coarsely crushing the gel into a size that can be put into the gel crushing apparatus described later. When the addition is carried out in the gel crushing step, it is preferable to add the water-absorbent resin solution before the gel crushing step and / or during the gel crushing step and sufficiently mix the mixture at the time of gel crushing. The amount of the water-absorbent resin solution added to the water-containing gel polymer is appropriately set in consideration of the degree of neutralization, the influence of physical properties on the obtained water-absorbent resin, the recovery efficiency, and the like. It is 1 to 100 parts by mass with respect to 100 parts by mass of the polymer. Further, in the monomer aqueous solution preparation step of (2-2-1), only a part of the acid group-containing unsaturated monomer was neutralized or neutralized, and the polymerization of (2--2-2) was carried out. In this case, neutralization can be performed in the present gel crushing step. Preferably, a part or all of the water-absorbent resin solution of the present invention can be used as a neutralizing agent. Further, a mixture and / or a granulated product obtained by adding an aqueous liquid (solvent) to the coarse particles removed in the granulation step described later or the fine powder obtained in the fine powder granulation step may be added to the gel pulverization step.

In the production method of the present invention, the type of gel crushing apparatus is not particularly limited as long as a particulate hydrogel having a predetermined particle size can be obtained without impairing the water absorption performance. For example, a gel crusher equipped with a plurality of rotary stirring blades such as a batch type or continuous type double-armed kneader, a single-screw extruder, a twin-screw extruder, a meat chopper and the like can be mentioned.

A gel fluidizing agent may be added before and / or during the gel crushing step. By adding the gel fluidizing agent, adhesion between the water-containing gel particles in the drying step described later is suppressed, and the water absorption rate of the obtained water-absorbent resin is improved. In addition, the load in the pulverization step after drying, which will be described later, is reduced, and the amount of fine powder generated is reduced. Even in the embodiment that does not require the gel crushing step, the above effect can be obtained by adding the gel fluidizing agent to the particulate hydrogel before the drying step.

Examples of this gel fluidizing agent include anionic, cationic, nonionic and amphoteric surfactants, these low molecular weight and high molecular weight surfactants, and high molecular weight lubricants. The polymer lubricant is another name for a specific nonionic surfactant, and examples thereof include polyalkylene oxides and maleic anhydride modified products thereof. A surfactant (particularly a non-polymeric surfactant) and a polymer lubricant may be used in combination.

The type and amount of the gel fluidizing agent are appropriately adjusted in consideration of the fluidity of the particulate hydrogel in the gel crushing step and the drying step. Further, as the third form, when the water-absorbent resin solution is added to the water-containing gel in this step, it may be mixed with the above-mentioned gel fluidizing agent and added separately, or may be added separately to the water-containing gel. .. As described above, the hydrogel may be crushed at the same time as the polymerization, in which case the forms 2 and 3 are performed in parallel.

The polymerization rate of the particulate hydrogel is preferably 90% by mass or more, more preferably 95, from the viewpoint of suppressing aggregation of the particulate hydrogel crosslinked polymer during drying and reducing residual monomers in the obtained water-absorbent resin. By mass or more, more preferably 98% by mass or more. When the drying step is carried out using a hydrogel having a low polymerization rate and containing a large amount of unreacted monomers, the polymerization reaction proceeds during drying, and gel particles having a small particle size are regenerated or secondary to a gel particle having a large particle size. May be born. The large particle size gel particles cause problems such as a decrease in the water absorption rate of the obtained water-absorbent resin, an increase in the size of the dried product, and the generation of fine particles due to re-grinding to the target product particle size. In order to avoid this problem, it is preferable to set the polymerization rate of the hydrogel to the above range.

The upper limit of the polymerization rate of the particulate hydrogel is not particularly limited, and 100% by mass is ideal. However, a high polymerization rate requires a long polymerization time and strict polymerization conditions, resulting in a decrease in productivity and physical properties. The upper limit is 99.9% by mass, further 99.9% by mass, and usually about 99.8% by mass is sufficient. Typically, it is 98 to 99.99% by mass.

The CRC (centrifugator holding capacity) of the polymer of the particulate hydrogel is preferably 5 g / g to 80 g / g, more preferably 10 g / g to 50 g / g, and further preferably 15 g / g in terms of solid content. It is ~ 45 g / g, particularly preferably 20 g / g ~ 40 g / g. The solid content conversion means that after measuring various physical properties such as CRC with a water-containing gel, the physical properties converted into the physical properties per water-absorbent resin solid content in the water-containing gel (for example, the water content is 50% (solid content 50%)). In the case of a water-containing gel, it is converted to the measured value of physical properties of the water-containing gel x 2 times).

The solid content of the particulate hydrogel (hereinafter referred to as gel solid content) is preferably 25% by mass or more. The gel solid content is more preferably 25% by mass to 75% by mass, more preferably 30% by mass to 70% by mass, from the viewpoints of suppressing aggregation of hydrogel particles after gel crushing, energy required for crushing, drying efficiency and absorption performance. Even more preferably, 35% by mass to 65% by mass is even more preferable, and 40% by mass to 60% by mass is particularly preferable. The gel solid content is measured by the method described in Examples described later.

[2-4] Drying Step This step is a step of drying the particulate water-containing gel obtained in the above-mentioned polymerization step and / or gel crushing step to a desired resin solid content to obtain a dry polymer. The resin solid content is determined by drying weight loss (mass change when 1 g of water-absorbent resin is heated at 180 ° C. for 3 hours), and is preferably 80% by mass or more, more preferably 85 to 99% by mass, and further preferably 90. It is ~ 98% by mass, particularly preferably 92 ~ 97% by mass.

The method for drying the particulate hydrogel is not particularly limited, but is, for example, heat drying, hot air drying, vacuum drying, fluidized layer drying, infrared drying, microwave drying, drum dryer drying, and co-boiling with a hydrophobic organic solvent. Examples include drying by dehydration and high-humidity drying using high-temperature steam. Of these, hot air drying is preferable from the viewpoint of drying efficiency.

Examples of the hot air drying method include a method of drying in a stationary state, a method of drying in a stirred state, a method of drying in a vibrating state, a method of drying in a flowing state, and a method of drying in an air flow. Among these, from the viewpoint of efficiency, static drying is preferable, ventilation band drying is more preferable, and hot air drying using continuous static drying (continuous ventilation band drying) is particularly preferably used.

The drying temperature (temperature of the hot air) in the hot air drying is preferably 120 to 250 ° C., more preferably 150 to 200 ° C. from the viewpoint of the color tone of the water-absorbent resin and the drying efficiency. Drying conditions other than the above-mentioned drying temperature, such as the wind speed and drying time of hot air, may be appropriately set according to the water content and total weight of the particulate hydrogel to be dried and the target resin solid content. When the band is dried, the conditions described in International Publication No. 2006/100300, No. 2011/025012, No. 2011/025013, No. 2011/11657, etc. are appropriately applied.

[2-5] Crushing Step, Classification Step In this step, the dry polymer obtained in the above drying step is crushed (grinding step), adjusted to a predetermined particle size (classification step), and the water-absorbent resin powder (classification step). This is a step of obtaining a powdery water-absorbent resin (referred to as "water-absorbent resin powder" for convenience) before surface cross-linking.

Examples of the equipment used in the crushing process of the present invention include high-speed rotary crushers such as roll mills, hammer mills, screw mills, and pin mills, vibration mills, knuckle type crushers, cylindrical mixers, and the like, if necessary. Used together.

The particle size adjusting method in the classification step of the present invention is not particularly limited, and examples thereof include sieve classification using a JIS standard sieve (JIS Z8801-1 (2000)) and air flow classification. The particle size adjustment of the water-absorbent resin is not limited to the above-mentioned pulverization step and classification step, and can be appropriately carried out in a polymerization step (particularly reverse phase suspension polymerization and spray droplet polymerization) and other steps. It is also possible to remove non-standard products (for example, fine powder) classified in the classification step, and the removed water-absorbent resin powder may be used as the recovered water-absorbent resin powder.

The water-absorbent resin powder (water-absorbent resin powder before the surface cross-linking step, so-called base polymer) obtained in the above step has a mass average particle diameter (D50) of preferably 200 to 600 μm, more preferably 200 to 550 μm, and even more preferably. Is 250 to 500 μm. The proportion of particles having a particle diameter of less than 150 μm is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 1% by mass or less, and the proportion of particles having a particle diameter of 850 μm or more is preferably 5. It is mass% or less, more preferably 3% by mass or less, still more preferably 1% by mass or less. In any case, the lower limit of the ratio of these particles is preferably 0% by mass, but may be about 0.1% by mass. Further, the logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.20 to 0.50, more preferably 0.25 to 0.40, and even more preferably 0.27 to 0.35. These particle sizes are described in US Pat. No. 7,638,570 and NWSP 220.0. It is measured using a standard sieve according to the measuring method disclosed in R2 (15).

The above-mentioned particle size is applied not only to the water-absorbent resin after surface cross-linking (hereinafter, may be referred to as “water-absorbent resin particles” for convenience), but also to the water-absorbent agent as a final product. Therefore, it is preferable that the water-absorbent resin particles are subjected to a surface cross-linking treatment (surface cross-linking step) so as to maintain the particle size in the above range. You may adjust.

[2-6] Fine powder granulation step This step is a step of granulating the fine powder classified in 2-5 and the fine powder obtained in the granulation step after the 2-8 surface cross-linking step described later. The granulated product obtained in this step is preferably recycled during the manufacturing process.

Granulation is to form particles larger than the original particles by adhering the particles to each other by a physical or chemical method.

The granulation is preferably performed by granulating with a solvent such as water or a hydrophilic solvent. Examples of the solvent include water; alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and t-butyl alcohol; and combinations thereof. The solvent is preferably water. At the time of granulation, the solvent used is preferably a method of spraying or dropping onto fine powder, and a method of spraying is more preferable. The amount of the solvent depends on the water content of the fine powder used, but is usually in the range of 25 to 250 parts by mass, preferably 25 to 200 parts by mass with respect to 100 parts by mass of the solid content of the water-absorbent resin.

The apparatus used for mixing the solvent and the fine powder is not particularly limited. For example, in the case of a container-fixed mixer, a mechanical stirring type mixer is preferable. Specific examples thereof include a tarview riser (manufactured by Hosokawa Micron), a radige mixer (manufactured by radige), and a mortar mixer (manufactured by West Japan Testing Machine Co., Ltd.). Further, either a batch type mixer or a continuous type mixer may be used for mixing.

The heating temperature in the mixing device at the time of mixing, preferably the inner wall surface of the mixing device, and / or the stirring means is preferably 60 ° C. or higher, more preferably 65 ° C. or higher, still more preferably 70 ° C. or higher, and preferably 70 ° C. or higher. It is 120 ° C. or lower, more preferably 100 ° C. or lower, still more preferably 90 ° C. or lower. By heating the mixer device (preferably either the inner wall surface or the stirring means, more preferably both), fine powder can be uniformly granulated in a short time, and productivity is improved. The temperature in the mixing device can be appropriately adjusted by, for example, supplying a heated gas or by conducting electric heating.

In this step, a water-absorbent resin solution can be added (form 4). In this case, it is preferable to use the above solvent and the water-absorbent resin solution in combination because the granulation strength and physical properties of the granulated product can be adjusted. In the case of combined use, the above solvent and the water-absorbent resin solution may be mixed, or may be dropped or sprayed on a line separate from the solvent.

When the solvent and the water-absorbent resin solution and the fine powder are mixed and granulated, it is preferable to use a preheated solvent and a water-absorbent resin solution. By using a heated solvent and a water-absorbent resin solution, fine powder can be uniformly granulated in a short time, and productivity is improved. The temperature of the solvent and / or the water-absorbent resin solution is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, still more preferably 60 ° C. or higher, particularly preferably 70 ° C. or higher, and preferably the boiling point or lower of the solvent. More preferably, it is 100 ° C. or lower. The boiling point can be adjusted by adding salts or solvents, pressure (decompression / pressurization), or the like.

The amount of the water-absorbent resin solution added to the fine powder is appropriately set in consideration of the influence of physical properties on the obtained water-absorbent resin, recovery efficiency, etc., and is, for example, 0.1 to 100 parts by mass of the fine powder. It is 100 parts by mass.

[2-7] Surface Crosslinking Step This step is a step of providing a portion having a higher crosslinking density on the surface layer of the water-absorbent resin powder (a portion several tens of μm from the surface of the water-absorbent resin powder) obtained through the above-mentioned step. It is composed of a mixing step, a heat treatment step and a cooling step (optional).

In the surface cross-linking step, a water-absorbent resin (water-absorbent resin particles) surface-crosslinked by radical cross-linking or surface polymerization on the surface of the water-absorbent resin powder, a cross-linking reaction with a surface cross-linking agent, or the like can be obtained.

A water-absorbent resin solution can be added in this step (form 5). In this case, the following surface cross-linking agent solution and the solution may be mixed and then added by mixing with the water-absorbent resin powder, or the following surface-cross-linking agent solution and the water-absorbent resin solution may be mixed in a separate line. You may.

The amount of the water-absorbent resin solution added to the water-absorbent resin is appropriately set in consideration of the influence of physical properties on the obtained water-absorbent resin, recovery efficiency, and the like. It is 0.1 to 100 parts by mass.

[2-7-1: Mixing process]
This step is a step of mixing the water-absorbent resin powder and the surface cross-linking agent. The method for mixing the surface cross-linking agent is not particularly limited, but a surface cross-linking agent solution is prepared in advance, and the solution is preferably sprayed or dropped onto the water-absorbent resin powder, and more preferably sprayed. And a method of mixing.

The apparatus for performing the mixing is not particularly limited, but preferably a high-speed stirring type mixer, and more preferably a high-speed stirring type continuous mixer.

The surface cross-linking agent used in the present invention is not particularly limited, and examples thereof include organic or inorganic surface cross-linking agents. Of these, an organic surface cross-linking agent that reacts with a carboxyl group is preferable from the viewpoint of the physical properties of the water-absorbent resin and the handleability of the surface cross-linking agent. For example, one or more surface cross-linking agents disclosed in US Pat. No. 7,183,456. More specifically, a polyhydric alcohol compound, an epoxy compound, a haloepoxy compound, a polyvalent amine compound or a condensate with the haloepoxy compound thereof, an oxazoline compound, an oxazolidinone compound, a polyvalent metal salt, an alkylene carbonate compound, a cyclic urea compound and the like. Can be mentioned.

Specific examples of the organic surface cross-linking agent include (di, tri, tetra, poly) ethylene glycol, (di, poly) propylene glycol, 1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, and (Poly) Glycerin, 2-butane-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, di or triethanol Polyalcohol compounds such as amine, pentaerythritol, sorbitol; epoxy compounds such as (poly) ethylene glycol diglycidyl ether, (di, poly) glycerol polyglycidyl ether, glycidole; 2-oxazolidone, N-hydroxyethyl-2-oxazolidone, Oxetane compounds such as 1,2-ethylenebisoxazoline; 1,3-dioxolan-2-one (ethylene carbonate), 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3- Dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one , 1,3-dioxetane-2-one, 4-methyl-1,3-dioxetane-2-one, 4,6-dimethyl-1,3-dioxetane-2-one, 1,3-dioxopan-2-one Oxetane compounds such as; haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin, and their polyvalent amine adducts (eg, Hercules Kaimen; registered trademark); γ-glycid. Silane coupling agents such as xipropyltrimethoxysilane and γ-aminopropyltriethoxysilane; 3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol, 3-butyl 3-oxetane methanol, 3-methyl- Oxetane compounds such as 3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl 3-oxetane ethanol, 3-chloromethyl-3-methyloxetane, 3-chloromethyl-3-ethyloxetane, and polyvalent oxetane compounds. , 2-Cyclic urea compounds such as imidazolidinone, and the like.

As the polyhydric alcohol, a polyhydric alcohol having 2 to 8 carbon atoms is preferable, a polyhydric alcohol having 3 to 6 carbon atoms is more preferable, and a polyhydric alcohol having 3 to 4 carbon atoms is further preferable. Further, diols are preferable, and ethylene glycol, propylene glycol, 1,3-propanediol and 1,4-butanediol are exemplified, and propylene glycol (1,2-propanediol), 1,3-propanediol and 1,4 are exemplified. -A polyhydric alcohol selected from butanediol is preferred.

Further, as the epoxy compound, a polyglycidyl compound is preferable, and ethylene glycol diglycidyl ether is preferably used.

In addition to the above-mentioned organic surface cross-linking agent, a polyamine-cationic polymer such as a polyamine polymer or a water-soluble polyvalent metal cation-containing compound may be used in combination as the ion-binding surface cross-linking agent. As the water-soluble polyvalent metal cation-containing compound, as the water-soluble polyvalent metal cation-containing compound, aluminum sulfate, aluminum chloride, zirconium chloride, ammonium zirconium carbonate, zirconium carbonate, potassium zirconium carbonate, zirconium sulfate, zirconium acetate, Examples thereof include inorganic salts of polyvalent metals such as zirconium nitrate, polyvalent metal compounds such as organic salts of polyvalent metals such as aluminum acetate, aluminum lactate, zirconium hydroxychloride, titanium triethanolaminate, and titanium lactate. Above all, a compound containing aluminum ions as a polyvalent metal cation is preferable.

The amount of the surface cross-linking agent used (total amount used in the case of a plurality of uses) is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the water-absorbent resin powder. Is. Further, the surface cross-linking agent is preferably added as an aqueous solution, and in this case, the amount of water used is preferably 0.1 to 20 parts by mass, more preferably 0, with respect to 100 parts by mass of the water-absorbent resin powder. It is 5 to 10 parts by mass. Further, when a hydrophilic organic solvent is used, the amount used is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, based on 100 parts by mass of the water-absorbent resin powder.

Further, as described above, the water-soluble polyvalent metal cation-containing compound may be added in the surface cross-linking step.

[2-7-2: Heat treatment process]
This step is a step of applying heat to the mixture discharged from the mixing step to cause a crosslinking reaction on the surface of the water-absorbent resin powder.

The apparatus for carrying out the crosslinking reaction is not particularly limited, but a paddle dryer is preferable. The reaction temperature in the crosslinking reaction is appropriately set according to the type of the surface crosslinking agent used, but is preferably 50 to 300 ° C, more preferably 100 to 200 ° C.

[2-7-3: Cooling process]
This step is an arbitrary step installed as needed after the heat treatment step.

The device for cooling is not particularly limited, but is preferably a device having the same specifications as the device used in the heat treatment step, and more preferably a paddle dryer. This is because it can be used as a cooling device by changing the heat medium to a refrigerant. The water-absorbent resin particles obtained in the heat treatment step are forcibly cooled to 40 to 80 ° C, more preferably 50 to 70 ° C, if necessary, in the cooling step.

[2-8] Granulation Step This step is a step of adjusting the particle size of the dry polymer or the surface-crosslinked (particulate) dry polymer. By performing the granulation step after the surface cross-linking step, a water-absorbent resin powder having a controlled particle size or particle size distribution at a high level can be obtained.

Preferably, the sizing step comprises a grinding step and / or a classification step.

The pulverization step is, for example, a step of pulverizing a lumpy dry polymer or a strongly aggregated particulate dry polymer obtained in the case of static drying in a drying step or a heat treatment step with a pulverizer to adjust the particle size. This pulverization step is different from the above-mentioned gel pulverization step in that the dry polymer to be pulverized has undergone a drying step.

Examples of the crusher used in the crushing step include a high-speed rotary crusher such as a roll mill, a hammer mill, a screw mill, and a pin mill, a vibration mill, a knuckle type crusher, and a cylindrical mixer. Among them, a roll mill is a preferable crusher from the viewpoint that the particle size distribution can be easily controlled.

The classification step is a step of removing coarse particles and fine particles from a (particulate) dry polymer, a surface-crosslinked (particulate) dry polymer, or a pulverized or crushed product thereof using a classifier. .. As the classifier used in the classification step, a vibration type or swing type sieve classifier using a sieve net is used. The coarse particles and fine particles removed in the classification step may be used as the water-absorbent resin A of the present invention. The coarse particles can use the crushed material as the water-absorbent resin A.

From the viewpoint of water absorption performance, the mass average particle size (D50) of the water-absorbent resin powder obtained through the granulation step is preferably 200 μm or more, more preferably 200 to 600 μm, still more preferably 250 to 550 μm, and particularly preferably. Is 300 to 500 μm.

[2-9] Addition Step of Other Additives This step is an arbitrary step carried out for the purpose of imparting various additional functions to the water-absorbent resin and improving the water-absorbing performance, and is any step. In the step of adding an additive. From the viewpoint of the addition effect, it is preferable that the following additives are present on the surface of each particle of the water-absorbent resin powder. Therefore, this step is preferably carried out simultaneously with or separately from the surface cross-linking step, and more preferably after the surface cross-linking step.

Other additives include chelating agents, organic reducing agents, inorganic reducing agents, oxidizing agents, hydroxycarboxylic acid compounds, surfactants, compounds having phosphorus atoms, organic powders such as metal soaps, deodorants, antibacterial agents, and pulps. , Thermoplastic fibers and the like are exemplified. Liquid permeability can be mentioned as an example of the water absorption performance imparted to the water-absorbent resin, and the following polyvalent metal salts, cationic polymers, and inorganic fine particles are exemplified as additives for improving the liquid permeability. Of these, it is preferable to use at least one of them.

-Multivalent metal salt As the polyvalent metal of the polyvalent metal salt, aluminum, zirconium and the like are preferable. The polyvalent metal salt that can be used is preferably aluminum lactate and aluminum sulfate, and more preferably aluminum sulfate.

As for the amount of the polyvalent metal salt added, the metal cation is preferably less than 3.6 × ^10-5 mol, more preferably less than 2.8 × ^10-5 mol, more preferably less than 1 g of the water-absorbent resin powder. Is less than 2.0 × ^10-5 mol.

Cationic Polymers Cationic polymers preferably include compounds exemplified by US Pat. No. 7,098284. Of these, vinylamine polymers are preferable. The amount of the cationic polymer added is preferably less than 2.5 parts by mass, more preferably less than 2.0 parts by mass, still more preferably less than 1.0 part by mass with respect to 100 parts by mass of the water-absorbent resin powder. be.

-Inorganic fine particles Specific examples of inorganic fine particles include mineral products such as talc, kaolin, fuller soil, hydrotalcite, bentonite, active white clay, heavy crystal stone, natural asphaltum, strontium ore, ilmenite, and pearlite; aluminum sulfate 14. ~ 18 water salt (or its anhydride), potassium aluminum sulfate 12 water salt, sodium aluminum sulfate 12 water salt, ammonium aluminum sulfate 12 water salt, aluminum chloride, polyaluminum chloride, aluminum oxide and other aluminum compounds; other such as calcium phosphate Polyvalent metal salts, polyvalent metal oxides and polyvalent metal hydroxides; hydrophilic amorphous silicas; silicon oxide / aluminum oxide / magnesium oxide complex, silicon oxide / aluminum oxide complex, silicon oxide / magnesium oxide Oxide complexes such as complexes; and the like. Of these, two or more may be used in combination. The amount of the inorganic fine particles added is preferably less than 2.0 parts by mass, more preferably less than 1.5 parts by mass, and further preferably less than 1.0 part by mass with respect to 100 parts by mass of the water-absorbent resin powder. ..

[2-10] Other Steps In addition to the above-mentioned steps, the manufacturing method according to the present invention includes, if necessary, a cooling step, a rewetting step, a crushing step, a classification step, a transportation step, a storage step, a packing step, and the like. It may further include a storage step and the like. Further, the conventional recovery / reuse of the water-absorbent resin powder (for example, recovery / reuse using granulation of fine powder) and the method for producing the water-absorbent agent of the present embodiment may be used in combination.

[3. Physical characteristics of the obtained water absorbent]
The present invention also provides a water absorbing agent obtained by the production method of the above embodiment. The physical characteristics of the water-absorbing agent are preferably as follows. The suitable range for the physical properties of the water-absorbent resin is the same as the suitable range for each physical property (CRC, etc.) of the following water-absorbing agent.

[3-1] CRC (centrifugal force holding capacity)
The CRC (centrifugal force holding capacity) of the water absorbent is usually 5 g / g or more, preferably 15 g / g or more, and more preferably 25 g / g or more. The upper limit is not particularly limited, and a higher CRC is preferable, but from the viewpoint of balance with other physical properties, it is preferably 70 g / g or less, more preferably 50 g / g or less, still more preferably 40 g / g or less. ..

When the CRC is less than 5 g / g, the amount of absorption is small and it is not suitable as an absorber for absorbent articles such as disposable diapers. Further, when the CRC exceeds 70 g / g, the rate of absorbing body fluids such as urine and blood decreases, so that it is not suitable for use in high water absorption rate type disposable diapers and the like. The CRC can be controlled by changing the type and amount of the internal cross-linking agent, the surface cross-linking agent, and the like.

[3-2] Particle size When the water-absorbing agent is a powder, the mass average particle size d3 (D50) of the water-absorbent resin is preferably 200 μm or more, more preferably 200 to 600 μm, still more preferably 250 to 550 μm, and particularly preferably. It is 300 to 500 μm. The proportion of particles having a particle diameter of less than 150 μm is usually 15% by mass or less, preferably 10% by mass or less, more preferably 8% by mass or less, and further preferably 6% by mass or less. The proportion of particles having a particle diameter of more than 850 μm is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 1% by mass or less. The water-absorbent resin contains particles having a particle diameter of 150 to 850 μm, preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 97% by mass or more, and particularly preferably 99% by mass or more. Ideally, it is 100% by mass. The logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.20 to 0.50, more preferably 0.25 to 0.40, and even more preferably 0.27 to 0.35.

[3-3] AAP (water absorption ratio under pressure)
The AAP (water absorption ratio under pressure) of the water absorbing agent is preferably 15 g / g or more, more preferably 20 g / g or more, further preferably 23 g / g or more, particularly preferably 24 g / g or more, and most preferably 25 g / g or more. Is. The upper limit is not particularly limited, but is preferably 40 g / g or less.

When the AAP is less than 15 g / g, the amount of liquid returned when pressure is applied to the absorber (sometimes referred to as "Re-Wet") increases, so that absorbent articles such as disposable diapers Not suitable as an absorber. The AAP can be controlled by adjusting the particle size, changing the surface cross-linking agent, and the like.

[3-4] Voltex (water absorption rate)
The Voltex (water absorption rate) of the water-absorbing agent is preferably 60 seconds or less, more preferably 50 seconds or less, still more preferably 40 seconds or less, and particularly preferably 30 seconds or less. The lower limit value is not particularly limited, but is preferably 5 seconds or longer, more preferably 10 seconds or longer.

By setting Vortex in the above range, it becomes possible to absorb a predetermined amount of liquid in a short time. When used as an absorber for absorbent articles such as disposable diapers, the time for the user to feel the skin wet is reduced, discomfort is less likely to occur, and the amount of leakage can be reduced.

[3-5] Amount of residual monomer The amount of residual monomer of the water absorbent is preferably 500 ppm or less, more preferably 450 ppm or less, and even more preferably 400 ppm or less. From the viewpoint of safety, the smaller the amount of residual monomer is, the more preferable.

[4] Uses of water-absorbing agent The use of the water-absorbing agent is not particularly limited, but preferably includes absorbents of absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads. In particular, it can be used as an absorber for high-concentration disposable diapers.

Further, as a raw material for the absorber, an absorbent material such as pulp fiber can be used together with the water absorbent. In this case, the content (core concentration) of the water-absorbent resin in the absorber is preferably 30% by mass to 100% by mass, more preferably 40% by mass to 100% by mass, and further preferably 50% by mass to 100% by mass. %, More preferably 60% by mass to 100% by mass, particularly preferably 70% by mass to 100% by mass, and most preferably 75% by mass to 95% by mass.

By setting the core concentration in the above range, when the absorber is used in the upper layer of the absorbent article, the absorbent article can be kept in a clean white state. Further, since the absorber is excellent in diffusivity of body fluids such as urine and blood, efficient liquid distribution is expected to improve the absorption amount.

The present invention will be described in more detail according to the following experimental examples, but the present invention is not limited to these explanations, and there are also experimental examples obtained by appropriately combining the technical means disclosed in each experimental example. , Shall be included in the scope of the present invention.

The "water-absorbent resin" described below means a granular dried product that has undergone a drying step, a surface-crosslinked granular dried product or a water-absorbent resin powder, and a surface-crosslinked water-absorbent resin powder, and is a "water-containing gel". Means a hydrogel-like crosslinked polymer or a particulate hydrogel-like crosslinked polymer that has not undergone a drying step.

Further, unless otherwise specified, a power supply of 200 V or 100 V at 60 Hz was used for the electric equipment used in the experimental example (including the equipment for measuring the physical properties of the water-absorbent resin). Unless otherwise specified, the physical characteristics of the water-absorbent resin and the water-containing gel described below were measured under the conditions of room temperature (20 ° C to 25 ° C) and a relative humidity of 50% RH ± 10%.

Further, for convenience, "liter" may be expressed as "l" or "L", and "mass fraction" or "weight%" may be expressed as "wt%". When measuring trace components, N.I. It may be expressed as D (Non Directed).

[Physical characteristic measurement method]
(A) CRC (centrifugal force holding capacity) of water-absorbent resin, water-absorbent agent, and water-containing gel
The CRC (centrifugal force holding capacity) of the water-absorbent resin was set to NWSP 241.0. Measured according to R2 (15). The CRC (centrifuge holding capacity) of the hydrogel was NWSP 241.0, except that the mass of the sample was 0.4 g as the hydrogel and the free swelling time was changed to 24 hours. The same operation as in R2 (15) was performed. Further, the solid content α of the hydrous gel was separately measured according to the following (f), and the CRC of the hydrogel (hereinafter, also referred to as gel CRC) was calculated according to the following (formula 1).

CRC (g / g) of hydrogel = {(mwi-mb) -msi × (α / 100)} / {msi × (α / 100)} ... (Equation 1)
Here, msi is the mass (unit; g) of the hydrogel before measurement, mb is the mass (unit: g) of Blank (non-woven fabric only) after free swelling and dehydration, and mwi is free swelling and after dehydration. The mass (unit: g) of the water-containing gel (including the non-woven fabric) and α are the solid content ratio (unit: mass%) of the water-containing gel before measurement.

(B) Moisture content and solid content of water-absorbent resin and water-absorbent resin The water content of the water-absorbent resin is described in NWSP 230.0. Measured according to R2 (15). In the measurement, the mass of the sample was changed to 1.0 g and the drying temperature was changed to 180 ° C., and the water content and solid content of the water-absorbent resin were calculated from the weight loss after drying for 3 hours.

(C) Particle size of water-absorbent resin and water-absorbent agent The particle size of the water-absorbent resin (particle size distribution, mass average particle size (D50) and logarithmic standard deviation (σζ) of particle size distribution) can be determined by using columns 27 and 28 of US Pat. No. 7,638,570. Measured according to the method described in.

(D) 150 pass rate: 150 μm mesh opening pass rate The same classification operation as the above-mentioned method for measuring the mass average particle size (D50) is performed, and the ratio (mass%) of the particles that have passed through the 150 μm open mesh sieve is the 150 pass rate. (Opening 150 μm sieve passing rate).

(E) Polymerization rate of hydrogel and amount of residual monomer Immediately after sampling the hydrogel, 1.00 g of the hydrogel was added to 1000 g of ion-exchanged water at room temperature (at this point, the polymerization reaction was substantially stopped). The insoluble matter was removed by stirring at 300 rpm for 2 hours and then filtering. The amount of the monomer extracted in the filtrate obtained by the above operation was measured using a liquid chromatograph. When the amount of the monomer is the residual monomer amount m (g), the polymerization rate C (mass%) of the hydrous gel is determined according to the following (formula 2), and the hydrous gel is determined according to the following (formula 3). The amount of residual monomer R (% by mass) was determined. It is preferable to measure the polymerization rate immediately after sampling the hydrogel, but if it takes time from sampling to measurement, the polymerization is stopped by forced cooling (dry ice, liquid nitrogen, contact with ice water, etc.). You need to perform an operation.

C (mass%) = 100 × {1-m / (α × M / 100)} ・ ・ ・ (Equation 2)
R (mass%) = 100-C ... (Equation 3)
However, in (Equation 2), M means the mass (g) of the hydrous gel, and α means the solid content ratio (mass%) of the hydrogel. In (Formula 3), C means the polymerization rate (mass%) of the hydrogel. The solid content α of the hydrogel is measured according to the following (f).

(F) Moisture content and solid content of the hydrogel The water content of the hydrogel is described in NWSP 230.0. Measured according to R2 (15). In the measurement, the mass of the sample was changed to 2.0 g, the drying temperature was changed to 180 ° C., and the drying time was changed to 24 hours. Specifically, 2.0 g of the water-containing gel was put into an aluminum cup having a bottom diameter of 50 mm, and then the total mass W1 (g) of the sample (water-containing gel and aluminum cup) was accurately weighed. Next, the sample was allowed to stand in an oven set to an atmospheric temperature of 180 ° C. After 24 hours, the sample was removed from the oven and the total mass W2 (g) was accurately weighed. When the mass of the hydrous gel used in this measurement was M (g), the water content (100-α) (mass%) of the hydrogel was determined according to the following (formula 4). In addition, α is a solid content ratio (mass%) of a hydrogel.

(100-α) (mass%) = {(W1-W2) / M} × 100 ... (Equation 4)
(G) Water-absorbing resin, water-absorbing agent Voltex (water absorption time)
The Voltex (water absorption time) of the water-absorbent resin was measured according to the following procedure. First, 0.02 part by mass of edible blue No. 1 (brilliant blue), which is a food additive, is added to 1000 parts by mass of a pre-prepared physiological saline solution (0.9 mass% sodium chloride aqueous solution), and then the liquid temperature is adjusted. The temperature was adjusted to 30 ° C.

Subsequently, 50 ml of the above physiological saline solution was weighed into a beaker having a capacity of 100 ml, and 2.0 g of the water-absorbent resin was added while stirring at 600 rpm using a stirrer chip having a length of 40 mm and a diameter of 8 mm. Starting from the time when the water-absorbent resin was added, the time until the water-absorbent resin absorbed the physiological saline solution and covered the stirrer chip was measured as Voltex (water absorption time) (unit: seconds).

(H) Amount of residual monomer of water-absorbent resin and water-absorbent agent The amount of residual monomer of water-absorbent resin is determined by NWSP 210.0. Measured according to R2 (15). Specifically, 1.0 g of a water-absorbent resin was added to 200 ml of a 0.9 mass% sodium chloride aqueous solution, and the mixture was stirred at 500 rpm for 1 hour using a stirrer chip having a length of 35 mm and then filtered to determine the amount of monomer eluted in the filtrate. It was measured by high performance liquid chromatography. The amount of residual monomer is expressed as a mass ratio to the water-absorbent resin (unit: ppm).

(I) AAP of water-absorbent resin and water-absorbing agent (water absorption ratio under pressure)
The AAP (water absorption magnification under pressure) of the water-absorbent resin was set to NWSP 242.0. Measured according to R2 (15). That is, 0.900 g (mass W3 (g)) of the water-absorbent resin was put into the measuring device, and the mass (W4 (g)) of the set of the measuring device was measured. Next, a 0.90 mass% sodium chloride aqueous solution adjusted to 23 ± 2 ° C. was absorbed under a load of 2.06 kPa (0.3 psi, 21 g / cm ² ). After 1 hour, the mass (W5 (g)) of the set of measuring devices was measured, and the obtained water absorption ratio under pressure was measured from W3 (g), W4 (g), and W5 (g) according to the following (formula 5). (AAP) was calculated.

AAP (g / g) = (W5-W4) / W3 ... (Equation 5)
[Reference Example 1]
(Polymerization process)
It consists of 422 g of acrylic acid, 106 g of 48.5 mass% sodium hydroxide aqueous solution, 0.92 g of polyethylene glycol diacrylate (weight average molecular weight 523), 25.8 g of 0.1 mass% diethylenetriamine 5 sodium acetate 3 sodium aqueous solution, and 374 g of deionized water. A monomeric solution was prepared. Next, 246 g of a 48.5 mass% sodium hydroxide aqueous solution was added while stirring the monomer solution whose temperature was adjusted to 42.5 ° C. The neutralization rate of acrylic acid was 73 mol%. In the following, the final neutralization rate of acrylic acid is the same for Examples and Comparative Examples. The heat of neutralization at this time increased the temperature to 92 ° C. When the temperature of the monomer aqueous solution reaches 90 ° C, 16.7 g of a 4.5 mass% sodium persulfate aqueous solution is added, and then the bottom surface is preheated to 50 ° C in an ambient temperature of 60 ° C. Polymerization was carried out by pouring it onto a Teflon (registered trademark) sheet (a 30 cm × 30 cm reaction vessel surrounded by a dam having a height of 1.5 cm on all sides). Fifteen seconds after the addition of the aqueous sodium persulfate solution, the polymerization system showed a maximum temperature of 105 ° C. After a further 3 minutes, the obtained polymer was taken out to obtain a hydrogel-like crosslinked polymer (G2).

(Gel crushing process)
The obtained hydrogel-like crosslinked polymer (G2) was cut into pieces in increments of 60 g. A water-containing gel-like crosslinked polymer (G2) was charged at 360 g / min into a meat chopper (manufactured by Remakomu Co., Ltd., model: HL-G22SN) equipped with a 9.5 mm die diameter plate, and at the same time, the temperature was raised to 90 ° C. A hydrogel-like crosslinked polymer pulverized product (MG2) was obtained by adding 22 g / min of warmed water and passing it once. The gel solid content of the pulverized water-containing gel-like crosslinked polymer (MG2) was 50.5% by mass, the gel CRC was 37.0 g / g, and the polymerization rate was 98.3%.

(Drying, crushing, classification process)
500 g of the obtained pulverized water-containing gel-like crosslinked polymer (MG2) was dried at 190 ° C. for 30 minutes in a hot air dryer (manufactured by Satake Chemical Industries, a ventilation band type dryer) to obtain a dried product. Then, it was pulverized with a roll mill (manufactured by Inoguchi Giken Co., Ltd.) to obtain a water-absorbent resin powder (F2-1). After sieving with a sieve having a mesh size of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, the particles were passed through an 850 μm sieve, and particles that did not pass through the 150 sieve were collected to obtain a water-absorbent resin powder (F2-2). The particle ratio (150 pass ratio) that passed through the 150 μm sieve was 13.9% by mass. The physical characteristics of the water-absorbent resin powder (F2-2) are shown in Table 1.

After sieving the water-absorbent resin powder (F2-2) with a sieve having an opening of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, particles that pass through 850 μm and do not pass through 600 μm pass through 3% by mass and 600 μm to 500 μm. Particles that do not pass through are 10% by mass, particles that pass through 500 μm and do not pass through 300 μm are 54% by mass, particles that pass through 300 μm and do not pass through 150 μm are 31% by mass, and particles that pass through 150 μm and do not pass through 45 μm are 2% by mass. By blending, a water-absorbent resin powder (F2-3) was obtained.

(Surface cross-linking process)
In 100 parts by mass of the water-absorbent resin powder (F2-3) prepared by particle size, 0.025 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of ethylene carbonate, 0.5 parts by mass of propylene glycol, and deionization A surface cross-linking agent solution consisting of 2.0 parts by mass of water was mixed. The above mixture was heat-treated at 200 ° C. for 35 minutes to obtain surface-crosslinked water-absorbent resin particles (R2). Table 2 shows the physical property values of the water-absorbent resin particles (R2).

[Manufacturing Example 1]
(Water Absorbent Resin A)
422 parts by mass of acrylic acid, 173.9 parts by mass of 48% by mass sodium hydroxide aqueous solution, 0.86 parts by mass of polyethylene glycol diacrylate (weight average molecular weight 523), 25.8 parts by mass of 0.1% by mass diethylenetriamine 5 acetate 3 sodium aqueous solution A monomer aqueous solution consisting of 372 parts by mass of deionized water was prepared. Next, the monomer aqueous solution (T1-1) whose temperature was adjusted to 38 ° C. was continuously supplied by a metering pump, and then 178.7 parts by mass of a 48 mass% sodium hydroxide aqueous solution was continuously line-mixed. At this time, the liquid temperature of the monomer aqueous solution (T1-2) rose to 82 ° C. due to the heat of neutralization.

Further, after continuously line-mixing 16.9 parts by mass of a 4% by mass sodium persulfate aqueous solution, the continuous polymerization machine having a flat polymerization belt provided with weirs at both ends was continuously subjected to a thickness of 10 mm. Supplied to. Then, polymerization (polymerization time of 3 minutes) was continuously carried out to obtain a band-shaped hydrogel-like crosslinked polymer (G1-1). By continuously cutting the obtained strip-shaped hydrogel (G1-1) in the width direction with respect to the traveling direction of the polymerization belt at equal intervals so that the cutting length is 300 mm, a strip-shaped hydrogel is formed. A crosslinked polymer (G1-2) was obtained.

The obtained hydrogel-like crosslinked polymer (G1-2) and a 3.1 mass% lauryldimethylaminoacetate betaine aqueous solution were simultaneously supplied to a screw extruder for gel pulverization. The supply amount of the aqueous solution of lauryldimethylaminoacetate betaine was 0.15% by mass with respect to the solid content of the hydrogel crosslinked polymer (G1-2). As the screw extruder, a meat chopper having a screw shaft with an outer diameter of 86 mm and a perforated plate having a diameter of 100 mm, a pore diameter of 12.5 mm, and a thickness of 10 mm at the tip thereof is used, and a hydrogel-like crosslinked polymer is used. At the same time as (G1-2), gel crushing was performed while supplying water and water vapor. The obtained pulverized water-containing gel-like crosslinked polymer (MG1) had a solid content of 44% by mass (water content of 56% by mass) and a polymerization rate of 98.6%.

The obtained pulverized water-containing gel-like crosslinked polymer (MG1) was dried using a continuous ventilation band type dryer. First, a hydrogel-like crosslinked polymer pulverized product (MG1) was sprayed on a ventilation plate (punching metal) of this dryer so as to have a thickness of about 10 cm, and dried with hot air at 185 ° C. for 35 minutes. The dried product obtained at the outlet of the dryer was integrated into a single plate block (the width is almost equivalent to the width of the drying belt, the length is endless, and the thickness is several cm) and solidified.

This integrated dried product is air-cooled, coarsely crushed by a crusher (first crusher) equipped with a rotating shaft having a plurality of wings, and then supplied to a three-stage roll mill (second crusher). The mixture was pulverized to obtain a water-absorbent resin powder (A). The obtained water-absorbent resin powder had a mass average particle diameter (d1) of 348 μm, a proportion of particles having a particle diameter of less than 150 μm was 9.8 mass%, and a solid content ratio was 97.6 mass%.

Subsequently, the water-absorbent resin powder (A) was classified using a JIS standard sieve having an opening of 850 μm and 180 μm. Fine powder (FP1), which is a water-absorbent resin A having a solid content of 95.2% by mass, was obtained as a passing material classified by a sieve having a mesh size of 180 μm. The fine powder (FP1) had a mass average particle diameter (d2) of 102 μm, a sieve passage rate of 93.9 mass% with an opening of 150 μm, and a CRC of 37.2 g / g.

[Example 1]
(Dissolution preparation process)
Add 106 g of 48.5 mass% sodium hydroxide aqueous solution to 374 g of deionized water to prepare a 10.7 mass% sodium hydroxide aqueous solution, and add 7.7 g of fine powder (FP1) while stirring so as not to become a splicing powder. Then, the mixture was stirred for 20 minutes to obtain a colorless and transparent water-absorbent resin solution (A1). The temperature of the alkaline aqueous solution when the fine powder (FP1) was added to the alkaline aqueous solution was 30 ° C.

(Preparation process of monomeric aqueous solution)
Water-absorbent resin fine powder solution while stirring a mixed solution of 422 g of acrylic acid, 0.92 g of polyethylene glycol diacrylate (weight average molecular weight 523), and 25.8 g of 0.1 mass% diethylenetriamine 5 sodium acetate 3 sodium aqueous solution. (A1) The whole amount was added to obtain an aqueous solution.

(Polymerization process)
Next, 246 g of a 48.5 mass% sodium hydroxide aqueous solution was added while stirring the aqueous solution whose temperature was adjusted to 42.5 ° C. to obtain a monomer aqueous solution. The heat of neutralization at this time increased the temperature to 92 ° C. When the temperature of the monomer aqueous solution reaches 90 ° C, 16.7 g of a 4.5 mass% sodium persulfate aqueous solution is added, and then the bottom surface is preheated to 50 ° C in an ambient temperature of 60 ° C. Polymerization was carried out by pouring it onto a Teflon (registered trademark) sheet (a 30 cm × 30 cm reaction vessel surrounded by a dam having a height of 1.5 cm on all sides). 16 seconds after the addition of the aqueous sodium persulfate solution, the polymerization system showed a maximum temperature of 106 ° C. After a further 3 minutes, the obtained polymer was taken out to obtain a hydrogel-like crosslinked polymer (G3).

(Gel crushing process)
The same operation as in the gel pulverization step of Reference Example 1 was carried out to obtain a hydrogel-like crosslinked polymer pulverized product (MG3).

The gel solid content of the pulverized water-containing gel-like crosslinked polymer (MG3) was 50.8% by mass, the gel CRC was 36.1 g / g, and the polymerization rate was 98.4%.

(Drying, crushing, classification process)
The same operations as in the drying, pulverizing, and classifying steps of Reference Example 1 were carried out to obtain water-absorbent resin powders (F3-1) and (F3-2). The particle ratio (150 pass ratio) that passed through the 150 μm sieve of (F3-1) was 12.1% by mass. Table 1 shows the physical property values of the water-absorbent resin powder (F3-2).

(Surface cross-linking process)
The same operation as in the surface cross-linking step of Reference Example 1 was carried out to obtain surface-crosslinked water-absorbent resin particles (water-absorbing agent) (R3). Table 2 shows the physical characteristics of the water-absorbing agent (R3).

[Comparative Example 1]
(Preparation of monomeric aqueous solution, polymerization process)
From 422 g of acrylic acid, 106 g of 48.5 mass% sodium hydroxide aqueous solution, 0.92 g of polyethylene glycol diacrylate (weight average molecular weight 523), 25.8 g of 0.1 mass% diethylenetriamine 5 sodium acetate 3 sodium aqueous solution, and 374 g of deionized water. A monomer solution (T4-1) was prepared. Next, 246 g of a 48.5 mass% sodium hydroxide aqueous solution was added while stirring the monomer solution (T4-1) whose temperature was adjusted to 42.5 ° C. The heat of neutralization at this time increased the temperature to 92 ° C. To this, 7.7 g of fine powder (FP1) was added and stirred for 60 seconds to obtain a monomer aqueous solution (T4-2). When the temperature of the monomer aqueous solution (T4-2) reaches 90 ° C., the 4.5 mass% sodium persulfate aqueous solution 16 remains in a state where suspended matter derived from fine powder added to the monomer aqueous solution can be confirmed. After adding 0.7 g, the bottom surface was preheated to 50 ° C in an atmospheric temperature of 60 ° C. Teflon® sheet (enclosed on all sides by a weir with a height of 1.5 cm). Polymerization was carried out by pouring it onto a 30 cm × 30 cm reaction vessel). Fifteen seconds after the addition of the aqueous sodium persulfate solution, the polymerization system showed a maximum temperature of 105 ° C. After a further 3 minutes, the obtained polymer was taken out to obtain a hydrogel-like crosslinked polymer (G4).

(Gel crushing process)
The same operation as in the gel pulverization step of Reference Example 1 was carried out to obtain a hydrogel-like crosslinked polymer pulverized product (MG4). The gel solid content of the pulverized water-containing gel-like crosslinked polymer (MG4) was 51.1% by mass, the gel CRC was 35.2 g / g, and the polymerization rate was 98.3%.

(Drying, crushing, classification process)
The same operations as in the drying, pulverizing, and classifying steps of Reference Example 1 were carried out to obtain water-absorbent resin powders (F4-1) and (F4-2). The particle ratio (150 pass ratio) that passed through the 150 μm sieve of (F4-1) was 13.1% by mass, and the particle ratio (150 pass ratio) that passed through the 150 μm sieve of the water-absorbent resin powder (F3-1) obtained in Example 1 (F4-1). 150 pass rate) It was more than 12.1 mass%. Table 1 shows the physical property values of the water-absorbent resin powder (F4-2).

(Surface cross-linking process)
The same operation as in the surface cross-linking step of Reference Example 1 was carried out to obtain surface-crosslinked water-absorbent resin particles (water-absorbing agent) (R4). Table 2 shows the physical characteristics of the water-absorbing agent (R4).

[Manufacturing Example 2]
(Water Absorbent Resin A)
The water-absorbent resin powder (A) obtained in Production Example 1 was sieved with a sieve having an opening of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, and then 3% by mass and 600 μm of particles passed through 850 μm and did not pass through 600 μm. Particles that pass through 500 μm but do not pass through 500 μm are 10% by mass, particles that pass through 500 μm and do not pass through 300 μm are 54% by mass, particles that pass through 300 μm and do not pass through 150 μm are 31% by mass, particles that pass through 150 μm and do not pass through 45 μm. Was mixed to 2% by mass to obtain a water-absorbent resin powder (B).

The mass average particle diameter (d3) of the water-absorbent resin powder (B) was 346 μm, and the CRC was 46.6 g / g.

In 100 parts by mass of the water-absorbent resin powder (B) obtained by adjusting the particle size, 0.025 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of ethylene carbonate, 0.5 parts by mass of propylene glycol, and deionization A surface cross-linking agent solution consisting of 2.0 parts by mass of water was mixed. The above mixture was heat-treated at 200 ° C. for 30 minutes to obtain surface-crosslinked water-absorbent resin particles (R1-1).

To 100 parts by mass of the surface-crosslinked water-absorbent resin particles (R1-1), 8 parts by mass of deionized water was added with stirring and mixed for 1 minute. Then, after leaving it in a hot air dryer at 60 ° C. for 30 minutes, it was passed through a wire mesh having an opening of 850 μm, and 0.6 parts by mass of hydrotalcite (DHT-6, Kyowa Chemical Industry Co., Ltd.) was mixed. To mix hydrotalcite, put 30 g of surface-crosslinked water-absorbent resin particles (R1-2) hydrated with deionized water into a 225 ml mayonnaise bottle together with hydrotalcite and shake for 3 minutes using a paint shaker. , A particulate water absorbing agent (S1) was obtained.

The obtained water-absorbing agent (S1) was classified using a JIS standard sieve having an opening of 850 μm and 180 μm. Fine powder (FP2), which is a water-absorbent resin A having a solid content of 88.9% by mass, was obtained as a passing material classified by a sieve having a mesh size of 180 μm. The fine powder (FP2) had a mass average particle diameter (d4) of 114 μm, a sieve passage rate of 87.2 mass% with an opening of 150 μm, and a CRC of 24.9 g / g.

[Example 2]
(Dissolution preparation process)
Add 106 g of 48.5 mass% sodium hydroxide aqueous solution to 374 g of deionized water to prepare a 10.7 mass% sodium hydroxide aqueous solution, and add 7.7 g of fine powder (FP2) while stirring so as not to become a splice. Then, the mixture was stirred for 20 minutes to obtain a colorless and transparent water-absorbent resin solution (A2). The temperature of the alkaline aqueous solution when the water-absorbent resin fine powder was added to the alkaline aqueous solution was 30 ° C.

(Preparation of monomeric aqueous solution, polymerization process)
A water-absorbent resin solution (water-absorbent resin solution) in a mixed solution of 422 g of acrylic acid, 0.92 g of polyethylene glycol diacrylate (weight average molecular weight 523), and 25.8 g of a 0.1 mass% diethylenetriamine 5-sodium acetate aqueous solution (25.8 g). A2) The whole amount was added to obtain an aqueous solution. Next, 246 g of a 48.5 mass% sodium hydroxide aqueous solution was added while stirring the aqueous solution whose temperature was adjusted to 42.5 ° C. to obtain a monomer aqueous solution. The heat of neutralization at this time increased the temperature to 92 ° C. When the temperature of the monomer aqueous solution reaches 90 ° C, 16.7 g of a 4.5 mass% sodium persulfate aqueous solution is added, and then the bottom surface is preheated to 50 ° C in an ambient temperature of 60 ° C. Polymerization was carried out by pouring it onto a Teflon (registered trademark) sheet (a 30 cm × 30 cm reaction vessel surrounded by a dam having a height of 1.5 cm on all sides). 14 seconds after the addition of the aqueous sodium persulfate solution, the polymerization system showed a maximum temperature of 105 ° C. After a further 3 minutes, the obtained polymer was taken out to obtain a hydrogel-like crosslinked polymer (G5).

(Gel crushing process)
A hydrogel-like crosslinked polymer pulverized product (MG5) was obtained in the same manner as in Reference Example 1.

The gel solid content of the pulverized water-containing gel-like crosslinked polymer (MG5) was 51.0% by mass, the gel CRC was 35.5 g / g, and the polymerization rate was 98.3%.

(Drying, crushing, classification process)
Water-absorbent resin powders (F5-1) and (F5-2) were obtained in the same manner as in Reference Example 1. The particle ratio (150 pass ratio) that passed through the 150 μm sieve of (F5-1) was 14.3% by mass. Table 1 shows the physical characteristics of the water-absorbent resin powder (F5-2).

(Surface cross-linking process)
In the same manner as in Reference Example 1, surface-crosslinked water-absorbent resin particles (water-absorbing agent) (R5) were obtained. Table 2 shows the physical characteristics of the water-absorbing agent (R5).

[Comparative Example 2]
(Preparation of monomeric aqueous solution, polymerization process)
From 422 g of acrylic acid, 106 g of 48.5 mass% sodium hydroxide aqueous solution, 0.92 g of polyethylene glycol diacrylate (weight average molecular weight 523), 25.8 g of 0.1 mass% diethylenetriamine 5 sodium acetate 3 sodium aqueous solution, and 374 g of deionized water. A monomer solution (T6-1) is prepared. Next, 246 g of a 48.5 mass% sodium hydroxide aqueous solution was added while stirring the monomer solution (T6-1) whose temperature was adjusted to 42.5 ° C. The heat of neutralization at this time increased the temperature to 92 ° C. To this, 7.7 g of fine powder (FP2) was added and stirred for 60 seconds. When the temperature of the monomer aqueous solution (T6-2) reached 90 ° C., the suspended matter derived from the fine powder added to the monomer aqueous solution. Teflon (registered trademark) whose bottom surface was preheated to 50 ° C in an ambient temperature of 60 ° C after adding 16.7 g of a 4.5 mass% sodium persulfate aqueous solution in a state where Polymerization was carried out by pouring it onto a sheet (a 30 cm × 30 cm reaction vessel surrounded by a dam having a height of 1.5 cm on all sides). Fifteen seconds after the addition of the aqueous sodium persulfate solution, the polymerization system showed a maximum temperature of 105 ° C. After a further 3 minutes, the obtained polymer was taken out to obtain a hydrogel-like crosslinked polymer (G6).

(Gel crushing process)
A hydrogel-like crosslinked polymer pulverized product (MG6) was obtained in the same manner as in Reference Example 1.

The gel solid content of the pulverized water-containing gel-like crosslinked polymer (MG6) was 51.5% by mass, the gel CRC was 34.6 g / g, and the polymerization rate was 98.4%.

(Drying, crushing, classification process)
Water-absorbent resin powders (F6-1) and (F6-2) were obtained in the same manner as in Reference Example 1. The particle ratio (150 pass ratio) that passed through the 150 μm sieve of (F6-1) was 14.3% by mass. Table 1 shows the physical property values of the water-absorbent resin powder (F6-2).

(Surface cross-linking process)
In the same manner as in Reference Example 1, surface-crosslinked water-absorbent resin particles (water-absorbing agent) (R6) were obtained. Table 2 shows the physical characteristics of the water-absorbing agent (R6).

[Example 3]
(Dissolution preparation process)
172 g of a 48.5 mass% sodium hydroxide aqueous solution is added to 374 g of deionized water to prepare a 15.3 mass% sodium hydroxide aqueous solution, and 4.0 g of the water-absorbent resin A fine powder (FP1) is sprinkled with stirring. The mixture was added so as not to become powder, and the mixture was stirred for 20 minutes to obtain a colorless and transparent water-absorbent resin solution (A3). The temperature of the alkaline aqueous solution when the fine powder (FP1) which is the water-absorbent resin A was added to the alkaline aqueous solution was 30 ° C.

(Preparation of monomeric aqueous solution, polymerization process)
200 g of acrylic acid, 0.73 g of N, N'-methylenebisacrylamide and 587 g of deionized water are put into a reaction vessel having a capacity of 1 L, and the monomer aqueous solution is stirred while maintaining the temperature of the contents at 20 ° C. (T7) was created. Subsequently, nitrogen gas was introduced until the dissolved oxygen concentration in the monomer aqueous solution (T7) became less than 0.02%, and then, in a sealed state, 2.44 g of 1% by mass hydrogen peroxide solution, 0.2% by mass. 2.92 g of an aqueous ascorbic acid solution and 6.82 g of a 2 mass% 2,2-azobisaminodipropanedihydrochloride aqueous solution were added to the monomer aqueous solution (T7) to initiate a polymerization reaction. After the temperature of the monomer aqueous solution (1) in the reaction vessel reached about 85 ° C., the mixture was continuously heated at 60 ° C. for 3 hours to obtain a hydrogel-like crosslinked polymer (G7).

(Gel crushing process)
The obtained hydrogel-like crosslinked polymer (G7) was shredded into blocks of 3 to 5 cm square. Next, a block-shaped meat chopper supply port equipped with a rotary blade and a perforated plate (diameter 70 mm, hole diameter 5 mm, number of holes 50, thickness 8 mm, made of SUS) at the tip and having a screw shaft with a length of 120 mm. 800 g (solid content 25.3% by mass) of the water-containing gel-like crosslinked polymer (G7) and 553.7 g of the water-absorbent resin solution (A3) (75 mol of carboxyl groups in the water-containing gel-like crosslinked polymer (G7)). (Corresponding to the amount of neutralizing%) was added and mixed while shredding to obtain a pulverized water-containing gel-like crosslinked polymer (MG7-1). The time from the addition of the water-containing gel-like crosslinked polymer (G7) to the discharge of the water-containing gel-like crosslinked polymer pulverized product (MG7-1) was about 30 seconds.

Subsequently, the obtained pulverized water-containing gel-like crosslinked polymer (MG7-1) was supplied again to the meat chopper of the same type as described above and pulverized by gel to obtain a pulverized hydrogel-containing crosslinked polymer (MG7-2). rice field. The solid content of the hydrous gel-like crosslinked polymer pulverized product (MG7-2) discharged from the meat chopper was 18.9% by mass.

(Drying, crushing, classification process)
Next, the same operations as in the drying, crushing, and classifying steps of Reference Example 1 were performed except that the drying time of the obtained pulverized water-containing gel-like crosslinked polymer (MG7-2) was lengthened to 35 minutes to absorb water. Sexual resin powders (F7-1) and (F7-2) were obtained. The particle ratio (150 pass ratio) that passed through the 150 μm sieve of (F7-1) was 13.2% by mass. Table 1 shows the physical characteristics of the water-absorbent resin powder (F7-2).

(Surface cross-linking process)
In the same manner as in Reference Example 1, surface-crosslinked water-absorbent resin particles (water-absorbing agent) (R7) were obtained. Table 2 shows the physical characteristics of the water-absorbing agent (R7).

[Comparative Example 3]
(Preparation of monomeric aqueous solution, polymerization process)
200 g of acrylic acid, 0.73 g of N, N'-methylenebisacrylamide and 587 g of deionized water are put into a reaction vessel having a capacity of 1 L, and the monomer aqueous solution is stirred while maintaining the temperature of the contents at 20 ° C. (T8) was created. Subsequently, nitrogen gas was introduced until the dissolved oxygen concentration in the monomer aqueous solution (T8) became less than 0.02%, and then, in a sealed state, 2.44 g of 1% by mass hydrogen peroxide solution, 0.2% by mass. 2.92 g of an aqueous ascorbic acid solution and 6.82 g of a 2 mass% 2,2-azobisaminodipropanedihydrochloride aqueous solution were added to the monomer aqueous solution (T8) to initiate a polymerization reaction. After the temperature of the monomer aqueous solution (1) in the reaction vessel reached about 85 ° C., the mixture was continuously heated at 60 ° C. for 3 hours to obtain a hydrogel-like crosslinked polymer (G8).

(Gel crushing process)
The obtained hydrogel-like crosslinked polymer (G8) was shredded into blocks of 3 to 5 cm square. Next, a block-shaped meat chopper supply port equipped with a rotary blade and a perforated plate (diameter 70 mm, hole diameter 5 mm, number of holes 50, thickness 8 mm, made of SUS) at the tip and having a screw shaft with a length of 120 mm. 800 g of the water-containing gel-like crosslinked polymer (G8) and 4.0 g of the water-absorbent resin A fine powder (FP1) were sufficiently mixed in a PE bag to 804 g and hydroxylation adjusted to 15.3% by mass. A water-containing gel-like crosslinked polymer is added by adding 546 g of an aqueous sodium solution (corresponding to an amount that neutralizes 75 mol% of carboxyl groups in the water-containing gel-like crosslinked polymer (G8)) and mixing while shredding. A pulverized product (MG8-1) was obtained. The time from the addition of the water-containing gel-like crosslinked polymer (G8) to the discharge of the water-containing gel-like crosslinked polymer pulverized product (MG8-1) was about 30 seconds.

Subsequently, the obtained pulverized water-containing gel-like crosslinked polymer (MG8-1) was again supplied to a meat chopper of the same type as described above and pulverized by gel to obtain a pulverized hydrogel-containing crosslinked polymer (MG8-2). rice field. The solid content of the hydrous gel-like crosslinked polymer pulverized product (MG8-2) discharged from the meat chopper was 18.8% by mass.

(Drying, crushing, classification process)
Next, the same operations as in the drying, pulverizing, and classifying steps of Reference Example 1 were performed except that the drying time of the obtained pulverized water-containing gel-like crosslinked polymer (MG8-2) was lengthened to 35 minutes to absorb water. Sexual resin powders (F8-1) and (F8-2) were obtained. The particle ratio (150 pass ratio) that passed through the 150 μm sieve of (F8-1) was 13.6% by mass. Table 1 shows the physical characteristics of the water-absorbent resin powder (F8-2).

(Surface cross-linking process)
In the same manner as in Reference Example 1, surface-crosslinked water-absorbent resin particles (water-absorbing agent) (R8) were obtained. Table 2 shows the physical property values of the water-absorbent resin particles (water-absorbing agent) (R8).

[Example 4]
(Dissolution preparation process)
106 g of 48.5 mass% sodium hydroxide aqueous solution is added to 374 g of deionized water to prepare a 10.7 mass% sodium hydroxide aqueous solution, and the water absorption obtained in Reference Example 1 which is the water-absorbent resin A is prepared while stirring. Add 7.7 g of resin powder (F2-1) so that it does not become a splicing powder, and stir for 10 minutes while soaking in an ultrasonic cleaner (KS-190N, manufactured by Kyowa Medical Science Co., Ltd.) to create a colorless and transparent water-absorbent resin. A lysate (A4) was obtained. The temperature of the alkaline aqueous solution when the water-absorbent resin powder (F2-1), which is the water-absorbent resin A, was added to the sodium hydroxide aqueous solution was 30 ° C.

(Monomer aqueous solution preparation step, polymerization step)
A mixed solution of 422 g of acrylic acid, 0.92 g of polyethylene glycol diacrylate (weight average molecular weight 523), and 25.8 g of 0.1 mass% diethylenetriamine 5 sodium acetic acid aqueous solution with a water-absorbent resin solution while stirring. The whole amount of a certain alkaline aqueous solution (A4) was added to obtain an aqueous solution.

Next, 246 g of a 48.5 mass% sodium hydroxide aqueous solution was added while stirring the aqueous solution whose temperature was adjusted to 42.5 ° C. to obtain a monomer aqueous solution. The heat of neutralization at this time increased the temperature to 92 ° C. When the temperature of the monomer aqueous solution reaches 90 ° C, 16.7 g of a 4.5 mass% sodium persulfate aqueous solution is added, and then the bottom surface is preheated to 50 ° C in an ambient temperature of 60 ° C. Polymerization was carried out by pouring it onto a Teflon (registered trademark) sheet (a 30 cm × 30 cm reaction vessel surrounded by a dam having a height of 1.5 cm on all sides). Thirteen seconds after the addition of the aqueous sodium persulfate solution, the polymerization system showed a maximum temperature of 105 ° C. After a further 3 minutes, the obtained polymer was taken out to obtain a hydrogel-like crosslinked polymer (G9).

(Gel crushing process)
A hydrogel-like crosslinked polymer pulverized product (MG9) was obtained in the same manner as in Reference Example 1.

The gel solid content of the pulverized water-containing gel-like crosslinked polymer (MG9) was 51.7% by mass, the gel CRC was 35.1 g / g, and the polymerization rate was 98.3%.

(Drying, crushing, classification process)
Water-absorbent resin powders (F9-1) and (F9-2) were obtained in the same manner as in Reference Example 1. Table 1 shows the physical characteristics of the water-absorbent resin powder (F9-2).

(Surface cross-linking process)
In the same manner as in Reference Example 1, surface-crosslinked water-absorbent resin particles (water-absorbing agent) (R9) were obtained. Table 2 shows the physical characteristics of the water-absorbing agent (R9).

[Comparative Example 4]
(Preparation of monomeric aqueous solution, polymerization process)
From 422 g of acrylic acid, 106 g of 48.5 mass% sodium hydroxide aqueous solution, 0.92 g of polyethylene glycol diacrylate (weight average molecular weight 523), 25.8 g of 0.1 mass% diethylenetriamine 5 sodium acetate 3 sodium aqueous solution, and 374 g of deionized water. A monomer solution (T10-1) is prepared.

Next, 246 g of a 48.5 mass% sodium hydroxide aqueous solution was added while stirring the monomer solution (T10-1) whose temperature was adjusted to 42.5 ° C. The heat of neutralization at this time increased the temperature to 92 ° C. To this, 7.7 g of the water-absorbent resin powder (F2-1) which is the water-absorbent resin A was added and stirred for 60 seconds. When the temperature of the monomer aqueous solution (T10-2) reached 90 ° C., a single amount was obtained. After adding 16.7 g of a 4.5 mass% sodium persulfate aqueous solution while the suspended matter derived from the water-absorbent resin powder (F2-1) added to the body aqueous solution can be confirmed, the atmosphere temperature is set to 60 ° C. Then, polymerization was carried out by pouring it onto a Teflon (registered trademark) sheet (a 30 cm × 30 cm reaction vessel surrounded by a dam having a height of 1.5 cm on all sides) whose bottom surface had been preheated to 50 ° C. .. Fifteen seconds after the addition of the aqueous sodium persulfate solution, the polymerization system showed a maximum temperature of 105 ° C. After a further 3 minutes, the obtained polymer was taken out to obtain a hydrogel-like crosslinked polymer (G10).

(Gel crushing process)
A hydrogel-like crosslinked polymer pulverized product (MG10) was obtained in the same manner as in Reference Example 1.

The gel solid content of the pulverized water-containing gel-like crosslinked polymer (MG10) was 51.2% by mass, the gel CRC was 35.6 g / g, and the polymerization rate was 98.2%.

(Drying, crushing, classification process)
Water-absorbent resin powders (F10-1) and (F10-2) were obtained in the same manner as in Reference Example 1. Table 1 shows the physical characteristics of the water-absorbent resin powder (F10-2).

(Surface cross-linking process)
In the same manner as in Reference Example 1, surface-crosslinked water-absorbent resin particles (water-absorbing agent) (R10) were obtained. Table 2 shows the physical property values of the water-absorbent resin particles (water-absorbing agent) (R10).

[Reference Example 2]
Reference Example 2 was carried out according to the procedure of Japanese Patent No. 4969778 Example 1.

A 2000 mL five-necked cylindrical round-bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas inlet tube with 340 g of n-heptane and 3.0 HLB sucrose fatty acid ester (Mitsubishi Chemical Corporation) Company trade name: S-370) 0.92 g was added, dispersed, heated, dissolved, and then cooled to 55 ° C.

Separately, 73.6 g of acrylic acid was charged into 1000 mL pack ace, and while cooling this from the outside, 153.1 g of a 20 mass% sodium hydroxide aqueous solution was added dropwise to neutralize 75 mol% of acrylic acid. did. Further, 3.9 g of deionized water, 0.11 g of 2,2'-azobis (2-amidinopropane) dihydrochloride as a water-soluble azo polymerization initiator, and 8.3 mg of ethylene glycol diglycidyl ether as an internal cross-linking agent were added. Then, a monomer aqueous solution for the first-stage polymerization was prepared.

The entire amount of this first-stage polymerization monomer aqueous solution is added to the above-mentioned five-necked cylindrical round-bottom flask under stirring to disperse it, the inside of the system is sufficiently replaced with nitrogen, and then the temperature is raised to a bath temperature. Was kept at 70 ° C., the polymerization reaction was carried out for 1 hour, and then the polymerized slurry liquid was cooled to room temperature.

In another 1000 mL pack ace, 95.3 g of acrylic acid was charged, and while cooling this, 156.0 g of a 25 mass% sodium hydroxide aqueous solution was added dropwise to neutralize 75 mol% of acrylic acid, and further water 3. Add 3 g, 2,2'-azobis (2-amidinopropane) dihydrochloride 0.14 g and ethylene glycol diglycidyl ether 10.7 mg to prepare a monomer aqueous solution for the second stage polymerization, and bathe in ice water. Used to cool.

After adding the entire amount of the monomer aqueous solution for the second stage polymerization to the polymerization slurry liquid, the inside of the system is sufficiently replaced with nitrogen, the temperature is raised, and the bath temperature is maintained at 70 ° C. for the second stage. The polymerization reaction of the eyes was carried out for 2 hours. After completion of the polymerization, the mixture was heated in an oil bath at 120 ° C. and only water was removed from the system by azeotropic distillation to obtain a gel-like product. Next, 7.81 g of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added as a post-crosslinking agent, mixed, and a post-crosslinking reaction was carried out. Further, water and n-heptane were removed by distillation and dried, and the mass average particle size (mass average particle size ( Water-absorbent resin particles (R11) having D50) cross-linked on the surface of 376 μm were obtained.

[Example 5]
(Dissolution preparation process)
Add 4.7 g of the water-absorbent resin particles (R11), which is the water-absorbent resin A obtained in Reference Example 2, to 153.1 g of the 20 mass% sodium hydroxide aqueous solution while stirring so as not to form a splicing powder, and perform ultrasonic cleaning. The mixture was stirred for 10 minutes in a container (KS-190N, manufactured by Kyowa Medical Science Co., Ltd.) to obtain an alkaline aqueous solution (A5) which is a colorless and transparent water-absorbent resin solution. The temperature of the alkaline aqueous solution when the water-absorbent resin particles (R11), which is the water-absorbent resin A, was added to the alkaline aqueous solution was 30 ° C.

(Monomer aqueous solution preparation step, polymerization step)
A 2000 mL five-necked cylindrical round-bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas inlet tube with 340 g of n-heptane and 3.0 HLB sucrose fatty acid ester (Mitsubishi Chemical Corporation) Company trade name: S-370) 0.92 g was added, dispersed, heated, dissolved, and then cooled to 55 ° C.

Separately, 73.6 g of acrylic acid was charged into 1000 mL pack ace, and while cooling this from the outside, 157.8 g of the alkaline aqueous solution (A5), which is a water-absorbent resin solution, was dropped to add acrylic acid. 75 mol% was neutralized. Further, 3.9 g of deionized water, 0.11 g of 2,2'-azobis (2-amidinopropane) dihydrochloride as a water-soluble azo polymerization initiator, and 8.3 mg of ethylene glycol diglycidyl ether as an internal cross-linking agent were added. Then, a monomer aqueous solution for the first-stage polymerization was prepared.

The entire amount of this first-stage polymerization monomer aqueous solution is added to the above-mentioned five-necked cylindrical round-bottom flask under stirring to disperse it, the inside of the system is sufficiently replaced with nitrogen, and then the temperature is raised to a bath temperature. Was kept at 70 ° C., the polymerization reaction was carried out for 1 hour, and then the polymerized slurry liquid was cooled to room temperature.

In another 1000 mL pack ace, 95.3 g of acrylic acid was charged, and while cooling this, 156.0 g of a 25 mass% sodium hydroxide aqueous solution was added dropwise to neutralize 75 mol% of acrylic acid, and further water 3. Add 3 g, 2,2'-azobis (2-amidinopropane) dihydrochloride 0.14 g and ethylene glycol diglycidyl ether 10.7 mg to prepare a monomer aqueous solution for the second stage polymerization, and bathe in ice water. Used to cool.

After adding the entire amount of the monomer aqueous solution for the second stage polymerization to the polymerization slurry liquid, the inside of the system is sufficiently replaced with nitrogen, the temperature is raised, and the bath temperature is maintained at 70 ° C. for the second stage. The polymerization reaction of the eyes was carried out for 2 hours. After completion of the polymerization, the mixture was heated in an oil bath at 120 ° C. and only water was removed from the system by azeotropic distillation to obtain a gel-like product. Next, 7.81 g of a 2% by mass ethylene glycol diglycidyl ether aqueous solution was added as a post-crosslinking agent, mixed, and a post-crosslinking reaction was carried out. Further, water and n-heptane were removed by distillation and dried, and the mass average particle size (mass average particle size ( Water-absorbent resin particles (water-absorbing agent) (R12) having D50) cross-linked on the surface of 435 μm were obtained. Table 2 shows the physical characteristics of the water-absorbing agent (R12).

[Comparative Example 5]
A 2000 mL five-necked cylindrical round-bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas inlet tube with 340 g of n-heptane and 3.0 HLB sucrose fatty acid ester (Mitsubishi Chemical Corporation) Company trade name: S-370) 0.92 g was added, dispersed, heated, dissolved, and then cooled to 55 ° C.

Separately, 73.6 g of acrylic acid was charged into 1000 mL pack ace, and while cooling this from the outside, 153.1 g of a 20 mass% sodium hydroxide aqueous solution was added dropwise to neutralize 75 mol% of acrylic acid. did. Further, 4.7 g of the water-absorbent resin particles (R11) which is the water-absorbent resin A, 3.9 g of deionized water, and 2,2'-azobis (2-amidinopropane) dihydrochloride of the water-soluble azo-based polymerization initiator 0. .11 g and 8.3 mg of ethylene glycol diglycidyl ether as an internal cross-linking agent were added to prepare a monomer aqueous solution for the first-stage polymerization.

The entire amount of this first-stage polymerization monomer aqueous solution is added to and dispersed in the five-necked cylindrical round-bottom flask under stirring, the inside of the system is sufficiently replaced with nitrogen, and then the temperature is raised to a bath temperature. Was kept at 70 ° C., the polymerization reaction was carried out for 1 hour, and then the polymerized slurry was cooled to room temperature. The polymerization reaction was canceled.

From the above results, the water-absorbing agent obtained by the production method of the present invention suppressed the deterioration of the basic physical properties of CRC and AAP (0.3 psi). In addition, the water-absorbing agent obtained by the production method of the present invention had a higher water-absorbing rate and a reduced amount of residual monomers as compared with the corresponding comparative example. In Comparative Example 5, the physical properties were not measured because the second-stage polymerization could not be performed.

Claims (7)

A method for producing a water-absorbent agent, in which a water-absorbent resin solution obtained by a water-absorbent resin and an alkaline agent is added to the process for producing the water-absorbent agent. The method for producing a water-absorbing agent according to claim 1, wherein the water-absorbent resin solution is added to any one or more of the following production steps (1) to (5).
(1) Monomer aqueous solution preparation step (2) Polymerization step (3) Gel crushing step (4) Fine powder granulation step (5) Surface cross-linking step. A method for producing a water-absorbing agent, wherein the water-absorbent resin solution is added to any one or more of the above-mentioned (1), (2) and (3) production steps. The method for producing a water-absorbing agent according to claim 3, wherein the water-absorbent resin solution is added to the production step of (1). The method for producing a water-absorbing agent according to any one of claims 1 to 4, wherein the alkaline agent is a hydroxide of an alkali metal. The method for producing a water-absorbent agent according to any one of claims 1 to 5, wherein the water-absorbent resin solution is obtained by mixing an aqueous solution of the alkaline agent and the water-absorbent resin. The water absorption according to any one of claims 1 to 6, wherein the water absorption resin dissolved in the water absorption resin solution contains a crosslinked polymer obtained by polymerizing an acid group-containing unsaturated monomer (salt). Method of manufacturing the agent.